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A general theory of fluidelastic instability for a tube array in crossflow is presented. Various techniques to obtain the motion-dependent fluid-force coefficients are discussed and the general instability characteristics are summarized. The theory is also used to evaluate the results of other mathematical models for crossflow-induced instability.
Artificial-feel system designed for general-aviation flight simulators. New system developed to replace directly lateral and longitudinal controls in general-aviation cockpit for use in flight-simulation research. Using peaucellier's cell to convert linear motion to rotary motion, control-loading system provides realistic control-force feedback to cockpit wheel and column controls.
In displaying computer-generated graphics, it is advantageous to have the facility to render any subset of polygons as a silhouette with respect to itself. While the silhouette problem has been addressed before, there has been no completely general solution. In this report, the silhouette problem for calligraphic drawings is solved for the most general case. This solution offers all possible combinations of silhouette and non-silhouette specifications for an arbitrary solid. It allows the flexibility to enhance the clarity of any three-dimensional scene presented in two dimensions.
A consistent linearization is provided for the element-dependent corotational formulation, providing the proper first and second variation of the strain energy. As a result, the warping problem that has plagued flat elements has been overcome, with beneficial effects carried over to linear solutions. True Newton quadratic convergence has been restored to the Structural Analysis of General Shells (STAGS) code for conservative loading using the full corotational implementation. Some implications for general finite element analysis are discussed, including what effect the automatic frame invariance provided by this work might have on the development of new, improved elements.
For all its activity statistics, general-aviation is the most vulnerable to hazardous weather. Of concern to the general aviation industry are: (1) the slow pace of getting units of the Automated Weather Observation System (AWOS) to the field; (2) the efforts of the National Weather Service to withdraw from both the observation and dissemination roles of the aviation weather system; (3) the need for more observation points to improve the accuracy of terminal and area forecasts; (4) the need for improvements in all area forecasts, terminal forecasts, and winds aloft forecasts; (5) slow progress in cockpit weather displays; (6) the erosion of transcribed weather broadcasts (TWEB) and other deficiencies in weather information dissemination; (7) the need to push to make the Direct User Access Terminal (DUAT) a reality; and (7) the need to improve severe weather (thunderstorm) warning systems.
Electrodynamic effects of thermospheric winds simulated with the NCAR thermospheric general circulation model (TGCM) were modeled and compared with observations for equinox solar minimum conditions. Two TGCM wind simulations were used: one driven only by in situ solar UV heating, the other also including lower boundary forcing that mimics the effects of upward propagating semidiurnal tides. It was found that, without tidal forcing, the TGCM winds produce ground magnetic variations that have the general pattern of observed Sq variations, but are only about half as strong. The addition of tidal forcing improved the agreement between calculated and observed magnetic variations and between calculated and observed electric fields.
Time-dependent aurora and magnetospheric convection parameterizations have been derived from solar wind and aurora particle data for November 21-22, 1981, and are used to drive the auroral and magnetospheric convection models that are embedded in the National Center for Atmospheric Research thermospheric general circulation model (TGCM). Neutral wind speeds and transition boundaries between the midlatitude solar-driven circulation and the high-latitude magnetospheric convection-driven circulation are examined on an orbit-by-orbit basis. The results show that TGCM-calculated winds and reversal boundary locations are in generally good agreement with Dynamics Explorer 2 measurements for the orbits studied. This suggests that, at least for this particular period of relatively moderate geomagnetic activity, the TGCM parameterizations on the eveningside of the auroral oval and polar cap are adequate.
The cycles of the water isotopic species (HDO and H2O-18) have been incorporated into the NASA Goddard Institute for Space Studies atmospheric general circulation model (GCM). The results of a three-year simulation for present-day conditions are discussed, with special emphasis on the comparison between predicted and observed isotopic distributions for both the seasonal and annual time scales. The observed seasonal cycles are generally well simulated. For the annual scale the observed linear relationship between delta O-18 and the surface temperature at middle and high latitudes, as well as the absence of any correlation between these fields in tropical and equatorial regions, are properly obeyed by the GCM simulation. In the tropical and equatorial regions the delta O-18 patterns for both observations and the GCM are influenced by the amount of rainfall. There is excellent agreement between the simulated and observed delta D-delta O-18 relationship throughout the world.
An attempt is made to demonstrate, by means of Hapke's (1981) photometric function, that a simple and reliable method exists for the estimation of phase integrals from limited higher phase angle measurements. This method is a generalization of the approximation first proposed by Russell (1916) and more recently treated by Veverka (1971). It is shown that this generalization of Russell's law can employ observations anywhere in the range of phase angles from 40 to 90 deg; optimum estimates of q will be obtained if the data near 70 deg are obtainable.
The paper presents a recursive method, designated the W exp (m)-algorithm, for implementing a generalization of the Richardson extrapolation process. Compared to the direct solution of the linear sytems of equations defining the extrapolation procedure, this method requires a small number of arithmetic operations and very little storage. The technique is also applied to solve recursively the coefficient problem associated with the rational approximations obtained by applying a d-transformation to power series. In the course of development a new recursive algorithm for implementing a very general extrapolation procedure is introduced, for solving the same problem. A FORTRAN program for the W exp (m)-algorithm is also appended.
