Multiple scattering by large particles
Multiple scattering by large particles - Neumann solution applied to scalar transfer equation in homogeneous layer of optical thickness
NEUMANN PROBLEM↗
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Symmetrical, equilibrium flow past a blunt body at superorbital re-entry speeds.
Symmetrical equilibrium flow past blunt body at superorbital reentry conditions calculated by integrating motion equations across shock layer
FLOW STABILITY↗
Free vibrations of semi-infinite multilayer composite cylinders.
Axisymmetric vibrations of semiinfinite cylindrical shell constructed of fiber reinforced composite layers, obtaining frequency equation from equations of motions
Boyd, W. W.↗
Aerothermodynamic environment for Jovian entry conditions
Solutions are presented for the aerothermal heating environments about blunt probes entering the atmosphere of Jupiter. The analysis employs a novel prediction procedure in which finite differences versions of the thin layer fluid dynamic equations are solved simultaneously with, and coupled to, a fully detailed radiation flux model. Predictions are presented and compared with those of earlier investigators. Radiative blowing corrections are presented for on- and off-stagnation point conditions. The use of a blowing correlation based on the retained mass was found to be useful for off-stagnation point conditions.
Nicolet, W. E.↗
Method for the rapid temperature correction of a transmission in an inhomogeneous atmosphere
The value of the transmission function in a heterogeneous atmosphere is determined by iterative correction of values in particular layers. The iterative equation and a set of absolute values of errors is presented in two tables.
Varnava, V. A.↗
Morphology of the Venus ultraviolet night airglow
Images of the nightside of Venus in the (0,1)delta band of nitric oxide have been obtained by the Pioneer Venus orbiter ultraviolet spectrometer (OUVS). The emission, which is produced by radiative association of N and O, shows a bright spot reaching 5 kR and located at 2 a.m. local solar time just south of the equator. The emitting layer is at 111 + or - 7-km altitude. A one dimensional vertical transport model shows that the hemispheric average brightness of 0.8 kR is consistent with the orbiter neutral mass spectrometer (ONMS) measurements of N and O near 167 km, and that the altitude of the emitting layer is consistent with the eddy mixing model proposed to explain the dayside helium profile measured by the bus neutral mass spectrometer. In the model, N reaches a peak of 7 x 10 to the 8th per cu cm at 114 km, and O reaches a peak of 2.6 x 10 to the 11th per cu cm at 106 km. There is a fair degree of consistency between the ONMS, OUVS, and other airglow measurements, except as regards the local time dependence.
Stewart, A. I. F.↗
SHARP: Subsonic High Altitude Research Platform
The Universities Space Research Association is sponsoring an undergraduate program which is geared to designing an aircraft that can study the ozone layer at the equator. This aircraft must be able to satisfy four mission profiles. Mission one is a polar mission that ranges from Chile to the South Pole and back to Chile, a total range of 6000 n.mi. at 100,000 ft with a 2500 lb payload. The second mission is also a polar mission, with an altitude of 70,000 ft and an increased payload of 4000 lbs. For the third mission, the aircraft will takeoff at NASA Ames, cruise at 100,000 ft carrying a 2500 lb payload, and land at Puerto Montt, Chile. The final mission requires the aircraft to take off at NASA Ames, cruise at 100,000 ft with a 1000 lb payload, make an excursion to 120,000 ft, and land at Howard AFB, Panama. Three missions require that a subsonic Mach number be maintained due to constraints imposed by the air sampling equipment. The aircraft need not be manned for all four missions. Three aircraft configurations have been determined to be the most suitable for meeting the above requirements. In the event that a requirement cannot be obtained within the given constraints, recommendations for proposal modifications are given.
Beals, Todd↗
Modeling the seasonal cycle of CO2 on Mars: A fit to the Viking lander pressure curves
We have constructed a more accurate Mars thermal model, similar to the one used by Leighton and Murray in 1966, which solves radiative, conductive, and latent heat balance at the surface as well as the one-dimensional heat conduction equation for 40 layers to a depth of 15 meters every 1/36 of a Martian day. The planet is divided into 42 latitude bands with a resolution of two degrees near the poles and five degrees at lower latitudes, with elevations relative to the 6.1 mbar reference areoid. This estimate of the Martian zonally averaged topography was derived primarily from radio occultations. We show that a realistic one-dimensional thermal model is able to reproduce the VL1 pressure curve reasonably well without having to invoke complicated atmospheric effects such as dust storms and polar hoods. Although these factors may cause our deduced values for each model parameter to differ from its true value, we believe that this simple model can be used as a platform to study many aspects of the Martian CO2 cycle over seasonal, interannual, and long-term climate timescales.
