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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 505 records · Page 28

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NASA NTRS1978

A digital computer program for the dynamic interaction simulation of controls and structure (DISCOS), volume 1

A theoretical development and associated digital computer program system for the dynamic simulation and stability analysis of passive and actively controlled spacecraft are presented. The dynamic system (spacecraft) is modeled as an assembly of rigid and/or flexible bodies not necessarily in a topological tree configuration. The computer program system is used to investigate total system dynamic characteristics, including interaction effects between rigid and/or flexible bodies, control systems, and a wide range of environmental loadings. In addition, the program system is used for designing attitude control systems and for evaluating total dynamic system performance, including time domain response and frequency domain stability analyses.

Bodley, C. S.↗

NASA NTRS1978

Analysis of dynamic system response to product random processes

The response of dynamic systems to the product of two independent Gaussian random processes is developed by use of the Fokker-Planck and associated moment equations. The development is applied to the amplitude modulated process which is used to model atmospheric turbulence in aeronautical applications. The exact solution for the system response is compared with the solution obtained by the quasi-steady approximation which omits the dynamic properties of the random amplitude modulation. The quasi-steady approximation is valid as a limiting case of the exact solution for the dynamic response of linear systems to amplitude modulated processes. In the nonlimiting case the quasi-steady approximation can be invalid for dynamic systems with low damping.

Sidwell, K.↗

NASA NTRS1978

Experiments on the dynamic behavior of cavitating pumps

This paper describes experiments performed to measure the dynamic transfer matrices for cavitating (and noncavitating) pumps. These transfer matrices describe the relationship between small linear oscillatory perturbations in the pressures and mass flow rates at inlet and discharge from the hydraulic machine. The matrices were deduced from direct measurements of these fluctuating quantities for different modes of excitation of the machine. Results for a cavitating inducer are presented as functions of frequency and mean operating state. Though some of the trends in the data are consistent with existing theoretical models of inducer dynamics, others are not, indicating a need for further theoretical investigation of the dynamic characteristics of such flows. The results exhibit increasingly complex dynamics with increasing cavitation; it appears that the hydraulic machine deviates from an essentially passive response without cavitation to an increasingly active response as the cavitation number is reduced.

Ng, S. L.↗

NASA NTRS1978

Development of a finite dynamic element for free vibration analysis of two-dimensional structures

The paper develops an efficient free-vibration analysis procedure of two-dimensional structures. This is achieved by employing a discretization technique based on a recently developed concept of finite dynamic elements, involving higher order dynamic correction terms in the associated stiffness and inertia matrices. A plane rectangular dynamic element is developed in detail. Numerical solution results of free-vibration analysis presented herein clearly indicate that these dynamic elements combined with a suitable quadratic matrix eigenproblem solution technique effect a most economical and efficient solution for such an analysis when compared with the usual finite element method.

Gupta, K. K.↗

NASA NTRS1979

Structural dynamics technology research in NASA: Perspective on future needs

The perspective of a NASA ad hoc study group on future research needs in structural dynamics within the aerospace industry is presented. The common aspects of the design process across the industry are identified and the role of structural dynamics is established through a discussion of various design considerations having their basis in structural dynamics. The specific structural dynamics issues involved are identified and assessed as to their current technological status and trends. Projections of future requirements based on this assessment are made and areas of research to meet them are identified.

Source record↗

NASA NTRS1978

Bubbly flow model for the dynamic characteristics of cavitating pumps

The recent experimental transfer matrices obtained by Ng and Brennen (1978) for some axial flow pumps revealed some dynamic characteristics which were unaccounted for by any existing theoretical analysis; their visual observations suggested that the bubbly cavitating flow in the blade passages could be responsible for these effects. A theoretical model of the dynamic response of this bubbly blade-passage flow is described in the present paper. Void-fraction fluctuations in this flow result not only from pressure fluctuations but also because the fluctuating angle of attack causes fluctuations in the rate of production of bubbles near the leading edge. The latter causes kinematic waves which interact through the boundary conditions with the dynamic waves caused by pressure fluctuation. The resulting theoretical transfer functions which results are in good qualitative agreement with the experiments; with appropriate choices of two parameters good quantitative agreement is also obtained. The theoretical model also provides one possible explanation of the observation that the pump changes from an essentially passive dynamic element in the absence of cavitation to a progressively more active element as the extent of cavitation increases.

Brennen, C.↗

NASA NTRS1979

Research needs in aerospace structural dynamics

The perspective of a NASA Ad Hoc Study Committee on future research needs in structural dynamics within the aerospace industry is presented. It identifies the common aspects of the design process across the industry and establishes the role of structural dynamics in it through a discussion of various design considerations having their basis in structural dynamics. The specific structural dynamics issues involved in these considerations are identified and assessed as to their current technological status and trends. Projections of future requirements based on this assessment are made and areas of research to meet them are identified.

