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1
Dinter, Simon. "Nucleon structure from lattice QCD." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2012. http://dx.doi.org/10.18452/16629.
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In dieser Arbeit berechnen wir mit Hilfe der Gitter-QCD Observablen, die in Beziehung zur Struktur des Nukleons stehen. Ein Teil dieser Arbeit beschäftigt sich mit Momenten von Parton-Verteilungsfunktionen. Solche Momente sind wichtig für das Verständnis der Nukleon-Struktur und werden durch globale Analysen von tief-inelastischen Streuexperimenten bestimmt. Eine theoretische, nicht-perturbative Rechnung der Momente in der Gitter-QCD ist möglich. Allerdings existiert, seit solche Gitter-QCD Rechnungen vorliegen, eine Diskrepanz zwischen diesen Rechnungen und den Ergebnissen globaler Analysen experimenteller Daten. Wir untersuchen, ob systematische Effekte für diese Diskrepanz verantwortlich sind, dabei studieren wir insbesondere die Effekte angeregter Zustände. Zudem führen wir eine erste Rechnung mit vier dynamischen Quark-Flavors durch. Ein weiterer Aspekt dieser Arbeit ist eine Machbarkeitsstudie zur Berechnung des skalaren Quark-Inhalts des Nukleons in der Gitter-QCD. Dieser bestimmt den Wirkungsquerschnitt der durch ein skalares Teilchen (z.B. ein Higgs-Teilchen) vermittelten Wechselwirkung eines schweren Teilchens mit einem Nukleon und kann somit einen Einfluss bei der Suche nach Dunkler Materie haben. Bisherige Gitter-Rechnungen dieser Größe besitzen große Unsicherheiten und sind daher von geringer Signifikanz für phenomenologische Anwendungen. Wir benutzen eine Varianz-Reduktions-Methode zur Auswertung von unverbundenen Diagrammen um ein präzises Ergebnis zu erhalten. Des Weiteren stellen wir eine neue stochastische Methode zur Berechnung von Nukleon-Dreipunkt-Korrelationsfunktionen vor, die für die Berechnung von Observablen der Nukleon-Struktur benötigt werden. Wir testen die Konkurrenzfähigkeit dieser neuen Methode gegenüber der Standard-Methode. In allen Rechnungen benutzen wir Wilson twisted-Mass Fermionen mit maximalem Twist, so dass die hier berechneten Observablen nur O(a^2) Diskretisierungsfehler aufweisen.In this thesis we compute within lattice QCD observables related to the structure of the nucleon. One part of this thesis is concerned with moments of parton distribution functions (PDFs). Those moments are essential elements for the understanding of nucleon structure and can be extracted from a global analysis of deep inelastic scattering experiments. On the theoretical side they can be computed non-perturbatively by means of lattice QCD. However, since the time lattice calculations of moments of PDFs are available, there is a tension between these lattice calculations and the results from a global analysis of experimental data. We examine whether systematic effects are responsible for this tension, and study particularly intensively the effects of excited states by a dedicated high precision computation. Moreover, we carry out a first computation with four dynamical flavors. Another aspect of this thesis is a feasibility study of a lattice QCD computation of the scalar quark content of the nucleon, which is an important element in the cross-section of a heavy particle with the nucleon mediated by a scalar particle (e.g. Higgs particle) and can therefore have an impact on Dark Matter searches. Existing lattice QCD calculations of this quantity usually have a large error and thus a low significance for phenomenological applications. We use a variance-reduction technique for quark-disconnected diagrams to obtain a precise result. Furthermore, we introduce a new stochastic method for the calculation of connected 3-point correlation functions, which are needed to compute nucleon structure observables, as an alternative to the usual sequential propagator method. In an explorative study we check whether this new method is competitive to the standard one. We use Wilson twisted mass fermions at maximal twist in all our calculations, such that all observables considered here have only O(a^2) discretization effects.
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Renner, Dru Bryant 1977. "Exploring proton structure using lattice QCD." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/29448.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2004.Includes bibliographical references (leaves 219-222).
We calculate moments of the generalized parton distributions of the nucleon using lattice QCD. The generalized parton distributions determine the angular momentum decomposition of the nucleon and the transverse distributions of partons within the nucleon. Additionally, the generalized parton distributions reduce to the elastic form factors and ordinary parton distributions in particular kinematic limits. Thus by calculating moments of the generalized parton distributions in lattice QCD we can explore many facets of the structure of the nucleon. In this effort, we have developed the building block method to determine all the lattice correlation functions which con- tribute to the off forward matrix elements of the twist two operators. These matrix elements determine the generalized form factors of the nucleon which in turn give the moments of the generalized parton distributions. Thus we use our building block method to calculate all the matrix elements of the lowest twist two operators. Fur- thermore, we use our method to construct an overdetermined set of matrix elements allowing a more accurate calculation of the generalized form factors.
by Dru Bryant Renner.
Ph.D.
3
Blair, Stuart R. "Lattice Boltzmann Methods for Fluid Structure Interaction." Thesis, Monterey, California. Naval Postgraduate School, 2012. http://hdl.handle.net/10945/17325.
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Approved for public release; distribution is unlimitedThe use of lattice Boltzmann methods (LBM) for fluid flow and its coupling with finite element method (FEM) structural models for fluid-structure interaction (FSI) is investigated. A body of high performance LBM software that exploits graphic processing unit (GPU) and multiprocessor programming models is developed and validated against a set of two- and three-dimensional benchmark problems. Computational performance is shown to exceed recently reported results for single-workstation implementations over a range of problem sizes. A mixed-precision LBM collision algorithm is presented that retains the accuracy of double-precision calculations with less computational cost than a full double-precision implementation. FSI modelling methodology and example applications are presented along with a novel heterogeneous parallel implementation that exploits task-level parallelism and workload sharing between the central processing unit (CPU) and GPU that allows significant speedup over other methods. Multi-component LBM fluid models are explicated and simple immiscible multi-component fluid flows in two-dimensions are presented. These multi-component fluid LBM models are also paired with structural dynamics solvers for two-dimensional FSI simulations. To enhance modeling capability for domains with complex surfaces, a novel coupling method is introduced that allows use of both classical LBM (CLBM) and a finite element LBM (FELBM) to be combined into a hybrid LBM that exploits the flexibility of FELBM while retaining the efficiency of CLBM.
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Xue, Boyu. "3D Printed Lattice Structure for Driveline Applications." Thesis, KTH, Materialvetenskap, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-299270.
