TECHNICAL NOTE

00457949/93 s6.w + 0.00 0 1993 Pergamon Press Ltd

AN INTERACTIVE GRAPHIC SOFTWARE FOR THE ANALYSIS OF ROTATIONALLY SYMMETRIC

STRUCTURES

R. KUMAR, J. AGARWAL and S. P. SHARMA

Structural Engineering Research Centre, Ghaziabad-201001, India

(Received 18 November 1991)

Abstract-Several efficient programs to analyse different kinds of structures have been developed at this centre. But the data preparation and comprehension of output have been time consuming. To facilitate data preparation some dedicated preprocessors were written but it has not been possible to make a visual check on structure modelling, deformations and stress patterns. With the availability of graphic facilities at this centre, the present project was taken up to develop graphic software for a program, ROTSYM, for the analysis of rotationally symmetric structures like cooling towers, chimneys, watertanks, etc. This software enables the designer to display the modelled structure, deformed geometry and stress patterns; thus cutting down the time required in data checking and output verification.

INTRODUCTION

Several general-purpose computer programs, namely SAP7, NASTRAN, ABACUS, etc., are in use for the analysis of structural engineering problems. Although these programs are very efficient and well known, input data preparation requires a lot of effort and the user has to enter various irrelevant data for a specific problem. Therefore, dedicated software developed f&r a specific type of problem is more problem-oriented and easier to handle. ROTSYM Il. 21 belongs to this category and was developed for the an&id of rotationally symmetric structures.

In the present work, a graphic processor has been devel- oped for this computer program with the view of making a visual check on structure modelling, deformations and stress patterns.

BRIEF DESCRIPTION OF ROTSYM

ROTSYM is a program to analyse thin-walled structures generated by rotating an arbitrary meridian about an axis. It can be used to analyse cooling towers, chimneys and water tanks with an accuracy sticient for engineering design purposes. In this program the structure is modelled as a combination of three basic elements, namely plate, cylinder and cone, then Flugge’s most general equations of bending theory of shells are so&d. To minimize errors at element boundaries due to discontinuity the structure is discretized into a sufficiently large number of elements. This makes the task of data preparation a time-consuming job. Similarly, it becomes difficult to comprehend the results of the program. Development of the graphic processor for this program has helped to remove these drawbacks to a large extent.

GRAPHIC LIBRARY

The development of the graphic processor required the use of graphic facilities; particularly a graphic subroutine package. @or the present work tge PcO?iO Interactive Graphic Library (IGL) package 131. as available on TEK- TR6NIX grap& wo;k&tions, has been used. The IGL routines can be called in any Fortran program when the IGL package is linked with the program. By their function,

IGL routines can be put into different categories such as system environment routines, text environment routines, text action environment routines, segment routines, 3D routines, etc. System environment routines set-up the graphic device for output; graphic environment routines set-up the environment for graphic action such as window, viewport, colour, dash style, etc. Graphic action routines take some action such as moving the cursor, drawing a line, drawing an arc, locating a point, etc. Text environment and text action routines help in putting text on a picture. ~r~~imen~onal routines make it possible to view an object in 3D space. There are many other routines which can be called as and when needed, thus providing a convenient tool for the application programmer to create and display graphics and text (Fig. 1).

GRAPHIC PROCESSOR FOR ROTSYM

Graphic processor

For ease of program usage the graphic processor is divided into two parts: (i) a preprocessor which can display the modelled structure on a graphic terminal or create a plot tile for plotting it later on an off-line plotter, (ii) a post- processor which can display or plot the deformed geometry or stress diagram depending upon the options chosen from the menu screen.

Preprocessor

In the preprocessor the strategy is to compute the joint coordinate from the geometry data file, set the environment for plotting geometry and then plot the structure. These three tasks are done by the routines GEM, ENV and PLT, respectively. In setting the environment, window size and scale are the two most important parameters. Window size is computed using the GEM routine and displayed to the user for a possible change. The choice of scale is left entirely to the user in the form of window-viewport mapping. The routines ENV and PLT make sub&tine c& t% the IGL oackaae to do their tasks. These in&de GRSTRT. GRSTOg for gystem environment, WINDOW, VWPORT; LINCLR, DASHPT, etc., for graphic environment, MOVE, DRAW, MAKER, etc., for graphic action, and so on.

1119

1120 Technical Note

ANALYSIS

PROGRAM

ROTSY M

C OUTPUT

GRAPHIC

PREPROCESSOR GRAPHIC

POSTPROCESSOR

c

c GRAPHIC DISPLAY

OF

STRUCTURAL MODEL

I GRAPHIC DISPLAY

DEFORMED GEOMETRY

AND STRESSES I

Fig. I. Conceptual plan of graphic software.

