Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Moving interface”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Algorithm and code development for unsteady three-dimensional Navier-Stokes equations

In the last two decades, there have been extensive developments in computational aerodynamics, which constitutes a major part of the general area of computational fluid dynamics. Such developments are essential to advance the understanding of the physics of complex flows, to complement expensive wind-tunnel tests, and to reduce the overall design cost of an aircraft, particularly in the area of aeroelasticity. Aeroelasticity plays an important role in the design and development of aircraft, particularly modern aircraft, which tend to be more flexible. Several phenomena that can be dangerous and limit the performance of an aircraft occur because of the interaction of the flow with flexible components. For example, an aircraft with highly swept wings may experience vortex-induced aeroelastic oscillations. Also, undesirable aeroelastic phenomena due to the presence and movement of shock waves occur in the transonic range. Aeroelastically critical phenomena, such as a low transonic flutter speed, have been known to occur through limited wind-tunnel tests and flight tests. Aeroelastic tests require extensive cost and risk. An aeroelastic wind-tunnel experiment is an order of magnitude more expensive than a parallel experiment involving only aerodynamics. By complementing the wind-tunnel experiments with numerical simulations the overall cost of the development of aircraft can be considerably reduced. In order to accurately compute aeroelastic phenomenon it is necessary to solve the unsteady Euler/Navier-Stokes equations simultaneously with the structural equations of motion. These equations accurately describe the flow phenomena for aeroelastic applications. At Ames a code, ENSAERO, is being developed for computing the unsteady aerodynamics and aeroelasticity of aircraft and it solves the Euler/Navier-Stokes equations. The purpose of this contract is to continue the algorithm enhancements of ENSAERO and to apply the code to complicated geometries. During the last year, the geometric capability of the code was extended to simulate transonic flows, a wing with oscillating control surface. Single-grid and zonal approaches were tested. For the zonal approach, a new interpolation technique was introduced. The key development of the algorithm was an interface treatment between moving zones for a control surface using the virtual-zone concept. The work performed during the period, 1 Apr. 1992 through 31 Mar. 1993 is summarized. Additional details on the various aspects of the study are given in the Appendices.

Obayashi, Shigeru↗
NASA NTRS1992

Finite element computation of incompressible flows

Among the solution techniques presented for FEM computation of incompressible flows are stabilized formulations designed to prevent the numerical oscillations that may be generated by (1) the presence of dominant advection terms in the governing equations, or (2) the failure to use an acceptable combination of interpolation functions to represent velocity and pressure fields. It is shown that the space-time formulation, in conjunction with the Galerkin-least squares methods, can be used to compute steady incompressible flows involving moving boundaries and interfaces; it is recommended that iteration methods be used to reduce the associated computational costs.

Tezduyar, T. E.↗
NASA NTRS2005

Stirling Analysis Comparison of Commercial Versus High-Order Methods

Recently, three-dimensional Stirling engine simulations have been accomplished utilizing commercial Computational Fluid Dynamics software. The validations reported can be somewhat inconclusive due to the lack of precise time accurate experimental results from engines, export control/proprietary concerns, and the lack of variation in the methods utilized. The last issue may be addressed by solving the same flow problem with alternate methods. In this work, a comprehensive examination of the methods utilized in the commercial codes is compared with more recently developed high-order methods. Specifically, Lele's compact scheme and Dyson's Ultra Hi-Fi method will be compared with the SIMPLE and PISO methods currently employed in CFD-ACE, FLUENT, CFX, and STAR-CD (all commercial codes which can in theory solve a three-dimensional Stirling model with sliding interfaces and their moving grids limit the effective time accuracy). We will initially look at one-dimensional flows since the current standard practice is to design and optimize Stirling engines with empirically corrected friction and heat transfer coefficients in an overall one-dimensional model. This comparison provides an idea of the range in which commercial CFD software for modeling Stirling engines may be expected to provide accurate results. In addition, this work provides a framework for improving current one-dimensional analysis codes.

