| Popis: |
Typically, complex components are designed with a CAD system, where free-form surfaces are usually described by B-Spline or NURBS surfaces. Especially in turbo machinery, design is performed for hot working conditions. However, for manufacturing a cold, unloaded CAD model is required. A deformed component with smooth surfaces may also be needed e.g. for flow calculations at different operating points. Engine-part deformations caused by loads and temperature changes are calculated by a finite element program which produces a displacement field as output. In such cases the original B-Spline description may be used and the shape of the relevant surfaces may be adjusted via displacement of the B-Spline control-points. The procedure is to decompose the solid into part-surfaces, identify corresponding FE nodes, apply the FE displacement field to the projected points of the FE nodes, and determine displacements of the control points by solving linear fitting problems. The required position and tangential continuity can be achieved by special treatment of the edge curves and their neighboring control points. Treatment of singularities of the linear fitting problem at trimmed surfaces and inadequate FE meshes requires special focus. The presented generic morphing method was implemented as an extension to the CAD system Unigraphics NX 7.5 and can now be used as the basis for automated hot-to-cold geometry transformations. Applications to a compressor aerofoil and an exhaust mixer segment demonstrate the robustness and accuracy of the method. |
