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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Structural response reconstruction using a system-equivalent singular vector basis

Here, this paper develops a novel method for reconstructing the full-field response of structural dynamic systems using sparse measurements. The singular value decomposition is applied to a frequency response matrix relating the structural response to physical loads, base motion, or modal loads. The left singular vectors form a non-physical reduced basis that can be used for response reconstruction with far fewer sensors than existing methods. The contributions of the singular vectors to measured response are termed singular-vector loads (SVLs) and are used in a regularized Bayesian framework to generate full-field response estimates and confidence intervals. The reconstruction framework is applicable to the estimation of single data records and power spectral densities from multiple records. Reconstruction is successfully performed in configurations where the number of SVLs to identify is less than, equal to, and greater than the number of sensors used for reconstruction. In a simulation featuring a seismically excited shear structure, SVL reconstruction significantly outperforms modal FRF-based reconstruction and successfully estimates full-field responses with as few as two uniaxial accelerometers. SVL reconstruction is further verified in a simulation featuring an acoustically excited cylinder. Finally, response reconstruction and uncertainty quantification are performed on an experimental structure with three shaker inputs and 27 triaxial accelerometer outputs.

42 ENGINEERING↗
DOE OSTI2024

Extraction of Vibration Data with Imaging

To date, the primary sensing technology used to measure the vibration response has been accelerometers and strain gages mounted directly to the structure and using either wired or, more recently, wireless telemetry. Cost issues with these sensors and the associated data acquisition systems typically limit the numbers that are deployed on in situ structures. Although there are a few structures with larger sensing counts that in some cases exceed over 1000 sensors, more typical numbers range from ten to one hundred sensors resulting in low spatial resolution when they are applied to physically large systems. When one considers that nuclear power plant structures usually have complex geometries, material properties, connectivity and boundary conditions, it is clear these current approaches to vibration measurements can only provide limited information about a system’s dynamics response characteristics. As an alternative, many non-contact measurement technologies have emerged, including point wise measurement methods such as Global Positioning System (GPS), microwave interferometry, and laser Doppler vibrometry (LDV), as well as simultaneous full-field measurement methods such as electronic speckle pattern interferometry, holography interferometry, and muon tomography, some of which can provide high spatial resolution measurements. Among these methods, digital video imaging techniques have emerged as a feasible solution for full-field vibration measurements that provide significantly more detailed dynamic response information because every pixel becomes a measurement point. Furthermore, recent advances in image processing and computer vision algorithms have been successfully used to process video data for experimental and operational modal analysis. Such full-field measurements have the potential to significantly improve many current structural assessment procedures including system identification (modal parameter estimation), structural health monitoring, load reconstruction, model validation, and model updating. Furthermore, more recent full-field imaging techniques can be accomplished with relatively low-cost, commercially-available off-the-shelf cameras. However, these measurement procedures have other limitations that must be considered such as the ability to only measure visibly accessible points on a structure and a more limited dynamic range and bandwidth than can be achieved with accelerometers or strain gages.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Earth-Centered, Earth-Fixed Inertial Navigation System & Error-State Kalman Filter Reference Manual

This is a self-contained reference document that derives the equations necessary to build a combined inertial navigation system and error-state Kalman filter. Coordinate transform, linear time invariant system, inertial sensing, and error-state Kalman filtering theory is built up from first principles. This theory is then leveraged to derive the system equations for two combined inertial navigation system and error-state Kalman filters: (1) a 15-state system modeling white-noise-integrating accelerometer and gyroscope biases, and (2) a 39-state system modeling static and first-order Gauss-Markov accelerometer and gyroscope biases, scale factor errors, and cross-axis sensitivity errors.

42 ENGINEERING↗
DOE OSTI2024

Experimental Investigation of Steel-Borne Acoustic Pulses for Fault Pinpointing in Pipe-Type Cable Systems: A Scaled-Down Model Approach

Pipe-type cable systems, including high-pressure fluid-filled (HPFF) and high-pressure gas-filled cables, are widely used for underground high-voltage transmission. These systems consist of insulated conductor cables within steel pipes, filled with pressurized fluids or gases for insulation and cooling. Despite their reliability, faults can occur due to insulation degradation, thermal expansion, and environmental factors. As many circuits exceed their 40-year design life, efficient fault localization becomes crucial. Fault location involves prelocation and pinpointing. Therefore, a novel pinpointing approach for pipe-type cable systems is proposed, utilizing accelerometers mounted on a steel pipe to capture fault-induced acoustic signals and employing the time difference of arrival method to accurately pinpoint the location of the fault. The experimental investigations utilized a scaled-down HPFF pipe-type cable system setup, featuring a carbon steel pipe, high-frequency accelerometers, and both mechanical and capacitive discharge methods for generating acoustic pulses. The tests evaluated the propagation velocity, attenuation, and pinpointing accuracy with the pipe in various embedment conditions. The experimental results demonstrated accurate fault pinpointing in the centimeter range, even when the pipe was fully embedded, with the acoustic pulse velocities aligning closely with the theoretical values. These experimental investigation findings highlight the potential of this novel acoustic pinpointing technique to improve fault localization in underground systems, enhance grid reliability, and reduce outage duration. Further research is recommended to validate this approach in full-scale systems.

