Development and application of a computer-based system for conceptual aircraft design

Development and application

of a computer-based system

for

conceptual aircraft design

TR diss

of a computer-based system

for

^(/u kv! conceptual aircraft design

Development and application

of a computer-based system

for

conceptual aircraft design

PROEFSCHRIFT

Ter verkrijging van de graad van doctor

aan de Technische Universiteit Delft,

op gezag van de Rector Magnificus,

prof.drs. P.A. Schenck,

in het openbaar te verdedigen

ten overstaan van een commissie

aangewezen door het College van Dekanen

op 8 november 1988 te 16.00 uur

door

Cornells Bil

Geboren te Oud-Beijerland

Vliegtuigbouwkundig ingenieur

Delft University Press / 1988

TR diss

1. De toepassing van een computergesteund voorontwerpsysteem b i j het

ontwerpen van vliegtuigen biedt de mogelijkheid het ontwerpproces t e

v e r s n e l l e n en t e komen t o t een b e t e r koncept-ontwerp ( z i e d i t

proefschrift).

2. B i j het gebruik van s t a t i s t i s c h e analyse methoden b i j multivarlabel

optimaliseren dient uiterste zorgvuldigheid te worden betracht.

3. Een ontwerpsysteem dient te worden ontwikkeld uitgaande van het tradi­

tionele ontwerpproces: een dergelijk systeem dient h i e r mogelijkheden

aan toe te voegen.

I

t. De toepassing van s t a t i s t i s c h e analyse methoden vanwege de o n v o l ­

ledigheid aan ontwerpgegevens, betekent slechts dat deze gegevens binnen

zekere grenzen impliciet worden vastgelegd.

5- De beschikbaarheid van steeds snellere computers stimuleert de tendens

fundamentele rekenmethoden s t e e d s vroeger in het ontwerpproces t e

gebruiken.

6. De introduktie van geïntegreerde ontwerpsystemen vereist een aanpassing

van de beslissingsstruktuur.

7. Het gebruik van een ontwerpsysteem ontslaat de gebruiker n i e t van het

hebben van fundamentele kennis en inzicht op het gebied van ontwerpen

van vliegtuigen.

8. Bij het ontwikkelen van computer programmatuur vormt het schrijven van

een deugdelijke handleiding ten onrechte een sluitpost.

werking met de Nederlandse vliegtuigindustrie op commerciële basis plaats te vinden.

10. Een sterke koppeling tussen het studierendement en de beschikbare financiële middelen bedreigt de kwaliteit van het onderwijs.

Delft University Press

Copyright © 1988 by author.

All rights reserved.

No part of the material protected by this copyright notice may be reproduced or utilized

in any form or by any means, electronic or mechanical, including photocopying,

recording or by any information storage and retrieval system, without written permission

from the publisher: Delft University Press.

List of Contents

page

List of symbols 6

PART 1: INTRODUCTION TO COMPUTER-AIDED AIRCRAFT DESIGN 12

1. COMPUTER-AIDED ENGINEERING IN AIRCRAFT DESIGN 13

1.1 A historical overview 13

1.2 Potential benefits of computer-aided engineering 17

1.3 Computer-aided engineering at the Delft University of

Technology 18

2. THE AIRCRAFT DESIGN PROCESS 21

2.1 The design synthesis 21

2.2 The search for the optimum design

22

2-3 Procedures for design optimization 25

PART 2: THE AIRCRAFT DESIGN AND ANALYSIS SYSTEM 27

3. THE AIRCRAFT DESIGN AND ANALYSIS SYSTEM 28

3.1 Principal requirements for ADAS 28

3.2 The ADAS system architecture 30

3.3 Project organization and data protection 32

4. DESIGN DEFINITION 34

4.1 The user-system interface 34

4.2 Configuration geometry definition 36

4.2.1 The MEDUSA drafting and modelling system 37

4.2.1.1 2D drafting 37

4.2.1.2 3D geometric modelling 38

4.3 Design data storage and retrieval 42 4.3.1 Database nanagement systems 42 4.3.2 The ADAS design database 42 4.3.3 The database data structure 44 4.4 Definition of design analysis methods 49

4.4.1 The analysis program 49 4.4.2 The program library 50

5. DESIGN ANALYSIS 52 5.1 The project file 52 5.2 ADAP compile, load and run step 53

5-3 The ADAP executive program 54 5-3-1 ADAP data storage and retrieval 55

5.3.2 ADAP analysis modes 57 5.3.2.1 Parametric survey mode 59

5.3-2.2 Optimization mode 60 5.3.2.3 Design point analysis mode 65

6. DESIGN EVALUATION 66 6.1 Data postprocessing with ADAS 66

6.2 Graphical representation of parametric data 67

6.2.1 Types of engineering diagrams 69

6.2.1.1 Carpet plots 69 6.2.1.2 Surface plots 71 6.2.1.3 Contour plots 71 6.2.2 Auto-scaling and annotation 73 6.2.3 Curve fitting and interpolation techniques 74

6.2.3.1 The osculatory method 74 6.2.3.2 Butland's method - 76

6.3 The ADAS ■* MEDUSA interface 76 PART 3: ANALYSIS METHODS FOR CONCEPTUAL AIRCRAFT DESIGN 81

7- WEIGHT ANALYSIS 82 7.1 Fuselage weight 83 7.2 Wing weight 86

7-3 Empennage weight 87 7.4 Undercarriage weight 89 7-5 Control systems weight 89 7.6 Propulsion group weight 90 7*7 Engine nacelles and pylons weight 91

7>8 Airframe systems and instruments weight 91

7.9 Furnishing and equipment weight 93 7.10 Operational items weight 94

7.11 Payload weight 95 7.12 Fuel weight 95

8. AERODYNAMIC ANALYSIS 97 8.1 Lifting surfaces 96

8.1.1 The wetted area of lifting surfaces 101

8.1.2 The mean aerodynamic chord 102 8.1.3 The flat-plate friction coefficient 103

8.2 Fuselage 105 8.3 Engine nacelles 109 8.4 Interference drag 110

8.5 Trim drag 110 8.6 Aerodynamic curves generation 110

9. ATMOSPHERIC PROPERTIES 116

10. RANGE PERFORMANCE 115 10.1 The equivalent range concept 115

10.2 Payload versus range 117

11. FIELD PERFORMANCE 124 11.1 Takeoff performance 124

11.1.1 The takeoff run 126 11.1.2 The rotation phase 127 11.1.3 The airborne phase 128 11.1.4 The stop distance 130 11.1.5 The Balanced Field Length 131

