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Structural optimization methods have been developed and applied to a variety of engineering practices. This study aims to overcome technical challenges in applying design and topology optimization techniques to large-scale structural systems with uncertainties. The specific goals of this dissertation are: (1) to develop an efficient scheme for topology optimization; (2) to introduce an efficient and accurate system reliability-based design optimization (SRBDO) procedure; and (3) to investigate the reliability-based topology optimization (RBTO) problem. First, it is noted that the material distribution method often requires a large number of design variables, especially in three-dimensional applications, which makes topology optimization computationally expensive. A multiresolution topology optimization (MTOP) scheme is thus developed to obtain high-resolution optimal topologies with relatively low computational cost by introducing distinct resolution levels to displacement, density and design variable fields: the finite element analysis is performed on a relatively coarse mesh; the optimization is performed on a moderately fine mesh for design variables; and the density is defined on a relatively fine mesh for material distribution. Second, it is challenging to deal with system events in reliability-based design optimization (RBDO) due to the complexity of system reliability analysis. A new single-loop system RBDO approach is developed by using the matrix-based system reliability (MSR) method. The SRBDO/MSR approach utilizes matrix calculations to evaluate the system failure probability and its parameter sensitivities accurately and efficiently. The approach is applicable to general system events consisting of statistically dependent component events. Third, existing RBDO approaches employing first-order reliability method (FORM) can induce significant error for highly nonlinear problems. To enhance the accuracy of component and system RBDO approaches, algorithms based on the second-order reliability method (SORM), termed as SORM-based RBDO, are proposed. These technical advances enable us to perform RBTO of large-scale structures efficiently. The proposed algorithms and approaches are tested and demonstrated by various numerical examples. The efficient and accurate approaches developed for design and topology optimization can be applied to large-scale problems in engineering design practices.
Next Generation HALT and HASS presents a major paradigm shift from reliability prediction-based methods to discovery of electronic systems reliability risks. This is achieved by integrating highly accelerated life test (HALT) and highly accelerated stress screen (HASS) into a physics-of-failure-based robust product and process development methodology. The new methodologies challenge misleading and sometimes costly mis-application of probabilistic failure prediction methods (FPM) and provide a new deterministic map for reliability development. The authors clearly explain the new approach with a logical progression of problem statement and solutions. The book helps engineers employ HALT and HASS by illustrating why the misleading assumptions used for FPM are invalid. Next, the application of HALT and HASS empirical discovery methods to quickly find unreliable elements in electronics systems gives readers practical insight to the techniques. The physics of HALT and HASS methodologies are highlighted, illustrating how they uncover and isolate software failures due to hardware-software interactions in digital systems. The use of empirical operational stress limits for the development of future tools and reliability discriminators is described. Key features: * Provides a clear basis for moving from statistical reliability prediction models to practical methods of insuring and improving reliability. * Challenges existing failure prediction methodologies by highlighting their limitations using real field data. * Explains a practical approach to why and how HALT and HASS are applied to electronics and electromechanical systems. * Presents opportunities to develop reliability test discriminators for prognostics using empirical stress limits. * Guides engineers and managers on the benefits of the deterministic and more efficient methods of HALT and HASS. * Integrates the empirical limit discovery methods of HALT and HASS into a physics of failure based robust product and process development process.
The book covers new developments in structural topology optimization. Basic features and limitations of Michell’s truss theory, its extension to a broader class of support conditions, generalizations of truss topology optimization, and Michell continua are reviewed. For elastic bodies, the layout problems in linear elasticity are discussed and the method of relaxation by homogenization is outlined. The classical problem of free material design is shown to be reducible to a locking material problem, even in the multiload case. For structures subjected to dynamic loads, it is explained how they can be designed so that the structural eigenfrequencies of vibration are as far away as possible from a prescribed external excitation frequency (or a band of excitation frequencies) in order to avoid resonance phenomena with high vibration and noise levels. For diffusive and convective transport processes and multiphysics problems, applications of the density method are discussed. In order to take uncertainty in material parameters, geometry, and operating conditions into account, techniques of reliability-based design optimization are introduced and reviewed for their applicability to topology optimization.
