A geometrically exact finite element for thin shells of revolution.
Geometrically exact finite element for thin shells of revolution, using approximation to predict boundary layer stress distribution during vibration
Adelman, H. M.↗
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Accuracy of modal stress calculations by the finite element method
Geometrically exact finite element for thin shells of revolution, using approximation to predict boundary layer stress distribution during vibration
Adelman, H. M.↗
An evaluation of approximations used in the analysis of chemically reacting, stagnation- point boundary layers with wall injection
Chemically reacting stagnation point boundary layers with wall injection of gas, comparing multicomponent solution with binary approximation and chemical simplifications
Craig, R. A.↗
Pressurized expulsion of nonisothermal single-phase cryogen
The performance of single-phase storage and expulsion systems as affected by temperature variations within the stored cryogen which are generated during heat transfer is discussed. Peculiar operating responses are indicated by spontaneous changes in fluid pressure which accompany g level changes, increased heater surface temperature, and durations of pressure cycles which differ considerably from that which is computed for an isothermal cryogen. The nonisothermal characteristics are predicted with a numerical model which includes the simultaneous solution of the time dependent conservation equations of mass, energy, and momentum in two space dimensions of Cartesian coordinates for boundary conditions which approximate those of the flight cryogenic system. The methodology of the numerical method and some comparisons between the predictions and the Apollo 12 flight data are included.
Forester, C. K.↗
Random excitation of a panel-cavity system
An experimental investigation of the influence of random external sound field on cavity pressure and panel vibration is presented. The panel used was 10 in. x 20 in. x 0.05 in. aluminum alloy plate that was bonded onto a rectangular frame consisting of aluminum channel members welded together at their ends. By bonding the plate to the cavity in this way, a clamped edge boundary condition was approximated. A sealed cavity was constructed beneath the panel in such a way that the cavity depth could be varied in 2 in. increments from 12 in. to 2 in. deep. In order to vary the cavity depth, the cavity was built in sections. Each 2 in. section of the cavity was bolted to the other sections with rubber gaskets between them. The panel was excited acoustically by a Wolverine LS15, 20 watt loudspeaker driven by a B and K random noise generator, Type 1402. The external sound field was measured on the panel surface, using the 6 percent bandwidth of the frequency analyzer.
Gorman, G. F., III↗
Partition function for a two dimensional plasma in the random phase approximation
The partition function for a two-dimensional plasma is evaluated within the random phase approximation. The periodic boundary conditions are fully taken into account by including the periodic image interactions. In the guiding-center limit, the negative temperature threshold energy is evaluated, and a value different from previous calculations results. When an identical random phase evaluated, and a value different from previous calculations results. When an identical random phase evaluation is applied to the finite gyroradius plasma, the Salzberg-Prager-May equation of state is recovered.
Seyler, C. E., Jr.↗
Partition function for a two-dimensional plasma in the random-phase approximation
The partition function for a two-dimensional plasma is evaluated within the random-phase approximation. The periodic boundary conditions are taken fully into account by including the periodic image interactions. In the guiding-center limit, the 'negative temperature' threshold energy is evaluated, and a value different from previous calculations results. When an identical random-phase evaluation is applied to the finite-gyroradius plasma, the Salzberg-Prager-May equation of state is recovered.
Seyler, C. E., Jr.↗
Application of the comparison principle to analysis of nonlinear systems
A comparison principle based on a Kamke theorem and Lipschitz conditions is presented along with its possible applications and modifications. It is shown that the comparison lemma can be used in the study of such areas as classical stability theory, higher order trajectory derivatives, Liapunov functions, boundary value problems, approximate dynamic systems, linear and nonlinear systems, and bifurcation analysis.
Gunderson, R. W.↗
Laser Doppler velocimeter system simulation for sensing aircraft wake vortices
A hydrodynamic model of aircraft vortex wakes in an irregular wind shear field near the ground is developed and used as a basis for modeling the characteristics of a laser Doppler detection and vortex location system. The trailing vortex sheet and the wind shear are represented by discrete free vortices distributed over a two-dimensional grid. The time dependent hydrodynamic equations are solved by direct numerical integration in the Boussinesq approximation. The ground boundary is simulated by images, and fast Fourier Transform techniques are used to evaluate the vorticity stream function. The atmospheric turbulence was simulated by constructing specific realizations at time equal to zero, assuming that Kolmogoroff's law applies, and that the dissipation rate is constant throughout the flow field. The response of a simulated laser Doppler velocimeter is analyzed by simulating the signal return from the flow field as sensed by a simulation of the optical/electronic system.
Thomson, J. A. L.↗
Simulation of three-dimensional separated flows with vortex filaments
A Lagrangian vorticity method for numerical simulation of three-dimensional separated flows with vortex filaments, about solid bodies, is discussed. The method is an extension of an earlier one for three-dimensional rotational flows away from solid boundaries e.g., jets, vortex rings, and aircraft trailing vortices after initial rollup. In this method an harmonic contribution to the velocity field is computed at each time step to ensure tangency of the velocity field at the boundary. The mechanics of the boundary layer are approximated with sufficient accuracy so that the separation lines are located correctly on the surface of the body.
Leonard, A.↗
Comparison of reusable insulation systems for cryogenically-tanked earth-based space vehicles
Three reusable insulation systems concepts were developed for use with cryogenic tanks of earth-based space vehicles. Two concepts utilized double-goldized Kapton (DGK) or double-aluminized Mylar (DAM) multilayer insulation (MLI), while the third utilized a hollow-glass-microsphere, loadbearing insulation (LBI). Thermal performance measurements were made under space-hold (vacuum) conditions for insulating warm boundary temperatures of approximately 291 K. The resulting effective thermal conductivity was approximately 0.00008 W/m-K (W = weight,Kg; m = measured; K = temperature) for the MLI systems (liquid hydrogen test results) and 0.00054 W/m-K for the LBI system (liquid nitrogen test results corrected to liquid hydrogen temperature).
