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NASA NTRS1983

Interpretation of radar returns from clear air: Discrimination against clutter

Different kinds of inteference may cause problems to the proper detection and analysis of the atmospheric signals, when using VHF and UHF radars. These are separated into passive and active contributions. Passive contributions are existent in the receiving system without the radar transmitter switched on. Active contributions are due to scatter and reflection of the own transmitted radar signal from unwanted targets, which are called clutter. Of major importance to radar systems are active interference contributions. Different methods can be applied for elimination or at least suppressing unwanted effects. These are; (1) Directional filtering, i.e., applying optimum suppression of antenna sidelobes, (2) Range filtering, i.e., suppressing unwanted signals only in affected range gates, (3) selection by amplitude distributions, (4) Temporal filtering, i.e., recognizing typical temporal variations of the clutter signals, through spectral characteristics, and applying matched filters.

Rottger, J.↗

NASA NTRS1991

Static performance of a multiaxis thrust vectoring cruciform nozzle

A multiaxis thrust vectoring nozzle designed to have equal flow turning capability in pitch and yaw is investigated, and methods for obtaining large multiaxis thrust vector angles without physical vectoring flap interference are studied. These methods include restricting the pitch flaps from the path of the yaw flaps, and shifting the flow path at the throat off the nozzle centerline in order to permit larger pitch flap deflections without interfering with operation of the yaw flaps. The results obtained show that unvectored performance of the cruciform nozzle is only slightly lower (0.5 to 1.0 percent) than that of previously tested axisymmetric and nonaxisymmetric nozzles, despite the complex internal geometry. The shifted-throat nozzle design has larger thrust vector angles at the nozzle pressure ratio of peak resultant thrust efficiency, but has 1 to 2 percent lower peak thrust performance than the restricted-flap nozzle design.

Wing, David J.↗

NASA NTRS1992

Production of H-3 at large momentum in alpha-(C-12) collisions at 2A GeV

Calculations of the longitudinal and transverse momentum distributions for H-3 production at large momentum in alpha-(C-12) collisions near 2A GeV are compared to experiment. Triton exchange and final-state interactions are shown to represent large corrections to the impulse approximation for proton knockout. A method for calculating interference effects for inelastic fragmentation is discussed. Good agreement with experiment using a phenomenological overlap function for (H-3)-p is found successful in describing H-3 production in pion-induced reactions. Comparisons to momentum distributions obtained through (p, 2p) and (e, ep) reactions on He-4 are made.

Cucinotta, Francis A.↗

NASA NTRS1956

The proper combination of lift loadings for least drag on a supersonic wing

Lagrange's method of undetermined multipliers is applied to the problem of properly combining lift loadings for the least drag at a given lift on supersonic wings. The method shows the interference drag between the optimum loading and any loading at the same lift coefficient to be constant. This is an integral form of the criterion established by Robert T. Jones for optimum loadings. The best combination of four loadings on a delta wing with subsonic leading edges is calculated as a numerical example. The loadings considered have finite pressures everywhere on the plan form. Through the sweepback range the optimum combination of the four nonsingular loadings has about the same drag coefficient as a flat plate with leading-edge thrust.

Grant, Frederick C↗

NASA NTRS2000

Sixth International Conference on Squeezed States and Uncertainty Relations

These proceedings contain contributions from about 200 participants to the 6th International Conference on Squeezed States and Uncertainty Relations (ICSSUR'99) held in Naples May 24-29, 1999, and organized jointly by the University of Naples "Federico II," the University of Maryland at College Park, and the Lebedev Institute, Moscow. This was the sixth of a series of very successful meetings started in 1990 at the College Park Campus of the University of Maryland. The other meetings in the series were held in Moscow (1992), Baltimore (1993), Taiyuan P.R.C. (1995) and Balatonfuered, Hungary (1997). The present one was held at the campus Monte Sant'Angelo of the University "Federico II" of Naples. The meeting sought to provide a forum for updating and reviewing a wide range of quantum optics disciplines, including device developments and applications, and related areas of quantum measurements and quantum noise. Over the years, the ICSSUR Conference evolved from a meeting on quantum measurement sector of quantum optics, to a wide range of quantum optics themes, including multifacet aspects of generation, measurement, and applications of nonclassical light (squeezed and Schrodinger cat radiation fields, etc.), and encompassing several related areas, ranging from quantum measurement to quantum noise. ICSSUR'99 brought together about 250 people active in the field of quantum optics, with special emphasis on nonclassical light sources and related areas. The Conference was organized in 8 Sections: Squeezed states and uncertainty relations; Harmonic oscillators and squeeze transformations; Methods of quantum interference and correlations; Quantum measurements; Generation and characterisation of non-classical light; Quantum noise; Quantum communication and information; and Quantum-like systems.

