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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 973 records · Page 54

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NASA NTRS1977

Modeling and Analysis of Power Processing Systems (MAPPS), initial phase 2

The overall objective of the program is to provide the engineering tools to reduce the analysis, design, and development effort, and thus the cost, in achieving the required performances for switching regulators and dc-dc converter systems. The program was both tutorial and application oriented. Various analytical methods were described in detail and supplemented with examples, and those with standardization appeals were reduced into computer-based subprograms. Major program efforts included those concerning small and large signal control-dependent performance analysis and simulation, control circuit design, power circuit design and optimization, system configuration study, and system performance simulation. Techniques including discrete time domain, conventional frequency domain, Lagrange multiplier, nonlinear programming, and control design synthesis were employed in these efforts. To enhance interactive conversation between the modeling and analysis subprograms and the user, a working prototype of the Data Management Program was also developed to facilitate expansion as future subprogram capabilities increase.

Yu, Y.↗

NASA NTRS1978

Analysis of stability contributions of high dihedral V-tails

An investigation was undertaken to determine the effectiveness of four analytical methods (empirical, modified empirical, vortex-lattice, and an inviscid, three dimensional, potential flow, wing body program) to estimate the lateral and longitudinal static stability characteristics of an isolated V-tail wind tunnel model. The experimental tests were conducted in the V/STOL tunnel at a Mach number of 0.18. Angle-of-attack data were obtained from -12 deg to 8 deg at 0 deg sideslip. Sideslip sweeps from -5 deg to 10 deg were made at angles of attack of 4 deg, 0 deg and -4 deg. The V-tail dihedral angles were 45 deg, 50 deg, 55 deg, and 60 deg.

Freeman, C. E.↗

NASA NTRS1978

Comparison of wing-span averaging effects on lift, rolling moment, and bending moment for two span load distributions and for two turbulence representations

An analytical method of computing the averaging effect of wing-span size on the loading of a wing induced by random turbulence was adapted for use on a digital electronic computer. The turbulence input was assumed to have a Dryden power spectral density. The computations were made for lift, rolling moment, and bending moment for two span load distributions, rectangular and elliptic. Data are presented to show the wing-span averaging effect for wing-span ratios encompassing current airplane sizes. The rectangular wing-span loading showed a slightly greater averaging effect than did the elliptic loading. In the frequency range most bothersome to airplane passengers, the wing-span averaging effect can reduce the normal lift load, and thus the acceleration, by about 7 percent for a typical medium-sized transport. Some calculations were made to evaluate the effect of using a Von Karman turbulence representation. These results showed that using the Von Karman representation generally resulted in a span averaging effect about 3 percent larger.

Lichtenstein, J. H.↗

NASA NTRS1978

Transient dynamics of a flexible rotor with squeeze film dampers

A series of simulated blade loss tests are reported on a test rotor designed to operate above its second bending critical speed. A series of analyses were performed which predicted the transient behavior of the test rig for each of the blade loss tests. The scope of the program included the investigation of transient rotor dynamics of a flexible rotor system, similar to modern flexible jet engine rotors, both with and without squeeze film dampers. The results substantiate the effectiveness of squeeze film dampers and document the ability of available analytical methods to predict their effectiveness and behavior.

Buono, D. F.↗

NASA NTRS1977

Effect of gravity-gradient torques on the dynamics of a spinning spacecraft with telescoping appendages

The effects of gravity-gradient torques during boom deployment maneuvers of a spinning spacecraft are examined with a combination of numerical and analytical methods. It is assumed that the spacecraft consists of a rigid central hub and movable rigid telescoping booms where the booms extend only along the hub principal axes. For the special case of symmetric deployment the stability boundaries are determined and a stability chart is used to study the system behavior. Possible cases of instability during this type of maneuver are identified.

Rajan, M.↗

NASA NTRS1977

Analysis and testing of adhesive bonds

An adhesive fracture mechanics approach is described with reference to the identification and design of the best tests for evaluating a given adhesive, the definition of the most meaningful fundamental parameters by which adhesives might be characterized, and the application of these parameters to the design of joints and to the prediction of their performance. Topics include standard adhesive test techniques, the theory of adhesive fracture, and adhesive fracture energy tests. Analytical methods and computer techniques for adhesive bonding, chemical and physical aspects of adhesive fracture, and specific applications and aspects of adhesive fracture mechanics are discussed.

