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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 1,459 records · Page 81
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

State of stress, faulting, and eruption characteristics of large volcanoes on Mars

The formation of a large volcano loads the underlying lithospheric plate and can lead to lithospheric flexure and faulting. In turn, lithospheric stresses affect the stress field beneath and within the volcanic edifice and can influence magma transport. Modeling the interaction of these processes is crucial to an understanding of the history of eruption characteristics and tectonic deformation of large volcanoes. We develop models of time-dependent stress and deformation of the Tharsis volcanoes on Mars. A finite element code is used that simulates viscoelastic flow in the mantle and elastic plate flexural behavior. We calculate stresses and displacements due to a volcano-shaped load emplaced on an elastic plate. Models variously incorporate growth of the volcanic load with time and a detachment between volcano and lithosphere. The models illustrate the manner in which time-dependent stresses induced by lithospheric plate flexure beneath the volcanic load may affect eruption histories, and the derived stress fields can be related to tectonic features on and surrounding martian volcanoes.

Mcgovern, Patrick J.↗
NASA NTRS1995

Three-dimensional CTOA and constraint effects during stable tearing in a thin-sheet material

A small strain theory, three-dimensional elastic-plastic finite element analysis was used to simulate fracture in thin sheet 2024-T3 aluminum alloy in the T-L orientation. Both straight and tunneled cracks were modeled. The tunneled crack front shapes as a function of applied stress were obtained from the fracture surface of tested specimens. The stable crack growth behavior was measured at the specimen surface as a function of applied stress. The fracture simulation modeled the crack tunneling and extension as a function of applied stress. The results indicated that the global constraint factor, alpha(sub g), initially dropped during stable crack growth. After peak applied stress was achieved, alpha(sub g) began to increase slightly. The effect of crack front shape on alpha(sub g) was small, but the crack front shape did greatly influence the local constraint and through-thickness crack-tip opening angle (CTOA) behavior. The surface values of CTOA for the tunneled crack front model agreed well with experimental measurements, showing the same initial decrease from high values during the initial 3mm of crack growth at the specimen's surface. At the same time, the interior CTOA values increased from low angles. After the initial stable tearing region, the CTOA was constant through the thickness. The three-dimensional analysis appears to confirm the potential of CTOA as a two-dimensional fracture criterion.

Dawicke, D. S.↗
NASA NTRS1996

Influence of Back-Up Bearings and Support Structure Dynamics on the Behavior of Rotors With Active Supports

This report presents a synopsis of the research work. Specific accomplishments are itemized below: (1) Experimental facilities have been developed. This includes a magnetic bearing test rig and an auxiliary bearing test rig. In addition, components have been designed, constructed, and tested for use with a rotordynamics test rig located at NASA Lewis Research Center. (2) A study of the rotordynamics of an auxiliary bearing supported T-501 engine model was performed. (3) An experimental/simulation study of auxiliary bearing rotordynamics has been performed. (4) A rotordynamical model for a magnetic bearing supported rotor system, including auxiliary bearing effects has been developed and simulation studies performed.(5) A finite element model for a foil bearing has been developed and studies of a rotor supported by foil bearings have been performed. (6) Two students affiliated with this project have graduated with M.S. degrees.

Flowers, George T.↗
NASA NTRS1998

Development of a Probabilistic Dynamic Synthesis Method for the Analysis of Nondeterministic Structures

Accounting for the statistical geometric and material variability of structures in analysis has been a topic of considerable research for the last 30 years. The determination of quantifiable measures of statistical probability of a desired response variable, such as natural frequency, maximum displacement, or stress, to replace experience-based "safety factors" has been a primary goal of these studies. There are, however, several problems associated with their satisfactory application to realistic structures, such as bladed disks in turbomachinery. These include the accurate definition of the input random variables (rv's), the large size of the finite element models frequently used to simulate these structures, which makes even a single deterministic analysis expensive, and accurate generation of the cumulative distribution function (CDF) necessary to obtain the probability of the desired response variables. The research presented here applies a methodology called probabilistic dynamic synthesis (PDS) to solve these problems. The PDS method uses dynamic characteristics of substructures measured from modal test as the input rv's, rather than "primitive" rv's such as material or geometric uncertainties. These dynamic characteristics, which are the free-free eigenvalues, eigenvectors, and residual flexibility (RF), are readily measured and for many substructures, a reasonable sample set of these measurements can be obtained. The statistics for these rv's accurately account for the entire random character of the substructure. Using the RF method of component mode synthesis, these dynamic characteristics are used to generate reduced-size sample models of the substructures, which are then coupled to form system models. These sample models are used to obtain the CDF of the response variable by either applying Monte Carlo simulation or by generating data points for use in the response surface reliability method, which can perform the probabilistic analysis with an order of magnitude less computational effort. Both free- and forced-response analyses have been performed, and the results indicate that, while there is considerable room for improvement, the method produces usable and more representative solutions for the design of realistic structures with a substantial savings in computer time.

