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  • 1984  (182)
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  • 1
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    Improved techniques of parallel gap welding and monitoring (1984)
    In:  CASI
    Details
    Publikationsdatum: 2006-02-14
    Beschreibung: Welding programs which show that parallel gas welding is a reliable process are discussed. When monitoring controls and nondestructive tests are incorporated into the process, parallel gap welding becomes more reliable and cost effective. The panel fabrication techniques and the HAC thermal cycling test indicate reliable product integrity. The design and building of automated tooling and fixturing for welding are discussed.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Space Photovoltaic Res. and Technol. 1983; p 228-234
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  • 2
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    Variable polarity plasma arc welding on the Space Shuttle external tank (1984)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-18
    Beschreibung: Variable polarity plasma arc (VPPA) techniques used at NASA's Marshall Space Flight Center for the fabrication of the Space Shuttle External Tank are presentedd. The high plasma arc jet velocities of 300-2000 m/s are produced by heating the plasma gas as it passes through a constraining orifice, with the plasma arc torch becoming a miniature jet engine. As compared to the GTA jet, the VPPA has the following advantages: (1) less sensitive to contamination, (2) a more symmetrical fusion zone, and (3) greater joint penetration. The VPPA welding system is computerized, operating with a microprocessor, to set welding variables in accordance with set points inputs, including the manipulator and wire feeder, as well as torch control and power supply. Some other VPPA welding technique advantages are: reduction in weld repair costs by elimination of porosity; reduction of joint preparation costs through elimination of the need to scrape or file faying surfaces; reduction in depeaking costs; eventual reduction of the 100 percent-X-ray inspection requirements. The paper includes a series of schematic and block diagrams.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Welding Journal (ISSN 0043-2296); 63; 27-35
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  • 3
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    Two-phase turbine staging (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Two-phase turbines would be useful in Rankine cycles using low-quality or saturated-liquid working fluids. The chief problem is low efficiency due to slip losses in nozzles and due to liquid impact and friction losses in rotors. To raise efficiency, a staging method was tested in which the first stage operated at high speed with low relative liquid velocity, and the second stage recovered the first-stage exit energy. The theoretical efficiency for an experimental turbine operating with Refrigerant-22 was raised from 55 percent to 66 percent, and the measured efficiency was raised from 52 percent to 57 percent.
    Schlagwort(e): MECHANICAL ENGINEERING
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  • 4
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    DOE/NASA Automotive Stirling Engine Project Overview 83 (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: An overview of the DOE/NASA Automotive Stirling Engine Project is presented. The background and objectives of the project are reviewed. Project activities are described and technical progress and status are presented and assessed. Prospects for achieving the objective 30 percent fuel economy improvement are considered good. The key remaining technology issues are primarily related to life, reliability and cost, such as piston rod seals, and low cost heat exchanges. Previously announced in STAR as N83-27924
    Schlagwort(e): MECHANICAL ENGINEERING
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  • 5
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    An analysis of temperature effect in a finite journal bearing with spatial tilt and viscous dissipation (1984)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The analysis presented herein deals with the evaluation of the pressure, velocity, and temperature profiles in a finite-length plane journal bearing. The geometry of the case under study consists of a spatially tilted shaft. The two-dimensional Reynolds equation accounts for the variation of the clearance gap h with x and z and is used to model the pressure field. The latter is solved for a variety of shaft tilt angles and then used to calculate the two-dimensional flow field. Finally, the flow field is used in the energy equation to solve for the film temperature profile, when the effect of viscous dissipation is taken into account.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: ASLE Transactions; 27; 405-412;
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  • 6
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    Influence of unbalance on the nonlinear dynamical response and stability of flexible rotor-bearing systems (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: In this paper, some of the effects of unbalance on the nonlinear response and stability of flexible rotor-bearing systems is presented from both a theoretical and experimental standpoint. In a linear system, operating above its stability threshold, the amplitude of motion grows exponentially with time and the orbits become unbounded. In an actual system, this is not necessarily the case. The actual amplitudes of motion may be bounded due to various nonlinear effects in the system. These nonlinear effects cause limit cycles of motion. Nonlinear effects are inherent in fluid film bearings and seals. Other contributors to nonlinear effects are shafts, couplings and foundations. In addition to affecting the threshold of stability, the nonlinear effects can cause jump phenomena to occur at not only the critical speeds, but also at stability onset or restabilization speeds.
    Schlagwort(e): MECHANICAL ENGINEERING
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  • 7
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    Ceramics potential in automotive powerplants (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The paper addresses the potential that ceramic materials can play an important role in future automotive powerplants - both advanced heat engines and advanced battery systems. A number of related experimental programs are reviewed including ceramics for gasoline and diesel piston engines, gas turbine and Stirling Engines and sodium-sulfur batteries. A strong integrated program to develop ceramics technology is recommended.
    Schlagwort(e): MECHANICAL ENGINEERING
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  • 8
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    Into mesh lubrication of spur gears with arbitrary offset oil jet. I - For jet velocity less than or equal to gear velocity (1983)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-19
    Beschreibung: An analysis was conducted for into mesh oil jet lubrication with an arbitrary offset and inclination angle from the pitch point for the case where the oil jet velocity is equal to or less than pitch line velocity. The analysis includes the case for the oil jet offset from the pitch point in the direction of the pinion and where the oil jet is inclined to intersect the common pitch point. Equations were developed for the minimum oil jet velocity required to impinge on the pinion or gear and the optimum oil jet velocity to obtain the maximum impingement depth.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: ASME; 713-718
    Format: text
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  • 9
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    Special cases of friction and applications (1984)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Two techniques for reducing friction forces are presented. The techniques are applied to the generalized problem of reducing the friction between kinematic pairs which connect a moveable link to a frame. The basic principles are: (1) Let the moveable link be supported by two bearings where the relative velocities of the link with respect to each bearing are of opposite directions. Thus the resultant force (torque) of friction acting on the link due to the bearings is approximately zero. Then, additional perturbation of motion parallel to the main motion of the moveable link will require only a very small force; (2) Let the perturbation in motion be perpendicular to the main motion. Equations are developed which explain these two methods. The results are discussed in relation to friction in geared couplings, gyroscope gimbal bearings and a rotary conveyor system. Design examples are presented.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: ASME; 256-260
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  • 10
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    Why ceramic engines? (1984)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Oil is still a problem for the U.S. and its allies. Transportation uses 61 percent of U.S. oil and its share is increasing, so more efficient technology should be concentrated there. Trucks' share of oil use is increasing because they are already much more efficient than autos. The primary truck opportunities are streamlining, more efficient engines, and shifting freight to railroads. More efficient engines are possible using ceramics to allow elimination of cooling systems and better use of waste exhaust heat. A 60 percent improvement seems possible if ceramics can be made tough enough and durable enough.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Ceramic Engineering and Science Proceedings (ISSN 0196-6219); 5; 281-284
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  • 11
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    Long term technology development program (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: In the Advanced Adiabatic Development program, the following technology were identified as critical: piston development for oil-less, adiabatic engine; positive displacement compounding and charge system; experimental evaluation of the preheat concept; combustion system with positive ignition assist; and ceramic manufacturing technology. Of these five areas, ceramic manufacturing technology is the pacing item, and is already being addressed by several organizations. Therefore the four remaining areas need immediate attention. Since the lead time involved in engine development and production is long, this technology development should be done concurrently with the AAD engine development. A four year program is outlined which will simultaneously study these first four areas. This program requires two test rigs; one single cylinder adiabatic engine; and one multicylinder adiabatic turbocompound engine.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Advan. Automotive Diesel Assessment Program; 7 p
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  • 12
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    A.A.D. engine noise evaluation (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: A critique of the various characteristics of engine design influencing noise and attempts to indicator areas where attention is required to obtain noise acceptable engine for automobiles are discussed. It was concluded that the engine has a potential to be quiet beccause a ion rated speed is chosen. Problems with high gas pressure, the fuel injection pump, and the expander/compressor are discussed.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Cummins Engine Co., Inc. Advan. Automotive Diesel Assessment Program; 29 p
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  • 13
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    Screw expander for light duty diesel engines (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Preliminary selection and sizing of a positive displacement screw compressor-expander subsystem for a light-duty adiabatic diesel engine; development of a mathematical model to describe overall efficiencies for the screw compressor and expander; simulation of operation to establish overall efficiency for a range of design parameters and at given engine operating points; simulation to establish potential net power output at light-duty diesel operating points; analytical determination of mass moments of inertia for the rotors and inertia of the compressor-expander subsystem; and preparation of engineering layout drawings of the compressor and expander are discussed. As a result of this work, it was concluded that the screw compressor and expander designed for light-duty diesel engine applications are viable alternatives to turbo-compound systems, with acceptable efficiencies for both units, and only a moderate effect on the transient response.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Cummins Engine Co., Inc. Advan. Automotive Diesel Assessment Program; 46 p
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  • 14
