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  • 1
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    Finite element solution of torsion and other 2-D Poisson equations (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The NASTRAN structural analysis computer program may be used, without modification, to solve two dimensional Poisson equations such as arise in the classical Saint Venant torsion problem. The nonhomogeneous term (the right-hand side) in the Poisson equation can be handled conveniently by specifying a gravitational load in a "structural" analysis. The use of an analogy between the equations of elasticity and those of classical mathematical physics is summarized in detail.
    Keywords: STRUCTURAL MECHANICS
    Type: Georgia Univ. 10th NASTRAN User's Colloq.; p 153-164
    Format: text
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  • 2
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    A general low frequency acoustic radiation capability for NASTRAN (1986)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A new capability called NASHUA is described for calculating the radiated acoustic sound pressure field exterior to a harmonically-excited arbitrary submerged 3-D elastic structure. The surface fluid pressures and velocities are first calculated by coupling a NASTRAN finite element model of the structure with a discretized form of the Helmholtz surface integral equation for the exterior fluid. After the fluid impedance is calculated, most of the required matrix operations are performed using the general matrix manipulation package (DMAP) available in NASTRAN. Far field radiated pressures are then calculated from the surface solution using the Helmholtz exterior integral equation. Other output quantities include the maximum sound pressure levels in each of the three coordinate planes, the rms and average surface pressures and normal velocities, the total radiated power and the radiation efficiency. The overall approach is illustrated and validated using known analytic solutions for submerged spherical shells subjected to both uniform and nonuniform applied loads.
    Keywords: ACOUSTICS
    Type: COSMIC 14th NASTRAN (R) Users' Colloquium; p 293-310
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  • 3
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    Recent improvements to BANDIT (1975)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The NASTRAN preprocessor BANDIT, which improves NASTRAN's computer efficiency by resequencing grid point labels for reduced matrix bandwidth is described. The addition of (1) the Gibbs-Poole-Stockmeyer (GPS) algorithm, and (2) the user option to reduce matrix profile rather than matrix bandwidth is also described. It is shown that, compared to the Cuthill-McKee algorithm on which BANDIT was originally based, GPS is faster and achieves similar results. Current capabilities and options of BANDIT are summarized.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center NASTRAN: Users' Experiences; p 511-521
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  • 4
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    The BANDIT computer program for the reduction of matrix bandwidth for NASTRAN (1972)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A computer program, BANDIT, is described which was developed for use as a preprocessor to NASTRAN to automatically resequence the grid point numbers for reduced matrix bandwidth. The BANDIT program accepts a standard NASTRAN data deck as input, resequences the grid point numbers for reduced bandwidth, and generates a set of SEQGP cards for insertion into the NASTRAN bulk data deck. BANDIT uses the Cuthill-McKee strategy for resequencing grid points. The program is operational on the CDC 6000 series of computers, the IBM 360, and the Univac 1108.
    Keywords: COMPUTERS
    Type: NASA. Langley Res. Center NASTRAN: Users' Experiences; p 407-414
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  • 5
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    Finite Element Prediction of Loss Factors for Structures with Frequency-dependent Damping Treatments (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A finite element procedure is described for calculating the loss factors for elastic structures to which frequency-dependent viscoelastic damping treatments were applied. The frequency dependence of the viscoelastic damping material is treated by approximating its shear modulus with a second-order polynomial so that the stiffnesses associated with the constant, linear, and quadratic terms can be combined, respectively, with the stiffness, damping, and mass matrices assembled for the rest of the structure. A single complex eigenvalue analysis is then performed in which the eigenvalues are purely imaginary. The loss factor is computed by the modal strain energy (MSE) approach. In the the MSE approach, the loss factor of a composite structure vibrating in one of its natural modes may be visualized as a weighted average of the loss factors of the component parts, with the relative stored energies as weighting constants. The finite element procedure, which can treat very general geometries, is illustrated for the case of a vibrating constrained-layer damped plate.
