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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 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Estimation of Forest Fuel Load from Radar Remote Sensing

Understanding fire behavior characteristics and planning for fire management require maps showing the distribution of wildfire fuel loads at medium to fine spatial resolution across large landscapes. Radar sensors from airborne or spaceborne platforms have the potential of providing quantitative information about the forest structure and biomass components that can be readily translated to meaningful fuel load estimates for fire management. In this paper, we used multifrequency polarimetric synthetic aperture radar imagery acquired over a large area of the Yellowstone National Park (YNP) by the AIRSAR sensor, to estimate the distribution of forest biomass and canopy fuel loads. Semi-empirical algorithms were developed to estimate crown and stem biomass and three major fuel load parameters, canopy fuel weight, canopy bulk density, and foliage moisture content. These estimates when compared directly to measurements made at plot and stand levels, provided more than 70% accuracy, and when partitioned into fuel load classes, provided more than 85% accuracy. Specifically, the radar generated fuel parameters were in good agreement with the field-based fuel measurements, resulting in coefficients of determination of R(sup 2) = 85 for the canopy fuel weight, R(sup 2)=.84 for canopy bulk density and R(sup 2) = 0.78 for the foliage biomass.

Saatchi, Sassan↗
NASA NTRS1989

Application of attachment modes in the control of large space structures

Various ways are examined to obtain reduced order mathematical models of structures for use in dynamic response analyses and in controller design studies. Attachment modes are deflection shapes of a structure subjected to specified unit load distributions. Attachment modes are frequently employed to supplement free-interface normal modes to improve the modeling of components (structures) employed in component mode synthesis analyses. Deflection shapes of structures subjected to generalized loads of some specified distribution and of unit magnitude can also be considered to be attachment modes. Several papers which were written under this contract are summarized herein.

Craig, Roy R., Jr.↗
NASA NTRS1981

Low-velocity impact tests on fibrous composite sandwich structures

The effect of low-velocity projectile impact on the load-carrying ability of the composite sandwich structural components is investigated experimentally, the impact simulating the damage caused by runway debris and the accidental dropping of hand tools during servicing on secondary aircraft structures made with composites. The sandwich-type beam specimens were fabricated with graphite/epoxy face sheets, aluminum honeycomb core, and a steel (back) plate. A four-point beam-loading apparatus was used, and the ultimate strength, ultimate strain, and residual strength of the composites were determined. A faired curve is presented indicating the lower bound of the failure threshold for each of the laminate configurations tested in compression and tension as a function of the projectile impact energy. It is shown that strength degradation due to impact is dependent on the laminate configuration and the fiber/matrix combination. The laminates having more angle plies near the impact surface and unidirectional plies elsewhere seem to show extensive interply and intraply fiber delaminations at failure relative to the laminates with a cross-ply on the impact surface.

Sharma, A. V.↗
NASA NTRS1961

A Versatile Drop Test Procedure for the Simulation of Impact Environments

In order to assure the reliability of space flight systems and spacecraft, it is necessary to subject these systems, vehicles, and their components to expected shock and impact environmental loads. The Langley Laboratory has found the apparatus and methods discussed in this paper useful in its work along these lines, and feels that other organizations might also find them of value.

Drop test↗
NASA NTRS1966

Compression springs at elevated temperatures

The behavior of compression springs is affected by increased temperatures. The most significant factors affecting springs are a loss of load and length (relaxation), and a change in the modulus of rigidity. Relaxation will reduce preset loads or change the location of supported components whereas a change in the modulus of rigidity will alter the spring rate. Both factors must be taken into account when designing compression springs. Curves and equations are presented (for music wire, 18-8 stainless steel, 17-7 PH, and Inconel-X) which can aid in the design of compression springs for use at elevated temperatures.

Spring↗
NASA NTRS1973

Apollo experience report: Command module crew-couch/restraint and load-attenuation systems

The Apollo command module crew-couch/restraint and load-attenuation system was required to support and restrain the crewman during mission phases and to limit the load imposed on the crewman during landing. Component designs evolved when requirements changed and tests were conducted. Advancement in the state of the art for energy-absorbing devices and changes in restraint philosophies for impact protection resulted from the efforts and experiences presented.

