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Dissertations / Theses on the topic 'Computational mechanics'

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Published: 4 June 2021
Last updated: 19 April 2025

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1

Denzer, Ralf. "Computational configurational mechanics." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=978669797.

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2

Zhu, Tulong. "Meshless methods in computational mechanics." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/11795.

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3

Alipour, Skandani Amir. "Computational and Experimental Nano Mechanics." Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/64869.

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The many advances of nano technology extensively revolutionize mechanics. A tremendous need is growing to further bridge the gap between the classical mechanics and the nano scale for many applications at different engineering fields. For instance, the themes of interdisciplinary and multidisciplinary topics are getting more and more attention especially when the coherency is needed in diagnosing and treating terminal diseases or overcoming environmental threats. The fact that how mechanical, biomedical and electrical engineering can contribute to diagnosing and treating a tumor per se is both interesting and unveiling the necessity of further investments in these fields. This dissertation presents three different investigations in the area of nano mechanics and nano materials spanning from computational bioengineering to making mechanically more versatile composites. The first part of this dissertation presents a numerical approach to study the effects of the carbon nano tubes (CNTs) on the human body in general and their absorbability into the lipid cell membranes in particular. Single wall carbon nano tubes (SWCNTs) are the elaborate examples of nano materials that departed from mere mechanical applications to the biomedical applications such as drug delivery vehicles. Recently, experimental biology provided detailed insights of the SWCNTs interaction with live organs. However, due to the instrumental and technical limitations, there are still numerous concerns yet to be addressed. In such situation, utilizing numerical simulation is a viable alternative to the experimental practices. From this perspective, this dissertation reports a molecular dynamics (MD) study to provide better insights on the effect of the carbon nano tubes chiralities and aspect ratios on their interaction with a lipid bilayer membrane as well as their reciprocal effects with surface functionalizing. Single walled carbon nano tubes can be utilized to diffuse selectively on the targeted cell via surface functionalizing. Many experimental attempts have smeared polyethylene glycol (PEG) as a biocompatible surfactant to carbon nano tubes. The simulation results indicated that SWCNTs have different time-evolving mechanisms to internalize within the lipid membrane. These mechanisms comprise both penetration and endocytosis. Also, this study revealed effects of length and chirality and surface functionalizing on the penetrability of different nano tubes. The second part of the dissertation introduces a novel in situ method for qualitative and quantitative measurements of the negative stiffness of a single crystal utilizing nano mechanical characterization; nano indentation. The concept of negative stiffness was first introduced by metastable structures and later by materials with negative stiffness when embedded in a stiffer (positive stiffness) matrix. However, this is the first time a direct quantitative method is developed to measure the exact value of the negative stiffness for triglycine sulfate (TGS) crystals. With the advancements in the precise measuring devices and sensors, instrumented nano indentation became a reliable tool for measuring submicron properties of variety of materials ranging from single phase humongous materials to nano composites with heterogeneous microstructures. The developed approach in this chapter of the dissertation outlines how some modifications of the standard nano indentation tests can be utilized to measure the negative stiffness of a ferroelectric material at its Curie temperature. Finally, the last two chapters outline the possible improvements in the mechanical properties of conventional carbon fiber composites by introducing 1D nano fillers to them. Particularly, their viscoelastic and viscoplastic behavior are studied extensively and different modeling techniques are utilized. Conventional structural materials are being replaced with the fiber-reinforced plastics (FRPs) in many different applications such as civil structures or aerospace and car industries. This is mainly due to their high strength to weight ratio and relatively easy fabrication methods. However, these composites did not reach their full potential due to durability limitations. The majorities of these limitations stem from the polymeric matrix or the interface between the matrix and fibers where poor adhesion fails to carry the desired mechanical loadings. Among such failures are the time-induced deformations or delayed failures that can cause fatal disasters if not taken care of properly. Many methodologies are offered so far to improve the FRPs' resistance to this category of time-induced deformations and delayed failures. Several researchers tried to modify the chemical formulation of polymers coming up with stiffer and less viscous matrices. Others tried to modify the adhesion of the fibers to the matrix by adding different chemically functional groups onto the fibers' surface. A third approach tried to modify the fiber to matrix adhesion and at the same time improve the viscous properties of the matrix itself. This can be achieved by growing 1D nano fillers on the fibers so that one side is bonded to the fiber and the other side embedded in the matrix enhancing the matrix with less viscous deformability. It is shown that resistance to creep deformation and stress relaxation of laminated composites improved considerably in the presence of the nano fillers such as multiwall carbon nano tubes (MWCNTs) and zinc oxide nano wires (ZnO- NWs). The constitutive behaviors of these hybrid composites were investigated further through the use of the time temperatures superposition (TTS) principle for the linear viscoelastic behavior and utilizing phenomenological models for the viscoplastic behavior.
Ph. D.
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4

Hughes, Michael. "Computational magnetohydrodynamics." Thesis, University of Greenwich, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284683.

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5

Barbaresi, Mattia. "Computational mechanics: from theory to practice." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/15649/.

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In the last fifty years, computational mechanics has gained the attention of a large number of disciplines, ranging from physics and mathematics to biology, involving all the disciplines that deal with complex systems or processes. With ϵ-machines, computational mechanics provides powerful models that can help characterizing these systems. To date, an increasing number of studies concern the use of such methodologies; nevertheless, an attempt to make this approach more accessible in practice is lacking yet. Starting from this point, this thesis aims at investigating a more practical approach to computational mechanics so as to make it suitable for applications in a wide spectrum of domains. ϵ-machines are analyzed more in the robotics scene, trying to understand if they can be exploited in contexts with typically complex dynamics like swarms. Experiments are conducted with random walk behavior and the aggregation task. Statistical complexity is first studied and tested on the logistical map and then exploited, as a more applicative case, in the analysis of electroencephalograms as a classification parameter, resulting in the discrimination between patients (with different sleep disorders) and healthy subjects. The number of applications that may benefit from the use of such a technique is enormous. Hopefully, this work has broadened the prospect towards a more applicative interest.
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6

Mocanita, Mihaela Ancuta. "Computational mechanics of welding complex structures." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0021/MQ57733.pdf.

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7

Borrvall, Thomas. "Computational topology optimization in continuum mechanics /." Linköping : Univ, 2002. http://www.bibl.liu.se/liupubl/disp/disp2002/tek744s.pdf.

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8

Pearce, C. J. "Computational plasticity in concrete failure mechanics." Thesis, Swansea University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638434.

