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1.
2.
In this paper,a complex variable function method for solving the hole shapeoptimization problem in an elastic plane is presented.In this method,the stresses in holeproblems are analysed by taking advantage of the efficiency of the complex variablefunction method.To optimize the hole shape,the coeffecients in conformal mappingfunctions are taken as design variables,and the sensitivity analysis and gradient methodsare used to reduce the largest circumferential stress in absolute value and at the same timeto make the second largest circumferential stress in absolute value not to exceed the largestone (in fact,these two stresses are the stationary values of the circumferential stresses).The coefficients in conformal mapping function are revised by iteration step by step until thelargest circumferential stress in absolute value is reduced to the second largest stress.Thismethod guarantees the continuity,differentiability and accuracy of the stress solution alongthe boundary,and it is evident that this method  相似文献   

3.
The cross-section profiles of polymer deformation in the hot embossing lithography process were studied by finite element method for various temperature, time and pressure. In order to successfully fabricate high-frequency grating lines, an optimal imprint condition was selected and the related experiments were carried out. The fabricated gratings were illuminated by the SEM image and AFM analysis, which agree well with the simulated results. Therefore, the finite element methods are helpful for a better comprehension of the polymer flow phenomena governing the pattern definition and the design of optimum processing conditions for successful grating fabrication.  相似文献   

4.
In this paper, a method for the design optimization of elasto-plastic truss structures is proposed based on parametric variational principles (PVPs). The optimization aims to find the minimum weight/volume solution under the constraints of allowable node displacements. The design optimization is a formulation of mathematical programming with equilibrium constraints (MPECs). To overcome the numerical difficulties of the complementary constraints in optimization, an iteration process, comprising a quadratic programming (QP) and an updating process, is employed as the optimization method. Furthermore, the elasto-plastic buckling of truss members is considered as a constraint in design optimization. A combinational optimization strategy is proposed for the displacement constraints and the buckling constraint, which comprises the method mentioned above and an optimal criterion. Three numerical examples are presented to show the validity of the methods proposed.  相似文献   

5.
SCATTERING OF CIRCULAR CAVITY IN RIGHT-ANGLE PLANAR SPACE TO STEADY SH-WAVE   总被引:1,自引:0,他引:1  
Complex function method and multi-polar coordinate transformation technology are used here to study scattering of circular cavity in right-angle planar space to SH-wave with out-of-plane loading on the horizontal straight boundary. At first, Green function of right-angle planar space which has no circular cavity is constructed; then the scattering solution which satisfies the free stress conditions of the two right-angle boundaries with the circular cavity existing in the space is formulated. Therefore, the total displacement field can be constructed using overlapping principle. An infinite algebraic equations of unknown coefficients existing in the scattering solution field can be gained using multi-polar coordinate and the free stress condition at the boundary of the circular cavity. It can be solved by using limit items in the infinite series which can give a high computation precision. An example is given to illustrate the variations of the tangential stress at the boundary of the circular cavity due to different dimensionless wave numbers, the location of the circular cavity, the loading center and the distributing range of the out-of-plane loading. The results show the efficiency and effectiveness of the method introduced here.  相似文献   

6.
The problem of nonlinear aerothermoelasticity of a two-dimension thin plate in supersonic airflow is examined. The strain-displacement relation of the von Karman's large deflection theory is employed to describe the geometric non-linearity and the aerodynamic piston theory is employed to account for the effects of the aerodynamic force. A new method, the differential quadrature method (DQM), is used to obtain the discrete form of the motion equations. Then the Runge-Kutta numerical method is applied to solve the nonlinear equations and the nonlinear response of the plate is obtained numerically. The results indicate that due to the aerodynamic heating, the plate stability is degenerated, and in a specific region of system parameters the chaos motion occurs, and the route to chaos motion is via doubling-period bifurcations.  相似文献   

7.
Stability for basic system of equations of atmospheric motion   总被引:1,自引:1,他引:0  
The topological characteristics for the basic system of equations of atmospheric motion were analyzed with the help of method provided by stratification theory. It was proved that in the local rectangular coordinate system the basic system of equations of atmospheric motion is stable in infinitely differentiable function class. In the sense of local solution, the necessary and sufficient conditions by which the typical problem for determining solution is well posed were also given. Such problems as something about "speculating future from past" in atmospheric dynamics and how to amend the conditions for determining solution as well as the choice of underlying surface when involving the practical application were further discussed. It is also pointed out that under the usual conditions, three motion equations and continuity equation in the basic system of equations determine entirely the property of this system of equations.  相似文献   

