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1
Rice, Christopher W. "Quantitative structural reliability assurance through finite element analysis." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1998. http://handle.dtic.mil/100.2/ADA355906.
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Thesis (Degreee of Aeronautical and Astronautical Engineering) Naval Postgraduate School, September 1998.<br>Thesis advisor(s): Edward M. Wu. "September 1998." Includes bibliographical references (p. 53). Also available online.
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Mahadevan, Sankaran. "Stochastic finite element-based structural reliability analysis and optimization." Diss., Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/19517.
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Koka, Exaud Noe. "Laterally loaded wood compression members : finite element and reliability analysis." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/26709.
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This thesis consists of two parts. The first part describes the analysis and implementation of a finite element computer model for the general prediction of failure of wood members in bending or in combined bending and axial compression. Both instability and material strength failures are included. The program is verified using available analytical and test results. A good agreement with the results predicted by this program is observed.
The second part describes a procedure for the structural reliability evaluation of a compression member assuming random loads and material variables. The program developed here for the reliability study links the finite element program and the Rackwitz-Fiessler algorithm for the calculation of the reliability index β. The gradient of the failure function, which is a necessary input to the Rackwitz-Fiessler algorithm, is computed numerically using the finite element routine. The results of the reliability study for a typical column problem are compared against the available results obtained by following the code procedures [as outlined in CAN3-086.1-M84 (1984)] for different slenderness ratios.
A performance factor ɸ⍴ = 0.75, for compression members of any length is recommended in order to obtain a more accurate and consistent level of reliability in the design process. It is estimated that if this factor ɸ⍴ = 0.75 adopted in the current design practices, a level reliability index of the order of 4.0 can be achieved.<br>Applied Science, Faculty of<br>Civil Engineering, Department of<br>Graduate
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Chodavarapu, Sandeep. "FINITE ELEMENT ANALYSIS AND RELIABILITY STUDY OF MULTI-PIECE RIMS." UKnowledge, 2004. http://uknowledge.uky.edu/gradschool_theses/329.
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Multi-piece wheels or rims used on large vehicles such as trucks, tractors, trailers, buses and off-road machines have often been known for their dangerous properties because of the large number of catastrophic accidents involving them. The main causes for these accidents range from dislocation of the rim components in the assembly, mismatch of the components, manufacturing tolerances, corrosion of components to tires. A finite element analysis of a two-piece rim design similar to one manufactured by some of the prominent rim manufacturers in the USA is undertaken. A linear static deformation analysis is performed with the appropriate loading and boundary conditions. The dislocation of the side ring with respect to the rim base and its original designer intent position is established using simulation results from ANSYS and actual rim failure cases. Reliability of the multi-piece rims is analyzed using the failure data provided by the rim manufacturers in connection with a lawsuit (Civil Action No. 88-C-1374). The data was analyzed using MINITAB. The effect of an OSHA standard (1910.177) on servicing multi-piece rims was studied for change in failure patterns of different rims. The hazard functions were plotted and failure rates were calculated for each type of rim. The failure rates were found to be increasing suggesting that the standard had minimal effect on the accidents and failures. The lack of proper service personnel training and design defects were suggested as the probable reasons for the increasing failure rates.
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Umetani, S. "Reliability and efficiency of the boundary element method in elastostatics." Thesis, University of Southampton, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375680.
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Huh, Jungwon. "Dynamic reliability analysis for nonlinear structures using stochastic finite element method." Diss., The University of Arizona, 1999. http://hdl.handle.net/10150/289087.
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An efficient and accurate algorithm is developed to evaluate reliability in the time domain for nonlinear structures subjected to short duration dynamic loadings, including earthquake loading. The algorithm is based on the nonlinear stochastic finite element method (SFEM). Uncertainties in the dynamic and seismic excitation, and resistance-related parameters are incorporated by modeling them as realistically as possible. The uncertainty in them is explicitly addressed. The proposed algorithm intelligently integrates the concepts of response surface method (RSM), finite element method (FEM), first-order reliability method (FORM), and an iterative linear interpolation scheme. This leads to the stochastic finite element concept. It has the potential to estimate the risk associated with any linear or nonlinear structure that can be represented by a finite element algorithm subjected to seismic loading or any short duration dynamic loadings. In the context of the finite element method, the assumed stress-based finite element algorithm is used to increase its efficiency. Two iterative response surface schemes consisting of second order polynomials (with and without cross terms) are proposed. A mixture of saturated and central composite designs is used to assure both efficiency and accuracy of the algorithm. Sensitivity analysis is used to improve the efficiency further. The unique feature of the algorithm is that it is capable of calculating risk using both serviceability and strength limit states and actual earthquake loading time histories can be used to excite structures, enabling a realistic representation of the loading condition. The uncertainty in the amplitude of the earthquake is successfully considered in the context of RSM. Uncertainty in the frequency content of an earthquake is considered indirectly by conducting a parametric study to quantify the effect of uncertainty in the frequency content of earthquakes on the overall reliability of structures. The algorithm has been extensively verified using the Monte Carlo simulation technique. The verified algorithm is used to study the reliability of structures excited by actual earthquake time histories. The results of the numerical examples show that the proposed algorithm can be used accurately and efficiently to estimate the risk for nonlinear structures subjected to short duration time-variant loadings including seismic loading.
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Yunusa, Valeri Aisha. "Reliability of Soldier Joints in Embedded Packages Using Finite Element Method." Thesis, Portland State University, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10843775.
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<p> Solder joints serve as both mechanical and electrical connections between elements in a package. They are subjected to shear strains generated as a result of the different behaviors of the elements in the package (tension and compression) due to the differences in coefficients of thermal expansion during service conditions. </p><p> Some of the causes of solder joint failures are due to the following: Vibration: small rapid displacements of parts of the assembly. This is not necessarily an issue with electronic components but larger parts like automobiles. </p><p> Humidity: the package being exposed to water or ionic species can undergo corrosion if an electrical bias exists resulting in electrical opens or electrical shorts if the corrosion products are electrically conductive. </p><p> Thermal Aging: this occurs during the lifetime of the solder interconnects, the package can be exposed to high ambient temperature or high dissipated heat during use. The micro-structure of the solder joint becomes more coarse and brittle. Mechanical Shock: the package undergoes shock during a short term exposure to high loads. </p><p> Thermo-mechanical fatigue: this type of failure arises as a result of the solder joints going through cyclic strains, due to different coefficients of thermal expansion of individual components in the package during service. </p><p> The most prevalent long-term reliability issues that can cause interconnect failure are thermal aging and thermo-mechanical fatigue. This study aims to evaluate the reliability of solder joints using finite element method, considering solder joint failure due to thermo-mechanical fatigue. </p><p> Three variations of the BGA (Ball Grid Array) package are evaluated using the finite element analysis. The SAC305 series lead (pb) free alloy of 96.5% tin, 3% silver, and 0.5% copper is employed for this study. </p><p>
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Yunusa, Valeri Aisha. "Reliability of Solder Joints in Embedded Packages Using Finite Element Methods." PDXScholar, 2018. https://pdxscholar.library.pdx.edu/open_access_etds/4558.
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Solder joints serve as both mechanical and electrical connections between elements in a package. They are subjected to shear strains generated as a result of the different behaviors of the elements in the package (tension and compression) due to the differences in coefficients of thermal expansion during service conditions.
Some of the causes of solder joint failures are due to the following:
Vibration: small rapid displacements of parts of the assembly. This is not necessarily an issue with electronic components but larger parts like automobiles.
Humidity: the package being exposed to water or ionic species can undergo corrosion if an electrical bias exists resulting in electrical opens or electrical shorts if the corrosion products are electrically conductive.
Thermal Aging: this occurs during the lifetime of the solder interconnects, the package can be exposed to high ambient temperature or high dissipated heat during use. The micro-structure of the solder joint becomes more coarse and brittle.
Mechanical Shock: the package undergoes shock during a short term exposure to high loads.
Thermo-mechanical fatigue: this type of failure arises as a result of the solder joints going through cyclic strains, due to different coefficients of thermal expansion of individual components in the package during service.
The most prevalent long-term reliability issues that can cause interconnect failure are thermal aging and thermo-mechanical fatigue. This study aims to evaluate the reliability of solder joints using finite element method, considering solder joint failure due to thermo-mechanical fatigue.
Three variations of the BGA (Ball Grid Array) package are evaluated using the finite element analysis. The SAC305 series lead (pb) free alloy of 96.5% tin, 3% silver, and 0.5% copper is employed for this study.
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Ma, Jiajie. "Accuracy and reliability of non-linear finite element analysis for surgical simulation." University of Western Australia. School of Mechanical Engineering, 2006. http://theses.library.uwa.edu.au/adt-WU2010.0089.
