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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.

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NASA NTRS2017

Boundary Condition Study for the Juncture Flow Experiment in the NASA Langley 14x22-Foot Subsonic Wind Tunnel

Because future wind tunnel tests associated with the NASA Juncture Flow project are being designed for the purpose of CFD validation, considerable effort is going into the characterization of the wind tunnel boundary conditions, particularly at inflow. This is important not only because wind tunnel flowfield nonuniformities can play a role in integrated testing uncertainties, but also because the better the boundary conditions are known, the better CFD can accurately represent the experiment. This paper describes recent investigative wind tunnel tests involving two methods to measure and characterize the oncoming flow in the NASA Langley 14- by 22-Foot Subsonic Tunnel. The features of each method, as well as some of their pros and cons, are highlighted. Boundary conditions and modeling tactics currently used by CFD for empty-tunnel simulations are also described, and some results using three different CFD codes are shown. Preliminary CFD parametric studies associated with the Juncture Flow model are summarized, to determine sensitivities of the flow near the wing-body juncture region of the model to a variety of modeling decisions.

Rumsey, C. L.↗

NASA NTRSDate not supplied

Artemis II Inertial Sensor Failure & Abort Condition Study

Given Artemis II as the first crewed lunar mission in decades, significant effort is directed towards understanding Space Launch System (SLS) response to failures of the three inertial sensors: two Ring-Laser Gyro Assemblies (RGAs) and the Redundant Inertial Navigation Unit (RINU). Parametric studies identify Loss of Mission (LOM) or Loss of Crew (LOC) sensitive mission phases. Fault Detection & Isolation (FDI) algorithms’ thresholds’ performance is assessed with respect to detecting LOM or LOC causing sensor failures. Monte Carlo studies are performed targeting specific trajectory phases for insight into re-optimizing FDI thresholds and improving knowledge of SLS sensor failure response statistics.

SLS↗

NASA NTRS1985

Parametric study of the aeroelastic stability of a bearingless rotor

A trade study was conducted to illustrate the sensitivity of the aeroelastic stability of a bearingless main rotor to the rotor hub coupling parameters that are available for the designer. The results are presented over the complete range of rotor speed and collective pitch available and the effects on air resonance of the 6 beam installation angles are compared together with the results of offsetting the cuff snubber attachment. The major part of the study was conducted using the FLAIR analysis which incorporates a uniform representation of the flexbeam. Results are also shown for a modified version of FLAIR in which the uniform beam is replaced by a member having the geometric tailoring resulting from structural optimization.

Hooper, W. E.↗

NASA NTRS1976

Practical considerations for the design of two-element duct liner noise suppressors

The results of analytical and experimental design studies for two-segment treatment configurations in rectangular ducts with mean flow are presented. The practical significance of the design optimization method, executed at a single frequency for measured modal input, is considered in the light of sensitivity to variations in wall impedance components and source modal content. The results of analytical parametric studies of the effects of frequency and segment length ratio are presented. The importance of designing for a measured modal content and the importance of the order of the liners in providing the multi-element suppression enhancement effects are demonstrated.

Kraft, R. E.↗

NASA NTRS1991

Calculation of aerosol backscatter from airborne continuous wave focused CO2 Doppler lidar measurements. II - Algorithm performance

This paper examines the performance of the Rothermel et al. (1991) algorithm for calculating aerosol backscatter coefficients from measurements by an airborne continuous wave focused CO2 Doppler lidar by using the algorithm to analyze measurements by the Laser True Airspeed System. The results show that, under optimum signal conditions, backscatter signals are detected unambiguously and the aerosol backscatter coefficients are determined accurately. However, under marginal or subthreshold conditions under which the system sensitivity is degraded, noise can be mistaken for signals. As determined from parametric studies, the 'false-alarm' rate under these conditions depends on the size of the search window and the SNR threshold for valid signals.

Rothermel, Jeffry↗

NASA NTRS2019

Bayesian Inference and the Effects of Varying Uncertainty Models in Charring Ablator Calibration and Uncertainty Quantification Problems

