Applied Mechanics and Materials Vols. 477-478

Abstract: Bi-directional Flying Wing (BFW) is a new supersonic civil transport shape concept that aims to meet the conflict requirements of high speed cruise and low speed take-off/landing missions. In this paper the Class-Shape-Transformation (CST) shape parameterization method is modified to represent the BFW shape, and new basis functions suitable for the BFW airfoil representation are constructed. The Far-field Composite Element (FCE) wave drag optimization is performed on both the flat bottom and symmetric BFW configurations, and the drag reduction effects and result precision are surveyed. It is suggested that significant wave drag reduction can be achieved by the FCE optimization for both the flat bottom and the symmetric BFW configurations. The wave drag coefficients with sufficient precision can be obtained in the FCE optimization of the symmetric configuration; while the FCE optimization results of the flat bottom one are not accurate enough.

Abstract: The fractional calculus approach has been taken into account in the Darcys law and the constitutive relationship of fluid model. Based on a modified Darcys law for a viscoelastic fluid, Stokes first problem is considered for a generalized Jeffreys fluid in a porous half space. By using the Fourier sine transform and the Laplace transform, two forms of exact solutions of Stokes first problem for a generalized Jeffreys fluid in the porous half space are obtained in term of generalized Mittag-Leffler function, and one of them is presented as the sum of the similar Newtonian solution and the corresponding non-Newtonian contributions. As the limiting cases, solutions of the Stokes first problem for the generalized second fluid, the fractional Maxwell fluid and the Newtonian fluid in the porous half space are also obtained.

Abstract: Linearized potential wave theory is applied to calculate the wave exciting loads on a CALM buoy in water of finite depth. The solution is based on the domain decomposition method and the unknown constants in the velocity potentials are determined by matched eigenfunction expansions. A comparison of the analytical solution with published experimental results on a vertical truncated cylinder is performed as part of the validation process. The effects of the disk on the wave exciting forces are discussed.

Abstract: This study establishes three-dimensional numerical wave tank based on the theory of viscous flow to simulate the unsteady motion response of a Wigley advancing in regular heading waves. The governing equations, Reynolds Averaged Navier-Stokes and continuity equations are discretized by finite volume method, a Reynolds-averaged NavierStokes solver is employed to predict the motions of ship, and volume of fluid method is adopted to capture the nonlinear free surface by writing user-defined functions. The outgoing waves are dissipated inside an artificial damping zone located at the rear part (about 1-2 wave lengths) of the wave tank. The numerical simulation results are compared with theoretical and experimental data from Delft University of Technology, and show good agreement with them. This research can be used to further analyze and predict hydrodynamic performance of ship and marine floating structures in waves and help to extend the applications of numerical wave tank.

Abstract: The physical phenomena of vortex suppression and flow patterns by deploying a very mall control cylinder in the near wake region of a main cylinder in low Reynolds numbers is studied numerically. The control diameter effect on vortex suppression and three flow patterns has been studied. The results shows the control cylinder can reduce vortex shedding frequency and suppress shedding partially or completely dependent on the diameter of control cylinder and Reynolds number. The results of a cylinder with control and without control agree with experimental and numerical studies.

Abstract: The magnetostriction-induced cavitation flow was numerically simulated by using a full cavitation model with the SST k-ω turbulence model and the dynamic mesh technique. The characteristics of ultrasonic cavitation flow and the cavitation erosion mechanism were revealed. The computational results show that the pressure fluctuation possesses the characteristics of pulse on the specimen. Intense pressure pluses and cavitation occur in the local flow adjacent to the specimen. As numerous bubbles collapse, intense pressure pulses form on the specimen. Cavitation intensity is serious at the center while it is slight at the edge. The pressure pulse and the vapor volumn fraction with the equal magnitude symmetrically distribute around the center, meaning that cavitatin erosion appears a symmetrical pattern around the center. The effective pressure fluctuation occurs in the local flow field within the distance of one third of the wave length to the specimen. It is validated that the wave energy dissipates very fast in the magnetostriction-induced cavitation flow.

Abstract: Aerodynamic characteristic analysis of hypersonic cruise aircraft is more difficult than that of conventional aircraft, for the complex flow field simulation and inadequate amount of results under limited flight conditions. In this paper, numerical schemes applicable for hypersonic flow field are adopted to acquire a set of aerodynamic characteristics of a typical hypersonic cruise aircraft as sample data, based on which response surface models (RSM) are constructed to provide approximation of aerodynamic characteristics under any flight conditions within the design domain, finally the overall approximation performance of the response surface models are analyzed.

Abstract: An immersed boundary method based on the ghost-cell approach is presented in this paper. The compressible Navier-Stokes equations are discretized using a flux-splitting method for inviscid fluxes and second-order central-difference for the viscous components. High-order accuracy is achieved by using weighted essentially non-oscillatory (WENO) and Runge-Kutta schemes. Boundary conditions are reconstructed by a serial of linear interpolation and inverse distance weighting interpolation of flow variables in fluid domain. Two classic flow problems (flow over a circular cylinder, and a NACA 0012 airfoil) are simulated using the present immersed boundary method, and the predictions show good agreement with previous computational results.

Abstract: There are many applications in marine engineering where two or more floating vessels are in close proximity. Probably the most significant one is related to the offshore installation engineering. On the background of the upper module installation operation of spar platform, this paper investigates the hydrodynamic interaction effects of multiple floating bodies in offshore installation engineering. The numerical simulation bases on the 3-D frequency domain linear potential theory. The calculations are carried out for the crane ship, the transport ship and the spar platform. Finally the best environmental parameters and the relative position of floating bodies are selected, which can provide good advice on installation operation scheme design.

Abstract: Based on the Lagrange finite element method, a simplified computational technique for sliding interface in oblique penetration is proposed in the paper. By applying the 3D finite element program developed on this technique to numerical analog computation of ogive-noded steel rod penetrating in the aluminum target, a result which is consistent with that of A.J.Piekutowskis experiment can be reached. Hence it proves the rationality and validity of the program and method discussed in this paper and that the method is useful in the numerical study of penetration and perforation.