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At least 1,477 records · Page 82

All sources NASA NTRS DOE OSTI

NASA NTRS1990

Probabilistic simulation of uncertainties in thermal structures

Development of probabilistic structural analysis methods for hot structures is a major activity at Lewis Research Center. It consists of five program elements: (1) probabilistic loads; (2) probabilistic finite element analysis; (3) probabilistic material behavior; (4) assessment of reliability and risk; and (5) probabilistic structural performance evaluation. Recent progress includes: (1) quantification of the effects of uncertainties for several variables on high pressure fuel turbopump (HPFT) blade temperature, pressure, and torque of the Space Shuttle Main Engine (SSME); (2) the evaluation of the cumulative distribution function for various structural response variables based on assumed uncertainties in primitive structural variables; (3) evaluation of the failure probability; (4) reliability and risk-cost assessment, and (5) an outline of an emerging approach for eventual hot structures certification. Collectively, the results demonstrate that the structural durability/reliability of hot structural components can be effectively evaluated in a formal probabilistic framework. In addition, the approach can be readily extended to computationally simulate certification of hot structures for aerospace environments.

Chamis, Christos C.↗

NASA NTRS1990

Probabilistic simulation of uncertainties in thermal structures

Development of probabilistic structural analysis methods for hot structures is a major activity at NASA-Lewis, and consists of five program elements: (1) probabilistic loads, (2) probabilistic finite element analysis, (3) probabilistic material behavior, (4) assessment of reliability and risk, and (5) probabilistic structural performance evaluation. Attention is given to quantification of the effects of uncertainties for several variables on High Pressure Fuel Turbopump blade temperature, pressure, and torque of the Space Shuttle Main Engine; the evaluation of the cumulative distribution function for various structural response variables based on assumed uncertainties in primitive structural variables; evaluation of the failure probability; reliability and risk-cost assessment; and an outline of an emerging approach for eventual hot structures certification. Collectively, the results demonstrate that the structural durability/reliability of hot structural components can be effectively evaluated in a formal probabilistic framework. In addition, the approach can be readily extended to computationally simulate certification of hot structures for aerospace environments.

Chamis, C. C.↗

NASA NTRS1992

Plasma dynamics on current-carrying magnetic flux tubes. II - Low potential simulation

The evolution of plasma in a current-carrying magnetic flux tube of variable cross section is investigated using a one-dimensional numerical simulation. The flux tube is narrow at the two ends and broad in the middle. The middle part of the flux tube is loaded with a hot, magnetically trapped population, and the two ends have a more dense, gravitationally bound population. A potential difference larger than the gravitational potential but less than the energy of the hot population is applied across the domain. The general result is that the potential change becomes distributed along the anode half of the domain, with negligible potential change on the cathode half. The potential is supported by the mirror force of magnetically trapped particles. The simulations show a steady depletion of plasma on the anode side of the flux tube. The current steadily decreases on a time scale of an ion transit time. The results may provide an explanation for the observed plasma depletions on auroral field lines carrying upward currents.

Swift, Daniel W.↗

NASA NTRS1992

Eigenvalue error analysis of viscously damped structures using a Ritz reduction method

The efficient solution of the eigenvalue problem that results from inserting passive dampers with variable stiffness and damping coefficients into a structure is addressed. Eigenanalysis of reduced models obtained by retaining a number of normal modes augmented with Ritz vectors corresponding to the static solutions resulting from the load patterns introduced by the dampers has been empirically shown to yield excellent approximations to the full eigenvalue problem. An analysis of this technique in the case of a single damper is presented. A priori and a posteriori error estimates are generated and tested on numerical examples. Comparison theorems with modally truncated models and a Markov parameter matching reduced-order model are derived. These theorems corroborate the heuristic that residual flexibility methods improve low-frequency approximation of the system. The analysis leads to other techniques for eigenvalue approximation. Approximate closed-form solutions are derived that include a refinement to eigenvalue derivative methods for approximation. An efficient Newton scheme is also developed. A numerical example is presented demonstrating the effectiveness of each of these methods.

