让神经网络按输入特性自动调整输出形状,提升力学建模效率。
Input Specific Neural Networks
- 根据不同输入设定凸性、单调性等约束,实现输出结构可控。
- 可嵌入有限元求解器,显式微分加速计算,比自动微分快数倍。
- 用二元门控机制自动识别是否需建模为多凸,适合多尺度材料建模。
神经网络的黑箱特性限制了对输入输出间结构关系的编码能力。现有方法大多仅对单一输入集施加约束,本文提出输入特异性神经网络(ISNN),使标量输出能同时满足多种约束:某些输入上强制凸性,另一些输入上兼具单调递增与凸性,其余输入则可为单调递增或任意关系。论文设计两种ISNN架构,并推导输出对输入的一阶与二阶导数公式。该方法广泛适用,本文聚焦于计算力学领域,用于拟合数据驱动的本构模型。训练后的本构律可嵌入有限元求解器,利用推导出的解析导数进行显式微分,相比自动微分显著提速。此外,通过二元门控机制,ISNN可学习输入输出间的结构关系,应用于解耦多尺度场景中各向异性自由能势函数建模,自动判断是否需建模为多凸,并仅保留相关层与最少输入,实现高效建模。
原文摘要 · Abstract (English)
The black-box nature of neural networks limits the ability to encode or impose specific structural relationships between inputs and outputs. While various studies have introduced architectures that ensure the network's output adheres to a particular form in relation to certain inputs, the majority of these approaches impose constraints on only a single set of inputs. This paper introduces a novel neural network architecture, termed the Input Specific Neural Network (ISNN), which extends this concept by allowing scalar-valued outputs to be subject to multiple constraints. Specifically, the ISNN can enforce convexity in some inputs, non-decreasing monotonicity combined with convexity with respect to others, and simple non-decreasing monotonicity or arbitrary relationships with additional inputs. The paper presents two distinct ISNN architectures, along with equations for the first and second derivatives of the output with respect to the inputs. These networks are broadly applicable. In this work, we restrict their usage to solving problems in computational mechanics. In particular, we show how they can be effectively applied to fitting data-driven constitutive models. We then embed our trained data-driven constitutive laws into a finite element solver where significant time savings can be achieved by using explicit manual differentiation using the derived equations as opposed to automatic differentiation. We also show how ISNNs can be used to learn structural relationships between inputs and outputs via a binary gating mechanism. Particularly, ISNNs are employed to model an anisotropic free energy potential to get the homogenized macroscopic response in a decoupled multiscale setting, where the network learns whether or not the potential should be modeled as polyconvex, and retains only the relevant layers while using the minimum number of inputs.
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