12. OPERATIONAL CLIMB PERFORMANCE 135

12.1 Angle of attack and climb angle for quasi-stationary

climb 135

12.2 Operational climb procedure 137

12.3 Maximum speed in horizontal flight 139

13. LOAD AND BALANCE ANALYSIS 140

13.1 Center of gravity at Operational Empty Weight I'M)

13.2 Center of gravity travel Hi

13.2.1 Passengers 141

13.2.2 Cargo 142

13.2.3 Fuel 143

14. DIRECT OPERATING COST 145

PART 4: APPLICATION EXAMPLE OF ADAS 152

15. DESIGN EXAMPLE OF A SHORT-HAUL PASSENGER AIRLINER 153

15.1 The design specification 153

15.2 The baseline design 154

15-3 Optimum aspect ratio and wing loading for minimum MTOW 158

15.3.1 Engines fixed 160

15.3.2 Engines sized for cruise 161

15.3.3 Engines sized for takeoff 163

15.3.4 Design with multivariate optimization 165

15.4 Optimum design evaluation 169

15.5 Effect of design range 170

15.6 Effect of alternative merit functions 173

16. CONCLUSION 17*

Appendices

A: ADAS COMMAND SUMMARY 197

B: The MEDUSA - ADAS Interface protocol 201

B-l Lifting surfaces planforms 203 B-2 Airfoil selection and positioning 204 B-3 High-lift devices and control surfaces 205

B-4 Wing fuel tanks geometry 206

B-5 Fuselage geometry 207 B-6 Doors and windows 211 B-7 Fuselage internal arrangement 214

B-8 Engine selection and positioning 217 B-9 Extended air intake ducts 219 B-10 Undercarriage geometry and disposition 220

B-ll Center of gravity locations 222 B-12 ADAS significant layer numbers 223

C: THE ENGINE LIBRARY 228 C-l Engine nacelle geometry 228

C-2 Engine performance data 229 C-3 Engine scaling techniques 231

D: THE AIRFOIL LIBRARY 243 D-l Airfoil geometry 243 D-2 Airfoil aerodynamic data 244

E : ADAS PROGRAM MODULES SUMMARY 247

Summary 252 Samenvatting 255 Curriculum Vitae 258

List of Symbols

a - a c c e l e r a t i o n , speed o f sound A - aspect r a t i o

b - span

B - bounds of free variables and constraints c - chord length, coefficient

C - rate of climb, cost, coefficient, circumference CO - constraint functions

D - drag, diameter e - Oswald factor exp - exponent

E - induced-drag factor for low-speed parabolic drag polar f - function, factor

fmt - print format, i.c the number of significant decimal digits F - form factor FV - free variables g - gravitational acceleration h - altitude, height H - Hessian matrix i - index, counter j - index, counter

k - equivalent sand grain size 1 - length

L - length, lift

m „--._ . m a s s _ _...._ _ M - pitching moment. Mach number

MAC - mean aerodynamic chord n - load factor

N - number of ... 0 - origin OBJ - objective function

dynamic pressure q = p p V , curve slope recovery factor

range

Reynolds number

area (no index: reference area) survey function

survey variable

airfoil thickness, time thrust, ambient temperature aircraft utilization

speed, volume, bounds of survey variables weight, curve-fit weight factor

angle of attack

Prandtl-Glauert compressibility factor, scale factor for finite-difference gradient approximations

climb angle, ratio of specific heats engine rating

flap/slat setting geometric twist angle difference

non-dimensional spanwise station pitch angle

taper ratio, fuselage slenderness ratio sweep angle

runway friction coefficient ambient kinematic viscosity ambient atmospheric density engine scale factors

lifting surface thickness ratio

subscripts

aircraft, aerodynamic center airconditioning system airframe

airframe spare parts additional items anti-icing system

afterbody, airborne phase Auxilary Power Unit Air Traffic Control avionics

span, basic bulkheads cargo cabin crew cabin crew pay

cabin crew provisions cabin crew seats compartment communications system cowling cruise diameter, dive depreciation doors and windows engines, empty electrical system escape provisions engines support engines spare parts fuselage, friction flight crew

floor covering flight crew pay

flight controls system flap control system flight deck

flight deck accommodations flight deck controls

fire detection and extinguishing system furnishing and equipment

flight, floor flaps

flight management system standard frames

fuel system fuel tank

fuel tank support ground, gross galley horizontal tailplane hydraulics system induced initial insurance inspection instruments lower

laminar boundary layer landing

lavatory provisions and water system lighting system

manoeuverlng control system nacelles navigation system non-optimum operational empty other instruments oxygen system

pass - passengers pay - payload pc - passenger cabin pcf - passenger cabin floor pcs - passenger cabin supplies pi - propulsion instruments prop - propeller

ps - pneumatic system

pwtc - potable water and toilet chemicals pyl - pylon

r - root ref - reference rev - thrust reversal rfo - residual fuel and oil R - rotation phase s - structural, steps

sbcs - speed brakes control system scs - slat control system

se - safety equipment serv - aircraft servicing sk - skin

sit - slats spb - speed brakes

spcs - spoilers control system spi - sound proofing and insulation stab - horizontal stabilizer

str - stringers and longerons struc - structures t --... .._.tail,._tip_ to - takeoff ts - tail support

turb - turbulent boundary layer T - boundary layer transition u - upper

uc - undercarriage ult - ultimate

V V S vscs

w

wb

ws

wss

variable stabilizer control system wing wheelbays windows windshield wing/fuselage support water/waste system

PART 1: INTRODUCTION TO COMPUTER-AIDED AIRCRAFT DESIGN

This part g i v e s a b r i e f and general Introduction Into the

field of computer-aided design and engineering. A h i s t o r i c a l

overview I s given, leading Into an assessment of the present

situation with respect to computer applications In a i r c r a f t

design In general and conceptual and preliminary design In

particular.

1. COMPUTER-AIDED ENGINEERING IN AIRCRAFT DESIGN

Computer applications have become commonplace in many areas of design and

engineering. Advances in computer technology have resulted in a continuous

improvement i n computational performance and memory c a p a c i t y . With the

introduction of single-user workstations, either stand-alone or included in

a network interlinked with other processors and peripheral d e v i c e s , con­

s i d e r a b l e dedicated computing resources have become a v a i l a b l e t o the

engineer at a relatively low cost [Ref. 8 2 ] . Besides the t r a d i t i o n a l func­

t i o n o f s o l v i n g l a r g e - s c a l e numerical problems ('number crunching'),

additional computer capabilities have emerged. For example, the so-called 4D

graphics workstations allow real-time object visualization for animation and

simulation. Special-purpose machines for symbolic manipulation have been

developed for the implementation of knowledge-based systems and other ap­

plications in the f i e l d of a r t i f i c i a l i n t e l l i g e n c e [Ref. 7 2 ] . Since the

beginning of the computer era, the aerospace industry in particular i s

playing a leading r o l e in the application of these new technologies to

improve aircraft development and manufacturing.

1.1 A historical overview

Before I960, the computer was hardly integrated into the design process. I t

was mainly used for running self-contained analysis programs, u s u a l l y i n a

batch-mode environment. Bach department Or design team availed of their own

specific analysis codes, generally developed and operated by s p e c i a l i s t s .

