Spline Based Design of Cam Contours for Improved Dynamic Performance

A method for the integrated design and manufacture of radial plate cams is discussed. Currently, a cam-follower system is designed by specifying constraints on the motion of the follower. The physical cam contour or cam pitch curve are not mathematically defined. The cam is manufactured from the discretized follower motion program. A new method for cam design is proposed which will produce a smooth, mathematically defined cam pitch curve while maintaining the proper constraints on the follower motion. Piecewise polynomial functions in the form of rational and/or non-rational splines may be used. Cams will be manufactured using smoothed profiles and tested for improved dynamic performance. The results of initial investigations of cam profile design for this research are presented.

Finite Element Modeling for Prediction of Residual Stresses in Fiber Reinforced Metal Matrix Composites

In metal matrix composites residual stresses developing during the cool-down process after consolidation due to mismatch in thermal expansion coefficients between the ceramic fibers and metal matrix have been predicted using finite element analysis. Conventionally, unit cell models consisting of a quarter fiber surrounded by the matrix material have been developed for analyzing this problem. Such models have successfully predicted the stresses at the fiber-matrix interface. However, experimental work to measure residual stresses have always been on surfaces far away from the interface region. In this paper, models based on the conventional unit cell (one quarter fiber), one fiber, two fibers have been analyzed. In addition, using the element birth/death options available in the FEM code, the surface layer removal process that is conventionally used in the residual stress measuring technique has been simulated in the model. Such layer removal technique allows us to determine the average surface residual stress after each layer is removed and a direct comparison with experimental results are therefore possible. The predictions are compared with experimental results of an eight-ply unidirectional composite with Ti-24Al-11 Nb as matrix material reinforced with SCS-6 fibers.

AXITURB: A Full Computer Implementation of the NASA Design Procedure for Axial-Flow Turbines

A recent task to design a Rankine-cycle space-power turbine system employing eutectic alloys of alkali metals prompted the present authors to re-examine the NASA design procedure for axial-flow turbines, as outlined by Glassman and Futral (and based on works of Stewart) in 1963. After clarifying the role of the singular case of a single-stage turbine, and organizing the procedure in clear steps, a computer program AXITURB was written. The present paper reports essentially the success of AXITURB in performing parametric studies of NaK and CsK turbines (using 78.4% and 23.1%, respectively, of potassium by weight), after re-generating all the reported NASA designs for turbines employing pure Na, K and Cs. An outline of design steps is also given. AXITURB has been put in public domain. Its heavily commented source code in FORTRAN is available to designers for adaption or modification.

Feature-Based Design: 4 Hypotheses for Future CAD Systems

Features are meaningful abstractions of geometry that engineers use to reason about components, products, and processes. For design activity, features are design primitives, serve as the basis for product representations, and can incorporate information relevant to life-cycle activities such as manufacturing. Research on feature-based design has matured to the point that results are being incorporated into commercial CAD systems. The intent here is to classify feature-based design literature to provide a solid historical basis for present research and to identify promising research directions that will affect computer-based design tools within the next few years. Applications of feature-based design and technologies of feature representations are reviewed. Open research issues are identified and put in the context of past and current work. Four hypotheses are proposed as challenges for future research: two on the existence of fundamental sub-feature elements and relationships for features, one that presents a new definition of design features, and one that argues for the successful development of concurrent engineering languages. Evidence for these hypotheses is provided from recent research results and from speculation about the future of feature-based design.

Integrated Microcomputer-LDV Instrumentation for Studying Finite Wing Aerodynamics

The effect of a simulated glaze ice accretion on the flow field of a three-dimensional wing is studied experimentally. A PC-based data acquisition and reduction system was used with a four-beam two-color fiber-optic laser Doppler velocimeter (LDV) to map the flow field along three spanwise cuts on the model. Results of the LDV measurements on the upper surface of the finite wing model without the simulated glaze ice accretion are presented for α = 0 degrees at Reynolds number of 1.5 million. Measurements on the centerline of the clean model compared favorably with theory.

3D-to-2D Mapping of Cutter Paths in NC Programming of Complex Engineering Parts

The concept of mapping a three dimensional (3D) contouring cutter path with major motion in a plane parallel to the Z axis onto the X-Y plane or one perpendicular to the Z axis is introduced. A systematic method is developed that can be used to program, in APT or other high-level languages, complex contouring cutter motion based on the concept introduced. As a result, NC programming of contouring motion for many complex engineering parts on a 3-axis numerically controlled (NC) milling machine, which is often considered difficult, can be greatly simplified. Part examples are discussed; and the APT programs defining the cutter path based on the 3D-to-2D mapping concept, are also analyzed in detail. The concept and method introduced proved to be a powerful tool for programming the NC machining process for many parts, particularly dies and molds.

Artificial Neural Networks Used As a Rule Selector for Fuzzy Logic Controllers

A feedforward, three-layer, partially-connected artificial neural network (ANN) is proposed to be used as a rule selector for a rule-based fuzzy logic controller. This will allow the controller to adapt to various control modes and operating conditions for different plants. A principal advantage of an ANN over a look up table is that the ANN can make good estimates to fill in for missing data. The control modes, operating conditions, and control rule sets are encoded into binary numbers as the inputs and outputs for the ANN. The General Delta Rule is used in the backpropagation learning process to update the ANN weights. The proposed ANN has a simple topological structure and results in a simple analysis and relatively easy implementation. The average square error and the maximal absolute error are used to judge if the correct connections between neurons are set up. Computer simulations are used to demonstrate the effectiveness of this ANN as a rule selector.

Knowledge Based Expert Systems for CAD/CAM Experience of an EDM Application

In this paper we present our experience from the use of two different expert system development environments to Wire-EDM CAD/CAM knowledge based application. The two systems used follow two different AI approaches: the one is based on the constraint propagation theory and provides a natural language oriented programming environment, while the other is a production rule system with backward-forward chaining mechanisms and a conventional-like programming style. Our experience showed that the natural language programming style offers an easier and more productive environment for knowledge based CAD/CAM systems development.

NERO: A Teleoperated Wall Climbing Vehicle for Assisting Inspection of a Nuclear Reactor Pressure Vessel

NERO is a series of teleoperated wall climbing vehicles. Each vehicle carries a specific tool for assisting inspection of a nuclear reactor pressure vessel in the U.K. They adopted a simple sliding frame walking mechanism to cope with 250mm head room and 25mm obstacles on the surface. Vacuum suckers are used by the vehicle for climbing vertical surface. The NERO vehicle is driven remotely by an operator via a control console. The status of the vehicle and the control console is displayed on the console’s computer monitor. These vehicles completed their tasks successfully by September 1992.

Teaching the Finite Element Method As a Design Tool for Mechanical Engineering

The importance of the finite element method as an engineering tool for design and analysis is emphasized in a senior level elective course taught at Michigan Technological University. The course emphasizes hands-on experience with computers and the pre- and post-analysis of results to establish confidence in solutions obtained. The students learn by using the finite element method to “solve” several design projects, rather than by being told about the method without significant actual experience. They also learn about the basis of the method, including formation of the matrix equations required and the numerical methods used in their solution. Intelligent use of the method requires that engineers understand both the mechanics of how to apply the method, i.e modeling requirements, and the limitations imposed by the basic solution process. The course provides the students with important experience in using the powerful finite element method as a design tool. It requires a strong background of fundamentals and stimulates the problem solving thinking skills so essential to industry.