An Analysis of Structural-Acoustic Coupling Band Gaps in a Fluid-Filled Periodic Pipe

A periodic pipe system composed of steel pipes and rubber hoses with the same inner radius is designed based on the theory of phononic crystals. Using the transfer matrix method, the band structure of the periodic pipe is calculated considering the structural-acoustic coupling. The results show that longitudinal vibration band gaps and acoustic band gaps can coexist in the fluid-filled periodic pipe. The formation of the band gap mechanism is further analyzed. The band gaps are validated by the sound transmission loss and vibration-frequency response functions calculated using the finite element method. The effect of the damp on the band gap is analyzed by calculating the complex band structure. The periodic pipe system can be used not only in the field of vibration reduction but also for noise elimination.

Structural-acoustic coupling characteristics of honeycomb sandwich plate based on parameter sensitivity analysis

The structural-acoustic coupling model for isotropic thin elastic plate was extended to honeycomb sandwich plate(HSP) by applying Green function method.Then an equivalent circuit model of the weakly-strongly coupled system was proposed.Based on that,the estimation formulae of the coupled eigenfrequency were derived.The accuracy of the theoretical predictions was checked against experimental data,with good agreement achieved.Finally,the effects of HSP design parameters on the system coupling degree,the acoustic cavity eigenfrequency,and sound pressure response were analyzed.The results show that mechanical and acoustical characteristics of HSP can be improved by increasing the thickness of face sheet and reducing the mass density of material.

基于声学FEM-BEM的户内变电站噪声场计算

准确计算户内变电站大型、复杂的噪声场分布,进而评价可采用降噪措施的减噪效果,是解决户内变电站噪声污染的关键问题。为此,综合声学有限元法(finite element method,FEM)求解复杂声场收敛性好及精度高的优点,及声学边界元法(boundary element method,BEM)降维求解大型声场的优势,提出了一种基于声学FEM-BEM的户内变电站噪声场求解算法。首先,建立变电站内部声源声固耦合模型,采用声学FEM求解混响噪声作用下的声固耦合响应;然后,基于声学FEM-BEM耦合理论,求解内、外耦合边界处结构单元受声固耦合激励产生的位移及应力载荷;最后,根据声压及应力载荷激发的外场声波扩散模型,基于常规Gauss数值积分法,建立外部空间声域2维BEM声学积分方程,求解外部声场。该算法在湖南某110 kV户内变电站噪声场的求解分析中得到了成功应用,与实测值的相对误差为3.61%~4.87%。

基于DEM-FEM耦合方法的碎屑流对桥墩最大冲击力的影响因素研究

碎屑流是我国山区最危险的地质灾害之一,山区桥墩常受到碎屑流冲击而开裂、倾斜甚至倒塌,给山区桥梁建设、运营带来严重的安全隐患。采用离散元方法(discrete element method,DEM)和有限元方法(finite element method,FEM)耦合的三维数值模拟方法模拟了碎屑流对双柱式桥墩的冲击效应,并结合斜槽试验,验证了耦合方法的准确性,进一步分析了碎屑流冲击坡度、距离和体积密度对桥墩冲击力的影响规律。结果表明,最大冲击力与碎屑流冲击坡度、距离和体积密度分别呈幂函数(指数大于1)、幂函数(指数小于1)和线性正相关。冲击坡度、距离和体积密度对最大冲击力的敏感度值分别为3.012、0.202、0.804,在桥梁碎屑流灾害防治时需重视冲击坡度和体积密度的影响。将冲击力的数值模拟值与流体动力学模型预测值对比分析表明,流体动力学模型理论公式能较好地预测桥墩所受的最大冲击力,最大预测误差低于23.6%。相关研究结果可为山区桥梁碎屑流灾害防治与设计提供一定的参考依据。

