SEARCH · Search NASA

Results for “Parametric and Sensitivity Studies”

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.

SourceResearch connectionFrom yearThrough year

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

At least 217 records · Page 12

All sources NASA NTRS DOE OSTI

NASA NTRS1986

Parametric analytical study of instability-related delamination growth

The effect of various parameters on instability-related delamination growth was studied analytially. The configuration studied consisted of a thick composite laminate with a single through-width delamination located near one surface. Both mechanical and thermal loads were considered. All conclusions were based on the assumption that GI and GII govern delamination growth. An approximate superposition stress analysis was developed which gives closed form expressions for GI and GII. The simplicity of the analysis permitted examination of numerous configurations. Both GI and GII were found to be very sensitive to delamination length and location through the thickness. The magnitude of GI was also very sensitive to initial imperfections, which might be the results of an inclusion of finite thickness in the delamination. Critical loads for delamination growth were calculated based on three growth criteria. Large differences in the predictions highlight the need for a verified mixed-mode delamination growth criterion.

Whitcomb, J. D.↗

NASA NTRS2012

Compression After Impact on Honeycomb Core Sandwich Panels with Thin Facesheets, Part 2: Analysis

A two part research study has been completed on the topic of compression after impact (CAI) of thin facesheet honeycomb core sandwich panels. The research has focused on both experiments and analysis in an effort to establish and validate a new understanding of the damage tolerance of these materials. Part 2, the subject of the current paper, is focused on the analysis, which corresponds to the CAI testings described in Part 1. Of interest, are sandwich panels, with aerospace applications, which consist of very thin, woven S2-fiberglass (with MTM45-1 epoxy) facesheets adhered to a Nomex honeycomb core. Two sets of materials, which were identical with the exception of the density of the honeycomb core, were tested in Part 1. The results highlighted the need for analysis methods which taken into account multiple failure modes. A finite element model (FEM) is developed here, in Part 2. A commercial implementation of the Multicontinuum Failure Theory (MCT) for progressive failure analysis (PFA) in composite laminates, Helius:MCT, is included in this model. The inclusion of PFA in the present model provided a new, unique ability to account for multiple failure modes. In addition, significant impact damage detail is included in the model. A sensitivity study, used to assess the effect of each damage parameter on overall analysis results, is included in an appendix. Analysis results are compared to the experimental results for each of the 32 CAI sandwich panel specimens tested to failure. The failure of each specimen is predicted using the high-fidelity, physicsbased analysis model developed here, and the results highlight key improvements in the understanding of honeycomb core sandwich panel CAI failure. Finally, a parametric study highlights the strength benefits compared to mass penalty for various core densities.

Mcquigg, Thomas D.↗

NASA NTRS2010

A Parametric Study on Using Active Debris Removal for LEO Environment Remediation

Recent analyses on the instability of the orbital debris population in the low Earth orbit (LEO) region and the collision between Iridium 33 and Cosmos 2251 have reignited the interest in using active debris removal (ADR) to remediate the environment. There are; however, monumental technical, resource, operational, legal, and political challenges in making economically viable ADR a reality. Before a consensus on the need for ADR can be reached, a careful analysis of its effectiveness must be conducted. The goal is to demonstrate the need and feasibility of using ADR to better preserve the future environment and to guide its implementation to maximize the benefit-to-cost ratio. This paper describes a new sensitivity study on using ADR to stabilize the future LEO debris environment. The NASA long-term orbital debris evolutionary model, LEGEND, is used to quantify the effects of several key parameters, including target selection criteria/constraints and the starting epoch of ADR implementation. Additional analyses on potential ADR targets among the currently existing satellites and the benefits of collision avoidance maneuvers are also included.

Source record↗

NASA NTRS1989

Generalized mathematical models in design optimization

The theory of optimality conditions of extremal problems can be extended to problems continuously deformed by an input vector. The connection between the sensitivity, well-posedness, stability and approximation of optimization problems is steadily emerging. The authors believe that the important realization here is that the underlying basis of all such work is still the study of point-to-set maps and of small perturbations, yet what has been identified previously as being just related to solution procedures is now being extended to study modeling itself in its own right. Many important studies related to the theoretical issues of parametric programming and large deformation in nonlinear programming have been reported in the last few years, and the challenge now seems to be in devising effective computational tools for solving these generalized design optimization models.

