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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Growth characteristics of a plane crack subjected to three-dimensional loading

The closed form expressions for the stress intensity factors due to concentrated forces applied to the surfaces of a half plane crack in an infinite body are used to generate solutions for distributed loads in this geometry. The stress intensity factors for uniformly distributed loads applied over a rectangular portion of the crack surface are given in closed form. An example of non-uniformly distributed loads which can be treated numerically is also included. In particular, combinations of normal and shear stresses on the crack which simulate the case of loading at an angle to the crack front are considered. The resulting stress intensity factors are combined with the strain energy density fracture criterion for the purpose of predicting the most likely direction of crack propagation. The critical value of the energy density factor can then be used for determining the allowable load on a specimen with a crack front not perpendicular to the tensile axis.

Hartranft, R. J.↗
DOE OSTI2020

Robust Distribution System Load Restoration With Time-Dependent Cold Load Pickup

Service restoration is one of the critical functions to enable the future self-healing distribution system. To restore the distribution system in a timely and reliable manner, the realistic system operating conditions need to be accurately characterized. Here, two main factors that have great impacts on distribution system restoration (DSR) in practice are investigated. First, cold load pickup (CLPU), generally caused by thermostatically controlled loads (TCLs), is a common phenomenon after an outage and shaped by the outage duration. However, the time-dependent behaviors of CLPU are rarely considered in literature. In this paper, the operating state evolution of TCLs after an outage is analyzed to characterize time-dependent CLPU. And the time-dependent CLPU is analytically embedded in DSR to accurately represent the actual behaviors of the restored loads. Second, it is difficult to predict loads that fluctuate during DSR due to the lack of real-time measurement data. Accordingly, a robust DSR based on the information gap decision theory (IGDT) is proposed to address this challenge, fully considering the uncertainty of CLPU. The proposed models are tested in IEEE 13-node and 123-node test feeders. Simulation results demonstrate that the time-dependent CLPU model and the uncertainty modeling of CLPU can accurately capture the actual behaviors of loads with TCLs after an outage, which greatly improves DSR decisions in practice.

24 POWER TRANSMISSION AND DISTRIBUTION↗
NASA NTRS1948

Application of Theodorsen's Theory to Propeller Design

A theoretical analysis is presented for obtaining by use of Theodorsen's propeller theory the load distribution along a propeller radius to give the optimum propeller efficiency for any design condition.The efficiencies realized by designing for the optimum load distribution are given in graphs, and the optimum efficiency for any design condition may be read directly from the graph without any laborious calculations. Examples are included to illustrate the method of obtaining the optimum load distributions for both single-rotating and dual-rotating propellers.

Crigler, John L↗
NASA NTRS1949

Application of Theodorsen's theory to propeller design

A theoretical analysis is presented for obtaining, by use of Theodorsen's propeller theory, the load distribution along a propeller radius to give the optimum propeller efficiency for any design condition. The efficiencies realized by designing for the optimum load distribution are given in graphs, and the optimum efficiency for any design condition may be read directly from the graph without any laborious calculations. Examples are included to illustrate the method of obtaining the optimum load distributions for both single-rotating and dual-rotating propellers.

Crigler, John L↗
NASA NTRS1979

Load support system analysis high speed input pinion configuration

An analysis and a series of computerized calculations were carried out to explore competing prototype design concepts of a shaft and two taper-roller bearings systems to support the high-speed input pinion of an advanced commercial helicopter transmission. The results were used to evaluate designs both for a straddle arrangement where the pinion gear is located between the bearings and for a cantilever arrangement where the pinion is outboard of the two bearings. Effects of varying parameters including applied gear load, preload, wall thickness, interference fits, bearing spacing and pinion gear location on system rigidity, load distribution and bearing rating life were assessed. A comparison of the bearing load distributions for these designs demonstrated that the straddle more equally distributes both radial and axial loads. The performance of these designs over a range of shaft rotational speeds, with lubrication and friction effects included, is also discussed.

Gassel, S. S.↗
NASA NTRS1979

Plotting max/min data envelopes

Study of maximum and minimum load distributions along structural section is aided by visual display of load distribution data. Maximum/minimum envelope plot program plots these envelopes of the stresses and shear loads at selected points in beam modeled by series of finite elements. Digital output for engineers and management is presented for quick analysis and understanding.

