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Articles 1  14 of 14
FullText Articles in Mechanical Engineering
Simulation Of Active Control Of Asymmetric Flows Around Slender Pointed Forebodies, Hazem Sharaf ElDin
Simulation Of Active Control Of Asymmetric Flows Around Slender Pointed Forebodies, Hazem Sharaf ElDin
Mechanical & Aerospace Engineering Theses & Dissertations
At high angles of attack, the flowfield over slender forebodies becomes asymmetric with substantial side force, which may exceed the available control capability. The unsteady compressible NavierStokes equations are used to investigate the effectiveness of different active control methods to alleviate and possibly eliminate the flow asymmetry and the subsequent side force. Although the research work focuses on active control methods, a passive control method has been investigated. The implicit, Roe fluxdifference splitting, finite volume scheme is used for the numerical computations. Both locallyconical and threedimensional solutions of the NavierStokes equations are obtained.
The asymmetric flow over fivedegree semiapex angle ...
Radiative Interactions In MultiDimensional Chemically Reacting Flows Using Monte Carlo Simulations, Jiwen Liu
Radiative Interactions In MultiDimensional Chemically Reacting Flows Using Monte Carlo Simulations, Jiwen Liu
Mechanical & Aerospace Engineering Theses & Dissertations
The Monte Carlo method (MCM) is applied to analyze radiative heat transfer in nongray gases. The nongray model employed is based on the statistical narrow band model with an exponentialtailed inverse intensity distribution. The amount and transfer of the emitted radiative energy in a finite volume element within a medium are considered in an exact manner. The spectral correlation between transmittances of two different segments of the same path in a medium makes the statistical relationship different from the conventional relationship, which only provides the noncorrelated results for nongray analysis. Two features of the MCM that are different from other ...
The Development Of A Method To Extract High Purity Oxygen From The Martian Atmosphere, Dongchuan Wu
The Development Of A Method To Extract High Purity Oxygen From The Martian Atmosphere, Dongchuan Wu
Mechanical & Aerospace Engineering Theses & Dissertations
A glowdischarge in an ambient Mars atmosphere (total pressure of 5 torr, composed of 95% carbon dioxide) results in the dissociation of carbon dioxide molecules into carbon monoxide and oxygen. If the glowdischarge zone is maintained adjacent and close to a silver membrane, operated at temperatures above 400°C, atomic and molecular oxygen, produced by the glowdischarge, can be separated from the other species by atomic diffusion through the membrane to an ultrahigh vacuum region where the desorbed O_{2} is then collected. Experiments have been conducted to study the behavior of the glow discharge in both molecular oxygen and ...
Investigation Of Wall Injectors For Supersonic Mixing Enhancement, Yaacov Haimovitch
Investigation Of Wall Injectors For Supersonic Mixing Enhancement, Yaacov Haimovitch
Mechanical & Aerospace Engineering Theses & Dissertations
A comparative study of the interaction between wall mounted sweptramp injectors and injector nozzle shape has been conducted in a constant area duct to explore techniques to enhance mixing in scramjet combustors. The scramjet combustors are currently being developed for propulsion systems applications on the envisioned hypersonic vehicles. Short combustor residence time, a requirement for fuel injection parallel to the main flow in the combustor, and an overall strong sensitivity of the vehicle performance to the propulsion system motivated the investigation. The sweptramp injector investigated in this study produces vortex shedding and local separation downstream of the injector's nozzle ...
Development Of Vibration And Sensitivity Analysis Capability Using The Theory Of Structural Variations, TingYu Rong
Development Of Vibration And Sensitivity Analysis Capability Using The Theory Of Structural Variations, TingYu Rong
Mechanical & Aerospace Engineering Theses & Dissertations
In the author's previous work entitled "General Theorems of Topological Variations of Elastic Structures and the Method of Topological Variation," 1985, some interesting properties of skeletal structures have been discovered. These properties have been described as five theorems and synthesized as a theory, called the theory of structural variations (TSV). Based upon this theory, an innovative analysis tool, called the structural variation method (SVM), has been derived for static analysis of skeletal structures (onedimensional finite element systems).
