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1.3.1 The basie design activities in CAD Systems

The CAD system provides generally the following design activities:

•    geometrie modeling,

•    engineering analysis,

•    design review and evaluation,

•    Computer drafting.

Above mentioned activities cover the all phases of generał design process.

Figurę.C: CAD system

Geometrie modeling is concemed with the mathematical description of the geometry of an object. This is the first and synthesis phase of product design. The basie operations of the modeling stage are generating basie geometrie elements such as points, lines, circles, primitives such as cubes and functions such as scaling, rotation, transformation, joining, wire frame representation and solid modeling.

Engineering analysis involves stress-strain calculations, heat-transfer computations and various analyses. Analysis of mass properties and fmite-element analysis is very reąuisite tool for providing of a solid object properties (surface area, weight, volume, centre of gravity, moment of inertia, etc.) and stress-strain and heat transfer performance. Engineer oftentimes applies differential equations to describe the dynamie behaviour of the system.

Design review and eva!uation provides for engineer the tools of design evaluation. For example kinematics is very important design review. The available kinematics tools enable to animate the motion of designed mechanisms. Afterwards there is a higher imagination. This capability enhances the designefs view and supports to avoid collision of designed objeets.

Computer drafting provides realising of the routine activities such as scaling of the drawing, autodimensioning, autohatching, various views ofthe drawings.

1.3.2 CAD database

All design activities such as geometrie modeling, various analysis, revie\v, evaluation and drafting are realised in data situated in some database. This database is called internal CAD database and data as CAD data,. Study of structure of the CAD database is a key to understanding of internal operations in the CAD system. There are programming tools to the access to CAD data. The database includes all inserted, modified and deleted objeets. Therefore it is possible to return to the previous designed and deleted features and to renew and updated the feature properties.