Transfer element method with application to acoustic design of aeroengine nacelle

In the present survey, various methods for the acoustic design of aeroengine nacelle are first briefly introduced along with the comments on their advantages and disadvantages for practi- cal application, and then detailed analysis and discussion focus on a kind of new method which is called ＂transfer element method＂ （TEM） with emphasis on its application in the following three problems： turbomachinery noise generations, sound transmission in ducts and radiation from the inlet and outlet of ducts, as well as the interaction between them. In the theoretical frame of the TEM, the solution of acoustic field in an infinite duct with stator sound source or liner is extended to that in a finite domain with all knows and unknowns on the interface plane, and the relevant acoustic field is solved by setting up matching equation. In addition, based on combining the TEM with the boundary element method （BEM） by establishing the pressure and its derivative con- tinuum conditions on the inlet and outlet surface, the sound radiation from the inlet and outlet of ducts can also be investigated. Finally, the effects of various interactions between the sound source and acoustic treatment have been discussed in this survey. The numerical examples indicate that it is quite important to consider the effect of such interactions on sound attenuation during the acoustic design of aeroengine nacelle.

Radiation heat transfer model for complex superalloy turbine blade in directional solidification process based on finite element method

For the sake of a more accurate shell boundary and calculation of radiation heat transfer in the Directional Solidification(DS) process, a radiation heat transfer model based on the Finite Element Method(FEM)is developed in this study. Key technologies, such as distinguishing boundaries automatically, local matrix and lumped heat capacity matrix, are also stated. In order to analyze the effect of withdrawing rate on DS process,the solidification processes of a complex superalloy turbine blade in the High Rate Solidification(HRS) process with different withdrawing rates are simulated; and by comparing the simulation results, it is found that the most suitable withdrawing rate is determined to be 5.0 mm·min^(-1). Finally, the accuracy and reliability of the radiation heat transfer model are verified, because of the accordance of simulation results with practical process.

Streamline upwind finite element method for conjugate heat transfer problems

This paper presents a combined finite element method for solving conjugate heat transfer problems where heat conduction in a solid is coupled with heat convection in viscous fluid flow. The streamline upwind finite element method is used for the analysis of thermal viscous flow in the fluid region, whereas the analysis of heat conduction in solid region is performed by the Galerkin method. The method uses the three-node triangular element with equal-order interpolation functions for all the variables of the velocity components, the pressure and the temperature. The main advantage of the proposed method is to consistently couple heat transfer along the fluid-solid interface. Three test cases, i.e. conjugate Couette flow problem in parallel plate channel, counter-flow in heat exchanger, and conjugate natural convection in a square cavity with a conducting wall, are selected to evaluate the efficiency of the present method.

Nodeless variable finite element method for heat transfer analysis by means of flux-based formulation and mesh adaptation

Based on flux-based formulation, a nodeless variable element method is developed to analyze two-dimensional steady-state and transient heat transfer problems. The nodeless variable element employs quadratic interpolation functions to provide higher solution accuracy without necessity to actually generate additional nodes. The flux-based formulation is applied to reduce the complexity in deriving the finite element equations as compared to the conventional finite element method, The solution accuracy is further improved by implementing an adaptive meshing technique to generaie finite element mesh that can adapt and move along corresponding to the solution behavior. The technique generates small elements in the regions of steep solution gradients to provide accurate solution, and meanwhile it generates larger elements in the other regions where the solution gradients are slight to reduce the computational time and the computer memory. The effectiveness of the combined procedure is demonstrated by heat transfer problems that have exact solutions. These problems tire： （a） a steady-state heat conduction analysis in a square plate subjected to a highly localized surface heating, and （b） a transient heat conduction analysis in a long plate subjected to moving heat source.

ANALYSIS OF THE HEAT TRANSFER IN FIN ASSEMBLIES BY THE BOUNDARY ELEMENT METHOD

The special formulation that allows an accurate and efficient solution to the heat transfer problems within fin assemblies with very large aspect ratios has been developed in this paper Numerically,it consists of the boundary element method in the wall region and the analytical solution in the fin region This modified BEM makes tractable a large class of heat transfer problems in the long and thin domains which are frequently encountered in practice.

ANALYSIS OF THE THERMOPHYSICAL PARAMETERS OF MOIST WOOD PARTICLE MATERIAL IN A COUPLED HEAT AND MASS TRANSFER PROCESS OF FREEZING BY USING FINITE ELEMENT METHOD

The coupled heat and moisture transfer in a freezing process of wood particle material was mathematically modeled in the paper. The models were interactively solved by using the numerical method(the finite element method and the finite difference method). By matching the theoretical calculation to an experiment, the nonlinear problem was analyzed and the variable thermophysical parameters concerned was evaluated. The analysis procedure and the evaluation of the parameters were presented in detail. The result of the study showed that by using the method as described in the paper, it was possible to determine the variable (with respect to temperature, moisture content and freezing state) thermophysical parameters which were unknown or difficult to measure as long as the governing equations for a considered process were available. The method can significantly reduces the experiment efforts for determining thermophysical parameters which arc very complicated to measure. The determined variable of the effective heat conductivity of wood particle material was given in the paper. The error of the numerical calculation was also estimated by the comparison with a matched experiment.