Brown, A. M.↗
NASA NTRS1997

Ice velocity at the ice front of the Filchner-Ronne Ice Shelf, Antarctica, as observed with ERS interferometry

ERS images of the two ends of the ice front of the Filchner-Ronne ice shelf (Antarctica) were utilized interferometrically to study the deformation rate of the ice shelf in response to viscous creep. On the western bank of Berkner Island (BI), near Hemmen Ice Rise (HIR), a time series of ERS data acquired in February 1992, in both ascending and descending mode, and with a three-day time interval, were utilized to map the ice velocity in two dimensions. Finite-element ice-shelf flow simulations are compared with the ERS interferograms to interpret the ice motion in terms of the physical constraints on ice-shelf flow. The efforts to fit artificial interferograms generated with model velocity output suggest that the flow regime is strongly influenced by three processes. First, a void-creation process responsible for rifts at coastal margins tends to uncouple the ice shelf from the ice rise and neighboring coast of BI. Secondly, sea ice within the void space appears to act as a binding agent between discrete ice-shelf fragments, allowing rigid-body rotations of these fragments. Third, strain rates appear to be enhanced in a narrow zone adjacent to HIR, implying significant strain softening along the boundary. It is believed that synthetic aperture radar (SAR) interferogram/model intercomparison represents a powerful impetus towards the development of better, more physically realistic ice-shelf flow models.

Rignot, Eric↗
NASA NTRS1999

Multiphysics Simulation of Active Hypersonic Lip Cooling

This article describes the application of the Multidisciplinary Analysis (MDA) solver, Spectrum, in analyzing a hydrogen-cooled hypersonic cowl leading-edge structure. Spectrum, a multiphysics simulation code based on the finite element method, addresses compressible and incompressible fluid flow, structural, and thermal modeling, as well as the interactions between these disciplines. Fluid-solid-thermal interactions in a hydrogen impingement-cooled leading edge are predicted using Spectrum. Two- and semi-three-dimensional models are considered for a leading edge impingement coolant, concept under either specified external heat flux or aerothermodynamic heating from a Mach 5 external flow interaction. The solution accuracy is demonstrated from mesh refinement analysis. With active cooling, the leading edge surface temperature is drastically reduced from 1807 K of the adiabatic condition to 418 K. The internal coolant temperature profile exhibits a sharp gradient near channel/solid interface. Results from two different cooling channel configurations are also presented to illustrate the different behavior of alternative active cooling schemes.

Melis, Matthew E.↗
NASA NTRS2000

Modeling and Characterization of Geometric Effects on the Performance of Rainbow and Thunder Actuators

Dome formation in Rainbow and Thunder actuators occurs to relieve thermal expansion mismatch stress between the metallic and piezoelectric layers during cooling from device fabrication temperatures. Accompanying this process is the generation of an internal stress profile within the devices and the development of significant tensile stresses within the surface region of the piezoelectric. These tensile stresses affect the domain configuration (ratio of c-to-a domains), and improve the 90 deg. domain wall movement response of the device in this region of the piezoelectric. This results in improved electromechanical performance compared to standard direct extensional and flextensional devices, presumably because of the contributions of stress to the non-linearity of the piezoelectric d-coefficients. 1 Interestingly, this improvement in response seems counterintuitive; a stress perpendicular to the direction of the applied electric field should impede, not contribute to 90' domain switching. Further consideration of the lower region of the piezoelectric that is under compressive stress thus appears warranted. The specified objectives of the research were to: 1. Conduct finite element and equivalent circuit simulation-based investigations to understand the effects of actuator geometry on internal stress distribution and actuator performance (displacement and load-bearing capabilities). 2. Use the results of the modeling studies to predict the processing conditions (geometry and thickness ratio) required for the fabrication of Rainbow ceramics with optimized performance.

