Reliability-based design optimization applied to structures submitted to random fatigue loads

Structural and Multidisciplinary Optimization - The reliability-based design optimization (RBDO) aims to find the most balanced design through a compromise between cost and safety when...     

Benchmark study of numerical methods for reliability-based design optimization

The reliability-based design optimization (RBDO) seeks for the best compromise between cost and safety, by considering system uncertainties. In order to overcome computational difficulties, many formulations have been recently developed, leading to confusion about what method should be selected for a given application, due to the lack of full-scale comparative studies. In this context, the present paper aims at giving an overview of various RBDO approaches which are tested on a benchmark constituted of four examples using mathematical and finite element models, with different levels of difficulties. The study is focused on the three main approaches, namely the two-level approach, the single loop approach and the decoupled approach; for each category, two RBDO formulations are discussed, implemented and tested for numerical examples. The benchmark study allows us to give comprehensive overview of various approaches, to give clear ideas about their capabilities and limitations, and to draw useful conclusions regarding robustness and numerical performance.     

Reliability-based optimization of structural systems by adaptive target safety – Application to RC frames

Reliability-based design optimization (RBDO) aims to find the best compromise between cost reduction and safety assurance. Traditionally, component optimization is defined by minimizing the structural cost under a prescribed reliability target for a single limit state. However, as structural failure is rarely devoted to only one component, the system approach becomes necessary to deal with realistic applications. In this paper, a methodology for system reliability-based design optimization (SRBDO) is proposed. Instead of specifying identical predefined component targets, the method is based on adaptive target reliabilities for structural components. An updating procedure is included in the optimization process to ensure the required system reliability. The proposed method aims to find the best compromise between satisfying the target system reliability and optimizing the component performance. The application to reinforced concrete structures shows the interest of the adaptive target reliabilities as well as the efficiency of the updating procedure.     

Reliability based design optimization of wire bonding in power microelectronic devices

This paper presents a numerical investigation of the probabilistic approach in estimating the reliability of wire bonding, and develops a reliability-based design optimization Methodology (RBDO) for microelectronic device structures. The objective of the RBDO method is to design structures which should be both economical and reliable where the solution reduces the structural weight in uncritical regions. It does not only provide an improved design, but also a higher level of confidence in the design. The Finite element simulation model intends to analyze the sequence of the failure events in power microelectronic devices. This numerical model is used to estimate the probability of failure of power module regarding the wire bonding connection. However, due to time-consuming of the multiphysics finite element simulation, a response surface method is used to approximate the response output of the limit state, in this way the reliability analysis is performed directly to the response surface by using the First and the Second Order Reliability Methods FORM/SORM. Subsequently the reliability analysis is integrated in the optimization process to improve the performance and reliability of structural design of wire bonding. The sequential RBDO algorithm is used to solve this problem and to find the best structural designs which realize the best compromise between cost and safety.     

Systematic forecasts of solar collector's performance in various sites of different climates in Algeria

This paper presents the results of theoretical models suggesting investigation of the performance of a solar air flat plate collector. The model can predict the temperature of the outlet air. This will be compared with the results obtained by the experimental results. The range of experimental results related to the thermal performances of plane–air solar collectors and various practical uses, inspires us to undertake this work in the context of a rational exploitation of local solar field. Indeed the setting up of a solar system to satisfy a well-determined need in a given site has to be done only after first having estimated the system productivity relative to the solar field actually available by fine weather (bright sky) or by bad days (covered sky) and then having an exact knowledge of the evolution of the climatic parameters.     

Performance investigation of single- and double-pass solar air heaters through the use of various fin geometries

This paper presents an experimental comparative study on the thermal performance of the following three single-pass types of solar air heaters (SAHs): (i) without obstacles, (ii) with rectangular obstacles and (iii) with a new form of obstacles in the air flow duct. Thus, we carried out studies to compare the best system with (iiii) a double-pass flat plate collector having the same type of obstacles in order to determine the best-performing model. All collectors were designed, constructed and tested in the University of Biskra (Algeria) in a stand facing South at an inclination angle equal to the local latitude. In comparison with the recent literature, at different air mass flows, the highest efficiencies were obtained from the double-pass SAH with trapezoidal obstacles. In addition, this study has allowed us to show that the use of obstacles, in the air flow duct of the SAHs, is an efficient method to improve their performances.