Showing papers in "Computer-aided Design in 1984"
TL;DR: In this article, a machined surface type is defined as a pattern of faces, and a syntactic pattern recognition method is used to find the machined surfaces from the boundary file.
Abstract: It has been proposed that a direct link between CAD and CAM be provided through a computer-automated process planning system. Described in this paper are algorithmic procedures to identify machined surfaces (ie, machining requirements) for a workpiece directly from its 3D geometric description. A machined surface is a portion of workpiece that can be generated by a certain mode of metal removal operation. Machined surfaces are algorithmically recognized from a 3D boundary file, and then their 2(built|1/2)D descriptions are obtained in a data structure (format) suitable for an automated process planning system. A simplified boundary file data structure is introduced in order to explain the machined surface recognition procedures. A machined surface type is defined as a pattern of faces, and a syntactic pattern recognition method is used to find the machined surface from the boundary file.
208 citations
TL;DR: The capabilities of a geometric modeller are extended towards finite element analysis by a mesh generator which extracts all its geometric and topological information from the model, which accomodates material properties, loadcase and analysis requirements.
Abstract: The capabilities of a geometric modeller are extended towards finite element analysis by a mesh generator which extracts all its geometric and topological information from the model. A coarse mesh is created and subsequently refined to a suitable finite element mesh, which accomodates material properties, loadcase and analysis requirements. The mesh may be optimized by adaptive refinement, ie according to estimates of the discretization errors. A survey of research and development in geometric modelling and finite element analysis is presented, then an implementation of a mesh generator for 3D curvilinear and solid objects is described in detail.
71 citations
TL;DR: An advanced demonstration system which brings together a number of recent developments in CAAD (computer-aided architectural design) and shows how an important new form of input device, a 3D modelling systemm can be linked with building performance software and 'indicative' computer output graphics.
Abstract: The paper describes an advanced demonstration system which brings together a number of recent developments in CAAD (computer-aided architectural design). This demonstration system illustrates how an important new form of input device, a 3D modelling systemm can be linked with building performance software and ‘indicative’ computer output graphics. The 3D modelling system uses electronically interrogable building elements. The user assembles these elements on a baseboard, providing a tangible model of the design. The model is then interrogated by the CAD system, which recovers the geometry data describing the topology of the model. The user changes the design by reassembling the model elements. A particular aspect of this demonstration is that the user has the option to generate building design data and assimilated building performance data without the need to handle this data in numeric form. It is likely that many of the features present in this demonstration system will be evident in future ‘production’ CAAD systems.
56 citations
TL;DR: A divide-and-conquer algorithm for finding all the intersection lines between two B-spline surfaces by employing an adaptive division strategy and by the careful choice of the representation basis of the patches on both surfaces.
Abstract: A divide-and-conquer algorithm is presented for finding all the intersection lines between two B-spline surfaces. Each surface is organized as an n- branch tree. For each intersection line, an initial point is detected after a depth-first search along one tree, ie the host tree. Extrapolation methods are then used to trace the entire length of the line, thus the line appears naturally in a continuous form. Efficiency of the algorithm is achieved by the employment of an adaptive division strategy and by the careful choice of the representation basis of the patches on both surfaces.
55 citations
TL;DR: In this article, the author's previous work on the application of probabilistic design methods to the particular case of the tolerancing of component dimensions is extended to the most general case, where there exist many interdependent modes by which the components may fail to assemble to specification.
Abstract: The author's previous work on the application of probabilistic design methods to the particular case of the tolerancing of component dimensions is here extended to the most general case, where there exist many interdependent modes by which the components may fail to assemble to specification. Other aspects of the analysis (particularly that of assumed distribution functions) are simplified, with due regard for manufacturing capabilities, with the intention of permitting the development of standard computing procedures (for design and analysis) to be employee in computer-aided design and manufacture.
40 citations
TL;DR: Two methods for improving the efficiency of ray casting in its present form are given here, which reduces computing time more than the first, but has the disadvantage that slivers may occasionally be lost from the image.
Abstract: In solid modelling based on constructive solid geometry and primitive instancing, ray casting is a very suitable technique for visualization of models on a raster display. In its present form, it is, however, too inefficient for interactive use. Two methods for improving the efficiency are given here. The first uses scan-line interval enclosures instead of box enclosures, and also bypasses non-contributing nodes during each traversal of the CSG (constructive solid geometry) tree. The second refines the image step by step by subdivision, thereby avoiding explicit computation of the intensities of many pixels of the image. The second method reduces computing time more than the first, but has the disadvantage that slivers may occasionally be lost from the image.
