带有环形阀片的阻尼阀可靠性研究

针对跑车试验时油气弹簧中节流阀片受冲击失效的现象,提出了研究阻尼阀水击压强的必要性,建立了带有环形节流阀片的阻尼阀物理模型. 运用水击理论及解偏微分方程的特征线法,创造性地对给定阻尼阀结构进行了水击建模计算. 编程分析节流阀片失效的原因,系统研究了常通孔结构参数变化对阻尼阀所受瞬态冲击及其阻力值的影响规律,提出需从屈服和疲劳强度两个方面入手对阀门可靠性进行校核,并给出计算实例,完善了现有阀系设计的算法. 所得结论可以作为可靠性研究的参考,同时避免了阀片断裂的再次发生.      

高温流体与变物性固体耦合系统温度场及热变形的数值计算

在腔体内部有高温流体,其外壳等固体材料的物性温度而为化的瞬态非线性问题中,其边界条件的确定十分困难。本文采用流一固“混合流”模式进行温度场的计算,由于方程计及了瞬态、复杂形状、浮动外边界条件等因系,采用变步长的控制容积法及时域有限元进行计算。对某个高温燃气配气阀的温度场及热变形进行了数值计算,得到与实测相符的结果。     

VIBRO-ACOUSTIC BEHAVIOR OF SUBMERGED CYLINDRICAL SHELLS: ANALYTICAL FORMULATION AND NUMERICAL MODEL

We propose both an analytical formulation and a numerical model to study the hydroelastic or vibroacoustic behaviour of cylindrical thin shells immersed in an unbounded, inviscid and heavy fluid. The analytical solution allows us to calculate the dynamic response and the pressure radiated in the far field by a baffled cylinder. This formulation uses the truncated modal basis of the dry structure to expand the displacements of the submerged shell. The analytical model is used as a reference in order to validate a numerical model which couples the finite element method (FEM) to the boundary element method (BEM). As opposed to the analytical formulation which is dedicated to baffled circular cylinders only, the numerical model allows us to treat any axisymmetric shell, such as cylindrical and spherical shells, or more complex shells of revolution. The structure is idealized by two-node ring finite elements and the boundary equation is solved using the method of singularities.     

Adaptive nodeless variable finite elements with flux-based formulation for thermal–structural analysis

A nodeless variable element method with the fluxbased formulation is developed to analyze two-dimensional thermal-structural problems. The nodeless variable formula- tion provides accurate temperature distributions to yield more accurate thermal stress solutions. The flux-based formulation is used 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 generate finite element meshes that can adapt and move along with the transient solution behavior. A version of a nearly optimal element size determination is proposed to provide high convergence rate of the predicted solutions. The combined procedure is evaluated by solving several thermal, structural, and thermal stress problems.     

Coupled thermoelasticity of functionally graded cylindrical shells

The coupled thermoelastic response of a functionally graded circular cylindrical shell is studied. The coupled thermoelastic and the energy equations are simultaneously solved for a functionally graded axisymmetric cylindrical shell subjected to thermal shock load. A second-order shear deformation shell theory that accounts for the transverse shear strains and rotations is considered. Including the thermo-mechanical coupling and rotary inertia, a Galerkin finite element formulation in space domain and the Laplace transform in time domain are used to formulate the problem. The inverse Laplace transform is obtained using a numerical algorithm. The shell is graded through the thickness assuming a volume fraction of metal and ceramic, using a power law distribution. The results are validated with the known data in the literature.     

Friction relaxation model for fast transient flows application to water hammer in two-phase flow – The WAHA code

The paper deals with the problem of the wall shear stress during rapid transient 1D flows in a piping system caused by water hammers in two-phase flow induced by a fast valve closure. The evolution of the transient wall shear stress is interpreted in terms of two steps. The first step is a sudden and dramatic change of the wall shear stress due to the passage of the pressure wave. The second step is a relaxation process of the shear stress which is modeled from the Extended Irreversible Thermodynamics theory. The friction relaxation model (FRM) presented in the first part of this paper describes both steps of the evolution of the wall shear stress during water hammers. The second part of the paper deals with the application of the FRM model as a closure law in the WAHA code. The main purpose of the WAHA code is to predict various situations relative to single- and two-phase water hammer transients in piping systems. The last part of the paper deals with the simulation of several cases from the UMSICHT databank using the adapted WAHA computer code with the FRM model. The results of these simulations are systematically compared with the experimental data. It is concluded that the new FRM model has a clear effect on water hammer pressure wave damping and on the pressure wave propagation velocity.     

Transient heat conduction in two-dimensional functionally graded hollow cylinder with finite length

In this paper a thick hollow cylinder with finite length made of two dimensional functionally graded material (2D-FGM) subjected to transient thermal boundary conditions is considered. The volume fraction distribution of materials, geometry and thermal boundary conditions are assumed to be axisymmetric but not uniform along the axial direction. The finite element method with graded material properties within each element is used to model the structure and the Crank–Nicolson finite difference method is implemented to solve time dependent equations of the heat transfer problem. Two-dimensional heat conduction in the cylinder is considered and variation of temperature with time as well as temperature distribution through the cylinder are investigated. Effects of variation of material distribution in two radial and axial directions on the temperature distribution and time response are studied. The achieved results show that using two-dimensional FGM leads to a more flexible design so that transient temperature, maximum amplitude and uniformity of temperature distributions can be modified to achieve required specifications by selecting a suitable material distribution profile in two directions.     