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Lattice structures have received a lot of attention as cellular materials in recent years because of their outstanding properties, such as high strength-to-weight ratio, heat transfer, energy absorption, and capability of improving noise, vibration and harshness (NVH) behavior. This type of structure received a boost from additive manufacturing (AM) technology, which can fabricate geometries in practically any shape. Due to economic and environmental requirements, lightweight design is increasingly used in automobile and construction equipment applications. NVH behavior is a crucial issue for construction equipment. However, the conventional structures' NVH behavior is mainly decided by the mass, so silence often requires heavy systems, leading to more energy consumption and emission. Therefore, the environmental trends and the resulting economic competition have limited traditional (heavy) solutions to improve NVH behavior and make the lightweight design more difficult. Novel solutions are necessary to light the difficulty and challenge of combining NVH and lightweight requirements. In this research, topology optimization was implemented on a New Articulated Hauler Transmission (NAHT) component to balance lightweight and NVH behavior. The topology- optimized 3D model was filled by a non-homogenous lattice structure with optimal lattice density via size optimization. Lattice structure optimization is one type of topology optimization, and it is the term for describing these procedures. To fabricate the complicated lattice structure, additive manufacturing (or 3D printing) is required (after topology and lattice structure optimization). The new models were analyzed using the finite element method (FEM), and the results of the analysis were compared with those of the original models. After the comparison, positive results were obtained, demonstrating that topology and lattice optimization can be applied in the design of construction equipment components. According to the results, lattice structure optimization can create a reliable lightweight design with good NVH behavior. Furthermore, lattice structure's organization and layout have a significant impact on the overall performance.Gitterstrukturer har fått mycket uppmärksamhet som cellulära material under de senaste åren på grund av deras enastående egenskaper, t.ex. hög hållfasthet i förhållande till vikt, värmeöverföring, energiabsorption och förmåga att förbättra buller-, vibrations- och bullerskador (NVH-beteende). Denna typ av struktur har fått ett uppsving av tekniken för additiv tillverkning (AM), som kan tillverka geometrier i praktiskt taget vilken form som helst. På grund av ekonomiska och miljömässiga krav används lättviktsdesign i allt större utsträckning inom bilindustrin och byggnadsutrustning. NVH-egenskaperna är en viktig fråga för anläggningsutrustning. De konventionella konstruktionernas NVH-beteende bestäms dock huvudsakligen av massan, vilket innebär att tystnad ofta kräver tunga system, vilket leder till ökad energiförbrukning och större utsläpp. Miljötrenderna och den ekonomiska konkurrens som följer av detta har därför begränsat de traditionella (tunga) lösningarna för att förbättra NVH-egenskaperna och gjort lättviktsdesignen svårare. Nya lösningar är nödvändiga för att lösa svårigheten och utmaningen med att kombinera NVH- och lättviktskrav. I den här forskningen genomfördes topologioptimering på en komponent för en ny ledad transportörtransmission (NAHT) för att balansera lättvikts- och NVH-beteende. Den topologioptimerade 3D-modellen fylldes med en icke-homogen gitterstruktur med optimal gittertäthet via storleksoptimering. Gitterstrukturoptimering är en typ av topologioptimering, och det är termen för att beskriva dessa förfaranden. För att tillverka den komplicerade gitterstrukturen krävs additiv tillverkning (eller 3D-utskrift) (efter topologi- och gitterstrukturoptimering). De nya modellerna analyserades med hjälp av finita elementmetoden (FEM), och resultaten av analysen jämfördes med resultaten av de ursprungliga modellerna. Efter jämförelsen erhölls positiva resultat, vilket visar att optimering av topologi och gitterstruktur kan tillämpas vid utformning av komponenter för byggutrustning. Enligt resultaten kan optimering av gitterstrukturen skapa en tillförlitlig lättviktsdesign med bra NVH-beteende. Dessutom har gitterstrukturens organisering och layout en betydande inverkan på den totala prestandan.
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ASHOK, RAMYA. "A DATABASE SYSTEM TO STORE AND RETRIEVE A CONCEPT LATTICE STRUCTURE." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1130552767.
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CAPOBIANCO, Silvio. "Structure and invertibility in cellular automata." Doctoral thesis, La Sapienza, 2005. http://hdl.handle.net/11573/917108.
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McConaha, Matthew. "Graded Lattice Structure Density Optimization for Additive Manufacturing." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1523634949822303.
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Downie, Lewis James. "Structure and properties of some triangular lattice materials." Thesis, University of St Andrews, 2014. http://hdl.handle.net/10023/4423.
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This thesis is concerned with the study of two families of materials which contain magnetically frustrated triangular lattices. Each material is concerned with a different use; the first, analogues of YMnO₃, is from a family of materials called multiferroics, the second, A₂MCu₃F₁₂ (where A = Rb¹⁺, Cs¹⁺, M = Zr⁴⁺, Sn⁴⁺, Ti⁴⁺, Hf⁴⁺), are materials which are of interest due to their potentially unusual magnetic properties deriving from a highly frustrated Cu²⁺-based kagome lattice. YFeO₃, YbFeO₃ and InFeO₃ have been synthesised as their hexagonal polymorphs. YFeO₃ and YbFeO₃ have been studied in depth by neutron powder diffraction, A.C. impedance spectroscopy, Mössbauer spectroscopy and magnetometry. It was found that YFeO₃ and YbFeO₃ are structurally similar to hexagonal YMnO₃ but there is evidence for a subtle phase separation in each case. Low temperature magnetic properties are also reported, and subtle correlations between the structural, electrical and magnetic properties of these materials have been found. InFeO₃ was found to adopt a higher symmetry and is structurally similar to the high temperature phase of YMnO₃. TbInO₃ and DyInO₃ have also been synthesised and studied at various temperatures. The phase behaviour of TbInO₃ was analysed in detail using neutron powder diffraction and internal structural changes versus temperature were mapped out – there is also evidence for a subtle isosymmetric phase transition. Neither DyInO₃ nor TbInO₃ show long-range magnetic order between 2 and 300 K, or any signs of ferroelectricity at room temperature. The new compounds Cs₂TiCu₃F₁₂ and Rb₂TiCu₃F₁₂ have both been synthesised and shown to be novel kagome lattice based materials. The former shows a transition from rhombohedral to monoclinic symmetry in the powder form and from rhombohedral to a larger rhombohedral unit cell in the single crystal – a particle size based transition pathway is suggested. For Rb₂TiCu₃F₁₂ a complex triclinic unit cell is found, which distorts with lowering temperature. Both materials show magnetic transitions with lowering temperature. The solid solution Cs₂₋ₓRbₓSnCu₃F₁₂ (x = 0, 0.5, 1.0, 1.5, 2.0) was synthesised and investigated crystallographically, demonstrating a range of behaviours. Rb₂SnCu₃F₁₂ displays a rare re-entrant structural phase transition. In contrast, Cs₀.₅Rb₁.₅SnCu₃F₁₂ shows only the first transition found in the Rb⁺ end member. CsRbSnCu₃F₁₂ adopts a lower symmetry at both room temperature and below. Cs₁.₅Rb₀.₅SnCu₃F₁₂ and Cs₂SnCu₃F₁₂ show a rhombohedral - monoclinic transition, which is similar to that found in Cs₂TiCu₃F₁₂.