Schwartz, Robert W.↗
NASA NTRS2001

Damage Tolerance of Sandwich Plates With Debonded Face Sheets

A nonlinear finite element analysis was performed to simulate axial compression of sandwich beams with debonded face sheets. The load - end-shortening diagrams were generated for a variety of specimens used in a previous experimental study. The energy release rate at the crack tip was computed using the J-integral, and plotted as a function of the load. A detailed stress analysis was performed and the critical stresses in the face sheet and the core were computed. The core was also modeled as an isotropic elastic-perfectly plastic material and a nonlinear post buckling analysis was performed. A Graeco-Latin factorial plan was used to study the effects of debond length, face sheet and core thicknesses, and core density on the load carrying capacity of the sandwich composite. It has been found that a linear buckling analysis is inadequate in determining the maximum load a debonded sandwich beam can carry. A nonlinear post-buckling analysis combined with an elastoplastic model of the core is required to predict the compression behavior of debonded sandwich beams.

Sankar, Bhavani V.↗
NASA NTRS2001

Thermal Fault Tolerance Analysis of Carbon Fiber Rope Barrier Systems for Use in the Reusable Solid Rocket Motor ( RSRM) Nozzle Joints

Carbon Fiber Rope (CFR) thermal barrier systems are being considered for use in several RSRM (Reusable Solid Rocket Motor) nozzle joints as a replacement for the current assembly gap close-out process/design. This study provides for development and test verification of analysis methods used for flow-thermal modeling of a CFR thermal barrier subject to fault conditions such as rope combustion gas blow-by and CFR splice failure. Global model development is based on a 1-D (one dimensional) transient volume filling approach where the flow conditions are calculated as a function of internal 'pipe' and porous media 'Darcy' flow correlations. Combustion gas flow rates are calculated for the CFR on a per-linear inch basis and solved simultaneously with a detailed thermal-gas dynamic model of a local region of gas blow by (or splice fault). Effects of gas compressibility, friction and heat transfer are accounted for the model. Computational Fluid Dynamic (CFD) solutions of the fault regions are used to characterize the local flow field, quantify the amount of free jet spreading and assist in the determination of impingement film coefficients on the nozzle housings. Gas to wall heat transfer is simulated by a large thermal finite element grid of the local structure. The employed numerical technique loosely couples the FE (Finite Element) solution with the gas dynamics solution of the faulted region. All free constants that appear in the governing equations are calibrated by hot fire sub-scale test. The calibrated model is used to make flight predictions using motor aft end environments and timelines. Model results indicate that CFR barrier systems provide a near 'vented joint' style of pressurization. Hypothetical fault conditions considered in this study (blow by, splice defect) are relatively benign in terms of overall heating to nozzle metal housing structures.

Clayton, J. Louie↗
NASA NTRS2002

Deployment, Foam Rigidization, and Structural Characterization of Inflatable Thin-Film Booms

Detailed investigation of the construction, packaging/deployment, foam rigidization, and structural characterization of polyimide film inflatable booms is described. These structures have considerable potential for use in space with solar concentrators, solar sails, space power systems including solar arrays, and other future missions. Numerous thin-film booms or struts were successfully constructed, inflated, injected with foam, and rigidized. Both solid-section and annular test articles were fabricated, using Kapton polyimide film, various adhesives, Styrofoam end plugs, and polyurethane pressurized foam. Numerous inflation/deployment experiments were conducted and compared to computer simulations using the MSC/DYTRAN code. Finite element models were developed for several foam-rigidized struts and compared to model test results. Several problems encountered in the construction, deployment, and foam injection/rigidization process are described. Areas of difficulty included inadequate adhesive strength, cracking of the film arid leakage, excessive bending of the structure during deployment, problems with foam distribution and curing properties, and control of foam leakage following injection into the structure. Many of these problems were overcome in the course of the research.

Schnell, Andrew R.↗
NASA NTRS2000

Coupled Thermo-Mechanical Analyses of Dynamically Loaded Rubber Cylinders

A procedure that models coupled thermo-mechanical deformations of viscoelastic rubber cylinders by employing the ABAQUS finite element code is described. Computational simulations of hysteretic heating are presented for several tall and short rubber cylinders both with and without a steel disk at their centers. The cylinders are compressed axially and are then cyclically loaded about the compressed state. The non-uniform hysteretic heating of the rubber cylinders containing a steel disk is presented. The analyses performed suggest that the coupling procedure should be considered for further development as a design tool for rubber degradation studies.

