The concept of a Figure-of-Merit (FoM) is developed to assess specific mission designs. The variables for a mission plan are so numerous and interdependent that a single parameter cannot accurately represent the overall design performance. The introduction of in-situ resource utilization (ISRU) and the use of advanced modular engines further complicate the problem. For these reasons, the FoM approach has been proposed to provide a more comprehensive look at the overall picture. The analysis encompasses the important design parameters in addition to the less tangible aspects such as long-term effects, reliability and reparability of the hardware, and the risks that are inevitably associated with new technologies. FoM's have been examined in detail for historical missions and for a proposed Mars Sample Return (MSR) mission. Results are presented for a conventional MSR mission along with missions incorporating ISRU and modular engines for comparison. It is concluded that this quantitative FoM approach may well become a key tool in the analysis and design of future space missions.

The hydrodynamic stability of a plane, two-dimensional, incompressible wall jet subjected to small disturbances is investigated by direct numerical integration of the complete Navier-Stokes equations. The numerical model allows growing or decaying of disturbances in the downstream direction as in physical experiments. In the past, various numerical investigations were published using the linear stability theory for the case of temporally growing disturbances. In this work, the investigations are made for the case of spatially growing disturbances. The neutral curves of the linear stability theory are displayed, and in addition, the downstream development of spatial growing disturbances is provided by using the complete Navier-Stokes equations. It is shown that the behavior of the disturbances is as predicted by the linear stability theory for a certain frequency using small disturbances. The changes in the downstream development of the flow subjected to large disturbances compared to the results using small disturbances is discussed. For large disturbance amplitudes, it was found that for the frequency of the disturbance waves used in the investigations the boundary layer mode clearly dominates the hydrodynamic stability.

A systematic search (Dow and Sykes 1988) for cometary dust trails in the Infrared Astronomical Satellite (IRAS) Sky Brightness Images (1988) resulted in the discovery of 466 sources (Dow et al. 1990) that are not in the IRAS Point Source Catalog (Version 2 1988) or in the IRAS Small Scale Structure Catalog (1988). Nearly all of the sources that were found are best explained as artificial satellites or pieces of Earth orbiting debris. This study addresses two questions. To what degrees have the Sky Brightness Images been contaminated by orbital debris? Second, can valuable information concerning the thermal characteristics of these sources be obtained by suitably analyzing IRAS data? Fifty-four sources, covering a range of positions and observed fluxes, were selected from the main sample to determine their angular motion, flux density and color temperature distributions. Four of these objects were correlated with known artificial satellites. (Abstract shortened with permission of author.)

<p> The goal of this work was to develop, introduce, and test a promising computational paradigm for the development of turbulence models for incompressible magnetohydrodynamics (MHD). MHD governs the behavior of an electrically conducting fluid in the presence of an external electromagnetic (EM) field. The incompressible MHD model is used in many engineering and scientific disciplines from the development of nuclear fusion as a sustainable energy source to the study of space weather and solar physics. Many interesting MHD systems exhibit the phenomenon of turbulence which remains an elusive problem from all scientific perspectives. This work focuses on the computational perspective and proposes techniques that enable the study of systems involving MHD turbulence. Direct numerical simulation (DNS) is not a feasible approach for studying MHD turbulence. In this work, turbulence models for incompressible MHD were developed from the variational multiscale (VMS) formulation wherein the solution fields were decomposed into resolved and unresolved components. The unresolved components were modeled with a term that is proportional to the residual of the resolved scales. Two additional MHD models were developed based off of the VMS formulation: a residual-based eddy viscosity (RBEV) model and a mixed model that partners the VMS formulation with the RBEV model. These models are endowed with several special numerical and physics features. Included in the numerical features is the internal numerical consistency of each of the models. Physically, the new models are able to capture desirable MHD physics such as the inverse cascade of magnetic energy and the subgrid dynamo effect. The models were tested with a Fourier-spectral numerical method and the finite element method (FEM). The primary test problem was the Taylor-Green vortex. Results comparing the performance of the new models to DNS were obtained. The performance of the new models was compared to classic and cutting-edge dynamic Smagorinsky eddy viscosity (DSEV) models. The new models typically outperform the classical models.</p>