8.
The turbulent flow of vertical plane wall plume with concentration variation was studied with the finite analytical method. The k-epsilon model with the effect of buoyancy on turbulent kinetic energy and its dissipation rate was adopted. There were similarity solutions in the uniform environment for the system of equations including the equation of continuity, the equation of momentum along the flow direction and concentration, and equations of k, epsilon. The finite analytic method was applied to obtain the similarity solution. The calculated data of velocity, relative density difference, the kinetic energy of turbulence and its dissipation rate distribution for vertical plane plumes are in good agreement with the experimental data at the turbulent Schmidt number equal to 1.0. The variations of their maximum value along the direction of main flow were also given. It shows that the present model is good, i.e., the effect of buoyancy on turbulent kinetic energy and its dissipation rate should be taken into account, and the finite analytic method is effective.  相似文献   

9.
A method for combining the CFD software,Fluent,with the iSIGHT design platform is presented to optimize a three-dimensional wing to ameliorate its aerodynamics performance.In the optimization design,two kinds of genetic algorithms,the Neighborhood Cultivation Genetic Algorithm(NCGA)and the Non-dominated Sorting Genetic Algorithm(NSGAII),are employed and the Navier-Stoke(N-S)equations are adopted to derive the aerodynamics functions of the 3D wing.The aerodynamic performance of the optimized wing has been significantly improved,which shows that the approach can be extended and employed in other cases.  相似文献   

10.
The state plane method has been used to search the singular pointand to determine their equilibrium state for a mass point sliding on aguide rail rotating about a vertical axis with friction disregarded.For the same purpose,this paper presents another method which mightbe briefly named“The Tangential Force method”.In contrast with thestate plane method.the new method is much simpler both in argumenta-tion and calculation,especially when one resorts to the five criteriain section XIII.throughout the paper the function for defining the guide rail wasintroduced,with great endeavor,in the equations newly set up,in or-der to avoid deducing them each time.i.e.,the useful equations areset up somewhat once for ever.Moreover,the condition of letting the tangential force vanishyields two solutions,the parabolic and the exponential curves of theshape of the guide rails;they are two additional orthogonal curvefamilies although not conjugate harmonics.In the last part of the paper,we present nine examples to showt  相似文献   

11.
An analytical model for a time dependent two dimensional flow around a moving profile is developed. The model is suitable for fast aerodynamic and aeroelastic coupling calculations. It determines the inviscid pressure distribution in the vicinity of one blade and the force on the blade in arbitrary two dimensional motion. The method is more flexible than previous analysis: it can represent any profile, pitching motion and blade attachment position. The method is based on conformal mapping techniques and Laurent's series decomposition and is faster and more accurate than standard panel methods. A main idea is to directly treat the singularities of the flow in a mapped plane where any geometrical plane is simplified to a circle. The vorticity is assumed to be shed in the form of a continuous vortex sheet near the trailing edge.  相似文献   

12.
基于IGA-SIMP法的连续体结构应力约束拓扑优化   总被引:1,自引:1,他引:0  
建立了一种IGA-SIMP框架下的连续体结构应力约束拓扑优化方法。基于常用的SIMP模型,将非均匀有理B样条(NURBS)函数用于几何建模、结构分析和设计参数化,实现了结构分析和优化设计的集成统一。利用高阶连续的NURBS基函数,等几何分析(IGA)提高了结构应力及其灵敏度的计算精度,增加了拓扑优化结果的可信性。为处理大量局部应力约束,提出了基于稳定转换法修正的P-norm应力约束策略,以克服拓扑优化中的迭代振荡和收敛困难。通过几个典型平面应力问题的拓扑优化算例表明了本文方法的有效性和精确性。应力约束下的体积最小化设计以及体积和应力约束下的柔顺度最小化设计的算例表明,基于稳定转换法修正的约束策略可以抑制应力约束体积最小化设计中的迭代振荡现象,获得稳定收敛的优化解;比较而言,体积和应力约束下的柔顺度最小化设计的迭代过程更加稳健,适合采用精确修正的应力约束策略。  相似文献   