Study of heat transfer by using DEM–CFD method in a randomly packed pebble-bed reactor

The pebble-bed reactor is one of the most promising designs for the nuclear energy industry. In this paper,a discrete element method-computational fluid dynamics(DEM-CFD) approach that includes thermal conduction, radiation, and natural convection mechanisms was proposed to simulate the thermal-fluid phenomena after the failure of forced circulation cooling system in a pebble-bed core. The whole large-scale packed bed was created using the DEM technique, and the calculated radial porosity of the bed was validated with empirical correlations reported by researchers. To reduce computational costs, a segment of the bed was extracted, which served as a good representative of the large-scale packed bed for CFD calculation. The temperature distributions simulated with two different fluids in this DEM-CFD approach were in good agreement with SANA experimental data. The influence of the natural convection mechanism on heat transfer must be taken into account for coolants with strong convective capacity. The proposed DEM-CFD methodology offers a computationally efficient and widely applied method for understanding the heat transfer process in a pebble-bed core. The method can also be easily extended to assess the passive safety features of newly designed fluoride-salt-cooled pebble-bed reactors.

SINGULAR INTEGRAL EQUATIONS AND BOUNDARY ELEMENT METHOD OF CRACKS IN THERMALLY STRESSED PLANAR SOLIDS

Using the method of the boundary integral equation, a set of singular integral equations of the hear transfer problems and the thermo-elastic problems of a crack embedded in a two-dimensional finite body is derived, and then,its numerical method is proposed by the numerical method of the singular integral equations combined with boundary element method. Moreover, the singular nature of temperature gradient field near the crack front is proved by the main-part analysis method of the singular integral equation, and the singular temperature gradients are exactly obtained. Finally, several typical examples calculated.

Finite Element Assisted Numerical Comparison of Single and Two Phase Inductively Coupled Power Transfer Systems

Inductively coupled power transfer systems (ICPT) are becoming ubiquitous in industry. Many such systems are excited with single or multi-phase input current. This leads to increased complexity in comparing such systems when solely using the magnetic frequency analysis. This paper utilizes modern finite element method analysis software to propose a novel software methodology for the numerical comparison of single and two phase ICPT systems as demonstrated on a three dimensional (3D) battery charging system. The sinusoidal magnetic frequency response of a single phase system is compared to the magnetic transient response of a multi-phase current system by use of a novel software methodology proposed in this paper. This consists of a transient response analysis to determine compute the resulting magnetic response over the duration of an input current period on the two phase system. The resulting non-sinusoidal response is then integrated over a whole period to extract the root-mean-square value for comparison with that of a single phase system across a 3D cubic power zone.

Numerical Simulation of Mold Filling in Resin Transfer Molding Using Isoparametric Method

The mold filling of RTM was simulated based on the control volume finite element method (CV/FEM). The formulat ion using isoparametric transformation was discussed in detail and a computation al code based on isoparametric technique was developed. The simulation results w ere compared with experimental data. Different isoparametric elements, quadrilat eral and triangular, were compared in the simulation.It demonstrates that the us e of bilinear quadrilateral isoparametric elements in simulating the process can produce a higher precision and cost a less time than the use of triangular ones .

Numerical Study of Natural Convection in Square Cavity with Inner Bodies Using Finite Element Method

A numerical study of heat transfer problem by natural convection of a fluid inside a square cavity with two inner bodies is presented. This subject is of great interest in the engineering area, mainly in applications involving development of heat exchangers and cooling or heating systems of bodies by natural convection mechanism. Two cases have been studied. The inner bodies are square in case 1 and circular in case 2. In both cases, the bodies are solid and thermally conductive, the cavity lower and upper horizontal surfaces are isothermal with high temperature Th and low temperature Tc, respectively. Both vertical surfaces are adiabatic. A FORTRAN code using Finite Element Method (FEM) is developed to simulate the problem and solve the governing equations. The distributions of stream function, ψ, dimensionless temperature, θ, and vorticity, ω, are determined. Heat transfer is evaluated by analyzing the behavior of the average Nusselt number. The Grashof number and thermal diffusivity ratio are considered in range from 2 × 104 to 105 and from 0.1 to 100, respectively. The fluid is air with Prandtl number fixed in 0.733.