Dyson, Rodger W.↗
NASA NTRS2007

Stirling Analysis Comparison of Commercial vs. High-Order Methods

Recently, three-dimensional Stirling engine simulations have been accomplished utilizing commercial Computational Fluid Dynamics software. The validations reported can be somewhat inconclusive due to the lack of precise time accurate experimental results from engines, export control/ proprietary concerns, and the lack of variation in the methods utilized. The last issue may be addressed by solving the same flow problem with alternate methods. In this work, a comprehensive examination of the methods utilized in the commercial codes is compared with more recently developed high-order methods. Specifically, Lele's Compact scheme and Dyson s Ultra Hi-Fi method will be compared with the SIMPLE and PISO methods currently employed in CFD-ACE, FLUENT, CFX, and STAR-CD (all commercial codes which can in theory solve a three-dimensional Stirling model although sliding interfaces and their moving grids limit the effective time accuracy). We will initially look at one-dimensional flows since the current standard practice is to design and optimize Stirling engines with empirically corrected friction and heat transfer coefficients in an overall one-dimensional model. This comparison provides an idea of the range in which commercial CFD software for modeling Stirling engines may be expected to provide accurate results. In addition, this work provides a framework for improving current one-dimensional analysis codes.

Dyson, Rodger W.↗
NASA NTRS2014

Avionics Architectures for Exploration: Building a Better Approach for (Human) Spaceflight Avionics

The field of Avionics is advancing far more rapidly in terrestrial applications than in space flight applications. Spaceflight Avionics are not keeping pace with expectations set by terrestrial experience, nor are they keeping pace with the need for increasingly complex automation and crew interfaces as we move beyond Low Earth Orbit. NASA must take advantage of the strides being made by both space-related and terrestrial industries to drive our development and sustaining costs down. This paper describes ongoing efforts by the Avionics Architectures for Exploration (AAE) project chartered by NASA's Advanced Exploration Systems (AES) Program to evaluate new avionic architectures and technologies, provide objective comparisons of them, and mature selected technologies for flight and for use by other AES projects. Results from the AAE project's FY13 efforts are discussed, along with the status of FY14 efforts and future plans.

Goforth, Montgomery B.↗
NASA NTRS2024

Molecular Dynamics Simulations of Microstructural Effects on Austenite-Martensite Interfaces in NiTi

Formation and migration of austenite-martensite interfaces plays the key role in reversible martensitic transformations of shape memory alloys (SMAs). How these interfaces interact with the SMA microstructure is a primary determining factor in important functional properties such as hysteresis and transformation span. As such, successful microstructural engineering of SMAs requires in-depth knowledge of interface behavior. The rapid nature of martensitic transformations makes experimental observations of moving austenite-martensite interfaces challenging. Molecular dynamics (MD) simulation is a unique tool which can probe the atomic-scale details of austenite-martensite interfaces as they migrate through different microstructures. However, in focusing on the entire transformation process, including the nucleation of new phases, MD studies are usually performed so far from equilibrium that their relevance to experiment is questionable. Here, we demonstrate new MD techniques to generate energetically preferred austenite-martensite interfaces in NiTi under near-equilibrium conditions. The interfaces are semi-coherent, exhibiting a series of structural disconnections, and they can migrate rapidly through single crystals under only small thermodynamic driving forces. In contrast, when interfaces migrate in polycrystals, their motion is impeded by thermoelastic effects as well as changes in orientation relationships at grain boundaries. Microstructures which accumulate large amounts of elastic energy tend to release some fraction through irreversible, hysteresis-inducing mechanisms. We demonstrate that engineering microstructures with less constraints is a viable strategy to produce SMAs with reduced hysteresis and transformation span. Similar thermoelastic and hysteresis-inducing mechanisms also arise when austenite-martensite interfaces encounter precipitates and can be controlled by tuning characteristics of the precipitate distribution.

