A Feature Extraction Interface for CAD Part Models

The concept of “Features” has been recognized as a neutral form of communication between design and manufacturing. Since virtually all CAD systems define part models using B-Rep or CSG formats, a facility is needed to convert geometry based part models to ones which are feature based. This paper outlines the framework of a facility which would enable part models from any type of CAD system to be converted to a format which could be analyzed using a knowledge based design system. This facility relies on the user to recognize and isolate the individual features of the model and then extracts the dimensions, locations and relative positioning of the features within the model. These features are then organized into a feature graph for the construction of a feature based part representation. The procedures for the construction of this part representation include feature instantiation, feature placement and functional specification.

SIXPAQ: A Comprehensive Software Package for Analysis and Synthesis of Six-Bar Dwell Linkages

SIXPAQ is a software package that was created for the interactive analysis and synthesis of six-bar dwell linkages. The package is structured so that any six-bar dwell planar linkage can be designed by simply choosing a reduced number of parameters. Robust algorithms are introduced that allow an accurate and reliable construction of the two loci on which the linkage synthesis procedure is based. Input-output plots and animation are available within the package as visualization aids. The package allows the user to interact with the program to satisfy the dwell and geometry conditions. Animation is achieved using a powerful graphics workstation.

HyperGear: An Object Oriented Design Program for Single Stage Gear Box Design

The need for superior design tools has lead to the development of better and more complex computer aided design programs. Two of the more important new developments in application tools being investigation are Object Oriented Languages, and HyperMedia. Object Oriented Languages allow the development of CAD tools where the parts being designed and the design procedures specified are conceptualized as objects. This allows for the development of design aids that are non-procedural and more readily manipulated by the user trying to accomplish a design task. HyperMedia allows for the easy inclusion of many different types of data, such as design charts and graphs, into the tool that are normally difficult to include in design tools programmed with more conventional programming languages. This paper explores the development of a computer aided design tool for the design of a single stage gear box using the development HyperCard® environment and the HyperTalk® programming language. The resulting program provides a user friendly interface, the ability to handle several kinds of design information including graphic and textual, and a non-procedural design tool to help the user design simple, one stage gear boxes. Help facilities in the program make it suitable for undergraduate instruction in a machine elements design course.

An Extensible Computer Environment for Modeling and Analysis in Mechanical Design

This paper investigates a computer environment approach for the exploration of design behavior in the mechanical design process. Generic component types and behavior modelers are developed based on the needs of mechanical designers and are represented in a computer environment. Built-in component types and physical behaviors are also developed. Extension can then occur as needed during design refinement. The resulting system can support exploration and knowledge refinement during design.

Modeling of Free Vertical Turbulent Diffusion Flames

A mathematical/empirical model compatible with the jet mixing theory for predicting the flow field properties, flame envelope, temperature distribution, and flame heights around a free vertical axi-symmetric turbulent diffusion flame has been developed. The model considers the effects of buoyancy force and the relative angle between the reactant jets. The flames are issued from a burner which consists of a central air jet and an annular fuel (commercial butane) jet. The annular jet is issued either vertically or at an angle to the flame axis. Experiments were performed earlier to measure the temperature distribution and concentration of carbon dioxide and oxygen in such flames. Three angular positions of the annular fuel jet and nine burner geometries were investigated. The model predictions in similar configurations are found to be in fair agreement with the experimental data.

An Integrated Joint Dynamics System for Elastically Jointed Structures

The dynamic behavior of elastic joints strongly affect the dynamic performance of a jointed mechanical system. The dynamic contacts introduced by joint clearances create a system with nonlinear characteristics. Special effort needs to be made to study jointed mechanical systems. This paper presents an integrated joint dynamics system, which can be used to predict the dynamic characteristics of a newly designed structure, or to analyze an existing jointed structure. This joint dynamics system can also be applied as a real time monitoring and diagnosis system when it is connected with a vibration measuring device. The joint dynamics system includes: 1) a theoretical model of jointed structures, in which the joint clearance and joint friction effects are considered; 2) a stochastic simulator which is used to generate vibration data and evaluate system dynamic characteristics; 3) a diagnostic monitoring algorithm for vibration state detection; and 4) a forecasting vibration control scheme. The joint dynamics system is applied to the dynamic analysis of a truss-cell unit structure. The results presented in this paper show that the joint dynamics system is effective.

