Geometric modeling and processing

This work presents a procedure aimed at automatically extracting the medulla duct outlines from a human femur radiographic image. The outlines are retrieved by referring to a suitable geometric model of the generic femoral cross section; the projection function deriving from such a model is fitted on the grey level values corresponding to the rows of the digitised radiographic image by means of a least square algorithm. The resulting outlines are used in a software system performing the hip prosthesis pre-operational planning.

Spacedesign is an innovative mixed reality (MR) application addressed to aesthetic design of free form curves and surfaces. It is a unique and comprehensive approach which uses task-specific configurations to support the design workflow from concept to mock-up evaluation and review. The first-phase conceptual design benefits from a workbench-like 3-D display for free hand sketching, surfacing and engineering visualization. Semitransparent stereo glasses augment the pre-production physical prototype by additional shapes, textures and annotations. Both workspaces share a common interface and allow collaboration and cooperation between different experts, who can configure the system for the specific task. A faster design workflow and CAD data consistency can be thus naturally achieved. Tests and collaborations with designers, mainly from automotive industry, are providing systematic feedback for this ongoing research. As far as the authors are concerned, there is no known similar approach that integrates the creation and editing phase of 3D curves and surfaces in virtual and augmented reality (VR/AR). Herein we see the major contribution of our new application.

Noise and vibrations levels are basic parameters in passenger comfort. Vibrations are commonly reduced by adding a layer of damping material to the metal sheet of parts of the vehicle body such as the floor, the roof, the firewall. In common practice the panels to be treated are uniformly covered by a layer of damping material; however this is not an efficient design solution especially with regard to the weight containment. In this paper a novel approach to the optimal damping material distribution will be presented. The proposed method is based on a genetic algorithm procedure which takes into account both the vibrational performance and the weight and cost reduction. A simple case study will be illustrated to demonstrate the capabilities of the developed procedure.

In this paper, B-spline curve fitting and sweep surface generation are used for the geometric design of involute gears. Tooth profiles are described by a B-spline formulation based on interpolating data points with first and second derivative constrains. Tooth surfaces are generated by sweeping the B-spline profiles along specified trajectories. This representation scheme enables tooth shapes to be interactively controlled by manipulating control polygons and sweep trajectories. A CAD-CAE integration allows the analysis of contact and structural three-dimensional problems for various geometric configurations. In the paper, the methodology is applied to the geometric design of involute pinions of face gear drives.

Keywords: B-splines , CAD , Curve fitting , Gear design , Geometric design , Sweep surfaces

Face gear drives have many advantageous characteristics compared to other angular transmissions but their complex geometry makes their design difficult with common approaches. This work is aimed at investigating the stress state of the teeth of a face gear and the mating pinion by integrating a 3D CAD system and a FEA code, and by simulating the meshing of a pinion and gear three teeth sector using contact elements and an automated contact algorithm. The procedures followed to create the 3D models of teeth in mesh are described and finite element analysis results are discussed.

Keywords: CAD , Contact analysis , FEM , Gear design

A CAD procedure has been developed to reduce lead times and development costs in the design of automobile components. The associative parametric capability of a CAD platform were applied to the design of a fuel tank lid. It comprises five macro phases: acquisition of the standards, definition of the main functional design constraints, implementation of a hardcopy design flow, transposition on the CAD platform and validation of the design flow. In this paper the first four topics will be discussed focussing on design functional constraints. The procedure is readily applicable to a vast number of complex components.

An important aspect in developing "intelligent" CAD systems is related to methodologies which are reliable both in handling the relevant information and in modelling the design processes themselves. The intrinsically dynamic nature of these last makes particularly difficult choosing the most suitable methodology to use. This paper describes a prototype Design System, which is capable of generating and dynamically modifying models of design processes and product data that can be considered as Engineering Knowledge Data Bases. The system, implemented in LPA-Prolog++, is based on a hybrid approach that enforces both the Object-Oriented and the Frame paradigms. Frames are mainly devoted to the implementation of the computational model required by the components involved in the design process, while classes are used to assure the inheritance of properties when objects are instantiated or specialized. Information in the Knowledge Data Base is structured using two types of frames: dataFrames, that support the static computational model of the low level components; and linkFrames, that allow for the collection of the low level components into more complex ones without restraining the activation sequence of the pointed frames. In addition, the management of history slots was added to the system in order to associate to the data and process models, at an atomic level, all information related to the rationale of the choices made. The functionality of the system is presented by means of relevant test cases. © 2001 Elsevier Science Ltd.