Gabriel Plummer↗
NASA NTRSDate not supplied

Molecular Dynamics Simulations of Microstructural Effects on Austenite-Martensite Interfaces in NiTi

The formation and migration of austenite-martensite interfaces plays the key role in reversible martensitic transformations of shape memory alloys (SMAs). How these interfaces interact with the SMA microstructure is a primary determining factor in important functional properties such as hysteresis and transformation span. As such, successful microstructural engineering of SMAs requires in-depth knowledge of interface behavior. The rapid nature of martensitic transformations makes experimental observations of moving austenite-martensite interfaces challenging. Molecular dynamics (MD) simulation is a unique tool which can probe the atomic-scale details of austenite-martensite interfaces as they migrate through different microstructures. However, in focusing on the entire transformation process, including the nucleation of new phases, MD studies are usually performed so far from equilibrium that their relevance to experiment is questionable. Here, we demonstrate new MD techniques to generate energetically preferred austenite-martensite interfaces in NiTi under near-equilibrium conditions. The interfaces are semi-coherent, exhibiting a series of structural disconnections, and they can migrate rapidly through single crystals under only small thermodynamic driving forces. In contrast, when interfaces migrate in polycrystals, their motion is impeded by thermoelastic effects as well as changes in orientation relationships at grain boundaries. Microstructures which accumulate large amounts of elastic energy tend to release some fraction through irreversible, hysteresis-inducing mechanisms. We demonstrate that engineering microstructures with less constraints is a viable strategy to produce SMAs with reduced hysteresis and transformation span. Similar thermoelastic and hysteresis-inducing mechanisms also arise when austenite-martensite interfaces encounter precipitates and can be controlled by tuning characteristics of the precipitate distribution.

Gabriel Plummer↗
NASA NTRSDate not supplied

Molecular Dynamics Simulations of Microstructural Effects on Austenite-Martensite Interfaces in NiTi

Formation and migration of austenite-martensite interfaces plays the key role in reversible martensitic transformations of shape memory alloys (SMAs). How these interfaces interact with the SMA microstructure is a primary determining factor in important functional properties such as hysteresis and transformation span. As such, successful microstructural engineering of SMAs requires in-depth knowledge of interface behavior. The rapid nature of martensitic transformations makes experimental observations of moving austenite-martensite interfaces challenging. Molecular dynamics (MD) simulation is a unique tool which can probe the atomic-scale details of austenite-martensite interfaces as they migrate through different microstructures. However, in focusing on the entire transformation process, including the nucleation of new phases, MD studies are usually performed so far from equilibrium that their relevance to experiment is questionable. Here, we demonstrate new MD techniques to generate energetically preferred austenite-martensite interfaces in NiTi under near-equilibrium conditions. The interfaces are semi-coherent, exhibiting a series of structural disconnections, and they can migrate rapidly through single crystals under only small thermodynamic driving forces. In contrast, when interfaces migrate in polycrystals, their motion is impeded by thermoelastic effects as well as changes in orientation relationships at grain boundaries. Microstructures which accumulate large amounts of elastic energy tend to release some fraction through irreversible, hysteresis-inducing mechanisms. We demonstrate that engineering microstructures with less constraints is a viable strategy to produce SMAs with reduced hysteresis and transformation span. Similar thermoelastic and hysteresis-inducing mechanisms also arise when austenite-martensite interfaces encounter precipitates and can be controlled by tuning characteristics of the precipitate distribution.

