GridTool: A surface modeling and grid generation tool

GridTool is designed around the concept that the surface grids are generated on a set of bi-linear patches. This type of grid generation is quite easy to implement, and it avoids the problems associated with complex CAD surface representations and associated surface parameterizations. However, the resulting surface grids are close to but not on the original CAD surfaces. This problem can be alleviated by projecting the resulting surface grids onto the original CAD surfaces. GridTool is designed primary for unstructured grid generation systems. Currently, GridTool supports VGRID and FELISA systems, and it can be easily extended to support other unstructured grid generation systems. The data in GridTool is stored parametrically so that once the problem is set up, one can modify the surfaces and the entire set of points, curves and patches will be updated automatically. This is very useful in a multidisciplinary design and optimization process. GridTool is written entirely in ANSI 'C', the interface is based on the FORMS library, and the graphics is based on the GL library. The code has been tested successfully on IRIS workstations running IRIX4.0 and above. The memory is allocated dynamically, therefore, memory size will depend on the complexity of geometry/grid. GridTool data structure is based on a link-list structure which allows the required memory to expand and contract dynamically according to the user's data size and action. Data structure contains several types of objects such as points, curves, patches, sources and surfaces. At any given time, there is always an active object which is drawn in magenta, or in their highlighted colors as defined by the resource file which will be discussed later

Topology and Grid Adaption for High-Speed Flow Computations

This study investigates the effects of grid topology and grid adaption on numerical solutions of the Navier-Stokes equations. In the first part of this study, a general procedure is presented for computation of high-speed flow over complex three-dimensional configurations. This includes the grid generation and solution algorithm for Navier-Stokes equations in a general three-dimensional curvilinear coordinate system. The flow field is simulated on the surface of a Butler wing in a uniform stream. Results are presented for Mach number 3.5 and a Reynolds number of 2,000,000. The O-type and H-type grids have been used for this study, and the results are compared together and with other theoretical and experimental results. The results demonstrate that while the H-type grid is suitable for the leading and trailing edges, a more accurate solution can be obtained for the middle part of the wing with an O-type grid. In spite of some discrepancies, the present numerical results compare favorably with the experimental results. In the second part of this study, methods of grid adaption are reviewed and a method is developed with the capability of adapting to several variables. This method is based on a variational approach and is an algebraic method. Also, the method has been formulated in such a way that there is no need for any matrix inversion. This method is used in conjunction with the calculation of hypersonic flow over a blunt-nose body. A movie has been produced which shows simultaneously the transient behavior of the solution and the grid adaption. For both cases, the simulations are done by integrating the viscous Navier-Stokes equations. These equations govern the unsteady, viscous, compressible and heat-conducting flow of an ideal gas, and all viscous terms are retained. The equations are written in curvilinear coordinates so that the body surface is represented accurately. The computer codes are written in FORTRAN, is vectorized and currently run on the CDC Vector Processing System (VPS-32, CYBER 205) computer. The results indicate the viability and validity of the proposed methods

Unstructured surface grid generation

Viewgraphs on unstructured surface grid generation are presented. Topics covered include: requirements for curves, surfaces, solids, and text; surface approximation; triangulation; advancing; projection; mapping; and parametric curves

Triangulation Of NURBS Surfaces

A technique is presented for triangulation of NURBS surfaces. This technique is built upon an advancing front technique combined with grid point projection. This combined approach has been successfully implemented for structured and unstructured grids. 2 Introduction Computer Aided Design (CAD) systems typically represent the surfaces of aerodynamic vehicles with a set of parametric surfaces such as NonUniform Rational B-Splines (NURBS). Then, CFD surface grids are generated on these NURBS surfaces. A surface grid can be generated either in a parameter space or on an approximated/simplified NURBS surface. Generating surface grid in a parameter space is very common in structured grid generation. This approach has two serious restrictions. The first restriction is that the choice of surface parameterization affects the CFD surface grid. As shown in [1], a poor parameterization may cause the CFD surface grid to be highly skewed. There are several ways to alleviate this problem which have..

A Grid Generation System For Multi-Disciplinary Design Optimization

A general multi-block three-dimensional volume grid generator is presented which is suitable for MultiDisciplinary Design Optimization. The code is timely, robust, highly automated, and written in ANSI "C" for platform independence. Algebraic techniques are used to generate and/or modify block face and volume grids to reflect geometric changes resulting from design optimization. Volume grids are generated/modified in a batch environment and controlled via an ASCII user input deck. This allows the code to be incorporated directly into the design loop. Generated volume grids are presented for a High Speed Civil Transport (HSCT) Wing/Body geometry as well a complex HSCT configuration including horizontal and vertical tails, engine nacelles and pylons, and canard surfaces. INTRODUCTION The continuing increase in computer speeds and the advancement of numerical algorithms has helped to increase the interest in Multi-disciplinary Design Optimization (MDO). MDO is a methodology for the desi..

A Grid Generation System For Multi-Disciplinary Design Optimization

A general multi-block three-dimensional volume grid generator is presented which is suitable for MultiDisciplinary Design Optimization. The code is fast, robust, highly automated, and written in ANSI "C" for platform independence. Algebraic techniques are used to generate and/or modify block face and volume grids to reflect geometric changes resulting from design optimization. Volume grids are generated/modified in a batch environment and controlled via an ASCII user input deck. This allows the code to be incorporated directly into the design loop. Generated volume grids are presented for a High Speed Civil Transport (HSCT) Wing/Body geometry as well a complex HSCT configuration including horizontal and vertical tails, engine nacelles and pylons, and canard surfaces. Nomenclature a,b = Blending functions C = Wing Chord c,d = Blending functions e,f = Edge arclengths g,h = Normalized edge arclengths P = Interpolant normalization R = Physical space coordinate vector r = Grid point ..

Unstructured Grids on NURBS Surfaces

A simple and efficient computational method is presented for unstructured surface grid generation. This method is built upon an advancing front technique combined with grid projection. The projection technique is based on a Newton-Raphson method. This combined approach has been successfully implemented for structured and unstructured grids. In this paper, the implementation for unstructured grid is discussed