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At least 1,027 records · Page 57

All sources NASA NTRS DOE OSTI

NASA NTRS2016

In-Situ Load System for Calibrating and Validating Aerodynamic Properties of Scaled Aircraft in Ground-Based Aerospace Testing Applications

An In-Situ Load System for calibrating and validating aerodynamic properties of scaled aircraft in ground-based aerospace testing applications includes an assembly having upper and lower components that are pivotably interconnected. A test weight can be connected to the lower component to apply a known force to a force balance. The orientation of the force balance can be varied, and the measured forces from the force balance can be compared to applied loads at various orientations to thereby develop calibration factors.

Commo, Sean A.↗

DOE OSTI2014

A Methodology to Analyze the Impact of 30-Minute Wind Scheduling on Load-Following Requirements

This paper proposes a new and systematic approach to investigating the impact of wind transfer between balancing authorities (BAs) with half-hour scheduling on load following requirements, which was traditionally scheduled on an hourly basis. The analysis is conducted for a few BAs in the Pacific Northwest of the U.S. that are described as source BAs (sending renewables) and sink BAs (receiving renewables). The main hypothesis is that if the source BA could schedule interchange for wind on a half-hourly basis, it would make the schedule follow its net load more closely. The scheduling change in the source BA is matched by adding the corresponding component to the net load in the sink BA. The load-following requirements are calculated as: (a) by the difference between the net load and modified schedule in the source BA, and (b) the difference between modified net load and unchanged hourly schedule in the sink BA. Results are presented as hourly upward and downward load following requirements in the source and sink BA, and compared with the results obtained with all generators scheduled on an hourly basis. Thus, the proposed method can effectively help utilities better understand the impact of 30-minute scheduling and make better business decisions.

Diao, Ruisheng↗

DOE OSTI2017

Topographically driven differences in energy and water constrain climatic control on forest carbon sequestration

Mountains are vital to ecosystems and human society given their influence on global carbon and water cycles. Yet the extent to which topography regulates montane forest carbon uptake and storage remains poorly understood. To address this knowledge gap, we compared forest aboveground carbon loading to topographic metrics describing energy balance and water availability across three headwater catchments of the Boulder Creek Watershed, Colorado, USA. The catchments range from 1800 to 3500 m above mean sea level with 46–102 cm/yr mean annual precipitation and -1.2° to 12.3°C mean annual temperature. In all three catchments, we found mean forest carbon loading consistently increased from ridges (27 ± 19 Mg C ha) to valley bottoms (60 ± 28 Mg C ha). Low topographic positions held up to 185 ± 76 Mg C ha, more than twice the peak value of upper positions. Toe slopes fostered disproportionately high net carbon uptake relative to other topographic positions. Carbon storage was on average 20–40 Mg C ha greater on north to northeast aspects than on south to southwest aspects, a pattern most pronounced in the highest elevation, coldest and wettest catchment. Both the peak and mean aboveground carbon storage of the three catchments, crossing an 11°C range in temperature and doubling of local precipitation, defied the expectation of an optimal elevation-gradient climatic zone for net primary production. These results have important implications for models of forest sensitivity to climate change, as well as to predicted estimates of continental carbon reservoirs.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2014

Joint Seasonal ARMA Approach for Modeling of Load Forecast Errors in Planning Studies

To make informed and robust decisions in the probabilistic power system operation and planning process, it is critical to conduct multiple simulations of the generated combinations of wind and load parameters and their forecast errors to handle the variability and uncertainty of these time series. In order for the simulation results to be trustworthy, the simulated series must preserve the salient statistical characteristics of the real series. In this paper, we analyze day-ahead load forecast error data from multiple balancing authority locations and characterize statistical properties such as mean, standard deviation, autocorrelation, correlation between series, time-of-day bias, and time-of-day autocorrelation. We then construct and validate a seasonal autoregressive moving average (ARMA) model to model these characteristics, and use the model to jointly simulate day-ahead load forecast error series for all BAs.

