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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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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Studies on Normal and Microgravity Annular Two Phase Flows

Two-phase gas-liquid flows occur in a wide variety of situations. In addition to normal gravity applications, such flows may occur in space operations such as active thermal control systems, power cycles, and storage and transfer of cryogenic fluids. Various flow patterns exhibiting characteristic spatial and temporal distribution of the two phases are observed in two-phase flows. The magnitude and orientation of gravity with respect to the flow has a strong impact on the flow patterns observed and on their boundaries. The identification of the flow pattern of a flow is somewhat subjective. The same two-phase flow (especially near a flow pattern transition boundary) may be categorized differently by different researchers. Two-phase flow patterns are somewhat simplified in microgravity, where only three flow patterns (bubble, slug and annular) have been observed. Annular flow is obtained for a wide range of gas and liquid flow rates, and it is expected to occur in many situations under microgravity conditions. Slug flow needs to be avoided, because vibrations caused by slugs result in unwanted accelerations. Therefore, it is important to be able to accurately predict the flow pattern which exists under given operating conditions. It is known that the wavy liquid film in annular flow has a profound influence on the transfer of momentum and heat between the phases. Thus, an understanding of the characteristics of the wavy film is essential for developing accurate correlations. In this work, we review our recent results on flow pattern transitions and wavy films in microgravity.

Balakotaiah, V.↗
NASA NTRS1993

Circuit and method for producing a flexible reference voltage

A flexible reference voltage circuit includes a circuit for producing a first digital signal representative of a range of reference voltage levels; a circuit for producing a second digital signal representative of a selected reference voltage level within the range of reference voltage levels; an adder for adding the first and second digital signals to produce a third digital signal; and a digital to analog converter for providing an output voltage in response to the third digital signal. The method of producing a flexible reference voltage performed by the circuit is also claimed. The invention can be used with a differential protection circuit to provide a series of trip level ranges, with a series of selectable trip levels in each range. This is accomplished in a high accuracy circuit which is relatively simple to construct, thereby minimizing size and complexity of the current sensor module, in differential protection applications, or the circuitry, if used in a power system controller. Standard digital logic components can be used to perform the necessary range/level decoding.

Thornton, Roger D.↗
NASA NTRSDate not supplied

Conceptual Integration Studies of Localized Active Flow Control on the Wing of a Commercial Aircraft

A study of conceptual integration and performance of localized active flow control technology onto wings of short-to-medium-range project passenger airplanes is summarized. Using predicted aerodynamic performance improvement opportunities on a computational fluid dynamics reference aircraft, this paper presents the estimated performance opportunities for conceptual implementation of studied wing localized active flow control technology for low-speed (takeoff and landing) application on a Project Research Aircraft configuration. Using conceptual active flow control systems and structural integration weight penalties for studied concepts, potential relevant net performance benefits can be obtained with reliable active flow control in takeoff and landing. The conceptual integration study identifies potential localized wing active flow control application opportunities for high-lift conditions using energy sources available on modern aircraft. Material benefits are estimated for takeoff and landing configurations for selected localized wing active flow control applications. The study concluded that substantial low-speed Maximum Lift and Lift/Drag related performance improvements may be possible with localized wing high-lift active flow control systems powered by auxiliary power unit, engine bleed, or electrical compressors - with due consideration of integration and weight impacts as well as availability requirements of such systems.