Johnson, Arthur R.↗
NASA NTRS1996

Impact Properties of Metal Fan Containment Materials Being Evaluated for the High-Speed Civil Transport (HSCT)

Under the Enabling Propulsion Materials (EPM) program - a partnership between NASA, Pratt & Whitney, and GE Aircraft Engines - the Materials and Structures Divisions of the NASA Lewis Research Center are involved in developing a fan-containment system for the High-Speed Civil Transport (HSCT). The program calls for a baseline system to be designed by the end of 1995, with subsequent testing of innovative concepts. Five metal candidate materials are currently being evaluated for the baseline system in the Structures Division's Ballistic Impact Facility. This facility was developed to provide the EPM program with cost-efficient and timely impact test data. At the facility, material specimens are impacted at speeds up to 350 m/sec by projectiles of various sizes and shapes to assess the specimens' ability to absorb energy and withstand impact. The tests can be conducted at either room or elevated temperatures. Posttest metallographic analysis is conducted to improve understanding of the failure modes. A dynamic finite element program is used to simulate the events and both guide the testing as well as aid in designing the fan-containment system.

Source record↗
NASA NTRS2006

Porous Media Approach for Modeling Closed Cell Foam

In order to minimize boil off of the liquid oxygen and liquid hydrogen and to prevent the formation of ice on its exterior surface, the Space Shuttle External Tank (ET) is insulated using various low-density, closed-cell polymeric foams. Improved analysis methods for these foam materials are needed to predict the foam structural response and to help identify the foam fracture behavior in order to help minimize foam shedding occurrences. This presentation describes a continuum based approach to modeling the foam thermo-mechanical behavior that accounts for the cellular nature of the material and explicitly addresses the effect of the internal cell gas pressure. A porous media approach is implemented in a finite element frame work to model the mechanical behavior of the closed cell foam. The ABAQUS general purpose finite element program is used to simulate the continuum behavior of the foam. The soil mechanics element is implemented to account for the cell internal pressure and its effect on the stress and strain fields. The pressure variation inside the closed cells is calculated using the ideal gas laws. The soil mechanics element is compatible with an orthotropic materials model to capture the different behavior between the rise and in-plane directions of the foam. The porous media approach is applied to model the foam thermal strain and calculate the foam effective coefficient of thermal expansion. The calculated foam coefficients of thermal expansion were able to simulate the measured thermal strain during heat up from cryogenic temperature to room temperature in vacuum. The porous media approach was applied to an insulated substrate with one inch foam and compared to a simple elastic solution without pore pressure. The porous media approach is also applied to model the foam mechanical behavior during subscale laboratory experiments. In this test, a foam layer sprayed on a metal substrate is subjected to a temperature variation while the metal substrate is stretched to simulate the structural response of the tank during operation. The thermal expansion mismatch between the foam and the metal substrate and the thermal gradient in the foam layer causes high tensile stresses near the metal/foam interface that can lead to delamination.

Ghosn, Louis J.↗
NASA NTRS2017

Heating and Thermal Control of Brazing Technique to Break Contamination Path for Potential Mars Sample Return

The potential return of Mars sample material is of great interest to the planetary science community, as it would enable extensive analysis of samples with highly sensitive laboratory instruments. It is important to make sure such a mission concept would not bring any living microbes, which may possibly exist on Mars, back to Earth’s environment. In order to ensure the isolation of Mars microbes from Earth’s Atmosphere, a brazing sealing and sterilizing technique was proposed to break the Mars-to-Earth contamination path. Effectively, heating the brazing zone in high vacuum space and controlling the sample temperature for integrity are key challenges to the implementation of this technique. The break-the-chain procedures for container configurations, which are being considered, were simulated by multi-physics finite element models. Different heating methods including induction and resistive/radiation were evaluated. The temperature profiles of Martian samples in a proposed container structure were predicted. The results show that the sealing and sterilizing process can be controlled such that the samples temperature is maintained below the level that may cause damage, and that the brazing technique is a feasible approach to breaking the contamination path.

