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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 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

An implicit finite-difference algorithm for hyperbolic systems in conservation-law form

An implicit finite-difference scheme is developed for the efficient numerical solution of nonlinear hyperbolic systems in conservation-law form. The algorithm is second-order time-accurate, noniterative, and in a spatially factored form. Second- or fourth-order central and second-order one-sided spatial differencing are accommodated within the solution of a block tridiagonal system of equations. Significant conceptual and computational simplifications are made for systems whose flux vectors are homogeneous functions (of degree one), e.g., the Eulerian gasdynamic equations. Conservative hybrid schemes, which switch from central to one-sided spatial differencing whenever the local characteristic speeds are of the same sign, are constructed to improve the resolution of weak solutions. Numerical solutions are presented for a nonlinear scalar model equation and the two-dimensional Eulerian gasdynamic equations.

Beam, R. M.↗
NASA NTRS1979

Two-dimensional, time-dependent MHD description of interplanetary disturbances Simulation of high speed solar wind interactions

A two-dimensional, time-dependent nonlinear MHD model is used to simulate the general features of multiply-interacting, transient solar wind flows. The major advantage of the two-dimensional model over the one-dimensional one is the proper consideration of azimuthal gradients. In addition, the new model can provide contour maps for disturbed plasma properties in the equatorial plane, thereby enabling one to perform essential tests of the physical assumptions through direct comparison with space probe data.

Wu, S. T.↗
NASA NTRS1980

Numerical calculation of steady inviscid full potential compressible flow about wind turbine blades

An exact nonlinear mathematical model that accounts for three-dimensional cascade effects about the inner portions of the rotor blades and compressibility effects about the tip regions of the blades was derived. An artificially time dependent version was iteratively solved by a finite volume technique involving an artificial viscosity and a three-level consecutive mesh refinement. The exact boundary conditions were applied by generating a boundary conforming periodic computation mesh.

Dulikravich, D. S.↗
NASA NTRS1980

Transient corona effects on a wire over the ground

The nuclear EMP effect on VLF/trailing wire antennas is investigated in relation to new features of corona effects. Previous experimental results on transmission lines with corona under E 80 kV/cm recorded in the nanosecond time frame are analyzed. A nonlinear macroscopic model which describes a transmission line with corona is discussed. The model not only accounts for overall waveform, but also describes the sharp changes in the waveform associated with the corona onset.

Chen, K. C.↗
NASA NTRS1980

Simulator results of an F-14A airplane utilizing an aileron-rudder interconnect during carrier approaches and landings

A piloted simulator study was conducted to evaluate an aileron rudder interconnect (ARI) control system for the F-14A airplane in the landing configuration. Effects on pilot performance and handling characteristics were investigated. Two ARI configurations were tested and compared to the standard F-14 fleet control system. A nonlinear aerodynamic model of the F-14 was used in conjunction with a six degree of freedom motion base simulator. The evaluation task, which utilized three subject pilots, consistent of a night carrier approach and landing. Both ARI configurations produced improved pilot performance and pilot ratings when compared to the standard control system. Sideslip due to adverse yaw as considerably reduced by the ARI systems and heading control was more stable and precise. Lateral deviation from centerline was reduced during the approach and lateral touchdown dispersion on the carrier deck was reduced with the ARI control systems.

Kelly, W. W.↗
NASA NTRS1980

Numerical calculation of steady inviscid full potential compressible flow about wind turbine blades

The air flow through a propeller-type wind turbine rotor is characterized by three-dimensional rotating cascade effects about the inner portions of the rotor blades and compressibility effects about the tip regions of the blades. In the case of large rotor diameter and/or increased rotor angular speed, the existence of small supersonic zones terminated by weak shocks is possible. An exact nonlinear mathematical model (called a steady Full Potential Equation - FPE) that accounts for the above phenomena has been rederived. An artificially time dependent version of FPE was iteratively solved by a finite volume technique involving an artificial viscosity and a three-level consecutive mesh refinement. The exact boundary conditions were applied by generating a boundary conforming periodic computation mesh.

Dulikravich, D. S.↗
NASA NTRS1982

Solution Accounts for Structural Damping

New analytical technique determines dynamic response of damped structures dominated by internal structural damping mechanisms. Though structural damping is often negligible compared with damping due to air friction and friction in joints, structural damping can be of major importance in structures having heavy damping treatments or in outer-space structures. Finite-element model includes nonlinear, nonviscous internal damping.

