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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 703 records · Page 39

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NASA NTRS1985

A Structural Dynamics Approach to the Simulation of Spacecraft Control/Structure Interaction

A relatively simple approach to the analysis of linear spacecraft control/structure interaction problems is presented. The approach uses a commercially available structural system dynamic analysis package for both controller and plant dynamics, thus obviating the need to transfer data between separate programs. The unilateral coupling between components in the control system block diagram is simulated using sparse matrix stiffness and damping elements available in the structural dynamic code. The approach is illustrated with a series of simple tutorial examples of a rigid spacecraft core with flexible appendages.

Young, J. W.↗

NASA NTRS1988

Wind-Wave-Current Tank Research Facility usage and status

This summary is to provide information as to: (1) research activities, and (2) facilities status of the wind-wave-current tank research facility located at the GSFC/WFF. Research Activities include: (1) Wave-Turbulence Interaction; (2) Velocity Structure Below Waves; (3) Short-Wave Modification by Long-Waves; (4) Wind-Wave Generation Time Scale; (5) Wave-Current Interaction; (6) Rain Effects on Microwave Scattering from the Sea-Surface; and (7) Gas Exchange Rates versus Scatterometer Power.

Bliven, L. F.↗

NASA NTRS1990

Adaptive-Control Experiments On A Large Flexible Structure

Antennalike flexible structure built for research in advanced technology including suppression of vibrations and control of initial deflections. Structure instrumented with sensors and actuators connected to digital electronic control system, programmed with control algorithms to be tested. Particular attention in this research focused on direct model-reference adaptive-control algorithm based on command generator tracker theory. Built to exhibit multiple vibrational modes, low modal frequencies, and low structural damping. Made three-dimensional so complicated interactions among components of structure and control system investigated.

Ih, Che-Hang C.↗

NASA NTRS1994

Expression and purification of recombinant polyomavirus VP2 protein and its interactions with polyomavirus proteins

Recombinant polyomavirus VP2 protein was expressed in Escherichia coli (RK1448), using the recombinant expression system pFPYV2. Recombinant VP2 was purified to near homogeneity by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, electroelution, and Extracti-Gel chromatography. Polyclonal serum to this protein which reacted specifically with recombinant VP2 as well as polyomavirus virion VP2 and VP3 on Western blots (immunoblots) was produced. Purified VP2 was used to establish an in vitro protein-protein interaction assay with polyomavirus structural proteins and purified recombinant VP1. Recombinant VP2 interacted with recombinant VP1, virion VP1, and the four virion histones. Recombinant VP1 coimmunoprecipitated with recombinant VP2 or truncated VP2 (delta C12VP2), which lacked the carboxy-terminal 12 amino acids. These experiments confirmed the interaction between VP1 and VP2 and revealed that the carboxyterminal 12 amino acids of VP2 and VP3 were not necessary for formation of this interaction. In vivo VP1-VP2 interaction study accomplished by cotransfection of COS-7 cells with VP2 and truncated VP1 (delta N11VP1) lacking the nuclear localization signal demonstrated that VP2 was capable of translocating delta N11VP1 into the nucleus. These studies suggest that complexes of VP1 and VP2 may be formed in the cytoplasm and cotransported to the nucleus for virion assembly to occur.

Non-NASA Center↗

NASA NTRS1988

PACOSS program

The objectives of the PACOSS program were to demonstrate the respective roles of passive and active control for structures that represented future Large Space Structures (LSS), to develop means to introduce passive vibration control, and to experimentally verify the damping predictions and the control algorithms. In order to meet the objectives, the program was divided into an analytical simulation phase to establish the respective roles of passive and active damping on a LSS-type structure, and a design, analysis, and test phase to validate the passive damping and the control algorithm performance for a structure. Predictable amounts of damping can be designed into a LSS structure, the best control strategy uses a combination of passive damping and active controls, and a more optimum system can be achieved by an early interaction between the structural designer, controls engineer, and the damping designer.