考虑强度速率衰减效应的地震滑坡SPH-FEM模拟

基于SPH和FEM耦合的数值计算方法,引入滑动面摩擦强度的速率衰减模型,提出了一种能够模拟地震诱发滑坡破坏过程的数值模拟方法。基于所提数值方法模拟了唐家山地震滑坡,模拟结果与现场勘查结果及室内试验现象较为一致。基于模拟的滑动面上摩擦系数的演化过程,将唐家山滑坡的发生分为4个阶段:启动阶段、摩擦衰减阶段、低摩擦滑移阶段和逐步稳定阶段。模拟结果表明速度增加和摩擦强度衰减的相互促进,是触发滑体的高速运动的根本原因。提出采用滑体上作用的动摩擦力fd和动下滑力Td的比值R作为判别指标用于判断大型滑坡的启动,当首次出现R小于1时认为滑动面发生整体贯通并出现失稳启动。基于滑动面不同位置摩擦系数的演化,揭示了滑坡启动中滑动面摩擦强度衰减和滑动面的渐进贯通过程,解释了地震作用与滑动面摩擦参数速率衰减效应共同作用触发大型滑坡发生破坏的内在机理。

基于DEM-FEM耦合的环锤式破碎机反击板可靠性分析

由于环锤式破碎机破碎物料的过程是一个极其复杂多变的过程,且与反击板所受的碰撞力是不连续、无规则的,因此,无法使用公式推导或使用单一软件对反击板受力进行计算,为了能够更好地确定破碎机破碎过程中反击板的载荷大小、分布和寿命,文中提出了一种基于离散元(DEM)和有限元(FEM)耦合计算的环锤式破碎机反击板可靠性分析方法,通过EDEM建立环锤式破碎机破碎物料仿真过程,并提取出破碎过程中反击板的载荷分布,与ANSYS Workbench建立耦合计算通道,计算得到在正常工作参数下反击板的受力大小和位置,在此基础上采用n Code Design Life疲劳分析软件对反击板进行寿命分析,得到反击板的受力云图和损伤云图,研究转子转速、反击板倾角、转子与筛板距离等不同因素下对反击板可靠性的影响,结果表明:转子转速为1000 r∕min时反击板的最大受力值为247.9 MPa、反击板角度为60°时应力最大值为206.48 MPa、转子与筛板距离为530 mm时受力最大值为268.37 MPa。

基于SPH-FEM耦合算法的台阶精准爆破延期时间研究及应用

电子雷管在大型露天矿爆破中广泛使用,利用其精准起爆特性通过设置合理延期时间可有效改善爆破质量,对矿山生产降本增效具有重要意义。基于光滑粒子流体动力学—有限单元(SPH-FEM)耦合算法,利用LS-Dyna软件建立了多个巴润矿常规台阶尺寸的三维数值模型。针对电子雷管起爆条件下不同孔间和排间延时分别建立双孔、三孔SPH-FEM三维模型,从矿岩体SPH粒子应力和移动2个维度研究了被爆矿岩体的受力破碎、抛掷位移特征,并重点分析了不同排间延时下后排炮孔爆破漏斗的偏移角度。据此确定了最佳孔间、排间延期时间范围,并通过现场验证对比试验,选出了适合该爆区的最优延时。研究结果表明:在巴润矿现行孔排距条件下利用电子雷管精准起爆,孔间延时在20~30 ms内可达到较好的破碎效果;排间延时大于35 ms时,先爆炮孔为后续炮孔提供新的自由面和抛掷空间,且大于40 ms时应力趋于稳定;在现场验证试验中,试验区内边长1 m以下的破碎矿岩体占比达91%,较非试验爆区中同尺寸岩块占比提高了14%,破碎效果得到有效改善。

基于SPH-FEM耦合方法的泥石流冲击输电塔基础的动力分析

泥石流是我国西南山区常见的地质灾害。架空输电杆塔在泥石流的冲击下往往发生基础破坏甚至会造成杆塔倒塌。首先采用光滑粒子流体动力学(smoothed particle hydrodynamics,简称SPH)方法和有限元方法(finite element method,简称FEM)相耦合的三维数值方法模拟了泥石流对杆塔基础的冲击作用;在与相关模型试验结果验证的基础上,开展了不同泥石流密度、黏度系数及初始速度条件下对输电塔基础的冲击力作用的参数分析;研究结果表明:随着泥石流初始速度的增加,冲击力峰值会随之增大;前排基础的冲击力峰值均大于后排基础;泥石流冲击过程特性受到泥石流密度和黏度系数影响。与稀性泥石流相比:黏性泥石流冲击基础后,基础下游真空区相对要小;此外,将数值模拟结果与Kwan冲击力公式及铁二院推荐的冲击压力设计公式预测值进行对比分析可以发现:Kwan冲击力公式能较好地预测出基础所受泥石流冲击力的平均趋势,最大预测误差低于30%,铁二院公式预测的稀性和黏性泥石流的冲击压力平均偏低分别约17%和28%。相关研究结果有望为泥石流频发区域输电塔基础的设计和风险评估提供一定的参考依据。