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A constitutive model for plain concrete is presented, centred around a fracture energy based plasticity formulation. The essential ingredients of a concrete strength envelope are realised (such as a non-linear hydrostatic pressure dependence, a non-circular deviatoric trace and a realistic biaxial trace) by utilising the well known Five Parameter Model of William/Warnke as the basis of an Enhanced Five Parameter Model. This model is capable of a complex loading surface evolution for capturing both the pre and post peak regimes of concrete. In particular, the post peak tensile softening is introduced exponentially, controlled by the fracture energy release rate. Several computational aspects of rate independent plasticity, with reference to the Enhanced Five Parameter Model are investigated. Finite stress increments are integrated using a backward Euler stress return formulation, solved by the Newton Raphson method. However, due to the complex nature of the proposed loading surface, this approach has been found not to be fully robust and in need of improvement. As such, controlled scaling of the stress update is introduced as well as improved starting predictions of the final solution via an analytical return to an intermediate auxiliary loading surface. The conditions necessary for discontinuous bifurcation of strain rates are discussed and the localisation tensor is introduced. Furthermore, spectral analysis of the localisation tensor is utilised to predict impending localisation and a scalar failure indicator is proposed to monitor the evolution of discontinuities. With particular application to the proposed concrete model, studies of localisation problems revealed that some form of mesh alignment is essential if impending bifurcation and orientation of discontinuities produced by the localisation analysis is to be resolved. Moreover, the effect on the overall response of a non-aligned mesh is shown to be significant.
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9

Mocanita, Mihaela Ancuta Carleton University Dissertation Engineering Mechanical and Aerospace. "Computational mechanics of welding complex structures." Ottawa, 2000.

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10

Wu, Fei. "Parallel computational methods for constrained mechanical systems." Diss., The University of Arizona, 1997. http://hdl.handle.net/10150/282561.

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Two methods suitable for parallel computation in the study of mechanical systems with holonomic and nonholonomic constraints are presented: one is an explicit solution based on generalized inverse algebra; the second solves problems of this class through the direct application of Gauss' principle of least constraint and genetic algorithms. Algorithms for both methods are presented for sequential and parallel implementations. The method using generalized inverses is able to solve problems that involve redundant, degenerate and intermittent constraints, and can identify inconsistent constraint sets. It also allows a single program to perform pure kinematic and dynamic analyses. Its computational cost is among the lowest in comparison with other methods. In addition, constraint violation control methods are investigated to improve integration accuracy and further reduce computational cost. Constrained dynamics problems are also solved using optimization methods by applying Gauss' principle directly. An objective function that incorporates constraints is derived using a symmetric scheme, which is implemented using genetic algorithms in a parallel computing environment. It is shown that this method is capable of solving the same cases of constraints as the former method. Examples and numerical experiments demonstrating the applications of the two methods to constrained multiparticle and multibody systems are presented.
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11

Walls, Kenneth Cline. "Multi-material contact for computational structural mechanics." Birmingham, Ala. : University of Alabama at Birmingham, 2008. https://www.mhsl.uab.edu/dt/2008m/walls.pdf.

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12

Gibbons, Melissa Marie. "Computational mechanics of nanoindentation of viral capsids." Diss., Restricted to subscribing institutions, 2008. http://proquest.umi.com/pqdweb?did=1709825191&sid=4&Fmt=2&clientId=1564&RQT=309&VName=PQD.

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13

Lew, Adrian Jose Ortiz Michael. "Variational time integrators in computational solid mechanics /." Diss., Pasadena, Calif. : California Institute of Technology, 2003. http://resolver.caltech.edu/CaltechETD:etd-05262003-200254.

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14

Christensen, Peter W. "Computational nonsmooth mechanics : contact, friction and plasticity /." Linköping : Department of mechanical engineering, 2000. http://catalogue.bnf.fr/ark:/12148/cb40921031z.

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15

Sachse, Frank B. "Computational cardiology : modeling of anatomy, electrophysiology, and mechanics /." Berlin [u.a.] : Springer, 2004. http://www.loc.gov/catdir/enhancements/fy0818/2004104242-d.html.

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16

Lee, Jack. "Computational Modelling of Coronary Structure and Flow Mechanics." Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526077.

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17

Fidkowski, Piotr. "A hybrid parallel framework for computational solid mechanics." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/67182.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 95-98).
A novel, hybrid parallel C++ framework for computational solid mechanics is developed and presented. The modular and extensible design of this framework allows it to support a wide variety of numerical schemes including discontinuous Galerkin formulations and higher order methods, multiphysics problems, hybrid meshes made of different types of elements and a number of different linear and non-linear solvers. In addition, native, seamless support is included for hardware acceleration by Graphics Processing Units (GPUs) via NVIDIA's CUDA architecture for both single GPU workstations and heterogenous clusters of GPUs. The capabilities of the framework are demonstrated through a series of sample problems, including a laser induced cylindrical shock propagation, a dynamic problem involving a micro-truss array made of millions of elements, and a tension problem involving a shape memory alloy with a multifield formulation to model the superelastic effect.
by Piotr Fidkowski.
S.M.
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18

Navarro, Zafra Joaquin. "Computational mechanics of fracture on advanced aerospace structures." Thesis, University of Sheffield, 2016. http://etheses.whiterose.ac.uk/16883/.

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In this thesis, the computational simulation of cracks in advanced composite structures subjected to biaxial loading is studied. A structural integrity analysis using the eXtended Finite Element Method (XFEM) is considered for simulating the crack behaviour of a chopped fibre-glass-reinforced polyester (CGRP) cruciform specimen subjected to a quasi-static tensile biaxial loading [99]. This is the first time this problem is accomplished for computing the stress intensity factors (SIFs) produced in the biaxially loaded area of the cruciform specimen. SIFs are calculated for infinite plates under biaxial loading as well as for the CGRP cruciform specimens in order to review the possible edge effects. A new ratio relating the side of the central zone of the cruciform and the crack length is proposed. Additionally, the initiation and evolution of a three-dimensional crack are successfully simulated. Specific challenges such as the 3D crack initiation, based on a principal stress criterion, and its front propagation, in perpendicular to the principal stress direction, are conveniently addressed. No initial crack location is pre-defined and an unique crack is developed. A three-dimensional progressive damage model (PDM) is implemented within a CGRP cruciform structure for modelling its damage under loading [100]. In order to simulate the computational behaviour of the composite, the constitutive model considers an initial elastic behaviour followed by strain-softening. The initiation criterion defined is based on the maximum principal stress of the composite and once this criterion is satisfied, stiffness degradation starts. For the computation of damage, the influence of the fibre and the matrix are taken into account within the damage rule. This is the first time a three-dimensional PDM is implemented into a composite cruciform structure subjected to biaxial loading. A new approach for dynamic analysis of stationary cracks using XFEM is derived. This approach is capable of addressing dynamic and static fracture mechanics problems. Additionally, by means of this relatively simple approach, it is possible to address correctly the crack pattern of the 10 degrees off-axis laminate manufactured solving the limitation observed with progressive damage modelling. During the whole thesis, the computational outcomes have been validated by means of comparison with theoretical and experimental results.
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19

Johnson, Paul C. "Parallel computational mechanics with a cluster of workstations." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0012121.

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20

Emerson, Tonya Lynn. "Ductile fracture mechanics : modeling, experiments, and computational simulation /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2002. http://uclibs.org/PID/11984.

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21

Panneerselvam, Dinesh. "Mechanics of Asphalt Concrete: Analytical and Computational Studies." online version, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=case1106341613.

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22

TIAN, BINYU. "COMPUTATIONAL AEROELASTIC ANALYSIS OF AIRCRAFT WINGS INCLUDING GEOMETRY NONLINEARITY." University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1070398084.

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23

Peshkin, David Annesley. "Computational fluid dymanics using transputer systems." Thesis, Queen's University Belfast, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335585.

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24

Alvarado, Walter. "Investigating Butyrylcholinesterase Inhibition via Molecular Mechanics." Thesis, California State University, Long Beach, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10639439.