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In this dissertation, the accuracy and reliability of non-linear finite element computations in application to surgical simulation is evaluated. The evaluation is performed through comparison between the experiment and finite element analysis of indentation of soft tissue phantom and human brain phantom. The evaluation is done in terms of the forces acting on the cylindrical Aluminium indenter and deformation of the phantoms due to these forces. The deformation of the phantoms is measured by tracking 3D motions of X-ray opaque markers implanted in the direct neighbourhood under the indenter using a custom-made biplane X-ray image intensifiers (XRII) system. The phantoms are made of Sylgard® 527 gel to simulate the hyperelastic constitutive behaviour of the brain tissue. The phantoms are prepared layer by layer to facilitate the implantation of the X-ray opaque markers. The modelling of soft tissue phantom indentation and human brain phantom indentation is performed using the ABAQUSTM/Standard finite element solver. Realistic geometry model of the human brain phantom obtained from Magnetic Resonance images is used. Specific constitutive properties of the phantom layers determined through uniaxial compression tests are used in the model. The models accurately predict the indentation force-displacement relations and marker displacements in both soft tissue phantom indentation and human brain phantom indentation. Good agreement between the experimental and modelling results verifies the reliability and accuracy of the finite element analysis techniques used in this study and confirms the predictive power of these techniques in application to surgical simulation.
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Jung, Hyung Chul. "A Study on Laser Forming Processes with Finite Element Analysis." Thesis, University of Canterbury. Mechanical Engineering, 2006. http://hdl.handle.net/10092/1099.
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Laser forming is an innovative technique that uses a defocused laser beam to form sheet metal by thermal stresses rather than external forces. Promising potential applications of laser forming include rapid prototyping, straightening, aligning and adjusting of macro/micro-metallic components. Research to-date on laser forming has been largely focused, theoretically and experimentally, on the problem of characterization of process parameters on the forming results, and computational simulations of laser forming remain limited only providing the insight into the process. This study investigates the laser forming processes using the finite element analysis with respect to material responses during the processes, including complex processes, process optimization, process reliability and the effects of thermal and mechanical material properties. The first part of this thesis describes a nonlinear transient three-dimensional heat transfer finite element model and a rate dependent three-dimensional deformation model, which are developed for the laser forming simulations. Simulations are performed using an indirect coupled thermal-structural method for the processes of a straight-line heating, a circle-line heating, and a laser micro-adjustment. The thermo-mechanical behaviours during the straight-line heating process are presented in terms of temperature, stress and strain, and displacement distributions. The emphasis in the circle-line heating simulations is placed on the characterization of the quality of the deformed geometry by obtaining the radial and circumferential waviness. The micron size movements induced by laser point heating are focused the simulations of the micro-adjustment process. Simulation results are validated by comparison with published data or correlation to engineering point of view. The second part of this thesis presents the development of an effective method to determine optimum process parameters in laser forming. For the process optimization, design optimisation techniques are introduced into the finite element analysis of the laser forming process. The optimum parameter values to produce a predefined bend angle of 3° in the straight-line heating process are sought by two optimization procedures - one is the procedure involving the non-gradient method and the other is the gradient-based method. Optimum values of laser power, feed rate, beam diameter and number of passes are determined to produce a predefined bend angle in a multiple straight-line heating process using the two optimization procedures. A more suitable optimisation method for laser forming is chosen, which is used for a new optimisation problem to generate a maximum bend angle in a single pass of laser forming. In the third part of this thesis, a strategy to assess the reliability of the laser forming process is established by employing a well-known reliability analysis method, the Monte Carlo simulation. Robustness of the straight-line heating process of producing 3° with the optimum parameters determined by process optimization is evaluated with regard to the uncertain input variables of laser power, feed rate, plate thickness and coefficient of thermal expansion via the Monte Carlo simulations based on the finite element simulations of the process. The final part of this thesis identifies the effects of material properties on the bend angle resulting from laser forming. Process sensitivity to the properties of coefficient of thermal expansion, thermal conductivity, specific heat capacity and elastic modulus is investigated by measuring the Pearson product-moment correlation coefficient between the properties and the bend angle, which are based on the Monte Carlo simulations of laser forming. The conclusion is that the developed finite element models contribute to a better understanding of the laser forming process, and the optimization procedure is able to be used for straightening, aligning and adjusting of components.
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Baingo, Darek. "A Framework for Stochastic Finite Element Analysis of Reinforced Concrete Beams Affected by Reinforcement Corrosion." Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/23063.
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Corrosion of reinforcing bars is the major cause of deterioration of reinforced concrete (RC) structures in North America, Europe, the Middle East, and many coastal regions around the world. This deterioration leads to a loss of serviceability and functionality and ultimately affects the structural safety. The objective of this research is to formulate and implement a general stochastic finite element analysis (SFEA) framework for the time-dependent reliability analysis of RC beams with corroding flexural reinforcement. The framework is based on the integration of nonlinear finite element and reliability analyses through an iterative response surface methodology (RSM). Corrosion-induced damage is modelled through the combined effects of gradual loss of the cross-sectional area of the steel reinforcement and the reduction bond between steel and concrete for increasing levels of corrosion. Uncertainties in corrosion rate, material properties, and imposed actions are modelled as random variables. Effective implementation of the framework is achieved by the coupling of commercial finite element and reliability software. Application of the software is demonstrated through a case study of a simply-supported RC girder with tension reinforcement subjected to the effects of uniform (general) corrosion, in which two limit states are considered: (i) a deflection serviceability limit state and (ii) flexural strength ultimate limit state. The results of the case study show that general corrosion leads to a very significant decrease in the reliability of the RC beam both in terms of flexural strength and maximum deflections. The loss of strength and serviceability was shown to be predominantly caused by the loss of bond strength, whereas the gradual reduction of the cross-sectional area of tension reinforcement was found to be insignificant. The load-deflection response is also significantly affected by the deterioration of bond strength (flexural strength and stiffness). The probability of failure at the end of service life, due to the effects of uniform corrosion-induced degradation, is observed to be approximately an order of magnitude higher than in the absence of corrosion. Furthermore, the results suggest that flexural resistance of corroded RC beams is controlled by the anchorage (bond) of the bars and not by the yielding of fully bonded tensile reinforcement at failure. This is significant since the end regions can be severely corroded due to chloride, moisture, and oxygen access at connections and expansion joints. The research strongly suggests that bond damage must be considered in the assessment of the time-dependent reliability of RC beams subjected to general corrosion.
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Lee, Kang. "Fabrication and Reliability Assessment of Embedded Passives in Organic Substrate." Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7643.
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In a typical printed circuit board assembly, over 70 percent of the electronic components are passives such as resistors, inductors, and capacitors, and these passives could take up to 50 percent of the entire printed circuit board area. By embedding the passive components within the substrate instead of being mounted on the surface, the embedded passives could reduce the system real estate, eliminate the need for surface-mounted discrete components, eliminate lead based interconnects, enhance electrical performance and reliability, and potentially reduce the overall cost. Even with these advantages, embedded passive technology, especially for organic substrates, is at an early stage of development, and thus a comprehensive experimental and theoretical modeling study is needed to understand the fabrication and reliability of embedded passives before they can be widely used.
This thesis aims to fabricate embedded passives in a multilayered organic substrate, perform extensive electrical and mechanical reliability tests, and develop physics-based models to predict the thermo-mechanical reliability of embedded capacitors. Embedded capacitors and resistors with different geometric shapes, planar dimensions, and thus different electrical characteristics have been fabricated on two different test vehicles. Capacitors are made with polymer/ceramic nanocomposite materials and have a capacitance in the range of 50 pF to 1.5 nF. Resistors are carbon ink based Polymer Thick Film (PTF) and NiCrAlSi and have a resistance in the range of 25 to 400 k. High frequency measurements have been done using Vector Network Analyzer (VNA) with 2 port signal-ground (S-G) probes. Accelerated thermal cycling (-55 to 125oC) and constant temperature and humidity tests (85oC/85RH) based on JEDEC and MIL standards have been performed. Furthermore, physics-based numerical models have been developed and validated using the experimental data. By focusing on the design and fabrication as well as the experimental and theoretical reliability assessments, this thesis aims to contribute to the overall development of embedded passive technology for Digital and Radio Frequency (RF) applications.
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Zhou, Yiguang. "Efficient stochastic finite element method for the reliability analysis of nonlinear frame structures." Diss., The University of Arizona, 1992. http://hdl.handle.net/10150/185746.
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An efficient stochastic finite element-based procedure is proposed for the reliability analysis of frame and truss structures with geometrical and material nonlinearities under static loading condition. The material properties, geometry and external loads of the structure are considered as random variables. The failure criteria of the structure are expressed in terms of limit-state functions. The method is based on the advanced first order second moment reliability analysis procedure. The assumed stress field approach is used in the finite element formulation to compute nonlinear structural responses and the corresponding response gradients. The proposed method is suitable for the reliability analysis of geometrically nonlinear frame structures with flexible connections. The mechanical properties of the nonlinear flexible connections can be deterministic or random. A random index parameter is introduced as a basic random variable to consider the uncertainties in the modeling of the connections. Structures with different types of connections can be handled by this method. An efficient method is also proposed for the reliability analysis of highly redundant elastic-perfectly-plastic frame structures with large deformations under proportional loading. The proposed method avoids dealing with the complicated failure mechanisms and stable configurations in the structure system reliability analysis, and has several advantages over the other available methods.