The objective of this dissertation research is to extend TSV and SVM from onedimensional finite element systems to multidimensional ones and from ...
ThreeDimensional Aerodynamic Shape Optimization Using Discrete Sensitivity Analysis, Gregory Wayne Burgreen
ThreeDimensional Aerodynamic Shape Optimization Using Discrete Sensitivity Analysis, Gregory Wayne Burgreen
Mechanical & Aerospace Engineering Theses & Dissertations
An aerodynamic shape optimization procedure based on discrete sensitivity analysis is extended to treat threedimensional geometries. The function of sensitivity analysis is to directly couple computational fluid dynamics (CFD) with numerical optimization techniques, which facilitates the construction of efficient directdesign methods. The development of a practical threedimensional design procedures entails many challenges, such as: (1) the demand for significant efficiency improvements over current design methods; (2) a general and flexible threedimensional surface representation; and (3) the efficient solution of very large systems of linear algebraic equations. It is demonstrated that each of these challenges is overcome by: (1) employing fully ...
Unsteady Flow Simulations About Moving Boundary Configurations Using Dynamic Domain Decomposition Techniques, GuanWei Yen
Unsteady Flow Simulations About Moving Boundary Configurations Using Dynamic Domain Decomposition Techniques, GuanWei Yen
Mechanical & Aerospace Engineering Theses & Dissertations
A computational method is developed to solve the coupled governing equations of an unsteady flowfield and those of rigidbody dynamics in six degreesoffreedom (6DOF). This method is capable of simulating the unsteady flowfields around multiple component configurations with at least one of the components in relative motion with respect to the others. Two of the important phenomena that such analyses can help us to understand are the unsteady aerodynamic interference and the boundaryinduced component of such a flowfield. By hybridizing two dynamic domain decomposition techniques, the grid generation task is simplified, the computer memory requirement is reduced, and the governing ...
Explicit And Iterative Lqg Controller Design, MinHung Hsiao
Explicit And Iterative Lqg Controller Design, MinHung Hsiao
Mechanical & Aerospace Engineering Theses & Dissertations
This dissertation presents two new LQG controller designs, namely, explicit and iterative designs. For the explicit design, the explicit solutions to the corresponding Riccati equations of controller design for large structures with collocated rate sensors and actuators are derived. Numerically solving the Riccati equations for state feedback and state estimation is no longer required. Since the number of design parameters for either state feedback or state estimation equals the number of controlled modes, the performance of each mode can be easily adjusted. NASA's Spacecraft COntrol Laboratory Experiment (SCOLE) configuration is used to demonstrate the effectiveness of the explicit design ...
Analysis Of Random StructureAcoustic Interaction Problems Using Coupled Boundary Element And Finite Element Methods, Carl S. Pates Iii
Analysis Of Random StructureAcoustic Interaction Problems Using Coupled Boundary Element And Finite Element Methods, Carl S. Pates Iii
Mechanical & Aerospace Engineering Theses & Dissertations
A coupled boundary element(BEM)finite element(FEM) approach is presented to accurately model structureacoustic interaction systems. The boundary element method is first applied to interior, two and threedimensional acoustic domains with complex geometry configurations. Boundary element results are very accurate when compared with limited exact solutions.
Structureinteraction problems are then analyzed with the coupled FEMBEM method, where the finite element method models the structure and the boundary element method models the interior acoustic domain. The coupled analysis is compared with exact and experimental results for a simplistic model. Composite panels are analyzed and compared with isotropic results. The coupled ...