The Mars Science Laboratory (MSL) vehicle utilized a heat shield constructed from NASA’s Phenolic-Impregnated Carbon Ablator (PICA) material to protect the main structure from the high enthalpy environment encountered during hypersonic atmospheric entry. During the vehicle’s descent through Martian atmosphere, multiple thermocouples embedded within the heat shield captured in-depth material temperature data that allow for studies to be conducted on current material response reconstruction tools. In the present work, material temperature data obtained from thermocouples within the MISP-4 plug (MEDLI (Mars Science Laboratory Entry, Descent, and Landing Instrument) Integrated Sensor Plug) are utilized in the calibration of Theoretical Ablative Composite for Open Testing (TACOT) model parameters in conjunction with NASA’s Porous material Analysis Toolbox (PATO) through Bayesian inference where uncertainty due to parametric, modeling, and experimental sources is simultaneously quantified. Prior to the study, a sensitivity analysis is performed through computation of the robust Sobol indices in an effort to study the relationship between input space and model response and to reduce the dimensionality of the statistical inverse problem. The Bayesian inference methodology necessitates an a-priori choice to be made for the uncertainty model for which numerous possibilities are available. Across most works, however, only basic additive or multiplicative models are utilized with pre-defined magnitudes of uncertainty based on a-priori knowledge or to-be-calibrated multipliers of static covariance matrix structures. The present effort explores the effects of informed uncertainty models, ones with temporal dependence that are simultaneously calibrated through Bayesian inference, on calibrated results for parameters that make up the uncertain input space.

Sensitivity Analysis↗

NASA NTRS2017

A Parametric Study of Actuator Requirements for Active Turbine Tip Clearance Control of a Modern High Bypass Turbofan Engine

The efficiency of aircraft gas turbine engines is sensitive to the distance between the tips of its turbine blades and its shroud, which serves as its containment structure. Maintaining tighter clearance between these components has been shown to increase turbine efficiency, increase fuel efficiency, and reduce the turbine inlet temperature, and this correlates to a longer time-on-wing for the engine. Therefore, there is a desire to maintain a tight clearance in the turbine, which requires fast response active clearance control. Fast response active tip clearance control will require an actuator to modify the physical or effective tip clearance in the turbine. This paper evaluates the requirements of a generic active turbine tip clearance actuator for a modern commercial aircraft engine using the Commercial Modular Aero-Propulsion System Simulation 40k (C-MAPSS40k) software that has previously been integrated with a dynamic tip clearance model. A parametric study was performed in an attempt to evaluate requirements for control actuators in terms of bandwidth, rate limits, saturation limits, and deadband. Constraints on the weight of the actuation system and some considerations as to the force which the actuator must be capable of exerting and maintaining are also investigated. From the results, the relevant range of the evaluated actuator parameters can be extracted. Some additional discussion is provided on the challenges posed by the tip clearance control problem and the implications for future small core aircraft engines.

Turbine↗

NASA NTRS1983

Sensitivity /comparison study between the Jacchia 1970, 1971, and 1977 upper atmospheric density models

The neutral upper atmospheric models for the Earth's thermosphere currently used in NASA-MSFC programs are the Jacchia 1970 (J70), 1971 (J71), and 1977 (J77). The Jacchia 1970 model (modified) is used in all MSFC orbital mechanics analyses. Since total density and its variations are the main environmental parameters of interest in orbital lifetime and attitude control studies, the total neutral density was selected for this analysis. This report presents the results of a parametric study of the total density (at 400 km altitude) as computed with three MSFC/Jacchia models. The sensitivity of each of the density models at the summer solstice to varying solar conditions (flux) and geomagnetic (index) values is discussed.

Johnson, D. L.↗

NASA NTRS1993

Image remapping strategies applied as protheses for the visually impaired

Maculopathy and retinitis pigmentosa (rp) are two vision defects which render the afflicted person with impaired ability to read and recognize visual patterns. For some time there has been interest and work on the use of image remapping techniques to provide a visual aid for individuals with these impairments. The basic concept is to remap an image according to some mathematical transformation such that the image is warped around a maculopathic defect (scotoma) or within the rp foveal region of retinal sensitivity. NASA/JSC has been pursuing this research using angle invariant transformations with testing of the resulting remapping using subjects and facilities of the University of Houston, College of Optometry. Testing is facilitated by use of a hardware device, the Programmable Remapper, to provide the remapping of video images. This report presents the results of studies of alternative remapping transformations with the objective of improving subject reading rates and pattern recognition. In particular a form of conformal transformation was developed which provides for a smooth warping of an image around a scotoma. In such a case it is shown that distortion of characters and lines of characters is minimized which should lead to enhanced character recognition. In addition studies were made of alternative transformations which, although not conformal, provide for similar low character distortion remapping. A second, non-conformal transformation was studied for remapping of images to aid rp impairments. In this case a transformation was investigated which allows remapping of a vision field into a circular area representing the foveal retina region. The size and spatial representation of the image are selectable. It is shown that parametric adjustments allow for a wide variation of how a visual field is presented to the sensitive retina. This study also presents some preliminary considerations of how a prosthetic device could be implemented in a practical sense, vis-a-vis, size, weight and portability.

