Finite element simulation of blood flow in a flexible carotid artery bifurcation

Numerical simulations for the blood flow are carried out to investigate the effect of the flexible artery wall on the flow field and to determine the wall shear stresses in the carotid artery wall. To solve the equation of motion for the structure in typical fluid-structure interaction (FSI) problems, it is necessary to calculate the fluid force on the surface of the structure explicitly. To avoid complexity due to the necessity of additional mechanical constraints, we use the combined formulation including both the fluid and structure equations of motion into a single coupled variational equation. The Navier-Stokes equations for fluid flow are solved using a P2P1 Galerkin finite element method (FEM) and mesh movement is achieved using arbitrary Lagrangian-Eulerian (ALE) formulation. The Newmark method is employed to solve the dynamic equilibrium equations for linear elastic solid mechanics. The time-dependent, three-dimensional, incompressible flows of Newtonian fluids constrained in the flexible wall are analyzed. The study shows strongly skewed axial velocity and flow separation in the internal carotid artery (ICA). Flow separation results in locally low wall shear stress. Further, strong secondary motion in the ICA is observed.     

热障涂层系统中TGO应力生成的数值模拟

采用有限元分析软件ABAQUS对热障涂层系统中TGO的应力生成进行了数值模拟.基于实验测得的TGO生成厚度和材料性能参数,研究了热氧化循环载荷中TGO应力产生的机理和影响因素,验证了材料属性转化方法模拟TGO生成过程的有效性.结果表明,热膨胀系数差异和TGO高温生长是导致TGO应力产生的主要原因,TGO厚度的增加导致了外层TGO中拉伸应力的产生,随着厚度的增加该应力逐渐增大.当TGO达到某一厚度时,该应力保持恒定.     

10 kV配电线路抵御强台风能力的数值研究

针对沿海地区配电线路抵御强台风能力不足的问题,对10k V配电线路抗台风的能力进行了数值研究,讨论了地基土与防风拉线对电杆防风能力的影响。采用ABAQUS/CAE建立了10k V单回路配电线路一个标准段的有限元模型,模型中包括导线、混凝土电杆、横担、拉线和地基土等;利用等效惯性加速度模拟线路所受风荷载,然后对模型在不同等级风速下进行了变形分析,通过数值解与理论解的对比,验证了数值模型的正确性。研究了3类线路的弯矩、扰度和应力等问题的变化规律,包括:考虑地基土作用、考虑拉线加固处理以及两者都没考虑的3类模型。研究结果表明,土体变形对电杆的扰度变化有叠加效应,安装拉线加固后电杆最大弯矩明显降低。     

热障涂层在多次热循环作用下残余应力的模拟

采用热弹塑性有限元方法,对热障涂层多次热循环降温过程中由于热梯度和材料参数不匹配而产生的残余应力进行了数值模拟,分析了平面和曲面的界面形貌对界面残余应力的影响.结果表明,在相同材料参数情况下,陶瓷层与粘接层的界面形状对残余应力及结构稳定状态有显著的影响,凹凸不平的界面将会使界面残余应力发生突变,不利于增强界面结合强度和涂层结构的热稳定性.该结果对分析涂层寿命及失效机制有指导意义.     

剪切力对动脉血管平滑肌细胞增殖分化的影响

目的：探讨剪切力作用下人脐动脉血管平滑肌细胞的增殖分化的变化。方法：利用改进的灌流及流动培养装置,通过蠕动泵提供稳定的剪切力,同时提供静态培养所需的其它条件,建立体外人脐动脉血管平滑肌流动培养模型。分别对体外培养的人脐动脉血管平滑肌细胞加载3,4,5,8,10dyn／cm^2的定长流剪切力24h,同时以静态培养的细胞为对照组。相差倒置显微镜观察玻片上细胞的数量并作细胞计数,α—actin免疫组化染色．结果：细胞记数显示,同对照组相比,七刀应力各组的增殖能力都有所下降,5dyn／cm^2切应力作用下,细胞增殖缓慢最为明显．α—actin免疫组化染色提示切应力各组的分化程度较对照组高。结论：初步研究表明,剪切力对人脐动脉血管平滑肌细胞的增殖有一定抑制作用,并且可能促进了细胞的分化。     

Numerical simulation of concrete pumping process and investigation of wear mechanism of the piping wall

A numerical simulation has been conducted to study the solid-fluid multi-phase flow problem in concrete pumping process. The kinematics and trajectory of the discrete particles as well as the particle-particle interaction were predicted by DEM while the motion of the continuous fluid phase was evaluated by a Navier-Stokes solver, and a pressure gradient force model was adopted to calculate the solid-fluid interaction force. A case of pneumatic conveying was utilized to demonstrate the capability of the coupling model. The concrete pumping process was then simulated, where several flow features were observed such as roping, particle segregation and particle concentration. The frequency of the particles impacting on the bended pipe was monitored, a new time average collision intensity model based on impact force has been proposed to investigate the wear mechanism of the elbow. The location of maximum erosive wear damage in the elbow was predicted. Statistical results were in good agreement with that observed in actual pumping process. It is found that the present multi-phase coupling model can predict the wear behavior of the bended pipe accurately, and consequently provide an effective guidance for the design of concrete pumping pipe.     