39 citations
TL;DR: The 3D extensible cell (EXCELL) index is presented together with algorithms for spatial search and for converting a complex polyhedron (boundary representation) into an octree-like block model.
Abstract: A spatial index is a data structure designed to facilitate spatial search, exemplified by the point-in-polyhedron inclusion problem. The 3D extensible cell (EXCELL) index is presented together with algorithms for spatial search and for converting a complex polyhedron (boundary representation) into an octree-like block model. We illustrate the techniques by an application to geometric mine modelling and demonstrate the efficiency of the approach by practical experiments.
38 citations
TL;DR: In this article, the authors report the progress of an SERC sponsored project on recursive subdivision over arbitrary topologies, where the limit surface is generally a standard B-spline surface except at the so-called extraordinary points, where, it is reported, tangent plane continuity can be guaranteed and discrepancies in the curvature can be confined to 10% or less.
Abstract: The paper reports the progress of an SERC sponsored project on recursive subdivision over arbitrary topologies. The limit surface is generally a standard B-spline surface except at the so called ‘extraordinary points’ where, it is reported, tangent plane continuity can be guaranteed and discrepancies in the curvature can be confined to 10% or less. The optimal subdivision procedure is currently being implemented in a designer-oriented form in collaboration with CADCentre Ltd Cambridge.
36 citations
TL;DR: A unified view of solid shape modelling systems that enables their classification and extension into particular application areas is presented.
Abstract: The potential benefits of using a canonical model for representing the shapes of solid objects has led to the design and implementation of a number of geometric modellers, with varying capabilities. This paper reviews the approaches taken in solid modelling by defining the well-formedness conditions which must be implemented in any modelling system. The methods for satisfying the well-formedness constraints in the various solid modelling methods are reviewed, using the concept of integrity constraint. The incorporation of integrity constraints, both explicitly and implicitly, into solid modellers are considered, with particular focus on boundary modellers. The use of integrity constraints for defining shape families and assembly families are also presented. The result is a unified view of solid shape modelling systems that enables their classification and extension into particular application areas.
35 citations
TL;DR: It is proved that algorithm presented generates for curves of some class, called spirals, the minimal number of circular arcs in Tchebycheff norm, which evaluates the published methods of piecewise circular approximation.
Abstract: The approximation of plane curves by smooth piecewise circular arc curves in Tchebycheff norm is analysed. The algorithm of approximation is proposed. It is proved that algorithm presented generates for curves of some class, called spirals, the minimal number of circular arcs. Results are used to evaluate the published methods of piecewise circular approximation.
34 citations
TL;DR: The main requirements for database management systems in a CAD environment are presented and some of the solutions which are currently being implemented are discussed.
Abstract: The main requirements for database management systems in a CAD environment are presented and some of the solutions which are currently being implemented are discussed.
TL;DR: In this article, a mathematical model of an automobile is described, which permits the study of simultaneous cornering and ride motions on irregular terrain, and a major departure from previous analytical treatments of vehicles is abandonment of the concept of a vehicle-fixed "Hinge" to approximate the changing virtual axis about which roll takes place.
Abstract: A mathematical model of an automobile is described, which permits the study of simultaneous cornering and ride motions on irregular terrain. A major departure from previous analytical treatments of vehicles is abandonment of the concept of a vehicle-fixed 'Hinge' to approximate the changing virtual axis about which roll takes place. To ease the task of interpretation of the extensive output information, a computer-graphics display technique has been developed to produce detailed perspective drawings of the vehicle and terrain at selected intervals of time during a simulated manoeuvre. Comparisons are presented of analytically predicted vehicle responses and test results. Future applications of the described mathematical model, in research related to highway safety, are briefly discussed.
TL;DR: In this paper, a consistent theory for the analysis of curvature and deflection of reinforced concrete beams in the cracking stage is presented, which assumes concrete to have a nonzero tensile carrying capacity, characterized by a uniaxial stress-strain diagram which characterizes progressive microcracking due to strain softening.
Abstract: A consistent theory for the analysis of curvature and deflections of reinforced concrete beams in the cracking stage is presented. The theory assumes concrete to have a nonzero tensile carrying capacity, characterized by a uniaxial stress-strain diagram which characterizes progressive microcracking due to strain softening. The tensile stressstrain properties are the same as those which are obtained in direct tensile tests and those which have recently been used with success in modeling fracture test results for concrete. The theory agrees well with the simpler formula of Branson within the range for which his formula is intended. The value of the proposed theory is its much broader applicability. Aside from demonstrating a good agreement with available test data for short-time deformations up to the ultimate load, it is shown that the theory also correctly predicts the longtime creep deformations of cracked beams. To this end, the average creep coefficient for tensile response including peak stress and strain softening needs to be taken about three times larger than that for compression states. The theory also predicts the reduction of creep deflections achieved by the use of compression reinforcement, and a comparison of modeling this effect is made with an ACI formula. As a simplified version of the model, it is proposed to replace the tensile strain-softening behavior by the use of an equivalent tensile area of concrete at the level of tensile steel, behaving linearly. Assuming this area to be a constant, realistic predictions for shorttime as well as longtime deformations in the service stress range can still be obtained.