However, the interchange of design information between these 'isolated

islands' was s t i l l a manual task and therefore time-demanding and error

prone. In 1950, the technical f e a s i b i l i t y to display computer-generated

p i c t u r e s on a CRT was demonstrated a t MIT [Ref. 9 9 ] . In 1962, a f t e r appreci­ a b l e a d v a n c e s i n i n t e r a c t i v e computer technology, t h i s new technique was implemented i n t h e f i r s t experimental d r a f t i n g system (SKETCHPAD). I n 1 9 6 5 , t h e Lockheed A i r c r a f t Company d e v e l o p e d t h e Computer-Aided Drafting And Manufacturing system (CADAM) [Refs. 18 and 1 1 7 ] , one of the f i r s t commercial d r a f t i n g s y s t e m s w h i c h i s a t p r e s e n t i n u s e w i t h many a i r c r a f t manufacturers. Around 1980, the CADAM c a p a b i l i t i e s were augmented w i t h t h e i n t r o d u c t i o n o f a s p e c i f i c 3 - d i m e n s i o n a l s y s t e m r e f e r r e d t o a s CATIA (Computer-graphics Aided Three-dimensional I n t e r a c t i v e Application s y s t e m ) , a l s o d e v e l o p e d by an a i r c r a f t manufacturer: the Avions Marcel Dassault -Breguet A v i a t i o n company [Ref. 2 2 ] . At p r e s e n t , a wide range o f CAD/CAM-s y CAD/CAM-s t e m CAD/CAM-s a r e c o m m e r c i a l l y a v a i l a b l e on variouCAD/CAM-s typeCAD/CAM-s of computer hardware. Drafting and modelling systems are u s u a l l y a s s o c i a t e d w i t h Computer-Aided Design (CAD).

The introduction o f the i n t e r a c t i v e computer graphics c a p a b i l i t y prompted a change i n the scope of computer a p p l i c a t i o n s . One became aware of the poten­ t i a l b e n e f i t s o f computer a p p l i c a t i o n i n the o v e r a l l d e s i g n p r o c e s s . T h i s i n i t i a t e d a t r e n d towards i n t e g r a t i n g s e l f - c o n t a i n e d engineering programs, e . g . mesh-generators f o r s t r u c t u r a l a n a l y s i s , g e o m e t r i c m o d e l l i n g and NC-t o o l i n g , i n NC-t o d e s i g n sysNC-tems. Usually, engineering programs are i n NC-t e r f a c e d w i t h , and configured around, c e n t r a l database systems. G r a d u a l l y , t h e r o l e o f t h e computer e v o l v e d i n t o a powerful design t o o l , p r a c t i c a l l y i n d i s p e n -s i b l e for the d e -s i g n and m a n u f a c t u r i n g o f t o d a y ' -s complex and e f f i c i e n t a e r o s p a c e v e h i c l e s . The i n f r a s t r u c t u r e o f computer systems for t h e o v e r a l l support o f a l l d e s i g n and e n g i n e e r i n g a c t i v i t i e s , u p t o m a n u f a c t u r i n g , i s g e n e r a l l y referred t o a s Computer-Aided Engineering (CAE).

A ~ c l a s s i f i c a t i ö n o f the c u r r e n t l y a v a i l a b l e CAE-systems a c c o r d i n g t o t h e i r d e p e n d e n c y on t y p e o f a p p l i c a t i o n , design phase and d i s c i p l i n e i s given i n Figure 1 . 1 [Ref. 5 1 ] . With the t r a d i t i o n a l CAD/CAM s y s t e m s p r a c t i c a l l y any o b j e c t c a n be g e o m e t r i c a l l y d e f i n e d and v i s u a l i z e d with a high degree of d e t a i l and accuracy. Therefore, t h e s e systems are c a t a g o r i z e d a s e x t r e m e l y a p p l i c a t i o n i n d e p e n d e n t . B e c a u s e o f t h e i r fundamental s o l u t i o n t o t h e problem, computer-assisted engineering systems, e . g . for s t r u c t u r a l and flow a n a l y s i s (CFD), are a l s o g e n e r a l l y a p p l i c a b l e . Inherent t o the u s e o f t h e s e

15

systems is that the object needs to be known in quite some detail, hence a large amount of data is involved and computing times are relatively long. Therefore, these systems can only be efficiently used in the detailed design phase when major changes in the configuration are no longer expected.

DESIGN STAGE

Figure 1 . 1 : C l a s s i f i c a t i o n of system types i n the current CAE-spectrum [Ref. 5 1 ] .

As y e t , CAE has not e s t a b l i s h e d i t s e l f as an a c c e p t e d d e s i g n t e c h n i q u e i n t h e i n i t i a l , i . e . conceptual and preliminary, phases o f the design p r o c e s s . There are some general f a c t o r s t h a t h a v e h i n d e r e d t h e p e n e t r a t i o n o f CAE i n t o the configuration development phase:

• Conceptual design i s u s u a l l y n o t a p r e d e t e r m i n e d and s t r i c t l y r a t i o n a l p r o c e s s . The h e u r i s t i c and i n t u i t i v e nature i s l e s s s u i t e d f o r the formal­ i z e d s t r u c t u r e required by a computer.

Computer programs tend t o appear l e s s transparent t o the d e s i g n e r . Hidden or obscured design d e c i s i o n s may confuse t h e d e c i s i o n m a k i n g p r o c e s s and r e s u l t s a r e n o t o r o n l y c a u t i o u s l y a c c e p t e d . E s p e c i a l l y In those cases

where many d e s i g n parameters a r e v a r i e d , e . g . i n automated d e s i g n , t h e a n a l y s i s nay become t o complex t o understand the p h y s i c a l r e l a t i o n s h i p s between the d i f f e r e n t d i s c i p l i n e s .

• C l o s e i n t e r a c t i o n b e t w e e n t h e computer and d e s i g n e r i s e s s e n t i a l and requires s p e c i a l a t t e n t i o n t o a u s e r - f r i e n d l y communication I n t e r f a c e and e a s e o f operation.