Richards, K. E., Jr.↗

NASA NTRS1976

A finite element-analytical method for modeling a structure in an infinite fluid

A method is described from which the interaction of an elastic structure with an infinite acoustic fluid is determined. The displacements of the structure and the pressure field of the immediate surrounding fluid are modeled by finite elements, and the remaining pressure field of the infinite fluid region is given by an analytical expression. This method yields a frequency dependent boundary condition for the outer fluid boundary when applied to the frequency response of an elastic beam in contact with an acoustic fluid. The frequency response of the beam is determined using NASTRAN, and compares favorably to the exact solution which is also presented. The effect of the fluid on the response of the structure at low and high frequencies is due to added mass and damping characteristics, respectively.

Zarda, P. R.↗

NASA NTRS1984

The Chemical Nature of the Fiber/resin Interface in Composite Materials

Carbon fiber/epoxy resin composites are considered. The nature of the fiber structure and the interaction that occurs at the interface between fiber and matrix are emphasized. Composite toughness can be improved by increased axial tensile and compressive strengths in the fibers. The structure of carbon fibers indicates that the fiber itself can fail transversely, and different transverse microstructures could provide better transverse strengths. The higher surface roughness of lower modulus and surface-treated carbon fibers provides better mechanical interlocking between the fiber and matrix. The chemical nature of the fiber surface was determined, and adsorption of species on this surface can be used to promote wetting and adhesion. Finally, the magnitude of the interfacial bond strength should be controlled such that a range of composites can be made with properties varying from relatively brittle and high interlaminar shear strength to tougher but lower interlaminar shear strength.

Diefendorf, R. J.↗

NASA NTRS1986

Thin-film temperature sensors for gas turbine engines Problems and prospects

The erosion and corrosion of thermocouples used to measure the temperature in turbine engines are studied. Structural and metallurgical interactions and instabilities at thermocouple interfaces are analyzed. Consideration is given to the adhesion, dielectric quality, surface topography, and hardness of the thermal oxides; it is observed that the structural and thermoelectric stability of thin-film thermocouple elements depends on adhesion, surface topography, and dielectric strength. The electrical conductivity and impurity content of the oxide scale are evaluated. Methods for improving the adhesion of thermocouples on the alumina surfaces are described. Compositional inhomogeneities in the sensors and contamination of the thermocouple elements are examined. The fabrication of the thermocouples is discussed. It is noted that Al2O3 and Si3N4 are useful for developing stable thermocouple elements on the surface of the blades and vanes.

Budhani, R. C.↗

NASA NTRS1997

Structural Verification of the Space Shuttle's External Tank Super LightWeight Design: A Lesson in Innovation

The Super LightWeight Tank (SLWT) team was tasked with a daunting challenge from the outset: boost the payload capability of the Shuttle System by safely removing 7500 lbs. from the existing 65,400 lb. External Tank (ET). Tools they had to work with included a promising new Aluminum Lithium alloy, the concept of a more efficient structural configuration for the Liquid Hydrogen (LH2) tank, and a highly successful, mature Light Weight Tank (LWT) program. The 44 month schedule which the SLWT team was given for the task was ambitious by any measure. During this time the team had to not only design, build, and verify the new tank, but they also had to move a material from the early stages of development to maturity. The aluminum lithium alloy showed great promise, with an approximately 29% increase in yield strength, 15% increase in ultimate strength, 5 deg/O increase in modulus and 5 deg/O decrease in density when compared to the current 2219 alloy. But processes had to be developed and brought under control, manufacturing techniques perfected, properties characterized, and design allowable generated. Because of the schedule constraint, this material development activity had to occur in parallel with design and manufacturing. Initial design was performed using design allowable believed to be achievable with the Aluminum Lithium alloy system, but based on limited test data. Preliminary structural development tests were performed with material still in the process of iteration. This parallel path approach posed obvious challenges and risks, but also allowed a unique opportunity for interaction between the structures and materials disciplines in the formulation of the material.

