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SIMULATION BASED DESIGN:
Broadly speaking research in the area of Simulation Based Design focuses in integrating advanced information technologies as well as techniques for enhancing design and engineering.
Until recently practical design merely consisted of experimentation and physical prototyping, which were not only very time consuming but also very expensive. Due to the increasing efficiency of computer hardware and the increasing sophistication of numerical methods, design and simulation in computer based virtual environments have become a realistic proposition. Thus, the trend nowadays is towards a situation in which many of the decisions affecting the final configuration of a design are taken as a result of computer simulation of the object's physical properties before the testing of the actual physical prototype. A fine example of this is the recent design simulation of the Boeing 777, which was designed, test flown, and the necessary repairs carried out before a single component was manufactured.
Within the framework of simulation based design three important research areas are presently being pursued at Bradford, namely Computer-Aided Design, Computer-Aided Analysis and Automatic Optimisation.
A major difficulty in creating practical objects on the computer is due to the lack of methods for defining them in an easy and intuitive fashion. From the point of view of a designer it is extremely important to be able to create realistic objects and be able to manipulate them in real time within a user-friendly interactive environment. Conventional methods typically use polynomial patches (e.g. Non Uniform Rational B-Splines or NURBS), which often require hundreds of control points in order to represent a realistic object. Furthermore, such "spline" based patches often do not exactly meet at the boundaries and consequently need to be 'trimmed' or stitched in order to close the surface of the object in question.
Research in this area at Bradford is based on a novel method for Computer-Aided Design, which is somewhat different from the conventional spline based techniques. The method enables to create the geometry of realistic objects based upon the surface information at the character lines or edges of the object to be designed. The approach regards surface design as solutions to Partial Differential Equations (PDEs), in particular elliptic PDEs, and creates a surface as a solution to an appropriately chosen boundary-value problem. Therefore, the method defines a surface in terms of data around its edges, i.e. along its boundary curves.
It has been demonstrated how the PDE Method can be used to describe the surfaces of complicated objects which can be created and manipulated in an interactive environment by a designer (see refs. below). In its simplest form the method can be thought of creating surfaces between a given set of curves in 3D chosen by a designer. Figure below describes this idea. The java applet [coming soon] describes the basic properties of the PDE surfaces and interactive design.
Examples of PDE geometry created in an interactive environment in real time.
Various threads under Computer-Aided Design using the PDE method have been identified to be essential. They are:
The aim here is to develop techniques, using the PDE method, so that a designer sitting at a workstation can create complex realistic objects and manipulate them in real time. Work is mainly focused on developing new techniques as well as improving the existing techniques to enhance the user interface from the point of view of Human Computer Interaction. Applications of such techniques include the development of new software for CAD as well as the integration of the interactive techniques within the exiting CAD software packages.
In parametric design the basic approach is to develop a generic description of an object or a class of objects, in which the shape is controlled by the values of a set of design variables or parameters. A new design, created for a particular application, is obtained from this generic template by selecting particular values for the design parameters so that the item has particular properties suited to that application. The PDE method allows the shape of the surface to be parametrised in terms of a few design variables. Being able to describe the shape in question in terms of few design parameters is paramount from the point of view functional design and automatic optimisation. Future work in this area is therefore to be concentrated on improving the existing techniques for shape parameterisation and furthermore the development of new methods for efficiently parameterising realistic objects.
Work in this area of research involves creating physically based simulation of complex deformable systems to generate motion for use in computer-generated animation. The ease by which complex shapes can be created and manipulated in real time, using the PDE method, allows a designer to create such computer-generated animation models. A basic feature of the animation schemes using the PDE method is that the animations of realistic objects are performed as a series of curve transformation where the curves correspond to the character lines or the boundaries of the object animated. Future work is to be concentrated on parameterising shapes so that realistic animation models such as animation of human figures and cartoon characters can be performed for use in computer games and video.
One of the major tasks in the Simulation Based Design is the computation of the functional properties of the object. Such functional properties may be the computation of heat transfer, strength, hydrodynamic, or aerodynamic characteristics. One of the major difficulties here is the proper linking of complicated surface geometry to analysis. In fact it has been identified that this is the major "bottleneck" in the implementation of simulated based design. Research in this area is therefore focused in developing techniques in order to bridge the gap between computer-aided design and computer based analysis. Present work involves the development of effective methods for surface mesh generation as well the development of sophisticated algorithms for use in the computer-based physical analysis.
Shear stress distribution of a vertically loaded structure with a fixed bottom.
The aim of design optimisation is to identify a design candidate meeting a given set of criteria out a given series of possible designs. In realistic terms an optimal product may be defined as the one that most economically meets its performance requirements. Thus, the idea behind shape optimisation is to automatically modify the shape of the object in question in order to obtain an optimised surface of the object subject to a given set of restrictions. Owing to its boundary-value approach, the PDE method can define complicated surfaces in terms of a small parameter set, which makes optimisation of these surfaces computationally feasible. One of the most important aspects of the work carried out here in Bradford is its use for automatic design for function. The aim of this part of the research is to develop a methodology whereby an initial design, parametrised by the PDE method, can automatically be optimised against suitable functional criteria, subject to constraints specified by the designer in order to ensure a sensible final design is achieved. Problems so far considered have included objects designed for their heat transfer, strength, hydrodynamic, or aerodynamic performance.
APPLICATIONS OF THE RESEARCH
This research has many practical applications, which include building new software as well as technological and biomedical applications. Work is to be carried out in order to incorporate the techniques already developed in existing CAD software packages for design and animation. Since many industrial problems require physical analysis and optimisation, in technology industry there exist a wide variety of application areas where this research has a direct relevance. On the biomedical front the research is applicable to a wide variety of biomedical applications ranging from the modelling of shape of biological membranes, human heart and limbs.
Some of the work carried out in the area of Simulation Based Design here at Bradford is in collaboration with Professors M. I. G. Bloor and M. J. Wilson, and S. Kubeisa at the Department of Applied Mathematics at University of Leeds.
This work has been sponsored through various research grants, which in the past have mainly been held at the School of Mathematics at University of Leeds. These grants include the PRIDE (Products by Rapid Integrated Detailed Engineering) Project funded by EU, and two other EPSRC funded research projects namely Efficient Parameterisation of Complex mechanical Parts and Optimal Design and Manufacture of Thin-Walled Structures.
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