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KALARICKEL, RAMAKRISHNAN PRAVEEN. "Reliability of finite element method for time harmonic electromagnetic problems involving moving bodies." Doctoral thesis, Università degli studi di Genova, 2018. http://hdl.handle.net/11567/930777.
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This work is mainly concerned about the time-harmonic electromagnetic problems involving moving bodies. Such a formulation is possible when the boundaries between different moving objects are stationary and the sources involved are time-harmonic. Even simple media present bianisotropic properties when they are in motion. This kind of problems find applications in diverse fields. Numerical solution is required for most of the practical problems. We examined the reliability of finite element simulator developed for solving such problems.
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Vanden, Berge Daniel. "Rapid Drawdown Analysis using the Finite Element Method." Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/56955.
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Rapid drawdown (RDD) occurs when the water level adjacent to a slope or embankment is lowered quickly after a long period of being elevated either at the normal operating level for a dam or in the case of levees, during a prolonged flood. The current state of practice for RDD analysis is a multi-stage undrained strength method based on limit equilibrium.
The primary objective of this research was to develop a new method for rapid drawdown based on the finite element method. The new method estimates undrained strengths based on effective consolidation stresses from finite element analysis and the results of isotropically consolidated undrained triaxial compression (ICU-TC) tests. The field strengths appropriate for use with this rapid drawdown method were found to be on average 70% of the strength measured in ICU-TC tests based on back analysis of rapid drawdown failures. For rapid drawdown, anisotropic consolidation, plane strain deformation, and principal stress rotation were shown to produce field undrained strengths in the range of 60 to 80% of the strengths measured in isotropically consolidated undrained (ICU) triaxial compression. The current limit equilibrium method for rapid drawdown was shown to produce a similar reduction in ICU-TC strength.
This study also investigated other issues related to RDD. Effective stress analysis of RDD, especially using uncoupled transient seepage analysis, was shown to be inappropriate because important aspects of soil behavior are ignored. Consolidated-undrained strength tests on compacted clay specimens highlighted the importance of relative compaction on undrained strength. Anisotropic consolidation was shown to produce lower undrained strengths in triaxial compression than isotropic consolidation, especially at higher consolidation stresses. The behavior of compacted specimens under principal stress rotation was investigated using triaxial and direct simple shear tests. Finally probabilistic methods were applied to RDD to assess the probability that the factor of safety is less than one, assuming RDD occurs.<br>Ph. D.
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Bradon, Jill Elizabeth. "Wire rope terminations and their influence on the reliability of offshore moorings." Thesis, University of Reading, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343175.
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Ba-abbad, Mazen. "Reliability-based Design Optimization of a Nonlinear Elastic Plastic Thin-Walled T-Section Beam." Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/27895.
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A two part study is performed to investigate the application of reliability-based design
optimization (RBDO) approach to design elastic-plastic stiffener beams with Tsection.
The objectives of this study are to evaluate the benefits of reliability-based
optimization over deterministic optimization, and to illustrate through a practical
design example some of the difficulties that a design engineer may encounter while
performing reliability-based optimization. Other objectives are to search for a
computationally economic RBDO method and to utilize that method to perform
RBDO to design an elastic-plastic T-stiffener under combined loads and with
flexural-torsional buckling and local buckling failure modes. First, a nonlinear
elastic-plastic T-beam was modeled using a simple 6 degree-of-freedom non-linear
beam element. To address the problems of RBDO, such as the high non-linearity and
derivative discontinuity of the reliability function, and to illustrate a situation where
RBDO fails to produce a significant improvement over the deterministic
optimization, a graphical method was developed. The method started by obtaining a
deterministic optimum design that has the lowest possible weight for a prescribed
safety factor (SF), and based on that design, the method obtains an improved
optimum design that has either a higher reliability or a lower weight or cost for the
same level of reliability as the deterministic design. Three failure modes were
considered for an elastic-plastic beam of T cross-section under combined axial and
bending loads. The failure modes are based on the total plastic failure in a beam
section, buckling, and maximum allowable deflection. The results of the first part
show that it is possible to get improved optimum designs (more reliable or lighter
weight) using reliability-based optimization as compared to the design given by
deterministic optimization. Also, the results show that the reliability function can be
highly non-linear with respect to the design variables and with discontinuous
derivatives. Subsequently, a more elaborate 14-degrees-of-freedom beam element
was developed and used to model the global failure modes, which include the
flexural-torsional and the out-of-plane buckling modes, in addition to local buckling
modes. For this subsequent study, four failure modes were specified for an elasticplastic
beam of T-cross-section under combined axial, bending, torsional and shear
loads. These failure modes were based on the maximum allowable in-plane, out-ofplane
and axial rotational deflections, in addition, to the web-tripping local buckling.
Finally, the beam was optimized using the sequential optimization with reliabilitybased
factors of safety (SORFS) RBDO technique, which was computationally very
economic as compared to the widely used nested optimization loop techniques. At
the same time, the SOPSF was successful in obtaining superior designs than the
deterministic optimum designs (either up to12% weight savings for the same level of
safety, or up to six digits improvement in the reliability for the same weight for a
design with Safety Factor 2.50).<br>Ph. D.
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Gu, Quan. "Finite element response sensitivity and reliability analysis of Soil-Foundation-Structure-Interaction (SFSI) systems." Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2008. http://wwwlib.umi.com/cr/ucsd/fullcit?p3290678.
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Thesis (Ph. D.)--University of California, San Diego, 2008.<br>Title from first page of PDF file (viewed February 5, 2008). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 569-594).
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Yan, Wei Johnson R. Wayne. "Process development of double bump flip chip with enhanced reliability and finite element analysis." Auburn, Ala., 2005. http://repo.lib.auburn.edu/2005%20Summer/doctoral/YAN_WEI_15.pdf.
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Rodriguez, Maria P. "Thermal characterisation and reliability study of advanced high power modules using finite element techniques." Thesis, Staffordshire University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364813.
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Gao, Liwei. "Stochastic finite element method for the reliability analysis of nonlinear frames with PR connections." Diss., The University of Arizona, 1994. http://hdl.handle.net/10150/186898.
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A nonlinear stochastic finite element-based procedure is developed for reliability analyses of structures. The procedure is based on the First Order Reliability Method. The failure criteria of structures are expressed in terms of the ultimate and serviceability state functions. The adjoint variable method is used to formulate the computation of the gradient vector. The assumed stress-based finite element method is used to compute nonlinear structural responses and the corresponding response gradients for steel frames. Nonlinearities due to geometry, material and partially restrained connections are considered in the procedure. A computational model based on the Richard model is developed to address the uncertain properties of partially restrained connections. The material properties, geometric properties, connections parameters and external loads are considered as random variables. Several observations with design implications are made from numerical examples. Frames designed considering strength may not be acceptable when serviceability is considered. The presence of partially restrained connections changes the stress distribution in frames and makes frames more flexible so that serviceability could become the governing limit state. It is essential to properly consider the presence of partially restrained connections in the analysis and design of frames. The proposed method can be used as an alternative to the currently available methods to design a structure and evaluate the corresponding reliability. As an extended study, an efficient finite element-based procedure is also developed for estimating nonlinear responses of complex two or three dimensional steel frames with partially restrained connections under dynamic and seismic excitations. The hysteretic behavior of partially restrained connections are modeled by using the Masing rule combined with the Richard model to describe the loading, unloading and reverse loading paths for connections. Numerical examples show that this procedure is accurate and efficient compared with other existing nonlinear methods.
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Tunga, Krishna Rajaram. "Experimental and Theoretical Assessment of PBGA Reliability in Conjunction with Field-Use Conditions." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5266.
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With the dramatic advances that have taken place in microelectronics over the past three decades, ball-grid array (BGA) packages are increasingly being used in microsystems applications. BGA packages with area-array configuration have several advantages: smaller footprint, faster signal transmission, testability, reworkability, handling easiness, etc. Although ceramic ball grid array (CBGA) packages have been used extensively in the microsystems industry, the use of plastic ball grid array (PBGA) packages is relatively new, especially for automotive and aerospace applications where harsh thermal conditions prevail.
