SEARCH · Engineering Papers

Results for “loading frequency”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17

All sources NASA NTRS DOE OSTI

NASA NTRS1970

The dynamic characteristics of a turbo-rotor simulator supported on gas-lubricated foil bearings. Part 2: Operation with heating and thermal gradients

A high speed rotor, supported by gas-lubricated foil bearings, is free from self-excited whirl and displays no loss of load capacity when vibrated at frequency equal to the rotational speed. It is demonstrated that in addition to tolerance of geometrical imperfections, misalignment and foreign particles, the foil bearing performs well at elevated temperatures and accommodates appreciable temperature gradients. The foil bearing is endowed with superior wipe-wear characteristics and the flexibility of the foil accounts not only for the stability of the foil bearing, but also for its accommodation of, and compensation for, distortion, contamination, and contact.

Licht, L.↗

NASA NTRS1974

Investigation of fatigue strength of multilayer advanced fiber composites

The analytical characterization of a multilayer fiber composite plate (without hole) was accomplished for both static and dynamic loading conditions using the finite difference technique. Thornel 300/5208 composites with and without holes were subjected to static and tensile fatigue testing. Five (5) fiber orientations were submitted to test. Tensile fatigue testing also included three (3) loading conditions and two (2) frequencies. The low-cycle test specimens demonstrated a shorter tensile fatigue life than the high-cycle test specimens. Failure surfaces demonstrated effect of testing conditions. Secondary failure mechanisms, such as: delamination, fiber breakage, and edge fiber delamination were present. Longitudinal delamination between plies also occurred in these specimens.

Thornton, H. R.↗

NASA NTRS1974

Fractional watt Vuillemier cryogenic refrigerator program engineering notebook. Volume 2: Stress analysis

A structural analysis performed on the 1/4-watt cryogenic refrigerator. The analysis covered the complete assembly except for the cooling jacket and mounting brackets. Maximum stresses, margin of safety, and natural frequencies were calculated for structurally loaded refrigerator components shown in assembly drawings. The stress analysis indicates that the design is satisfactory for the specified vibration environment, and the proof, burst, and normal operating loads.

Miller, W. S.↗

NASA NTRS1979

PEP solar array definition study

The conceptual design of a large, flexible, lightweight solar array is presented focusing on a solar array overview assessment, solar array blanket definition, structural-mechanical systems definition, and launch/reentry blanket protection features. The overview assessment includes a requirements and constraints review, the thermal environment assessment on the design selection, an evaluation of blanket integration sequence, a conceptual blanket/harness design, and a hot spot analysis considering the effects of shadowing and cell failures on overall array reliability. The solar array blanket definition includes the substrate design, hinge designs and blanket/harness flexibility assessment. The structural/mechanical systems definition includes an overall loads and deflection assessment, a frequency analysis of the deployed assembly, a components weights estimate, design of the blanket housing and tensioning mechanism. The launch/reentry blanket protection task includes assessment of solar cell/cover glass cushioning concepts during ascent and reentry flight condition.

Source record↗

NASA NTRS1980

Noise due to tip vortex formation on lifting rotors

The high frequency broadband noise radiated by the local separated flow at rotor blade tips is analyzed. The aeroacoustic model is based on the convection of the tip region's separated flow pressure fluctuations past the trailing edge of the blade. The tip vortex formation and separation are modeled from available experimental studies. The separated flow pressure fluctuations are estimated using available separated flow experimental data and correlations. The trailing edge noise was approximated using a point dipole model. The point dipole strengths were evaluated by a method based on the trailing edge noise theory of Amiet. The point dipole approach compares favorably to stationary airfoil trailing edge noise analyses and experiments except near the plane of the airfoil. The rotor tip separation noise results are compared to other noise mechanism calculations and to experiments. The tip noise mechanism is shown to be quite important in the high frequency range. It is likely to be the major contributor to high frequency broadband noise for heavily loaded rotors with low turbulence inflow.