Posrprocessor

In the interactive postprocessor, the user can opt for deformations and stresses through menu options. These are either shown superimposed on the undeformed structure or on a X-Y graph where superposition is not possible. To have a better understanding of the structure it can be viewed in elevation as well as in plan. In elevation the user can see the deformations/stresses at a section denoted by 0. While in plan the same can be seen along the circumference. Radial deformations can be viewed in elevation and plan both along the structure and vertical deformations can be viewed in elevation. Tangential deformations in plan are plotted against 0 values ranging from 0 to 2n.

The ROTSYM program computes all the in-plane forces, shear forces and bending moments, but only four are summed and printed at a time. The four stresses chosen for the graphic processor are meridional force and moment and circumferential force and moment. All the four stresses can be viewed in elevation along the structure boundaries and in plan on a force vs o graph. If a user is interested in some other stress component, he/she can also view other stresses.

The programming strategy in the postprocessor is much the same as the preprocessor and it is the same for displaying deformations and stresses. The undeformed structure coor- dinates are generated and stored for later use (routine GEM), then the deformations are read from a sequential data file and are rewritten to a random file in order of joint number and section for flexible and quick retrieval (routine DEFIL). Then a choice is made whether to display defor- mations in plan or elevation. For a display in elevation, coordinates for the deformed structure are computed (routine DEFI). ENV sets the environment, PLT plots the undeformed structure and DEF2 routine plots the deformed geometry. The stress diagrams are plotted the same way; subroutines STRI and STR2 take the place of routines DEFI and DEFZ, respectively. Similarly, for display in plan, deformations and stresses are plotted by

calling PLANDEF and PLSNSTR routines, respectively. Figure 2 shows the organization of routines in the graphic processor for the ROTSYM program.

User inrerface

ROTSYM is an interactive program and the user is expected to make a choice from the menu presented or to enter his/her responses against the queries put before him/her after the program has been loaded. The menus which might appear are shown below. The main menu is displayed at the start of the program while the pre- and post-menu appear after it has been requested from the main menu.

Each of the pre- and post-menu options initiates calls to appropriate routines and then the user is prompted for various inputs. As the deformations and stresses are read from files, obvious prompts are for these file names. Each time a new image is desired, the user is prompted to enter the window size. For a screen display, viewport size is also required. For a plot, default page size is used and the user is prompted for a new plot file name. A few queries are shown below

‘Input window ordinates-wminx, wmaxx, wmiuy, wmaxy’ ‘(Maximum size: nnn, nnn, nnn, nnn)’ ‘(For same scale in X, Y direction, choose proper window) ‘Input viewport ordinates-vminx, vmaxx, vminy, vmaxy’ ‘(Maximum size: nnn, nnn, nnn, nnn)’ ‘Enter plot file name (max 6 char)‘.

There are many other queries for choosing the defor- mations in plan or elevation and for choosing a section at which deformations are required. There are also queries relating to stress components. If the user enters an invalid response, the program ignores it and in most cases returns to the same query. After the desired functions have been completed, the user can go back to the main menu and then exit from the program in a normal way.

Technical Note 1121

I .

PREMENU

MAIN MENU

I

ROTSYM

1

POSTMEtu

I I

GEM ENU PLT GEM DEFIL DEFl ENU PLT DEF2

’ ‘)jf $$+$Ei,U I(; ,.‘lr.

IGL ROUTINES IGL ROUTINES

Fig. 2. Organization of routines in graphic processor for program ROTSYM.

The graphic processor reads one file each for geometry, deformations and stresses. The formats for these files are given in the Appendix. Typical input and output is explained in the next section through an example.

EXAMPLE: COOLING TOWER

A cooling tower with a height of 122m and throat diameter 25.3 m was analysed under wind loads using the ROTSYM program; the graphic processor was used to view the structure modelling, deformations and stresses. The user inputs for this are given below in sequence.

THETA 1.000 !

! ! I i

To view structure moa’elling

Main menu 1 Pre-menu 2 Enter geometry file name > bis.dat Is the numbering top to bottom (O/l)? I Input window ordinates-wminx, wmaxx, wminy, wmaxy (Maxm size: -4869, 4869, - 11632, 0.) (For same scale in X, Y directions, select proper window) -6000 6000 - 11900 100 Input viewport ordinates-vminx, vmaxx, vminy, vmaxy (Maxm size: 0, 130,0, 100) 0, lOO,O, 100 (Display appears.)

SIGN CONVENTION RADIAL MFORMATION + ve AWAY FROM AXIS

VERTICAL DEFORMATION + ve IF UPWORDS

_ ______ ___ ____ ___-____.__--___ t _____.___________________________-_rpa_._ _

Fig. 3. Alongwind deformations for a cooling tower under wind load.