Johnson, Curtis D.↗

NASA NTRS1980

Parametric study of modern airship productivity

A method for estimating the specific productivity of both hybrid and fully buoyant airships is developed. Various methods of estimating structural weight of deltoid hybrids are discussed and a derived weight estimating relationship is presented. Specific productivity is used as a figure of merit in a parametric study of fully buoyant ellipsoidal and deltoid hybrid semi-buoyant vehicles. The sensitivity of results as a function of assumptions is also determined. No airship configurations were found to have superior specific productivity to transport airplanes.

Ardema, M. D.↗

NASA NTRS2019

Development and Analysis of the Automated Object Reentry Survival Analysis Tool Parametric Study Wrapper

The NASA Orbital Debris Program Office (ODPO) Safety Group at the Johnson Space Center analyzes reentering spacecraft at the end of life. The program primarily used by ODPO in this effort is the Object Reentry Survival Analysis Tool (ORSAT). ORSAT utilizes shape primitives as well as a variety of other parameters (material, size, thickness, aerodynamic mass, orbit inclination, etc.) to simulate the reentry process and ultimately, to determine if a spacecraft could be hazardous to the population on the ground. The NASA ODPO plans to automate the ORSAT process to run multiple ORSAT input files either concurrently or consecutively. This type of automation program will provide several benefits. First, there is a need to run large parametric studies for ORSAT analysts to gain a greater understanding of reentering object’s sensitivity to certain input variables. Secondly, a database of pre-run ORSAT cases will be used to develop a survivability model, which could be made available to spacecraft developers as a design for demise (D4D) tool. The recently completed Automated Object Reentry Survival Analysis Tool (AutoORSAT) Wrapper is currently being used to build a survivability database, the first step in developing a survivability model. Already, the data that AutoORSAT has produced provides a greater understanding of the sensitivity of variables such as the initial temperature of the spacecraft, spacecraft breakup altitude, and the aerodynamic mass of spacecraft.

Smith, Andrew N.↗

NASA NTRS1991

Tiltrotor ground noise reduction from rotor parametric changes as predicted by ROTONET

A simple acoustic footprint trend study has been performed to determine the sensitivity of a tiltrotor aircraft to simple rotor design variations. Using the XV-15 aircraft as a baseline, the effects of blade number, rotor RPM, and chord on tone and broadband noise were predicted with the ROTONET noise code. Effects on EPNL, PNLT, and OASPL for level forward flight were considered.

Jumper, Stephen J.↗

NASA NTRS1994

Numerical Simulation of Inlet Bleed with Circular Holes on Plate Under Shock-Wave/Boundary-Layer Interactions

A numerical study was performed to investigate the shock-wave/boundary-layer interactions on a flat plate with bleed through one or more circular holes that vent into a plenum. The bleed-hole patterns considered for the study include in-line multiple holes and staggered multiple-row holes that are configured to simulate the patterns used in inlet bleed systems of high performance aircraft. The focus of the study was to examine how the bleed through multiple holes affect bleed rate and the pressure and Mach number distributions. Since the bleed performance was found sensitive to the change in bleed conditions, a computational procedure was developed to give a good turnaround computational time for parametric studies involving changes in bleed hole geometry and the structure of shock-wave/boundary-layer flowfield. The procedure includes the grid-generation methodology and the flow simulation with solutions from the Navier-Stokes equations. The computational techniques permit analysis of complex bleed systems and make possible the investigation of a broader range of design variables associated with inlet bleed operation.

Chyu, Wei J.↗

NASA NTRS1991

Simplified micromechanical equations for thermal residual stress analysis of coated fiber composites

The fabrication of metal matrix composites poses unique problems to the materials engineer. The large thermal expansion coefficient (CTE) mismatch between the fiber and matrix leads to high tensile residual stresses at the fiber/matrix (F/M) interface which could lead to premature matrix cracking during cooldown. Fiber coatings could be used to reduce thermal residual stresses. A simple closed form analysis, based on a three phase composite cylinder model, was developed to calculate thermal residual stresses in a fiber/interphase/matrix system. Parametric studies showed that the tensile thermal residual stresses at the F/M interface were very sensitive to the CTE and thickness of the interphase layer. The modulus of the layer had only a moderate effect on tensile residual stresses. For a silicon carbide titanium aluminide composite, the tangential stresses were 20 to 30 pct. larger than the axial stresses, over a wide range of interphase layer properties, indicating a tendency to form radial matrix cracks during cooldown. Guidelines for the selection of appropriate material properties of the fiber coating were also derived in order to minimize thermal residual stresses in the matrix during fabrication.

