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Numerical study on the effective thermal conductivity and thermal tortuosity of porous media with different morphologies

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Science China(Technological Sciences) 2024年第6期67卷 1685-1694页

作者： DU Shen LI Dong LI Meng-Jie HE Ya-Ling key laboratory of Thermo-fluid Science and engineering of Ministry of Education School of Energy and Power EngineeringXi’an Jiaotong UniversityXi’an710049China

Effective thermal conductivity and thermal tortuosity are crucial parameters for evaluating the effectiveness of heat conduction within porous *** direct pore-scale numerical simulation method is applied to investigate the heat conduction processes inside porous structures with different *** thermal conduction performances of idealized porous structures are directly compared with real foams across a wide range of *** foam structures are reconstructed using X-ray computed tomography and image processing techniques,while Kelvin and Weaire-Phelan structures are generated through periodic unit cell *** detailed temperature fields inside the porous structures are determined by solving the heat conduction equation at the pore *** results present that the equivalent thermal conductivity of Kelvin and Weaire-Phelan structures is similar to and greater than that of the real foam structure with the same strut *** thermal tortuosity of real foam structure is relatively larger and the heat conduction path becomes straighter by adopting the anisotropic *** thermal tortuosity of the fluid channels for Kelvin,Weaire-Phelan,and real foam structures is close to *** thermal conductivity of porous structures with heat transfer fluid increases as the thermal conductivity ratio of fluid to solid becomes larger.A small porosity of porous media leads to a larger equivalent thermal conductivity due to the dominant contribution of porous skeleton in the heat conduction *** derived from parallel and series models,as well as the Maxwell-Eucken models,provide decent predictions of effective thermal conductivity,with an average error of less than 8%in the entire range of thermal conductivity ratio.

关键词： volumetric solar receiver porous morphology direct pore-scale simulation equivalent thermal conductivity thermal tortuosity empirical correlation

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Diameter-dependent ultra-high thermoelectric performance of ZnO nanowires

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Chinese Physics B 2024年第4期33卷 86-94页

作者：聂祎楠唐桂华李一斐张敏赵欣 MOE key laboratory of Thermo-fluid Science and engineering School of Energy and Power EngineeringXi’an Jiaotong UniversityXi’an 710049China

Zinc oxide(ZnO)shows great potential in electronics,but its large intrinsic thermal conductivity limits its thermoelectric *** this work,we explore the significant carrier transport capacity and diameter-dependent thermoelectric characteristics of wurtzite-ZnO(0001)nanowires based on first-principles and molecular dynamics *** the synergistic effect of band degeneracy and weak phonon-electron scattering,P-type(ZnO)_(73) nanowires achieve an ultrahigh power factor above 1500μW·cm^(-1)·K^(-2)over a wide temperature *** lattice thermal conductivity and carrier transport properties of ZnO nanowires exhibit a strong diameter size *** the ZnO nanowire diameter exceeds 12.72A,the carrier transport properties increase significantly,while the thermal conductivity shows a slight increase with the diameter size,resulting in a ZT value of up to 6.4 at 700 K for P-type(ZnO)_(73).For the first time,the size effect is also illustrated by introducing two geometrical configurations of the ZnO *** work theoretically depicts the size optimization strategy for the thermoelectric conversion of ZnO nanowires.

关键词： ZnO nanowire size effect thermoelectric performance deformation potential theory

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Biomimetic Lightweight Design of Legged Robot Hydraulic Drive Unit Shell Inspired by Geometric Shape of Fish Bone Rib Structure

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Journal of Bionic engineering 2024年第3期21卷 1238-1252页

作者： Zhipeng Huang Xinjie Li Xikang Guan Xueqing Sun Chenxu Wang Yuepeng Xu Bin Yu Xiangdong Kong School of Mechanical engineering Yanshan UniversityQinhuangdao066004China School of Arts and Design Yanshan UniversityQinhuangdao066004China Hebei Provincial key laboratory of Heavy machinery fluid power Transmission and Control Qinhuangdao066004China

The lightweight design of hydraulic quadruped robots,especially the lightweight design of the leg joint Hydraulic Drive Unit(HDU),can improve the robot's response speed,motion speed,endurance,and load ***,the lightweight design of HDU is a huge challenge due to the need for structural *** paper is inspired by the geometric shape of fish bones and biomimetic reinforcing ribs on the surface of the HDU shell are designed to increase its strength and reduce its ***,a HDU shell with biomimetic fish bone reinforcing ribs structure is ***,the MATLAB toolbox and ANSYS finite element analysis module are used to optimize the parameters of the biomimetic reinforcing ribs structure and the overall layout of the ***,the HDU shell is manufactured using additive manufacturing technology,and a performance testing platform is built to conduct dynamic and static performance tests on the designed *** experimental results show that the HDU with biomimetic fish bone reinforcing ribs has excellent dynamic performance and better static performance than the prototype model,and the weight of the shell is reduced by 20%compared to the prototype *** work has broad application prospects in the lightweight and high-strength design of closed-pressure vessel components.