Heat Distribution in Rectangular Fins Using Efficient Finite Element and Differential Quadrature Methods

Finite element method (FEM) and differential quadrature method (DQM) are among important numerical techniques used in engineering analyses. Usually elements are sub-divided uniformly in FEM (conventional FEM, CFEM) to obtain temperature distribution behavior in a fin or plate. Hence, extra computational complexity is needed to obtain a fair solution with required accuracy. In this paper, non-uniform sub-elements are considered for FEM (efficient FEM, EFEM) solution to reduce the computational complex-ity. Then this EFEM is applied for the solution of one-dimensional heat transfer problem in a rectangular thin fin. The obtained results are compared with CFEM and efficient DQM (EDQM), with non-uniform mesh generation). It is found that the EFEM exhibit more accurate results than CFEM and EDQM showing its potentiality.

基于功率流有限元法的涡旋压缩机振动特性研究

针对涡旋压缩机内部振动传递路径复杂,采用传统的传递函数法往往不能真实地描述振动产生与传递的本质问题,引入功率流有限元法从能量角度分析振动传递特性,进行涡旋压缩机内部振动产生、传递与空间分布的可视化研究。在分析涡旋压缩机的动力拓扑关系基础上建立激励源,提取与振动响应模型并进行仿真分析;利用实体试验和响应分析结果对比进行模型有效性分析;在验证后的模型上定义8个能量输出面,分析谐波与激励作用下上支撑和下支撑的振动能量传递特性,并且计算节点的功率流矢量确定振源的空间分布。结果表明,涡旋压缩机曲轴在运转到280°时,振动频率在1 000 Hz与1 890 Hz时振动能量传递率较高,上支撑能量分布均匀并集于自身,下支撑能量集中于支脚并向外传递。研究方法和研究成果对于涡旋压缩机振动分布及传递、振动控制和优化设计等方面具有一定借鉴意义。

基于CFD-DEM耦合的梯级溜槽的设计与分析

针对传统物料转运过程中溜槽和输送带磨损严重、出口处粉尘浓度过高的问题,建立含臂架的梯级溜槽几何模型,采用基于计算流体力学与离散单元法(CFD-DEM)耦合的数值模拟方法,分析了臂架对转运溜槽的磨损以及对其出口处粉尘排放浓度的影响。仿真结果表明:含臂架的梯级溜槽可以有效控制物料流的速度和方向,降低对溜槽内表面的冲击磨损,降低出口处的粉尘量。

常泰长江大桥组合索塔锚固结构钢-混传剪构造足尺模型试验研究

常泰长江大桥索塔锚固结构采用钢箱-核芯混凝土组合结构,为研究该新型组合索塔锚固结构钢-混传剪构造的受力特性,进行钢-混传剪构造足尺模型试验研究。制作2个锚固结构足尺节段试验模型,通过压剪试验研究锚固结构的荷载~滑移曲线及应力、应变分布等受力特性,并通过有限元模型分析锚固结构的传力机理和各组件的内力分配比例,推导剪力钉剪力计算方法。结果表明:在2.14倍单索最大索力荷载作用下,锚固结构保持弹性状态,钢壁板未产生明显滑移,钢-混界面最大滑移不超过0.25 mm,该锚固结构中钢-混传剪构造至少具有2.14倍的安全系数;荷载作用下,剪力钉剪力从上至下逐渐增大,锚腹板附近底部3排剪力钉剪力较大,钢-混传剪构造至少存在剪力钉和界面摩擦力2种传剪机制,钢-混传剪构造的承载能力显著提高;钢-混传剪构造受力过程分为粘结力传力阶段和局部滑移阶段,剪力钉剪力分布不仅与沿剪切方向长度分布有关,也与荷载的大小线性相关。

基于声电类比的低频消音结构优化设计

基于声电类比,设计了与电滤波器性能相似的低频消音结构,并结合传递矩阵法和模拟退火法,构造了声学结构的优化设计策略。首先,采用归一化方法,以四阶切比雪夫高通电滤波器为基准,设计了电学带阻滤波器;然后,基于声电类比,将电路中的电感电容转换为声学结构中的细管和圆柱腔,构造了消音结构原型,并利用传递矩阵法,建立其数学模型,推导声波传递损失表达式;最后,结合声学结构的数学模型和模拟退火法,以有效衰减带宽最大为目标,以消音结构的尺寸参数为变量,对原型结构进行优化设计。结果表明:基于声电类比,能获得合理的消音结构原型,克服了仅依靠经典消音结构进行设计的局限;结合推导的传递损失数学模型和模拟退火法,对消音结构原型进行参数优化,能显著提高其消音效果,表现在传递损失超过20 dB的带宽拓宽至410~2 165 Hz,是优化前带宽的202%,特别是优化后的结构克服了原型结构在466~537 Hz频率内不能实现有效消音的缺陷,获得了连续的大跨度有效带宽,且传递损失曲线平均增幅达22.8%。

