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arXiv 1902.04562math.OCcs.NAmath.NA
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在不确定性下使用随机梯度方法的拓扑优化

Topology Optimization under Uncertainty using a Stochastic Gradient-based Approach

University of Colorado, Boulder(科罗拉多大学博尔德分校)

Subhayan De, Jerrad Hampton, Kurt Maute, Alireza Doostan

AI总结:

本文提出了一种在不确定性下进行拓扑优化的方法,通过少量的伴随(和/或正向)求解生成随机近似的目标、约束及其梯度,从而减少计算成本,适用于大规模优化问题。

摘要:

在不确定性下的拓扑优化(TOuU)通常通过感兴趣几何和物理量的统计矩来定义目标和约束。大多数传统TOuU方法使用基于梯度的优化算法,并依赖于准确的统计矩及其梯度估计,例如通过伴随计算。当不确定输入的数量很大或感兴趣量表现出大的变异性时,可能需要大量的伴随(和/或正向)求解以确保这些梯度的准确性。优化过程本身通常需要大量的迭代,这可能会使TOuU计算成本高昂,甚至不可行。为了解决这个问题,我们提出了一种优化方法,通过少量的伴随(和/或正向)求解,每迭代生成目标、约束及其梯度的随机近似。在每个优化迭代中,生成统计独立(随机)的这些量的近似值。这种方法的总成本仅比相应的确定性TO问题大一小部分。我们将目标、约束及其设计灵敏度的随机近似纳入两种优化算法中。首先,我们研究了随机梯度下降(SGD)方法及其多种变体,这些方法已成功应用于大规模优化问题。其次,我们研究了所提出的随机近似方法在传统非线性规划方法中的应用,重点是全局收敛的渐近法(GCMMA)。通过结构设计优化问题,利用固有材料惩罚(SIMP)以及显式水平集方法,检验了这些算法的性能。

英文摘要:

Topology optimization under uncertainty (TOuU) often defines objectives and constraints by statistical moments of geometric and physical quantities of interest. Most traditional TOuU methods use gradient-based optimization algorithms and rely on accurate estimates of the statistical moments and their gradients, e.g., via adjoint calculations. When the number of uncertain inputs is large or the quantities of interest exhibit large variability, a large number of adjoint (and/or forward) solves may be required to ensure the accuracy of these gradients. The optimization procedure itself often requires a large number of iterations, which may render TOuU computationally expensive, if not infeasible. To tackle this difficulty, we here propose an optimization approach that generates a stochastic approximation of the objective, constraints, and their gradients via a small number of adjoint (and/or forward) solves, per iteration. A statistically independent (stochastic) approximation of these quantities is generated at each optimization iteration. The total cost of this approach is only a small factor larger than that of the corresponding deterministic TO problem. We incorporate the stochastic approximation of objective, constraints and their design sensitivities into two classes of optimization algorithms. First, we investigate the stochastic gradient descent (SGD) method and a number of its variants, which have been successfully applied to large-scale optimization problems for machine learning. Second, we study the use of the proposed stochastic approximation approach within conventional nonlinear programming methods, focusing on the Globally Convergent Method of Moving Asymptotes (GCMMA). The performance of these algorithms is investigated with structural design optimization problems utilizing a Solid Isotropic Material with Penalization (SIMP), as well as an explicit level set method.

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