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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Reliability of equivalent sphere model in blood-forming organ dose estimation

The radiation dose equivalents to blood-forming organs (BFO's) of the astronauts at the Martian surface due to major solar flare events are calculated using the detailed body geometry of Langley and Billings. The solar flare spectra of February 1956, November 1960, and August 1972 events are employed instead of the idealized Webber form. The detailed geometry results are compared with those based on the 5-cm sphere model which was used often in the past to approximate BFO dose or dose equivalent. Larger discrepancies are found for the later two events possibly due to the lower numbers of highly penetrating protons. It is concluded that the 5-cm sphere model is not suitable for quantitative use in connection with future NASA deep-space, long-duration mission shield design studies.

Shinn, Judy L.↗
NASA NTRS1994

Overview of nebula models: Potential chondrule-forming environments

Observations of T Tauri stars and their circumstellar disks, combined with broadly applied theoretical principles, permit the construction of solar nebular models that are potentially useful for the interpretation of meteoritic data. Quantitative comparisons of model results with meteoritic and planetary data is used to test several propositions regarding the bulk properties of chondrites and chondrule precursor material.

Cassen, P.↗
NASA NTRS1972

An eclectic integrated circuit reliability model

A general form of a comprehensive reliability modeling rationale was formulated for the integrated circuit. Integrated device failure models amenable to long term applications were investigated.

Fetcher, B. C.↗
NASA NTRS1998

Modeling the Benchmark Active Control Technology Wind-Tunnel Model for Active Control Design Applications

This report describes the formulation of a model of the dynamic behavior of the Benchmark Active Controls Technology (BACT) wind tunnel model for active control design and analysis applications. The model is formed by combining the equations of motion for the BACT wind tunnel model with actuator models and a model of wind tunnel turbulence. The primary focus of this report is the development of the equations of motion from first principles by using Lagrange's equations and the principle of virtual work. A numerical form of the model is generated by making use of parameters obtained from both experiment and analysis. Comparisons between experimental and analytical data obtained from the numerical model show excellent agreement and suggest that simple coefficient-based aerodynamics are sufficient to accurately characterize the aeroelastic response of the BACT wind tunnel model. The equations of motion developed herein have been used to aid in the design and analysis of a number of flutter suppression controllers that have been successfully implemented.

Waszak, Martin R.↗
NASA NTRS1996

Modeling the Benchmark Active Control Technology Wind-Tunnel Model for Application to Flutter Suppression

This paper describes the formulation of a model of the dynamic behavior of the Benchmark Active Controls Technology (BACT) wind-tunnel model for application to design and analysis of flutter suppression controllers. The model is formed by combining the equations of motion for the BACT wind-tunnel model with actuator models and a model of wind-tunnel turbulence. The primary focus of this paper is the development of the equations of motion from first principles using Lagrange's equations and the principle of virtual work. A numerical form of the model is generated using values for parameters obtained from both experiment and analysis. A unique aspect of the BACT wind-tunnel model is that it has upper- and lower-surface spoilers for active control. Comparisons with experimental frequency responses and other data show excellent agreement and suggest that simple coefficient-based aerodynamics are sufficient to accurately characterize the aeroelastic response of the BACT wind-tunnel model. The equations of motion developed herein have been used to assist the design and analysis of a number of flutter suppression controllers that have been successfully implemented.

Waszak, Martin R.↗
NASA NTRS1981

A four-dimensional primitive equation model for coupled coastal-deep ocean studies

A prototype four dimensional continental shelf/deep ocean model is described. In its present form, the model incorporates the effects of finite amplitude topography, advective nonlinearities, and variable stratification and rotation. The model can be forced either directly by imposed atmospheric windstress and surface pressure distributions, and energetic mean currents imposed by the exterior oceanic circulation; or indirectly by initial distributions of shoreward propagation mesoscale waves and eddies. To avoid concerns over the appropriate specification of 'open' boundary conditions on the cross-shelf and seaward model boundaries, a periodic channel geometry (oriented along-coast) is used. The model employs a traditional finite difference expansion in the cross-shelf direction, and a Fourier (periodic) representation in the long-shelf coordinate.

Haidvogel, D. B.↗
NASA NTRS1988

Turbulence modeling in non-inertial frames of reference

The effect of an arbitrary change of frame on the structure of turbulence models is examined from a fundamental theoretical standpoint. It is proven, as a rigorous consequence of the Navier-Stokes equations, that turbulence models must be form invariant under arbitrary translational accelerations of the reference frame and should only be affected by rotations through the intrinsic mean vorticity. A direct application of the invariance property along with the Taylor-Proudman Theorem, material frame-indifference in the limit of two-dimensional turbulence and Rapid Distortion Theory is shown to yield powerful constraints on the allowable form of turbulence models. Most of the commonly used turbulence models are demonstrated to be in serious violation of these constraints and consequently are inconsistent with the Navier-Stokes equations in non-inertial frames. Alternative models with improved non-inertial properties are developed and some simple applications to rotating turbulent flows are considered.