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Souvatzis, Petros. "Electronic Structure and Lattice Dynamics of Elements and Compounds." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8198.
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Misawa, Masaki, Naoki Takada, Hiroshi Yamashita, Shingo Satake, and Kazuhiro Yamamoto. "Lattice Boltzmann simulation on porous structure and soot accumulation." Elsevier, 2006. http://hdl.handle.net/2237/20046.
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Lambrou, Eliana. "Phase structure of five-dimensional anisotropic lattice gauge theories." Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/19579.
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The idea that we live in a higher-dimensional space was first introduced almost 100 years ago. In the past two decades many extra-dimensional models have been proposed in order to solve fundamental problems of nature such as the hierarchy problem. Most of them need exploration via non-perturbative approaches and Lattice Gauge Theory provides a tool for doing this. In this thesis, we make attempts to find a non-perturbative way to localize gauge fields that arise from five-dimensional SU(2) gauge theories on 3-branes. In 1984, it was proposed that the phase diagram of anisotropic extra-dimensional lattice gauge theories inherits a new phase, called the "layered" phase, where the gauge fields behave as four-dimensional ones. This was shown for the abelian case, but the existence of this new phase for the simplest non-abelian group, SU(2), was still in doubt. We investigated this system in large volumes using Monte Carlo simulations and we could not find a second order phase transition from a five-dimensional to a continuous four-dimensional theory when all directions were kept large. This made the model unattractive for further exploration as nothing suggests that a non-trivial fixed point could exist. The above investigation was done in a flat background metric. We extended the previous work by putting our theory into a slice of AdS5 space, usually called the warped background. The motivation for this is that our SU(2) theory looks like the gauge-sector of the Randall-Sundrum model, which does not have a concrete solution to the problem of localization of the gauge fields on a 3-brane. We carried out our investigation using the Mean-Field Approach and we present novel results for the phase diagram and measurements of important observables. In our implementation we have a finite extent of the extra dimension and one layer (or 3-brane) on each extra-dimensional coordinate. At weak coupling, we observed that each layer decouples one at a time in the transition to the fully layered phase of the system, forming a mixed phase, whereas there is a strong and sharp transition between the fully layered and the strong-coupling phase. Within the mixed phase, close to the transition into the layered phase, we found evidence that the system is four-dimensional acquiring a Yukawa mass and resembling a Higgs-like phase. The mixed phase grows as the curvature increases suggesting that for an infinite extra dimension the entire weak-coupling phase is mixed.
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Ramakrishnan, S. 1964. "Micro-structure in particulate media: A lattice type approach." Thesis, The University of Arizona, 1993. http://hdl.handle.net/10150/291671.
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The behavior of particulate media, in contrast to the behavior of continuous media, is governed by the interaction of particles/grains at contacts. The current approach to model particulate media is through a disc model assembly composed of rigid discs linked by normal and tangential springs at contacts. In this project, a novel approach using a lattice type model is investigated. The mathematical concepts related to the formulation of the lattice model are developed and are numerically implemented by a computer code. Numerical experiments were conducted on a two dimensional assembly of spheres subjected to a vertical load and a simple shear strain. The results of numerical simulation are in general agreement with observations from simple shear tests.
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Goel, Archak. "Design of Functionally Graded BCC Type Lattice Structures Using B-spline Surfaces for Additive Manufacturing." University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1552398559313737.
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Seiler, Anja [Verfasser], and Ingo [Akademischer Betreuer] Krossing. "Growth, structure and lattice dynamics of rare earth silicide nanostructures." Freiburg : Universität, 2016. http://d-nb.info/1119452961/34.
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Syritsyn, Sergey Nikolaevich. "Exploration of nucleon structure in lattice QCD with chiral quarks." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/68978.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 185-195).
In this work, we calculate various nucleon structure observables using the fundamental theory of quarks and gluons, QCD, simulated on a lattice. In our simulations, we use the full QCD action including Nf = 2+ 1 dynamical quarks in the SU(2) isospin limit. We compute the nucleon vector and axial vector form factors as well as the generalized form factors, and analyze the nucleon charge, magnetization, and axial radii, anomalous magnetic moment, and axial charge. In addition, we compute quark contributions to the nucleon momentum and spin. Our calculation is novel for three reasons. It is a first full QCD calculation using both sea and valence chiral quarks with pion masses as low as m[pi] = 300 MeV. We develop a method to keep systematic effects in the lattice nucleon matrix elements under control, which helps us to obtain a better signal-to-noise ratio, to achieve higher precision and to test the applicability of low-energy effective theories. Finally, we compare the results from lattice QCD calculations with two different discretization methods and lattice spacings, with the rest of the calculation technique kept equal. The level of agreement between these results indicates that our calculations are not significantly affected by discretization effects.
by Sergey Nikolaevich Syritsyn.
Ph.D.
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Valdez, Andrés Ricardo. "On lattice Boltzmann method for solving fluid-structure interaction problems." Universidade Federal de Juiz de Fora (UFJF), 2017. https://repositorio.ufjf.br/jspui/handle/ufjf/6104.
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Neste trabalho são apresentados aspectos de modelagem computacional para o estudo de Interação Fluido-Estrutura (FSI). Numericamente, o Método de Lattice Boltzmann (LBM) é usado para resolver a mecânica dos fluidos, em particular as equações de Navier-Stokes incompressíveis. Neste contexto, são abordados problemas de escoamentos complexos, caracterizado pela presença de obstáculos. A imposição das restrições na interface fluido-sólido é feita utilizando princípios variacionais, empregando o Princípio de Balanço de Potências Virtuais (PVPB) para obter as equações de Euler-Lagrange. Esta metodologia permite determinar as dependências entre carregamentos cinematicamente compatíveis e o estado mecânico adotado. Neste sentido, as condições de interface fluido-sólido são abordadas pelo Método de Fronteira Imersa (IBM) visando técnicas computacionais de baixo custo. A metodologia IBM trata o equilíbrio das equações na interface fluido-sólido através da interpolação entre os nós Lagrangianos (sólidos) e os nós Eulerianos (fluidos). Neste contexto, uma modificação desta estratégia que fornece soluções mais precisas é estudada. Para mostrar as capacidades do acoplamento LBM-IBM são apresentados vários experimentos computacionais que demonstram grande fidelidade entre as soluções obtidas e as soluções disponíveis na literatura.
