Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “model exploration”

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 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Exploring the Low-Thrust Transfer Design Space in an Ephemeris Model via Multi-Objective Reinforcement Learning

Multi-Reward Proximal Policy Optimization (MRPPO) is a multi-objective reinforcement learning algorithm used to train multiple policies to uncover solutions within a multi-objective solution space. MRPPO is used in this paper to train policies to construct low-thrust transfers for a SmallSat from the vicinity of L2 to an L5 short period orbit in the Sun-Earth-Moon system. First, the policies are trained in this scenario in the circular restricted three-body problem. This information is used to initialize the policies before training in a higher-fidelity ephemeris model; a process known as transfer learning. The recovered segments of the solution space will be compared to fundamental dynamical structures to both examine the results of MRPPO in this complex design scenario and explore the effectiveness of transfer learning.

Christopher J. Sullivan↗
NASA NTRS2022

Exploring the Low-Thrust Transfer Design Space in an Ephemeris Model via Multi-Objective Reinforcement Learning

Multi-Reward Proximal Policy Optimization (MRPPO) is a multi-objective reinforcement learning algorithm used to train multiple policies to uncover solutions within a multi-objective solution space. MRPPO is used in this paper to train policies to construct low-thrust transfers for a SmallSat from the vicinity of 𝐿2 to an 𝐿5 short period orbit in the Sun-Earth-Moon system. First, the policies are trained in this scenario in the circular restricted three-body problem. This information is used to initialize the policies before training in a higher-fidelity ephemeris model; a process known as transfer learning. The recovered segments of the solution space will be compared to fundamental dynamical structures to both examine the results of MRPPO in this complex design scenario and explore the effectiveness of transfer learning.

Mashiku, Alinda K.↗
NASA NTRS2024

NASA HECC Geometry and Performance Review Part 1: Validation of a Computational Model for the Vaneless Diffuser Configuration with As-Manufactured Impeller Geometry

An investigation of the NASA High Efficiency Centrifugal Compressor (HECC) vaneless diffuser configuration was performed. This multipart investigation presents an extensive validation of the computational model against experimental data. The validated model was then used to explore the effects geometric differences between the as-manufactured and design-intent impellers. Lastly, the validated model was used for comparison against an experimental tip clearance study. Part I of the investigation focused on describing the HECC vaneless computational model and its validation against the experimental data published in GT2023-103128. To generate the model, a verification of the manufactured impeller was performed and was confirmed to match the impeller CAD. Section data from the impeller CAD, referred to as the As-Manufactured geometry, were used for development of the computational model. Steady RANS simulations utilizing the Wilcox K-Omega 98 turbulence model and a multiblock structured mesh were used to conduct a mesh convergence study. The resultant mesh was then used for simulations at both design-speed and off-design speed conditions. The simulations compared well to data in both 1D and 2D terms for the major performance metrics of efficiency, total pressure rise, and total temperature rise. Based on the observed results the model was deemed validated and was used in the latter two parts of the multipart investigation.