Power system planning, Operations, Probabilistic m↗

NASA NTRS1980

An investigation of a stoppable helicopter rotor with circulation control

A stoppable helicopter rotor with circulation control was investigated in the Ames 40 by 80 foot wind tunnel. The model was tested as a rotating wing, a fixed wing, and during transition start/stop sequences. The capability of the model's control system to maintain pitch and roll moment balance during the start/stop sequence, the ability of the blades to withstand the start/stop loads, the adequacy of the control system to maintain balance in the helicopter mode, and the control system capabilities in the fixed-wind mode were assessed. Time-history data of several start/stop sequences of the X-wing rotor, and the steady-state data relating to the model as both a rotor and as a fixed-wing aircraft are presented. In addition, stability data are presented which were acquired during open-loop and closed-loop tests of the hub moment feedback control system.

Ballard, J. D.↗

NASA NTRS1981

Liquid oxygen turbopump technology

A small, high-pressure, LOX turbopump was designed, fabricated and tested. The pump is a single-stage centrifugal type with power to the pump supplied by a single-stage partial-admission axial-impulse turbine. Design conditions included an operating speed of 7330 rad/s (70,000 rpm), pump discharge pressure of 2977 N/sqcm (4318 psia), and a pump flowrate of 16.4 Kg/s (36.21 lb/s). The turbopump contains a self-compensating axial thrust balance piston to eliminate axial thrust loads on the bearings during steady-state operation. Testing of the turbopump was achieved usng a gaseous hydrogen high-pressure flow to drive the turbine, which generally is propelled by LOX/LH2 combustion products, at 1041K (1874 R) inlet temperature and at a design pressure ratio of 1.424. Test data obtained with the turbopump are presented which include head-flow-efficiency performance, suction performance, balance piston performance and LOX seal performance. Mechanical performance of the turbopump is also discussed.

Nielson, C. E.↗

NASA NTRSDate not supplied

Rollable Corrugated Tubular Booms

A promising candidate for a new class of deployable composite boom is the COrrugated ROllable TUbular Boom (COROTUB), which is to be employed on future large space structures by the National Aeronautics and Space Administration (NASA). The COROTUB’s two corrugated thin shells form a closed section, which yields high bending and torsional stiffness, allowing for high dimensional stability. The corrugation geometry that dictates the boom cross-section shape was completely defined by closed-form analytical equations given a set of key design parameters. Parametric studies of two geometric variables were used to evaluate which parameters most influence the cross-section’s area moment of inertia and torsional constant. The number of corrugations, flattened height of the boom, and concave and convex corrugation radii were varied to study the complete boom design space. Deeper corrugations increased the local buckling (crimpling) loads of the thin-shell boom but reduced the area moment of inertia and therefore the global buckling load of the beam-column member, and thus a fine balance was sought. Finite element analyses of pure bending and compression load cases for short, 1.22-m-long fully-deployed booms ofeither the same size (flattened height) or similar inertia properties, were first carried out to efficiently study this design trade-off in detail.A second computational study evaluated the boom transition shape and the structural response of a 6-m-long partially-deployed boom, where the effects of partially bracing the root of the boom were also assessed. It was found that bracing length could greatly affect the strength and stiffness of this boom.Bracing type (as in the discrete number of clamps at the root) had no effect on stiffness, but particularly impacted strength for loading cases and boundary conditions that promoted the onset of local web buckling at the root. The corrugated designs were also found to improve, by as much as 20%, the boom bending and axial strength and boom transition length from flat to deployed when compared to a state-of-the-art boom alternative of the same size, for short bracing distances, such as those that would be required by small satellite applications. In addition, they showed a comparable structural response for longer bracing supports.

Booms↗

NASA NTRS2017

Wind Tunnel Strain-Gage Balance Calibration Data Analysis Using a Weighted Least Squares Approach

A new approach is presented that uses a weighted least squares fit to analyze wind tunnel strain-gage balance calibration data. The weighted least squares fit is specifically designed to increase the influence of single-component loadings during the regression analysis. The weighted least squares fit also reduces the impact of calibration load schedule asymmetries on the predicted primary sensitivities of the balance gages. A weighting factor between zero and one is assigned to each calibration data point that depends on a simple count of its intentionally loaded load components or gages. The greater the number of a data point's intentionally loaded load components or gages is, the smaller its weighting factor becomes. The proposed approach is applicable to both the Iterative and Non-Iterative Methods that are used for the analysis of strain-gage balance calibration data in the aerospace testing community. The Iterative Method uses a reasonable estimate of the tare corrected load set as input for the determination of the weighting factors. The Non-Iterative Method, on the other hand, uses gage output differences relative to the natural zeros as input for the determination of the weighting factors. Machine calibration data of a six-component force balance is used to illustrate benefits of the proposed weighted least squares fit. In addition, a detailed derivation of the PRESS residuals associated with a weighted least squares fit is given in the appendices of the paper as this information could not be found in the literature. These PRESS residuals may be needed to evaluate the predictive capabilities of the final regression models that result from a weighted least squares fit of the balance calibration data.

