SEARCH · Search NASA

Results for “problems”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 865 records · Page 48

All sources NASA NTRS DOE OSTI

NASA NTRS1979

ATLAS, an integrated structural analysis and design system. Volume 5: System demonstration problems

One of a series of documents describing the ATLAS System for structural analysis and design is presented. A set of problems is described that demonstrate the various analysis and design capabilities of the ATLAS System proper as well as capabilities available by means of interfaces with other computer programs. Input data and results for each demonstration problem are discussed. Results are compared to theoretical solutions or experimental data where possible. Listings of all input data are included.

Samuel, R. A.↗

NASA NTRS1979

The generalized pole assignment problem

Two dynamic output feedback problems for a linear, strictly proper system are considered, along with their interrelationships. The problems are formulated in the frequency domain and investigated in terms of linear equations over rings of polynomials. Necessary and sufficient conditions are expressed using genericity.

Djaferis, T. E.↗

NASA NTRS1979

Geophysical approaches to inverse problems: A methodological comparison. Part 1: A Posteriori approach

The relationships of a variety of general computational methods (and variances) for treating illposed problems such as geophysical inverse problems are considered. Differences in approach and interpretation based on varying assumptions as to, e.g., the nature of measurement uncertainties are discussed along with the factors to be considered in selecting an approach. The reliability of the results of such computation is addressed.

Seidman, T. I.↗

NASA NTRS1977

An interactive computer approach to performing resource analysis for a multi-resource/multi-project problem

New planning techniques and supporting computer tools are needed for the optimization of resources and costs for space transportation and payload systems. Heavy emphasis on cost effective utilization of resources has caused NASA program planners to look at the impact of various independent variables that affect procurement buying. A description is presented of a category of resource planning which deals with Spacelab inventory procurement analysis. Spacelab is a joint payload project between NASA and the European Space Agency and will be flown aboard the Space Shuttle starting in 1980. In order to respond rapidly to the various procurement planning exercises, a system was built that could perform resource analysis in a quick and efficient manner. This system is known as the Interactive Resource Utilization Program (IRUP). Attention is given to aspects of problem definition, an IRUP system description, questions of data base entry, the approach used for project scheduling, and problems of resource allocation.

Schlagheck, R. A.↗

NASA NTRS1978

Calculation of Pareto-optimal solutions to multiple-objective problems using threshold-of-acceptability constraints

A technique is presented for the calculation of Pareto-optimal solutions to a multiple-objective constrained optimization problem by solving a series of single-objective problems. Threshold-of-acceptability constraints are placed on the objective functions at each stage to both limit the area of search and to mathematically guarantee convergence to a Pareto optimum.

Giesy, D. P.↗

NASA NTRS1979

The problem of an inclined crack in an orthotropic strip

The elastostatic problem for an infinite orthotropic strip containing a crack is considered. It is assumed that the orthogonal axes of material orthotropy may have an arbitrary angular orientation with respect to the orthogonal axes of geometric symmetry of the uncracked strip. The crack is located along an axis of orthotropy, hence at an arbitrary angle with respect to the sides of the strip. The general problem is formulated in terms of a system of singular integral equations for arbitrary crack surface tractions. As examples Modes I and II stress-intensity factors are calculated for the strip having an internal or an edge crack with various lengths and angular orientations. In most calculations uniform tension or uniform bending away from the crack region is used as the external load. Limited results are also given for uniform normal or shear tractions on the crack surface.

Delale, F.↗

NASA NTRS1979

Second-order estimates in singular perturbation of output regulator problems

A method of order reduction in singular perturbation problems due to Chow and Kokotovic is studied. The method is used for an output regulator problem in control theory. The quadratic term in the asymptotic expansion of Chow and Kokotovic is calculated and it is shown by some examples how this term can give evidence of the accuracy of the procedure.

Rublein, G.↗

NASA NTRS1979

Application of a velocity-split Navier-Stokes solution technique to external flow problems

A method for solving the Navier-Stokes equations based on splitting the velocity vector into its rotational and irrotational parts has recently been applied successfully to internal flow computations. In this paper, the applicability of the method to external flows is examined by studying two model problems; laminar incompressible flow over semiinfinite and finite flat plates. For these problems the procedure accurately reproduces the known solutions and is computationally very efficient even at high Reynolds numbers. Computational aspects of the method are discussed along with the possibility of using the procedure to retrofit a viscous capability into existing transonic potential flow codes.

Dwoyer, D. L.↗

NASA NTRS1979

An accurate method for two-point boundary value problems

A second-order method for solving two-point boundary value problems on a uniform mesh is presented where the local truncation error is obtained for use with the deferred correction process. In this simple finite difference method the tridiagonal nature of the classical method is preserved but the magnitude of each term in the truncation error is reduced by a factor of two. The method is applied to a number of linear and nonlinear problems and it is shown to produce more accurate results than either the classical method or the technique proposed by Keller (1969).

Walker, J. D. A.↗

NASA NTRS1980

Linear stochastic optimal control and estimation problem

Problem involves design of controls for linear time-invariant system disturbed by white noise. Solution is Kalman filter coupled through set of optimal regulator gains to produce desired control signal. Key to solution is solving matrix Riccati differential equation. LSOCE effectively solves problem for wide range of practical applications. Program is written in FORTRAN IV for batch execution and has been implemented on IBM 360.