Keywords: Computer-aided design , Dynamic management , Product data

The evolution of computer aided design (CAD) systems and related technologies has promoted the development of software for the automatic configuration of mechanical systems. This occurred with the introduction of knowledge aided engineering (KAE) systems that enable computers to support the designer during the decision-making process. This paper presents a knowledge-based application that allows the designer to automatically compute and evaluate mass properties of racing cars. The system is constituted by two main components: the computing core, which determines the car model, and the graphic user interface, because of which the system may be used also by nonprogrammers. The computing core creates the model of the car based on a tree structure, which contains all car subsystems (e.g., suspension and chassis). Different part-subpart relationships define the tree model and link an object (e.g., suspension) to its components (e.g., wishbones and wheel). The definition of independent parameters (including design variables) and relationships definition allows the model to configure itself by evaluating all properties related to dimension, position, mass, etc. The graphic user interface allows the end user to interact with the car model by editing independent design parameters. It visualizes the main outputs of the model, which consist in numeric data (mass, center of mass of both the car and its subsystems) and graphic elements (car and subsystems 3D representation).

A genetic algorithm has been designed to optimize the arrangement of stiffening ribs that serve to reduce vibrations and noise in dynamically excited panels. The algorithm was tested on the finite element model of a flat panel whose ribs were modeled by raising some of the nodes. The proposed algorithm, validated by comparison with a panel derived from a commercial software package optimization procedure, allows designers to investigate unconventional rib arrangements and evaluate their performance.

This work illustrates a computer program designed to aid surgeons in selecting the hip prosthesis femoral component during the preoperation planning stage of hip replacement surgery. Starting from the processing of the patient's coxo-femoral region X-ray image, the program, called Hippin, interacts with the user to outline the femoral region, including the head and the inner contour of the proximal femur. It automatically examines all possible couplings with the patient's femur outlines from a database containing the outlines of the available prostheses created by digitizing the templates normally used in preoperation planning. The resulting images enable the surgeon to visually compare all the alternatives. In addition, the program provides numerical values for the distances between the physiological rotation and prosthesis centers, helping the surgeon in selecting from among the possibilities. The program has been validated by comparing the computer results with actual surgeon selections. (C) 2000 Elsevier Science Ireland Ltd.

Keywords: Hip prosthesis , Image processing , Preoperation planning

A new approach to the finite element simulation of the dynamic behavior of trimmed panels with an equivalent material is illustrated. By taking into account both the bending and membrane effects in a shell element, the proposed method overcomes the drawbacks of conventional methods, i.e., excessive calculation times and, in the case of software using equivalent shells, application limited solely to flat plates. Testing conducted on several finite element models of various complexities has validated the simplicity and reliability of the method.

A new approach to the finite element simulation of the dynamic behavior of trimmed panels with an equivalent material is illustrated. By taking into account both the bending and membrane effects in a shell element, the proposed method overcomes the drawbacks of conventional methods, i.e., excessive calculation times and, in the case of software using equivalent shells, application limited solely to flat plates. Testing conducted on several finite element models of various complexities has validated the simplicity and reliability of the method.

Damping must be accurately determined in the design and/or optimization of vehicle and aircraft trim. Yet, owing to the complexity of the dynamic interaction among the components in trimmed panel systems, until now it has been difficult to obtain reliable damping estimates. In this work, the power input method (PIM), which compares dissipated energy to the structure's strain energy, was evaluated as a damping evaluation tool. Numerical simulations were used to analyze the lumped mass system (with custom software) and the plates (with commercial finite element software) and consequently to evaluate the assumptions required to apply the PIM. It was thus possible to find a way of minimizing the effect of the assumptions on the results, whose importance would be fundamental in the successive phase involving the experimental application of the method. © 1999 by ASME.