黏弹性管道水柱分离弥合水锤有限体积法模型

基于有限体积法二阶Godunov求解格式对黏弹性输水管道中水柱分离弥合现象进行建模和模拟研究. 在传统的弹性管道模型基础上考虑管道黏弹性效应的影响. 在瞬变流控制方程中引入管道黏弹性项和动态摩阻项, 采用有限体积法进行求解, 考虑压力修正系数来模拟自由气体对计算单元的影响, 同时为避免数值模拟结果产生虚假震荡引入斜率限制器MINMOD函数; 通过虚拟单元法进行边界构建, 实现了计算区域的统一计算. 将所建模型计算结果与已有模型结果、试验结果进行对比, 并对影响模型的各参数进行敏感性分析. 结果表明, 本文模型能够准确模拟出纯水锤、水柱分离弥合水锤两种情况下的瞬态压力变化, 均能与试验数据高度吻合; 与传统的特征线方法相比, 当库朗数C_r小于1时, 有限体积法二阶Godunov格式计算结果更准确、稳定; 在压力波动的衰减过程中, 黏弹性效应相比于管道摩阻起主导作用; 与弹性管道模型相比, 考虑管道黏弹性效应后可显著提高模拟结果的准确性, 尤其是压力波峰值的相对误差明显降低.      

圆管流动水击压力波测量及水力计算

为探索水击现象的物理过程和机理,研制了自循环定常流动管路瞬态特性计算机控制试验装置,并利用该装置进行圆管流动水击压力波实验测量。用12只扩散硅压力传感器测定圆管流动水击压力波瞬态分布及最大、最小压力值,由试验数据拟合出水击波波形,揭示了水击压力波传播方式、特性及衰减规律。通过分析随机捕捉测量技术方法,理论上推断出测量数据达到可信精度。在归纳分析试验数据基础上,得出最大压力随关阀时间的关系曲线,对圆管流动直接水击等概念进行了探讨,用数值分析方法拟合出水击最大压力水力计算修正方程式。     

Nonlinear axisymmetric deformations of an elastic tube under external pressure

The problem of the finite axisymmetric deformation of a thick-walled circular cylindrical elastic tube subject to pressure on its external lateral boundaries and zero displacement on its ends is formulated for an incompressible isotropic neo-Hookean material. The formulation is fully nonlinear and can accommodate large strains and large displacements. The governing system of nonlinear partial differential equations is derived and then solved numerically using the C++ based object-oriented finite element library Libmesh. The weighted residual-Galerkin method and the Newton-Krylov nonlinear solver are adopted for solving the governing equations. Since the nonlinear problem is highly sensitive to small changes in the numerical scheme, convergence was obtained only when the analytical Jacobian matrix was used. A Lagrangian mesh is used to discretize the governing partial differential equations. Results are presented for different parameters, such as wall thickness and aspect ratio, and comparison is made with the corresponding linear elasticity formulation of the problem, the results of which agree with those of the nonlinear formulation only for small external pressure. Not surprisingly, the nonlinear results depart significantly from the linear ones for larger values of the pressure and when the strains in the tube wall become large. Typical nonlinear characteristics exhibited are the “corner bulging” of short tubes, and multiple modes of deformation for longer tubes.     

基于有限体积水锤方程的Godunov格式离散

基于有限体积法建立了管道瞬变流的离散格式,采用特征分解技术计算界面通量,并通过重构和通量限制建立二阶精度的TVD格式。此格式保证了质量和动量的守恒性,物理意义明确,计算速度快,适用范围广。通过Riemann问题算例、水锤实例和各种阀门组合情况下的管网水锤实例验证了格式具有高分辨率、无虚假振荡和对克朗数灵敏度低等优点。     

A time-domain high-order spectral finite element for the simulation of symmetric and anti-symmetric guided waves in laminated composite strips

A time domain spectral finite element is developed for improving the efficiency of numerical simulations of guided waves in laminated composite strips. The finite element relies on a new generalized laminate mechanics model formulated to represent symmetric and anti-symmetric Lamb waves. The laminate mechanics incorporate third-order polynomial terms for the approximation of axial and transverse displacement fields through the thickness and consider the displacements of the upper and lower surfaces as degrees of freedom. The laminate theory formulation is easily expanded to a high-order layerwise model. Based on the resultant governing equations of the laminate section, a new finite element with 8 nodal degrees of freedom is formulated; its nodes are collocated with Gauss–Lobatto–Legendre integration points in order to improve computational efficiency. Stiffness and mass matrices are assembled and the transient response is predicted using the explicit central differences time integration scheme. The transient response of Aluminum, Carbon Fiber Reinforced Polymer laminated and sandwich strips is investigated. Numerical results are validated against a semi-analytical solution. The accuracy and computational efficiency of the introduced element regarding the prediction of symmetric and anti-symmetric wave propagation is also quantified.     