Computer a p p l i c a t i o n s In the pre-design phase a r e g e n e r a l l y r e s t r i c t e d t o ( l a r g e ) custom-coded programs developed and used on an ad hoc b a s i s . Since 1965, research has been d i r e c t e d toward i n t e g r a t i n g d e s i g n methods i n t o s y n t h e s i s programs. A c l a s s i c a l example i s SYNAC (Synthesis o f Aircraft) for configuration development o f m i l i t a r y a i r c r a f t a t General Dynamics [Ref. 9 1 ] . A more r e c e n t example i s the ACSYNT-program (Aircraft S y n t h e s i s ) de­ veloped by NASA [Ref. 1 5 ] . T h i s program a l s o forms a p a r t o f N o r t h r o p ' s Conceptual Design System (CDS) [Refs. 105 and 1 0 6 ] . Some o f t h e s e s y n t h e s i s programs e v e n p r o v i d e t h e o p t i o n t o a u t o m a t i c a l l y perform s e n s i t i v i t y s t u d i e s and a i r c r a f t s i z i n g . However, the incorporated design methods and t h e i r r e s p e c t i v e Input and output v a r i a b l e s are p r e - s e l e c t e d and can n o t be e a s i l y m o d i f i e d by t h e d e s i g n e r . T h e r e f o r e , t h e s e programs are l i k e l y t o require reprogramming o r a d d i t i o n a l code f o r e a c h new a p p l i c a t i o n , n o t accommodated by t h e o r i g i n a l program. Thus, innovative design i s r e s i s t e d . In a d d i t i o n , the time required t o adapt the program may r e n d e r i t a l r e a d y o b s o l e t e before i t becomes productive. Because of the b u i l t - i n design proce­ dures and p r o c e s s e s , the d e s i g n e r tends t o adjust the way of thinking t o the c a p a b i l i t i e s and the mode o f program operation.

E s s e n t i a l t o the development o f a generic preliminary design system, i s that the a n a l y s i s methods are t o -be_considered_as Input t o the system, s i m i l a r t o data, rather than i n t e g r a t i n g , i . e . f i x i n g , them i n t o t h e s y s t e m i t s e l f . Thus, t h e s e m o d u l e s , embodying the design knowledge, should r e s i d e outside the system, where they can be e a s i l y modified and reorganized by t h e d e s i g ­ n e r and be t a i l o r e d t o t h e s p e c i f i c design problem s t r u c t u r e and a i r c r a f t category. The Boeing's Computer-aided Preliminary Design System (CPDS) [Ref. 132] i s a t y p i c a l example o f t h i s concept.

17

1.2 Potential benefits of computer-aided engineering

Although the objectives to Introduce CAE may differ per Industry and type of application, some general areas of practical and economic potential can be Identified with respect to aircraft design [Ref. 70]:

• Reduced design time

CAE can reduce the development time needed t o introduce a new design.

Early Introduction and availability, ahead of competative designs, can be

an advantage.

• A better product through Improved design

Within a given time frame, more alternative design solutions can be consi­

dered, which potentially leads to an Improved design quality.

• A greater design capacity

For a given design s t a f f , several design p r o j e c t s can be accommodated

simultaneously. A f a s t e r response to customer queries and requests i s

possible.

• Solving outslzed design problems

CAE introduces opportunities and c a p a b i l i t i e s , which are practically

impossible t o do i n a t r a d i t i o n a l design environment. S o p h i s t i c a t e d

analysis codes require computer-assisted pre- and postprocessing.

• Reduced design cost

A reduction In design and development cost can be expected. In particular In the areas of drafting and manufacturing [Ref. 54].

In principle, these advantages also apply to conceptual design. However, although at least 80X of the development and production cost of a project is related to decisions made in the early stages of design, the actual invest­ ments during the conceptual design are relatively small. Therefore, emphasis Is put on Improving the design quality rather than cost reduction, In gene­ ral:

• An Improved e f f i c i e n c y o f the design p r o c e s s .

Automation of routine and r e p e t a t i v e a c t i v i t i e s r e l i e v e s t h e d e s i g n e r o f s t a n d a r d t a s k s . F o r m a l i z a t i o n of design data improves data exchange be­ tween d i s c i p l i n a r y teams and down-stream design l e v e l s .

• An improved design quality.

Within a given t i m e / c o s t frame, more design a l t e r n a t i v e s can be evaluated. S e n s i t i v i t y s t u d i e s , t r a d e - o f f s t u d i e s and m u l t i v a r i a t e optimization can be more e a s i l y applied i n an i n t e g r a t e d design environment.

Although t h e procurement o f CAD/CAE h a r d - and software i s c o s t l y and the implementation w i l l undoubtedly have an impact on t h e company's o r g a n i z a ­ t i o n , i n f r a s t r u c t u r e and working procedures, these i n i t i a l problems do not outweigh t h e long-term b e n e f i t s and the implementation o f CAB i n t h e a e r o ­ s p a c e i n d u s t r i e s and r e s e a r c h l a b o r a t o r i e s i s w e l l under way: A b e t t e r concept i s e s s e n t i a l for a b e t t e r a i r c r a f t d e s i g n .

1.3 Computer-aided engineering a t the D e l f t U n i v e r s i t y of Technology

Considering these rapid developments i n the aerospace industry w i t h r e s p e c t t o CAE, i t i s t o be expected that aerospace engineers w i l l become i n c r e a s ­ i n g l y more involved with computer a p p l i c a t i o n s i n a i r c r a f t d e s i g n . There­ f o r e , t h e a e r o n a u t i c a l f a c u l t i e s must adjust t h e i r c u r r i c u l a to t h i s trend and prepare future d e s i g n engineers f o r t h i s new environment.

Around 1980, the D e l f t U n i v e r s i t y o f Technology furnished funds t o stimulate general research i n CAE. In September 1983, a g e n e r a l - p u r p o s e CAD-system, referred t o as t h e I n t e r f a c u i t y CAD-Installation ( I C I ) , became a v a i l a b l e for u n i v e r s i t y - w i d e use^r The-ICI i s a "turnkey? CAD-system based on.a PRIME 75Q computer on which the MEDUSA d r a f t i n g and modelling package i s implemented. The ICI hardware configuration i s s c h e m a t i c a l l y i l l u s t r a t e d i n F i g u r e 1 . 2 . I t shows r e s e m b l a n c e w i t h t h e s y s t e m i n u s e a t t h e NASA Langly Research Center f o r Computer-Aided Research (CAR) [Ref. 1 1 8 ] . The central p r o c e s s i n g u n i t (PRIME 7 5 0 ) and i t s p e r i p h e r a l d e v i c e s a r e s i t u a t e d a t t h e DUT's Computing C e n t r e . The h o s t can a c c o m m o d a t e s e v e r a l r e m o t e

MEDUSA-19

w o r k s t a t i o n s and o t h e r terminals i n a m u l t i - u s e r operation mode. A MEDUSA-workstation comprises a g r a p h i c s and an alphanumeric d i s p l a y w i t h l o c a l h a r d c o p y and p r i n t i n g f a c i l i t i e s . A s m a l l d a t a t a b l e t i s used for menu-driven command input and d i g i t i z i n g . A d i r e c t communication l i n k e x i s t s with t h e C e n t r a l D i g i t a l I n s t a l l a t i o n (CDI), an IBM 3083-JX1 mainframe, for Remote Job Entry (RJE).

IBM 3083 mo in frame remote j o b T e n t r y CRJE3 A0 digitizer 630 Mb d i s k tape un it PRIME 750 8 Mb memory Vir. Men. 0/S (CENTRAL HARDWARE)

(WORKSTATION) graphics terminal.

printer

Ï

H

-r

Figure 1 . 2 : The DUT's c e n t r a l CAD hardware configuration ( I C I ) .

