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Dissertations / Theses on the topic 'Edge modeling'
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1
Trosclair, Kevin J. "Wave transformation at a saltmarsh edge and resulting marsh edge erosion: observations and modeling." ScholarWorks@UNO, 2013. http://scholarworks.uno.edu/td/1777.
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This study examines wind generated waves during winter storms, their transformation/attenuation near the marsh edge, and the resulting saltmarsh edge erosion. A simple numerical model for wave generation, transmission and marsh edge erosion was developed and validated against observations from Lake Borgne, Louisiana. Results suggest that meteorological conditions modify the local water depth via wind or wave setup and atmospheric pressure, thus exerting a first order control on the location of wave attack, which in turn determines the type of wave forces (shear vs. impact) that dominate the erosion process. Scarp failure follows, at a location determined by water level, creating multiple erosive scarps and terraces. High measured erosion, likely due to marsh edge destabilization followed by subsequent frontal passage forces differential marsh erosion, exposing underlying substrate to further erosion. A conceptual model for marsh edge retreat is developed using these observations and supported further by model predictions.
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Slota, George M. Wolfe Douglas E. "Finite element modeling of leading edge curl phenomenon." [University Park, Pa.] : Pennsylvania State University, 2009. http://honors.libraries.psu.edu/theses/approved/WorldWideIndex/EHT-4/index.html.
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Eddins, Steven L. "Subband analysis-synthesis and edge modeling methods for image coding." Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/15697.
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Fundamenski, Wojciech R. "Tokamak edge plasma modeling using an improved onion-skin method." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0021/NQ45640.pdf.
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Liu, Chao. "Optical modeling and resist metrology for deep-UV photolithography." Texas A&M University, 2005. http://hdl.handle.net/1969.1/4233.
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This thesis first presents a novel and highly accurate methodology for investigating
the kinetics of photoacid diffusion and catalyzed-deprotection of positive-tone
chemically amplified resists during post exposure bake (PEB) by in-situ monitoring the
change of resist and capacitance (RC) of resist film during PEB. Deprotection converts
the protecting group to volatile group, which changes the dielectric constant of resist. So
the deprotection rate can be extracted from the change of capacitance. The photoacid
diffusivity is extracted from the resistance change because diffusivity determines the rate
of change of the acid distribution. Furthermore, by comparing the R and C curves, the
dependence of acid diffusivity on reaction state can be extracted. The kinetics of
non-Fickean acid transportation, deprotection, free volume generation and
absorption/escaping, and resist shrinkage is analyzed and a comprehensive model is
proposed that includes these chemical/physical mechanisms.
Then in this thesis a novel lithographic technique, liquid immersion contact
lithography (LICL) is proposed and the simulations are performed to illustrate its main features and advantages. Significant depth-of-field (DOF) enhancement can be achieved
for large pitch gratings with deep-UV light (û=248nm) illumination with both TM and
TE polarizations by liquid immersion. Better than 100nm DOF can be achieved by when
printing 70nm apertures. The simulation results show that it is very promising to apply
this technique in scanning near field optical microscopy.
Finally, a rigorous, full vector imaging model of non-ideal mask is developed and
the simulation of the imaging of such a mask with 2D roughness is performed. Line edge
roughness (LER) has been a major issue limiting the performance of sub-100nm
photolithography. A lot of factors contribute to LER, including mask roughness, lens
imperfection, resist chemistry, process variation, etc. To evaluate the effect of mask
roughness on LER, a rigorous full vector model has been developed by the author. We
calculate the electromagnetic (EM) field immediately after a rough mask by using
TEMPEST and simulate the projected wafer image with SPLAT. The EM field and wafer
image deviate from those from an ideal mask. LER is finally calculated based on the
projected image.
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Yilmaz, Asim Egemen. "Finite Element Modeling Of Electromagnetic Scattering Problems Via Hexahedral Edge Elements." Phd thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608587/index.pdf.
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In this thesis, quadratic hexahedral edge elements have been applied to the three dimensional for open region electromagnetic scattering problems. For this purpose, a semi-automatic all-hexahedral mesh generation algorithm is developed and implemented. Material properties inside the elements and along the edges are also determined and prescribed during the mesh generation phase in order to be used in the solution phase. Based on the condition number quality metric, the generated mesh is optimized by means of the Particle Swarm Optimization (PSO) technique. A framework implementing hierarchical hexahedral edge elements is implemented to investigate the performance of linear and quadratic hexahedral edge elements. Perfectly Matched Layers (PMLs), which are implemented by using a complex coordinate transformation, have been used for mesh truncation in the software. Sparse storage and relevant efficient matrix ordering are used for the representation of the system of equations. Both direct and indirect sparse matrix solution methods are implemented and used.
Performance of quadratic hexahedral edge elements is deeply investigated over the radar cross-sections of several curved or flat objects with or without patches. Instead of the de-facto standard of 0.1 wavelength linear element size, 0.3-0.4 wavelength quadratic element size was observed to be a new potential criterion for electromagnetic scattering and radiation problems.
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Tüllmann, Ralph. "Observations and modeling of diffuse ionized gas in edge-on galaxies." [S.l.] : [s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=964998548.
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Ramos, Sangrós Diego. "Development of a Bridge SteelEdge Beam Design : FE Modelling for a Vehicle Collision andCase Study." Thesis, KTH, Bro- och stålbyggnad, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-177492.
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The degradation of bridge edge beam systems in Sweden entailed the study of new alternativedesigns, which may become more optimal from a life-cycle perspective than the currenttypical solution used (concrete integrated). Subsequently, a U-shaped steel edge beamproposed by the consulting engineering group Ramböll was considered by the SwedishTransport Administration for its use in a real bridge project. This thesis follows theimplementation of this alternative in a bridge project.The goals of the thesis are to study the development of the U-shaped steel edge beam solutionin the case study, and to identify the key factors behind it. The case study consists of a roadframe bridge where a heavily damaged bridge edge beam system is going to be replaced.For the structural design of the solution, a static linear analysis of a vehicle collision has beencarried out with the help of Finite Element Modelling and current codes. The report shows themodelling of the design solution throughout different development phases in the project. Thecommercial software used has been LUSAS.As an outcome of the project, four models have been designed and analysed, two of themdeveloped by the author as proposed solutions. The factors behind the different changes in thedesign have been identified as: (1) structural resistance, (2) constructability and (3) the use ofstainless steel. Moreover, the connection between the steel edge beam and the concrete slabhas been the main critical part for the structural resistance. Finally, the current preliminarymodel at the moment this thesis is written, which was proposed in the project meetings, meetsthe requirements from a structural point of view.
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Lo, Piccolo Anna. "Arctic ocean submesoscale brine driven eddies: modeling of a sea ice edge front." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.
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Characteristic features of the wintertime Arctic Ocean are narrow and elongated fractures in the sea ice cover, up to hundreds of kilometers long and up to tens of kilometers wide, called leads. Leads expose the ocean to the cold atmosphere, establishing air-sea heat fluxes which freeze the oceanic surface. During new sea ice formation, dense and salt-enriched plumes of brine are rejected into the oceanic mixed-layer. Due to brine rejection, lateral density gradients appear at sea ice edges, creating fronts. Fronts store potential energy and are subjected to gravitational overturning. The effect of Earth's rotation prevents the complete slumping establishing along sea sea ice edge currents in a geostrophic balance state, known as geostrophic adjustment, leaving the isopycnals tilted. Baroclinic instabilities develop and grow into submesoscale eddies - typical vortical coherent structures of the oceanic mixed-layer. Transferring momentum and tracer properties laterally, submesoscale eddies are the leading order process of mixed-layer restratification. Current global climate models can not resolve this small scale turbulence and Arctic Ocean observations are limited due to the presence of sea ice. High resolution numerical models are therefore a powerful tool for investigating these unknown processes. In this work, idealized high resolution model experiments are setup in order to study the wintertime refreezing of an open ocean area near a sea ice edge. The results confirm that submesoscale eddies enhance the mixed-layer restratification subtracting energy from the mean flow and increasing the turbulent kinetic energy. Through the study of lateral density transfer scaling rate, a departure from the deformation radius emerges in geostrophic adjustment experiments and more strongly under ageostrophy predominance. The presence of an ageostrophic diffusion process can explain the frontal region widening.
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Al-Zkeri, Ibrahim Abdullah. "Finite element modeling of hard turning." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1181928433.
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Kandibanda, Rajesh. "TOPOLOGY-BASED MODELING AND ANALYSIS OF ORTHOGONAL CUTTING PROCESS." UKnowledge, 2008. http://uknowledge.uky.edu/gradschool_theses/512.
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This thesis presents the application of topology to machining at the micro and macro levels through an experimental study, modeling and analysis. Uncoated carbide tools of four different cutting edge radii and four different feed rates are used to perform orthogonal machining on AISI 1045 steel disks. The study analyzes the cutting forces, changing grain boundary parameters, micro-hardness, temperature and correlates them to the residual stresses that hold a key to the product life. This analysis helps to understand and evaluate the aspects of grain boundary engineering that influence the fatigue life of a component. The two components of residual stresses (axial and circumferential) are measured, and are correlated with the different cutting edge radii and feed conditions. A topology-based modeling approach is applied to study and understand various outputs in the machining process. The various micro and macro topological parameters that influence the machining process are studied to develop a model to establish the effects of topological parameters in machining using Maple program.
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Wise, Andre. "A spatial approach to edge effect modelling for plantation forestry." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/85876.
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Thesis (MScFor)--Stellenbosch University, 2013.ENGLISH ABSTRACT: One of the major objectives in plantation forestry is to achieve a high level of homogeneity of distribution and dimension of trees within the stand. Precise planting geometries, intensive silviculture and genetic selection are used to achieve this homogeneity. However, a natural variability is still introduced by micro-‐site conditions and disturbances. A substantial source of variation is caused by edge effects of neighbouring stands or other land use forms. The edge effect causes trees at the stand edge to develop differently from trees in the interior of the stand. The overarching objective of this study is to simulate the edge effect based on average stand interior variables as typically received from an enumeration and spatial information on the current and historic stand neighbourhood. With re-‐introducing this natural variance as well as its spatial pattern, we expect to derive improved planning information. A major aim is thus separating the effect of the edge interaction from the other factors contributing to stand variance and quantifying the result in terms of stand output. A methodology is introduced for quantifying interaction at stand edges between a given stand and its neighbouring stands over its lifetime. Transferring the edge interaction value from the edges to all the trees within the stand is then done by applying inverse distance weighting interpolation from the edges to the tree position within the stand. Once an edge interaction value has been calculated for each point, the extent of the edge effect is quantified. The spatial extent of the edge effect is derived empirically from an existing fully spatially mapped stand by means of breakpoint regression. The expected variance as a result of edge influence is then quantified by producing a set of models, which can reproduce the effect of the edge interaction on tree height, diameter and volume. The edge effect is treated as a dynamic interaction for which the temporal aspect needs to be considered, because the current spatial structure of a stand is influenced by its current neighbourhood, but also by the historic development of the neighbourhood in relation to the stand in question. Each stand therefore undergoes an edge effect which is completely unique to that stand, within a given time period. For this reason the presented methodology is a spatial-‐temporal one, aimed at providing a way in which growth and yield forest modelling can be augmented by the inclusion of the edge effect in a practical way. To explicitly quantify edge effects, the natural variance had to be separated into a component explained by edge effect and a second component introduced by other factors such as micro site conditions and disturbance. The second component is treated as an unexplained residual variance. In order to provide a realistic simulation of a stand output at a finer, tree level, this second stand variance needs nonetheless to be quantified. The variance attributable to factors other than the edge effect is mimicked by generating a random number by means of a parameterised stochastic process based on the variance of the inner stand region, which is beyond the reach of the edge effect. In this way, a realistic spatial pattern of a plantation forest stand, taking into account the edge effect and combining it with the natural stand variance is achieved. This study, within the field of plantation forest management, aspires to land use optimization both in terms of productive capacity estimation and for the provision of information for effective land use management planning. It makes use of open source software resources namely the R framework and QGIS and explores aerial stereophotogrammetry as an option for data collection.