基于自适应FEM-SPH耦合算法的飞机典型部位破片冲击战伤的数值研究

针对飞机典型部位在遭到高速破片攻击后结构整体的战伤状态及破片的剩余行为开展数值模拟。应用LS-DYNA软件,结合有限单元方法(finite element method,FEM)和光滑粒子流体动力学(smoothed particle hydrodynamics,SPH)两者的优势,建立自适应的FEM-SPH耦合模拟方法,并构建2种飞机典型部位的计算模型,采用六面体网格局部细化方法实现了核心位置的精确模拟,并进行试验来验证数值模型;开展了一系列高速冲击战伤模拟,对比了不同工况下破片高速冲击结构后形成的碎片云和破口形貌,并对破片的剩余速度和质量进行分析,确定了破片在结构蒙皮上的临界跳飞角。结果表明:自适应FEM-SPH耦合算法的计算结果与试验结果吻合良好,能够对破片高速冲击战伤进行有效准确模拟;碎片云分布形状随破片速度增加变得狭长,冲击角度会改变碎片云和结构破口形状朝向;碎片云高度和扩散速度随破片速度或角度的变化趋势基本一致并都呈线性关系;破片的速度减少量不随初始速度变化,质量减少量则与冲击速度正相关,两者与冲击角度都负相关;破片临界跳飞角与冲击速度大小基本呈线性关系。

An iterative algorithm for analysis of coupled structural-acoustic systems subject to random excitations

This paper analyzes the random response of structural-acoustic coupled systems. Most existing works on coupled structural-acoustic analysis are limited to systems under deterministic excitations due to high computational cost required by a random response analysis. To reduce the computational burden involved in the coupled random analysis, an iterative procedure based on the Pseudo excitation method has been developed. It is found that this algorithm has an overwhelming advantage in computing efficiency over traditional methods, as demonstrated by some numerical examples given in this paper.

基于DEM-FEM耦合模型的质量流量对喷丸强化效果的影响

目的提出一种将有限元(FEM)与离散元(DEM)相耦合的新方法,即通过定义关键字的方式在ABAQUS软件内实现DEM-FEM耦合功能,并应用此方法建立喷丸强化模型。方法将弹丸视为等直径刚体,利用刚体动力学模拟弹丸-弹丸和弹丸-靶材之间相互作用以及整个弹丸流。通过建立的DEM-FEM耦合喷丸强化模型研究质量流量对残余应力场和表面粗糙度的影响。结果质量流量对喷丸强化效果有显著影响,最大残余应力随质量流量的增加而减小,由2 kg/min时的–596.77 MPa下降到6 kg/min时的–581.91 MPa;表面残余应力随质量流量的增加先增大后减小,由2 kg/min时的–420.86 MPa增大到4 kg/min时的472.06 MPa,随后减小到6 kg/min时的–450.50 MPa;表面粗糙度Ra随质量流量的增加减小,由2 kg/min时的11.21μm减小到6 kg/min时的9.82μm。设计了喷丸强化实验,对质量流量2 kg/min的结果进行了验证。结论实测值与模拟值吻合较好,所建立的模型可以准确反映实际喷丸强化过程。质量流量对喷丸强化效果具有显著影响。

FEM COUPLING FIELD ITERATION AND ITS CONVERGENCE FOR A GMM ACTURATOR

The coupling iteration (CI) of the finite element method(FEM) is used to simulate the magnetic and mechanical characteristics for a GMM actuator. The convergent ability under different prestress and different load types is investigated. Then the calculated deformations are compared with the experimental values. The results convince that the CI of FEM is suitable for the simulation of energy coupling and transformation mechanism of the GMM. At last, the output deformation properties are studied under different input currents, showing that there is a good compromise between good linearity and large strain under the prestress 6 MPa.