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    Thermal and mechanical analysis of major components for the advanced adiabatic diesel engine (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The proposed design for the light duty diesel is an in-line four cylinder spark assisted diesel engine mounted transversely in the front of the vehicle. The engine has a one piece cylinder head, with one intake valve and one exhaust valve per cylinder. A flat topped piston is used with a cylindrical combustion chamber recessed into the cylinder head directly under the exhaust valve. A single ceramic insert is cast into the cylinder head to insulate both the combustion chamber and the exhaust port. A similar ceramic insert is cast into the head to insulate the intake port. A ceramic faceplate is pressed into the combustion face of the head to insulate the face of the head from hot combustion gas. The valve seats are machined directly into the ceramic faceplate for the intake valve and into the ceramic exhaust pot insert for the exhaust valve. Additional ceramic applications in the head are the use of ceramic valve guides and ceramic insulated valves. The ceramic valve guides are press fit into the head and are used for increased wear resistance. The ceramic insulated valves are conventional valves with the valve faces plasma spray coated with ceramic for insulation.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Advan. Automotive Diesel Assessment Program; 65 p
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  • 15
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    Advanced automotive diesel engine system study (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: A conceptual study of an advanced automotive diesel engine is discussed. The engine concept selected for vehicle installation was a supercharged 1.4 liter, 4 cylinder spark assisted diesel of 14:1 compression ratio. A compounding unit consisting of a Lysholm compressor and expander is connected to the engine crankshaft by a belt drive. The inlet air charge is heated by the expander exhaust gas via a heat exchanger. Four levels of technology achievement on the selected engine concept were evaluated, from state-of-the-art to the ideal case. This resulted in the fuel economy increasing from 53.2 mpg to 81.7 mpg, and the 0-60 mph time decreasing from 17.6 seconds to 10.9 seconds.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Cummins Engine Co., Inc. Advan. Automotive Diesel Assessment Program; 18 p
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  • 16
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    A study of the Armstrong Whitworth swing beam engine for automotive application (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The introduction of ceramics to those parts suffering high thermal loading was successfully demonstrated, and there is no question that the 100 kw (134 hp) naturally aspirated engine of the future will be developed to produce up to 300 kw (402 hp) by the application of turbocharging or its equivalent. However, at the 60 - 80 kw (80 - 107 hp) size needed for the economic automotive engine, scaling down the 300 kw (402 hp) is beset by the laws of scale. The conventional four stroke diesel was not shown to be successful at the small high speed engine size. The opposed piston two stroke engine does not suffer the same laws of scale and engines in the low power range have already been marketed successfully. The half liter/cylinder Armstrong Whitworth Swing Beam Engine is the latest to be designed with the automotive market in mind. Its low noise structure and balanced linkage system coupled with advantages for easy start and potential use of low grade fuels, derived from its variable compression ratio and slow piston motion, qualifies it for the application.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Cummins Engine Co., Inc. Advan. Automotive Diesel Assessment Program; 3 p
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  • 17
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    Roller crosshead analysis (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: An analysis of the frictional behavior of a roller crosshead configuration is given. This configuration consists of a piston which carries at the wristpin position a roller of large diameter which can roll on the cylinder liner surfaces. A preliminary assessment is given of whether the roller can roll on the cylinder liner without skidding, and what, if any, are the tribological implications of this approach to a dry lubricated design. The rotational speed of the roller must change during the stroke if it is not to slip on the cylinder liner. The maximum value of angular acceleration occurs at top dead center and bottom dead center. If the traction force on the rim of the roller, which is the product of the normal force due to piston side load and the coefficient of friction, is not sufficient to drive the roller through the necessary angular acceleration, sliding will occur. At 1,000 rpm, it appears that there will be a definite area of slip near each end of the stroke. The length of the area of slip may be of the order of 1/8 inch at each of these points.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Advan. Automotive Diesel Assessment Program; 9 p
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  • 18
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    Advanced Automotive Diesel Assessment Program, executive summary (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The objectives of this analytical study were: to select one advanced automotive diesel engine (AAD) concept which would increase the tank mileage of a 3,000 pound passenger car from the present 35 mpg to at least 52 mpg; to identify long term component research and development work required to bring the selected concept to fruition; and to prepare a development strategy that will bring the selected concept to a prototype testing phase. Cummins Engine Company has completed this study. The selected concept is a 4 stroke cycle, direct injection, spark assisted, advanced adiabatic diesel engine with positive displacement compounding plus expander and part load air preheating. The engine does not use a liquid coolant nor liquid lubricants. It is a 4 cylinder, in-line, 77 mm bore x 77 mm stroke, 1.434 liters displacement engine weighing 300 lb, and rated at 70 BHP at 3000 rpm. Installation dimensions are 621 mm length x 589 mm width x 479 mm height (24.4 inch x 22 inch x 18.9 inch).
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Advan. Automotive Diesel Assessment Program p; 59 p
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  • 19
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    Detailed performance analysis of the A.A.D. - concept B (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: New concepts for engine performance improvement are seen through the adoption of heat regeneration techniques; advanced methods to enhance the combustion; and higher efficiency air handling machinery, such as the positive displacement helical screw expander and compressor. Each of these concepts plays a particular role in engine performance improvement. First regeneration has a great potential for achieving higher engine thermal efficiency through the recovery of waste energy. Although the concept itself is not new (this technique is used in the gas turbine), the application to reciprocating internal combustion engines is quite unusual and presents conceptual difficulties. The second important area is better control of the combustion process in terms of heat transfer characteristics, combustion products, and heat release rate. The third area for performance improvement is in the adoption of high efficiency air handling machinery. In particular, positive displacement helical expander and compressor exhibit an extremely high efficiency over a wide range of operating conditions.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Advan. Automotive Diesel Assessment Program; 46 p
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  • 20
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    NASA transmission research and its probable effects on helicopter transmission design (1984)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Transmissions studied for application to helicopters in addition to the more conventional geared transmissions include hybrid (traction/gear), bearingless planetary, and split torque transmissions. Research is being performed to establish the validity of analysis and computer codes developed to predict the performance, efficiency, life, and reliability of these transmissions. Results of this research should provide the transmission designer with analytical tools to design for minimum weight and noise with maximum life and efficiency. In addition, the advantages and limitations of drive systems as well as the more conventional systems will be defined.
    Schlagwort(e): MECHANICAL ENGINEERING
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  • 21
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    Feasibility analysis of a spiral groove ring seal for counter-rotating shafts (1984)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Journal of Aircraft (ISSN 0021-8669); 21; 618-622
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  • 22
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    Pivoting and slip in an angular contact bearing (1984)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Pivoting slips are calculated for the ball-race and ball-ball contacts in a retainerless bearing. The calculation is kinematic, ignoring all inertial loadings. Pure spin and uniform precession of the balls are considered. Pivoting slip magnitudes are compared with several other kinds of slip which were previously reported in an R4 size bearing. Previously announced in STAR as N83-26079
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: ASLE Transactions; 27; 259-262
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  • 23
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    Elastic model of the traction behavior of two traction lubricants (1984)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: In the analysis of rolling-sliding concentrated contacts, such as gears, bearings and traction drives, the traction characteristics of the lubricant are of prime importance. The elastic shear modulus and limiting shear stress properties of the lubricant dictate the traction/slip characteristics and power loss associated with an EHD contact undergoing slip and/or spin. These properties can be deducted directly from the initial slope m and maximum traction coefficient micron of an experimental traction curve. In this investigation, correlation equations are presented to predict m and micron for two modern traction fluids based on the regression analysis of 334 separate traction disk machine experiments. The effects of contact pressure, temperature, surface velocity, ellipticity ratio are examined. Problems in deducing lubricant shear moduli from disk machine tests are discussed. Previously announced in STAR as N83-20116
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: ASLE Transactions; 27; 129-137;
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  • 24
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    Practical small-scale explosive seam welding (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: A small-scale explosive seam welding process has been developed that can significantly contribute to remote metal joining operations under hazardous or inaccessible conditions, such as nuclear reactor repair and assembly of structure in space. This paper describes this explosive seam welding process in terms of joining principles, variables, types of joints created, capabilities, and applications. Very small quantities of explosive in a ribbon configuration are used to create narrow (less than 0.5 inch), long-length, uniform, hermetically sealed joints that exhibit parent metal properties in a wide variety of metals, alloys, and combinations. The practicality of this process has been demonstrated by its current acceptance, as well as its capabilities that are superior in many applications to the universally accepted joining processes, such as mechanical fasteners, fusion and resistance welding, and adhesives. Previously announced in STAR as N83-24896
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: (ISSN 0025-6501)
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  • 25
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    Dynamic stiffness characteristics of high eccentricity ratio bearings and seals by perturbation testing (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The complex behavior of cylindrical bearings and seals that are statically loaded to eccentricities in excess of 0.7 are examined. The stiffness algorithms as a function of static load are developed from perturbation methodology by empirical modeling.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 481-501
    Format: application/pdf
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  • 26
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    Damping capacity of a sealed squeeze film bearing (1984)
    In:  CASI
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    Publikationsdatum: 2016-06-07
    Beschreibung: The advantages of incorporating an open-ended or weakly-sealed squeeze-film bearing in a flexible support structure simulating an aero-engine assembly were examined. Attention is given to empirically modelling the hydrodynamics of the more usual tightly-sealed squeeze-film bearing, with a view to assessing its damping performance.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 407-428