AFRIKAANSE OPSOMMING: Een van die hoofdoelwitte in plantasie bosbou praktyk is hoё vlakke van homogeniteit met betrekking tot die verspreiding en die dimensies van die bome in die plantasie opstand. Simetriese aanplantings, intensiewe bosboupraktyk en genetiese seleksie word gebruik om hierdie homogeniteit te verkry. Natuurlike verskille word egter nog steeds gevind as gevolg van groeiplek mikro toestande en ander versteurings in die opstand. Een van die hoofbronne van hierdie variasie is die randeffekte van buurplantasies en ander gebruike van grond. Hierdie randeffekte veroorsaak dat bome aan die rand van die opstand anders ontwikkel as die bome binne in die opstand. Die oorhoofse doelwit met hierdie navorsing is om die randeffekte te simuleer. Hierdie randeffekte is gegrond op die gemiddelde binneopstand boom veranderlikes soos afgelei uit die opmeting en uit ruimtelike inligting oor die huidige en geskiedkundige toestande in die omgewing. As hierdie natuurlike variasies asook die ruimtelike patrone weer in berekening gebring word, verwag ons om beter beplanningsinligting te bekom. ’n Belangrike doelwit tydens hierdie navorsing is dus om die effek van die rand-‐interaksie te skei van die effek van ander faktore wat bydra tot variasies binne-‐in die opstand en om die resultaat in terme van plantasie produksie te kwantifiseer. ’n Metodiek word voorgestel vir die kwantifisering van die interaksie op die rande tussen die opstand en die buuropstande tydens die leeftyd van die opstand. Die oorplasing van die rand interaksie waarde van die rand af na al die bome in die plantasie word dan gedoen deur om geweegde inverse afstand interpolasie vanaf die rand tot by die ligging van die boom, toe te pas. As die rand interaksie waarde vir elke punt bereken is, kan die omvang van die randeffek gekwantifiseer word. Die ruimtelike omvang van die rand effek is, met die gebruik van breekpunt regressie, empiries afgelei van ’n bestaande ten volle karteerde plantasie. Die verwagte variasie as gevolg van die randeffek word dan met die gebruik van ’n stel modelle gekwantifiseer, wat dan die effek van die rand interaksie op boomhoogte, deursnit en volume kan weergee. Die randeffek word as ’n dinamiese interaksie beskou waarvan die tydsaspek in ag geneem moet word, want die huidige ruimtelike struktuur van die plantasie word beïnvloed deur die huidige omgewing asook deur die historiese ontwikkeling van die omgewing met betrekking tot die opstand onder bespreking. Elke opstand ondergaan ’n randeffek wat uniek is aan daardie plantasie op die gegewe tydstip. Die doelwit is om ’n wyse te vind waarvolgens groei-‐en-‐opbrengs plantasie modellering deur die insluiting van randeffek op ’n praktiese wyse, aangevul kan word. Om hierdie rede is die aanbevole metodiek ruimtelik-‐tydelik en gerig daarop om ’n wyse te vind waarvolgens groei-‐en-‐opbrengs modellering deur die insluiting van die randeffek, op ’n praktiese wyse aangevul kan word. Om randeffek eksplisiet te kwantifiseer, moes die natuurlike afwyking gedeel word in die komponent wat die gevolg is van die randeffek, en ’n tweede komponent wat die gevolg is van ander faktore soos mikroligging toestande en versteurings. Die tweede komponent word behandel as ’n onverklaarde oorblywende afwyking. Hierdie tweede plantasie afwyking moet nogtans kwantifiseer word om sodoende ’n realistiese simulasie van plantasie opbrengs op ’n fyner boom vlak te verkry. Die afwyking wat toegeskryf kan word aan faktore buiten die randeffek, word nageboots deur om ’n lukrake nommer (wat gebaseer word op die afwyking van die binne-‐plantasie gebied wat buite die strekwydte van die randeffek is) deur middel van ‘n geparameteriseerde stogastiese proses te genereer. Sodoende word ’n realistiese ruimtelike patroon van ’n plantasie opstand verkry, wat die randeffek in ag neem en dit kombineer met die natuurlike plantasie afwyking.
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Holly, Carlo [Verfasser]. "Modeling of the Lateral Emission Characteristics of High-Power Edge-Emitting Semiconductor Lasers / Carlo Holly." Düren : Shaker, 2019. http://d-nb.info/1198600349/34.
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Tu, Hong. "Strong lensing and CFHTLS : searching edge-on galaxy lenses and modeling Einstein rings in clusters." Paris 6, 2010. http://www.theses.fr/2010PA066596.
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Colin, Clothilde. "Turbulent transport modeling in the edge plasma of tokamaks : verification, validation, simulation and synthetic diagnostics." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4350/document.
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La possibilité de produire de l'énergie en utilisant la fusion par confinement magnétique est un défi scientifique et technologique. La perspective d'ITER transmet des signaux forts afin d'intensifier les efforts de modélisation pour les plasmas de fusion. Le succès de la fusion est conditionnée par la qualité du confinement du plasma dans le cœur du réacteur et par le contrôle des flux de particules et de chaleur qui arrivent sur la paroi. Les deux phénomènes sont liés au transport turbulent. L'étude de ces phénomènes est d'autant plus compliquée que la géométrie magnétique est complexe. Cela nécessite une amélioration de notre capacité à développer des outils numériques capables de reproduire les propriétés du transport turbulent fiables.Cette thèse présente le modèle fluide du code TOKAM3X pour simuler plasma de bord turbulent. Une attention particulière a été portée sur la vérification et la validation de ce code, ce qui est une étape nécessaire avant d'utiliser un code comme un outil prédictif. Ensuite, de nouvelles études sur les propriétés physiques de la turbulence bord du plasma sont examinées. En particulier, les asymétries poloïdales induites par la turbulence et observées expérimentalement côté faible champ sont étudiées en détail. Un grand soin est dédié à la reproduction du scénario MISTRAL, qui consiste à changer la configuration magnétique et à en observer l'impact sur les flux parallèles dans le plan poloïdal. Les simulations reproduisent les mesures expérimentales et fournissent de nouvelles informations sur l'effet du point de contact plasma-paroi sur les caractéristiques de la turbulence, qui ne sont pas accessibles dans les expériencesThe possibility to produce power by using magnetically confined fusion is a scientific and technological challenge. The perspective of ITER conveys strong signals to intensify modeling effort on magnetized fusion plasmas. The success of the fusion operation is conditioned by the quality of plasma confinement in the core of the reactor and by the control of plasma exhaust on the wall. Both phenomena are related to turbulent cross-field transport that is at the heart of the notion of magnetic confinement studies, particle and heat losses. The study of edge phenomena is therefore complicated by a particularly complex magnetic geometry.This calls for an improvement of our capacity to develop numerical tools able to reproduce turbulent transport properties reliable to predict particle and energy fluxes on the plasma facing components. This thesis introduces the TOKAM3X fluid model to simulate edge plasma turbulence. A special focus is made on the code Verification and the Validation. It is a necessary step before using a code as a predictive tool. Then new insights on physical properties of the edge plasma turbulence are explored. In particular, the poloidal asymmetries induced by turbulence and observed experimentally in the Low-Field-Side of the devices are investigated in details. Great care is dedicated to the reproduction of the MISTRAL base case which consists in changing the magnetic configuration and observing the impact on parallel flows in the poloidal plane. The simulations recover experimental measurements and provide new insights on the effect of the plasma-wall contact position location on the turbulent features, which were not accessible in experiments
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Hosder, Serhat. "Clean Wing Airframe Noise Modeling for Multidisciplinary Design and Optimization." Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/28886.
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A new noise metric has been developed that may be used for optimization problems involving aerodynamic noise from a clean wing. The modeling approach uses a classical trailing edge noise theory as the starting point. The final form of the noise metric includes characteristic velocity and length scales that are obtained from three-dimensional, steady, RANS simulations with a two- equation k-omega turbulence model. The noise metric is not the absolute value of the noise intensity, but an accurate relative noise measure as shown in the validation studies. One of the unique features of the new noise metric is the modeling of the length scale, which is directly related to the turbulent structure of the flow at the trailing edge. The proposed noise metric model has been formulated so that it can capture the effect of different design variables on the clean wing airframe noise such as the aircraft speed, lift coefficient, and wing geometry. It can also capture three-dimensional effects which become important at high lift coefficients, since the characteristic velocity and the length scales are allowed to vary along the span of the wing.
Noise metric validation was performed with seven test cases that were selected from a two-dimensional NACA 0012 experimental database. The agreement between the experiment and the predictions obtained with the new noise metric was very good at various speeds, angles of attack, and Reynolds Number, which showed that the noise metric is capable of capturing the variations in the trailing edge noise as a relative noise measure when different flow conditions and parameters are changed.
Parametric studies were performed to investigate the effect of different design variables on the noise metric. Two-dimensional parametric studies were done using two symmetric NACA four-digit airfoils (NACA 0012 and NACA 0009) and two supercritical (SC(2)-0710 and SC(2)-0714) airfoils. The three-dimensional studies were performed with two versions of a conventional transport wing at realistic approach conditions. The twist distribution of the baseline wing was changed to obtain a modified wing which was used to investigate the effect of the twist on the trailing edge noise.
An example study with NACA 0012 and NACA 0009 airfoils demonstrated a reduction in the trailing edge noise by decreasing the thickness ratio and the lift coefficient, while increasing the chord length to keep the same lift at a constant speed. Both two- and three-dimensional studies demonstrated that the trailing edge noise remains almost constant at low lift coefficients and gets larger at higher lift values. The increase in the noise metric can be dramatic when there is separation on the wing. Three-dimensional effects observed in the wing cases indicate the importance of calculating the noise metric with a characteristic velocity and length scale that vary along the span. The twist change does not have a significant effect on the noise at low lift coefficients, however it may give significant noise reduction at higher lift values.