Flow Simulations About SteadyComplex And Unsteady Moving Configurations Using StructuredOverlapped And Unstructured Grids, James Charles Newman Iii
Flow Simulations About SteadyComplex And Unsteady Moving Configurations Using StructuredOverlapped And Unstructured Grids, James Charles Newman Iii
Mechanical & Aerospace Engineering Theses & Dissertations
The limiting factor in simulating flows past realistic configurations of interest has been the discretization of the physical domain on which the governing equations of fluid flow may be solved. In an attempt to circumvent this problem, many Computational Fluid Dynamic (CFD) methodologies that are based on different grid generation and domain decomposition techniques have been developed. However, due to the costs involved and expertise required, very few comparative studies between these methods have been performed. In the present work, the two CFD methodologies which show the most promise for treating complex threedimensional configurations as well as unsteady moving boundary ...
Multigrid Acceleration Of TimeDependent Solutions Of NavierStokes Equations, Sarafa Oladele Ibraheem
Multigrid Acceleration Of TimeDependent Solutions Of NavierStokes Equations, Sarafa Oladele Ibraheem
Mechanical & Aerospace Engineering Theses & Dissertations
Recent progress in Computational Fluid Dynamics is encouraging scientists to look at fine details of flow physics of problems in which natural unsteady phenomena have hitherto been neglected. The acceleration methods that have proven very successful in steady state computations can be explored for time dependent computations. In this work, an efficient multigrid methods is developed to solve the timedependent Euler and NavierStokes equations. The BeamWarming ADI method is used as the base algorithm for time stepping calculations. Application of the developed algorithm proved very efficient in selected steady and unsteady test problems. For instance, the inherent unsteadiness present in ...
Vibration Control With Piezoelectric Actuation Applied To Nonlinear Panel Flutter Suppression, Zhihong Lai
Vibration Control With Piezoelectric Actuation Applied To Nonlinear Panel Flutter Suppression, Zhihong Lai
Mechanical & Aerospace Engineering Theses & Dissertations
Panel flutter is a largedeflection limitcycle motion excited by the airflow, which is only on one side of a panel. The objective of this research is to analytically study the panel flutter limitcycle suppression using nonlinear vibration control techniques with piezoelectric actuation. It is well known that piezoelectric materials are characterized by their ability to produce an electrical charge when subjected to a mechanical strain. The converse piezoelectric effect can be utilized to actuate a panel by applying an electrical field. Piezoelectric actuators are driven by feedback controllers, and control the panel dynamics. For a simply supported panel with piezoelectric ...
Numerical Simulation Of The Nonlinear Response Of Composite Plates Under Combined Thermal And Acoustic Loading, Jayashree Moorthy
Numerical Simulation Of The Nonlinear Response Of Composite Plates Under Combined Thermal And Acoustic Loading, Jayashree Moorthy
Mechanical & Aerospace Engineering Theses & Dissertations
A timedomain study of the random response of a laminated plate subjected to combined acoustic and thermal loads is carried out. The features of this problem also include given uniform static inplane forces. The formulation takes into consideration a possible initial imperfection in the flatness of the plate. High decibel sound pressure levels along with high thermal gradients across thickness drive the plate response into nonlinear regimes. This calls for the analysis to use von Karman large deflection straindisplacement relationships. A finite element model that combines the von Karman strains with the firstorder shear deformation plate theory is developed. The ...
Finite Element Analysis For Nonlinear Flutter Suppression Of Composite Panels At Elevated Temperatures Using Piezoelectric Materials, Run Chen Zhou
Finite Element Analysis For Nonlinear Flutter Suppression Of Composite Panels At Elevated Temperatures Using Piezoelectric Materials, Run Chen Zhou
Mechanical & Aerospace Engineering Theses & Dissertations
Nonlinear coupled finite element equations of motion are derived for composite panels with embedded piezoelectric layers subjected to aerodynamic, thermal loads and applied electric fields. The nonlinear equations of motion describe the coupling between a structure and an electrical network through the piezoelectric effect. The von Karman largedeflection straindisplacement relations, quasisteady firstorder piston theory aerodynamics, quasisteady thermal stress theory and linear piezoelectricity theory are used to formulate the nonlinear coupled panel flutter finite element equations of motion in nodal displacements. The governing equations, which are referred to actuator and sensor equations, form a basis for piezoelectric actuation and sensing. Following ...