Speziale, Charles G.↗
NASA NTRS1989

Turbulence modeling in noninertial frames of reference

The effect of an arbitrary change of frame on the structure of turbulence models is examined from a fundamental theoretical standpoint. It is proven, as a rigorous consequence of the Navier-Stokes equations, that turbulence models must be form invariant under arbitrary translational accelerations of the reference frame and should only be affected by rotations through the intrinsic mean vorticity. A direct application of the invariance property along with the Taylor-Proudman Theorem, material frame-indifference in the limit of two-dimensional turbulence and Rapid Distortion Theory is shown to yield powerful constraints on the allowable form of turbulence models. Most of the commonly used turbulence models are demonstrated to be in serious violation of these constraints and consequently are inconsistent with the Navier-Stokes equations in non-inertial frames. Alternative models with improved non-inertial properties are developed and some simple applications to rotating turbulent flows are considered.

Speziale, Charles G.↗
NASA NTRS1992

Closed-form solution of decomposable stochastic models

Equations to compute failure probabilities of the total (combined) model without a complete solution of the combined model are presented. A closed-form analytical approach to presentation of probabilities is used on the bases of the Symbolic Hierarchical Automated Reliability and Performance Evaluator tool. The techniques under consideration make it possible to compute the probability function for a much wider class of systems at a reduced computational cost.

Sjogren, Jon A.↗
NASA NTRS1993

Establishing the relationship between manufacturing and component performance in stretch formed thermoplastic composites

Flexible manufacturing methods are needed to reduce the cost of using advanced composites in structural applications. One method that allows for this is the stretch forming of long discontinuous fiber materials with thermoplastic matrices. In order to exploit this flexibility in an economical way, a thorough understanding of the relationship between manufacturing and component performance must be developed. This paper reviews some of the recent work geared toward establishing this understanding. Micromechanics models have been developed to predict the formability of the material during processing. The latest improvement of these models includes the viscoelastic nature of the matrix and comparison with experimental data. A finite element scheme is described which can be used to model the forming process. This model uses equivalent anisotropic viscosities from the micromechanics models and predicts the microstructure in the formed part. In addition, structural models have been built to account for the material property gradients that can result from the manufacturing procedures. Recent developments in this area include the analysis of stress concentrations and a failure model each accounting for the heterogeneous material fields.

Santare, Michael H.↗
NASA NTRS1996

A model for closing the inviscid form of the average passage equation system

A mathematical model for closing or mathematically completing the system of equations is proposed. The model describes the time average flow field through the blade passages of multistage turbomachinery. These average-passage equation systems govern a conceptual model useful in turbomachinery aerodynamic design and analysis. The closure model was developed to insure a consistency between these equations and the axisymmetric through-flow equations. The closure model was incorporated into a calculation code for use in the simulation of the flow field about a high-speed counter rotating propeller and a high-speed fan stage.

Adamczyk, John J.↗
NASA NTRS1974

Development of technology for fluid-structure interaction modeling of a 1/8-scale dynamic model of shuttle External Tank (ET). Volume i: Technical report

A NASTRAN analysis of the external tank (ET) substructure of the 1/8-scale space shuttle structural dynamics model is described. The NASTRAN hydroelastic procedures were used to form a model of the liquid oxygen portion of the ET. Large computer storage requirements and running times were required unless these procedures were modified. Several possibilities were demonstrated including the substitution of the real for the complex eigenvalue routine and the use of the OMIT capability to reduce the number of fluid coordinates. A NASTRAN model of the complete ET was formed and reduced to 252 degrees of freedom. A review of the eigenvector extracted, using the unsymmetrical inverse power method, indicated that the structural OMIT's resulted in unsatisfactory modal deflections. Modifications to the NASTRAN hydroelastic capability appeared necessary to generate a successful ET model. An approach is described which, by assuming incompressibility, reduces the fluid representation to a symmetric mass matrix which can be added to the structural mass. The problem is solved using faster and more efficient eigenvalue routines. Using this approach the ET NASTRAN model was analyzed for three separate weight conditions.

