Intelligent Patching of Conceptual Geometry for CFD Analysis

NASA Tech Briefs, September 2010 The iPatch computer code for intelligently patching surface grids was developed to convert conceptual geometry to computational fluid dynamics (CFD) geometry (see figure). It automatically uses bicubic B-splines to extrapolate (if necessary) each surface in a conceptual geometry so that all the independently defined geometric components (such as wing and fuselage) can be intersected to form a watertight CFD geometry. The software also computes the intersection curves of surface patches at any resolution (up to 10–4 accuracy) specified by the user, and it writes the B-spline surface patches, and the corresponding boundary points, for the watertight CFD geometry in the format that can be directly used by the grid generation tool VGRID. iPatch requires that input geometry be in PLOT3D format where each component surface is defined by a rectangular grid {(x(i,j), y(i,j), z(i,j)): 1 ≤ i ≤ m, 1 ≤ j ≤ n} that represents a smooth B-spline surface. All surfaces in the PLOT3D file conceptually represent a watertight geometry of components of an aircraft on the half-space y ≥ 0. Overlapping surfaces are not allowed, but could be fixed by a utility code “fixp3d”. The fixp3d utility code first finds the two grid lines on the two surface grids that are closest to each other in Hausdorff distance (a metric to measure the discrepancies of two sets); then uses one of the grid lines as the transition line, extending grid lines on one grid to the other grid to form a merged grid. Any two connecting surfaces shall have a “visually” common boundary curve, or can be described by an interIntelligent Patching of Conceptual Geometry for CFD Analysis Langley Research Center, Hampton, Virginia image 2 of any point on the plane in image 1. Any feature pair that is inconsistent with the homography is thrown out. The output of the process is a set of feature pairs, and the homography. The algorithms in this innovation are well known, but the new implementation improves the process in several ways. It runs in real-time at 2 Hz on 64megapixel imagery. The new Shi-Tomasi corner de tector tries to produce the requested number of features by automatically adjusting the minimum distance between found features. The homography-finding code now uses an implementation of the RANSAC algorithm that adjusts the number of iterations automatically to achieve a pre-set probability of missing a set of inliers. The new interface allows the caller to pass in a set of predetermined points in one of the images. This allows the ability to track the same set of points through multipleframes. This work was done by Daniel S. Clouse, Yang Cheng, Adnan I. Ansar, David C. Trotz, and Curtis W. Padgett of Caltech for NASA’s Jet Propulsion Laboratory. Further information is contained in a TSP (see page 1). The software used in this innovation is available for commercial licensing. Please contact Daniel Broderick of the California Institute of Technology at [email protected]. Refer to NPO-46916.