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Theses/Dissertations

1994

Structures and Materials

Articles 1 - 10 of 10

Full-Text Articles in Engineering

An Experimental Investigation Of Sandwich Flat Panels Under Low Velocity Impact, Timberlyn M. Harrington Dec 1994

An Experimental Investigation Of Sandwich Flat Panels Under Low Velocity Impact, Timberlyn M. Harrington

Theses and Dissertations

This study evaluated the failure modes and mechanisms associated with increasing face sheet thickness of flat sandwich panels under low velocity impact. The sandwich panels were fabricated using 1.27 cm thick, 145 kg-m3 (9 lb-ft3), 3.175 mm (1-8 in.) cell size Nomex honeycomb core, FM 300-2 film adhesive and AS4-3501-6 graphite-epoxy face sheets. The thickness of the core remained 1.27 cm, and the thickness of the adhesive remained 0.25 mm. The thickness of the face sheets varied using the following stacking sequences: [0-90]s, [0-90]2s, [0-90]4s, [0-90]8s, and [0-90]12s …

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Finite Element Methods For Nonlinear Static Analysis Of Sandwich Plates, Damin J. Siler Dec 1994

Finite Element Methods For Nonlinear Static Analysis Of Sandwich Plates, Damin J. Siler

Theses and Dissertations

A finite element method, developed for static analysis of composite plates, was enhanced to be used with sandwich plates. The theory considers geometric nonlinearity and transverse shear. Furthermore, a new postprocessor was written to check for initial failure using the maximum stress criteria. It also includes a procedure for evaluating transverse normal stresses by enforcing equilibrium. The code modifications for sandwiches were verified by comparing finite element solutions to closed-form sandwich theories. Both methods showed good correlation. In addition, comparisons between one type of composite plate and a similar sandwich plate found that the sandwich had better specific stiffness for …

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The Collapse Of Composite Cylindrical Panels With Various Thickness Using Finite Element Analysis, Christopher P. Chaplin Dec 1994

The Collapse Of Composite Cylindrical Panels With Various Thickness Using Finite Element Analysis, Christopher P. Chaplin

Theses and Dissertations

This study compared numerical collapse results of graphite-epoxy cylindrical panels with free vertical edges undergoing axial compression for three different shell theories. Symmetric quasi-isotropic laminates were investigated using solid panels and panels with five different centralized cutouts with three thicknesses. The theories compared in the study were the Simplified Large displacement moderate Rotation (SLR) theory, the Donnell Cylindrical Shell (Modified Donnell) theory, and the Classical Donnell theory. The purpose of the study was to determine when large rotations and through-the-thickness shear become important in the numerical collapse analysis of cylindrical composite shells. By observing cases where the numerical collapse results …

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Investigation Of Wall Injectors For Supersonic Mixing Enhancement, Yaacov Haimovitch Jul 1994

Investigation Of Wall Injectors For Supersonic Mixing Enhancement, Yaacov Haimovitch

Mechanical & Aerospace Engineering Theses & Dissertations

A comparative study of the interaction between wall mounted swept-ramp 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 swept-ramp injector investigated in this study produces vortex shedding and local separation downstream of the injector's nozzle exit, …

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Flow Simulations About Steady-Complex And Unsteady Moving Configurations Using Structured-Overlapped And Unstructured Grids, James Charles Newman Iii Apr 1994

Flow Simulations About Steady-Complex And Unsteady Moving Configurations Using Structured-Overlapped 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 three-dimensional configurations as well as unsteady moving boundary …

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Unsteady Flow Simulations About Moving Boundary Configurations Using Dynamic Domain Decomposition Techniques, Guan-Wei Yen Apr 1994

Unsteady Flow Simulations About Moving Boundary Configurations Using Dynamic Domain Decomposition Techniques, Guan-Wei Yen

Mechanical & Aerospace Engineering Theses & Dissertations

A computational method is developed to solve the coupled governing equations of an unsteady flowfield and those of rigid-body dynamics in six degrees-of-freedom (6-DOF). 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 boundary-induced 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 …

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Finite Element Analysis For Nonlinear Flutter Suppression Of Composite Panels At Elevated Temperatures Using Piezoelectric Materials, Run Chen Zhou Jan 1994

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 large-deflection strain-displacement relations, quasi-steady first-order piston theory aerodynamics, quasi-steady 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 …

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Numerical Simulation Of The Nonlinear Response Of Composite Plates Under Combined Thermal And Acoustic Loading, Jayashree Moorthy Jan 1994

Numerical Simulation Of The Nonlinear Response Of Composite Plates Under Combined Thermal And Acoustic Loading, Jayashree Moorthy

Mechanical & Aerospace Engineering Theses & Dissertations

A time-domain 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 strain-displacement relationships. A finite element model that combines the von Karman strains with the first-order shear deformation plate theory is developed. The …

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Vibration Control With Piezoelectric Actuation Applied To Nonlinear Panel Flutter Suppression, Zhihong Lai Jan 1994

Vibration Control With Piezoelectric Actuation Applied To Nonlinear Panel Flutter Suppression, Zhihong Lai

Mechanical & Aerospace Engineering Theses & Dissertations

Panel flutter is a large-deflection limit-cycle 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 limit-cycle 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 …

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Multigrid Acceleration Of Time-Dependent Solutions Of Navier-Stokes Equations, Sarafa Oladele Ibraheem Jan 1994

Multigrid Acceleration Of Time-Dependent Solutions Of Navier-Stokes 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 time-dependent Euler and Navier-Stokes equations. The Beam-Warming 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 …

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