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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 1,153 records · Page 64
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Structural optimization of rotor blades with integrated dynamics and aerodynamics

The problem of structural optimization of helicopter rotor blades with integrated dynamic and aerodynamic design considerations is addressed. Results of recent optimization work on rotor blades for minimum weight with constraints on multiple coupled natural flap-lag frequencies, blade autorotational inertia and centrifugal stress has been reviewed. A strategy has been defined for the ongoing activities in the integrated dynamic/aerodynamic optimization of rotor blades. As a first step, the integrated dynamic/airload optimization problem has been formulated. To calculate system sensitivity derivatives necessary for the optimization recently developed, Global Sensitivity Equations (GSE) are being investigated. A need for multiple objective functions for the integrated optimization problem has been demonstrated and various techniques for solving the multiple objective function optimization are being investigated. The method called the Global Criteria Approach has been applied to a test problem with the blade in vacuum and the blade weight and the centrifugal stress as the multiple objectives. The results indicate that the method is quite effective in solving optimization problems with conflicting objective functions.

Chattopadhyay, Aditi↗
NASA NTRS1989

Demonstration of decomposition and optimization in the design of experimental space systems

Effective design strategies for a class of systems which may be termed Experimental Space Systems (ESS) are needed. These systems, which include large space antenna and observatories, space platforms, earth satellites and deep space explorers, have special characteristics which make them particularly difficult to design. It is argued here that these same characteristics encourage the use of advanced computer-aided optimization and planning techniques. The broad goal of this research is to develop optimization strategies for the design of ESS. These strategics would account for the possibly conflicting requirements of mission life, safety, scientific payoffs, initial system cost, launch limitations and maintenance costs. The strategies must also preserve the coupling between disciplines or between subsystems. Here, the specific purpose is to describe a computer-aided planning and scheduling technique. This technique provides the designer with a way to map the flow of data between multidisciplinary analyses. The technique is important because it enables the designer to decompose the system design problem into a number of smaller subproblems. The planning and scheduling technique is demonstrated by its application to a specific preliminary design problem.

Padula, Sharon↗
NASA NTRS1989

ASTROS: A multidisciplinary automated structural design tool

ASTROS (Automated Structural Optimization System) is a finite-element-based multidisciplinary structural optimization procedure developed under Air Force sponsorship to perform automated preliminary structural design. The design task is the determination of the structural sizes that provide an optimal structure while satisfying numerous constraints from many disciplines. In addition to its automated design features, ASTROS provides a general transient and frequency response capability, as well as a special feature to perform a transient analysis of a vehicle subjected to a nuclear blast. The motivation for the development of a single multidisciplinary design tool is that such a tool can provide improved structural designs in less time than is currently needed. The role of such a tool is even more apparent as modern materials come into widespread use. Balancing conflicting requirements for the structure's strength and stiffness while exploiting the benefits of material anisotropy is perhaps an impossible task without assistance from an automated design tool. Finally, the use of a single tool can bring the design task into better focus among design team members, thereby improving their insight into the overall task.

Neill, D. J.↗
NASA NTRS1989

Digital robust control law synthesis using constrained optimization

Development of digital robust control laws for active control of high performance flexible aircraft and large space structures is a research area of significant practical importance. The flexible system is typically modeled by a large order state space system of equations in order to accurately represent the dynamics. The active control law must satisy multiple conflicting design requirements and maintain certain stability margins, yet should be simple enough to be implementable on an onboard digital computer. Described here is an application of a generic digital control law synthesis procedure for such a system, using optimal control theory and constrained optimization technique. A linear quadratic Gaussian type cost function is minimized by updating the free parameters of the digital control law, while trying to satisfy a set of constraints on the design loads, responses and stability margins. Analytical expressions for the gradients of the cost function and the constraints with respect to the control law design variables are used to facilitate rapid numerical convergence. These gradients can be used for sensitivity study and may be integrated into a simultaneous structure and control optimization scheme.

Mukhopadhyay, Vivekananda↗
NASA NTRS1989

Experiences in applying optimization techniques to configurations for the Control of Flexible Structures (COFS) program

Optimization procedures are developed to systematically provide closely-spaced vibration frequencies. A general purpose finite-element program for eigenvalue and sensitivity analyses is combined with formal mathematical programming techniques. Results are presented for three studies. The first study uses a simple model to obtain a design with two pairs of closely-spaced frequencies. Two formulations are developed: an objective function-based formulation and constraint-based formulation for the frequency spacing. It is found that conflicting goals are handled better by a constraint-based formulation. The second study uses a detailed model to obtain a design with one pair of closely-spaced frequencies while satisfying requirements on local member frequencies and manufacturing tolerances. Two formulations are developed. Both the constraint-based and the objective function-based formulations perform reasonably well and converge to the same results. However, no feasible design solution exists which satisfies all design requirements for the choices of design variables and the upper and lower design variable values used. More design freedom is needed to achieve a fully satisfactory design. The third study is part of a redesign activity in which a detailed model is used.

