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Based on overset grid method, the problems about flow past circular cylinder were numerically studied, which include the flow around a single circular cylinder at Reynolds number Re=100 and Reynolds number Re=200, the flow past two tandem circular cylinders at Reynolds number Re=200 and dimensionless distance g * =4, and the flow around a lateral oscillating circular cylinder at Reynolds number Re=200. Overset grid method is effective in dealing with the problems of flow over multi-body and flow with moving boundaries. This grid method couple overlapping regions in an arbitrary manner through flow field information updating over acceptor cells in one region suing its donor cells in another region. The computed drag coefficient and lift coefficients of the circular cylinder, vortical structure in the flow wake and vortex shedding P+S mode are agreed well with the results in previous experiment investigations and numerical simulations.

Aquatic and aerial animals have developed their superior and complete mechanisms of swimming and flight. These mechanisms bring excellent locomotion performances to natural creatures, including high efficiency, long endurance ability, high maneuverability and low noise, and can potentially provide inspiration for the design of the man-made vehicles. As an efficient research approach, numerical modeling becomes more and more important in studying the mechanisms of swimming and flight. This review is focused on assessing the recent progress in numerical techniques of solving animal swimming and flight problems. According to the complexity of the problems considered, numerical studies are classified into five stages, of which the main characteristics and the numerical strategies are described and discussed. In addition, the body-conformal mesh, Cartesian-mesh, overset-grid, and meshfree methods are briefly introduced. Finally, several open issues in numerical modeling in this field are highlighted.

[...]when the gear rotates, the gear surface has a very complicated movement, which is becoming an important problem in CFD analysis. When the male rotor rotates by φ around the female rotor, the male rotor is rotated by θ (θ=Rf+RmRmφ) in the x-y plane. [...]the conversion formula of the x-y and u-v coordinate systems is defined in Equation (1) [13,14]: [xy]=[(Rf+Rm)cosφ(Rf+Rm)sinφ]+[cosθ−sinθsinθcosθ][uv] If the rotor profile curve of the driving rotor can be defined from the relation function of Equation (1), a rotor profile of the dependent rotor could be produced that satisfies a pair of meshing conditions. Table 3 shows the boundary condition for the CFD analysis. Since the inner flow field of the screw compressor is in unsteady state, and appropriate boundary conditions affect the convergence rate of the flow analysis, the working fluid is regarded as an ideal gas. The measured sample data are the mean values of the pressure measured at the place where the five pressure transducers are installed, and the exit pressure boundary condition is set as the interpolation value for the pressure value at each position, because the number of sample data is small. [...]it is confirmed that the error rate with respect to the pressure value increases after 200° of rotation angle.

Purpose This paper aims to study the fluid flow and forced convection heat transfer from an isothermal circular cylinder with control rods in the laminar unsteady flow regime. Design/methodology/approach The overset grid method was used for accurate simulation of the unsteady flows around different arrangements of the cylinders. Grid generation for overset grids was performed using a general orthogonal boundary fitted coordinate system. The method of solution was based on a finite volume discretization of the Navier-Stokes equations. Simulations were carried out for the Prandtl numbers of 0.7 and 7.0 with the Reynolds numbers ranging from 60 to 300. Findings The results indicate that the performance of multiple control rods depends strongly on the spacing ratio. Furthermore, in a manner similar to the flow patterns, four different thermal regimes were recognized based on the variations of mean Nusselt number versus G/D, as the thermal regimes follow the categories of flow regimes at different diameter ratios. However, for different Prandtl numbers, no single trend of heat transfer variation versus the spacing ratio exists for same regime. Originality/value Few studies have been conducted to investigate the heat transfer characteristics from control rods. The results of this study provide a comprehensive knowledge on the dynamical and thermal behavior of the flow around multiple cylinders.

Finite-Difference Time-Domain (FDTD) method is a simple and powerful tool used to solve electromagnetic (EM) problems. However, the drawbacks of FDTD method are difficult to model the curved boundaries and small features due to its restriction to inherent orthogonal grids. We have previously proposed that the B2-spline or biquadratic spline interpolation technique for Overset Grid Generation and Finite- Difference Time-Domain (OGG-FDTD) method be utilised to overcome the limitations of FDTD method. This proposed method has the ability to accurately measure a scattered field around an unknown object. In this paper, the OGG-FDTD method with B2-spline interpolation in Forward-Backward Time-Stepping (FBTS) inverse scattering technique was proposed for the detection and reconstruction of arbitrary shaped objects in Case A and malignant breast tumour detection in Case B. The results showed that the Mean Square Error (MSE) of reconstructed dielectric profiles by using the proposed method has achieved significantly lower values than the FDTD method in FBTS. In Case A, the accuracy difference between the two methods was 26.67% for relative permittivity and 27.63% for conductivity, respectively. In Case B, it was found that the implementation of the proposed method increased the accuracy of reconstructed the relative permittivity image by 50.54%, and conductivity by 74.42% as compared to the FDTD method in FBTS technique. Furthermore, the values of normalised error function for the proposed method were also lower than the FDTD method in FBTS. Hence, it is proven that this numerical method can provide clearer and better reconstructed images to improve the quality of retrieve the dielectric profiles of the investigation area.

