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At least 1,423 records · Page 79

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NASA NTRS1979

Dynamic properties of elastomer cartridge specimens under a rotating load

This paper presents the results of a program of analysis and test to determine the dynamic properties of elastomer cartridges operating under a rotating load. These measured properties were compared to predictions based on results of unidirectional tests with the same elastomer material. The test method for the dynamic stiffness and damping measurements was essentially the same as the Base Excitation Resonant Mass Method. The primary difference is that the exciting force used for these most recent tests was exerted by rotating unbalance in a rotational test rig rather than a shake table. The specimens tested were: two rectangular cross-section, continuous ring cartridges of different cross-section and three cylindrical button cartridges of different button thickness. Tests were performed for strains from about 0.0001 to about 0.01 (double amplitude). Material properties and prediction equations determined from reciprocating tests were used to make numerical predictions of stiffness, damping, and loss coefficient for the test elements, with encouraging results. Strain was shown to be an important parameter in determining these dynamic properties, particularly damping and loss coefficient.

Darlow, M. S.↗

NASA NTRS1979

Evaluation of finite element formulations for transient conduction forced-convection analysis

Conventional versus upwind convective finite elements, and lumped versus consistent formulations for practical conduction/forced convection analysis are evaluated on the basis of numerical studies, with finite element and finite difference lumped-parameter temperatures compared to closed-form analytical solutions for convection problems. Attention is given to two practical combined conduction and forced convection applications, stressing that the finite element method, showing superior accuracy, is competitive with the finite difference lumped-parameter method. Also considered are the computational time savings offered by the zero capacitance nodes procedure and comparative finite element and finite difference lumped-parameter computer times. The present study has reference to the design of actively cooled engine and airframe structures for hypersonic flight.

Thornton, E. A.↗

NASA NTRS1982

Application of an airfoil stall flutter computer prediction program to a three-dimensional wing: Prediction versus experiment

An aerodynamic computer code, capable of predicting unsteady and C sub m values for an airfoil undergoing dynamic stall, is used to predict the amplitudes and frequencies of a wing undergoing torsional stall flutter. The code, developed at United Technologies Research Corporation (UTRC), is an empirical prediction method designed to yield unsteady values of normal force and moment, given the airfoil's static coefficient characteristics and the unsteady aerodynamic values, alpha, A and B. In this experiment, conducted in the PSU 4' x 5' subsonic wind tunnel, the wing's elastic axis, torsional spring constant and initial angle of attack are varied, and the oscillation amplitudes and frequencies of the wing, while undergoing torsional stall flutter, are recorded. These experimental values show only fair comparisons with the predicted responses. Predictions tend to be good at low velocities and rather poor at higher velocities.

Muffoletto, A. J.↗

NASA NTRS1985

Theoretical calculation of ozone vibrational infrared intensities

An ab initio dipole moment function for ozone has been computed using the CASSCF (complete active space self-consistent field) method, and forms the basis for a calculation of ozone infrared band intensities. Vibrational wave functions were generated using the variational method with potential energy surfaces derived from experimental force constants. Computed values of the permanent dipole moment, dipole moment derivatives, and infrared band strengths are all found to be in remarkably good agreement with experiment. Intensities are predicted for hot bands for which experimental values are unavailable, and implications for atmospheric ozone spectroscopy are discussed. As the dipole moment matrix element signs are now established for nearly all of the observed bands, further refinement of the dipole moment function is possible.

Adler-Golden, S. M.↗

NASA NTRS1987

Data analysis and interpretation of UVSP and other experiments on board solar maximum mission

During the period of this contract (February 1 1980 to February 1987) there were two separate efforts involved: one was programmetric, i.e., the coordination of scientific working groups and the organization of workshops in the solar physics discipline; the second was scientific, i.e., to perform research to investigate the fundamental physical mechanisms of the energy and momentum transport from the solar surface to interplanetary space. In the former, 19 workshops, involving 88 scientists were organized. In the latter aspect, the following were investigated: solar flare energy buildup and release, coronal dynamics, energy and momentum transport from lower solar atmosphere to interplanetary space, numerical methods for the calculation of the nonlinear force-free field, and the evolution of the solar magnetic field.

