通过基于预训练转换器(Transformer)双向编码器表征的文本卷积神经网络(text convolutional neural network model based on pre-training bidirectional encoder representations from transformer,BERT-TextCNN)模型实现汽车网站评论...通过基于预训练转换器(Transformer)双向编码器表征的文本卷积神经网络(text convolutional neural network model based on pre-training bidirectional encoder representations from transformer,BERT-TextCNN)模型实现汽车网站评论的情感分析,其目的在于研究用户对汽车产品和汽车服务的情感态度。首先采用基于Transformer的双向编码器表征(bidirectional encoder representations from transformer,BERT)模型能有效解决汽车评论中存在的一词多义问题,并产生包含丰富信息的动态词向量,然后结合文本卷积神经网络(text convolutional neural network,TextCNN)模型中的卷积运算和池化运算提取关键特征,最后通过softmax函数计算评论文本情感的概率分布。试验结果表明,BERT-TextCNN模型在情感分类中相比几种常见的神经网络模型的精度、召回率和F1值均有所提升。展开更多
带钢表面缺陷检测是生产过程智能检测的重要任务。针对目前带钢表面缺陷检测算法效率低、实时性差的问题,本文提出了基于卷积神经网络的轻量级目标检测器。该方法以YOLOv4-tiny模型为框架,针对带钢表面缺陷检测任务的特殊性,结合了多尺...带钢表面缺陷检测是生产过程智能检测的重要任务。针对目前带钢表面缺陷检测算法效率低、实时性差的问题,本文提出了基于卷积神经网络的轻量级目标检测器。该方法以YOLOv4-tiny模型为框架,针对带钢表面缺陷检测任务的特殊性,结合了多尺度检测与空间注意力机制的优化策略,在保证检测效率的同时提高了轻量级目标检测器的精度。实验证明,所提出的改进的YOLOv4-tiny模型能够精确地检测带钢表面缺陷,平均均值精度mAP(mean Average precision)为73.29%,并且每秒帧数FPS(Frames per second)达到163,满足实际工业落地的实时性要求。展开更多
The pitching motions of supercavitating vehicles could not be avoided due to the lost water buoyancy. In order to have some insight for the design of the supercavitating vehicles, the fixed frequency and free pitching...The pitching motions of supercavitating vehicles could not be avoided due to the lost water buoyancy. In order to have some insight for the design of the supercavitating vehicles, the fixed frequency and free pitching motions are investigated. A numerical predicting method based on the relative motion principle and the non-inertia coordinate system is proposed to simulate the free pitching motions of supercavitating vehicles in the longitudinal plane. Homogeneous and two fluid multiphase models are used to predict the natural and the ventilated supercavitating flows. In the fixed frequency pitching motions, a variety of working conditions are considered, including the pitching angular velocities and the supercavity scales and the results are found to be consistent with the available experimental results in literature. The mesh deformation technology controlled by the moment of momentum equation is adopted to study the free pitching motions and finally to obtain the planing states proposed by Savchenko. The numerical method is validated for predicting the pitching motions of supercavitating vehicles and is found to enjoy better calculation efficiency as comparing with the mesh regeneration technology.展开更多
A numerical method consisted of the cavitation number correction and the model coefficient correction algorithms is presented to simulate the supercavity in water tunnel considering blockage and gravity effects based ...A numerical method consisted of the cavitation number correction and the model coefficient correction algorithms is presented to simulate the supercavity in water tunnel considering blockage and gravity effects based on the Logvinovich model.A model of the minimum cavitation number is also proposed based on the dimensional analysis theory,and the minimum cavitation number is formulated based on the model and numerical results using the nonlinear least square method(NLLS).The formula is verified by experiment to some extent.展开更多
The curvilinear motion in a vertical plane is one of the most important features of the supercavitating vehicle. It is of great significance to study the controllability and the maneuverability of the supercavitating ...The curvilinear motion in a vertical plane is one of the most important features of the supercavitating vehicle. It is of great significance to study the controllability and the maneuverability of the supercavitating vehicle. Models are built for the effects of the angle of attack, the gravity and the inertial force in the curvilinear motion in the vertical p｜ane. Numerica~ simulations are carried out for the supercavity motion based on these models combined with the Logvinovich model. It is shown that the maximum deviation displacement in the outward normal direction of the trajectory with a constant curvature, which occurs in the tail of the supercavity, increases as the cavitation number or the curvature radius of the supercavity trajectory decreases under the condition that other model and flow parameters are kept constant. For a varied curvature, the supercavity shape changes evidently because of the change of the ambient pressure, but with the same trend as in constant curvature. The deviation displacement increases along the supercavity length gradually.展开更多
This paper analyses theoretically the effect of transportation and housing subsidies on urban sprawl,modal choice decisions and urban spatial structure using a spatial general equilibrium model in a monocentric city w...This paper analyses theoretically the effect of transportation and housing subsidies on urban sprawl,modal choice decisions and urban spatial structure using a spatial general equilibrium model in a monocentric city with two transport modes. Our analysis shows that public transit subsidy leads to urban shrink,whilst subsidizing automobile and housing make the city sprawl. We also find the effects of the other factors on urban sprawl,such as households income and demand,rural land rent,the income tax rate,the total fixed cost of public transit and automobile and the travelling marginal cost of public transit and automobile. Furthermore,this paper also studies how to maximize the urban-area-wide spatial equilibrium utility level.展开更多
