White papers

• How to Express Design Intent in Rhino 3D. Part I. Assembly Design and Kinematic Simulation (pdf)
  by Dmitry Ushakov, Director, Product Management & Marketing, LEDAS Ltd.

  Rhinoceros is a 3D computer-aided design (CAD) application developed for Windows since 1992 by Robert McNeel and Associates (Seattle, WA, USA). It is popularly known as “Rhino”, and is used by more than 150,000 professionals around the globe for its powerful freeform modeling. Rhino’s license fees start below $1,000, yet its functionality is similar to that found in products typically costing 20 to 50 times more. It is based on the open 3DM file format, which is available to any software developer for reading/writing in the framework of the openNURBS initiative. As a result, Rhino is bundled with 120+ third-party plug-ins. Its interface, features, and commands are familiar to CAD users, and allow them to easily work out complex 3D design problems. Rhino, however, lacks of one important capability: it cannot specify the behavior that should occur when its 3D models are changed.

• Variational Direct Modeling: How to Keep Design Intent in History-Free CAD (pdf)
  by Dmitry Ushakov, Director, Product Management & Marketing, LEDAS Ltd.

  What is better: history-based modeling or direct modeling for 3D design and editing? Both approaches have their advantages and their drawbacks. Can smart parametric editing be combined with simplicity of user's manipulations? The answer is in the new technology - variational direct modeling: using geometric and dimensional constraints to define the desired model behavior when modifying the model. A variational direct modeler simultaneously satisfies all constraints in contrast to the history-based consequence in parametric modeling. The set of constraints is a declarative construction to be interpreted uniformly regardless of their history. At the same time, constraints expressivities are sufficient to specify features and links between them. Constrains are set not only by a system user but also by the system itself which automatically identifies them building the original model or importing the model from another system. As a result, there is an easy-to-use tool to control feature concept of a product, which can adequately replace the current history-based and direct geometric modeling systems, combining their pluses and concealing their minuses. This paper describes advantages of variational direct modeling applications for the end-users.

• Common Pitfalls in Parametric CAD Systems (pdf)
  by Dr.-Ing. Edgar A. Gerteisen, Group Research & Advanced Engineering, Product Modeling and Knowledge Integration, Daimler AG

  Parametric CAD Systems promise great potential with regard to product optimization. A given parametric set may be varied to produce variant instances of the geometry that further are going to be functionally assessed by means of computational methods, so-called CAE methods. If such a methodology is being embedded within a numerical optimization procedure, e.g. evolutionary strategies, the parametric set that rules the geometric and thereafter the functional behavior may converge to an optimum or at least may lead to an improvement of the corresponding product. In the present investigation some limitations of parametric CAD systems are figured, if intended to be applied in the context of numerical optimization. Specifically, the non-uniqueness of geometric constraint solving leads to robustness issues when applied in automatic geometry update cycles upon parameter variation. The suggested enhancement with regard to the geometric interpretation of distance and tangency strives towards a more reliable parametric CAD system.

• Using LEDAS Computational Software Toolkits to Shorten Development Cycle of Variational CAD Systems (pdf)
  by Dmitry Ushakov, Chief Technology Officer, LEDAS Ltd.

  In the paper we present the strategy of the LEDAS Company aimed at providing ready-to-integrate toolkits of computational software modules for developers of commercial CAD/CAM/CAE systems. The modules provided by LEDAS are supposed to be integrated into an application for implementation of the so-called variational approach to parametric design (further on referred to as variational design). The paper describes the main advantages of variational design over traditional history-based parametric design. It presents the main computational engine — a geometric constraint solver — and discusses its applications in CAD/CAM/CAE domain. Describing the basic functionality of typical CAD/CAM/CAE applications (2D sketcher, 3D part modeler, assembly design, drafting, kinematics analysis, and others), we emphasize the advantages of variational approach for end-users. In conclusion we list some prospective applications of variational design in other domains.