To see the other types of publications on this topic, follow the link: Multi-axial.
Dissertations / Theses on the topic 'Multi-axial'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Multi-axial.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Pijlman, Hermen Hendrik. "Sheet material characterisation by multi-axial experiments." [S.l. : s.n.], 2001. http://doc.utwente.nl/59366.
Full text
2
Hilmy, Irfan. "Multi-Axial Damage Modelling of Adhesive Bonding." Thesis, University of Surrey, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.493035.
Full textAbstract:
The behaviour of damage parameters in adhesive bonding has been investigated in order to predict the location of the initial crack in the adhesive region. Research started using bulk adhesive in which the loading is uniaxial, In this case the triaxiality, a variable that defines the stress state will have a value around unity.
3
Sander, Christian [Verfasser], and Oliver [Akademischer Betreuer] Paul. "Multi-axial hall devices in silicon technology." Freiburg : Universität, 2018. http://d-nb.info/1156532663/34.
Full text
4
Andrejack, Theresa Louise Wartman Joseph. "A multi-axial tension test for geotextiles /." Philadelphia, Pa. : Drexel University, 2010. http://hdl.handle.net/1860/3212.
Full text
5
Gallimore, Simon John. "Spanwise mixing in multi-stage axial compressors." Thesis, University of Cambridge, 1986. https://www.repository.cam.ac.uk/handle/1810/250879.
Full text
6
Dempers, Richard William. "Multi-axial creep behaviour of gamma titanium aluminide." Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368165.
Full text
7
Abdul, Majid Mohd Shukry Bin. "Behaviour of composite pipes under multi-axial stress." Thesis, University of Newcastle Upon Tyne, 2011. http://hdl.handle.net/10443/1351.
Full textAbstract:
This thesis describes an experimental investigation of the behaviour of filament wound glass fibre reinforced epoxy (GRE) composite pipe under hydrostatic and biaxial load conditions at temperatures up to 95⁰C. The project was intended to lead to improvements in reliability and quality, and ultimately a reduction in the cost of qualifying GRE oil and gas pipelines. The experiments were designed to be compatible with the procedure currently used by Future Pipe Industries (FPI), employing the concept of ultimate elastic wall stress (UEWS) in the qualification and production control of GRE pipe. The UEWS test appears to provide an attractive means of rating GRE pipes, where weepage resulting from the accumulation of matrix cracks is a common failure mechanism. A novel test rig capable of performing UEWS tests under various loading conditions from hydrostatic to multi-axial loadings was designed and developed. UEWS tests were conducted under six different stress ratios ranging from pure axial to pure hoop loading at room temperature (RT), 65°C and 95°C. The tests involved the application of groups of ten 1-minute hydrostatic pressure cycles at increasing pressure levels. The intention is to identify, by examining the stress-strain response, a stress level below which damage growth is either negligible or at least sufficiently low to prevent long term failure within the design life. In addition, acoustic emission measurements were also conducted to investigate the nature of the damage mechanisms involved as well as its compatibility to the UEWS results. Three distinct failure modes were observed: tensile axial failure under pure axial loading, weepage under axial dominated loading from 0.5:1 to 2:1 and localized leakage failure under hoop dominated loading of 4:1 and 1:0. Full tensile-tensile UEWS and leakage based failure envelopes were developed at a range of temperatures from 20°C (RT) to 95°C. Both envelopes showed a strong dependence on stress ratio and test temperature. It was also shown that the UEWS based failure envelope at elevated temperatures generally degraded, except for the 2:1 loading where UEWS strength increased. The Miner‟s law model developed, gives a good account of the effects of cyclic and static loading in UEWS tests. Using a crack growth model similar to Paris Law, damage development can be directly linked to the progressive nucleation of matrix micro cracks. It is also shown that cyclic rather than static loading dominates the UEWS test response. The general lifetime damage model developed in the study shows good agreement with the experimental data from the multiaxial UEWS tests. This approach may therefore be an appropriate procedure for describing the long term performance of GRE pipes under any required combination of static, cyclic fatigue, hydrostatic and non-hydrostatic loading.
8
Najafi, Ali. "AXIAL COLLAPSE OF THIN-WALLED, MULTI-CORNER, SINGLE- AND MULTI-CELL TUBES." MSSTATE, 2009. http://sun.library.msstate.edu/ETD-db/theses/available/etd-06152009-125424/.
Full textAbstract:
Nonlinear explicit finite element (FE) simulations are used to study the axial collapse behavior of multi-corner. single- and multi-cell crush tubes under quasi-static and dynamic loading conditions. It is shown that the higher hardening modulus and yield stress increases the crush force and its resulting energy absorption. Moreover, the multi-cell tubes are found to have complicated collapse modes because of the geometrical complexity of the corner region unlike single-cell tubes. it was also shown that the stress wave propagation has a significant effect on the formation of crush modes in the tubes without imperfections whereas this effect can be ignored in tubes with imperfection or trigger mechanism. An analytical formula for the prediction of mean crush force of multi-corner multi-cell tubes is derived based on the super folding element theory. The analytical predictions for the mean crush force are found to be in good agreement with the FE solutions. Results also show a strong correlation between the cross-sectional geometry and the crash behavior with the method of connecting the inner to the outer walls having large influence on the energy absorption.
9
Abdel, Karim Nabil. "Optimisation multi-critères et multi-physique d'aérogénérateurs à aimants permanents à flux axial." Phd thesis, Université du Havre, 2008. http://tel.archives-ouvertes.fr/tel-00880881.
Full textAbstract:
Nous avons abordé, dans ce travail, la problématique posée par la conception des machines synchrones à aimants permanents à flux axial (MSAPFA) intégrées dans un système éolien de petite puissance. Les objectifs ont été de mettre au point une méthodologie générale de dimensionnement et le développement d'une méthode de modélisation de MSAPFAs par le calcul analytique des champs à partir du formalisme de Maxwell. Le défi de cette modélisation demeure toujours le compromis à faire entre temps de calcul et précision des résultats. Un outil d'analyse analytique issu de la résolution des équations de Maxwell par la méthode de séparation des variables dans les différentes régions de la machine, a donc été développé. Un modèle thermique nodale de la structure de MSAPFA est ensuite mis au point. La construction de ce modèle conduit à un système d'équations algébriques linéaires dont la solution nous renseigne sur la température aux nœuds sensibles de la machine. Ce modèle thermique est suivi par un modèle mécanique qui s'appuie sur les expressions proposées par le modèle de Young permettant ainsi de contrôler la déflexion des disques rotoriques en choisissant la bonne épaisseur de ces derniers à partir des efforts axiaux. Ces trois modèles constituent le modèle dimensionnant multi-physique de la machine. Pour l'optimisation non linéaire, un algorithme génétique d'optimisation multi-contrainte (GENOCOP) associé un algorithme d'optimisation multi-objectif (SPEA_II) sont choisis. C'est une méthode élitiste qui utilise une archive externe pour le stockage des solutions Pareto et effectue sa mise à jour au fur et à mesure des générations. Le couplage du SPEA_II avec le GENOCOP nous a permis de développer le code d'optimisation OPTIMSAP implémenté sous Matlab et dédié au dimensionnement des machines électriques. Le code d'optimisation OPTIMSAP développé a été enfin utilisé pour le dimensionnement d'un système aérogénérateur de 10 kW à base d'une machine synchrone à aimants permanents à flux axial couplée à un redresseur à diodes suivi d'un hacheur dévolteur et débitant sur un banc de batteries de 120V en parallèle avec une charge de consommation.
10
Lau, Hin Chung. "Development of a multi-axial load distribution measurement device." Thesis, University of Strathclyde, 2013. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=24966.
Full textAbstract:
Diabetic foot ulceration is a global health problem that often leads to amputation. While peripheral vascular disease and neuropathy are common risk factors for foot ulcers, excessive mechanical stress would directly cause the breakdown of plantar tissue. Once the skin is broken, many factors may contribute to defective healing and putting one at greater risk for ulceration. Clinical measurement of plantar pressure distribution, therefore, is commonly used to identify feet at risk of ulceration. However, plantar pressures are poor predictors and there is evidence that shear load is at least equally important in ulcer development. Compared to the numerous commercial systems available for plantar pressure distribution measurement, only a few experimental devices exist for shear distribution measurement. These are typically either too large for high spatial resolution measurement or expensive to manufacture, limiting their suitability for routine clinical use. The aim of this study was to develop a low-cost multi-axial load transducer array to measure the distribution of stress beneath the human foot during walking. A preexisting piezoelectric-based load transducer and several novel transducer designs using hydraulic, optoelectronic and magnetic-based technologies were manufactured and their performance relative to 29 criteria evaluated. The magnetic-based design was found to possess the highest performance (accuracy <3%RC, hysteresis <4%RC, non-linearity <2%RC) and physical characteristics (sensing area 10x10mm). Subsequently, an array consisting of 20 discrete magnetic-based transducers was constructed. In a single subject trial, the total shear load measured by the array was <2N of that measured by a Kistler® force platform. Although the array was capable of measuring biaxial shear load distribution, further work is required to expand the current design to measure load distribution beneath the entire plantar surface. Once realised, such a system has the potential to provide valuable biomechanical data that may help clinicians identify diabetic feet at risk of ulceration.
11
McFall, Bruce Daniel. "The Effects of Multi-Axial Loading on Adhesive Joints." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1515074800550415.
Full text
12
Maqsood, Muhammad Waqas. "Metal waveguides for multi-axial light guiding at nanometer scales." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/40001.
Full textAbstract:
A basic component of most optical systems is an optical waveguide. There has been an increased interest in nanofabricated optical waveguides that incorporate metal layers due to their fabrication compatibility with existing complimentary-metal-oxide-semiconductor (CMOS) processes and, their ability to sustain sub-wavelength confined electromagnetic modes. In this work, we have developed analytical techniques for designing metal waveguides that achieve tailored optical functionalities. The developed techniques are applied in two design examples which address contemporary problems related to waveguiding at sub-wavelength and nanometer scales.In the first example, we apply our analytical technique to optimize a bi-axial waveguide that can bend light at 90 degree, constructed from two uni-axial metal waveguides. The optimization procedure consists of mapping out wavevector values of the electromagnetic modes sustained by the two waveguides over the operational frequency range. The constituent materials and geometry of the waveguides are selected such that each waveguide sustains only one low-loss mode. The geometry of each of the waveguides is tailored in a way that the in-plane wavevector components for both waveguide modes are matched. The wavevector matching results in efficient coupling between the two modes, yielding predicted bending efficiencies over 90%. In the second example, we apply our analytical technique to optimize a bi-axial waveguide structure for coupling free-space light into surface plasmon polaritons (SPP), electromagnetic excitations bounded to the surface of a metal. We study the simple geometry consisting of a slit in a metal film, filled and covered with a dielectric. We break the configuration down into two uni-axial waveguide components. Using our approach, we optimize the materials and geometry of the slit so that wavevector matching is achieved between the light emanating from the slit and the adjacent SPP modes, yielding coupling efficiency over 68%.