Bao, Xiaoqi↗
NASA NTRS2019

X-57 Mod 2 Motor Thermal Analysis

This work covers the refinement of thermal models from design estimates to actual fabricated performance. Matching the experimental data of the first fully electrified version of the X-57 Maxwell experimental vehicle requires high fidelity thermal analysis to sufficiently capture the electric motor and inverter temperature profiles. Qualification test data of the motors and inverters is used to validate finite element analysis models used to simulate thermal performance over mission transients. An additional thermal-hydraulic models is used to estimate flow characteristics through the propulsor nacelle and component heat sinks. After calibration of the higher order models, overall component sizing and peak temperature constraints can be distilled to reduced order models, to improve modelflexibility and utility.

Chin, Jeffrey C.↗
NASA NTRS2018

Modeling Space Radiation Induced Bone Changes in Rat Femurs through Finite Element Analysis

As the duration of manned missions outside of the Earth’s protective shielding increase, astronauts are at risk for exposure to space radiation. Various organ systems may be damaged due to exposure. This study investigates the bonestrength changes using finite element modeling of Long Evans rats (n=85) subjected to graded, head-only proton (0, 10, 25, and 100 cGy, 150 MeV/n) and 28silicon (0, 10, 25, and 50 cGy, 300 MeV/n) radiation. The strength of the femoral neck will be examined due its clinical relevance to hip fractures. It has been shown in previous studies that bone mineral density was not reduced at the site of fracture. These findings question whether measurements of bone mineral density may be used to assess risk of hip fracture. The mechanisms leading to the irregular relationship between bone density and strength are still uncertain within literature and investigated to greater extent in clinical applications. Finite element analysis within this study simulated physiological loading of the femoral neck. No significant changes in femoral neck strength were found across doses of proton or 28silicon head-only radiation. Future work includes performing mechanical testing of the bone samples. Moving from mouse to larger animal models may also provide the increased lifespan for assessing the long-term outcomes of radiation exposure.

Dale Johnson↗
DOE OSTI2015

Evaluation of Test Methods for Triaxially Braided Composites using a Meso-Scale Finite Element Model

The characterization of triaxially braided composite is complicate due to the nonuniformity of deformation within the unit cell as well as the possibility of the freeedge effect related to the large size of the unit cell. Extensive experimental investigation has been conducted to develop more accurate test approaches in characterizing the actual mechanical properties of the material we are studying. In this work, a meso-scale finite element model is utilized to simulate two complex specimens: notched tensile specimen and tube tensile specimen, which are designed to avoid the free-edge effect and free-edge effect induced premature edge damage. The full field strain data is predicted numerically and compared with experimental data obtained by Digit Image Correlation. The numerically predicted tensile strength values are compared with experimentally measured results. The discrepancy between numerically predicted and experimentally measured data, the capability of different test approaches are analyzed and discussed. The presented numerical model could serve as assistance to the evaluation of different test methods, and is especially useful in identifying potential local damage events.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2016

An Assessment of Some Design Constraints on Heat Production of a 3D Conceptual EGS Model Using an Open-Source Geothermal Reservoir Simulation Code

Performance of heat production process over a 30-year period is assessed in a conceptual EGS model with a geothermal gradient of 65K per km depth in the reservoir. Water is circulated through a pair of parallel wells connected by a set of single large wing fractures. The results indicate that the desirable output electric power rate and lifespan could be obtained under suitable material properties and system parameters. A sensitivity analysis on some design constraints and operation parameters indicates that 1) the fracture horizontal spacing has profound effect on the long-term performance of heat production, 2) the downward deviation angle for the parallel doublet wells may help overcome the difficulty of vertical drilling to reach a favorable production temperature, and 3) the thermal energy production rate and lifespan has close dependence on water mass flow rate. The results also indicate that the heat production can be improved when the horizontal fracture spacing, well deviation angle, and production flow rate are under reasonable conditions. To conduct the reservoir modeling and simulations, an open-source, finite element based, fully implicit, fully coupled hydrothermal code, namely FALCON, has been developed and used in this work. Compared with most other existing codes that are either closed-source or commercially available in this area, this new open-source code has demonstrated a code development strategy that aims to provide an unparalleled easiness for user-customization and multi-physics coupling. Test results have shown that the FALCON code is able to complete the long-term tests efficiently and accurately, thanks to the state-of-the-art nonlinear and linear solver algorithms implemented in the code.

enhanced geothermal system↗