MHD flow and heat transfer over permeable stretching sheet with slip conditions

The magnetohydrodynamic (MHD) flow and heat transfer characteristics for the boundary layer flow over a permeable stretching sheet are considered. Velocity and thermal slip conditions are taken into account. Problem formulation is developed in the presence of thermal radiation. Governing non‐linear problem is solved by a homotopy analysis method. Convergence of the derived solutions is studied. Numerical values of skin‐friction coefficient and local Nusselt number are tabulated. Effects of pertinent parameters on the velocity and temperature profiles are discussed. Comparison between the present and previous limiting results is shown. Copyright © 2010 John Wiley & Sons, Ltd.     

Unsteady shrinking sheet with mass transfer in a rotating fluid

In this paper, the problem of unsteady flow induced by a shrinking sheet with mass transfer in a rotating fluid is studied. The transformed boundary layer equations are solved numerically by an implicit finite‐difference scheme known as the Keller‐box method. The influence of rotation, unsteadiness and mass suction parameters on the reduced skin friction coefficients f″(0) and g′(0), as well as the lateral velocity and velocity profiles are presented and discussed in detail. Copyright © 2010 John Wiley & Sons, Ltd.     

Unsteady CFD computations using vertex‐centered finite volumes for unstructured grids on Graphics Processing Units

This paper presents a Navier–Stokes solver for steady and unsteady turbulent flows on unstructured/hybrid grids, with triangular and quadrilateral elements, which was implemented to run on Graphics Processing Units (GPUs). The paper focuses on programming issues for efficiently porting the CPU code to the GPU, using the CUDA language. Compared with cell‐centered schemes, the use of a vertex‐centered finite volume scheme on unstructured grids increases the programming complexity since the number of nodes connected by edge to any other node might vary a lot. Thus, delicate GPU memory handling is absolutely necessary in order to maximize the speed‐up of the GPU implementation with respect to the Fortran code running on a single CPU core. The developed GPU‐enabled code is used to numerically study steady and unsteady flows around the supercritical airfoil OAT15A, by laying emphasis on the transonic buffet phenomenon. The computations were carried out on NVIDIA's Ge‐Force GTX 285 graphics cards and speed‐ups up to ～46 × (on a single GPU, with double precision arithmetic) are reported. Copyright © 2010 John Wiley & Sons, Ltd.     

Robust airfoil optimization based on improved particle swarm optimization method

A robust airfoil optimization platform is constructed based on the modified particle swarm optimization method (i.e., the second-order oscillating particle swarm method), which consists of an efficient optimization algorithm, a precise aerodynamic analysis program, a high accuracy surrogate model, and a classical airfoil parametric method. There are two improvements for the modified particle swarm method compared with the standard particle swarm method. First, the particle velocity is represented by the combination of the particle position and the variation of position, which makes the particle swarm algorithm a second-order precision method with respect to the particle position. Second, for the sake of adding diversity to the swarm and enlarging the parameter searching domain to improve the global convergence performance of the algorithm, an oscillating term is introduced to the update formula of the particle velocity. At last, taking two airfoils as examples, the aerodynamic shapes are optimized on this optimization platform. It is shown from the optimization results that the aerodynamic characteristic of the airfoils is greatly improved in a broad design range.     

Computation of two‐dimensional flows past ram‐air parachutes

Computational results for flow past a two‐dimensional model of a ram‐air parachute with leading edge cut are presented. Both laminar (Re=10⁴) and turbulent (Re=10⁶) flows are computed. A well‐proven stabilized finite element method (FEM), which has been applied to various flow problems earlier, is utilized to solve the incompressible Navier–Stokes equations in the primitive variables formulation. The Baldwin–Lomax model is employed for turbulence closure. Turbulent flow computations past a Clarck‐Y airfoil without a leading edge cut, for α=7.5°, result in an attached flow. The leading edge cut causes the flow to become unsteady and leads to a significant loss in lift and an increase in drag. The flow inside the parafoil cell remains almost stagnant, resulting in a high value of pressure, which is responsible for giving the parafoil its shape. The value of the lift‐to‐drag ratio obtained with the present computations is in good agreement with those reported in the literature. The effect of the size and location of the leading edge cut is studied. It is found that the flow on the upper surface of the parafoil is fairly insensitive to the configuration of the cut. However, the flow quality on the lower surface improves as the leading edge cut becomes smaller. The lift‐to‐drag ratio for various configurations of the leading edge cut varies between 3.4 and 5.8. It is observed that even though the time histories of the aerodynamic coefficients from the laminar and turbulent flow computations are quite different, their time‐averaged values are quite similar. Copyright © 2001 John Wiley & Sons, Ltd.     