关键词： Hydraulic drive unit Lightweight design of shell Biomimetic fish bone structure design Dynamic and static performance testing

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Observer-Based Adaptive Robust Precision Motion Control of a Multi-Joint Hydraulic Manipulator

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IEEE/CAA Journal of Automatica Sinica 2024年第5期11卷 1213-1226页

作者： Zheng Chen Shizhao Zhou Chong Shen Litong Lyu Junhui Zhang Bin Yao State key laboratory of fluid power and Mechatronic Systems Zhejiang UniversityHangzhou 310027 Ocean College Zhejiang UniversityZhoushan 316021China School of Mechanical engineering Shijiazhuang Tiedao UniversityShijiazhuang 050000 State key laboratory of fluid power and Mechatronic Systems Zhejiang UniversityHangzhou 310027China School of Mechanical engineering Purdue UniversityWest LafayetteIN 47907 USA

Hydraulic manipulators are usually applied in heavy-load and harsh operation ***,when faced with a complex operation,the traditional proportional-integral-derivative(PID)control may not meet requirements for high control ***-based full-state-feedback control is an effective alternative,but the states of a hydraulic manipulator are not always available and reliable in practical applications,particularly the joint angular velocity *** that it is not suitable to obtain the velocity signal directly from differentiating of position measurement,the low-pass filtering is commonly used,but it will definitely restrict the closed-loop bandwidth of the whole *** avoid this problem and realize better control performance,this paper proposes a novel observerbased adaptive robust controller(obARC)for a multi-joint hydraulic manipulator subjected to both parametric uncertainties and the lack of accurate velocity ***,a nonlinear adaptive observer is first designed to handle the lack of velocity measurement with the consideration of parametric ***,the adaptive robust control is developed to compensate for the dynamic uncertainties,and the close-loop system robust stability is theoretically proved under the observation and control ***,comparative experiments are carried out to show that the designed controller can achieve a performance improvement over the traditional methods,specifically yielding better control accuracy owing to the closed-loop bandwidth breakthrough,which is limited by low-pass filtering in fullstate-feedback control.

关键词： handle Observer filtering

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Numerical and experimental study of the effects of wind turbine operation on sand-dust transport characteristics

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Science China(Physics,Mechanics & Astronomy) 2024年第4期67卷 97-113页

作者： Gaosheng Ma Hong Han Ye Li Deshun Li Yan Wang Ning Fu Quan Zheng Rennian Li School of Energy and power engineering Lanzhou University of TechnologyLanzhou 730050China Gansu Provincial Technology Center for Wind Turbines Lanzhou 730050China key laboratory of fluid machinery and Systems Lanzhou 730050China Multiple Function Towing Tank laboratory State Key Laboratory of Ocean EngineeringSchool of Naval ArchitectureOcean and Civil EngineeringShanghai Jiao Tong UniversityShanghai 200240China

Given factors such as reduced land availability for onshore wind farms,wind resource enrichment levels,and costs,there is a growing trend of establishing wind farms in deserts,the Gobi,and other arid ***,the relationship between sanddust weather environments and wind turbine operations has garnered significant *** investigate the impact of wind turbine wakes on sand-dust transportation,this study employs large eddy simulation to model flow fields,coupled with an actuator line model for simulating rotating blades and a multiphase particle in cell model for simulating sand *** research focuses on a horizontal axis wind turbine model and examines the motion and spatiotemporal distribution characteristics of four typical sizes of sand particles in the turbine *** findings reveal that sand particles of varying sizes exhibit a spiral settling pattern after traversing the rotating plane of wind turbine blades,influenced by blade shedding vortex and *** particles tend to cluster in the peripheries of the vortex cores of low vorticity in the wind turbine *** rotation of wind turbines generates a wake vortex structure that causes a significant clustering of sand particles at the tip *** the wake distance increases,the particles that cluster at the turbine's tip gradually spread outward to approximately twice the rotor diameter and then begin to mix with the incoming flow *** turbines have a noticeable impact on sand-dust transportation,hindering their movement to a significant *** average sand-blocking rate exhibits a trend of initially increasing and then decreasing as the wake distance *** its peak,the sand-blocking rate reaches an impressive 67.55%.The presence of wind turbines induces the advanced settling of sand particles,resulting in a“triangular”distribution of the deposition within the ground projection area of the wake.

关键词： wind turbine particle transportation actuator line model dry deposition particle clustering

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