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On the role of minicomputers in structural design
Abstract
Results are presented of exploratory studies on the use of a minicomputer in conjunction with large-scale computers to perform structural design tasks, including data and program management, use of interactive graphics, and computations for structural analysis and design. An assessment is made of minicomputer use for the structural model definition and checking and for interpreting results. Included are results of computational experiments demonstrating the advantages of using both a minicomputer and a large computer to solve a large aircraft structural design problem.
The efficiency of the application of mini-computers to the solution of many problems by means of the finite element method is well recognized, and the importance of the percentage of time devoted to the solution of the resultant systems of linear equations is also noteworthy.Here, we present a comparative study of six programs of the solution of systems of linear equations, implemented in a 64-Kbyte mini-computer (HP1000F). The methods and algorithms on which the programs are based are described.Then, six finite element problems are presented with various degrees of discretization, giving rise to 19 different cases. In each case computation times, the number of disk input-output transfers and the number of arithmetic operations carried out are compared. It is concluded that the programs based on algorithms of variable bandwidth are always superior to those of constant bandwidth. In some cases, the optimum results are obtained with the algorithm of hypermatrices.
Floating roofs are used in oil storage tanks to reduce evaporation and handling losses, decrease corrosion, and reduce the fire hazard. A pontoon roof is used in this paper. It consists of a circular central plating attached at the edge to a compartmented; buoyant ring. The primary design loadings for this roof are due to accumulated rainwater or a punctured deck. The design loads typically cause the deck to deflect several hundred times its thickness and consequently the deck is usually designed and analyzed as a membrane.The complicated nature of the loading on the membrane together with the unusual boundary conditions require numerical integration of the coupled, non-linear differential equations which govern the behavior. A skilled analyst is needed to vary the starting parameters necessary for the integration. This paper describes the procedure that should be followed in the analysis and design of the roofs, and shows why an interactive computer is so important in the understanding of the forces in this structure and in the design necessary to transmit them.
Investigation of the Taylor expansion accuracy, when applied as an approximation to a modified structure solution, was carried out using a highly idealized finite element representation of a skin-stringer-frame fuselage midsection as a test model. It was found that for the sample structure, this approximation's error is less than 16% over a range of minus 100% (element removal) to plus 500% for modification of a single element, and minus 50% to 50% for simultaneous multielement modifications.
Status and recent developments of substructuring techniques and their application to structural analysis and design are summarized. Discussion focuses on a number of aspects including: multilevel substructuring algorithms; use of hypermatrix and other sparse matrix schemes, use of substructuring in automated design systems and application of substructuring in elasto-plastic problems. Numerical examples are presented to demoostrate the reduction in the number of arithmetic operations and disk storage requirements obtained by using multilevel substructuring techniques. Also discussed are the potential benefits of using such techniques with new computing hardware such as CDC STAR-100 and minicomputer systems.
Minicomputers are receiving increased use throughout the aerospace industry. Until recently, their use focused primarily on process control and numerically controlled tooling applications, while their exposure to and the opportunity for structural calculations has been limited. With the increased availability of this computer hardware, the question arises as to the feasibility and practicality of carrying out comprehensive structural analysis on a minicomputer. This paper presents results on the potential for using minicomputers for structural analysis by (1) selecting a comprehensive, finite-element structural analysis system in use on large mainframe computers; (2) implementing the system on a minicomputer; and (3) comparing the performance of the minicomputers with that of a large mainframe computer for the solution to a wide range of finite element structural analysis problems.
The use of superminicomputers for solving a series of increasingly complex thermal analysis problems is investigated. The approach involved (1) installation and verification of the SPAR thermal analyzer software on superminicomputers at Langley Research Center and Goddard Space Flight Center, (2) solution of six increasingly complex thermal problems on this equipment, and (3) comparison of solution (accuracy, CPU time, turnaround time, and cost) with solutions on large mainframe computers.
A description is given of a powerful computer-operated graphic system, used from design through manufacture at McDonnell Aircraft Company (MCAIR). This system has made designers many times more productive than when they are using conventional drawing hoard methods. High engineering productivity, however, is only an initial benefit. When fully developed, the system will allow Manufacturing to machine parts, utilizing the programmed data created by the designer at the console, without writing additional programmed instructions to drive the milling machines. In addition, Tool Design and Quality Assurance have direct access to the original three-dimensional geometric data, thus eliminating misinterpretation of design intentions. With lofted surfaces developed, defined mathematically, and stored in a shared-computer file, a designer is able to indicate the plane in which a lofted contour is desired, and in a matter of seconds, he can have the contour displayed on the CRT. This enables the designer to create a design almost as fast as he can think. Further, his designs are defined mathematically at a degree of accuracy never before known. Other disciplines which interface with design are strength, aerodynamics, thermodynamics, and propulsion. With continued use and development of this system, even greater time and cost-saving techniques will be realized. © 1973, American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
Stuctures Technology is oriented to the total vehicle with disciplines involving primarily stress, loads, flutter and fatigue, and with major data interfaces to others. Boeing's ATLAS System provides a tool for broad aeroelastic vehicle studies, involving multi-disciplines. ATLAS handles small and large strength design problems. On these problems both total cost and flowtime have been reduced by 90%. ATLAS produces 3 cycles of fully stressed design (20,000 design variables) for approximately 60 cp minutes on the CDC 6600 (2000 total computer cost).
Investigation of the Taylor expansion accuracy, when applied as an approximation to a modified structure solution, was carried out using a highly idealized finite element representation of a skin-stringer-frame fuselage midsection as a test model. It was found that for the sample structure, this approximation's error is less than 16% over a range of minus 100% (element removal) to plus 500% for modification of a single element, and minus 50% to 50% for simultaneous multielement modifications.
The architecture of the FLEXSTAB system and the important internal blocks of logic within each program of the system are described. General information flow schematics depiciting major areas where data are input to and output from each program are also shown. Program maintenance, updating, and modification are discussed.
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