FINITE ELEMENT ANALYSIS FOR LAMINAR FLOW AND HEAT TRANSFER IN FINITE ROD BUNDLES

This investigation deals with the application of finite element method to solve the thermohydraulic problem of laminar fully developed flow in the interior and wall sub-channels of finite fuel rod bundles. A variational principle has been used for the solution of the momentum and energy equations. Wall shear stress and temperature distributions, ƒRe and Nusselt numbers are obtained for the sub-channels of different configurations. The results are compared with solutions generated by collocation and finite difference methods.     

ADAPTIVE AND STOCHASTIC FINITE ELEMENT ANALYSIS IN DRYING

ABSTRACT

The focus of this paper is on the use of new advances in the finite element method to model and analyze drying problems, with emphasis on biological, food and grain materials. It presents the current status of the use of numerical analysis for such process, and emphasizes the need and advantages of incorporating adaptive and stochastic strategies into the finite element analysts. The existing literature on the application of the adaptive and stochastic finite elements is reviewed in conjunction with the relevant advances in this area. A new perturbation-based stochastic methodology far nonlinear and transient drying problems is formulated and presented in detail. The specific application of this new methodology to drying is under development. In conclusion, tracks for future research in this field are proposed.     

I. THEORY AND FINITE ELEMENT FORMULATION

ABSTRACT

A theoretical basis for a nonlinear thermo-hydro viscoelastic boundary value problem was developed. An incremental finite element formulation was derlved using the principle of virtual work. The effects of non-uniform temparature and moisture gradients and solution dependent material property functions are outlined. An appropriate     

GENERALIZED FINITE DIFFERENCE SOLUTION FOR HEAT AND MASS TRANSFER FROM A FINITE CYLINDER DURING QUENCH

A generalized nondimensional solution is presented that describes heat or mass transfer from a finite cylinder during quench. The solution is applicable to three important cases:

Conduction with convection heat transfer at the surface during any single step hot or cold quench.

Conduction with radiation heat transfer at the surface during a single step cold quench with negligible background radiation.

Diffusion with surface desorption of a diatomic gas from a metal specimen during a single step quench in a high vacuum with negligible background pressure.

Application of the generalized solution, which utilizes the numerical method of finite differences with forward stepping, is illustrated by determining a cylinder's transient temperature distribution and surface transfer rate (both instantaneous and cumulative) for an example L/D ratio of 2.0. Selected results are graphed and tabulated for the three cases. The results for the conduction/convection case are verified using the familiar analytical product solution as well as the lumped solution. For the conduction/radiation and diffusion/desorption cases, no analytical solutions are available other than the lumped limit which is in agreement.     

ADAPTIVE AND STOCHASTIC FINITE ELEMENT ANALYSIS IN DRYING

The focus of this paper is on the use of new advances in the finite element method to model and analyze drying problems, with emphasis on biological, food and grain materials. It presents the current status of the use of numerical analysis for such process, and emphasizes the need and advantages of incorporating adaptive and stochastic strategies into the finite element analysts. The existing literature on the application of the adaptive and stochastic finite elements is reviewed in conjunction with the relevant advances in this area. A new perturbation-based stochastic methodology far nonlinear and transient drying problems is formulated and presented in detail. The specific application of this new methodology to drying is under development. In conclusion, tracks for future research in this field are proposed.     

TRANSIENT FILM CONDENSATION ON FINITE HORIZONTAL PLATE

An analytical study of the transient film condensation on a finite horizontal plate is carried out. The flow across the edges of the horizontal surface is determined by a simple model based on the gravitational force exerted on the fluid. The transient heat transfer to the plate and the growth of the condensate film thickness are determined for various boundary conditions of practical interest. For short times, the semi-infinite solution is considered and it is shown that the solution merges into that for a finite plate thickness as time elapses. The temperature variation across the plate is considered in the analysis of the transient conduction problem and numerical results are obtained to determine the effect of the imposed boundary conditions and the various governing parameters. The results obtained are found to be strongly dependent on the boundary condition at the plate surface. The variation, with time, of the heat transfer to the plate, of the film thickness and of the plate temperature are determined.     