centrifugal compressor↗
NASA NTRS2017

Hydrological Modeling of the Jezero Crater Outlet-Forming Flood

Abundant evidence exists for lakes on Mars both from orbital observations [e.g., 1-3] and in situ exploration [e.g., 4-5]. These lakes can be divided into two classes: those that were hydrologically closed, so their source valley(s) terminated at the basin [3], and those that were hydrologically open, where there was sufficient flow from inlet valley(s) to cause the lake to breach and form an outlet valley [2]. It is easier to be confident from orbital data alone that a standing body of water must have existed in open basins, because there is no other way for their perched outlet valleys to form. The majority of basins fed by valley networks, rather than by isolated inlet valleys, are open [6], with some important exceptions (e.g., Gale Crater). Jezero crater (Fig. 1) is one of the most well-studied open basin paleolakes on Mars, with a breach that re-mains well above the lowest part of the crater floor, and two sedimentary fans at its northwestern margin that are likely deltaic in origin [7-9]. CRISM observations of these sediments indicate they host a variety of alteration minerals [9-11], including smectite and carbonate, and both the mineralogy of the sediments and their settings suggest they have a strong potential for preserving organic materials [10]. As a result, Jezero is a strong candidate landing site for the Mars 2020 rover. Approximate formative discharges have been estimated for its well-preserved western fan (Q approximately 500m3/s) [7], but to our knowledge, no estimates for the dis-charges associated with formation and incision of its outlet valley have been presented. Indeed, only a few studies [e.g., 12-14] have attempted to reconstruct the formation of outlet breaches broadly similar to Jezero anywhere on Mars, despite the apparent commonality of basins with large outlets [e.g., 2]. The outlet valley formed as a dam breach when the lake overflowed. In such an event, the growth and incision of the breach is directly coupled to flood discharge. In the case of Jezero, the discharge through the breach eventually lacked the energy needed to erode through the dam further, preventing complete drainage of the lake. After the initial flood, further incision can take place if additional water flows into, and thus out of, the hydrologically open lake, though the rate of this erosion occurs under more typical fluvial conditions. Despite this qualitative understanding of the process, it is useful to explore numerically what range of model parameters are potentially consistent with obser-vations of the outlet. We ultimately seek to address questions that include: (1) What was the flood hydro-graph?, (2) What sediment transport processes were involved and what can we infer about the erosion process? (3) Can most or all of the Jezero outlet's morphology be explained as a consequence of catastrophic formation, or is additional longer-term erosion required?

geology↗
NASA NTRS2001

The Origin of Hot Subluminous Horizontal-Branch Stars in Omega Cen and NGC 2808

Ultraviolet observations of the globular clusters omega Cen and NGC 2808 have revealed an unexpected population of hot subluminous stars lying up to 0.7 mag below the extreme horizontal branch (EHB), which axe not explained by canonical stellar models. In order to explore the evolutionary status of these stars, we have evolved a set of low-mass stars from the main sequence through the helium flash to the horizontal branch (HB) for a wide range in the mass loss along the red-giant branch (RGB). Stars with the largest mass loss evolve off the RGB to high effective temperatures before igniting helium in their cores. Our results indicate that the subluminous stars can be explained if these stars undergo a late helium flash while descending the white dwarf cooling curve. Under these conditions the convection zone produced by the helium flash will penetrate into the stellar envelope, thereby mixing the envelope hydrogen into the hot helium-burning interior, where it is rapidly consumed. Such "flashmixed" stars will have helium- and carbon-rich envelopes and will lie at higher effective temperatures than the hottest canonical (i.e., unmixed) EHB stars. Using new stellar atmospheres, we show that these changes in the envelope abundances will suppress the ultraviolet flux in the spectra of the flash-mixed stars by the amount needed to explain the hot subluminous stars in w Cen and NGC 2808. To test this evolutionary scenario, we have obtained medium resolution spectra of a sample of the hottest HB stars in omega Cen. We find that these stars axe indeed helium-rich compared to classical EHB stars and also considerably hotter than the hottest EHB models without flash mixing.

Sweigart, A. V.↗
NASA NTRS1983

Multishaker modal testing

Procedures for improving the modal modeling of structures using test data and to determine appropriate analytical models based on substructure experimental data were explored. Two related research topics were considered in modal modeling: using several independently acquired columns of frequency response data, and modal modeling using simultaneous multi-point excitation. In component mode synthesis modeling, the emphasis is on determining the best way to employ complex modes and residuals.

Craig, R. R., Jr.↗
NASA NTRS1989

Simulation-modeling tool for evaluation of space telerobotic control strategies

An object-oriented software graphic simulation and modeling tool is developed to explore human/autonomous control allocation for varied operational scenarios. The system provides designers with LISP workstations through which to simulate telerobotic operations, model human performance in those operations, examine task performance profiles, and investigate control and diagnostic strategies. It is suggested that the provision of such analytic tools along with the presentation of performance projections can assist designers in rapidly and conveniently exploring design alternatives for telerobotic system control.

