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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Use of asymptotic methods in vibration analysis

The derivation of dynamic differential equations, suitable for studying the vibrations of rotating, curved, slender structures was examined, and the Hamiltonian procedure was advocated for this purpose. Various reductions of the full system are displayed, which govern the vibrating troposkien when various order of magnitude restrictions are placed on important parameters. Possible advantages of the WKB asymptotic method for solving these classes of problems are discussed. A special case of this method is used illustratively to calculate eigenvalues and eigenfunctions for a flat turbine blade with small flexural stiffness.

Ashley, H.↗
NASA NTRS1976

Real eigenvalue analysis in NASTRAN by the tridiagonal reduction (FEER) method

Implementation of the tridiagonal reduction method for real eigenvalue extraction in structural vibration and buckling problems is described. The basic concepts underlying the method are summarized and special features, such as the computation of error bounds and default modes of operation are discussed. In addition, the new user information and error messages and optional diagnostic output relating to the tridiagonal reduction method are presented. Some numerical results and initial experiences relating to usage in the NASTRAN environment are provided, including comparisons with other existing NASTRAN eigenvalue methods.

Newman, M.↗
NASA NTRS1981

Thermal design of the Space Shuttle External Tank

The history of the engineering and manufacturing requirements leading to the final Thermal Protection System (TPS) for the External Tank (ET) is presented. The thermal design for the ET must be optimized, based on considerations of cost, weight, and application of the TPS. The significant thermal requirements include the structural and component temperature limits, the propellant quality, the minimization of ice and frost, no air liquefaction, and no film boiling. The TPS materials selected to meet the requirements are a low density closed cell foam (CPR-488) and two light-weight ablators (SLA-56 and MA-25s). The first four flights of the Space Shuttle (1981) will measure and evaluate external environmental, structural, propulsion, electrical, and engine performance data. The ET will be instrumented to measure acoustics, pressures, heat transfer, vibration, temperatures, and structural strains. TPS weight reductions are planned for future ETs through the use of a comprehensive thermal instrumentation system.

Warmbrod, J. D.↗
NASA NTRS1993

Noise control in aeroacoustics; Proceedings of the 1993 National Conference on Noise Control Engineering, NOISE-CON 93, Williamsburg, VA, May 2-5, 1993

In the conference over 100 papers were presented in eight sessions: (1) Emission: Noise Sources; (2) Physical Phenomena; (3) Noise ControlElements; (4) Vibration and Shock: Generation, Transmission, Isolation, and Reduction; (5) Immission: Physical Aspects of Environmental Noise; (6) Immission: Effects of Noise; (7) Analysis; and (8) Requirements. In addition, the distinguished lecture series included presentations on the High Speed Civil Transport and on research from the United Kingdom on aircraft noise effects.

Hubbard, Harvey H.↗
NASA NTRS2009

Wind Tunnel Test of the SMART Active Flap Rotor

Boeing and a team from Air Force, NASA, Army, DARPA, MIT, UCLA, and U. of Maryland have successfully completed a wind-tunnel test of the smart material actuated rotor technology (SMART) rotor in the 40- by 80-foot wind-tunnel of the National Full-Scale Aerodynamic Complex at NASA Ames Research Center. The Boeing SMART rotor is a full-scale, five-bladed bearingless MD 900 helicopter rotor modified with a piezoelectric-actuated trailing edge flap on each blade. The eleven-week test program evaluated the forward flight characteristics of the active-flap rotor at speeds up to 155 knots, gathered data to validate state-of-the-art codes for rotor aero-acoustic analysis, and quantified the effects of open and closed loop active flap control on rotor loads, noise, and performance. The test demonstrated on-blade smart material control of flaps on a full-scale rotor for the first time in a wind tunnel. The effectiveness of the active flap control on noise and vibration was conclusively demonstrated. Results showed significant reductions up to 6dB in blade-vortex-interaction and in-plane noise, as well as reductions in vibratory hub loads up to 80%. Trailing-edge flap deflections were controlled within 0.1 degrees of the commanded value. The impact of the active flap on control power, rotor smoothing, and performance was also demonstrated. Finally, the reliability of the flap actuation system was successfully proven in more than 60 hours of wind-tunnel testing.

