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Results for “transference number”
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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System evaluation from impulse response fragments
By use of rational approximation, a procedure was found which allows calculation of the z-transfer function from a restricted number of time sequence values. The order of the system need not be known. Transformation to the s-domain is easily provided.
Effects of multiple scattering on light pulses reflected by turbid atmospheres
Multiple scattering contributions to lidar returns from turbid atmospheres are derived by means of an analytical theory. It is assumed that scattering takes place mainly at small angles except for one event that scatters the light backward. The phase functions are approximated by the sum of Gaussian functions of the scattering angle in both the forward and backward directions. The three-dimensional radiative transfer equation is transformed to a one-dimensional problem by means of Fourier transforms. Neumann solutions to the transformed equation of radiative transfer are then found. A number of examples are presented for cloud, fog and haze models. The results are found to be in satisfactory agreement with results obtained from the Monte Carlo analysis of Kunkel (1974) and the theory of light pulses doubly scattered by turbid atmospheres which was developed by Eloranta (1972).
Quasi-three-dimensional laminar boundary-layer separations in supersonic flow
A numerical algorithm is presented for solving laminar, steady, supersonic interacting boundary-layer flows for quasi-three-dimensional configurations. The interaction problem is treated as a boundary-value problem and a salient feature of the scheme is the direct implementation of the downstream boundary condition. Solutions are presented for axisymmetric and swept (yawed) compression ramps for both adiabatic and heat transfer conditions over a Mach number range of 2-6. The results are in good agreement with experimental data and existing theories for axisymmetric cases. For the swept (yawed) configurations, lack of experimental data makes a direct comparison impossible, but the present solutions are found to be in qualitative agreement with earlier studies. In addition it is shown that the trends obtained here for the sweep effects are well predicted by a simple extension of the two-dimensional asymptotic theory.
Numerical solution of the Navier-Stokes equations for laminar, transonic flows
An implicit finite difference solution of the Navier-Stokes equations yielded time histories of the transonic laminar flow development about a circular cylinder and NACA-0018 airfoil. Reynolds numbers ranged from those corresponding to purely laminar flow to those corresponding to significant turbulence in the boundary layer. Body thermal conditions of an adiabatic wall and a specified body temperature were considered. Versatility in treating arbitrary bodies was incorporated by using numerically generated, body-fitted coordinate transformations. Solution of the simultaneous difference equations for the dependent variables was obtained using an accelerated Gauss-Seidel iterative scheme. Computational results are presented in the form of velocity vector fields, Mach number contours, aerodynamic coefficients, heat transfer rates at the body surface, and body temperature distributions. Truncation analyses of first and second derivative difference approximations resulted in general criteria for numerically generated coordinates so that flow near a body is more accurately represented.
The Martian polar vortex - Theory of seasonal variation and observations of eolian features
Observations of eolian features in the south polar region of Mars show strikingly axisymmetric patterns. The paper presents an explanation for the patterns in terms of the simplest dynamical model possible. Piraglia's (1975) model is simplified by neglecting compressibility and by assuming a cylindrical rather than spherical geometry, but this model is extended by including the nonlinear transport terms (of order Rossby number) and the seasonal mass transfer terms. The proposed model is therefore focused on determining the surface stress in polar regions rather than the atmospheric structure. The model is described, the parameter values are discussed, and the solutions are compared with observations. It is shown that the model predicts seasonal behavior which can be divided into four periods: formation of the south polar cap, its maximum extent, sublimation, and absence.
Orbital transfer of large space structures with nuclear electric rockets
This paper discusses the potential application of electric propulsion for orbit transfer of a large spacecraft structure from low earth orbit to geosynchronous altitude in a deployed configuration. The electric power was provided by the spacecraft nuclear reactor space power system on a shared basis during transfer operations. Factors considered with respect to system effectiveness included nuclear power source sizing, electric propulsion thruster concept, spacecraft deployment constraints, and orbital operations and safety. It is shown that the favorable total impulse capability inherent in electric propulsion provides a potential economic advantage over chemical propulsion orbit transfer vehicles by reducing the number of Space Shuttle flights in ground-to-orbit transportation requirements.