calibration analysis↗

NASA NTRS1921

Torsion of wing trusses at diving speeds

The purpose of this report is to indicate what effect the distortion of a typical loaded wing truss will have upon the load distribution. The case of high angle of incidence may be dismissed immediately from consideration as the loads on the front and rear trusses are balanced, and consequently there will be little angular distortion. A given angular distortion will have the maximum effect upon load distribution in the region of the angle of no-lift, because the slope of the lift curve is highest here, and it is here that the greatest angular distortion will occur, because the load on the front truss acts downward while the load on the rear truss acts upward.

Miller, Roy G↗

DOE OSTI2016

Three-phase Four-leg Inverter LabVIEW FPGA Control Code [SWR-16-26]

In the area of power electronics control, Field Programmable Gate Arrays (FPGAs) have the capability to outperform their Digital Signal Processor (DSP) counterparts due to the FPGA’s ability to implement true parallel processing and therefore facilitate higher switching frequencies, higher control bandwidth, and/or enhanced functionality. National Instruments (NI) has developed two platforms, Compact RIO (cRIO) and Single Board RIO (sbRIO), which combine a real-time processor with an FPGA. The FPGA can be programmed with a subset of the well-known LabVIEW graphical programming language. The use of cRIO and sbRIO for power electronics control has developed over the last few years to include control of three-phase inverters. Most three-phase inverter topologies include three switching legs. The addition of a fourth-leg to natively generate the neutral connection allows the inverter to serve single-phase loads in a microgrid or stand-alone power system and to balance the three-phase voltages in the presence of significant load imbalance. However, the control of a four-leg inverter is much more complex. In particular, instead of standard two-dimensional space vector modulation (SVM), the inverter requires three-dimensional space vector modulation (3D-SVM). The candidate software implements complete control algorithms in LabVIEW FPGA for a three-phase four-leg inverter. The software includes feedback control loops, three-dimensional space vector modulation gate-drive algorithms, advanced alarm handling capabilities, contactor control, power measurements, and debugging and tuning tools. The feedback control loops allow inverter operation in AC voltage control, AC current control, or DC bus voltage control modes based on external mode selection by a user or supervisory controller. The software includes the ability to synchronize its AC output to the grid or other voltage-source before connection. The software also includes provisions to allow inverter operation in parallel with other voltage regulating devices on the AC or DC buses. This flexibility allows the Inverter to operate as a stand-alone voltage source, connected to the grid, or in parallel with other controllable voltage sources as part of a microgrid or remote power system. In addition, as the inverter is expected to operate under severe unbalanced conditions, the software includes algorithms to accurately compute real and reactive power for each phase based on definitions provided in the IEEE Standard 1459: IEEE Standard Definitions for the Measurement of Electric Power Quantities Under Sinusoidal, Nonsinusoidal, Balanced, or Unbalanced Conditions. Finally, the software includes code to output analog signals for debugging and for tuning of control loops. The software fits on the Xilinx Virtex V LX110 FPGA embedded in the NI cRIO-9118 FPGA chassis, and with a 40 MHz base clock, supports a modulation update rate of 40 MHz, user-settable switching frequencies and synchronized control loop update rates of tens of kHz, and reference waveform generation, including Phase Lock Loop (PLL), update rate of 100 kHz.

Martin, Gregory↗

NASA NTRSDate not supplied

A Single-Piece Wind Tunnel Balance with a Universal Metric End

The metric attachment strategies for single and multi-piece wind tunnel balances have historically been distinct. This limits the interchangeability of single and multi-piece balances in wind tunnel models. In this work, a single-piece balance with a metric attachment compatible with a multi-piece balance (universal metric end) is designed, fabricated, and calibrated. The calibration results including the balance accuracies and deflections are reported for the new balance and compared to a single-piece balance with a conventional metric end designed to the same loads.

