An Octree Method for Interference Detection in Computer Aided 3-D Packing

In simulating the three dimensional packing process with arbitrary shaped objects, the task of detecting interference between objects is important and very difficult. This paper, representing the three dimensional packing space and objects with an octree, presents an effective interference detection algorithm, which can overcome the performance shortcomings that the conventional methods have in terms of real-time response, computer memory and computational accuracy. By recording the distribution status of packing space in the “bits” of short integers, the data space can be compressed to 1/16 of that used by conventional algorithms.

Concurrent Designing of Airframes: State of the Art and Trends

We will first recall that the organization of airframe designing stands in direct relation to the performance capabilities of available tools, which is, in fact, what determines the number and the nature of project iterations. We then present and analyze an organization type which can nowadays be recommended in view of the currently available CAD, computation and mathematical optimization means. This leads to a first design which is followed by experimental verification, with a key role for flight tests. The final design is checked with the aid of computation models that have been calibrated with the results of the performed tests. We will then examine new tools, since they are factors in the future evolution of the design methodology, including: • availability of the “design history”, as a set of all data of the whole process, • structure optimization with parametric CAD and multidisciplinary optimization • “feature” modeling • enhancement of the computation methods As a conclusion, we show that significant gains in terms of productivity and quality can be expected from these new products, both at design and at production level. What remains, however, to be found, are the most appropriate concurrent engineering organizations that are best suited to these new tools.

Path Planning for Spheres in Three Dimensional Environments With Low Interference Index

We consider the path planning problem for a spherical object moving through a three-dimensional environment composed of spherical obstacles. Given a starting point and a terminal or target point, we wish to determine a collision free path from start to target for the moving sphere. We define an interference index to count the number of configuration space obstacles whose surfaces interfere simultaneously. In this paper, we present algorithms for navigating the sphere when the interference index is ≤ 2. While a global calculation is necessary to characterize the environment as a whole, only local knowledge is needed for path construction.

A Knowledge-Based Approach to Design Partial Journal Bearings

Various methods for designing hydrodynamic partial journal bearings are reviewed and an integrated and dependable design procedure is (developed. Knowledge and rule bases pertaining to the design of journal bearings having arcs of 180°, 120°. and 60° are either gathered or derived and represented properly. An expert system is developed using the databases and rulebases. The bearing design is based on one of the following decision criteria: the maximum load, the minimum friction, or the optimal clearance The expert system makes an exhaustive search for all the design solutions. Utility value of each of the final solutions is calculated and the design solutions having utility values above a certain limit are stored The results are presented to demonstrate the usefulness of the knowledge-based approach.

An Effective Method for Modelling Flexible Surfaces of Cloth Objects

In this paper a method for modelling the deformation of flexible objects such as cloth is presented in which the physical analysis can be imported into the geometric simulation. The geometric representations as well as the physical properties of flexible objects are considered. A so-called basic configuration and a constraint finite element method are given to improve previous methods for modelling flexible objects. The basic configuration is a primitive 3-D surface of a flexible object, and the constraint finite element method is a special finite element method with respect to the constraint conditions of the deformed flexible objects. The basic configuration of a deformed flexible surface can be directly obtained from its initial 2-D shape by using some control points and curves. Subsequently, according to the geometric constraint conditions of deformation, the basic configuration is adjusted to a satisfactory flexible surface by the constraint finite element method.

Behavior of Structures Using Simple Plastic Hinge Theory

The behavior of structures under the impact or crash situations demands an efficient modeling of the system for its behavior to be predicted close to practical situations. The various formulations that are possible to model such systems are spring mass models, finite element models and plastic hinge models. Of these three techniques, the plastic hinge theory offers a more accurate model compared to the spring mass formulation and is much simpler than the finite element models. Therefore, it is desired to model the structure using plastic hinges and to use a computational program to predict the behavior of structures. In this paper, the behavior of some simple structures, ranging from an elementary cantilever beam to a torque box are predicted. It is also shown that the plastic hinge theory is a reliable method by comparing the results obtained from a plastic hinge model of an aviation seat structure with that obtained from a finite element model.

Heuristics Based Feature Recognition: A Graph Approach

Feature based modeling has been used as a means to bridge the gap between engineering design and manufacturing. Features can represent an artifact with higher level entities which relate directly to its design functionalities and manufacturing characteristics, such as surface finish, manufacturability, fits, tolerance etc. In this study, a heuristic based feature recognition approach is proposed by using the graph representation of a design. The process consists of two steps: subgraph construction, and subgraph to feature identification. In this study, the subgraph construction is accomplished by using a set of heuristic rules. The process of subgraph to feature identification is carried out with a set of integers and characters which represent the geometric, topological, and semantic characteristics of the corresponding feature. This feature recognition scheme is used for the identification of machine features in a design.

Computerized Simulation of Transmission Errors and Shift of Bearing Contact for Hypoid Gear Drive With Conjugate Gear Tooth Surfaces

Computerized investigation of the influence of alignment errors on the transmission errors and the shift of the bearing contact is proposed. The investigation is performed for an imaginary hypoid gear drive with conjugate tooth surfaces. It is proven that the transmission functions caused by misalignment are periodic discontinues almost linear functions with the frequency of cycle of meshing. The above functions can be totally absorbed by a predesigned parabolic function. The shift of the bearing contact caused by misalignment has been determined as well. The performed investigation is based on computerized simulation of meshing and contact of gear tooth surfaces. The machine-tool settings for the generation of the designed gear drive have been determined. Numerical example that illustrates the developed theory is given. The performed investigation allows to determine the influence of gear misalignment on transmission errors, and design a low-noise hypoid gear drive by a properly predesigned parabolic function of transmission errors.

Computer-Aided Design Synthesis Using Syntactic Solid Modeling

This paper presents a new Computer-Aided Design (CAD) synthesis model which uses Plex Grammar as structural relationship descriptors and NURBS surface representation for constructing standard and non-standard solid entities. Here, the designer uses a syntactic design methodology for early topological and geometrical definition of the structure of concept alternatives resulting from the design process. This syntactic scheme provides the capability of describing a large set of complex structures by using a small set of simple entities. The recursive nature of the grammar and the hierarchical representation of the structure makes the description of complex structures simple and under the direct control of the designer. An object structure constructive tree is generated and subsequently translated into Plex Grammar production rules in order to form an Interconnection Matrix (ICM) expressing. The resulting Plex structure defined in the ICM expresses the topological information among entities which form the specific types of objects. By modifying the Plex grammar rules, various objects with different geometry and topology can easily be reconstructed. Compared to conventional solid modeling techniques, this approach provides more systematic object generation, easy manipulation and modification, control over congruity and the ability to represent sculptured shapes. Several examples of syntactic solid modeling applied in design synthesis will be presented for further usage in downstream applications.

Form Feature Recognition Using Base Volume Decomposition

A new feature recognition method is presented that generates volumetric feature representations from conventional boundary representations of mechanical parts. Recognition is accomplished by decomposing the known total feature volume of a part into a set of smaller volumes through analytic face extension. The decomposed volumes are combined to generate an initial set of features. Alternative sets of features are generated by maintaining and evaluating information on intersections of the initial feature set. The capabilities of the method are demonstrated through both a hypothetical and a real world design example. The method’s ability to locate features despite interactions with other features, and its ability to generate alternative sets of features, distinguishes it from existing recognition techniques.