结构的全过程设计优化

建立了结构生命期内的设计优化模型。根据该模型,不仅可以得到结构的最优设计－维修策略,而且可以得以结构的寿命期。对在役结构,给出当前结构的剩余承载力,模型将给出结构以后的最优维修决策。该模型的优点在于理论简单易懂,计算方便,便于实际应用。     

Optimization of travelling wave ultrasonic motors using a three-dimensional analysis of the contact mechanism at the stator–rotor interface

The present paper investigates optimization rules and new design methodologies dealing with the contact mechanics in rotative travelling wave ultrasonic motors (TWUM). The proposed approaches focus on the design of the rotor, including the friction layer that is usually deposited onto its lower surface, while the stator is supposed to be preliminary designed. Contact aspects such as the transmission of mechanical power as well as the wear mechanism of the friction layer are investigated, according to the analysis of the stator–rotor contact mechanics in both hoop and radial directions. Considering a classical wear criterion in a preliminary step, a contact ratio, that allows the mechanical power to be optimized, is pointed out in the hoop direction. In a further step, the contact conditions in the radial direction are improved through the elastic fitting of the stator and rotor radial deflexions, therefore allowing the material's wear to be decreased. Some experimental tests, that have been recently performed, give a comparison of wear marks, which occur onto optimal and non-optimal rotor geometries. A first mechanism synthesis is finally proposed in such a way to allow the mechanical architecture of the rotor (including the friction layer) to be automatically designed according to a given set of mechanical constraints.     

锚杆支护的神经网络设计系统及其应用

本文简要地概括了锚杆支护设计理论存在的局限性。强调锚杆支护理论应用必须考虑地下工程的类型。为此,作者将地下工程划分为3类,指出每一类地下工程特性及其支护设计应遵循的准则,第3类采场巷道工程的锚杆支护设计应以工程类比和设计经验为主;并介绍了作者已经开发的锚杆支护神经网络设计系统。     

A general approach for computing unsteady 3D thin lifting and/or propulsive systems derived from a complete theory

This paper presents the basis of a numerical method for unsteady aerodynamic computation around thin lifting and/or propulsive systems with arbitrary variable geometries, involving the velocity field, the velocity potential, the pressure field and the wake characteristics (geometry and vortex strength). Most of the corresponding theory actually stems from the unsteady wake model established by Mudry, in which the wake is considered to be a median layer, characterized by a pair of functions on which Mudry founded the concept of continuous vortex particle. The governing relations of the continuous problem are then the flow tangency condition, the wake integro‐differential evolution equation, and a flow regularity condition at the trailing edge. This constitutes a rigorous and complete theoretical formulation of this problem, from which a discretization scheme and a numerical method of solution are derived. The view of the vortex wake is similar to the one in the classical vortex lattice approaches, but uses a discrete vortex particle concept, particularly well suited for the prediction of the unsteady wake deformation. This, together with the continuous theory, ensures the computing method compares favorably with the classical methods in terms of flexibility and computing costs. In order to demonstrate the capabilities of the present method, the calculation of flapping wings of variable geometry is also presented. Copyright © 1999 John Wiley & Sons, Ltd.     

基于区间的不确定多目标优化方法研究

基于非线性区间优化,提出了一种不确定多目标优化方法.基于区间序关系和区间可能度,把不确定多目标的目标函数和约束转化为确定性的目标函数和确定性的约束.对于复杂的工程优化问题,为了提高效率,采用拉丁方试验设计方法,构建响应面近似模型,并基于近似模型进行不确定多目标优化,从而形成了非线性区间优化方法与近似模型相结合的高效不确定多目标优化方法.数值算例表明了该方法的有效性和工程实用性.