基于Riccati传递矩阵法的永磁涡流联轴器固有频率分析

在对永磁涡流联轴器进行模态特性研究时,为了提高对联轴器转子系统的固有频率分析计算的准确度,利用传递矩阵法构建了转子的动力学分析模型。将永磁体的磁力统一化为零质量铰链连接,简化了涡流联轴器的磁电作用力,将复杂的研究模型转化为一个机械强度问题,使用Riccati传递矩阵法对完成等效化处理的转子进行模态分析,得到联轴器的固有频率与对应振型。在此基础上,将分析结果与精细三维有限元仿真结果进行了对比。结果表明,该方法能够较准确地对永磁涡流联轴器进行固有频率分析,与高精度仿真模型分析产生的结果误差不超过8%。通过改进计算数据与有限元分析结果进行对比研究,为永磁涡流联轴器的动力学特性研究提供了理论依据。

半自由声场下车辆开闭件的时频优化

乘用车关门工况下半自由声场测量需要在整车制造完成之后才能进行,因此对关门声辐射的提前预测与优化分析显得至关重要。首先,通过设计整车试验和台架试验获取加速度振动响应和频率响应函数,实现关门工况下瞬态冲击载荷的离散化,进一步联合传递路径分析(TPA)与连续小波变换(CWT)提出TPA-CWT方法进行离散化瞬态冲击载荷时频分析。其次,根据关门工况下车门的动力学特性,将求取的离散化瞬态冲击载荷输入至已建立的车门有限元模型中,进而将车门有限元瞬态加速度振动响应映射至车身时域边界元模型预测半自由声场辐射噪声,并与整车试验中麦克风处的实测结果进行对比,声压曲线整体趋势与局部峰值的一致性证明了时域边界元仿真可以精准捕捉到关门工况下瞬态声压特性;最后,通过等效辐射声功率选取低频噪声贡献量前3的部件作为设计变量,再利用多目标粒子群优化对车门质量与关门声辐射进行优化,优化后车门质量减小1.8%,关门声辐射减小1.7%,达到了多目标优化的目的。结果表明,仿真数据与试验结果一致性较好,验证了通过将车门关闭瞬态载荷离散化处理方式和声固耦合分析在关门工况下多目标优化中的可行性,并为后续改款车型的车门设计提供一定的指导方向。

螺栓连接结构冲击载荷传递特性及冲击响应行为研究进展综述

目的通过探讨复杂装备结构中螺栓连接结构在冲击载荷条件下的力学响应特征,以及这些特征如何影响装备结构的应力波传播、能量耗散和整体结构响应;同时,关注螺栓自身的变形和破坏对关键部件乃至整个系统稳定性和安全性的潜在影响,特别是在武器装备中可能引发的灾难性后果,旨在进一步优化螺栓连接结构的设计,提高其在极端载荷条件下的性能和可靠性。方法系统调研国内外文献,总结螺栓连接结构冲击载荷传递特性及冲击响应行为的研究进展,涉及的研究方法包括试验研究、有限元模拟和理论分析等。结论螺栓连接结构的冲击响应行为对装备整体的稳定性和安全性具有重要影响。通过对现有文献的分析,提出了未来研究的建议。

复杂场地变电站基础中预应力管桩荷载传递规律的有限元分析

在山区修建变电站等工程时,经常会遇到复杂场地基础的问题。倾斜软土地基是其中的一种特殊基础,具有独特的工程特性,给变电站的施工带来很大困难。为了研究复杂场地基础中预应力管桩的加固效果,指导预应力管桩设计。利用有限元软件建立了预应力管桩加固斜坡软土地基模型,研究了不同桩间距、桩长对路堤安全系数的影响,分析了预应力管桩的荷载传递规律、沉降以及路堤破坏机理。结果表明,在倾斜软土地基中设置预应力管桩,可以有效减少基础的变形,提高其稳定性;桩间距和桩长的改变对加固效果的影响显著,随着桩间距的减小和桩长的增加,倾斜软土地基变形逐渐减小,路堤安全系数逐渐增大;桩长应深入到嵌固层以下,过度减小桩间距后加固效果提高不大;路堤中部的桩基主要提供承载力,产生竖向位移较大,两侧的桩基主要提供抗滑力,产生横向位移较大;桩身轴力沿桩身先增大再减小,以软土层底面为分界线,上部桩身与下部桩身受剪应力相反,主要受力部位集中在桩端。在相关工程中,可根据需要合理设计预应力管桩的桩长、桩数和桩间距等参数,实现更加经济合理的加固方案。