Gabriel Plummer↗
NASA NTRSDate not supplied

Visualizing Geospatial Data through ESRI Story Maps for Earth Science Education: Lessons Learned from My NASA Data

For 20 years My NASA Data (MND) has curated NASA Earth science data and provided the data to educators in engaging learner-centered resources. MND has recently featured story maps as an innovative way to engage students in NASA Earth data. A story map is a cloud-based lesson that engages the learner in interactive geospatial maps using NASA data, and other multimedia content, text, and tasks that can be seamlessly incorporated in classroom instruction. This immersive technology eliminates the need for the user to move among tricky interfaces to access and visualize Earth science data, and no special software is required to be downloaded. Each story map integrates data from different NASA satellite missions, retrieved from Distributed Active Archive Centers (DAACs). Story maps also employ data analysis tools, such as time series options and swipe tools that allow learners to view and analyze relationships between scientific variables. MND has produced 25 story map lesson plans on the topics of air quality, the urban heat island effect, Earth’s energy budget, phytoplankton distribution, hurricane formation, solar eclipses, ocean circulation patterns, sea ice extent, and volcanic eruptions. Nine of them are extended story maps and written in the 5E format, which is internationally recognized as best practice based on how children learn science. Each story map resource is developed by the MND team featuring a GIS programming specialist, a lead scientist, and educational specialist/s to ensure the context, content, and methods are scientifically and educationally sound. The MND story maps are written for middle and high school science teachers and students as they connect with the Earth Systems Science phenomena featured in the Next Generation Science Standards. Each story map includes supporting resources for smooth integration in the classroom. During Fiscal Year 2023, The My NASA Data website received over 100,000 story map engagements during. These metrics highlight the interest in story maps as an Earth Science educational resource.

Desiray Wilson↗
NASA NTRS1990

Submillimeter Wave Astronomy Satellite Conceptual Design Review

The SWAS instrument consists of the moving telescope assembly, the interface baseplate assembly, and the thermal control housing. The movin g telescope structure holds the primary mirror, secondary mirror, and receiver front end in precise alignment. This structure also carries the receiver cold plate radiators, which view cold space both directl y and through reflection off the primary mirror. The moving telescope assembly attaches to the interface baseplate with an open pivot frame through which flex leads from the receiver front end also pass. Two flexure-mounted linear actuators tilt the moving telescope assembly u p to +/-3 deg in two axes. The interface plate serves as a mounting for these actuators as well as the acousto-optic spectrometer, the inst rument control electronics, the star tracker, and the balance of the receiver components. The thermal control housing attaches to the inte rface baseplate around its edge. The top cylindrical part of this hou sing serves to shade the receiver cold plate radiators from Sun and Earth influence. The bottom "D" shaped portion of the housing is therma lly isolated from the top and forms the electronlcs radiator. Heat is conducted from the Interface baseplate into this lower portion of the shell. The radiator geometry and conduction paths create a very stab le thermal environment in the center of the interface baseplate where the AOS and receiver IF amplifiers are heat sinked. The outer surface of the thermal control housing is covered with fused silica second s urface mirrors that reflect visible light and radiate infrared energy . The instrument is mounted to the spacecraft through four thermally- isolating titanium flexures an the underside of the interface basepla te.

Source record↗
NASA NTRS2015

The January 2015 Repressurization of ISS ATCS Loop B - Analysis Limitations and Concerns

In January 2013 a false ammonia leak alarm resulted in the shutdown and partial depressurization of one of the two International Space Station (ISS) External Active Thermal Control System (EATCS) loops. The depressurization resulted in a vapor bubble of 18 liters in warm parts of the stagnant loop. To repressurize the loop and regain system operation, liquid would have to be moved from the Ammonia Tank Assembly (ATA) into the loop. This resulted in the possibility of moving cold (as low as ‐30 C) ammonia into the water‐filled Internal Active Thermal Control System (IATCS) interface heat exchangers. Before moving forward, the freezing potential of the repressurization was evaluated through analysis - using both a Thermal Desktop SINDA/FLUINT model and hand calculations. The models yielded very different results, but both models indicated that heat exchanger freezing was not an issue. Therefore, the repressurization proceeded. The presentation describes the physical situation of the EATCS prior to repressurization and discusses the potential limits and pitfalls of the repressurization. The pre‐repressurization analytical models and their results are discussed. The successful repressurization is describled and the results of a post‐event model assessment is detailed.