TL;DR: A new channel routing algorithm is presented, based on reduction of the problem to the case of a ( 2 × n ) grid and on consistent utilization of a ‘divide-and-conquer’ approach, which consistently outperforms several known routers in quality of wiring.
Abstract: The channel routing problem is a special case of the wire routing problem when interconnections have to be performed within a rectangular strip having no obstructions between terminals located on opposite sides of the rectangle. We present here a new channel routing algorithm, based on reduction of the problem to the case of a ( 2 × n ) grid and on consistent utilization of a ‘divide-and-conquer’ approach. For the current implementation of the algorithm, the running time is proportional to N ∗ n log (m) where N is the number of nets, n the length of the channel (number of columns) and m the width of the channel (number of tracks). Traditional technological restrictions are assumed, ie, net terminals are located on vertical grid lines, two wiring layers are available for interconnections. One layer is used exclusively for vertical segments and another for horizontal. Vias are introduced for each layer change. This algorithm consistently outperforms several known routers in quality of wiring. We tested the algorithm on several benchmark problems. One of them, Deutsch's ‘difficult example’, was routed with only 19 horizontal wiring tracks (the absolute minimum for this case), whereas all other known routers required 20 or more tracks.
TL;DR: A structure model is presented which can represent not only the simplified geometry of an individual part but also the whole structure of a machine, which plays an important role in developing a CAD system to aid designers in the primary design stage.
Abstract: A structure model is presented which can represent not only the simplified geometry of an individual part but also the whole structure of a machine. The model is derived from observation of the general features of a machine, ie the hierarchy and the topology (connectivity) among parts. The model plays an important role in developing a CAD system to aid designers in the primary design stage, because a general method for representing the whole structure of a machine is needed at that stage. An interactive machine design system named HIMADES-1 has been developed. The data structure of the system is based on the above structure model. The system has some original features, the most distinctive of which is the unified algorithm for dimension matching and motion analysis which reduces design labour in the primary stages of machine design.
TL;DR: The paper commences with a discussion on new ways of using computers based on knowledge engineering and examples of prototypical expert systems based on a general expert system builder are provided.
Abstract: The paper commences with a discussion on new ways of using computers based on knowledge engineering. Expert systems are defined and their components explicated. Simple architectural examples are provided for each class of knowledge expert systems can deal with. The generic areas in architecture in which expert systems can play a role are described and examples of prototypical expert systems based on a general expert system builder are provided. The examples are drawn from an expert system system builder written in Prolog.
TL;DR: In this article, a spatially segmented set-theoretic structure copes with the complexity of toolpath verification by controlling the spatial division process, which has been a major feature of the tool path verification work but is also important to the development of this type of modelling system in general.
Abstract: Toolpath verification is a natural application of solid modelling However, the large amount of data that must be handled renders many existing techniques unsuitable This paper shows how the authors' spatially segmented set-theoretic structure copes with this complexity Developments in controlling the spatial division process are outlined These have been a major feature of the toolpath verification work but are also important to the development of this type of modelling system in general
TL;DR: In this article, the authors describe an implementation of double quadratic surface patches in the BUILD geometric modeller, along with some details of the methods used in the modeller for geometric calculations on them.
Abstract: This paper reports on a project that brings together sculptured surface techniques and volume modelling. It describes an implementation of ‘double quadratic surface patches’ in the BUILD geometric modeller. An outline of the mathematics of these surface patches is given together with some details of the methods used in the modeller for geometric calculations on them. Some of the general problems encountered in the synthesis of sculptured surfaces and geometric modelling are also discussed.
TL;DR: A programme is described for ship hull definition and fairing using a B-spline tensor product surface reached using CRT, by moving and digitizing control points in three projection planes.
Abstract: A programme is described for ship hull definition and fairing using a B-spline tensor product surface. The definition is reached using CRT, by moving and digitizing control points in three projection planes. Longitudinal parameter curves are compared to fixed offset points. Plotting the surface is done perspectively or by plane sections in one of the three coordinate-planes.
TL;DR: A scanline algorithm is presented which generates a realistic picture of a solid object bounded by curved surfaces which is saved by delaying subdivision, and by using a novel garbage collection technique.
