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4th IAHR Asian Working Group Symposium on Hydraulic Machinery and Systems

作者： Cai, Jinhan Zhou, Xuejun Luo, Hongying Wang, Zhengwei Tianjin Key Laboratory for Advanced Mechatronic System Design and Intelligent Control School of Mechanical Engineering Tianjin University of Technology Tianjin300384 China National Demonstration Center for Experimental Mechanical and Electrical Engineering Education Tianjin University of Technology China College of Mechanical Engineering Tianjin Sino-German University of Applied Science No. 2 Yashen Road Tianjin China College of Hydraulic and Civil Engineering Tibet Agricultural and Animal Husbandry University China Department of Energy and Power Engineering Tsinghua University China

In recent years, with the continuous development of China's hydropower projects, Pelton turbines are gradually being valued, and the focus of development has shifted from plain areas to plateau areas. Environmental impacts such as high altitude, water temperature, and high sediment content in the plateau area have caused serious interference to equipment that originally worked in a stable environment, for example, the failure of the cooperation between the parts of the turbine and the mutual seizure, the increased wear of the nozzle needle, the decrease of the flow rate and the water outlet speed of the nozzle, and the decrease of the air pressure in the plateau environment lead to the change of the flow state of the nozzle. In view of the above problems, this paper puts forward the design scheme of impulse turbine test-bed, using the method of changing specific speed to determine the basic parameters of impulse turbine unit, so as to eliminate the influence of plateau environment on the normal operation of turbine, obtain the efficiency condition of model experiment under low ambient pressure, and improve the operation efficiency and reliability of turbine unit. © 2024 Institute of Physics Publishing. All rights reserved.

关键词： Nozzles

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Pressure-assisted Silver Sintering Structure Optimization for Power Modules 5

Pressure-assisted Silver Sintering Structure Optimization fo...

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5th International Conference on Optoelectronic Science and Materials, ICOSM 2023

作者： Zhang, Hao Xing, Yulong Gao, Lilan Liu, Zheng Tan, Yansong Lu, Guoquan Tianjin Key Laboratory for Advanced Mechatronic System Design and Intelligent Control Tianjin University of Technology Tianjin300384 China National Demonstration Center or Experimental Mechanical and Electrical Engineering Education Tianjin University of Technology Tianjin300384 China Tianjin Yixunyuan New Material Technology Co. Ltd. Tianjin300380 China School of Chemical Engineering Tianjin University Tianjin300350 China School of Materials Science and Engineering Virginia Polytechnic Institute and State University BlacksburgVA24061 United States

ISBN: (纸本)9781510674547

As mobile technology evolves from 5G to 6G, the demand for third-generation semiconductors such as SiC with higher power and frequency capabilities is increasing. Silicon Carbide power modules generate significant heat during operation, requiring large-area nano-silver sintering technology to improve module performance and reliability. However, in large-area sintering processes, low exhaust efficiency of solder paste by-products and uneven sintering pressure of the nano-silver paste result in poor sintering quality of the silver layer. This study aims to improve the sintering quality of interconnected silver layers by optimizing the sintering pressure distribution and adding rubber spacers to the sintering structure. ABAQUS was used to quantitatively analyze the effects of pressure methods and gasket material, diameter, and thickness on the stress distribution in the silver layer. Finally, based on the simulation results, an optimized sintering structure was proposed to unify the pressure and reduce the stress concentration in the silver layer, and verified experimentally by sintering tests. Compared with the traditional sintering structure, the application of a 2 mm thick fluoro rubber gasket with the same surface area as the silver layer in the optimized structure reduced the porosity to 2.15% and achieved a more dense sintered silver layer. © 2024 SPIE.

关键词： Finite element method

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Investigation of the Conjugate Heat Transfer and Flow Field for a Flat Plate with Combined Film and Impingement Cooling

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Journal of Thermal Science 2020年第4期29卷 955-971页

作者： FU Jinglun CAO Ying ZHANG Chao ZHU Junqiang Institute of Engineering Thermophysics Chinese Academy of SciencesBeijing 100190China University of Chinese Academy of Sciences Beijing 100049China Tianjin Key Laboratory for Advanced Mechatronic System Design and Intelligent Control Tianjin 300384China

Film cooling combined with internal impingement cooling is one of the most effective technologies to protect the gas turbine vanes and blades from the hot gas. In this study, conjugate heat transfer CFD study was undertaken for a flat plate with combined film cooling and impingement cooling. An experiment on conjugate heat transfer of a flat plate with combined film and impingement cooling was performed to validate the code. Then the effects of several parameters including Biot number, blowing ratio, film hole shape and impingement hole diameter on the overall cooling effectiveness were numerically studied. The results show that for a specific combined cooling scheme and a given blowing ratio, the coolant potential can be reasonably allocated to the internal and the external cooling to achieve the overall cooling effectiveness. As the blowing ratio increases, the overall cooling effectiveness trends to reach a maximum value. For different film hole geometrical, the maximum values of the overall cooling effectiveness at high blowing ratio approximate to the same value. At a given mass flow rate of coolant, the increase of the impingement hole diameter leads to the reduction of the overall cooling effectiveness.

