The application of the thermal analysis phase of NASTRAN in engineering is described. Some illustrative samples are presented to demonstrate the applicability and limitation of NASTRAN thermal analysis capability. The results of the evaluation of the relative efficiency, applicability and accuracy among NASTRAN, other finite element programs, and finite difference programs are also presented

Go, J. C. D.

English

NASA Technical Reports Server

APPLICATION EXPERIENCES OF NASTRAN THERMAL ANALYSIS
IN ENGINEERING
James Chi-Dian Go
Computer Sciences Corporation
ABSTRACT
This paper summarizes the experiences of the application of the thermal analysis
hase of NASTRAN in engineering. Some illustrative samples are presented to
emonstrate the applicability and limitation of NASTRAN thermal analysis capability
engineering. The results of the evaluation of the relative efficiency, applicability
and accuracy among NASTRAN, other finite element programs and finite difference
?rograms are also presented.
INTRODUCTION
Prior to the development of the finite element method, finite difference was one of
the most practical analysis techniques for engineering thermal problems. Computer
codes such as HEATING, TAP, etc. were developed and widely used. E.L.
Wilson and others had shown that thermal problems could also be solved by finite
element techniques. Subsequently, several finite element thermal analysis computer
programs were developed; most of these were developed as part of a general purpose
structural analysis code. For example, lJohn Swanson implemented the finite
element thermal analysis method into his proprietary program ANSYS in 1970 and it
proved to be extremely popular among the structural engineers.
NASTRAN, being one of the most popular general purpose structural analysis
programs, introduced many thermal analysts to finite element thermal analysis tech-
niques. Subsequently, the application of finite element thermal analysis method was
widely accepted by engineers and applied scientists. This paper summarizes some
experiences of the application of NASTRAN in the analysis of engineering thermal
problems.
529
https://ntrs.nasa.gov/search.jsp?R=19750023444 2020-03-22T20:31:27+00:00Z
COMPARISONS OF FINITE DIFFERENCE AND FINITE ELEMENT
COMPUTER PROGRAMS
In assessing the relative merits of finite difference and finite element thermal
analysis programs, we have to consider computational accuracy, efficiency of input
preparation and output interpretation, computer requirements and some other factors.
Some experiences are summarized in this section. It should be noted that the informa-
tion was derived from a limited number of computer runs on currently readily obtain-
able programs.
In our evaluation of the accuracies of finite difference and finite element we
selected several problems of various sizes and types covering ranges of our practical
applications. In all cases the desired accuracies were easily obtained by adjusting
the mesh or element sizes. Thus, the accuracy comparison by itself does not indicate
preference among various finite difference and finite element computer programs.
Input preparation comparisons and output interpretation are more difficult to assess
due to various degrees of familiarity with each of the computer codes. However, some
distinctive advantages of finite element are evident:
• subsequent utilization of thermal analysis model for structural analysis
• thermal outputs conversion to structural analysis inputs
• program maintenance
minimizing new users' learning time by running both thermal and
structural analyses in one general purpose finite element analysis
program.
Computer requirements comparison is based on central memory, I/O and elapsed
run time. For small problems, with two minutes or less run time and 140000 (octal)
or less core, the relative efficiencies of the finite difference and finite element pro-
grams are not significant. However, some problems with run time of five minutes or
over and requiring 142000 (octal) core for finite element programs required 300000
(octal) core and about the same run time for finite difference programs. It seems
reasonable to project that this difference in core requirement will be widened as the
problem sizes increase.
53O
ADDITIONAL DESIRABLE FEATURES
l In any computer program some additional features become desirable only after
xtensive actual applications. Based on our experiences, the following features would
,e extremely useful to the NASTRAN thermal analysis users:
Internal Data Generation: During the course of our application of NASTRAN
we developed several small programs to generate externally some NASTRAN
input cards. After extensive application of NASTRAN and other finite element
programs it has become apparent that internal data generation significantly
increases users' efficiency.
Simplification of Radiation Heat Transfer Inputs: The radiation heat transfer
input cards RADMTX and RADLST should be simplified to reduce the input
data preparation efforts.
Contour Plot: A simple contour plotting for stress and temperature would be
useful for the interpretation of the outputs.
Addition of a Heat Transfer-Fluid Flow Element: This element is to be
defined by two grids, each with only one degree of freedom. It should be
capable of transfering heat and fluid between the two grids. The heat
transfer should include the heat conduction within the fluid and the mass
transport of the fluid.
CONC LUDING REMARKS
Based on our application experience, we have found that the finite element thermal
analysis cede significantly reduced analyst time and, in most cases, required less
computer resources than finite difference codes. Current research and development of
_init e element programs by various groups is far more extensive than that of finite diff-
erence thermal analysis programs. This will lead to an even greater efficiency of finite
/element thermal analysis programs in the near future. This will provide another incen-
ftive for the adoption of the finite element method as a standard thermal analysis tool.
531


Application Experiences of NASTRAN Thermal Analysis in Engineering

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server