Damping must be accurately determined in the design and/or optimization of vehicle and aircraft trim. Yet, owing to the complexity of the dynamic interaction among the components in trimmed panel systems, until now it has been difficult to obtain reliable damping estimates. The power input method (PIM) was numerically investigated in Part 1 of this work. The results regarding how to reduce the effects of the assumptions required to apply the method were put into practice through the experimental activity with impact hammer excitation described in this work. The experimental testing was conducted on flat and bent steel plates of various sizes trimmed with damping material. A method, called the “numerical updating technique” (NUT), was developed to reduce the number of measuring points and the effects of the discretization on the kinetic energy estimation. Comparison of the numerical and experimental results has validated the reliability and suitability of the proposed method. © 1999 by ASME.

The design of mechanical assemblies carried out using today's CAD systems is mainly developed by modelling single parts, and then assembling them in a subsequent design phase. This bottom-up approach is not congruent and not satisfying the way designers are used to design assemblies. Besides, most of the CAD systems are weak for what concerns several functionalities. For example, the manipulation or the modification of the part geometry or the mating conditions of a created assembly is not supported. The introduction of the feature-based approach in assembly design, already successfully used in the design of single parts, would offer several advantages. For example, it would allow designers to start drawing the assembly from a top view, leaving the design of details and subsystems to a following phase. This paper describes some results of research work done within a project funded by the European Union aiming at extending and validating the use of features, to help in the solution of assembly problems in aeronautical applications. Copyright © 1999 Inderscience Enterprises Ltd.

Keywords: Assembly feature , Feature-based design , Knowledge formalization , Knowledge-based system

A prst step towards a semi-immersive Virtual Reality (L!R) interface for Finite Element Analysis (FEA) is presented in this paper. During recent years, user interfaces of FM solvers have matured from characterbased command-line driven implementations into easy-touse graphical user interfaces (GUS). This new generation of GUIs provides access to intuitive and productive tools for the management and analysis of structural problems. Many pre-And post-processors have been implemented targeting the simplification of the manmachine interface in order to increase the ease of use and provide better visual analysis of FEA solver results. Nevertheless, none of these packages provides a real 3Denabled interface. The main objective of this project is to join state-of-The-Art visualization technology, VT devices, and FM solvers into the integrated development environment VRFM.

Keywords: 3D Modeling , Finite Element Analysis , Interactive Modeling , Simulation. , Virtual Reality

A method for a conservative reconstruction of damaged or incomplete geometrical models into flawless and consistent Brep based solid models are introduced. Practical experiments employing the approach of space point tolerance driven face sewing within a prototype testbed implemented showed already promising results for a limited range of investigated models containing structural errors and data exchange inflicted errors.

The problem of damping representation and measurement is investigated. Among the many parameters found in literature, the most comprehensive is loss factor η. Several definitions of η are feasible, but in linear problems they all should reduce to the ratio of the in-phase and quadrature parts of the associated complex modulus. This work surveys measuring methods for materials and structures with respect to the way they express η, either by approximated or correct expressions. Since some commonly used techniques such as the Oberst method do not follow the definition of η, special care is required when dealing with damping values obtained by different methods and in different environments. On the whole, non-homogeneous values must be expected, owing to the physical differences among the phenomena that enable damping measurement.

This work describes the third phase in the authors' development of an experimental procedure for determining the loss factor by the power input method (PIM). Unlike in the second phase in which the excitation was provided by an impact hammer, the excitation in the third phase was provided by a shaker. Experimental testing performed on a special-design setup validated the effects of parameters such as shaker mass, excitation point position, non-perpendicular force input, and specimen size and shape, as well as repeatability. In the fourth phase, the number and shape of the structure portions to be used in the measuring procedure will be determined.

Current research trends are extending from partially integrated product and process modeling to life cycle modeling, in order to provide a framework and methodologies based on a holistic approach for the support of sustainable product development. Within given scope we are interested to investigate, if feature technology, introduced in the late seventies and developed over the paste twenty years provides the potential, if further enhanced, to be used as a means to provide basic integration for geometry related processes and models over different product life cycle stages. In a first approach, feature neighborhoods are developed and introduced as an extension, to foster evaluation of disassembly / reassembly on grounds of feature-based product descriptions. An attempt to support product maintenance and material recycling within life cycle modeling while investigating structural dimension and limits of improved feature models as a means of geometrybased model integration.