This paper considers the concept of magnetic reconnection from a general point of view, with special consideration given to magnetic reconnection in nonvanishing magnetic fields, i.e., finite-B reconnection as distinct from zero-B reconnection. It is shown that the electric field component parallel to the magnetic field (E-parallel) plays a crucial physical role in finite-B reconnection. Two theorems involving E-parallel are proposed. The first defines a necessary and sufficient condition of E-parallel for global reconnection to occur. The second theorem is concerned with the change of magnetic helicity to E-parallel for cases where the electric field vanishes at large distances. The general magnetic reconnection concept is tested by applying it to the process of plasmoid formation process.
The traditional definition of the transmission error of parallel-axis gear pairs is reviewed and shown to be unsuitable for characterizing the deviation from conjugate action of bevel gear pairs for vibration excitation characterization purposes. This situation is rectified by generalizing the concept of the transmission error of parallel-axis gears to a three-component transmission error for spiral bevel gears of nominal spherical involute design. A general relationship is derived which expresses the contributions to the three-component transmission error from each gear of a meshing spiral bevel pair as a linear transformation of the six coordinates that describe the deviation of the shaft centerline position of each gear of the pair from the position of its rigid perfect involute counterpart.
The vibratory excitation arising from a gear pair is widely recognized to be a consequence of the nonuniform transmission of motion by the gear pair. In the preceding paper in this issue, it is shown that a three-component transmission error is required to describe the nonuniform transmission of motion by bevel gears for vibration excitation characterization purposes. The expression for the three-component transmission error derived in that paper is combined in the present paper with an analysis of the mesh forces and mesh elasticity to yield an equation of constraint involving the six degree-of-freedom unknown vibratory displacements of the gear shaft centerliners, the three unknown components of the generalized force transmitted by the mesh, and the geometric deviations of the tooth running surfaces from perfect involute surfaces which are assumed known. This matrix equation can be combined with the equations of motion of a gear system to predict the vibratory response of the system to the generalized transmission error excitation arising from meshing gear pairs within the system.
The generalized first adiabatic invariant, an extension of the magnetic moment for regions of large field gradients, has been applied to the study of particles in the magnetotail current sheet. Boundaries in phase space are obtained which form a generalized loss cone and separate particles drifting into and out of the layer from particles trapped within the layer, and the boundaries can be employed in the moment integrals for densities and currents when the drifting particles differ in temperature. It is shown that the parallel pressure of the drifting particles must exceed the transverse pressure for self-consistent solutions to exist. Fully self-consistent solutions are obtained using bi-Maxwellian ion and Maxwellian electron distributions.
The image correspondence problem is considered the most difficult step in both stereo and motion analysis. Stereo vision is useful in determining the 3-D positions of points on visible surface in a scene. Motion analysis is useful in determining the spatial and temporal relationships of objects in an environment. Besides stereo and motion analysis, there is the image correspondence problem. Most of this work is based on point or local area properties of the observed gray level values in 2-D images. A global and general approach to this problem is described by using a knowledge-based system. The knowledge it uses consists of both physical properties and spatial relationships of the edges and regions extracted from the given images. The physical component depends on features of the edge or region) in isolation. The spatial component involves the set of edges and regions adjacent to a given edge (or region) of the first image and the set of edges and regions adjacent to each potentially matching edge (or region) of the second image; thus the spatial context of each edge or region is considered. A computational network is used to represent this knowledge, it allows the computation of the likelihood of matching two edges or regions with logical and heuristic operators. An expert system shell called AGNESS (A Generalized Network-based Expert System Shell) is used to build a prototype system.
An object is an abstract software model of a problem domain entity. Objects are packages of both data and operations of that data (Goldberg 83, Booch 83). The Ada (tm) package construct is representative of this general notion of an object. Object-oriented design is the technique of using objects as the basic unit of modularity in systems design. The Software Engineering Laboratory at the Goddard Space Flight Center is currently involved in a pilot program to develop a flight dynamics simulator in Ada (approximately 40,000 statements) using object-oriented methods. Several authors have applied object-oriented concepts to Ada (e.g., Booch 83, Cherry 85). It was found that these methodologies are limited. As a result a more general approach was synthesized with allows a designer to apply powerful object-oriented principles to a wide range of applications and at all stages of design. An overview is provided of this approach. Further, how object-oriented design fits into the overall software life-cycle is considered.
Inviscid flux Jacobian matrices and their properties used in numerical solutions of conservation laws are extended to general, equilibrium gas laws. Exact and approximate generalizations of the Roe average are presented. Results are given for one-dimensional flow, and then extended to three-dimensional flow with time-varying grids.
The application of a generalized optimality criteria to framed structures is presented. The optimality conditions, Lagrangian multipliers, resizing algorithm, and scaling procedures are all represented as a function of the objective and constraint functions along with their respective gradients. The optimization of two plane frames under multiple loading conditions subject to stress, displacement, generalized stiffness, and side constraints is presented. These results are compared to those found by optimizing the frames using a nonlinear mathematical programming technique.