Corker, Kevin↗
NASA NTRS1991

Surface knowledge and risks to landing and roving - The scale problem

The role of surface information in the performance of surface exploration missions is discussed. Accurate surface models based on direct measurements or inference are considered to be an important component in mission risk management. These models can be obtained using high resolution orbital photography or a combination of laser profiling, thermal inertia measurements, and/or radar. It is concluded that strategies for Martian exploration should use high confidence models to achieve maximum performance and low risk.

Bourke, Roger D.↗
NASA NTRS2018

Challenges in Clinical Management of Radiation-Induced Illnesses in Exploration Spaceflight

Historical solar particle events (SPEs) provide context for some understanding of acute radiation exposure risk to astronauts traveling outside of low Earth orbit. Modeling of potential doses delivered to exploration crewmembers anticipates limited radiation-induced health impacts, including prodromal symptoms of nausea, emesis, and fatigue, but suggests that more severe clinical manifestations are unlikely. Recent large animal-model research in space-analogs closely mimicking SPEs has identified coagulopathic events independent of the hematopoietic sequelae of higher radiation doses, similar in manifestation to disseminated intravascular coagulation (DIC). We explored the challenges of clinical management of radiation-related clinical manifestations, using currently accepted modeling techniques and anticipated physiological sequelae, to identify medical capabilities needed to successfully manage SPE-induced radiation illnesses during exploration spaceflight.

Blue, Rebecca↗
NASA NTRS2003

A Subjective Assessment of Alternative Mission Architecture Operations Concepts for the Human Exploration of Mars at NASA Using a Three-Dimensional Multi-Criteria Decision Making Model

The primary driver for developing missions to send humans to other planets is to generate significant scientific return. NASA plans human planetary explorations with an acceptable level of risk consistent with other manned operations. Space exploration risks can not be completely eliminated. Therefore, an acceptable level of cost, technical, safety, schedule, and political risks and benefits must be established for exploratory missions. This study uses a three-dimensional multi-criteria decision making model to identify the risks and benefits associated with three alternative mission architecture operations concepts for the human exploration of Mars identified by the Mission Operations Directorate at Johnson Space Center. The three alternatives considered in this study include split, combo lander, and dual scenarios. The model considers the seven phases of the mission including: 1) Earth Vicinity/Departure; 2) Mars Transfer; 3) Mars Arrival; 4) Planetary Surface; 5) Mars Vicinity/Departure; 6) Earth Transfer; and 7) Earth Arrival. Analytic Hierarchy Process (AHP) and subjective probability estimation are used to captures the experts belief concerning the risks and benefits of the three alternative scenarios through a series of sequential, rational, and analytical processes.

Tavana, Madjid↗
NASA NTRS2015

Phobos: Simulation-Driven Design for Exploration

Dr. Edwin "Zack" Crues presented an overview of the current use of modeling and simulation technologies by the NASA Exploration Systems Simulations (NExSyS) team in investigating the spacecraft and missions for the human exploration of Mars' moon Phobos.

Crues, Edwin↗
NASA NTRS2024

NASA HECC Geometry and Performance Review Part 2: Geometric Differences Between the As-Manufactured and Design-Intent Impeller Geometry and their Effects on the Vaneless Diffuser Configuration Performance