    Keywords: STRUCTURAL MECHANICS
    Type: COSMIC 13th NASTRAN (R) Users' Colloq.; p 419-430
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  • 6
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    Finite Element Prediction of Acoustic Scattering and Radiation from Submerged Elastic Structures (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A finite element formulation is derived for the scattering and radiation of acoustic waves from submerged elastic structures. The formulation uses as fundamental unknowns the displacement in the structure and a velocity potential in the field. Symmetric coefficient matrices result. The outer boundary of the fluid region is terminated with an approximate local wave-absorbing boundary condition which assumes that outgoing waves are locally planar. The finite element model is capable of predicting only the near-field acoustic pressures. Far-field sound pressure levels may be determined by integrating the surface pressures and velocities over the wet boundary of the structure using the Helmholtz integral. Comparison of finite element results with analytic results show excellent agreement. The coupled fluid-structure problem may be solved with general purpose finite element codes by using an analogy between the equations of elasticity and the wave equation of linear acoustics.
    Keywords: STRUCTURAL MECHANICS
    Type: COSMIC Twelfth NASTRAN (R) Users' Colloq.; p 192-209
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  • 7
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    Reduction of matrix wavefront for NASTRAN (1978)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The three grid point resequencing algorithms most often run by NASTRAN users are compared for their ability to reduce matrix root-mean-square (rms) wavefront, which is the most critical parameter in determining matrix decomposition time in NASTRAN. The three algorithms are Cuthill-McKee (CM), Gibbs-Poole-Stockmeyer (GPS), and Levy. The first two (CM and GPS) are in the BANDIT program, and the Levy algorithm is in WAVEFRONT. Results are presented for a diversified collection of 30 test problems ranging in size from 59 to 2680 nodes. It is concluded that GPS is exceptionally fast and, for the conditions under which the test was made, the algorithm best able to reduce rms wavefront consistently well.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Marshall Space Flight Center Seventh NASTRAN User's Colloq.; p 111-121
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  • 8
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    The dynamic analysis of submerged structures (1975)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Methods are described by which the dynamic interaction of structures with surrounding fluids can be computed by using finite element techniques. In all cases, the fluid is assumed to behave as an acoustic medium and is initially stationary. Such problems are solved either by explicitly modeling the fluid (using pressure or displacement as the basic fluid unknown) or by using decoupling approximations which take account of the fluid effects without actually modeling the fluid.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Res. Center NASTRAN: Users' Experiences; p 419-429
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  • 9
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    A NASTRAN implementation of the doubly asymptotic approximation for underwater shock response (1976)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A detailed description is given of how the decoupling approximation known as the doubly asymptotic approximation is implemented with NASTRAN to solve shock problems for submerged structures. The general approach involves locating the nonsymmetric terms (which couple structural and fluid variables) on the right hand side of the equations. This approach results in coefficient matrices of acceptable bandwidth but degrades numerical stability, requiring a smaller time step size than would otherwise be used. It is also shown how the structure's added (virtual) mass matrix, is calculated with NASTRAN.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Res. Center NASTRAN: User's Experiences; p 207-228
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  • 10
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    Comparison of finite element analysis of a piping tee using NASTRAN and CORTES/SA (1980)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A comparison of finite element analyses of a piping tee was made using NASTRAN and CORTES/SA, a modified version of SAP3 having a special purpose input processor for generating geometries for a wide variety of tee joints. Four finite element models were subjected in force, moment, and pressure loadings. Flexibility factors and principal stresses were computed for each model and compared with results obtained experimentally by Combustion Engineering, Inc. Results from the NASTRAN analyses were in good agreement with experimental results for all loadings except internal pressure. The CORTES/SA analyses gave good results for the internal pressure loading, but poorer results for out of plane bending moments or forces resulting in out of plane bending. Two of the basic load cases in CORTES/SA were found to contain errors that could not be easily corrected. COST COMPARison of NASTRAN and CORTES/SA showed NASTRAN to be less expensive to two than CORTES/SA for identical meshes.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Kennedy Space Center 9th NASTRAN (R) Users' Colloq.; p 224-242
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