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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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The nonlinear phenomena of signal beam saturation, pump beam depletion, and optically controlled coupling coefficient of two-beam interaction in photorefractive materials are analyzed. Applications of these phenomena to digital logic operations is discussed and supported by experimental results obtained in photorefractive BaTiO3.
The matching of a boundary layer and a rotational inviscid flow is reexamined by extending the Johnson and Sockol (1979) coupling conditions to include the case where the boundary layer solution includes the second-order effects of the freestream vorticity and the total temperature gradient. It is pointed out that two of the three conditions are not independent. If the boundary layer solution satisfies the appropriate momentum and energy integral equations, it follows that the imposition of the normal mass flux condition insures that the conditions on a normal flux of streamwise momentum and total enthalpy will also be satisfied.
A simple analytical model for the structural dynamics of a rotating flexible blade/rigid disk/flexible cantilevered shaft system yields the equations of motion expressed in the rotating frame, showing that the blade's one-nodal diameter modes dynamically couple to the rigid body whirling motion of the shaft-disk system. This analytical model is correlated with the results of a structural dynamic experiment performed on an aeroelastic rotor fan that is similar to a high bypass ratio shroudless turbofan. The agreement between the predicted and experimental natural frequencies is good, and suggests significant interaction of the one-nodal diameter blade modes with the shaft-disk modes.
The MacCormack implicit predictor-corrector model (1981) for numerical solution of the coupled Navier-Stokes equations for turbulent flows is extended to nonconservative multiequation turbulence models, as well as the inclusion of second-order Reynolds stress turbulence closure. A scalar effective pressure turbulent contribution to the pressure field is defined to approximate the effects of the Reynolds stress in strongly sheared flows. The Jacobian matrices of the transport equations are diagonalized to reduce the required computer memory and run time. Techniques are defined for including turbulence in the diagonalization. Application of the method is demonstrated with solutions generated for transonic nozzle flow and for the interaction between a supersonic flat plate boundary layer and a 12 deg compression-expansion ramp.
The analytical basis and the application of a Rotor/Airframe Comprehensive Aeroelastic Program (RACAP) are described in detail. The rationale behind each analytical choice is outlined and the modular procedure is described. The program is verified by application to the AH-1G helicopter. The applicability of various airload prediction models is examined, and both the steady and vibratory responses of the blade are compared with flight test data. Reasonable correlation is found between measured and calculated blade response, with excellent correlation for vibration amplitudes at various locations on the fuselage such as engine, pilot seat, and gunner. Within the analytical model, comparisons are drawn between an isolated blade analysis and a coupled rotor/fuselage model. The deficiency of the former in the context of the AH-1G is highlighted.
A programmable transformer coupled converter (PTCC) is being developed by NASA/Marshall Space Flight Center for application in future large space power systems. The PTCC uses an internal microprocessor to control the output characteristics of its three Cuk integrated magnetics type power stages which have a combined capability of 5.4 kW (30 V at 180 A). Details of design trade-offs and test results are presented.
Numerical methods adapted to concurrent processing. Algorithm solves set of coupled partial differential equations by numerical integration. Adapted to run on hypercube computer, algorithm separates problem into smaller problems solved concurrently. Increase in computing speed with concurrent processing over that achievable with conventional sequential processing appreciable, especially for large problems.
Misaligned machine shafts operating at low speeds coupled with cheap, simple mechanism made in part from wire rope. Wire rope bends to accommodate angular and lateral misalignments and dampens vibrations that accompany, or caused by, rotation of shafts.
Semiconductor-laser arrays more reliable, more powerful, and easier to make. Improved design intended to eliminate undesired electromagnetic modes and mode shifts sometimes occuring in gain-guided variety. Reflected from mirror/window at end of common resonator section of laser, energy refracted from each laser enters adjacent laser. Mutual coupling establishes phase relationships among lasers. Monolithic laser array made by standard epitaxial techniques. Made in part with polymeric materials to mitigate some deleterious effects of all-expitaxial processing. Potential applications include optical communications, ranging, printing, and recording.
For a rapid preparation of solutions intended for analysis by inductively coupled plasma emission spectrometry or atomic absorption spectrometry, an automatic device called Plasmasol was developed. This apparatus used the property of nonwettability of glassy C to fuse the sample in an appropriate flux. The sample-flux mixture is placed in a composite crucible, then heated at high temperature, swirled until full dissolution is achieved, and then poured into a water-filled beaker. After acid addition, dissolution of the melt, and filling to the mark, the solution is ready for analysis. The analytical results obtained, either for oxide samples or for prereduced iron ores show that the solutions prepared with this device are undistinguished from those obtained by manual dissolutions done by acid digestion or by high temperature fusion. Preparation reproducibility and analytical tests illustrate the performance of Plasmasol.