Naik, R. A.↗

NASA NTRS2001

Nonlinear Analysis and Scaling Laws for Noncircular Composite Structures Subjected to Combined Loads

Results from an analytical study of the response of a built-up, multi-cell noncircular composite structure subjected to combined internal pressure and mechanical loads are presented. Nondimensional parameters and scaling laws based on a first-order shear-deformation plate theory are derived for this noncircular composite structure. The scaling laws are used to design sub-scale structural models for predicting the structural response of a full-scale structure representative of a portion of a blended-wing-body transport aircraft. Because of the complexity of the full-scale structure, some of the similitude conditions are relaxed for the sub-scale structural models. Results from a systematic parametric study are used to determine the effects of relaxing selected similitude conditions on the sensitivity of the effectiveness of using the sub-scale structural model response characteristics for predicting the full-scale structure response characteristics.

Hilburger, Mark W.↗

NASA NTRS2018

Methodologies for Verification and Validation of Space Launch System (SLS) Structural Dynamic Models

Responses to challenges associated with verification and validation (V&V) of Space Launch System (SLS) structural dynamics models are presented in this paper. Four methodologies addressing specific requirements for V&V are discussed. (1) Residual Mode Augmentation (RMA), which has gained acceptance by various principals in the NASA community, defines efficient and accurate FEM modal sensitivity models that are useful in test-analysis correlation and reconciliation and parametric uncertainty studies. (2) Modified Guyan Reduction (MGR) and Harmonic Reduction (HR, introduced in 1976), developed to remedy difficulties encountered with the widely used Classical Guyan Reduction (CGR) method, are presented. MGR and HR are particularly relevant for estimation of "body dominant" target modes of shell-type SLS assemblies that have numerous "body", "breathing" and local component constituents. Realities associated with configuration features and "imperfections" cause "body" and "breathing" mode characteristics to mix resulting in a lack of clarity in the understanding and correlation of FEM- and test-derived modal data. (3) Mode Consolidation (MC) is a newly introduced procedure designed to effectively "de-feature" FEM and experimental modes of detailed structural shell assemblies for unambiguous estimation of "body" dominant target modes. Finally, (4) Experimental Mode Verification (EMV) is a procedure that addresses ambiguities associated with experimental modal analysis of complex structural systems. Specifically, EMV directly separates well-defined modal data from spurious and poorly excited modal data employing newly introduced graphical and coherence metrics.

Coppolino, Robert N.↗

NASA NTRS1976

Georgia Institute of Technology research on the Gas Core Actinide Transmutation Reactor (GCATR)

The program reviewed is a study of the feasibility, design, and optimization of the GCATR. The program is designed to take advantage of initial results and to continue work carried out on the Gas Core Breeder Reactor. The program complements NASA's program of developing UF6 fueled cavity reactors for power, nuclear pumped lasers, and other advanced technology applications. The program comprises: (1) General Studies--Parametric survey calculations performed to examine the effects of reactor spectrum and flux level on the actinide transmutation for GCATR conditions. The sensitivity of the results to neutron cross sections are to be assessed. Specifically, the parametric calculations of the actinide transmutation are to include the mass, isotope composition, fission and capture rates, reactivity effects, and neutron activity of recycled actinides. (2) GCATR Design Studies--This task is a major thrust of the proposed research program. Several subtasks are considered: optimization criteria studies of the blanket and fuel reprocessing, the actinide insertion and recirculation system, and the system integration. A brief review of the background of the GCATR and ongoing research is presented.

Clement, J. D.↗

NASA NTRS1983

Retrieval of stratospheric aerosol size distribution from atmospheric extinction of solar radiation at two wavelengths

A parametric study is presented of the effects of the size distribution and composition of stratospheric aerosols on the value R, the ratio of the extinction of solar radiation at wavelength 0.45 micron to the extinction at wavelength 1.0 micron. The aerosol size distributions under study comprise nine analytical expressions, including most of the stratospheric aerosol models used by investigators. The aerosol compositions considered are the supercooled sulfuric-acid droplets, with different weight percentages of H2SO4 in the aerosol. It is found that whereas R is not very sensitive to either the composition or the radii limits of the stratospheric aerosols under consideration, it is quite sensitive to the value of the variable parameter governing the mode radius of the size distribution of aerosol particles. The results of the parametric study underlie the method proposed here of retrieving the size distribution of aerosol particles in the stratosphere from the experimental results of the extinction of solar radiation at two wavelengths.

Yue, G. K.↗