Abstract

Extraction and recognition of the features of flow field is an important research area of fluid mechanics. However, the wake flow field of object immersed in fluid is complicated in the case of medium- and high-Reynolds number, thus it is difficult to extract and recognize the key features by using traditional physical models and mathematical methods. The continuous development of deep learning theory provides us with a new method of recognizing the complex flow features. A new method of extracting the features of the flow time history is proposed based on deep learning in this work. The accuracy of four deep learning model for feature recognition is studied. The results show that the proposed model can identify different characteristics of the wake time history and object shapes accurately. Some conclusions can be obtained below (i) The model based on convolutional layers has higher accuracy and is suitable for analyzing the features of flow time history data. (ii) The residual convolutional network, with a deeper structure and more complex inter-layer structure, has highest accuracy for feature recognition. (iii) The proposed method can extract and recognize the flow features from the perspective of physical quantities time history, which is a high-accuracy method, and it is an important new way to study the features of flow physical quantities.

Highlights

  • The results show that the proposed model can identify different characteristics of the wake time history and object shapes accurately

  • Technol. 47 75 (in Chinese) [战庆亮, 周志勇, 葛耀君 2015 哈尔滨工业 大学学报 47 75]

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Summary

DL model

全连接网络又称多层感知网络, 是最简单、应 用最广泛的深度学习模型, 其特点是任意层的神经 元与上一层的所有神经元都是相连的, 这些相连的 关系称为权重. 式中 y 为第 n 层全连接层的输出, F 和 b 为第 n 层 全连接层的权重和偏移矩阵. 从其结构原理可以发 现, 每一个神经元都与上层的各神经元相关, 这将 导致时程数据的每一个元素与上一层中其他元素 的关系是完全等价的, 丢失了时程数据中各个时刻 前后之间的关系. 同时, 在全连接层前增加 Dropout 层, 用来防止训练过程中的过拟合 [24], 保证模型的 收敛. 本文构建了适用于流场时程数据的 RCNN 网络, 如图 4 所示, 该网络由 3 个残差块组 成, 每个残差块包含 3 个卷积层. Structure of Fully connected convolution neural network. 图 6 各形状棱柱的瞬态流场云图 (a) 三棱柱压力云图; (b) 方柱压力云图; (c) 六棱柱压力云图; (d) 三棱柱速度云 图; (e) 方柱速度云图; (f) 六棱柱速度云图 Fig. 6. 学习模型参数要远多于 TCNN; 4 种模型中, 结构 最复杂的 RCNN 网络参数也远多于 FCNN 网络, 依然少于 MLP 模型. 学习模型参数要远多于 TCNN; 4 种模型中, 结构 最复杂的 RCNN 网络参数也远多于 FCNN 网络, 依然少于 MLP 模型. 在训练过程中, 从测点集中 随机选取 10% 的样本作为训练集, 剩余 90% 样本 作为验证集, 计算的迭代次数均为 100 次

Flow Prism
FCNN 卷积层
MLP TCNN FCNN RCNN

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