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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Finite Element Based Model of Fiber-optic Strain Sensor Mounted on a Semi-monocoque Structure

Fiber-optic strain sensing (FOSS) provides an opportunity for additional awareness and can enable other mitigations such as flutter suppression or gust load alleviation but requires an accurate computational model as part of a design process that integrates structures and controls. A modeling approach for fiber-optic strain sensors has been developed using a shell element formulation in a detailed finite element model. The new FOSS modeling approach is designed to better scale to more complex realistic structures and fiber layouts than previous approaches. The modeling method was applied to the X-56A vehicle and results were compared to experimental static ground-test data. Additionally, the experimental sensor noise of these fiber optic sensors was assessed for the correlations in time and correlations along the fiber. The noise does show significant correlations both in time and along the fibers. These correlations of the noise should also be considered in modeling and assessing algorithms that will use FOSS.

Jeffrey Ouellette↗
NASA NTRSDate not supplied

Finite Element Based Model of Fiber-optic Strain Sensor Mounted on a Semi-monocoque Structure

Fiber-optic strain sensing (FOSS) provides an opportunity for additional awareness and can enable other mitigations such as flutter suppression or gust load alleviation but requires an accurate computational model as part of a design process that integrates structures and controls. A modeling approach for fiber-optic strain sensors has been developed using a shell element formulation in a detailed finite element model. The new FOSS modeling approach is designed to better scale to more complex realistic structures and fiber layouts than previous approaches. The modeling method was applied to the X-56A vehicle and results were compared to experimental static ground-test data. Additionally, the experimental sensor noise of these fiber optic sensors was assessed for the correlations in time and correlations along the fiber. The noise does show significant correlations both in time and along the fibers. These correlations of the noise should also be considered in modeling and assessing algorithms that will use FOSS.

Jeffrey Ouellette↗
NASA NTRS1984

Effect of airfoil mean loading on convected gust interaction noise

The present theoretical model for noise generation when a convected vortical or entropic gust encounters an airfoil at a nonzero angle-of-attack is based on a linearization of the Euler equations for the steady, subsonic flow past the airfoil. Noise generation is found to be concentrated at local regions which scale on the gust wavelength and are present at airfoil leading and trailing edges. Steady loading of the airfoil affects noise generation at the leading and trailing edges in significantly different ways. Parametric calculations are presented which illustrate that, at high frequencies, moderate levels of airfoil steady loading can drastically increase the noise level produced by airfoil-convected gust interactions.

Myers, M. R.↗
NASA NTRS1972

Load relief and gust alleviation control study

The results of a study are presented in which a computerized optimal control techique was applied to the synthesis of a load relief control system for an advanced Saturn 5 derivative launch vehicle. This technique included selection of a load relief control law and computerized optimization of the controller gain schedules for a set of preselected adverse synthetic wind speed profiles. The gain optimization was effected using a hybrid optimizer program to minimize (optimize) a direct performance functional which specified the design goal (load relief) in engineering terms (explicit representation of maximum bending moments).

Vieweg, R. R.↗
NASA NTRS1986

Influence of airfoil mean loading on convected gust interaction noise

A theoretical model is developed for the noise generated when a convected vortical or entropic gust encounters an airfoil at nonzero angle of attack. The analysis is based on Rapid Distortion Theory. High frequency gusts, whose wavelengths are short compared to the airfoil chord, are considered. The noise generation is shown to be concentrated near the airfoil leading edge. The level of the generated noise is increased by airfoil mean loading, with the appropriate scaling parameter being the local leading edge incidence angle. The trailing edge simply scatters the leading edge sound field, and here the mean loading effects scale on the airfoil total lift. Calculations are presented which illustrate that, at high frequencies, moderate levels of airfoil steady loading can dramatically increase the noise produced by airfoil convected gust interactions.

Kerschen, E. J.↗
NASA NTRS1987

A parametric study of mean loading effects on airfoil gust interaction noise

The influence of airfoil mean loading parameters on the sound generated by interaction with short wavelength vorticity and entropy gusts is examined. It is found that there are two mean flow parameters of importance, the effective leading edge incidence angle and the airfoil lift coefficient. The former controls the total sound power level, while the latter has an important effect on the directivity pattern. For vorticity gusts, positive gust angles result in noise levels which increase with leading edge loading (LEL), while for negative gust angles an increase in LEL may actually reduce the noise level. For low levels of LEL, entropy gusts generate less sound than vorticity gusts, while for larger values of LEL, entropy gusts are at least as important as vorticity gusts.