Wu, S. T.↗

NASA NTRS1986

Application of a full potential method for analysis of complex aircraft geometries

A supersonic potential flow solver was developed to analyze the flow over complex realistic aircraft geometries. Enhancements to the method were made to accommodate regions of subsonic flow, the effect of trailing wakes on other aircraft components, and the modeling/gridding of complete configurations. Validation of the method was demonstrated by comparisons with experimental aerodynamic force and surface pressure measurements. The predicted results are in very good agreement with the experimental data. The bibliography contains additional information on the use of the potential flow code to predict the aerodynamics of high-speed wing/body configurations, waverider concepts, TAV, and the Space Shuttle orbiter package.

Jones, Kenneth M.↗

NASA NTRS1988

Development and applications of optical interferometric micrometrology in the Angstrom and subangstrom range

The characteristics of the scanning tunneling microscope and atomic force microscope (AFM) are briefly reviewed, and optical methods, mainly interferometry, of sufficient resolution to measure AFM deflections are discussed. The methods include optical resonators, laser interferometry, multiple-beam interferometry, and evanescent wave detection. Experimental results using AFM are reviewed.

Lauer, James L.↗

NASA NTRS1989

Experience with strain-gage balances for cryogenic wind tunnels

The U.S. National Transonic Facility (NTF) is a cryogenic wind tunnel build to meet the United States' needs for high Reynolds number testing. The facility was declared operational in August 1984, and since that time numerous models were tested in the NTF using unheated strain-gage balances to measure aerodynamic forces. The difficulty in accurately measuring forces and moments of models in conventional wind tunnels becomes more challenging at cryogenic conditions. The Force and Strain Instrumentation Section of the Instrument Research Division at NASA Langley Research Center designed and fabricated the balances to measure forces at cryogenic temperatures without thermally controlling the balance temperature. Presented are balance results from a recent cryogenic test program in the NTF. The data indicated the accuracy with which aerodynamic forces are determined using current instrumentation and test methods as well as identified areas for future research.

Williams, M. Susan↗

NASA NTRS1990

Thin-walled composite beams under bending, torsional, and extensional loads

Symmetric and antisymmetric layup graphite-epoxy composite beams with thin-walled rectangular cross sections are fabricated using an autoclave molding technique and tested under bending, torsional, and extensional loads. The bending slope and elastic twist at a station are measured using an optical system, and the results correlated with predicted values from a simple beam analysis as well as a refined finite element analysis. A symmetric ply layup results in bending-twist coupling whereas an antisymmetric layup causes extension-twist coupling. Simple analytical results with plane-stress assumption agree better with measured data as well as finite element predictions than with plane-strain assumption. For symmetric layup beams, the bending-induced twist and torsion-induced bending slope are predicted satisfactorily using simple analytical solution. Correlations with measured data, however, are generally improved using a finite element solution. For antisymmetric beams, axial force-induced twist is predicted satisfactorily by both methods.

Chandra, Ramesh↗

NASA NTRS1989

Finite element large-amplitude free and forced vibrations of rectangular thin composite plates

A finite element formulation is presented for determining the large-amplitude free and steady-state forced vibration response of arbitrarily laminated anisotropic composite rectangular thin plates. The nonlinear stiffness and harmonic force matrices of an arbitrarily laminated composite rectangular plate element are developed for nonlinear free and forced vibration analyses. The linearized updated-mode method with nonlinear time function approximation is employed for the solution of the system nonlinear eigenvalue equations. The amplitude-frequency relations for convergence with gridwork refinement, different boundary conditions, aspect ratios, lamination angles and number of plies are presented. The finite element results are compared with available approximate continuum solutions.

Chiang, C. K.↗

NASA NTRS1991

Performance and stability of telemanipulators using bilateral impedance control

A new method of control for telemanipulators called bilateral impedance control is investigated. This new method differs from previous approaches in that interaction forces are used as the communication signals between the master and slave robots. The new control architecture has several advantages: (1) It allows the master robot and the slave robot to be stabilized independently without becoming involved in the overall system dynamics; (2) It permits the system designers to arbitrarily specify desired performance characteristics such as the force and position ratios between the master and slave; (3) The impedance at both ends of the telerobotic system can be modulated to suit the requirements of the task. The main goals of the research are to characterize the performance and stability of the new control architecture. The dynamics of the telerobotic system are described by a bond graph model that illustrates how energy is transformed, stored, and dissipated. Performance can be completely described by a set of three independent parameters. These parameters are fundamentally related to the structure of the H matrix that regulates the communication of force signals within the system. Stability is analyzed with two mathematical techniques: the Small Gain Theorem and the Multivariable Nyquist Criterion. The theoretical predictions for performance and stability are experimentally verified by implementing the new control architecture on a multidegree of freedom telemanipulator.