The ICI i s currently i n use with f e n g i n e e r i n g f a c u l t i e s , i . e . I n d u s t r i a l Design, Naval Engineering, Mechanical Engineering and Aerospace Engineering. The DUT's Computing Center i s r e s p o n s i b l e f o r s y s t e m s u p e r v i s i o n , main­

t e n a n c e and s u p p o r t . I n 1 9 8 5 . t h e s e f a c u l t i e s drew up and s u b m i t t e d a proposal for a joined p r o j e c t , e x t e n d i n g f o r a 10 y e a r s p e r i o d , c o v e r i n g s e v e r a l r e l a t e d t o p i c s i n t h e f i e l d of CAD/CAM/CAE for which each f a c u l t y would put i n a s p e c i f i c research e f f o r t .

A contribution to this project from the Faculty of Aerospace Engineering i s

represented by the development of a computer-aided system for conceptual

a i r c r a f t design. The purpose of t h i s p r o j e c t , i n i t i a t e d in 1983, was to

assess the practical capabilities and p i t f a l l s of computer-aided design as

applied t o conceptual aircraft design and to obtain hands-on experience in

this f i e l d . The system should be general and f l e x i b l e enough to be ap­

p l i c a b l e i n a wide spectrum of design problems, both for research, e.g.

a l t e r n a t i v e design concepts, m u l t i v a r i a t e o p t i m i z a t i o n , a s w e l l as

aeronautical teaching, e.g. design synthesis, parameter studies. This design

system i s referred to as the Aircraft Design and Analysis System (ADAS).

This d i s s e r t a t i o n concludes a 4-years period of development work in which

the design process was analyzed, functional requirements were drawn up, the

system a r c h i t e c t u r e was conceived and the individual programs were coded.

Although, development work on ADAS w i l l be an on-going process as new r e ­

quirements a r i s e and additional enhancements are implemented, the current

pilot-version of ADAS meets the basic requirements s e t for an a i r c r a f t

design system geared toward a university environment. This dissertation

gives a general overview of ADAS as i t i s currently implemented on the ICI.

Individual modules w i l l be highlighted and discussed in d e t a i l . In con­

clusion, Chapter 15 describes a typical design problem and i l l u s t r a t e s how

ADAS can be employed to obtain an optimum design solution.

2. THE AIRCRAFT DESIGN PROCESS

The design and development of a new aircraft type involves a great financial

investment. Therefore, the decision to i n i t i a t e a new a i r c r a f t project i s

preceded by intensive market surveys to assess the commercial prospects and

to inventory the requirements of potential customers for a future air trans­

p o r t . However, conceptual and preliminary design studies are also carried

out just to assess e.g. the impact of emerging technologies or t o study the

f e a s i b i l i t y of alternative concepts, but without the implicit intention to

ultimately build the aircraft: a new aircraft type appears only about every

20 years!

2.1 The design synthesis

Aircraft design i s generally not a continuous and straightforward process:

i t involves many repetative procedures and feedbacks. However, i t i s common

p r a c t i c e t o divide the overall a i r c r a f t design process i n t o 3 l o g i c a l

phases, as shown in Figure 2.1 [Ref. 124]. The objective i n the conceptual

design phase i s t o conceive a global definition of a number of design con­

figurations that best comply with the design requirements. Typical for

conceptual design i s the design synthesis: the designer attempts to combine

a l l technical disciplines, e.g. weight and balance, aerodynamics, s t a b i l i t y

and c o n t r o l , performance, c o s t s and n o i s e , i n t o a well-balanced design

solution. As only l i t t l e design information i s a v a i l a b l e at t h i s s t a g e ,

relatively simple analysis methods have to be used. These prediction methods

are referred to as class I methods and are g e n e r a l l y derived from (semi-)

empirical and s t a t i s t i c a l analysis on existing aircraft designs.

DESIGN PHASE ^ TECHNOLOGICAL RESEARCH DEVELOPMENT MARKET ANALVSIS \ I | CONCEPTUAL DESIGN | | | | | | | I I |PRELlHlNARV DESIGN' (CONFIGURATION FROZEN | DETAIL DESIGN | , IMANUFACTUR/NG GO-AHEAD' 1 ' | ,m i u. AIRKORTHINESS CERTIFICATION CONFIGURATION ^ DELIVER? OF FIRST 1 'PRODUCTION AIRCRAFT SUPPORT \ CUSTOMER DEVELOPMENT DESIGN SUPPORT

Figure 2.1: Typical phases in the aircraft design process [Ref. 124].

A selection of the most promising conceptual designs are subsequently analysed with more sophisticated methods, e.g. finite-element modelling and computational fluid dynamics. Usually, at this stage, the design staff.is divided into disciplinary teams each with their specific specialism. A final selection is made and the design configuration is frozen. In the detail design phase, the aircraft is designed at a component level resulting in many engineering drawings. Windtunnel experiments and structural tests are carried out. At this time, the management must decide whether to "go-ahead" and build the aircraft as development cost will increase progressively beyond this point.

Although the general concept of the ADAS system does not restrict its ap­ plication to a particular design stage, it is in principle intended for conceptual design.

2.2 The search for the optimum design

In order to develop a suitable design system, it is essential to identify the basic activities and procedures that take place in the initial stages of design. Design is generally an iterative process which starts with an in­ itial, tentative design configuration, referred to as the baseline design. Given the design requirements and objectives, the configuration is repeated­ ly modified in subsequent design cycles until a satisfactory design solution is found. A design cycle can in turn be divided into 3 basic steps:

1. Design definition

A new or modified design configuration is geometrically defined in suffi­ cient detail.

2. Design analysis

Suitable analysis methods are utilized to compute selected design charac­ teristics.

3. Design evaluation

The design i s evaluated by comparing the analysis r e s u l t s with t h e given

design requirements and objectives. If deemed necessary, the design con­

figuration i s changed and the process r e p e a t s .

This procedure can be r e p r e s e n t e d i n a schematic flow chart, adopted for

implementation on a computer (Figure 2 . 2 ) :

TENTATIVE DESIGN

CHANGE DESIGH

DESIGN DEFINITION

define configuration geometry and operational requirements

(descriptive model) INDEPENDENT VARIABLES

t

render design characteristics and evaluate design according

to specified requirements

DESIGN REQUIREMENTS/ FIGURE OF HER IT

m

Figure 2.2 shows that conceptual design Is basically a search process: design data and analysis Methods are manipulated until the process Is con­ verged to an acceptable design solution. In Mathematical terms there are 4 Ingredients Involved:

1. Independent variables or design parameters which can have arbitrary values within certain limits. Design parameters can be assigned a value either directly by the designer or indirectly by an executive program. Design data that is not subject to change during a design study are referred to as design constants. Examples of typical design parameters are wing aspect ratio, wing loading, thrust/weight ratio and tailplane dimensions.