New short constraint length, rate 1/N convolutional codes which minimize the required SNR for given desired bit error rates
It is pointed out that for a convolutional coding system, the Bit Error Rate (BER) at the Viterbi decoder output is upper-bounded by the transfer function bound. A large number of rate 1/N convolutional codes have been reported. The criteria used for determining the quality of a code in code search procedures, however, may not be very suited for cases in which the required BER is in the moderate range. For this reason, it may be best to select the code with the aim to minimize the required SNR for a given disired BER. Partial code searching techniques are presented, and a table listing the code search results is provided.
Instability of capillary jets with thermocapillarity
Long axisymmetric liquid zones are subject to axial temperature gradients which induce steady viscous flows driven by thermocapillarity. The approximately parallel flow in a cylindrical zone is examined for linearized instabilities. Capillary, surface-wave and thermal modes are found. Capillary breakup can be retarded or even suppressed for small Prandtl number and large Biot number B, which measures heat transfer from the liquid to the surrounding atmosphere. In the limiting case B approaches infinity the zone becomes an isothermal jet subject to axial 'wind stress' on its interface. It is then possible to suppress capillary breakup entirely so that one can maintain long coherent jets.
Stability characteristics of a supersonic boundary layer and their relation to the position of the laminar-turbulent transition point
By comparing the calculated results with experimental data, it is demonstrated that the position of the laminar-boundary transition point of a boundary layer can be estimated by using the e-exp-n method. The effect of the Mach number, pressure gradient, and heat transfer on the laminar-turbulent transition is discussed. It is found that under conditions of strong cooling, the effect of the pressure gradient on the position of the transition point is less pronounced than in the absence of heat transfer.
Benefits to the nation from astronomy and astrophysics
It is argued that astronomy makes unexpectantly large contributions to formal and informal science education, given the small number of research astronomers. Technology transfer and spin-offs from astronomy have important applications in medicine, industry, defence, environmental monitoring, and consumer products. Astronomy provides unusually promising opportunities for international cooperation. Other sciences benefit from synergistic interactions with astronomy. A review is given of astronomy education and teacher training. The role of astronomy in medicine, industry, defence, energy technology, the environment, and everyday life is reviewed.
Performance characteristics of a thermal energy storage module - A transient PCM/forced convection conjugate analysis
The performance of a thermal energy storage module is simulated numerically. The change of phase of the phase-change material (PCM) and the transient forced convective heat transfer for the transfer fluid with low Prandtl numbers are solved simultaneously as a conjugate problem. A parametric study and a system optimization are conducted. The numerical results show that module geometry is crucial to the design of a space-based thermal energy storage system.
Fluid acquisition system for superfluid helium
To enable the resupply of liquid helium users on orbit, the technology for helium transfer in space is being developed. A key element of the resupply process is the fluid acquisition in the supply dewar; feeding the liquid to the pump. For the Superfluid Helium On-Orbit Transfer (SHOOT) flight experiment a number of fluid acquisition techniques have been examined. Subscale tests performed in one gravity on two of the candidates are described. The hope is that these results may be scaled to much larger systems in low gravity. These two types are a screened channel device and a capillary device. Flow rates versus negative head height are presented. Difficulties with each device and the test environment are explained. Some of the measurements to be made on orbit on the fluid acquisition for SHOOT are described.
Minimum-fuel, power-limited transfers between coplanar elliptical orbits
Two techniques of computing coplanar, minimum-fuel, power-limited transfers are presented, based on approximate solutions obtained by the averaging method. For the first technique, the average solution provides estimates of the initial adjoint variables, and the second provides approximations of the optimal controls in feedback form. The accuracy of the techniques for computing coplanar, minimum-fuel, power-limited transfers is evaluated for a number of initial and final orbits.