This work presents computational modeling aspects for studying Fluid-Structure Interaction (FSI). The Lattice Boltzmann Method (LBM) is employed to solve the fluid mechanics considering the incompressible Navier-Stokes equations. The flows studied are complex due to the presence of arbitrary shaped obstacles. The obstacles alters the bulk flow adding complexity to the analysis. In this work the Euler-Lagrange equations are obtained employing the Principle of Virtual Power Balance (PVPB). Consequently, the functional dependencies between the mechanical state and every kinematic compatible loadings are established employing variational arguments. This modeling technique allows to study the fluid-solid boundary constraint. In this context the fluid-solid interface is handled employing the Immersed Boundary Method (IBM). The IBM deals with the fluid-solid interface equilibrium equations performing an interpolation of forces between Lagrangian nodes (solid domain) and Eulerian Lattice grid (fluid domain). In this work a different version of this methodology is studied that allows to obtain more accurate solutions. To show the capabilities of the implemented LBM-IBM solver several experiments are done showing the agreement with the benchmarks results available in literature.
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Burchell, T. D. "Studies of fracture in nuclear graphite." Thesis, University of Bath, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374615.
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Livsey, I. "A light scattering study of non-aqueous colloidal dispersions." Thesis, University of Bristol, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355344.
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Fathelbab, F. A. "The effect of joints on the stability of shallow single layer lattice domes." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233896.
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Considerable improvements in the technology of space frame joints have been achieved in recent years. The conventional procedure for the analysis and study of space structure stability assumes that the joints of these structures behave as either pure pins or are fully rigid despite the fact that the joints of most space structures are semi-rigid. The actual behaviour of joints has been shown to have a significant effect on the behaviour of space structures, especially for shallow single layer lattice domes. In this thesis the development of a general space frame member tangent stiffness matrix is reported. This matrix incorporates, in addition to the effects of axial force and bowing, the effects of joint characteristics. An algorithm for following the pre and post buckling behaviour of shallow single layer lattice domes has also been developed. The new tangent stiffness matrix and the new algorithm have been implemented in a computer program for the geometrically nonlinear analysis of space frames. Results obtained using the modified computer program have been tested against the available published results. The computer program developed is then used to analyse and study the stability of a number of experimental shallow single layer lattice dome models. In these tests, various combinations of member size, joint type, and load pattern were tested. The results of all these tests along with the corresponding computer predictions are presented in this thesis. The ability of the program to model accurately the observed experimental behaviour is clearly demonstrated as is the significant influence that joint bending stiffness has on the behaviour of shallow single layer lattice domes. In particular, realistic levels of joint bending stiffness are shown to produce a considerable improvement in load carrying capacity as compared with predictions based on pin jointed behaviour.
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O'Connor, Joseph. "Fluid-structure interactions of wall-mounted flexible slender structures." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/fluidstructure-interactions-of-wallmounted-flexible-slender-structures(1dab2986-b78f-4ff9-9b2e-5d2181cfa009).html.
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The fluid-structure interactions of wall-mounted slender structures, such as cilia, filaments, flaps, and flags, play an important role in a broad range of physical processes: from the coherent waving motion of vegetation, to the passive flow control capability of hair-like surface coatings. While these systems are ubiquitous, their coupled nonlinear response exhibits a wide variety of behaviours that is yet to be fully understood, especially when multiple structures are considered. The purpose of this work is to investigate, via numerical simulation, the fluid-structure interactions of arrays of slender structures over a range of input conditions. A direct modelling approach, whereby the individual structures and their dynamics are fully resolved, is realised via a lattice Boltzmann-immersed boundary model, which is coupled to two different structural solvers: an Euler-Bernoulli beam model, and a finite element model. Results are presented for three selected test cases - which build in scale from a single flap in a periodic array, to a small finite array of flaps, and finally to a large finite array - and the key behaviour modes are characterised and quantified. Results show a broad range of behaviours, which depend on the flow conditions and structural properties. In particular, the emergence of coherent waving motions are shown to be closely related to the natural frequency of the array. Furthermore, this behaviour is associated with a lock-in between the natural frequency of the array and the predicted frequency of the fluid instabilities. The original contributions of this work are: the development and application of a numerical tool for direct modelling of large arrays of slender structures; the characterisation of the behaviour of slender structures over a range of input conditions; and the exposition of key behaviour modes of slender structures and their relation to input conditions.
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Javadi, Motaghi Narjes [Verfasser], and Gunnar [Akademischer Betreuer] Bali. "Pion structure form lattice QCD / Narjes Javadi Motaghi. Betreuer: Gunnar Bali." Regensburg : Universitätsbibliothek Regensburg, 2015. http://d-nb.info/107229379X/34.
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McKenzie, Stuart Lamont James. "The order structure of some spaces of Banach lattice valued functions." Thesis, Queen's University Belfast, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.675660.
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Spaces of real valued functions form many examples in the theory of ordered vector spaces and vector lattices. For example the space of real -valued polynomials on a bounded subset of the reals is not in general a vector lattice but does have the Riesz interpolation property (RIP). Another example of an ordered vector space which is in general not a lattice is the space of differentiable functions, again this space has the Riesz decomposition property (RDP) which is equivalent to the RIP for ordered vector spaces. In this thesis we replace the real -valued function versions of these spaces with Banach lattice-valued functions with appropriate definitions and investigate when they have the RIP/RDP. We also consider when the Banach lattice-valued polynomials form a vector lattice. Spaces of continuous real-valued functions on a (locally) compact Hausdorff space are very important in Banach lattice theory. Generalisations to Banach lattice-valued functions have already been made and many analogous results to the real case have been proved. Including some extension and separation results. In the thesis this space is further generalised by considering functions which are continuous with respect to the weak topology on the Banach lattice instead of the norm topology. These spaces of functions may not be Banach lattices in general in contrast to the norm continuous versions which always are. We provide conditions under which it will be a Banach lattice and prove several other desirable properties for a Banach lattice under varying conditions. We also give some extension and separtion results under fairly restrictive conditions.
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Al-wattar, Tahseen Abdulridha Ali. "Developing equivalent solid model for lattice cell structure using numerical approaches." Wright State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=wright1610335304435815.
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De, Rosis Alessandro <1984>. "Fluid-structure interaction by a coupled lattice Boltzmann-finite element approach." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5934/1/derosis_alessandro_tesi.pdf.
Full textAbstract:
In this thesis, a strategy to model the behavior of fluids and their interaction with deformable bodies is proposed. The fluid domain is modeled by using the lattice Boltzmann method, thus analyzing the fluid dynamics by a mesoscopic point of view. It has been proved that the solution provided by this method is equivalent to solve the Navier-Stokes equations for an incompressible flow with a second-order accuracy. Slender elastic structures idealized through beam finite elements are used. Large displacements are accounted for by using the corotational formulation. Structural dynamics is computed by using the Time Discontinuous Galerkin method. Therefore, two different solution procedures are used, one for the fluid domain and the other for the structural part, respectively. These two solvers need to communicate and to transfer each other several information, i.e. stresses, velocities, displacements. In order to guarantee a continuous, effective, and mutual exchange of information, a coupling strategy, consisting of three different algorithms, has been developed and numerically tested. In particular, the effectiveness of the three algorithms is shown in terms of interface energy artificially produced by the approximate fulfilling of compatibility and equilibrium conditions at the fluid-structure interface.