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  • 27
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    Influence of stationary components on unsteady flow in industrial centrifugal compressors (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: An experimental investigation was performed to determine the characteristics of the onset and the growth of rotating nonuniform flow in a standard low specific speed stage, normally utilized in high pressure applications, in relation to change of stationary component geometry. Four configurations, differing only in the return channel and crossover geometry were tested on an atmospheric pressure open loop test rig. Experimental results make conspicious the effect of return channel geometry and give the possibility of shifting the unstable zone onset varying such geometry. An attempt was made to interpret the experimental results in the Emmons - Stenning's rotating stall theory.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 429-480
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  • 28
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    Squeeze-film dampers for turbomachinery stabilization (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: A technique for investigating the stability and damping present in centrally preloaded radially symmetric multi-mass flexible rotor bearing systems is presented. In general, one needs to find the eigenvalues of the linearized perturbation equations, though zero frequency stability maps may be found by solving as many simultaneous non-linear equations as there are dampers; and in the case of a single damper, such maps may be found directly, regardless of the number of degrees of freedom. The technique is illustrated for a simple symmetric four degree of freedom flexible rotor with an unpressurized damper. This example shows that whereas zero frequency stability maps are likely to prove to be a simple way to delineate multiple solution possibilities, they do not provide full stability information. Further, particularly for low bearing parameters, the introduction of an unpressurized squeeze film damper may promote instability in an otherwise stable system.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 391-406
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  • 29
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    Design of electromagnetic bearing for vibration control of flexible transmission shaft (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: Recently magnetic bearings were proposed by several researchers and shown to be viable on a variety of rotor assemblies. The design and construction of such a bearing, which employs features hitherto not used by other workers is examined. These include an original approach to the design of the electromagnets and their amplifiers, and to software in a digital control system, to condition the control signals so as to make the magnets appear to be linear and uncoupled. The resulting system is used to control a rotor-bearing assembly, whose speed range covers two flexural-critical speeds.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 351-364
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  • 30
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    Effects of fluid inertia and turbulence on force coefficients for squeeze film dampers (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The effects of fluid inertia and turbulence on the force coefficients of squeeze film dampers are investigated analytically. Both the convective and the temporal terms are included in the analysis of inertia effects. The analysis of turbulence is based on friction coefficients currently found in the literature for Poiseuille flow. The effect of fluid inertia on the magnitude of the radial direct inertia coefficient (i.e., to produce an apparent added mass at small eccentricity ratios, due to the temporal terms) is found to be completely reversed at large eccentricity ratios. The reversal is due entirely to the inclusion of the convective inertia terms in the analysis. Turbulence is found to produce a large effect on the direct damping coefficient at high eccentricity ratios. For the long or sealed squeeze film damper at high eccentricity ratios, the damping prediction with turbulence included is an order of magnitude higher than the laminar solution.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 365-390
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  • 31
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    Analysis for leakage and rotordynamic coefficients of surface roughened tapered annular gas seals (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: In order to soften the effects of rub, the smooth stators of turbine gas seals are sometimes replaced by a honeycomb surface. This deliberately roughened stator and smooth rotor combination retards the seal leakage and may lead to enhanced rotor stability. However, many factors determine the rotordynamic coefficients and little is known as to the effectiveness of these honeycomb seals under various changes in the independent seal parameters. An analytical-computational method to solve for the rotordynamic coefficients of this type of compressible-flow seal is developed. The governing equations for surface roughned tapered annular gas seals are based on a modified Hirs' turbulent bulk flow model. A perturbation analysis is employed to develop zeroth and first-order perturbation equations. These equations are numerically integrated to solve for the leakage, pressure, density, and velocity for small motion of the shaft about the centered position. The resulting pressure distribution is then integrated to find the corresponding rotor-dynamic coefficients.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 341-350
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  • 32
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    Analysis and testing for rotordynamic coefficients of turbulent annular seals with different, directionally homogeneous surface-roughness treatment for rotor and stator elements (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: A theory is presented, based on a simple modification of Hirs' turbulent lubrication equations, to account for different but directionally-homogeneous surface roughness treatments for the rotor and stator of annular seals. The theoretical results agree with von Pragenau's predictions that a damper seal which uses a smooth rotor and a rough stator yields more net damping than a conventional seal which has the same roughness for both the rotor and stator. Experimental results for four stators confirm that properly-designed roughened stators yield higher net damping values and substantially less leakage than seals with smooth surfaces. The best seal from both damping and leakage viewpoints uses a round-hole-pattern stator. Initial results for this stator suggest that, within limits, seals can be designed to yield specified ratios of stiffness to damping.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 313-340
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  • 33
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    Identification of dynamic coefficients of annular turbulent seals (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: An identification procedure to determine dynamic coefficients of annular turbulent seals in turbopumps is presented. Measurements were carried out at a built test rig with two symmetrical arranged seals. A rigid rotating shaft is surrounded by an elastically supported housing, which is excited by impact forces. The relative radial motion between the rotating parts and the housing, respectively between the seal surfaces, is measured by displacement pick-ups and from the time signals complex frequency response functions can be calculated. Finally an analytical model, depending on the seal parameters, is fitted to the measured data, to find the dynamic coefficients.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 295-312
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  • 34
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    Preliminary investigation of labyrinth packing pressure drops at onset of swirl-induced rotor instability (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: Backward and forward subsynchronous instability was observed in a flexible model test rotor under the influence of swirl flow in a straight-through labyrinth packing. The packing pressure drop at the onset of instability was then measured for a range of operating speeds, clearances and inlet swirl conditions. The trend in these measurements for forward swirl and forward instability is generally consistent with the short packing rotor force formulations of Benchert and Wachter. Diverging clearances were also destabilizing and had a forward orbit with forward swirl and a backward orbit with reverse swirl. A larger, stiff rotor model system is now being assembled which will permit testing steam turbine-type straight-through and hi-lo labyrinth packings. With calibrated and adjustable bearings in this new apparatus, direct measure of the net destabilizing force generated by the packings can be made.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 281-294
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  • 35
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    An iwatsubo-based solution for labyrinth seals - comparison with experimental results (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The basic equations are derived for compressible flow in a labyrinth seal. The flow is assumed to be completely turbulent in the circumferential direction where the friction factor is determined by the Blasius relation. Linearized zeroth and first-order perturbation equations are developed for small motion about a centered position by an expansion in the eccentricity ratio. The zeroth-order pressure distribution is found by satisfying the leakage equation while the circumferential velocity distribution is determined by satisfying the momentum equation. The first-order equations are solved by a separation of variables solution. Integration of the resultant pressure distribution along and around the seal defines the reaction force developed by the seal and the corresponding dynamic coefficients. The results of this analysis are compared to published test results.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 257-280
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  • 36
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    Prediction of force coefficients for labyrinth seals (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The development of a linear model for the prediction of labyrinth seal forces and on its comparison to available stiffness data is presented. A discussion of the relevance of fluid damping forces and the preliminary stages of a program to obtain data on these forces are examined. Fluid-dynamic forces arising from nonuniform pressure patterns in labyrinth seal glands are known to be potentially destablizing in high power turbomachinery. A well documented case in point is that of the space Shuttle Main Engine turbopumps. Seal forces are also an important factor for the stability of shrouded turbines, acting in that case in conjunction with the effects of blade-tip clearance variations.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 235-256
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  • 37
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    Analysis of dynamic characteristics of fluid force induced by labyrinth seal (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: Flow patterns of the labyrinth seal are experimentally investigated for making a mathematical model of labyrinth seal and to obtain the flow induced force of the seal. First, the flow patterns in the labyrinth chamber are studied on the circumferential flow using bubble and on the cross section of the seal chamber using aluminum powder as tracers. And next, the fluid force and its phase angle are obtained from the measured pressure distribution in the chamber and the fluid force coefficients are derived from the fluid force and the phase angle. Those are similar to the expression of oil film coefficients. As a result, it is found that the vortices exist in the labyrinth chambers and its center moves up and down periodically. The pressure drop is biggest in the first stage of chambers and next in the last stage of chambers.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 211-234
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  • 38
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    Experimental investigation of lateral forces induced by flow through model labyrinth glands (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The lateral forces induced by flow through model labyrinth glands were investigated. Circumferential pressure distributions, lateral forces and stiffness coefficients data obtained are discussed. The force system is represented as a negative spring and a tangential force orthogonal to eccentricity. The magnitude of these forces are dependent on eccentricity, entry swirl, rotor peripheral velocity and seal size. A pressure equalization chamber at midgland tests should in significantly reduced forces and stiffness coefficients.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 187-210
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  • 39