Furuike, T.↗
NASA NTRS1998

Evaluation of 3D Inverse Code Using Rotor 67 as Test Case

A design modification of Rotor 67 is carried out with a full 3D inverse method. The blade camber surface is modified to produce a prescribed pressure loading distribution, with the blade tangential thickness distribution and the blade stacking line at midchord kept the same as the original Rotor 67 design. Because of the inviscid-flow assumption used in the current version of the method, Rotor 67 geometry is modified for use at a design point different from the original design value. A parametric study with the prescribed pressure loading distribution yields the following results. In the subsonic section, smooth pressure loading shapes generally produce blades with well-behaved blade surface pressure distributions. In the supersonic section, the study shows that the strength and position of the passage shock correlate with the characteristics of the blade pressure loading shape. In general, "smooth" prescribed blade pressure loading distributions generate blade designs with reverse cambers which have the effect of weakening the passage shock.

Dang, T.↗
NASA NTRS1968

Development of helical seal for high temperature /2000 degrees F/ application

Helical seal is used to seal bolted flange joints in a high temperature environment. The seal design incorporates a new cross-sectional shape, a metal strip with a slight radius, and the use of premolded asbestos. It provides equal load distribution under compression loads, allows for minimum loss and recovery values, and increases the temperature range.

Held, C.↗
NASA NTRS1989

Composite load spectra for select space propulsion structural components

The objective of the Composite Load Spectra (CLS) project is to build a knowledge based system to synthesize probabilistic loads for selected space propulsion engine components. The knowledge based system has a load expert system module and a load calculation module. The load expert system provides load information and the load calculation module generates the probabilistic load distributions. The engine loads are divided into 4 broad classes: the engine independent loads, the engine system dependent load, the component local independent loads and the component loads. These classes are defined and illustrated.

Ho, H.↗
NASA NTRS1993

Denver TMA assessment

This report describes the assessment of the Traffic Management Advisor (TMA) conducted at the Denver Center and TRACON, January 11-February 5, 1993. The assessment addressed the effectiveness of TMA for supporting various traffic management activities. At the Center, traffic management coordinators (TMC's) shadowed traffic operations, using TMA to make metering time and internal release decisions. At the TRACON, TMC's accessed TMA in an advisory mode for different planning activities such as staffing, distributing the traffic load, and changing the airport acceptance rate. These different opportunities for assessing TMA provide insight into TMA as a potential communication aid and planning tool. Findings from this assessment indicate that TMA can be used to support traffic management planning and decisions. TMC's at the center were able to use information provided by TMA to determine metering times as well as internal release times. At the TRACON, TMA supported decisions on airport configuration, airport acceptance rate, load distribution, proactive coordination with the center, and staffing. While findings of TMA use are generally positive, it must be kept in mind that this assessment is a snapshot in time. Not all TMA capabilities were assessed, nor were TMC's fully trained and knowledgeable on all features. Feature use will continue to evolve and strategies emerge as the TMC's gain experience with TMA over a variety of traffic situations and their understanding of TMA capabilities broadens with continued training.

Harwood, Kelly↗
NASA NTRS1997

Buckling Behavior of Long Symmetrically Laminated Plates Subjected to Shear and Linearly Varying Axial Edge Loads

A parametric study of the buckling behavior of infinitely long symmetrically laminated anisotropic plates that are subjected to linearly varying edge loads, uniform shear loads, or combinations of these loads is presented. The study focuses on the effects of the shape of linearly varying edge load distribution, plate orthotropy, and plate flexural anisotropy on plate buckling behavior. In addition, the study exmines the interaction of linearly varying edge loads and uniform shear loads with plate flexural anisotropy and orthotropy. Results obtained by using a special purpose nondimensional analysis that is well suited for parametric studies of clamped and simply supported plates are presented for [+/- theta](sub s), thin graphite-epoxy laminates that are representative of spacecraft structural components. Also, numerous generic buckling-design charts are presented for a wide range of nondimensional parameters that are applicable to a broad class of laminate constructions. These charts show explicitly the effects of flexural orthotropy and flexural anisotropy on plate buckling behavior for linearly varying edge loads, uniform shear loads, or combinations of these loads. The most important finding of the present study is that specially orthotropic and flexurally anisotropic plates that are subjected to an axial edge load distribution that is tension dominated can support shear loads that are larger in magnitude than the shear buckling load.