Sumner, I. E.↗
Comparison of reusable insulation systems for cryogenically-tanked earth-based space vehicles
Three reusable insulation systems concepts have been developed for use with cryogenic tanks of earth-based space vehicles. Two concepts utilized double-goldized Kapton (DGK) or double-aluminized Mylar (DAM) multilayer insulation (MLI), while the third utilized a hollow-glass-microsphere, load-bearing insulation (LBI). All three insulation systems have recently undergone experimental testing and evaluation under NASA-sponsored programs. Thermal performance measurements were made under space-hold (vacuum) conditions for insulation warm boundary temperatures of approximately 291 K. The resulting effective thermal conductivity was approximately .00008 W/m-K for the MLI systems (liquid hydrogen test results) and .00054 W/m-K for the LBI system (liquid nitrogen test results corrected to liquid hydrogen temperature). The DGK MLI system experienced a maximum thermal degradation of 38 percent, the DAM MLI system 14 percent, and the LBI system 6.7 percent due to repeated thermal cycling representing typical space flight conditions. Repeated exposure of the DAM MLI system to a high humidity environment for periods as long as 8 weeks provided a maximum degradation of only 24 percent.
Sumner, I. E.↗
Transonic flow over the NACA 64A006 with an oscillating flap-calculations based on the Euler equations
Exploratory calculations of transonic flows over the airfoil with a quarter-chord oscillating flap were made using a program which obtains approximate solutions to the Euler equations with an explicit, shock-capturing, finite-difference scheme. The calculations, essentially inviscid and for the airfoil at zero angle-of-attack in a free-stream, are at Mach numbers and reduced frequencies which were tested in experiments by Tijdeman. The oscillatory lifts from analogus calculations by various investigators generally agree with one another better than they agree with Tijdeman's data. Inclusion in the calculations of an approximate modelling of boundary conditions expected at slotted wind tunnel walls tends to shift some of the results closer to the experimental values.
Magnus, R. J.↗
A fast Cauchy-Riemann solver
The inhomogeneous Cauchy-Riemann equations in a rectangle are discretized by a finite difference approximation. Several different boundary conditions are treated explicitly, leading to algorithms which have overall second-order accuracy. All boundary conditions with either u or v prescribed along a side of the rectangle can be treated by similar methods. The algorithms presented here have nearly minimal time and storage requirements and seem suitable for development into a general-purpose direct Cauchy-Riemann solver for arbitrary boundary conditions.
Ghil, M.↗
Three dimensional thermal pollution models. Volume 1: Review of mathematical formulations
A mathematical model package for thermal pollution analyses and prediction is presented. These models, intended as user's manuals, are three dimensional and time dependent using the primitive equation approach. Although they have sufficient generality for application at sites with diverse topographical features; they also present specific instructions regarding data preparation for program execution and sample problems. The mathematical formulation of these models is presented including assumptions, approximations, governing equations, boundary and initial conditions, numerical method of solution, and same results.
Lee, S. S.↗
Adaptive-wall wind-tunnel research at NASA-Ames Research Center
Adaptive wall wind tunnel research is summarized. Small scale two and three dimensional wind tunnel experiments and numerical experiments with a three dimensional adaptive wall simulator are included. A NACA 0012 airfoil was tested in a 25 by 13 cm slotted wall test section. Airflow through the test section walls was controlled by adjusting the pressures in segmented plenums. Interference free conditions were successfully attained in subsonic and transonic flows. For the three dimensional experiment, the 25 by 13 cm wind tunnel was modified to permit cross stream wall adjustments. The test model was a semispan wing mounted to one sidewall. Wall interference was substantially reduced at several angles of attack at Mach 0.60. A wing on wall configuration was also modeled in the numerical experiments. These flow simulations showed that free air conditions can be approximated by adjusting boundary conditions at only the floor and ceiling of the test section. No sidewall control was necessary. Typical results from these experiments are discussed.
Schairer, E. T.↗
Adaptive-wall wind-tunnel research at Ames Research Center
Adaptive-wall wind-tunnel research is summarized. This research includes small-scale two- and three-dimensional wind-tunnel experiments and numerical experiments with a three-dimensional adaptive-wall simulator. Airflow through the test-section walls is controlled by adjusting the pressures in segmented plenums. Interference free conditions are successfully attained in subsonic and transonic flows. An adaptive wall test section is constructed for the transonic wind tunnel. Wall interference was reduced in the three dimensional experiment at several angles of attack at Mach 0.60. A wing on wall configuration was modeled in the numerical experiments. These flow simulations showed that free air conditions can be approximated by adjusting boundary conditions at only the floor and ceiling of the test section. No sidewall control was necessary.
Schairer, E. T.↗
A numerical model of acoustic choking. I - Shock free solutions
The phenomenon of acoustic choking in near sonic flows is investigated using the one-dimensional gasdynamic equations for an ideal gas. It is pointed out that this approach eliminates the need to make the classical small disturbance assumption. A finite difference scheme is elaborated to approximate these equations. Boundary conditions that correctly model the physics of the acoustics problems are chosen. The use of a fast Fourier transform routine allows the results to be compared with those obtained by using the conventional harmonic assumptions. Only solutions in which shocks have not fully developed are reported. Continuous solutions are sought, and these are compared with the Fubini solution and with certain results of Myers and Callegari (1977, 1978, 1979).
Walkington, N. J.↗