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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 631 records · Page 35

All sources NASA NTRS DOE OSTI

NASA NTRS1989

Spatial operator algebra framework for multibody system dynamics

The Spatial Operator Algebra framework for the dynamics of general multibody systems is described. The use of a spatial operator-based methodology permits the formulation of the dynamical equations of motion of multibody systems in a concise and systematic way. The dynamical equations of progressively more complex grid multibody systems are developed in an evolutionary manner beginning with a serial chain system, followed by a tree topology system and finally, systems with arbitrary closed loops. Operator factorizations and identities are used to develop novel recursive algorithms for the forward dynamics of systems with closed loops. Extensions required to deal with flexible elements are also discussed.

Rodriguez, G.↗

NASA NTRS1992

Spatial Operator Algebra for multibody system dynamics

Rodriguez, G.↗

NASA NTRS1993

Contact-impact analysis of deployable space systems

This paper presents simulation results of a flexible, deployable space system with multiple contact-impact events, using three different modeling approaches. In the first two approaches, the equations of motion of the system are written in terms of generalized coordinates of each component, with modal coordinates used to account for flexibility in the components. Two different methods are used to model contact-impact events in the systems. In the momentum balance method, as contact-impact occurs, momentum equations of the systems are solved for the jump discontinuity in velocity of generalized coordinates. Integration of the system is restarted with the new initial conditions from solutions of momentum equations. In the logical function method, a virtual spring connecting the two contact points is assumed. The virtual spring is active only when impact occurs. No special treatment is needed in the integration algorithm using this method. In the third approach, instead of using modal coordinates, a finite element based formulation for the transient dynamics of mechanical system is used to model flexibility of the components. The logical function method is used to model contact-impact in the third approach.

Wu, Shih-Chin↗

NASA NTRS1999

Control of a Thrust Alignment Table for Modeling the Coning Dynamics of a Spinning Spacecraft with a Follower Force

This document presents a system controlling the motion of a spherical air bearing used in the modeling of spacecraft dynamics and controls in a laboratory environment. The system is part of the Spinning Rocket Simulator (SRS), used to simulate the coning of spacecraft during a thrusting stage. The reaction force at the spherical air bearing supporting the spacecraft model must coincide with the thrust axis of the model for proper simulation. Therefore, the bearing is translated in a circular path to introduce a centrifugal force. This horizontal force along with the gravitational reaction force at the bearing combines to simulate the direction of the spacecraft's thrust force. The control system receives attitude information from the spacecraft model via a laser beam embedded in the model that impinges on a photosensitive array. The non-linear system is controlled using high-speed lookup tables and digital techniques. A vector-controlled motor and a stepper motor are given the necessary signals to accurately control the turntable and platform supporting the air bearing. Preliminary performance data is presented. Mechanical elements of the table and platform are described in detail. A wireless (RF) data path for all devices on the spacecraft model to an off-table command computer is also described.

Halsmer, Dominic↗

NASA NTRS1998

The TSS-1R Electrodynamic Tether Experiment: Scientific and Technological Results

The Tethered Satellite System (TSS) program was designed to provide the opportunity to explore certain space plasma-electrodynamic processes (associated with high-voltage bodies and electrical currents in space) and the orbital mechanics of a gravity-gradient stabilized system of two satellites linked by a long conducting tether. A unique data set was obtained during the TSS-1 R mission in which the tether emf and current reached values in excess of 3500 volts and 1 amp, respectively. The insight this has allowed into the current collection process and the physics of high-voltage plasma sheaths is significant. Previous theoretical models of current collection were electro-static assuming that the orbital motion of the system, which is highly sub-sonic with respect to electron thermal motion, was unimportant. This may still be acceptable for the case of relatively slow-moving sounding rockets. However, the TSS-1 R results show that motion relative to the plasma does affect current collection and must be accounted for in orbiting systems.

Stone, Nobie H.↗

DOE OSTI2024

An Approach to Realize Generalized Optimal Motion Primitives Using Physics Informed Neural Networks

Autonomous manipulation is a challenging problem in field robotics due to uncertainty in object properties, constraints, and coupling phenomenon with robot control systems. Humans learn motion primitives over time to effectively interact with the environment. We postulate that autonomous manipulation can be enabled by basic sets of motion primitives as well, but do not necessitate mimicking human motion primitives. Here, this work presents an approach to generalized optimal motion primitives using physics-informed neural networks. Our simulated and experimental results demonstrate that optimality is notionally maintained where the mean maximum observed final position percent error was 0.564% and the average mean error for all the trajectories was 1.53%. These results indicate that notional generalization is attained using a physics-informed neural network approach that enables near optimal real-time adaptation of primitive motion profiles.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2020