Chu, Cheng-Chih↗

NASA NTRS1994

Kinematic modeling of a double octahedral Variable Geometry Truss (VGT) as an extensible gimbal

This paper presents the complete forward and inverse kinematics solutions for control of the three degree-of-freedom (DOF) double octahedral variable geometry truss (VGT) module as an extensible gimbal. A VGT is a truss structure partially comprised of linearly actuated members. A VGT can be used as joints in a large, lightweight, high load-bearing manipulator for earth- and space-based remote operations, plus industrial applications. The results have been used to control the NASA VGT hardware as an extensible gimbal, demonstrating the capability of this device to be a joint in a VGT-based manipulator. This work is an integral part of a VGT-based manipulator design, simulation, and control tool.

Williams, Robert L., II↗

NASA NTRS1994

Probabilistic Simulation of the Human Factor in Structural Reliability

The formal approach described herein computationally simulates the probable ranges of uncertainties for the human factor in probabilistic assessments of structural reliability. Human factors such as marital status, professional status, home life, job satisfaction, work load, and health are studied by using a multifactor interaction equation (MFIE) model to demonstrate the approach. Parametric studies in conjunction with judgment are used to select reasonable values for the participating factors (primitive variables). Subsequently performed probabilistic sensitivity studies assess the suitability of the MFIE as well as the validity of the whole approach. Results show that uncertainties range from 5 to 30 percent for the most optimistic case, assuming 100 percent for no error (perfect performance).

Chamis, Christos C.↗

NASA NTRS1997

Application of Thioether for Vapor Phase Lubrication

The objective of these studies was to identify the optimal conditions for vapor phase lubrication using Thioether for both sliding and rolling wear. The important variable include; (1) The component materials including M50 steel, monel and silicon nitride. (2) The vapor concentration and flow rate. (3) The temperature in the range of 600 F to 1500 F. (4) The loads and rolling and/or sliding speeds.

Graham, E. Earl↗

NASA NTRS2003

Evaluation of the Spherical Flange Concept for a Rocket Engine

Due to the inherent tolerance variability of hardware, flange misalignments occur during installation of mating components for a liquid propellant rocket engine. Flange misalignments include axial, lateral, and angular offsets. If these misalignments are high, they can impart significant loads into the two mating components. These significant loads can then be a driver in the design of the propellant ducts. Such was the case for the Rocketdyne RS-83 engine design for the Space Launch Initiative Program. To address this flange misalignment issue, Marshall Space Flight Center joined with Rocketdyne to develop and test a spherical flange system that allows for misalignment, yet reduces loads imparted, and at the same time provides sufficient sealing against leakage. The flange design was tested to evaluate and compare performance parameters such as misalignment and leakage. The environmental conditions ranged from -100 to 400 degrees Fahrenheit (F) with 1000 to 4000 pounds per square inch gage (psig) pressure. The desirable design features will be extracted and synthesized into a new flange design concept. This paper will address the spherical flange design and the test results.

Nichols, Jay↗

NASA NTRS2003

Air Cargo Transportation Route Choice Analysis

Using a unique feature of air cargo transshipment data in the Northeast Asian region, this paper identifies the critical factors that determine the transshipment route choice. Taking advantage of the variations in the transport characteristics in each origin-destination airports pair, the paper uses a discrete choice model to describe the transshipping route choice decision made by an agent (i.e., freight forwarder, consolidator, and large shipper). The analysis incorporates two major factors, monetary cost (such as line-haul cost and landing fee) and time cost (i.e., aircraft turnaround time, including loading and unloading time, custom clearance time, and expected scheduled delay), along with other controls. The estimation method considers the presence of unobserved attributes, and corrects for resulting endogeneity by use of appropriate instrumental variables. Estimation results find that transshipment volumes are more sensitive to time cost, and that the reduction in aircraft turnaround time by 1 hour would be worth the increase in airport charges by more than $1000. Simulation exercises measures the impacts of alternative policy scenarios for a Korean airport, which has recently declared their intention to be a future regional hub in the Northeast Asian region. The results suggest that reducing aircraft turnaround time at the airport be an effective strategy, rather than subsidizing to reduce airport charges.