Han, D.↗

NASA NTRS2006

CFD-Predicted Tile Heating Bump Factors Due to Tile Overlay Repairs

A Computational Fluid Dynamics investigation of the Orbiter's Tile Overlay Repair (TOR) is performed to assess the aeroheating Damage Assessment Team's (DAT) existing heating correlation method for protuberance interference heating on the surrounding thermal protection system. Aerothermodynamic heating analyses are performed for TORs at the design reference damage locations body points 1800 and 1075 for a Mach 17.9 and a=39deg STS-107 flight trajectory point with laminar flow. Six different cases are considered. The computed peak heating bump factor on the surrounding tiles are below the DAT's heating bump factor values for smooth tile cases. However, for the uneven tiles cases the peak interference heating is shown to be considerably higher than the existing correlation prediction.

Lessard, Victor R.↗

NASA NTRS2019

Investigation of Transonic Truss-Braced Wing Aircraft Transonic Wing-Strut Interference Effects Using FUN3D

This paper presents a computational study of transonic wing-strut interference effects of Transonic Truss-Braced Wing (TTBW) aircraft using the high-fidelity CFD (Computational Fluid Dynamics) code FUN3D (Fully Unstructured Navier-Stokes Three Dimensional). The study is conducted for the wing-strut and the wing-alone configurations at different Mach numbers and Reynolds numbers. The interference effects are calculated by comparing the wing aerodynamics along the spanwise direction between the wing-strut and the wing-alone configurations. The presence of the strut underneath the wing induces a suction peak on the lower surface of the wing, which causes changes in aerodynamic forces and moments, as well as the aerodynamic center location. The interference effects become more pronounced as the Mach number increases. The Reynolds number has less impact on the interference effects. A transonic wing-strut interference aerodynamic correction method is developed for use in a lower-fidelity tool, VSPAERO [a vortex lattice flow solver], coupled to a finite-element model for rapid flutter analysis.

Xiong, Juntao↗

NASA NTRSDate not supplied

Experimental Testing of Data Fusion in A Distributed Ground-Based Sensing Network for Advanced Air Mobility

Advanced Air Mobility (AAM) is an active area of development which foresees the integration of autonomous uncrewed aircraft into the civil airspace for air transportation of people and cargo. Safe integration requires significant technological developments and extensive testing phases of sensing and surveillance strategies in dense airspace. Compared to well-assessed manned aviation systems scenarios, surveillance strategies in the AAM and small Uncrewed Aircraft Vehicles(UAVs) context need to detect smaller platforms flying at lower altitude against cluttered backgrounds in dense airspace. Fusion of data provided by a network of distributed sensing nodes is a powerful tool to enable detection and tracking in such complex conditions. This paper contributes to this research direction by proposing a surveillance strategy for the AAM environment based on sensor fusion of data acquired by distributed ground-based radars. Specifically, experimental data collected with two independent radars, observing the flight of two small UAVs, are used. Data fusion at tracking level is based on a leader-helper strategy where the leader radar uses the helper’s measurements to increase the lifespan of its generated tracks. This solution shows promising results with a 10%increase in track coverage with respect to the standalone leader radar tracking solution. The paper also proposes an interference removal processing method which is applied on the data collected by one of the two radars.