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We show that a combination of different theoretical methods is a viable approach to calculate and explain the relative binding affinities of inhibitors of the human butyrylcholinesterase enzyme. We probe structural properties of the enzyme-inhibitor complex in the presence of dialkyl phenyl phosphates and derivatives that include changes to the aromatic group and alkane-to-cholinyl substitutions that help these inhibitors mimic physiological substrates. Monte Carlo docking allowed for the identification of three regions within the active site of the enzyme where substituents of the phosphate group could be structurally stabilized. Computational clustering was used to identify distinct binding modes and their relative stabilities. Molecular dynamics suggest an essential asparagine residue not previously characterized as strongly influencing inhibitor strength which may serve as a crucial component in catalytic and inhibitory activity. This study provides a framework for suggesting future inhibitors that we expect will be effective at sub-micromolar concentrations.

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25

Tang, Baobao. "Development of Mathematical and Computational Models to Design Selectively Reinforced Composite Materials." Thesis, University of Louisiana at Lafayette, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10163313.

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Different positions of a material used for structures experience different stresses, sometimes at both extremes, when undergoing processing, manufacturing, and serving. Taking the three-point bending as an example, the plate experiences higher stress in the middle span area and lower stress in both sides of the plate. In order to ensure the performance and reduce the cost of the composite, placement of different composite material with different mechanical properties, i.e. selective reinforcement, is proposed.

Very few study has been conducted on selective reinforcement. Therefore, basic understanding on the relationship between the selective reinforcing variables and the overall properties of composite material is still unclear and there is still no clear methodology to design composite materials under different types of loads.

This study started from the analysis of composite laminate under three point bending test. From the mechanical analysis and simulation result of homogeneously reinforced composite materials, it is found that the stress is not evenly distributed on the plate based on through-thickness direction and longitudinal direction. Based on these results, a map for the stress distribution under three point bending was developed. Next, the composite plate was selectively designed using two types of configurations. Mathematical and finite element analysis (FEA) models were built based on these designs. Experimental data from tests of hybrid composite materials was used to verify the mathematical and FEA models. Analysis of the mathematical model indicates that the increase in stiffness of the material at the top and bottom surfaces and middle-span area is the most effective way to improve the flexural modulus in three point bending test. At the end of this study, a complete methodology to perform the selective design was developed.

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Betancourt, Arturo. "Computational study of the heat transfer and fluid structure of a shell and tube heat exchanger." Thesis, Florida Atlantic University, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10172609.

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A common technique to improve the performance of shell and tube heat exchangers (STHE) is by redirecting the flow in the shell side with a series of baffles. A key aspect in this technique is to understand the interaction of the fluid dynamics and heat transfer. Computational fluid dynamics simulations and experiments were performed to analysis the 3-dimensional flow and heat transfer on the shell side of an STHE with and without baffles. Although, it was found that there was a small difference in the average exit temperature between the two cases, the heat transfer coefficient was locally enhanced in the baffled case due to flow structures. The flow in the unbaffled case was highly streamed, while for the baffled case the flow was a highly complex flow with vortex structures formed by the tip of the baffles, the tubes, and the interaction of flow with the shell wall.

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27

JUNIOR, EDGARD POIATE. "ROCK MECHANICS AND COMPUTATIONAL MECHANICS FOR THE DESIGN OF OIL WELLS IN SALT ZONES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2012. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=34904@1.

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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
O objetivo deste estudo foi ampliar o conhecimento em mecânica de rochas evaporíticas e aplicar a mecânica computacional na modelagem numérica do comportamento estrutural de poços de petróleo em zonas de sal. Amostras de rochas evaporíticas de anidrita, halita, carnalita e taquidrita pertencentes à sequência evaporítica Ibura da Formação Muribeca, testemunhadas em poços de petróleo, foram submetidas a ensaios laboratoriais de mecânicas de rochas, em especial a ensaios triaxiais de fluência sob diferentes condições de estado de tensões e temperaturas. Nas mesmas condições de ensaio triaxial de fluência a taquidrita desenvolveu deformação axial específica de cerca de 107 vezes maior que a halita e 2,7 vezes maior que a carnalita, sendo que a anidrita permanece essencialmente indeformável. Para os ensaios triaxiais de fluência com a halita na temperatura de 86 graus Celsius foi possível definir o mecanismo duplo de deformação por fluência, enquanto que para a carnalita e a taquidrita isto ocorreu nas temperaturas de 130 e 86 graus Celsius, respectivamente. A taxa de deformação por fluência em regime permanente obtida por simulação numérica reproduziu fielmente os resultados experimentais dos ensaios triaxias de fluência, com erro relativo inferior a 1 por cento. Através dos ensaios laboratoriais foram obtidos os parâmetros geomecânicos de fluência das rochas ensaiadas e a seguir aplicados nos modelos numéricos de simulação, construídos para avaliar a influência de diversos parâmetros nos estudos de estabilidade de poços e integridade de revestimentos. A desconsideração da interação geomecânica entre estruturas salíferas e o maciço hospedeiro pode conduzir a falhas na perfuração de poços próximos a tais estruturas devido ao processo de halocinése do sal que altera o estado de tensões gravitacional.
The aim of this study was to increase knowledge of evaporitic rock mechanics and apply computational mechanics in numerical modeling of structural behavior of oil wells in areas of salt. Evaporitic rock samples of anhydrite, halite, carnallite e tachyhydrite and belonging to the evaporitic sequence Ibura from the Muribeca formation, coring in oil wells, were subjected to laboratory tests of rock mechanics, especially the triaxial creep under different states of stress and temperature. Under the same conditions of triaxial creep tachyhydrite developed specific axial strain rate about 107 times that of halite and 2.7 times that of carnallite, and anhydrite remains essentially undeformed. For the triaxial creep of halite in the temperature of 86 degrees Celsius it was possible to define the double mechanism creep law, while for carnallite and tachyhydrite this occurred at temperatures of 130 and 86 degrees Celsius, respectively. The creep rate in steady state condition obtained by numerical simulation accurately reproduced the experimental results of the triaxial creep tests, with a relative error less than 1 percent. Through laboratory tests geomechanical creep parameters of the tested rocks were obtained and then applied in numerical simulation models, designed to evaluate the influence of various parameters in the well stability and casing design. The lack of consideration of the geomechanical interaction between the salt structures and the host rock can lead to drilling failures in wells near such structures due to the salt halokinesis process that changes the gravitational stress state.
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Li, Dongli. "Computational and experimental study of shock wave interactions with cells." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:38beffe8-06c9-4b49-89f8-f5318c527800.

