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Fatigue crack growth rate test using a frequency sweep method

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2008年第3期9卷 346-350页

作者： Xun ZHOU xiao-li yu College of Mechanical and Energy Engineering Zhejiang University Hangzhou 31002 7 China

Fatigue crack propagation characteristics of a diesel engine crankshaft are studied by measuring the fatigue crack growth rate using a frequency sweep method on a resonant fatigue test rig. Based on the phenomenon that the system frequency will change when the crack becomes large, this method can be directly applied to a complex component or structure. Finite element analyses （FEAs） are performed to calibrate the relation between the frequency change and the crack size, and to obtain the natural frequency of the test rig and the stress intensity factor （SIF） of growing cracks. The crack growth rate i.e. da/dN-AK of each crack size is obtained by combining the testing-time monitored data and FEA results. The results show that the crack growth rate of engine crankshaft, which is a component with complex geometry and special surface treatment, is quite different from that of a pure material. There is an apparent turning point in the Paris＇s crack partition. The cause of the fatigue crack growth is also discussed.

关键词： Crack growth rate Residual stress Frequency sweep method Engine crankshaft Reliability

Numerical simulation and optimization design of the EGR cooler in vehicle

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2008年第9期9卷 1270-1276页

作者： yu-qi HUANG xiao-li yu Guo-dong LU Power Machinery and Vehicular Engineering Institute Zhejiang University Hangzhou 310027 China Zhejiang Yinlun Machinery Co. Ltd. Tiantai 317200 China

The EGR (exhaust gas recirculation) technique can greatly reduce the NOx emission of diesel engines, especially when an EGR cooler is employed. Numerical simulations are applied to study the flow field and temperature distributions inside the EGR cooler. Three different models of EGR cooler are investigated, among which model A is a traditional one, and models B and C are improved by adding a helical baffle in the cooling area. In models B and C the entry directions of cooling water are different, which mostly influences the flow resistance. The results show that the improved structures not only lengthen the flow path of the cooling water, but also enhance the heat exchange rate between the cool and hot media. In conclusion we suggest that the improved structures are more powerful than the traditional one.

关键词： Exhaust gas recirculation (EGR) cooler Computational fluid dynamics (CFD) Shell-and-tube heat exchanger Helical baffle

Simulation, experimentation, and collaborative analysis of adjacent heat exchange modules in a vehicular cooling system

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2013年第6期14卷 417-426页

作者： yu-qi HUANG Rui HUANG xiao-li yu Feng LV Power Machinery and Vehicular Engineering Institute Zhejiang University Department of Mechanical and Aerospace Engineering Monash University-Clayton

A cooling system consisting of several heat exchange modules is a necessary part of an automobile, and its performance has a direct effect on a vehicle's energy consumption. Heat exchangers, such as a charged air cooler (CAC), radiator, oil cooler, or condenser have different structures and can be arranged in various orders, and each combination may produce different effects because of interactions among them. In this study, we aimed to explore the principles governing interactions among adjacent heat exchangers in a cooling system, using numerical simulation and experimental technology. 3D models with different combinations were developed, compared, and analyzed comprehensively. A wind tunnel test platform was constructed to validate the computational results. We found that the heat dissipation of the modules was affected slightly by their relative position (the rules basically comply with the field synergy principle), but was independent of the modules' spacing within a certain distance range. The heat dissipation of one module could be effectively improved by restructuring, but with a penalty of higher resistance. However, the negative effect on the downstream module was much less than expected. The results indicated that the intensity of heat transfer depends not only on the average temperature difference between cold and hot mediums, but also on the temperature distribution.

