Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Well”

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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Recent Developments in Quantum-Well Infrared Photodetectors

Intrinsic infrared (IR) detectors in the long wavelength range (8-20 Am) are based on an optically excited interband transition, which promotes an electron across the band gap (E(sub g)) from the valence band to the conduction band as shown. These photoelectrons can be collected efficiently, thereby producing a photocurrent in the external circuit. Since the incoming photon has to promote an electron from the valence band to the conduction band, the energy of the photon (h(sub upsilon)) must be higher than the E(sub g) of the photosensitive material. Therefore, the spectral response of the detectors can be controlled by controlling the E(sub g) of the photosensitive material. Examples for such materials are Hg(1-x), Cd(x), Te, and Pb(1-x), Sn(x), Te, in which the energy gap can be controlled by varying x. This means detection of very-long-wavelength IR radiation up to 20 microns requires small band gaps down to 62 meV. It is well known that these low band gap materials, characterized by weak bonding and low melting points, are more difficult to grow and process than large-band gap semiconductors such as GaAs. These difficulties motivate the exploration of utilizing the intersub-band transitions in multiquantum well (MQW) structures made of more refractory large-band gap semiconductors. The idea of using MQW structures to detect IR radiation can be explained by using the basic principles of quantum mechanics. The quantum well is equivalent to the well-known particle in a box problem in quantum mechanics, which can be solved by the time independent Schroudiner equation.

Gunapala, S. D.↗
NASA NTRS1998

Quantum Well Infrared Photodetectors for Low Background Applications

High performance long-wavelength GaAs/Al(x)Ga(1-x)As quantum well infrared photodetectors for low background applications have been demonstrated. This is the first theoretical analysis of quantum well infrared photodetectors for low background applications and the detectivity D* of 6 x 10(exp 13) cm.square root of Hz/W has been achieved at T = 40 K with 2 x 10(exp 9) photons/cm2/sec background. In addition, this paper describes the demonstration of mid-wavelength/long-wavelength dualband quantum well infrared photodetectors and long-wavelength/very long-wavelength dualband quantum well infrared photodetectors in 4-26 micrometers wavelength region.

Gunapala, S. D.↗
NASA NTRS2006

Transient Flow Dynamics in Optical Micro Well Involving Gas Bubbles

The Lab-On-a-Chip Application Development (LOCAD) team at NASA s Marshall Space Flight Center is utilizing Lab-On-a-Chip to support technology development specifically for Space Exploration. In this paper, we investigate the transient two-phase flow patterns in an optic well configuration with an entrapped bubble through numerical simulation. Specifically, the filling processes of a liquid inside an expanded chamber that has bubbles entrapped. Due to the back flow created by channel expansion, the entrapped bubbles tend to stay stationary at the immediate downstream of the expansion. Due to the huge difference between the gas and liquid densities, mass conservation issues associated with numerical diffusion need to be specially addressed. The results are presented in terms of the movement of the bubble through the optic well. Bubble removal strategies are developed that involve only pressure gradients across the optic well. Results show that for the bubble to be moved through the well, pressure pulsations must be utilized in order to create pressure gradients across the bubble itself.

Johnson, B.↗
NASA NTRS2014

How Well Does the Latest Anthropomorphic Test Device Mimic Human Impact Responses?

One of the goals of the NASA Occupant Protection Group is to understand the human tolerance to dynamic loading. This knowledge has to come through indirect approaches such as existing human response databases, anthropometric test devices (ATD), animal testing, post‐mortem human subjects, and models. This study investigated the biofidelity of the National Highway Traffic Safety Administration's ATD named the THOR (test device for human occupant restraint). If THOR responds comparably to humans, then it could potentially be used as a human surrogate to help validate space vehicle requirements for occupant protection. The THOR responses to frontal and spinal impacts (ranging from 8 to 12 G with rise times of 40, 70, and 100 ms) were measured and compared to human volunteer responses (95 trials in frontal and 58 in spinal) previously collected by the U. S. Air Force on the same horizontal impact accelerator. The impact acceleration profiles tested are within the expected range of multi‐purpose crew vehicle (MPCV) landing dynamics. A correlation score was calculated for each THOR to human comparison using CORA (CORrelation and Analysis) software. A two‐parameter beta distribution model fit was obtained for each dependent variable using maximum likelihood estimation. For frontal impacts, the THOR head x‐acceleration peak response correlated with the human response at 8 and 10‐G 100 ms but not 10‐G 70 ms. The phase lagged the human response. Head z‐acceleration was not correlated. Chest x‐acceleration was in phase, had a higher peak response, and was well correlated with lighter subjects (Cora = 0.8 for 46 kg vs. Cora = 0.4 for 126 kg). Head x‐displacement had a leading phase. Several subjects responded with the same peak displacement but the mean of the group was lower. The shoulder x‐displacement was in phase but had higher peaks than the human response. For spinal impacts, the THOR head x‐acceleration was not well correlated. Head and chest z‐acceleration was in phase but had a higher peak response. Chest z‐acceleration was highly correlated with heavier subjects at lower G pulses (Cora = 0.86 for 125 kg at 8 G). The human response was variable in shoulder z‐displacement but the THOR was in phase and was comparable to the mean peak response. Head xand z‐displacement was in phase but had higher peaks. Seat pan forces were well correlated, were in phase, but had a larger peak response than most subjects. The THOR does not respond to frontal and spinal impacts exactly the same way that a human does. Some responses are well matched and others are not. Understanding the strengths and weaknesses of this ATD is an important first step in determining its usefulness in occupant protection at NASA