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This thesis presents a combined numerical and experimental study on the response of kidney cells to shock waves. The motivation was to develop a mechanistic model of cell deformation in order to improve the clinical use of shock waves, by either enhancing their therapeutic action against target cells or minimising their impact on healthy cells. An ultra-high speed camera was used to visualise individual cells, embedded in tissue-mimicking gel, in order to measure their deformation when subject to a shock wave from a clinical shock wave source. Advanced image processing was employed to extract the contour of the cell from the images. The evolution of the observed cell contour revealed a relatively small deformation during the compressional phase and a much larger deformation during the tensile phases of a shock wave. The experimental observations were captured by a numerical model which describes the volumetric cell response with a bilinear Equation of State and the deviatoric cell response with a viscoelastic framework. Experiments using human kidney cancer cells (CAKI-2) and noncancerous kidney cells (HRE and HK-2) were compared to the model in order to determine their mechanical properties. The differences between cancerous and noncancerous cells were exploited to demonstrate a design process by which shock waves may be able to improve the specificity on targeted cancer cells while having minimal effect on normal cells. The cell response to shock waves was studied in a more biophysically realistic environment to include influence of cell size, shape and orientation, and the presence of neighbouring cells. The most significant difference was predicted when cells were in a cluster in which case the presence of neighbouring cells resulted in a four-fold increase on the von Mises stress and the membrane strain. Finally the numerical model was extended to capture the effect of cell damage using one of two paradigms. In the first paradigm the model captured microdamage during one shock wave but then assumed that the cell recovered by the time the next shock wave arrived. The second model allowed microdamage to accumulate with increasing number of shock waves. These models may be able to explain the strong effect that shock wave loading rate has on tissue damage. In conclusion a validated numerical model has been developed which provides a mechanistic understanding of how cells respond to shock waves. The model has application in suggesting improved strategies for current uses of shock waves, e.g., lithotripsy, as well as opening up new indications such as cancer treatment.
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Sjöholm, Linnea. "Computational handbook for power line engineers." Thesis, KTH, Hållfasthetslära (Avd.), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-217480.

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The high voltage power network in Sweden consists mainly of overhead power lines, that is conductors suspended in the air by supports. Ideally when projecting a power line, all supports should be placed equidistantly and the conductors should be suspended at equal height. When this is not applied, the support placement may have consequences, such as uplifting forces in a support, which should be avoided. The objective of this thesis was to investigate both what in　uences the support placement, and what consequences that may come out of it. This was investigated using mainly analytical calculations on poles and conductors, but was also implemented on a specic case. When solving the case, support placement and FEM software were also used and compared with the analytical calculations. It was found that the support placement is in　uenced by both environmental factors; such as terrain, obstacles and solidity of the ground, as well as how long spans that are possible to construct. The span length is the distance between two nearby supports and is limited by sag, that is the de　ection of the conductors, and the strength of the supports. The sag is dependent on the tension in the conductor, which is dependent on wind and ice loads, temperature and creep; a permanent elongation that for certain materials occur over time even if the load is constant. Since the sag will increase over time, and especially at high temperatures, the distance between the conductors and the ground will decrease. This extra de　ection must be accounted for when designing the power line and determining the span length. When it comes to support designing, both bending and buckling should be accounted for. The greatest loads the supports are in　uenced by are transferred from the conductors, and therefore are dependent of the span length. An analysis of buckling and bending as function of span length was therefore conducted on non-guyed timber pole supports. It was concluded that bending stresses; due to wind loads on the support and especially on the conductors, are usually the critical aspect when designing standard power line supports.
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Eguzkitza, Bazar Ane Beatriz. "HERMESH : a geometrical domain composition method in computational mechanics." Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/276177.

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With this thesis we present the HERMESH method which has been classified by us as a a composition domain method. This term comes from the idea that HERMESH obtains a global solution of the problem from two independent meshes as a result of the mesh coupling. The global mesh maintains the same number of degrees of freedom as the sum of the independent meshes, which are coupled in the interfaces via new elements referred to by us as extension elements. For this reason we enunciate that the domain composition method is geometrical. The result of the global mesh is a non-conforming mesh in the interfaces between independent meshes due to these new connectivities formed with existing nodes and represented by the new extension elements. The first requirements were that the method be implicit, be valid for any partial differential equation and not imply any additional effort or loss in efficiency in the parallel performance of the code in which the method has been implemented. In our opinion, these properties constitute the main contribution in mesh coupling for the computational mechanics framework. From these requirements, we have been able to develop an automatic and topology-independent tool to compose independent meshes. The method can couple overlapping meshes with minimal intervention on the user's part. The overlapping can be partial or complete in the sense of overset meshes. The meshes can be disjoint with or without a gap between them. And we have demonstrated the flexibility of the method in the relative mesh size. In this work we present a detailed description of HERMESH which has been implemented in a high-performance computing computational mechanics code within the framework of the finite element methods. This code is called Alya. The numerical properties will be proved with different benchmark-type problems and the manufactured solution technique. Finally, the results in complex problems solved with HERMESH will be presented, clearly showing the versatility of the method.
En este trabajo presentamos el metodo HERMESH al que hemos catalogado como un método de composición de dominios puesto que a partir de mallas independientes se obtiene una solución global del problema como la unión de los subproblemas que forman las mallas independientes. Como resultado, la malla global mantiene el mismo número de grados de libertad que la suma de los grados de libertad de las mallas independientes, las cuales se acoplan en las interfases internas a través de nuevos elementos a los que nos referimos como elementos de extensión. Por este motivo decimos que el método de composición de dominio es geométrico. El resultado de la malla global es una malla que no es conforme en las interfases entre las distintas mallas debido a las nuevas conectividades generadas sobre los nodos existentes. Los requerimientos de partida fueron que el método se implemente de forma implícita, sea válido para cualquier PDE y no implique ningún esfuerzo adicional ni perdida de eficiencia para el funcionamiento paralelo del código de altas prestaciones en el que ha sido implementado. Creemos que estas propiedades son las principales aportaciones de esta tesis dentro del marco de acoplamiento de mallas en mecánica computacional. A partir de estas premisas, hemos conseguido una herramienta automática e independiente de la topología para componer mallas. Es capaz de acoplar sin necesidad de intervención del usuario, mallas con solapamiento parcial o total así como mallas disjuntas con o sin "gap" entre ellas. También hemos visto que ofrece cierta flexibilidad en relación al tamaños relativos entre las mallas siendo un método válido como técnica de remallado local. Presentamos una descripción detallada de la implementación de esta técnica, llevada a cabo en un código de altas prestaciones de mecánica computacional en el contexto de elementos finitos, Alya. Se demostrarán todas las propiedades numéricas que ofrece el métodos a través de distintos problemas tipo benchmark y el método de la solución manufacturada. Finalmente se mostrarán los resultados en problemas complejos resueltos con el método HERMESH, que a su vez es una prueba de la gran flexibilidad que nos brinda.
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31

Farhat, Hikmat. "Studies in computational methods for statistical mechanics of fluids." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape10/PQDD_0026/NQ50157.pdf.

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32

Kurdila, Andrew John. "Concurrent multiprocessors in computational mechanics for constrained dynamical systems." Diss., Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/15845.

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33

Kelly, David. "Computational mechanics in practice : mathematical adaptions and experimental applications." Thesis, University of Bristol, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.570852.