Wind tunnel balance↗

NASA NTRS2002

Inducer Hydrodynamic Load Measurement Devices

Marshall Space Flight Center (MSFC) has demonstrated two measurement devices for sensing and resolving the hydrodynamic loads on fluid machinery. The first - a derivative of the six component wind tunnel balance - senses the forces and moments on the rotating device through a weakened shaft section instrumented with a series of strain gauges. This "rotating balance" was designed to directly measure the steady and unsteady hydrodynamic loads on an inducer, thereby defining both the amplitude and frequency content associated with operating in various cavitation modes. The second device - a high frequency response pressure transducer surface mounted on a rotating component - was merely an extension of existing technology for application in water. MSFC has recently completed experimental evaluations of both the rotating balance and surface-mount transducers in a water test loop. The measurement bandwidth of the rotating balance was severely limited by the relative flexibility of the device itself, resulting in an unexpectedly low structural bending mode and invalidating the higher frequency response data. Despite these limitations, measurements confirmed that the integrated loads on the four-bladed inducer respond to both cavitation intensity and cavitation phenomena. Likewise, the surface-mount pressure transducers were subjected to a range of temperatures and flow conditions in a non-rotating environment to record bias shifts and transfer functions between the transducers and a reference device. The pressure transducer static performance was within manufacturer's specifications and dynamic response accurately followed that of the reference.

Skelley, Stephen E.↗

NASA NTRS2012

High-Reynolds Number Active Blowing Semi-Span Force Measurement System Development

Recent wind-tunnel tests at the NASA Langley Research Center National Transonic Facility utilized high-pressure bellows to route air to the model for evaluating aircraft circulation control. The introduction of these bellows within the Sidewall Model Support System significantly impacted the performance of the external sidewall mounted semi-span balance. As a result of this impact on the semi-span balance measurement performance, it became apparent that a new capability needed to be built into the National Transonic Facility s infrastructure to allow for performing pressure tare calibrations on the balance in order to properly characterize its performance under the influence of static bellows pressure tare loads and bellows thermal effects. The objective of this study was to design both mechanical calibration hardware and an experimental calibration design that can be employed at the facility in order to efficiently and precisely perform the necessary loadings in order to characterize the semi-span balance under the influence of multiple calibration factors (balance forces/moments and bellows pressure/temperature). Using statistical design of experiments, an experimental design was developed allowing for strategically characterizing the behavior of the semi-span balance for use in circulation control and propulsion-type flow control testing at the National Transonic Facility.

Lynn, Keith C.↗

NASA NTRS2000

The Effect of Age in the Alteration in Fluid Balance of Rats in Response to Centrifugation

With an increase in gravity load induced by centrifugation or upon return to Earth following spaceflight, there is a period of adjustment in fluid balance in rats. With centrifugation there is a reduced fluid intake with maintenance of the rate of urine excretion. Following spaceflight there is an increase in urine output and maintenance of fluid intake. The initial period of acclimation to hypergravity is associated with a net loss of fluids. In the present study in response to centrifugation at 2.0 G this period of acclimation is present in mature rats for a longer period of time, about 24 hours. Following this initial response a period of over compensation has previously been reported. In the present study this was not observed. The net effect of these alterations in water intake and output in response to centrifugation for 14 days was slight increase in the percent total body water, with effective compensation seen in both young and mature rats. Older rats have been shown to have a reduced relative thirst and compensatory renal function in response to hypohydration, hyperosmolality and pharmacological stimuli. Responsiveness to these stimuli are delayed and/or attenuated in older animals. Similar findings were noted in the present study in the initial response to centrifugation. The older animal had a delayed return of fluid intake to control levels. The delay of one day did not appear to effect long-term fluid homeostasis, as there was difference in the response of percent total body water at the end of 14 days of centrifugation with both age groups having a slight but significant increase. This increase has been attributed to the increase in lean body mass induced by centrifugation.