关键词： Collaborative analysis Heat exchangers Field synergy principle Computational fluid dynamics (CFD) Wind tunnel

Simulation and experimental study of electro-pneumatic valve used in air-powered engine

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2009年第3期10卷 377-383页

作者： Ping-lu CHEN xiao-li yu lin liU College of Mechanical and Energy Engineering Zhejiang University Hangzhou 310027 China College of Engineering Jiangxi Agricultural University Nanchang 330045 China

To evaluate the performance of newly designed electro-pneumatic valves (EPVs) for the air-powered engine (APE) and study laws of parameters affecting them, a simulation model was established based on the thermodynamics and mechanics theories. Experiments were set up to determine the instantaneous effective orifice area of solenoid valve by the constant volume discharge method. The simulation model was also validated by comparing the measured displacement curve with the simulated displacement curve of the valve in the pressure of 0.16 and 0.49 MPa. Simulation and experimental results showed that maximum working frequency of the designed EPV could reach 30 Hz corresponding to 2000 r/min of engine rotating speed. Based on simulation results, impacts of temperature and pressure of control air on delay time, full opening/closing time and seating velocity of EPV were analyzed. The simulation model could also act as EPV simulation prototype in designing the air exchange control system of APE.

关键词： Pneumatic Variable valve actuation (VVA) Air-powered engine (APE) Simulation

Entrance-channel dynamics in the reaction 40Ca+208Pb

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Science China(Physics,Mechanics & Astronomy) 2019年第12期62卷 34-40页

作者： xiao yu li Zhen Ji Wu Lu Guo School of Nuclear Science and Technology University of Chinese Academy of SciencesBeijing J00049China Institute of Theoretical Physics Chinese Academy of SciencesBeijing 100190China

The entrance-channel dynamics including capture, fusion, and quasifission processes for the reaction ^40Ca+^208Pb is investigated in the fully microscopic time-dependent Hartree-Fock(TDHF) theory. The calculations are performed in three-dimensional Cartesian coordinate without any symmetry restrictions, in which the full Skyrme energy functional SLy4d and SLy5 are *** study the energy dependence of capture cross sections, and find that the experimental data are well reproduced by the TDHF calculations. Both fusion and quasifission events are observed in the reaction ^40Ca+^208Pb. The contact time, mass and charge of quasifission fragments show a wide distribution in SLy4d compared with SLy5, implying that more nucleons are transferred in the SLy4d calculations. We find that the total kinetic energy of quasifission fragments in the TDHF calculations is distributed around Viola systematics, indicating that most of the relative kinetic energy is dissipated in quasifission dynamics.

关键词： capture fusion quasifission TDHF

Flow pattern analysis of linear gradient flow distribution

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Applied Mathematics and Mechanics(English Edition) 2015年第1期36卷 81-106页

作者： Da-ming li xiao-yu li Yan-qing li R.J.FARAHANI School of Civil Engineering & Key Laboratory of Harbor & Ocean Engineering Ministry of Education Tianjin University Civil and Environmental Engineering Johns Hopkins University Civil Engineering The University of Adelaide

This paper uses the Oseen transformation to solve the differential equations governing motion of the vertical linear gradient flow distribution close to a wall surface. The Navier-Stokes equations are used to consider the inertia term along the flow direction. A novel contour integral method is used to solve the complex Airy function. The boundary conditions of linear gradient flow distribution for finite problems are determined. The vorticity function, the pressure function, and the turbulent velocity profiles are provided, and the stability of particle trajectories is studied. An Lx-function form of the third derivative circulation is used to to simplify the solution. Theoretical results are compared with the experimental measurements with satisfactory agreement.

关键词： linear gradient distribution flow contour integral stability analysis Airyfunction Oseen transformation

INVERSE OPAliNE STRUCTURE TITANIA PHOTONIC CRYSTALS BY FUNCTIONALLY MODIFIED COLLOIDAL CRYSTALS TEMPLATING

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Chinese Journal of Polymer Science 2007年第2期25卷 217-220页

作者： Hong-yu li Zhi-qiang Chen Hai-qiao Wang Bo Meng xiao-yu li Department of Chemistry Anyang Teachers College Anyang Henan 455000 China The Key Laboratory of Nanomaterials of Ministry of Education College of Materials Science and Engineering Beijing University of Chemical Technology Beijing 100029 China

Ordered macroporous titania photonic crystals （PCs） and photonic balls were fabricated by functional modified polymer colloidal crystals. The TiO2 PCs and balls formed through this method exhibit no cracks and lacun... 详细信息

关键词： Photonic crystals Photonic balls Ordered macroporous titania Polymer colloidal crystals.