Bernstein, M.↗
NASA NTRS2010

Roughness Based Crossflow Transition Control for a Swept Airfoil Design Relevant to Subsonic Transports

A high fidelity transition prediction methodology has been applied to a swept airfoil design at a Mach number of 0.75 and chord Reynolds number of approximately 17 million, with the dual goal of an assessment of the design for the implementation and testing of roughness based crossflow transition control and continued maturation of such methodology in the context of realistic aerodynamic configurations. Roughness based transition control involves controlled seeding of suitable, subdominant crossflow modes in order to weaken the growth of naturally occurring, linearly more unstable instability modes via a nonlinear modification of the mean boundary layer profiles. Therefore, a synthesis of receptivity, linear and nonlinear growth of crossflow disturbances, and high-frequency secondary instabilities becomes desirable to model this form of control. Because experimental data is currently unavailable for passive crossflow transition control for such high Reynolds number configurations, a holistic computational approach is used to assess the feasibility of roughness based control methodology. Potential challenges inherent to this control application as well as associated difficulties in modeling this form of control in a computational setting are highlighted. At high Reynolds numbers, a broad spectrum of stationary crossflow disturbances amplify and, while it may be possible to control a specific target mode using Discrete Roughness Elements (DREs), nonlinear interaction between the control and target modes may yield strong amplification of the difference mode that could have an adverse impact on the transition delay using spanwise periodic roughness elements.

Li, Fei↗
NASA NTRS1985

A model for closing the inviscid form of the average-passage equation system

A mathematical model is proposed for closing or mathematically completing the system of equations which describes the time average flow field through the blade passages of multistage turbomachinery. These equations referred to as the average passage equation system govern a conceptual model which has proven useful in turbomachinery aerodynamic design and analysis. The closure model is developed so as to insure a consistency between these equations and the axisymmetric through flow equations. The closure model was incorporated into a computer code for use in simulating the flow field about a high speed counter rotating propeller and a high speed fan stage. Results from these simulations are presented.

Adamczyk, J. J.↗
NASA NTRS1986

A model for closing the inviscid form of the average-passage equation system

A mathematical model is proposed for closing or mathematically completing the system of equations which describes the time average flow field through the blade passages of multistage turbomachinery. These equations referred to as the average passage equation system govern a conceptual model which has proven useful in turbomachinery aerodynamic design and analysis. The closure model is developed so as to insure a consistency between these equations and the axisymmetric through flow equations. The closure model was incorporated into a computer code for use in simulating the flow field about a high speed counter rotating propeller and a high speed fan stage. Results from these simulations are presented.

Adamczyk, J. J.↗
NASA NTRS1994

Modeling of the magnetosphere-ionosphere-atmosphere system

During the period covered by this report we continued to investigate basic processes in magnetosphere-ionosphere coupling and to develop algorithms for analyzing ultraviolet, visible, and X-ray images that will be acquired on the POLAR spacecraft. An image analysis procedure combines several numerical models to obtain a self-consistent picture of the ionosphere and thermosphere. Our ionosphere-aurora model was extended by the inclusion of the magnetic mirror force and a self-consistent parallel electric field in the ionosphere. The electron transport model which forms a critical part of the aurora model was evaluated by comparison with laboratory measurements and auroral observations. We determined the uncertainties that arise from our limited knowledge of cross sections and energy degradation functions for electron neutral interaction.

Source record↗
NASA NTRS1937

Hydrodynamic Tests in the N.A.C.A. Tank of a Model of the Hull of the Short Calcutta Flying Boat

The hydrodynamic characteristics of a model of the hull of the Short Calcutta (N.A.C.A. Model 47) are presented in non-dimensional form. This model represents one of a series of hulls of successful foreign and domestic flying boats the characteristics of which are being obtained under similar test conditions in the N.A.C.A. tank. The take-off distance and time for a flying boat having the hull of the Calcutta are compared at two values of the gross load with the corresponding distances and times for the same flying boat having hulls of two representative American types, the Sikorsky S-40 and the N.A.C.A. 11-A. This comparison indicates that for hulls of the widely different forms compared, the differences in take-off time and distance are negligible.

Ward, Kenneth E↗
NASA NTRS1989

Comparison of measured induced velocities with results from a closed-form finite state wake model in forward flight

An unsteady, three-dimensional induced-flow model is applied to compute the induced-flow distribution of a rotor in forward flight, and numerical results are compared against LDV measurements for both time-averaged and unsteady induced flow at the disk. The former flow shows good agreement with measured data, except just behind the pylon at the lowest advanced ratio and near the blade tips for rectangular blades at high advance ratios. The method performs as well or better than other codes that have been applied to these data, takes less computing time, and is better suited to aeroelastic analysis. Results with only four harmonics and 15 state variables converge to all fundamental characteristics of the time-averaged flow.

Peters, David A.↗