Newby, N.↗
NASA NTRS2014

How Well Does the Latest Anthropomorphic Test Device Mimic Human Impact Responses?

One of the goals of the NASA Occupant Protection Group is to understand the human tolerance to dynamic loading. This knowledge has to come through indirect approaches such as existing human response databases, anthropometric test devices (ATD), animal testing, post-­‐mortem human subjects, and models. This study investigated the biofidelity of the National Highway Traffic Safety Administration's ATD named the THOR (test device for human occupant restraint). If THOR responds comparably to humans, then it could potentially be used as a human surrogate to help validate space vehicle requirements for occupant protection. The THOR responses to frontal and spinal impacts (ranging from 8 to 12 G with rise times of 40, 70, and 100 ms) were measured and compared to human volunteer responses (95 trials in frontal and 58 in spinal) previously collected by the U. S. Air Force on the same horizontal impact accelerator. The impact acceleration profiles tested are within the expected range of multi-­‐purpose crew vehicle (MPCV) landing dynamics. A correlation score was calculated for each THOR to human comparison using CORA (CORrelation and Analysis) software. A two-­‐parameter beta distribution model fit was obtained for each dependent variable using maximum likelihood estimation. For frontal impacts, the THOR head x-­‐acceleration peak response correlated with the human response at 8 and 10-­‐G 100 ms but not 10-­‐G 70 ms. The phase lagged the human response. Head z-­‐acceleration was not correlated. Chest x-­‐acceleration was in phase, had a higher peak response, and was well correlated with lighter subjects (Cora = 0.8 for 46 kg vs. Cora = 0.4 for 126 kg). Head x-­‐displacement had a leading phase. Several subjects responded with the same peak displacement but the mean of the group was lower. The shoulder x-­‐displacement was in phase but had higher peaks than the human response. For spinal impacts, the THOR head x-­‐acceleration was not well correlated. Head and chest z-­‐acceleration was in phase but had a higher peak response. Chest z-­‐acceleration was highly correlated with heavier subjects at lower G pulses (Cora = 0.86 for 125 kg at 8 G). The human response was variable in shoulder z-­‐displacement but the THOR was in phase and was comparable to the mean peak response. Head x-­‐ and z-­‐displacement was in phase but had higher peaks. Seat pan forces were well correlated, were in phase, but had a larger peak response than most subjects. The THOR does not respond to frontal and spinal impacts exactly the same way that a human does. Some responses are well matched and others are not. Understanding the strengths and weaknesses of this ATD is an important first step in determining its usefulness in occupant protection at NASA

Newby, Nate↗
NASA NTRS2018

En Route Detect and Avoid Well Clear in Terminal Area Landing Pattern

A fast time simulation was conducted to test the detect and avoid Well Clear definition designed for en route use when an unmanned aircraft (UA) is approaching the landing pattern of the terminal area. Measures focused on were loss of well clear and alerts intended to help the pilot avoid loss of well clear. Data indicated warning-level alerts will occur outside the typical Class D airspace which may prevent the UA from normal operations in the terminal airspace. Other aircraft on 45o entry could result in “nuisance” alerts which may also prevent the UA from normal operations in the terminal airspace. However, eliminating horizontal proximity (τmod) has the potential to increase “nuisance” alerts on the 45o entry and downwind legs. Overall, this suggests that a more stringent definition of Well Clear may be advisable in the landing pattern of the terminal area.