13
Mailler, Philippe. "Rhéologie des membranes composites souples orthotropes sous chargement multi-axial." Lyon 1, 1996. http://www.theses.fr/1996LYO10143.
Full textAbstract:
La recherche aborde l'identification et la modelisation du comportement rheologique de composites souples (tissu de fibres de polyester enduit de polychlorure de vinyle) utilises sous forme de membranes pour l'architecture tensible. Le bilan bibliographique met en evidence l'absence de methodes de caracterisation de ces composites orthotropes sous sollicitations multiaxiales et l'absence de methodes previsionnelles pour decrire le comportement rheologique de ces materiaux et prevoir l'evolution du comportement en rigidite et a rupture en fonction du temps et de l'environnement. La premiere partie de la these est consacree a la conception et a la validation d'une machine d'essai de traction biaxiale regulee en charge et en deplacement. La methodologie experimentale porte d'une part sur des mesures de champs de deplacement par des techniques d'extensometrie optique et sur l'analyse des champs de contraintes corriges en fonction des geometries des eprouvettes et de l'anisotropie du materiau. L'etude du comportement rheologique et l'identification des fonctions fluage et relaxation des membranes est abordee en realisant des essais de fluage thermostimules et en appliquant le principe d'equivalence temps temperatures. Parallelement a partir de la mesure des proprietes viscoelastiques des fibres et de la matrice et de l'identification de modeles rheologiques ou de derivees fractionnaires, en appliquant des expressions previsionnelles de calcul des caracteristiques en rigidite des structures textiles considerees a l'echelle microscopique, nous proposons une formulation des fonctions fluage et relaxation. La validation de ces methodologies theorico-experimentales est faite par une confrontation avec des resultats de fluage obtenus dans des bases de temps et dans des conditions d'environnement reelles
14
Tan, Julian Lip Yi. "Multi-axial fracture behaviour of notched carbon-fibre/epoxy laminates." Thesis, University of Cambridge, 2015. https://www.repository.cam.ac.uk/handle/1810/247924.
Full textAbstract:
Carbon-fibre reinforced polymer (CFRP) laminates are widely used in various engineering applications, such as in race cars and aircrafts, because they are light, stiff and strong. They commonly contain stress raisers in the form of holes and notches (for mechanical joining methods, routing of pipes and cables etc.) and are also often subjected to complex combined multi-axial stress conditions during service. Yet their notched multi-axial fracture behaviour remains largely unexplored. This is the main contribution of the thesis. First, a novel loading fixture for applying a wide range of in-plane loading modes is developed based on the popular Arcan’s method. Termed the ‘modified Arcan rig’, it utilises friction gripping to transfer loads into tabbed specimens. This loading fixture is used to test centre-notched multi-directional CFRP laminates under different combinations of tension and shear stresses. Together with penetrant-enhanced X-ray CT and laminate de-ply, the fracture behaviour of quasi-isotropic CFRP specimens is investigated for the following loading modes: pure tension, pure compression, in-plane shear, and combined tension and shear. Two notch geometries (sharp notch and circular hole) are investigated to allow for an assessment of the role of stress concentration upon strength and damage development to be performed. Three distinct fracture modes are observed in a tensile/compressive-shear stress space (termed Mechanism A, Mechanism B and Mechanism C). It is observed that quasi-isotropic specimens with a central sharp notch are consistently stronger than equivalent specimens with a central circular hole (for all stress states investigated). An underlying micromechanical explanation concerning the effects of damage upon strength is proposed. Second, a finite element (FE) model is developed using the commercial FE program, Abaqus FEA to simulate the observed progressive damage and failure in the quasi-isotropic specimens. The FE model employs independent material property data as inputs. Overall, good correlation between the simulations and the experiments is obtained, validating the FE strategy. The capabilities of the model are extended to predict the notched fracture behaviour of the specimens under combined compression and shear loading, for which experimental work has not been done by the author, but for which literature data exists. Finally, the effect of laminate lay-up upon the notched multi-axial fracture behaviour of the CFRP specimens is explored by considering a 0° ply-dominated lay-up, a ±45° ply-dominated lay-up and a cross-ply lay-up, alongside the quasi-isotropic lay-up. Experiments reveal that all lay-ups exhibit Mechanisms A, B and C. However, the extent of damage in each Mechanism as well as the regime in which each Mechanism operates in (in the failure envelopes) strongly depend on the lay-up of the specimen. As expected, the tensile strengths and compressive strengths increase with the proportion of 0° plies. Surprisingly, the shear strengths do not scale with the proportion of ±45° plies; the specimen geometry and material orthotropy are attributed as reasons for this. In contrast to the case of the quasi-isotropic lay-up, the extent of subcritical damage induced by the circular hole is not always lower than that induced by the sharp notch for the other lay-ups. The difference in the extent of damage between both notch geometries is reflected in the notched strengths of the lay-up in question. These experimental observations are adequately predicted by the FE strategy, which further validates it as a reliable predictive tool for composite fracture.
15
Chung, Timothy Kwang-Joon. "Study of multi-axial failure properties of planar biological soft tissues." Diss., University of Iowa, 2017. https://ir.uiowa.edu/etd/5732.
Full textAbstract:
Rupture of abdominal aortic aneurysm (AAA) is a catastrophic event that leads to high mortality and morbidity in patients. The primary causes associated with aneurysm rupture remain poorly understood despite rigorous investigations. Reports have shown that AAA that went on to rupture or present ruptured had higher peak wall tension (stress resultant) than those that did not go on to rupture or present ruptured. Studies investigating the material strength of ruptured AAA and unruptured AAA revealed that the uniaxial failure strength in ruptured AAA is no different on average than unruptured AAA. However, it is poorly understood whether uniaxial failure properties are reliable as they are not indicative of the manner in which failure occurs in biological soft tissues. Multi-axial failure properties using a bubble inflation test (BIT) have been implemented by various groups but have not been directly compared against uniaxial failure properties. The current study seeks to develop a BIT apparatus, to compare multi-axial and uniaxial failure properties of fibrous anisotropic biological soft tissues (bovine aorta) and non-fibrous isotropic molded silicon, and to perform a survey of computational indices at the rupture sites of four ruptured AAA. Two versions of the BIT apparatus were developed: a manual that was developed allows for a large amount of failure properties to be extracted that can identify localized weaknesses. It was found that circumferentially oriented multi-axial failure was correlated with longitudinally oriented uniaxial failure properties, however, for oblique oriented multi-axial failure the correlation decreased. Utilizing the insights gained from the multi-axial experiments it was determined that the failure properties used in the computational study with the data from Raghavan et al. were appropriate for use in retrospective assessment of the rupture site in four ruptured AAA computational models. Although the study was inconclusive in finding causation, the rupture line of each aneurysm had indices ranging between the third quartile and peak values for tension to failure tension ratio, nodal displacement magnitude, strain energy per unit volume and strain energy per unit surface area. This study provides a framework for interrogating failure properties at a higher density of measurement and a heterogeneous computational model that has the potential to predict AAA rupture in the future.
16
Kulkarni, Prakash K. "Identification and contouring control of multi-axial machine tool feed drives /." The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487325740717862.
Full text
17
Ohka, Masahiro, Yasuhiro Sawamoto, Shiho Matsukawa, Tetsu Miyaoka, and Yasunaga Mitsuya. "Parallel Type Two-axial Actuator Controlled by a Multi-layered Neural Network." IEEE, 2007. http://hdl.handle.net/2237/9510.
Full text
18
Hou, Bing. "Dynamic enhancement and multi-axial behavior of honeycombs under combined shear-compression." Phd thesis, École normale supérieure de Cachan - ENS Cachan, 2011. http://tel.archives-ouvertes.fr/tel-00675750.
Full textAbstract:
The study consists mainly of two parts. The first part is related to the dynamic strength enhancement of honeycombs under uniaxial compression. We firstly study numerically this particular phenomenon of thin-walled structure by using three micro-size FE models and this allows us to reveal the role played by lateral inertia in the dynamic enhancement. Further more, the dynamic enhancement of a series of honeycombs with different cell-size, cell-wall thickness and base material is studied experimentally and the influence of these geometric parameters and the base material on honeycomb strength as well as the dynamic enhancement rate is investigated. The second part of this study concerns the biaxial behavior of honeycombs under combined shear-compression. We firstly present a combined dynamic shear-compression loading device basing on a large-diameter Nylon Split Hopkinson Pressure Bar system. Then, a series of quasi-static and dynamic experiments on an aluminium honeycomb is performed with loading angles ranging from 0o to 60o (part of shear more and more important). It shows a strong effect of the additional shear loading to honeycomb overall strength. A notable strength enhancement under impact loading is observed for all the honeycomby b specimens. Images captured during tests permit for the determination of the two co-existing deforming patterns under combined shear-compression. Finally, the combined shear-compression tests on honeycombs are reproduced by a numerical virtual model and the separated normal and shear behaviors of honeycombs under combined shear-compression are obtained. A crushing envelope in normal strength vs. shear strength plane was obtained on the basis of these simulations, which shows an isotropic expansion behavior from the quasi-static loading to the dynamic loading.
19
Van, Antwerpen Werner. "Multi-quadrant performance simulation for subsonic axial flow compressors / Werner van Antwerpen." Thesis, North-West University, 2007. http://hdl.handle.net/10394/1271.
Full textAbstract:
The emergence of closed-loop Brayton cycle power plants, such as the PBMR, resulted in the
need to simulate start-up transients for industrial multi-stage axial flow compressors operating at
subsonic conditions. This implies that the delivery pressure and power requirements must be
predicted for different mass flow rates and rotational speeds while operating in the first and fourth
quadrants on the compressor performance charts.
Therefore, an analytical performance prediction model for subsonic multi-stage axial flow
compressors had to be developed that can be integrated into a generic network analysis software
code such as Flownex. For this purpose, performance calculations based on one-dimensional
mean-line analysis demonstrated good accuracy, provided that the correct models for losses,
incidence and deviation are used. Such a model is therefore the focus of this study.