This thesis work has developed an experimental and a theoretical modeling program to study the reliability of two PBGA packages. The physics-based theoretical models take into consideration the time-dependent creep behavior through power law creep and time-independent plastic behavior through multi-linear kinematic hardening. In addition, unified viscoplastic constitutive models are also taken into consideration. The models employ two damage-metrics, namely inelastic strain and inelastic strain energy density, to predict the solder joint fatigue life. The theoretical predictions have been validated through air-to-air in-house thermal cycling tests carried out between 55 and #61616;C and 125 and #61616;C. In addition, laser-moir interferometry has been used to determine the displacement contours in a cross-section of the package at various temperatures. These contours measured through moir interferometry have also been used to validate the thermally-induced displacement contours, predicted by the models. Excellent agreement is seen between the experimental data and the theoretical predictions.
In addition to life prediction, the models have been extended to map the field-use conditions with the accelerated thermal cycling conditions. Both linear and non-linear mapping techniques have been developed employing inelastic strain and strain energy density as the damage metric. It is shown through this research that the symmetric MIL-STD accelerated thermal cycles, currently in practice in industry, have to be modified to account for the higher percentage of creep deformation experienced by the solder joints in the field-use conditions. Design guidelines have been developed for such modifications in the accelerated thermal cycles.
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Trattles, John T. "Finite element simulation of VLSI interconnections with application to reliability design optimisation and electromigration modelling." Thesis, University of Newcastle Upon Tyne, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334059.
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Chatterjee, Aritra. "Structural System Reliability with Application to Light Steel-Framed Buildings." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/74879.
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A general framework to design structural systems for a system-reliability goal is proposed.
Component-based structural design proceeds on a member to member basis, insuring acceptable failure probabilities for every single structural member without explicitly assessing
the overall system safety, whereas structural failure consequences are related to the whole
system performance (the cost of a building or a bridge destroyed by an earthquake) rather
than a single beam or column failure. Engineering intuition tells us that the system is
safer than each individual component due to the likelihood of load redistribution and al-
ternate load paths, however such conservatism cannot be guaranteed without an explicit
system-level safety check. As a result, component-based structural designs can lead to both
over-conservative components and a less-than-anticipated system reliability.
System performance depends on component properties as well as the load-sharing network,
which can possess a wide range of behaviors varying from a dense redundant system with
scope for load redistribution after failure initiates, to a weakest-link type network that fails as
soon as the first member exceeds its capacity. The load-sharing network is characterized by
its overall system reliability and the system-reliability sensitivity, which quantifies the change in system safety due to component reliability modifications. A general algorithm is proposed
to calculate modified component reliabilities using the sensitivity vector for the load-sharing
network. The modifications represent an improvement on the structural properties of more
critical components (more capacity, better ductility), and provide savings on less important
members which do not play a significant role.
The general methodology is applied to light steel-framed buildings under seismic loads.
The building is modeled with non-linear spring elements representing its subsystems. The
stochastic response of this model under seismic ground motions provides load-sharing, system
reliability and sensitivity information, which are used to propose target diaphragm and shear
wall reliability to meet a building reliability goal. Finally, diaphragm target reliability is
used to propose modified component designs using stochastic simulations on geometric and
materially non-linear finite-element models including every individual component.<br>Ph. D.
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Barbato, Michele. "Finite element response sensitivity, probabilistic response and reliability analyses of structural systems with applications to earthquake engineering." Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2007. http://wwwlib.umi.com/cr/ucsd/fullcit?p3274842.
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Thesis (Ph. D.)--University of California, San Diego, 2007.<br>Title from first page of PDF file (viewed October 9, 2007). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.
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Henriques, De Sena Cardoso Francisco Manuel. "System reliability-based criteria for designing cold-formed steel structures by advanced analysis." Thesis, The University of Sydney, 2015. http://hdl.handle.net/2123/14498.
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This doctoral thesis develops a system-reliability based approach for designing cold-formed steel structures by advanced analysis. Specifically, this doctoral thesis carries out the underpinning structural analyses and reliability studies that enable the implementation of the next generation of system-based design-by-analysis steel specifications, i.e., specifications that establish a design approach where analysis and capacity checks are carried out in a single step. The study begins by developing and validating finite element (FE) models and advanced analyses that are capable of accurately predicting the behaviour and system strength of cold-formed steel structures. The modelling scheme includes a rational methodology for incorporating frame, member and sectional geometric imperfections, the ability to assign semi-rigid behaviour to the joints, the flexibility to represent the geometry of complex cross-sections and takes into account the detrimental effect of local and distortional buckling while determining the ultimate capacity of the structure. It follows the survey and statistical characterisation of the variability of the geometric and material parameters affecting the strength of cold-formed structures. Based on the collected data and the developed FE models, Monte-Carlo type of simulations are performed to determine system strength distributions and statistics of several representative frame configurations and failure modes. Reliability studies using the first-order reliability method (FORM) are then carried out to derive system resistance factors s corresponding to certain system reliability indices and representative frames are categorised on their structural reliability features. The study concludes by establishing guidelines for the design of cold-formed steel structures based on the nominal system strength as obtained by advanced analysis and category of structural reliability.
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Warren, J. E. Jr. "Nonlinear Stability Analysis of Frame-Type Structures with Random Geometric Imperfections Using a Total-Lagrangian Finite Element Formulation." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/30338.
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With the increasing use of lightweight frame-type structures that span long distances, there is a need for a method to determine the probability that a structure having random initial geometric imperfections will become unstable at a load less than a spe cified fraction of the perfect critical load. The overall objective of this dissertation is to present such a method for frame-type structures that become unstable at limit points.
The overall objective may be broken into three parts. The first part concerns the development of a three-dimensional total Lagrangian beam finite element that is used to determine the critical load for the structure. The second part deals with a least squares method for modeling the random initial imperfections using the mo de shapes from a linear buckling analysis, and a specified maximum allowable magnitude for the imperfection at any imperfect node in the structure. The third part deals with the calculation of the probability of failure using a combined response surface/ first-order second-moment method. Numerical results are presented for two example problems, and indicate that the proposed method is reasonably accurate. Several problems with the proposed method were noted during the course of this work and are discussed in the final chapter.<br>Ph. D.
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Papaioannou, Iason [Verfasser], Ernst Akademischer Betreuer] Rank, Daniel [Akademischer Betreuer] Straub, and Manolis [Akademischer Betreuer] [Papadrakakis. "Non-intrusive finite element reliability analysis methods / Iason Papaioannou. Gutachter: Daniel Straub ; Ernst Rank ; Manolis Papadrakakis. Betreuer: Ernst Rank." München : Universitätsbibliothek der TU München, 2012. http://d-nb.info/1024161439/34.
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Nobeen, Nadeesh. "Design and reliability of polymeric packages for high voltage power semiconductors." Thesis, Loughborough University, 2011. https://dspace.lboro.ac.uk/2134/8957.
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This thesis focuses on the development of a novel polymer based housing for power thyristor devices typically used in long distance high voltage direct current (HVDC) transmission. Power thyristor devices used in HVDC power conversion stations are typically packaged in a hermetically sealed ceramic housing and have demonstrated an excellent history of reliability and performance. However, to avoid increasing the number of thyristors in future higher powered HVDC schemes thyristors having higher power ratings at 8.5 kV and sizes at 125 mm and 150 mm diameters are sought for implementation to achieve higher transmission ratings of, for example, 4000 A at +/- 800 kV. The main disadvantages of such large ceramic-based packages are higher processing cost and weight whilst robustness is also a concern. To overcome these issues, replacing the current ceramic housing with a polymeric material has been investigated in this project. The advantages it is anticipated such packages will provide include lower cost, less weight, robustness, recyclability, etc. However, some challenges it will also offer are: non-hermeticity i.e. polymers are moisture and gas permeable, potentially more complex manufacturing routes, and different electrical, mechanical and thermal properties compared to ceramic materials. The work presented in this thesis was part of a larger project where these challenges have been addressed by developing and testing a prototype polymeric thyristor housing. The prototype is aimed at demonstrating that polymer packages can deliver performance and reliability comparable to, if not better than, current ceramic packages. In this thesis, it is the package development and reliability related studies that are discussed. Because the housings will experience severe electrical stresses and various thermal excursions during their service life, the electrical and thermo-mechanical behaviour of the polymer housing was studied using finite element analysis to gain an understanding of the effects of various design variables and materials properties on performance and the tradeoffs between performance and manufacturability. From these modelling studies, design guidelines have been established for the future development of polymer housings. On the other hand, to identify the physics-of-failure of the prototype that was manufactured as part of the project, accelerated life tests were performed to study its reliability. The knowledge gained from the polymer prototype development was then applied to the design of a larger 125 mm diameter housing using the Taguchi method of experimental design.
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Yang, Jin. "Quality inspection and reliability study of solder bumps in packaged electronic devices [electronic resource] : using laser ultrasound and finite element methods." Diss., Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26593.