Papalambros, Panos Y.↗

NASA NTRS2010

A Parametric Study on Using Active Debris Removal to Stabilize the Future LEO Debris Environment

Recent analyses of the instability of the orbital debris population in the low Earth orbit (LEO) region and the collision between Iridium 33 and Cosmos 2251 have reignited the interest in using active debris removal (ADR) to remediate the environment. There are; however, monumental technical, resources, operational, legal, and political challenges in making economically viable ADR a reality. Before a consensus on the need for ADR can be reached, a careful analysis of the effectiveness of ADR must be conducted. The goal is to demonstrate the feasibility of using ADR to preserve the future environment and to guide its implementation to maximize the benefit-cost ratio. This paper describes a comprehensive sensitivity study on using ADR to stabilize the future LEO debris environment. The NASA long-term, orbital debris evolutionary model, LEGEND, is used to quantify the effects of many key parameters. These parameters include (1) the starting epoch of ADR implementation, (2) various target selection criteria, (3) the benefits of collision avoidance maneuvers, (4) the consequence of targeting specific inclination or altitude regimes, (5) the consequence of targeting specific classes of vehicles, and (6) the timescale of removal. Additional analyses on the importance of postmission disposal and how future launches might affect the requirements to stabilize the environment are also included.

Liou, J.C.↗

NASA NTRS1985

Parametric study of supersonic STOVL flight characteristics

A number of different control devices and techniques are evaluated to determine their suitability for increasing the short takeoff performance of a supersonic short-takeoff/vertical landing (STOVL) aircraft. Analysis was based on a rigid-body mathematical model of the General Dynamics E-7, a single engine configuration that utilizes ejectors and thrust deflection for propulsive lift. Alternatives investigated include increased static pitch, the addition of a close-coupled canard, use of boundary layer control to increase the takeoff lift coefficient, and the addition of a vectorable aft fan air nozzle. Other performance studies included the impact of individual E-7 features, the sensitivity to ejector performance, the effect of removing the afterburners, and a determination of optional takeoff and landing transition methods. The results pertain to both the E-7 and other configurations. Several alternatives were not as well suited to the E-7 characteristics as they would be to an alternative configuration, and vice versa. A large amount of supporting data for each analysis is included.

Rapp, David C.↗

NASA NTRS1984

Aerodynamic canard/wing parametric analysis for general aviation applications

Vortex panel and vortex lattice methods have been utilized in an analytic study to determine the two- and three-dimensional aerodynamic behavior of canard and wing configurations. The purpose was to generate data useful for the design of general aviation canard aircraft. Essentially no two-dimensional coupling was encountered and the vertical distance between the lifting surfaces was found to be the main contributor to interference effects of the three-dimensional analysis. All canard configurations were less efficient than a forward wing with an aft horizontal tail, but were less sensitive to off-optimum division of total lift between the two surfaces, such that trim drag could be less for canard configurations. For designing a general aviation canard aircraft, results point toward large horizontal and vertical distance between the canard and wing, a large wing-to-canard area ratio, and with the canard at a low incidence angle relative to the wing.

Keith, M. W.↗

NASA NTRS1986

Aeroelastic considerations for torsionally soft rotors

A research study was initiated to systematically determine the impact of selected blade tip geometric parameters on conformable rotor performance and loads characteristics. The model articulated rotors included baseline and torsionally soft blades with interchangeable tips. Seven blade tip designs were evaluated on the baseline rotor and six tip designs were tested on the torsionally soft blades. The designs incorporated a systemmatic variation in geometric parameters including sweep, taper, and anhedral. The rotors were evaluated in the NASA Langley Transonic Dynamics Tunnel at several advance ratios, lift and propulsive force values, and tip Mach numbers. A track sensitivity study was also conducted at several advance ratios for both rotors. Based on the test results, tip parameter variations generated significant rotor performance and loads differences for both baseline and torsionally soft blades. Azimuthal variation of elastic twist generated by variations in the tip parameters strongly correlated with rotor performance and loads, but the magnitude of advancing blade elastic twist did not. In addition, fixed system vibratory loads and rotor track for potential conformable rotor candidates appears very sensitive to parametric rotor changes.

Mantay, W. R.↗

NASA NTRS1984

Aeroelastic considerations for torsionally soft rotors

Mantay, W. R.↗

NASA NTRS1991

A mass sensitivity analysis of lunar orbiting beam power systems

At NASA Lewis Research Center, the feasibility of beaming power from orbiting satellites to the surface of the moon was studied. Reference microwave and laser beam power concepts were found to be 1/3 to 1/6 the mass of surface solar systems. Further analysis was performed to determine the sensitivity of the reference concepts to technology performance levels and mission architecture scenarios, such as beaming to multiple surface sites and lunar rovers. Previous studies concluded that frequencies above 35 GHz for the microwave systems were not critical for reducing the main base mass; however, when multiple sites and rovers are considered, this may become necessary. In addition, for the laser system, the pointing accuracy of the satellites becomes a critical factor for rover applications. These issues and other important results of the parametric studies, are discussed.