Trujillo, Anna C.↗
NASA NTRS2019

A Comparison of Two Terminal Area Detect and Avoid Well Clear Definitions

Technical requirements are currently under development for a detect and avoid system (DAA) that would support the operation of Unmanned Aircraft Systems (UAS) within the National Airspace System (NAS). Such a system would aid UAS operators in maintaining sufficient separation, or "well clear", from other aircraft in their vicinity. The first set of technical standards for a UAS DAA system (referred to as "Phase 1" requirements) was limited to UAS operations transiting through Class D, E, and G airspace to, or from, Class A (or special-use) airspace. Explicitly out of scope of the Phase 1 requirements was the operation of UAS within terminal airspace in the NAS. Fern, Rorie, Roberts and Monk (2018) explored the application of a Phase 1 DAA system within Class D terminal airspace in a human-in-the-loop simulation. The results of the study demonstrated a poor fit of the Phase 1 DAA well clear (DWC) definition to these terminal operations. The original DWC definition was designed for the en-route environment and could not account for the complex, tightly-choreographed nature of traffic typically found near an airport. The interaction of the en-route DWC definition and the terminal area traffic led to excessive DAA alerting against safely-separated traffic. The frequent alerting quickly degraded pilots' ability to discriminate between encounters where a maneuver was or was not necessary. This resulted in slower response times, higher rates of losses of DAA well clear, and more severe losses of DAA well clear than had been observed in previous DAA research (e.g., Rorie et al., 2017). The current paper reports on a follow-on study to Fern et al. (2018) that tested two DWC definitions designed to accommodate standard terminal area operating procedures, such as traffic in the downwind leg of a VFR traffic pattern while the UAS is on final. The two definitions utilized identical horizontal and vertical thresholds but differed in whether or not Tau (a function that takes into account the closure rate of two aircraft) was included as a part of the DWC hazard zone. The "Tau" DWC candidate definition nominally extended the DWC hazard zone by 15 seconds in the direction of the intruder aircraft, while the "No Tau" DWC candidate definition did not extend the DWC hazard zone. The results of this follow-on study indicated that both candidate definitions improved pilot and DAA system performance relative to Fern et al (2018). Pilot response times and rates of losses of DWC returned to levels comparable to earlier research in the en-route environment. Several important differences between the two DWC candidate definitions, however, are also discussed.

Terminal Area↗
NASA NTRS2014

Final Overview of ACES Simulation for Evaluation SARP Well-Clear Definitions

The UAS in the NAS project is studying the minimum operational performance standards for unmanned aerial systems (UAS's) detect-and-avoid (DAA) system in order to operate in the National Airspace System. The DoD's Science and research Panel (SARP) Well-Clear Workshop is investigating the time and spatial boundary at which an UAS violates well-clear. NASA is supporting this effort through use of its Airspace Concept Evaluation System (ACES) simulation platform. This briefing presents the final results to the SARP, which will be used to judge the three candidate well-clear definitions, and for the selection of the most operationally suitable option.

detect and avoid↗
NASA NTRS2017

UAS Well Clear Recovery Against Non-Cooperative Intruders Using Vertical Maneuvers

This paper documents a study that drove the development of a mathematical expression in the minimum operational performance standards (MOPS) of detect-and-avoid (DAA) systems for unmanned aircraft systems (UAS). This equation describes the conditions under which vertical maneuver guidance could be provided during recovery of well clear separation with a non-cooperative VFR aircraft in addition to horizontal maneuver guidance. Although suppressing vertical maneuver guidance in these situations increased the minimum horizontal separation from 500 to 800 feet, the maximum severity of loss of well clear increased in about 35 of the encounters compared to when a vertical maneuver was preferred and allowed. Additionally, analysis of individual cases led to the identification of a class of encounter where vertical rate error had a large effect on horizontal maneuvers due to the difficulty of making the correct left-right turn decision: crossing conflict with intruder changing altitude. These results supported allowing vertical maneuvers when UAS vertical performance exceeds the relative vertical position and velocity accuracy of the DAA tracker given the current velocity of the UAS and the relative vertical position and velocity estimated by the DAA tracker. Looking ahead, these results indicate a need to improve guidance algorithms by utilizing maneuver stability and near mid-air collision risk when determining maneuver guidance to regain well clear separation.