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Consumer demands are driving the current trend in the microelectronics industry to make electronic products that are miniature, fast, compact, high-density, reliable and low-cost. The use of surface mount devices (SMDs) has helped to decrease the size of electronic packages through the use of solder bump interconnections between the devices and the substrates/printed wiring boards (PWBs). Solder bumps act as not only mechanical, but also electrical interconnections between the device and the substrate/PWB. Common manufacturing defects ¨C such as open, cracked, missing, and misaligned solder bumps ¨C are difficult to detect because solder bumps are hidden between the device and the substrate/PWB after assembly. The reliability of packaged electronic devices in storage and usage is a major concern in the microelectronics industry. Therefore, quality inspection of solder bumps has become a critical process in the microelectronics industry to help ensure product quality and reliability.
In this thesis, a methodology for quality evaluation and reliability study of solder bumps in electronic packages has been developed using the non-destructive and non-contact laser ultrasound-interferometric technique, finite element and statistical methods in this research work. This methodology includes the following aspects: 1) inspection pattern ¨C specific inspection patterns are created according to inspection purpose and package formats, 2) laser pulse energy density calibration ¨C specific laser pulse power and excitation laser spot size are selected in terms of package formats, 3) processing and analysis methods, including integrated analytical, finite element and experimental modal analyses approach, advanced signal processing methods and statistical analysis method, 4) approach combining modal analysis and advanced signal processing to improve measurement sensitivity of laser ultrasound-interferometric inspection technique, and 5) calibration curve using energy based simulation method and laser ultrasound inspection technique to predict thermomechanical reliability of solder bumps in electronic packages.
Because of the successful completion of the research objectives, the system has been used to evaluate a broad range of solder bump defects in a variety of packaged electronic devices. The development of this system will help tremendously to improve the quality and reliability of electronic packages.
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Zarmai, Musa Tanko. "Modelling of solder interconnection's performance in photovoltaic modules for reliability prediction." Thesis, University of Wolverhampton, 2016. http://hdl.handle.net/2436/617782.
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Standard crystalline silicon photovoltaic (PV) modules are designed to continuously convert solar energy into electricity for 25 years. However, the continual generation of electricity by the PV modules throughout their designed service life has been a concern. The key challenge has been the untimely fatigue failure of solder interconnections of solar cells in the modules due to accelerated thermo-mechanical degradation. The goal of this research is to provide adequate information for proper design of solar cell solder joint against fatigue failure through the study of cyclic thermo-mechanical stresses and strains in the joint. This is carried-out through finite element analysis (FEA) using ANSYS software to develop the solar cell assembly geometric models followed by simulations. Appropriate material constitutive model for solder alloy is employed to predict number of cycles to failure of solder joint, hence predicting its fatigue life. The results obtained from this study indicate that intermetallic compound thickness (TIMC); solder joint thickness (TSJ) and width (WSJ) have significant impacts on fatigue life of solder joint. The impacts of TIMC and TSJ are such that as the thicknesses increases solder joint fatigue life decreases. Conversely, as solder joint width (WSJ) increases, fatigue life increases. Furthermore, optimization of the joint is carried-out towards thermo-mechanical reliability improvement. Analysis of results shows the design with optimal parameter setting to be: TIMC -2.5μm, TSJ -20μm and WSJ -1000μm. In addition, the optimized model has 16,264 cycles to failure which is 18.82% more than the expected 13,688 cycles to failure of a PV module designed to last for 25 years.
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Chen, Silin. "Reliability-based design of concrete-filled steel tubular (CFST) truss systems by advanced analysis." Thesis, The University of Sydney, 2021. https://hdl.handle.net/2123/24557.
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Concrete-filled steel tubular (CFST) truss is a type of composite structure with CFST chords and hollow tubular braces. CFST trusses have been increasingly used in large-scale structures such as towers, bridge girders, piers and arch ribs. The compression and flexural behaviour of CFST trusses are greatly improved compared to hollow tubular trusses due to the concrete infill in chords. For such complex composite structural systems, traditional structural analysis approaches are readily applied for the safety checks of individual members and connections, whilst system-level inelastic analysis and reliability calibration are very limited. In the past, relevant studies on the reliability of CFST structures mostly focused on structural components such as individual columns and beams, and there is no mature system-based design regulations nor reliability evaluations on this complex composite system. This thesis aims to address this gap by adopting stochastic finite element analysis (FEA) modellings of CFST truss systems through numerical approach considering both the structural nonlinearities and random uncertainties.
With the complex configuration, nonlinear material interaction and sophisticated construction process, initial imperfections may largely affect the strength and stability of a CFST truss structure. The deterministic and probabilistic studies of CFST trusses with random imperfections based on the statistics of imperfections obtained through experiments and on-site measurements are carried out first, which lays a foundation for further study on the comprehensive reliability analysis of composite truss structures with uncertainties in material properties, structural configurations, initial imperfections and model uncertainties.
The verified FEA models of CFST truss systems (two-chord, three-chord and four-chord) are then further developed to implement random uncertainties, including the elastic modulus of steel (Es), the yield strength of steel (fy), the thickness of steel (ts), the cylinder strength of concrete (fc’), the initial steel imperfection (χs) and the initial concrete imperfection (χc1, χc2), to facilitate a comprehensive reliability analysis. To consider the random variation of these uncertainties based on statistics, the Monte Carlo (MC) simulation and the Latin Hypercube Sampling (LHS) technique are incorporated on the basis of the above-described Abaqus modelling. A large number of stochastic FEA models of CFST truss samples are randomly analysed using Abaqus-Python technique with random variables considered to estimate the statistics of the flexural strengths of CFST trusses.
Using the obtained statistics of system resistance, reliability analysis is then undertaken to calculate the system reliability indices (β) of the three typical CFST truss systems. Random dead loads and live loads are implemented to the FEA models. The structure reliability of the CFST trusses is evaluated in MATLAB using the First-Order Reliability Method (FORM). The relationship between reliability indices (β) and system resistance factors (ϕs) under various load cases is obtained. Finally, a comprehensive reliability-based design guideline of CFST truss systems by advanced analysis is suggested. The proposed novel computational approach and the reliability analysis contribute to both the practical design and the standard drafting for CFST truss systems.
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Nešpůrek, Lukáš. "STOCHASTIC CRACK PROPAGATION MODELLING USING THE EXTENDED FINITE ELEMENT METHOD." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2010. http://www.nusl.cz/ntk/nusl-233900.
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Tato disertační práce vychází z výzkumu v rámci francouzsko-českého programu doktorátu pod dvojím vedením na pracovišti Institut français de mécanique avancée v Clermont-Ferrand a na Ústavu fyziky materiálu AV v Brně. Úvodní výzkumný úkol na brněnském pracovišti se zabýval numerickou analýzou pole napětí v okolí čela trhliny v tenké kovové fólii. Zvláštní pozornost byla zaměřena na vliv speciálního typu singularity v průsečíku čela trhliny s volným povrchem. Těžiště disertační práce spočívá v numerickém modelování a stochastické analýze problémů šíření trhlin se složitou geometrií v dvojrozměrném prostoru. Při analýze těchto problémů se dříve zřídka používaly numerické metody, a to z důvodu vysoké náročnosti na výpočtový čas. V této disertaci je ukázáno, že aplikací moderních metod numerické mechaniky a vhodných technik v analýze spolehlivosti lze tyto problémy řešit s pomocí numerických metod i na PC. Ve spolehlivostní analýze byla využita lineární aproximační metoda FORM. Pro rychlost šíření trhlin se vycházelo z Parisova-Erdoganova vztahu. Pro parametry tohoto vztahu byl použit dvourozměrný statistický model, který postihuje vysokou citlivost na korelaci obou parametrů. Mechanická odezva byla počítána rozšířenou metodou konečných prvků (XFEM), která eliminuje výpočetní náročnost a numerický šum související se změnou sítě v klasické metodě konečných prvků. Prostřednictvím přímé diferenciace bylo odvozeno několik vztahů pro derivace funkce odezvy, čímž se dosáhlo lepší numerické stability a konvergence spolehlivostní analýzy a výrazného zkrácení doby výpočtu. Problém zatížení s proměnou amplitudou byl řešen aplikací transformace zatížení metodou PREFFAS. Využití distribuce výpočtů v síti PC umožnilo další zrychlení analýzy.
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Miller, Ian Timothy. "Probabilistic finite element modeling of aerospace engine components incorporating time-dependent inelastic properties for ceramic matrix composite (CMC) materials." Akron, OH : University of Akron, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=akron1144941702.
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Thesis (M.S.)--University of Akron, Dept. of Mathematics, 2006.<br>"May, 2006." Title from electronic thesis title page (viewed 11/29/2007) Advisor, Vinod Arya; Co-Advisor, Ali Hajjafar; Faculty reader, Shantaram S. Pai; Department Chair, Kevin Kreider; Dean of the College, Ronald F. Levant; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.
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Pacheco, Roman Oscar. "Evaluation of Finite Element simulation methods for High Cycle Fatigue on engine components." Thesis, Linköpings universitet, Mekanik och hållfasthetslära, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-148779.