文摘通过基于预训练转换器(Transformer)双向编码器表征的文本卷积神经网络(text convolutional neural network model based on pre-training bidirectional encoder representations from transformer,BERT-TextCNN)模型实现汽车网站评论的情感分析,其目的在于研究用户对汽车产品和汽车服务的情感态度。首先采用基于Transformer的双向编码器表征(bidirectional encoder representations from transformer,BERT)模型能有效解决汽车评论中存在的一词多义问题,并产生包含丰富信息的动态词向量,然后结合文本卷积神经网络(text convolutional neural network,TextCNN)模型中的卷积运算和池化运算提取关键特征,最后通过softmax函数计算评论文本情感的概率分布。试验结果表明,BERT-TextCNN模型在情感分类中相比几种常见的神经网络模型的精度、召回率和F1值均有所提升。
文摘带钢表面缺陷检测是生产过程智能检测的重要任务。针对目前带钢表面缺陷检测算法效率低、实时性差的问题,本文提出了基于卷积神经网络的轻量级目标检测器。该方法以YOLOv4-tiny模型为框架,针对带钢表面缺陷检测任务的特殊性,结合了多尺度检测与空间注意力机制的优化策略,在保证检测效率的同时提高了轻量级目标检测器的精度。实验证明,所提出的改进的YOLOv4-tiny模型能够精确地检测带钢表面缺陷,平均均值精度mAP(mean Average precision)为73.29%,并且每秒帧数FPS(Frames per second)达到163,满足实际工业落地的实时性要求。
基金Project support by the Major National Natural Science Founation of China(Grant No.10832007)
文摘The pitching motions of supercavitating vehicles could not be avoided due to the lost water buoyancy. In order to have some insight for the design of the supercavitating vehicles, the fixed frequency and free pitching motions are investigated. A numerical predicting method based on the relative motion principle and the non-inertia coordinate system is proposed to simulate the free pitching motions of supercavitating vehicles in the longitudinal plane. Homogeneous and two fluid multiphase models are used to predict the natural and the ventilated supercavitating flows. In the fixed frequency pitching motions, a variety of working conditions are considered, including the pitching angular velocities and the supercavity scales and the results are found to be consistent with the available experimental results in literature. The mesh deformation technology controlled by the moment of momentum equation is adopted to study the free pitching motions and finally to obtain the planing states proposed by Savchenko. The numerical method is validated for predicting the pitching motions of supercavitating vehicles and is found to enjoy better calculation efficiency as comparing with the mesh regeneration technology.
基金supported by the National Natural Science Foundation of China(Grant No.10832007)
文摘A numerical method consisted of the cavitation number correction and the model coefficient correction algorithms is presented to simulate the supercavity in water tunnel considering blockage and gravity effects based on the Logvinovich model.A model of the minimum cavitation number is also proposed based on the dimensional analysis theory,and the minimum cavitation number is formulated based on the model and numerical results using the nonlinear least square method(NLLS).The formula is verified by experiment to some extent.
基金supported by the National Natural Science Foundation of China(Grant No.10832007)
文摘The curvilinear motion in a vertical plane is one of the most important features of the supercavitating vehicle. It is of great significance to study the controllability and the maneuverability of the supercavitating vehicle. Models are built for the effects of the angle of attack, the gravity and the inertial force in the curvilinear motion in the vertical p｜ane. Numerica~ simulations are carried out for the supercavity motion based on these models combined with the Logvinovich model. It is shown that the maximum deviation displacement in the outward normal direction of the trajectory with a constant curvature, which occurs in the tail of the supercavity, increases as the cavitation number or the curvature radius of the supercavity trajectory decreases under the condition that other model and flow parameters are kept constant. For a varied curvature, the supercavity shape changes evidently because of the change of the ambient pressure, but with the same trend as in constant curvature. The deviation displacement increases along the supercavity length gradually.
基金Supported by Humanities and Social Sciences of Beijing Jiaotong University(B16JB00190)the National Natural Science Foundation of China(71501012)the Social Science Foundation of Beijing(16GLC054)
文摘This paper analyses theoretically the effect of transportation and housing subsidies on urban sprawl,modal choice decisions and urban spatial structure using a spatial general equilibrium model in a monocentric city with two transport modes. Our analysis shows that public transit subsidy leads to urban shrink,whilst subsidizing automobile and housing make the city sprawl. We also find the effects of the other factors on urban sprawl,such as households income and demand,rural land rent,the income tax rate,the total fixed cost of public transit and automobile and the travelling marginal cost of public transit and automobile. Furthermore,this paper also studies how to maximize the urban-area-wide spatial equilibrium utility level.