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The definition and quantification of complexity is a source of debate. A promising answer, from Crutch field, Shalizi and co-workers, identifies complexity with the amount of information required to optimally predict the future of a process. Computational mechanics computes this quantity for discrete time series; quantifying the complexity and generating minimal, optimally predictive models. Here we adapt and apply these methods to two very different problems. First, we extend computational mechanics to continuous data which cluster around discrete values. This is applied to the analysis of single molecule experimental data; allowing us to infer hidden Markov models without the necessity of assuming model architecture and allowing for the inference of degenerate states, giving advantages over previous analysis methods. The new analysis methods are demonstrated to perform well on both simulated data, in high noise and sparse data conditions; and experimental data, namely fluorescence resonance energy transfer spectra of Holliday junction conformational dynamics. Secondly, we apply computational mechanics to investigations of the HP model of protein folding. Computational mechanics was used to investigate the properties of the sequence sets folding to the highly designable structures. A hypothesised correlation between structures' designability and the statistical complexity of its sequence set was unsupported. However, methods were developed to succinctly encapsulate the non-local statistical regularities of sequence sets and used to accurately predict the structure of designing and randomly generated sequences. Finally, limitations of the standard algorithm for reconstructing predictive models are addressed. The algorithm can fail due to pair-wise comparisons of conditional distributions. A clustering method, considering all distributions simultaneously has been developed. This also makes clear when the algorithm may be effectively employed. A second issue concerns a class of processes for which computational mechanics cannot infer the correct, optimally predictive models. Adaptions to allow the inference of these processes have been devised.
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LIRA, WILLIAM WAGNER MATOS. "AN INTEGRATED SYSTEM FOR NUMERICAL SIMULATIONS IN COMPUTATIONAL MECHANICS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1998. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=1471@1.

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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Este trabalho dá continuidade ao desenvolvimento de uma metodologia para extensão e configuração de aplicações gráficas interativas utilizadas em simulações baseadas no método dos elementos finitos (MEF). Novos atributos requisitados pelos módulos de análise podem ser facilmente incluídos nos pré- e pós-processadores. Os atributos são definidos, através de uma linguagem de extensão interpretada relativamente simples, em um arquivo de configuração. A configuração e extensão é feita a partir da criação de classes e métodos, no contexto da programação orientada a objetos, de atributos da simulação. Esta metodologia foi implementada no desenvolvimento de um sistema integrado para simulações numéricas de problemas bidimensionais em geotecnia pelo MEF. A tese apresenta, inicialmente, uma discussão sobre a evolução dos sistemas utilizados para simulações numéricas na mecânica computacional, desenvolvidos no Departamento de Engenharia Civil da PUC-Rio, indicando os problemas existentes. A seguir, é apresentada uma extensão da arquitetura do módulo utilizado para o gerenciamento e extensão configurável dos atributos (ESAM), que, originalmente, considerava uma abordagem onde atributos só podiam ser aplicados a entidades geométricas. A nova arquitetura permite que atributos também possam ser aplicados diretamente em nós e elementos de uma malha de elementos finitos. O sistema implementado através da integração dos módulos utilizados para pré-processamento, análise numérica e pós- processamento com o módulo de gerenciamento de atributos resultou em um sistema bastante flexível, podendo ser estendido por um usuário configurador para diversos outros tipos de simulação. As fases envolvidas em um processo de simulação na mecânica computacional (definição da geometria, especificação dos atributos, geração da malha de elementos finitos, análise numérica e visualização dos resultados) são ilustradas em um exemplo de aplicação do sistema proposto.
This work continues the development of a methodology for extension and configuration of interactive graphics applications utilized on a finite element simulations. New attributes necessary for the analysis modules can be easily included in pre- and post-processor modules. The attributes are defined, through a relatively simple interpreted extension language, in a configuration file. The extension and configuration is performed through the creation of classes and methods, in the context of object oriented programming, of simulation attributes. This methodology was implemented in development of an integrated system for two- dimensional numerical simulation of geotechnical problems by the finite element method. The dissertation presents, initially, a discussion on the evolution of the systems used for numerical simulations in computational mechanics, developed in Department of Civil Engineering of PUC-Rio, pointing the existing problems. In the sequence, it is presented an extension of architecture of module that manager extension the simulation attributes (ESAM), that, originally, considerated only an approach where attributes could be applied in geometrical entities. The new architecture permits that attributes may also be applied directly to nodes and elements of a finite element mesh. The system implemented through the integration of the pre- processing, numerical analysis and post-processing modules, with the attribute management module resulted in a very flexible system, that can be extended for several other types of simulations. The phases involved in a simulations of a computational mechanics process (geometry defined, attributes specification, automatic mesh generation, numerical analysis and visualization of results) are illustrated in an application example of the proposed system.
Este trabajo da continuidad al desarrollo de una metodología para extensión y configuración de aplicaciones gráficas interactivas utilizadas en simulaciones que tiene como base el método de los elementos finitos (MEF). Los nuevos atributos que requieran los módulos de análisis pueden ser facilmente incluidos en los pre y pos procesadores. Los atributos son definidos, a través de un lenguaje de extensión interpretada relativamente simple, en un archivo de configuración. La configuración y extensión se realiza a partir de la creación de clases y métodos, en el contexto de la programación orientada a objetos, de atributos de la simulación. Esta metodología fue implementada en el desarrollo de un sistema integrado para simulaciones numéricas de problemas bidimensionales en geotecnía por el MEF. La tesis presenta, inicialmente, una discusión sobre la evolución de los sistemas utilizados para simulaciones numéricas en la mecánica computacional, desarrollados por el Departamento de Ingeniería Cívil de la PUC-Rio, indicando los problemas existentes. A seguir, se presenta una extensión de la arquitectura del módulo utilizado para el gerenciamiento y extensión configurable de los atributos (ESAM) que, originalmente, consideraba una abordaje donde los atributos solo podían ser aplicados a entidades geométricas. La nueva arquitectura permite que los atributos también puedan ser aplicados directamente en nodos y elementos de una malla de elementos finitos. El sistema implementado a través de la integración de los módulos utilizados para preprocesamiento, análisis numérico y posprocesamiento con el módulo de gerenciamento de atributos tuvo como resultado un sistema bastante flexible, que puede ser extendido por un usuario configurador para diversos otros tipos de simulación. Las fases involucradas en un proceso de simulación en la mecánica computacional (definición de la geometría, especificación de los atributos, generación de la malla de elementos finitos, análisis numérico y visualización de los resultados) son ilustradas en un ejemplo.
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35

Capelli, R. "COMPUTATIONAL MODELING OF PROTEINS: FROM STATISTICAL MECHANICS TO IMMUNOLOGY." Doctoral thesis, Università degli Studi di Milano, 2017. http://hdl.handle.net/2434/527950.