drag reduction↗
NASA NTRS1991

Communications and control for electric power systems

The first section of the report describes the AbNET system, a hardware and software communications system designed for distribution automation (it can also find application in substation monitoring and control). The topology of the power system fixes the topology of the communications network, which can therefore be expected to include a larger number of branch points, tap points, and interconnections. These features make this communications network unlike any other. The network operating software has to solve the problem of communicating to all the nodes of a very complex network in as reliable a way as possible even if the network is damaged, and it has to do so with minimum transmission delays and at minimum cost. The design of the operating protocols is described within the framework of the seven-layer Open System Interconnection hierarchy of the International Standards Organization. Section 2 of the report describes the development and testing of a high voltage sensor based on an electro-optic polymer. The theory of operation is reviewed. Bulk fabrication of the polymer is discussed, as well as results of testing of the electro-optic coefficient of the material. Fabrication of a complete prototype sensor suitable for use in the range 1-20 kV is described. The electro-optic polymer is shown to be an important material for fiber optic sensing applications. Appendix A is theoretical support for this work. The third section of the report presents the application of an artificial neural network, Kohonen's self-organizing feature map, for the classification of power system states. This classifier maps vectors of an N-dimensional space to a 2-dimensional neural net in a nonlinear way preserving the topological order of the input vectors. These mappings are studied using a nonlinear power system model.

Kirkham, H.↗
NASA NTRS1976

Solid state remote power controllers for 120 Vdc power systems

Solid state Remote Power Controllers (RPCs) developed for use in any dc power system with voltage up to 120 Vdc and distributed power up to 3.6 kW per bus are described. The RPCs were demonstrated to be reliable, 99 percent efficient, comparatively simple, and potentially low in cost. Advantages of the RPCs include: contactless switching; controlled rates of current rise and fall; current limiting; and fast, well-defined, repeatable response to overloads and faults.

Sundberg, G. R.↗
NASA NTRS1975

Solid state remote power controllers for 120 VDC power systems

Solid state remote power controllers can be applied to any dc power system up to 120 Vdc and distribute power up to 3.6 kW per hour. Devices have demonstrated total electrical efficiencies of 98.5 percent to 99.0 percent at rated load currents.

Sundberg, G. R.↗
NASA NTRS1975

Design and performance of a no-single-failure control system for the mini-Brayton power conversion system

The control system consists of the ac-dc conversion, voltage regulation, speed regulation through parasitic load control, and overload control. A no-single-failure configuration was developed to attain the required reliability for a 10-year design life of unattended operation. The design principles, complete schematics, and performance are reported. Testing was performed on an alternator simulator pending construction of the actual Mini-Brayton alternator.

Brichenough, A. G.↗
NASA NTRS1989

Three approaches to reliability analysis

It is noted that current reliability analysis tools differ not only in their solution techniques, but also in their approach to model abstraction. The analyst must be satisfied with the constraints that are intrinsic to any combination of solution technique and model abstraction. To get a better idea of the nature of these constraints, three reliability analysis tools (HARP, ASSIST/SURE, and CAME) were used to model portions of the Integrated Airframe/Propulsion Control System architecture. When presented with the example problem, all three tools failed to produce correct results. In all cases, either the tool or the model had to be modified. It is suggested that most of the difficulty is rooted in the large model size and long computational times which are characteristic of Markov model solutions.

Mesh networks↗
NASA NTRS1993

Stirling Converters For Solar Power

Two designs expected to meet long-term goals for performance and cost. Proposed for advanced systems to convert solar thermal power to electrical power. Each system, designed to operate with 11-m-diameter paraboloidal reflector, includes solar-energy receiver, liquid-metal heat-transport subsystem, free-piston Stirling engine, cooling subsystem, alternator or generator coupled directly or indirectly to commercial electric-power system, and control and power-conditioning circuitry. System converts approximately 75 kW of input solar thermal power falling on collector to about 25 kW of output electrical power.

Shaltens, Richard K.↗
NASA NTRS1994

YAV-8B reaction control system bleed and control power usage in hover and transition

Using a calibrated Rolls-Royce Pegasus engine and existing aircraft instrumentation and pressure taps, total and individual nozzle reaction control system (RCS) bleed flow rates have been measured on a YAV-8B Harrier during typical short takeoff, transition, hover, and vertical landing maneuvers. RCS thrust forces were calculated from RCS nozzle total pressure measurements, and control power was determined from the moments produced by these thrusts and the aircraft's moments of inertia. These data document the characteristics of the YAV-8B RCS with its basic stability augmentation system (SAS) engaged. Advanced control system designs for the YAV-8B can be compared to the original SAS based on the total bleed use and the percentage of available bleed used. In addition, the peak and mean values of the bleed and control power data can be used for sizing the reaction controls for a future short takeoff and vertical landing (STOVL) aircraft.

