Shigehiro Sakamoto

Simulation of multi-dimensional non-gaussian non-stationary random fields

Abstract This paper presents a method for simulating multi-dimensional stochastic processes. The target process is specified by its marginal density function which can vary along the indexing set, and by its two point correlation function, which need not be stationary. The polynomial chaos expansion is used to match the marginal densities while the Karhunen–Loeve representation is used to fine tune the match of the correlation function. The resulting representation of the process is in the form of a polynomial chaos expansion, which can be readily realized.

Numerical study on velocity-pressure field and wind forces for bluff bodies by κ-ϵ, ASM and LES

Abstract Velocity-pressure fields and wind-induced forces on and around a building model are analyzed by means of numerical simulations. In this study, three types of well-known turbulrnce models, namely κ-ϵ Eddy Viscosity Model (κ—ϵ EVM), Algebraic Stress Model (ASM) and Large Eddy Simulation (LES) are used. In the first half of the paper, three-dimensional (3D), time-averaged flowfields around a cube within a surface boundary layer are predicted using these three turbulence models with similar boundary conditions. The accuracy of these simulations is assessed by comparison with results of wind tunnel tests. The results of LES show the best agreement with the experimental data. In the latter part, unsteady flowfield around a square prism is predicted by LES. Results of 2D and 3D computations are compared with experimental data. It is confirmed that the results of the 3D computation correspond very well to the experimental ones, while the results of the 2D computation include some significant discepancies.

Numerical prediction of wind loading on buildings and structures : Activities of AIJ cooperative project on CFD

This study presents the activities of the Architectural Institute of Japan (AIJ) concerning the Computational Fluid Dynamics (CFD) for a numerical prediction of wind loading on buildings and structures. In the AIJ project, the flows and the pressures around a low-rise building (breadth : depth : height = 1 : 1 : 0.5) have been computed by 10 members of the working group, who mainly employed the κ-e model or the large eddy simulation for turbulent flows. Here, on the basis of the results of the AIJ project, future subjects for further development of the CFD technique are discussed. Also we present how to find the way to realize the practical use of the CFD technique on prediction of wind loading.

Numerical study on flow past 2D square cylinder by Large Eddy Simulation: Comparison between 2D and 3D computations

The unsteady flowfield past a two-dimensional(2D) square cylinder at Re=1.0 × 105 is predicted by Large Eddy Simulation(LES). Results of two-dimensional (2D) and three-dimensional(3D) computations are compared with results of previous experiments[1–4]. It is confirmed that the LES results based on 3D computation correspond very well with the experimental results, but the LES results based on 2D computation are different from those based on 3D computation as well as those based on experiments. Distributions of mean vorticity, vorticity fluctuations and turbulence terms in the mean vorticity equation are discussed in order to examine structural difference between the results of 2D and 3D LES computations.

CFD analysis of wind-structure interaction for oscillating square cylinders

Abstract This paper deals with the interaction between fluid and body, i.e., the flowfields around oscillating square cylinders both in cases of forced oscillation and wind-induced free oscillation. Computations are based on three-dimensional (3D) LES using the standard Smagorinsky sub-grid scale model to describe the unsteady pressure fields. A very simple procedure to incorporate the influence of body motion on the flowfield is used. The accuracy of the computations using this procedure is made clear by comparing them with the experimental results of Bearman et al. [J. Fluid. Mech. 119 (1982) 297–321] and Nakamura et al. [J. Eng. Mech. Div. ASCE No. EM6 (1975) 855–871].

Unsteady pressure field around oscillating prism predicted by LES

Abstract Unsteady velocity-pressure fields around an oscillating square prism are analyzed by means of Large Eddy Simulation (LES). The accuracy of the numerical results is assessed by comparing them with the experimental results of Bearman et al.[3]. The prism is forced to oscillate in a sinusoidal motion in the x2 (lateral) direction. In order to incorporate the influence of the body motion, an inertia force term, whose magnitude is equal to the acceleration of the body, but with the opposite sign, is added to the transport equation of u 2 , as an external force at each grid point of the fluid. The reduced velocity, Uo/NpD, in this study ranges from 7.5 to 10.0. It was confirmed that the numerical results successfully reproduce the lock-in phenomena in this range. Furthermore, the results of LES showed a good agreement with the results of experiment, in terms of: 1. 1) the phase angle between the displacement of the oscillating prism and the negative pressure acting on the side face, and 2. 2) the correlation between pressures across the side face.