George, A. R.↗

NASA NTRS1981

DSS 14 64-meter antenna. Computed RF pathlength changes under gravity loadings

Using a computer model of the reflector structure and its supporting assembly of the 64-m antenna rotating about the elevation axis, the radio frequency (RF) pathlengths changes resulting from gravity loadings were computed. A check on the computed values was made by comparing the computed foci offsets with actual field readings of the Z or axial focussing required for elevation angle changes.

Katow, M. S.↗

NASA NTRS1981

Coal/rock interface detection by sensitized pick, part A

In order to increase the operating margins of the detector for safe, reliable operation under difficult in-mine conditions the transmitted signal strength was increased to provide additional signal margin for in-mine conditions and the transmitter section was redesigned to reduce frequency pulling of the transmitter frequency with variations in antenna load. The linearity of the pick load SCO signal with true pick load was increased, and hysteresis effects were minimized. The sensitized pick hardware was ruggedized for rough inmine use. The sensitized pick and telemetry system provided excellent, high quality signals proportional to cutting load under all conditions experienced during testing.

Wu, P. T. K.↗

NASA NTRS1983

Static versus dynamic loads as an influence on bone remodelling

Bone remodelling activity in the avian ulna was assessed under conditions of disuse alone, disuse with a superimposed continuous compressive load, and disuse interrupted by a short daily period of intermittent loading. The ulna preparation is made by two submetaphyseal osteotomies, the cut ends of the bone being covered with stainless steel caps which, together with the bone they enclosed, are pierced by pins emerging transcutaneously on the dorsal and ventral surfaces of the wing. The 110 mm long undisturbed section of the bone shaft can be protected from functional loading, loaded continuously in compression by joining the pins with springs, or loaded intermittently in compression by engaging the pins in an Instron machine. Similar loads (525 n) were used in both static and dynamic cases engendering similar peak strains at the bone's midshaft (-2000 x 10-6). The intermitent load was applied at a frequency of 1 Hz during a single 100 second period per day as a ramped square wave, with a rate of change of strain during the ramp of 0.01 per second.

Lanyon, L. E.↗

NASA NTRS1990

Minimum Weight Design of a Leaf Spring Tapered in Thickness and Width for the Hubble Space Telescope-Space Support Equipment

A linear elastic solution to the problem of minimum weight design of cantilever beams with variable width and depth is presented. The solution shown is for the specific application of the Hubble Space Telescope maintenance mission hardware. During these maintenance missions, delicate instruments must be isolated from the potentially damaging vibration environment of the space shuttle cargo bay during the ascent and descent phases. The leaf springs are designed to maintain the isolation system natural frequency at a level where load transmission to the instruments in a minimum. Nonlinear programming is used for the optimization process. The weight of the beams is the objective function with the deflection and allowable bending stress as the constraint equations. The design variables are the width and depth of the beams at both the free and the fixed ends.

Rodriguez, P. I.↗

NASA NTRS1992

Optical Link For Readout From Focal-Plane Array

Outputs of photodetectors modulate beam of light. Proposed optical link carries analog readout signals from photodetectors in focal-plane array to external signal-processing circuitry. Insensitive to electromagnetic interference at suboptical frequencies, and imposes smaller heat load on cryogenic apparatus because it does not include high-power electronic amplifier or laser transmitter within cold chamber.

Fossum, Eric R.↗

NASA NTRS1992

Modal Test/Analysis Correlation of Space Station Structures Using Nonlinear Sensitivity

The modal correlation problem is formulated as a constrained optimization problem for validation of finite element models (FEM's). For large-scale structural applications, a pragmatic procedure for substructuring, model verification, and system integration is described to achieve effective modal correlation. The space station substructure FEM's are reduced using Lanczos vectors and integrated into a system FEM using Craig-Bampton component modal synthesis. The optimization code is interfaced with MSC/NASTRAN to solve the problem of modal test/analysis correlation; that is, the problem of validating FEM's for launch and on-orbit coupled loads analysis against experimentally observed frequencies and mode shapes. An iterative perturbation algorithm is derived and implemented to update nonlinear sensitivity (derivatives of eigenvalues and eigenvectors) during optimizer iterations, which reduced the number of finite element analyses.