A preliminary analytical performance prediction code, with the capability of interchanging between
different deviation and loss models is presented. Reasonably complex loss models are
integrated in association with the correct incidence and deviation models in a software package
called "Engineering Equation Solver" (EES). The total pressure loss calculations are based on a
superposition of theoretically separable loss components that include the following: blade profile
losses, secondary losses and annulus losses. The fundamental conservation equations for
mass, momentum and energy for compressible "rotating pipe" flow were implemented into the
performance prediction code. Performance prediction models were validated against
experimental data and evaluated according to their ease of implementation. Verification was
done by comparing simulation results with experimental work done by Von Backstrom. This
includes a calculation to determine the uncertainty in the experimental results.
Furthermore, since the conventional definition of isentropic efficiency breaks down at the
boundaries of quadrants on the performance charts, a new non-dimensional power formulation is
presented that allows for the calculation of the compressor power in all of the relevant quadrants.
Good comparison was found between simulation results and measurements in the first and fourth
quadrant of operation.Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2007.
20
Blanvillain, Emmanuel 1979. "Dynamic stability analysis of a multi-stage axial compressor with design implications." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/82255.
Full text
21
BELHABIB, MUSTAPHA. "Aerodynamique tridimensionnelle instationnaire dans un compresseur axial multi-etages a basse vitesse." Paris 6, 1995. http://www.theses.fr/1995PA066255.
Full textAbstract:
Il s'agit dans cette these, d'une etude experimentale des caracteristiques de l'ecoulement dans un compresseur axial a quatre etages. Des mesures tridimensionnelles instationnaires tres fines ont ete realisees au niveau des etages 1, 3 et 4. Deux methodes de traitement du signal ont ete developpees pour exploiter correctement la quantite importante des resultats des mesures instationnaires. La premiere technique consiste a extraire la composante periodique des signaux bruts et la seconde permet de generaliser la periodicite chorochronique a l'environnement multi-etages. Les signaux temporels des grandeurs physiques mesurees au premier etage montrent la presence de fortes interactions entre la roue mobile de cet etage et celle de l'etage aval. Elles se traduisent par des fluctuations supplementaires de l'ecoulement dont les frequences sont liees a celles des passages des deux roues en interaction. L'application de la periodicite chorochronique dans le compresseur a permis d'observer egalement, des interactions instantanees entre une roue fixe et une roue mobile voisine. Le comportement de la couche limite aux parois d'un redresseur a fait l'objet de mesures tres fines au moyen d'une jauge a films minces. Celles ci montrent que la couche limite est constituee de trois zones. La premiere region situee pres du bord d'attaque du redresseur est affectee par les sillages amont. La deuxieme partie est observee pres du bord de fuite. Elle est le siege des effets potentiels du rotor aval. La troisieme region se trouve entre les deux premieres. On y rencontre a la fois une trace des sillages amont et la presence des effets potentiels de la roue mobile aval. On s'est interesse egalement durant cette these, aux effets d'un soutirage entre les etages 3 et 4 sur les performances energetique du compresseur. Les resultats obtenus montrent que le prelevement d'air entre deux etages affecte a la fois le debit a l'entree de la machine, le rapport global de pression et perturbe fortement le champ de l'ecoulement pres du carter a la sortie des rotors des etages concernes. Outre la comprehension des phenomenes physiques existants dans le compresseur, les resultats des mesures constituent une base importante de donnees pour la validation de codes de calcul
22
Scott-Emuakpor, Onome Ejaro. "Development of a novel energy-based method for multi-axial fatigue strength assessment." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1196280356.
Full text
23
Escuret, Jean-Francois. "The prediction and active control of surge in multi-stage axial-flow compressors." Thesis, Cranfield University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333133.
Full text
24
Feulner, Matthew Roger 1967. "Modeling and control of rotating stall in high speed multi-stage axial compressors." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/11941.
Full text
25
Tsantrizos, Anthony. "Internal deformation and strain of human lumbar intervertebral discs subjected to multi-axial loads." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=86056.
Full textAbstract:
Morphological and clinical signs of lumbar intervertebral disc disruption are pronounced in the posterior and postero-lateral inner annulus fibrosus. The regional intervertebral disc predisposition to disruption suggests that intradiscal stresses and strains may also be region specific and possibly initiate the disruption. Quantitative data describing intradiscal deformations have been limited to the mid-sagittal plane using techniques that compromise the intervertebral disc integrity. No experimental study has quantified intradiscal strain patterns. The initial objectives of the present work were to use experimental cadaveric methods and finite element techniques to develop and validate methods of measuring intradiscal deformations and strains along the complete mid-transversal plane using a fine wire grid.Subsequently, these methods were used to quantify intradiscal deformations and strains in healthy and degenerated intervertebral discs during sub-maximal loads. Eighteen healthy and degenerated intervertebral discs were subjected with wires placed within and beads glued along their mid-traversal plane surface, to compression, extension, flexion and lateral bending. Cramo-caudal radiographs at unloaded and loaded steps documented wire and bead positions. Intradiscal nucleus pulposus displacements, circumferential, radial and shear strains in the annulus fibrosus and transitional zone under load were compared among all anatomical regions and between healthy and degenerated intervertebral discs.
The methods develop to estimate intradiscal strains from intradiscal wire intersection displacements demonstrated a relative overall accuracy of 2.9% (i.e. percent error from theoretical estimations). Generally, intradiscal circumferential and radial strains decreased from the transitional zone to the annulus fibrosus and increased at the side of bending during all bending conditions. Circumferential and radial strain peaks were observed in the postero-lateral regions even in healthy intervertebral discs during extension and lateral bending. Shear strains were generally uniform within the healthy intervertebral disc. Degeneration significantly increased intradiscal circumferential, radial and shear strains during all bending conditions (particularly in the postero-lateral regions). The increased nucleus pulposus migration in degenerative intervertebral discs appeared to have caused the increases in circumferential and radial strains and to some extent perhaps increases in shears strains.
The inner postero-lateral annulus fibrosus is predisposed to excessive normal circumferential and radial strains early on which coincide with morphological changes observed in the same regions. This observation suggests a predisposition to failure likely due to an inability of resisting delaminating normal strains. Furthermore, the increased nucleus pulposus migration observed in degenerated intervertebral discs appears to shift the pivot point during bending movements more posterior, which consequently forces the postero-lateral regions to consistently experience higher circumferential and radial strains. These effects may contribute to the segmental instability observed in degenerated motion segments prior to intervertebral disc failure.
26
Martinez, Alejandro. "Multi-scale studies of particulate-continuum interface systems under axial and torsional loading conditions." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54423.
Full textAbstract:
The study of the shear behavior of particulate (soil) – continuum (man-made material) interfaces has received significant attention during the last three decades. The historical belief that the particulate – continuum interface represents the weak link in most geotechnical systems has been shown to be incorrect for many situations. Namely, prescribing properties of the continuum material, such as its surface roughness and hardness, can result in interface strengths that are equal to the contacting soil mass internal shear strength. This research expands the engineering implications of these findings by studying the response of interface systems in different loading conditions. Specifically, the axial and torsional shear modes are studied in detail. Throughout this thesis it is shown that taking an engineering approach to design the loading conditions induced to the interface system can result in interface strengths that exceed the previously considered limiting shear strength of the contacting soil.
Fundamental experimental and numerical studies on specimens of different types of sand subjected to torsional and axial interface shear highlighted the inherent differences of these processes. Specifically, micro-scale soil deformation measurements showed that torsional shear induces larger soil deformations as compared to axial shear, as well as complex volume-change tendencies consisting of dilation and contraction in the primary and secondary shear zones. Studies on the global response of torsional and axial shear tests showed that they are affected differently by soil properties such as particle angularity and roughness. This difference in global behavior highlights the benefits of making systems that transfer load to the contacting soil in different manners available for use in geotechnical engineering. Discrete Element Modeling (DEM) simulations allowed for internal information of the specimens to be studied, such as their fabric and shear-induced loading conditions. These findings allowed for the development of links between the measured micro-scale behavior and the observed global-scale response.
The understanding of the behavior of torsional and axial interfaces has allowed provides a framework for the development of enhanced geotechnical systems and applications. The global response of torsional shear found to induce larger cyclic contractive tendencies within the contacting soil mass. Therefore, this shear mode is more desirable than the conventional axial shear for the study of phenomena that depend on soil contractive behavior, such as liquefaction. A study on the influence of surface roughness form revealed that surfaces with periodic profiles of protruding elements that prevent clogging are capable of mobilizing interface friction angles that are 20 to 60% larger than the soil friction angle. These findings have direct implications in engineering design since their implementation can result in more resilient and sustainable geotechnical systems.
27
Swift, William James. "Modelling of losses in multi-stage axial compressors with subsonic conditions / William James Swift." Thesis, North-West University, 2003. http://hdl.handle.net/10394/431.
Full textAbstract:
The need was identified to develop an analytical performance prediction code for subsonic multistage
axial compressors that can be included in network analysis software. It was found that
performance calculations based on an elementary one-dimensional meanline prediction method
could achieve remarkable accuracy, provided that sound models are used for the losses, deviation
and the onset of rotating stall. Consequently, this study focuses on gaining more expertise on the
modelling of losses in such compressors through investigating the mechanisms responsible, the
methods of predicting them, their implementation and possible usage.
Internal losses are seen as mechanisms that increase the entropy of the working fluid through the
compressor and it was found that, at a fundamental level, all internal losses are a direct result of
viscous shearing that occurs wherever there are velocity gradients. Usually the methodology
employed to predict the magnitudes of these mechanisms uses theoretically separable loss
components, ignoring the mechanisms with negligible velocity gradients. For this study these
components were presented as: Blade profile losses, endwall losses including tip leakage and
secondary losses, part span shroud losses, other losses, losses due to high subsonic Mach numbers
and incidence loss. A preliminary performance prediction code, with the capability of
interchanging of the different loss models, is presented. Verification was done by comparing the
results with those predicted by a commercial software package and the loss models were
evaluated according to their ease of implementation and deviation from the predictions of the
commercial package. Conclusions were made about the sensitivity of performance prediction to
using the different loss models.
Furthermore, the combination of loss models that include the most parameters and gave the best
comparison to the commercial software predictions was selected in the code to perform
parametric studies of the loss parameters on stage efficiency. This was done to illustrate the
ability of the code for performing such studies to be used as an aid in understanding compressor
design and performance or for basic optimization problems.
It can therefore be recommended that the preliminary code can be implemented in an engineering
tool or network analysis software. This may however require further verification, with a broader
spectrum of test cases, for increased confidence as well as further study regarding aspects like
multi-stage annulus blockage and deviationThesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2004.
28
Crevel, Flore. "Simulation numérique de l'écoulement en régime de pompage dans un compresseur axial multi-étage." Phd thesis, Ecole Centrale de Lyon, 2013. http://tel.archives-ouvertes.fr/tel-00929734.
