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At least 307 records · Page 17

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DOE OSTI2025

Structural origin of disorder-induced ion conduction in NaFePO 4 cathode materials

Diffusion in NaFePO 4 can be enhanced through amorphization. Based on computations using DFT and machine learning potentials, we ascribe this phenomenon to the formation of less constrained Na-ion environments upon disordering. Most modern battery technologies depend on solid-state crystalline cathode materials. However, some of these materials are constrained by the low ionic conductivity of their most stable phases. An example of this is maricite (NaFePO 4 ). Interestingly, experiments have shown that maricite can improve its rate capability through disordering (amorphization). However, experimental characterization of amorphous cathode materials remains a major challenge, hindering a clear understanding of the structural origin of the disorder-induced improvement in sodium-ion mobility. To address this, we here employ molecular dynamics simulations by first training a machine learning potential for NaFePO 4 based on the atomic cluster expansion approach and a batch active learning potential parameterization scheme. This potential is then applied to explore the structural and dynamical properties of NaFePO 4 glasses as cathode materials. Specifically, we investigate the effect of glass structure on sodium-ion diffusion, revealing the relative influences of short-range and medium-range order features. We find significant heterogeneity in sodium-ion diffusivity in the glass, with fast-conducting ions residing in less constrained atomic environments with fewer P and Fe neighbors. These more mobile ions are also surrounded by larger ring-type structures. Overall, the results and developed approach present promising avenues for developing high-performance glassy cathodes for next-generation batteries.

Christensen, Rasmus↗

NASA NTRSDate not supplied

Advancing Electric Propulsion Aircraft Evaluation for Urban Air Mobility: Insights from NASA-Ames

This presentation delves into a recent evaluation conducted at NASA-Ames on the Vertical Motion Simulator, focusing on the handling qualities of Distributed Electric Propulsion VTOL (eVTOL) aircraft, specifically tailored for Urban Air Mobility (UAM) applications. The presentation will focus on the recent effort to adapt and refine use of the Aeronautical Design Standard -33 (ADS-33) rotorcraft handling qualities developed by the U.S. Army and NASA to meet the diverse needs of civilian (eVTOL) concept evaluation. A brief discussion of the author’s personal test pilot insights in the early development of military Fly-By-Wire evaluation methods will also be provided. The emergence of innovative eVTOL designs with unique lift capabilities and flight control systems, present both opportunities and challenges, particularly in ensuring safety amidst technological complexity. To navigate these challenges, our investigation examined evaluation criteria designed to accommodate the varied configurations and advanced automation systems inherent in modern eVTOL aircraft. By establishing a standardized approach to evaluation, our research not only fosters innovation but also upholds safety standards in the dynamic landscape of urban air mobility. Through this endeavor, we help to facilitate the seamless integration of novel aircraft capabilities into new operations, contributing to a new era of safe and efficient aerial transportation.

Loran Allen Haworth↗

NASA NTRS1995

Narrowband and wideband characterisation of satellite mobile/PCN channel

This paper presents models characterizing satellite mobile channel. Statistical narrowband models based on the CSER high elevation angle channel measurement campaign are reported. Such models are understood to be useful for communication system simulations. It has been shown from the modelling results that for the mobile satellite links at high elevation angles line-of-sight (LOS) signal is available most of the time, even under the heavy shadowing conditions. Wideband measurement campaign which CSER is about to undertake, and subsequently the modelling approach to be adopted is also discussed. It is noted that a wideband channel model is expected to provide a useful tool in investigating CDMA applications.

Butt, G.↗

NASA NTRSDate not supplied

Comparing Planetary Helicopter Brownout Observations with Numerical Predictions for Ingenuity

Ingenuity is considered the Martian equivalent of the Wright Flyer. Its sustained flights on Mars proved that non-terrestrial powered flight is possible, even on planets with thin atmospheres. However, Ingenuity was small and carried no payload. Future planetary rotorcraft will be bigger and heavier to accomplish new scientific and exploratory goals. On dusty planets, the associated increase in rotor thrust poses a potential challenge well known to helicopter pilots who have flown in desert environments: dust clouds forming during take-off and landing due to rotor wash, referred to as brownout. This work evaluates the effectiveness of existing numerical simulation models in predicting the severity of this phenomenon for planetary rotorcraft. We compare the output of a CFD-based dust mobilization model with data recently gathered using image processing techniques of Ingenuity’s flights. The simulation results suggest that the sensitivity of the wall friction velocity to the rotorcraft height may be lower than previously assessed. We further evaluate the sensitivity of the total mass of mobilized dust to other model parameters such as the sandblasting efficiency and the saltation threshold velocity. Finally, we discuss the limitations of this comparison due to uncertainty in both the observation and the numerical model.

