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Selected Publications:
Svalbonas, V., "Numerical Analysis of Stiffened Shells of Revolution," NASA CR-2273, 1973
V. Svalbonas (Engineering Department, The Franklin Institute Research Laboratories, Philadelphia, Pennsylvania 19103, USA), “Transient dynamic and inelastic analysis of shells of revolution — a survey of programs”, Nuclear Engineering and Design, Vol. 37, No. 1, April 1976, pp. 73-93,
doi:10.1016/0029-5493(76)90054-6
ABSTRACT: Advances in the limits of structural use in the areospace and nuclear power industries over the past years have increased the requirements upon the applicable analytical computer programs to include accurate capabilities for inelastic and transient dynamic analyses. In many minds, however, this advanced capability is unequivocally linked with the large scale, general purpose, finite element programs. This idea is also combined with the view that such analyses are therefore prohibitively expensive and should be relegated to the “last resort” classification. While this, in the general sense, may indeed be the case, if the user needs only to analyze structures falling into limited categories, however, he may find that a variety of smaller special purpose programs are available which do not put an undue strain upon his resources. One such structural category is shells of revolution. This survey of programs will concentrate upon the analytical tools which have been developed predominantly for shells of revolution. The survey will be subdivided into three parts: (a) consideration of programs for transient dynamic analysis; (b) consideration of programs for inelastic analysis and finally; (c) consideration of programs capable of dynamic plasticity analysis. In each part, programs based upon finite difference, finite element, and numerical integration methods will be considered. The programs will be compared on the basis of analytical capabilities, and ease of idealization and use. In each part of the survey sample problems will be utilized to exemplify the state-of-the-art.
V. Svalbonas (1) and A. Kalnins (2)
(1) Engineering Department, The Franklin Institute Research Laboratories, Philadelphia, PA, 19103, USA
(2) Department of Mechanical Engineering and Mechanics, Lehigh University, Bethlehem, PA, 18015, USA
“Dynamic buckling of shells: Evaluation of various methods”, Nuclear Engineering and Design, Vol. 44, No. 3, December 1977, pp. 331-356, doi:10.1016/0029-5493(77)90169-8
ABSTRACT: The problem of dynamic stability is substantially more complex than the buckling analysis of a shell subjected to static loads. Even at this date suitable criteria for dynamic buckling of shells, which are both logically sound and practically applicable, are not easily available. Thus, a variety of analyses are available to the user, encompassing various degrees of complexity, and involving a range of simplifying assumptions. The purpose of this paper is to compare and evaluate some of these solutions by applying them to a specific problem. A shallow spherical cap, subjected to an axisymmetric, uniform-pressure, step loading, is used as the structural example. The predictions, by various methods, of the dynamic buckling of this shell into unsymmetric modes, are then investigated and compared. The approximate methods used by Akkas are compared to the more rigorous and general solutions of the KSHEL, STARS, DYNASOR, and SATANS computer programs, and the various simplifying assumptions utilized are evaluated. Also included in the comparisons, are the predictions of the relatively simple “dynamic buckling model” approach of Budiansky and Hutchinson. The approaches utilized by the more complex programs [KSHEL (spatial integration, modal superposition, perturbation approach), DYNASOR (finite elements, time integration of non-linear dynamic equilibrium equations), SATANS (finite differences, pseudo load method, time integration), STARS (spatial and time integration, non-linear equilibrium or perturbation approaches)] will in turn be compared in terms of accuracy, idealization complexity, ease of use, and user expertise and experience required for analysis. The comparisons show that the more approximate methods underpredict the dynamic buckling loads for this problem. In addition, some basic assumptions of the simpler solutions are found to be invalid.
V. Svalbonas (1) and J. Key (2)
(1) Grumman Aerospace Corporation, Bethpage, New York 11714, USA
(2) NASA Marshall Space Flight Center, Huntsville, Alabama, USA
“Static, stability, and dynamic analysis of shells of revolution by numerical integration — A comparison”, Nuclear Engineering and Design, Vol. 27, No.1, March 1974, pp. 30-45, doi:10.1016/0029-5493(74)90022-3
ABSTRACT: The use of numerical integration for the analysis of practical shell-of-revolution structures was documented almost simultaneously in the United States by three independent groups of researchers (Cohen, Kalnins, Mason et al.). These early efforts have been refined, reformulated, and increased in scope and applicability to become major program systems (SRA, Kalnins, STARS). While all three programs utilize basically the same mathematical formulation for integrating the shell differential equations, the matrix solution procedures from this point are basically different. The purpose of this paper is twofold, as follows: (1) to present the differences in solution procedures of the largest system (the Grumman — NASA STARS) from the other two, and point out the inherent advantages of this approach; and (2) compare the numerical integration procedure, as utilized in the STARS, with finite difference and finite element procedures, noting the relative advantages of each in the analysis of shells of revolution for static, buckling, and dynamic loadings. To fulfill the above purpose, a brief review of the numerical integration procedure for the analysis of shells of revolution is presented, and the matrix solution procedures of the SRA, Kalnins, and STARS programs are contrasted. The limitations imposed by the relative procedures are discussed. The unique formulation utilized by STARS for the solution of stability and vibration problems, and its advantages, are discussed in detail. The STARS program's analytical capabilities, capacity, and user options are compared with those of other major systems utilizing either finite differences or finite elements for the analysis of shells of revolution. Comparisons are made in terms of program size, program accuracy, number of degrees of freedom required for analysis, ease of idealization and user inputs, limitations imposed on analysis capability or output, running time, and so forth. All advantages and differences are demonstrated by use of solutions for realistic shell problems in the areas of statics, stability (including dead and live load distributions), vibrations, and dynamic response of shells subjected to time-dependent loadings.
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