Full textAbstract:
Dans le contexte économique et environnemental actuel, la prochaine génération de moteurs d'avion devra offrir opérabilité, compacité et hauts rendements. Les compresseurs demeurent une des pièces critiques de ces moteurs, et leur conception un challenge. À débit réduit, leur plage de fonctionnement est contrainte par la limite de pompage, phénomène hautement instable et dangereux. À ce jour, peu d'études expérimentales sur un compresseur en situation de pompage ont été réalisées, étant donné le danger inhérent pour les installations. Dans ce cadre, la simulation numérique peut apporter des informations sur le développement des instabilités aérodynamiques et aider à la prévision de la limite de pompage. L'objectif du travail présenté dans cette thèse est de mettre en place une méthode afin de simuler numériquement l'entrée en pompage et un cycle complet de l'instabilité avec le code elsA. Le cas test retenu est le compresseur de recherche axial multi-étage CREATE dessiné par Snecma, et étudié expérimentalement par le LMFA. Des études antérieures ont montré le rôle joué par les volumes entourant le compresseur ; l'originalité de cette étude réside donc dans l'inclusion des volumes du banc d'essai dans la simulation du compresseur. Une des difficultés inhérentes à la simulation de ces instabilités est leur temps caractéristique, qui représente plus d'une centaine de rotations de la machine. Le calcul a donc nécessité le recours à une approche massivement parallèle ; environ un million d'heures CPU ont été utilisées pour décrire le cycle. Enfin, compte tenu du retournement de l'écoulement dans le compresseur, les conditions aux limites ont été modifiées pour pouvoir s'adapter aux changements de sens de l'écoulement. La simulation a permis de décrire l'entrée en pompage et un cycle complet de l'instabilité. La comparaison avec les données expérimentales montre que les caractéristiques du cycle sont correctement prédites (phénomènes physiques précurseurs de l'instabilité, durée du cycle..). En parallèle, une étude acoustique a été menée afin de mettre en évidence les modes propres du banc d'essai. L'analyse de ces résultats a notamment montré le rôle de l'acoustique dans le déclenchement du pompage. Les différentes phases du cycle de pompage sont ensuite étudiées, et caractérisées (déclenchement, débit inversé, récupération et recompression). Ce travail a généré une base de données qui permet de mieux comprendre les instabilités qui se développent dans ce type de machine. À terme, ces résultats pourront être utilisés pour élaborer et valider des modélisations du phénomène de pompage moins coûteuses, pouvant intervenir dans un cycle de conception.
29
Baker, Jonathan D. "Analysis of the sensitivity of multi-stage axial compressors to fouling at various stages." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02Sep%5FBaker.pdf.
Full text
30
Austin, Philip Daniel. "International Delphi study to assess the need for multiaxial criteria in diagnosis and management of functional gastrointestinal disorders." Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/15842.
Full textAbstract:
Purpose: While there are diagnostic criteria for functional gastrointestinal disorders (FGIDs), their evaluation is challenging. This is because criteria are based on symptoms, and the underlying pathophysiology is not clear; as such, there are no gold standard tests. Diagnosis is further challenged by considerable clinical overlap between different FGIDs as well as other organic diseases, while many people with FGIDs have more anxiety and depression than healthy individuals. I hypothesised that assessment of separate components of FGIDs that also indicate their effect on the patient could improve diagnosis. My aim was to investigate the evolution of opinions from experts involved in the development of FGID diagnostic criteria on the proposal for the development of multiaxial assessment criteria (MAC) for FGIDs. Methods: I conducted a web-based Delphi study using a group of purposively sampled experts identified from committees of the Rome Foundation and the International Foundation for Gastrointestinal Disorders. From a systematic search of relevant articles, I generated132 items that were sent to experts as a first round survey. The items assessed risk and contributing factors, the therapeutic relationship, areas of evaluation and the advantages and disadvantages of multiaxial assessment. Consensus on an item was reached when 75% of experts indicated that they agreed or strongly agreed with the statement. Key results: 36 of 68 eligible participants (52%) responded to the first round. Consensus was reached on 96 items. Using participant feedback, thematic analysis was used to generate 33 additional items for round two. Thirty-one of 36 participants (86%) replied to rounds two and three. In round two, 19 items gained consensus, and in round three, nine items gained consensus. Participants agreed that multiaxial assessment was needed, using a systematic approach to establish the physiological and psychosocial components of FGIDs. Participants were unable to agree on the importance of physical risk factors such as previous surgery and genetic association. Overall, 124 of the 167 items achieved consensus. Conclusion and inferences: The key finding from my study shows that experts agree that multiaxial assessment of FGIDs is needed. I also identified expert agreement on the consideration of psychological risk factors and the importance of the impact of FGID symptoms on daily life. Findings also show that experts disagreed on the impact of physical risk factors, socioeconomic status and spirituality on people with FGIDs. While experts could not agree on genetic and gender-based risk factors, they considered that these areas are important and require further research.
31
Esumi, Kazuya, Masahiro Ohka, Yasuhiro Sawamoto, Shiho Matsukawa, and Tetsu Miyaoka. "Improvement of a Parallel Type Two-axial Actuator Controlled by a Multi-layered Neural Network." IEEE, 2008. http://hdl.handle.net/2237/12135.
Full text
32
Rameau, Jean-Michel. "Multi-axial damage and failure models for thick composite lugs under static and cyclic loading." Thesis, KTH, Lättkonstruktioner, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-185174.
Full textAbstract:
The thesis deals with quasi-static and fatigue simulations of thick composite lugs subjected to three-dimensional stress states. This includes damage prediction of hybrid laminates made of GRFP and CRFP containing unidirectional and woven fabric plies.Focus lies on the development of a progressive damage model in fatigue which accounts for sti˙ness and strength degra-dations. Two methods based on Puck’s failure criterion are proposed to predict failure of unidirectional plies: one for plane stress analysis and and the other which takes out-of-plane damage into account.Virtual testing in FEM is conducted in quasi-static and fatigue analysis on thick composite lugs subjected to uni-axial loading. Damage, strength and life predictions are then compared with experimental results to validate the numerical models under investigations.In der vorliegenden Arbeit wird die Berechnung der Festig-keit von dickwandigen Lochleibungslaminaten im Faserver-bundwerksto˙en unter dreidimensionalen Spannungszustän-den untersucht. Nichtlineare Materialverhalten von Hybrid-laminaten in CFK und GFK werden für Unidirektionalfa-serlagen und Gewebelagen berücksichtigt.Der Schwerpunkt liegt auf der Entwicklung von progressi-ven Versagensmodellen unter der Berüsichtigung von Rest-festigkeit und Reststeifigkeit des Materials. Zwei Modelli-erungsmethoden nach Puck-Kriterium zur Vorhersage des Versagens in UD-Lagen werden vorgeschlagen: eine Degra-dierungstechnik für ebene Spannungszustände und ein me-hrachsiges Modell.Numerische Simulationen mit der Finite-Elemente-Methode werden in Statik- und Ermüdungsanalyse an dickwandigen Lochleibungslaminaten unter einachsiger Belastung durch-geführt. Beschädigungen, Festigkeiten und Ermüdungsle-bensdauer werden dann mit experimentiellen Daten ver-glichen, um die numerischen Methoden zu validieren.
33
Gill, Andrew. "Four quadrant axial flow compressor performance." Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/20075.
Full textAbstract:
Thesis (PhD)--Stellenbosch University, 2012.ENGLISH ABSTRACT: The aims of this thesis are to identify all possible modes of operaton for a multi-stage axial flow compressor; then to characterise the performance, attempt to numerically model operation, and determine the main flow field features for each mode. Four quadrant axial flow compressor operation occurs when the direction of flow through the compressor or the sign of the pressure difference across the compressor reverses, or any combination of these. Depending on the direction of rotation of the compressor, six modes of operation are possible in the four quadrants of the performance map. The rotor rotates in the design direction for three modes, and in the opposite direction for the other three. The stationary-rotor pressure characteristic is S-shaped and passes through the second and fourth quadrants. A three-stage axial flow compressor operating in the incompressible flow regime was used for the experimental investigation. Flow through the compressor was reversed or augmented by means of an auxiliary axial flow fan. Compressor performance was measured by means of static pressure tappings, a turbine anemometer calibrated to measure forward and reversed volumetric flow and a load cell for torque measurement. The inter-blade row flow fields were measured with pneumatic probes and 50 μm cylindrical hot film probes. Three dimensional single blade-passage Navier-Stokes simulations were performed using the Numeca FineTurbo package. Steady state simulations used a mixing plane approach. A nonlinear harmonic approximation was used for time-unsteady simulations. Unstalled first quadrant operation was unremarkable, and good agreement was obtained between experimental and numerical data. A single stall cell was detected experimentally during stalled operation, which was not modelled numerically. In the fourth quadrant for positive rotation, (windmilling), the compressor acts as an inefficient turbine. Flow separates from the pressure surface of the blade, rendering the steady-state mixing plane approach unsuitable. The performance characteristic curves for second quadrant for positive rotation, are discontinuous with those of first quadrant operation. The temperature rise in the working fluid is significantly higher than at design point. Periodic flow structures occurring across two blade passages were detected at all flow coefficients investigated, invalidating numerical modelling assumptions. Better agreement was obtained between experimental and numerical data from a case found in literature. If the compressor operates as a compressor in reverse (third quadrant operation), significant separation occurs on the pressure surface of all blades, and flow conditions resemble severe first quadrant stall. Separation becomes less severe at larger flow rates, allowing numerical simulation, though this is sensitive to the initial flow field. In the the part of the second quadrant, where the compressor rotates in reverse, it operates as a turbine. The blade angles and the direction of curvature match the flow angles and turning well, leading to high turbine efficiencies. Numerical simulations yielded good agreement with measured results, but were again sensitive to the initial flow field. Fourth quadrant operation with negative rotation occurs when flow is forced through the compressor in the design direction. Large separation bubbles are attached to the pressure surfaces of rotor and stator blades, so virtually all throughflow occurs near the hub and casing
