An Efficient Time-Variant Reliability Analysis Method with Mixed Uncertainties

In practical engineering, due to the lack of information, it is impossible to accurately determine the distribution of all variables. Therefore, time-variant reliability problems with both random and interval variables may be encountered. However, this kind of problem usually involves a complex multilevel nested optimization problem, which leads to a substantial computational burden, and it is difficult to meet the requirements of complex engineering problem analysis. This study proposes a decoupling strategy to efficiently analyze the time-variant reliability based on the mixed uncertainty model. The interval variables are treated with independent random variables that are uniformly distributed in their respective intervals. Then the time-variant reliability-equivalent model, containing only random variables, is established, to avoid multi-layer nesting optimization. The stochastic process is first discretized to obtain several static limit state functions at different times. The time-variant reliability problem is changed into the conventional time-invariant system reliability problem. First order reliability analysis method (FORM) is used to analyze the reliability of each time. Thus, an efficient and robust convergence hybrid time-variant reliability calculation algorithm is proposed based on the equivalent model. Finally, numerical examples shows the effectiveness of the proposed method.

A Time-Variant Reliability Analysis Method Based on the Stochastic Process Discretization under Random and Interval Variables

In practical engineering, it is a cost-consuming problem to consider the time-variant reliability of both random variables and interval variables, which usually requires a lot of calculation. Therefore, a time-variant reliability analysis approach with hybrid uncertain variables is proposed in this paper. In the design period, the stochastic process is discretized into random variables. Simultaneously, the original random variables and the discrete random variables are converted into independent normal variables, and the interval variables are changed into standard variables. Then it is transformed into a hybrid reliability problem of static series system. At different times, the limited state functions are linearized at the most probable point (MPP) and at the most unfavorable point (MUP). The transformed static system reliability problem with hybrid uncertain variables can be solved effectively by introducing random variables. To solve the double-loop nested optimization in the hybrid reliability calculation, an effective iterative method is proposed. Two numerical examples and an engineering example demonstrate the validity of the present approach.

Personal and professional reliability in the structure of professional qualities of a specialist of the EMERCOM of Russia

The article considers the structure of personal and professional reliability of specialists of EMERCOM of Russia, working in the conditions interfaced to risk for life. The analysis of factors influencing the professional and personal reliability of a specialist of the EMERCOM of Russia is given. The relevance of this research is due to the need to study various parameters of reliability of the EMERCOM of Russia specialist. The author shows that the personal and professional reliability of a specialist of the EMERCOM of Russia is a characteristic of personal characteristics and qualities that determine the stability of standard normative behavior in terms of personal reliability in professional activities. At the same time, another important parameter of personal and professional reliability is the moral qualities of the specialist, his spiritual and moral maturity. In modern conditions of performing professional duties, the problem of studying the personal and professional qualities of EMERCOM specialists in Russia is of particular importance. The author conducted a theoretical and methodological analysis of psychological and pedagogical literature on the topic. The results of research conducted with the EMERCOM of Russia specialists on the study of personal and professional qualities are presented. Theoretical and methodological analysis of the reliability problem shows that it is not considered as an independent task and is not established in the traditionally existing systems of selection( selection), training, and support of specialists.

Overview of mathematical methods for power system reliability evaluation

Nowadays, with the strong development of the world's economy, the power system reliability issue is increasingly concerned. A high reliable power system brings peace of mind in production investment, stability in national security, citizen's satisfaction… Therefore, serious researches of the power system reliability problem is very necessary. Based on that researches, we can accurately evaluate the situation, propose operational scenarios, troubleshoot reasonably, plan properly for the future. From there, we can implement the ultimate goal of the power system reliability problem is to maximize the reliability, meeting the nation's development need. However, at present, power system reliability problems in many countries have not yet applied updated and objective assessment tools, only exploiting the surface of the problem. Through the research process, the authors publish this paper to outline the basic concepts, the classification and the parameters of the power system reliability problem. Besides, the paper summarizes in detail the methods of calculating and evaluating power system reliability based on the current mathematical models (Analytical Graph method, State Space method, Failure Tree method, Monte - Carlo method) with examples of each method. Thereby, these methods are compared and indicated the applications in specific situations.

Efficient System Reliability-Based Design Optimization Study for Replaced Hip Prosthesis Using New Optimized Anisotropic Bone Formulations

An efficient reliability algorithm is developed to transfer the system reliability problem to a single-component reliability problem, considering the uncertainty of loading cases and the material properties. The main difficulty is that femoral bone densities change after hip arthroplasty and, thus, the mechanical properties of the distinctive bone tissues and, therefore, the corresponding elasticity modulus and yield stress values change. Therefore, taking these changes into account during the hip prosthesis design process is strongly needed. As the bone possesses anisotropic behaviors, as the material properties in both radial and tangential directions in long bone (femur, tibia) are almost similar, the bone anisotropy is represented in this study by transversal isotropy. Two optimized formulations for yield stress against the elasticity modulus relationship are first developed and then integrated into an efficient reliability algorithm. Thus, a coupling between reliability and optimization, so-called reliability-based design optimization (RBDO), is introduced in order to control the reliability level. The proposed RBDO algorithm using optimum safety factors (OSF) takes into account the material uncertainties and leads to new stem dimensions. An in-depth numerical analysis on a cementless hip prosthesis is implemented to demonstrate the appropriateness of the proposed algorithm with the consideration of many different loading cases. The results show that the studied model can be effectively used when compared to previous works, which concerns the changes in both geometry and material properties.