<p> With the increasing size of wind turbines and the use of flexible and light materials in aerodynamic applications, aeroelastic tailoring for power generation and blade stability has become an important subject in the study of wind turbine dynamics. To this day, coupling of bending and torsion in wind turbine rotor blades has been studied primarily as an elastic mechanism due to a coupling laminate construction. In this report, inertial coupling of bending and torsion, due to offset of axis of elasticity and axis of center of mass, is investigated and numerical simulations are performed to test the validity of the constructed model using an in-house developed aeroelastic numerical tool. A computationally efficient aeroelastic numerical tool, based on Goldstein's helicoidal vortex model with a prescribed wake model and modal coupling of bending and torsion in the blades, is developed for 2-bladed horizontal axis wind turbines and a conceptual study is performed in order to argue the validity of the proposed formulation and numerical construction. The aeroelastic numerical tool, without bending-torsion coupling, was validated (Chattot 2007) using NREL Phase VI wind turbine data, which has become the baseline model in the wind turbine community. Due to novelty of the proposed inertial bending-torsion coupling in the aeroelastic model of the rotor and lack of field data, as well as, other numerical tools available for code to code comparison studies, a thorough numerical investigation of the proposed formulation is performed in order to validate the aeroelastic numerical tool Finally, formulations of geometrically nonlinear beams, elastically nonlinear plates and shells, and a piecewise linear, two degree of freedom, quasi steady, aerodynamic model are presented as an extension for nonlinear wind turbine aeroelastic simulations. Preliminary results of nonlinear beams, plates, shells, and 2 DOF NACA0012 aeroelastic model are presented.</p>

The complex yet important unsteady flow problem of dynamic stall was studied using the random-walk vortex blob method. A fast summation technique was used, which reduced the computational operations for n vortices from $O(n\sp2)$ to O(n log n). Viscous flows about a NACA 0012 airfoil and about a parabolic leading edge were investigated. The Reynolds number based on the chord length was 5000. The purposes of this study were to enhance understanding of the physical process of dynamic stall, and to investigate efficient ways to prevent the stall. The numerical results showed that the development of unsteady separation at the leading edge caused the development of a dynamic stall vortex. In the further development, the dynamic-stall vortex dominated the flow field, and its motion affected the lift greatly. Flow control methods to improve the lift coefficient were also investigated. These included a moving surface and suction through the surface. It was found that a careful implementation of these two methods could be effective for dynamic stall prevention. The computational results also demonstrated that early application was necessary to control dynamic stall. / Source: Dissertation Abstracts International, Volume: 56-12, Section: B, page: 6885. / Major Professor: Leon L. Van Dommelen. / Thesis (Ph.D.)--The Florida State University, 1995.

A crucial issue in the application of Metal Matrix Composites (MMCs) is the presence of processing induced stresses caused by the significant difference in the coefficients of thermal expansion (CTE) of the fiber and the matrix. A micromechanics based elastic-plastic finite element model is developed to study the effects of thermal stresses induced during the fabrication of typical titanium based MMC systems. Computational results show that, in SCS-6/Ti-24Al-11Nb composite, processing induced residual stresses are high enough to cause substantial plastic deformation in the matrix, leading to increased matrix damage. / Interfacial debonding is one of the common damage mechanisms in most of the continuous fiber-reinforced MMCs. A model for describing the behavior of the fiber-matrix interface with minimum number of physically based and experimentally measurable parameters is developed in this work. A stress based failure criterion and a frictional resistance based criterion are used to simulate the occurrence of debonding and sliding respectively, at the interface. The transverse mechanical behavior of typical MMCs are predicted using this interface model. / Push-out test is widely used to determine the interfacial shear properties of MMCs. But, the interpretation of test results in the case of thin-slice MMC specimens is difficult due to the interaction of processing induced residual stresses and other geometric parameters on the test results. Single fiber push-out test is analyzed in detail using the interface model described above. The numerical simulation is able to explain many of the physical phenomena observed in the experiments. A method is developed for predicting the interfacial shear strength of the composite by correlating the numerical results with the experimental data. / Source: Dissertation Abstracts International, Volume: 56-08, Section: B, page: 4533. / Major Professor: N. Chandra. / Thesis (Ph.D.)--The Florida State University, 1995.