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    Theoretical approach to labyrinth seal forces - cross-coupled stiffness of a straight-through labyrinth seal (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: Two kinds of three dimensional flows in a labyrinth seal, a jet flow and a core flow, are considered and theoretical equations are set up concerning the motion of each flow. The pressure distribution within the labyrinth is calculated, when the rotor shaft makes a small displacement from the center line of the casing, keeping parallel with it. The theoretical values of cross coupled stiffness obtained by integrating the pressure under different labyrinth geometries and operating conditions through these formulas are compared with the experimental data.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 173-186
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  • 40
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    Two-dimensional unsteady analysis of fluid forces on a whirling centrifugal impeller in a volute (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: Destabilizing fluid forces on a whirling centrifugal impeller rotating in a volute were observed. A quasisteady analysis neglecting shed vorticity or an unsteady analysis without a volute does not predict the existence of such destabilizing fluid forces on a whirling impeller. The effects of a volute and the shed vorticity are considered. We treat cases when an impeller with an infinite number of vanes rotates with a constant velocity omega and its center whirls with a constant eccentric radius epsilon and a constant whirling velocity psi. It is assumed that: (1) the number of the vanes is so large that the impeller can be treated as an actuator impeller in which the flow is perfectly guided; (2) flow is inviscid, incompressible and two dimensional; (3) the eccentricity epsilon is so small that unsteady components can be linearized; (4) vorticity is transported on a prescribed mean flow, the operating point is near design flow rate; and (5) the volute can be represented by a curved plate.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 161-172
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  • 41
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    Hydrodynamic impeller stiffness, damping, and inertia in the rotordynamics of centrifugal flow pumps (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The lateral hydrodynamic forces experienced by a centrifugal pump impeller performing circular whirl motions within several volute geometries were measured. The lateral forces were decomposed into: (1) time averaged lateral forces and (2) hydrodynamic force matrices representing the variation of the lateral forces with position of the impeller center. It is found that these force matrices essentially consist of equal diagonal terms and skew symmetric off diagonal terms. One consequence of this is that during its whirl motion the impeller experiences forces acting normal and tangential to the locus of whirl. Data on these normal and tangential forces are presented; it is shown that there exists a region of positive reduced whirl frequencies, within which the hydrodynamic forces can be destablizing with respect to whirl.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 137-160
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  • 42
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    Hydraulic forces on a centrifugal impeller undergoing synchronous whirl (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: High speed centrifugal rotating machinery with large vibrations caused by aerodynamic forces on impellers was examined. A method to calculate forces in a two dimensional orbiting impeller in an unbounded fluid with nonuniform entering flow was developed. A finite element model of the full impeller is employed to solve the inviscid flow equations. Five forces acting on the impeller are: Coriolis forces, centripetal forces, changes in linear momentum, changes in pressure due to rotation and pressure changes due to linear momentum. Both principal and cross coupled stiffness coefficients are calculated for the impeller.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 123-136
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  • 43
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    Lateral fluid forces acting on a whirling centrifugal impeller in vaneless and vaned diffuser (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: Fluid forces on a rotating centrifugal impeller in whirling motion were studied. A two dimensional impeller installed in a parallel-walled vaneless and vaned diffuser whirled on a circular orbit with various positive and negative angular velocities. It is shown that the fluid forces exert a damping effect on the rotor in most operating conditions, but become excitatory when the impeller operates at very low partial discharge while rotating far faster than the whirl speed. The fluid forces were expressed in terms of mass, damping and stiffness matrices. Impellers with the same geometry and whirl condition are calculated. Quantitative agreement is obtained especially in positive whirl.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 109-122
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  • 44
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    Internal hysteresis experienced on a high pressure syn gas compressor (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: A vibration instability phenomenon experienced in operating high pressure syn gas centrifugal compressors in two ammonia plants is described. The compressors were monitored by orbit and spectrum analysis for changes from baseline readings. It is found that internal hysteresis was the major destabilizing force; however, the problem was further complicated by seal lockup at the suction end of the compressor. A coupling lockup problem and a coupling fit problem, which frettage of the shaft, are also considered as contributors to the self excited vibrations.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Rotordynamic Instability Problems in High-Performance Turbomachinery; p 97-108
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  • 45
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    Experimental on-stream elimination of resonant whirl in a large centrifugal compressor (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: Resonant whirl condition during operation of a multi-stage centrifugal compressor at higher than anticipated speeds and loads was reported. The condition was diagnosed by a large scale computerized Machinery Condition Monitoring System (MACMOS). This computerized system verified that the predominant subsynchronous whirl frequency locked in on the first resonant frequency of the compressor rotor and did not vary with compressor speed. Compressor stability calculations showed the rotor system had excessive hearing stiffness and inadequate effective damping. An optimum bearing design which was developed to minimize the unbalance response and to maximize the stability threshold is presented.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 81-95
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  • 46
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    Control of rotordynamic instability in a typical gas turbine's power system (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The effect of rotor internal friction on the system's stability was studied when operated above the first critical speed. This internal friction is commonly caused by sliding press fits or sliding splines. Under conditions of high speed and low bearing damping, these systems will occassionally whirl at a frequency less than the shaft's rotational speed. This subsynchronous precession is a self excited phenomenon and stress reversals are created. This phenomenon was observed during engine testing. The reduction of spline friction and/or the inclusion of squeeze film damping have controlled the instability. Case history and the detail design of the squeeze film dampers is discussed.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 53-80
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  • 47
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    Experiences with nonsynchronous forced vibration in centrifugal compressors (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The high subsynchronous vibrations which are often forced vibrations caused by flow instabilities, such as stage stall were examined. Modifications to improve the rotor stability by changing the bearings or seals have little effects on the subsynchronous vibrations. Understanding of the differences between forced vibrations and self excited vibrations to properly diagnose the problem and to correct it, is recommended. A list of characteristics of the two types of subsynchronous vibration is presented.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 37-52
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  • 48
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    Subsynchronous vibrations in a high pressure centrifugal compressor: A case history (1984)
    In:  CASI
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    Publikationsdatum: 2016-06-07
    Beschreibung: Two distinct aerodynamically excited vibrations in a high pressure low flow centrifugal compressor are documented. A measured vibration near 21% of running speed was identified as a nonresonant forced vibration which results from rotating stall in the diffuser; a measured vibration near 50% of running speed was identified as a self excited vibration sustained by cross coupling forces acting at the compressor wheels. The dependence of these characteristics on speed, discharge pressure, and changes in bearing design are shown. The exciting mechanisms of diffuser stall and aerodynamic cross coupling are evidenced. It is shown how the rotor characteristics are expected to change as a result of modifications. The operation of the compressor after the modifications is described.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 17-36
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  • 49
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    Full load testing in the platform module prior to tow-out: A case history of subsynchronous instability (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: An electric motor driven centrifugal compressor to supply gas for further compression and reinjection on a petroleum production platform in the North Sea was examined. The compressor design, raised concerns about susceptibility to subsynchronous instability. Log decrement, aerodynamic features, and the experience of other compressors with similar ratios of operating to critical speed ratio versus gas density led to the decision to full load test. Mixed hydrocarbon gas was chosen for the test to meet discharge temperature restrictions. The module was used as the test site. Subsynchronous vibrations made the compressor inoperable above approximately one-half the rated discharge pressure of 14500 kPa. Modifications, which includes shortening the bearing span, change of leakage inlet flow direction on the back to back labyrinth, and removal of the vaned diffusers on all stages were made simultaneously. The compressor is operating with satisfactory vibration levels.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 1-16
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  • 50
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    Structural Optimization in automotive design (1984)
    In:  CASI
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    Publikationsdatum: 2016-06-07
    Beschreibung: Although mathematical structural optimization has been an active research area for twenty years, there has been relatively little penetration into the design process. Experience indicates that often this is due to the traditional layout-analysis design process. In many cases, optimization efforts have been outgrowths of analysis groups which are themselves appendages to the traditional design process. As a result, optimization is often introduced into the design process too late to have a significant effect because many potential design variables have already been fixed. A series of examples are given to indicate how structural optimization has been effectively integrated into the design process.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Langley Research Center Recent Experiences in Multidisciplinary Analysis and Optimization, Part 1; 16 p
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  • 51
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    Inherent Problems in Designing Two-Failure Tolerant Electromechanical Actuators (1984)
    In:  CASI
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    Publikationsdatum: 2016-06-07
    Beschreibung: An electromechanical ac-powered rotary actuated four-bar linkage system for rotating the Shuttle/Centaur deployment adapter is described. The essential features of the deployment adapter rotation system (DARS) are increased reliability for mission success and maximum practical hazard control for safety. The requirements, concept development, hardware configuration, quality assurance provisions, and techniques used to meet two-fault tolerance requirements are highlighted. The rationale used to achieve a degree of safety equivalent of that of two-failure tolerance is presented. Conditions that make this approach acceptable, including single failure point components with regard to redundancy versus credibility of failure modes, are also discussed.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Goddard Space Flight Center The 18th Aerospace Mech. Symp.; p 155-170