The results obtained in this study show the importance of the lift coefficient on the airframe noise of a clean wing and favors having a larger wing area to reduce the lift coefficient for minimizing the noise. The results also point to the fact that the noise reduction studies should be performed in a multidisciplinary design and optimization framework, since many of the parameters that change the trailing edge noise also affect the other aircraft design requirements. It's hoped that the noise metric developed here can aid in such multidisciplinary design and optimization studies.Ph. D.
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Baxter, Iain A. "Finite Element Modeling of the Mitral Valve and Mitral Valve Repair." Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/22876.
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As the most commonly diseased valve of the heart, the mitral valve has been the subject of extensive research for many years. Prior research has focused on the development of surgical repair techniques and mainly consists of in vivo clinical studies into the efficacy and long-term effects of different procedures. There is a need for a means of studying the mitral valve ex vivo, incorporating patient data and the effects of different repair techniques on the valve prior to surgery. In this study, a method was developed for reconstructing the mitral valve from patient-specific data. Three-dimensional transthoracic and transesophageal echocardiography (3D-TTE and 3D-TEE) were used to obtain ultrasound images from a normal subject and a patient with mitral valve regurgitation. Geometric information was extracted from the images defining the primary structures of the mitral valve and a special program in MATLAB was created to automatically construct a finite element model of a valve. A dynamic finite element analysis solver, LS-DYNA 971, was used to simulate the dynamics of the valves and the non-linear, anisotropic behaviour of biological tissue. The two models were successful in simulating the dynamics of the mitral valve, with the subject model displaying normal function and the patient model showing the dysfunction displayed in the ultrasound images. A method was then developed to modify the original patient model, in a way that maintains its patient-specific nature, to model mitral valve repair. Four mitral valve repair techniques were simulated using the patient model: the annuloplasty ring, the double-orifice Alfieri stitch, the paracommissural Alfieri stitch, and the quadrangular resection. The former was coupled with the other three techniques, as is standard protocol in mitral valve repair. The effects of these techniques on the mitral valve were successfully determined, with varying degrees of improvement in valve function.
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Qin, Na. "Modeling and experimental investigation on ultrasonic-vibration-assisted grinding." Diss., Kansas State University, 2011. http://hdl.handle.net/2097/8537.
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Doctor of PhilosophyDepartment of Industrial & Manufacturing Systems Engineering
Zhijian Pei
Poor machinability of hard-to-machine materials (such as advanced ceramics and titanium) limits their applications in industries. Ultrasonic-vibration-assisted grinding (UVAG), a hybrid machining process combining material-removal mechanisms of diamond grinding and ultrasonic machining, is one cost-effective machining method for these materials. Compared to ultrasonic machining, UVAG has much higher material removal rate while maintaining lower cutting pressure and torque, reduced edge chipping and surface damage, improved accuracy, and lower tool wear rate. However, physics-based models to predict cutting force in UVAG have not been reported to date. Furthermore, edge chipping is one of the technical challenges in UVAG of brittle materials. There is no report related to effects of cutting tool design on edge chipping in UVAG of brittle materials. The goal of this research is to provide new knowledge of machining these hard-to-machine materials with UVAG for further improvements in machining cost and surface quality. First, a thorough literature review is given to show what has been done in this field. Then, a physics-based predictive cutting force model and a mechanistic cutting force model are developed for UVAG of ductile and brittle materials, respectively. Effects of input variables (diamond grain number, diamond grain diameter, vibration amplitude, vibration frequency, spindle speed, and federate) on cutting force are studied based on the developed models. Interaction effects of input variables on cutting force are also studied. In addition, an FEA model is developed to study effects of cutting tool design and input variables on edge chipping. Furthermore, some trends predicted from the developed models are verified through experiments. The results in this dissertation could provide guidance for choosing reasonable process variables and designing diamond tools for UVAG.
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Orain, Francois. "Edge Localized Mode control by Resonant Magnetic Perturbations in tokamak plasmas." Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4749/document.
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Dans les tokamaks, les instabilités nommées ELMs (pour ``Edge Localized Modes'') génèrent des relaxations quasi-périodiques du plasma, potentiellement néfastes pour le divertor d'ITER. Une méthode de contrôle des ELMs prévue pour ITER est l'application de Perturbations Magnétiques Résonantes (RMPs), capables de mitiger ou supprimer les ELMs dans les tokamaks existants. Afin d'améliorer la compréhension de l'interaction entre les ELMs, les RMPs et les écoulements du plasma et de réaliser des prédictions fiables pour ITER, la simulation non-linéaire des ELMs et des RMPs est réalisée avec le code de MHD réduite JOREK, en géométrie réaliste. Les effets bi-fluides diamagnétiques, la friction poloidale néoclassique, une source de rotation parallèle et les RMPs ont été ajoutés dans JOREK pour simuler la pénétration des RMP en prenant en compte la réponse cohérente du plasma. Dans un premier temps, la réponse du plasma aux RMPs (sans ELMs) est étudiée dans le cas des tokamaks JET, MAST et ITER, pour des paramètres réalistes. Ensuite, la dynamique cyclique des ELMs (sans RMPs) est modélisée pour la première fois en géométrie réaliste. La compétition entre la stabilisation du plasma par la rotation diamagnétique et sa déstabilisation par la source de chaleur induit la reconstruction cyclique du piédestal. Enfin la mitigation et la suppression des ELMs sont obtenues pour la première fois dans nos simulations. Le couplage non-linéaire des RMPs avec des modes instables du plasma induit une activité MHD continue à la place des violentes relaxations d'ELMs. Au-delà d'un seuil de perturbation magnétique, la suppression totale des ELMs est également observéeThe growth of plasma instabilities called Edge Localized Modes (ELMs) in tokamaks results in the quasi-periodic relaxations of the edge plasma, potentially harmful for the divertor in ITER. One of the promising ELM control methods planned in ITER is the application of external resonant magnetic perturbations (RMPs), already efficient for ELM mitigation/suppression in current tokamak experiments. However a better understanding of the interaction between ELMs, RMPs and plasma flows is needed to make reliable predictions for ITER. In this perspective, non-linear modeling of ELMs and RMPs is done with the reduced MHD code JOREK, in realisitic geometry including the X-point and the Scrape-Off Layer. The two-fluid diamagnetic drifts, the neoclassical friction, a source of parallel rotation and RMPs have been implemented to simulate the RMP penetration consistently with the plasma response. As a first step, the plasma response to RMPs (without ELMs) is studied for JET, MAST and ITER realistic plasma parameters and geometry. Then the cyclic dynamics of the ELMs (without RMPs) is modeled for the first time in realistic geometry. After an ELM crash, the diamagnetic rotation is found to be instrumental to stabilize the plasma and to model the cyclic reconstruction and collapse of the plasma pressure profile. Last the ELM mitigation and suppression by RMPs is observed for the first time in modeling. The non-linear coupling of the RMPs with unstable modes is found to induce a continuous MHD activity in place of a large ELM crash, resulting in the mitigation of the ELMs. Over a threshold in magnetic perturbation, the full ELM suppression is also observed
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Park, Jinseok. "Sample-Data Modeling for Double Edge Current Programmed Mode Control in High Frequency and Wide Range DC-DC converters." NCSU, 2010. http://www.lib.ncsu.edu/theses/available/etd-12162009-141235/.
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This dissertation focuses on sample-data modeling for double edge current programmed mode control (DECPM) and its application to high frequency and wide range DC-DC converters. Steady state conditions and subharmonic oscillation issues for DECPM are addressed. By combining the conventional peak and valley current programmed mode control, a sample-data model for DECPM is proposed. A small signal model for DECPM is developed by deriving the modulation gains (Fm) and the sampling gains (He) for DECPM from the proposed sample-data model. The sampling frequency dependence on the duty ratio and a large current loop gain at high frequency for DECPM are emphasized. The analytical results are verified by the simulation. Finally, DECPM is proposed as a method to control the high frequency and wide range DC-DC converters. A 10MHz four switch buck boost converter is implemented with DECPM to verify the viability of its application to high frequency and wide range converters.
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Holly, Carlo [Verfasser], Reinhart [Akademischer Betreuer] Poprawe, and Günther [Akademischer Betreuer] Tränkle. "Modeling of the lateral emission characteristics of high-power edge-emitting semiconductor lasers / Carlo Holly ; Reinhart Poprawe, Günther Tränkle." Aachen : Universitätsbibliothek der RWTH Aachen, 2019. http://d-nb.info/1211345920/34.
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Horndahl, Ludvig, and Emil Andersson. "Utvärdering av featurebaserad modellering och direktmodellering." Thesis, Tekniska Högskolan, Högskolan i Jönköping, JTH, Produktutveckling, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-41668.
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The benefits of using feature-based CAD methodology and direct modelling are discussed inthe thesis. An experimental CAD study has been performed in which three different cases hasbeen modelled to get an overview of how direct modelling works in Solid Edge ST10 and to determine how the methodology could be integrated into product development. These two ways of modelling in Solid Edge are evaluated using previous research and data from thestudy to do a SWOT analysis and a Pugh matrix. Further on a comparison is made to find respective methodologies’ area of use.The experimental CAD study explores three cases in which each uses one type of product thatis investigated. The CAD models used as reference for the experiment are originally created using feature-based modelling, in the ordered module of Solid Edge. The intent is to recreate the models using direct modelling. The products of interest are created using different manufacturing processes which enables most tools in the Synchronous module to be put tothe test. Points of interests for the study is the workflow of direct modelling, to define the useand limits of Synchronous and investigate the synergy between the tools of the modules.It is concluded that direct modelling excels in certain area of operations where precision engineering can be ignored. When developing concepts for a new product, time could be savedby using the swift surface editing tool of direct modelling. When the CAD user does not need to rely on already set dimensions and is free to explore different shapes to create a 3D-model,direct modelling will come in handy due to its ability to model without taking history data into account. Direct modelling can also be used as a tool for creating redesigns of products containing complex feature trees. Cooperation between different CAD software could be strengthened using direct modelling where the need to redesign imported CAD files featuring “dead geometries” and empty history trees. These types of 3D-models, step, Parasolid’s etc can be easily modified using directmodelling in Solid Edge. Further research can be made to determine in which areas direct modeling can be applied and excel compared to the standard feature-based CAD methodology.
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VELAYUTHAM, PRAKASH SANKAREN. "AN EFFICIENT ALGORITHM FOR CONVERTING POLYHEDRAL OBJECTS WITH WINGED-EDGE DATA STRUCTURE TO OCTREE DATA STRUCTURE." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1109366602.
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Garland, Michael. "Quadric-Based Polygonal Surface Simplification." Research Showcase @ CMU, 1999. http://repository.cmu.edu/dissertations/282.