AFRIKAANSE OPSOMMING: Die doelwitte van hierdie tesis is om al die moontlike werkmodusse vir ’n bestaande multi-stadium aksiaalvloei kompressor uit te ken; om dan die gedrag te gekarakteriseer, ’n poging aan te wend om die werking numeries te modelleer, en die belangrikste vloeiveldkenmerke vir elke modus te bepaal. Vier-kwadrant aksiaalvloei kompressor werking vind plaas as die rigting van die vloei deur die kompressor, of die teken van die drukverskil oor die kompressor omkeer, of enige kombinasie daarvan. Afhangende van die rigting van rotasie van die kompressor is ses operasionele modusse moontlik in die vier kwadrante van die kompressorkaart. Die rotor draai in die ontwerprigting vir drie van die modes, en in die teenoorgestelde rigting vir die ander drie. Die stilstaande-rotor drukkarakteristiek is S-vormig gaan deur die tweede en vierde kwadrante. ’n Drie-stadium onsamedrukbare vloei aksiaalvloei kompressor is vir die eksperimentele ondersoek gebruik. Vloei deur die kompressor is omgekeer of aangehelp deur middel van ’n aksiaalvloei hulpwaaier. Kompressor werking is gemeet deur middel van statiese druk meetpunte in die omhulsel, ’n turbine anemometer wat gekalibreer is om vorentoe en omgekeerde volumetriese vloei te meet, en ’n lassel vir wringmoment meting. Interlemryvloeivelde is opgemeet met pneumatiese sensors en 50-μm silindriese warm film sensors. Drie-dimensionele Navier-Stokes simulasies is uitgevoer vir ’n enkele lem van elke lemry, met behulp van die Numeca FineTurbo sagtewarepakket. ’n Mengvlakbenadering is gebruik vir bestendige toestand simulasies, terwyl ’n nie-linere harmoniese benadering gebruik is vir die tyd-afhanklike simulasies. Ongestaakte eerste kwadrant werking was alledaags, en goeie ooreenkoms is gevind tussen die eksperimentele en numeriese data. ’n Enkele staak-sel is eksperimenteel ontdek tydens gestaakte werking. Gestaakte werking is nie numeries gemodelleer nie. In die vierde kwadrant vir positiewe rotasie, (”windmeulwerking”), werk die kompressor as ’n ondoeltreffende turbine. Vloei-wegbrekinging op die lem drukoppervlaktes maak die bestendige toestand mengvlakbenadering ongeskik. In die kenlyne vir tweede kwadrant positiewe rotasie, is daar ’n diskontinu¨ıteit in die prestasie karakteristiekkrommes vir die eerste en tweede kwadrant werking. Die temperatuurstyging in die werk- vloeistof is beduidend ho¨er as as by die ontwerppunt. Periodiese vloeistrukture wat oor twee lemme plaasvind is gevind by alle vloei ko¨effisi¨ente wat ondersoek is, en dit maak die numeriese modellering aannames ongeldig. Beter ooreenkoms tussen die eksperimentele en numeriese data iss verkry met ’n geval wat uit die literatuur gevind is. Indien die kompressor werk as ’n kompressor in omgekeerde (derde kwadrant weking), vind beduidende wegbreking op die drukoppervlak van al die lemme plaas, wat lyk soos ernstige gestaakte eerste kwadrant werking. Die vloeiskeiding raak minder ernstig by ’n groter vloeitempo, wat numeriese nabootsing toelaat, maar die nabootsings is sensitief vir die aanvanklike vloeiveld. In die tweede kwadrant, by omgekeerde rotasie, werk die kompressor as ’n turbine. Die lemhoeke en die rigting van lemkromming stem ooreen met die vloeihoeke en verwringing, wat lei tot ho¨er turbine doeltreffendheid. Numeriese nabootsings stem goed ooreen met gemete resultate, maar is weereens sensitief vir die keuse van die aanvanklike vloeiveld. Vierde kwadrant werking met negatiewe rotasie vind plaas wanneer die lug gedwing word om deur die kompressor in die ontwerprigting te vloei. Groot skeidingborrels sit vas aan die drukoppervlaktes van alle lemme, sodat meeste deurvloei naby die naaf en die omhulsel plaas vind.
34
Zhang, Jie. "Multi-axial damage model for numerical simulation of metal forming processes using 3D adaptive remeshing procedure." Troyes, 2013. http://www.theses.fr/2013TROY0005.
Full textAbstract:
Dans ce travail, nous avons d’abord développé un modèle thermo-élasto-viscoplastique fortement couplé à l’endommagement dans différents états de contraintes pour simuler divers procédés de mise en forme. Il est basé sur un paramètre d'état de contrainte dépendant de l'angle de Lode et de la triaxialité pour tenir compte des chargements multiaxiaux de compression, de tension et de cisaillement. Le modèle proposé est couplé à l’écrouissage plastique de Johnson-Cook et implémenté dans la plate-forme de simulation ABAQUS pour simuler virtuellement le formage par déformation plastique des métaux et les procédés d'usinage à différentes températures et vitesse de déformation. Un outil de remaillage adaptatif 3D « OPTIFORM » est construit pour contrôler dynamiquement les discrétisations spatio-temporels des domaines déformables en tenant compte des grandes variations géométriques et physiques des procédés. Des scripts python sont mis au point pour interfacer ABAQUS avec OPTIFORM soit pour identifier les propriétés des matériaux par méthode inverse soit pour simuler divers procédés de forgeage, de découpage de tôles minces et de couple orthogonal. La méthodologie proposée est validée en étudiant les effets des différents paramètres technologiques et procédé sur la formabilité et la qualité des produits finauxIn this work, we firstly developed a model that can accurately predict the thermo-elastoviscoplastic and damage behaviour in different stress states for metal forming. It can adapt to multiaxial loadings conditions like compression, tension and shear state based on a stress state parameter that considers synthetically triaxiality and Lode angle. For the coupling of John-Cook hardening law, the proposed constitutive equations can virtually simulate metal forming and machining processes in different temperature and strain rate conditions. An advanced 3D adaptive remeshing « OPTIFORM » procedure is developed in order to control dynamically the finite element discretizations at each time of areas following with the changing of geometry and physical fields. Python scripts are developed to interface with ABAQUS and OPTIFORM mesher in order to identify the material properties by inverse method and to simulate numerically various processes of forging, sheet metal cutting and orthogonal cutting. The proposed methodology is validated by studying the effects of various parameters on the process formability and final products quality
35
Löfstrand, Grip Rasmus. "A mechanical model of an axial piston machine." Licentiate thesis, KTH, Machine Design (Div.), 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10948.
Full textAbstract:
A mechanical model of an axial piston-type machine with a so-called wobble plate and Z-shaft mechanism is presented. The overall aim is to design and construct an oil-free piston expander demonstrator as a first step to realizing an advanced and compact small-scale steam engine system. The benefits of a small steam engine are negligible NOx emissions (due to continuous, low-temperature combustion), no gearbox needed, fuel flexibility (e.g., can run on biofuel and solar), high part-load efficiency, and low noise. Piston expanders, compared with turbines or clearance-sealed rotary displacement machines, have higher mechanical losses but lower leakage losses, much better part-load efficiency, and for many applications a more favourable (i.e., lower) speed. A piston expander is thus feasible for directly propelling small systems in the vehicular power range. An axial piston machine with minimized contact pressures and sliding velocities, and with properly selected construction materials for steam/water lubrication, should enable completely oil-free operation. An oil-free piston machine also has potential for other applications, for example, as a refrigerant (e.g., CO2) expander in a low-temperature Rankine cycle or as a refrigerant compressor.
An analytical rigid-body kinematics and inverse dynamics model of the machine is presented. The kinematical analysis generates the resulting motion of the integral parts of the machine, fully parameterized. Inverse dynamics is applied when the system motion is completely known, and the method yields required external and internal forces and torques. The analytical model made use of the “Sophia” plug-in developed by Lesser for the simple derivation of rotational matrices relating different coordinate systems and for vector differentiation. Numerical solutions were computed in MATLAB. The results indicate a large load bearing in the conical contact surface between the mechanism’s wobble plate and engine block. The lateral force between piston and cylinder is small compared with that of a comparable machine with a conventional crank mechanism.
This study aims to predict contact loads and sliding velocities in the component interfaces. Such data are needed for bearing and component dimensioning and for selecting materials and coatings. Predicted contact loads together with contact geometries can also be used as input for tribological rig testing. Results from the model have been used to dimension the integral parts, bearings and materials of a physical demonstrator of the super-critical steam expander application as well as in component design and concept studies.
36
Akiki, Paul. "Conception multi-physique de machines électriques à flux radial et axial pour des applications à entraînement direct." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLC055/document.
Full textAbstract:
Les travaux présentés dans cette thèse portent sur la modélisation et l’optimisation de machines électriques pour des applications à entraînement direct. Ils s’inscrivent dans un contexte de réduction de l’utilisation des aimants en terres rares et d’amélioration du rendement énergétique. Un état de l’art des machines électriques est réalisé et l’accent est mis sur les machines à flux radial et axial pour les applications à fort couple et basse vitesse. Une classification est établie visant à identifier les structures intéressantes et innovantes. L’étude de la machine radiale est d’abord réalisée. Une étude comparative de différentes machines issues de l’étude bibliographique est effectuée. Cette étude a permis de choisir une structure originale à bobinage concentré sur dents et aimants en multi-V. Dans le but de calculer les performances du moteur avec un temps de calcul réduit, une modélisation analytique multi-physique de la structure est réalisée. Un premier dimensionnement de la machine a conduit à la définition d’un prototype qui a servi à la validation expérimentale du modèle multi-physique. Une approche de conception par optimisation multi-objectifs est adoptée pour obtenir les machines optimales répondant à un cahier des charges industriel. La suite de l’étude concerne une machine à flux axial à structure innovante. Il s’agit d’une machine à double rotor et simple stator avec plusieurs barrières de flux par pôle. Une étude par éléments finis est d’abord réalisée afin de valider le passage d’un modèle tridimensionnel à modèle bidimensionnel. L’analyse des pertes fer a permis de choisir les matériaux utilisés au stator et aux rotors. L’étape suivante consiste à établir un modèle analytique multiphysique de la machine à flux axial et de l’optimiser selon le même cahier des charges que celui de la machine radiale. Finalement, une comparaison entre les deux structures radiale et axiale est effectuée pour évaluer les avantages en termes de densité de coupleThe work presented in this thesis deals with the modeling and optimization of electrical machines for direct drive applications. The objective is to reduce the use of rare earth permanent magnets along with the improvement of the motor’s efficiency. A state of the art of electrical machines is realized. It focused on radial and axial flow structures for high torque and low speed applications. A classification is established to identify interesting and innovative structures. Firstly, the radial machine is studied. The choice of the structure is made after a finite element comparison of different machines resulting from the literature. This led to an original structure with concentrated winding and multi-V shape barriers. Then, a multi-physics analytical modeling of the structure is detailed in order to calculate the performances with a reduced calculation time. A preliminary design led to the definition of a prototype which was used to experimentally validate the multi-physics model. An optimization design approach is adopted to obtain optimal machines meeting industrial specifications. Secondly, a novel axial flux structure is studied. It is a machine with double rotor and single stator with several barriers per pole. A finite element study is carried out in order to validate the transition from a three dimensional to a two-dimensional model. The analysis of iron losses made it possible to choose the materials used in the stator and the rotors. Then, the development of a multi-physics analytical model for the axial machine is proposed. It is used to optimize the structure according to the same specifications defined for the radial machine. Finally, a comparison between the radial and axial structures is performed in order to evaluate the advantages in terms of torque density
37
Sargeant, Ramon Bradley. "A multi-axial optical fibre and linear polarizer based force and torque sensor for dexterous robotic fingertips." Thesis, King's College London (University of London), 2014. http://kclpure.kcl.ac.uk/portal/en/theses/a-multiaxial-optical-fibre-and-linear-polarizer-based-force-and-torque-sensor-for-dexterous-robotic-fingertips(a9c419a3-901e-4a56-9b02-00648539d17e).html.
