Recent experiences with incorporating NASTRAN as a teaching tool in undergraduate courses was found pedagogically sound. Students with no previous computerized structures background are able to readily grasp the program's logic and begin solving realistic problems rapidly. The educational benefit is significantly enhanced by NASTRAN's plotting feature. However, the cost of operating the level 12 version makes the program difficult to justify

Wilkinson, M. T.

English

NASA Technical Reports Server

USE OF NASTRAN AS A m C H I N G  A I D  
By Michael T. Wilkinson 
Louisiana Tech University 
SUMMARY 
Recent experiences wi th  incorporating NASTRAN as a teaching tool 
i n  undergraduate cowses has been found pedagogically sound. Students 
w i t h  no previous computerized structures background are able to readily 
grasp the program's logic and begin solving r e a l i s t i c  problems rapidly. 
The educational benefit  i s  s ignif icant ly  enhanced by NASTRAN's plot t ing 
feature.  However, the cost of operating the leve l  12 version presently 
makes the program d i f f i c u l t  to jus t i fy .  
SEJ3CTION OF A FINITE EI.XMENT PROGRAM 
Undergraduate instruction i n  the area of s t ruc tura l  analysis must 
begin by placing major emphasis on the fundamentals such as s t r e s s ,  s t ra in ,  
Mohr's c i r c l e ,  flexure formula, e tc .  However, a l l  too often the under- 
graduate's progress does not extend far beyond problems i n  which a beam 
i s  e i ther  bent, sheared, twisted or buckled under a wide variety of end 
conditions. 
It seems highly desirable that the undergraduate should also be 
exposed to more r e a l i s t i c  s t ruc tura l  problems such as are encountered 
i n  practice.  
obstacles -- 1) they axe usually too large fo r  hand calculations and 
2 )  they often cannot be analyzed using the simple formulas w i t h  which 
the studect is  familiar.  
These r e a l i s t i c  problems generally present two major 
It i s ,  of course, c lear  t h a t  the addition of large s t ruc tura l  
-problems in to  the undergraduate curriculum should not precede a study 
of the fundamentals. However, r e a l i s t i c  problems not only give the 
senior-level student a prac t ica l  f e e l  for  the resu l t s  but a lso provide 
a s ignif icant  motivation factor .  That i s ,  students generally f e e l  a 
greater sense of achievement when they successfully solve a s ignif icant  
engineering problem. 
With t h i s  purpose i n  mind, the general f i n i t e  element programs 
have s ignif icant  potent ia l  as a teaching aid. In the selection of a 
https://ntrs.nasa.gov/search.jsp?R=19720025244 2020-03-23T10:19:15+00:00Z
f i n i t e  element program, the instructor  must consider the following 
character is t ics  of the programs: 
1) IS it easy to use? 
2)  W i l l  it handle a suf f ic ien t ly  broad c lass  of problems? 
3 )  Is it a program the student could be expected to 
encounter a f t e r  graduation? 
4) IS it expensive to use? 
With regard to the first question, it i s  important t h a t  a min imum 
amount of classroom time i s  spent "checking out" the student on the 
program. 
and extensive e r ror  checks. 
ment fo r  a program which i s  dependable -- nothing dampens student 
enthusiasm l i k e  a program which fa i ls  to work! 
Consequently, the program must be user oriented w i t h  easy input 
A corollary to t h i s  question i s  a require- 
The second question concerns the v e r s a t i l i t y  of the program. This 
requirement a r i s e s  fo r  several  reasons. 
senior l e v e l  design work, the var ie ty  of problems w i l l  almost cer ta inly 
require a general program. Furthermore, many students remain f o r  graduate 
school and want to use the program as a research tool. Thus, while it 
i s  not  mandatory, it cer ta in ly  i s  desirable to acquaint the undergraduate 
student w i t h  a program which can also be used f o r  graduate research. 
If the program i s  used f o r  
The t h i r d  question asks not only i s  the program presently widely 
used by s t ruc tu ra l  engineers, but a lso i s  it one of l a s t ing  quali ty? 
This question i s  very d i f f i c u l t  to answer and tends to be more of an 
opinion than anything e l se .  All too frequently the answer i s  biased 
wi th  how well the instructor  can use the program i n  comparison to similar 
programs with which he is  familiar. Fortunately, it is  not imperative 
that  the student be l'trained" on a univeral  program, provided the program 
used has the same major character is t ics  of the more commonly used ones. 
The f i n a l  question i s  more pragmatic and i s  one which cannot be 
ignored i n  view of the current f inancial  pressure on ins t i tu t ions  of 
higher learning. The cost  of operating the  program depends s ignif icant ly  
on the txpe of computer i n s t a l l a t ion  and the method of charging f o r  
computer services.  It is  important that  the instructor  monitor the 
computer expenses to ensure they do not ge t  out of hand. 
While several  excellent f i n i t e  element programs are available 
(Ref. l), the NASTRAN program w a s  selected f o r  the present study f o r  
the following reasons. F i r s t  and foremost, the author f e l t  NASTRAN 
416 
st ruck a proper balance between easy usage and v e r s a t i l i t y  (Ref. 2 ) .  
w a s  a lso f e l t  t h a t  the government's commitment (Ref. 3) t o  maintain and 
improve the program w i l l  assure an even wider acceptance of NASTRAN i n  
the future.  With regard t o  the question of cost ,  it is  acknowledged 