Stavnes, Mark W.↗

NASA NTRS2023

CFD Modeling of Bi-Directional PMD inside Cryogenic Propellant Tanks Onboard Parabolic Flights

Future cryogenic propulsion systems will require efficient methods with which to transfer cryogenic propellants from a depot storage tank to a customer receiver tank to minimize cost and maximize reusability. The Reduced Gravity Cryogenic Transfer project is currently developing advanced cryogenic fluid management technology and developing and validating new numerical models for three phases of transfer: line chilldown, tank chilldown, and tank fill. Additionally, multiple liquid nitrogen (LN 2 ) parabolic flight transfer rigs are being designed by universities and NASA to investigate the gravitational sensitivities that exist in these three technologies. In order to maximize the collection of low-g data during flights, it is required to extract as much (LN 2 as possible from the supply tank, despite variable gravity levels. The purpose of this paper is to present computational fluid dynamics (CFD) volume of fluid simulations of (LN 2 behavior in the supply tank onboard parabolic flights to validate the optimal design of a bi-directional propellant management device (PMD) using the commercial software FLOW-3D. A parametric study is conducted on the effects of gravity level, fill level, pore size, open area, thickness, and type of baffle on PMD performance. Based on results, the PMD as designed exceeds the targeted expulsion efficiency.

Jason Hartwig↗

NASA NTRS1995

Hypersonic Combustor Model Inlet CFD Simulations and Experimental Comparisons

Numerous two-and three-dimensional computational simulations were performed for the inlet associated with the combustor model for the hypersonic propulsion experiment in the NASA Ames 16-Inch Shock Tunnel. The inlet was designed to produce a combustor-inlet flow that is nearly two-dimensional and of sufficient mass flow rate for large scale combustor testing. The three-dimensional simulations demonstrated that the inlet design met all the design objectives and that the inlet produced a very nearly two-dimensional combustor inflow profile. Numerous two-dimensional simulations were performed with various levels of approximations such as in the choice of chemical and physical models, as well as numerical approximations. Parametric studies were conducted to better understand and to characterize the inlet flow. Results from the two-and three-dimensional simulations were used to predict the mass flux entering the combustor and a mass flux correlation as a function of facility stagnation pressure was developed. Surface heat flux and pressure measurements were compared with the computed results and good agreement was found. The computational simulations helped determine the inlet low characteristics in the high enthalpy environment, the important parameters that affect the combustor-inlet flow, and the sensitivity of the inlet flow to various modeling assumptions.

Venkatapathy, E.↗

NASA NTRS1976

Theoretical optimization and parametric study of n-on-p Al/x/Ga/1-x/As-GaAs graded band-gap solar cell

A comprehensive theoretical model of the graded band-gap Al(x)Ga(1-x)As-GaAs solar cell is used to optimize the n-on-p cell. The model includes power losses due to surface, bulk, and junction minority-carrier recombination, series resistance, and photon reflection from an SiO antireflection coating of optimum thickness. The optimized cell has a junction depth/graded band-gap layer thickness of 1.0 micron, respective donor and acceptor concentrations of 4 x 10 to the 17th power and 2 x 10 to the 17th power per cu cm, and a surface AlAs mode fraction of x = 0.35. The optimized graded band-gap cell has an air-mass-zero efficiency of 17.7% (not corrected for a 13% front surface contact area) and is shown to be less sensitive than a similar n-on-p GaAs cell to material degradation in the form of decreased minority-carrier diffusion lengths and increased surface-recombination velocity

Hutchby, J. A.↗

NASA NTRS2013

Investigation of Maximum Blade Loading Capability of Lift-Offset Rotors

Maximum blade loading capability of a coaxial, lift-offset rotor is investigated using a rotorcraft configuration designed in the context of short-haul, medium-size civil and military missions. The aircraft was sized for a 6600-lb payload and a range of 300 nm. The rotor planform and twist were optimized for hover and cruise performance. For the present rotor performance calculations, the collective pitch angle is progressively increased up to and through stall with the shaft angle set to zero. The effects of lift offset on rotor lift, power, controls, and blade airloads and structural loads are examined. The maximum lift capability of the coaxial rotor increases as lift offset increases and extends well beyond the McHugh lift boundary as the lift potential of the advancing blades are fully realized. A parametric study is conducted to examine the differences between the present coaxial rotor and the McHugh rotor in terms of maximum lift capabilities and to identify important design parameters that define the maximum lift capability of the rotor. The effects of lift offset on rotor blade airloads and structural loads are also investigated. Flap bending moment increases substantially as lift offset increases to carry the hub roll moment even at low collective values. The magnitude of flap bending moment is dictated by the lift-offset value (hub roll moment) but is less sensitive to collective and speed.