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Many applications in computer graphics and related fields can benefit fromautomatic simplification of complex polygonal surface models. Applications areoften confronted with either very densely over-sampled surfaces or models toocomplex for the limited available hardware capacity. An effective algorithmfor rapidly producing high-quality approximations of the original model is avaluable tool for managing data complexity.
In this dissertation, I present my simplification algorithm, based on iterativevertex pair contraction. This technique provides an effective compromisebetween the fastest algorithms, which often produce poor quality results, andthe highest-quality algorithms, which are generally very slow. For example, a1000 face approximation of a 100,000 face model can be produced in about 10seconds on a PentiumPro 200. The algorithm can simplify both the geometryand topology of manifold as well as non-manifold surfaces. In addition toproducing single approximations, my algorithm can also be used to generatemultiresolution representations such as progressive meshes and vertex hierarchiesfor view-dependent refinement.
The foundation of my simplification algorithm, is the quadric error metricwhich I have developed. It provides a useful and economical characterization oflocal surface shape, and I have proven a direct mathematical connection betweenthe quadric metric and surface curvature. A generalized form of this metric canaccommodate surfaces with material properties, such as RGB color or texturecoordinates.
I have also developed a closely related technique for constructing a hierarchyof well-defined surface regions composed of disjoint sets of faces. This algorithminvolves applying a dual form of my simplification algorithm to the dual graphof the input surface. The resulting structure is a hierarchy of face clusters whichis an effective multiresolution representation for applications such as radiosity.
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Grey, Christopher Norton. "Cold-Formed Steel Behavior: Elastic Buckling Simplified Methods for Structural Members with Edge-Stiffened Holes and Purlin Distortional Buckling Strength Under Gravity Loading." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/32829.
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Elastic Buckling Simplified Methods for Structural Members with Edge-Stiffened Holes:
Presently, the current design methods available to engineers to predict the strength of cold-formed steel members with edge-stiffened holes remains largely unaddressed in the North American Specification for the Design of Cold-Formed Steel Structural Members (NAS). Research was conducted to explore and develop a further understanding of the effects of stiffened edge holes on the elastic buckling parameters for local, distortional, and global buckling. Elastic buckling parameter studies have been conducted on a suite of cold-formed members including recently developed DeltaSTUDs manufactured by Steelform Building Products, Inc. and a series of common Steel Stud Manufacturers Association (SSMA) members. Furthermore, a suite of simplified methods for determining elastic buckling parameters used to predict capacity with the Direct Strength Method (DSM) for members with edge stiffened holes were developed and validated. The elastic buckling studies are used to validate the simplified methods presented in this thesis. All simplified methods are further validated with thin shell finite element eigen-buckling parameter studies where the edge-stiffened holes are explicitly modeled.
Purlin Distortional Buckling Strength Under Gravity Loading:
Laterally braced cold-formed steel beams generally fail due to local and/or distortional buckling in combination with yielding. For many members, distortional buckling is the dominant buckling mode and is addressed in the current North American Specification for the Design of Cold-formed Steel Structural Members. The current main code equation, AISI C3.1.4-10 for calculating the available distortional buckling stress was derived experimentally based on a series of four-point bending tests at John Hopkins University. Where this provides a good basis for determining capacity, in most loading conditions purlins are subjected to a downward uniform loading that provides additional resistance to distortional buckling in the top flange beyond the resistance of the steel roofing panel. This research describes an experimental study to explore and quantify the difference in distortional buckling flexural capacity of metal building Z-purlins treated as isolated components and Z-purlins loaded with a constant pressure applied to metal roof panels. A series of three different types of tests have been developed to quantify the system effect provided by the metal roof panels as well as downward pressure on distortional buckling. Results are also extended to validate the Direct Strength Method when predicting flexural capacity of purlins in a roof system.Master of Science
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Saillet, Alan. "Implementace a aplikace metody párování obráběných materiálů a břitů při orbitálním vrtání." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-451199.
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This internship's objective is to implement modeling of uncut chip thicknesses and milling forces in 3-axis milling, and apply it to orbital drilling. The goal is to understand deeper the process, and develop a tool which permits to model a wide range of end-mill tool geometries, and most of 3-axis milling operations.In this report, the following axis will be developed: • The modeling of the complex tool geometry • The modeling of uncut chip thicknesses in slot milling, and for any 3-axis milling operation • The strategy which has been chosen to identify cutting forces coefficients, and their use. • The obtained results and prospects for development.
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Yen, Yung-Chang. "Modeling of metal cutting and ball burnishing prediction of tool wear and surface properties /." Columbus, Ohio : Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1073065455.
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Thesis (Ph. D.)--Ohio State University, 2004.Title from first page of PDF file. Document formatted into pages; contains xxviii, 254 p.; also includes graphics. Includes abstract and vita. Advisor: Taylan Altan, Dept. of Industrial and Systems Engineering. Includes bibliographical references (p. 240-248).
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Baudouin, Jean-Baptiste. "Modeling and simulation with molecular dynamics of the edge dislocation behavior in the presence of Frank loops in austenitic stainless steels Fe-Ni-Cr." Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0055/document.
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Les aciers inoxydables austénitiques sont très utilisés dans l’industrie nucléaire comme structure interne. Ces structures se retrouvent en grande majorité dans la cuve du réacteur et, du fait de leur proximité avec les assemblages combustibles, sont soumis à de rudes conditions d’utilisation. Ces éléments sont donc exposés à des doses d’irradiation élevées et peuvent atteindre 100 dpa après 40 ans d’utilisation, à une température proche de 350°C. Ces conditions d’utilisation modifient la microstructure de l’acier et son comportement mécanique, ce qui entraîne une dégradation de leurs propriétés mécaniques et de leur résistance à la corrosion. L’objectif de cette thèse est d’établir à l’échelle atomique une loi de comportement décrivant le déplacement d’une dislocation coin dans une solution solide Fe-Ni10-Cr20, d’apporter une compréhension des mécanismes d’interaction entre une dislocation coin et une boucle de Frank et d’investiguer l’effet de la température, du générateur aléatoire d’alliage, de l’orientation et du diamètre de la boucle sur la contrainte mécanique. Pour atteindre ces objectifs, des simulations en dynamique moléculaire sont réalisées, basées sur potentiel FeNiCr récemment développé pour imiter le comportement de l’acier austénitique inoxydable. Les simulations sont réalisées en conditions statiques, à 300 K, 600 K et 900 K et les interactions effectuées pour des tailles de boucle de Frank de 2 nm et 10 nm. nous proposons une loi de comportement où sont incluses la température et la vitesse de déformation; l’interaction entre la dislocation coin et la boucle de Frank révèle trois types de mécanismes d’interactions : le cisaillement simple, le défautement et l’absorption de la boucle. L’absorption est le mécanisme le plus stable ; Les analyses des propriétés mécaniques résultantes ont montré que le mécanisme de défautement requiert la contrainte la plus élevée pour que la dislocation franchisse l’obstacle. D’autre part, contrairement aux études précédentes, le défautement de la surface de la boucle n’a lieu que lorsque celle-ci entre en contact avec la dislocation coin ; dans le cas de la boucle de Frank de 2 nm, la corrélation entre la probabilité du mécanisme d’interaction et la force moyenne de l’obstacle constitue des données utiles pour les simulations en Dynamique des Dislocations. Les observations des configurations résultantes de la boucle de Frank suite à l’interaction avec la dislocation permettent de justifier l’apparition de bandes claires observées au MET. Ce travail a été partiellement soutenu par la Commission européenne FP7 par le numéro de subvention 232612 dans le cadre du projet PERFORM 60Austenitic stainless steels are widely used in the nuclear industry as internals. These structures reside mainly in the reactor vessel and, due to their proximity with fuel assemblies, are subjected to severe operating conditions. These elements are exposed to high irradiation doses which can reach 100 dpa after 40 years of operating, at a temperature close to 350°C. These operating conditions affect the microstructure of steels and their mechanical behavior, which leads to the deterioration of their mechanical properties and their corrosion resistance. The objective of this PhD research work is to establish at the atomic scale a constitutive law describing the edge dislocation motion in a random Fe-Ni10-Cr20 solid solute solution, to bring a comprehensive understanding of the interaction mechanism between the edge dislocation and the Frank loops and to investigate the effect of temperature, alloying random generator, orientation and size of the Frank loop on the mechanical stress. To achieve these objectives, molecular dynamics simulations were conducted with a recently developed FeNiCr potential used to mimic the behavior of austenitic stainless steels. These simulations have been performed in static conditions as well as at 300 K, 600 K and 900 K and the interactions realized for loop sizes of 2nm and 10nm. A constitutive law taking into account the temperature and strain rate is proposed; the interaction between the edge dislocation and the Frank loop revealed 3 kinds of interaction mechanisms: simple shearing, unfaulting and absorption of the loop. Absorption is the most stable mechanism; the analyses of the resulting mechanical properties have shown that the unfaulting mechanism requires the highest stress to make the dislocation overcome the obstacle. On the other hand, contrary to previous studies, the unfaulting of the loop surface occurs only when the dislocation comes into contact with the edge dislocation; for the 2 nm Frank loop size, the coupling between the probability of the outcome of the reaction and the average strength of the obstacle constitutes useful data for Dislocation Dynamics simulations. The observations of the resulting Frank loop configurations following the interaction with the dislocation allow justifying the emergence of clear bands observed in TEM. This work has been partially supported by the European Commission FP7 with the grant number 232612 as part of the PERFORM 60 project
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Zhang, Chao. "Multi-Scale Characterization and Failure Modeling of Carbon/Epoxy Triaxially Braided Composite." University of Akron / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1384174136.
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Nadal, Sala Daniel. "Living on the edge: modeling climate change impacts on sub-humid forests growing in semi-arid environments = Vivint al límit: modelant els impactes del canvi climàtic sobre els boscos semi-humits creixent en entorns semi-àrids." Doctoral thesis, Universitat de Barcelona, 2019. http://hdl.handle.net/10803/668301.
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Semi-arid environments are zones where annual precipitation is less than a half of annual potential evapotranspiration, yet water availability is high enough to allow tree growth. Climate change is expected to have a major impact on forests growing at those regions. Rising atmospheric [CO2] (Ca) is expected to increase forest productivity. However, this fertilizing effect may be partially offset by an increase in water stress, either by reductions in water availability or by increases in atmospheric evaporative demand. Additionally, species-specific responses to climate change may further promote invasive tree species expansion.
GOTILWA+ process-based model was used to project the performance of sub-humid forests growing in semi-arid conditions under climate change. However, a carpenter is just as good as the least sharpened of his tools. So, firstly it was developed and tested the RheaG Weather Generator Algorithm, a first-order Markov transition matrix-based WGA, in order to assure the ability to generate statistically robust meteorological time-series. Then, Bayesian inverse modeling was applied in order to calibrate GOTILWA+ model from “in situ” observations from two different forest stands, both occupied by water-demanding tree species growing surrounded by semi-arid conditions.