饱和地基中劲芯水泥土墙隔振的二维BEM-FEM耦合分析

振动污染在国际上已被列入“七大环境公害”之一,填充沟是振动污染治理的一种常用隔振屏障。传统的填充沟受工程造价和施工工艺等限制工程中应用较困难;为克服上述问题,提出一种新型隔振屏障-内插预制芯墙的劲芯水泥土墙。对于饱和地基中劲芯水泥土墙的隔振问题,饱和地基采用饱和土半解析边界元法(boundary element method,BEM)建模,劲芯水泥土墙采用有限元法(finite element method,FEM)建模,根据饱和地基-水泥土墙交界面的平衡和连续性条件,分别建立了劲芯水泥土墙对入射Rayleigh波(瑞利波)的远场被动隔振和对动力机器基础振动近场主动隔振的半解析BEM-FEM耦合分析方法,并对劲芯水泥土墙的隔振效果进行了计算分析。研究结果表明:饱和地基中设置劲芯水泥土墙能够起到较好的隔振作用,其隔振效果与混凝土墙基本相当且远优于纯水泥土墙;预制芯墙在劲芯水泥土墙隔振系统中起关键作用,为避免弹性波从芯墙底绕射而降低隔振效果,预制芯墙深度应与水泥土墙深度保持一致;增大芯墙厚度对隔振效果提升不大。在等深芯墙条件下,增大墙深能显著提高远场隔振效果,但对近场隔振效果提升较小;增大墙厚也可提高隔振效果,但提高幅度不大。实际工程中,建议结合工程造价和施工工艺,选择合适的水泥土墙和预制芯墙墙厚。此外,屏障距振源距离对主动隔振效果影响较小,建议根据被保护建筑与振源之间的实际情况,选择合适位置构建隔振屏障。

基于PD-FEM混合模型的材料热力耦合损伤分析

提出了一种新的近场动力学-有限元方法(peridynamics-finite element method,PD-FEM)混合模型.该模型用于求解材料热力耦合损伤问题,将求解域划分为近场动力学(PD)区域和有限元方法(FEM)区域,通过FEM节点与PD物质点构成的混合键连接各个子区域.采用该模型对氧化铝陶瓷板在热冲击载荷作用下的损伤行为进行了模拟分析,计算结果表明,采用该混合模型获得的裂纹萌生及扩展与实验研究结果吻合良好,验证了该模型的正确性.该PD-FEM混合模型继承了PD处理不连续问题的优势,同时,由于FEM的引入,大大提高了PD方法在研究材料热力耦合损伤问题时的求解效率.

基于SPH-FEM算法的森林灭火弹爆炸抛撒灭火剂初速的数模拟研究

针对森林灭火弹爆炸抛撒问题,应用LS-DYNA软件对森林灭火弹爆炸抛撒灭火剂初速进行数值模拟研究。依据森林灭火弹爆炸抛撒实验的数据,对Gurney公式进行修正;建立森林灭火弹的仿真模型,将仿真模型所得灭火剂初速与修正后Gurney公式所得灭火剂初速进行对比,验证SPH-FEM耦合算法研究此类问题的可行性;对森林灭火弹装药结构进行优化,分析阶梯装药结构对灭火剂初速的影响。结果表明,修正后Gurney公式能够更好地适用于灭火剂初速的计算;采用SPH-FEM耦合算法模拟所得灭火剂初速与修正后Gurney公式所得灭火剂初速的吻合度高,表明采用SPH-FEM耦合算法研究此类问题是可行的;对森林灭火弹装药结构进行阶梯化改进可以增大灭火剂抛撒面积与提升灭火剂抛撒均匀性,提高森林灭火弹灭火效率。

FEM analyses for influences of pressure solution on thermo-hydro-mechanical coupling in porous rock mass

