Search NASA⌕ Search

Engineering topics

Williams, F. W.

Publications and source records attributed to Williams, F. W..

15 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Optimum design using VICONOPT, a buckling and strength constraint program for prismatic assemblies of anisotropic plates

A computer program for obtaining the optimum (least mass) dimensions of the kind of prismatic assemblies of laminated, composite plates which occur in advanced aerospace construction is described. Rigorous buckling analysis (derived from exact member theory) and a tailored design procedure are used to produce designs which satisfy buckling and material strength constraints and configurational requirements. Analysis is two to three orders of magnitude quicker than FEM, keeps track of all the governing modes of failure and is efficiently adapted to give sensitivities and to maintain feasibility. Tailoring encourages convergence in fewer sizing cycles than competing programs and permits start designs which are a long way from feasible and/or optimum. Comparisons with its predecessor, PASCO, show that the program is more likely to produce an optimum, will do so more quickly in some cases, and remains accurate for a wider range of problems.

Butler, R.↗
NASA NTRS1992

Designing Assemblies Of Plates

VICONOPT calculates vibrations and instabilities of assemblies of prismatic plates. Designed for efficient, accurate analysis of buckling and vibration, and for optimum design of panels of composite materials. Written in FORTRAN 77.

Williams, F. W.↗
NASA NTRS1990

User manual for VICONOPT: An exact analysis and optimum design program covering the buckling and vibration of prismatic assemblies of flat in-plane loaded, anisotropic plates, with approximations for discrete supports, and transverse stiffeners

A computer program which is designed for efficient, accurate buckling and vibration analysis and optimum design of composite panels is described. The capabilities of the program are given along with detailed user instructions. It is written in FORTRAN 77 and is operational on VAX, IBM, and CDC computers and should be readily adapted to others. Several illustrations of the various aspects of the input are given along the example problems illustrating the use and application of the program.

Williams, F. W.↗
NASA NTRS1989

Calculating Buckling And Vibrations Of Lattice Structures

BUNVIS-RG computer program designed to calculate vibration frequencies or buckling loads of prestressed lattice structures used in outer space. For buckling and vibration problems, BUNVIS-RG calculates deadload axial forces caused in members by any combination of externally-applied static point forces and moments at nodes, axial preload or prestrain in members, and such acceleration loads as those due to gravity. BUNVIS-RG is FORTRAN 77 computer program implemented on CDC CYBER and VAX computer.

Anderson, M. S.↗
NASA NTRS1988

Reliable use of determinants to solve nonlinear structural eigenvalue problems efficiently

The analytical derivation, numerical implementation, and performance of a multiple-determinant parabolic interpolation method (MDPIM) for use in solving transcendental eigenvalue (critical buckling or undamped free vibration) problems in structural mechanics are presented. The overall bounding, eigenvalue-separation, qualified parabolic interpolation, accuracy-confirmation, and convergence-recovery stages of the MDPIM are described in detail, and the numbers of iterations required to solve sample plane-frame problems using the MDPIM are compared with those for a conventional bisection method and for the Newtonian method of Simpson (1984) in extensive tables. The MDPIM is shown to use 31 percent less computation time than bisection when accuracy of 0.0001 is required, but 62 percent less when accuracy of 10 to the -8th is required; the time savings over the Newtonian method are about 10 percent.

Williams, F. W.↗
NASA NTRS1986

Exact Bernoulli-Euler static stiffness matrix for a range of tapered beam-columns

The static stiffnesses for torsional and flexural deformation of a tapered beam under axial loading are determined analytically, extending the Bernoulli-Euler/Bessel-function approach of Banerjee and Williams (1985). The derivation of the expressions is explained in detail, and numerical results for sample problems are presented in tables and shown to be in excellent agreement with those obtained using stepped beams of 400 or 500 elements.