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  • 52
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    Design and test of a low-temperature liner driver/rate controller (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The design and testing of a force/rate control device used to deploy an Earth shield on an orbiting satellite is described. Test experience, failure modes, and applications are emphasized.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: The 18th Aerospace Mech. Symp.; p 65-77
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  • 53
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    A passively controlled appendage deployment system for the San Marco D/L spacecraft (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The analytical simulation of deployment dynamics of these two axis concepts as well as the evolution of practical designs for the add on deployable inertia boom units is described. With the boom free to swing back in response to Coriolis forces as well as outwards in response to centrifugal forces, the kinematics of motion are complex but admit the possibility of absorbing deployment energy in frictional or other damping devices about the radial axis, where large amplitude motions can occur and where the design envelope allows more available volume. An acceptable range is defined for frictional damping for any given spin rate. Inadequate damping allows boom motions which strike the spacecraft; excessive damping causes the boom to swing out and latch with damaging violence. The acceptable range is a design parameter and must accommodate spin rate tolerance and also the tolerance and repeatability of the damping mechanisms.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: The 18th Aerospace Mech. Symp.; p 29-48
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  • 54
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    Evolution from a hinge actuator mechanism to an antenna deployment mechanism for use on the European large communications satellite (L-SAT/OLYMPUS) (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The evolution of an Antenna Deployment Mechanism (ADM) from a Hinge Actuator Mechanism (HAM) is described as it pertains to the deployment of large satellite antennas. Design analysis and mechanical tests are examined in detail.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Goddard Space Flight Center The 18th Aerospace Mech. Symp.; p 79-91
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    Unified Analysis for Antenna Pointing and Structural Errors. Part 1. Review (1983)
    In:  CASI
    Details
    Publikationsdatum: 2014-09-10
    Beschreibung: A necessary step in the design of a high accuracy microwave antenna system is to establish the signal error budget due to structural, pointing, and environmental parameters. A unified approach in performing error budget analysis as applicable to ground-based microwave antennas of different size and operating frequency is discussed. Major error sources contributing to the resultant deviation in antenna boresighting in pointing and tracking modes and the derivation of the governing equations are presented. Two computer programs (SAMCON and EBAP) were developed in-house, including the antenna servo-control program, as valuable tools in the error budget determination. A list of possible errors giving their relative contributions and levels is presented.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: The Telecommun. and Data Acquisition Rept.; p 40-59
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  • 56
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    Status of Understanding for Seal Materials (1984)
    In:  CASI
    Details
    Publikationsdatum: 2014-09-11
    Beschreibung: Material selection for mainshaft face and ring seals, labyrinth seals, accessory gearbox face seals, and lip seals are discussed in light of tribology requirements and a given seal application. Carbon graphite has been found to be one of the best sealing materials and it is widely used in current gas turbine mainshaft and accessory gearbox seals. Its popularity is due to its unique combination of properties which consists of dimensional stability, corrosion resistance, low friction, good self lubricating characteristics, high thermal conductivity and low thermal expansion, the latter two properties combining to provide good thermal shock resistance. A brief description of the seals and the requirements they must meet are discussed to provide insight into the limitations and advantages of the seals in containing the lubricant. A forecast is made of the operational requirements of main shaft and gearbox seals for advanced engines and candidate materials and coatings that may satisfy these advanced engine requirements.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA Lewis Research Center Tribology in the 80's, vol. 2; p 811-829
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  • 57
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    Status of Understanding for Gear Materials (1984)
    In:  CASI
    Details
    Publikationsdatum: 2014-09-11
    Beschreibung: A wide variety of gear materials is available today for the gear designer. The choice of which material to use should be based on the requirements of the application and will include the operating conditions of load, speed, and temperature in addition to reliability, weight, noise limitation, accuracy, and cost. In aircraft applications such as helicopters, V/STOL aircraft, and turboprops, the dominant factors to be considered are reliability and weight. The following gear materials are reviewed herein with an emphasis upon mechanical properties, cost, and durability: plastics, nonferrous metals, copper alloys, iron alloys, metal powders, and steels.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Tribology in the 80's, vol. 2; p 795-809
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  • 58
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    Sputtering as a Technique for Applying Tribological Coatings (1984)
    In:  CASI
    Details
    Publikationsdatum: 2014-09-11
    Beschreibung: Friction and wear-induced mechanical failures may be controlled to extend the life of tribological components through the interposition of selected solid materials between contacting surfaces. Thin solid films of soft and hard materials are appropriate to lower friction and enhance the wear resistance of precision tribo-elements. Tribological characteristics of thin hard coats deposited on a variety of ferrous and non-ferrous substrates were tested. The thin hard coats used were titanium nitride films deposited by reactive magnetron sputtering of metallic titanium. High contact stress, low speed tests showed wear rate reductions of one or more magnitude, even with films a few micrometers in thickness. Low contact stress, high speed tests carried out under rather severe test conditions showed that thin films of TiN afforded significant friction reduction and wear protection. Thin hard coats were shown to improve the friction and wear performance of rolling contacts. Satisfactory film-to-substrate adhesion strengths can be obtained with reactive magnetron sputtering. X-ray diffraction and microhardness tests were employed to assess the effectiveness of the sputtering technique.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA Lewis Research Center Tribology in the 80's, vol. 2; p 753-772
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    Micro-elastohydrodynamic Lubrication (1984)
    In:  CASI
    Details
    Publikationsdatum: 2014-09-11
    Beschreibung: Conventional elastohydrodynamics, which is based on assumption of smooth surfaces, is reviewed to show its insufficiency for explaining the failure processes in these contacts. For conditions approaching failure, lubrication breakdown occurs locally at asperity contacts where the lubrication behavior is controlled by microelastohydrodynamic lubrication (micro-EHL). The film formation mechanisms in micro-EHL conjunctions is described. The level of film thickness due to normal approach and sliding of a single asperity and due to asperity-asperity collision between two asperities is assessed. Possible influence of the micro-EHL to incipient scuffing failure, surface crack propagation and wear are discussed.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA Lewis Research Center Tribology in the 80's, vol. 2; p 615-639
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  • 60
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    Transient EHL Effects in Starved Ball Bearings (1984)
    In:  CASI
    Details
    Publikationsdatum: 2014-09-11
    Beschreibung: The independent variables used in most calculations for EHL film thickness in ball bearings involve lubricant properties, contact elasticity, load, and bearing kinematics. The calculations are for steady state, and they give a time constant film thickness. Four distinct processes in starved ball bearings which are explained by assuming a time varying film thickness are shown. The four processes and another transient EHL effect which does not involve the thickness of the film are described. A simple model allows direct calculation of several of the thickness transients.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA Lewis Research Center Tribology in the 80's, vol. 2; p 641-649
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  • 61
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    Real Surface Effects in Elastohydrodynamic Lubrication (1984)
    In:  CASI
    Details
    Publikationsdatum: 2014-09-11
    Beschreibung: The real effects in electrohydrodynamic lubrication (EHL,) are discussed and the role of stochastic roughness superimposed on the nominal solid boundaries is considered. The full film EHL regime where incipient asperity contact bears a negligible fraction of the load is analyzed. Flow, from which an averaged Reynolds equation can be formed, is nonetheless modified by the amplitude and texture of the roughness patterns. It is found that only two extra parameters are needed, the rms surface height and the ratio of the correlation lengths in the two principal roughness directions. In a lowest order perturbation expansion of these flow factors in powers of the ratio of rms roughness to nominal film thickness, no other properties of the roughness appear. The factors describing Poiseuille flow are separable into the sum of two single surface flow factors which means that a combination of a single equivalent rough surface versus an ideal smooth surface is found. For flow entrained by slip velocity the factors separate instead into a difference of single surface factors and it becomes significant which of the two surfaces carries the equivalent roughness. Applications of the averaged Reynolds equation based on the flow factor method to the EHL line contact problem are discussed. The partial EHL regime is considered where comparable load fractions are carried by the hydrodynamic film and by incipient mechanical contact. An extension of the method into this regime by combining it with asperity contact models appears most encouraging.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA Lewis Research Center Tribology in the 80's, vol. 2; p 595-614
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  • 62
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    Non-steady State Effects in EHL (1984)
    In:  CASI
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    Publikationsdatum: 2014-09-11
    Beschreibung: Lubricated machine elements are subjected to cyclic variations of load and speed, particularly in reciprocating machinery. Squeeze film action plays an important role in preserving satisfactory lubricating films in many cases in which the entraining velocities fall to zero during each cycle, as in the reciprocating seal and synovial joints. The essential features of combined entraining and normal motion for hydrodynamic and elastohydrodynamic conditions are described. It is shown that very small squeeze film velocities lead to substantial hydrodynamic action. A squeeze film lubrication between spheres or cylinders and a plane is reviewed by an analysis of ankle joint lubrication. It is shown that elastohydrodynamic lubrication might be encountered in the conjunction between a piston ring and cylinder liner and that combined entraining and squeeze film action is important. The 2 stroke Diesel engine shows that variations in squeeze film velocity throughout the conjunction, associated with time rates of change of elastic deformation, must be considered in a full elastohydrodynamic lubrication analysis.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA Lewis Research Center Tribology in the 80's, vol. 2; p 579-592
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    Lubricant Rheology in Concentrated Contacts (1984)
    In:  CASI
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    Publikationsdatum: 2014-09-11
