Linking Expert Group Technology With Parametric Design

Expert systems can be integrated with databases and CAD/CAM systems using group technology (GT). By using information in a database, geometric features of parts can be specified by GT codes, and CAD models can be generated automatically using parameterized generic templates. This paper describes a microcomputer-based prototype implementation that merges database, expert, and CAD systems in order to perform GT classification and create CAD models with minimal manual intervention.

Restructuring Applied Thermodynamics: Exploratory Thermodynamics

A graphical method is proposed for removing the “drudge work” of looking up property values and solving the conservation equations and second law in an Applied Thermodynamics course. The vehicle used is VisSim simulation software. The method requires the student to perform the thermodynamic analysis and set up the equations, but the computer finds the property values and solves the equations. This concept allows the student to explore various aspects of the topics covered in such a course, including power and refrigeration cycles, mixtures and psychrometrics, and combustion and equilibrium. Substantial design type problems can be solved easily, as can complicated analyses that are too difficult and time consuming for traditional solution methods.

Use of Finite-Element Stress Analysis in the Design of a Tank-Cannon-Launched Training Projectile

The U.S. Army Armament Research. Development, and Engineering Center (ARDEC) recently expressed a need for a tank-cannon-launched training projectile with reduced penetration capability. The expressed primary design goals for this projectile were to minimize the probability of personnel injury and materiel loss in the event of an accidental impact during a training exercise. In order to meet these design goals, the solid-steel flight body of a current kinetic energy (KE) training projectile, the M865IP, was replaced with a hollow aluminum configuration. Because of the incorporation of aluminum, the structural integrity of the entire projectile during launch was put in question. Thus, a thorough stress analysis of the new design was conducted to alleviate concerns about its structural integrity. Two-dimensional, axisymmetric, quasi-static stress analyses were performed on two new KE training projectile designs. The first analysis indicated that structural failure was possible in the aft portion of the projectile due to compressive loading by the gun gases. Structural failure in this case would be circumferential yielding of the hollow flight body. The aft portion of the round was redesigned, and subsequent stress analysis showed the possibility of structural failure to be resolved. The finite-element modeling approach, the applied boundary conditions, and the results of the stress analyses conducted, based on use of the von Mises failure criterion, will be discussed in detail.

Dynamic Response of Composites to Impact Loading

This paper shares some of our experiences in the use of a supercomputer to facilitate the analysis of impact process in thick composites, and also in the benefits of color animation of the results on a Macintosh computer. An explicit nonlinear finite element program has been ported to the CRAY-2 Supercomputer at the National Center for Supercomputing Applications (NCSA) of the University of Illinois at Urbana-Champaign (UIUC). The calculations were carried out using an impact model developed for high velocity impact of fiber-reinforced layered composites. The model is built on a continuum approach and includes a basic orthotopic constitutive material behavior. It has been validated to some degree with ballistic tests and therefore can provide a reasonable estimate of the effectiveness of a fiber-reinforced layered composite construction as a protective system. A computer program was developed to convert the results of the analysis for hundreds of time steps to 8-bit raster images. The images stored in NCSA’s Hierarchical Data Format (HDF) were then transferred to a color Macintosh workstation and animated using graphics tools developed at NCSA. The same set of images were also directly recorded on a video tape and displayed on any standard VCR. This animation capability allowed us to see important detailed information about various quantities like deformation, pressure, stress, etc., which cannot be easily observed by any other means.

Numerical Solution to the Radial Sink Flow Between Two Disks

A numerical solution to the sink flow between two disks is presented. The numerically predicted pressure is shown to correlate well with the experiment. By comparison to the previous results of the linearized theory, the axial distribution of the radial velocity has been found to be lower at the mid-plane and larger near the disk wall.

Maximum Stress at Intersecting Bores of Pressurized Blocks

In high pressure applications, rectangular blocks of steel are used instead of cylinders as pressure vessels. Bores are drilled in these blocks for fluid flow. Intersecting bores with axes normal to each other and of almost equal diameters, produce stresses which can be many times higher than the internal pressure. Experimental results for the magnitude of maximum tensile stress along the intersection contour were available. A parametric finite element model simulated the experimental set up, followed by correlation between finite element analysis and experimental results. Finally, empirical methods are applied to generate models for the maximum tensile stress σ11 at cross bores of open and close ended blocks. Results from finite element analysis and empirical methods are further matched. Design optimization of cross bores is discussed.

