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考虑随机场载荷不确定性的连续体结构可靠性拓扑优化

RELIABILITY-BASED TOPOLOGY OPTIMIZATION OF CONTINUUM STRUCTURES CONSIDERING RANDOM FIELD LOAD UNCERTAINTY

  • 摘要: 本文提出了一种基于多项式混沌展开(Polynomial Chaos Expansions, PCE)代理模型的高效可靠性拓扑优化(reliability-based topology optimization, RBTO)方法, 用于处理考虑随机场载荷不确定性的可靠性设计问题. 为此, 建立了基于柔度响应定义的概率约束下的结构体积分数最小化的单层循环RBTO模型, 采用Karhunen-Loève(K-L)展开式描述载荷随机场, 利用蒙特卡罗模拟计算结构的失效概率. 为了克服蒙特卡罗模拟方法在计算结构响应时计算成本高昂的问题, 本文引入了PCE作为代理模型, 高效地捕捉随机场载荷与结构柔度之间的复杂非线性关系. 通过少量的高精度有限元分析样本, 可以构建出高精度的PCE代理模型, 一旦构建好代理模型的显式表达式, 就可以直接基于代理模型在随机样本处计算失效概率, 后续无需再进行有限元分析, 从而在不牺牲太多精度的情况下, 大幅减少后续计算的时间成本. 详细推导了概率约束函数关于设计变量的灵敏度, 采用移动渐近线方法(method of moving asymptotes, MMA)求解优化问题, 将基于分析模型的RBTO方法与基于代理模型的RBTO方法作对比, 验证了所提方法的有效性和优越性, 并通过4个数值算例讨论了失效概率限值、柔度限值、载荷随机场均值与标准差以及相关长度对优化结果的影响. 结果表明, 不确定性因素增强时, 结构需要消耗更多的材料来抵抗不确定性因素的干扰, 另外基于代理模型的RBTO方法相对于基于分析模型的RBTO计算时间大幅缩短, 提高了优化效率.

     

    Abstract: This paper proposes an efficient reliability-based topology optimization (RBTO) method based on the P-olynomial Chaos Expansions (PCE) surrogate model to address design problems considering random field load uncer-tainty. To this end, a single-loop RBTO model is established to minimize the structural volume fraction under probabi-listic constraint defined by compliance response. The Karhunen-Loève (K-L) expansion is utilized to characterize the random field of loads, while Monte Carlo Simulation is employed to estimate the probability of structural failure. In order to mitigate the substantial computational demands of Monte Carlo Simulation method in calculating structural response, the PCE is implemented as a surrogate model, effectively capturing the intricate nonlinear relationship bet-ween random field loads and structural compliance. A high-precision PCE surrogate model can be constructed using a limited number of high-fidelity finite element analysis samples, Once the explicit expression of the surrogate model is constructed, the failure probability can be directly calculated at random samples based on the surrogate model, without the need for further finite element analysis, thereby significantly reducing computational time without compr-omising accuracy. The sensitivity of the probabilistic constraint function with respect to design variables is thoroughly derived, and the optimization problem is addressed using the Method of Moving Asymptotes (MMA). The efficacy and superiority of the proposed surrogate model-based RBTO method are validated through comparisons with an an-alytical model-based RBTO approach. In addition, the effects of failure probability thresholds, compliance limits, m-ean and standard deviations of load random fields, and correlation lengths on the optimization outcomes was discusse-d through four numerical examples. The results indicate that when uncertainty factors increase, the structure needs t-o consume more materials to resist the interference of uncertainty factors. In the bargain, the surrogate model-based RBTO method significantly reduces the computation time and improves the optimization efficiency compared to the analytical model-based RBTO approach.

     

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