Chapter5

Chapter5 - Geometric Modelling Systems Ch. 5 Objectives:...

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Geometric Modelling Systems – Ch. 5 Objectives: Wireframe modelling systems. Surface modelling systems. Solid modelling systems. Nonmanifold modelling systems. Assembly modelling capabilities. Web-based modelling.

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Geometric Modelling Systems Used to overcome problems encountered with physical models in design process. Easier for designer to deform, add, and cut pieces off, and 3D virtual model comes with mathematical description. Three types – wireframe modelling systems, surface modelling systems, and nonmanifold modelling systems (in order of evolutionary history).
Popular when geometric modelling first introduced. Easy for users to develop modelling system and only simple user input needed to create shape. Mathematical description consists of list of curve equations, coordinates of points, and connectivity information. Wireframe Modelling Systems

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Wireframe Modelling Systems Figure 5.1 Ambiguous wireframe modelling. Ambiguity in wireframe models makes it difficult to calculate object mass properties, derive tool paths to machine its surfaces or generate finite meshes for FEA.
Mathematical description of visual model includes surface information. Equation list now includes surface equations, which are also updated as visual model manipulated on graphics screen. Mathematical description includes surface connectivity, otherwise, NC tool path programs must derive surface boundaries in their connectivity information. Surface Modelling Systems

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Three methods to create surface in surface modelling system: 1) Interpolating input points 2) Interpolating curve nets specified 3) Translating or revolving specified curve Surface Modelling Systems
Surface Modelling Systems Figure 5.2 Modelling of an automobile body.

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Surface Modelling Systems Figure 5.3 Calculation and verification of NC tool paths (OPEN MIND Software Technologies GmbH., HyperMILL®).
Solid Modelling Systems A set of surfaces must describe a shape having a closed volume . Information contained by system now includes information of locations inside, outside, or on closed volume. Application programs now can be written to do operations at volume level instead of surface level. Complete solid models require large amounts of input data. Nonmanifold modelling systems developed to overcome this. Solid modelling systems contain functions that are simple and natural for users to manipulate solid shape.

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Solid Modelling Systems – Modelling Functions Primitive Creation Functions – create simple shapes from solids stored in advance. Boolean Operations – add or subtract one solid from another. First Group – simple shape creation
Solid Modelling Systems – Modelling Functions Figure 5.4 Primitives generally supported.

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Functions Figure 5.5 Union (addition) operation. Figure 5.6
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This note was uploaded on 09/16/2009 for the course ENGR 3030 taught by Professor Vinhquan during the Spring '09 term at UOIT.

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Chapter5 - Geometric Modelling Systems Ch. 5 Objectives:...

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