"Motivated by the need of high reliability and safety in complex engineering systems, recently reliability-based design has been increasingly applied in multidisciplinary design optimization (MDO). However, a direct integration of reliability-based design that has been successful in many single disciplinary fields into MDO may present tremendous implementation and numerical difficulties. The reliability analysis and reliability based designs are highly expensive for MDO considering various disciplines that are dependent on each other or coupled. Hence, the present work proposes a methodology of Sequential Optimization and Reliability Assessment for multidisciplinary systems design, to improve the efficiency of reliability-based MDO. The central idea is to decouple the reliability analysis from MDO with sequential cycles of reliability analysis and deterministic MDO and hence to reduce the computational demand"--Abstract, leaf iii.
"This thesis focuses on developing a methodology for accurately estimating series system probability of failure. Existing methods for series system based design optimization are not that accurate because they assign reliability to each failure mode; as a result complete system reliability goes down. According to method proposed in this work, the user will assign required system reliability at the start and then optimizer will apportion reliability to every failure mode in order to meet required system reliability level. Detlevson second order upper bounds are used to estimate system probability of failure. Several examples have been shown to verify the results obtained"--Abstract, leaf iii
This thesis discusses two topics pertaining to structural topology optimization: reliability-based topology optimization and the topological derivative. We first perform reliability-based topology optimization by combining reliability analysis and material distribution topology design methods to design linear elastic structures subject to random loadings. Both component reliability and system reliability are considered. In component reliability, we satisfy numerous probabilistic constraints which quantify the failure of different events. In system reliability, we satisfy a single probabilistic constraint which encompasses the component events. To solve the probabilistic optimization problem, we use a variant of the single loop method, which eliminates the need for an inner reliability analysis loop. The proposed method is amenable to implementation with existing deterministic topology optimization software, and hence suitable for practical applications. The topological derivative provides the variation of a functional when an infinitesimal hole is introduced in the domain. It was first introduced in the context of topology optimization as means to nucleate holes within a structure. Here we use the topological derivative to approximate the energy release rate field corresponding to a small crack at any boundary location and at any orientation. Our proposed method offers significant computational advantages over current finite element based methods since it requires a single analysis whereas the others require a distinct analysis for each crack size-location-orientation combination. Moreover, the proposed method evaluates the topological derivative in the non-cracked domain which eliminates the need for tailored meshes in the crack region. To improve our fracture mechanics analyses we next propose an algorithm to obtain higher order terms in the topological derivative expansion corresponding to the introduction of a circular hole, not a crack, in this preliminary study. In this way, we are able to obtain better estimates for the response functional when larger circular holes, and eventually cracks, are introduced into the domain. The primary element of our algorithm involves the asymptotic expansion for the stress on the hole boundary as the hole size approaches zero.
Keeping abreast of the latest developments in materials technology and techniques is vital to a wide range of sectors such as aerospace, the automotive industry, and mechanical and civil engineering. A knowledge and understanding of the latest research is crucial to facilitate the adoption of appropriate solutions in tackling those challenges that will inevitably be encountered. This book presents the proceedings of MSAM 2023, the 6th International Conference on Material Strength and Applied Mechanics, held as a hybrid event from 4-7 July 2023 in Macau, China. This annual conference provides a platform for all those engaged in basic or applied research, technology development, application, and innovation in material strength and applied mechanics to exchange information and ideas about the latest research in the field, and is attended by scientists and experts from academia and industry from around the world. The book contains 17 papers accepted from 50 submissions received for presentation at the conference. These were selected following a rigorous peer-review process, in which each paper was assessed by two or three reviewers on the basis of criteria including scope, application, research merit, and experimental techniques. Topics covered include applied mechanics, intelligent manufacturing technology, mechanical engineering, optimal design of structures, advanced materials sciences, computational methods and modeling, simulation processes, and industrial applications. The book offers an overview of the latest advancements in material strength and applied mechanics, and will be of interest to all those working in the field.
This volume gathers the latest advances, innovations, and applications in the field of seismic engineering, as presented by leading researchers and engineers at the 1st International Workshop on Energy-Based Seismic Engineering (IWEBSE), held in Madrid, Spain, on May 24-26, 2021. The contributions cover a diverse range of topics, including energy-based EDPs, damage potential of ground motion, structural modeling in energy-based damage assessment of structures, energy dissipation demand on structural components, innovative structures with energy dissipation systems or seismic isolation, as well as seismic design and analysis. Selected by means of a rigorous peer-review process, they will spur novel research directions and foster future multidisciplinary collaborations.