Aj Robotham

The use of function/means trees for modelling technical, semantic and business functions

This paper considers the feasibility of using the function/means tree to create a single tree for a complete motor vehicle. It is argued that function/means trees can be used for modelling technical and semantic functions, but it is an inappropriate method for business functions when one tree of the vehicle is required. Life-cycle modelling provides an effective means for determining all the required purpose functions and is considered a more effective method than the function/means tree for this task when the structure and mode of operation of the vehicle is well defined and understood.

Numerical and experimental investigation of aircraft panel deformations during riveting process

In collaboration with Airbus-UK, the dimensional growth of aircraft panels while being riveted with stiffeners is investigated. Small panels are used in this investigation. The stiffeners have been fastened to the panels with rivets and it has been observed that during this operation the panels expand in the longitudinal and transverse directions. It has been observed that the growth is variable and the challenge is to control the riveting process to minimize this variability. In this investigation, the assembly of the small panels and longitudinal stiffeners has been simulated using static stress and nonlinear explicit finite element models. The models have been validated against a limited set of experimental measurements; it was found that more accurate predictions of the riveting process are achieved using explicit finite element models. Yet, the static stress finite element model is more time efficient, and more practical to simulate hundreds of rivets and the stochastic nature of the process. Furthermore, through a series of numerical simulations and probabilistic analyses, the manufacturing process control parameters that influence panel growth have been identified. Alternative fastening approaches were examined and it was found that dimensional growth can be controlled by changing the design of the dies used for forming the rivets.

Modulation of Visually Evoked Postural Responses by Contextual Visual, Haptic and Auditory Information: A 'Virtual Reality Check'

Externally generated visual motion signals can cause the illusion of self-motion in space (vection) and corresponding visually evoked postural responses (VEPR). These VEPRs are not simple responses to optokinetic stimulation, but are modulated by the configuration of the environment. The aim of this paper is to explore what factors modulate VEPRs in a high quality virtual reality (VR) environment where real and virtual foreground objects served as static visual, auditory and haptic reference points. Data from four experiments on visually evoked postural responses show that: 1) visually evoked postural sway in the lateral direction is modulated by the presence of static anchor points that can be haptic, visual and auditory reference signals; 2) real objects and their matching virtual reality representations as visual anchors have different effects on postural sway; 3) visual motion in the anterior-posterior plane induces robust postural responses that are not modulated by the presence of reference signals or the reality of objects that can serve as visual anchors in the scene. We conclude that automatic postural responses for laterally moving visual stimuli are strongly influenced by the configuration and interpretation of the environment and draw on multisensory representations. Different postural responses were observed for real and virtual visual reference objects. On the basis that automatic visually evoked postural responses in high fidelity virtual environments should mimic those seen in real situations we propose to use the observed effect as a robust objective test for presence and fidelity in VR.

Computer-aided drawing and design

1 Introduction.- 2 Computer graphics hardware.- 3 Computer graphics software.- 4 Three-dimensional modelling software.- 5 Two-dimensional shape generation.- 6 Orthographic projection.- 7 Libraries of symbols and parts drawings.- 8 Three-dimensional (3-D) drawing.- 9 Towards integration: draughting and 3-D modeling.- 10 Towards integration: solid modeling.- 11 The fully integrated CAE system.- 12 Exercises.- Appendix A Matrix notation for graphical transformations.- A.1 Two-dimensional transformations.- A. 2 Translation.- A.3 Scaling.- A.4 Rotation.- A.5 Homogeneous co-ordinates.- A.6 Three-dimensional transformations.- Appendix B Graphs.- B.1 Introduction.- B.2 Two-dimensional graphs.- B.3 Three-dimensional graphs.- B.4 Using the computer to display graphs.- Appendix C Sources.- C.1 Hardware and software.- C.2 Plotting and printing.- C.3 Word processing and desk editing.- C.4 Useful addresses.

The fully integrated CAE system

We shall consider in this chapter the integration of CAD with other computer-aided engineering tasks (analysis, manufacture, etc.). We have seen in previous chapters the advantages to be gained from a two-way exchange of data and information in CAD. For example, if a 3-D model of an item is created using a solid modelling system, orthographic views of the item can be generated automatically from the geometric information archived in the solid modelling system database. If the solid modeller is integrated with a 2-D draughting system, then geometric information about the size and shape of the item can be exchanged between the two activities, e.g. the orthographic views of the component can be passed to the 2-D draughting package to produce a fully dimensioned detail drawing of the component. The advantage of this approach is that the integration of these two activities prevents the designer from having to specify the geometric characteristics of an item more than once on the CAD system. This not only saves time, e.g. because the designer does not have to construct the orthographic views of the item from scratch, but ensures that the geometry of a component is represented accurately in both systems. Similarly, if the CAD packages are linked to CAE packages, the same benefits will accrue because the exchange of data can occur across the whole CAE system.

Computer graphics hardware

The term ‘hardware’ is used to cover all those pieces of equipment which are used to implement computer programs. The computer programs themselves are referred to as ‘software’ and are considered in detail in Chapter 3. A third term ‘firmware’ covers those software instructions which have been implemented permanently into the electronic hardware, usually to enable increased speed of computation to be achieved.

Three-dimensional modelling software

The general way in which three-dimensional modelling works and how it differs from 2-D systems will now be discussed.

Towards integration: solid modelling

Solid modelling is the most advanced technique available to the designer for generating a 3-D representation of an item on a CAD system. The solid model represents both the full surface geometry of the item and the interior volume bounded by the surface faces. Consequently, an unambiguous representation of an item can be generated using this technique. The Boolean operators allow ‘material’ simply to be added to, or subtracted from, the item currently modelled on the CAD system. Any new edges or surfaces created by a Boolean operation are calculated immediately by the modelling software and incorporated into the object model. Once an item has been solid modelled, its 3-D representation can be used to integrate the design activity with other CAE activities. The importance of this approach to 3-D modelling can be gauged by its increasing frequency of use in industry for a range of diverse engineering applications. Also the importance of the 2-D database as the basis of an integrated CAE system has declined in preference to the 3-D solid model database.

Libraries of symbols and parts drawings

One of the most valuable facilities offered by CAD software is the option of being able to store files of drawing entities. When required any of these entity files can be recalled to be included in drawings. Sets of such files are known as libraries. The use of library files saves a great deal of time. A detail or symbol can be added to a drawing merely by calling up the necessary entity file from its library disk.

Three-dimensional (3-D) drawing

Of the three CAD packages with which we have been dealing in Chapters 5, 6 and 7, only AutoCAD offers both isometric and true 3-D drawing and modelling facilities. AutoSketch does not have an isometric facility, although isometric drawings can be produced by setting the grid and snap points to different x and y sizes (approximately x = 5.0 and y = 2.9). However like much of the inexpensive software of this type, AutoSketch cannot produce isometric circles (ellipses), isometric drawing is thus mostly restricted to straight lines. Techsoft Designer possesses an isometric capability — GRID and SNAP can be set isometrically by stating the angles required for the x and y grids (30° and 150°) when setting grid points on screen. This software also allows ellipses to be drawn. Examples of isometric drawings created using these three CAD packages are shown in Figs. 8.1, 8.2 and 8.3.