Anderson, G. P.↗

NASA NTRS1978

A review and assessment of the stress-intensity factors for surface cracks

The stress-intensity factor solutions proposed for a surface crack in a finite plate subjected to uniform tension are reviewed. Fourteen different solutions for the stress-intensity factors are compared. These solutions were obtained over the past 16 years using approximate analytical methods, experimental methods, and engineering estimates. The accuracy is assessed of the various solutions by correlating fracture data on surface-cracked tension specimens made of a brittle epoxy material. Fracture of the epoxy material was characterized by a constant value of stress-intensity factor at failure. Thus, the correctness of the various solutions is judged by the variations in the stress-intensity factors at failure. The solutions were ranked in order of minimum standard deviation. The highest ranking solutions correlated 95 percent of data analyzed within + or - 10 percent, whereas the lowest ranking solutions correlated 95 percent of data analyzed within + or - 20 percent. However, some solutions could be applied to all data considered, whereas others are limited with respect to crack shapes and crack sizes that could be analyzed.

Newman, J. C., Jr.↗

NASA NTRS1978

Formulation of consumables management models. Volume 1: Mission planning

Development of an STS (Space Transportation System) interactive computer program MPP (Mission Planning Processor) working model was conducted. A summary of the computer program development and those supporting tasks conducted is presented. Development of the MPP Computer Program is discussed. This development was supported by several parallel tasks. These tasks either directly supported the program development, or provided information for future application and/or modification to the program in relation to the flight planning and flight operations of the STS and advanced spacecraft. The supporting tasks also included development of a Space Station MPP to demonstrate the applicability of the analytical methods developed under this RTOP to more advanced spacecraft than the STS.

Torian, J. G.↗

NASA NTRS1978

Problems and advances in monitoring horizontal strain

The modern instrumentation is described for use in geodesy for the detection of the deformations of the crust of the earth. Problems are listed. Needs are discussed for the survey of the physical quantities of interest in geodesy, geology, geophysics, and engineering such as the strain invariants, the optimal network of baselines and the accuracy. An analytic method is also given for the computation of the effect of a source of dilatation in a spherical earth.

Caputo, M.↗

NASA NTRS1978

Advanced rotorcraft technology: Task force report

The technological needs and opportunities related to future civil and military rotorcraft were determined and a program plan for NASA research which was responsive to the needs and opportunities was prepared. In general, the program plan places the primary emphasis on design methodology where the development and verification of analytical methods is built upon a sound data base. The four advanced rotorcraft technology elements identified are aerodynamics and structures, flight control and avionic systems, propulsion, and vehicle configurations. Estimates of the total funding levels that would be required to support the proposed program plan are included.

Source record↗

NASA NTRS1979

Hypersonic airframe structures: Technology needs and flight test requirements

Hypersonic vehicles, that may be produced by the year 2000, were identified. Candidate thermal/structural concepts that merit consideration for these vehicles were described. The current status of analytical methods, materials, manufacturing techniques, and conceptual developments pertaining to these concepts were reviewed. Guidelines establishing meaningful technology goals were defined and twenty-eight specific technology needs were identified. The extent to which these technology needs can be satisfied, using existing capabilities and facilities without the benefit of a hypersonic research aircraft, was assessed. The role that a research aircraft can fill in advancing this technology was discussed and a flight test program was outlined. Research aircraft thermal/structural design philosophy was also discussed. Programs, integrating technology advancements with the projected vehicle needs, were presented. Program options were provided to reflect various scheduling and cost possibilities.

Stone, J. E.↗

NASA NTRS1979

Gyrotron: A high-frequency microwave amplifier

A proposed microwave amplifier mechanism for future generations of millimeter high power uplinks to spacecraft and planetary radar transmitters is introduced. Basic electron-electromagnetic field interaction theory for RF power gain is explained. The starting point for general analytical methods leading to detailed design results is presented.