2. Dependent variables whose values depend on the independent variables. Typical dependent variables are design characteristics such as per­ formance criteria, cost, noise, etc.

3- Analysis methods which define the physical relationships between the independent and dependent variables. Analysis methods may be relatively simple or extremely complex, dependent on the accuracy required and the amount of input information available.

l\. Design requirements and figure of merit to assess the feasibility and

efficiency of the design configuration. The design requirements impose technical constraints which may originate from operational performance and mission requirements, airworthiness requirements, technological aspects and practical considerations.

JThe selection of Jhe primaryjwing and tailplane parameters such that the

aircraft meets the defined mission requirements ("sizing"), is common prac­ tice in conceptual design. However, it is generally found that several different design concepts represent a feasible design. The total collection of feasible designs is referred to as the design space. An additional re­ quirement, a figure of merit, may then be considered according to which the best possible (feasible) design can be selected. This process is referred to as design optimization.

2.3 Procedures for design optimization

There are 3 basically different procedures which the designer can employ to search for the best conceivable ("optimum") design [Refs. 113 and 126]: • In the traditional intuitive (optimum) design approach, the designer

relies mainly on intuition and experience to select and change design parameters. The principal advantages (+) and disadvantages (-) of this approach are:

+ The designer can make full use of experience, augmented by proven and simple design methods;

+ Simple or no programming is required; + Number of designs to be analyzed is limited; + Maximum use is made of calculated results; + No a priori choice of one merit function;

+ Arbitrary, though limited number of variations and design modifications; - No guarantee that a real optimum is obtained;

- No useful result outside the designer's experience;

- It is time consuming: the designer will therefore tend to resist desirable changes in the design specifications or other previous decisions.

• With explicit or parametric optimization, a multitude of designs, each with different parameter values, are generated and analyzed. All designs are subsequently evaluated and the "best" design is selected. The ad­ vantages (+) and disadvantages (-) are:

+ It is rooted in the industrial approach; + Requires relatively simple programming;

+ The designer has complete control over decisions; + No a priori choice of a single merit function;

+ Sensitivity of off-optimum design conditions remains visible;

- No guarantee that a global optimum Is obtained: it may be outside the selected design space;

- Many designs are evaluated, only a few are actually used;

- The designer is not encouraged to extend the number of variables: the amount of data to be analyzed Increases exponentially;

- Changes in the design specification make previously generated results obsolete and are resisted.

• Implicit or multlvariate optimization requires the design process to be fully automated. The figure of merit and design requirements are quantita­ tively formulated as an objective function and constraints respectively. An optimization algorithm (optimizer) changes the specified design parameters (free variables) based on mathematical information acquired during the optimization process. The advantages ( + ) and disadvantages (-) are:

+ It potentially leads to an improved design quality due to the rigorous approach;

+ Especially useful for multi-variable systems; + Effect of "biased" decisions is eliminated; + Changes in design specifications are easily met; - Programming and debugging are difficult;

- Optimization algorithms are not always effective; - Convergence problems may occur: no solution is found;

- No insight into design sensitivity: only one design is obtained; - Inexperienced designers may produce and accept unrealistic results. In the presented order, these optimization techniques involve a higher degree of design automation in which control of the search process is dele­ gated to the computer. By comparing the pros and cons, it can be concluded ~that - these~3~optimization--techniques-are_complementary,_Jhence,_an_effectiye_

design system should give the designer the freedom to choose a suitable combination for a given design problem.

PART 2: THE AIRCRAFT DESIGN AND ANALYSIS SYSTEM

3. THE AIRCRAFT DESIGN AND ANALYSIS SYSTEM

3-1 Principal requirements for ADAS

Based on the considerations discussed in the previous Chapters, some princi­

pal requirements were formulated for the ADAS-system, with respect to i t s

functionality and practical implementation, i . e . :

• As teaching and research in conceptual/preliminary design i s traditionally

the r e s p o n s i b i l i t y of the d i s c i p l i n a r y group Aircraft D e s i g n / F l i g h t

Mechanics of the Faculty of Aerospace Engineering, ADAS i s primarily

intended for aircraft configuration development. However, an e f f e c t i v e

design system should include the c a p a b i l i t y to communicate with other

design systems/programs to be able to carry-on the design to down-stream

design l e v e l s (open-ended system).

• A design system must be f l e x i b l e in handling a wide range of different

design problems with l i t t l e or no modifications required. This implies a

oodularly structured system architecture that simplifies future modifica­

tions and enhancements.

• The designer must be able t o s e l e c t s e n s i t i v i t y a n a l y s i s and/or

multi-v a r i a t e optimization as an optional feature, but an analysis study of a

given configuration must remain possible.

• A conceptual design system i s highly i n t e r a c t i v e , therefore a u s e r

-friendly operating environment i s essential for the general acceptance and

use of the system. This entails e . g . computer checking and reporting of

logical and syntactical errors, use of default keywords where appropriate, an on-line help facility and elaborate documentation.

• Built-in design decisions within analysis programs mist be avoided as much as possible, as they can hinder the Interpretation of results and confuse the decisionmaking process. The primary task of a design system is to produce selected analysis results in an efficient way. Design decisions should be the sole responsibility of the designer, even when design con­ trol is delegated to the computer, e.g. in case of numerical optimization. Hence, design and analysis are two different functions that should be clearly separated.

• A design system can potentially reduce time and effort required particu­ larly for data pre- and postprocessing. Substantial benefits can be gained in this area. The implementation of a database system, interactive geome­ try Input through a CAD-system and options for interactive plotting of engineering diagrams are a logical consequence of this requirement.

• ADAS should logically be implemented on the ICI, as the most readily available system for Interactive CAD-applications at the DUT, although this may Impose some hard- and software limitations. As yet no attempt has been made to make ADAS completely hardware independent. However, hardware dependency is mainly restricted to the handling of global variables and system calls.

• Ample use should be made of available (commercial) software products in order to reduce development time and cost. In this respect, ADAS requires the MEDUSA-system for graphics (drafting and graph plotting) and the NAG-library for standard numerical routines although other equivalent software can In principle be used.

Note that the ADAS-version described in this dissertation, is a pilot-system: a starting point for further research and development. Currently, the analysis methods and geometry definition capabilities are.geared toward. conventional subsonic transport aircraft.

3-2 The ADAS-system a r c h i t e c t u r e

On t h e b a s i s o f t h e f u n c t i o n a l requirements and a v a i l a b l e hard- and s o f t ­ ware described above, a system a r c h i t e c t u r e has been d e v e l o p e d f o r ADAS. This ADAS system a r c h i t e c t u r e i s s c h e m a t i c a l l y i l l u s t r a t e d i n Figure 3 - l;

$UZ

Figure 3 . 1 : The ADAS-system general a r c h i t e c t u r e .