The proposed coupled approach is used in order to solve different fluid-structure interaction problems, i.e. cantilever beams immersed in a viscous fluid, the impact of the hull of the ship on the marine free-surface, blood flow in a deformable vessels, and even flapping wings simulating the take-off of a butterfly. The good results achieved in each application highlight the effectiveness of the proposed methodology and of the C++ developed software to successfully approach several two-dimensional fluid-structure interaction problems.
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De, Rosis Alessandro <1984>. "Fluid-structure interaction by a coupled lattice Boltzmann-finite element approach." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5934/.
Full textAbstract:
In this thesis, a strategy to model the behavior of fluids and their interaction with deformable bodies is proposed. The fluid domain is modeled by using the lattice Boltzmann method, thus analyzing the fluid dynamics by a mesoscopic point of view. It has been proved that the solution provided by this method is equivalent to solve the Navier-Stokes equations for an incompressible flow with a second-order accuracy. Slender elastic structures idealized through beam finite elements are used. Large displacements are accounted for by using the corotational formulation. Structural dynamics is computed by using the Time Discontinuous Galerkin method. Therefore, two different solution procedures are used, one for the fluid domain and the other for the structural part, respectively. These two solvers need to communicate and to transfer each other several information, i.e. stresses, velocities, displacements. In order to guarantee a continuous, effective, and mutual exchange of information, a coupling strategy, consisting of three different algorithms, has been developed and numerically tested. In particular, the effectiveness of the three algorithms is shown in terms of interface energy artificially produced by the approximate fulfilling of compatibility and equilibrium conditions at the fluid-structure interface.
The proposed coupled approach is used in order to solve different fluid-structure interaction problems, i.e. cantilever beams immersed in a viscous fluid, the impact of the hull of the ship on the marine free-surface, blood flow in a deformable vessels, and even flapping wings simulating the take-off of a butterfly. The good results achieved in each application highlight the effectiveness of the proposed methodology and of the C++ developed software to successfully approach several two-dimensional fluid-structure interaction problems.
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Caiazzo, Alfonso. "Asymptotic Analysis of lattice Boltzmann method for Fluid-Structure interaction problems." Doctoral thesis, Scuola Normale Superiore, 2007. http://hdl.handle.net/11384/85682.
Full textAbstract:
The lattice Boltzmann method (LBM) is a numerical solver for the Navier-Stokes
equation, based on an underlying molecular dynamic model. Recently, it has
been extended towards the simulation of complex
fluids.
In this thesis, we use the asymptotic expansion technique to investigate the standard
scheme, the initialization problem and possible developments towards moving
boundary and
fluid-structure interaction problems. At the same time, it will
be shown how the mathematical analysis can be used to understand and improve
the algorithm.
First of all, we elaborate the tool "asymptotic analysis", explaining the methods
and the strategy we use for the investigation. A first application to the LBM is described,
recovering the approximation of the Navier-Stokes solution starting from
the lattice Boltzmann equation. As next, we extend the analysis, to investigate
the origin and the dynamic of initial layers. A class of initialization algorithms to
generate accurate initial values within the LB framework is described in detail.
Then we study the features of a simple moving boundary LBM. In particular, we
concentrate on the initialization of new
uid nodes created by the variations of
the computational
fluid domain.
Finally, to set up an LBM for
uid structure interaction, efficient routines to
evaluate forces are required. We describe the Momentum Exchange algorithm
(MEA). Precise accuracy estimates are derived, and the analysis leads to the
construction of an improved method to evaluate the interface stresses.
In conclusion, we test the defined code and validate the results of the analysis on
several simple benchmarks.
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Caiazzo, Alfonso. "Asymptotic analysis of lattice Boltzmann method for fluid-structure interaction problems." [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=983804214.
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Mawson, Mark. "Interactive fluid-structure interaction with many-core accelerators." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/interactive-fluidstructure-interaction-with-manycore-accelerators(a4fc2068-bac7-4511-960d-41d2560a0ea1).html.
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The use of accelerator technology, particularly Graphics Processing Units (GPUs), for scientific computing has increased greatly over the last decade. While this technology allows larger and more complicated problems to be solved faster than before it also presents another opportunity: the real-time and interactive solution of problems. This work aims to investigate the progress that GPU technology has made towards allowing fluid-structure interaction (FSI) problems to be solved in real-time, and to facilitate user interaction with such a solver. A mesoscopic scale fluid flow solver is implemented on third generation nVidia ‘Kepler’ GPUs in two and three dimensions, and its performance studied and compared with existing literature. Following careful optimisation the solvers are found to be at least as efficient as existing work, reaching peak efficiencies of 93% compared with theoretical values. These solvers are then coupled with a novel immersed boundary method, allowing boundaries defined at arbitrary coordinates to interact with the structured fluid domain through a set of singular forces. The limiting factor of the performance of this method is found to be the integration of forces and velocities over the fluid and boundaries; the arbitrary location of boundary markers makes the memory accesses during these integrations largely random, leading to poor utilisation of the available memory bandwidth. In sample cases, the efficiency of the method is found to be as low as 2.7%, although in most scenarios this inefficiency is masked by the fact that the time taken to evolve the fluid flow dominates the overall execution time of the solver. Finally, techniques to visualise the fluid flow in-situ are implemented, and used to allow user interaction with the solvers. Initially this is achieved via keyboard and mouse to control the fluid properties and create boundaries within the fluid, and later by using an image based depth sensor to import real world geometry into the fluid. The work concludes that, for 2D problems, real-time interactive FSI solvers can be implemented on a single laptop-based GPU. In 3D the memory (both size and bandwidth) of the GPU limits the solver to relatively simple cases. Recommendations for future work to allow larger and more complicated test cases to be solved in real-time are then made to complete the work.
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Wilmoth, Nathan G. "Determining the Mechanical Properties of Lattice Block Structures." Cleveland State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=csu1366275566.
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Moliner, Marion Cabra Daniel Carlos Pujol Pierre. "Effects of lattice distortions on low-dimensional strongly correlated systems." Strasbourg : Université de Strasbourg, 2009. http://eprints-scd-ulp.u-strasbg.fr:8080/1100/01/MOLINER_Marion_2009.pdf.
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Okeke, Somtochukwu Francis. "Analisi numerica del comportamento a compressione di strutture "lattice"." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2017.
Find full textAbstract:
In questo lavoro due strutture lattice sono state analizzate e sottoposte a prove di compressione assiale a buckling con la volontà di capire quali sono i parametri più influenti in tale analisi. Infatti tale analisi si è rivelata fondamentale poiché si è potuto notare che la geometria di tali strutture ricopre un ruolo fondamentale ai fini delle caratteristiche meccaniche delle stesse. Un materiale omogeneo isotropo (AISI 316) è stato usato nella modellazione della struttura.