Borchers, Paul F.↗
NASA NTRS1980

Attitude control study for a large flexible spacecraft using a Solar Electric Propulsion System (SEPS)

The attitude control performance of the solar electric propulsion system (SEPS) was evaluated. A thrust vector control system for powered flight control was examined along with a gas jet reaction control system, and a reaction wheel system, both of which have been proposed for nonpowered flight control. Comprehensive computer simulations of each control system were made and evaluated using a 30 mode spacecraft model. Results obtained indicate that thrust vector control and reaction wheel systems offer acceptable smooth proportional control. The gas jet control system is shown to be risky for a flexible structure such as SEPS, and is therefore, not recommended as a primary control method.

Tolivar, A. F.↗
NASA NTRS1996

Solar Dynamic Power System Stability Analysis and Control

The objective of this research is to conduct dynamic analysis, control design, and control performance test of solar power system. Solar power system consists of generation system and distribution network system. A bench mark system is used in this research, which includes a generator with excitation system and governor, an ac/dc converter, six DDCU's and forty-eight loads. A detailed model is used for modeling generator. Excitation system is represented by a third order model. DDCU is represented by a seventh order system. The load is modeled by the combination of constant power and constant impedance. Eigen-analysis and eigen-sensitivity analysis are used for system dynamic analysis. The effects of excitation system, governor, ac/dc converter control, and the type of load on system stability are discussed. In order to improve system transient stability, nonlinear ac/dc converter control is introduced. The direct linearization method is used for control design. The dynamic analysis results show that these controls affect system stability in different ways. The parameter coordination of controllers are recommended based on the dynamic analysis. It is concluded from the present studies that system stability is improved by the coordination of control parameters and the nonlinear ac/dc converter control stabilize system oscillation caused by the load change and system fault efficiently.

Momoh, James A.↗
NASA NTRS1975

Commonality Study of the Pressure-Volume-Temperature Based Propellant Gaging Software Modules for the Auxiliary Power Unit, Reaction Control System, and Orbital Maneuvering System

Computer storage requirements can be reduced if areas of commonality exist in two or more programs placed in the same computer and identical code can be used by more than one program. The pressure-volume-temperature (P-V-T) relationship for the propellant tank pressurant agent is utilized as the basis for either a primary of a backup propellant gaging program for the auxiliary power unit (APU), the reaction control system (RCS), and the orbital maneuvering system (OMS). These three propellant gaging programs were investigated. It was revealed that a very limited degree of software commonality exits among them. An examination of this common software indicated that only the computation of the helium compressibility factor in an external function subprogram accessible to both the RCS and OMS propellant gaging programs appears to offer a savings in computer storage requirements.

Duhon, D. D.↗
NASA NTRS1980

A ground based phase control system for the solar power satellite. Executive summary, volume 1, phase 3

The Solar Power Satellite (SPS) concept and the reference phase control system investigated in earlier efforts are reviewed. A summary overview of the analysis and selection of the pilot signal and power transponder design is presented along with the SOLARSIM program development and the simulated SPS phase control performance. Evaluations of the ground based phase control system as an alternate phase control concept are summarized.

Chie, C. M.↗
NASA NTRS1978

Accuracy analysis of pointing control system of solar power station

The first-phase effort concentrated on defining the minimum basic functions that the retrodirective array must perform, identifying circuits that are capable of satisfying the basic functions, and looking at some of the error sources in the system and how they affect accuracy. The initial effort also examined three methods for generating torques for mechanical antenna control, performed a rough analysis of the flexible body characteristics of the solar collector, and defined a control system configuration for mechanical pointing control of the array.

Hung, J. C.↗