Full textAbstract:
As robots play a more pervasive role in our everyday activities more and more research emphasis is being placed on having robots interact directly with humans, whether in terms of taking care of the elderly, medical interventions or performing dangerous or hazardous tasks. Another trend is for robots to use existing human tools to perform desired actions since it is also not always possible or cost effective to design special tools for every robot. This trend has led to the development of anthropomorphic dexterous manipulators that can perform equally or better than the human hand. Thus the accelerating trend is not only to design a dexterous manipulator but to focus on its ability to grasp and manipulate different and sometimes unknown objects. One of the most researched types of grasp is the precision grasp which accounts for over 80 % of the grasps performed by humans on a daily basis. Precision grasps are grasps involving the fingertips and are generally used for tasks that require fine manipulation skills. Fingertip sensors are therefore important for dexterous manipulators since humans can identify salient properties of an object and formulate effective manipulation strategies solely by grasping the object. This PhD project focuses on developing fingertip sensors, specifically force and torque fingertip sensors that can be integrated into the fingertip of an existing dexterous manipulator and gather contact force and torque information during a grasping event. Another goal is to make the sensor magnetic resonant (MR) compatible so that it can be used in high magnetic environments, as in the case of medical, magnetic resonance imagining applications. To accomplish these goals two sensors were developed based on light intensity modulation and novel sensing structures. Optical sensing schemes were chosen because they are not susceptible to magnetic interference, the sensor and its light source can be separated by long distances without significant signal attenuation and the size and weight of the actual sensing element can be reduced since the processing electronics can be positioned far from the sensing structure. The first sensor developed, as part of this PhD work, was a 2-DOF sensor which used a combination of axially-aligned fibres and linear polarizers to modulate the light to measure the applied force and torque respectively. The use of linear polarizers as the main sensing technique for force and torque sensing is a new area of research since linear polarizers have a defined response curve and can be easily cut into any desired shape and size. The experiments conducted with the 2-DOF sensor showed that the linear polarizer response was superior to traditional axially-aligned and reflective techniques and it was tolerant of small deviations and twists in the sensing structure. The second sensor improved on the first sensor by increasing the number of degrees of freedom from two to six by using a parallel-type 3-UPS (Universal Prismatic Spherical) sensing structure to allow measuring six degrees of movement. All of the joints of the sensing structure were made of nitinol flexures to reduce friction and all of the links were made of plastic and bonded together to produce a flexible but light and strong structure. Another improvement was that all of the optical modulation sensors on the sensing structure were based on linear polarizers thereby reducing the possibility of misalignment errors caused by the transmitting and receiving fibres moving out of axial alignment. The new sensor therefore satisfies the design requirements and the experiments conducted showed that Light Intensity Modulation (LIM) using linear polarizers and an appropriate sensing structure can produce an accurate and versatile force and torque sensor.
38
DiPietro, Anthony Louis. "Effects of temperature transients on the stall and stall recovery aerodynamics of a multi-stage axial flow compressor." Diss., This resource online, 1997. http://scholar.lib.vt.edu/theses/available/etd-10052007-143638/.
Full text
39
Dunand, Matthieu. "Hybrid experimental-numerical determination of the loading path to fracture in TRIP780 sheets subjected to multi-axial loading." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/57573.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student submitted PDF version of thesis.
Includes bibliographical references (p. 104-110).
The development of ductile fracture models of metals requires reliable measurements of the stress and strain histories up to the onset of fracture in multi-axial experiments. In the present work, a hybrid experimental-numerical approach is taken to determine the loading path in various fracture experiments on TRIP780 steel sheets. In most mechanical experiments on sheet metal, the localization of plastic deformation precedes the onset of fracture. After the beginning of necking, the stress fields within the specimen gage section become non-uniform and of three dimensional nature. Consequently, the stress history prior to fracture can no longer be estimated based on the force history measurements using simple analytical formulas. A detailed finite element analysis of each experiment is required to identify the local stress and strain fields. The results of the hybrid experimental-numerical analysis of a fracture experiment depend strongly on the chosen constitutive model. Here, an extensive bi-axial experimental program comprising more than 20 distinct loading conditions is performed to characterize the monotonic large deformation behavior of the TRIP780 steel. It is found that an anisotropic quadratic yield function along with a non-associated flow rule can accurately describe the inelastic behavior of the TRIP material.
(cont.) A first series of fracture experiments is carried out on three types of full-thickness fracture specimens. This experimental program characterizes the onset of fracture for stress states between uniaxial tension and equi-biaxial tension. An effort is made to quantify and minimize the errors affecting the hybrid experimental-numerical analysis of those experiments. Inaccuracies affecting the stress triaxiality and plastic strain histories to fracture are evaluated by comparing surface strains measured by Digital Image Correlation (DIC) and computed by Finite Element Analysis (FEA). A second series of fracture experiments is carried out on a newly designed butterfly-shaped specimen, which allows for multi-axial testing under combinations of normal and tangential loads. Experiments for four different loading conditions are performed and used to analyze the onset of fracture for stress states ranging from pure shear to transverse plane strain tension.
by Matthieu Dunand
S.M.
40
Pechet, Gatien. "Génération de trajectoires pour la réalisation de pièces de grandes dimensions en fabrication additive par dépôt de fil. : Application au secteur naval." Thesis, Ecole centrale de Nantes, 2020. http://www.theses.fr/2020ECDN0015.
Full textAbstract:
La fabrication additive se caractérise par l’ajout successif de couches pour obtenir la pièce désirée. Parmi les nombreux procédés existants, le WAAM (Wire+Arc Additive Manufacturing) s’adapte particulièrement bien à la fabrication de pièces de grandes dimensions. Il se caractérise par un apport de chaleur sous forme d’arc électrique (produit par un générateur de soudage) et un apport de matière sous forme de fil lui permettant un taux de dépôt supérieur aux procédés de fabrication additive avec apport sous forme de poudre. Pour permettre la mise en service de pièces fonctionnelles, la géométrie des dépôts et la santé matière doivent être maitrisées. Cela se traduit par un bon couplage entre les paramètres opératoires et les trajectoires. Ces travaux de thèse vont mettre en avant une méthodologie dans le choix des paramètres en utilisant des plans d’expériences ou de la simulation numérique par éléments finis. Par la suite, nous nous pencherons sur la simulation des trajectoires sur un environnement numérique qui permet de prédire le comportement du porteur. Nous montrerons l’importance de la concordance des environnements numériques et réels et proposerons des règles pour contrôler la redondance cinématique. Enfin, une méthodologie de fabrication pour des pièces de grandes dimensions sera développée. Suite à une identification des zones à complexités géométriques, différentes stratégies de fabrication ont été proposées et appliquées avec succès. Ces travaux seront illustrés par la réalisation de plusieurs démonstrateurs, provenant notamment du domaine naval. Plus particulièrement, une pale creuse d’hélice a été réalisée en profitant des capacités de trajectoires multi-axiales (6+2 axes) et en employant la méthodologie développée dans la thèseAdditive manufacturing is characterized by the successive addition of layers to obtain the desired part. Among the many existing processes, WAAM (Wire + Arc Additive Manufacturing) is particularly well suited to the manufacturing of large parts. It is characterized by a supply of heat in the form of an electric arc (produced by a welding generator) and a supply of material in the form of wire, allowing it a deposition rate higher than additive manufacturing processes with supply in the form of powder. To allow the commissioning of functional parts, the geometry of the weld beads and the material health must be controlled. This results in a good coupling between the operating parameters and the toolpath. This thesis work will highlight a methodology in the choice of parameters using experimental designs or numerical simulation by finite elements. Thereafter, we will study the simulation of the trajectories on a virtual environment, which makes it possible to predict the behavior of the device. We will show the importance of the concordance of virtual and real environments and will propose rules to control the kinematic redundancy. Finally, a manufacturing methodology for large parts will be developed. Following the identification of areas with geometric complexity, different manufacturing strategies have been proposed and successfully applied. This work will be illustrated by the production of various demonstrators, notably from the naval field. More specifically, a hollow propeller blade was produced by taking advantage of the capabilities of multi-axial toolpath (6 + 2 axes) and by using the methodology developed in this thesis
41
Bernachy-Barbé, Fabien. "Caractérisation des mécanismes d'endommagement et modélisation du comportement mécanique sous chargements multi-axiaux de tubes composites SiC/SiC." Thesis, Paris, ENMP, 2014. http://www.theses.fr/2014ENMP0031/document.