    Beschreibung: Lubricant behavior in highly stressed situtations shows that a Newtonian model for lubricant rheology is insufficient for explanation of traction behavior. The oil film build up is predicted by using a Newtonian lubricant model except at high slide to roll ratios and at very high loads, where the nonNewtonian behavior starts to be important already outside the Hertzian contact area. Static and dynamic experiments are reported. In static experiments the pressure is applied to the lubricant more than a million times longer than in an EHD contact. Depending on the pressure-temperature history of the experiment the lubricant will become a crystallized or amorphous solid at high pressures. In dynamic experiments, the oil is in an amorphous solid state. Depending on the viscosity, time scale, elasticity of the oil and the bearing surfaces, the oil film pressure, shear strain rate and the type of lubricant, different properties of the oil are important for prediction of shear stresses in the oil. The different proposed models for the lubricant, which describe it to a Newtonian liquid, an elastic liquid, a plastic liquid and an elastic-plastic solid.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA Lewis Research Center Tribology in the 80's, vol. 2; p 555-572
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    Elastohydrodynamic Lubrication. Status of Understanding (1984)
    In:  CASI
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    Publikationsdatum: 2014-09-11
    Beschreibung: The development of elastohydrodynamic lubrication which was divided into three main stages is discussed. The first stage is the development of the idealized form of elastohydrodynamic lubrication, where the surfaces are smooth, the fluid behavior is assumed to be Newtonian, and isothermal considerations are assumed. The complete spectrum of contact geometries contact materials and lubricant availability are presented. The second state of development incorporates the effects of a nonNewtonian fluid model, thermal effects, and surface roughness effects into the elastohydrodynamic lubrication model developed in stage one. Recent developments in this stage are presented. The third stage considers the items considered in stage two, the lubrication of real surfaces in their operating environments is examined.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Tribology in the 80's, vol. 2; p 507-531
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    Temperature Effects in Elastohydrodynamically Lubricated Contacts (1984)
    In:  CASI
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    Publikationsdatum: 2014-09-11
    Beschreibung: Thermal phenomena in elastohydrodynamic contacts are reviewed. Measured temperatures are presented for representative conditions and ranges of operating parameters. Temperatures can range from bulk ambient temperature to several hundred degrees centigrade in fully separated elastohydrodynamic films. The mixed elastohydrodynamic films are outlined. These mixed conditions are common in tribological systems and conditions that border on unsuccessful run-in and failure of the elastohydrodynamic contact. In mixed film conditions local hot spots can have temperatures of the order of 1000 C which cause increased reactivity of the surfaces with surrounding materials and changes of the surface physical properties so important to the operation of concentrated contacts. The bulk system thermal transients which occur in tribological systems is discussed. These transients are frequently long in duration and have a direct bearing on the elastohydrodynamic film thickness and traction.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA Lewis Research Center Tribology in the 80's, vol. 2; p 533-548
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    Antiwear Additive Mechanisms in Sliding Contacts (1984)
    In:  CASI
    Details
    Publikationsdatum: 2014-09-11
    Beschreibung: The possible mechanisms associated with wear in a sliding contact and how an oil and antiwear additive can mitigate wear or prevent catastropic seizure of the contacting parts was examined. The various load and temperature regimes are examined and the mechanisms which are predominant under these conditions are determined. The critical mechanism(s) depend on the test parameters, particularly load and temperature, although sliding speed is also a factor. Different ways to improve the efficiency of antiwear additives are suggested.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA Lewis Research Center Tribology in the 80's. Vol. 1; p 391-413
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    Considerations in Friction and Wear (1984)
    In:  CASI
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    Publikationsdatum: 2014-09-11
    Beschreibung: The abrasion of ceramic materials is discussed. The friction and wear properties of ceramics which arise primarily from adhesion between sliding surfaces in contact was examined. The role of chemical bonding in adhesion and friction and the influence of surface films, temperature, and crystallographic orientation effects on tribological response with respect to adhesion, friction, and wear are discussed. The complex interaction of various deformation and fracture mechanisms in ceramics, the effect of crystallographic orientation on abrasion, friction, and fracture behavior is addressed.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Tribology in the 80's. Vol. 1; p 291-320
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    Importance of Properties of Solids to Friction and Wear Behaviour (1984)
    In:  CASI
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    Publikationsdatum: 2014-09-11
    Beschreibung: The main properties of solids which influence friction and wear are discussed and published rules which relate material properties to friction and wear are considered. In addition, recent experimental results on the tribological behaviour of metals and polymers illustrating the effect of some important interaction characteristics on friction and wear are presented. Finally, a framework for the systematic compilation and documentation of relevant tribological parameters in experimental friction and wear investigations is given.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA Lewis Research Center Tribology in the 80's. Vol. 1; p 71-106
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    Future Directions of Research in Adhesion and Friction. Status of Understanding (1984)
    In:  CASI
    Details
    Publikationsdatum: 2014-09-11
    Beschreibung: Four main classes of materials are covered: metals, ceramics, elastomers and polymers. In dealing with adhesion a distinction is drawn between adhesion (which often involves thermodynamic concepts) and the observed adhesive strength, here designated as the pull-off force. With metals the level of understanding of the interfacial bond is well understood theoretically and was elegantly studied experimentally. However the role of surface roughness and especially ductility needs to be incorporated into an overall view of metallic adhesion. The effect of contaminant films has not gone far beyond purely descriptive language. The friction of metals is understood in terms of surface topography, adhesion and deformation and there are now promising solutions using slipline-field theory. These do not however, cope very satisfactorily with work hardening. For surfaces sliding at higher speeds there are now good models which deal with asperity instabilities produced by frictional heating.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA Lewis Research Center Tribology in the 80's. Vol. 1; p 119-139
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  • 70
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    Ferrographic and spectrometer oil analysis from a failed gas turbine engine (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: An experimental gas turbine engine was destroyed as a result of the combustion of its titanium components. It was concluded that a severe surge may have caused interference between rotating and stationary compressor parts that either directly or indirectly ignited the titanium components. Several engine oil samples (before and after the failure) were analyzed with a Ferrograph, and with plasma, atomic absorption, and emission spectrometers to see if this information would aid in the engine failure diagnosis. The analyses indicated that a lubrication system failure was not a causative factor in the engine failure. Neither an abnormal wear mechanism nor a high level of wear debris was detected in the engine oil sample taken just prior to the test in which the failure occurred. However, low concentrations (0.2 to 0.5 ppm) of titanium were evident in this sample and samples taken earlier. After the failure, higher titanium concentrations (2 ppm) were detected in oil samples taken from different engine locations. Ferrographic analysis indicated that most of the titanium was contained in spherical metallic debris after the failure. The oil analyses eliminated a lubrication system bearing or shaft seal failure as the cause of the engine failure. Previously announced in STAR as N83-12433
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Wear (ISSN 0043-1648); 90; 239-249
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    Metal shell technology (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Metallic shells are fabricated for a size range from several millimeters down to less than 500 microns in diameter. The technology, developed at JPL, is based on the hollow-jet instability for the large-shell formation, and in addition, on the Bernoulli's force for the microbubble generation. Various materials were processed into hollow spheres, such as AL1100, tin, lead, and a metallic glass-forming alloy, AuPbSb. They exhibited a range of contrasting solidification behaviors and surface characteristics. Some of their potential applications will be explored in this paper.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: SAMPE Journal (ISSN 0091-1062); 19; 7-11
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  • 72
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    Thermodynamic analysis of journal bearings operating under steady state loading in laminar regime (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Thermohydrodynamic effects in journal bearings operating under steady load in laminar regime are investigated. An analytical model for the finite and infinitely long journal bearings is formulated. The model includes correction factors for the cavitation effects in the unloaded region of the bearing and the mixing of the recirculating oil and supply oil at the oil inlet. A finite difference computer program is developed to numerically solve the governing equations of the continuity, Reynolds, energy, Laplace heat conduction, and a viscosity-temperature relation simultaneously. The program includes a numerical technique for obtaining an isothermal shaft temperature. The numerical results of temperature distribution and the heat effects on the bearing load carrying capacity agree closely with those of experimental findings. Several different sets of simpler boundary conditions for the energy equation are studied.
    Schlagwort(e): MECHANICAL ENGINEERING
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  • 73
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    Frictional and morphological properties of Au-MoS2 films sputtered from a compact target (1984)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: AuMoS2 films 0.02 to 1.2 microns thick were sputtered from target compacted from 5 wt pct. Au + 95 wt pct. MoS2, to investigate the frictional and morphological film growth characteristics. The gold dispersion effects in MoS2 films are of interest to increase the densitification and strengthening of the film structure. Three microstructural growth stages were identified on the nano-micro-macrostructural level. During sliding both sputtered Au-MoS2 and MoS2 films have a tendency to break within the columner region. The remaining or effective film, about 0.2 microns thick, performs the lubrication. The Au-MoS2 films displayed a lower friction coefficient with a high degree of frictional stability and less wear debris generation as compared to pure MoS2 films. The more favorable frictional characteristics of the Au-MoS2 films are attributed to the effective film thickness and the high density packed columner zone which has a reduced effect on the fragmentation of the tapered crystallites during fracture.
    Schlagwort(e): MECHANICAL ENGINEERING
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  • 74
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    Substrate heating rates for planar and cylindrical-post magnetron sputtering sources (1984)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Results are presented for the substrate heating energy/atom required in the planar magnetron sputtering of Al, Cr, Ni, Cu, Mo, In, Ta, W, and Pt in Ar, as well as Al and Cr in O2. Data are also obtained for cylindrical magnetron sputtering of Nb, Ag, Ta, W, and Pb-Sn in Ar, and Mo sputtered in Ne, Ar, Kr, and Xe. Planar and cylindrical magnetron heating rates were comparable. Special experiments were conducted to examine the contributions to substrate heating of plasma species and ion neutralization and reflection at the cathode; the results obtained indicate that charged plasma species do not significantly contribute to the heating, but that neutralized and reflected ions play a significant role in the planar as well as cylindrical cases despite the differences in cathode geometry.