Numerical simulation of a pool fire

Thermo-fluid mechanical characteristics as well as flame structure of a pool fire were numerically simulated in this study. The small scale pool fire was treated as a gaseous jet flame with low initial velocity as an approximation. The combustion model postulated infinitely fast chemical reaction and the soot formation model included soot nucleation, surface growth, coagulation, thermophoresis, and oxidation. Valuable data were obtained in the temperature distribution, velocity profiles, soot volume fraction and major species concentrations. Especially, the periodic formation of the large scale structures were successfully simulated. Its frequency agreed well with experimental results. Research Institute of Industrial Science and Technology Heat and Fluid Flow Research Team     

航空发动机短舱空间温度分布数值模拟与分析

通过分析飞机发动机短舱的结构特点,发展了短舱空间温度分布的一维和三维数值计算方法.针对某型涡扇发动机的几种飞行状态,确立了其短舱流动和换热的计算模型,数值模拟了发动机短舱内的温度分布,并对计算结果进行了比较和分析.从计算结果可以看出,沿轴向短舱内的温度分布规律几乎与涡扇发动机沿轴向的温度分布规律是一致的.因此,若保证短舱内的温度不超温,必须降低涡扇发动机向短舱内的热传递,特别是涡扇发动机高温部件向短舱内的传热.     

Numerical simulation on the local stress and local deformation in multi-point stretch forming process

Multi-point stretch forming (MPSF) is a new flexible forming technique to form aircraft outer skin parts. The multi-point stretching die (MPSD) replaces the traditional fixed shape stretching die, and the sheet metal is formed over a MPSD composed by the punch element. The MPSD is a discontinuous surface of discrete stretching die, and the stress concentration and local strain occur on formed parts. These lead to generate dimples on the surface of formed part. In this paper, a series of numerical simulations on MPSF processes for stretching parabolic cylindrical, spherical, and saddle-shaped parts were carried out. The local stress and local strain in thickness distribution of MPSF part were analyzed by dispersed the blank into solid elements. The forming results of MPSF were compared with those that use traditional stretch forming, and the influences of thickness of elastic cushion and the size of punch element on the stress concentration and local strain were surveyed. The simulation results show the distribution of local stress and local deformation in different layers, and the elastic cushion and the small size of punch element can reduce the stress concentration and local deformation. The results may understand the stress distribution on the sheet and prevent the defect of dimple.     

固液两相流离心泵内颗粒运动规律的数值研究

针对分析固相参数对颗粒在流道内运动规律影响的问题,对不同固相参数工况下流道内颗粒运动轨迹、固相速度分布和颗粒雷诺数分布规律进行了研究,对颗粒直径以及颗粒浓度对颗粒运动规律影响进行了归纳。应用RNG k-ε湍流模型以及离散相模型进行了离心泵内部固液两相流场数值模拟。研究结果表明,颗粒与蜗壳碰撞的次数随着直径和颗粒浓度的增大而减少;叶轮流道内,颗粒与叶片发生碰撞的位置在叶片工作面;流道内的固相速度随着直径的增大整体会有减小的趋势;蜗壳和叶轮流道内两相分离严重,两相滑移速度较大。     

Scaling laws for wall shear stress through stenoses under steady and pulsatile flow conditions.

Most patients with atherosclerosis exhibit isolated stenoses of one or more epicardial coronary arteries. The wall shear stresses produced in high-grade stenosis are important in the understanding of atheromatous plaque rupture and thrombosis. This study is designed to establish a method which can be used to scale the different wall shear stresses obtained under different flow conditions to be normalized and subsequently collapsed on to a single general curve. The simulations include both steady and pulsatile flow. The reduced area percentages of the stenoses studied are 50, 75 and 90 per cent. Scaling laws for steady and pulsatile flow conditions are proposed and presented. It can be found from the results that the scaling analysis for pulsatile flow conditions is more complicated than for steady flow conditions and is restricted to, and only valid at, certain time intervals.     

Numerical simulation of ultrasonic minimum reflection for residual stress evaluation in 2D case

A number of interesting phenomena at fluid-solid interfaces can be observed when the incident angle approaches the Rayleigh angle, including Schoch displacement and leaky Rayleigh waves. Besides the experimental and theoretical research on these problems, numerical tools have been more and more widely used for these complex problems. Based on previous experimental and numerical researches, a 2D finite element model has been built to reproduce the Schoch effects. With the same model, the minimum reflection profile is investigated for the feasibility of material characterization, especially for residual stress evaluation. Residual stress is one of the important properties for structures, and its measurement is a popular research topic in nondestructive evaluation. However, it is not possible to put the residual stress into the numerical model directly. According to the relation of residual stress with mechanical properties, the material damping and wave speed have been alternatively adopted in this work. The influence of minimum reflection profile by residual stress has been shown by the change of wave speed and damping factor. Simulation results show that the minimum reflection profile is a potential method for residual stress evaluation.     