Full textAbstract:
Les composites SiC/SiC sont envisagés comme matériaux pour des composants de cœur de réacteurs nucléaires du futur. Le dimensionnement de ces structures par la simulation numérique repose sur une modélisation du comportement mécanique de ces matériaux. Ces travaux visent à améliorer la compréhension de leurs mécanismes de déformation afin de construire une loi de comportement à même de prédire la réponse du matériau sous chargements complexes. Une caractérisation approfondie du comportement macroscopique de tubes SiC/SiC multicouches - similaires aux concepts de gaines de combustibles - a été entreprise, par des essais de traction-pression interne, traction-torsion et flexion multi-instrumentés, et a permis de constituer une importante base expérimentale pour la compréhension des mécanismes d'endommagement et l'identification de modèles. Des observations in-situ et après rupture ont permis de quantifier l'orientation des fissures matricielles observées en surface en fonction du type de chargement appliqué. Des mesures de champs de déplacement par Corrélation d'Images Numériques à l'échelle d'un motif du textile ont permis d'apporter des informations fines sur la cinématique de la surface du composite, telles que l'ouverture des fissures ou la déformation des fragments matriciels. Ces mesures ont également permis de mettre en évidence l'importance de la réorientation des torons dans la direction de chargement, mécanisme pouvant expliquer certaines spécificités du comportement macroscopique du fait de son couplage avec la fissuration matricielle. Enfin, ces différentes données expérimentales ont permis de construire un modèle phénoménologique, identifiable sur quatre essais uniaxiaux, permettant de prédire de manière satisfaisante le comportement macroscopique sous divers chargements bi-axés. L'accord de certaines quantités locales, telles que les caractéristiques de la fissuration en traction, ont également été vérifiéesSiC/SiC composites are candidate materials for in-core components of future nuclear reactors. The analysis of these structures using numerical simulations requires material constitutive laws. The present work focuses on understanding the deformation mechanisms of these materials in order to build a constitutive model able to predict their stress-strain response under complex loadings. An extensive characterization of the mechanical behaviour of SiC/SiC multi-layered tubes – similar to fuel cladding concepts - was carried out, using tension-internal pressure, tension-torsion and bending tests, that allowed to build an important experimental basis for the understanding of the mechanisms and the identification of constitutive laws. In-situ and post-failure observations have allowed quantifying the orientation of surface matrix cracks as a function of the loading type. Full-field measurements using Digital Image Correlation at the tow scale brought precise information on the composite surface kinematics, such as the crack opening or the deformation of the matrix fragments. These measurements also evidence the importance of the tow reorientation, that could explain specific features of the macroscopic behaviour because of its coupling with matrix cracking. Finally, these experimental data allowed to build a constitutive model, identified on only four uniaxial tests, able to predict satisfactorily the macroscopic behaviour under several biaxial loadings. The correct prediction of local quantities, such as the characteristics of the matrix cracking in tension, has also been verified
42
Kalhor, Roozbeh. "Energy Absorption of Metal-FRP Hybrid Square Tubes." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/74960.
Full textAbstract:
Lower-cost manufacturing methods have increased the anticipation for economical mass production of vehicles manufactured from composite materials. One of the potential applications of composite materials in vehicles is in energy-absorbing components such as hollow shells and struts (these components may be in the form of circular cylindrical shells, square and rectangular tubes, conical shells, and frusta). However, constructions which result in brittle fracture of the composite tubes in the form of circumferential or longitudinal corner crack propagation may lead to unstable collapse failure mode and concomitant very low energy absorption. As a result, metal-composite hollow tubes have been developed that combine the benefits of stable ductile collapse of the metal (which can absorb crushing energy in a controlled manner) and the high strength-to-weight ratio of the composites. The relative and absolute thicknesses of metal or FRP section has a substantial effect on energy absorption of the hybrid tubes. In particular, likelihood of delamination occurrence raises with increase in FRP thickness. This can reduce the energy absorption capability of the metal-FRP hybrid tubes. Additionally, adding a very thick FRP section may result in a global buckling failure mode (rather than local folding). Until now, there are no studies specifically addressing the effect of FRP thickness on energy absorption of hybrid tubes. In this study, the effects of fiber orientation and FRP thickness (the number of layers) on the energy absorption of S2-glass/epoxy-304 stainless steel square tubes were experimentally investigated. In addition, a new geometrical trigger was demonstrated which has positive effects on the collapse modes, delamination in the FRP, and the crush load efficiency of the hybrid tube.
To complete this study, a new methodology including the combination of experimental results, numerical modeling, and a multi-objective optimization process was introduced to obtain the best combination of design variables for hybrid metal-composite tubes for crashworthiness applications. The experimental results for the S2 glass/epoxy-304 stainless steel square tubes with different configurations tested under quasi-static compression loading were used to validate numerical models implemented in LS-DYNA software. The models were able to capture progressive failure mechanisms of the hybrid tubes. In addition, the effects of the design variables on the energy absorption and failure modes of the hybrid tubes were explained. Subsequently, the results from the numerical models were used to obtain optimum crashworthiness functions. The load efficiency factor (the ratio of mean crushing load to maximum load) and ratio between the difference of mean crushing load of hybrid and metal tube and thickness of the FRP section were introduced as objective functions. To connect the variables and the functions, back-propagation artificial neural networks (ANN) were used. The Non-dominated Sorting Genetic Algorithm–II (NSGAII) was applied to the constructed ANNs to obtain optimal results. The results were presented in the form of Pareto frontiers to help designers choose optimized configurations based on their manufacturing limitations. Such restrictions may include, but are not limited to, cost (related to the number of layers), laminate architecture (fiber orientation and stacking sequence) which can be constrained by the manufacturing techniques (i.e. filament winding) and thickness (as an example of physical constraints).Ph. D.
43
Lockwood, C. "Comparison of average-passage equation closures through simulation of single and multi-row axial compressors : the limitations of using a commercial CFD code." Thesis, Cranfield University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323824.
Full text
44
Delattre, Alexis. "Caractérisation et modélisation du comportement hyper-viscoelastique d'un élastomère chargé pour la simulation de pièces lamifiées élastomère-métal et étude en fatigue." Thesis, Tours, 2014. http://www.theses.fr/2014TOUR4039/document.
Full textAbstract:
Dans le cadre d’une Cifre avec Airbus Helicopters, le projet a pour but le développement d’un modèle pour le pré-dimensionnement de pièces lamifiées élastomère-métal dont le rôle est critique en termes de conception et de sécurité pour les architectures de rotors d’hélicoptères. Pour cela, un premier volet de la thèse a consisté à caractériser le comportement élasto-dissipatif du matériau d’étude (un butadiène chargé de noir de carbone) via une campagne d’essais statiques et dynamiques, sous différents modes de sollicitations (uniaxiales et biaxiales) et sur un spectre assez large de fréquences, d’amplitudes et de températures. A partir de ces observations, un modèle phénoménologique de comportement hyper-viscoélastique est proposé. Sur la base d’un modèle de Maxwell généralisé, il permet de traduire les phénomènes observés sur la gamme de sollicitations visées. Un accent particulier a été porté sur la prise en compte de l’effet Payne en adoptant une approche originale. Les paramètres du modèle sont identifiés par une méthode robuste et rapide. Le modèle est ensuite développé à la fois dans un code commercial de calcul par éléments finis et dans un outil de calcul basé sur une méthode de réduction de modèles. Enfin, une étude du comportement en fatigue est réalisée à travers une campagne d’essais originaux servant de point de départ à la proposition d’une loi d’endommagement continuIn association with Airbus Helicopters, the aim of the project is to develop a model to pre-size elastomer-metal laminated devices whose role is critical in terms of design and safety for helicopters rotor architectures. To do so, the first part of this thesis consisted in characterizing the elasto-dissipatice behavior of the studied material (a carbon black filled butadiene rubber) thanks to static and dynamic tests, with several kind of loading (uni-axial and bi-axial) and over a wide range of frequences, amplitudes and temperatures. From these observations, a phenomenological hyper-viscoelastic model is proposed. Based on a generalized Maxwell model, it is able to describe the phenomena over the loading range of concern. A particular focus is made to take in account the Payne effect thanks to an original approach. The model parameters are identified with a fast and robust method. The model is then implemented in a commercial finite element code and in a tool based on a model reduction method. Last, a study of the behaviour in fatigue is performed with an original characterization campaign from which a continuous damage law is proposed
45
Kim, Taeho, and Monika Ivantysynova. "Active Vibration Control of Axial Piston Machine using Higher Harmonic Least Mean Square Control of Swash Plate." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-199412.
Full textAbstract:
Noise emission is a major drawback of the positive displacement machine. The noise source can be divided into structure borne noise source (SBNS) and fluid borne noise source (FBNS). Passive techniques such as valve plate optimization have been used for noise reduction of axial piston machines. However, passive techniques are only effective for limited operating conditions or at least need compromises in design. In this paper, active vibration control of swash plate is investigated for vibration and noise reduction over a wide range of operating conditions as an additional method to passive noise reduction techniques. A 75cc pump has been modified for implementation of active vibration control using the swash plate. One tri-axial acceleration sensor and one angle sensor are installed on the swash plate and a high speed servovalve is used for the swash plate actuation. The multi-frequency two-weight least mean square (LMS) filter synthesizes the servovalve input signal to generate a destructive interference force which minimizes the swash plate vibration. An experimental test setup has been realized using Labview field-programmable gate array (FPGA) via cRIO. Simulation and experimental studies are conducted to investigate the possibility of active vibration control.
46
Ramirez, Adriana. "Young Adults in General Psychiatry." Doctoral thesis, Uppsala universitet, Psykiatri, Akademiska sjukhuset, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-151504.
Full textAbstract:
Mental illness is common, and usually starts early in life. However, the majority of those affected never seek mental health care. The overall aim of this thesis was to increase knowledge about help-seeking young adults with mental illness in order to improve diagnostic procedures in clinical psychiatry. A group of young adult psychiatric out-patients (n=217) were consecutively invited to participate in the study between October 2002 and September 2003. Altogether 200 (92%) agreed to participate. Among them, there were 161 (80%) women and 39 (20%) men. Participants’ mean age was 22.4±1.9 years. All participants were carefully and comprehensively assessed with respect to axes I, II, IV and V in the DSM-IV. Psychiatric disorders and personality disorders were assessed using the Structured Clinical Interview for DSM-IV for axis I disorders and the Structured Clinical Interview for DSM-IV for axis II disorders. Psychosocial and environmental problems (axis IV) were evaluated through structured interviewing by a social worker and by self-assessment with a questionnaire. Professional and patient ratings on the Global Assessment of Functioning scale were compared before and after treatment. Patients also reported on the Swedish universities Scales of Personality, the Child and Adolescent Psychiatric Screening Inventory-Retrospect and the Coddington’s life event scale. Taken together, the young adult, psychiatric outpatients were characterized by an early onset of their mental disorders, by co-morbidity, by being female and by having mood or anxiety disorders. There were no significant differences between self-referred and those referred by medical professionals according to either number of current or lifetime diagnoses. Childhood onset of depression was associated with more severe symptoms, more psychosocial risk factors, and more childhood developmental delays. Axis IV psychosocial stress categories were related to the presence of axis I disorders, personality disorders, co-morbidity, and impaired functioning. Agreement between patients’ and professionals’ ratings on the GAF scale was good before treatment and excellent after treatment. In summary, the findings suggest that direct self-referral to specialized psychiatric care does not seem to be associated with overutilization of such care. Childhood onset of depression is associated with a more complex illness. The revised axis IV according to DSM-IV seems to have concurrent validity, but is still hampered by limited reliability. And finally, the results support the usefulness of the self-report GAF instrument for measuring outcome in psychiatric care.
47
Bertin, Morgan. "Mechanical and fatigue properties of bellows determined with Integrated DIC and IR Thermography." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLN031/document.