HEC↗

NASA NTRSDate not supplied

DLES Unreal Simulation Tool (DUST)

NASA’s future Artemis missions to the Moon seek to explore areas around the Lunar South Pole. Though humans have previously set foot on the lunar surface, the proposed region provides unique and challenging environments that require insight and investigation prior to arrival. Several teams throughout the agency are performing this site and mission planning, design, and analysis to support areas like the Human Landing System (HLS), surface mobility, habitation elements, and scientific exploration. The NASA Exploration Systems Simulation (NExSyS) team at Johnson Space Center is developing a graphical environment of the Lunar South Pole region. Lunar terrain information collected from the Lunar Reconnaissance Orbiter (LRO) is compiled and made available through Johnson Space Center’s Digital Lunar Exploration Sites (DLES) data sets. The DLES data is used to build this graphic environment. The process of ingesting and accurately modeling this information in a meaningful way for analysis creates its own challenges such as generating a performant model from the source data and the application of curvature. Additionally, the area around the Lunar South Pole experiences different lighting conditions than those observed from the Apollo missions. The need to use the lunar environmental data products provided by DLES combined with the capability to calculate date specific ephemerides in real-time has given rise to the development of the DLES Unreal Simulation Tool (DUST). DUST incorporates augmented terrain from the DLES product into a desktop application that allows exploration of the Lunar South Pole region and its complex lighting conditions. DUST leverages advanced capabilities in the recently released Unreal Engine 5 renderer by Epic Games such as double precision for positioning of planetary bodies and surface elements, multiple infinite light sources to represent the Sun and eventually Earthshine, high resolution shadow maps for dynamic shadow accuracy, real-time software ray-tracing for multi-surface bounce lighting to render sunlight reflected off surface elements and terrain features, and performance optimized level of detail shifting as the eyepoint changes in a scene. This paper details the DUST application, the technologies of the engine platform that enable scientific and engineering analysis, the unique techniques and processes developed to consume the DLES data sets, and how the tool is being used to support the Artemis program.

Lunar Visualization↗

NASA NTRSDate not supplied

Dynamic Vehicle Assessment for Intelligent Contingency Management of Urban Air Mobility Vehicles

New algorithms will be required to ensure passenger and bystander safety during the expected era of autonomous urban air mobility (UAM) aircraft. This paper examines an approach for assessing the vehicle capability to fly itself and to complete a mission safely. The concepts combine elements of system identification, adaptive control, flight dynamics, envelope predictions, and handling qualities, as well as human pilot intuition. The approach is applied to a simulation of a generic distributed electric propulsion urban air mobility-type aircraft, which was developed under the NASA Transformational Tools and Technologies (TTT) project, Autonomous Systems / Intelligent Contingency Management subproject.

flight envelope↗

NASA NTRSDate not supplied

Dynamic Vehicle Assessment for Intelligent Contingency Management for Urban Air Mobility Vehicles

flight envelope prediction↗

DOE OSTI2024

Electrochemical grand potential-based phase-field simulation of electric field-assisted sintering

Here, an electrochemical grand potential functional was proposed to describe the sintering of an ionic ceramic green body. The resultant phase-field description enables simulation of the consolidation of an arbitrary number of granular particles and their interactions with the surrounding void phase. The model includes the effects of charged vacancies and the associated interactions between internal and applied electric fields. Defect segregation to grain boundaries is also accounted for, as well as enhanced interfacial defect mobilities. The model was parameterized for Y 2 O 3 . Simulations of two-particle systems showed that the applied electric field had an increasingly important impact on neck growth as particle size increased. A sudden rapid increase in temperature occurred for larger field strengths, which has been reported to be correlated to the onset of a flash event in flash sintering. Simulations of many particles showed that internal heat generation by Joule heating was localized at particle–particle contacts (grain boundaries), even though their conductivities were lower than nearby internal particle-void interfaces. A percolative path for ionic charge across the green body and the ceramic sintered solid was thus defined, accelerating the Joule heating process as the porosity of the green body is removed.