Influence of the Turing instability on the motion of domain boundaries

Turing's theory of pattern formation has provided crucial insights into the behavior of various biological, geographical, and chemical systems over the last few decades. Existing studies have focused on moving-boundary Turing systems for which the motion of the boundary is prescribed by an external agent. In this paper, we present an extension of this theory to a class of systems in which the front motion is governed by the physical processes that occur within the domain. Biological systems exhibiting apically dominant growth and corrosion of metals and alloys highlight some of the noteworthy examples of such systems. In this study, we characterize the nature of interaction between the moving front and the Turing-instability for both an activator-inhibitor and an activator-substrate model. Behavioral regimes of periodic, as well as nonperiodic (nonconstant), growth rates are obtained. Furthermore, the trends in the first show striking similarities with the cyclic-boundary-kinetics observed in experimental systems. In general, a stationary, periodic structure is also left behind the moving front. If the periodicity of the boundary kinetics agrees with the allowed range of the stable-periodic solutions, the pattern formed tends to persist. Lastly, it evolves to a nearby energy-minimum either by peak-splitting, peak-decay, or by settling down to a spatially homogeneous state.

99 GENERAL AND MISCELLANEOUS↗

NASA NTRS1972

Note on the origin of Jupiter's magnetic field

The effect of the coriolis force was examined for stability of rotating hydromagnetic systems. It is shown that the effect of this force is to inhibit the onset of instability which leads to convective motion in these systems. The possibility of the existence of a dynamo process in Jupiter's interior is discussed, taking into account the effect of the coriolis force.

Sakurai, K.↗

NASA NTRS1994

Implementation of a state of the art automated system for the production of cloud/water vapor motion winds from geostationary satellites

Significant progress was attained in this reporting period towards the overall goal of improving the CIMSS satellite wind algorithms through incorporation of new processing options, and testing/evaluating these options on data sets and through case studies. Several new strategies were implemented, and these are outlined. In addition, data from GOES-8 have recently become available during system check-out and evaluation. Initial testing and software adjustments necessary to handle this new and improved data are briefly touched upon in this summary, and will be a main focus of the remaining funds and efforts under this contract.

Velden, Christopher↗

NASA NTRS1973

Crystal motion measurement by means of satellite techniques

A system for monitoring precursory crustal motions is presented. It involves a set of automated corner reflector stations tracked by means of a laser operating in the Geopause satellite. It is possible to range some three times during every Geopause pass to each of the sites in such an ensemble, weather permitting. One centimeter range data gathered during a quarter of a year can yield position component accuracies of the order of a couple of centimeters. A laser beam of a tenth of a milliradian in diameter would, illuminate a single station in such an array. A broader beam would generate reflections from several sites, yielding overlapping data. A chain or pattern of such overlapping regions can strengthen the solution for site positions. Pressure, temperature and humidity gauges can provide refraction correction data. Turnaround transponders interrogated by the Geopause radio tracking system can furnish corresponding data in excessively cloudy regions.

Siry, J. W.↗

NASA NTRS1992

Dual-arm supervisory and shared control space servicing task experiments

A dual-arm task execution primitive has been implemented for cooperative dual-arm telerobotic task execution utilizing multiple sensors concurrently. The primitive has been integrated into a telerobot task execution system and can be called by a task planning system for execution of tasks requiring dual-arm sensor based motion, e.g., force control, teleoperation, and shared control. The primitive has a large input parameter set which is used to specify the desired behavior of the motion. Move-squeeze decomposition is utilized to decompose forces sensed at the wrists of the two manipulators into forces in the move subspace, which cause system motion, and forces in the squeeze subspaces, which cause internal forces. The move and squeeze forces are then separately controlled. Several space servicing tasks utilizing the cooperative dual-arm control capability are described, and experimental results from the tasks are given. The supervisory and shared control tasks include capture of a rotating satellite, orbital replacement unit changeout, fluid coupler seating and locking, and contour following.

Backes, Paul G.↗

NASA NTRS1979

Energy-state formulation of lumped volume dynamic equations with application to a simplified free piston Stirling engine

Lumped volume dynamic equations are derived using an energy state formulation. This technique requires that kinetic and potential energy state functions be written for the physical system being investigated. To account for losses in the system, a Rayleigh dissipation function is formed. Using these functions, a Lagrangian is formed and using Lagrange's equation, the equations of motion for the system are derived. The results of the application of this technique to a lumped volume are used to derive a model for the free piston Stirling engine. The model was simplified and programmed on an analog computer. Results are given comparing the model response with experimental data.

