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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 19 records

All sources NASA NTRS DOE OSTI

NASA NTRS1972

Analysis of dashpot performance for rotating control drums of a lithium cooled fast reactor concept

A dashpot was incorporated in the design of the drive train of the rotating control drum to prevent shock damage to the control drum and drive train at the termination of a scram action. A rotating vane dashpot using reactor coolant lithium as a damping fluid appears to be the best candidate of the various damping devices explored. A performance analysis, results and discussion of vane type dashpots are presented.

Wenzler, C. J.↗

NASA NTRS1994

Dashpot Damps Oscillations In Check Valve

Operation of check valve improved by redesigning poppet and adding two new components: dashpot and dashpot ring between dashpot and poppet. Modifications eliminate self-sustaining poppet oscillations that cause premature wear and jamming of poppet mechanism.

Morris, Brian G.↗

NASA NTRS1941

Damping characteristics of dashpots

An investigation of the damping characteristics of dashpots was carried out combining theory and experiment. Laminar flow was assumed and three equations for the steady velocity of a piston moving in a cylinder filled with liquid were derived. In the first equation, the piston was assumed coaxial in the cylinder and, in the second equation, the piston was assumed eccentric in the cylinder with an element of the piston in contact with the cylinder wall. The third equation is for a piston of circular cross section in an elliptical cylinder. Experiments showed that the piston is normally eccentric in the cylinder. The pistons tested were 1.25 and 2 inches in diameter 0.062 to 1.00 inch long, and the clearances varied from 1.36 to 5.16 x 10 to the 3rd power inch. The difference in pressure on the two sides of the piston varied from about 2 to 55 pounds per square inch. The piston velocities for each assembly were measured with damping liquids of three different viscosities. At high piston velocities, when turbulent flow exists, the observed velocities were much lower than the velocities calculated on the basis of laminar flow. Results for a wide range of Reynolds numbers are presented in graphical form.

INSTRUMENTS-MICROMETERS↗

NASA NTRS1983

Test results and description of a 1-kW free-piston Stirling engine with a dashpot load

A 1 kW (1.33 hp) single cylinder free piston Stirling engine was installed in the test facilities at the Lewis laboratory. The engine was designed specifically for research of the dynamics of its operation. A more complete description of the engine and its instrumentation is provided in a prior NASA paper TM-82999 by J. G. Schreiber. Initial tests at Lewis showed the power level and efficiency of the engine to be below design level. Tests were performed to help determine the specific problems in the engine causing the below design level performance. Modifications to engine hardware and to the facility where performed in an effort to bring the power output and efficiency to their design values. As finally configured the engine generated more than 1250 watts of output power at an engine efficiency greater than 32 percent. This report presents the tests performed to help determine the specific problems, the results if the problem was eliminated, the fix performed to the hardware, and the test results after the engine was tested. In cases where the fix did not cause the anticipated effects, a possible explanation is given.

Schreiber, J.↗

NASA NTRS1983

Test results and description of a 1 kW free-piston Stirling engine with a dashpot load

Schreiber, J.↗

NASA NTRS1993

Check valve with poppet dashpot/frictional damping mechanism

An inline check valve for a flow line where the valve element is guided for inline travel forward and rearward of a valve sealing member and is spring biased to a closed sealing condition is presented. One of the guides for the valve element includes a dashpot housing with a bore and plunger member to control the rate of travel of the valve element in either direction, providing a guiding function. The plunger member is arranged with a dashpot ring to frictionally contact the dashpot bore and has an interior tortuous flow path from one side to the other side of the dashpot ring. The dashpot housing is not anchored to the valve body so that the valve can be functional even if the dashpot ring becomes jammed in the dashpot housing.

Morris, Brian G.↗

NASA NTRS1993

Check valve with poppet damping mechanism

An inline check valve for a flow line is presented where the valve element is guided for inline travel forward and rearward of a valve sealing member and is spring biased to a closed sealing condition. One of the guides for the valve element includes a dashpot bore and plunger member to control the rate of travel of the valve element in either direction as well as provided a guiding function. The dashpot is not anchored to the valve body so that the valve can be functional even if the plunger member becomes jammed in the dashpot.

Morris, Brian G.↗

NASA NTRS1987

Active damping of vibrations in SCOLE excited by slewing

Control simulations were performed to study active damping of vibrations in SCOLE excited by minimum-time rapid slewing. Highlights of the numerical results are presented. Some conclusions reached are: (1) modal-dashpot and modal-spring controllers provide quick and effective vibration control; (2) high gain problems can be avoided by proper selection of modeled modes and proper level of augmentation; (3) modal dashpots and modal springs are most effective during the initial period of large vibrations; and (4) line of sight error due solely to each mode excited by the disturbance provides a sound measure of importance of individual modes.