Yeo, Hyeonsoo↗

NASA NTRS1980

Experimental combustor study program

Advanced combustor concepts are evaluated as a means of accommodating possible future broad specification fuels. The three advanced double annular combustor concepts consisted of (1) a concept employing high pressure drop fuel nozzles for improved atomization, (2) a concept with premixing tubes in the main stage, and (3) a concept with the pilot stage on the inside and the main stage on the sideout, which is the reverse of the other two concepts. All of the advanced concepts show promise for reduced sensitivity to fuel hydrogen content. Some hardware problems were encountered, but these problems could be quickly resolved if refinement tests were conducted. The design with the premixing main stage was selected for a parametric test because of its low NOx emissions level, carbon free dome, and very low dome temperatures which were essentially independent of fuel type. The other advanced designs also had low done temperatures. The premixing dome design liner temperatures exhibited less sensitivity to fuel type than did the base-line combustor, although more sensitivity than observed for concept 1. The inner liner hot spot and the observed smoke results for the premixing design suggest that the fuel-air mixture was not as uniform as desired.

Kasper, J. M.↗

NASA NTRS2017

NIAC Swarm Flyby Gravimetry Phase II Report

This NASA Innovative Advanced Concept (NIAC) grant has enabled the research and development of a method for conducting small body gravimetry from a spacecraft, using relative measurements to a set of deployed test-masses. The test-masses are tracked from a host spacecraft, which dispenses them near to the small body's surface. Thanks to this close proximity, the probes' orbits can be highly perturbed, which yields useful gravimetric measurements. The most readily achievable approach for tracking the probes is to use an optical instrument on- board the spacecraft. The probes then need only be reflective to sunlight. This implementation, called optical gravimetry (OpGrav), has the fewest requirements for the host spacecraft and probes.The results of this study indicate that OpGrav is feasible and offers meaningful improvement over existing methods. Parametric studies suggest roughly an order of magnitude improvement in accuracy or asteroid accessibility (how small an asteroid one can measure) over Earth-based Doppler-only mass estimation. This exponentially expands the number of potential near-Earth objects that one could study, which has implications for planetary defense.As a sample mission, we evaluated OpGrav as an added instrument on a main- belt asteroid tour mission. In this case, simulations show that OpGrav would increase the number of asteroid mass estimates from 3 of 9 to 7 of 9. That is, OpGrav has sufficient sensitivity to offer utility in missions for which it is not explicitly designed for.We designed and fabricated a prototype hardware implementation for this concept called the Small-body In-situ Multi-probe Mass Estimation Experiment (SIMMEE). This hardware provides a basis for many inputs into the simulations and grounds the models with physical values. The primary design driver for the hardware is a long life, on the order of five years prior to operation, and a need for high pointing accuracy to enable flybys of the smallest objects.The next steps include further hardware testing and extension of the concept to rendezvous cases. We believe that this concept offers planetary scientists a new and relevant means of better understanding small-bodies.

Atchison, Justin A.↗

NASA NTRS1992

Composite propellant tank study for very low cost space transportation

A study of life-cycle cost is conducted to determine acceptable options for composite propellant tanks at low cost and weight and for use at moderate pressures. The review examines all cost issues relevant to the production, mass, applications, and reliability of the tanks for pressure-fed rockets. Specific attention is given to the manufacturing and life-cycle issues relevant to the use of composite materials in this application since composites are effective materials for liquid propellant tanks. Specific costs and parametric considerations are given for several tank candidates with 62,303-lb capacities. The mass sensitivity of the fourth stage for the concept vehicle is shown to be high, and the use of a 325-psi fourth-stage tank is shown to yield the minimum cost/lb for the stage. Wound S-glass/epoxy composites can be employed as cost-effective replacements for steel in the design of liquid-propellant tanks.

Moser, D. J.↗

NASA NTRS2018

Modeling Fiber Kinking at the Microscale and Mesoscale

A computational micromechanics (CMM) model is employed to interrogate the assumptions of a recently developed mesoscale continuum damage mechanics (CDM) model for fiber kinking. The CMM model considers an individually discretized three dimensional fiber and surrounding matrix accounting for nonlinearity in the fiber, matrix plasticity, fiber/matrix interface debonding, and geometric nonlinearity. Key parameters of the CMM model were measured through experiments. In particular, a novel experimental technique to characterize the in situ longitudinal compressive strength of carbon fibers through indentation of micropillars is presented. The CDM model is formulated on the basis of Budiansky's fiber kinking theory (FKT) with a constitutive deformation-decomposition approach to alleviate mesh size sensitivity. In contrast to conventional mesoscale CDM models that prescribe a constitutive response directly, the response of the proposed model is an outcome of material nonlinearity and large rotations of the fiber direction following FKT. Comparison of the predictions from the CMM and CDM models shows remarkable correlation in strength, post-peak residual stress, and fiber rotation, with less than 10% difference between the two models in most cases. Additional comparisons are made with several fiber kinking models proposed in the literature to highlight the efficacy of the two models. Finally, the CMM model is exercised in parametric studies to explore opportunities to improve the longitudinal compression strength of a ply through the use of nonconventional microstructures.

Herraez, Miguel↗