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One of the biggest revolutions occurred during the second half of the 20th century in physics was the introduction of computers in research. In particular, the use of fast computing machines opened the possibility to study complex systems by simulating their dynamics, without the need to pursue analytical solutions, otherwise impossible to tackle. The consequences of this breakthrough were huge both in the study of equilibrium and non-equilibrium many-body problems, with the strong limitation given by the number of atoms involved in the calculation. The first technique used in biology-related problems was the Monte Carlo Method, and some years later Molecular Dynamics (MD) was formalized. In MD, for each atom of the system one can solve its Newton equations of motion, obtaining a trajectory in the phase space for the entire system, and study its behavior in equilibrium and non-equilibrium conditions. The constant rise in computational power gave the possibility to scientists to study larger and larger systems, while the advances in experimental techniques enhanced the possibility for direct comparisons between wet and in silico data at similar levels of resolution. Despite the validity of Moore’s Law (i.e., the exponential growth of the computing power due to transistors miniaturization) until now, the timescale of the events that can be simulated has an upper limit of the millisecond with tailor-made computers, which is not enough to study all the biologically-relevant phenomena. Since the birth of computational chemistry, a huge number of different statistical mechanics-based methods has been implemented to permit, given the computing power limit, an effective reliable use of MD simulations in biochemistry. One of the most relevant problems tackled by MD is the calculation of free energy differences, both in conformational changes and in sequence mutations of a protein. The main reason of this difficulty is represented by the frustrated nature of interactions in proteins and the size of these systems: this leads to a complex energy landscape which in principle needs very long sampling times to overcome all possible energy barriers. In the present thesis, we studied and improved a path-independent and system-independent free energy calculation technique, called Simplified Confinement Method. We describe this work in Chapter 1. Although MD has been successful in most of its applications, there are still many open problems: as mentioned before, the available parametrizations of interaction potentials (called force fields) are not completely reliable. In particular, the choice of force field parameters is performed comparing experimental data on a fixed set of (usually small) molecules with computed data on the same molecules. This raises a significant problem: large molecules can have a more complex behavior, and using these potentials can lead to a systematic error; furthermore, the timescale in which the force field is tested needs to be limited. Another strong limitation of MD depends on the equilibrium experiments used for parametrization: the kinetic properties of a system are not considered. Given the impossibility to reparametrize a general force field with non-equilibrium experimental data, we implemented a technique that uses equilibrium-based force fields, adding a potential term based on time series resulting from kinetic experiments. This approach, based on the principle of Maximum Caliber, restrains the system with an experimental-based bias, returning a more realistic behavior of the simulation in condition where the usual force fields show their limitations. We describe this work in Chapter 2. The application of computational methods in the study of proteins confirms its efficacy in other fields of life sciences: an actual and emerging topic is represented by vaccinology. With techniques developed by Louis Pasteur at the end of the 19 th century (isolation of the pathogen, its inactivation and subsequent inoculation in the host), various scientists developed vaccines for deadly diseases like poliomyelitis, diphterite and measles. None of the mentioned was developed with molecular biology-based approaches. Almost 50 years after the birth of molecular biology, the Human Genome Project decoded human DNA and, at the same time, the genome of the most dangerous pathogen was screened. This has laid the foundation of Reverse Vaccinology (RV), where the proteins responsible for immune reaction can be identified from the pathogen DNA and tested directly on animal models, obtaining a new vaccine candidate with little or no risk for the host, having removed the pathogen itself. At the beginning of the 21st century the first vaccine against Meningococcus B, responsible for the 50% of the meningococcal meningitis, was developed using this protocol. Since then, crystallographic data was inserted in RV workflow to exploit conformational data, creating the so-called Structural Vaccinology (SV). To enhance its efficacy, SV exploits all the aspects of molecular modeling like computer-aided drug/protein design and MD to integrate information that come from experimental sources. One of the most promising technique in this field is the grafting of an immunogenic sequence (i.e., a portion of a protein recognized by the immune system) on a foreign protein; this approach could lead to a new vaccine component which have no risk for the patient. To date, the grafting technique has been carried out by human-driven workflows. Motivated by this reason, we studied immunogenic peptides from a family of pathogens involved in respiratory diseases, exploiting Structural Vaccinology principles with both computational and experimental approach. Furthermore, we developed and implemented an unsupervisionated automated tool to design grafted protein sequences. We describe this work in Chapter 3.
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36

Schmidt, Peter. "Computational Models of Adhesively Bonded Joints." Doctoral thesis, Linköping : Division of Mechanics, Department of Management and Engineering, Linköping University, 2007. http://www.bibl.liu.se/liupubl/disp/disp2007/tek1076s.pdf.

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37

Arteaga-Gomez, Joaquin M. "Development of crack generation and propagation algorithms for computational structural mechanics." Fairfax, VA : George Mason University, 2009. http://hdl.handle.net/1920/3430.

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Thesis (M.S.)--George Mason University, 2009.
Vita: p. 64. Thesis director: Rainald Löhner. Submitted in partial fulfillment of the requirements for the degree of Master of Science in Computational Sciences. Title from PDF t.p. (viewed June 10, 2009). Includes bibliographical references (p. 60-63). Also issued in print.
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38

Ward, Paul. "A computational and experimental study on respiratory oscillation mechanics for the control of mechanical ventilation." Thesis, King's College London (University of London), 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.435804.

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39

Scheldt, Therese. "Comparison of continuous and discontinuous modelling for computational rock mechanics." Doctoral thesis, Norwegian University of Science and Technology, Department of Geology and Mineral Resources Engineering, 2003. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-943.

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Computational rock mechanics becomes more and more popular. New programs are constantly under development, and the modelling process has become a natural part of the planning process for many caverns and tunnels, as well as for the mining and petroleum industry.

Computational rock mechanics becomes more and more popular. New programs are constantly under development, and the modelling process has become a natural part of the planning process for many caverns and tunnels, as well as for the mining and petroleum industry.

When to use continuous modelling in preference to discontinuous modelling and vice versa, is an important question that has been discussed for a long time.

For this purpose, in this work continuous and discontinuous modelling is applied in order to analyze the stability of the Gjøvik Olympic Mountain Hall. The large span cavern (62m) was built in connection with the XVII Winter Olympic Games 1994 at Lillehammer, and is a unique case study because of the large amount of available input data from a comprehensive stress and deformation monitoring program carried out during and after the excavation, as well as thorough pre-investigations. Phase2, a two-dimensional non-linear finite element program, and the Discontinuous Deformation Analysis (DDA) are used as representative tools for continuous and discontinuous modelling, respectively. DDA is both a theory and a computer program. The modelling procedure is similar to the distinct element modelling, while it more closely parallels the finite element method with respect to: i) Minimizing the total potential energy to establish equilibrium equations, ii) Choosing displacements as unknowns of the simultaneous equations and iii) Adding stiffness, mass and loading submatrices to the coefficient matrix of the simultaneous equation.

In general, the decision to use either continuous or discontinuous modelling should be based on data from the geological field mapping process. Mapping techniques which remove subjectivity from the results, for example scanline/area mapping or semi-automatic mapping, are recommended. If the rock mass is basically free of discontinuities, or if the discontinuities are very closely spaced in comparison to the dimensions of the problem to be analysed, continuous modelling is preferable. If large deformations including slip, rotation and separation are dominant, as for rock slope stability problems, discontinuous modelling may be selected. If the problem to be analysed cannot be classified within one of the two groups, the quality of required input parameters and the purpose of the modelling should be taken into consideration.

For underground hard rock problems as the Gjøvik Olympic Mountain Hall, continuous modelling is strongly recommended. Today’s mapping techniques are not good enough to give satisfactory information about the required and most crucial input for discontinuous modelling, namely the joint pattern, and the process for implementation of measured discontinuities into a numerical model is based on too many approximations. In addition, the discontinuous modelling process is very time consuming. A fast and high capacity computer is required.

Crucial input parameters for continuous modelling are strength and deformability parameters of the rock mass, and estimation of these parameters is dependent on the selected failure criterion, usually either Mohr-Coulomb or Hoek-Brown.

The magnitude of in-situ stresses, particularly the horizontal stresses, may have crucial influence on the general stability, and independent of whether continuous or discontinuous modelling is selected, in-situ stress measurements are strongly recommended in order to estimate a reasonably correct stress level for the problem to be analysed.