Straub, Friedrich K.↗
NASA NTRS2013

High-Powered, Ultrasonically Assisted Thermal Stir Welding

This method is a solid-state weld process capable of joining metallic alloys without melting. The weld workpieces to be joined by thermal stir welding (TSW) are drawn, by heavy forces, between containment plates past the TSW stir tool that then causes joining of the weld workpiece. TSW is similar to friction stir welding (FSW) in that material is heated into a plastic state (not melted) and stirred using a stir rod. The FSW pin tool is an integrated geometrical structure consisting of a large-diameter shoulder, and a smaller-diameter stir pin protruding from the shoulder. When the pin is plunged into a weld workpiece, the shoulder spins on the surface of the weld workpiece, thus inducing frictional heat into the part. The pin stirs the fraying surfaces of the weld joint, thus joining the weld workpiece into one structure. The shoulder and stir pin of the FSW pin tool must rotate together at a desired rotational speed. The induced frictional energy control and stir pin control of the pin tool cannot be de-coupled. The two work as one integrated unit. TSW, on the other hand, de-couples the heating and stirring of FSW, and allows for independent control of each process element. A uniquely designed induction coil heats the weld workpiece to a desired temperature, and once heated, the part moves into a stir rod whose RPM is also independently controlled. As the weld workpiece moves into the stir rod, the piece is positioned, or sandwiched, between upper and lower containment plates. The plate squeezes together, thus compressing the upper and lower surfaces of the weld workpiece. This compressive force, also called consolidation force, consolidates the plastic material within the weld nugget material as it is being stirred by the stir rod. The stir rod is positioned through the center of the top containment plate and protrudes midway through the opposite lower containment plate where it is mechanically captured. The upper and lower containment plates are separated by a distance equal to the thickness of the material being welded. The TSW process can be significantly improved by reducing the draw forces. This can be achieved by reducing the friction forces between the weld workpieces and the containment plates. High-power ultrasonic (HPU) vibrations of the containment plates achieve friction reduction in the TSW process. Furthermore, integration of the HPU energy into the TSW stir rod can increase tool life of the stir rod, and can reduce shear forces to which the stir rod is subjected during the welding process. TSW has been used to successfully join 0.500-in (≈13-mm) thick commercially pure (CP) titanium, titanium 6AL- 4V, and titanium 6AL-4V ELI in weld joint lengths up to 9 ft (≈2.75-m) long. In addition, the TSW process was used to fabricate a sub-scale hexagonally shaped gun turret component for the U.S. Navy. The turret is comprised of six 0.5000-in (≈13-mm) thick angled welds. Each angled weld joint was prepared by machining the mating surfaces to 120deg. The angled weld joint was then fixtured using an upper and lower containment plate of the same geometry of the angled weld joint. The weld joint was then stirred by the stir rod as it and the upper and lower containment plates traverse through the angled joint prep.

Ding, Robert↗
NASA NTRS1983

Application of stiffened cylinder analysis to ATP interior noise studies

An analytical model developed to predict the interior noise of propeller driven aircraft was applied to experimental configurations for a Fairchild Swearingen Metro II fuselage exposed to simulated propeller excitation. The floor structure of the test fuselage was of unusual construction - mounted on air springs. As a consequence, the analytical model was extended to include a floor treatment transmission coefficient which could be used to describe vibration attenuation through the mounts. Good agreement was obtained between measured and predicted noise reductions when the foor treatment transmission loss was about 20 dB - a value which is consistent with the vibration attenuation provided by the mounts. The analytical model was also adapted to allow the prediction of noise reductions associated with boundary layer excitation as well as propeller and reverberant noise.

Wilby, E. G.↗
NASA NTRS1992

Active control of interior noise in a large scale cylinder using piezoelectric actuators

The noise reduction effectiveness of two types of control force actuator models has been analytically investigated: (1) a point actuator, and (2) an in-plane, piezoelectric actuator. The actuators were attached to the wall of a simply supported, elastic cylinder closed with rigid end caps. Control inputs to the actuators were determined such that the integrated square of the pressure over the interior of the vibrating cylinder was a minimum. Significant interior noise reductions were achieved for all actuator configurations, but especially for the structurally dominated response. Noise reduction of 9 dB to 26 dB were achieved using point force actuators, as well as localized and extended piezoelectric actuators. Control spillover was found to limit overall performance for all cases. However, the use of extended piezoelectric actuators was effective in reducing control spillover, without increasing the number of control degrees of freedom.