Kerschen, E. J.↗
NASA NTRS1956

An investigation of the loads on the vertical tail of a jet-bomber airplane resulting from flight through rough air

Vertical-tail loads were measured in turbulent air on a four-engine jet bomber. Results showed large load oscillations which were lightly damped. Comparison of experimental results with discrete-load calculations indicated that discrete-gust calculations underestimated the loads by 30 to 40 percent and gave no indication of the low damping. Power spectral analysis, on the other hand, indicated the general frequency characteristics and gave a somewhat better estimate of the peak-load distributions. The present results strongly suggest that discrete-gust calculation for gust loads on vertical tails may seriously underestimate the gust loads for airplanes having lightly damped lateral oscillations.

GUSTS, FREQUENCY↗
NASA NTRS1990

Cascade aerodynamic gust response including steady loading effects

To predict the unsteady convected gust aerodynamic response of a cascade comprised of arbitrary thick and cambered aerofoils in an incompressible, inviscid, flow field, a complete first-order model is formulated. The flow is analyzed by considering a periodic flow channel. The velocity potential is separated into steady and unsteady harmonic components, each described by a Laplace equation. The strong dependence of the unsteady aerodynamics on the steady effects of aerofoil and cascade geometry and incidence angle is manifested in the coupling of the unsteady and steady flow fields through the unsteady boundary conditions. Analytical solutions in individual grid elements of a body-fitted computational grid are then determined, with the complete solution obtained by assembly of these local solutions. The validity and capabilities of this model and solution technique are then demonstrated by analyzing the steady and unsteady aerodynamics of both theoretical and experimental cascade configurations.

Chiang, Hsiao-Wei D.↗
NASA NTRS1981

The nature of operating flight loads and their effect on propulsion system structures

Past diagnostics studies revealed the primary causes of performance deterioration of high by-pass turbofan engines to be flight loads, erosion, and thermal distortion. The various types of airplane loads that are imposed on the engine throughout the lifetime of an airplane are examined. These include flight loads from gusts and maneuvers and ground loads from takeoff, landing, and taxi conditions. Clarification is made in definitions of the airframer's limit and ultimate design loads and the engine manufacturer's operating design loads. Finally, the influence of these loads on the propulsion system structures is discussed.

Dickenson, K. H.↗
NASA NTRS1950

Gust-Tunnel Investigation to Determine the Load at the Joint of a Coupled Airplane Configuration Encountering a Gust

An investigation has been made in the Langley gust tunnel with two identical airplane models approximating 1/40-scale models of the B-29, coupled in tandem with a boom so that the individual centers of gravity were equidistant from the single coupling joint at the tail of the lead airplane. Time histories of the boom joint load were obtained as the models were flown through a gust. The results indicate that on a similar configuration involving airplanes the size of B-29 airplanes a load on the boom joint of 10,000 to 14,000 pounds could be induced by encountering a gust of 50 feet per second and having a gradient distance of 17 chords, at a forward speed of 380 feet per second and that the total load is extremely sensitive to the steadiness of flight that can be maintained with or without a gust. It is felt that the results are probably satisfactory to show order of magnitude, but it does not appear possible that a precise determination of the joint load that would be applicable to the full-scale airplanes can be obtained by gust-tunnel tests.

Cahen, George L.↗
NASA NTRS1971

Progress report on the NASA V-G/VGH general aviation program

An analysis is presented of 79 000 hours of data obtained from NASA V -G and VGH flight recorders installed on 134 general aviation aircraft engaged in eight types of operations. Information is presented on typical mission characteristics, on airspeed practices, on gust accelerations and derived gust velocities encountered, on maneuver -acceleration experience, and on the initial positive landing-impact accelerations. Comparisons are also made of the actual gust and maneuver loads experienced with the design gust and maneuver loads.

Joseph W. Jewel, Jr.↗
NASA NTRS1985

Preliminary study of inphase gusts and moment force wind loads over the first 150 meters at KSC, Florida

A mathematical/statistical analysis of inphase gusts and wind velocity moment forces over the first 150 m at the Kennedy Space Center (KSC) is presented. The wind velocity profile data were acquired at the KSC 150 m ground wind tower. The results show that planetary boundary layer (PBL) winds can sustain near peak speeds for periods up to 60 sec and longer. This is proven from calculating the autocorrelation functions of moment forces for several 10 min cases of wind profile data. The results show that lower atmospheric planetary boundary layer winds have periodic variations for long periods of time. This flow characteristic is valuable as aerospace vehicle engineering and design criteria where wind loading must be determined.

Kaufman, J. W.↗