detect and avoid↗
NASA NTRS2018

Simulated Water Well Performance on Mars

The surface of Mars once had abundant water flowing on its surface, but now there is a general perception that this surface is completely dry. Several lines of research have shown that there are sources of potentially large quantities of water at many locations on the surface, including regions considered as candidates for future human missions. Recent discovery of exposed water ice scarps in Martian mid-latitudes has bolstered the evidence for massive amounts of almost pure water in these regions. These favorable indications of massive quantities of water have initiated studies of changes that could be made to human Mars missions if a means could be devised that would make this water available to these crews. The proposed paper will describe progress towards developing one approach for accessing and extracting water from these mid-latitude sources. This approach relies on mechanical drills to access the water ice through overlying debris. Once the ice has been accessed, a technique known as a Rodriguez Well is used to melt the ice, store the resulting water until it is needed, and then pump the water to the surface for use. Previous work in this area has utilized a computer simulation to predict the performance of the Rodriguez Well. This simulation was developed originally to predict performance in terrestrial polar regions. While the basic approach used in this model is appropriate for a similar well on Mars, several parameters were known to require a change to correctly model the Martian environment. Some of these parameters are empirical and require experiments simulating the Martian environment to determine their value. The proposed paper will describe the experiments set up to determine the value of these parameters and compare their numerical value to the terrestrial equivalent. Finally, the proposed paper will show results from the updated computer simulation and compare results with those determined from the original version of the simulation.

water↗
NASA NTRS2014

Pilot Evaluation of a UAS Detect-and-Avoid System's Effectiveness in Remaining Well Clear

Unmanned aircraft will equip with a detect-and-avoid (DAA) system that enables them to comply with the requirement to "see and avoid" other aircraft, an important layer in the overall set of procedural, strategic and tactical separation methods designed to prevent mid-air collisions. Regulators will establish minimum operating standards for DAA effectiveness, but different combinations of algorithms, displays and procedures could be used to meet those standards. The research presented in this paper indicates the effectiveness of the combined pilot-DAA system as a function of the DAA design requirements and provides data that may be used to model the behavior of pilots when employing such systems. Two simulations involving 21 professional unmanned aircraft system (UAS) pilots evaluated eight different DAA system designs in order to assess their ability to maintain the "well clear" separation standard, i.e., the state of maintaining a safe distance from other aircraft that would not normally cause the initiation of a collision avoidance maneuver by either aircraft. When the traffic display was integrated with the primary mission map directly in front of the pilot, there were fewer losses of well clear. Greater warning time provided to the pilot was strongly correlated with success in remaining well clear. Pilots' ability to separate from aircraft with cooperative and non-cooperative surveillance systems was nearly the same after accounting for the amount of alert time provided in each encounter, although the limited surveillance volume for the airborne-equipped aircraft meant alerts tended to occur later and therefore were more difficult to resolve.

detect-and-avoid↗
NASA NTRSDate not supplied

Progress in Simulated Water Well Performance on Mars

Recent studies of human Mars missions considered the impacts of an abundant supply of in-situ, accessible water on these mission scenarios. Discovery of exposed water ice scarps in Martian mid-latitudes has bolstered the evidence for massive amounts of almost pure water in buried deposits in regions considered candidates for these future human missions. This paper describes progress towards adapting a long-standing terrestrial technique for accessing and extracting water from these mid-latitude sources of ice. This approach relies on mechanical drills to access the ice through overlying debris. Once the ice layer has been reached, a technique known as a Rodriguez Well, or Rodwell, is used to melt the ice, store the resulting water in a subsurface cavity until needed, and then pump the water to the surface for use. Previous work by the authors utilized a computer simulation to predict the performance of a Martian Rodwell. This simulation was originally developed to predict performance in terrestrial Polar Regions. Whereas the basic approach is appropriate for a similar well on Mars, several parameters had been empirically derived and required experiments simulating the Martian environment to determine the values appropriate for a Martian Rodwell simulation. These experiments have now been completed and preliminary values have been determined for the empirical parameters. Test results are consistent with a dimensionless Sh(Ra) correlation developed by Bower and Saylor (2009) and based on lab tests of water evaporating from a pool into a large air chamber. They are also consistent with correlations derived by Ingersoll (1970) and by Hecht (2002), based on natural-convection heat transfer. Each of these earlier correlations found Sh~Ra1/3, with the 1/3rd power characteristic of large Ra where the boundary layer over the pool surface is turbulent. A somewhat surprising result was that this power-law was found to extend into a range of Ra where laminar flow would be expected. Another surprising result was found in that instead of following established correlations for natural-convection heat transfer over flat plates, the dimensionless heat-transfer rates (Nu) were much larger and approximately independent of Ra. This suggests that mass transfer from the pool enhances convective heat transfer, possibly by enhanced mixing in the boundary layer. Although this possibility has been suggested in the literature, if it is proven to be true under these conditions it could play an important role in the use of a Rodwell on Mars, where evaporative mass transfer is enhanced relative to terrestrial wells.