Wood, S. E.↗
High-altitude reconnaissance aircraft
At the equator the ozone layer ranges from 65,000 to 130,000+ ft, which is beyond the capabilities of the ER-2, NASA's current high-altitude reconnaissance aircraft. This project is geared to designing an aircraft that can study the ozone layer. The aircraft must be able to satisfy four mission profiles. The first is a polar mission that ranges from Chile to the South Pole and back to Chile, a total range of 6000 n.m. at 100,000 ft with a 2500-lb payload. The second mission is also a polar mission with a decreased altitude and an increased payload. For the third mission, the aircraft will take off at NASA Ames, cruise at 100,000 ft, and land in Chile. The final mission requires the aircraft to make an excursion to 120,000 ft. All four missions require that a subsonic Mach number be maintained because of constraints imposed by the air sampling equipment. Three aircraft configurations were determined to be the most suitable for meeting the requirements. The performance of each is analyzed to investigate the feasibility of the mission requirements.
Yazdi, Renee Anna↗
Direct simulation of the stably stratified turbulent Ekman layer
The Navier-Stokes equations and the Boussinesq approximation were used to compute a 3D time-dependent turbulent flow in the stably stratified Ekman layer over a smooth surface. The simulation data are found to be in very good agreement with atmospheric measurements when nondimensionalized according to Nieuwstadt's local scaling scheme. Results suggest that, when Reynolds number effects are taken into account, the 'constant Froud number' stable layer model (Brost and Wyngaard, 1978) and the 'shearing length' stable layer model (Hunt, 1985) for the dissipitation rate of turbulent kinetic energy are both valid. It is concluded that there is good agreement between the direct numerical simulation results and large-eddy simulation results obtained by Mason and Derbyshire (1990).
Coleman, G. N.↗
Numerical simulation of helicopter engine plume in forward flight
Flowfields around helicopters contain complex flow features such as large separated flow regions, vortices, shear layers, blown and suction surfaces and an inherently unsteady flow imposed by the rotor system. Another complicated feature of helicopters is their infrared signature. Typically, the aircraft's exhaust plume interacts with the rotor downwash, the fuselage's complicated flowfield, and the fuselage itself giving each aircraft a unique IR signature at given flight conditions. The goal of this project was to compute the flow about a realistic helicopter fuselage including the interaction of the engine air intakes and exhaust plume. The computations solve the Think-Layer Navier Stokes equations using overset type grids and in particular use the OVERFLOW code by Buning of NASA Ames. During this three month effort, an existing grid system of the Comanche Helicopter was to be modified to include the engine inlet and the hot engine exhaust. The engine exhaust was to be modeled as hot air exhaust. However, considerable changes in the fuselage geometry required a complete regriding of the surface and volume grids. The engine plume computations have been delayed to future efforts. The results of the current work consists of a complete regeneration of the surface and volume grids of the most recent Comanche fuselage along with a flowfield computation.
Dimanlig, Arsenio C. B.↗
Unsteady aerodynamic analyses for turbomachinery aeroelastic predictions
Applications for unsteady aerodynamics analysis in this report are: (1) aeroelastic: blade flutter and forced vibration; (2) aeroacoustic: noise generation; (3) vibration and noise control; and (4) effects of unsteadiness on performance. This requires that the numerical simulations and analytical modeling be accurate and efficient and contain realistic operating conditions and arbitrary modes of unsteady excitation. The assumptions of this application contend that: (1) turbulence and transition can be modeled with the Reynolds averaged and using Navier-Stokes equations; (2) 'attached' flow with high Reynolds number will require thin-layer Navier-Stokes equations, or inviscid/viscid interaction analyses; (3) small-amplitude unsteady excitations will need nonlinear steady and linearized unsteady analyses; and (4) Re to infinity will concern inviscid flow. Several computer programs (LINFLO, CLT, UNSVIS, AND SFLOW-IVI) are utilized for these analyses. Results and computerized grid examples are shown. This report was given during NASA LeRC Workshop on Forced Response in Turbomachinery in August of 1993.
Verdon, Joseph M.↗
Topography of the northern hemisphere of Mars from the Mars Orbiter Laser Altimeter
The first 18 tracks of laser altimeter data across the northern hemisphere of Mars from the Mars Global Surveyor spacecraft show that the planet at latitudes north of 50 degrees is exceptionally flat; slopes and surface roughness increase toward the equator. The polar layered terrain appears to be a thick ice-rich formation with a non-equilibrium planform indicative of ablation near the periphery. Slope relations suggest that the northern Tharsis province was uplifted in the past. A profile across Ares Vallis channel suggests that the discharge through the channel was much greater than previously estimated. The martian atmosphere shows significant 1-micrometer atmospheric opacities, particularly in low-lying areas such as Valles Marineris.