1122 Technical Note

Fig. 4. Radial deformations at joint 9.

NS THETA l*OOG

ht

G-- .-.

Fig. 5. Hoop force along the circumference at joint 9.

Ns

THETA G*GOO

SIGN CONVENTION

TESILE FORCE cvc PLOTTED ON INNER SIDE

MOMENT DIAGRAM PLOTTED ON TENSION SIGE

Fig. 5. Meridiouaat face.

Technical Note 1123

changes to data files. For example, if in a program after the first run, stress concentration is seen at some location then the mesh could be refined graphically and the data file updated accordingly for the next run.

To view deformations

Main menu Post menu . . *

3 3

Enter deformation file name > Enter number of sections (max 20) > Defn in plan (u, v) or elevn (u, w) p/e? (To terminate enter any other char) Which section, enter two theta values > (to terminate enter -ve numbers) Enter magnification factor for defn >

bis.def 9 e

0.0, 1.0

100

. . (Display appears as in Fig. 3.) Defn in plan (u, v) or elevn (v, w) p/e? P

Deformations at which joint, 0 to exit > 9 Which component: u - 1, v - 2, 0 to exit > 2 Enter magnification factor for defn > 100 (Display appears as in Fig. 4.) Deformations at which joint, 0 to exit > 9 Which component: u - 1, v - 2, 0 to exit > 1 Enter magnifi~tion factor for defn > 100

(Display appears.)

To view stresses

Main menu Post menu .,,

3 4

Enter stress file name > Enter number of sections > Stress in plan or elevn p/e? (to terminate enter any char) . . .

bisstr 9 P

. . Stress for which element, 0 to exit 8 Which component: Nt - 1, Mt - 2, 0 to exit 1 Enter rna~i~~tion factor for stress > 5

(Display appears as in Fig. 5.) Stress in plan or elevn p/e? e (to terminate enter any other char) Which section, enter two theta values > 0.0, 1 .o Which stress component: Ns - 1, MS - 2, Nt - 3 > 1 Enter scale factor > 1 . . . (Display appears as in Fig. 6.) Any more stress component (O/l)? 1 Which stress components: Ns - 1, MS - 2, Nt - 3 > 2 Enter scale factor > 0.1 . . . . . (Display appears.)

CONCLUSIONS

The present work, which was carried out primarily with a view to understand the graphic software, has resulted in a graphic processor for the program ROTSYM. This graphic processor cuts down time significantly in checking the geometry of the structure as well as the deformations. Without going through the numerical output, the user is able to understand the structural behaviour and identify the mistakes in input and ouput.

Learning from the experience on this work, it is opined that graphics software can help in preparing files from structural layouts. Not only this, it is also possible to remodel the structure graphically and then write back the

REFERENCES

1. S. P. Sharma, 8. K. Goyal and J. Ahmad, Thin walled structures generated by rotating arbitrary meridian about an axis. SERC. Roorkee, India (1980).

2. J. Aganval, ROTSYM: A program for thin walled rotationally symmetric structures. SERC, Ghaziabad, India (1991).

3. Tek user’s manual, PLOT 10, Interactive Graphic Library. Tektronix (1986).

4. C. I. Pesqudra, W. Mcquire and J. F. Abel, Interactive graphical preprocessing of 3D framed structures. Comput. Struct. 17, 1-12 (1983).

APPENDIX A. Geometry jile

I. Blank Card II. Control card (313).

Nm No. of joints NPL: No. of elements.

III. Connectivity card (313. 4F12.4).

B.

NPL: Element number NE: Near end NF: Far end RNE: Radius at near end ALFA: Angle that element makes with horizontal T: Thickness of element PL: Length of the element.

Deformation file

I. Two blank cards. II. (a) Location card (47X, F6.3)

TH( .): Deformation at location. (b) Blank card.

III. Defo~ation card (7X, 4816.8). (Repeat as many times as the number of joints)

U: Deformation in u-direction V: Deformation in v-direction W: Deformation in w-direction SI: Deformation in B-direction

(Repeat the set as many times as the number of locations at which deformations are given).

C. Stress jile

I. Two blank cards. II. (a) Location card (45X, F6.3).

THI.): Stress at location. (b) Blank card.

III. Stress card (3X, 213,4E16.8). (Repeat as many times as the number of elements). (a) At near end

IPL: Element number IJTI: Joint number at near end NS: Ns component of stress NT: No component of stress MS: MS component of stress MT: MO component of stress.

(b) At far end IPL: Element number IJTZ: Joint number at far end NS: Ns component of stress NT: No component of stress MS: MS comnonent of stress. MT: MO component of stress.

(Repeat the set as many times as the number of locations at which deformations are given).