The o v e r a l l s y s t e m c o m p r i s e s 3 s e l f - c o n t a i n e d programs which communicate through a common database system, i . e . :

• The ADAS program controls the user-system dialogue through a command-oriented language. This program also contains functions to interactively perform data pre- and postprocessing, e.g. database query, graph plotting, text editing, etc. The ADAS-program forms the nucleus of the system, any function or subsystem can be invoked from a central command level.

• The Aircraft Design and Analysis Program (ADAP) is a general executive program that controls the processing of a user-supplied analysis program. Optionally, ADAP can be run In parametric survey and/or optimization mode. ADAP is non-interactive, hence it can run independently once all the necessary input Information has been prepared.

• The MEDUSA drafting and modelling system is used within ADAS to define a design configuration layout in the form of a schematic 3~view drawing. An interface has been developed to transfer geometry information between a MEDUSA sheet file to the ADAP-executive program for analysis and to place a newly computed (optimum) design configuration from ADAP back into a MEDUSA drawing.

ADAS and MEDUSA are effectively integrated into one program. One invokes the MEDUSA 2D drafting module on any suitable workstation or alphanumeric terminal and can subsequently switch between the MEDUSA and ADAS command level as required. For example, plotting of engineering diagrams is done by ADAS directly Into a MEDUSA drawing through the MEDUSA graphical Inter­ face. Subsequently, the designer can switch to MEDUSA command level and apply any of the available MEDUSA drafting commands to edit the plot or to make a high-quality copy.

All available options are input at ADAS or MEDUSA command level and control subsequently returns to this command level after the operation has been completed. The user is generally unaware of the underlying processes taking place, although knowledge thereof is useful for understanding the workings of the system.

In the following Chapters these individual system components will be de­ scribed in more detail and their specific features will be highlighted by going through an imaginary design sequence as described In Section 2.2.

3^3 Project organization and data protection

When utilizing ADAS in a design project, it is likely that data will be generated that is to be retained for some period of tine. Such data is placed In a file, under a given filename, and resides on a secondary storage device, usually a Magnetic disk unit. The system manager will regularly make copies of all the disk files onto a magnetic tape for back-up purposes.

The file organization structure employed on the 1C1 is referred to as a hierarchical file structure, as shown in Figure 3-2:

root directory

LUD

Login

C0D

A

tfJ

ÖlD

/

,

/

Figure 3 - 2 : Organization s t r u c t u r e o f f i l e s and d i r e c t o r i e s .

L o g i c a l l y - r e l a t e d f l i e s . , _ e . g . - d a t a b a s e f l i e s ,_MEDUSA^sheet f i l e s . , jsource code, e t c . , may be placed i n t o a User F i l e Directory (UFD). A child-UFD i s sub-ordinate t o another UFD, referred to a s the parent UFD. In t h i s way, the f i l e o r g a n i z a t i o n s t r u c t u r e r e s e m b l e s an i n v e r t e d t r e e , w i t h e a c h node r e p r e s e n t i n g a UFD. A filename must be unique w i t h i n the UFD i t r e s i d e s i n . To r e f e r t o a p a r t i c u l a r f i l e , one must s p e c i f y i t s complete pathname, i . e . a l l t h e UFD-names down t o t h e filename i t s e l f . In a pathname, UFD-names are separated by the > symbol, e . g . VL>V0>ADAS>ENGINE>ALF-502D.

As t y p i n g o f r e l a t i v e l y l o n g pathnames may become cumbersome, the system maintains a p o i n t e r t o the current OFD: the working d i r e c t o r y . When o n l y a f i l e n a m e i s g i v e n , t h e system automatically assumes t h a t f i l e t o r e s i d e i n the current UFD. Each u s e r has an attach-UFD which automatically becomes the c u r r e n t UFD a f t e r s i g n i n g on the ICI: the home d i r e c t o r y . The user i s f r e e t o c r e a t e any sub-UFD a s required. Before a new design p r o j e c t i s I n i t i a t e d , t h e d e s i g n e r s h o u l d s e t up a convenient UFD-structure, p a r t i c u l a r l y i f the p r o j e c t comprises s e v e r a l s u b j e c t s or when a group o f d e s i g n e r s a r e working on one p r o j e c t . ADAS allows the user t o s t o r e design data i n any s p e c i f i e d UFD and t o a p p l y any f i l e management command p r o v i d e d by t h e o p e r a t i n g system.

The user can a l s o a s s i g n a c c e s s r i g h t s e i t h e r t o a f i l e o r t o a complete UFD and which may a f f e c t an individual u s e r or a group o f u s e r s . Access r i g h t s Include f o r example d e l e t e , r e a d , l i s t , u s e and w r i t e . By s e t t i n g a c c e s s r i g h t s , an owner can p r o t e c t o r secure t h e f i l e s a g a i n s t e . g . unauthorized a c c e s s or u n i n t e n t i o n a l d e l e t e .

4. DESIGN DEFINITION

D e s i g n d e f i n i t i o n forms a l o g i c a l f i r s t s t e p i n a t y p i c a l design study with ADAS. This means t h a t design data has t o be a c q u i r e d and e n t e r e d i n t o t h e system. These a c t i v i t i e s are g e n e r a l l y i n t e r a c t i v e and are c o n t r o l l e d by the ADAS program. The ADAS program forms t h e n u c l e u s o f t h e ADAS s y s t e m and a l l o w s t h e u s e r t o a c c e s s any a v a i l a b l e function or subsystem by means o f a command-oriented language.

4 . 1 The user-system i n t e r f a c e

As mentioned i n S e c t i o n 3 - 2 , the MEDUSA and ADAS systems are i n t e g r a t e d i n t o one program. The u s e r can s w i t c h between both command l e v e l s with only a simple i n s t r u c t i o n . This does not a f f e c t t h e s t a t e o f t h e MEDUSA and ADAS programs or the information held i n primary memory.

The advantages and disadvantages o f t h i s approach are:

+ Graphs g e n e r a t e d by ADAS and s t o r e d i n a MEDUSA s h e e t can be e d i t e d and p l o t t e d u s i n g the standard MEDUSA d r a f t i n g o p t i o n s .

+ Use" o f t h e " MEDUSA~built- i n - g r a p h i c a l i n t e r f a c e e l i m i n a t e s the _need__ tp_ adjust ADAS t o d i f f e r e n t g r a p h i c a l i n t e r f a c e s f o r d i f f e r e n t t e r m i n a l t y p e s .

- ADAS requires the availability of the MEDUSA software or an equivalent CAD-system.

- To start the ADAS system, one must invoke the MEDUSA system on a specially configured graphical workstation or alphanumeric terminal.