Lin, Jiguan Gene↗

NASA NTRS1987

RE-1000 free-piston Stirling engine hydraulic output system description

The NASA Lewis Research Center was involved in free-piston Stirling engine research since 1976. Most of the work performed in-house was related to characterization of the RE-1000 engine. The data collected from the RE-1000 tests were intended to provide a data base for the validation of Stirling cycle simulations. The RE-1000 was originally build with a dashpot load system which did not convert the output of the engine into useful power, but was merely used as a load for the engine to work against during testing. As part of the interagency program between NASA Lewis and the Oak Ridge National Laboratory, (ORNL), the RE-1000 was converted into a configuration that produces useable hydraulic power. A goal of the hydraulic output conversion effort was to retain the same thermodynamic cycle that existed with the dashpot loaded engine. It was required that the design must provide a hermetic seal between the hydraulic fluid and the working gas of the engine. The design was completed and the hardware was fabricated. The RE-1000 was modified in 1985 to the hydraulic output configuration. The early part of the RE-1000 hydraulic output program consisted of modifying hardware and software to allow the engine to run at steady-state conditions. A complete description of the engine is presented in sufficient detail so that the device can be simulated on a computer. Tables are presented showing the masses of the oscillating components and key dimensions needed for modeling purposes. Graphs are used to indicate the spring rate of the diaphragms used to separate the helium of the working and bounce space from the hydraulic fluid.

Schreiber, Jeffrey G.↗

NASA NTRS1987

Control design challenges of large space systems and spacecraft control laboratory experiment (SCOLE)

The quick suppression of the structural vibrations excited by bang-bang (BB) type time-optional slew maneuvers via modal-dashpot design of velocity output feedback control was investigated. Simulation studies were conducted, and modal dashpots were designed for the SCOLE flexible body dynamics. A two-stage approach was proposed for rapid slewing and precision pointing/retargeting of large, flexible space systems: (1) slew the whole system like a rigid body in a minimum time under specified limits on the control moments and forces, and (2) damp out the excited structural vibrations afterwards. This approach was found promising. High-power modal/dashpots can suppress very large vibrations, and can add a desirable amount of active damping to modeled modes. Unmodeled modes can also receive some concomitant active damping, as a benefit of spillover. Results also show that not all BB type rapid pointing maneuvers will excite large structural vibrations. When properly selected small forces (e.g., vernier thrusters) are used to complete the specified slew maneuver in the shortest time, even BB-type maneuvers will excite only small vibrations (e.g., 0.3 ft peak deflection for a 130 ft beam).

Lin, Jiguan Gene↗

NASA NTRS1988

Slewing and vibration control of the SCOLE

A discussion of Slewing and Vibration Control makes the following conclusions: (1) A 2-stage approach is feasible and promising for rapid slewing and precision pointing of SCOLE; (2) Not all bang-bang type of time-minimized slew maneuvers will excite large structural vibrations in SCOLE; and (3) Modal dashpots can be a concentrated high-power vibration control, as well as the usual diffuse (broadband, low-power (low-authority) control. The following recommendations are made: (1) Limit the magnitude of applied forces on reflector to either the 25-lb limit of vernier thrusters on the real Space Shuttle or the 150-lb level equivalent to the cold-gas jets of laboratory SCOLE; (2) to complete stage 2, add an integrated design of LQF/LTR (Linear-Quadratic-Gaussian/Loop-Transfer Recovery) and Modal Dashpots; and, (3) Validate the 2-stage approach using the SCOLE laboratory facility with a comprehensive sequence of integrated designs and experiments coupling nonlinear rigid-body motions with flexible-body dynamics.

Lin, Jiguan Gene↗

NASA NTRS1989

Simulation of flexible structures with impact: Experimental validation

The simulation of the dynamic behavior of flexible structures with impact, is experimentally and numerically investigated. A radially rotating flexible beam attached to a rigid shaft is considered. Both experimental and numerical studies are undertaken. Experimental studies how excellent agreement with simulation studies using both the momentum balance (coefficient of friction), and spring-dashpot (impact pair) models. The simulation studies are even capable of predicting the high-speed multiple impacts which occur due to structural flexibility and which are experimentally observed using high-speed video photography. The results of the studies show that a simple momentum balance (coefficient of restitution) method for simulating the impact is sufficiently accurate in predicting the dynamic behavior of the system for most engineering applications. The momentum balance method cannot simulate the impact force which develops during the contact duration, but is computationally very efficient. The spring-dashpot model is more difficult to develop and requires significantly larger computation time, but can simulate impact forces and stresses due to impact. The momentum balance (coefficient of restitution) method, although strictly not applicable to flexible bodies, has been shown to provide an accurate and computationally efficient method for simulating the dynamic behavior of flexible structures with impact when contact stresses are not needed.