7075铝合金板淬火残余应力模拟及实验研究

铝合金板在淬火过程中产生较大的残余应力,导致构件出现变形、翘曲。采用准耦合法对7075铝合金板在淬火过程中的温度场和应力场进行数值模拟,利用盲孔法对淬火后的残余应力分布进行实验测量。结果表明,7075铝合金板淬火后残余应力呈现出外压内拉的分布状态,淬火过程中形成的较大温度梯度造成的不均匀塑性变形是应力产生的主要因素,铝板表层和心部冷却速度的变化导致了应力分布状态的转变。实验结果验证了准耦合模拟方法的可行性,研究结论为残余应力控制提供重要依据。     

超微粉碎过程中气/固两相流场的数值模拟

为认知超微粉碎机粉碎腔内的流场结构和流动状态,采用离散相模型对粉碎机粉碎腔内的气/固两相三维定常流场进行了数值模拟.气相采用重整化群k-ε双方程模型,颗粒相采用随机颗粒轨道模型,同时综合考虑了颗粒受力和湍流扩散对流场状态的影响.模拟结果直观显示了粉碎腔内的速度、总压和流线等特征,研究结果对进行超微粉碎设备关键结构优化设计提供了一定的理论指导.     

柴油机冷却系统的数值模拟

对某柴油机的冷却系统进行数值模拟,包括了机体和气缸盖的水套.运用CFD(Computational Fluid Dynamics)分析软件SC/Tetra计算温度场及流场.通过计算发现水套存在诸多不足,如机体水套冷却不均匀,机体进气侧与非进气侧冷却液流速相差大,鼻梁区流量偏小等缺陷.然后对其结构进行改进,取得了比较好的效果.     

Design of a micro floating element shear stress sensor

A silicon-based micro-machined, floating element sensor for wall shear-stress measurement has been developed. Sensor with the dimension of 4×3×0.5 mm³ has been fabricated by inductively coupled plasma (ICP) etching techniques with single mask. An optical system was designed to identify whether there is defect in the structure of the fabricated sensor. Detection of the floating element motion induced by shear stress of fluid is accomplished using differential capacitance measurement. A special package was used to reduce the parasitic capacitance and realize flush mounted between the sensor and the wall. Calibration tests were carried out in a laminar flow channel; the result indicates that the sensitivity of the sensor is measured to be 27 mv/Pa. The measured non-linearity is less than 3.4% while the repeatability is within 4.9% in the regime of 0–35 Pa.     

Al-Cu合金定向凝固脉冲磁场分布数值模拟

采用ANSYS8.0有限元软件对脉冲磁场作用下的Al-Cu合金定向凝固磁场分布作了数值模拟。并对脉冲磁场强度进行了实验测量。结果表明:在合金试样中心附近磁感应强度较强,而在端部较弱。模拟结果和实验测得结果相符合。通过数值模拟,可以初步了解定向凝固过程中的磁场分布状态,而且有助于进一步研究凝固组织细化的原因。     

基于ANSYS/LS-DYNA的进近灯光杆塔撞击应力数值仿真

本文针对机场内进近灯光站点所使用的进近灯光杆塔,从应力分析的角度出发,利用有限元分析软件ANSYS,建立了飞机撞击进近灯光杆塔应力仿真的有限元模型,得到了灯塔的应力、速度、位移等参数.从而为进近灯光杆塔易折结构设计、维护和损伤评估等提供理论上的支持.验证了基于ANSYS/LS-DYNA非线性动力有限元分析方法在求解高速碰撞响应分析问题中的可行性.     

Numerical investigation of dynamic behavior of a compound drop in shear flow

We present a numerical investigation of the deformation and breakup of a compound drop in shear flow. The numerical method used in this study is a two-dimensional front-tracking/finite difference technique for representing the interface separating two fluids by connected elements. The compound drop with the initially circular and concentric inner and outer fronts is placed at the center of a domain whose top and bottom boundaries move in the opposite direction. Because of the shear rate, the compound drop deforms and can break up into drops, depending on the flow conditions based on the Reynolds number Re, the Capillary number Ca and the interfacial tension ratio σ₂₁ of the outer to inner interfaces. We vary Re in the range of 0.1-3.16, Ca in the range of 0.05-0.6 and σ₂₁ in the range of 0.8-3.2 to reveal the transition from the non-breakup to breakup regimes. Numerical results indicate that the compound drop breaks up into drops when there's an increase in Re or Ca or a decrease in σ₂₁ beyond the corresponding critical values. We also propose a phase diagram of Ca versus Re that shows the region in which the compound drop changes from the deformation mode to the breakup mode.     

Numerical simulation of a reflective diffraction fiber interferometer

Numerical simulation was used to demonstrate the possibility of designing a two-mirror multibeam reflective diffraction interferometer using a single-mode fiber with a cladding. The method is based on the calculation of the multimode and multibeam interference of the cladding modes in the fiber describing the diffraction on a diffuser made in the form of an insert of a different fiber as part of one of the interferometer mirrors. It is shown based on bulk optics that using certain optimization, one can obtain a reflection-response function profile of this interferometer similar to that of the transmission-response function of a Fabry-Perot interferometer.