Banerjee, J. R.↗
NASA NTRS1986

Boundary layer measurements on an airfoil in cascade using laser Doppler anemometry

Laser Doppler anemometry (LDA) was used to obtain detailed boundary layer data at 89.3 percent chord on the pressure surface of a double circular arc compressor blade in cascade. The measurements were taken at a chord Reynolds number of 5.0 x 10 to the 5th and a cascade angle of 53 degrees. The mean velocity, local turbulence intensity, skewness, and kurtosis were determined from the measured velocity probability distributions. The mean velocity profile and the local turbulence intensity profile had classical shapes. Also, the skewness and kurtosis had commonly observed shapes through out the boundary layer, reaching maximum values for Y/delta between 0.5 and 1.1 and Gaussian values for Y/delta greater than 1.1. A comparison was made between data taken with and without the Bragg cell and no significant differences were found.

Williams, F. W.↗
NASA NTRS1986

Inclusion of elastically connected members in exact buckling and frequency calculations

A standard stiffness matrix procedure which permits any combination of rigid, elastic, pinned or sliding connections of the degrees of freedom at the ends of a member to the nodes of its parent structure is described, in order to show how easily it can be extended to allow an existing algorithm to be used to ensure that no eigenvalues of the parent structure can be missed even when 'exact' member theory is used. The eigenvalues are the natural frequencies of undamped free vibration analyses or the critical load factors of buckling problems. The method preserves the exactness of the member theory and an efficient method for computer application is indicated. The theory also permits any combination of rigid, elastic, pinned or sliding connections between the freedoms of a substructure and those of its parent structure.

Williams, F. W.↗
NASA NTRS1986

BUNVIS-RG - An exact buckling and vibration program for lattice structures, with repetitive geometry and substructuring options

The exact FORTRAN computer program BUNVIS-RG which uses an exact stiffness matrix method to find eigenvalues and modes of three-dimensional planes, is presented in detail. It is shown that BUNVIS-RG solution times can be predicted fairly accurately from two computer dependent constants, the number of nodes and members in the frame, and the maximum node number difference of any pair of connected nodes. The program's use of repetitive geometry, stayed column substructures and nonuniform member options was found to enhance efficiency and range of application.

Anderson, M. S.↗
NASA NTRS1985

Buckling of simply supported plate assemblies subject to shear loading

An analysis is presented of the shear buckling load of an arbitrary simply-supported prismatic plate assembly or stiffened panel configuration. The method utilizes stiffness matrices developed by Wittrick (1968). For the restraint of simple support along edges perpendicular to the longitudinal direction, various wavelengths of response are combined using an energy method that involves only a boundary integral. Numerical results for plate and panel configurations show the accuracy and convergence of the method.

Anderson, M. S.↗
NASA NTRS1984

Vibration and buckling of general periodic lattice structures

A method is presented for vibration and buckling analysis of arbitrary lattice structures having repetitive geometry in any combination of coordinate directions. The approach is based on exact member theory for representing the stiffness of an individual member subject to axial load, and in the case of vibration, undergoing harmonic oscillation. The method is an extension of previous work that was limited to specific geometries. The resulting eigenvalue problem is of the size associated with the repeating element of the structure. A computer program has been developed incorporating the theory and results are given for vibration of rectangular platforms and a large antenna structure having rotational symmetry. Buckling and vibration results for cable-stiffened rings are also given.

Anderson, M. S.↗
NASA NTRS1983

Buckling and vibration of any prismatic assembly of shear and compression loaded anisotropic plates with an arbitrary supporting structure

The computer program designated 'VIPASA', which accurately treats buckling and vibration in prismatic plate assemblies with a response that varies sinusoidally in the longitudinal direction, has been found to be limited by the production of an in-plane shear loading of component plates that produces skewed mode shapes. These do not conform to desired support conditions. This problem is presently overcome through a coupling of the VIPASA stiffness matrices for different wavelength responses by means of the Lagrangian Multipliers method. The theory extends to supports at arbitrary locations, and even to the support provided by any elastic structure. The generality and capabilities of VIPASA have been retained in the computer program designated 'VICON', which permits constraints and a supporting structure consisting of any number of transverse beam columns.

Anderson, M. S.↗