Ulsoy, A. Galip↗

NASA NTRS1995

Robust stability of second-order systems

It has been shown recently how virtual passive controllers can be designed for second-order dynamic systems to achieve robust stability. The virtual controllers were visualized as systems made up of spring, mass and damping elements. In this paper, a new approach emphasizing on the notion of positive realness to the same second-order dynamic systems is used. Necessary and sufficient conditions for positive realness are presented for scalar spring-mass-dashpot systems. For multi-input multi-output systems, we show how a mass-spring-dashpot system can be made positive real by properly choosing its output variables. In particular, sufficient conditions are shown for the system without output velocity. Furthermore, if velocity cannot be measured then the system parameters must be precise to keep the system positive real. In practice, system parameters are not always constant and cannot be measured precisely. Therefore, in order to be useful positive real systems must be robust to some degrees. This can be achieved with the design presented in this paper.

Chuang, C.-H.↗

NASA NTRS1971

Dynamic responses of railroad car models to vertical and lateral rail inputs

Simplified dynamic models were applied in a study of vibration in a high-speed railroad car. The mathematical models used were a four-degree-of-freedom model for vertical responses to vertical rail inputs and a ten-degree-of-freedom model for lateral response to lateral or rolling (cross-level) inputs from the rails. Elastic properties of the passenger car body were represented by bending and torsion of a uniform beam. Rail-to-car (truck) suspensions were modeled as spring-mass-dashpot oscillators. Lateral spring nonlinearities approximating certain complicated truck mechanisms were introduced. The models were excited by displacement and, in some cases, velocity inputs from the rails by both deterministic (including sinusoidal) and random input functions. Results were obtained both in the frequency and time domains. Solutions in the time domain for the lateral model were obtained for a wide variety of transient and random inputs generated on-line by an analog computer. Variations in one of the damping properties of the lateral car suspension gave large fluctuations in response over a range of car speeds for a given input. This damping coefficient was significant in reducing lateral car responses that were higher for nonlinear springs for three different inputs.

Sewall, J. L.↗

NASA NTRS1972

Resonance-inert stabilization for space stations

An approach to stabilizing control systems is presented which structures controllers like passive mechanical systems. The controller is visualized as a structural part with a passive behavior similar to springs, dashpots, and masses. If such a controller is connected by a proper feedback arrangement, then a passive mechanical plant cannot upset stability, regardless of masses, resonances, and three-dimensional coupling. The concept of resonance-inert stabilization is explained by structuring the controller of a simple feedback loop. Reactive functions, connections, and matrices are defined and used in the stabilization concept. The realization of a possible Skylab control system is discussed and compared with the present design. This example demonstrates the applicability to three-dimensional problems with lagging controllers.

Vonpragenau, G. L.↗

NASA NTRS1973

Computer program for the load and trajectory analysis of two DOF bodies connected by an elastic tether: Users manual

The derivation of the differential equations of motion of a 3 Degrees of Freedom body joined to a 3 Degrees of Freedom body by an elastic tether. The tether is represented by a spring and dashpot in parallel. A computer program which integrates the equations of motion is also described. Although the derivation of the equations of motions are for a general system, the computer program is written for defining loads in large boosters recovered by parachutes.

Doyle, G. R., Jr.↗

NASA NTRS1974

Users manual: Dynamics of two bodies connected by an elastic tether, six degrees of freedom forebody and five degrees of freedom decelerator

The equations of motion and a computer program for the dynamics of a six degree of freedom body joined to a five degree of freedom body by a quasilinear elastic tether are presented. The forebody is assumed to be a completely general rigid body with six degrees of freedom; the decelerator is also assumed to be rigid, but with only five degrees of freedom (symmetric about its longitudinal axis). The tether is represented by a spring and dashpot in parallel, where the spring constant is a function of tether elongation. Lagrange's equation is used to derive the equations of motion with the Lagrange multiplier technique used to express the constraint provided by the tether. A computer program is included which provides a time history of the dynamics of both bodies and the tension in the tether.

Doyle, G. R., Jr.↗

NASA NTRS1975

Method for evaluating gravity effects in the testing of nutation dampers

A method is developed for determining the effect of gravity in the testing of nutation dampers on symmetric single or dual spin satellites. The basic theory is developed and then applied to the partially filled viscous ring damper and the spring-mass-dashpot damper. A comparison with test results for the viscous ring damper is also given.-

Alfriend, K. T.↗