Ungar, Eugene↗
NASA NTRS2000

NEA Multi-Chamber Sample Return Container with Hermetic Sealing

A sample return container is being developed by Honeybee Robotics to receive samples from a derivative of the Champollion/ST4 Sample Acquisition and Transfer Mechanism or other samplers such as the 'Touch and Go' Surface Sampler (TGSS), and then hermetically seal the samples for a sample return mission. The container is enclosed in a phase change material (PCM) chamber to prevent phase change during return and re-entry to earth. This container is designed to operate passively with no motors and actuators. Using the rotation axis of the TGSS sampler for interfacing, transferring and sealing samples, the container consumes no electrical power and therefore minimizes sample temperature change. The circular container houses multiple isolated canisters, which will be sealed individually for samples acquired from different sites or depths. The TGSS based sampler indexes each canister to the sample transfer position, below the index interface for sample transfer. After sample transfer is completed, the sampler indexes a seal carrier, which lines up seals with the openings of the canisters. The sampler moves to the sealing interface and seals the sample canisters one by one. The sealing interface can be designed to work with C-seals, knife edge seals and cup seals. This sample return container is being developed by Honeybee Robotics in collaboration with the JPL Exploration Technology program. A breadboard system of the sample return container has been recently completed and tested. Additional information is contained in the original extended abstract.

Rafeek, Shaheed↗
NASA NTRS2000

A Sample Return Container with Hermetic Seal

A sample return container is being developed by Honeybee Robotics to receive samples from a derivative of the Champollion/ST4 Sample Acquisition and Transfer Mechanism or other samplers and then hermetically seal samples for a sample return mission. The container is enclosed in a phase change material (PCM) chamber to prevent phase change during return and re-entry to earth. This container is designed to operate passively with no motors and actuators. Using the sampler's featured drill tip for interfacing, transfer-ring and sealing samples, the container consumes no electrical power and therefore minimizes sample temperature change. The circular container houses a few isolated canisters, which will be sealed individually for samples acquired from different sites or depths. The drill based sampler indexes each canister to the sample transfer position, below the index interface for sample transfer. After sample transfer is completed, the sampler indexes a seal carrier, which lines up seals with the openings of the canisters. The sampler moves to the sealing interface and seals the sample canisters one by one. The sealing interface can be designed to work with C-seals, knife edge seals and cup seals. Again, the sampler provides all sealing actuation. This sample return container and co-engineered sample acquisition system are being developed by Honeybee Robotics in collaboration with the JPL Exploration Technology program.

Kin Yuen Kong↗
NASA NTRS2016

Modification of Surface Density of a Porous Medium

A method for increasing density of a region of a porous, phenolic bonded ("PPB") body adjacent to a selected surface to increase failure tensile strength of the adjacent region and/or to decrease surface recession at elevated temperatures. When the surface-densified PPB body is brought together with a substrate, having a higher failure tensile strength, to form a composite body with a PPB body/substrate interface, the location of tensile failure is moved to a location spaced apart from the interface, the failure tensile strength of the PPB body is increased, and surface recession of the material at elevated temperature is reduced. The method deposits and allows diffusion of a phenolic substance on the selected surface. The PPB body and the substrate may be heated and brought together to form the composite body. The phenolic substance is allowed to diffuse into the PPB body, to volatilize and to cure, to provide a processed body with an increased surface density.