Federica Vitiello↗

NASA NTRS2025

Demonstration of Data Processing and Fusion from Distributed Radars for AAM Surveillance

Advanced Air Mobility (AAM) is an active area of development which foresees the integration of autonomous uncrewed aircraft into the civil airspace for air transportation of people and cargo. Safe integration requires significant technological developments and extensive testing phases of sensing and surveillance strategies in dense airspace. Compared to well-assessed manned aviation systems scenarios, surveillance strategies in the AAM and small Uncrewed Aircraft Vehicles (UAVs) context need to detect smaller platforms flying at lower altitude against cluttered backgrounds in dense airspace. Fusion of data provided by a network of distributed sensing nodes is a powerful tool to enable detection and tracking in such complex conditions. This paper contributes to this research direction by proposing a surveillance strategy for the AAM environment based on sensor fusion of data acquired by distributed ground-based radars. Specifically, experimental data collected with three independent radars, observing the flight of two small UAVs, are used. Data fusion at tracking level is based on a leader-helper strategy where the leader radar uses the helper’s measurements to increase the lifespan of its generated tracks. This solution shows promising results with a 10% increase in track coverage with respect to the standalone leader radar tracking solution. The paper also proposes an interference removal processing method which is applied on the data collected by two of the radars.

Federica Vitiello↗

NASA NTRS1988

Emerging technology for transonic wind-tunnel-wall interference assessment and corrections

Several nonlinear transonic codes and a panel method code for wind tunnel/wall interference assessment and correction (WIAC) studies are reviewed. Contrasts between two- and three-dimensional transonic testing factors which affect WIAC procedures are illustrated with airfoil data from the NASA/Langley 0.3-meter transonic cyrogenic tunnel and Pathfinder I data. Also, three-dimensional transonic WIAC results for Mach number and angle-of-attack corrections to data from a relatively large 20 deg swept semispan wing in the solid wall NASA/Ames high Reynolds number Channel I are verified by three-dimensional thin-layer Navier-Stokes free-air solutions.

Newman, P. A.↗

NASA NTRS1938

Interference of Wing and Fuselage from Tests of 17 Combinations in the NACA Variable-density Tunnel Combination with Special Junctures

As part of the wing-fuselage interference program in progress in the NACA variable-density wind tunnel, a method of eliminating the interference bubble associated with critical mid wing combinations was investigated. The interference bubble of the critical mid wing combination was shown to respond to modification at the nose of the juncture and to be entirely suppressed with little or no adverse effect on the high-speed drag by special leading edge fillets.

Sherman, Albert↗

NASA NTRS2017

A Fast, Accurate and Sensitive GC-FID Method for the Analyses of Glycols in Water and Urine

Glycols, specifically ethylene glycol and 1,2-propanediol, are some of the major organic compounds found in the humidity condensate samples collected on the International Space Station. The current analytical method for glycols is a GC/MS method with direct sample injection. This method is simple and fast, but it is not very sensitive. Reporting limits for ethylene glycol and 1,2-propanediol are only 1 ppm. A much more sensitive GC/FID method was developed, in which glycols were derivatized with benzoyl chloride for 10 minutes before being extracted with hexane. Using 1,3-propanediol as an internal standard, the detection limits for the GC/FID method was determined to be 50 ppb and the analysis only takes 7 minutes. Data from the GC/MS and the new GC/FID methods shows excellent agreement with each other. Factors affecting the sensitivity, including sample volume, NaOH concentration and volume, volume of benzoyl chloride, reaction time and temperature, were investigated. Interferences during derivatization and possible method to reduce interferences were also investigated.

Kuo, C. Mike↗

NASA NTRS1992

Static performance of a cruciform nozzle with multiaxis thrust-vectoring and reverse-thrust capabilities

A multiaxis thrust vectoring nozzle designed to have equal flow turning capability in pitch and yaw was conceived and experimentally tested for internal, static performance. The cruciform-shaped convergent-divergent nozzle turned the flow for thrust vectoring by deflecting the divergent surfaces of the nozzle, called flaps. Methods for eliminating physical interference between pitch and yaw flaps at the larger multiaxis deflection angles was studied. These methods included restricting the pitch flaps from the path of the yaw flaps and shifting the flow path at the throat off the nozzle centerline to permit larger pitch-flap deflections without interfering with the operation of the yaw flaps. Two flap widths were tested at both dry and afterburning settings. Vertical and reverse thrust configurations at dry power were also tested. Comparison with two dimensional convergent-divergent nozzles showed lower but still competitive thrust performance and thrust vectoring capability.