FULLY DEVELOPED LAMINAR FLOW IN A HELICALLY COILED TUBE OF FINITE PITCH

Solutions for steady, fully developed, laminar flow of an incompressible Newtonian fluid through a helically coiled tube of finite pitch were obtained by finite difference calculations. Prior theoretical solutions have apparently been limited to toroidal flow (with zero pitch). The computed results are consistent with those for this limiting case and with prior experimental data for finite pitch. The behavior for helical coils is intermediate between that for a straight pipe and a torus, and, for a moderate degree of pitch differs only slightly from that for a torus. A correlating equation was developed for the friction factor for all Reynolds numbers, all ratios of coil radius to lube radius and all ratios of pitch to coil radius for which the flow remains laminar.     

陶瓷全自动液压压砖机有限元分析

本文对陶瓷全自动液压压砖机架（ 包括上梁、立柱、底座） 进行了整体有限元应力分析和单独分析，两者分析结果表明，危险部位的应力吻合，得出的全场应力分布比传统的计算方法更精确更详细，为压机结构整体强度分析提供了重要依据。     

I. THEORY AND FINITE ELEMENT FORMULATION

A theoretical basis for a nonlinear thermo-hydro viscoelastic boundary value problem was developed. An incremental finite element formulation was derlved using the principle of virtual work. The effects of non-uniform temparature and moisture gradients and solution dependent material property functions are outlined. An appropriate     

非均质复合材料力学性能分析的多边形有限元方法

有限元方法是材料力学性能分析的主要工具.对于颗粒增强复合材料,其增强相或夹杂多为不规则的多边形,共采用经典有限元分析,需划分稠密的计算网格,降低分析效率.本文以多边形为有限元计算单元,采用Wachspress作为试函数,建立分析非均质材料力学性能的多边形有限元方法,给出形函数计算的简化公式.多边形单元的位移插值采用Wachspress插值,能自动满足不同形状单元间的协调性.计算网格按照材料分布的真实结构划分为若干多边形单元.数值算例验证了多边形有限元在模拟非均质材料力学性能方面的有效性和计算精度.     

基于MSC.Nastran的无人机复合材料机翼有限元分析

以某型无人机复合材料机翼为基础,基于MCS．Patran建立四种不同结构机翼有限元模型,并利用MCS．Nastran进行强度校核和模态分析。分析各元件的承载情况,对机翼的结构进行优化,从而提高机翼的寿命,降低生产成本。     

玻璃钢信号灯架的有限元分析与应用

现代交通工程中大量使用信号灯架,其质量、耐久性、造价是工程建设的重要指标.本文介绍了复合材料性能,并用大型结构分析软件ANSYS对一个玻璃钢复合材料制作的红绿灯架进行了有限元分析,与普通钢材红绿灯架进行了分析和比较.     

陶瓷全自动液压压机接触有限元分析

利用有限元接触分析法对６００吨陶瓷全自动液压压机立柱的预紧进行了研究。传统的压机有限元分析是将上梁、立柱、底腐和为单独部分进行的,在整机分析中将各部件作为固连的整体,忽略了接触的非线性特性;本文还分别按传统的有限元方法和接触有限元方法对压机计算结果进行对比,分析结果表明,两者计算结果有较大的差异,考虑接触科技司的压机有限元分析更接近实际工况。本文采用的分析方法对其它立柱式压机同样适用。     

FINITE ELEMENT SIMULATION OF ROUGH RICE DRYING

Milled, brown and rough rice samples were dried in the laboratory with heated air and diffusivities of the endosperm, bran and husk were evaluated with a search technique using the finite element method. The endosperm had the highest diffusivity. The husk had a slightly higher diffusivity than the bran because the trapped air inside the husk was considered as an integral part of the husk. The finite element method predicted rough rice drying that was in good agreement with experimental results.     

