Search NASA⌕ Search

SEARCH · Search NASA

Results for “analytical models”

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.

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

At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Sensitivity of Hingeless Rotor Blade Flap-lag Stability in Hover to Analytical Modelling Assumptions

Prediction of flap-lag stability using a single bending mode for each degree-of-freedom is examined in the case in which the bending modes are assumed to be the same in the flap and lag directions and are independent of pitch angle and stiffness distribution. It is shown that this model gives results analogous to those obtained by Ormiston employing a rigid blade model with the blade and hub stiffness represented by springs in the limiting cases of the elastic coupling parameter R = 0 and 1. For intermediate values of R the results are shown to be quite different. The mode shape assumptions are shown to result in what is referred to as the parallel spring model in contrast to Ormiston's model which is referred to as a series spring model. The similarities and differences between these two models are developed in some details. The differences between these two models are examined for various typical rotor blade characteristics. Other aspects of the sensitivity of this problem are also considered.

Curtiss, H. C., Jr.↗
NASA NTRS1977

Charging characteristics of materials: Comparison of experimental results with simple analytical models

An understanding of the behavior of materials, of dielectrics in particular, under charged particle bombardment is essential to the prediction and prevention of the adverse effects of spacecraft charging. A one-dimensional model for charging of samples in a test facility was used in conjunction with experimental data taken to develop "material charging characteristics" for silvered Teflon. These characteristics were then used in a one-dimensional model for charging in space to examine expected response. Relative charging rates as well as relative charging levels for silvered Teflon and metal are discussed.

Purvis, C. K.↗
NASA NTRS1977

An analytical model for highly seperated flow on airfoils at low speeds

A computer program was developed to solve the low speed flow around airfoils with highly separated flow. A new flow model included all of the major physical features in the separated region. Flow visualization tests also were made which gave substantiation to the validity of the model. The computation involves the matching of the potential flow, boundary layer and flows in the separated regions. Head's entrainment theory was used for boundary layer calculations and Korst's jet mixing analysis was used in the separated regions. A free stagnation point aft of the airfoil and a standing vortex in the separated region were modelled and computed.

Zunnalt, G. W.↗
NASA NTRS1977

Analytical model of the combustion of multicomponent solid propellants

Multiple flame models derived for simple composite propellants are extended to describe the combustion of propellants containing multimodal particle sizes, mixed oxidizers and monopropellant binders. Models combining the component contributions to propellant surface structure, flame structure and energy distribution are based in part upon experimental observations and in part upon hypotheses constrained to provide reasonable agreement with measured burning rate characteristics. The methods employed consist of superposition, interaction and iteration. The computerized model is applied to explain the effects of multiple ingredients and to discuss burning rate tailoring problems of current interest.

Cohen, N. S.↗
NASA NTRS1977

Charging characteristics of materials: Comparison of experimental results with simple analytical models

A one-dimensional model for charging of samples is used in conjunction with experimental data taken to develop material charging characteristics for silvered Teflon. These characteristics are then used in a one dimensional model for charging in space to examine expected response. Relative charging rates as well as relative charging levels for silvered Teflon and metal are discussed.

Purvis, C. K.↗
NASA NTRS1978

An improved analytical model of the separation region on boattail nozzles at subsonic speeds

A practical engineering calculation was developed to model the viscous effects of a separated, reverse flow region on afterbody pressures and drag. This viscous calculation was iteratively coupled with an inviscid flow calculation by means of an aerodynamic interface. A standard boundary layer displacement thickness was used to modify the afterbody shape where the flow was attached. A discriminating streamline calculation was developed to account for displacement effects of the reverse flow in separated regions with and without a flowing jet. The viscous flow calculation was coupled with a potential flow calculation. The analysis accurately predicted afterbody pressures and drag with variations in Reynolds number, Mach number, and afterbody shape.

Presz, W. M., Jr.↗
NASA NTRS1978

Analytical model of high pressure burning rates in a transient environment

A transient ballistics and combustion model is derived to represent the closed vessel experiment that is widely used to characterize the high pressure burning rates of solid propellants. The model is applied to explain why burning rates deduced from the closed vessel are in basic agreement with those measured from an equilibrium strand burner in the case of homogeneous propellants, but differ significantly in the case of nitramine composite propellants. Thermal profile time lag effects become small at high pressure because the burning rates become high. However, the development of the burning surface structure of those nitramine propellants which exhibit shifts in pressure exponent causes the mass burning rate to lag and then exceed the equilibrium value. It is necessary to consider this mechanism in applications dealing with high pressures and pressurization rates.

Cohen, N. S.↗
NASA NTRS1978

An improved analytical model of the separated region on nozzle boattails

A viscous flow calculation is formulated for modelling the effects of separated, reverse flow regions on nozzle afterbody pressures and drags at subsonic Mach numbers. A discriminating streamline approach is used. Effects of skin friction, axial pressure gradient, and nozzle jet entrainment on the separated discriminating streamline shape are included. The viscous flow calculation is coupled to a potential flow calculation. The combined analysis is found to accurately predict both the magnitude of the measured afterbody pressures and drag, and also their variation with Reynolds number, Mach number and afterbody shape.