This research involves development and testing of a tactile control prosthesis to aid human operators in control of dynamic vehicles. Specifically, this work includes development and demonstration of a torso mounted tactile drift display that allowed helicopter pilots to hover a Blackhawk helicopter with degraded vision (equivalent to 20/200 acuity), a NASA sponsored pilot-in-the-loop simulator study for a hover display and development and analysis of a tactile control prosthesis to help pilots correctly control an airplane experiencing an engine failure on takeoff. Results of a ten-subject experiment indicate that use of a tactile display in conjunction with a visual display reduces operator delay by 65 msec (SD of 28 msec), (P < 0.001) without a significant increase in error rate. In the pilot-in-the-loop simulation experiment pilots hovered a simulated helicopter better under increased workload conditions with the tactile control prosthesis than without it. The increased workload consisted of an addition drill in which the subject had to agree or disagree with a computer generated sum. Pilots were able to hover more precisely with the tactile display (mean of 5.19, SD of 2.57 feet) than without (mean of 6.39 and SD of 3.31 feet) especially when the secondary task was required (P < 0.001). Although learning effects were exhibited throughout the trials (P < 0.001), the tactile display was of greater benefit in higher workload conditions / acase@tulane.edu

An experimental study of a high-temperature, supersonic jet operating at ideal and off-design conditions is conducted using both standard pressure and temperature instrumentation, and particle image velocimetry (PIV). The purpose is to determine the effects of shock-cell structure and of temperature on the growth and development of the jet plume. The study uses a two stage approach to introduce shock and expansion waves into the flow. First a single axisymmetric, convergent-divergent nozzle having a design exit Mach number of 2.0, is operated at three varying pressure ratios, corresponding to isentropic flow Mach numbers of 1.8, 2.0, and 2.15. In the second stage, three axisymmetric, convergent-divergent nozzles with matched throat areas, and varying area ratios are utilized. These nozzles consist of the Mach number 2.0 nozzle previously used, as well as nozzles having design exit Mach numbers of 1.8 and 2.15. These nozzles are operated at a constant pressure ratio corresponding to an isentropic Mach number of 2.0. Results indicate that shock cells in the near field do not significantly affect the growth of the shear layers. Furthermore, flow in the fully developed region of the jet appear unaffected by the presence of the shocks. Increasing temperature ratio results in an increase of the jet spreading rates and centerline velocity decay. Normalized shear layer growth rates in the initial jet regions are consistent with that of a planer shear layer. The PIV data is found to be consistent with that measured using probe instrumentation. / Source: Dissertation Abstracts International, Volume: 56-03, Section: B, page: 1673. / Major Professor: Anjaneyulu Krothapalli. / Thesis (Ph.D.)--The Florida State University, 1995.

This thesis presents a greedy method for the solution of differential equations that accelerates convergence versus standard Finite Element Methods. The Sequentially Optimized Meshfree Approximation method unites meshfree methods, sequential optimization processes, and radial basis functions to solve the strong form of governing equations. The ability to solve the strong form eliminates the need to develop expensive and time consuming variational and/or weak forms of the governing equations currently employed in many numerical methods. The first section introduces and explains the procedures for using this method and then uses increasingly complex examples to detail the finer points of the method across a range of algebraic and differential equations. The second section explains why this method fails for equations and systems that involve discontinuities and explores future avenues through which these shortcomings might be remedied.