An investigation of the NASA High Efficiency Centrifugal Compressor (HECC) vaneless diffuser configuration was performed. This multipart investigation focused on validating the computational model against experimental data. The validated model was then used to explore the effects of observed geometric differences between the As-Manufactured and Design-Intent impellers. Lastly, the validated model was used for comparison against an experimental tip clearance study. Part II of the investigation of the NASA HECC vaneless diffuser configuration focused on understanding the differences in geometry and performance between the As-Manufactured impeller and the Design-Intent impeller. This was achieved through comparison of the As-Manufactured HECC vaneless computational model, developed from the solid model of the impeller and validated in Part I, against a new model developed from the Design-Intent blade sections published in NASA/CR-2014-218114/Rev1. The 1D performance values showed that the As-Manufactured impeller underperformed compared to the Design-Intent for all four speedlines that were simulated. Further investigation of profiles, loading and contours showed consistent underperformance of the As-Manufactured relative to the Design-Intent. An investigation into the source of the performance differences led to the discovery of several significant variations in the impeller geometries. The differences that were observed can be summarized into four categories: fillets, trailing-edge exit radii variation, dissimilarity in the splitter leading-edge geometry and main blade thickness differences. The investigation then shifted its effort to quantify the performance effects caused by geometric differences. The investigation showed that out of the four geometric differences that were explored, the differences in the splitter blade had the largest impact. These differences most notably changed flow physics near the splitter leading edge, especially near the tip of the impeller.

centrifugal compressor↗
NASA NTRSDate not supplied

NASA HECC Geometry and Performance Review Part 2: Geometric Differences Between the as-Manufactured and Design-Intent Impeller Geometry and Their Effects on the Vaneless Diffuser Configuration Performance

An investigation of the NASA High Efficiency Centrifugal Compressor (HECC) vaneless diffuser configuration was performed. This multipart investigation focused on validating the computational model against experimental data. The validated model was then used to explore the effects of observed geometric differences between the as-manufactured and design-intent impellers. Lastly, the validated model was used for comparison against an experimental tip clearance study. Details regarding each of the parts are detailed below: This second part of a multipart investigation of the NASA HECC vaneless diffuser configuration focused on the comparison of the as-manufactured HECC vaneless computational model validated in Part I against a new model that used the same grid and solver settings but replaced the impeller section data with the design-intent sections from NASA/CR-2014-218114/Rev1. The 1D performance values showed that the as-manufactured impeller underperformed compared to the design-intent for all four speedlines that were simulated. Further investigation of radial profiles, loading and contours showed consistent underperformance of the as-manufactured. An investigation into the source of the difference led to the discovery of several geometric differences in the two impellers of magnitudes that could not be explained outside of manufacturing. The differences that were observed can be summarized into four categories: fillets, TE exit radius differences, splitter LE differences and main blade thickness differences. The investigation then shifted to attempting to isolate the geometric differences as best as possible and to understand their contribution to the observed underperformance. The investigation showed that out of the four geometric differences that were explored, the differences in the splitter blade had the largest effect.

centrifugal compressor↗
NASA NTRS1994

EUVAC: A solar EUV flux model for aeronomic calculations

This paper presents a new solar Extreme Ultraviolet (EUV) flux model for aeronomic calulations (EUVAC), which is based on the measured F74113 solar EUV reference spectrum. The model provides fluxes in the 37 wavelength bins that are in widespread use. This paper also presents cross sections to be used with the EUVAC flux model to calculate photoionization rates. The flux scaling for solar activity is accomplished using a proxy-based on the F10.7 index and its 81-day average together with the measured solar flux variation from the EUVS instrument on the Atmosphere Explorer E satellite. This new model produces 50-575 A integrated EUV fluxes in good agreement with rocket observations. The solar cycle variation of the chromospheric fluxes agrees well with the measured variation of the Lyman alpha flux between 1982 and 1988. In addition, the theoretical photoelectron fluxes, calculated using the new EUV flux model, are in good agreement with the solar minimum photoelectron fluxes from the Atmosphere Explorer E satellite and also with the solar maximum photoelectron fluxes from the Dynamics Explorer satellite. Its relative simplicity coupled with its ability to reproduce the 50-575 A solar EUV flux as well as the measured photoelectron spectrum makes the model well suited for aeronomic applications. However, EUVAC is not designed to accurately predict the solar flux variability for numerous individual lines.