    Schlagwort(e): MECHANICAL ENGINEERING
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  • 75
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    The influence of surface dents and grooves on traction in sliding EHD point contacts (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Changes in traction, caused by dents and grooves on a highly polished ball, are investigated as these defects approach and go through sliding elastohydrodynamic point contacts. The contacts are formed with the ball loading against a transparent disk. The ball and thus the topographical features are held stationary at various locations in the vicinity and within the contact while the disk is rotating. These topographical features can cause substantial changes in the traction when compared to traction obtained with smooth surfaces. Previously announced in STAR as N82-32734
    Schlagwort(e): MECHANICAL ENGINEERING
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  • 76
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    Plastic deformation and wear process at a surface during unlubricated sliding (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The plastic deformation and wear of a 304 stainless steel surface sliding against an aluminum oxide rider with a spherical surface (the radius of curvature: 1.3 cm) were observed by using scanning electron and optical microscopes. Experiments were conducted in a vacuum of one million Pa and in an environment of fifty thousandth Pa of chlorine gas at 25 C. The load was 500 grams and the sliding velocity was 0.5 centimeter per second. The deformed surface layer which accumulates and develops successively is left behind the rider, and step shaped proturbances are developed even after single pass sliding under both environmental conditions. A fully developed surface layer is gradually torn off leaving a characteristic pattern. The mechanism for tearing away of the surface layer from the contact area and sliding track contour is explained assuming the simplified process of material removal based on the adhesion theory for the wear of materials. Previously announced in STAR as N82-32735
    Schlagwort(e): MECHANICAL ENGINEERING
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    Vibration of a hydrostatic gas bearing due to supply pressure oscillations (1984)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The vibration of a statically loaded, inherently compensated hydrostatic journal bearing due to oscillating supply pressure is investigated. Both angular and radial vibration modes are analyzed. The time-dependent Reynolds equation governing the pressure distribution between the oscillating journal and the sleeve is solved numerically together with the journal equation of motion to obtain the response characteristics of the bearing. The Reynolds equation and the equation of motion are simplified by applying regular perturbation theory for small displacements. The results presented include Bode plots of bearing oscillation gain and phase for a particular bearing configuration for various combinations of parameters over a range of frequencies, including the resonant frequency. The results are compared with the results of an earlier study involving the response of a similar bearing to oscillating exhaust pressure.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Wear (ISSN 0043-1648); 95; 199-212
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  • 78
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    Formation and destruction of vortices in a motored four-stroke piston-cylinder configuration (1984)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Previously cited in issue 05, p. 652, Accession no. A83-16749
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: AIAA Journal (ISSN 0001-1452); 22; 948
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    Dynamic characteristics of a hydrostatic gas bearing driven by oscillating exhaust pressure (1984)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Vibration of a statically loaded, inherently compensated hydrostatic journal bearing due to oscillating exhaust pressure is investigated. Both angular and radial vibration modes are analyzed. The time-dependent Reynolds equation governing the pressure distribution between the oscillating journal and sleeve is solved together with the journal equation of motion to obtain the response characteristics of the bearing. The Reynolds equation and the equation of motion are simplified by applying regular perturbation theory for small displacements. The numerical solutions of the perturbation equations are obtained by discretizing the pressure field using finite-difference aproximations with a discrete, nonuniform line-source model which excludes effects due to feeding hole volume. An iterative scheme is used to simultaneously satisfy the equations of motion for the journal. The results presented include Bode plots of bearing-oscillation gain and phase for a particular bearing configuration for various combinations of parameters over a range of frequencies, including the resonant frequency.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: ASME, Transactions, Journal of Tribology (ISSN 0742-4787); 106; 477-483
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    A device for applying plastic film antireflection coatings to optical elements (1984)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-19
    Beschreibung: To simplify the process of thermally bonding thin plastic films to optical elements and to help eliminate the source of the flaws, a film-application device (FAD) is developed. Any plastic film may be used to make the coatings, but thin polyethylene is particularly useful for this application since it is readily available. If more than one layer of polyethylene is required, several layers may be applied, one layer at a time. The coatings may be used for protecting optical elements or to reduce surface reflection of radiation with wavelengths greater than 20 microns. When the FAD is used without the central plate it may be used to stretch single sheets of plastic material to make pellicles or beam-splitters for many applications.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Infrared Physics (ISSN 0020-0891); 24; 567-569
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  • 81
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    Frictional and morphological properties of Au-MoS2 films sputtered from a compact target (1984)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-19
    Beschreibung: AuMoS2 films 0.02 to 1.2 microns thick were sputtered from target compacted from 5 wt percent Au + 95 wt percent MoS2, to investigate the frictional and morphological film growth characteristics. The gold dispersion effects in MoS2 films are of interest to increase the densification and strengthening of the film structure. Three microstructural growth stages were identified on the nano-micro-macrostructural level. During sliding both sputtered Au-MoS2 and MoS2 films have a tendency to break within the columner region. The remaining or effective film, about 0.2 microns thick, performs the lubrication. The Au-MoS2 films displayed a lower friction coefficient with a high degree of frictional stability and less wear debris generation as compared to pure MoS2 films. The more favorable frictional characteristics of the Au-MoS2 films are attributed to the effective film thickness and the high density packed columner zone which has a reduced effect on the fragmentation of the tapered crystallites during fracture.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Thin Solid Films (ISSN 0040-6090); 118; 375-384
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  • 82
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    Elastohydrodynamic lubrication of line contacts (1984)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-19
    Beschreibung: An isothermal elastohydrodynamically lubricated rectangular contact was evaluated numerically. This required the simultaneous solution of the elasticity and Reynolds equations. In the elasticity analysis the contact zone was divided into equal rectangular areas, and it was assumed that a uniform pressure was applied over each area. The elastohydrodynamic lubrication theory thus developed was used to investigate the influence of the dimensionless speed, load, and materials parameters on minimum film thickness. Ten cases were used in obtaining the minimum film thickness formula. Plots are shown that indicate the details of the pressure distribution, film shape, and flow. The characteristic pressure spike is clearly in evidence as is the parallel film shape through the central portion of the contact, with a minimum film thickness occurring near the outlet of the contact.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: ASLE Transactions; 27; 275-286;
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  • 83
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    Two-region analysis of interface shape in continuous casting with superheated liquid (1984)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-18
    Beschreibung: A slab ingot is being formed as a continuous casting by withdrawal from a mold with parallel walls. The sides of the ingot below the mold are cooled to remove heat of fusion and energy transferred to the solidification interface by superheated liquid metal in the mold. A two-region analysis is made to determine the non-uniform heat conduction from the liquid metal to the interface, and then from the interface to the cooled ingot sides. The solidification interface shape is found that is compatible with the removal of fusion energy and nonuniform heating from the liquid. The solution is obtained by two applications of a Cauchy boundary value method.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: ASME, Transactions, Journal of Heat Transfer (ISSN 0022-1481); 106; 506-511
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  • 84
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    Overview of Advanced Stirling and Gas Turbine Engine Development Programs and Implications for Solar Thermal Electrical Applications (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The DOE automotive advanced engine development projects managed by the NASA Lewis Research Center were described. These included one Stirling cycle engine development and two air Brayton cycle development. Other engine research activities included: (1) an air Brayton engine development sponsored by the Gas Research Institute, and (2) plans for development of a Stirling cycle engine for space use. Current and potential use of these various engines with solar parabolic dishes were discussed.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: JPL Proc. of the 5th Parabolic Dish Solar Thermal Power Program; p 49
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  • 85
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    Design of a precision etalon position control system for a cryogenic spectrometer (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The Upper Atmosphere Research Satellite (UARS) will be launched in 1988 to study the distribution of a series of trace elements in the upper atmosphere and to study atmospheric dynamics. The UARS carries on board a cryogenically cooled infrared spectrometer to measure the concentration of a series of chemical species that are important for understanding the ozone layer in the stratosphere. This device, known as the Cryogenic Limb Array Etalon Spectrometer (CLAES), uses a multiposition filter wheel combined with tilt-scanned Fabry Perot etalons to obtain the high resolution required for these experiments. The CLAES optical system is sealed in a dewar where it is maintained at cryogenic temperatures by a supply of solid hydrogen. Operating temperatures for CLAES range from 130 K at the entrance aperture to 13 K at the focal plane. The design and test of a special control system using a unique actuator concept to provide position and can control for the CLAES etalon are described. Results of performance tests at cryogenic temperatures simulating the CLAES on-orbit environment are discussed.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Goddard Space Flight Center The 18th Aerospace Mech. Symp.; p 243-262
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  • 86
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    The design and development of a release mechanism for space shuttle life-science experiments (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The design, development, and testing of a release mechanism for use in two life science experiments on the Spacelab 1, 4, and D1 missions is described. The mechanism is a self latching ball lock device actuated by a linear solenoid. An unusual feature is the tapering of the ball lock plunger to give it a near constant breakout force for release under a wide range of loads. The selection of the design, based on the design requirements, is discussed. A number of problems occurred during development and test, including problems caused by human factors that became apparent after initial delivery for crewtraining sessions. These problems and their solutions are described to assist in the design and testing of similar mechanisms.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: The 18th Aerospace Mech. Symp.; p 1-14
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  • 87
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    Load positioning system with gravity compensation (1984)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: A load positioning system with gravity compensation has a servomotor, position sensing feedback potentiometer and velocity sensing tachometer in a conventional closed loop servo arrangement to cause a lead screw and a ball nut to vertically position a load. Gravity compensating components comprise the DC motor, gears, which couple torque from the motor to the lead screw, and constant current power supply. The constant weight of the load applied to the lead screw via the ball nut tend to cause the lead screw to rotate, the constant torque of which is opposed by the constant torque produced by the motor when fed from the constant current source. The constant current is preset as required by the potentiometer to effect equilibration of the load which thereby enables the positioning servomotor to see the load as weightless under both static and dynamic conditions. Positioning acceleration and velocity performance are therefore symmetrical.