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This document reflects the results of evaluating three computational methods to analyse the fatigue life of components mounted on the cylinder block; two currently in use at Scania and one that has been further developed from its previous state. Due to the cost of testing and the exponential increase in computational power throughout the years, the cheaper computational analyses have gained in popularity. When a component is mounted in a fairly complex assembly such as an engine, simplifications need to be made in order to make the analysis as less expensive as possible while keeping a high degree of accuracy. The methods of Virtual Vibrations, VROM and VFEM have been evaluated and compared in terms of accuracy, computational cost, user friendliness and general capacities. Additionally, the method VFEM has been further developed and improved from its previous state. A in-depth investigation regarding the differences of the methods has been conducted and improvements to make them more efficient are suggested herein. The reader can also find a decision matrix and recommendations regarding which method to use depending on the general characteristics of the component of interest and other factors. Two components, which differ in complexity and mounting nature, have been used to do the research.
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BAMIRO, OLUYINKA OLUGBENGA. "ANALYSIS OF THERMAL STRESS AND PLASTIC STRAIN IN STUDS/VIAS OF MULTILEVEL INTEGRATED CIRCUITS." University of Toledo / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1099778888.
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Pondugala, Lakshmi Vara Prasad. "Stochastic J-integral and reliability of composite laminates based on a computational methodology combining experimental investigation, stochastic finite element analysis and maximum entropy method." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0017/MQ54327.pdf.
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Yilmaz, Okan. "Service Life Assessment Of Solid Rocket Propellants Considering Random Thermal And Vibratory Loads." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614555/index.pdf.
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In this study, a detailed service life assessment procedure for solid propellant rockets under random environmental temperature and transportation loads is introduced. During storage and deployment of rocket motors, uncontrolled thermal environments and random vibratory loads due to transportation induce random stresses and strains in the propellant which provoke mechanical damage. In addition, structural capability degrades due to environmental conditions and induced stresses and strains as well as material capability parameters have inherent uncertainties. In this proposed probabilistic service life prediction, uncertainties along with degradation mechanisms are taken into consideration. Vibration loads are accounted by utilizing acceleration spectral density values which are induced during various deployment scenarios of ground, air and sea transportation. Furthermore, thermal loads are represented with a mathematical model being a harmonic function of time. Throughout the finite element analyses, a linear viscoelastic material model is to be used for the propellant. Change in the structural capability of the propellant with time is calculated using Laheru'<br>s cumulative damage model. Moreover, to include aging effect of the propellant, Layton model is used. To determine the effects of induced stress and strains under variations and uncertainties in the random loads and material constants, mathematical surrogate models are constructed using response surface method. Limit state functions are utilized to predict failure modes of the solid rocket motor. First order reliability method is used to calculate reliability and probability of failure of the propellant grain. With the proposed methodology, instantaneous reliability of the propellant grain is determined within a confidence interval.
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Li, Yixiang Li. "Numerical modeling of supported excavations considering soil spatial variability." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1510322541966921.
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Leonel, Edson Denner. "Modelos não lineares do método dos elementos de contorno para análise de problemas de fratura e aplicação de modelos de confiabilidade e otimização em estruturas submetidas à fadiga." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-26012010-092236/.
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Apresentam-se neste trabalho formulações do método dos elementos de contorno (MEC), visando sua utilização em problemas de fratura e também de modelos de confiabilidade e otimização aplicados na análise de problemas de fadiga. Com relação aos progressos e avanços nas formulações do MEC, apresentam-se modelos que representam o processo de crescimento de fissuras em domínios planos constituídos por materiais frágeis, quase-frágeis e dúcteis. Considerando esses diferentes tipos de materiais, a formulação numérica adotada na análise descreve o comportamento estrutural não linear decorrente do processo de propagação das fissuras e conseqüente degradação estrutural. Nos modelos de fratura é empregada a formulação MEC dual, a qual é mais adequada para a análise da propagação aleatória de fissuras. São também apresentadas as expressões dos operadores tangente para as formulações não lineares que tratam os problemas de fratura elástico linear e coesiva, problemas de contato e os problemas de domínios enrijecidos. Com relação às análises de confiabilidade estrutural, o modelo mecânico de fadiga é acoplado a algoritmos de confiabilidade para a determinação do índice de confiabilidade e do conjunto de valores aleatórios com maior probabilidade de ocorrência. São testados alguns algoritmos de confiabilidade, podendo-se claramente definir um deles como mais eficiente para a análise de problemas de fadiga. A esse modelo é acoplado um algoritmo de otimização para a determinação das dimensões do elemento estrutural e dos intervalos para os procedimentos de manutenção e inspeção, que levam ao mínimo custo estrutural com base nas incertezas determinadas pelo modelo de confiabilidade. São apresentados vários exemplos validando e mostrando a eficiência das formulações desenvolvidas.<br>This work deals with the development of boundary element method (BEM) formulations to be used in engineering problems. Particular attention is given to using these formulations in development of reliability and optimization models applied to fatigue problems. Contributions to BEM formulations are developed, particularly, models that deal with crack growth in plane domains composed by brittle, quasi-brittle and ductile materials. Taking into account these different types of materials, the proposed formulation properly represents the nonlinear structural behaviour induced by crack growth and the resulting structural damage. The dual BEM formulation is adopted here for the proposed crack model and to analyse random crack propagation. In this thesis tangent operators are used in the non-linear BEM formulations, in order to deal with cohesive crack, contact problems and debonding problems in reinforced domains. Regarding structural reliability analysis, the fatigue mechanical model was coupled with appropriate reliability algorithms to compute the reliability index and other important random values. Several reliability algorithms were tested for this coupled model, in order to find the most efficient in the analysis of fatigue problems. An optimization model was also coupled with the fatigue reliability model, in order to evaluate the optimal structural element dimensions and also to schedule the intervals for maintenance and inspection procedures, taking into account the minimum cost and problem uncertainties. Many examples are presented in order to show the efficiency and accuracy of the proposed formulations in dealing with crack propagation, fatigue reliability analysis and optimization problems.
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Tunga, Krishna Rajaram. "Study of Sn-Ag-Cu reliability through material microstructure evolution and laser moire interferometry." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24805.
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Butler, Martin A. "Fracture Critical Analysis Procedure for Pony Truss Bridges." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin155351691314481.
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Boiger, Wolfgang Josef. "Stabilised finite element approximation for degenerate convex minimisation problems." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät II, 2013. http://dx.doi.org/10.18452/16790.
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Infimalfolgen nichtkonvexer Variationsprobleme haben aufgrund feiner Oszillationen häufig keinen starken Grenzwert in Sobolevräumen. Diese Oszillationen haben eine physikalische Bedeutung; Finite-Element-Approximationen können sie jedoch im Allgemeinen nicht auflösen. Relaxationsmethoden ersetzen die nichtkonvexe Energie durch ihre (semi)konvexe Hülle. Das entstehende makroskopische Modell ist degeneriert: es ist nicht strikt konvex und hat eventuell mehrere Minimalstellen. Die fehlende Kontrolle der primalen Variablen führt zu Schwierigkeiten bei der a priori und a posteriori Fehlerschätzung, wie der Zuverlässigkeits- Effizienz-Lücke und fehlender starker Konvergenz. Zur Überwindung dieser Schwierigkeiten erweitern Stabilisierungstechniken die relaxierte Energie um einen diskreten, positiv definiten Term. Bartels et al. (IFB, 2004) wenden Stabilisierung auf zweidimensionale Probleme an und beweisen dabei starke Konvergenz der Gradienten. Dieses Ergebnis ist auf glatte Lösungen und quasi-uniforme Netze beschränkt, was adaptive Netzverfeinerungen ausschließt. Die vorliegende Arbeit behandelt einen modifizierten Stabilisierungsterm und beweist auf unstrukturierten Netzen sowohl Konvergenz der Spannungstensoren, als auch starke Konvergenz der Gradienten für glatte Lösungen. Ferner wird der sogenannte Fluss-Fehlerschätzer hergeleitet und dessen Zuverlässigkeit und Effizienz gezeigt. Für Interface-Probleme mit stückweise glatter Lösung wird eine Verfeinerung des Fehlerschätzers entwickelt, die den Fehler der primalen Variablen und ihres Gradienten beschränkt und so starke Konvergenz der Gradienten sichert. Der verfeinerte Fehlerschätzer konvergiert schneller als der Fluss- Fehlerschätzer, und verringert so die Zuverlässigkeits-Effizienz-Lücke. Numerische Experimente mit fünf Benchmark-Tests der Mikrostruktursimulation und Topologieoptimierung ergänzen und bestätigen die theoretischen Ergebnisse.<br>Infimising sequences of nonconvex variational problems often do not converge strongly in Sobolev spaces due to fine oscillations. These oscillations are physically meaningful; finite element approximations, however, fail to resolve them in general. Relaxation methods replace the nonconvex energy with its (semi)convex hull. This leads to a macroscopic model which is degenerate in the sense that it is not strictly convex and possibly admits multiple minimisers. The lack of control on the primal variable leads to difficulties in the a priori and a posteriori finite element error analysis, such as the reliability-efficiency gap and no strong convergence. To overcome these difficulties, stabilisation techniques add a discrete positive definite term to the relaxed energy. Bartels et al. (IFB, 2004) apply stabilisation to two-dimensional problems and thereby prove strong convergence of gradients. This result is restricted to smooth solutions and quasi-uniform meshes, which prohibit adaptive mesh refinements. This thesis concerns a modified stabilisation term and proves convergence of the stress and, for smooth solutions, strong convergence of gradients, even on unstructured meshes. Furthermore, the thesis derives the so-called flux error estimator and proves its reliability and efficiency. For interface problems with piecewise smooth solutions, a refined version of this error estimator is developed, which provides control of the error of the primal variable and its gradient and thus yields strong convergence of gradients. The refined error estimator converges faster than the flux error estimator and therefore narrows the reliability-efficiency gap. Numerical experiments with five benchmark examples from computational microstructure and topology optimisation complement and confirm the theoretical results.