Firstly, combined effects of increased vapor pressure deficit (D), increased Ca and decreased water availability in an S.W. Australian Eucalyptus salinga Sm. plantation were evaluated. Increasing Ca up to 700 ppm alone was projected to increase E. saligna productivity up to a 33%, and forest carbon stock up to a ~60%. However, combined reductions in water availability and D increases offset part of this fertilizing effect, down to 13% and 35%, respectively. Furthermore, limitations on forest productivity due to D increases were projected to occur in a magnitude similar than productivity reductions due to reduced soil water availability.
Afterwards, in a N.E. Iberian Mediterranean riparian forest where black locust (Robinia pseudoacacia L.) is outcompeting three autochthonous deciduous tree species, sap flow observations were used to calibrate GOTILWA+ model for black locust and European Ash tree (Fraxinus excelsior L.). Field observations suggested that black locust success was explained by its facultative phreatophytic behavior, as well as an increased water use efficiency in stem growth, when compared with co-occurring autochthonous tree species. GOTILWA+ projections, including regionalized climate change scenarios, suggested that under global warming black locust productivity and growth would be further enhanced than its native counterpart, the European ash. The reasons are an increase on daily productivity as Ca increases, and an enlargement of its vegetative period as temperature rises.
As conclusions, the invasive black locust growth performance is expected to be favored by global warming in Mediterranean riparian forests. On the other hand, E. saligna responses to climate change will strongly depend on the balance between the beneficial effects of increasing Ca and physiological limitations due to water stress increase. At stand level, results highlight the importance of accounting for the water available for the trees at the whole soil column, and not only at the superficial soil layers, a challenging issue that is often not resolved in simulation models. Moreover, results also highlight that properly accounting for vapor pressure deficit changes is of a major importance when projecting forest responses to climate change, as it will strongly determine stand changes in productivity and water use efficiency. This thesis also highlights the importance of training simulation models from field observations, not only to describe ecophysiological processes, but also to obtain the most likely set of parameters providing "in situ" observations.
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Kohoutek, Michal. "Metoda fyzikálního modelování přechodových hran v obraze pro určení skutečné pozice obrysu předmětu." Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2009. http://www.nusl.cz/ntk/nusl-233452.
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Doctoral thesis is focused on a design of a new original image transition edge physical modeling method for exact object shape position determination. Automatic Optical Inspection systems for the high accuracy optical measurements is main application area for designed method. The new method design is based on precise physical analysis of a defined imaging system. Object side telecentric lens, telecentric backlight source and CCD video camera are main parts of the analyzed imaging system. New image transition edge physical model and method for accurate shape position detection within the model are derived by geometrical and Fourier optics imaging system analysis. Possible influences of the model parameters changes to the accuracy of shape position detection are studied precisely. A new modeling function suitable for implementation in a new optimal approximation method is derived from the physical transition edge model. The modeling function optimal approximation method is implemented in to a Tester2D measuring system and verified by length etalon measurements. The Tester2D measuring system was successfully accredited for dimensions measurement in range with accuracy up to . Documentation of results of the accreditation process with the record of obtained results from measurement system in scope of preformed interlaboratory comparison tests are appended to the doctoral thesis.
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Sinha, Priyanjana [Verfasser], Thomas Sunn [Akademischer Betreuer] Pedersen, Thomas Sunn [Gutachter] Pedersen, and Bruce [Gutachter] Lipschultz. "Edge and scrape-off layer physics modeling for Wendelstein 7-X in preparation of the operation phases OP1.2 and OP2 / Priyanjana Sinha ; Gutachter: Thomas Sunn Pedersen, Bruce Lipschultz ; Betreuer: Thomas Sunn Pedersen." Greifswald : Universität Greifswald, 2020. http://d-nb.info/1213447569/34.
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Rajaonarison, Tahiry Andriantsoa. "A Geodynamic Investigation of Continental Rifting and Mantle Rheology: Madagascar and East African Rift case studies." Diss., Virginia Tech, 2021. http://hdl.handle.net/10919/102410.
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Continental rifting is an important geodynamic process during which the Earth's outer-most rigid shell undergoes continuous stretching resulting in continental break-up and theformation of new oceanic basins. The East African Rift System, which has two continentalsegments comprising largely of the East African Rift (EAR) to the West and the easternmostsegment Madagascar, is the largest narrow rift on Earth. However, the driving mechanismsof continental rifting remain poorly understood due to a lack of numerical infrastructure tosimulate rifting, the lack of knowledge of the underlying mantle dynamics, and poor knowl-edge of mantle rheology. Here, we use state-of-art computational modeling of the upper660 km of the Earth to: 1) provide a better understanding of mantle flow patterns and themantle rheology beneath Madagascar, 2) to elucidate the main driving forces of observedpresent-day∼E-W opening in the EAR, and 3) to investigate the role of multiple plumesor a superplume in driving surface deformation in the EAR. In chapter 1, we simulate EdgeDriven convection (EDC), constrained by a lithospheric thickness model beneath Madagas-car. The mantle flow associated with the EDC is used to calculate induced olivine aggregates'Lattice Preferred Orientation (LPO), known as seismic anisotropy. The predicted LPO isthen used to calculate synthetic seismic anisotropy, which were compared with observationsacross the island. Through a series of comparisons, we found that asthenospheric flow result-ing from undulations in lithospheric thickness variations is the dominant source of the seismicanisotropy, but fossilized structures from an ancient shear zone may play a role in southern
Madagascar. Our results suggest that the rheological conditions needed for the formationof seismic anisotropy, dislocation creep, dominates the upper asthenosphere beneath Mada-gascar and likely other continental regions. In chapter 2, we use a 3D numerical model ofthe lithosphere-asthenosphere system to simulate instantaneous lithospheric deformation inthe EAR and surroundings. We test the hypothesis that the∼E-W extension of the EAR isdriven by large scale forces arising from topography and internal density gradients, known aslithospheric buoyancy forces. We calculate surface deformation solely driven by lithosphericbuoyancy forces and compare them with surface velocity observations. The lithosphericbuoyancy forces are implemented by imposing observed topography at the model surfaceand lateral density variations in the crust and mantle down to a compensation depth of 100km. Our results indicate that the large-scale∼E-W extension across East Africa is driven bylithospheric buoyancy forces, but not along-rift surface motions in deforming zones. In chap-ter 3, we test the hypothesis that the anomalous northward rift-parallel deformation observedin the deforming zones of the EAR is driven by viscous coupling between the lithosphereand deep upwelling mantle material, known as a superplume, flowing northward. We testtwo end-member plume models including a multiple plumes model simulated using high res-olution shear wave tomography-derived thermal anomaly and a superplume model (Africansuperplume) simulated by imposing a northward mantle-wind on the multiple plumes model.Our results suggest that the horizontal tractions from northward mantle flow associated withthe African Superplume is needed to explain observations of rift-parallel surface motions indeforming zones from GNSS/GPS data and northward oriented seismic anisotropy beneaththe EAR. Overall, this work yields a better understanding of the geodynamics of Africa.Doctor of Philosophy
Continental rifting is an important geodynamic process during which the Earth's outer-most rigid shell undergoes continuous stretching resulting in continental break-up and theformation of new oceanic basins. The East African Rift System, which has two continentalsegments comprising largely of the East African Rift (EAR) to the West and the easternmostsegment Madagascar, is the largest narrow rift on Earth. However, the driving mechanismsof continental rifting remain poorly understood due to a lack of numerical infrastructure tosimulate rifting, the lack of knowledge of the underlying mantle dynamics, and poor knowl-edge of mantle rheology. Here, we use state-of-art computational modeling of the upper660 km of the Earth to: 1) provide a better understanding of mantle flow patterns and themantle rheology beneath Madagascar, 2) to elucidate the main driving forces of observedpresent-day∼E-W opening in the EAR, and 3) to investigate the role of multiple plumesor a superplume in driving surface deformation in the EAR. In chapter 1, we simulate EdgeDriven convection (EDC), constrained by a lithospheric thickness model beneath Madagas-car. The mantle flow associated with the EDC is used to calculate induced olivine aggregates'Lattice Preferred Orientation (LPO), known as seismic anisotropy. The predicted LPO isthen used to calculate synthetic seismic anisotropy, which were compared with observationsacross the island. Through a series of comparisons, we found that asthenospheric flow result-ing from undulations in lithospheric thickness variations is the dominant source of the seismicanisotropy, but fossilized structures from an ancient shear zone may play a role in southern Madagascar. Our results suggest that the rheological conditions needed for the formationof seismic anisotropy, dislocation creep, dominates the upper asthenosphere beneath Mada-gascar and likely other continental regions. In chapter 2, we use a 3D numerical model ofthe lithosphere-asthenosphere system to simulate instantaneous lithospheric deformation inthe EAR and surroundings. We test the hypothesis that the∼E-W extension of the EAR isdriven by large scale forces arising from topography and internal density gradients, known aslithospheric buoyancy forces. We calculate surface deformation solely driven by lithosphericbuoyancy forces and compare them with surface velocity observations. The lithosphericbuoyancy forces are implemented by imposing observed topography at the model surfaceand lateral density variations in the crust and mantle down to a compensation depth of 100km. Our results indicate that the large-scale∼E-W extension across East Africa is driven bylithospheric buoyancy forces, but not along-rift surface motions in deforming zones. In chap-ter 3, we test the hypothesis that the anomalous northward rift-parallel deformation observedin the deforming zones of the EAR is driven by viscous coupling between the lithosphereand deep upwelling mantle material, known as a superplume, flowing northward. We testtwo end-member plume models including a multiple plumes model simulated using high res-olution shear wave tomography-derived thermal anomaly and a superplume model (Africansuperplume) simulated by imposing a northward mantle-wind on the multiple plumes model.Our results suggest that the horizontal tractions from northward mantle flow associated withthe African Superplume is needed to explain observations of rift-parallel surface motions indeforming zones from GNSS/GPS data and northward oriented seismic anisotropy beneaththe EAR. Overall, this work yields a better understanding of the geodynamics of Africa.
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Duport, Chloé. "Modeling with consideration of the fluid-structure interaction of the behavior under load of a kite for auxiliary traction of ships." Thesis, Brest, École nationale supérieure de techniques avancées Bretagne, 2018. http://www.theses.fr/2018ENTA0011/document.