Lester, H. C.↗
NASA NTRS1991

Active control of interior noise in a large scale cylinder using piezoelectric actuators

The noise reduction effectiveness of two types of control force actuator models has been analytically investigated: (1) a point actuator, and (2) an in-plane, piezoelectric actuator. The actuators were attached to the wall of a simply supported, elastic cylinder closed with rigid end caps. Control inputs to the actuators were determined such that the integrated square of the pressure over the interior of the vibrating cylinder was a minimum. Significant interior noise reductions were achieved for all actuator configurations, but especially for the structurally dominated response. Noise reduction of 9 dB to 26 dB were achieved using point force actuators, as well as localized and extended piezoelectric actuators. Control spillover was found to limit overall performance for all cases. However, the use of extended piezoelectric actuators was effective in reducing control spillover, without increasing the number of control degrees of freedom.

Lester, H. C.↗
NASA NTRS1966

Air bearing analysis

Numerical analysis of air bearing system to reduce high frequency noise from vertical vibrations

NUMERICAL ANALYSIS↗
NASA NTRS1984

Helicopter individual-blade-control and its applications

A new, advanced type of active control for helicopters and its applications are described. The system, based on previously developed M.I.T. Individual-Blade-Control hardware, employs blade-mounted accelerometers to sense blade motion and feeds back information to control blade pitch in such a manner as to reduce the response of selected blade modes. A linear model of the blade and control system dynamics is used to give guidance in the design process as well as to aid in analysis of experimental results. System performance in wind tunnel tests is described, and evidence is given of the system's ability to provide substantial reduction in blade modal responses, including blade bending vibration.

Ham, N. D.↗
NASA NTRS2004

Reduced Order Methods for Prediction of Thermal-Acoustic Fatigue

The goal of this investigation is to assess the quality of high-cycle-fatigue life estimation via a reduced order method, for structures undergoing random nonlinear vibrations in a presence of thermal loading. Modal reduction is performed with several different suites of basis functions. After numerically solving the reduced order system equations of motion, the physical displacement time history is obtained by an inverse transformation and stresses are recovered. Stress ranges obtained through the rainflow counting procedure are used in a linear damage accumulation method to yield fatigue estimates. Fatigue life estimates obtained using various basis functions in the reduced order method are compared with those obtained from numerical simulation in physical degrees-of-freedom.

Przekop, A.↗
NASA NTRS1960

Some Measurements of Noise Transmission and Stress Response of a 0.020-Inch Duralumin Panel in the Presence of Air Flow

Noise transmission measurements were made for a 0.020-inch panel with and without air flow on its surface. Tests were conducted with both an absorbent and reverberant chamber behind the panel. Panel stresses for some of these tests were also determined. Noise spectra obtained inside the absorbent chamber with flow attached and flow not attached to the panel appeared to contain several peaks corresponding in frequency to panel vibration modes. These peaks were notably absent when the chamber was reverberant. The noise reduction through the test panel measured with the aid of an absorbent chamber for the flow-not-attached case is in general agreement with values predicted by the theoretical weight law, which assumes negligible panel stiffness. Corresponding data for the flow-attached case do not follow the weight law but rather indicate less noise reduction at the high frequencies. The main stress responses of the panel without air flow occurred at its fundamental vibration mode. In the presence of air flow the main response occurs in a vibration mode having a node line perpendicular to the direction of air flow.

