提出新型损失函数GMSE,让机器学习更高效模拟流体流动。
A generalised novel loss function for computational fluid dynamics
- 根据局部方差动态加权,自动识别流场重要区域
- 生成结果与真实模拟相比结构相似性误差降低83.6%
- 适合需要快速流体模拟的工程领域,如汽车与航空
计算流体动力学(CFD)在汽车、航空、航海和医疗等领域至关重要,但因直接求解流动的复杂性、成本高及计算需求大,常需数天时间。基于控制生成对抗网络(cGAN)的机器学习方法有望加速或替代传统CFD,因其可逼近数据分布。然而,传统cGAN对图像各部分同等重视,而CFD数据中仅有小范围高变区域具重要意义,其余大部分为低方差背景。为此,本文提出梯度均方误差(GMSE)损失函数,能按场域动态识别重要区域并赋予相应权重。通过三组相同网络分别使用MSE、GMSE和动态变体DGMSE训练对比,结果显示:新损失函数加快收敛,显著缩短训练时间;生成场与真实模拟间结构相似性误差降低83.6%,损失下降速率提升76.6%,且更具欺骗判别器的能力。该方法有望推动机器学习在CFD中的加速应用。
原文摘要 · Abstract (English)
Computational fluid dynamics (CFD) simulations are crucial in automotive, aerospace, maritime and medical applications, but are limited by the complexity, cost and computational requirements of directly calculating the flow, often taking days of compute time. Machine-learning architectures, such as controlled generative adversarial networks (cGANs) hold significant potential in enhancing or replacing CFD investigations, due to cGANs ability to approximate the underlying data distribution of a dataset. Unlike traditional cGAN applications, where the entire image carries information, CFD data contains small regions of highly variant data, immersed in a large context of low variance that is of minimal importance. This renders most existing deep learning techniques that give equal importance to every portion of the data during training, inefficient. To mitigate this, a novel loss function is proposed called Gradient Mean Squared Error (GMSE) which automatically and dynamically identifies the regions of importance on a field-by-field basis, assigning appropriate weights according to the local variance. To assess the effectiveness of the proposed solution, three identical networks were trained; optimised with Mean Squared Error (MSE) loss, proposed GMSE loss and a dynamic variant of GMSE (DGMSE). The novel loss function resulted in faster loss convergence, correlating to reduced training time, whilst also displaying an 83.6% reduction in structural similarity error between the generated field and ground truth simulations, a 76.6% higher maximum rate of loss and an increased ability to fool a discriminator network. It is hoped that this loss function will enable accelerated machine learning within computational fluid dynamics.
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