36 MATERIALS SCIENCE↗

NASA NTRS2012

Liquid Water in the Extremely Shallow Martian Subsurface

Availability of liquid water is one of the major constraints for the potential Martian biosphere. Although liquid water is unstable on the surface of Mars due to low atmospheric pressures, it has been suggested that liquid films of water could be present in the Martian soil. Here we explored a possibility of the liquid water formation in the extremely shallow (1-3 cm) subsurface layer under low atmospheric pressures (0.1-10 mbar) and low ("Martian") surface temperatures (approx.-50 C-0 C). We used a new Goddard Martian simulation chamber to demonstrate that even in the clean frozen soil with temperatures as low as -25C the amount of mobile water can reach several percents. We also showed that during brief periods of simulated daylight warming the shallow subsurface ice sublimates, the water vapor diffuses through porous surface layer of soil temporarily producing supersaturated conditions in the soil, which leads to the formation of additional liquid water. Our results suggest that despite cold temperatures and low atmospheric pressures, Martian soil just several cm below the surface can be habitable.

Pavlov, A.↗

DOE OSTI2025

Simulation and generalized Langevin equation study of lipid subdiffusion in biomembrane phases

In biomembranes lipid mobility exhibits deviations from the classical diffusive behavior of Brownian particles, i.e. ‘anomalous’ diffusion. The question arises as to how this anomalous diffusive behavior varies in gel, ripple, and fluid biomembrane phases. Here, in this study, we perform all-atom molecular dynamics (MD) simulations of dimyristoylphosphatidylcholine (DMPC) bilayers in the three different phases and analyze the results using the framework of the Generalized Langevin Equation (GLE). This analysis emphasizes sub-diffusive behavior on the relatively short, picosecond-nanosecond timescales, capturing local molecular constraints and transient caging effects during the crossover of atomic dynamics from vibrational to incipient anharmonic motion. The ripple and gel phases are found to exhibit strong transient caging and prolonged memory effects resulting in distinct sub-diffusive behavior. The role of hydrogen bonding in lipid confinement is also examined, demonstrating its influence on phase-dependent molecular ordering and on short-time diffusional constraints. These findings demonstrate the GLE framework’s utility in characterizing molecular transport and lipid dynamics, with implications for longer timescale membrane dynamics.

Malik, Sheeba [Oak Ridge National Laboratory (ORNL↗

NASA NTRS2005

Mars Tumbleweed Simulation Using Singular Perturbation Theory

The Mars Tumbleweed is a new surface rover concept that utilizes Martian winds as the primary source of mobility. Several designs have been proposed for the Mars Tumbleweed, all using aerodynamic drag to generate force for traveling about the surface. The Mars Tumbleweed, in its deployed configuration, must be large and lightweight to provide the ratio of drag force to rolling resistance necessary to initiate motion from the Martian surface. This paper discusses the dynamic simulation details of a candidate Tumbleweed design. The dynamic simulation model must properly evaluate and characterize the motion of the tumbleweed rover to support proper selection of system design parameters. Several factors, such as model flexibility, simulation run times, and model accuracy needed to be considered in modeling assumptions. The simulation was required to address the flexibility of the rover and its interaction with the ground, and properly evaluate its mobility. Proper assumptions needed to be made such that the simulated dynamic motion is accurate and realistic while not overly burdened by long simulation run times. This paper also shows results that provided reasonable correlation between the simulation and a drop/roll test of a tumbleweed prototype.

Raiszadeh, Behzad↗

NASA NTRS2009

Simulation of SRAM SEU Sensitivity at Reduced Operating Temperatures

A new NanoTCAD-to-Spectre interface is applied to perform mixed-mode SEU simulations of an SRAM cell. Results using newly calibrated TCAD cold temperature substrate mobility models, and BSIM3 compact models extracted explicitly for the cold temperature designs, indicate a 33% reduction in SEU threshold for the range of temperatures simulated.