内衬涂塑预应力钢筒混凝土管应力分析

传统预应力钢筒混凝土管(prestressed concrete cylinder pipe,PCCP)容易开裂、预应力丝锈蚀而爆管失效.提出了耐腐蚀内衬涂塑钢筒预应力混凝土管(prestressed concrete cylinder pipe with plastic,PCCP-P),建立了PCCP-P线弹性轴对称分层圆筒平面应变模型,考虑预应力引起的内部径向压力,针对喷射砂浆保护层在管道预制阶段不受力以及缠丝、运行阶段混凝土弹性模量不同的特点,对PCCP-P分阶段进行分析,得到各结构层的应力解析解,并建立有限元模型进行验证.本研究可为PCCP-P和传统PCCP设计提供依据.     

有限长圆柱壳中轴对称弹性瞬态波

有限长的计及剪切变形和转动惯性的弹性圆柱壳的轴对称运动方程经过Laplace变换后转化为一组相空间中的方程。对该方程组作了一些适当的处理后,应用广义射线法,得到了相空间中位移和内力的射线法表达式。采用快速Fourier变换作Laplacl逆变换,即可得到圆柱壳受轴对称冲击载荷时的弹性瞬态波解。     

Finite element analysis of the viscous flow in a vaned radial diffuser

A new finite element method was used to analyze an experimental model of a radial vaned diffuser. The new method includes a streamline upwind formulation for the advection terms in the governing equations. The streamline upwind significantly reduces numerical diffusion while maintaining the stability of the conventional upwind formulation. The new finite element method also incorporates an iterative equal-order, velocity-pressure solution method based on the well-known SIMPLER algorithm. The results of the analysis are compared to flow visualization studies of the experimental model. The flow separation point for the four blade diffuser was predicted to occur at 19, 6% of the blade length from the leading edge. The experimentally determined value was 23% of the blade length. For the eight blade diffuser model, separation was predicted to occur at 43% of the blade length from the leading edge, as compared to the experimentally observed value of 50% of the blade length. With this performance comparison, the proposed finite element method has been demonstrated to be reliable for predicting complex fluid flows.     

含复合铠装层的非黏结柔性立管轴对称载荷响应

针对新型含复合材料铠装层的非黏结柔性立管,推导了各向异性复合材料拉力铠装层在内、外压和轴拉力作用下的控制方程,且考虑了载荷作用下可能出现的层间间隙,建立了非黏结柔性立管的轴对称载荷响应模型。采用循环验证算法求解,获得了管道的抗拉刚度、抗扭刚度、层间压力、层间间隙等重要参数。建立了有限元仿真模型,验证了理论模型的可靠性。算例研究表明:层间间隙出现在螺旋层与圆筒层之间,不考虑间隙时,抗拉刚度的预测值较高;相较于传统的钢质铠装层柔性管,复合铠装层管的抗拉刚度以及抗扭刚度均更大,且抗拉刚度随着管外压力增大而降低程度更小,复合铠装层在柔性立管的应用中能够达到铠装层的刚度性能要求。     

Higher order spectral/hp finite element models of the Navier–Stokes equations

In this paper, we present higher order least-squares finite element formulations for viscous, incompressible, isothermal Navier–Stokes equations using spectral/hp basis functions. The second-order Navier–Stokes equations are recast as first-order system of equations using stresses as auxiliary variables. Both steady-state and transient problems are considered. For a better coupling of pressure and velocity, especially in transient flows, an iterative penalisation strategy is employed. The outflow-type boundary conditions are applied in a weak sense through the least-squares functional. The formulation is verified by solving various benchmark problems like the lid-driven cavity, backward-facing step and flow over cylinder problems using direct serial solver UMFPACK.     

Adaptive finite element methods for high-speed compressible flows

We describe an adaptive finite element algorithm for solving the unsteady Euler equations. The finite element algorithm is based on a Taylor/Galerkin formulation and uses a very fast and efficient data structure to refine and unrefine the grid in order to optimize the approximation. We give a general version of the method which can be applied to moving grids with sliding interfaces and we present the results for a transient supersonic calculation of rotor-stator interaction.     

Finite element solutions of axisymmetric Euler equations for an incompressible and inviscid fluid

In this paper we present a finite element method for the numerical solution of axisymmetric flows. The governing equations of the flow are the axisymmetric Euler equations. We use a streamfunction angular velocity and vorticity formulation of these equations, and we consider the non-stationary and the stationary problems. For industrial applications we have developed a general model which computes the flow past an annular aerofoil and a duct propeller. It is able to take into account jumps of angular velocity and vorticiy in order to model the flow in the presence of a propeller. Moreover, we compute the complete flow around the after-body of a ship and the interaction between a ducted propeller and the stern. In the stationary case we have developed a simple and efficient version of the characteristics/finite element method. Numerical tests have shown that this last method leads to a very fast solver for the Euler equations. The numerical results are in good agreement with experimental data.