Richards, P. G.↗
NASA NTRS2010

Evaluation of Enhanced High Resolution MODIS/AMSR-E SSTs and the Impact on Regional Weather Forecast

Over the last few years, the NASA Short-term Prediction Research and Transition (SPoRT) Center has been generating a 1-km sea surface temperature (SST) composite derived from retrievals of the Moderate Resolution Imaging Spectroradiometer (MODIS) for use in operational diagnostics and regional model initialization. With the assumption that the day-to-day variation in the SST is nominal, individual MODIS passes aboard the Earth Observing System (EOS) Aqua and Terra satellites are used to create and update four composite SST products each day at 0400, 0700, 1600, and 1900 UTC, valid over the western Atlantic and Caribbean waters. A six month study from February to August 2007 over the marine areas surrounding southern Florida was conducted to compare the use of the MODIS SST composite versus the Real-Time Global SST analysis to initialize the Weather Research and Forecasting (WRF) model. Substantial changes in the forecast heat fluxes were seen at times in the marine boundary layer, but relatively little overall improvement was measured in the sensible weather elements. The limited improvement in the WRF model forecasts could be attributed to the diurnal changes in SST seen in the MODIS SST composites but not accounted for by the model. Furthermore, cloud contamination caused extended periods when individual passes of MODIS were unable to update the SSTs, leading to substantial SST latency and a cool bias during the early summer months. In order to alleviate the latency problems, the SPoRT Center recently enhanced its MODIS SST composite by incorporating information from the Advanced Microwave Scanning Radiometer-EOS (AMSR-E) instruments as well as the Operational Sea Surface Temperature and Sea Ice Analysis. These enhancements substantially decreased the latency due to cloud cover and improved the bias and correlation of the composites at available marine point observations. While these enhancements improved upon the modeled cold bias using the original MODIS SSTs, the discernable impacts on the WRF model were still somewhat limited. This paper explores several factors that may have contributed to this result. First, the original methodology to initialize the model used the most recent SST composite available in a hypothetical real ]time configuration, often matching the forecast initial time with an SST field that was 5-8 hours offset. To minimize the differences that result from the diurnal variations in SST, the previous day fs SST composite is incorporated at a time closest to the model initialization hour (e.g. 1600 UTC composite at 1500 UTC model initialization). Second, the diurnal change seen in the MODIS SST composites was not represented by the WRF model in previous simulations, since the SSTs were held constant throughout the model integration. To address this issue, we explore the use of a water skin-temperature diurnal cycle prediction capability within v3.1 of the WRF model to better represent fluctuations in marine surface forcing. Finally, the verification of the WRF model is limited to very few over-water sites, many of which are located near the coastlines. In order to measure the open ocean improvements from the AMSR-E, we could use an independent 2-dimensional, satellite-derived data set to validate the forecast model by applying an object-based verification method. Such a validation technique could aid in better understanding the benefits of the mesoscale SST spatial structure to regional models applications.

Schiferl, Luke D.↗
NASA NTRS1990

Plasmasphere-ionosphere coupling. II - Ion composition measurements at plasmaspheric and ionospheric altitudes and comparison with modeling results

This paper presents Dynamic Explorer data on the plasma coupling between the plasmasphere and ionosphere. DE 1 measurements of ion composition and temperatures at 1.4-3.5 R(F) in the plasmasphere were combined with DE-2 measurements of ion composition and electron and ion temperatures in the upper F region/topside ionosphere, closely spaced in universal and local time for cases in the November 6-11, 1981 period. The observations are compared directly with the field-line interhemispheric plasma (FLIP) model calculations of altitudinal ion density and temperature profiles. It was found that, when the FLIP model permitted fractional trapping of ionospheric photoelectrons and consequent plasmaspheric heating, good agreement with the observations was obtained.

Horwitz, J. L.↗