Sanathanamurthy, S.↗

DOE OSTI2024

Perpendicular crossing chains enable high mobility in a noncrystalline conjugated polymer

The nature of interchain π-system contacts, and their relationship to hole transport, are elucidated for the high-mobility, noncrystalline conjugated polymer C16-IDTBT by the application of scanning tunneling microscopy, molecular dynamics, and quantum chemical calculations. The microstructure is shown to favor an unusual packing motif in which paired chains cross-over one another at near-perpendicular angles. By linking to mesoscale microstructural features, revealed by coarse-grained molecular dynamics and previous studies, and performing simulations of charge transport, it is demonstrated that the high mobility of C16-IDTBT can be explained by the promotion of a highly interconnected transport network, stemming from the adoption of perpendicular contacts at the nanoscale, in combination with fast intrachain transport.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRSDate not supplied

A Preliminary Assessment of Physical Demand during Simulated Lunar Surface Extravehicular Activities

Returning to the moon requires many advances in current space technology. One major aspect of this development is a new exploration spacesuit (xEMU). Taking lessons learned from Apollo era suitsand the Extravehicular Mobility Unit (EMU) used on the International Space Station (ISS), xEMU will have increased mobility, dust mitigation, headspace, glove fit, and life support capabilities. Artemis astronauts in xEMU will complete a far more rigorous Extravehicular Activity (EVA) schedule than Apolloand ISS. Notably, metabolic rates during Apollo lunar EVA tasks were observed to be up to 50% lower than similar tasks performed in a ground analog environment under simulated partial gravity with newer suits. Therefore, understanding the physical demands of lunar surface exploration operations is criticalto ensuring best outcomes operating within the constraints of xEMU and planning for exploration EVA activities. This study utilized the Active Response Gravity Offload System (ARGOS) to simulate the lunar environment and continuously offload subjects to lunar gravity. Two male subjects completed two days of EVAs wearing the pressurized Mark III spacesuit, completing suit fit and mobility checks, as well as simulated lander operations, cable routing, crew rescue, geology, payload relocation, and traverse tasks in an end-to-end EVA (E2E) task block and standalone (SA) task blocks. We recorded continuous values of metabolic rate (MR) and heart rate (HR) to assess physical demand. During the E2E task block, subjects did not rest between tasks to simulate continuous effort from task to task, as in real EVAs. In comparison, subjects had a 5-minute break after each SA task block to allow for the metabolic rate and heart rate to return to baseline.MR values were categorized as low (≤ 700 BTU/hr), medium (700-1000 BTU/HR), and high (≥ 1000 BTU/hr), while HR values were categorized as low (≤150) and high (>150). During the 16 tasks in the E2E block, subjects averaged low MR in 6% of tasks, medium MR in 47% of tasks, and high MR in 47% of tasks. While MR was consistent between subjects, Subject 1 averaged low HR for 100% of these tasks, while Subject 2 averaged low HR in 44% of tasks. During the 23 tasks in the SA task blocks, subjects averaged low MR in 26% of tasks, medium MR in 52% of tasks, and high MR in 22% of tasks. Again, HR was different between subjects, with subject 1 averaging low HR in 100% of these tasks while subject 2 averaged low HR in 70%. Across all tasks in this study, subjects reached maximum MR and HR values during a 500m traverse at 30% grade in the E2E block (subject 1: 1747 BTU/hr, 150 BPM; subject 2: 1656 BTU/hr, 177 BPM).Understanding the physical demand to complete exploration EVA tasks will be instrumental to the future success of exploration spacesuit designs and missions. Further work in this study will be needed to characterize MR during exploration EVA tasks, including expanding the subject pool and testing new suit designs.

Taylor E Schlotman↗

NASA NTRS1989

Space station dynamics, attitude control and momentum management

The Space Station Attitude Control System software test-bed provides a rigorous environment for the design, development and functional verification of GN and C algorithms and software. The approach taken for the simulation of the vehicle dynamics and environmental models using a computationally efficient algorithm is discussed. The simulation includes capabilities for docking/berthing dynamics, prescribed motion dynamics associated with the Mobile Remote Manipulator System (MRMS) and microgravity disturbances. The vehicle dynamics module interfaces with the test-bed through the central Communicator facility which is in turn driven by the Station Control Simulator (SCS) Executive. The Communicator addresses issues such as the interface between the discrete flight software and the continuous vehicle dynamics, and multi-programming aspects such as the complex flow of control in real-time programs. Combined with the flight software and redundancy management modules, the facility provides a flexible, user-oriented simulation platform.