Simulation of Two-Dimensional Turbulent Recirculating Flow Field Behind a V-Shaped Bluff Body

The two-dimensional turbulent recirculating flow fields behind a V-shaped bluff body have been investigated numerically. Similar bluff bodies are used in combustion chambers for flame stabilization. The governing transport equations in conservative form are solved by a pressure based predictor-corrector method. The standard k-ϵ turbulence closure model and a boundary fitted multi-block curvilinear grid system are used in the computation. The code is validated against turbulent flow over a backward facing step problem. The predicted flow field behind the bluff body is also compared with experiment. It is found that while the qualitative features of the flow are well predicted, there is quantitative disagreement between the measurement and prediction. This disagreement can be partially attributed to the k-ϵ turbulence model which is known to be inadequate for recirculating flows. Parametric investigation of the flow field by varying the shape and size of the bluff body is also performed and the results are reported.

Preliminary Phase in Cell Level Modelling

This paper addresses the need to add a preliminary phase to cell level modelling. It is accepted that the Cell level plays an important role within a CIM structure. To assist implementation and research into cell systems, an appropriate modelling technology is required. However, existing modelling methods are not sufficiently adequate. A consolidated approach towards cell level modelling is desirable. Requirements capture and representation is one of the most critical processes in system modelling. The proposed modelling phase is considered as an enabling mechanism through which improved communication between system modellers and users, and consequently better representation of users requirement, can be achieved. This paper discusses the need for a preliminary phase of cell level modelling, especially at the requirements analysis stage of the system life cycle. The essential constituents of this phase are discussed. A partial method, specially designed for the modelling process in this strategy, is briefly introduced.

Analysis of a Balanced Breech System for the M1A1 Main Gun System Using Finite Element Techniques

A series of experiments were recently conducted in an attempt to reduce the dynamic motions of the M256 gun system during firing. Data collected during these experiments included the motion of the gun tube and breech mechanism for both the standard (unbalanced) configuration and a modified system in which mass was added such that the breech center of gravity (CG) was coincident with the gun tube centerline. The results indicated a noticeable change in the dynamic motions between these two configurations. Prior experiments indicated that the unbalanced breech drops several tenths of a millimeter during the firing cycle. Also, the gun tube whipping motion, which is induced by the powder pressure couple, vibrates the gun in a similar fashion regardless of ammunition type. Furthermore, the gun tube shape at shot exit always resembles a distorted sine wave. This behavior was noted for both heat and kinetic energy (KE) munitions in previous unbalanced breech tests conducted with the M256 gun. However, when the breech is balanced, the dynamics of the entire system change in both shape and magnitude of displacement. This report attempts to explain the results of the tests performed. This was accomplished using a three-dimensional (3-D), transient, finite element (FE) model of the entire system, which included breech, gun tube, trunnion mount, recoil, and projectile. Results from these calculations provide an explanation of the observed behavior of the system. Insight acquired about the nature of the system’s behavior was then used to propose several simple improvements to the M256 gun system which can be applied to gun systems in general. Implementation of these changes should decrease the shot-to-shot variability associated with gun accuracy.

Handling Blending Features in Form Feature Recognition Using Convex Decomposition

Form features intrinsic to the product shape can be recognized using a convex decomposition called Alternating Sum of Volumes with Partitioning (ASVP). However, the domain of geometric objects to which ASVP decomposition can be applied had been limited to polyhedral solids due to the difficulty of convex hull construction for solids with curved boundary faces. We develop an approach to extend the geometric domain to solids having cylindrical and blending features. Blending surfaces are identified and removed from the boundary representation of the solid, and a polyhedral model of the unblended solid is generated while storing the cylindrical geometric information. From the ASVP decomposition of the polyhedral model, polyhedral form features are recognized. Form feature decomposition of the original solid is then obtained by reattaching the stored blending and cylindrical information to the form feature components of its polyhedral model. In this way, a larger domain of solids can be covered by the feature recognition method using ASVP decomposition. In this paper, handling of blending features in this approach is described.