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Ginga, Nicholas J. "On-chip dielectric cohesive fracture characterization and mitigation investigation through off-chip carbon nanotube interconnects." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52225.
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The cohesive fracture of thin films is a concern for the reliability of many devices in microelectronics, MEMS, photovoltaics, and other applications. In microelectronic packaging the cohesive fracture toughness has become a concern with new low-k dielectric materials currently being used. To obtain the low-k values needed to meet electrical performance goals, the mechanical strength of the material has decreased. This has resulted in cohesive cracks occurring in the Back End of Line (BEoL) dielectric layers of the microelectronic packages. These cracks lead to electronic failures and occur after thermal loading (due to CTE mismatch of materials) and mechanical loading. To prevent these cohesive cracks, it is necessary to measure the cohesive fracture resistance of these thin films to implement during the design and analysis process. Many of the current tests to measure the cohesive fracture resistance of thin films are based on methods developed for larger scale specimens. These methods can be difficult to apply to thin films due to their size and require mechanical fixturing, physical contact near the crack tip, and complicated stress fields. Therefore, a fixtureless cohesive fracture resistance measurement technique has been developed that utilizes photolithography fabrication processes. This technique uses a superlayer thin film with a high intrinsic stress deposited on top of the desired test material to drive cohesive fracture through the thickness of test material. In addition to developing a technique to measure the fracture resistance of dielectric thin films, the use of carbon nanotube (CNT) forests as off-chip interconnects is investigated as a potential method to mitigate the fracture of these materials. The compressive and tensile modulus of CNT forests is characterized, and it is seen that the modulus is several orders of magnitude less than that of a single straight CNT. The low-modulus CNT forest will help mechanically decouple the chip from the board and reduce stress occurring in the dielectric layers as compared to the current technology of solder ball interconnects and therefore improve reliability. The mechanical performance of these CNT interconnects is investigated by creating a finite-element model of a flip chip electronic package utilizing CNT interconnects and comparing the chip stresses to a traditional solder ball interconnect scenario. Additionally, flip chips are fabricated with CNT forest interconnects, assembled to an FR4 substrate, and subjected to accelerated thermomechanical testing to experimentally investigate their performance.
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Achkar, Hikmat. "Modélisation et conception des micro commutateurs RF MEMS à actionnement électrostatique et/ou piézoélectrique." Toulouse 3, 2009. http://thesesups.ups-tlse.fr/594/.
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MEMS est un système électromécanique à l'échelle du micron comprenant des capteurs ainsi que des actionneurs (micro moteurs, micro miroirs, micro relais. . . ) fabriqués avec les techniques de la micro-électronique conventionnelle (croissance d'oxyde, dépôt de matériaux, lithographie). Les plupart des commutateurs RF MEMS sont actionnés à l'aide des forces électrostatique pour faire changer la distance entre deux électrodes pour couper ou transmettre le signal. Ce type d'actionnement, malgré ces avantages, il a un inconvénient majeur qu'il s'agit du chargement du diélectrique qui mène à l'échec de ce commutateur. Pour résoudre ce problème, on a travaillé en parallèle sur deux axes différents. Le premier axe s'agit de changer le type d'actionnement qui est la raison du chargement en actionnement piézoélectrique tandis que le deuxième consiste à garder l'actionnement électrostatique mais en améliorant le comportement des structures utilisées en augmentant la force de rappel pour surmonter le phénomène du collage sans changer la tension d'actionnement. Une étape a succédé ce travail qui s'agissait d'une validation de la plateforme numérique avant de l'utiliser à modéliser nos structures<br>MEMS are electromechanical system that have a micrometric scale including sensors as well as actuators (micro motor, micro mirrors, micro switches. . . ) manufactured using the conventional micro-electronics techniques (growth of oxide, material deposition, lithography). The majority of RF MEMS switches are actuated using the electrostatic forces to vary the distance between the two electrodes to cut or transmit the signal. This type of actuation, despite its advantages, has a major drawback which is the dielectric charging which leads to the failure of the switch. To solve this problem, we worked in parallel in two directions. The first direction consists of changing the type of actuation, which is the main reason for charging and failure, to piezoelectric while the second consists of keeping the electrostatic actuation while improving the behavior of the structures by increasing the restoring force used to overcome this charging phenomenon without increasing the actuation voltage. This work has succeeded a major step which is the numeric platform validation before using it to simulate the structure
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Paliga, Charlei Marcelo. "Análise probabilística de vigas de concreto armado recuperadas à flexão, através do método de Monte Carlo utilizando um modelo de elementos finitos." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2008. http://hdl.handle.net/10183/13455.
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O objetivo deste trabalho é apresentar um modelo para análise probabilística de vigas de concreto armado recuperadas à flexão, através da utilização conjunta do método de simulação de Monte Carlo e do método dos Elementos Finitos. Para uma análise da confiabilidade, foram projetadas vigas de concreto armado seguindo as recomendações da NRR 6118:2003. Após, foi considerado que as armaduras tracionadas de flexão sofreram reduções de 10%, 20% e 30% na sua área da seção transversal, sendo, então, feita uma análise da segurança estrutural remanescente. Para o projeto de recuperação das vigas danificadas, estão apresentados os procedimentos do Bulletin 14 da fédération internationale du béton (fib) para o dimensionamento de sistemas de reforço com material compósito colado externamente às estruturas. Assim, a confiabilidade destas vigas recuperadas pôde ser estimada e comparada à confiabilidade das vigas originais. Dentro do processo de simulação, a resposta em termos da carga de ruptura das vigas de concreto armado recuperadas foi obtida através de uma análise numérica não-linear utilizando um modelo de elementos finitos. Devido à importância do deslizamento entre o substrato de concreto e o sistema de reforço estrutural, foram implementados dentro do modelo de elementos finitos, elementos unidimensionais de interface, quadráticos com seis pontos nodais para a captura deste comportamento. As análises probabilísticas através do método de simulação de Monte Carlo usando um modelo de elementos finitos mostraram que se atinge bom nível de segurança no projeto de vigas de concreto armado seguindo as recomendações da NBR 6118:2003. Entretanto, danos nas armaduras tracionadas de flexão podem fazer com que a confiabilidade caía para níveis inaceitáveis. Como solução, o projeto de recuperação estrutural de acordo com o Bulletin 14 da fib fez com que a confiabilidade das vigas recuperadas fosse no mínimo igual à confiabilidade das vigas originais. Assim, a probabilidade de falha das vigas recuperadas foi menor quando comparado à probabilidade de falha das vigas originais.<br>The objective of this work is to present a model for probabilistic analysis of RC beams rehabilitated for flexure, through the simultaneous utilization of the Monte Carlo method and the finite element method. Initially, three RC beams were designed following the NBR 6118:2003 recommendations. In the next step, it was considered that a reduction of the steel reinforcement area of 10%, 20% and 30% had occurred. Then the procedures for strengthening systems design with externally bonded carbon fiber reinforced polymers (fib, Bulletin 14) were employed for the rehabilitation of the damaged RC beams. Finally, the reliability of the RC beams rehabilitated for flexure could be evaluated and compared to that of the damaged and undamaged RC beams. In the Monte Carlo method, the RC beams failure load was obtained numerically through a nonlinear finite element model. Due to the importance of the slip between the concrete substrate and the external reinforcement, it was introduced in the finite element model a special one-dimensional interface element, with six nodal points and quadratic shape functions. The probabilistic analysis through the Monte Carlo method using a finite element model showed the high reliability attained in the RC beams design following the NBR 6118:2003 recommendations. However, the damage in the internal steel reinforcement can lead to an unacceptable reliability level. As a solution, the design of structural recovery according to the Bulletin 14 produced a reliability level for the RC beams rehabilitated for flexure at least equal to the reliability level of the undamaged RC beams. Consequently, the failure probability of the RC beams rehabilitated for flexure was lower then the failure probability of the undamaged RC beams.