Otte, Neil↗

NASA NTRS1981

Finite element analyses of plane thermal entry-length flows

It is pointed out that the design of actively cooled engine and airframe structures for hypersonic flight requires strong interaction between fluid, thermal, and structural analyses. Research programs are being conducted to develop an integrated thermal-structural analysis capability based upon the finite element method. In connection with these programs, a finite element engineering approach has been developed based upon a number of assumptions customarily used in practical heat transfer analysis. An evaluation is conducted of the finite element engineering approach for entry-length flows. The evaluation makes use of an analysis of plane thermal entry-length flows by a finite element approach utilizing mean fluid temperatures with a convection coefficient. Another analysis is based on a finite element continuum approach, taking into account the rigorous momentum, mass, and energy equations of viscous, incompressible flow. The engineering approach was found to give excellent agreement with the rigorous continuum approach for Peclet number values not less than 100.

Thornton, E. A.↗

NASA NTRS1982

The self-excited axisymmetric jet

The results of a number of investigations suggest that large-scale coherent structures and their interactions play key roles in the transport of heat, mass, and momentum, and in the generation of aerodynamic noise. Investigations related to the study of a large-scale coherent structure in the circular jet are considered, taking into account the advantages of inducing controlled perturbation through self-sustained excitation with the whistler nozzle. The primary objective of the present study was to document the jet response to self-excitation and the sensitivity of this response to the initial condition and the Reynolds number R(D). It was also felt that the results would find use in the control of mixing and aerodynamic noise in a jet.

Hasan, M. A. Z.↗

NASA NTRS1989

Hubble Space Telescope-Space Shuttle interface dynamic verification test

A test program has been developed for the interface between the Space Shuttle Orbiter and the Hubble Space Telescope which couples a standard modal test for a simple suspended structure with a novel, 'interface verification' test. While the free-free modal test is used to verify the high loads generating structural modes due to the interaction of internal components of the structure with the rest of the structure, the interface verification test verifies the character of the high-loading generating modes in which the structure reacts against the booster interface. The novel method excites the structure at a single payload-booster interface DOF, while all other interfaces are left free to move.

Blair, Mark A.↗

NASA NTRS2010

The Prediction of Broadband Shock-Associated Noise from Dualstream and Rectangular Jets Using RANS CFD

Supersonic jets operating off-design produce broadband shock-associated noise. Broadband shock-associated noise is characterized by multiple broadband peaks in the far-field and is often the dominant source of noise towards the sideline and upstream direction relative to the jet axis. It is due to large scale coherent turbulence structures in the jet shear layers interacting with the shock cell structure. A broadband shock-associated noise model recently developed by the authors predicts this noise component from solutions to the Reynolds averaged Navier-Stokes equations using a two-equation turbulence model. The broadband shock-associated noise model is applied to dualstream and rectangular nozzles operating supersonically, heated, and off-design. The dualstream jet broadband shock-associated noise predictions are conducted for cases when the core jet is supersonic and the fan jet is subsonic, the core jet is subsonic and the fan jet is supersonic, and when both jet streams operate supersonically. Rectangular jet predictions are shown for a convergent-divergent nozzle operating both over- and under-expanded for cold and heated conditions. The original model implementation has been heavily modified to make accurate predictions for the dualstream jets. It is also argued that for over-expanded jets the oblique shock wave attached to the nozzle lip contributes little to broadband shock-associated noise. All predictions are compared with experiments.

Miller, Steven A.↗

NASA NTRS1988

Navier-Stokes simulation of unsteady three-dimensional blade-vortex interactions

The unsteady, viscous, three-dimensional flow field of a helicopter rotor blade encountering a passing vortex is calculated by solving the thin layer Navier-Stokes equations by a finite-difference numerical procedure. A prescribed vortex method is adopted to preserve the structure of the interacting concentrated vortex. The test cases considered correspond to the experimental model rotor test conditions of Caradonna et al.