关键词： conjugate heat transfer combined film and impingement cooling overall cooling effectiveness Biot number blowing ratio

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Tailoring structural, mechanical, and electronic properties of (Ti0.25Ta0.25Zr0.25Nb0.25-xLax)C high-entropy carbide ceramics via rare-earth La incorporation: A comprehensive first-principles study

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Ceramics International 2025年

作者： Wang, Zhipeng Yu, Zhaowen Zhang, Linkun Liu, Feng Huang, Lan Wang, Yan Tan, Liming Wang, Zi Ma, Li Tang, Pingying School of Materials Science and Engineering Dongguan University of Technology Guangdong Province Dongguan523808 China State Key Laboratory of Advanced Design and Manufacturing Technology for Vehicle Hunan University Hunan Province Changsha410082 China State Key Laboratory for Powder Metallurgy Central South University Hunan Province Changsha410083 China Guangxi Key Laboratory of Functional Information Materials and Intelligent Information Processing Nanning Normal University Guangxi Province Nanning530001 China

High-entropy carbide ceramics (HECCs) exhibit exceptional material properties, but their underlying physical mechanisms are underexplored. This study utilizes first-principles calculations to examine the influence of rare-earth La on the structural, mechanical, dislocation, and electronic properties of (Ti0.25Ta0.25Zr0.25Nb0.25-xLax)C (x = 0∼18.75 %) HECCs. key parameters, including formation enthalpy, lattice distortion, elastic constants, mechanical modulus, and density of states, are systematically analyzed as a function of La content. Results show that La preferentially substitutes Nb sites, forming thermodynamically stable rock-salt structures. Increased La content induces severe lattice distortion, reduces resistance to bulk, elastic, and shear deformation, and enhances ductility while decreasing brittleness. La incorporation also lowers Vickers hardness and yield strength, weakening crack resistance. Notably, (Ti0.25Ta0.25Zr0.25Nb0.0625La0.1875)C exhibits minimal energy factors and maximum dislocation width, facilitating dislocation nucleation and twinning. A rightward shift and reduced peak heights in valence band of total density of states curves with increasing La content indicate enhanced electron delocalization and reduced brittleness. These findings highlight the potential of La substitution to tailor structural, mechanical, and electronic properties in (Ti0.25Ta0.25Zr0.25Nb0.25-xLax)C HECCs, offering insights for designing ductile HECCs. © 2025 Elsevier Ltd and Techna Group S.r.l.

关键词： Vickers hardness

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A NOVEL STRATEGY TO FABRICATE LOW-MELTING-POINT ALLOY AND ITS COMPOSITE PARTS USING EXTRUSION ADDITIVE MANUFACTURING 50

A NOVEL STRATEGY TO FABRICATE LOW-MELTING-POINT ALLOY AND IT...

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50th International Conference on Computers and Industrial Engineering: Sustainable Digital Transformation, CIE 2023

作者： Jiang, Jingchao Jin, Liuchao Zhai, Xiaoya Zhang, Kang Chen, Jun Liao, Wei-Hsin Department of Mechanical and Automation Engineering The Chinese University of Hong Kong Shatin Hong Kong School of Mathematical Sciences University of Science and Technology of China China Zhejiang Provincial Key Laboratory of Advanced Chemical Engineering Manufacture Technology College of Chemical and Biological Engineering Zhejiang University Hangzhou China Institute of Zhejiang University- Quzhou Quzhou China Institute of Intelligent Design and Manufacturing The Chinese University of Hong Kong Shatin Hong Kong

ISBN: (纸本)9781713886952

Additive manufacturing (AM) has been continuously developed for more than 30 years. Different novel AM techniques, including electric-assisted, magnetic-assisted, robot-assisted, and UAV-assisted AM technologies have been created with various objectives. In this paper, we propose a new strategy for fabricating complex and/or multifunctional components of low-melting-point alloys (LMPA) using extrusion additive manufacturing (EAM). The main idea is using two nozzles in EAM, one for extruding polymers (e.g., PLA, PVA) while another for extruding LMPA. By using the proposed EAM system, there are three novel aspects of this study. First, the proposed system can achieve composite parts (polymer & LMPA) fabrication with improved mechanical properties. Second, the proposed system can be used to fabricate 3D products with LMPA wire inside acting as electrical wire. This achieves electrical wire inside a product without assembly, unlike conventional method which needs further step to insert the wires. Third, complex pure LMPA parts can be fabricated by dissolving the polymer after manufacturing, achieving complex LMPA parts fabrication using EAM (a low-cost AM technique, compared with traditional metal AM). © 2023 Computers and Industrial Engineering. All rights reserved.

