Overset Grid Generation Research Articles

Overset grid generation with inverse scattering technique for object and crack detection

This paper presents the forward backward time stepping (FBTS) technique with finite difference time domain (FDTD) method and overset grid generation (OGG) method was applied for the reconstruction of object and crack detection. Object and crack detection is widely used in structural health monitoring (SHM) application especially in civil structure to detect the buried object and also cracks. The proposed numerical approach has been validated by investigating different kind of ratio of grid size between the main mesh and sub-mesh. Then, the proposed numerical approach is implemented in the analysis of the detection of objects such as concrete blocks and cracks underground. Here, the numerical errors between the actual result and simulated result had been calculated by using relative error. It is shown that the proposed approach has 5.22% error and nearer to the actual value.

B<sub>2</sub>-SPLINE INTERPOLATION TECHNIQUE FOR OVERSET GRID GENERATION AND FINITE-DIFFERENCE TIME-DOMAIN METHOD

—In this paper, B2-spline interpolation technique for Overset Grid Generation and FiniteDifference Time-Domain (OGG-FDTD) method was developed. B2-spline or biquadratic spline interpolation offers better accuracy than bilinear interpolation. Two-dimensional (2D) numerical simulations were carried out for electromagnetic (EM) field analysis to measure the scattered fields for an unknown object in free space and dielectric medium. In this work, two antennas were utilised as transmitter and receiver sequentially to transmit microwave pulses and collect the scattered fields for an unknown object in OGG-FDTD lattice. In order to analyse the stability and efficiency of the proposed method, the scattered fields for the unknown object were investigated with error analysis. The results showed that the OGG-FDTD method with B2-spline interpolation gave lower relative error than bilinear interpolation with 0.0009% of difference in free space, 0.0033% of difference in Case A dielectric medium, 0.236% of difference in Case B dielectric medium, and 0.003% of difference in Case C dielectric medium. Besides, the Mean Square Error (MSE) for the OGG-FDTD method with B2-spline interpolation was also lower than the bilinear interpolation. Hence, it proves that the OGG-FDTD method with B2-spline interpolation has the ability to measure the scattered fields around an unknown object accurately. For future work, the proposed method can be applied to inverse scattering to detect and reconstruct buried objects with arbitrary shapes in a complex media.

Numerical Analysis of Electromagnetic Scattering From a Moving Target by the Lorentz Precise Integration Time-Domain Method

A novel numerical method, referred to as Lorentz precise integration time-domain (Lorentz-PITD) method, is proposed to deal with the scattering problem from a moving conducting slab. Both the overset grid generation technique and the Lorentz transformation are employed in this method. By using the Lorentz transformation and the linear interpolation technique, the incident plane wave in the rest frame is introduced to the moving frame; the scattered fields are transformed from the moving frame to the rest frame. Numerical experiments validate the Lorentz-PITD method and show that the Lorentz-PITD method is more computationally efficient compared with the Lorentz finite-difference time-domain method. An accompanied find is that there must be a tradeoff between the applicable frequency range and the computation cost in the proposed method.

A New Approach for Solving Inverse Scattering Problems with Overset Grid Generation Method

This paper presents a new approach of Forward-Backward Time-Stepping (FBTS) utilizing Finite-Difference Time-Domain (FDTD) method with Overset Grid Generation (OGG) method to solve the inverse scattering problems for electromagnetic (EM) waves. The proposed FDTD method is combined with OGG method to reduce the geometrically complex problem to a simple set of grids. The grids can be modified easily without the need to regenerate the grid system, thus, it provide an efficient approach to integrate with the FBTS technique. Here, the characteristics of the EM waves are analyzed. For the research mentioned in this paper, the ‘measured’ signals are syntactic data generated by FDTD simulations. While the ‘simulated’ signals are the calculated data. The accuracy of the proposed approach is validated. Good agreements are obtained between simulation data and measured data. The proposed approach has the potential to provide useful quantitative information of the unknown object particularly for shape reconstruction, object detection and others.

A New Approach for Solving Inverse Scattering Problems with Overset Grid Generation Method

A New Approach for Solving Inverse Scattering Problems with Overset Grid Generation Method

FDTD Analysis with Overset Grid Generation Method for Rotating Body and Evaluation of Its Accuracy

This paper presents an alternative approach for the analysis of EM field by a rotating body with FDTD method and Overset Grid Generation method, considering Lorentz transformation for the higher velocity cases. This approach has been previously proposed for the case of linear and uniformly moving body against/to the incident wave. Here, the approach is expanded to a rotating body which includes the interpolation technique in the space and time increment along the cylindrical rotation at the fixed axis. First, the grid size ratios between the main mesh and the sub-mesh are studied. The appropriate choice of the grid size ratio is obtained. Then, the modulations of the EM field when the incident wave hits the rotating body in high velocity cases are analyzed. The relationship of the phase shift and the velocity is further observed. The observed EM fields are compared with the theoretical results and achieved good agreements in high relative velocities. The assessment of the numerical errors in a rotating environment is also highlighted. This numerical approach may have numerous situations to which it can be applied. This may be involved with the design of rotating devices such as microactuator, commutator and others.

CFL3D/OVERFLOW Results for DLR-F6 Wing/Body and Drag Prediction Workshop Wing

A series of overset grids was generated in response to the Third AIAA CFD Drag Prediction Workshop (DPW-III) which preceded the 25th Applied Aerodynamics Conference in June 2006. DPW-III focused on accurate drag prediction for wing/body and wing-alone configurations. The grid series built for each configuration consists of a coarse, medium, fine, and extra-fine mesh. The medium mesh is first constructed using the current state of best practices for overset grid generation. The medium mesh is then coarsened and enhanced by applying a factor of 1.5 to each (I, J, K) dimension. The resulting set of parametrically equivalent grids increase in size by a factor of roughly 3.5 from one level to the next denser level. Computational fluid dynamics simulations were performed on the overset grids using two different Reynolds-averaged Navier-Stokes flow solvers: CFL3D and OVERFLOW. The results were postprocessed using Richardson extrapolation to approximate grid-converged values of lift, drag, pitching moment, and angle of attack at the design condition. This technique appears to work well if the solution does not contain large regions of separated flow (similar to that seen in the DLR-F6 results) and appropriate grid densities are selected. The extra-fine grid data helped to establish asymptotic grid convergence for both the OVERFLOW FX2B wing/body results and the OVERFLOW DPW-W1/W2 wing-alone results. More CFL3D data are needed to establish grid convergence trends. The medium grid was used beyond the grid convergence study by running each configuration at several angles of attack so drag polars and lift/pitching moment curves could be evaluated. The alpha sweep results are used to compare data across configurations as well as across flow solvers. With the exception of the wing/body drag polar, the two codes compare well qualitatively showing consistent incremental trends and similar wing pressure comparisons.

Unstructured Moving Patched-Grid Method Using Concept of Overset Grid

From a point of view of grid generation, an overset grid generation method is suitable for a flow around moving complicated-shaped body. The overset grid method treats two grid-types which are a main-grid placed on all over the flow field and a sub-grid placed around the body. However it is difficult to satisfy a physical conservation law since the overset grid method interpolates the value between the main-grid and the sub-grid. To assure the conservation law on the overlapped region, we propose a new method that the overset grid method is combined to the unstructured moving grid finite volume method. In this method the sub-grid and the main-grid are joined by the unstructured grid. The feature of the method is that a control volume on which a space-time unified domain is adopted, and the method assures the geometric conservation law too even if the sub-grid moves and deforms. The method is applied to a problem such that complicated-shaped body flies in supersonic flow.