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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Singular plastic element: NASTRAN implementation and application

The elastic and plastic singularities near a crack tip are obtained from higher order isoparametric elements. This is simply accomplished by collapsing the quadrilateral element into the triangular element and by judicious choice of adjacent mid-side nodes. Specifically for the cubic element the elastic singularity is obtained by placing the mid-side nodes adjacent to the crack tip at 1/9th and 4/9th locations. The plastic singularity is constructed using the sliding node concept. These elements have been implemented in NASTRAN as user dummy elements.

Hussain, M. A.↗
NASA NTRS1977

Development of an automated multi-stage modal synthesis system for NASTRAN

A mode synthesis development to be scheduled in the NASTRAN multi-level substructuring system for general dynamics applications is described. The method combines the better features of several state of the art mode synthesis techniques, yet is general enough to provide for any arbitrary combination of boundary degrees of freedom and normal mode boundary conditions. Normal modes or complex eigenvectors may be used in the definition of a structure component which may be combined with other components of any type. Combination structures fabricated from component modes may be processed as normal substructures, including further multi-stage mode synthesis reductions. Included are discussions of the user control of the system and advantages in actual application.

Herting, D. N.↗
NASA NTRS1977

Addition of rigid elements to NASTRAN

Four rigid elements, namely, a rigid rod element (CRIGDR) and three rigid body elements (CRIGD1, GRIGD2 and CRIGD3), have recently been added to NASTRAN and will be available in the next public release of the program. The theoretical formulation, the bulk data information and the programming details pertaining and realistic problems are illustrated by employing them in the solution of two helicopter structural analysis problems.

Pamidi, P. R.↗
NASA NTRS1978

Dynamic storage expansion in NASTRAN

Some functions of NASTRAN require a large block of working computer storage to execute. The method of meeting this requirement, because of insufficient data, was to specify in advance an excessive amount of data to avoid a fatal exit. A method was developed to calculate the amount of working space needed for the analysis and to inform the analyst of this data or, in the case of Univac computers, to acquire this extra storage and continue the analysis.

Hess, E. N.↗
NASA NTRS1978

NASTRAN computer resource management for the matrix decomposition modules

Detailed computer resource measurements of the NASTRAN matrix decomposition spill logic were made using a software input/output monitor. These measurements showed that, in general, job cost can be reduced by avoiding spill. The results indicated that job cost can be minimized by using dynamic memory management. A prototype memory management system is being implemented and evaluated for the CDC Cyber computer.

Bolz, C. W.↗
NASA NTRS1978

Typical uses of NASTRAN in a petrochemical industry

NASTRAN was principally used to perform failure analysis and redesign process equipment. It was also employed in the evaluation of vendor designs and proposed design modifications to existing process equipment. Stress analysis of forced draft fans, distillation trays, metal stacks, jacketed pipes, heat exchangers, large centrifugal fans, and agitator support structures are described.

Winter, J. R.↗
NASA NTRS1978

Use of NASTRAN in a university environment

A survey was conducted in the middle of the 1977-78 school year. Each faculty member of the civil engineering, engineering mechanics, and mechanical and aerospace engineering departments was asked to give information on the present (Level 15.5) and future projected (Level 17) usage of NASTRAN programs. Results from the survey study are summarized.

Mei, C.↗
NASA NTRS1978

Application of NASTRAN to TFTR toroidal field coil structures

The primary applied loads on the TF coils were electromagnetic and thermal. The complex structure and the tremendous applied loads necessitated computer type of solutions for the design problems. In the early stage of the TF coil design, many simplified finite element models were developed for the purpose of investigating the effects of material properties, supporting schemes, and coil case material on the stress levels in the case and in the copper coil. In the more sophisticated models that followed the parametric and scoping studies, the isoparametric elements, such as QUAD4, HEX8, and HEXA, were used. The analysis results from using these finite element models and the NASTRAN system were considered accurate enough to provide timely design information.

Chen, S. J.↗
NASA NTRS1978

Solving magnetostatic field problems with NASTRAN

Determining the three-dimensional magnetostatic field in current-induced situations has usually involved vector potentials, which can lead to excessive computational times. How such magnetic fields may be determined using scalar potentials is reviewed. It is shown how the heat transfer capability of NASTRAN level 17 was modified to take advantage of the new method.

