Some notes on numerical simulation and error analyses of the attached turbulent cavitating flow by LES

In this letter, the attached turbulent cavitating flow around the Clark-Y hydrofoil is investigated by the numerical simulation with special emphasis on error analysis of large eddy simulation(LES) for the unsteady cavitation simulation. The numerical results indicate that the present simulation can capture the periodic cavity shedding behavior and show a fairly good agreement with the available experimental data. Further analysis demonstrates that the cavitation has a great influence on LES numerical error and modeling error. The modeling error and numerical error are almost on the same order of magnitude, while the modeling error often shows a little bit larger magnitude than numerical error. The numerical error and modeling error sometimes can partially offset each other if they have the opposite sign. Besides, our results show that cavitation can extend the magnitudes and oscillation levels of numerical error and modeling error.     

Numerical Simulations of Tungsten Alloy Rods Penetration into Alumina Ceramic/Armor Steel Composite Target

The Johnson-Holmquist constitutive ceramic model is re-implemented into the LS-DYNA3D program to simulate the penetration of long rod projectile into ceramic/armor steel composite targets. The damage evolution, fracture propagation, and spall damage in the ceramic/armor targets is represented during the simulation procedure and the accuracy of the penetration depth comparing between the simulating and experimental results is reliable with an error less than 8%. The relationship between the mass efficiency factor, differential factor and ceramic tiles thickness is given out for the penetration results with/without a cover plate.     

Numerical simulation of parallel hole cut blasting with uncharged holes

The cavity formation and propagation process of stress wave from parallel hole cut blasting was simulated with ANSYS/LS-DYNA 3D nonlinear dynamic finite element software. The distribution of element plastic strain, node velocity, node time-acceleration history and the blasting cartridge volume ratio during the process were analyzed. It was found that the detonation of charged holes would cause the interaction of stress wave with the wall of uncharged holes. Initial rock cracking and displacement to neighboring uncharged holes become the main mechanism of cavity formation in early stage.2008 University of Science and Technology Beijing. All rights reserved.     

数字模拟——一种军用车辆防护设计的工具

本专题分为以下四部分:背景、材料、技术以及防护车辆,分别对世界装甲车辆防护发展历史和面临威胁的变化,车辆肪护陶瓷材料与透明装甲、"硬杀伤"主动防护系统以及车辆信号管理和数字模拟技术在车辆防护中的应用、防护在车辆设计概念中的变化等方面进行了介绍。     

Effects of Loading Paths on Hydrodynamic Deep Drawing with Independent Radial Hydraulic Pressure of Aluminum Alloy Based on Numerical Simulation

In order to meet the forming demands for low plasticity materials and large height-diameter ratio parts, a new process of hydrodynamic deep drawing （HDD） with independent radial hydraulic pressure is proposed. To investigate the effects of loading paths on the HDD with independent radial hydraulic pressure, the forming process of 5A06 aluminum alloy cylindrical cup with a hemispherical bottom was studied by numerical simulation. By employing the dynamic explicit analytical software ETA/Dynaform based on LS-DYNA3D, the effects of loading paths on the sheet-thickness distribution and surface quality were analyzed. The corresponding relations of the radial hydraulic pressure loading paths and the part＇s strain status on the forming limit diagram （FLD） were also discussed. The results indicated that a sound match between liquid chamber pressure and independent radial hydraulic pressure could restrain the serious thinning at the hemisphere bottom and that through adjusting radial hydraulic pressure could reduce the radial tensile strain and change the strain paths. Therefore, the drawing limit of the aluminum cylindrical cup with a hemispherical bottom could be increased significantly.     

小波变换在数字埋入云纹技术中的应用

埋入云纹技术可以用于三维力学问题的全场测量,对接触问题和物体内部力学场的测量具有很大的优势。将小波变换引入到数字埋入云纹技术中,可以方便快捷地消除条纹图中的噪声,模拟出清晰光滑的条纹图。介绍了应用小波变换生成云纹条纹的原理,并且进行了实验测试,结果表明该方法是可行的。     

Numerical simulation of flow instabilities in high speed multistage compressors

INTRODUCTIONTheusefuloperatingrangeofturbomachinerycompressionsystemsislimitedbytheonsetoffluiddynamicinstabilities.Bothformsofinstabilities,rotatingstallandsurge,willdegradecompressionsystemperformanceanddurabilityll].naditionally,thisundesirablebeh...     

Experimental and theoretical analysis of fiber Bragg gratings under Transverse Force to a Small Grating Section

Fiber Bragg grating (FBG) technology has been de-veloped rapidlyinrecent years ,and has beenextensivelystudied in today′s optical communication and sensingsystems . Because of the linearity between the Braggwavelength and outside environmental parameters ,theaxial strain response of FBGhas been fullyinvestigatedand usedin measurement for strain,pressure,andther-mal expansion coefficient etc . By contrast ,fewstudieshave been carried out onthe transverseload response ofFBG[1-3].Gafsi and …     

风力发电传动系统的建模与数字模拟研究

通过分析风力发电机组中传动系统的特性,针对不同类型的风力发电机组提出了灵活的传动系统建模方法(包括4种模型:刚性轴感应发电机模型、柔性轴感应发电机模型、刚性轴变速发电机模型和柔性轴变速发电机模型),并采用数字模拟方法在软件中加以实现,与商业风力机计算分析软件GH-Bladed中的风力发电系统运行结果进行对比,验证了模型的准确性,运行结果表明,该文提出的建模方法能够满足不同传动系统的惯性要求,并且能方便的在软件中根据实际风力机参数进行模型选择和参数设置,为实验室模拟风力发电系统提供了理论依据和模拟方法。     

ESOTERIC K-03数字音源设备

ESOTERIC新推出了K-01,这款机型是厂家的先进级数字模拟转换器及Super Audio CD／CD一体式播放机系列中的旗舰型号,集中了Esoteric的顶尖技术,