unmanned↗
A Multi-scale Refined Zigzag Theory for Multilayered Composite and Sandwich Plates with Improved Transverse Shear Stresses
The Refined Zigzag Theory (RZT) enables accurate predictions of the in-plane displacements, strains, and stresses. The transverse shear stresses obtained from constitutive equations are layer-wise constant. Although these transverse shear stresses are generally accurate in the average, layer-wise sense, they are nevertheless discontinuous at layer interfaces, and thus they violate the requisite interlaminar continuity of transverse stresses. Recently, Tessler applied Reissner's mixed variational theorem and RZT kinematic assumptions to derive an accurate and efficient shear-deformation theory for homogeneous, laminated composite, and sandwich beams, called RZT(m), where "m" stands for "mixed". Herein, the RZT(m) for beams is extended to plate analysis, where two alternative assumptions for the transverse shear stresses field are examined: the first follows Tessler's formulation, whereas the second is based on Murakami's polynomial approach. Results for elasto-static simply supported and cantilever plates demonstrate that Tessler's formulation results in a powerful and efficient structural theory that is well-suited for the analysis of multilayered composite and sandwich panels.
Iurlaro, Luigi↗
A Solution Adaptive Structured/Unstructured Overset Grid Flow Solver with Applications to Helicopter Rotor Flows
This paper summarizes a method that solves both the three dimensional thin-layer Navier-Stokes equations and the Euler equations using overset structured and solution adaptive unstructured grids with applications to helicopter rotor flowfields. The overset structured grids use an implicit finite-difference method to solve the thin-layer Navier-Stokes/Euler equations while the unstructured grid uses an explicit finite-volume method to solve the Euler equations. Solutions on a helicopter rotor in hover show the ability to accurately convect the rotor wake. However, isotropic subdivision of the tetrahedral mesh rapidly increases the overall problem size.
Duque, Earl P. N.↗
A cracked orthotropic sheet stiffened by a semi-infinite orthotropic sheet
The stress intensity factor is determined for a cracked orthotropic sheet adhesively bonded to an orthotropic stringer. Since the stringer is modeled as a semiinfinite sheet, the solution is most appropriate for a crack tip located near a stringer edge. Both adherends are treated as homogeneous, orthotropic media. It is assumed they are in plane stress and the adhesive is in pure shear. From Green's functions and the complex variable theory of orthotropic elasticity developed by Lekhnitskiy, a set of integral equations is obtained. The integral equations are replaced by an equivalent set of algebraic equations which is solved to obtain the shear stress distribution in the adhesive layer. With these stresses, equations for the stress intensity factors at both crack tips are found. A parametric study is conducted to determine the sensitivity of the system to material properties and specimen configuration. Unless the crack tip is very close to or under the stringer the stress intensity factor is approximately that of an unstiffened sheet. However, as the crack propagates beneath the stringer, the stress intensity factor decreases significantly. Increasing the stiffness of the stringer or the adhesive also results in a decrease in the stress intensity factor.
Bigelow, C. A.↗
Point-Mass Aircraft Trajectory Prediction Using a Hierarchical, Highly-Adaptable Software Design
A highly adaptable and extensible method for predicting four-dimensional trajectories of civil aircraft has been developed. This method, Behavior-Based Trajectory Prediction, is based on taxonomic concepts developed for the description and comparison of trajectory prediction software. A hierarchical approach to the "behavioral" layer of a point-mass model of aircraft flight, a clear separation between the "behavioral" and "mathematical" layers of the model, and an abstraction of the methods of integrating differential equations in the "mathematical" layer have been demonstrated to support aircraft models of different types (in particular, turbojet vs. turboprop aircraft) using performance models at different levels of detail and in different formats, and promise to be easily extensible to other aircraft types and sources of data. The resulting trajectories predict location, altitude, lateral and vertical speeds, and fuel consumption along the flight path of the subject aircraft accurately and quickly, accounting for local conditions of wind and outside air temperature. The Behavior-Based Trajectory Prediction concept was implemented in NASA's Traffic Aware Planner (TAP) flight-optimizing cockpit software application.
Karr, David A.↗
Upwind relaxation algorithms for the Navier Stokes equations
The development of upwind relaxation algorithms for obtaining efficient steady-state solutions to the compressible Navier-Stokes equations is described. The method is second-order accurate spatially and naturally disipative, using third-order flux splitting of the pressure and convective terms and second-order central differencing for shear and heat flux terms. A line Gauss-Seidel relaxation approach, shown to be unconditionally stable for model convection and diffusion equations, is used. The algorithm is demonstrated for several flows using the thin-layer form of the equations, including the problem of shock-induced separation over a flat plate.
Thomas, J. L.↗