    Schlagwort(e): MECHANICAL ENGINEERING
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  • 88
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    Separator plugs for liquid helium (1984)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Work performed during Summer 1984 (from June to Sept. 30) in the area of porous media for use in low temperature applications is discussed. Recent applications are in the area of vapor - liquid phase separation, pumping based on the fountain effect and related subsystems. Areas of potential applications of the latter are outlined in supplementary work. Experimental data have been developed. The linear equations of the two-fluid model are inspected critically in the light of forced convection evidence reported recently. It is emphasized that the Darcy permeability is a unique throughput quantity in the porous media application areas whose use will permit meaningful comparisons of data not only in one lab but also within a group of labs doing porous plug studies.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA-CR-176545 , NAS 1.26:176545 , UCLA-ENG-8436
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  • 89
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    Design and performance analysis of gas sorption compressors (1984)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Compressor kinetics based on gas adsorption and desorption processes by charcoal and for gas absorption and desorption processes by LaNi5 were analyzed using a two-phase model and a three-component model, respectively. The assumption of the modeling involved thermal and mechanical equilibria between phases or among the components. The analyses predicted performance well for compressors which have heaters located outside the adsorbent or the absorbent bed. For the rapidly-cycled compressor, where the heater was centrally located, only the transient pressure compared well with the experimental data.
    Schlagwort(e): MECHANICAL ENGINEERING
    Format: text
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  • 90
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    Magnetic Refrigeration Development (1984)
    In:  CASI
    Details
    Publikationsdatum: 2014-09-12
    Beschreibung: Magnetic refrigeration is being developed to determine whether it may be used as an alternative to the Joule-Thomson circuit of a closed cycle refrigerator for providing 4 K refrigeration. An engineering model 4-15 K magnetic refrigerator has been designed and is being fabricated. This article describes the overall design of the magnetic refrigerator.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: The Telecommun. and Data Acquisition Rept.; p 49-58
    Format: text
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  • 91
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    Status and Direction of Tribology as a Science in the 80's. Understanding and Prediction (1984)
    In:  CASI
    Details
    Publikationsdatum: 2014-09-10
    Beschreibung: The most challenging research problems in tribology for the next decade or beyond are classified horizontally into two categories: (1) understanding of basic mechanisms and (2) prediction of practical performance. Vertical classifications are in terms of particular themes or fields of interest. Areas where more fundamental work is required are: adhesion and friction of clean and contaminated surfaces; lubrication; new materials; surface characterization at the engineering level (topography) and at the atomic levels (various spectroscopies); and wear.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA Lewis Research Center Tribology in the 80's. Vol. 1; p 1-17
    Format: text
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  • 92
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    Linear and Nonlinear Aspects of Rotordynamics (1983)
    In:  CASI
    Details
    Publikationsdatum: 2014-09-10
    Beschreibung: Excessive vibrations of the liquid oxygen pump in the Space Shuttle's Main Engine have been recorded during hot firing ground testing. In order to determine mathematical explanations of this possibility, destructive phenomenon differential equations have been examined which describe the rotordynamics of the pump. Modeling the rotor as a random eigenvalue problem was considered. Analytical expressions were derived for the solution in the case of symmetric damping and stiffness. This enables one to determine accuracy estimates when testing numerical techniques to solve both asymmetric and nonlinear problems. Finally, the rotor model has had nonlinear elements incorporated to improve its simulation of the pump and to expand the corresponding mathematical theory.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Alabama Univ. Res. Rept.: 1983 NASA(ASEE Summer Faculty Fellowship Program; 22 p
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  • 93
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    Sensor Control of Robot Arc Welding (1983)
    In:  CASI
    Details
    Publikationsdatum: 2014-09-12
    Beschreibung: The potential for using computer vision as sensory feedback for robot gas-tungsten arc welding is investigated. The basic parameters that must be controlled while directing the movement of an arc welding torch are defined. The actions of a human welder are examined to aid in determining the sensory information that would permit a robot to make reproducible high strength welds. Special constraints imposed by both robot hardware and software are considered. Several sensory modalities that would potentially improve weld quality are examined. Special emphasis is directed to the use of computer vision for controlling gas-tungsten arc welding. Vendors of available automated seam tracking arc welding systems and of computer vision systems are surveyed. An assessment is made of the state of the art and the problems that must be solved in order to apply computer vision to robot controlled arc welding on the Space Shuttle Main Engine.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Alabama Univ. Res. Rept.: 1983 NASA(ASEE Summer Faculty Fellowship Program; 56 p
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  • 94
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    Secondary electric power generation with minimum engine bleed (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: Secondary electric power generation with minimum engine bleed is discussed. Present and future jet engine systems are compared. The role of auxiliary power units is evaluated. Details of secondary electric power generation systems with and without auxiliary power units are given. Advanced bleed systems are compared with minimum bleed systems. A cost model of ownership is given. The difference in the cost of ownership between a minimum bleed system and an advanced bleed system is given.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Lewis Research Center Aircraft Elect. Secondary Power; p 37-50
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  • 95
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    Hinge latch mechanism (1983)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The device described in this paper is a modular hinge latch mechanism. It is used to latch and preload four motorized hinges after their deployment. The paper describes design requirements, hardware development and initial testing of this hinge latch module. A special effort has been made to cover the design philosophy incorporated into this hardware.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: JPL The 17th Aerospace Mech. Symp.; p 343-356
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  • 96
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    The electron Echo 6 mechanical deployment systems (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The Echo 6 sounding rocket payload was flown on a Terrier boosted Black Brant vehicle on March 30, 1983. The experiment requirements resulted in the new design of a rocket propelled Throw Away Detector System (TADS) with onboard Doppler radar, a free-flyer forward experiment designated the Plasma Diagnostic Package (PDP), and numerous other basic systems. The design, developmental testing, and flight preparations of the payload and the mechanical deployment systems are described.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: The 18th Aerospace Mech. Symp.; p 263-276
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  • 97
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    Antenna tracking mechanism for geostationary satellites (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The design and development of a continuous duty cycle antenna tracking mechanism (ATM) for geostationary communications satellites is described. The FACC requirements for an ATM and description of the development mechanism designed and built for the program are presented. The mechanism mechanical configuration and component performance is documented along with its launch and operational constraints. The proposed development tests and the results of computer simulations are discussed. The advantages of this mechanism are its simplicity with inherent reliability, low mass, high stiffness, and ability to accurately point a wide range of antenna sizes.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Goddard Space Flight Center The 18th Aerospace Mech. Symp.; p 203-214
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  • 98
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    The design and development of a solar tracking unit (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The solar tracking unit was developed to support the Laser Heterodyne Spectrometer (LHS) airborne instrument, but has application to a general class of airborne solar occultation research instruments. The unit consists of a mirror mounted on two gimbals, one of which is hollow. The mirror reflects a 7.6 cm (3.0 in.) diameter beam of sunlight through the hollow gimbal into the research instrument optical axis. A portion of the reflected sunlight is directed into a tracking telescope which uses a four quadrant silicon detector to produce the servo error signals. The colinearity of the tracker output beam and the research instrument optical axis is maintained to better than + or - 1 arc-minute. The unit is microcomputer controlled and is capable of stand alone operation, including automatic Sun acquisition or operation under the control of the research instrument.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Goddard Space Flight Center The 18th Aerospace Mech. Symp.; p 187-201
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  • 99
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    The design and development of two-failure tolerant mechanisms for the Spaceborne Imaging Radar (SIR-B) antenna (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The performance requirements, design constraints, and design qualification status of the mechanisms necessary to restrain, deploy, and stow the Spaceborne Imaging Radar (SIR) B antenna experiment on the Shuttle Orbiters are described.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Goddard Space Flight Center The 18th Aerospace Mech. Symp.; p 131-154
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  • 100
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    The importance of thermal-vacuum testing in achieving high reliability of spacecraft mechanisms (1984)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The work performed on thermal vacuum testing of complex mechanisms is described. The objective of these tests is to assess the mechanism reliability by monitoring performance in an environment that closely resembles the environment that will occur during flight. To be both valid and cost effective, these tests are performed in a detailed, formally controlled manner. A review of the major test observations is given, during which time some failure modes are detected. Full confidence now exists in many mechanism and component designs, and much valuable data obtained.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: NASA. Goddard Space Flight Center The 18th Aerospace Mech. Symp.; p 93-109
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