It is very difficult to estimate reliable input parameters for numerical modelling and a critical evaluation of the analysis results is absolutely recommended. Thus, analysis results should be considered as valuable additional input to field observations, in-situ and laboratory measurements, and experience rather than a precise answer for the given problem.

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Jakobsson, Håkan. "Adaptive reduction of finite element models in computational solid mechanics." Doctoral thesis, Umeå universitet, Institutionen för matematik och matematisk statistik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-43750.

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41

Jang, Jae Won. "Characterization of live modeling performance boundaries for computational structural mechanics /." Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/10178.

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42

Nikopour, Deilami Hasan. "Mechanics of fibre reinforced composite plates: Experiments and computational modelling." Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=114500.

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Fibre-reinforced composite plates consist of bonded layers of either unidirectionally or multi-directionally reinforced sub-elements, which are arranged in a way to achieve optimum deformability and failure characteristics. This thesis examines the effective elasticity properties of a unidirectionally reinforced carbon fibre-polyester composite. A computational simulation of an experimentally determined fibre arrangement is used to derive the effective elasticity properties of the transversely isotropic composite. The computational estimates for the elastic constants are compared with several theoretical estimates for the effective elasticity properties that are based on regular arrangement of the reinforcing fibres, their volume fraction and the elasticity properties of the constituents. This study also examines the flexural behavior of a locally loaded rectangular Carbon Fibre-Reinforced Polymer (CFRP) composite plate under different edge support conditions. The assembly of the laminae is used to construct a computational model of the plate. The layered composite CFRP plate used in the experimental investigation consisted of 11 layers of a polyester matrix reinforced with carbon fibres. The bulk fibre volume fraction in the plate was approximately 66%. The experimental results for the deflected shape of the plate were used to establish the validity of a computational approach that accounts for large deflections of the plate within the small strain range. This thesis also examines the role of a crack on the overall flexural behaviour of a circular layered composite CFRP plate with fixed boundary and different through crack configurations, which is subjected to uniform air pressure loading. In particular, the effect of crack length and orientation on the overall pressure-deflection behaviour of the plate is investigated. The assembly of the cracked laminae is also used to construct a non-linear model of the cracked plate.
Les plaques composites à renforts fibreux constituent en des ensembles de couches assemblées selon leur épaisseur de manière uni- ou multidirectionnelle afin d'obtenir des propriétiés de déformabilité ou de résistance optimales. Cette thèse se propose d'étudier les propriétiés élastiques effectives d'un composite à matrice de polyester renforcé par des fibres de carbone unidirectionnelle. Une simulation numérique est utilisée pour determiner les propriétiés élastiques equivalents dans l'hypothèse d'un comportement isotrope transverse au moyen d'un arrangement des fibres obtenu expérimentalement. Les estimation de ces constates élastiques obtenue par voie numérique sont comparées avec plusieurs estimations théoriques basées sur l'hypothèse d'un arrangement régulier des fibres et sur les fractions volumiques des constituants et leurs propriétés. Le travail est également étendu à l'identification des modules de glissement en plan et hors-plan d'une bande rectangulaire composite en polymère renforcée par des fibres de carbone. Les modules de glissement sont obtenus à partir de la rigidité torsionnelle déterminée expérimentalement et de technique de réduction de données basées sur le modèle de torsion de plaques rectangulaires orthotropes de Lekhnitskii. Cette etude examine également le comportement flexionnel d'une telle plaque rectangulaire chargée ponctuellement pour différentes conditions aux limites appliquées. L'assemblage du laminé est utilisé pour construire un modèle numérique de la plaque. La plaque laminée de composite utilisée dans les investigations expérimentales consiste en un ensemble de 11 couches à matrice polyester renforcée par des fibres de carbone. La fraction volumique de fibre dans la plaque est approximativement de 66%. Les résultats expérimentaux obtenus pour la déformée de la plaque ont été utilisée en vue de valider l'approche numérique qui prend en compte les grandes déflections sous l'hypothèse de petites déformations. Le travail investigue aussi l'effet d'une fissure sur le comportement global d'une plaque composite circulaire pour des conditions aux limites fixées et pour différentes configurations de fissures à travers la plaque, et soumise à une pression d'air uniforme. En particulier, l'influence de la longueur de fissure et de son orientation sur la réponse globale pression-déplacement est étudiée. L'assemblage de couches fissurées est également utilisé afin de construire un modèle non linéaire matériel de la plaque fissurée.
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43

Bhatti, Ayjwat Awais. "Computational weld mechanics : Towards simplified and cost effective FE simulations." Doctoral thesis, KTH, Lättkonstruktioner, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-168174.

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It is the demand of the world’s ever increasing energy crisis to reduce fuel consumption wherever possible. One way of meeting this demand is by reducing the weight of a structure by replacing thick plates of low strength steel with thin plates of high strength steel in the structure. Fusion welding process is extensively used in the manufacturing industry, however, despite many advantages different problems such as weld defects, residual stresses and permanent distortions are associated with this process. Finite element (FE) method has proved itself as an alternative and acceptable tool for prediction of welding residual stresses and distortions. However, the highly nonlinear and transient nature of the welding process makes the FE simulation computationally intensive and complex. Thus, simplified and efficient welding simulations are required so that they can be applied to industrial scale problems. In this research work an alternative FE simulation approach for the assessment of welding residual stresses, called rapid dumping is developed. This approach proved to be efficient and predicted the residual stress with acceptable accuracy for different small scale welded joints. This approach was further implemented on a large scale welded structures along with other available approaches. It was found that the computational time involved in the welding simulations for large structures using rapid dumping approach can be reduced but at the cost of accuracy of the results. Furthermore, influence of thermo-mechanical material properties of different steel grades (S355-S960) on welding residual stresses and angular distortion in T-fillet joints is investigated. It is observed that for assessment of residual stresses, except yield stress, all of the thermo-mechanical properties can be considered as constant. For the prediction of angular distortions with acceptable accuracy, heat capacity, yield stress and thermal expansion should be employed as temperature dependent in the welding simulations. Finally, the influence of two different LTT (Low Transformation Temperature) weld filler material on residual stress state and fatigue strength was investigated. It was observed that a reduction in tensile residual stresses at the weld toe of the joint was observed. Furthermore, at higher R-ratio no significant increase in the fatigue strength was observed . However, at low R-ratio significant  increase in fatigue strength was observed.

QC 20150529

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Kadel, Saurav. "Computational Assessment of Aortic Valve Function and Mechanics under Hypertension." Wright State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=wright1594243694736478.

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45

Tran, Hai Thanh. "Experimental and Computational Study on Fracture Mechanics of Multilayered Structures." Scholar Commons, 2016. http://scholarcommons.usf.edu/etd/6595.