Amos, A. K.↗

NASA NTRS1980

Wind tunnel determination of dynamic cross-coupling derivatives - A new approach

The latest developments in the NAE ongoing dynamic stability research program are briefly summarized. Emphasis is placed on the recently developed wind-tunnel data reduction procedures used to obtain cross and cross-coupling derivatives due to an oscillatory motion. These procedures, which account for the dynamic behaviour of the model-balance subsystem, are described for the balance configurations currently in use. The principles on which they are based, however, are quite general and can therefore be applied to other balance configurations. Two full-model dynamic stability apparatuses are described and typical results, obtained from dynamic calibrations as well as from wind-tunnel experiments, are presented.

Hanff, E. S.↗

NASA NTRS1981

Spacecraft dynamic environments

Zero-gravity conditions in Earth orbit cannot be obtained in the Shuttle Orbiter, however, through careful planning, the dynamic environment and its effects on experiments can be minimized. Futhermore, although the dynamic environment of the Shuttle Orbiter is to a large degree stochastics, it is possible to predict characteristics of this environments so that scientists and technologists can plan their experiments and mission managers can plan missions with a view toward minimizing the effects of spacecraft dynamics on experiments. Characteristics of the dynamic environment that might be predicted include typical and "worst case" values of vehicle acceleration for the anticipated acceleration sources, typical number of acceleration event, duration times of disctete acceleration events, bandwidth of acceleration time history, etc.

Fichtl, G. H.↗

NASA NTRS1982

Dynamic switch matrix for the TDMA satellite switching system

Future high capacity satellite communication systems require signal processing on board satellites. The on-board signal processing includes switching of RF signals between multiple antennas to provide interconnection between the uplink and downlink beams. This paper describes the development of a dynamic switch matrix for a TDMA satellite switching system to be used in the next generation communications satellites. In this paper, a dynamic switch matrix, which includes the microwave switch matrix, the distribution control unit and the timing source, will be described. Several different microwave switch matrix architectures and switching devices were evaluated and compared. A unique coupler crossbar switch matrix architecture with dual-gate field effect transistor as switching element was developed. Experimental results of both microwave switch matrix (MSM) and distribution control unit (DCU) are presented. These test results verify the MSM with coupler crossbar architecture and dual-gate FET as switching element will meet the future SS-TDMA system requirements. Finally, the reliability of the dynamic switch matrix is addressed. The analysis shows reliability of 0.9981 for 7 year space operation can be achieved for the designed dynamic switch matrix.

Ho, P. T.↗

NASA NTRS1981

Observations of the interaction of ozone and dynamics

Data on the global distribution of temperature and ozone obtained with the Limb Radiance Inversion Radiometer which flew on the Nimbus 6 spacecraft are analyzed within the conceptual framework of Hartmann and Garcia (1979). The analysis supports the conclusion that ozone perturbations are dynamically controlled when the photochemical time constant is much greater than the dynamical time constant; when the photochemical constant is much less than the dynamical constant, ozone perturbations are photochemically controlled. It is also shown that the transports of planetary waves, or eddy transports, appear to be strongly localized in the region between the regimes in which dynamical and photochemical controls operate.

Gille, J. C.↗

NASA NTRS1982

Dynamics of rotating and oscillating free drops

The Dynamics of Rotating and Oscillating Free Drops (DROP) experiment is to be performed using the Drop Dynamics Module (DDM). The main scientific objectives of the DROP experiment are the study of the equilibrium figures of a rotating drop and the study of the large-amplitude oscillations of a liquid drop. The objective of the DROP experiment in relation to the DDM is to establish the advantages of conducting future drops and bubbles experiments in space. The DROP experiment will be subjected to continual to ensure that the experiments are scientifically current and available. The two component experiments (rotation and oscillation) of the DROP experiment have been chosen as the simplest experiments representative of the entire class of drop dynamics experiments. The component experiment on the equilibrium shapes of a rotating liquid drop of a simple liquid is not only an important and interesting experiment in its own right, but is also the simplest gyrostatic experiment that can be performed. In later experiments, more complicated liquids can be used; bubbles can be included; and the dynamics of rotating drops can be studied. This experiment, as it now stands, is an important exercise of the module's ability to provide drop rotation and the requisite science data.