Hurwitz, M. M.↗
NASA NTRS1978

Comparison of several NASTRAN analytical techniques for large structures

In order to plan for the finite element structural analysis of future aircraft, five static analysis techniques using the MacNeal-Schwendler Corporation version of NASTRAN were evaluated. The structure was analyzed as: (1) a single model with a symmetric loading condition; (2) a single model with symmetric/nonsymmetric loading conditions; (3) three substructures in three phases using tape storage with a symmetric loading condition; (4) three superelements using data base storage with a symmetric loading condition; and (5) three superelements using data base storage with cyclic symmetry for symmetric/nonsymmetric loading conditions. The superelement techniques proved superior to the single model approaches by reducing computer time for redesign work by as much as 70 percent.

Zemer, D. T.↗
NASA NTRS1978

NASTRAN analysis of Tokamak vacuum vessel using interactive graphics

Isoparametric quadrilateral and triangular elements were used to represent the vacuum vessel shell structure. For toroidally symmetric loadings, MPCs were employed across model boundaries and rigid format 24 was invoked. Nonsymmetric loadings required the use of the cyclic symmetry analysis available with rigid format 49. NASTRAN served as an important analysis tool in the Tokamak design effort by providing a reliable means for assessing structural integrity. Interactive graphics were employed in the finite element model generation and in the post-processing of results. It was felt that model generation and checkout with interactive graphics reduced the modelling effort and debugging man-hours significantly.

Miller, A.↗
NASA NTRS1978

Accuracy of results with NASTRAN modal synthesis

A new method for component mode synthesis was developed for installation in NASTRAN level 17.5. Results obtained from the new method are presented, and these results are compared with existing modal synthesis methods.

Herting, D. N.↗
NASA NTRS1979

Effect of element density on the NASTRAN calculated mechanical and thermal stresses of a spar

A NASTRAN model of a spar was examined to determine the sensitivity of calculated axial thermal stresses and bending stresses to changes in element density of the model. The thermal stresses calculated with three different element densities resulted in drastically differing values. The position of the constraint also significantly affected the value of the calculated thermal stresses. Mechanical stresses calculated from an applied loading were insensitive to element density.

Jenkins, J. M.↗
NASA NTRS1980

Eighth NASTRAN User's Colloquium

The general application of finite element methodology and the specific application of NASTRAN to a wide variety of static and dynamic structural problems are discussed.

Source record↗
NASA NTRS1980

On the congruent feature in NASTRAN

The congruent feature, which is a capability in NASTRAN that can contribute to significant increases in computational efficiencies, is discussed. The usage of the capability and the software design characteristics affecting it are explained. The factors affecting the efficiency of the feature are pointed out. The details pertaining to the software design of the congruent feature are presented; in particular, the congruent element table is described. Serveral examples employing the congruent feature are considered and comparisons of Element Matrix Generator module computer program update times with and without this feature are presented. The results clearly demonstrate the role of the congruent feature in increasing computational efficiencies and its applicability to large-size problems.

Pamidi, P. R.↗
NASA NTRS1980

Implementation of a trapezoidal ring element in NASTRAN for elastic-plastic analysis

The explicit expressions for an elastic-plastic trapezoidal ring element are presented and implemented in NASTRAN computer program. The material is assumed to obey the von Mises' yield criterion, isotropic hardening rule and the Prandtl-Reuss flow relations. For the purpose of demonstration, two elastic-plastic problems are solved and compared with previous results. The first is a plane-strain tube under uniform internal pressure and the second, a finite-length tube loaded over part of its inner surface. A very good agreement was found in both test problems.

Chen, P. C. T.↗
NASA NTRS1979

The NASTRAN user's manual (level 17.0)

NASTRAN embodies a lumped element approach, wherein the distributed physical properties of a structure are represented by a model consisting of a finite number of idealized substructures or elements that are interconnected at a finite of grid points, to which loads are applied. All input and output data pertain to the idealized structural model. The general procedures for defining structural models are described and instructions are given for each of the bulk data cards and case control cards. Additional information on the case control cards and use of parameters is included for each rigid format.

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