13.
低压涡轮内部流动及其气动设计研究进展   总被引:3,自引:0,他引:3  
邹正平  叶建  刘火星  李维  杨琳  冯涛 《力学进展》2007,37(4):551-562
随着高空无人飞行器研究的不断升温, 高空低雷诺数条件下动力装置的研究越来越受到人们的重视. 结合近年来国内外相关领域的研究工作, 对低雷诺数低压涡轮内部复杂流动机理的研究进展进行了介 绍, 包括低雷诺数情况下低压涡轮内部非定常流动的特点, 叶片边界层分离及转捩现象机理, 上游周期性 尾迹与下游叶片边界层相互作用机理等. 在此基础上给出了适合低雷诺数条件的低压涡轮气动设计方法: 尾迹通过与边界层的相互作用, 能够抑制分离, 进而减小叶型损失, 在气动设计中有效引入非定常效应可 以大幅度提高低压涡轮的气动负荷或降低气动损失, 最终达到提高性能的目的;数值及实验结果验证了这 种设计方法的有效性.  相似文献   

14.
基于近似技术的涡轮叶片气动优化设计   总被引:4,自引:1,他引:3  
根据五次多项式方法进行三维涡轮叶片的参数化建模,采用N-S方程和湍流模型进行三维流场分析计算,以K-S函数法作为优化方法,利用近似技术加速循环优化速度,建立了一种基于近似技术的涡轮叶片的气动优化方法。将气动效率和总压比作为目标函数,对涡轮叶片进行多目标气动优化、形状优化。算例表明本文提出的涡轮叶片优化设计方法是有效的。  相似文献   

15.
本文中提出了一种求解有限长径向滑动轴承非线性油膜力的近似解析方法.在滑动轴承-转子系统非线性动力行为分析中,油膜力计算模型通常采用"π"油膜假设,但是,实际工况中油膜的存在区域并非是"π"区域,运行时油膜中出现气穴,破裂成条纹状(即具有Reynolds边界条件).本文中的近似解析方法采用Reynolds边界条件,基于变分原理,运用分离变量法求解油膜的压力分布,其中油膜压力的周向分离函数通过无限长轴承的油膜压力分布获得,油膜的破裂终止位置角通过连续条件确定,轴向分离函数运用变分原理并结合周向函数求得.计算结果表明:本文中提出的方法和有限元方法的结果吻合得很好.在此基础上,分析了一些轴承参数对油膜压力分布的影响.  相似文献   

16.
Two techniques that improve the aerodynamic performance of wind turbine airfoils are described. The airfoil S809, designed specially for wind turbine blades, and the airfoil FX60-100, having a higher lift-drag ratio, are selected to verify the flow control techniques. The flow deflector, fixed at the leading edge, is employed to control the boundary layer separation on the airfoil at a high angle of attack. The multi-island genetic algorithm is used to optimize the parameters of the flow deflector. The results indicate that the flow deflector can suppress the flow separation, delay the stall, and enhance the lift. The characteristics of the blade tip vortex, the wake vortex, and the surface pressure distributions of the blades are analyzed. The vortex diffuser, set up at the blade tip, is employed to control the blade tip vortex. The results show that the vortex diffuser can increase the total pressure coefficient of the core of the vortex, decrease the strength of the blade tip vortex, lower the noise, and improve the efficiency of the blade.  相似文献   

17.
运用了基于相场描述的拓扑优化方法,来寻找在拉伸和压缩中表现出不对称强度行为的连续体结构的最优布局。依据Drucker-Prager屈服准则和幂率插值方案,优化问题可以描述为在局部应力约束下的最小化结构的体积。用qp放松法来解决应力约束的奇异性,并采用基于P-norm函数的聚合方法对应力约束进行凝聚,该方法实现了约束个数的降低,同时引入了稳定转化法来处理大量的局部应力约束和高度非线性的应力行为,以修正应力,提高优化收敛的稳定性。在优化问题求解时,使用拉格朗日乘子法对目标函数和应力约束进行处理。利用伴随变量法进行灵敏度分析,并通过求解Allen-Cahn方程更新相场函数设计变量。数值算例证明了该优化模型和相应数值技术的有效性,相关算例还揭示了考虑拉压不同强度和考虑同拉压强度约束时得到的结构优化拓扑构型具有显著的差异。  相似文献   