Fuller, Charles A.↗

NASA NTRS2017

Inverse Force Determination on a Small Scale Launch Vehicle Model Using a Dynamic Balance

A launch vehicle can experience large unsteady aerodynamic forces in the transonic regime that, while usually only lasting for tens of seconds during launch, could be devastating if structural components and electronic hardware are not designed to account for them. These aerodynamic loads are difficult to experimentally measure and even harder to computationally estimate. The current method for estimating buffet loads is through the use of a few hundred unsteady pressure transducers and wind tunnel test. Even with a large number of point measurements, the computed integrated load is not an accurate enough representation of the total load caused by buffeting. This paper discusses an attempt at using a dynamic balance to experimentally determine buffet loads on a generic scale hammer head launch vehicle model tested at NASA Ames Research Center's 11' x 11' transonic wind tunnel. To use a dynamic balance, the structural characteristics of the model needed to be identified so that the natural modal response could be and removed from the aerodynamic forces. A finite element model was created on a simplified version of the model to evaluate the natural modes of the balance flexures, assist in model design, and to compare to experimental data. Several modal tests were conducted on the model in two different configurations to check for non-linearity, and to estimate the dynamic characteristics of the model. The experimental results were used in an inverse force determination technique with a psuedo inverse frequency response function. Due to the non linearity, the model not being axisymmetric, and inconsistent data between the two shake tests from different mounting configuration, it was difficult to create a frequency response matrix that satisfied all input and output conditions for wind tunnel configuration to accurately predict unsteady aerodynamic loads.

testing↗

DOE OSTI2021

Power System Event Identification Based on Deep Neural Network With Information Loading

Online power system event identification and classification are crucial to enhancing the reliability of transmission systems. In this study, we develop a deep neural network (DNN) based approach to identify and classify power system events by leveraging real-world measurements from hundreds of phasor measurement units (PMUs) and labels from thousands of events. Two innovative designs are embedded into the baseline model built on convolutional neural networks (CNNs) to improve the event classification accuracy. First, we propose a graph signal processing based PMU sorting algorithm to improve the learning efficiency of CNNs. Second, we deploy information loading based regularization to strike the right balance between memorization and generalization for the DNN. Numerical results based on real-world dataset from the Eastern Interconnection of the U.S power transmission grid show that the combination of PMU based sorting and the information loading based regularization techniques help the proposed DNN approach achieve highly accurate event identification and classification results.

24 POWER TRANSMISSION AND DISTRIBUTION↗

NASA NTRS2002

Inducer Hydrodynamic Load Measurement Devices

Marshall Space Flight Center (MSFC) has demonstrated two measurement devices for sensing and resolving the hydrodynamic loads on fluid machinery. The first - a derivative of the six-component wind tunnel balance - senses the forces and moments on the rotating device through a weakened shaft section instrumented with a series of strain gauges. This rotating balance was designed to directly measure the steady and unsteady hydrodynamic loads on an inducer, thereby defining both the amplitude and frequency content associated with operating in various cavitation modes. The second device - a high frequency response pressure transducer surface mounted on a rotating component - was merely an extension of existing technology for application in water. MSFC has recently completed experimental evaluations of both the rotating balance and surface-mount transducers in a water test loop. The measurement bandwidth of the rotating balance was severely limited by the relative flexibility of the device itself, resulting in an unexpectedly low structural bending mode and invalidating the higher-frequency response data. Despite these limitations, measurements confirmed that the integrated loads on the four-bladed inducer respond to both cavitation intensity and cavitation phenomena. Likewise, the surface-mount pressure transducers were subjected to a range of temperatures and flow conditions in a non-rotating environment to record bias shifts and transfer functions between the transducers and a reference device. The pressure transducer static performance was within manufacturer's specifications and dynamic response accurately followed that of the reference.

Skelley, Stephen E.↗

NASA NTRS1990

Cryogenic temperature effects on sting-balance deflections in the National Transonic Facility

An investigation was conducted at the National Transonic Facility (NTF) to document the change in sting-balance deflections from ambient to cryogenic temperatures. Space limitations in some NTF models do not allow the use of on-board angle of attack instrumentation. In order to obtain angle of attack data, pre-determined sting-balance bending data must be combined with arc sector angle measurements. Presently, obtaining pretest sting-balance data requires several cryogenic cycles and cold loadings over a period of several days. A method of reducing the calibration time required is to obtain only ambient temperature sting-balance bending data and correct for changes in material properties at cryogenic temperatures. To validate this method, two typical NTF sting-balance combinations were tested. The test results show excellent agreement with the predicted values and the repeatability of the data was 0.01 degree.

Popernack, Thomas G., Jr.↗