Presz, W. M., Jr.↗
NASA NTRS1979

Elementary analytic models of climate. 1: The mean global heat balance

Climate models based on global radiative equilibrium are normally so complicated that they require extensive computer codes to provide adequate accuracy. However, by simply modifying the concept of a gray atmosphere, a reasonably correct mean global temperature is obtained. This elementary model is then used to estimate the effects of changes in the abundances of minor infrared absorbers and changes in the solar constant or earth albedo. When applied to a Budyko-Sellers zonally averaged model, the quasi-gray model could give a physical basis for the latitude dependence of outgoing radiation and of opacity due to H2O vapor content. The latter effect constitutes an important positive feedback on surface temperature.

Chamberlain, J. W.↗
NASA NTRS1980

A comprehensive analytical model of rotorcraft aerodynamics and dynamics. Part 1: Analysis development

Structural, inertia, and aerodynamic models were combined to form a comprehensive model of rotor aerodynamics and dynamics that is applicable to a wide range of problems and a wide class of vehicles. A digital computer program is used to calculate rotor performance, loads, and noise; helicopter vibration and gust response; flight dynamics and handling qualities; and system aeroelastic stability. The analysis is intended for use in the design, testing, and evaluation of rotors and rotorcraft, and to be a basis for further development of rotary wing theories.

Johnson, W.↗
NASA NTRS1982

Prediction of aircraft handling qualities using analytical models of the human pilot

The optimal control model (OCM) of the human pilot is applied to the study of aircraft handling qualities. Attention is focused primarily on longitudinal tasks. The modeling technique differs from previous applications of the OCM in that considerable effort is expended in simplifying the pilot/vehicle analysis. After briefly reviewing the OCM, a technique for modeling the pilot controlling higher order systems is introduced. Following this, a simple criterion for determining the susceptibility of an aircraft to pilot induced oscillations is formulated. Finally, a model based metric for pilot rating prediction is discussed. The resulting modeling procedure provides a relatively simple, yet unified approach to the study of a variety of handling qualities problems.

Hess, R. A.↗
NASA NTRS1982

Development and validation of preliminary analytical models for aircraft interior noise prediction

Predictions are made of the transmission of sound into an unpressurized and unstiffened cylinder under random and harmonic excitations, in order to validate the preliminary version of an airplane interior noise prediction model which is based on an analysis of the power flow type. The predictions are compared to experimental results, and statistically significant differences between predictions and measurements are found to be primarily due to input data deficiencies. Because the model requires only the value of a simple integral for determining interior spatial coupling, and resonance frequencies to determine frequency coupling, the known dynamics of the fuselage can be utilized without difficulty.

Pope, L. D.↗
NASA NTRS1982

Prediction of aircraft handling qualities using analytical models of the human pilot

The optimal control model (OCM) of the human pilot is applied to the study of aircraft handling qualities. Attention is focused primarily on longitudinal tasks. The modeling technique differs from previous applications of the OCM in that considerable effort is expended in simplifying the pilot/vehicle analysis. After briefly reviewing the OCM, a technique for modeling the pilot controlling higher order systems is introduced. Following this, a simple criterion for determining the susceptibility of an aircraft to pilot-induced oscillations (PIO) is formulated. Finally, a model-based metric for pilot rating prediction is discussed. The resulting modeling procedure provides a relatively simple, yet unified approach to the study of a variety of handling qualities problems.

Hess, R. A.↗
NASA NTRS1982

Analytical modeling of operating characteristics of premixing-prevaporizing fuel-air mixing passages. Volume 1: Analysis and results

A model for predicting the distribution of liquid fuel droplets and fuel vapor in premixing-prevaporizing fuel-air mixing passages of the direct injection type is reported. This model consists of three computer programs; a calculation of the two dimensional or axisymmetric air flow field neglecting the effects of fuel; a calculation of the three dimensional fuel droplet trajectories and evaporation rates in a known, moving air flow; a calculation of fuel vapor diffusing into a moving three dimensional air flow with source terms dependent on the droplet evaporation rates. The fuel droplets are treated as individual particle classes each satisfying Newton's law, a heat transfer, and a mass transfer equation. This fuel droplet model treats multicomponent fuels and incorporates the physics required for the treatment of elastic droplet collisions, droplet shattering, droplet coalescence and droplet wall interactions. The vapor diffusion calculation treats three dimensional, gas phase, turbulent diffusion processes. The analysis includes a model for the autoignition of the fuel air mixture based upon the rate of formation of an important intermediate chemical species during the preignition period.

Anderson, O. L.↗
NASA NTRS1983

Analytical modeling of transport aircraft crash scenarios to obtain floor pulses

The KRAS program was used to analyze transport aircraft candidate crash scenarios. Aircraft floor pulses and seat/occupant responses are presented. Results show that: (1) longitudinal only pulses can be represented by equivalent step inputs and/or static requirements; (2) the L1649 crash test floor longitudinal pulse for the aft direction (forward inertia) is less than 9g static or an equivalent 5g pulse; aft inertia accelerations are extremely small ((ch76) 3g) for representative crash scenarios; (3) a viable procedure to relate crash scenario floor pulses to standard laboratory dynamic and static test data using state of the art analysis and test procedures was demonstrated; and (4) floor pulse magnitudes are expected to be lower for wide body aircraft than for smaller narrow body aircraft.

Wittlin, G.↗