Geyser, L. C.↗

NASA NTRS1980

Decision making and problem solving with computer assistance

In modern guidance and control systems, the human as manager, supervisor, decision maker, problem solver and trouble shooter, often has to cope with a marginal mental workload. To improve this situation, computers should be used to reduce the operator from mental stress. This should not solely be done by increased automation, but by a reasonable sharing of tasks in a human-computer team, where the computer supports the human intelligence. Recent developments in this area are summarized. It is shown that interactive support of operator by intelligent computer is feasible during information evaluation, decision making and problem solving. The applied artificial intelligence algorithms comprehend pattern recognition and classification, adaptation and machine learning as well as dynamic and heuristic programming. Elementary examples are presented to explain basic principles.

Kraiss, F.↗

NASA NTRS1980

Flight-deck automation: Promises and problems

The state of the art in human factors in flight-deck automation is presented. A number of critical problem areas are identified and broad design guidelines are offered. Automation-related aircraft accidents and incidents are discussed as examples of human factors problems in automated flight.

Wiener, E. L.↗

NASA NTRS1980

Potential problems relative to TDRS/IUS tilt table elevation with failed VRCS

Operational concerns and preliminary solution alternatives related to elevating the inertial upper stage/tracking and data relay satellite (IUS/TDRS) with a failed orbiter vernier reaction control system (VRCS) are presented. Problems arise from the combination of TDRS thermal constraints and tilt table constraints (the primary reaction control system (PRCS) cannot be used to hold attitude while the tilt table is being elevated), and the problems are compounded by the minimum PRCS attitude deadband. The potential solution options are affected by the launch window, flight profile, crew procedures, vehicle capability and constraints, and flight rules.

Bell, J.↗

NASA NTRS1980

Newton's method: A link between continuous and discrete solutions of nonlinear problems

Newton's method for nonlinear mechanics problems replaces the governing nonlinear equations by an iterative sequence of linear equations. When the linear equations are linear differential equations, the equations are usually solved by numerical methods. The iterative sequence in Newton's method can exhibit poor convergence properties when the nonlinear problem has multiple solutions for a fixed set of parameters, unless the iterative sequences are aimed at solving for each solution separately. The theory of the linear differential operators is often a better guide for solution strategies in applying Newton's method than the theory of linear algebra associated with the numerical analogs of the differential operators. In fact, the theory for the differential operators can suggest the choice of numerical linear operators. In this paper the method of variation of parameters from the theory of linear ordinary differential equations is examined in detail in the context of Newton's method to demonstrate how it might be used as a guide for numerical solutions.

Thurston, G. A.↗

NASA NTRS1980

Straightening of a wavy strip: An elastic-plastic contact problem including snap-through

The nonlinear behavior of a wave like deformed metal strip during the levelling process were calculated. Elastic-plastic material behavior as well as nonlinearities due to large deformations were considered. The considered problem lead to a combined stability and contact problem. It is shown that, despite the initially concentrated loading, neglecting the change of loading conditions due to altered contact domains may lead to a significant error in the evaluation of the nonlinear behavior and particularly to an underestimation of the stability limit load. The stability was examined by considering the load deflection path and the behavior of a load-dependent current stiffness parameter in combination with the determinant of the current stiffness matrix.

Fischer, D. F.↗

NASA NTRS1980

Finite elements for contact problems in two-dimensional elastodynamics

A finite element approach for contact problems in two dimensional elastodynamics was proposed. Sticking, sliding, and frictional contact were taken into account. The method consisted of a modification of the shape functions, in the contact region, in order to involve the nodes of the contacting body. The formulation was symmetric (both bodies were contactors and targets), in order to avoid interpenetration. Compatibility over the interfaces was satisfied. The method was applied to the impact of a block on a rigid target. It is shown that the formulation can be applied to fluid structure interaction, and to problems involving material nonlinearity.

Zimmermann, T. K.↗

NASA NTRS1980

Solution sensitivity and accuracy study of NASTRAN for large dynamic problems involving structural damping

Large dynamic problems involving NASTRAN SOLUTION 8 (i.e., the steady state dynamic response option wherein all response quantities vary as e sub i omega t, where omega is the driving frequency and t is time) are considered. Using a submerged steel plate with a viscoelastic layer layer as the bench mark sample, the solution sensitivity and solution accuracy are checked. The solution sensitivity is examined by running the same finite element model on different computers, different versions of NASTRAN, and different precision levels. The solution accuracy is evaluated for these same runs by comparing the NASTRAN results with the exact solution of the same problem.

Kalinowski, A. J.↗

NASA NTRS1979

Boundary conditions for exterior acoustic problems

Problems of acoustics are generally posed in unbounded regions. Numerical computations require that the infinite regions be truncated with artificial finite boundaries. Boundary conditions must be developed at these artificial boundaries which approximate the conditions for outgoing waves. These conditions should be asymptotic in the distance of the boundaries from the source terms and should give rise to well posed problems interior to fairly arbitrary regions, which can be chosen on the basis of computational efficiency rather than for mathematical (i.e., well posedness) reasons. A family of such conditions is presented and their properties are discussed. These conditions can be thought of as extensions of the Sommerfeld radiation condition for outgoing waves.

Bayliss, A.↗