Walsh, Joanne L.↗
NASA NTRS1988

Is the Sun really a rigid rotator

Attention is drawn to observations of surface rotational bands in subgiants which indicate that a deep-seated reservoir of angular momentum must exist in these stars. This interpretation is compatible with theoretical studies of the rotational history of the Sun and Sun-like stars, but is in conflict with observations of p-mode splittings in the Sun. In order to understand better the source of this discrepancy, the predicted rotational splittings of several test rotation curves are compared to solar data.

Demarque, P.↗
NASA NTRS1989

Controller evaluations of the descent advisor automation aid

An automation aid to assist air traffic controllers in efficiently spacing traffic and meeting arrival times at a fix has been developed at NASA Ames Research Center. The automation aid, referred to as the descent advisor (DA), is based on accurate models of aircraft performance and weather conditions. The DA generates suggested clearances, including both top-of-descent point and speed profile data, for one or more aircraft in order to achieve specific time or distance separation objectives. The DA algorithm is interfaced with a mouse-based, menu-driven controller display that allows the air traffic controller to interactively use its accurate predictive capability to resolve conflicts and issue advisories to arrival aircraft. This paper focuses on operational issues concerning the utilization of the DA, specifically, how the DA can be used for prediction, intrail spacing, and metering. In order to evaluate the DA, a real time simulation was conducted using both current and retired controller subjects. Controllers operated in teams of two, as they do in the present environment; issues of training and team interaction will be discussed. Evaluations by controllers indicated considerable enthusiasm for the DA aid, and provided specific recommendations for using the tool effectively.

Tobias, Leonard↗
NASA NTRS1989

Descent strategy comparisons for TNAV-equipped aircraft under airplane-preferred operating conditions

Three 4-D descent strategies were evaluated which were employed by TNAV-equipped aircraft in an advanced metering air traffic control environment. The Flow Management Evaluation Model (FMEM) was used to assess performance using three criteria when traffic enters the simulation under preferred cruise operating conditions (altitude and speed): throughput, fuel usage, and conflict probability. In comparison to an evaluation previously performed under NASA contract, the current analysis indicates that the optimal descent strategy is preferred over the clean-idle and constant descent angle (CFPA) strategies when all three criteria are considered.

Izumi, K. H.↗
NASA NTRS1989

Rationale for Mars Rover/Sampler Return mission

A Mars Rover/Sample Return (MRSR) mission is currently being studied for the late 1990's. The objectives of the mission are to better understand the origin and evolution of Mars, to search for evidence of former life, and to improve the knowledge of the Martian environment in preparation for subsequent human exploration. Having formed in a different part of the Solar System from Earth, Mars will provide clues that will better enable the discrimination between conflicting theories of Solar System formations. Mars is also a natural laboratory on which a wide range of geologic and meteorological processes have operated under conditions very different from those on Earth. Samples are needed so that the full range of analytical techniques available here on Earth can be applied to the study of these issues. The rover provides the mobility needed to access different materials, and can be equipped with an analytical capability so that the planet can be sampled intelligently. The rover will also provide the means of exploring the planet on a human scale and performing a wide range of in situ measurements at different locations. Different mission scenarios are currently being studied with the goal of achieveing sample return before the end of the century.

Carr, Michael H.↗
NASA NTRS1989

CSM research: Testbed development

The Computational Structural Mechanics (CSM) Activity at Langley Research Center is developing methods for structural analysis on modern computers. To facilitate that research effort, a Testbed Development environment is being constructed. It is the purpose of the Testbed to insulate researchers from differences in the computer operating systems of modern computer systems and permit concentrated effort on the analytical problem rather than the analytical tools required to solve that problem. While modern computers enable the solution of larger problems of increasing complexity, they do so at a cost. Distributed computer environments, vector processing hardware and multiple processors dominate the current computer environment and threaten to overwhelm future analysis software. The systems software for current computers becomes more complex in order to manage the increasing complexity. The applications developer is caught between conflicting goals. They must take advantage of the computing power of new computer systems while maintaining a stable software development system. The CSM Testbed is being developed to address this problem for the computational structural analysis research community. The Langley CSM activity was initiated in October 1984. The current directions for the Testbed Development Team of the Langley CSM activity are discussed.

Gillian, Ronnie E.↗
NASA NTRS1988

Intrinsic and artificial bias in the KONUS cumulative number distribution

The known biases affecting the KONUS gamma burst cumulative number distribution are discussed and categorized as intrinsic (unavoidable) and artificial (avoidable). Artificial biases are removed to obtain a revised, more faithful representation of the true KONUS log N-log Pc, where Pc is in counts (1/0.25 s). A low Pc turnover is still apparent in the revised log N-log Pc. Conflicting claims that the KONUS log N-log Pc is compatible with a nearby disk or an isotropic, homogeneous distribution are tested using the revised log N-log Pc and a rigorous treatment of the KONUS intrinsic gamma background bias. The claims are shown to be improbable. Other possibilities and problms concerning log N-log Pc are discussed, but the need for a complete explanation of the low Pc turnover remains.