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Wang, Yaou. "Failure mechanism and reliability prediction for bonded layered structure due to cracks initiating at the interface." Columbus, Ohio : Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1236645979.
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Naccache, Eduardo Assad Kaba. "Confiabilidade aplicada ao problema de interação estaca-solo." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/3/3144/tde-23062016-160800/.
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Este trabalho busca aplicar técnicas de confiabilidade ao problema de grupo de estacas utilizadas como fundação de estruturas correntes. Para isso, lança-se mão de um modelo tridimensional de interação estaca-solo onde estão presentes o Método dos Elementos de Contorno (MEC) e o método dos Elementos Finitos (MEF) que atuam de forma acoplada. O MEC, com as soluções fundamentais de Mindlin (meio semi-infinito, homogêneo, isotrópico e elástico-linear é utiliza), é utilizado para modelar o solo. Já o MEF é utilizado para modelar as estacas. Definido o modelo de funcionamento estrutural das estacas, parte-se para a aplicação de métodos trazidos da confiabilidade estrutural para avaliação da adequabilidade em relação aos estados limite de serviço e estados limites últimos. Os métodos de confiabilidade utilizados foram o Método de Monte Carlo, o método FOSM (First-Order Second-Moment) e o método FORM (First-Order Reliability Method).<br>This work seeks to apply reliability techniques to the problem of piles groups used as current structures foundation. For this, makes use of a three-dimensional model of pile-soil interaction with the boundary element method (BEM) and the finite element method (FEM) working coupled. The BEM, with Mindlin fundamental solutions (semi-infinite medium, homogeneous, isotropic and linear elastic) is used to model the soil. The MEF is used to model the piles. Defined the model of structural functioning of the piles, the aim goes to the application of structural reliability for assessing the adequacy of the serviceability limit states and ultimate limit states. Reliability methods used were the Monte Carlo method, the FOSM (First-Order Second-Moment) method and the FORM method (First-Order Reliability Method).
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Bringmann, Philipp. "Adaptive least-squares finite element method with optimal convergence rates." Doctoral thesis, Humboldt-Universität zu Berlin, 2021. http://dx.doi.org/10.18452/22350.
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Die Least-Squares Finite-Elemente-Methoden (LSFEMn) basieren auf der Minimierung des Least-Squares-Funktionals, das aus quadrierten Normen der Residuen eines Systems von partiellen Differentialgleichungen erster Ordnung besteht. Dieses Funktional liefert einen a posteriori Fehlerschätzer und ermöglicht die adaptive Verfeinerung des zugrundeliegenden Netzes. Aus zwei Gründen versagen die gängigen Methoden zum Beweis optimaler Konvergenzraten, wie sie in Carstensen, Feischl, Page und Praetorius (Comp. Math. Appl., 67(6), 2014) zusammengefasst werden. Erstens scheinen fehlende Vorfaktoren proportional zur Netzweite den Beweis einer schrittweisen Reduktion der Least-Squares-Schätzerterme zu verhindern. Zweitens kontrolliert das Least-Squares-Funktional den Fehler der Fluss- beziehungsweise Spannungsvariablen in der H(div)-Norm, wodurch ein Datenapproximationsfehler der rechten Seite f auftritt. Diese Schwierigkeiten führten zu einem zweifachen Paradigmenwechsel in der Konvergenzanalyse adaptiver LSFEMn in Carstensen und Park (SIAM J. Numer. Anal., 53(1), 2015) für das 2D-Poisson-Modellproblem mit Diskretisierung niedrigster Ordnung und homogenen Dirichlet-Randdaten. Ein neuartiger expliziter residuenbasierter Fehlerschätzer ermöglicht den Beweis der Reduktionseigenschaft. Durch separiertes Markieren im adaptiven Algorithmus wird zudem der Datenapproximationsfehler reduziert.
Die vorliegende Arbeit verallgemeinert diese Techniken auf die drei linearen Modellprobleme das Poisson-Problem, die Stokes-Gleichungen und das lineare Elastizitätsproblem. Die Axiome der Adaptivität mit separiertem Markieren nach Carstensen und Rabus (SIAM J. Numer. Anal., 55(6), 2017) werden in drei Raumdimensionen nachgewiesen. Die Analysis umfasst Diskretisierungen mit beliebigem Polynomgrad sowie inhomogene Dirichlet- und Neumann-Randbedingungen. Abschließend bestätigen numerische Experimente mit dem h-adaptiven Algorithmus die theoretisch bewiesenen optimalen Konvergenzraten.<br>The least-squares finite element methods (LSFEMs) base on the minimisation of the least-squares functional consisting of the squared norms of the residuals of first-order systems of partial differential equations. This functional provides a reliable and efficient built-in a posteriori error estimator and allows for adaptive mesh-refinement. The established convergence analysis with rates for adaptive algorithms, as summarised in the axiomatic framework by Carstensen, Feischl, Page, and Praetorius (Comp. Math. Appl., 67(6), 2014), fails for two reasons. First, the least-squares estimator lacks prefactors in terms of the mesh-size, what seemingly prevents a reduction under mesh-refinement. Second, the first-order divergence LSFEMs measure the flux or stress errors in the H(div) norm and, thus, involve a data resolution error of the right-hand side f. These difficulties led to a twofold paradigm shift in the convergence analysis with rates for adaptive LSFEMs in Carstensen and Park (SIAM J. Numer. Anal., 53(1), 2015) for the lowest-order discretisation of the 2D Poisson model problem with homogeneous Dirichlet boundary conditions. Accordingly, some novel explicit residual-based a posteriori error estimator accomplishes the reduction property. Furthermore, a separate marking strategy in the adaptive algorithm ensures the sufficient data resolution.
This thesis presents the generalisation of these techniques to three linear model problems, namely, the Poisson problem, the Stokes equations, and the linear elasticity problem. It verifies the axioms of adaptivity with separate marking by Carstensen and Rabus (SIAM J. Numer. Anal., 55(6), 2017) in three spatial dimensions. The analysis covers discretisations with arbitrary polynomial degree and inhomogeneous Dirichlet and Neumann boundary conditions. Numerical experiments confirm the theoretically proven optimal convergence rates of the h-adaptive algorithm.
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Neves, Rodrigo de Azevêdo. "Desenvolvimento de modelos mecânico-probabilísticos para estruturas de pavimentos de edifícios." Universidade de São Paulo, 2004. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-13042005-081959/.
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Neste trabalho, são desenvolvidas novas técnicas aproximadas de análise de confiabilidade para grelhas de concreto armado levando-se em consideração as probabilidades de falha de vários modos importantes. Realiza-se um acoplamento entre os métodos de Monte Carlo, elementos finitos e procedimentos de otimização para considerar esses modos de falha importantes e classificá-los. Esse acoplamento também permite a redução do número de chamadas ao modelo de elementos finitos. Os cenários de falha são caracterizados como o encurtamento excessivo do concreto e o alongamento do aço. Estes cenários determinam a capacidade última da estrutura, e podem ser representados por um coeficiente escalar que multiplica todas as ações presentes na estrutura. Para a determinação desses estados estruturais últimos, um procedimento incremental-iterativo é utilizado. A análise de confiabilidade é realizada em diferentes conjuntos de realizações aleatórias das variáveis de projeto. O conjunto de respostas estruturais e de realizações permite a determinação dos coeficientes da superfície de respostas da estrutura. O acoplamento realizado permite também o tratamento com estruturas de concreto com elevado número de modos de falha. Aplicam-se as técnicas em exemplos de grelhas de concreto armado<br>In this work, new local approaches of reliability analysis applied to reinforced concrete grid structures are developed, taking into account several critical cross-section failure probabilities. Monte Carlo simulations are coupled with finite element analyses and optimization techniques with techniques to take into account the failure in the most important cross-sections, in order to classify the severity of failure modes. The failure scenario is depicted when either a concrete fiber or a steel bar reaches the predefined conventional limit. This scenario gives the structural ultimate capacity, which can be represented by a scalar coefficient multiplying all the loads acting on the structure. To achieve the failure scenario, an incremental and iterative procedure is used. To carry out the reliability analysis, the mechanical analysis has to be performed for different sets of random variable realizations of the mechanical, material and geometrical properties. The set of ultimate coefficients obtained from several mechanical analyses defines the response surface. The coupling between Monte Carlo simulations and response surface techniques applied in this work aims to reduce significantly the number of the finite element model calls, and hence to deal with real, or high-scale, reinforced concrete grids where large number of failure components can be found. The proposed procedure is then applied to reinforced concrete grids in order to show some more complex reinforced concrete examples