t h a t  NASTRAN is an expensive system t o  operate (Ref. 2 ) .  
the s ignif icant  time savings available between Levels 12 and 15, it 
appears the cost of operation can s t i l l  be reduced. 
It 
However, with 
PROGRAM UTILIZATION 
The presentation of computer methods of s t ructures  primarily 
consists of three topics with which the student is unfamiliar: 
1) Struc tura l  theory 
2)  Computer code 
3) User experience 
The ins t ruc tor  i s  faced with the problem of maintaining a proper balance 
between the three.  If he devotes h is  time exclusively t o  presenting 
s t ruc tu ra l  theory, he creates an "ivory tower" product who may make an 
excellent graduate student but a poor prospect f o r  industry. On the other 
hand, t o t a l  emphasis on user experience produces a "technician" who knows 
how to use a "black box" but who knows very l i t t l e  about how the %lack 
box" works. 
A balanced approach has been taken by the author i n  two separate 
The two courses. d i f f e r  i n  t h a t  the 
senior-level courses -- one i n  a i r c r a f t  s t ructures  and another i n  machine 
design i n  mechanical engineering. 
a i r c r a f t  s t ructures  course has an  assigned problem of a small a i r c r a f t  
component whereas the machine design course allows the students t o  se lec t  
individual projects .  
students are: 
Typical projects  which have been selected by 
1) Automobile brake drum 
2)  Concrete beam with spliced reinforcing s t e e l  
3 )  Automobile car  roof 
4)  Railroad tank car 
5 )  Motorcycle helmet 
6) Outboard motor propellear 
The d ivers i ty  of subjects points out the wide var ie ty  of in te res t s  and 
backgrounds among engineering students 
In each course it has been found possible to start w i t h  a sequence 
By relying upon of lectures  on how t o  use MSTRAN fo r  s t a t i c  analysis.  
the physical concepts of the f i n i t e  elements, it has been found that  
three periods are suf f ic ien t  to check out students who have had no previous 
s t ruc tu ra l  programming experience. This i n i t i a l  check out enables the 
students to spend the remainder of the course working on t h e i r  par t icu lar  
s t ruc tu ra l  problem. Following the f irst  three periods, the remaining 
lectures  are devoted to s t ruc tu ra l  theory and computer coding. 
The topic  of computer coding i s  covered w i t h  a presentation of a 
simple f i n i t e  element program wri t ten by the instructor  to i l l u s t r a t e  
the major s teps  i n  program code development. Explanation of t h i s  simple 
program i s  intended to show the student the ar t  of building a program. 
Thus, the student i s  spared the time consuming labors of writ ing h is  own 
computer code, debugging it, and f ina l ly  t rying to obtain some prac t ica l  
r e su l t s  before the course ends. The f ac t  tha t  the student can understand 
how to use NASTRAN before he has the s t ruc tu ra l  theory and coding back- 
ground s igni f icant ly  increases the amount of time he cam spend developing 
first-hand experience. 
picture" before becoming entangled i n  the de t a i l s  
Thus, i n  a sense, he i s  able to see the "big 
.Based upon student accomplishments, understanding, and endorsement, 
t h i s  par t icu lar  approach has apparently been successful. Its greatest  
shortcoming is  t h a t  MSTRAN i s  expensive to operate. 
on an IBM 370/145 computer w i t h  256K core. 
are figured at  $400 per CPU hour. 
s t ructures  course used approximately one hour of CPU time, whereas the 
machine design students required an average of two CPU hours. Thus, the 
compter costs per student f e l l  within the range of $400-$800. 
comparison, a similar study on course instruct ion i n  basic  Fj6RTRAN was 
found to cost l e s s  than $40 per student. 
The program was run 
The charges f o r  t h i s  machine 
The average student i n  the aerospace 
For 
The author's experience has also shown t h a t  use of NASTRAN's p lo t t ing  
feature dramatically improves student acceptance of the r e su l t s .  The 
importance of the student seeing a scaled model of the s t ruc ture ,  as 
opposed to simply scanning pages of numbers, cannot be over-emphasized. 
After gaining a f e e l  f o r  his  problem, he i s  much more wil l ing to study 
the tabulated r e su l t s .  
PROPOSED WORK 
A t  f irst  glance, students tend to be overwhelmed by the magnitude 
and bulk of the NASTRAN User's Manual. This i n i t i a l  shock could be eased 
418 
with the ava i l ab i l i t y  of a "Mini-Manual" which describes the essent ia l  
steps f o r  writing a NASTRAN program. 
simple example problems. After graduating from the "Ivlini-Manual, the 
student can then use the more extensive documentation contained i n  the 
present User's Manual. 
This manual should a l so  contain 
IiEFERENCES 
1. T. G. Butler, "On the Reduction of Prol i ferat ion of F in i te  Element 
Programs I' paper contained i n  "NASTRAN: 
NASA X-2378, 1971. 
Users ' Experiences, 'I 
2. J. L. Tocher and E. D. Herness, "A C r i t i c a l  View of NASTRAN," paper 
presented at the Internat ional  Symposium on Numerical and Computer 
Methods i n  S t ruc tura l  Mechanics, Urbana-Champaign, Ill., Sept. 
8-10, 1971. 
3 .  J. P. Raney, D. J. Weidman, and H. M. Adelman, "NASTRAN: Status ,  
Maintenance, and Future Development of New Capability, I'  paper 
contained i n  "NASTRAN: Users ' Experiences, 'I NASA TM X-2378, 1971. 


Use of NASTRAN as a teaching aid

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