Parametric Geometry Creation Methodology and Utility for the Stars Cfd Analysis Package

Differing methodologies and approaches for the creation of STARS CFD test case geometry models and support files were examined. The current methods for model geometry creation have been identified by past researchers as an area needing improvement. Methods of geometric data transfer, storage, and processing were examined for their applicability and usefulness in the STARS solution procedure. A CFD model creation utility was then developed for STARS. The utility converts existing CAD geometry into the set of files needed for a general CFD analysis. A graphical user interface was also created in order to aid the user in the specification of geometric, meshing, and solution parameters.Mechanical & Aerospace Engineerin

PDE-Based Parameterisation Techniques for Planar Multipatch Domains

This paper presents a PDE-based parameterisation framework for addressing the planar surface-to-volume (StV) problem of finding a valid description of the domain's interior given no more than a spline-based description of its boundary contours. The framework is geared towards isogeometric analysis (IGA) applications wherein the physical domain is comprised of more than four sides, hence requiring more than one patch. We adopt the concept of harmonic maps and propose several PDE-based problem formulations capable of finding a valid map between a convex parametric multipatch domain and the piecewise-smooth physical domain with an equal number of sides. In line with the isoparametric paradigm of IGA, we treat the StV problem using techniques that are characteristic for the analysis step. As such, this study proposes several IGA-based numerical algorithms for the problem's governing equations that can be effortlessly integrated into a well-developed IGA software suite. We augment the framework with mechanisms that enable controlling the parametric properties of the outcome. Parametric control is accomplished by, among other techniques, the introduction of a curvilinear coordinate system in the convex parametric domain that, depending on the application, builds desired features into the computed harmonic map, such as homogeneous cell sizes or boundary layers

A Generalized Blending Scheme for Arbitrary Order of Continuity

In this thesis, new templates and formulas of blending functions, schemes, and algorithms are derived for solving the scattered data interpolation problem. The resulting data fitting scheme interpolates the positions and derivatives of a triangular mesh, and for each triangle of the mesh blends three triangular sub-surfaces, and creates a triangular patch. Similar to some existing schemes, the resulting surface inherits the derivatives of the sub-surfaces on the boundaries. In contrast with existing schemes, the new scheme has additional properties: The order of interpolated derivatives is extended to arbitrary values, and the restrictions of the sub-surfaces are relaxed. Then based on the properties of the new blending functions, an algorithm for constructing smooth triangular surfaces with global geometric continuity is described. The new blending functions and the scheme are then extended to multi-sided faces. The algorithm using these new blending functions accepts data sites formed by multi-sided polygons

Real-time Realistic Rendering Of Nature Scenes With Dynamic Lighting

Rendering of natural scenes has interested the scientific community for a long time due to its numerous applications. The targeted goal is to create images that are similar to what a viewer can see in real life with his/her eyes. The main obstacle is complexity: nature scenes from real life contain a huge number of small details that are hard to model, take a lot of time to render and require a huge amount of memory unavailable in current computers. This complexity mainly comes from geometry and lighting. The goal of our research is to overcome this complexity and to achieve real-time rendering of nature scenes while providing visually convincing dynamic global illumination. Our work focuses on grass and trees as they are commonly visible in everyday life. We handle geometry and lighting complexities for grass to render millions of grass blades interactively with dynamic lighting. As for lighting complexity, we address real-time rendering of trees by proposing a lighting model that handles indirect lighting. Our work makes extensive use of the current generation of Graphics Processing Units (GPUs) to meet the real-time requirement and to leave the CPU free to carry out other tasks

Hybrid Rugosity Mesostructures (HRMs) for fast and accurate rendering of fine haptic detail

The haptic rendering of surface mesostructure (fine relief features) in dense triangle meshes requires special structures, equipment, and high sampling rates for detailed perception of rugged models. Low cost approaches render haptic texture at the expense of fidelity of perception. We propose a faster method for surface haptic rendering using image-based Hybrid Rugosity Mesostructures (HRMs), paired maps with per-face heightfield displacements and normal maps, which are layered on top of a much decimated mesh, effectively adding greater surface detail than actually present in the geometry. The haptic probe’s force response algorithm is modulated using the blended HRM coat to render dense surface features at much lower costs. The proposed method solves typical problems at edge crossings, concave foldings and texture transitions. To prove the wellness of the approach, a usability testbed framework was built to measure and compare experimental results of haptic rendering approaches in a common set of specially devised meshes, HRMs, and performance tests. Trial results of user testing evaluations show the goodness of the proposed HRM technique, rendering accurate 3D surface detail at high sampling rates, deriving useful modeling and perception thresholds for this technique.Peer ReviewedPostprint (published version

Pseudoedge--a hierarchical skeletal modeler for the computer aided design of structural components

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1991.Includes bibliographical references (p. 121-122).by David Leo Bonner.M.S

A new local basis for designing with tensioned splines

Journal ArticleRecently there has been a great deal of interest in the use of "tension" parameters to augment control mesh vertices as design handles for piecewise polynomials. A particular local cubic basis called p-splines, which has been termed a "generalization of B-splines", has been proposed as an appropriate basis. These functions are defined only for floating knot sequences. This paper uses the known property of B-splines that with appropriate knot vectors they span what are called here spaces of tensioned splines, and that particular combinations of them, called LT-splines, form bases for the spaces of tensioned splines. In addition, this paper shows that these new proposed bases have the variation diminishing property, the convex hull property, and straightforward knot insertion algorithms, and that both curves and individual basis functions can be easily computed. Sometimes it is desirable to interpolate points and also use these tension parameters so interpolation methods using the LT-spline bases are presented. Finally, the above properties are established for uniform and nonuniform knot vectors, open and floating end conditions, and homogeneous and nonhomogeneous tension parameter pairs

A Computational Study of Blood Flow and Vascular Nitric Oxide Transport

Atherosclerosis occurs in a spatially heterogeneous fashion within the arterial system. The patchy nature of the disease is thought to reflect spatial variation in haemodynamic factors such as wall shear stress (WSS) and in the concentration of vascular species. This thesis numerically investigates blood flow and vascular transport of the atheroprotective agent nitric oxide (NO) using a spectral/hp element method. Firstly, NO distribution is analysed within a parallel-plate flow chamber coated with endothelial cells. Contrary to the accepted hypothesis that NO concentration increases with WSS (as does NO production), it is observed that NO concentration depends on WSS in a non-monotonic fashion. Furthermore, these results emphasise the effect of convection on in vitro NO transport, which has been overlooked or misinterpreted in most previous computational studies. Secondly, blood flow and NO transport are investigated within a detailed representation of the rabbit thoracic aorta and its branches, which was reconstructed using high resolution computed tomography (CT) scan data of a vascular corrosion cast. The computed WSS distribution exhibits significant spatial heterogeneity, reflecting the complexity of the blood flow. In particular it is observed that two Dean-type vortices (associated with a skewed velocity profile) form in the aortic arch and propagate along the descending aorta. This results in streaks of WSS similar in nature to the fatty streaks of early stage atherosclerosis observed in mature rabbits. This finding provides further support for the hypothesis that blood flow mediates atherogenesis. The vascular distribution of NO is found to depend significantly on the relationship between NO production and WSS. Furthermore, it is concluded that mechanisms preventing NO consumption by haemoglobin (such as diffusional barriers) must exist in order for NO to exert its atheroprotective action. This study represents the first effort to model NO transport in a realistic representation of the major arteries