Moutassem, Zaki↗
NASA NTRS1973

Study of an experimental technique for application to structural dynamic problems

An experimental program was conducted to determine the feasibility of using subscale plastic models to determine the response of full-scale aerospace structural components to impulsive, pyrotechnic loadings. A monocoque cylinder was impulsively loaded around the circumference of one end, causing a compressive stress wave to propagate in the axial direction. The resulting structural responses of two configurations of the cylinder (with and without a cutout) were recorded by photoelasticity, strain gages, and accelerometers. A maximum dynamic stress concentration was photoelastically determined and the accelerations calculated from strain-gage data were in good agreement with those recorded by accelerometers. It is concluded that reliable, quantitative structural response data can be obtained by the experimental techniques described in this report.

Snell, R. F.↗
NASA NTRS1973

Acoustic emission studies of large advanced composite rocket motor cases.

Acoustic emission (AE) patterns were measured during pressure testing of advanced composite rocket motor cases made of boron/epoxy and graphite/epoxy. Both accelerometers and high frequency AE transducers were used, and both frequency spectrum and amplitude distribution were studied. The AE patterns suggest that precursor emission might be used in certain cases to anticipate failure. The technique of hold-cycle AE monitoring was also evaluated and could become a valuable decision gate for test continuation/termination. Data presented show similarity of accelerometers and AE transducer responses despite the different frequency response, and suggest that structural AE phenomena are broadband.

Robinson, E. Y.↗
NASA NTRS1973

Failure detection and isolation methods for redundant gimballed inertial measurement units.

Skewed alignment of two redundant conventional inertial measuring units permits nonambiguous detection and isolation of hard and soft failures in real time by an airborne computer. Accelerometer outputs and gimbal readouts are monitored periodically, and attitude rate and velocity error vectors are computed from these data. Magnitudes of these vectors provide failure detection, and projection of these error vectors onto the coordinate axes of the two clusters permits isolation. A detailed Monte Carlo simulation of one version of the mechanization as applied to Space Shuttle boost trajectories demonstrates effectiveness down to very low levels of inertial instrument performance failures. The results indicate that worst case overall navigation performance occurs when accelerometer failures are of the order of 20 sigma and gyro failures are about 100 sigma for conventional state-of-the-art IMU instruments.

Solov, E. G.↗
NASA NTRS1974

Investigation of new radar-data-reduction techniques used to determine drag characteristics of a free-flight vehicle

An investigation was conducted of new techniques used to determine the complete transonic drag characteristics of a series of free-flight drop-test models using principally radar tracking data. The full capabilities of the radar tracking and meteorological measurement systems were utilized. In addition, preflight trajectory design, exact kinematic equations, and visual-analytical filtering procedures were employed. The results of this study were compared with the results obtained from analysis of the onboard, accelerometer and pressure sensor data of the only drop-test model that was instrumented. The accelerometer-pressure drag curve was approximated by the radar-data drag curve. However, a small amplitude oscillation on the latter curve precluded a precise definition of its drag rise.

Woodbury, G. E.↗
NASA NTRS1975

Accelerations experienced during low-G flight of Black Brant VC (NAS 21.015) on 4 October 1974

This investigation was to determine whether a Black Brant VC (BBVC) sounding rocket equipped with the Goddard Space Flight Center (GSFC) rate control system (RCS) would produce g-levels which are satisfactory for space processing. Accelerations measured by the Marshall Space Flight Center (MSFC) low-g accelerometer system (LGAS) were compared with accelerations calculated from measured payload RCS gyro data during a low-g flight of BBVC NAS 21.015 at White Sands Missile Range, N.M., on October 4, 1974. Accelerations of up to 0.0002 g existed at the LGAS accelerometers from 70 through 420 sec (5.8 min), with the exception of a spike at 101 sec of 0.0004 g which occurred when the RCS was activated the second time. Accelerations of 0.0001 g existed from 140 through 400 sec (4.3 min). Accelerations of 0.0002 g along the roll axis up to 150 sec and of 0.0015 g in the lateral plane at about 135 sec are being investigated by GSFC. They may be associated with leaking thruster valves or a leak in one of the heat pipe experiments. The vehicle rate buildup each time after the RCS nulls out are also being investigated by GSFC. This rate caused most of the 0.0001 g acceleration experienced after 150 sec into the flight. Aerodynamic drag produced no significant accelerations after about 80 sec. The principal conclusion was that the BBVC with the GSFC RCS produces g-levels satisfactory for space processing.