Abstract This paper presents a new approach of Forward-Backward Time-Stepping (FBTS) utilizing FiniteDifference Time-Domain (FDTD) method with Overset Grid Generation (OGG) method to solve the inverse scattering problems for electromagnetic (EM) waves. Keywords: finite-difference time-domain, forward-backward time-stepping, inverse scattering problems, overset grid generation method Copyright © 2017 Universitas Ahmad Dahlan. (ProQuest: ... denotes formulae omitted.) 1.Introduction Microwave inverse scattering technique is generally used to determine the location, shape and dielectric properties of unknown objects that are scattered by the objects [1]. Here, the FDTD need to refine the computational domain globally to solve the problem. First solve the problem in the whole domain on a coarse grid, then part of the FDTD grid is replaced with a finer grid called the sub-grid to solve the sub-problem on finer grid and combine the results [22-25]. The electric properties include the permittivity (s), permeability (u) and conductivity (a). The H, Takenaka T, Johnson JE, Tanaka T. A Breast Imaging Model Using Microwaves and a Time Domain Three Dimensional Reconstruction Method. Estimation of The Frequency-Dependent Average Dielectric Properties of Breast Tissue Using a Time-Domain Inverse Scattering Technique. Confocal Microwave Imaging for Breast Cancer Detection: Localization of Tumors in Three Dimensions. [29] Sahrani S, Kuroda M. FDTD Analysis with Overset Grid Generation Method for Rotating Body and Evaluation of Its Accuracy.

In this paper, a novel approach which combines the FDTD method with overset grid generation method is proposed for the analysis of the EM field with rotating body. The analysis is carried out together with the Lorentz transformation to comprise with the higher velocity cases. To apply the Lorentz transformation to the FDTD method, at least two frames are required, and we primitively modelled it with the overset grid generation method. With the Lorentz transformation, the time component changes at each of the grid point. The time component that has been changed by Lorentz transformation must be fixed as the numerical procedure. Through the interpolation technique, it is possible to fix the time component easily. We have previously proposed this novel approach for a stationary and uniformly moving body. Here, this analysis is further expanded and has included a more detailed discussion of the EM field interactions in a rotating environment. The numerical results show the characteristics of the EM field when the incident wave strikes the rotating body. For validation, the numerical results are compared with the theoretical results, and good agreements were obtained. The proposed novel approach has shown its consistency over higher relative velocity cases.

An unsteady Reynolds averaged Navier–Stokes solver with a structured overset grid method has been developed. Velocity–pressure coupling is achieved using an artificial compressibility approach, spatial discretization is based on a finite-volume method, and convective fluxes are evaluated by a third-order upwind scheme based on flux-difference splitting. Body motions are considered using the grid deformation technique and grid velocities in the convective term. Viscous fluxes are evaluated via second-order centered differencing. The full multigrid (FMG) method is applied to obtain fast convergence. The cell flag on a coarse grid level is determined using the cell flag on a fine grid level. In the coarse grid-level calculations at the FMG stage, the data are interpolated until the finest grid level is achieved at an overset update interval. Then, the data are updated based on the overset relations at the finest grid level and then transferred to a coarser grid level. For free surface treatments, a single-phase localized level-set method is employed. The computations for flows around a hull form, including an unsteady simulation with regular waves, are demonstrated.

We consider the numerical solution of Poisson’s equation on structured grids using geometric multigrid with nonstandard coarse grids and coarse-level operators. We are motivated by the problem of developing high-order accurate numerical solvers for elliptic boundary value problems on complex geometry using overset grids. For flexibility in grid generation, we would like to consider lower-order accurate coarse-level approximations, and coarsening factors other than two. We show that second-order accurate coarse-level approximations are very effective for fourth- or sixth-order accurate fine-level finite-difference discretizations. We study the use of different Galerkin and non-Galerkin coarse-level operators. Using local Fourier analysis (LFA) we choose the smoothing parameter ω and the coarse-level operators to optimize the overall multigrid convergence rate. We show that the results based on LFA for periodic problems also hold for more general boundary conditions provided these are discretized using compatibility conditions . Numerical results for Poisson’s equation on a sample overset grid show that our multigrid solver is many times faster, and uses less memory, than selected Krylov solvers and an algebraic multigrid solver. We also study grid coarsening by a general factor and show that good convergence rates are retained for a range of coarsening factors around two. We ask the question of which coarsening factor leads to the most efficient multigrid algorithm.