Kupiszewski, A.↗

NASA NTRS1979

Off-axis impact of unidirectional composites with cracks: Dynamic stress intensification

The dynamic response of unidirectional composites under off axis (angle loading) impact is analyzed by assuming that the composite contains an initial flaw in the matrix material. The analytical method utilizes Fourier transform for the space variable and Laplace transform for the time variable. The off axis impact is separated into two parts, one being symmetric and the other skew-symmetric with reference to the crack plane. Transient boundary conditions of normal and shear tractions are applied to a crack embedded in the matrix of the unidirectional composite. The two boundary conditions are solved independently and the results superimposed. Mathematically, these conditions reduce the problem to a system of dual integral equations which are solved in the Laplace transform plane for the transformation of the dynamic stress intensity factor. The time inversion is carried out numerically for various combinations of the material properties of the composite and the results are displayed graphically.

Sih, G. C.↗

NASA NTRS1978

Recent theoretical developments and experimental studies pertinent to vortex flow aerodynamics - With a view towards design

A review is presented of recent progress in a research program directed towards the development of an improved vortex-flow technology base. It is pointed out that separation induced vortex-flows from the leading and side edges play an important role in the high angle-of-attack aerodynamic characteristics of a wide range of modern aircraft. In the analysis and design of high-speed aircraft, a detailed knowledge of this type of separation is required, particularly with regard to critical wind loads and the stability and performance at various off-design conditions. A description of analytical methods is presented. The theoretical methods employed are divided into two classes which are dependent upon the underlying aerodynamic assumptions. One conical flow method is considered along with three different nonconical flow methods. Comparisons are conducted between the described methods and available aerodynamic data. Attention is also given to a vortex flow drag study and a vortex flow wing design using suction analogy.

Lamar, J. E.↗

NASA NTRS1979

A semi-analytic theory for the motion of a close-earth artificial satellite with drag

A semi-analytic method is used to estimate the decay history/lifetime and to generate orbital ephemeris for close-earth satellites perturbed by the atmospheric drag and earth oblateness due to the spherical harmonics J2, J3, and J4. The theory maintains efficiency through the application of the theory of a method of averaging and employs sufficient numerical emphasis to include a rather sophisticated atmospheric density model. The averaged drag effects with respect to mean anomaly are evaluated by a Gauss-Legendre quadrature while the averaged variational equations of motion are integrated numerically with automatic step size and error control.

Liu, J. J. F.↗

NASA NTRS1979

Noise from struts and splitters in turbofan exit ducts

An analytical method for calculating noise radiation from isolated airfoils in turbulent flow was combined with a method for calculating transmission of sound through a subsonic exit duct and with an empirical far field directivity shape. This combination provides a method for predicting engine internally generated noise from radial struts and stators and annular splitter rings. Calculated sound power spectra, directivity, and acoustic pressure spectra are compared with data. These data were for noise caused by a fan exit duct splitter ring, large-chord stator blades, and turbine exit struts. However, the lack of turbulence intensity and scale length measurements for these flow ducts prevented an absolute validation of the prediction method.

Fink, M. R.↗

NASA NTRS1979

Master Plan for prediction of vehicle interior noise

Substantial advances have been made in improving the analytical methods available for prediction of interior noise and providing an experimental data base for their assessment and validation. A review of recent accomplishments, including representative results, is presented in the context of a Master Plan. It is suggested that modal representations of structural walls and acoustic cavities provide a useful conceptual and computational theoretical framework for including the mass, stiffness and damping of both the structure and acoustic cavity. Geometrical details and acoustic damping (absorption) are included in a rigorous manner. Future efforts, both near term and long term, are identified which are required to complete the Master Plan and provide the noise control practitioner with access to these improved methods.

Dowell, E. H.↗

NASA NTRS1979

Application of the superposition principle to solar-cell analysis

The superposition principle of differential-equation theory - which applies if and only if the relevant boundary-value problems are linear - is used to derive the widely used shifting approximation that the current-voltage characteristic of an illuminated solar cell is the dark current-voltage characteristic shifted by the short-circuit photocurrent. Analytical methods are presented to treat cases where shifting is not strictly valid. Well-defined conditions necessary for superposition to apply are established. For high injection in the base region, the method of analysis accurately yields the dependence of the open-circuit voltage on the short-circuit current (or the illumination level).

Lindholm, F. A.↗