Nemeth, Michael P.↗
NASA NTRS1984

Incompressible lifting-surface aerodynamics for a rotor-stator combination

Current literature on the three dimensional flow through compressor cascades deals with a row of rotor blades in isolation. Since the distance between the rotor and stator is usually 10 to 20 percent of the blade chord, the aerodynamic interference between them has to be considered for a proper evaluation of the aerothermodynamic performance of the stage. A unified approach to the aerodynamics of the incompressible flow through a stage is presented that uses the lifting surface theory for a compressor cascade of arbitrary camber and thickness distribution. The effects of rotor stator interference are represented as a linear function of the rotor and stator flows separately. The loading distribution on the rotor and stator flows separately. The loading distribution on the rotor and stator blades and the interference factor are determined concurrently through a matrix iteration process.

Ramachandra, S. M.↗
NASA NTRS1981

A study of the viscous dissipation and surface loading on a vibrating surface

The energy dissipated by viscosity at the edge of a vibrating flat plate is calculated and compared to the radiated acoustic energy. A correction to the Kirchhoff integral estimate of the noise is derived. For Helmholtz number of order unity and smaller the dissipation can be comparable to or greater than the acoustic energy. A viscous compressible theory of the load distribution on a vibrating two dimensional body is developed. First it is shown that load calculations based on potential theory and the Newmann uniqueness condition (continuity of potential or pressure on the surface) are not in agreement with experiment or the more correct viscous theory. For a flat plate airfoil the eigensolution of potential theory is indeterminant while viscous theory yields a unique solution that has square root singularities at the edges. It is also shown that for compact surfaces the far field acoustics depend only on the magnitude of the eigensolutions of potential theoy and so will be uniquely determined by the viscous theory. It is suggested that the general viscous theory of vibrating surfaces with cross sectional geometry will lead to results in agreement with expermentally measured load distributions.

Yates, J. E.↗
DOE OSTI2021

Coordinated Optimal Control of PV Inverters and HVAC Loads in Distribution Systems

The increasing integration of distributed energy resources (DERs), such as photovoltaics (PVs) and smart buildings into distribution systems complicate power system operation and controls. This paper proposes a coordinated optimal control strategy for PV inverters and Heating, ventilation, and air conditioning (HVAC) loads in smart buildings to minimize the total network loss in a distribution system. For the HVAC units, we enforce minimum on and off time constraints to avoid frequent switching that can degrade the unit. The proposed control will dispatch optimal control signals of active and reactive power to PV inverters and on/off commands to HVAC units while maintaining the nodal voltage within a secure range and the temperature of HVAC units at a comfort level. The simulation results on a modified IEEE 33-node distribution system demonstrate that the proposed coordinated control scheme can reduce the network loss.

Pani, Naveen↗
NASA NTRS1972

Aerodynamic characteristics of the Scout 133R vehicle determined from wind tunnel tests

Bending moments and other associated parameters were measured on a Scout vehicle during a launch through high velocity horizontal winds. Comparison of the measured data with predictions revealed some unexplained discrepancies. Possible sources of error in the experimental data and predictions were considered; one of which is the predicted aerodynamic characteristics. A wind tunnel investigation was initiated, including supersonic force and pressure tests, to better define the aerodynamics. In addition to basic aerodynamic coefficients from the force test, detailed pressure and load distributions along the body were established from the pressure test. Pressure coefficients were integrated to determine normal load distributions, total normal force, and total pitching moment of the body. Comparison of the normal forces from pressure and force tests resulted in agreement within 15%. Comparison of pitching moment data from the two tests resulted in larger differences.

Abramson, F. B.↗
NASA NTRS1993

Optimization of a Centrifugal Impeller Design Through CFD Analysis

This paper discusses the procedure, approach and Rocketdyne CFD results for the optimization of the NASA consortium impeller design. Two different approaches have been investigated. The first one is to use a tandem blade arrangement, the main impeller blade is split into two separate rows with the second blade row offset circumferentially with respect to the first row. The second approach is to control the high losses related to secondary flows within the impeller passage. Many key parameters have been identified and each consortium team member involved will optimize a specific parameter using 3-D CFD analysis. Rocketdyne has provided a series of CFD grids for the consortium team members. SECA will complete the tandem blade study, SRA will study the effect of the splitter blade solidity change, NASA LeRC will evaluate the effect of circumferential position of the splitter blade, VPI will work on the hub to shroud blade loading distribution, NASA Ames will examine the impeller discharge leakage flow impacts and Rocketdyne will continue to work on the meridional contour and the blade leading to trailing edge work distribution. This paper will also present Rocketdyne results from the tandem blade study and from the blade loading distribution study. It is the ultimate goal of this consortium team to integrate the available CFD analysis to design an advanced technology impeller that is suitable for use in the NASA Space Transportation Main Engine (STME) fuel turbopump.

Chen, W. C.↗