Vijay Srinivasan

Automatic mesh generation using the symmetric axis transformation of polygonal domains

An automatic method for generating finite element meshes for multiply connected planar domains with polygonal boundaries (i.e. planar polygons with polygonal holes) is described. The symmetric axis transform is used to obtain a planar graph that partitions the given domain. This transformation may introduce edges in the graph that are too long or too short for generating good meshes. A silver processing algorithm, which transforms the graph into another graph devoid of such edges, is presented. Finally, additional modes are placed on the edges of the graph to obtain a triangulation, and this process is applied iteratively, yielding the final mesh. The method automatically increases the mesh density in regions of rapid change in shape and allows both global and local control of the mesh density. The method also admits the imposition of node compatibility constraints along domain boundaries, thus making the method suitable for meshing planar cell complexes (i.e multiple polygonal domains with shared boundaries in two-dimensional space) and for generating boundary elements for polyhedra in three-dimensional space. >

Voronoi diagram for multiply-connected polygonal domains 1: algorithm

Voronoi diagrams of multiply-connected polygonal domains (polygons with holes) can be of use in computer-aided design. We describe a simple algorithm that computes such Voronoi diagrams in O(N(log 2 N+H)) time, where N is the number of edges and H is the number of holes.

An integration framework for product lifecycle management

Abstract The need for integrating business and technical information systems, allowing partners to collaborate effectively in creating innovative products, has motivated the design and deployment of a novel integration framework for product lifecycle management. The time is ripe for such an integration framework because of the convergence of three important developments, almost in a perfect storm: (1) maturity of standardized product data and meta-data models, and standardized engineering and business processes; (2) emergence of service-oriented architecture for information sharing; and (3) availability of robust middleware to implement them. These developments allow engineering and business objects and processes to be built or composed as modular pieces of software in the form of services that can communicate with each other and be used across different parts of a business. These modular software pieces can be reused and reconfigured in new ways as business conditions change, thereby saving time and money for companies. This paper describes the business and technical aspects of an integration framework for product lifecycle management using open standards and service-oriented architecture.

Geometric tolerancing: 2. conditional tolerances

In a companion paper, we examined the representation of geometric tolerances in solid models from the perspective of certain functional requirements. We showed that assembly and material bulk requirements can be specified as virtual boundary requirements (VBRs). Here, we study the related issue of deriving equivalent alternative specifications. Specifically, we first explore the reasons for converting VBRs to another form of tolerances designated as conditional tolerances (CTs). We then develop a theoretical basis for converting VBRs to CTs and derive CTs for some common and practical VBRs. We thereby demonstrate the difficulties in finding a general-purpose algorithm for such conversions and also show that some of the CT formulas used in current practice are incorrect.

A geometrical product specification language based on a classification of symmetry groups

Abstract A relatively old and deeply entrenched engineering “language” universally used by draughtsmen for specifying product geometry is undergoing renovation for the modern information age. Part of the renovation process is to find a set of firm mathematical principles that can support much of the edifice that has served industry well thus far. This search has turned up a set of surprisingly powerful results based on an elegant classification of continuous subgroups of rigid motion. Among them is a compact classification of surface features and lower order kinematic pairs, their reduction to simpler geometric elements that preserve the classification and serve as datums, and a rationale for parameterizing the relative positioning of geometric objects. These results are now being enthusiastically embraced by the International Organization for Standardization (ISO) as part of the basic principles to define the next generation of a product geometry specification language. The paper tells this story.

Computational Metrology for the Design and Manufacture of Product Geometry: A Classification and Synthesis

The increasing use of advanced measurement tools and technology in industry over the past 30 years has ushered in a new set of challenging computational problems. These problems can be broadly classified as fitting and filtering of discrete geometric data collected by measurements made on manufactured products. Collectively, they define the field of computational metrology for the design specification, production, and verification of product geometry. The fitting problems can be posed and solved as optimization problems; they involve both continuous and combinatorial optimization problems. The filtering problems can be unified under convolution problems, which include convolutions of functions as well as convolutions of sets. This paper presents the status of research and standardization efforts in computational metrology, with an emphasis on its classification and synthesis.

The optimal zigzag direction for filling a two‐dimensional region

Many engineering and scientific problems require the filling of a two‐dimensional region with scan lines of finite width. The number of contiguous scan line segments required for the filling depends on the direction used for scanning. When the cost of the filling operation increases with the number of scan line segments, as is the case in numerically controlled machining, layered fabrication and computer graphics applications, then it is desirable to select a direction that minimizes this number. In this paper we provide a method for efficiently computing such an optimal direction when the region to be filled is bounded by straight‐line segments and/or circular arcs.

ISO Deliberates Statistical Tolerancing

ISO is currently in the first of its three-phase process for developing an international standard for statistical tolerancing of mechanical parts. In this phase the technical scope of the future standard is being defined by a group of international experts. This paper describes the technical deliberations that have been undertake thus far and the standards development process used for this purpose.

Towards an ISO Standard for Statistical Tolerancing

Although statistical tolerancing has been practiced in industry for a long time, standards have paid only limited attention to it. This is changing now because of economic reasons, and ISO is investigating how to standardize statistical tolerancing. In this paper we trace the history and document the current state of the knowledge in standardizing statistical tolerancing. Our objective is to disseminate this information as widely as possible so that the international community is aware of, and has an opportunity to influence, the thinking behind the future ISO standard.

On Architecting and Implementing a Product Information Sharing Service

Recent developments in information technology are influencing the field of engineering informatics in some profound ways. Nowhere is the influence more evident than in the use of Internet-based technologies and standards to share engineering and business information across a worldwide enterprise. In turn, the business need for collaboration among various players and partners in a globally integrated enterprise is driving the development and deployment of open standards, service-oriented architecture, and middleware. The convergence of these developments has provided us an opportunity to architect and implement a product information sharing service described in this paper. The architecture is service oriented and is based on the Object Management Groups PLM Services 1.0 specifications. It is implemented using IBMs WebSphere Process Server middleware and PROSTEPs OpenPDM software. This product information sharing service is one of the first industrial examples of a successful application of service-oriented architecture to product lifecycle management.