Gupta, Viney K.↗

NASA NTRS1992

Tilt rotor hover aeroacoustics

The methodology, results, and conclusions of a study of tilt rotor hover aeroacoustics and aerodynamics are presented. Flow visualization and hot wire velocity measurement were performed on a 1/12-scale model of the XV-15 Tilt Rotor Aircraft in hover. The wing and fuselage below the rotor cause a complex recirculating flow. Results indicate the physical dimensions and details of the flow including the relative unsteadiness and turbulence characteristics of the flow. Discrete frequency harmonic thickness and the loading noise mechanism were predicted using WOPWOP for the standard metal blades and the Advanced Technology Blades. The recirculating flow created by the wing below the rotor is a primary sound mechanism for a hovering tilt rotor. The effects of dynamic blade response should be included for fountain flow conditions which produce impulsive blade loading. Broadband noise mechanisms were studied using Amiet's method with azimuthally varying turbulence characteristics derived from the measurements. The recirculating fountain flow with high turbulence levels in the recirculating zone is the dominant source of broadband noise for a hovering rotor. It is shown that tilt rotor hover aeroacoustic noise mechanisms are now understood. Noise predictions can be made based on reasonably accurate aerodynamic models developed here.

Coffen, Charles David↗

NASA NTRS1992

Modal test/analysis correlation of Space Station structures using nonlinear sensitivity

The modal correlation problem is formulated as a constrained optimization problem for validation of finite element models (FEM's). For large-scale structural applications, a pragmatic procedure for substructuring, model verification, and system integration is described to achieve effective modal correlations. The space station substructure FEM's are reduced using Lanczos vectors and integrated into a system FEM using Craig-Bampton component modal synthesis. The optimization code is interfaced with MSC/NASTRAN to solve the problem of modal test/analysis correlation; that is, the problem of validating FEM's for launch and on-orbit coupled loads analysis against experimentally observed frequencies and mode shapes. An iterative perturbation algorithm is derived and implemented to update nonlinear sensitivity (derivatives of eigenvalues and eigenvectors) during optimizer iterations, which reduced the number of finite element analyses.

Gupta, Viney K.↗

NASA NTRS1995

PC Software graphics tool for conceptual design of space/planetary electrical power systems

This paper describes the Decision Support System (DSS), a personal computer software graphics tool for designing conceptual space and/or planetary electrical power systems. By using the DSS, users can obtain desirable system design and operating parameters, such as system weight, electrical distribution efficiency, and bus power. With this tool, a large-scale specific power system was designed in a matter of days. It is an excellent tool to help designers make tradeoffs between system components, hardware architectures, and operation parameters in the early stages of the design cycle. The DSS is a user-friendly, menu-driven tool with online help and a custom graphical user interface. An example design and results are illustrated for a typical space power system with multiple types of power sources, frequencies, energy storage systems, and loads.

Truong, Long V.↗

NASA NTRS1996

Full scale GLARE fuselage panel tests

A GLARE fuselage panel, representative of the crown section of the Fokker 100 fuselage in front of the wing, was tested. The panels were loaded by air pressure resulting in tangential stress in the panel by axial loading, representative of both the cabin pressure and the fuselage bending due to taxiing and gust loading. A fatigue test, simulating 180000 flights, followed by static tests were performed. The panel was loaded to failure at 1.32 ultimate load. The test set-up, the uniform strain distribution of the panel, and the fatigue loads applied at high test frequency are described. The use of GLARE leads to a substantial weight reduction without affecting the fatigue static strength.