Sunkel, John W.↗

NASA NTRS2019

Simulating Fleet Noise for Notional UAM Vehicles and Operations in New York

This paper presents the results of systems-level simulations using Metrosim that were conducted for notional Urban Air Mobility (UAM)-style vehicles analyzed for two different scenarios for New York (NY). UAM is an aviation industry term for passenger or cargo-carrying air transportation services, which are often automated, operating in an urban/city environment. UAM-style vehicles are expected to use vertical takeoff and landing with fixed wing cruise flight. Metrosim is a metroplex-wide route and airport planning tool that can also be used in standalone mode as a simulation tool. The scenarios described and reported in this paper were used to evaluate a fleet noise prediction capability for this tool. The work was a collaborative effort between the National Aeronautics and Space Administration (NASA), Intelligent Automation, Inc (IAI), and the Port Authority of New York and New Jersey (PANYNJ). One scenario was designed to represent an expanded air-taxi operation from existing helipads around Manhattan to the major New York airports. The other case represented a farther term vision case with commuters using personal air vehicles to hub locations just outside New York, with an air-taxi service running frequent connector trips to a few key locations inside Manhattan. For both scenarios, the trajectories created for the entire fleet were passed to the Aircraft Environmental Design Tool (AEDT) to generate Day-Night Level (DNL) noise contours for inspection. Without data for actual UAM vehicles available, surrogate AEDT empirical Noise-Power-Distance (NPD) tables used a similar sized current day helicopter as the Baseline, and a version of that same data linearly scaled as a first guess at possible UAM noise data. Details are provided for each of the two scenario configurations, and the output noise contours are presented for the Baseline and reduced noise DNL cases.

Glaab, Patricia↗

NASA NTRS2020

Computational Study of NASA's Quadrotor Urban Air Taxi Concept

High-fidelity computational fluid dynamics simulations have been carried out in order to analyze NASA's quadrotor urban air taxi concept for urban air mobility, also know as on-demand mobility applications. High-order accurate schemes, dual-time stepping, and the delayed detached-eddy simulation model have been employed. The ow solver has been loosely coupled with a rotorcraft comprehensive analysis code. The vehicle simulated is a six-passenger quadrotor for air taxi operations. A study of power reduction as a function of the rear-rotor to front-rotors vertical separation has been performed, for a quad-rotor without the airframe, in cruise flight conditions. Then, the quadrotor without the airframe has been simulated in hover. The airloads and wake geometries are analyzed. To finish the study the complete quadrotor vehicle is presented. NASA's quadrotor air taxi concept is one of the many concepts being developed by NASA in support of aircraft development for vertical take-o and landing air taxi operations.

Ventura Diaz, Patricia↗

DOE OSTI2025

What is the Role of Relative Humidity on Conductivity in Polymer Electrolytes?

Ion transport properties in polymer electrolytes have been widely studied under rigorously dry and highly water-swollen conditions. However, the transition between these extremes, i.e., the low hydration regime, is still poorly understood at the molecular level and relevant to applications ranging from battery electrolytes to electrophoretic separations. Here, in this study, we apply atomistic molecular dynamics simulations to probe the role of hydration on ion mobilities and conductivities in LiTFSI-doped polyethers at low water content (less than 10% water by volume), which corresponds to 0−80% relative humidity conditions. With increasing water content, Li + ions exhibit two distinct regimes in their mobilities. At low water content, the majority of the Li + ions are weakly hydrated (two or fewer water molecules per Li + ion), maintaining strong interactions with their polymer solvation cage, and therefore exhibit only a weak increase in mobility relative to dry conditions. As water content increases, Li + ions form complete hydration shells, residing within water-rich domains that promote faster mobilities. Further, Li + mobilities increase more significantly in polymer electrolytes composed of more hydrophilic polymers and higher salt concentrations due to the formation of larger water-rich domains. In contrast, TFSI − has comparatively weak interactions with both the polymer and water, exhibiting a monotonic increase in mobility as a function of water content. Overall, these results help clarify the molecular mechanisms underlying ionic mobilities and conductivities in polymer electrolytes at low water content.

36 MATERIALS SCIENCE↗