Roussos, L. A.↗
NASA NTRS1981

Parameter estimation of large flexible aerospace structures with application to the control of the Maypole Deployable Reflector

Systems such as the Maypole deployable reflector have a distributed parameter nature. The flexible column and hoop structure and the circular antenna of 30-100 meter diameter which it supports are described by partial, rather than ordinary, differential equations. Progress completed in reduced order modelling andd controller design and digital parameter estimation and control is summarized. Topics covered include depolyment and on-orbit operation; quasi-static (steady state) operation; dynamic distributed parameter system; autoregressive moving average identification; frequency domain procedures; direct or implicit active control; adaptive observers; parameter estimation using a linear reinforcement learning factor; feedback control; and reduced order modeling for nonlinear systems.

Balas, M. J.↗
NASA NTRS1981

V/STOL propulsion control technology

Results of a NASA sponsored study of V/STOL Propulsion Control Analysis are presented. The study involved propulsion control requirements, design concepts and procedures, and control designs for supersonic V/STOL. A variable cycle engine with a remote augmented lift system was used as a basis for establishing typical operating requirements and control concepts, and a nonlinear engine model was developed for control development as a precursor to a real-time simulation capability. A simplified aircraft model was also used to investigate transition requirements, and a long-range technology plan was developed to define subsequent program requirements for achieving a real-time piloted simulation capability.

Brown, H.↗
NASA NTRS1981

Control system development for an organic Rankine cycle engine

The development of a control logic to govern the toluene throttle valve and verify the stability of the speed control approach for multiple engines connected to a 1 MWe point focus solar generator installation for distributed applications is presented. The toluene is is pumped by booster and main feed pumps through a regenerator to the parabolic focus receiver, with the flow rate controlled by a valve to remain at critical level of 4.1 MPa. The valve changes the inlet pressure at the turbine nozzle block. Each concentrator would produce 76 kWth and 20 kWe. Dynamic variables in the logic account for insolation variation, fluid temperature, ac grid voltage, the thermal dynamics of the regenerator, and variations in the head supplied by the feed pump. Separate analyses are presented for the turbine shaft speed and toluene loop dynamics. The resulting logic is considered preliminary and suitable only in full insolation conditions. Extension of the model to nonlinear perturbations is indicated.

Bergthold, F. M., Jr.↗
NASA NTRS1981

Is energy conserved at the foot of the solar chromosphere?

The current empirical models of the solar atmosphere which have kinetic temperatures that are too low at the temperature minimum to balance radiative heating and cooling are examined. It was noted that when there is additional energy input from the dissipation of hydrodynamic waves the apparent imbalance is aggravated. It is suggested that the problem lies in the assumption of a static upper photosphere. It is proposed that the mechanical waves, which further out cause the chromospheric temperature rise, traverse the temperature minimum region with large amplitude and produce the apparent nonconservation of energy as well as other difficulties of the empirical models through nonlinear, time dependent effects.

Kalkofen, W.↗
NASA NTRS1983

A simple propulsion system model for the simulation of nonlinear dynamic thrust response

A simple mathematical jet engine description is presented where the measured transition functions of the engine thrust can be simulated in a quasi-stationary operation as well as in acceleration or deceleration schedules. Because of its simplicity and high fidelity, it is especially suited for representing jet engines in digital simulation programs.

Schaenzer, G.↗
NASA NTRS1982

Dynamic and static modeling of the shuttle orbiter's thermal protection system

The dynamic and static analysis methods used to model the nonlinear structural behavior of the Shuttle Orbiter's tile/pad thermal protection system are discussed. The structural evaluation of the tile/pad system is complicated by the nonlinear stiffening, hysteresis and viscosity exhibited by the pad material. Application of the analysis to square tiles subject to sinusoidal and random excitation is presented along with appropriate test data. Correlation is considered good. In order to treat the stress analysis of thousands of individual tiles, a nonlinear static analysis was developed which utilizes equivalent static loads derived from the dynamic environment. Tensile stress at the bondline is examined in thousands of unique tiles.

Housner, J. M.↗
NASA NTRS1984

Development of a global model for atmospheric backscatter at CO2 wavelengths

The effect of gravitational sedimentation on the atmospheric aerosol size distribution has been simulated using a one layer numerical model. A nonlinear curve fitting program is being developed to study aerosol size parameters. The Sage/Sam 2 data establishing the geographical and temporal variations of aerosol concentration in the troposphere are being studied. The basic version of the Sam 2 program and the alternative version of the Sage 2 program are operational. Above 6 km, latitudinal differences are more important in determining aerosol concentration than surface conditions.

Source record↗
NASA NTRS1983

Linking numbers, spin, and statistics of solitons

The spin and statistics of solitons in the (2 + 1)- and (3 + 1)-dimensional nonlinear sigma models is considered. For the (2 + 1)-dimensional case, there is the possibility of fractional spin and exotic statistics; for 3 + 1 dimensions, the usual spin-statistics relation is demonstrated. The linking-number interpretation of the Hopf invariant and the use of suspension considerably simplify the analysis.

Wilczek, F.↗