Obashi, Hiroshi↗

NASA NTRS2012

Probabilistic Sensitivity Analysis for Launch Vehicles with Varying Payloads and Adapters for Structural Dynamics and Loads

This paper examines Probabilistic Sensitivity Analysis (PSA) methods and tools in an effort to understand their utility in vehicle loads and dynamic analysis. Specifically, this study addresses how these methods may be used to establish limits on payload mass and cg location and requirements on adaptor stiffnesses while maintaining vehicle loads and frequencies within established bounds. To this end, PSA methods and tools are applied to a realistic, but manageable, integrated launch vehicle analysis where payload and payload adaptor parameters are modeled as random variables. This analysis is used to study both Regional Response PSA (RRPSA) and Global Response PSA (GRPSA) methods, with a primary focus on sampling based techniques. For contrast, some MPP based approaches are also examined.

McGhee, David S.↗

DOE OSTI2022

Impact of feed variability on cesium removal with multiple actual waste samples from the Hanford site

Here, the Tank Side Cesium Removal (TSCR) system, under development by Washington River Protection Solutions (WRPS), will send initial low-activity Hanford waste tank supernate feeds to the Hanford Waste Treatment and Immobilization Plant (WTP) Low-Activity Waste (LAW) Facility. In addition to entrained solids removal from the supernate, the primary goal of TSCR is to remove cesium-137 ( 137 Cs) by ion exchange, allowing contact handling of the liquid effluent product at WTP. Crystalline silicotitanate (CST) ion exchange media, manufactured by Honeywell UOP (product IONSIV™ R9140-B), was selected as the ion exchange media at TSCR. This lot of material was found to have superior performance in comparison to historic batches of CST. Ion exchange column and batch contact testing with supernate from Hanford tanks AP-105, AP-107 and AW-102 was performed to assess the impact of feed variability on system performance. These tests demonstrated that batch contact measurements provide a reasonable prediction of column capacities with some deviation in performance attributed to column dynamics. In addition, the variability in CST capacity for cesium in the various actual waste samples does not track with historical understanding of the competing cations, suggesting that tank waste samples contain other components that may significantly impact cesium loading.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2020

Control of Output Power in Primary Side LCC and Secondary Series Tuned Wireless Power Transfer System without Secondary Side Sensors

The output power of a wireless power transfer (WPT) system varies with load and coupling factor of the inductively coupled coils. This paper presents a method to control the output power of primary side LCC and secondary side series tuned WPT system using information of primary side variables. In this approach, a secondary side control system or secondary side sensors are not needed. Detailed mathematical derivations are given to identify and justify the suitable primary side variable that accomplishes the desired purpose without the need of any secondary side communications. Simulation results presented validate the proposed scheme.

Mukherjee, Subho↗

DOE OSTI2025

Real-time Simulation Model of a Vanadium Redox Flow Battery Energy Storage System with Power Electronics Integration

This paper presents a real-time (RT) model of a 20 kW multi-stack vanadium redox flow battery (VRFB) system including power electronics converters in a single real-time framework. Implemented on a Typhoon HIL 604 device, this model is designed to simulate the operation of the flow battery with system-level controls. To provide a realistic overview of a VRFB system, the model incorporates a closed-loop control system for managing the speeds of two centrifugal pumps and an electro-thermal model of the battery stacks, enabling realtime temperature estimation. Furthermore, a two-stage power electronics topology and associated control solution are presented, operating with distinct strategies for interfacing the battery model with the main grid and a local load. Results from simulations demonstrate that the VRFB model is well suited for RT environment, and system can manage power during both charging and discharging cycles, while a SCADA monitor is used to display critical variables for safe, efficient, and reliable operation of the VRFB systems.