An Algorithm to Slice 3-D Shapes for Reconstruction in Prototyping Systems

Rapid Prototyping (RP) processes reduce the time consumed in the manufacture of a prototype by producing parts directly from a CAD representation, without tooling. The StereoLithography Apparatus (SLA), and most other recent RP processes build a 3-D object from 2.5-D layers. Slicing is the process of defining layers to be built by the system. In this paper a framework is proposed for the development of algorithms for the representation and definition of layers for use in the SLA, with a view to determine if the slicing algorithms will affect surface finish in any significant manner. Currently, it is not possible to automatically vary slice thicknesses within the same object, using the existent algorithm. Also, it would be useful to use a dense grid for hatching or skin filling any given layer, or to change the hatch-pattern if desired. In addition, simulation of the layered building process would be helpful, so that the user can prespecify parameters that need to be varied during the process. The proposed framework incorporates these and other features. Two approaches for determining contours on each slice are suggested and their implementation is discussed. In the first, the layers are defined by the intersections of a plane with the surfaces defining the object. The plane is moved up from the base of the object as it is being built in increments. All intersections found are stored in a data structure, and sorted in head to tail fashion to define a contour for all closed areas on a layer. The second approach uses a scanline-type search to look for an intersection that will trigger a contour-tracing procedure. The contour-tracer is invoked whenever an unused edge is found in the search. This saves storage and sorting times, because the contour is determined as a chain of edges, in cyclic order. It is envisaged that results of this work on the SLA can be applied to other RP processes entailing layered building.

An Automated Layout Design System for Industrial Plant Piping

This paper describes a new approach to an automated layout design system for industrial plant piping. The routing system, which is the main part of this layout system, is composed of three steps, according to the practical layout design process. By dividing the layout design into the optimal routing phase (Step 1, Step 2) and the arrangement phase (Step 3), it is possible to design without depending on the routing order, and with small computer memory storage capacities. The optimal route is obtained by using the routing algorithm and heuristic search, based on expert knowledge. The arrangements are made by applying the enumeration method, taking the strong and weak constraints into account.

Numerical Simulation of Supersonic Combustion in Quasi One-Dimensional Flow

Supersonic combustion induced by a two-shock system has been studied using a chemical nonequilibrium, quasi one-dimensional flow model. The combustion of stoichiometric, premixed H2-air is described by a chemistry model which consists of 11 species and 28 reactions. The freestream Mach numbers used in this calculations are 8, 10 and 12. The initial pressure is 0.01 atm and temperature 300 K. The first of the two shocks is a conical shock and the second is its reflection. Supersonic combustion has been predicted to occur at combustor pressures between 0.8 and 2.9 atmospheres, and temperatures between 1500 and 3000 K. The Mach number of the flow in the combustor is between 1.7 and 4. These combustor conditions are typical of the future hypersonic propulsion systems. The results also show the changes in the composition of the flow during the induction and heat release phases. The two-shock system is assumed to be generated by a cone. For Mach 8, 10 and 12, the minimum cone angle for generating a strong enough two-shock system to induce supersonic combustion has also been identified.

A Combined Knowledge-Based and Finite Element Approach to Forging Die Design

This paper presents the use of a knowledge-based system to provide the link between computer-aided rule-of-thumb procedures and a finite element simulation package for the design of forging dies. The knowledge-based system automates the mesh generation and regeneration procedure that is traditionally the most cumbersome aspect of such a process. The system is programmed in Prolog, C, and Fortran. It is based on parametric mapping approach and generates 2-D quadrilateral meshes. Results are presented to show its effectiveness in reducing the effort and skill required for conducting forging simulations.