18.
风力机通常运行在非定常工况中,其气动性能及尾迹会随着工况的变化而变化. 风剪切是风力机长期所处的环境,它会影响到叶片气动载荷、尾迹形状、总体性能等,分析风剪切作用下的叶片气动性能对风力机的设计有重要意义.本文采用一种时间步进自由涡尾迹(free vortex wake, FVW)方法,耦合FVW方法与风剪切模型,计算不同风剪切因子作用下叶片的气动力系数、推力以及风轮后的尾迹形状变化,研究尾迹形状变化对风轮旋转平面诱导速度及风力机叶片气动性能的影响. 结果表明:在风剪切入流条件下, 随着风剪切因子的增大,风力机的气动力系数随时间做周期性波动的幅度加剧, 推力的平均值逐渐减小,尾迹倾斜程度增大, 尾迹在轮毂下方的倾斜程度更明显;尾迹形状的变化使风轮平面轴向诱导速度因子分布不均匀,同时使风力机的总体性能降低且偏离较大;倾斜尾迹相比于对称尾迹对风轮平面处的诱导影响有明显差别, 波动幅值增大,气动力系数在波谷处的偏差比波峰处大. 尾迹越倾斜,风轮旋转平面处的载荷不对称性越明显.   相似文献   

19.
Determination of the aerodynamic configuration of wake is the key to analysis and evaluation of the rotor aerodynamic characteristics of a horizontal-axis wind turbine.According to the aerodynamic configuration, the real magnitude and direction of the onflow velocity at the rotor blade can be determined, and subsequently, the aerodynamic force on the rotor can be determined. The commonly employed wake aerodynamic models are of the cylindrical form instead of the actual expanding one. This is because the influence of the radial component of the induced velocity on the wake configuration is neglected. Therefore, this model should be called a "linear model". Using this model means that the induced velocities at the rotor blades and aerodynamic loads on them would be inexact. An approximately accurate approach is proposed in this paper to determine the so-called "nonlinear" wake aerodynamic configuration by means of the potential theory,where the influence of all three coordinate components of the induced velocity on wake aerodynamic configuration is taken into account to obtain a kind of expanding wake that approximately looks like an actual one. First, the rotor aerodynamic model composed of axial(central), bound, and trailing vortexes is established with the help of the finite aspect wing theory. Then, the Biot-Savart formula for the potential flow theory is used to derive a set of integral equations to evaluate the three components of the induced velocity at any point within the wake. The numerical solution to the integral equations is found,and the loci of all elementary trailing vortex filaments behind the rotor are determined thereafter. Finally, to formulate an actual wind turbine rotor, using the nonlinear wake model, the induced velocity everywhere in the wake, especially that at the rotor blade,is obtained in the case of various tip speed ratios and compared with the wake boundary in a neutral atmospheric boundary layer. Hereby, some useful and referential conclusions are offered for the aerodynamic computation and design of the rotor of the horizontal-axis wind turbine.  相似文献   

20.
A numerical finite-volume solution of Euler equations is performed in the meridional plane of complete axial flow turbomachinery. The throughflow equations contain blade force terms that model the effects of the real blades on the flow and are resolved by further equations. Under the axisymmetric flow assumption, incidence involves a discontinuity through the leading edge, which introduces strong unphysical losses. Incidence is modeled by solving an inverse problem in the front part of the bladed region. The inverse method provides the geometry of the throughflow surface that replaces the discontinuous profile of swirl velocity with a specified, conveniently smooth profile across the leading edge region. The specified velocity profile and computed ideal geometry are used to update the blade force. The Euler solution is compared to a streamline curvature solution in analyzing a three-stage turbine. In the design condition with up to 2° of spanwise-averaged incidence, the method does not significantly affect the prediction of overall performance. In a strong off-design condition with up to 13° of average incidence, performance is predicted with the same accuracy as in the design case.  相似文献   

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