Kantarges, George T.↗
NASA NTRS2015

SMART Rotor Wind Tunnel Test Report

The Boeing Company, Mesa Arizona, has been developing smart material actuated rotor technology (SMART) under in-house, DARPA (Defense Advanced Research Projects Agency), NASA and Army funding. A whirl tower test of the SMART active flap rotor system was successfully conducted at the remote test facility (RTF) in Mesa, Arizona, in 2003. Under DARPA and NASA funding, the SMART rotor system was tested in the NASA Ames National Full Scale Aerodynamic Complex (NFAC) 40- by 80-Foot Wind Tunnel in 2008. The DARPA program objectives were to demonstrate the active flap impact on rotor acoustics in forward flight and establish a validation database for noise prediction tools. Under NASA funding, additional wind tunnel tests were conducted, with the objective to demonstrate and quantify vibration, noise, and performance improvements.Wind tunnel testing was successfully and safely concluded, meeting all high priority objectives. The authority, effectiveness, and reliability of the flap actuation system were demonstrated in 65 hours of testing at up to 155 knots and 7,700 pound thrust. Validation data was successfully acquired for four test conditions; blade loads were too high for the high speed condition. The effectiveness of the flap for noise and vibration control was demonstrated conclusively, with results showing significant reductions in BVI (Blade-Vortex Interaction) and in-plane noise as well as vibratory hub loads. The impact of the flap on control power and rotor smoothing was also demonstrated. Data evaluating any benefits in aerodynamic performance and impact on flight controls were acquired, but will need more detailed evaluation. Both open loop control and closed loop feedback control, using continuous time and higher harmonic controllers, were applied.The purpose of the Test Report is to provide a comprehensive document that describes the preparation for and conduct of the wind tunnel test and summarizes the processing and evaluation of wind tunnel test data for the DARPA and the NASA portion of the test. An overview of the wind tunnel test and results can be found in Reference 1. Details on the testing and results for BVI noise, in-plane noise, and vibrations can be found in References 2-4, respectively. These references are four papers, presented at the American Helicopter Society Annual Forum in 2009. A brief description of the delivered electronic data is provided in Reference 5.

Rotor↗
NASA NTRS1996

Active Vibration Isolation of Microgravity Experiments with Spring Umbilicals Using an Electrodynamic Actuator

Microgravity experiments will require active vibration isolation in the low to mid frequency range of 0.1 Hz to 10 Hz. Approximately two orders of acceleration reduction (40 dB) will be required. Previous works have reported results for accelerations transmitted through the umbilical. This paper describes experimental and theoretical results for vibration isolation in one dimension (horizontal) where the simulated experiment is connected to the spacecraft by a spring umbilical. The experiment consisted of a spacecraft (shaker), experiment (mass), umbilical, accelerometer, control electronics, and Lorentz actuator. The experiment mass was supported in magnetic bearings to avoid any stiction problems. Acceleration feedback control was employed to obtain the vibration isolation. Three different spring umbilicals were employed. Acceleration reductions on the order of 40 dB were obtained over the frequency range of 0.1 Hz to 10 Hz. Good agreement was obtained between theory and experiment.

Banerjee, B. B.↗
NASA NTRS1978

Helicopter internal noise reduction research and development application to the SA 360 and SA 365 Dauphin

Noise sources inside helicopter cabins are considered with emphasis on the mechanisms of vibration generation inside the main gear box and mechanisms of transmission between source and cabin. The dynamic behavior of the main gear box components is examined in relation to the transfer of vibration energy to the structure. It is indicated that although improvements can be made in noise reduction at the source, a soundproofing treatment isolating the passenger from the noise source is necessary. Soundproofing treatments installed and optimized include: (1) an acoustic screen using the weight effect to isolate the passenger from the noise source; (2) a damping treatment to limit the conversion of the vibratory energy into acoustic energy; and (3) an absorbing treatment achieved either through HELMHOLTZ resonators or through a glass wool blanket to limit the propagation of acoustic waves and the wave reflection effects in the cabin. The application of treatments at the source and the optimization of the sound barriers improved the noise level by about 30 db.

Marze, H. J.↗
NASA NTRS1994

Low-Noise Spiral Bevel Gears

Modified spiral bevel gears that generate relatively little noise and vibration designed and fabricated for use in U.S. Army OH-58D helicopter. Noise reduced by 12 to 19 dB. Similar low-noise, low-vibration spiral bevel gears used in other helicopters, with consequent benefits in comfort and health of pilots and passengers, enhancement of pilots' performance and safety through reduction of audible distraction, and reduction in cost and weight of helicopters through reduction in amount of sound-proofing material. Low-noise, low-vibration spiral bevel gears also used in drive axles of cars and trucks for smoother, quieter rides.

Lewicki, David G.↗