The model of pressure solution for granular aggregate was introduced into the FEM code for analysis of thermo-hydro- mechanical （T-H-M） coupling in porous medium. Aiming at a hypothetical nuclear waste repository in an unsaturated quartz rock mass, two computation conditions were designed： 1） the porosity and the permeability of rock mass are fimctions of pressure solution; 2） the porosity and the permeability are constants. Then the corresponding numerical simulations for a disposal period of 4 a were carried out, and the states of temperatures, porosities and permeabilities, pore pressures, flow velocities and stresses in the rock mass were investigated. The results show that at the end of the calculation in Case 1, pressure solution makes the porosities and the permeabilities decrease to 10%-45% and 0.05%-1.4% of their initial values, respectively. Under the action of the release heat of nuclear waste, the negative pore pressures both in Case 1 and Case 2 are 1.2-1.4 and 1.01-l.06 times of the initial values, respectively. So, the former represents an obvious effect of pressure solution. The magnitudes and distributions of stresses within the rock mass in the two calculation cases are the same.

FEM-BEM Coupling for the MHD Pipe Flow in an Exterior Region

In this study, the magnetohydrodynamic (MHD) flow through a circular pipe under the influence of a transverse mag- netic field when the outside medium is also electrically conducting is solved numerically by using FEM-BEM coupling approach. The coupled partial differential equations defined for the interior medium are transformed into homogenous modified Helmholtz equations. For the exterior medium on an infinite region, the Laplace equation is considered for the exterior magnetic field. Unknowns in the equations are also related with the corresponding Dirichlet and Neumann type coupled boundary conditions. Unknown values of the magnetic field on the boundary and for the exterior region are obtained by using BEM, and the unknown velocity and magnetic field inside the pipe are obtained by using SUPG type stabilized FEM. Computations are carried for very high values of magnetic Reynolds numbers Rm1, Reynolds number Re and magnetic pressure Rh of the fluid. The results show that using stabilized method enables us to get stable and accurate numerical approximations consistent with the physical configuration of the problem over rough mesh which also results a cheap computational cost.

Abrasive Waterjet Machining Simulation by Coupling Smoothed Particle Hydrodynamics /Finite Element Method

In dealing with abrasive waterjet machining（AWJM） simulation,most literatures apply finite element method（FEM） to build pure waterjet models or single abrasive particle erosion models.To overcome the mesh distortion caused by large deformation using FEM and to consider the effects of both water and abrasive,the smoothed particle hydrodynamics（SPH） coupled FEM modeling for AWJM simulation is presented,in which the abrasive waterjet is modeled by SPH particles and the target material is modeled by FEM.The two parts interact through contact algorithm.Utilizing this model,abrasive waterjet with high velocity penetrating the target materials is simulated and the mechanism of erosion is depicted.The relationships between the depth of penetration and jet parameters,including water pressure and traverse speed,etc,are analyzed based on the simulation.The simulation results agree well with the existed experimental data.The mixing multi-materials SPH particles,which contain abrasive and water,are adopted by means of the randomized algorithm and material model for the abrasive is presented.The study will not only provide a new powerful tool for the simulation of abrasive waterjet machining,but also be beneficial to understand its cutting mechanism and optimize the operating parameters.

Finite Element Simulation of Hot Strip Continuous Rolling Process Coupling Microstructural Evolution

Using the nonlinear rigid-viscoplastic finite element method （FEM）, a finite element simulation of the hot strip continuous rolling process was done, which completely integrates different phenomena such as the metallurgical behavior of the strip and the thermo-mechanics in the strip based on the physical metallurgical microstructural evolution law. By combining with the process parameters of certain 2 050 mm hot strip rolling, an actual roll- ing process of low carbon steel SS400 was simulated using the FEM model. Based on the simulation results, the distributions of the strain field, the temperature field, and the microstructure were presented. Meanwhile, the simulated rolling force, temperature, and microstructure are in good agreement with the measured results.

COUPLED THERMO MECHANICAL FEM ANALYSIS OF TWIST COMPRESSION DEFORMATION PROCESS

3-D rigid-viscoplastic FEM of compressible materials was applied to analyze the deformation behavior during twist compression forming of axisymmetrical body at high temperatures. When calculating the temperature fields, considering the thermo mechanical coupling effect between temperature and deformation, 2-D FEM and CNG methods were adopted, and the up winding technique was used to avoid the influences of numerical instability on calculated results.