Abstract: A scanline algorithm is presented which generates a realistic picture of a solid object bounded by curved surfaces. Externally, a surface is described by parametric equations. The internal representation is comprised of meshes of cubic splines which may be subdivided. Memory is saved by delaying subdivision, and by using a novel garbage collection technique. Time is saved by exploiting depth coherence. A viewpoint and scanline fix a cross-section represented as a set of curves. There are usually only a few of these to compare, and the curve nearest the viewer often remains nearest over much of its length.
TL;DR: Parametric design in the MEDUSA system is based on the technique of variational geometry, which is superior to parameterised text macros because it uses the draftman's natural language — dimensioning.
Abstract: Parametric design in the MEDUSA system is based on the technique of variational geometry. A drawing or object is dimensioned in the normal way. The dimensions are interpreted as constraints on the object, and the system then automatically modifies the geometry of the object to satisfy those constraints. This approach is superior to parameterised text macros because it uses the draftman's natural language — dimensioning.
TL;DR: In this paper, the authors assess types of visualization and flexible layout programs for CAAD and discuss the areas which knowledge-based design systems should cover, and the areas in which CAAD tools should cover.
Abstract: CAAD tools have gradually come into use in architecture over the past years. Appraisal and evaluation of designs and design tools and the preparation of production innovations are discussed. Types of visualization and flexible layout programs for CAAD are assessed. The areas which knowledge-based design systems should cover are discussed.
TL;DR: Improved proposal on segmented Bezier curves 1 has been improved and a new type of characteristic polygon which can generate inflection points is introduced.
Abstract: The author's proposal on segmented Bezier curves 1 has been improved. The modifications are the: 1. • generalization and automatic determination of the parameter c which controls the shape of interpolants 2. • introduction of a new type of characteristic polygon which can generate inflection points 3. • utilization of the length of tangent vectors These improvements enable our proposal to be applied to wider range sets of data points.
TL;DR: In this article, the state-of-the-art of finite element analysis in a CAD environment and factors influencing it are discussed, and the technological state of the art is briefly reviewed, with special consideration given to shell elements and solution methods.
Abstract: Current use of the finite element method in engineering practice is considered The increasing use of finite element analysis in a CAD environment and factors influencing it are discussed The technological state of the art is briefly reviewed Special consideration is given to shell elements and solution methods, illustrating the progress being made in these and other areas of finite element technology Future trends are predicted
TL;DR: The role and history of CAD in the mechanical engineering industry is briefly discussed, and the greatest progress is expected in geometric modelling, in the application of knowledge engineering technologies and in advanced database systems.
Abstract: The role and history of CAD in the mechanical engineering industry are briefly discussed. Dominant among recent developments have been the sharp increase in the cost-effectiveness of CAD and CAM systems and the imperatives imposed by the economic climate. Combined with the increasing availability of mature software, these have led to a very rapid proliferation even among small and medium-sized companies, despite the economic recession. Social and competitive pressures are leading to more user-friendly systemś. The greatest progress is expected in geometric modelling, in the application of knowledge engineering technologies and in advanced database systems, permitting the closer integration of CAD and CAM activities.
TL;DR: This paper explores the derivation of new rules of thumb from Pareto optimization and presents examples for the design of one-way concrete floor slabs in office buildings.
Abstract: Rules of thumb are of great importance in providing a first approximation in structural design. This paper explores the derivation of new rules of thumb from Pareto optimization and presents examples for the design of one-way concrete floor slabs in office buildings. The encoding of such rules using knowledge engineering concepts is discussed as a mechanism for the acquisition of knowledge for expert systems.
TL;DR: In this article, the progress that has been made in hardware and software is described, and some trends are deduced, giving a picture of the not too distant future, while decrit les progres accomplis par les moyens materiels and logiciels necessaires a son developpement.
Abstract: After briefly reviewing the major stages of CAD/CAM, the progress that has been made in hardware and software is described. From these facts, are deduced some trends, giving a picture of the not too distant future. Apres un bref rappel des etapes principales de l'evolution de la CFAO, on decrit les progres accomplis par les moyens materiels et logiciels necessaires a son developpement. De ces donnees, on essaie de deduire quelle pourrait etre l'evolution dans les annees prochaines.
TL;DR: Algorithms are presented for placement and for modifying existing placements to be used in channel routing solutions for custom VLSI layout, based on mathematical results characterizing the structure of channel routing order constraints.
Abstract: Algorithms are presented for placement and for modifying existing placements to be used in channel routing solutions for custom VLSI layout. The placements are produced so as not to have channel routing order constraint cycles, which constitute a familiar problem for custom VLSI. The algorithms are based on mathematical results characterizing the structure of channel routing order constraints.