Jennings, Mark C.↗
NASA NTRS1988

Reasoning with inaccurate spatial knowledge

This paper describes work in progress on spatial planning for a semiautonomous mobile robot vehicle. The overall objective is to design a semiautonomous rover to plan routes in unknown, natural terrains. The approach to spatial planning involves deduction of common-sense spatial knowledge using geographical information, natural terrain representations, and assimilation of new and possibly conflicting terrain information. This report describes the ongoing research and implementation.

Doshi, Rajkumar S.↗
NASA NTRS1988

Accuracy versus convergence rates for a three dimensional multistage Euler code

Using a central difference scheme, it is necessary to add an artificial viscosity in order to reach a steady state. This viscosity usually consists of a linear fourth difference to eliminate odd-even oscillations and a nonlinear second difference to suppress oscillations in the neighborhood of steep gradients. There are free constants in these differences. As one increases the artificial viscosity, the high modes are dissipated more and the scheme converges more rapidly. However, this higher level of viscosity smooths the shocks and eliminates other features of the flow. Thus, there is a conflict between the requirements of accuracy and efficiency. Examples are presented for a variety of three-dimensional inviscid solutions over isolated wings.

Turkel, Eli↗
NASA NTRS1988

Origin of the solar system

The current status of the classical model of solar-system formation is surveyed, reviewing the results of recent observational and theoretical investigations. Topics addressed include interstellar clouds, the collapse of interstellar gas, the primitive solar nebula, the formation of the sun, planetesimal accumulation, planetary accumulation, major planetary collisions, the development of planetary atmospheres, and comets. The relative merits of conflicting theories on many key problems are indicated, with reference to more detailed reviews in the literature.

Cameron, A. G. W.↗
NASA NTRS1988

Mass and energy flow near sunspots

Sunspots block the flow of energy to the solar surface. The blocked energy heats the volume beneath the spot, producing a pressure excess which drives an outflow of mass. Linear numerical models of the mass and energy flow around spots were constructed to estimate the predictions of this physical picture against the observed properties of sunspot bright rings and moat flows. The width of the bright ring and moat are predicted to be proportional to the depth of the spot penumbra, in conflict with the observed proportionality of the moat width to the spot diameter. Postulating that spot depths are proportional to spot diameters would bury the moat flow too deeply to be observed, because the radial velocity at the surface is found to be inversely proportional to the depth of the spot penumbra. The radial velocity at the surface is of order a few hundred meters per second after 1 day, in agreement with the observed excess of moat velocities over supergranule velocities.

Nye, Alan↗
NASA NTRS1988

Astrophysical implications of presolar grains

The widely accepted hypothesis that presolar materials survive intact in meteorites and can be studied in our laboratories is of great potential astrophysical significance. Two first-order conclusions have been drawn from the evidence supporting this hypothesis: graphitic grains are rare in the interstellar medium and grain lifetimes are considerably longer than 100 million yr. Both conclusions are in conflict with currently accepted astrophysical models, but might still be consistent with astronomical observations. Many more astrophysical revelations could be concealed within the meteorites, but until astronomers are again given some training in meteoritics, only the meteoritics community has the tools necessary to decipher the message.

Nuth, Joseph A., III↗
NASA NTRS1988

Knowledge acquisition for autonomous systems

Knowledge-based capabilities for autonomous aerospace systems, such as the NASA Space Station, must encompass conflict-resolution functions comparable to those of human operators, with all elements of the system working toward system goals in a concurrent, asynchronous-but-coordinated fashion. Knowledge extracted from a design database will support robotic systems by furnishing geometric, structural, and causal descriptions required for repair, disassembly, and assembly. The factual knowledge for these databases will be obtained from a master database through a technical management information system, and it will in many cases have to be augmented by domain-specific heuristic knowledge acquired from domain experts.

Lum, Henry↗
NASA NTRS1989

Images of the 10-micron source in the Cygnus 'Egg'

Mid-IR images of AFGL 2688, the Egg nebula, obtained with a 16 x 16 pixel array camera (field of view 12.5 x 12.5 arcsec) resolve the central source. It appears as a centrally peaked ellipsoid with major axis of symmetry parallel to the axis of the visible nebulosity. This is contrary to the expected extension perpendicular to this axis implied by proposed dust-toroid models of the IR source. Maps of the spatial distribution of 8-13 micron color temperature and warm dust opacity derived from the multiwavelength images further characterize the IR emission. The remarkable flatness of the color temperature conflicts with the radial temperature gradient expected across a thick shell of material with a single heat source at its center. The new data suggest instead that the source consists of a central star surrounded by a dust shell that is too thin to provide a detectable temperature gradient and too small to permit the resolution of limb brightening.

Jaye, D.↗