The ADAS/MEDUSA command p r o c e s s i n g c o n t r o l scheme I s I l l u s t r a t e d I n F i g u r e 4 . 1 : execute MEDUSA command YES ^command prompt ^

MEDUSA program

ADAS program

Figure 4 . 1 : ADAS/MEDUSA command p r o c e s s i n g control flow.

At ADAS command l e v e l , t h e u s e r i s prompted f o r any o f t h e commands described I n t h e ADAS Command R e f e r e n c e Manual [ R e f . 2 5 ] . A summary o f a v a i l a b l e commands I s given In Appendix A. Commands can be e i t h e r s p e c i f i c ADAS commands or operating system commands. I f a command name I s not a v a l i d ADAS command, i t w i l l be p a s s e d t o t h e operating system as a system c a l l . After a command i s executed, c o n t r o l returns t o ADAS command l e v e l . A b u i l t -i n b r e a k - h a n d l e r can be used t o Interrupt command p r o c e s s -i n g at any t-ime. The keyboard i s the standard input d e v i c e . Experiments have shown t h a t ADAS can e a s i l y b e adopted f o r menu-driven i n p u t , i f s o required. These pro­ v i s i o n s however, make t h e s y s t e m e x t r e m e l y hardware-dependent and have

4.2 Configuration geometry definition

Geometry information constitutes a large part of the total collection of design data. A logical means of geometry data input is through a drafting system. With a drafting system, the configuration layout is directly visu­ alized and errors are easily detected. In 19&1, a graphics program (SKETCH) was developed to generate a schematic 3-view configuration drawing or a 3D

wire-frame model from only a few, basic shape parameters [Ref. 2 3 ] . At a later stage, SKETCH was coupled to the ADAS system to display optimized design configurations. An example is shown in Figure 4.2:

Figure 4.2: Sample 3-view configuration drawing from the SKETCH-program.

However, as it was only intended for postprocessing, the SKETCH program could not handle interactive drawing manipulation. After the implementation of the MEDUSA system on the ICI, development work was directed toward Inter­ facing MEDUSA with ADAS, which rendered the SKETCH program obsolete.

4.2.1 The MEDUSA drafting and modelling system

The MEDUSA drafting and modelling system is a software product developed by Cambridge Interactive Systems (CIS) in the United Kingdom and it is offered as a "turnkey" CAD-system on several mini- and micro-computers, e.g. PRIME, VAX and SUN [Ref. 9]. The MEDUSA system architecture consists of a collec­ tion of separately available program modules configured around a general-purpose 2D drafting program, as shown in Figure 4.3:

DESIGNER

IMB***

E

Figure 4.3: The MEDUSA-system modular configuration.

In general however, the ADAS-user will only be concerned with the 2D draft­ ing and, occasionally, with the 3n modelling module. Therefore, only these

programs will be briefly discussed.

4.2.1.1 2D drafting

The MEDUSA system can be i n v o k e d from ADAS command l e v e l o r d i r e c t l y a t o p e r a t i n g s y s t e m l e v e l . A f t e r s t a r t - u p , the user w i l l be a t the d r a f t i n g module command l e v e l . Command input i s p r i m a r i l y m e n u - o r i e n t e d , t h e r e f o r e MEDUSA can only be operated from an ICI-workstation with a data t a b l e t .

At t h i s p o i n t , an already e x i s t i n g drawing can be r e t r i e v e d for modification (drawing e d i t i n g ) or a new drawing can be c r e a t e d . MEDUSA features numerous

options to perform basic as well as complicated drawing operations [Ref. 11], e.g.:

- Automatic cross-hatching; - Different line types;

- Different text types and fonts;

- Automatic dimensioning (DIN, ANSI or ISO standard); - Transformation and duplication of drawing parts; - Line editing ("rubber banding");

- Curve fitting (conies); - Variable grids;

- Internal programming language (BaCIS2);

- Parametrics.

It i s beyond the scope of t h i s d i s s e r t a t i o n to d i s c u s s these options in

detail, since they are standard for most CAD/CAM-systems.

4.2.1.2 3D geometric modelling

The 3D module comprises a solid modelling and a viewing program [Ref. 10].

The s o l i d modeller generates of 3

dimensional description of an object

(model) while the viewer d i s p l a y s a projected image onto the graphics

terminal.

• The solid modeller

The MEDUSA 3D module requires Input of a s p e c i a l l y prepared 2D drawing,

referred to as a ' d e f i n i t i o n drawing. A d e f i n i t i o n drawing defines the

object in terms of profile lines in one or more, orthogonal or oblique,

views, --interconnected~by.-80rcalled._llnkJLines

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gene-rates a 3~dimensional description in terms of polygons ( t i l e s ) , wire-lines

and faces and s t o r e s the result in a model f i l e . By default, the objects

are modelled as s o l i d s , but special modelling commands are a v a i l a b l e to

generate e . g . s h e l l s and wire-frame models. The solid modeller provides

different model generators, which can be applied to objects with s p e c i f i c

geometric properties, e . g . :

- Volume of revolution: a profile line is rotated around a specified axis. VOLUME OF

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- Ruled surface: linear lofting between two parallel endfaces.

Pipe/slide: a cross-sectional profile line is extruded along a spatial curve.

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Free for» Modelling: the 10061 i s constructed froa an a r b i t r a r y number of longitudinal and latitudinal profile l i n e s .

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In addition, more complicated objects can be modelled with boolean opera­ tions. Boolean operations are used to join, subtract or take the com­ plementary volume of two or more, separately defined objects. An object may be broken down into subcomponents which can in turn be modelled from separate definition drawings. The resulting object can subsequently be assembled in another drawing by indicating their relative locations and by referring to their corresponding model names (instancing).

• The (interactive) viewer and shader

The viewer projects a model onto the graphics display according to a user-specified orientation. Typical viewer options are hidden line removal, display of tiles or boundary lines, isometric or perspective views, etc. The 3n viewer places generated views back into the definition drawing

(reconstruction) so they can be saved in the drawing database or option­ ally sent to a line-plotter. The interactive viewer program module takes the viewing commands directly from the user rather than from a definition drawing. In this case, views cannot be saved or plotted, except for a local hardcopy. The functionality of the shader is similar to that of the interactive viewer, except that the shader is intended for rendering colour or greyscale images on a raster of bit-map terminal.

4.2.2 The ADAS ■> MEDUSA interface

To obtain better insight into the principles of the ADAS-MEDUSA interface a brief discussion will be given on the way MEDUSA organizes and stores In­ formation in a drawing. The information representing a MEDUSA drawing re­ sides in a drawing*database, stored under a user-specified name (sheet name). A drawing is a composition of graphical elements of which there are 3 basic classes, i.e.: LINE, TEXT and PRIM. A PRIM is a standard symbol, composed of LINE- and TEXT-elements, which is referenced as a single entity. The individual elements however can not be changed directly by the user. Each element class is associated with a number of specific attributes, shown in Table 4.1. These attributes define the shape, orientation and location of a graphical element in the -drawing.