No description available.

No description available.

No description available.

No description available.

No description available.

A general nonlinear, nonplanar unsteady vortex panel method for potential-flow is developed. The surface is modeled as a collection of triangular elements on which the vorticity vector is piecewise linearly varying. The wake emanates from the sides and trailing edges of the thin lilting surfaces and is modeled as a progressively formed collection of vortex filaments. This model provides a continuous pressure distribution on the surface while allowing the wake to roll up as tightly as needed. The wake position is determined as part of the solution and no prior knowledge of the position or strength is assumed. An adaptive grid technique is used to redistribute the circulation of the vortex filaments of the wake as the wake sheet spreads. The aerodynamic model is coupled with dynamic equations of motion. Forced oscillation tests are conducted on flat rectangular and delta wings. Dynamic tests are performed to predict wing rock of a slender delta wing restricted to one degree of freedom in roll. The aerodynamic/dynamic model is coupled with control laws that govern the motion of flaperons so that a prescribed pitch motion is executed and wing rock is suppressed. ( 300 pages, 107 figures ) / Ph. D.

A modeling approach suitable for simulating solid-state-controlled machine systems, including component failures within either the electronics or machine(s), is presented in detail. The capability of modeling unbalanced-machine operation is included in the modeling approach. The approach is directly amenable to computer implementation. Computer implementation of the modeling approach was performed and the simulated results were compared with actual oscillograms, obtained from the performance tests of an Electric Vehicle Propulsion Unit, in order to verify the proposed modeling approach. Excellent correlation between the simulated waveforms and the oscillograms existed in all the simulated cases. The modeling approach was used also to simulate the electrical behavior of a brushless-excitation system used for large turbine generators. The simulations consisted of normal steady-state operation as well as a scenario of fault conditions occurring within the rotating rectifier assembly of the brushless exciter. The simulated results are displayed and a discussion of intrinsic features of these results needed to identify the specific fault is presented. Fault detection schemes are warranted for such expensive systems. Actual voltage and/or current waveforms could be telemetered to an controller for fault detection and classification. The elements of this modeling approach which allow inexpensive computer simulation of such systems, that can contain nonlinearities and/or spontaneous faults in any of its components, are listed as follows: 1. The capability of automatically generating the systems' governing state equations, from a minimal set of topological data and component values, at any point within the simulation run; 2. Inclusion of unbalanced machine operation is a result of having no topological restrictions placed upon the mutual coupling. 3. Using piece-wise linear I-V characteristics of the solid-state switching components decreases the computation time needed for a given simulation run since iteration for the status of the equivalent resistance values for each switch is only required at their threshold (I-V) points. 4. Employment of an implicit (predictor-corrector) integration algorithm designed specifically for solving stiff differential equations, typically associated with solid-state controlled machine systems, allows realistic modeling of the solid-state switches' equivalent resistance values. Also, implicit algorithms (like the one employed in this work) result in a drastic reduction of computer execution time and an increase in accuracy, when compared to explicit algorithms, systems. for simulating these types of stiff systems. / Ph. D.

A systems approach for manufacturing system design calls for the division of a system design into sub-designs, and their specification over multiple levels of detail. Through an iterative design and evaluation process, a system design progresses from an abstraction to an implemental specification. To facilitate the evaluation process, models of sub-designs must be applicable to modular assembly, even if the sub-designs are heterogeneously specified. Computer simulation modeling is currently the most flexible method of manufacturing system analysis. When used in the multi-level design process, two forms of simulation models are encountered, uni-level and multi-level. A simulation model of a manufacturing system is considered uni-level if objects of equivalent type within the system are modeled at the same level of detail. On the other hand, a model is considered multi-level if objects of equivalent type are not modeled at the same level of detail. Unfortunately, current simulation frameworks do not integrate modular construction with the various discrete event and continuous simulation techniques needed to support multi-level modeling. This dissertation describes GIBSS (Generalized Interaction Based Simulation Specification), a simulation framework which supports the modular construction of uni-level and multi-level simulation models. Under GIBSS, the mechanisms and attributes of a manufacturing system simulation are distributed among various classes of independent sub-models. These classes are passive, internal interaction, external interaction, and master simulation. GIBSS describes the mechanics of each of these classes, as well as their method of synchronization. Using GIBSS, sub-models are created, executed, and validated independently, and then brought together to execute in parallel or near parallel fashion. As a result, uni-level and multi-level system simulation models are assembled from multiple sub-models. GIBSS eliminates a barrier to the rapid evaluation of manufacturing system designs. It facilitates the multi-level design process, and is the basis of a research effort, dedicated to the development of a new generation of computer-aided manufacturing system design environments. / Ph. D.

An engineering model designed for the analysis of high angle-of-attack flight characteristics is developed and applied to the problem of aircraft poststall departure. The model consists of an aerodynamics package used interactively with a six-degree-of-freedom flight simulator. The aerodynamics are computed via a nonlinear lifting line theory with unsteady wake effects due to a discrete, nonplanar vortex system. A fully configured aircraft (main wing, horizontal tail and vertical fin) is mathematically constructed by modeling all lifting surfaces with bound, discrete vortex segments and associated control points; vehicle geometric influence on high angle-of-attack flight characteristics is included through complete variability in the relative locations, orientations and sizes of the flight surfaces. This aircraft model is “flown” through prescribed maneuvers by integrating the equations of motion. Selected results of trajectory simulations presented for a typical general aviation aircraft provide the following insights to wing-drop departure subsequent to stall. The abruptness of poststall roll-off depends on the presence of flight asymmetries at the stall break and the rate of stall penetration. Such out-of-trim flight conditions induce asymmetric wing panel unstall subsequent to deep stall penetration resulting in large wing-drop-producing roll moments. However, the abrupt departure from symmetric flight conditions is also found to be mathematically possible. This is a consequence of multiple lifting line solutions which exist for bound vortex systems assigned the lift properties of airfoils having stall discontinuities. The dynamic model is well suited to the prediction of departure resistance benefits realized through passive aerodynamic modifications, for example, drooped leading edge outboard wing panels. The model can also be applied to the generation of dynamic stability derivatives by analytically simulating forced oscillation test procedures. / Ph. D.

The nonlinear modeling and analysis of dc-dc converters in the continuous mode and discontinuous mode has been done by averaging and discrete-sampling techniques. The averaging technique is simple to use and averages the output voltage. The discrete technique is very complex and cumbersome, but accurately predicts the envelope of the output voltage. A new model is developed by combining the aforementioned techniques. This new model, the discrete-average model, accurately predicts the envelope of the output voltage and is easy to implement in circuit and state variable forms. The major points of this dissertation are as follows: 1. The proposed model is shown to be dependent on the type of duty cycle control. 2. The proper selection of the power stage model, between average and discrete-average, is largely a function of the error processor in the feedback loop. 3. The accuracy of the measurement data taken by a conventional technique is affected by the conditions at which the data is collected. / Ph. D.