Multidisciplinary Design Optimization Based On Time-variant Reliability Theory

Modern engineering design is faced with more and more design requirements for complex structures. In order to design efficiently and ensure the safety and reliability of complex products, reliability based multidisciplinary design optimization(RBMDO) is applied. The conventional RBMDO consider the uncertainties as time-invariant factors. However, in real engineering design problems there are a lot of time-variant uncertainties, such as load, the wear degradation factors and so on. This paper focuses on the transmission and quantization of the time-variant uncertainties in a multidisciplinary environment, and the corresponding MDO models are developed. The main research contents are as follows:Firstly, the time-invariant reliability based MDO under correlated uncertainties is analyzed. the concept of correlated uncertainties is presented, then a mathematical model based on the ellipsoidal set theory is built to estimate correlated uncertainties. Building upon the constructed mathematical model the new collaborative optimization MDO method considering correlated uncertainties is presented. The purposed method is illustrated with a case study of an engineering example system.Secondly, the time-variant reliability based MDO under time-variant design parameters is presented. The transmission, quantification and modeling of the timevariant design parameters in a multidisciplinary environment are analyzed. Then, the time-variant reliability of the design parameters based MDO is developed on the basis of the improved RBDO model. The corresponding CO calculation framework is conducted. The purposed method is illustrated with four-high mill design.At last, the reliability based MDO under time-variant design variables is proposed. Based on the maintenance cost concept, out-crossing rate and the maintenance cost are considered, and the deterministic MDO is quantified with the Research and development costs(R&D) costs. The R&D costs and maintenance costs are regarded as different disciplines and the lowest cost in entire life cycle is objective function. The optimization process is given to coordinate the variable transmission between time-variant reliability optimization and the deterministic multidisciplinary design optimization.