The Space Transportation System summer environment on launch pad
This paper describes a 2D flow and thermalanalysis to determine the solar effect on the Space Shuttle launch components subsequent to the external tank (ET) loading operation in extremely hot conditions. An existing CFD code Parabolic Hyperbolic or Elliptical Numerical Integration Code Series was used in the study. The analysis was done for a 2D slice between planes perpendicular to the longitudinal axis of the STS and passing through the lower portions of the Redesigned Solid Rocket Motors (RSRMs), the ET, and the wing of the Orbiter. The results are presented as local and average values of the heat transfer coefficient, and the Nusselt number, and the surface temperature around the RSRMs and the ET. Solar heating effects increased the surface temperatures of the RSRMs by 9-11 F. Higher prelaunch surface temperatures measured on the east and west RSRMs (in the inboard region between the RSRMs and the ET) during 19 most recent launches of the STS are correlated as a function of the ambient temperature.
Ultra low-noise charge coupled device
Special purpose CCD designed for ultra low-noise imaging and spectroscopy applications that require subelectron read noise floors, wherein a non-destructive output circuit operating near its 1/f noise regime is clocked in a special manner to read a single pixel multiple times. Off-chip electronics average the multiple values, reducing the random noise by the square-root of the number of samples taken. Noise floors below 0.5 electrons rms are possible in this manner. In a preferred embodiment of the invention, a three-phase CCD horizontal register is used to bring a pixel charge packet to an input gate adjacent a floating gate amplifier. The charge is then repeatedly clocked back and forth between the input gate and the floating gate. Each time the charge is injected into the potential well of the floating gate, it is sensed non-destructively. The floating gate amplifier is provided with a reference voltage of a fixed value and a pre-charge gate for resetting the amplifier between charge samples to a constant gain. After the charge is repeatedly sampled a selected number of times, it is transferred by means of output gates, back into the horizontal register, where it is clocked in a conventional manner to a diffusion MOSFET amplifier. It can then be either sampled (destructively) one more time or otherwise discarded.
Hypervelocity Impact Initiation of Explosive Transfer Lines
The Gemini, Apollo and Space Shuttle spacecraft utilized explosive transfer lines (ETL) in a number of applications. In each case the ETL was located behind substantial structure and the risk of impact initiation by micrometeoroids and orbital debris was negligible. A current NASA program is considering an ETL to synchronize the actuation of pyrobolts to release 12 capture latches in a contingency. The space constraints require placing the ETL 50 mm below the 1 mm thick 2024-T72 Whipple shield. The proximity of the ETL to the thin shield prompted analysts at NASA to perform a scoping analysis with a finite-difference hydrocode to calculate impact parameters that would initiate the ETL. The results suggest testing is required and a 12 shot test program with surplused Shuttle ETL is scheduled for February 2012 at the NASA White Sands Test Facility. Explosive initiation models are essential to the analysis and one exists in the CTH library for HNS I, but not the HNS II used in the Shuttle 2.5 gr/ft rigid shielded mild detonating cord (SMDC). HNS II is less sensitive than HNS I so it is anticipated that these results using the HNS I model are conservative. Until the hypervelocity impact test results are available, the only check on the analysis was comparison with the Shuttle qualification test result that a 22 long bullet would not initiate the SMDC. This result was reproduced by the hydrocode simulation. Simulations of the direct impact of a 7 km/s aluminum ball, impacting at 0 degree angle of incidence, onto the SMDC resulted in a 1.5 mm diameter ball initiating the SMDC and 1.0 mm ball failing to initiate it. Where one 1.0 mm ball could not initiate the SMDC, a cluster of six 1.0 mm diameter aluminum balls striking simultaneously could. Thus the impact parameters that will result in initiating SMDC located behind a Whipple shield will depend on how well the shield fragments the projectile and spreads the fragments. An end-to-end simulation of the impact of an aluminum ball onto a Whipple shield covering SMDC is problematic due to the hydrocode fracture models. Regardless, two simulations were performed resulting in a 5 mm ball initiating the SMDC and a 4 mm ball failing to initiate the SMDC.
Comparison of Numerical Models for Computing Underwater Light Fields
Seven models for computing underwater radiances and irradianes by numberical solution of the radiative transfer equation are compared. The models are applied to the solution of several problems drawn from optical oceanography.