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Balthazar, Matthis. "Conception d’outillage de mise en forme des composites à haute dynamique thermique via l’utilisation de structures lattices à porosité contrôlée." Electronic Thesis or Diss., Nantes Université, 2024. http://www.theses.fr/2024NANU4031.
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La mise en forme des matériaux composites nécessite un apport et une évacuation contrôlés de la chaleur dans la pièce afin de garantir sa qualité tout en permettant une productivité maximale. Dans les procédés nécessitant un outillage pour le formage des matériaux, la régulation thermique est assurée par des canaux où circule un fluide à débit et température contrôlés. Ces canaux doivent être proches de la surface de la cavité moulante pour une réponse thermique rapide, mais leur distance est limitée par la résistance mécanique et le risque de marquage thermique des pièces. Une alternative aux approches classiques est l'utilisation d’un milieu poreux constitué de structures lattices dans lequel un fluide de régulation va circuler. Ces structures poreuses peuvent être intégrées dans les outillages au plus près de la surface car elles apportent un renfort structurel, et évitent le marquage thermique grâce à un écoulement sous forme de « nappe ». L’inertie thermique peut alors être fortement réduite. Cette solution a pour objectif de réduire au maximum le temps de réponse thermique de l'outillage lorsqu'il est soumis à des variations de température, de réduire la consommation énergétique du procédé, mais aussi de pouvoir concentrer localement les puissances à évacuer ou apporter en adaptant spatialement la porosité de la structure. Ce travail de thèse s’interesse à l’analyse des transferts thermiques couplés à l’écoulement du fluide au sein de l’outillage. Pour cela, le travail comporte une étude numérique et une expérimentale. Les résultats fournissent une compréhension des paramètres de conception sur la performance de l’outillage et démontrent la pertinence de l’utilisation de telles structures pour la gestion thermiqueThe forming of composite parts requires a controlled supply and release of heat to and from the part, in order to guarantee quality while maximizing productivity. In processes requiring tooling for material forming, thermal regulation is ensured by channels through which a fluid circulates at a controlled flow rate and temperature. These channels need to be close to the surface of the mold cavity for rapid thermal response, but their distance is limited by mechanical strength and the risk of thermal marking of the parts. An alternative to conventional approaches is to use a porous medium consisting of lattice structures in which a fluid will circulate. These porous structures can be integrated into tooling as close as possible to the surface, as they provide structural reinforcement and avoid thermal marking thanks to a "sheet" flow. Thermal inertia can thus be greatly reduced. The aim of this solution is to minimize the thermal response time of the tooling when subjected to temperature variations, to reduce the energy consumption of the process, and to locally concentrate the power to be evacuated or supplied by spatially adapting the porosity of the structure. This research focuses on the analysis of heat transfer coupled with fluid flow within the tooling. To this end, the work includes a numerical and an experimental study. The results provide an understanding of the impact of design parameters on tooling performance, and demonstrate the relevance of using such structures for thermal management
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Benamour, Malek. "Développement d'une méthode de pénalisation volumique en lattice Boltzmann : application aux domaines mobiles." Thesis, La Rochelle, 2015. http://www.theses.fr/2015LAROS017/document.
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Les écoulements autour de structures en mouvement font l'objet de plusieurs travaux numériques et expérimentaux. L'objectif de ce travail de thèse consiste à montrer la pertinence de la combinaison de la pénalisation volumique avec la méthode de lattice Boltzmann (LBM), dans l'étude du mouvement d'obstacles mobiles dans un écoulement, et de leur interaction avec celui-ci. La LBM,qui est simple et précise à mettre en œuvre, a prouvé ces dernières années son efficacité dans le domaine de la mécanique des fluides. Par ailleurs, la méthode de pénalisation volumique consiste à introduire un terme de pénalisation dans l'équation que l'on souhaite résoudre, afin de prendre en compte l'influence de l'obstacle sur le domaine fluide. Comme cette équation est résolue sur l'ensemble du domaine composé du fluide et du solide, les conditions aux limites à l'interface fluide-solide sont appliquées de façon naturelle. Il semble donc aisé de combiner cette technique avec la méthode de lattice Boltzmann. Nous avons dans un premier temps rappelé les notions de base et les principales caractéristiques de la méthode de lattice Boltzmann. On a présenté quelques exemples d'applications sur des cas tests, que nous avons programmés. Ensuite, une étude bibliographique faisant état des différentes approches qui utilisent la LBM dans l'étude des problèmes d'interaction fluide structure (IFS) a été réalisée. Puis, la combinaison de la pénalisation volumique avec la LBM a été testée avec succès sur l'équation de Burgers monodimensionnelle. La validation s'est portée en premier lieu, sur un écoulement autour d'un solide fixe, puis sur un écoulement autour d'une structure dont le mouvement est imposé, et finalement sur un problème d'IFS de type masse-ressort. La méthode développée a été ensuite testée sur les équations de Navier-Stokes, en considérant un fluide incompressible et une structure rigide. La validation s'est portée tout d'abord sur un écoulement autour d'obstacles immobiles (carré et cylindre), puis autour d'un cylindre mobile en oscillations forcées et libres. Enfin, une dernière application a été portée sur un écoulement entre deux plaques mobiles dans un canal. Nous avons montré que pour tous les cas étudiés, l'approche développée donne de bons résultats, elle reproduit avec précision les résultats de référenceFlows around moving bodies are the subject of several numerical and experimental studies. The work presented in this document deals with the implementation of a volume penalization technique in a lattice Boltzmann model (LBM), in order to compute flows around moving obstacles. The LBM, which is accurate and easy to implement, has been successfully applied in fluid mechanics during the last decades. It was thus chosen in the present work, for flow computation. Furthermore, the volume penalization technique consists in introducing a volume penalization term into the equation that needs to be solved, in order to take into account the influence of the obstacle on the fluid domain. Since this equation is solved on both fluid and solid domains, the boundary conditions at the fluid-solid interface are naturally applied. Hence this technique seems easy to implement in a lattice Boltzmann framework. In the first chapter, the foundations and the main features of the lattice Boltzmann method are recalled, and several test cases that we simulated are presented. The second chapter deals with a literature review of the techniques developed for the simulation of fluid structure interaction problems in combination with the LBM. In the third chapter, the volume penalization method combined with the LBM was first applied to the one dimensional Burgers equation, considering motionless and moving obstacles (forced motion, and coupling between the fluid force calculated with the penalized Burgers equation and the motion of the obstacle). The combination of the volume penalization approach and the LBM was then employed to solve the incompressible NavierStokes equations, for cases of flows past motionless obstacles (flows over a square obstacle, and past a circular cylinder), and past an oscillating cylinder (where forced and free oscillations of the cylinder were simulated). Finally, this method was also applied to a symmetric Couette flow. For all these simulated cases, a good agreement with numerical results obtained with other techniques, and with results found in literature, was obtained
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Misawa, Masaki, Naoki Takada, and Kazuhiro Yamamoto. "Combustion simulation with Lattice Boltzmann method in a three-dimensional porous structure." Elsevier, 2005. http://hdl.handle.net/2237/20031.