颗粒增强复合材料有限覆盖技术数值模拟研究

本文将有限覆盖技术应用于颗粒增强复合材料的数值模拟。通过引入数学与物重网格,将有限元的插值域与积分域分别定义在两个不同的覆盖上,即在数学网格上进行插值函数的构造,在物理网格上完成系统能量泛函的积分运算,最后通过覆盖权函数将二者联结在一起。它的优点是单元网格划分随意,不受复杂边界形状和二相材料界面的限制,单元可以是任意形状,是较之于有限元方法更普遍的数值模拟方法。最后给出了有限元网格覆盖颗粒增强复合材料的数值模拟算例,并与现有的方法进行了比较和讨论。     

基于非线性本构关系的有限元计算复合材料层合板的强度

复合材料的桥联模型本构理论考虑了基体材料的非线性特性.本文根据联模型理论编制出用户自定义材料库程序,与有限元软件ABAQUS实现接口,以方便地分析计算复合材料层合板结构的非线性响应与极限强度问题.在限元计算中荷载采用逐步加载的方式施加,最终得到复合材料层合板极限坏时的内力包罗图和应力应变曲线.有限元模拟的结果与桥联模型解析解结果吻合得很好,并且与实验结果相一致.     

FINITE ELEMENT SIMULATION OF THE THERMO-HYDRO STRESSES IN A VISCOELASTIC SPHERE DURING DRYING

The objective of this study is the formulation of a finite element model that could be used to analyze the stress crack formation in a viscoelastic sphere resulting from temperature and moisture gradients during the drying process. Numerical solutions to the simultaneous moisture and heat diffusion equations describing moisture removal and heat intake process for the sphere are obtained. The distribution and gradients of temperature and moisture developed inside the sphere during drying are established. The calculated temperature and moisture gradients are used in a finite element analysis of the thermo-hydro viscoelastic boundary value problem to simulate the stresses in the body.

The model is used to solve a sample problem of drying a soybean kernel. The simulated drying curve for the soybean model is obtained and compared favorably with the experimental results reported in the literature. Tangential stress, as a criteria for failure, is shown to change from compressive to tensile stress as it approaches the surface. It reaches its peak value at the surface in one hour and then decays slowly. The effect of different drying conditions is studied and the results are discussed.     

碳纤维缠绕复合气瓶爆破压力的有限元分析

本文主要采用有限元法分析复合气瓶的爆破,按最大应力准则和最大应变准则预测爆破压力,并与《DOT CFFC》标准规定的最小爆破压力进行比较,计算误差百分比,由误差百分比分析得出,按最大应变准则预测爆破压力较为接近最小爆破压力,对工程实践有较大的指导意义。     

三维中空复合材料天线罩的有限元结构分析

某类型天线罩外形尺寸较大,减重要求高,三维中空复合材料可满足该类型天线罩透波和结构高强的要求。针对上述使用要求和实际工况,选择三维中空织物复合材料为主体结构,玻璃纤维增强环氧树脂复合材料为补强面层,制备三维中空结构天线罩,采用有限元分析软件建立三维中空结构天线罩的有限元模型,对该类型天线罩在使用工况下的刚度、强度和稳定性进行分析,其计算结果满足刚度、强度和稳定性的要求,并通过压力试验验证中空夹层天线罩的变形量与有限元分析结果保持一致,从而指导该天线罩的铺层设计、优化及材料的选用。     

有限体积法解多场耦合下散射性非灰介质内的辐射换热

将有限体积法与谱带模型结合 ,求解了吸收、散射性非灰介质内的耦合换热 .经与光线踪迹法、离散传递法的计算结果比较表明 :提出的数值方法具有较高的精度 ;有限体积法适合辐射导热的多场耦合计算 ;对非灰介质建议选用谱带模型 ;并应考虑折射率对传热的影响