Wang, T. G.↗

NASA NTRS1983

Safe on-orbit experiment for measurement of large structures dynamics

The Solar Array Flight Experiment (SAFE) on-orbit experiment for measurement of large structures dynamics consists of a dynamic sensing system designed to record and analyze the dynamic characteristics of the SAFE. The early availability of the SAFE and its basic large space structure characteristics make it a logical candidate for verification of the sensing system and the evaluation technique. The characteristics of the solar array which place it well within the generic class of large space structures are: (1) large size, (2) low natural frequencies, (3) mechanical complexity of its extendable/retractable mast, and (4) the inability to dynamically test in the Earth's atmosphere and in one g. The fourth characteristic is due to its size, air damping dominance of the blanket, and structural instability in one g. The specific characteristics of the solar array are shown and the applicability to large space structures is illustrated.

Schock, R. W.↗

NASA NTRS1982

Calculation of exact vibration modes for plane grillages by the dynamic stiffness method

A dynamic stiffness method is developed for the calculation of the exact modal parameters for plane grillages which consist of straight and uniform beams with coincident elastic and inertial axes. Elementary bending-torsion beam theory is utilized, and bending translation is restricted to one direction. The exact bending-torsion dynamic stiffness matrix is obtained for a straight and uniform beam element with coincident elastic and inertial axes. The element stiffness matrices are assembled using the standard procedure of the static stiffness method to form the dynamic stiffness matrix of the complete grillage. The exact natural frequencies, mode shapes, and generalized masses of the grillage are then calculated by solving a nonlinear eigenvalue problem based on the dynamic stiffness matrix. The exact modal solutions for an example grillage are calculated and compared with the approximate solutions obtained by using the finite element method.

Hallauer, W. L., Jr.↗

NASA NTRS1983

Dynamics and control of a Shuttle attached antenna experiment

Study results obtained to date identify the requirements for a large space system flight experiment. This paper considers the dynamics and control of an offset feed wrap-rib antenna attached to the Shuttle for such an experiment. Results reported in this paper are primarily based on the analysis and simulation of the combined Shuttle and antenna flexible dynamics model, and the Shuttle Vernier Reaction Control Subsystem. These results establish the technical feasibility of the Shuttle attached antenna flight experiment. Static and dynamic disturbances examined do not cause significant dynamic interactions to the experiment. Shuttle Vernier jets can be used for control purpose or as controlled excitation sources for experiment. Interface between the Shuttle and the antenna can be rigid or actively decoupled depending on the experiment objective. Key large space systems control technologies such as distributed sensing and actuation, system identification, figure estimation and control, and control for slew or reconfiguration can be validated with the experiment configuration described in this paper.

Wang, S. J.↗

NASA NTRS1984

Shuttle on-orbit dynamics

Shuttle on-orbit dynamics are outlined. Topics discussed include: on-orbit dynamic environment; on-orbit dynamic interaction; accelerated g-levels and sources; phase plane controller; maximum average RCS pulsing rate; maximum RCS accelerations; manual pulse mode; dynamic interaction; generic screening.

Fay, S.↗

NASA NTRS1984

Identification of multivariable high-performance turbofan engine dynamics from closed loop data

A typical engine control design cycle consists of developing a dynamic engine simulation from steady-state component performance data, designing a control based upon this simulation, and then testing and modifying the control in an engine test cell to meet performance requirements. This design cycle was successful for state-of-the-art engines. However, for more advanced multivariable engines that exhibit strong variable interactions, this procedure will result in substantial trial and error modification of the control during the testing phase. One method to automate the design process and reduce control modification testing and development cost would be to identify accurate dynamic models directly from the closed-loop test data. These identified models would then be used in conjunction with a synthesis procedure to systematically refine the control. Recent advances in closed-loop identifiability present a methodology for this direct identification of engine model dynamics from closed-loop test data. The application of an identification method to simulated and actual closed-loop F100 engine data is described. This study was undertaken to determine if useful dynamic engine models could be identified directly from closed-loop engine test data.

Merrill, W. C.↗

NASA NTRS1983

Frequency-domain identification of XV-15 tilt-rotor aircraft dynamics

Frequency-domain methods are used to identify the open-loop dynamics of the XV-15 tilt-rotor aircraft from flight tests. Piloting and data analysis techniques are presented to determine frequency response plots and equivalent transfer function models. The open-loop pitch and roll dynamics for the hover flight condition exhibit unstable low-frequency oscillations, whereas the dynamics in the remaining degrees of freedom are lightly damped and generally decoupled. Comparisons of SV-13 flight-test and simulator data are more favorable for high-frequency inputs (omega greater than 1.0 rad/sec) than low-frequency inputs. The identification of symmetric and asymmetric beam-bending modes compares favorably with previous flight-test data. The results presented in this paper demonstrate the utility of the frequency-domain techniques for dynamics identification and simulator fidelity studies.

Tischler, M. B.↗