Daniele, C. J.↗

NASA NTRS1992

Finite element nonlinear panel flutter with arbitrary temperatures in supersonic flow

A finite element frequency domain method for predicting nonlinear flutter response of panels with temperature effects is presented. By using the principle of virtual work, the element nonlinear stiffness formulation for a panel under a combined thermal and aerodynamic loads is derived on the bases of von Karman's large deflection plate theory, the first-order piston theory aerodynamics and the quasi-steady thermal stress theory. The system equations of motion can be mathematically separated into two sets of equations and then solved in sequence. The first set of equations yields the panel thermal-aerodynamic equilibrium and the second set of equations of motion leads to the flutter limit-cycle oscillations. Stability and flutter boundaries can also be obtained from the two sets of system equations. Finite element large amplitude limit-cycle flutter results at different uniform temperatures are obtained for a simply supported square panel and are compared with existing Galerkin/time integration and other finite element solutions. Effects of nonuniform temperature distributions, panel length-to-width ratios, and boundary conditions on flutter responses of rectangular and triangular panels are presented.

Xue, David Y.↗

NASA NTRS1982

An integration scheme to determine the dynamic response of a launch vehicle with several payloads

The coupled equations of motion of a system composed of a launch vehicle and multiple payloads are derived. In the process, it is shown how superfluous interface degrees of freedom on the booster side can be accommodated in the formulation. The discrete system equations are directly integrated, avoiding the solution of an expensive system eigenvalue problem. A modified Newmark-Chan-Beta numerical integration scheme is used to obtain the response. The unique form of the equations of motion allow for a quick and accurate solution both for the response and the internal loads. Although completely general, the presented technique is most effective when the number of interface degrees of freedom is relatively small compared to the overall number of degrees of freedom of the system. The technique is applied to the case of the S.T.S.-S.T.-OMS Kit system. Finally, an evaluation of the presented method is included.

Engels, R. C.↗

NASA NTRS1972

Stability of certain periodic solutions of a forced system with hysteresis

Many physical systems exhibit the phenomenon of nonlinear hysteresis when the amplitude of oscillation exceeds some small limit. It was shown that under certain conditions there are periodic motions of such a system with small forcing which are near the largest periodic motion of the corresponding unforced system. Conditions for the stability of these periodic motions are derived.

Drew, J. H.↗

NASA NTRS1991

The radio 'lobes' of Scorpius X-1 are unrelated background sources

The VLA between 1981 and 1990 are used to produce high-resolution images of the radio emission from the region near Sco X-1. The radio proper motion of Sco X-1 was measured at 0.0148 +/-0.0011/yr, which agrees with the optical determination for the X-ray-emitting binary system. The proper motions of two nearby radio sources, juxtaposed 1 arcmin to the NE and to the SW, were measured and found to be stationary in the sky with upper limits of 0.004 arcsec/yr. A deep radio image of the 10-arcsec extended SW source shows a morphology strikingly similar to that of a typical luminous extragalactic radio source, which contains two edge-brightened lobes, a jet, and a core. The possibilities that the NE source, although nearly stationary in the sky, is associated with Sco X-1, are discussed, and it is concluded that it is an unrelated background source. It is inferred that Sco X-1 is not a miniature triple source or a 'microquasar', and its radio emission is confined to the binary system.

Fomalont, E. B.↗

NASA NTRS1979

Energy-state formulation of lumped volume dynamic equations with application to a simplified free piston Stirling engine

Lumped volume dynamic equations are derived using an energy-state formulation. This technique requires that kinetic and potential energy state functions be written for the physical system being investigated. To account for losses in the system, a Rayleigh dissipation function is also formed. Using these functions, a Lagrangian is formed and using Lagrange's equation, the equations of motion for the system are derived. The results of the application of this technique to a lumped volume are used to derive a model for the free-piston Stirling engine. The model was simplified and programmed on an analog computer. Results are given comparing the model response with experimental data.

Daniele, C. J.↗

NASA NTRS1972

Analog analysis of a tracked air-cushion vehicle.

The dynamics of tracked air-cushion vehicles considered for high-speed ground transportation systems are examined using a vehicle model represented by a one-degree-of-freedom system. The respective equations of motion are derived, and the control system is discussed. The equations obtained for the cushion are solved using an analog computer. The computer showed the effect of the control technique on the relative motion between vehicle and guideway.

Leatherwood, J. D.↗