Stackpoole, Margaret M.↗
NASA NTRS2002

The Effects of Ultra Thin Films on Dynamic Wetting

Dynamic wetting, the displacement of one fluid by another immiscible fluid on a surface, controls many natural and technological phenomena, such as coating, printing, spray painting and lubricating. Particularly in coating and spraying applications, contact lines advance across pre-existing fluid films. Most previous work has focused on contact lines advancing across films sufficiently thick that they behave as simple Newtonian fluids. Ultrathin films, where the film thickness may impinge on fundamental length scales in the fluid, have received less attention. In this talk, we will discuss the effects of ultrathin polymer films on dynamic wetting. We measure the interface shape within microns of moving contact lines advancing across preexisting films and compare the measurements to existing models of viscous bending for interfaces advancing across dry surfaces and 'thick' (in the sense that they behave as liquids) films. In the experiments, we advance a contact line of 10-poise and 1-poise polydimethylsiloxane (silicone oil) across pre-coated films of the same fluid with thickness from a single chain thickness (approx. 10 A) through a couple of radii of gyration (100-200 A) to films so thick they are likely bulk in behavior (10(exp 3) A). All films are physisorbed, i.e. they readily rinse from the surface. Thus, molecules in the film are not anchored to the surface and can move within the film if the hydrodynamics dictate such motion. For films of the thickness of a single chain (approx. 10 A), our experiments indicate that the advancing fluid behaves just as it would if it advanced over a dry surface. For the thicker films (10(exp 3) A), we find behavior indicating that the molecules in the film are acting as a fluid with the bulk properties. In this regime, results for the two different fluids are identical when the experiments are performed at the same pre-existing film thickness and advancing capillary number, Ca. For film of thickness of a few radii of gyration (approx. 100-200 A), the behavior depends on Ca of the advancing meniscus. At low Ca, the viscous bending of the interface near the contact line does not behave as it would on a dry surface. It has a lower curvature than expected. However, at higher Ca, the viscous bending is described by the model for spreading over a dry surface. These results show that the fluid flow in the film does behave differently than bulk as the film thickness becomes comparable to molecular length scale. But even more intriguing is the unusual velocity dependence of that behavior where the film behaves more solid-like at higher contact line speeds. We will discuss these results in terms of the properties of confined polymer melts.

Chen, Xia↗
NASA NTRS1999

The Isothermal Dendritic Growth Experiment (IDGE): USMP-4 One-Year-Report

Dendrites describe the tree-like crystal morphology commonly assumed in many material systems--particularly in metals and alloys that freeze from supercooled or supersaturated melts. There remains a high level of engineering interest in dendritic solidification because of the role of dendrites in the determination of cast alloy microstructures. Microstructure plays a key role in determining the physical properties of cast or welded products. In addition, dendritic solidification provides an example of non-equilibrium physics and is one of the simplest non-trivial examples of dynamic pattern formation, where an amorphous melt, under simple starting conditions, evolves into a complex ramified microstructure. Although it is well-known that dendritic growth is controlled by the transport of latent heat from the moving solid-melt interface as the dendrite advances into a supercooled melt, an accurate, and predictive model has not been developed. Current theories consider: 1) the transfer of heat or solute from the solid-liquid interface into the melt, and 2) the interfacial crystal growth and growth selection physics for the interface. However, the effects of gravity-induced convection on the transfer of heat from the interface prevent either element from being adequately tested solely under terrestrial conditions. The Isothermal Dendritic Growth Experiment (IDGE) constituted a series of three NASA-supported microgravity experiments, all of which flew aboard the space shuttle, Columbia. This experimental space flight series was designed and operated to grow and record dendrite solidification in the absence of gravity-induced convective heat transfer, and thereby produce a wealth of benchmark-quality data for testing solidification scaling laws. The data collection from the on-orbit phase of the IDGE flight series is now complete. We are currently completing analyses and moving towards final data archiving.

Glicksman, M. E.↗
NASA NTRS1987

Adaptive finite element methods for high-speed compressible flows

An adaptive finite element algorithm for solving the unsteady Euler equations is described. The finite element algorithm is based on a Taylor/Galerkin formulation and uses a very fast and efficient data structure to refine and unrefine the grid in order to optimize the approximation. A general version of the method which can be applied to moving grids with sliding interfaces is given, and results for a transient supersonic calculation of rotor-stator interaction are presented.

Oden, J. T.↗