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Cette thèse fait partie du projet beyond the sea® qui a pour but de développer la traction par cerf-volant à boudins gonflés (kite) comme système de propulsion auxiliaire des navires. Comme le kite est une structure souple, il est nécessaire de mettre en place une boucle d’interaction fluide-structure pour calculer la géométrie du kite en vol et ses performances aérodynamiques. Un modèle de Ligne Portante 3D Non-Linéaire a été développé pour pouvoir gérer ces ailes non planes, avec des angles de dièdre et de flèche qui varient le long de l’envergure, et également pour pouvoir prendre en compte la non-linéarité du coefficient de portance de la section aérodynamique. Le modèle a été vérifié par des simulations RANSE sur différentes géométries et donne des résultats satisfaisants pour des angles d’incidence et de dérapage variant jusqu’à 15°, avec des différences relatives de quelques pour cent pour l’estimation de la portance globale de l’aile. Les résultats locaux sont aussi correctement estimés, le modèle est capable d’estimer la position du minimum et du maximum de chargement local, selon l’envergure de l’aile, et cela même pour une aile en dérapage. En parallèle, un modèle structure a été développé. L’idée principale du modèle Kite as a Beam est de réduire le kite à un ensemble d’éléments poutre, chacun équivalent à une partie du kite composé d’une section du boudin d’attaque, de deux lattes gonflées et de la canopée correspondante. Le modèle Kite as a Beam a été comparé à un modèle éléments finis complet du kite sur des cas de déplacements élémentaires. Les résultats montrent certaines différences de comportement entre les deux modèles, avec notamment une surestimation de la raideur en torsion pour le modèle Kite as a Beam. Finalement, le modèle Kite as a Beam a été couplé avec la Ligne Portante 3D Non-Linéaire, puis comparé au modèle éléments finis, couplé également avec la Ligne Portante. La réduction du temps de calcul est réellement importante mais les résultats de la comparaison montrent la nécessité de calibrer le modèle Kite as a Beam pour pouvoir retrouver correctement les résultats du modèle éléments finisThe present thesis is part of the beyond the sea® project which aims to develop tethered kite systems as auxiliary devices for ship propulsion. As a kite is a flexible structure, fluid-structure interaction has to be taken into account to calculate the flying shape and aerodynamic performances of the wing. A 3D Non-Linear Lifting Line model has been developed to deal with non-straight kite wings, with dihedral and sweep angles variable along the span and take into account the non-linearity of the section lift coefficient. The model has been checked with 3D RANSE simulations over various geometries and produces satisfactory results for range of incidence and sideslip up to 15°, with typical relative differences of few percent for the overall lift. The local results are also correctly estimated, the model is able to predict the position of the minimum and maximum loading along the span, even for a wing in sideslip. Simultaneously, a structure model has been developed. The core idea of the Kite as a Beam model is to approximate a Leading Edge Inflatable kite by an assembly of beam elements, equivalent each to a part of the kite composed of a portion of the inflatable leading edge, two inflatable battens and the corresponding canopy. The Kite as a Beam model has been compared to a complete kite Finite Element model over elementary comparison cases. The results show the behaviour differences of the two models, for example the torsion stiffness is globally overestimated by the Kite as a Beam model. Eventually, the Kite as a Beam model coupled with the 3D Non-Linear Lifting Line model is compared to the complete finite element model coupled with the 3D Non-Linear Lifting Line model. The gain in computation time is really significant but the results show the necessity of model calibration if the Kite as a Beam model should be used to predict the results of the complete finite element model
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Giez, Justine. "Effets de charge et de géométrie sur le bruit d'interaction rotor-rotor des doublets d'hélices contra-rotatives." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEC005.
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Le développement de systèmes de propulsion alternatifs aux turboréacteurs actuels constitue un axe de recherche important dans le contexte aéronautique. L’open-rotor, moteur à hélices contrarotatives, constitue une piste sérieuse car il permet à la fois de réduire fortement la consommation de carburant et les émissions de gaz. Toutefois, les émissions sonores restent un défi pour ce type d’architecture, notamment du fait de l’absence de carénage. La compréhension des sources acoustiques et leur prévision est nécessaire afin de pouvoir, par la suite, réduire le bruit de ces moteurs. Les écoulements d’un doublet d’hélices contrarotatives sont complexes, en particulier pour l’hélice aval qui constitue l’axe d’étude de la thèse. Le travail présenté est dédié à une étude numérique, expérimentale et analytique et intervient dans le cadre de la chaire industrielle ADOPSYS entre Safran Aircraft Engines et l’Ecole Centrale de Lyon. L’objectif de ce travail est double. Il s’agit d’une part de réaliser une campagne expérimentale afin d’observer et de mieux comprendre le comportement de l’écoulement et de l’acoustique d’une pale en flèche, notamment en réponse à la présence d’un tourbillon de bord d’attaque. Un second objectif de la thèse était de constituer une base de données afin de comparer les prévisions obtenues avec un modèle analytique. Une méthode de calcul semi-analytique de la réponse aéroacoustique d’une pale aval en réponse à une excitation provenant de l’amont et prenant en compte les effets de charge et de géométrie a été développée. Une étude numérique d’un doublet d’hélices contrarotatives a servi de base à la définition de la géométrie de pale utilisée pendant l’étude. Celle-ci a été définie de façon à observer un tourbillon de bord d’attaque pour certains angles d’incidence. La maquette a ensuite été placée dans une soufflerie anéchoïque de l’Ecole Centrale de Lyon afin de réaliser une étude paramétrique. Des visualisations par enduit visqueux et des mesures de pression pariétale permettent de rendre compte de la présence du tourbillon de bord d’attaque à certains angles d’incidence. L’étude des spectres en champ lointain permet de distinguer un comportement en trois régimes, associés aux trois comportements du tourbillon de bord d’attaque. Des mesures de localisation de sources permettent de corroborer ces observations. Des prévisions analytiques du bruit émis par la pale et se basant sur le modèle d’Amiet ont également été réalisées. Dans un premier temps, les effets de la flèche sont pris en compte dans le modèle et celui-ci est alors appliqué à la pale de l’étude. Une meilleure adéquation des résultats est alors trouvée quand les effets de flèche sont pris en compte, en particulier dans les directions perpendiculaires à la pale. Le modèle est ensuite étendu afin de prendre en compte les effets de la jonction en pied de pale. Cette partie est exploratoire et le développement reste à approfondir. Un complément à l’expérience a consisté en l’étude de l’impact de sillages défilants sur la pale. Un système de barreaux rotatifs permet de générer des sillages périodiques représentatifs d’une interaction de sillages rotor-rotor. Les mesures réalisées montrent le comportement quasi-stationnaire du tourbillonThe development of alternative propeller systems to turbojets is a main issue for research in the current context of aeronautical transport. Counter rotating open rotors are a candidate solution because they allow reduction of fuel consumption and gas emission. However, noise emissions are still a challenge for these types of configuration, in particular because they cannot benefit from the nacelle and the liners currently used in turbojet. The understanding of acoustic sources and their prediction is necessary in order to be able to reduce noise emission in the near future. Flows in an open-rotor are complex, in particular for the downstream propeller which is the subject of this approach.This work based on a numerical, experimental and analytical study and takes part in the ADOPSYS chair between Safran Aircraft Engines and l’Ecole Centrale de Lyon. This PhD has two main goals. The first one is to complete an experimental study in order to elucidate the behavior of the flow on a swept airfoil and the resulting acoustics, with a possibly developing leading-edge vortex. The measurements will be a data base for further comparison with analytical prediction. The second objective of the PhD consists in developing a semi-analytical modeling of the noise emitted by an airfoil in response to an incoming perturbation, taking into account the loading and geometry effects. A numerical study of a full counter-rotating system was used as a basis for designing the investigated airfoil. The latter was designed so that a leading-edge vortex could be formed on the surface for some angles of attack. The mock-up was then tested in an anechoic wind tunnel of Ecole Centrale de Lyon for various sets of parameters. Flow visualization and wall-pressure measurements indicated the presence of the leading-edge vortex for some angles of attack. The far-field measurements indicated three acoustic regimes, which can be associated with three behaviors of the leading-edge vortex. Source localization measurements corroborate these observations. Analytical predictions of the noise emitted by the airfoil and based on Amiet’s model were also performed. Firstly, the sweep angle is taken into account in the model. Secondly it is applied to the studied airfoil. A better match of the results is found when the sweep is considered, in particular in the perpendicular directions. The model in then extended in order to include the wall-junction. This part is exploratory and should be further developed. Finally, a complementary experimental investigation of the impingement of periodic wakes on the airfoil has been performed, using a system made of rotating bars, mimics true wake interactions. The measurements suggest that the leading-edge vortex has a quasi-steady behavior
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Morgan, Philip Alan. "Boundary element modelling and full scale measurement of the acoustic performance of outdoor noise barriers." Thesis, Brunel University, 1999. http://bura.brunel.ac.uk/handle/2438/4921.
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The performance of various designs of outdoor noise barrier has been investigated using numerical modelling and full scale experiments. The numerical modelling has been performed using a two-dimensional boundary element method. The model has been extended to allow the efficient simulation of barrier arrangements on ground having two distinct impedance values and cross-sections incorporating cuttings. It has been reported previously that the performance of a plane screen can be enhanced by adding a device to the top of the barrier to induce destructive interference. Full scale modelling and boundary element simulations have been performed on one such commercially available device. It has been shown that, taking the height increase into account, the major contribution to the improved performance is the presence of two diffracting edges rather than any interference effects generated. It is known that the performance of a single barrier is degraded following the introduction of a barrier on the opposite side of a source. Boundary element simulations of such parallel arrangements have been performed. Modifications have been proposed to reduce the over-estimation of multiple reflections within the model, together with a method for converting predictions to the equivalent point source values. Sound absorptive, tilted and median barriers have been shown to be effective in reducing the degradation. A multiple-edge barrier configuration is known to offer improved screening performance over a plane screen. Reported in-situ measurements have suggested the behaviour to be influenced by site geometry. Boundary element calculations have been performed to identify a more efficient variant of the device. The results suggest the addition of an inclined base panel to be most effective. The boundary element model has been used to investigate the effect of shape and surface treatment upon railway noise barriers. The model has been adapted to allow the use of dipole sources characteristic of railway noise. The cross-section of the rolling stock has been shown to affect the performance of rigid barriers. If the upper edges are coincident, the results suggest that simple absorptive barriers provide better screening than tilted designs. The addition of multiple edges further enhances performance.
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Schawohl, Elke. "Der Weg zum digitalen Zwilling mit Mainstream CAD-Lösungen." Technische Universität Chemnitz, 2018. https://monarch.qucosa.de/id/qucosa%3A21533.
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Von der ersten Idee bis zur Auslieferung eines Produktes laufen verschiedene Prozesse ab, die koordiniert und optimiert werden, um Produkte schnell zur Marktreife zu entwickeln. Die Digitalisierung von Prozessen sowie eine firmenweit einheitliche Datenplattform sind in der Produktentwicklung zwingend notwendig. Digitaler Zwilling, und PLM rücken in den Fokus. Die Herausforderung der Industrie liegt in der Optimierung von Produkten. Wo beginnt die Optimierung? Während der Konstruktion greifen verschiedene Optimierungstools in die Entwicklungsphase ein. Skalierbare FEM-Tools ermöglichen konstruktionsbegleitende Analysen. Verschiedene Konstruktions-Tools in der CAD-Lösung sparen Zeit und Kosten. Die Konstruktion der nächsten Generation Generative Konstruktion – bei der Modellerzeugung werden die Vorteile der additiven Fertigung einbezogen und somit die Bauteilkonstruktion optimiert. Reverse Engineering bietet die Möglichkeit direkt mit Facettendaten zu arbeiten und Flächen zu generieren. Convergent Modeling bietet die nahtlose Kombination von „B-Rep“-Volumen und „Facetten“-Modellen. Solid Edge Portfolio - die Zukunft der Produktentwicklung Solid Edge Apps erweitern den Funktionsumfang. Auf bestimmte Marktsegmente entwickelte Applikationen runden die Anwendungsmöglichkeiten ab.