Human Mars Mission↗
NASA NTRS1998

Quantum Well Infrared Photodetectors for Long Wavelength Infrared Applications

Quantum Well Infrared Photodetectors (QWIPs) offer greater flexibility than usual extrinsically doped semiconductor IR detectors because the wavelength of the peak response and cutoff can be continuously tailored by varying layer thickness (well width), barrier composition (barrier height), and carrier density (well doping density).

Quantum↗
NASA NTRSDate not supplied

Mars Water Well Performance: Experimental Heat Transfer Results Supporting Simulations

Favorable indications of massive quantities of water on Mars have initiated studies of potential changes to human Mars missions. Using a technique known as a Rodriguez Well to melt the ice, store the resulting water in a subsurface ice cavity until needed, and then pump water to the surface for use is one potential means to effect these changes. A computer simulation of the Rodriguez Well in a terrestrial environment is one of the engineering tools being used to characterize the performance of this type of well on Mars. An experiment at the NASA Johnson Space Center is gathering data for convective heat transfer and evaporation rates at Mars surface conditions so that this computer simulation can be properly modified to predict performance on Mars. While quantitative results await processing, tests have indicated that a pool of water can be maintained at 1°C to 2° C while at Mars surface temperatures and pressures.

Mars↗
NASA NTRS2024

Monitoring Well Installation Completion Report for Ransom Road Landfill, Vertical Processing Facility, and Environmental Health Facility, Solid Waste Management Units: 003, 077, and 079

The intended purpose of the Monitoring Well Installation project is to support the Kennedy Space Center (KSC) Environmental Remediation Department’s Resource Conservation and Recovery Act Program by installing new monitoring wells. The wells are installed in accordance with the Brevard County Health Department and St. Johns River Water Management Districts rules and guidelines.

Well Installation↗
NASA NTRS1974

Geothermal down well pumping system

A key technical problem in the exploitation of hot water geothermal energy resources is down-well pumping to inhibit mineral precipitation, improve thermal efficiency, and enhance flow. A novel approach to this problem involves the use of a small fraction of the thermal energy of the well water to boil and super-heat a clean feedwater flow in a down-hole exchanger adjacent to the pump. This steam powers a high-speed turbine-driven pump. The exhaust steam is brought to the surface through an exhaust pipe, condensed, and recirculated. A small fraction of the high-pressure clean feedwater is diverted to lubricate the turbine pump bearings and prevent leakage of brine into the turbine-pump unit. A project demonstrating the feasibility of this approach by means of both laboratory and down-well tests is discussed.

Matthews, H. B.↗
NASA NTRS1975

Investigation of space shuttle vehicle 140C configuration orbiter (model 16-0) wheel well pressure loads in the Rockwell International 7.75 x 11 foot wind tunnel (OA143)

Experimental aerodynamic investigations were conducted on a sting mounted .0405-scale representation of the 140C outer mold line space shuttle orbiter configuration in the Rockwell International 7.75 x 11.00 foot low speed wind tunnel. The primary test objectives were to define the orbiter wheel well pressure loading and its effects on landing gear thermal insulation and to investigate the pressure environment experienced by both the horizontal flight nose probe and air vent door probes. Steady state and dynamic pressure values were recorded in the orbiter nose gear well, left main landing gear well, horizontal flight nose probe, and both left and right air vent door probe. All steady state pressure levels were measured by Statham differential pressure transducers while dynamic pressure levels were recorded by Kulite high frequency response pressure sensors.

Mennell, R. C.↗
NASA NTRS1978

A well posed boundary value problem in transonic gas dynamics

A new approach considered by Garabedian and Korn (1976) to solve a problem of airfoil design has led to a transonic boundary value problem. It remains to be shown that this problem is well posed. A description is presented of an investigation in which it is shown that a corresponding problem for the Tricomi equation is well posed. The solution to the boundary value problem is characterized, in a unique way, as a sum of two particular solutions. The Poisson formulas for the unit semicircle for the Euler-Poisson-Darboux equation are considered and reflection laws for solutions of the general Euler-Poisson-Darboux equation are established. It is proved that the considered boundary value problem for the case in which the involved function is periodic and continuous is well posed within the specified class of solutions.

Sanz, J. M.↗