Wing, David J.↗

NASA NTRS1998

The Real-Time Wall Interference Correction System of the NASA Ames 12-Foot Pressure Wind Tunnel

An improved version of the Wall Signature Method was developed to compute wall interference effects in three-dimensional subsonic wind tunnel testing of aircraft models in real-time. The method may be applied to a full-span or a semispan model. A simplified singularity representation of the aircraft model is used. Fuselage, support system, propulsion simulator, and separation wake volume blockage effects are represented by point sources and sinks. Lifting effects are represented by semi-infinite line doublets. The singularity representation of the test article is combined with the measurement of wind tunnel test reference conditions, wall pressure, lift force, thrust force, pitching moment, rolling moment, and pre-computed solutions of the subsonic potential equation to determine first order wall interference corrections. Second order wall interference corrections for pitching and rolling moment coefficient are also determined. A new procedure is presented that estimates a rolling moment coefficient correction for wings with non-symmetric lift distribution. Experimental data obtained during the calibration of the Ames Bipod model support system and during tests of two semispan models mounted on an image plane in the NASA Ames 12 ft. Pressure Wind Tunnel are used to demonstrate the application of the wall interference correction method.

Ulbrich, Norbert↗

NASA NTRS1980

Flutter spectral measurements using stationary pressure transducers

Engine-order sampling was used to eliminate the integral harmonics from the flutter spectra corresponding to a case-mounted static pressure transducer. Using the optical displacement data, it was demonstrated that the blade-order sampling of pressure data may yield erroneous results due to the interference caused by blade vibration. Two methods are presented which effectively eliminate this interference yielding the blade-pressure-difference spectra. The phase difference between the differential-pressure and the displacement spectra was evaluated.

Kurkov, A. P.↗

NASA NTRS1984

Experiments suitable for wind tunnel wall interference assessment/correction

Three experiments suitable for wall interference assessment and evaluation of proposed correction methods are presented. The experiments are: (1) a series of airfoil tests using a newly designed transonic flow facility that employs side-wall boundary layer suction and upper- and lower-wall shaping; (2) tests on a swept airfoil section spanning a solid-wall wind tunnel with fixed contouring on all four walls; and (3) tests on a swept wing of aspect ratio 3 mounted in a solid-wall wind tunnel with fixed flat walls. Each of the experiments provides data on the airfoil sections as well as on the wind tunnel walls. All the experiments were performed in solid wall wind tunnels corrected for boundary layer displacement effects. Although the experiments were performed primarily to evaluate computer code performance, it is believed that they also provide information that can be used to evaluate methods for assessing and correcting wall interference effects.

Marvin, J. G.↗

NASA NTRS1991

Engineering calculations for communications satellite systems planning

The final phase of a satellite synthesis project is described. Several methods for generating satellite positionings with improved aggregate carrier to interference characteristics were studied. Two general methods for modifying required separation values are presented. Also, two methods for improving aggregate carrier to interference (C/I) performance of given satellite synthesis solutions are presented. A perturbation of the World Administrative Radio Conference (WARC) synthesis is presented.

Walton, E.↗

NASA NTRS1992

Computing high-speed flows past an oscillating cylinder near a vertical wall

A computational method to simulate unsteady flows involving moving rigid boundaries and interference has been developed. The method is used to solve inviscid equations governing the fluid flow and the dynamic equations governing the motion of rigid bodies. A second-order accurate, upwind-biased, and alterating-direction-implicit method is used to solve the governing equations of the flow. A kinematic domain decomposition (KDD) procedure is extended to treat 3D problems with a high degree of accuracy and generality. The method under consideration is applied to both transonic and supertransonic flows. Both cases involve flow past a cylinder which is forced to pitch sinusoidally near a vertical wall. Benefits of the proposed approach include accurate calculation of the flow around 3D moving multiple bodies with interference; reduction of a numerical error; in particular, the dispersion error which strongly affects wave propagation; and minimization of the phase error which is accumulated according to the time advance procedure.

Yen, Guan-Wei↗