Drexel, R. E.↗
NASA NTRS1974

Space shuttle SRM interim contract, part 1

Essential studies and analyses required to integrate the SRM into the booster and overall space shuttle system. Emphasis was placed on the case, nozzle, insulation, and propellant components with resulting performance, weight, and structural load characteristics being generated. Effort conducted during the time period of this contract included studies, analyses, planning, and preliminary design activities. Technical requirements identified in the SRM Project Request for Proposal No. 8-1-4-94-98401 and Thiokol's proposed SRM design (designated Configuration 0) established the basis for this effort. The requirements were evaluated jointly with MSFC and altered where necessary to incorporate new information that evolved after issuance of the RFP and during the course of this interim contract. Revised water impact loads and load distributions were provided based on additional model test data and analytical effort conducted by NASA subsequent to the RFP release. Launch pad peaking loads into the SRM aft skirt were provided which also represented a change from RFP requirements. A modified SRM/External Tank (ET) attachment configuration with new structural load data was supplied by NASA, and direction was received to include a 2 percent inert weight contingency.

Source record↗
NASA NTRS1982

Environmental and high strain rate effects on composites for engine applications

The complex environmental and loading conditions experienced by many turbine engine components impose severe durability and damage tolerance requirements for component materials. Programs are being conducted to establish the structural performance of composite materials under anticipated engine operating environments. A description is presented of the results obtained in connection with several of these programs. A comparison of predicted and measured hygrothermal effects is considered along with hygrothermal effects on defect growth, high strain rate effects on composite mechanical properties, dynamic stress intensity factors for composites, and the indentation laws for composite impact analysis.

Chamis, C. C.↗
NASA NTRS1983

Predicted and experimental performance of large-bore high-speed ball and roller bearings

The values of inner and outer race temperature, cage speed, and heat transferred to the lubricant or bearing power loss, calculated using the computer programs Shaberth and Cybean, with the corresponding experimental data for the large bore ball and roller bearings were compared. After the development of computer program, it is important that values calculated using such program are compared with actual bearing performance data to assess the programs predictive capability. Several comprehensive computer programs currently in use are capable of predicting rolling bearing operating and performance characteristics. These programs accept input data of bearing internal geometry, bearing material and lubricant properties, and bearing operating conditions. The programs solve several sets of equations that characterize rolling element bearings. The output produced typically consists of rolling element loads and Hertz stresses, operating contact angles, component speed, heat generation, local temperatures, bearing fatigue life, and power loss. Two of these programs, Shaberth and Cybean were developed.

Coe, H. H.↗
NASA NTRS1983

NASTRAN forced vibration analysis of rotating cyclic structures

Theoretical aspects of a new capability, developed and added to the general purpose finite element program NASTRAN Level 17.7, to conduct forced vibration analysis of turned cyclic structures rotating about their axis of symmetry, are presented. The effects of Coriolis and centripetal accelerations as well as those due to the translational acceleration of the axis of rotation, are included. The equations of motion are first derived for an arbitrary grid point of the cyclic sector finite element model and then extended for the complete model. The equations are solved by four principal steps: (1) transformation of applied loads at frequency-dependent circumferential harmonic components; (2) application of circumferential harmonic-dependent intersegment compatibility constraints; (3) solution of frequency-dependent circumferential harmonic components of displacements; and (4) recovery of frequency-dependent response in various segments of the total structure. Five interrelated examples are presented to illustrate the various features of the development.

Elchuri, V.↗
NASA NTRS1988

Data requirements to model creep in 9Cr-1Mo-V steel

Models for creep behavior are helpful in predicting response of components experiencing stress redistributions due to cyclic loads, and often the analyst would like information that correlates strain rate with history assuming simple hardening rules such as those based on time or strain. On the one hand, much progress has been made in the development of unified constitutive equations that include both hardening and softening through the introduction of state variables whose evolutions are history dependent. Although it is difficult to estimate specific data requirements for general application, there are several simple measurements that can be made in the course of creep testing and results reported in data bases. The issue is whether or not such data could be helpful in developing unified equations, and, if so, how should such data be reported. Data produced on a martensitic 9Cr-1Mo-V-Nb steel were examined with these issues in mind.