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Fuhry, David P. "PLASMA-HD: Probing the LAttice Structure and MAkeup of High-dimensional Data." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1440431146.
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Siegel, Jakob. "A CUDA optimized Lattice Boltzmann method implementation using control-structure splitting techniques." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 69 p, 2009. http://proquest.umi.com/pqdweb?did=1885754631&sid=4&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Nguyen, Jason Nam. "A heuristic optimization method for the design of meso-scale truss structure for complex-shaped parts." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/44810.
Full textAbstract:
Advances in additive manufacturing technologies have brought a new paradigm shift to both design and manufacturing. There is a much bigger design space in which designers can achieve a level of complexity and customizability, which are infeasible using traditional manufacturing processes. One application of this technology is for fabrication of meso-scale lattice structures (MSLS). These types of structures are designed to have material where it is needed for specific applications. They are suitable for any weight-critical applications, particularly in industries where both low weight and high strength are desired. MSLS can easily have hundreds to thousands of individual strut, where the diameter of each strut can be treated as a design variable. As a result, the design process poses a computational challenge. Since the computational complexity of the design problem often scales exponentially with the number of design variables, topological optimization that requires multi-variable optimization algorithm is infeasible for large-scale problems.
In previous research, a new method was presented for efficiently optimizing MSLS by utilizing a heuristic that reduces the multivariable optimization problem to a problem of only two variables. The method is called the Size Matching and Scaling (SMS) method, which combines solid-body analysis and predefined unit-cell library to generate the topology of the structure. However, the method lacks a systematic methodology to generate the initial ground geometry for the design process, which limits the previous implementations of the SMS method to only simple, axis-aligned structures.
In this research, an augmented SMS method is presented. The augmented method includes the integration of free-mesh approach in generating the initial ground geometry. The software that embodies that ground geometry generation process is integrated to commercial CAD system that allows designer to set lattice size parameters through graphical user interface. In this thesis, the augmented method and the unit-cell library are applied to various design examples.
The augmented SMS method can be applied effectively in the design of conformal lattice structure with highly optimized stiffness and volume for complex surface. Conformal lattice structures are those conformed to the shape of a part's surface and that can used to stiffen or strengthen a complex and curved surface. This design approach removes the need for a rigorous topology optimization, which is a main bottleneck in designing MSLS.
38
Gervais, Claire. "Proposition of a model generating derived crystal structures from a given lattice." Rouen, 2002. http://www.theses.fr/2002ROUES057.
Full textAbstract:
Un modèle de construction de structures cristallines basé sur l'utilisation d'un empilement cristallin existant est présenté. Le protocole de construction de ce modèle appelé " Derived Crystal Packings " (DCP) peut se résumer en deux étapes :(i)extraction de fragments périodiques (PF) d'une structure expérimentale et (ii) application d'opérateurs de symétrie sur ces PFs, permettant de régénérer de nouveaux empilements cristallins. Le modèle DCP est appliqué à une famille de 5-alkyl-5-aryl-hydantoines, ainsi qu'à des structures provenant de la Cambridge Structural Database. Sa capacité à prédire des formes polymorphiques, à mettre en évidence des relations structurales entre énantiomères et composés racémiques, et à analyser des phénomènes de macles et d'épitaxie lamellaire est démontrée. Néanmoins, à l'issue de ces premiers travaux il apparaît que la comparaison entre les structures prédites et celles trouvées expérimentalement est actuellement limitée par la minimisationA simple model generating crystal structures derived from a given lattice is presented. The two-step procedure of the model called "Derived Crystal Packings" (DCP) consists of (i) extracting one- or two-dimensional periodic fragments (PF) from a known structure and (ii) of adding symmetry operators to these PFs, generating new three-dimensional crystal structures. The DCP model is applied to a family of 5-alkyl-5-aryl-hydantoins as well as couples of known structures retrieved from the Cambridge Structural Database. Its ability to predict polymorphs, to highlight relationships between enantiomer and racemic compounds structures, and to analyse twins and lamellar epitaxy phenomena is demonstrated. However, it appears that the comparison between the predicted structures and the experimentally observed structures is strongly limited by the minimisation procedure
39
Rawas, A. "The crystal structure of some biphenyl derivatives and X-ray diffraction studies of some liquid crystal materials." Thesis, University of Hull, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377046.
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OLIVEIRA, MYRIAN COE DE. "A STUDY OF THE SENSITIVITY OF THE LATTICE-LADER STRUCTURE USING STATE VARIABLES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1991. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=9394@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICONa construção de filtros digitais os coeficientes da sua função de transferência, calculados teoricamente, nem sempre podem ser implementados com exatidão. Isto gera o erro de quantização. A análise de sensibilidade permite conhecer tal alteração das especificações teóricas como também avaliar o desempenho do filtro. Este trabalho examina a estrutura Lattice-Ladder, tipo de filtro digital, descrita por equações de estado genéricas. O objetivo é estabelecer expressões de sensibilidade nos domínios do tempo e da freqüência, para resposta impulsional e resposta a uma excitação qualquer.
In the construction of digital filters the coeficientes of its transfer function, calculated theorically, can´t often be implemented with accuracy. This leads to the quantization error. The sensitivy analysis allows to know this deviation from theoretical specifications and allows to estimate filter´s performance. This work examines Lattice- Ladder structure, a type of digital filter, described by generic state equations. The purpose is to establish sensivity expressions in time and frequency domains, for impulse and generic responses.
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Day, Graeme Matthew. "Lattice dynamical studies of molecular crystals with application to polymorphism and structure prediction." Thesis, University College London (University of London), 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404411.
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Yoshino, Masato. "Numerical Analysis of Transport Phenomena in Porous Structure by the Lattice Boltzmann Method." Kyoto University, 2000. http://hdl.handle.net/2433/157089.
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本文データは平成22年度国立国会図書館の学位論文(博士)のデジタル化実施により作成された画像ファイルを基にpdf変換したものであるKyoto University (京都大学)
0048
新制・課程博士
博士(工学)
甲第8403号
工博第1968号
新制||工||1178(附属図書館)
UT51-2000-F307
京都大学大学院工学研究科化学工学専攻
(主査)教授 荻野 文丸, 教授 小森 悟, 教授 田門 肇
学位規則第4条第1項該当
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Hauglin, Harald. "Vortex lattice structure in single crystal YBCO studied with atomic beam magnetic resonance /." The Ohio State University, 1997. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487943341526625.
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Hasan, Nesreen [Verfasser]. "A lattice QCD study of nucleon structure with physical quark masses / Nesreen Hasan." Wuppertal : Universitätsbibliothek Wuppertal, 2020. http://d-nb.info/1207005657/34.
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Wiese, Christian. "Investigating new lattice approaches to the momentum and spin structure of the nucleon." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2016. http://dx.doi.org/10.18452/17522.