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Zacks, J. "Edge Modelling of Carbon Imputies in JET Plasmas." Thesis, Queen's University Belfast, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.517623.
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Lunniss, Amelia E. L. "Modelling eruptions and edge stability in tokamak plasmas." Thesis, University of York, 2016. http://etheses.whiterose.ac.uk/16638/.
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In the high confinement mode (H-mode) of tokamak operation, sharp gradients and the resulting high bootstrap current near the edge of a tokamak plasma (the pedestal) typically trigger eruptions called edge localised modes (ELMs). On the ITER scale, these have the potential to cause unacceptable erosion of materials. However, there exist scenarios, such as the quiescent H-mode (QH), where there are no ELMs. The ELITE code was originally developed to efficiently calculate the edge ideal MHD stability properties of tokamaks, optimised for the intermediate-high toroidal mode number, n, modes associated with ELMs. In QH-mode the limiting MHD is typically low n. Chapter 3 presents the extension of the ELITE code to arbitrary n. Chapter 4 presents successful benchmarks against the original ELITE code as well as GATO and MARG2D at low n. A first application of the new ELITE code was to study the stability of the QH-mode pedestal in DIII-D. Results from this study are presented in Chapter 5, which show the presence of low n phenomena. Additionally, understanding the pedestal performance losses in JET ITER-like wall (ILW) plasmas is vital to the success of future JET and ITER experiments. Chapter 6 presents an inter-ELM pedestal stability study, which compares the pedestal evolution to the criteria of the pedestal structure model, EPED. These results suggest that maximising the region of plasma that has second stability access will lead to the highest pedestal heights and, therefore, best confinement - a key result for optimising the fusion performance of JET and future tokamaks, such as ITER.
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Pun, Kwok Cheung. "New directions in image modelling based on human perceptual mechanisms." Thesis, Heriot-Watt University, 1995. http://hdl.handle.net/10399/1329.
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Dewhurst, Joseph Michael. "Statistical description and modelling of fusion plasma edge turbulence." Thesis, University of Warwick, 2010. http://wrap.warwick.ac.uk/3903/.
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In tokamaks, heat and particle fluxes reaching the wall are often bursty and intermittent and understanding this behaviour is vital for the design of future reactors. Plasma edge turbulence plays an important role, its quantitative characterisation and modelling under different operating regimes is therefore an important area of research. Ion saturation current (Isat) measurements made in the edge region of the Large Helical Device (LHD) and Mega-Amp Spherical Tokamak (MAST) are analysed. Absolute moment analysis is used to quantify properties on different temporal scales of the measured signals, which are bursty and intermittent. In all data sets, two regions of power-law scaling are found, with the temporal scale τ≈40μs separating the two regimes. A monotonic relationship between connection length and skewness of the probability density function is found for LHD. A new numerical code, ‘HAWK,’ which solves the Hasegawa-Wakatani (HW) equations is presented. The HAWK code is successfully tested and used to study the HW model and modifications. The curvature-Hasegawa-Wakatani (CHW) equations include a magnetic field strength inhomogeneity, C = −∂lnB/∂x. The zonal-Hasegawa- Wakatani (ZHW) equations allow the self-generation of zonal flows. The statistical properties of the turbulent fluctuations produced by the HW model and variations thereof are studied. In particular, the probability density function of E × B density flux Γn = −n∂φ/∂y, structure functions, the bispectrum and transfer functions are investigated. Test particle transport is studied. For the CHW model, the conservation of potential vorticity Π = ∇2φ − n + (κ − C)x accounts for much of the phenomenology. Simple analytical arguments yield a Fickian relation Γn = (κ − C)Dx between the radial density flux Γn and the radial tracer diffusivity Dx. For the ZHW model, a subtle interplay between trapping in small scale vortices and entrainment in larger scale zonal flows determines the rate, character and Larmor radius dependence of the test particle transport. When zonal flows are allowed non-Gaussian statistics are observed. Radial transport (across the zones) is subdiffusive and decreases with the Larmor radius. Poloidal transport (along the zones), however, is superdiffusive and increases with small values of the Larmor radius.
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Leddy, Jarrod. "Integrated modelling of tokamak core and edge plasma turbulence." Thesis, University of York, 2016. http://etheses.whiterose.ac.uk/13207/.
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The accurate prediction of turbulent transport and its effect on tokamak operation is vital for the performance and development of operational scenarios for present and future fusion devices. For problems of this complexity, a common approach is integrated modelling where multiple, well-benchmarked codes are coupled together to form a code that covers a larger domain and range of physics than each of the constituents. The main goal of this work is to develop such a code that integrates core and edge physics for long-time simulation of the tokamak plasma. Three questions are addressed that contribute to the ultimate end goal of this core/edge coupling, each of which spans a chapter. Firstly, the choice of model for edge and core must be fluid for the time scales of interest, but the validity of a common further simplification to the physics models (i.e. the drift-reduction) is explored for regions of interest within a tokamak. Secondly, maintaining a high computational efficiency in such integrated frameworks is challenging, and increasing this while maintaining accurate simulations is important. The use of sub-grid dissipation models is ubiquitous and useful, so the accuracy of such models is explored. Thirdly, the challenging geometry of a tokamak necessitates the use of a field-aligned coordinate system in the edge plasma, which has limitations. A new coordinate system is developed and tested to improve upon the standard system and remove some of its constraints. Finally, the investigation of these topics culminates in the coupling of an edge and core code (BOUT++ and CENTORI, respectively) to produce a novel, three-dimensional, two-fluid plasma turbulence simulation.
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Jidling, Carl. "Strain Field Modelling using Gaussian Processes." Thesis, Uppsala universitet, Avdelningen för systemteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-315254.
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This report deals with reconstruction of strain fields within deformed materials. The method relies upon data generated from Bragg edge measurements, in which information is gained from neutron beams that are sent through the sample. The reconstruction has been made by modelling the strain field as a Gaussian process, assigned a covariance structure customized by incorporation of the so-called equilibrium constraints. By making use of an approximation scheme well suited for the problem, the complexity of the computations has been significantly reduced. The results from numerical simulations indicates a better performance as compared to previous work in this area.
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Watson, David Stewart. "Modelling aspects of the influence of edge effects on expansion anchors." Thesis, University of Glasgow, 2006. http://theses.gla.ac.uk/8049/.
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The principal aim of this work was to investigate and develop modelling techniques capable of accurately and robustly analysing expansion anchor bolts in concrete under tensile loading. Of special interest was the influence of low edge distances on such devices. Since the 20th century increased demands for flexibility, safety and cost have lead to significant development of new anchor products. Modern design methods for new products follow a scientific approach but still rely on substantial and expensive programs of experimental testing. Current design methods for structural designers using anchors are based on semi-empirical approaches derived from extensive experimental testing. It is proposed that much of this experimental work can be replaced with numerical modelling. A number of suitable finite element constitutive models are considered. Initially a Multisurface Plasticity Model and a Traditional Crack Model using a Multiple Fixed Crack (MFC) formulation are considered. Both are shown to give satisfactory results when used to analyse a common, plane-stress benchmark problem. However, although the Plasticity Model gave a better post peak response a 3D implementation was not available within the chosen FE framework. Spurious stress accumulation was identified as the cause of the problems with the MFC Model and its various causes are investigated in detail. A Total Strain Based Rotating Crack Model was chosen as an alternative constitutive model and together with suitable modelling parameters was able to reduce these spurious stress accumulation effects to an acceptable level. 3D modelling of a non-expanding, fully bonded anchor at various distances to the free edge accurately predicted the expected reduction in strength and compared well with reduction factors supplied by anchor manufacturers. The study was extended to include the effect of two free edges and results allowed the strength reduction to be calculated for any arbitrary position rather than for just the single edge approach given in the anchor design guides. Modelling of anchor expansion was tackled on two fronts. Firstly anchor-concrete interfacial behaviour was considered. A Coulomb Friction Model applied to zero thickness structural interface elements to simulate the pressure dependant frictional bond. The role of FE model geometry and material properties in producing a realistic interfacial stress profile was studied in detail. For the kinematics of the expansion modelling of the expander mechanism as a contact problem was found to be the most accurate approach. However, limitations of the modelling framework required that the contact analysis be performed separately and resulting contact stress profile be applied to the existing, noncontact problem. This approach, although somewhat inflexible, provided a useful insight into the important factors pertaining to both the geometric and constitutive models. Results showed realistic crack patterns and demonstrated the effect of varying expansion pressures on the structural response of the anchor bolt. The modelling approach used in this study was highly complex in terms of the multiple non-linear material models and the associated solution process. This resulted in problems with robustness and stability. As an alternative and inherently stable modelling framework a Sequentially Linear (SL) Model was developed. In its isotropic form it proved fast, accurate and reliable for plane-stress anchor problems. Orthotropic fracturing and 3D analysis capabilities were introduced to the model and a number of rules for crack initiation and orientation were tested. Although limitations in the possible crack orientations produced significant mesh bias to the crack pattern, the model was able to capture the changes in anchor behaviour associated with reduced edge distance. The overall assessment is that that SL Model has great potential especially for highly nonlinear problems where stability and robustness are issues.
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Thorsell, Thomas. "Advances in Thermal Insulation : Vacuum Insulation Panels and Thermal Efficiency to Reduce Energy Usage in Buildings." Doctoral thesis, KTH, Byggnadsteknik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-90745.