Vercammen, Roland W. A.↗

NASA NTRS1994

Integrated Tail Buffet Loads on the F/A-18

The unsteady pressures acting on the vertical tails of a full-scale F/A-18 fighter aircraft were studied to gain a better understanding of tail-buffet loads that frequently occur on fighter aircraft operating at high angles-of-attack. Data for the study were acquired during two test entries in the 80- by 120-Foot Wind Tunnel wherein the aircraft was tested at wind speeds up to 100 knots and at angles-of-attack from 20deg to 40deg. For the purposes of this paper, the primary difference between the two tests is that, during the first wind-tunnel entry, the pressure transducers were more sparsely spaced and covered less of the fin than during the second entry. In addition to a brief description of the spectral analysis methods used for the unsteady aerodynamic pressures and loads, an analysis of the effects of sensor density on estimating integrated loads is presented. It was found that the integrated loads determined from sparse sensor arrays are significantly higher than actual loads. However, a modest increase in the number of sensors can greatly reduce the error and a method for correcting load estimates from sparse sensor arrays is also suggested. The results for the time-averaged, power-spectral analysis are then presented for the tail-fin bending moments. Power spectra are presented for the aircraft at zero sideslip over an angle-of-attack range from 20deg to 40deg and for the aircraft at an angle-of-attack of 30deg over a sideslip range from -16deg to 16deg. Since the aircraft was equipped with a removable leading-edge extension (LEX) fence to reduce tail-buffet loads, the tail-fin bending moment loads are also presented for that configuration. The LEX fence is shown to significantly reduce bending moment loads over a broad range frequencies, for all the aircraft attitudes presented.

Meyn, Larry A.↗

NASA NTRS2002

Methodology of Blade Unsteady Pressure Measurement in the NASA Transonic Flutter Cascade

In this report the methodology adopted to measure unsteady pressures on blade surfaces in the NASA Transonic Flutter Cascade under conditions of simulated blade flutter is described. The previous work done in this cascade reported that the oscillating cascade produced waves, which for some interblade phase angles reflected off the wind tunnel walls back into the cascade, interfered with the cascade unsteady aerodynamics, and contaminated the acquired data. To alleviate the problems with data contamination due to the back wall interference, a method of influence coefficients was selected for the future unsteady work in this cascade. In this approach only one blade in the cascade is oscillated at a time. The majority of the report is concerned with the experimental technique used and the experimental data generated in the facility. The report presents a list of all test conditions for the small amplitude of blade oscillations, and shows examples of some of the results achieved. The report does not discuss data analysis procedures like ensemble averaging, frequency analysis, and unsteady blade loading diagrams reconstructed using the influence coefficient method. Finally, the report presents the lessons learned from this phase of the experimental effort, and suggests the improvements and directions of the experimental work for tests to be carried out for large oscillation amplitudes.

Lepicovsky, J.↗

NASA NTRS2006

Structural Analysis and Test Comparison of a 20-Meter Inflation-Deployed Solar Sail

Under the direction of the NASA In-Space Propulsion Technology Office, the team of L Garde, NASA Jet Propulsion Laboratory, Ball Aerospace, and NASA Langley Research Center has been developing a scalable solar sail configuration to address NASA s future space propulsion needs. Prior to a flight experiment of a full-scale solar sail, a comprehensive test program was implemented to advance the technology readiness level of the solar sail design. These tests consisted of solar sail component, subsystem, and sub-scale system ground tests that simulated the aspects of the space environment such as vacuum and thermal conditions. In July 2005, a 20-m four-quadrant solar sail system test article was tested in the NASA Glenn Research Center s Space Power Facility to measure its static and dynamic structural responses. Key to the maturation of solar sail technology is the development of validated finite element analysis (FEA) models that can be used for design and analysis of solar sails. A major objective of the program was to utilize the test data to validate the FEA models simulating the solar sail ground tests. The FEA software, ABAQUS, was used to perform the structural analyses to simulate the ground tests performed on the 20-m solar sail test article. This paper presents the details of the FEA modeling, the structural analyses simulating the ground tests, and a comparison of the pretest and post-test analysis predictions with the ground test results for the 20-m solar sail system test article. The structural responses that are compared in the paper include load-deflection curves and natural frequencies for the beam structural assembly and static shape, natural frequencies, and mode shapes for the solar sail membrane. The analysis predictions were in reasonable agreement with the test data. Factors that precluded better correlation of the analyses and the tests were unmeasured initial conditions in the test set-up.

Sleight, David W.↗