Moore, Christopher Lane↗

NASA NTRS1993

Nonlinear vibrations of thin arbitrarily laminated composite plates subjected to harmonic excitations using DKT elements

A finite element formulation is presented for determining the large-amplitude free and steady-state forced vibration response of arbitrarily laminated anisotropic composite thin plates using the Discrete Kirchhoff Theory (DKT) triangular elements. The nonlinear stiffness and harmonic force matrices of an arbitrarily laminated composite triangular plate element are developed for nonlinear free and forced vibration analyses. The linearized updated-mode method with nonlinear time function approximation is employed for the solution of the system nonlinear eigenvalue equations. The amplitude-frequency relations for convergence with gridwork refinement, triangular plates, different boundary conditions, lamination angles, number of plies, and uniform versus concentrated loads are presented.

Chiang, C. K.↗

NASA NTRS1995

The Clementine mechanisms

The Clementine spacecraft was developed under the 'faster, better, cheaper' theme. The constraints of a low budget coupled with an unusually tight schedule forced many departures from the normal spacecraft development methods. This paper discusses technical lessons learned about several of the mechanisms on the Clementine spacecraft as well as managerial lessons learned for the entire mechanisms subsystem. A quick overview of the Clementine mission is included; the mission schedule and environment during the mechanisms releases and deployment are highlighted. This paper then describes the entire mechanisms subsystem. The design and test approach and key philosophies for a fast-track program are discussed during the description of the mechanisms subsystem. The mechanism subsystem included a marman clamp separation system, a separation nut separation system, a solar panel deployment and pointing system, a high gain antenna feed deployment system, and two separate sensor cover systems. Each mechanism is briefly discussed. Additional technical discussion is given on the marman clamp design, the sensor cover designs, and the design and testing practices for systems driven by heated actuators (specifically paraffin actuators and frangibolts). All of the other mechanisms were of conventional designs and will receive less emphasis. Lessons learned are discussed throughout the paper as they applied to the systems being discussed. Since there is information on many different systems, this paper is organized so that information on a particular topic can be quickly referenced.

Purdy, William↗

NASA NTRS1998

3D Navier-Stokes Time Accurate Solutions Using Multipartitioning Parallel Computation Methodology

A parallel CFD code solving 3D time accurate Navier-Stokes equations with multipartitioning parallel Methodology is being developed in collaboration with Ohio State University within the Air Vehicle Directorate, at Wright Patterson Air Force Base. The advantage of the multipartitioning parallel method is that the domain decomposition will not introduce domain boundaries for the implicit operators. A ring structure data communication is employed so that the implicit time accurate method can be implemented for multi-processors with the same accuracy as for the single processor. No sub-iteration is needed at the domain boundaries. The code has been validated for some typical unsteady flows, which include Coutte Flow, flow passing a cylinder. The code now is being employed for a large scale time accurate wall jet transient flow computation. 'ne preliminary results are promising. The mesh has been refined to capture more details of the flow field. The mesh refinement computation is in progress and would be difficult to successfully implement without the parallel computation techniques used. A modified version of the code with more efficient inversion of the diagonalized block matrix is currently being tested.

Zha, Ge-Cheng↗

NASA NTRS2000

Using Modern Design Tools for Digital Avionics Development

Using Modem Design Tools for Digital Avionics Development Shrinking development time and increased complexity of new avionics forces the designer to use modem tools and methods during hardware development. Engineers at the Marshall Space Flight Center have successfully upgraded their design flow and used it to develop a Mongoose V based radiation tolerant processor board for the International Space Station's Water Recovery System. The design flow, based on hardware description languages, simulation, synthesis, hardware models, and full functional software model libraries, allowed designers to fully simulate the processor board from reset, through initialization before any boards were built. The fidelity of a digital simulation is limited to the accuracy of the models used and how realistically the designer drives the circuit's inputs during simulation. By using the actual silicon during simulation, device modeling errors are reduced. Numerous design flaws were discovered early in the design phase when they could be easily fixed. The use of hardware models and actual MIPS software loaded into full functional memory models also provided checkout of the software development environment. This paper will describe the design flow used to develop the processor board and give examples of errors that were found using the tools. An overview of the processor board firmware will also be covered.