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We are coming to realize that there is an urgent need to reduce energy usage in buildings and it has to be done in a sustainable way. This thesis focuses on the performance of the building envelope; more precisely thermal performance of walls and super insulation material in the form of vacuum insulation. However, the building envelope is just one part of the whole building system, and super insulators have one major flaw: they are easily adversely affected by other problems in the built environment. Vacuum Insulation Panels are one fresh addition to the arsenal of insulation materials available to the building industry. They are composite material with a core and an enclosure which, as a composite, can reach thermal conductivities as low as 0.004 W/(mK). However, the exceptional performance relies on the barrier material preventing gas permeation, maintaining a near vacuum into the core and a minimized thermal bridge effect from the wrapping of barrier material round the edge of a panel. A serpentine edge is proposed to decrease the heat loss at the edge. Modeling and testing shows a reduction of 60% if a reasonable serpentine edge is used. A diffusion model of permeation through multilayered barrier films with metallization coatings was developed to predict ultimate service life. The model combines numerical calculations with analytical field theory allowing for more precise determination than current models. The results using the proposed model indicate that it is possible to manufacture panels with lifetimes exceeding 50 years with existing manufacturing. Switching from the component scale to the building scale; an approach of integrated testing and modeling is proposed. Four wall types have been tested in a large range of environments with the aim to assess the hygrothermal nature and significance of thermal bridges and air leakages. The test procedure was also examined as a means for a more representative performance indicator than R-value (in USA). The procedure incorporates specific steps exposing the wall to different climate conditions, ranging from cold and dry to hot and humid, with and without a pressure gradient. This study showed that air infiltration alone might decrease the thermal resistance of a residential wall by 15%, more for industrial walls. Results from the research underpin a discussion concerning the importance of a holistic approach to building design if we are to meet the challenge of energy savings and sustainability. Thermal insulation efficiency is a main concept used throughout, and since it measures utilization it is a partial measure of sustainability. It is therefore proposed as a necessary design parameter in addition to a performance indicator when designing building envelopes. The thermal insulation efficiency ranges from below 50% for a wood stud wall poorly designed with incorporated VIP, while an optimized design with VIP placed in an uninterrupted external layer shows an efficiency of 99%, almost perfect. Thermal insulation efficiency reflects the measured wall performance full scale test, thus indicating efficiency under varied environmental loads: heat, moisture and pressure. The building design must be as a system, integrating all the subsystems together to function in concert. New design methodologies must be created along with new, more reliable and comprehensive measuring, testing and integrating procedures. New super insulators are capable of reducing energy usage below zero energy in buildings. It would be a shame to waste them by not taking care of the rest of the system. This thesis details the steps that went into this study and shows how this can be done.QC 20120228
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Boguslawski, Pawel. "Modelling and analysing 3D building interiors with the dual half-edge data structure." Thesis, University of South Wales, 2011. https://pure.southwales.ac.uk/en/studentthesis/modelling-and-analysing-3d-building-interiors-with-the-dual-halfedge-data-structure(ac1af643-835a-4093-90cd-3d51c696e280).html.
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While many systems and standards like CAD systems or CityGML permit the user to represent the geometry and the semantics of building interior models, their use for applications where spatial analysis and/or real-time modifications are required are limited since they lack the possibility to store topological relationships between the elements. In this thesis a new topological data structure, the dual half-edge (DHE) is presented. It permits the representation of the topology of building models with the interior included. It is based on the idea of simultaneously storing a graph in 3D space and its dual graph, and to link the two. Euler-type operators for incrementally constructing 3D models (for adding individual edges, faces and volumes to the model while updating the dual structure simultaneously), and navigation operators (for example to navigate from a given point to all the connected planes or polyhedra) are proposed. The DHE also permits the assigning of attributes to any element. This technique allows the handling of important query types and performs analysis based on the building structure, for example finding the nearest exterior exit to a given room, as in disaster management planning. As the structure is locally modifiable the model may be adapted whenever a particular pathway is no longer available. The proposed DHE structure adds significant analytic value to the increasingly popular CityGML model, and to the CAD field where the dual structure is of growing interest.
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Galassi, Davide. "Numerical modelling of transport and turbulence in tokamak edge plasma with divertor configuration." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0632/document.
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La fusion nucléaire pourrait offrir une nouvelle source d'énergie stable, non émettrice de CO$_2$ et pérenne. Aujourd’hui, les tokamaks offrent les meilleures performances, en confinant un plasma à haute température au moyen d’un champ magnétique. Deux des enjeux technologiques majeurs pour l'exploitation des tokamaks sont l’extraction de puissance et le confinement du plasma sur des temps longs. Ces enjeux sont associés au transport de particules et de chaleur, déterminé par la turbulence, depuis le plasma centrale vers la zone de bord. Dans cette thèse, nous modélisons la turbulence dans le plasma de bord. Nous étudions en particulier la configuration divertor, dans laquelle le plasma central est isolé des parois au moyen d’un champ magnétique additionnel. Cette géométrie magnétique complexe est simulée avec le code de turbulence fluide TOKAM3X, né de la collaboration de l'IRFM au CEA et du laboratoire M2P2 de l'Université Aix-Marseille.Une comparaison avec des simulations en géométrie simplifiée montre une nature intermittente similaire de la turbulence. Néanmoins, l'amplitude des fluctuations, maximale au plan équatorial, est fortement réduite près du point X, où les lignes de champ deviennent purement toroïdales, en accord avec les données expérimentales récentes. Les simulations en configuration divertor montrent un confinement significativement plus élevé que en géométrie circulaire. Une inhibition partielle du transport radial de matière au niveau du point X contribue à cette amélioration. Ce mécanisme est potentiellement important pour comprendre la transition du mode de confinement faible au mode de confinement élevé, le mode opérationnel prévu pour ITERNuclear fusion could offer a new source of stable, non-CO2 emitting energy. Today, tokamaks offer the best performance by confining a high temperature plasma by means of a magnetic field. Two of the major technological challenges for the operation of tokamaks are the power extraction and the confinement of plasma over long periods. These issues are associated with the transport of particles and heat, which is determined by turbulence, from the central plasma to the edge zone. In this thesis, we model turbulence in the edge plasma. We study in particular the divertor configuration, in which the central plasma is isolated from the walls by means of an additional magnetic field. This complex magnetic geometry is simulated with the fluid turbulence code TOKAM3X, developed in collaboration between the IRFM at CEA and the M2P2 laboratory of the University of Aix-Marseille.A comparison with simulations in simplified geometry shows a similar intermittent nature of turbulence. Nevertheless, the amplitude of the fluctuations, which has a maximum at the equatorial plane, is greatly reduced near the X-point, where the field lines become purely toroidal, in agreement with the recent experimental data. The simulations in divertor configuration show a significantly higher confinement than in circular geometry. A partial inhibition of the radial transport of particles at the X-point contributes to this improvement. This mechanism is potentially important for understanding the transition from low confinement mode to high confinement mode, the intended operational mode for ITER
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Duboc, Bastien. "Modélisation hybride de la chimie pour la simulation numérique de la combustion." Thesis, Normandie, 2017. http://www.theses.fr/2017NORMIR23/document.
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Malgré l'augmentation constante des ressources informatiques dédiées au calcul scientifique, simuler des écoulements réactifs mettant en jeu une chimie complexe reste aujourd'hui encore un véritable challenge. L'objectif de cette thèse est le développement de la méthode Hybrid Transported-Tabulated Chemistry (HTTC), destinée aux simulations DNS/LES de flammes avec des mécanismes cinétiques détaillés, en offrant un temps de calcul acceptable. Cette nouvelle approche consiste à transporter les espèces majoritaires de l'écoulement, tandis que les espèces minoritaires sont extraites d'une table chimique. La méthode HTTC a été implémentée dans un code DNS/LES et validée sur des flammes 1D de méthane et de kérosène, mettant en évidence une réduction extrêmement importante du temps de calcul, comparé aux solveurs classiques de chimie détaillée. HTTC a ensuite été mis en œuvre avec succès sur des flammes triples de méthane en présence de forts gradients de fraction de mélange. L'impact des méthodes choisies pour prolonger la table chimique et pour calculer les variables de contrôle, utilisées pour paramétrer la table, a été étudiée avec une attention particulière. Un très bon accord a été trouvé avec les résultats de référence, obtenus avec un solveur de chimie détailléeEven if significant progress is being made to improve the power of high-performance computers, the numerical simulation of reactive flows involving complex chemistry is still a challenging task. The objective of this work is the development of the Hybrid Transported-Tabulated Chemistry method (HTTC), designed for the DNS/LES simulations of flames with detailed kinetic mechanisms, with an acceptable cost. This novel approach combines the transport of the main species in the flow with the tabulation of the radical species. It has been implemented in a DNS/LES code and validated on 1D methane and kerosene flames. The cost of the simulations has been considerably decreased, compared to classic detailed chemistry solvers. Then, simulations of methane edge flames, featuring large gradients of mixture fraction, have been performed with HTTC. In particular, the impact of the methods used to extend the chemical tables and to compute the control variables have been analyzed in details. A very good agreement has been found by comparison with detailed chemistry
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Jahani, Faezeh. "Modelling of dynamic edge loading in total hip replacements with ceramic on polyethylene bearings." Thesis, University of Leeds, 2017. http://etheses.whiterose.ac.uk/19913/.
Full textAbstract:
The performance of total hip replacement (THR) devices can be affected by various factors such as quality of the tissues surrounding the joint, mismatch of the component centres or the cup positioning during hip replacement surgery. Experimental studies have shown that these factors can cause the separation of the two components during the walking cycle (dynamic separation) and the contact of the femoral head with the rim of the acetabular liner (edge loading), which can lead to increased wear and shortened implant lifespan. There is a need for flexible pre-clinical testing tools which allow THR devices to be assessed under these adverse conditions. In this work, a novel dynamic finite element model was developed that is able to generate dynamic separation as it occurs during the gait cycle. In addition, the ability to interrogate contact mechanics and material strain under separation conditions provides a unique means of assessing the severity of edge loading. This study demonstrates these model capabilities for a range of simulated surgical translational mismatch values, cup inclination angles and swing phase loads for ceramic-on-polyethylene implants. The computational model was developed to replicate one station of the Leeds II hip simulator that mimic in vitro adverse conditions. Firstly, a computational sensitivity model was developed under standard conditions for a stable computational contact. The mechanism of separation was also added. The finite element model was able to predict medial-lateral separation as it occurred dynamically in the gait cycle, including cases where the femoral head was in contact with the rim of the cup. The increase in medial-lateral separation with increased translational mismatch, cup inclination angle and decreased swing phase load were in broad agreement with existing experimental data. The factors that increased the separation level, also increased the permeant deformation on the cup. However, steep cup inclination angle resulted in a higher number of conditions with permanent deformation than the standard cup inclination angle. Moreover, despite the low axial load during swing phase, under some separation conditions, reduced contact area created stress value higher than those at the peak axial load. The developed computational tool can be used to understand the effect of various factors on the separation and contact mechanics simultaneously. As separation is a multi-factorial phenomenon, this model can assist to focus on the selected factors that affect the separation experimentally. Moreover, the effect of components specifications such as materials, geometry, and the cup thickness can be investigated with this model.
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Pinoli, Jean-Charles. "Contribution à la modélisation, au traitement et à l'analyse d'image." Saint-Etienne, 1987. http://www.theses.fr/1987STET4005.
Full textAbstract:
Etude du seuillage automatique d'image. Etude des opérateurs Gradient et Laplace. Etude sur la rugosité locale utilisée comme outil pour la segmentation d'image. Etude sur le rehaussement d'image et plus particulièrement sur la suppression de flou dans les images. Traitement des images de nature logarithmique telles les images obtenues en lumière transmise ou celle issue de la vision luminaire. Proposition d'un modèle. La faisabilité industrielle porte sur un problème d'interférométrie automatique en temps réel