| Advances in computer and Computational Fluid Dynamics (CFD) techniques are allowing mathematical models and simulations to have ever-increasing level of precision and complexity. Tremendously large amounts of heterogeneous, massive data are being generated and collected. These data consist of scalar data (temperature, pressure, etc) and vector data (velocity, etc), which are commonly defined on unstructured grids with complex topology. Without effective tools, it is usually impossible to gain understanding and insight into the data. Scientific visualization encompasses and unifies the fields of computer graphics, image processing, computer vision, computer-aided design, signal processing, and human-computer interaction to represent vast amounts of numerical data in an effective way using graphical representations for researchers to comprehend or manipulate the data. The larger the data set, the more important it is to have capable and flexible visual tools from which to choose.Scientific visualization is a relatively new computer-based field that is in rapid and constant progress; hence one of the primary concerns in design a new visualization system is the extendibility to embrace newly emerging technology. To achieve this goal, structured, object-oriented principles should be followed. The quality'of a software system can be improved to a large extent by following these principles. The primary concern in structured, object-oriented design is to get a large system broken down into many small ones by combined functional and data abstract. Each module is independent, reusable, comprehensible and extensible.The technique and ideas in developing a CFD visualization system are described elaborately. The design and implementation of the system has been strongly influenced by structured, object-oriented principles.The Visualization ToolKit (VTK) is an open source, freely available software system for three-dimensional (3D) computer graphics, imageprocessing, and visualization used by thousands of researchers and developers around the world. VTK consists of a C++ class library, and several interpreted interface layers including Tcl/Tk, Java, and Python. VTK and Visual C++ 6.0 are taken to develop the visualization system. The system is developed in the following structured, object-oriented manner: (1) each new specific visualization algorithm is encapsulated with a C++ class; (2) Some VTK classes are enhanced or extended with new attributes and functions; (3) Classes are assembled to carry out a particular visualization task.For visualization geometrical data generated in numerical simulations, two subdivision methods are used and described in full detail. The two methods, which are triangular subdivision and quadrilateral subdivision, are incorporated into the visualization system with VTK for surface and volume rendering. The system supports a wide variety of visualization algorithms including scalar, vector, tensor, texture, and volumetric methods; and advanced modeling techniques such as implicit modeling, polygon reduction, mesh smoothing, cutting, and contouring. In addition, dozens of imaging algorithms have been directly integrated to manage two-dimensional (2D) image / 3D graphics data. The merits and demerits of each algorithm are fully addressed.The results of CFD computations are commonly stored in different file formats; a visualization system should be able to recognize these file formats. For this purpose, the visualization system supports many wide-used CFD data file formats.The visualization system also features a user-friendly graphical user interface (GUI). The user can easily master most of the system operations, change visualization parameters, and view the results interactively. Users are encouraged to use mouse to interact with the system, although advanced users can use keyboard shortcuts for speed.Visualization examples in ship mechanics are given in several chapters for demonstration and discussion.
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