关键词： 3D printing

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Investigating 3d Object Detection Using Stereo Camera and LiDAR Fusion with Bird'S-Eye View Representation

SSRN

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SSRN 2024年

作者： Zhu, Lin Nie, Xin He, Zhicheng Cheng, Aiguo Li, Eric Zhong, ShengZheng State Key Laboratory of Advanced Design and Manufacture Technology for Vehicle Hunan University Changsha410082 China Wuling New Energy Automobile Co. Ltd. Liuzhou545007 China School of Computing Engineering & Digital Technologies Teesside University Middlesbrough United Kingdom

Multi-sensor fusion for 3D object detection is a crucial development in autonomous vehicle technology. Current research primarily explores the combination of monocular cameras with LiDARs. However, there is a notable gap in the integration of stereo cameras with LiDARs. A significant drawback of the fusion between monocular cameras and LiDARs is its vulnerability to sensor failures, which can completely disable the system. This paper presents a novel end-to-end framework called SLBEVFusion, which leverages the effective combination of stereo cameras and LiDARs for 3D object detection. The framework utilizes the rich semantic and depth data from stereo images along with spatial data from LiDAR point clouds to improve detection accuracy. Moreover, it addresses sensor failures by isolating the data streams of each sensor and implementing straightforward feature fusion in Bird's Eye View (BEV) space. Comprehensive testing on the challenging KITTI dataset demonstrates that our approach significantly enhances performance in 3D object detection by merging stereo cameras with LiDARs. © 2024, The Authors. All rights reserved.

关键词： Semantics

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Hierarchical Clustering-Based State Grouping Reinforcement Learning for Switching Decision of Autonomous Vehicles

Hierarchical Clustering-Based State Grouping Reinforcement L...

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2023 IEEE International Conference on Unmanned Systems, ICUS 2023

作者： Ouyang, Wenjie Jiao, Yiwen Liu, Yang Li, Yang Hu, Manjiang Qin, Hongmao College of Mechanical and Vehicle Engineering Hunan University Changsha China College of Computer Science and Electronic Engineering Hunan University Changsha China College of Electrical Mechanical and Computer Science Delft University of Technology Delft Netherlands College of Mechanical and Vehicle Engineering Hunan University State Key Laboratory of Advanced Design and Manufacturing Technology for Vehicle Changsha China Institute of Hunan University Wuxi Intelligent Control Research Wuxi China

ISBN: (纸本)9798350316308

Reinforcement learning (RL) has gained wide attention, but its implementation in autonomous vehicles is still limited by insufficient sample efficiency and heavy training costs. The training efficiency of RL agents is influenced by the dimension of the state space, which can be partitioned to reduce the complexity of sampling and computation. This study proposes a hierarchical clustering-based state grouping reinforcement learning (HCSG-RL) method for the switching decision of autonomous vehicles. First, we partition the base state space into groups and generate a hierarchical tree of state space groups. Then, we train multiple sub-agents for each node in the hierarchical tree. Finally, we add these trained-well sub-model into master policy. This method allows us to fully explore all state spaces and improve the training efficiency of individual agents, which handles the 'long-tail' issue and the curse of dimensionality issue. We conduct experiments in a simulation environment and results show that the proposed method has 16-72% reward improvement compared to the tree model in different road length. © 2023 IEEE.

关键词： Reinforcement learning

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Research on Robust Measurement Method of Heart Rate Using Remote Photoplethysmography Based on Adversarial Learning Network with High and Low Frequency Features

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IEEE Transactions on Circuits and Systems for Video Technology 2025年第6期35卷 5208-5222页

作者： Zhai, Dezhao Chen, Wei Ding, Yinghao Yu, Ming Li, Qinwei Wu, Hang Tianjin University of Technology Tianjin Key Laboratory for Advanced Mechatronic System Design and Intelligent Control School of Mechanical Engineering Tianjin300384 China National Demonstration Center for Experimental Mechanical and Electrical Engineering Education Tianjin University of Technology China People's Liberation Army Systems Engineering Institute Academy of Military Sciences Tianjin300161 China Civil Aviation University of China Tianjin Key Laboratory for Advanced Signal Processing Tianjin300300 China Nankai University School of Artificial Intelligence Tianjin300381 China