Kissel, R.↗
NASA NTRS1976

Satellite borne gravity gradiometer study

Gravity gradiometry is recognized to be a very difficult instrumentation problem because extremely small differential acceleration levels have to be measured, 0.1 EU corresponds to an acceleration of 10 to the minus 11th power g at two points 1 meter apart. A feasibility model of a gravity gradiometer is being developed for airborne applications using four modified versions of the proven Model VII accelerometers mounted on a slowly rotating fixture. Gravity gradients are being measured to 1.07 EU in a vertical rotation axis orientation. Equally significant are the outstanding operational characteristics such as fast reaction time, low temperature coefficients and high degree of bias stability over long periods of time. The rotating accelerometer gravity gradiometer approach and its present status is discussed and it is the foundation for the orbital gravity gradiometer analyzed. The performance levels achieved in a 1 g environment of the earth and under relatively high seismic disturbances, lend the orbital gravity gradiometer a high confidence level of success.

Metzger, E.↗
NASA NTRS1977

Studies of orbital Eoetvoes experiments

A direct force-balance technique was analyzed for carrying out the Eoetvoes experiment in space, which is intended to give sufficient sensitivity to allow investigation of the gravitational interactions of energy stored in the weak interaction. The heart of experiment is an exceedingly sensitive dual accelerometer, containing two proof masses constructed of the materials whose Eoetvoes ratio is to be compared. For use in development of the accelerometer, a magnetic microbalance is proposed in which the weight of the proof mass is supported by magnetic forces which vary very slowly with the proof mass position. It is shown that at least two different mechanizations of the magnetic suspension may be feasible.

Chapman, P. K.↗
NASA NTRS1977

Redundant integrated flight control/navigation inertial sensor complex

A redundant strapdown inertial navigation system for integrated flight control/navigation use is described. Design of the system, which consists of four tuned-gimbal gyros, eight accelerometers, and four processors, is discussed, with emphasis on its compact configuration (13 by 13 by 14 in.), based on symmetry properties of an octahedron. A matrix operator for least-squares combination of data from an arbitrary number of two-degree-of-freedom gyros is derived, and general parity equations for error analysis are given. Self-contained detection and isolation of a two-axis gyro failure is considered; system failure probability, which depends on component failure rates and self-correction capacities, is analyzed. Test data, including typical parity equation responses during motion and simulated gyro and accelerometer failures, are also presented.

Ebner, R. E.↗
NASA NTRS1978

Detection of boundary-layer transitions in wind tunnels

Accelerometer replaces stethoscope in technique for detection of laminar-to-turbulent boundary-layer transitions on wind-tunnel models. Technique allows measurements above or below atmospheric pressure because human operator is not required within tunnel. Data may be taken from accelerometer, and pressure transducer simultaneously, and delivered to systems for analysis.

Wood, W. R.↗
NASA NTRS1979

Coal-shale interface detection

A penetrometer for coal-shale interface detection is presented. It is used with coal cutting equipment consisting of a reciprocating hammer, having an accelerometer mounted thereon to measure the impact of the hammer as it penetrates the ceiling or floor surface of a mine. Additionally, a pair of reflectometers simultaneously view the same surface, and the outputs from the accelerometer and reflectometers are detected and jointly registered to determine when an interface between coal and shale is being cut through.

Broussard, P. H.↗
NASA NTRS1979

Ferrographic analysis of wear debris from full-scale bearing fatigue tests

The Ferrograph was used to determine the types and quantities of wear particles generated during full scale bearing fatigue tests. Deep-groove ball bearings made from steel were used. A tetraester lubricant was used in a recirculating lubricant system containing a 49 micrometers absolute filter. Test conditions include a maximum Hertz stress of 2.4 GPa, a shaft speed of 15,000 rpm, and a lubricant supply temperature of 74 C (165 F). Four fatigue failures were detected by accelerometers in this test set. In general, the Ferrograph was more sensitive (up to 23 hr) in detecting spall initiation than either accelerometers or the normal spectrographic oil analysis. Four particle types were observed: normal rubbing weather particles, spheres, nonferrous particles, and severe wear (spall) fragments.

Jones, W. R., Jr.↗
NASA NTRS1980

Detecting a coal/shale interface

Detector, intended for use with longwall shearer, determines when cut has pierced through coal layer. Accelerometer measures hardness of material struck by penetrometer ram, while reflectometers measure reflectivity of surface on either side of penetrometer. Signals are combined in voting circuit that indicates "coal" or "shale", depending on information supplied by three sensors. It distinguishes by differences in accelerometer waveforms.

Broussard, P. H.↗
NASA NTRS1979

Coal-shale interface detection system

A coal-shale interface detection system for use with coal cutting equipment consists of a reciprocating hammer on which an accelerometer is mounted to measure the impact of the hammer as it penetrates the ceiling or floor surface of a mine. A pair of reflectometers simultaneously view the same surface. The outputs of the accelerometer and reflectometers are detected and jointly registered to determine when an interface between coal and shale is being cut through.

Campbell, R. A.↗