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Many devices in electronics are in the form of multilayered structures. These structures can fail catastrophically if they contain defects or cracks. Enhancing their fracture properties is therefore critical to improve the reliability of the systems. The interface-dominated fracture mechanics of multilayered structure was studied using experiments and finite element (FE) modeling by considering two examples: thin films on polymer substrates in flexible electronics and Cu leadframe/epoxy molding compound (EMC) in micro-electronics packaging. In the first example, aluminum-manganese (Al-Mn) thin films with Mn concentration up to 20.5 at.% were deposited on polyimide (PI) substrates. A variety of phases, including supersaturated fcc (5.2 at.% Mn), duplex fcc and amorphous (11.5 at.% Mn), and completely amorphous phase (20.5 at.% Mn) were obtained by adjusting alloying concentration in the film. In comparison with crystalline and dual phase counterparts, the amorphous thin film exhibits the highest fracture stress and fracture toughness, but limited elongation. Based on a fracture mechanism model, a multilayer scheme was adopted to optimize the ductility and the fracture properties of the amorphous film/PI system. Tensile deformation and subsequent fracture of strained Al-Mn films on PI were investigated experimentally and by FE simulations. It was found that by sandwiching the amorphous film (20.5 at.% Mn) between two ductile copper (Cu) layers, the elongation can be improved by more than ten times, and the interfacial fracture toughness by twenty four times with a limited sacrifice of the film's fracture toughness (less than 18%). This design provides important guidelines to obtain optimized mechanical properties of future flexible electronics devices. The reliability of amorphous brittle Al-Mn (20.5 at.% Mn) thin films deposited on PI substrates is strongly influenced by the film/substrate interface adhesion. Some strategies to improve the adhesion of the interface were conducted, including roughening the surface of the PI substrate, adding a buffer layer and then tuning its thickness. Tensile testing and FE analysis of amorphous Al-Mn thin films with and without buffer layers coated on intact and plasma etched rough PI were investigated. It was found that by adding a chromium buffer layer of 75 nm on a rough PI substrate, the interface adhesion of the film/substrate can increase by almost twenty times. The obtained results would thus shed light on the interfacial engineering strategies for improving interface adhesion for flexible electronics. In the second example, a systematic investigation and characterization of the interfacial fracture toughness of the bimaterial Cu leadframe/EMC was carried out. Experiments and FE simulations were used to investigate delamination and interfacial fracture toughness of the biomaterial system. Two dimensional simulations using computational fracture mechanics tools, such as virtual crack closure technique, virtual crack extension and J-integral proved to be computationally cheap and accurate to find the interfacial fracture toughness of the bimaterial structures. The effects of temperature, moisture diffusion and mode-mixity on the interfacial fracture toughness were investigated. Testing temperature and moisture exposure significantly reduce the interfacial fracture toughness, and its relationship with the mode-mixity was achieved by fitting the results with an analytic formula.
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46

Yeganeh-Bakhtiary, Abbas. "Computational mechanics of bed-load transport at high bottom shear." Kyoto University, 1999. http://hdl.handle.net/2433/181776.

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47

Saavedra, Flores Erick Isaac. "Computational multi-scale constitutive model for wood cell-wall mechanics." Thesis, Swansea University, 2011. https://cronfa.swan.ac.uk/Record/cronfa43160.

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48

Singh, Dara. "A COMPUTATIONAL STUDY OF PATCH IMPLANTATION AND MITRAL VALVE MECHANICS." UKnowledge, 2019. https://uknowledge.uky.edu/me_etds/137.

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Myocardial infarction (i.e., a heart attack) is the most common heart disease in the United States. Mitral valve regurgitation, or the backflow of blood into the atrium from the left ventricle, is one of the complications associated with myocardial infarction. In this dissertation, a validated model of a sheep heart that has suffered myocardial infarction has been employed to study mitral valve regurgitation. The model was rebuilt with the knowledge of geometrical changes captured with MRI technique and is assigned with anisotropic, inhomogeneous, nearly incompressible and highly non-linear material properties. Patch augmentation was performed on its anterior leaflet, using a simplified approach, and its posterior leaflet, using a more realistic approach. In this finite element simulation, we virtually installed an elliptical patch within the central portion of the posterior leaflet. To the best of the author’s knowledge, this type of simulation has not been performed previously. In another simulation, the effect of patch within the anterior leaflet was simulated. The results from the two different surgical simulations show that patch implantation helps the free edges of the leaflets come close to one another, which leads to improved coaptation. Additionally, the changes in chordal force distributions are also reported. Finally, this study answers a few questions regarding mitral valve patch augmentation surgeries and emphasizes the importance of further investigations on the influence of patch positioning and material properties on key outcomes. The ultimate goal is to use the proposed techniques to assess human models that are patient-specific.
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49

Dhruv, Akash. "A Multiphase Solver for High-Fidelity Phase-Change Simulations over Complex Geometries." Thesis, The George Washington University, 2021. http://pqdtopen.proquest.com/#viewpdf?dispub=28256871.

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Complex interactions between solid, liquid and gas occur in many practical engineering applications, and are often difficult to quantify experimentally. A few examples include boiling over solid heaters, solidification melt-dynamics in metal casting, and convective cooling of electronic components. With the availability of scalable computational tools, high-fidelity simulations can provide new insight into these phenomena and answer open questions. In the present work, a multiphase solver is presented which can simulate problems involving phase transition over complex geometries. The dynamics of liquid-gas interface are modeled using a level-set technique, which utilizes Ghost Fluid Method (GFM) to account for sharp jump in pressure, velocity, and temperature across the multiphase boundary. The fluid-solid interactions are modeled using an Immersed Boundary Method (IBM) which uses a Moving Least Squared (MLS) reconstruction to calculate fluid-flow around the solid, along with an additional GFM forcing to model its effect on pressure, temperature and Conjugate Heat Transfer (CHT). The resulting three dimensional solver is fully explicit in time and uses a fractional step method for Navier-Stokes, energy, and mass transfer equations. Validation and verification cases are presented to demonstrate the accuracy of the solver in comparison to experimental and analytical problems, and results of high fidelity pool boiling simulations in varying gravity environments are discussed in detail.
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50

Emmanuelli, Gustavo. "An Assessment of State Equations of Air for Modeling a Blast Load Simulator." Thesis, Mississippi State University, 2019. http://pqdtopen.proquest.com/#viewpdf?dispub=10979719.

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When an explosive detonates above ground, air is principally the only material involved in the transmission of shock waves that can result in damage. Hydrodynamic codes that simulate these explosions use equations of state (EOSs) for modeling the behavior of air at these high-pressure, high-velocity conditions. An investigation is made into the effect that the EOS selection for air has on the calculated overpressure-time waveforms of a blast event. Specifically, the ideal gas, Doan-Nickel, and SESAME EOSs in the SHAMRC code were used to reproduce experiments conducted at the Blast Load Simulator (BLS), a large-scale shock tube operated by the U.S. Army Engineer Research and Development Center, that consisted of subjecting an instrumented rigid box at three angles of orientation inside the BLS to a blast environment. Numerical comparisons were made against experimentally-derived confidence intervals using peak values and several error metrics, and an attempt was made to rank the EOS based on performance. Issues were noted with the duration of decay from maximum pressure to negative phase that resulted in a general underprediction of the integrated impulse regardless of EOS, while the largest errors were noted for gages on faces at 45 to 90 degrees from the initial flow direction. Although no significant differences were noticed in the pressure histories from different EOSs, the ideal gas consistently ranked last in terms of the error metrics considered and simultaneously required the least computing resources. Similarly, the Doan-Nickel EOS slightly performed better than SESAME while requiring additional wallclock time. The study showed that the Doan-Nickel and SESAME EOSs can produce blast signatures with less errors and more matches in peak pressure and impulse than the ideal gas EOS at the expense of more computational requirements.

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