Swindeman, R. W.↗
NASA NTRS1986

Independent Orbiter Assessment (IOA): Analysis of the backup flight system

The results of the Independent Orbiter Assessment (IOA) of the Failure Modes and Effects Analysis (FMEA) and Critical Items List (CIL) are presented. The IOA approach features a top-down analysis of the hardware to determine failure modes, criticality, and potential critical items. To preserve independence, this analysis was accomplished without reliance upon the results contained within the NASA FMEA/CIL documentation. This report documents the analysis results corresponding to the Orbiter Backup Flight System (BFS) hardware. The BFS hardware consists of one General Purpose Computer (GPC) loaded with backup flight software and the components used to engage/disengage that unique GPC. Specifically, the BFS hardware includes the following: DDU (Display Driver Unit), BFC (Backup Flight Controller), GPC (General Purpose Computer), switches (engage, disengage, GPC, CRT), and circuit protectors (fuses, circuit breakers). The IOA analysis process utilized available BFS hardware drawings and schematics for defining hardware assemblies, components, and hardware items. Each level of hardware was evaluated and analyzed for possible failure modes and effects. Criticality was assigned based upon the severity of the effect for each failure mode. Of the failure modes analyzed, 19 could potentially result in a loss of life and/or loss of vehicle.

Prust, E. E.↗
NASA NTRS1992

The Space Transportation System summer environment on launch pad

This paper describes a 2D flow and thermalanalysis to determine the solar effect on the Space Shuttle launch components subsequent to the external tank (ET) loading operation in extremely hot conditions. An existing CFD code Parabolic Hyperbolic or Elliptical Numerical Integration Code Series was used in the study. The analysis was done for a 2D slice between planes perpendicular to the longitudinal axis of the STS and passing through the lower portions of the Redesigned Solid Rocket Motors (RSRMs), the ET, and the wing of the Orbiter. The results are presented as local and average values of the heat transfer coefficient, and the Nusselt number, and the surface temperature around the RSRMs and the ET. Solar heating effects increased the surface temperatures of the RSRMs by 9-11 F. Higher prelaunch surface temperatures measured on the east and west RSRMs (in the inboard region between the RSRMs and the ET) during 19 most recent launches of the STS are correlated as a function of the ambient temperature.

Ahmad, R. A.↗
NASA NTRS1918

Airplane Stress Analysis

Report presents stress analysis of individual components of an airplane. Normal and abnormal loads, sudden loads, simple stresses, indirect simple stresses, resultant unit stress, repetitive and equivalent stress, maximum steady load and stress are considered.

Zahm, A F↗
NASA NTRS1999

Euler Flow Computations on Non-Matching Unstructured Meshes

Advanced fluid solvers to predict aerodynamic performance-coupled treatment of multiple fields are described. The interaction between the fluid and structural components in the bladed regions of the engine is investigated with respect to known blade failures caused by either flutter or forced vibrations. Methods are developed to describe aeroelastic phenomena for internal flows in turbomachinery by accounting for the increased geometric complexity, mutual interaction between adjacent structural components and presence of thermal and geometric loading. The computer code developed solves the full three dimensional aeroelastic problem of-stage. The results obtained show that flow computations can be performed on non-matching finite-volume unstructured meshes with second order spatial accuracy.

Gumaste, Udayan↗
NASA NTRS2011

Development of the Vibration Isolation System for the Advanced Resistive Exercise Device

This paper describes the development of the Vibration Isolation System for the Advanced Resistive Exercise Device from conceptual design to lessons learned. Maintaining a micro-g environment on the International Space Station requires that experiment racks and major vibration sources be isolated. The challenge in characterizing exercise loads and testing the system in the presence of gravity led to a decision to qualify the system by analysis. Available data suggests that the system is successful in attenuating loads, yet there has been a major component failure and several procedural issues during its 3 years of operational use.

Niebuhr, Jason H.↗