Full textAbstract:
Afin de participer à l’émergence de technologies innovantes et contribuer aux objectifs de développement durable, un consortium composé de 13 partenaires (3 laboratoires académiques et 10 entreprises industrielles) a été formé. Le projet Thermofluid-RT consiste à développer un système de refroidissement à boucle de fluide diphasique à pompage mécanique. Le LMT-Cachan contribue à la conception de l'élément essentiel de la pompe, à savoir, le soufflet. Celui-ci est obtenu en soudant des feuilles d’acier inoxydable à durcissement structural très mince (70 µm) et doit fonctionner sans défaillance pendant 20 ans. Un dimensionnement fiabiliste du soufflet basé sur la théorie du maillon le plus faible est réalisé. Une méthode d'optimisation basée sur la technique d’identification intégrée à la corrélation d'images numériques aboutit à une géométrie d’éprouvette qui minimise l'incertitude des paramètres recherchés. Toutes les données brutes sont combinées à leur juste valeur grâce à une formulation Bayésienne basée sur l’hypothèse de bruits blanc gaussiens. La géométrie optimisée est testée sur Mini-Astrée, la nouvelle machine biaxiale du LMT. Plusieurs lois de comportements sont étudiées et testées sur le matériau étudié. De très fines feuilles du même acier, sont de même testées à l’aide d’essais uni-axiaux et multiaxiaux. Une analyse microscopique est conduite au travers d’un micro-essai de traction sur 2 grains et l’identification de paramètres d’une loi de plasticité cristalline. Enfin, le dimensionnement probabiliste du soufflet est validé à partir de plusieurs mesures expérimentales infra-rouges sur un nouveau banc d’essai. Un modèle probabiliste à deux échelles permet la caractérisation des phénomènes observés relatifs au matériau d’étude et au composant lui-mêmeIn the context of leveraging and accelerating innovative technological solutions that contribute to meeting sustainable goals, a consortium composed of 13 partners (3 academic laboratories and 10 industrial companies) has been formed. The THERMOFLUID-RT project consists in developing a two-phase fluid loop driven by a mechanical pump. LMT-Cachan contributes to the design of the critical component of the pump, i.e., bellows. This component obtained by welding very thin (70 µm) pre-deformed sheets made of precipitation-hardened stainless steel is expected to operate without failure for 20 years. First, a new probabilistic design methodology allows for the fatigue design of the component. Second, an optimization methodology based on full field measurements and Integrated Digital Image Correlation (IDIC) allows the sample geometry to be designed with the least uncertainty of the sought parameters. All data account for the latter thanks to a Bayesian foundation that equitably weights all measurements. Third, the optimized cruciform geometry has been tested in a new compact biaxial machine, mini-Astrée that allows for a fast, yet robust identification. Several elasto-plastic models with increasing complexity are investigated to probe the material behavior. Ultra-thin sheets are also tested in uniaxial and biaxial experiments thanks to an anti-wrinkling setup. Fourth, a microscopic analysis is also performed via quasi-3D IDIC and a uniaxial micro-specimen allow a crystal plasticity law to be characterized. Last, the probabilistic fatigue design of the bellows based on the weakest link theory and a two-scale probabilistic model is validated with infrared measurements in the high cycle fatigue regime
48
Dumas, Florian. "Contribution à l'étude des machines polyentrefers à aimants permanents et à entrefer réduit.Applications aux machines à flux axial à hautes performances sous contrainte d'encombrement." Thesis, Montpellier 2, 2011. http://www.theses.fr/2011MON20151.
Full textAbstract:
Cette thèse porte sur l'étude de machines polyentrefers et leurs limitations, dans le contexte d'avion plus électrique et du projet de déplacement des avions au sol. Ces moteurs, basés sur l'utilisation de plusieurs éléments mobiles et fixes mis en parallèle, permettent d'obtenir de hautes performances. Une étude sur les tolérances des dimensions des éléments actifs montre que les performances peuvent être dégradées si des précautions lors de la réalisation ne sont pas prises et si les entrefers utilisés ne sont pas faibles. Ce manuscrit présente un système totalement innovant permettant d'utiliser un entrefer réduit à son minimum sans que les performances ne soient dégradées par de la friction. Ce système est appelé système de compensation des efforts de plaquage. Afin de développer un moteur tournant à entraînement direct dans le cadre du taxiage des avions, deux topologies différentes de machines discoïdes sont étudiées et dimensionnées. Les résultats favorisent l'utilisation d'une des deux structures, à entrefer réduit, pour réaliser un maximum de couple dans le volume donné. Afin de prouver la faisabilité du système innovant sur un moteur discoïde, la réalisation d'un prototype laboratoire complet est proposée. Des simulations thermiques et du comportement du système innovant permettront de valider ces étudesThis thesis focuses on the study of multi-air gap machines and their limitations, in the framework of more electric aircraft and the project of moving aircrafts on the ground without the main engines. These motors, based on the use of mobile and fixed parts disposed in parallel, induce high performance. A study concerning the tolerance for the dimensions of active parts shows that performance can decrease if precautions are not taken during manufacturing and if the air gaps are not small. This manuscript presents a totally innovative system that permits the use of an air gap reduced to its minimum without reducing performance by friction. This system is called system of attraction control. In order to develop a direct-drive motor for aircraft taxiing, two different topologies of disc-type machines are studied and sized. The obtained results encourage the use of one of the two structures with reduced air gap to realize maximum torque in the fixed volume. To prove the feasibility of the innovative system on a disc-type motor, the conception of an entire laboratory prototype is proposed. Thermal modelling and simulations on the innovative system behaviour will validate the presented work
49
Amerineni, Rajesh. "BRAIN-INSPIRED MACHINE LEARNING CLASSIFICATION MODELS." OpenSIUC, 2020. https://opensiuc.lib.siu.edu/dissertations/1806.
Full textAbstract:
This dissertation focuses on the development of three classes of brain-inspired machine learning classification models. The models attempt to emulate (a) multi-sensory integration, (b) context-integration, and (c) visual information processing in the brain.The multi-sensory integration models are aimed at enhancing object classification through the integration of semantically congruent unimodal stimuli. Two multimodal classification models are introduced: the feature integrating (FI) model and the decision integrating (DI) model. The FI model, inspired by multisensory integration in the subcortical superior colliculus, combines unimodal features which are subsequently classified by a multimodal classifier. The DI model, inspired by integration in primary cortical areas, classifies unimodal stimuli independently using unimodal classifiers and classifies the combined decisions using a multimodal classifier. The multimodal classifier models are be implemented using multilayer perceptrons and multivariate statistical classifiers. Experiments involving the classification of noisy and attenuated auditory and visual representations of ten digits are designed to demonstrate the properties of the multimodal classifiers and to compare the performances of multimodal and unimodal classifiers. The experimental results show that the multimodal classification systems exhibit an important aspect of the “inverse effectiveness principle” by yielding significantly higher classification accuracies when compared with those of the unimodal classifiers. Furthermore, the flexibility offered by the generalized models enables the simulations and evaluations of various combinations of multimodal stimuli and classifiers under varying uncertainty conditions. The context-integrating model emulates the brain’s ability to use contextual information to uniquely resolve the interpretation of ambiguous stimuli. A deep learning neural network classification model that emulates this ability by integrating weighted bidirectional context into the classification process is introduced. The model, referred to as the CINET, is implemented using a convolution neural network (CNN), which is shown to be ideal for combining target and context stimuli and for extracting coupled target-context features. The CINET parameters can be manipulated to simulate congruent and incongruent context environments and to manipulate target-context stimuli relationships. The formulation of the CINET is quite general; consequently, it is not restricted to stimuli in any particular sensory modality nor to the dimensionality of the stimuli. A broad range of experiments are designed to demonstrate the effectiveness of the CINET in resolving ambiguous visual stimuli and in improving the classification of non-ambiguous visual stimuli in various contextual environments. The fact that the performance improves through the inclusion of context can be exploited to design robust brain-inspired machine learning algorithms. It is interesting to note that the CINET is a classification model that is inspired by a combination of brain’s ability to integrate contextual information and the CNN, which is inspired by the hierarchical processing of visual information in the visual cortex. A convolution neural network (CNN) model, inspired by the hierarchical processing of visual information in the brain, is introduced to fuse information from an ensemble of multi-axial sensors in order to classify strikes such as boxing punches and taekwondo kicks in combat sports. Although CNNs are not an obvious choice for non-array data nor for signals with non-linear variations, it will be shown that CNN models can effectively classify multi-axial multi-sensor signals. Experiments involving the classification of three-axis accelerometer and three-axes gyroscope signals measuring boxing punches and taekwondo kicks showed that the performance of the fusion classifiers were significantly superior to the uni-axial classifiers. Interestingly, the classification accuracies of the CNN fusion classifiers were significantly higher than those of the DTW fusion classifiers. Through training with representative signals and the local feature extraction property, the CNNs tend to be invariant to the latency shifts and non-linear variations. Moreover, by increasing the number of network layers and the training set, the CNN classifiers offer the potential for even better performance as well as the ability to handle a larger number of classes. Finally, due to the generalized formulations, the classifier models can be easily adapted to classify multi-dimensional signals of multiple sensors in various other applications.
50
Nordborg, Tobias, and Alexander Lyrbo. "Produktutveckling av skalkonstruktion för 3-axiellt styrt maskinstativ." Thesis, Linnéuniversitetet, Institutionen för maskinteknik (MT), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-54235.
Full textAbstract:
Detta examensarbete omfattar produktutvecklingen av ett multiaxiellt styrt maskinstativ, som senare vid en slutlig produkt skall vara ämnad för användning inom additiv tillverkning. Arbetet som utförts har lett fram till konceptframtagning, materialval och tillverkning av en skalkonstruktion för ett 3-axiellt styrt maskinstativ. Tester och simuleringar har gjorts för att se om maskinkonstruktionen går att använda efter de kravspecifikationer som ställts av värdföretaget. Konstruktionen höll sig väl inom sin tolerans på 100 mikrometer vid rumstemperatur men visade vissa felmarginaler vid arbetstemperaturen på 600 grader Celsius. Resultaten som erhållits har analyserats för att kunna ge vidare förslag på förbättringar av konstruktionen då det ännu kvarstår implikationer vid säkerställandet av toleranserna vid arbetstemperaturen.This thesis covers the product development of a multi-axial driven machine frame, which at a later stage will be intended to be used in additive manufacturing. The work that has been performed has led to concept development, material selection and manufacturing of a shell construction for a 3-axially driven machine construction. Tests and simulations have been done to verify if the machine design can be used by the specifications set by the host company. The construction was well within its tolerance of 100 microns at room temperature but showed some error margins at the operating temperature of 600 degrees Celsius. The results obtained have been analyzed in order to provide further suggestions for improvement of the structure when there still remain implications in ensuring the tolerances at operating temperature.