Remote Photoplethysmography (rPPG) is a non-contact method for measuring heart rate (HR) through facial video, breaking the constraints of contact measurements and offering broad application prospects. However, in real monitoring scenarios, the distance of subjects and facial illumination often vary. This leads to degradation of rPPG signals due to changes in facial resolution and light intensity. This paper presents the High and Low Frequency Feature Adversarial Learning Network (HLFF-AL), which utilizes feature space interpolation and composite feature capture to perform multi-band global and local signal extraction. By adopting an adversarial learning strategy, it enhances the capability to capture semantic information of rPPG under varying resolutions and lighting, bridging the differences in rPPG signal generation due to resolution changes. While maintaining accuracy in HR measuring, the robustness of the network is improved to achieve robust measurement of HR via rPPG. Even under high-resolution conditions, the Mean Absolute Error (MAE) for the three public datasets - unchanging lighting (COHFACE, UBFC-rPPG) and varying lighting (BUAA-MIHR) - reached 1.10 bpm, 1.64 bpm, and 4.41 bpm, respectively, with a mere 0.29 bpm difference in MAE between high and low resolutions on the BUAA-MIHR dataset. This demonstrates that HLFF-AL can predict more robust rPPG signals in various resolutions and lighting scenarios, achieving competitive results compared to state-of-the-art methods. © 1991-2012 IEEE.

关键词： Heart

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Precision loss of ball screw mechanism under sliding-rolling mixed motion behavior

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Journal of Central South University 2021年第5期28卷 1357-1376页

作者： QI Bao-bao CHENG Qiang LI Shun-lei LIU Zhi-feng YANG Cong-bin Institute of Advanced Manufacturing and Intelligent Technology Beijing University of TechnologyBeijing 100124China Beijing Key Laboratory of Advanced Manufacturing Technology Beijing University of TechnologyBeijing 100124China Mechanical Industry Key Laboratory of Heavy Machine Tool Digital Design and Testing Beijing University of TechnologyBeijing 100124China

The sliding-rolling mixed motion behavior degrades the ball screw’s precision at different *** on the sliding-rolling mixed motion between ball and screw/nut raceway,the ball screw’s precision loss considering different given axial loading and rotational speed working conditions was *** creep and lubrication relate to sliding and rolling motion wear,the creep and lubrication characteristics are analyzed under different working ***,the precision loss was calculated considering the sole influence of sliding behavior between ball and screw and compared with the results from other current ***,research on precision loss owing to the sliding-rolling mixed motion behavior was realized under given working conditions,and suitable wear tests were carried *** analytical results of precision loss are in good agreement with the experimental test conclusions,which is conducive to better predicting the law of precision loss in stable wear period.

关键词： ball screw mechanism precision loss sliding-rolling mixed motion creep lubrication

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Numerical and Experimental Investigation on Heat Transfer Characteristics, Grain Refinement Mechanism and Mechanical Properties in Synchronous Tailing Heat Sink Assisted Laser Welding

SSRN

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SSRN 2022年

作者： Liu, Guo Jin, Xiangzhong Zhang, Junyi Hao, Zhongjia Li, Junhao Chen, Huiyang State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body Hunan University Hunan Changsha410082 China Hunan Provincial Key Laboratory of Intelligent Laser Manufacturing Hunan University Hunan Changsha410082 China

In this paper, a synchronous heat sink assisted laser welding method is first used to weld SUS301L stainless steel with 0.6mm thickness through an independently designed experimental platform, and the dynamic characteristics of molten pool in heat sink + laser welding (Heat sink + LW) together with those in the process of laser welding (LW) are observed by a high-speed camera. Different image processing steps are applied to extract the longitudinal characteristic length of weld pool and the dynamic characteristics of plume on the upper surface of keyhole. Then, the effect of heat sink parameters on the characteristic length of molten pool is studied. In addition, based on the experimental observation, a simulation model of Heat sink + LW is established. The simulation results illustrate that heat sink will form a rapid cooling zone at the tail of weld pool, which leads to the disappearance of weld comet characteristics, and improves the temperature field at the tail of weld pool. With the increase of heat sink strength, the weld temperature gradient decreases. When the heat sink is 200ml and the distance is 5mm, the temperature gradient decreases by 305 [[EQUATION]] . Meanwhile, the relationship between grain refinement and cooling rate shows that heat sink also helps to refine the microstructure of the fusion zone and promote the transformation from columnar dendrite to equiaxed dendrite. Furthermore, the heat sink increases the constitutional supercooling (CS) during solidification by reducing the temperature gradient of the melt pool, and subsequently creates an environment conducive to particle nucleation, growth and survival. This new understanding provides an opportunity to make better use of heat sink to control grain structure, and in turn to improve the mechanical properties of the welds, which is also verified by the test results of the properties of the welds. The measurement resuls show that the heat sink enhances the micro hardness and improves the tens

关键词： High speed cameras

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