An orbiter and its payload substructure are linked together by five trunnion joints which have thirty degrees-of-freedom. Geometric compatibility conditions require fourteen of the interface physical coordinates of the orbiter and payload to be equal to each other and the remaining sixteen are free to have relative motions under Coulomb friction. The component modes synthesis method using fourteen inertia relief attachment modes for the formulation of the coupled system is presented. The exact nonlinear friction function is derived based on the characteristics of the joints. Formulation is applicable to an orbiter that carries any number of payload substructures.
As spacecraft structural concepts increase in size and flexibility, the vibration frequencies become more closely-spaced. The identification and control of such closely-spaced frequencies present a significant challenge. To validate system identification and control methods prior to actual flight, simpler space structures will be flown. To challenge the above technologies, it will be necessary to design these structures with closely-spaced or coupled vibration modes. Thus, there exists a need to develop a systematic method to design a structure which has closely-spaced vibration frequencies. This paper describes an optimization procedure which is used to design a large flexible structure to have closely-spaced vibration frequencies. The procedure uses a general-purpose finite element analysis program for the vibration and sensitivity analyses and a general-purpose optimization program. Results are presented from two studies. The first study uses a detailed model of a large flexible structure to design a structure with one pair of closely-spaced frequencies. The second study uses a simple equivalent beam model of a large flexible structure to obtain a design with two pairs of closely-spaced frequencies.
A versatile large-signal, two-dimensional computer program is used by NASA to model coupled-cavity travelling-wave tubes (TWTs). In this model, the electron beam is divided into a series of disks, each of which is further divided into axially symmetric rings which can expand and contract. The trajectories of the electron rings and the radiofrequency (RF) fields are determined from the calculated axial and radial space-charge, RF, and magnetic forces as the rings pass through a sequence of cavities. By varying electrical and geometric properties of individual cavities, the model is capable of simulating severs, velocity tapers, and voltage jumps. The calculated electron ring trajectories can be used in designing magnetic focusing and multidepressed collectors. The details of using the program are presented, and results are compared with experimental data.
A finite element approach to coupling flow, thermal and structural analyses of aerodynamically heated panels is presented. The Navier-Stokes equations for laminar compressible flow are solved together with the energy equation and quasi-static structural equations of the panel. Interactions between the flow, panel heat transfer and deformations are studied for thin stainless steel panels aerodynamically heated by Mach 6.6 flow.
The problem of the thermal stresses in coupled deformable bodies is formulated for the case where the heat-transfer coefficient at the common boundary depends on the stress-strain state of the bodies (e.g., is a function of the normal pressure at the common boundary). Several one-dimensional problems are solved in this formulation. Among these problems is the determination of the thermal stresses in an n-layer plate and in a two-layer cylinder.
Samples of two GEC charge coupled devices with enhanced X-ray performance have been tested. The P8607, fabricated with reduced linear dimensions, gives the lowest detector noise reported for Fe-55 with a CCD. The deep depletion device P8600-HR gives the best combination of energy resolution and quantum efficiency at 6 keV. The energy resolution vs quantum efficiency trade-off curve are discussed.
The goal set forth here is to continue the work started by Braun et al. (1984-1985) and present an integrated analysis of the behavior of the two row, 20 staggered pockets, hydrostatic cryogenic bearing used by the turbopumps of the Space Shuttle main engine. The variable properties Reynolds equation is fully coupled with the two-dimensional fluid film energy equation. The three-dimensional equations of the shaft and bushing model the boundary conditions of the fluid film energy equation. The effects of shaft eccentricity, angular velocity, and inertia pressure drops at pocket edge are incorporated in the model. Their effects on the bearing fluid properties, load carrying capacity, mass flow, pressure, velocity, and temperature form the ultimate object of this paper.
An exact analytical solution is given to the problem of long-time propellant thermal response to a specified pressure oscillation. Coupling to the gas phase is made using the quasisteady Zeldovich-Novozhilov approximation. Explicit linear and lowest order (quadratic) nonlinear expressions for propellant response are obtained from the implicit nonlinear solutions. Using these expressions, response curves are presented for an ammonium perchlorate composite propellant and HMX monopropellant.