Hyde, David W.↗

NASA NTRS2001

Semiclassical Models for Virtual Antiparticle Pairs, the Unit of Charge e, and the QCD Coupling alpha(sub s)

New semiclassical models of virtual antiparticle pairs are used to compute the pair lifetimes, and good agreement with the Heisenberg lifetimes from quantum field theory (QFT) is found. The modeling method applies to both the electromagnetic and color forces. Evaluation of the action integral of potential field fluctuation for each interaction potential yields approximately Planck's constant/2 for both electromagnetic and color fluctuations, in agreement with QFT. Thus each model is a quantized semiclassical representation for such virtual antiparticle pairs, to good approximation. When the results of the new models and QFT are combined, formulae for e and alpha(sub s)(q) are derived in terms of only Planck's constant and c.

Batchelor, David↗

NASA NTRS2005

The Effect of Infrastructure Sharing in Estimating Operations Cost of Future Space Transportation Systems

NASA and the aerospace industry are extremely serious about reducing the cost and improving the performance of launch vehicles both manned or unmanned. In the aerospace industry, sharing infrastructure for manufacturing more than one type spacecraft is becoming a trend to achieve economy of scale. An example is the Boeing Decatur facility where both Delta II and Delta IV launch vehicles are made. The author is not sure how Boeing estimates the costs of each spacecraft made in the same facility. Regardless of how a contractor estimates the cost, NASA in its popular cost estimating tool, NASA Air force Cost Modeling (NAFCOM) has to have a method built in to account for the effect of infrastructure sharing. Since there is no provision in the most recent version of NAFCOM2002 to take care of this, it has been found by the Engineering Cost Community at MSFC that the tool overestimates the manufacturing cost by as much as 30%. Therefore, the objective of this study is to develop a methodology to assess the impact of infrastructure sharing so that better operations cost estimates may be made.

Sundaram, Meenakshi↗

NASA NTRS2008

Advanced Active-Magnetic-Bearing Thrust-Measurement System

An advanced thrust-measurement system utilizes active magnetic bearings to both (1) levitate a floating frame in all six degrees of freedom and (2) measure the levitation forces between the floating frame and a grounded frame. This system was developed for original use in measuring the thrust exerted by a rocket engine mounted on the floating frame, but can just as well be used in other force-measurement applications. This system offers several advantages over prior thrust-measurement systems based on mechanical support by flexures and/or load cells: The system includes multiple active magnetic bearings for each degree of freedom, so that by selective use of one, some, or all of these bearings, it is possible to test a given article over a wide force range in the same fixture, eliminating the need to transfer the article to different test fixtures to obtain the benefit of full-scale accuracy of different force-measurement devices for different force ranges. Like other active magnetic bearings, the active magnetic bearings of this system include closed-loop control subsystems, through which the stiffness and damping characteristics of the magnetic bearings can be modified electronically. The design of the system minimizes or eliminates cross-axis force-measurement errors. The active magnetic bearings are configured to provide support against movement along all three orthogonal Cartesian axes, and such that the support along a given axis does not produce force along any other axis. Moreover, by eliminating the need for such mechanical connections as flexures used in prior thrust-measurement systems, magnetic levitation of the floating frame eliminates what would otherwise be major sources of cross-axis forces and the associated measurement errors. Overall, relative to prior mechanical-support thrust-measurement systems, this system offers greater versatility for adaptation to a variety of test conditions and requirements. The basic idea of most prior active-magnetic-bearing force-measurement systems is to calculate levitation forces on the basis of simple proportionalities between changes in those forces and changes in feedback-controlled currents applied to levitating electromagnetic coils. In the prior systems, the effects of gap lengths on fringing magnetic fields and the concomitant effects on magnetic forces were neglected. In the present system, the control subsystems of the active magnetic bearings are coupled with a computer-based automatic calibration system running special-purpose software wherein gap-length-dependent fringing factors are applied to current and magnetic-flux-based force equations and combined with a multipoint calibration method to obtain greater accuracy.

Imlach, Joseph↗