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Diese Arbeit beschäftigt sich mit der Berechnung von für die Struktur des Nukleons relevanten Observablen, die experimentell durch inklusive und semi-inklusive Streuexperimente bestimmt werden können. Es werden zwei Pilotstudien erörtert, welche die Spin- und Impulsstruktur des Nukleons mithilfe von Gitter-QCD untersuchen. Hierfür wird der Twisted-Mass-Formalismus mit dynamischen Fermionen verwendet, um sicherzustellen, dass die untersuchten Größen einen verbesserten Kontinuumslimes aufweisen. Der erste Teil dieser Arbeit untersucht die Umsetzbarkeit einer Rechnung, die sich mit dem durchschnittlichen Impulsanteil der Gluonen im Nukleon auseinandersetzt. Diese Größe wurde bisher kaum im Rahmen der Gitter-QCD behandelt. In diesem Zusammenhang werden zwei verschiedene Gittermethoden untersucht: das Feynman-Hellman-Theorem, sowie die direkte Berechnung der relevanten Formfaktoren. Mithilfe der zweiten Methode und mehreren Iterationen des Schmierens der Eichlinks ist es möglich, statistisch aussagekräftige Resultate zu erhalten. Die zweite Studie beschäftigt sich mit der direkten Berechnung der vollständigen Impuls- und Spinverteilung von Quarks und Antiquarks im Nukleon. Hierfür wird untersucht, ob eine kürzlich publizierte Methode praktikabel ist, nach der eine räumliche Quasiverteilung zu berechnen und aus dieser die physikalische Verteilung abzuleiten ist. In diesem Zusammenhang wird der Einfluß des Schmierens der Eichlinks und unterschiedlicher Impulsboosts des Nukleons erprobt. Die anschließend berechneten Isovektor-Quarkverteilungen (unpolarisiert und polarisiert) weisen eine gute qualitative Übereinstimmung mit Verteilungen auf, die mithilfe von phänomenologischen Analysen bestimmt wurden. Zentrale Erkenntnis dieser Arbeit ist der Nachweis, dass es auf dem Gitter prinzipiell möglich ist, beide Observablen zu berechnen. Trotzdem muss noch erheblich mehr Arbeit aufgewendet werden, um verlässliche Resultate für diese Größen zu erhalten.This thesis deals with the theoretical computation of nucleon structure observables as they can be experimentally obtained from inclusive and semi-inclusive scattering experiments. I present two exploratory studies on spin and momentum structure observables of the nucleon in the framework of lattice QCD. Throughout this work, I use the twisted mass formalism with dynamical fermions at maximal twist, which ensures an improved continuum limit scaling for the relevant quantities. In the first part, I investigate the feasibility of a lattice calculation of the gluons’ average momentum fraction in the nucleon, a quantity that is rarely studied in lattice QCD. For this purpose, I study two different methods, namely the Feynman-Hellman theorem and the direct computation of the relevant form factor. Applying the latter method and combining it with several steps of stout gauge link smearing, I obtain a statistically significant results for the gluon content. The second study is concerned with the direct computation of the full momentum and spin distribution of quarks and antiquarks within the nucleon. I investigate the feasibility of a recently published approach proposing the computation of a purely spatial quasi-distribution that can be related to the physical distribution. I test the influence of gauge link smearing and different nucleon momentum boosts on the lattice data. Ultimately, I obtain iso-vector quark distributions for the unpolarized and polarize case that featuring a decent qualitative agreement to quark distributions acquired from phenomenological fits. As a key result of this work, I demonstrate that the demanding calculation of gluon content and the novel approach of computing quark distributions directly within lattice QCD are feasible in principle, although significantly more effort has to be invested into obtaining accurate results with reliable uncertainties.
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Liu, Biheng. "Reduced order models for the analysis of offshore lattice structures." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2022.
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The lattice is a common frame applied in offshore structures benefiting from their economic construction and easily accessible, for example, the jacket platform of the offshore wind turbine. In order to accelerate the design process of a model, this thesis proposed a method to reduce the order of the offshore lattice structure models. The full order model is constructed based on the FEM. Applying the MDOF mass discrete concept lumps the structure mass on each story center. Meanwhile, apply the DSM to determine the displacement and the forces implied on the mass center for accomplishing the unitary displacement of each DOF of the mass center node. Finally, a reduced order model for the lattice structure will be obtained. That model composed of the stiffness matrix of the mass center node has the same fundamental flexural frequency as the original model. The model can be expressed by symbolic relationship as well as possible to package as a function for further quotation. All computation processes of this thesis were executed on the Python platform.
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Iacob, Alexandru Sorin. "Studio comparativo tra configurazioni alari convenzionali e con struttura lattice." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
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Lo studio effettuato ha lo scopo di confrontare un’ala per impiego aerospaziale o automotive con configurazione convenzionale e una con riempimento con struttura di tipo lattice regolare cubica non conforme, al fine di determinare se un’ala ottenuta mediante stampa con tecniche di additive manufacturing è in grado di competere con un’ala ottenuta attraverso metodi convenzionali a livello di massa a parità di sollecitazione massima.
Il confronto è stato effettuato sia a pari peso calcolando le massime tensioni, sia ad equivalenti sollecitazioni esterne, andando a verificare i pesi ottenuti.
A tale scopo è stata impiegata una analisi 1-way FSI che coinvolge sia simulazioni CFD che FEM.
È stato anche messo in pratica un approccio di analisi semplificativo che consiste nello studiare la struttura lattice come se fosse un materiale continuo, cercando di capire se il cosiddetto metodo di omogeneizzazione applicato al caso di studio in questione, permette di ottenere risultati soddisfacenti riducendo di gran lunga i tempi di calcolo.
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Venturini, Nicolas. "Valutazione numerica del comportamento meccanico di strutture "lattice"." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/13304/.
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In questo lavoro diverse strutture di tipo lattice sono state realizzate mediante un CAD e sottoposte a diverse prove a tensioni numeriche per capire quali parametri influiscono sul loro comportamento sotto carico tensionale e con lo scopo di identificare la migliore configurazione tra quelle realizzate. Mediante i risultati ottenuti, si è dimostrata l’importanza fondamentale che ricopre la geometria di tali strutture rispetto alla scelta del materiale, che rimane un problema piuttosto secondario. Poi è stato ricavato un parametro adimensionale capace di indicare la validità di una configurazione rispetto ad un’altra.
Infine, la miglior lattice structure realizzata è stata integrata ad un componente meccanico e sottoposta ad una forza tensionale per valutarne vantaggi e svantaggi in un’applicazione.
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Zhang, Botao. "Design of Variable-Density Structures for Additive Manufacturing Using Gyroid Lattices." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1535374427634743.
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Graf, Gregory C. "Development of specialized base primitives for meso-scale conforming truss structures." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28238.
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