Poly(methyl methacrylate)-induced Microstructure and Hydrolysis Behavior Changes of Poly(L-lactic acid)/Carbon Nanotubes Composites

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Chinese Journal of Polymer Science 2020年第2期38卷 195-204,I0008页

作者： Xu yu Xin-Zheng Jin Ting Huang Nan Zhang xiao-yu li Yong Wang School of Materials Science&Engineering Key Laboratory of Advanced Technologies of Materials(Ministry of Education)Southwest Jiaotong UniversityChengdu 610031China College of Polymer Science and Engineering Sichuan UniversityChengdu 610065China

Poly(L-lactic acid)(PLLA)-based composites exhibit wide applications in many ***,most of hydrophilic fillers usually accelerate the hydrolytic degradation of PLLA,which is unfavorable for the prolonging of the service life of the *** this work,a small quantity of poly(methyl methacrylate)(PMMA)(2 wt%-10 wt%)was incorporated into the PLLA/carbon nanotubes(CNTs)*** effects of PMMA content on the dispersion of CNTs as well as the microstructure and hydrolytic degradation behaviors of the composites were systematically *** results showed that PMMA promoted the dispersion of CNTs in the *** PLLA was obtained in all the *** enhanced hydrolytic degradation resistance was achieved by incorporating PMMA,especially at relatively high PMMA *** 10 wt%PMMA led to a dramatic decrease in the hydrolytic degradation rate from 0.19%/h of the PLLA/CNT composite sample to 0.059%/h of the PLLA/PMMA-10/CNT composite *** microstructure evolution of the composites was also detected,and the results showed that no crystallization occurred in the PLLA *** results based on the interfacial tension calculation showed that the enhanced hydrolytic degradation resistance of the PLLA matrix was mainly attributed to the relatively strong interfacial affinity between PMMA and CNTs,which prevented the occurrence of hydrolytic degradation at the interface between PLLA and *** work provides an alternative method for tailoring the hydrolytic degradation ability of the PLLA-based composites.

关键词： Poly(L-lactic acid)composites Poly(methyl methacrylate) Microstructure Hydrolytic degradation

Possible shape coexistence in Ne isotopes and the impurity effect of Λ hyperon

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Science China(Physics,Mechanics & Astronomy) 2021年第8期64卷 29-40页

作者： Chen Chen Qian-Kun Sun yu-xiao li Ting-Ting Sun School of Physics and Microelectronics Zhengzhou UniversityZhengzhou 450001China

The possible shape coexistence in even-even Ne isotopes and the impurity effects of the sΛ and pΛ hyperons are explored employing the multidimensionally constrained relativistic-mean-field(MDC-RMF) model with the PK1 parameter set for the N N interaction and PK1-Y1 for the ΛN interaction. The quadrupole deformation potential energy surfaces(PESs), nuclear deformations, nuclear radii, binding energies, and density distributions of the hypernuclei and core nuclei are examined. The possible shape coexistence in ^(24,26,28)Ne is predicted with small energy differences of 140, 336, and 128 keV, respectively, between the two local energy minima. Different impurity effects of the sΛand pΛ hyperons are revealed. The sΛ hyperon exhibits clear shrinkage effects, which reduce the nuclear size and facilitate a spherical nuclear shape. The prolate pΛhyperon on the 1/2^(-)[110] orbital renders the nuclear shape more prolate, while the oblate pΛ hyperon on the 3/2^(-)[101] or 1/2^(-)[101] orbital renders the nuclei more oblate. Moreover, the Λ hyperon can increase the probabilities of the shape coexistence by reducing the energy differences between the two local energy minima, although the shape coexistence may disappear owing to the vanishment of one energy minimum on the flat energy surface.

关键词： single-Λhypernuclei shape coexistence impurity effects Ne isotope