The features on freeform surface are common in products with complex curved surfaces, such as gas film holes attached on turbine blade surface or pressing head on the multi-spots bending press. The freeform surfaces generally have tiny geometric structure, the large number and regular arrangement, which makes it hard to extract analysis parameters from CAD structures and construct equivalent analysis features. Therefore, the analysis models generation will be accelerated if parameters for analysis could be extracted automatically rather than manually. In this paper, the analysis-oriented parameter extraction problem is proposed and analyzed. The geometry pattern parameter and physical attribute parameter are summarized and defined as the research kernel based on common analysis scenarios. Based on Hough transform and k-means clustering method, a geometry pattern parameter extraction method is proposed, which can convert analytic criterion of extraction requirements into clear pattern recognition problems. A physical attribute parameter extraction method based on rule reasoning is also put forward to extract numeric analysis parameters with physical meanings. Finally, two representative cases are taken to illustrate the implementation steps of the proposed method, and to verify the effectiveness and practicability in engineering. The instance demonstrates that the proposed method could significantly reduce the time consumption of analysis model generation and improve the integration degree of CAD/CAE.

The Non-Uniform Rational B-spline (NURBS) surface not only has the characteristics of the rational Bézier surface, but also has changeable knot vectors and weights, which can express the quadric surface accurately. In this paper, we investigated new bounds of the first- and second-order partial derivatives of NURBS surfaces. A pilot study was performed using inequality theorems and degree reduction of B-spline basis functions. Theoretical analysis provides simple forms of the new bounds. Numerical examples are performed to illustrate that our method has sharper bounds than the existing ones.

This paper proposes a method for the geometric design of axial compressor blades. First, a novel approach for creating 2D blade sections is proposed, where each 2D blade section is obtained by imposing the defined thickness distribution along the camber line. The camber line of each 2D blade section is defined by specifying the angle change of each point on the camber line. In order to make this method applicable to a wider range of blade section design, the camber line of each section can be designed in several (usually 2 or 3) segments. It takes into account the change rule of blade section along the flow channel, which is the most concerned in the aerodynamic design, rather than the specific curve form of blade section. Then, the 2D blade sections are mapped to the corresponding arbitrary rotational flow surface. Finally, the 3D blade model is generated by lofting the blade sections in the flow surfaces. Some typical examples are presented. It shows that this method has good applicability and flexibility to realize the geometric design of multiple types of blades.