Srinivasan, G. R.↗

NASA NTRS1988

Studying Turbulence Using Numerical Simulation Databases, 2. Proceedings of the 1988 Summer Program

The focus of the program was on the use of direct numerical simulations of turbulent flow for study of turbulence physics and modeling. A special interest was placed on turbulent mixing layers. The required data for these investigations were generated from four newly developed codes for simulation of time and spatially developing incompressible and compressible mixing layers. Also of interest were the structure of wall bounded turbulent and transitional flows, evaluation of diagnostic techniques for detection of organized motions, energy transfer in isotropic turbulence, optical propagation through turbulent media, and detailed analysis of the interaction of vortical structures.

Source record↗

NASA NTRS1995

Solar wind interaction with small bodies. 1: Whistler wing signatures near to Gaspra and Ida

Data from Galileo's two asteroid flybys reveal magnetic fluctuations that we interpret as perturbations of the solar wind magnetic field caused by an interaction with the nearby asteroid. The scale sizes of the bodies (approximately 14 km for Gaspra and approximately 30 km for Ida) are intermediate between the ion and electron gyroradii, which implies that the asteroid-imposed perturbations propagate in the whistler mode. Special properties of the whistler mode include phase phase velocities that can exceed the solar wind speed and confinement of the disturbance to directions nearly aligned with the magnetic field. These features of the interaction impose a structure on the solar wind disturbance that differs greatly from the forms familiar for either magnetized or unmagnetized bodies of magnetohydrodynamic spatial scales. We examine both data and computer simulations of the interaction with special attention to what can be inferred about the interaction itself from analysis of the data.

Wang, Z.↗

NASA NTRS1994

Axis switching and spreading of an asymmetric jet: Role of vorticity dynamics

The effects of vortex generators and periodic excitation on vorticity dynamics and the phenomenon of axis switching in a free asymmetric jet are studied experimentally. Most of the data reported are for a 3:1 rectangular jet at a Reynolds number of 450,000 and a Mach number of 0.31. The vortex generators are in the form of 'delta tabs', triangular shaped protrusions into the flow, placed at the nozzle exit. With suitable placement of the tabs, axis switching could be either stopped or augmented. Two mechanisms are identified governing the phenomenon. One, as described by previous researchers and referred to here as the omega(sub theta)-induced dynamics, is due to difference in induced velocities for different segments of a rolled up azimuthal vortical structure. The other, omega(sub x)-induced dynamics, is due to the induced velocities of streamwise vortex pairs in the flow. Both dynamics can be active in a natural asymmetric jet; the tendency for axis switching caused by the omega(sub theta)-induced dynamics may be, depending on the streamwise vorticity distribution, either resisted or enhanced by the omega(sub x)-induced dynamics. While this simple framework qualitatively explains the various observations made on axis switching, mechanisms actually in play may be much more complex. The two dynamics are not independent as the flow field is replete with both azimuthal and streamwise vortical structures which continually interact. Phase averaged flow field data for a periodically forced case, over a volume of the flow field, are presented and discussed in an effort to gain insight into the dynamics of these vortical structures.

Zaman, K. B. M. Q.↗

NASA NTRS1989

Unsteady interaction of a rotor with a vortex

The unsteady, three-dimensional flow field of a helicopter rotor blade encountering a passing vortex is calculated by solving the Euler/thin layer Navier-Stokes equations by a finite-difference numerical procedure. A prescribed vortex method is adopted to preserve the structure of the interacting vortex. The cases considered for computation correspond to the experimental model rotor test conditions of Caradonna, et al. and consist of parallel and oblique interactions. Comparison of the numerical results with test data show good agreement for both parallel and oblique interactions at subsonic and transonic tip speeds.

Srinivasan, G. R.↗