Rezende Da Costa Reis Kimpara, Renata [ORNL] (ORCI↗

NASA NTRS1975

Experimental quiet engine program

Full-scale low-tip-speed fans, a full-scale high-tip-speed fan, scale model versions of fans, and two full-scale high-bypass-ratio turbofan engines, were designed, fabricated, tested, and evaluated. Turbine noise suppression was investigated. Preliminary design studies of flight propulsion system concepts were used in application studies to determine acoustic-economic tradeoffs. Salient results are as follows: tradeoff evaluation of fan tip speed and blade loading; systematic data on source noise characteristics and suppression effectiveness; documentation of high- and low-fan-speed aerodynamic and acoustic technology; aerodynamic and acoustic evaluation of acoustic treatment configurations, casing tip bleed, serrated and variable pitch rotor blades, leaned outlet guide vanes, slotted tip casings, rotor blade shape modifications, and inlet noise suppression; systematic evaluation of aerodynamic and acoustic effects; flyover noise projections of engine test data; turbine noise suppression technology development; and tradeoff evaluation of preliminary design high-fan-speed and low-fan-speed flight engines.

Cornell, W. G.↗

NASA NTRS1975

Fatigue crack propagation behavior of the Ni-Ni3Cb eutectic composite

The experimental procedures used in the investigation are considered, taking into account solidification and heat treatment, fatigue testing, questions of test specimen and loading fixture design verification, metallographic techniques, and electron microscopy techniques. Attention is given to the characteristics of the microstructure, aspects of fatigue crack propagation (FCP) in the Ni-Ni3Nb composite, the effect of test variables on FCP, the effect of metallurgical variables on FCP, and fatigue fracture mechanisms. Fractographic and metallographic observations are discussed.

Mills, W. J.↗

NASA NTRS1975

Inviscid to turbulent transition of trailing vortices

The plateau region in which trailing vortices initially exhibit slow decay of maximum tangential speed is demonstrated with the aid of constant and variable eddy viscosity models. The existence of the plateau is explained by the presence of the viscous core and by the necessity for transition of the initial, nearly inviscid profile to similarity far downstream. Span loading is shown to affect the initial maximum tangential speed as well as the duration of the plateau region. Triangular span loading is shown to present less hazard to trailing aircraft, at least in the near field, than elliptic loading because the inviscid profile for triangular loading exhibits a finite tangential speed at the vortex centerline and a large inviscid core.

Iversen, J. D.↗

NASA NTRS1977

A computer software system for the generation of global ocean tides including self-gravitation and crustal loading effects

A computer software system is described which computes global numerical solutions of the integro-differential Laplace tidal equations, including dissipation terms and ocean loading and self-gravitation effects, for arbitrary diurnal and semidiurnal tidal constituents. The integration algorithm features a successive approximation scheme for the integro-differential system, with time stepping forward differences in the time variable and central differences in spatial variables.

Estes, R. H.↗

NASA NTRS1977

Aerodynamic characteristics of a 1/6-scale powered model of the rotor systems research aircraft

A wind-tunnel investigation was conducted to determine the effects of the main-rotor wake on the aerodynamic characteristics of the rotor systems research aircraft (RSRA). For the investigation, a 1/6-scale model with a four-blade articulated main rotor was used. Tests were conducted with and without the main rotor. Both the helicopter and the compound helicopter were tested. The latter configuration included the auxiliary thrust engines and the variable-incidence wing. Data were obtained over ranges of angle of attack, angle of sideslip, and main-rotor collective pitch angle at several main-rotor advance ratios. Results are presented for the total loads on the airframe as well as the loads on the rotor, the wing, and the tail. The results indicated that without the effect of the rotor wake, the RSRA had static longitudinal and directional stability and positive effective dihedral. With the effect of the main rotor and its wake, the RSRA exhibited longitudinal instability but retained static directional stability and positive effective dihedral.

Mineck, R. E.↗