Engineering Mechanics Commons^™

A Fracture Mechanics Analysis Of A 38 Inch Diameter Hot Pressed Beryllium Telescope Mirror, Phillip L. Brown

Mechanical & Aerospace Engineering Theses & Dissertations

A 38 inch diameter hot pressed beryllium telescope mirror was analyzed for structural integrity using finite-element modeling and a fracture mechanics analysis program, ZIP3D, developed for three-dimensional (3-0) solid and cracked bodies. The calculation of stress and mixed-mode fracture mechanics parameters for the mirror critical stress area was the objective of the mirror analysis.

Finite-element modeling for ZIP3D solution was performed in two stages. The first stage modeling modeled the mirror configuration on a global basis for calculation of accurate nodal displacements. The second stage modeling reduced the modeled mirror configuration to a set of localized models for calculation of …

Elastic Buckling Of Stiffened Composite Curved Panels, Navin R. R. Jaunky

Mechanical & Aerospace Engineering Theses & Dissertations

Continuous filament grid-stiffened structure is a stiffening concept that combines structural efficiency and damage tolerance. However, buckle resistant design of such structures using finite elements methods is expensive and time consuming. An analytical model of a general grid stiffened structure is developed using a smeared theory with a first order shear deformation theory to account for transverse shear flexibilities. The solution for buckling of a simply supported panel subjected to combined loading is developed using energy method and a Rayleigh-Ritz technique. The smeared theory results are compared with finite element results. The results smeared theory compare well with the finite …

Design Considerations For An Astronaut Monorail System For Large Space Structures And The Structural Characterization Of Its Positioning Arm, Judith J. Watson

Mechanical & Aerospace Engineering Theses & Dissertations

An astronaut monorail system (AMS) is presented as a vehicle to transport and position EV A astronauts along large space truss structures. The AMS is proposed specifically as an alternative to the crew and equipment transfer aid for Space Station Freedom. Design considerations for the AMS were discussed and a reference configuration was selected for the study. Equations were developed to characterize the stiffness and frequency behavior of the AMS positioning arm. Experimental data showed that these equations gave an fairly accurate representation of the stiffness and frequency behavior of the arm. A study was presented to show trends for …

Analysis Of Impact Damage Of Composite Laminates Using Five-Point Bending, Mark Edward Robeson

Mechanical & Aerospace Engineering Theses & Dissertations

The low-velocity impact of composite laminates can induce high transverse shear strains, resulting in severe damage within the laminate. This type of damage may be studied in a quasi-static manner by use of a multi-span beam shear test in five-point bending configuration. A five-point bending arrangement induces high transverse shear strains in sections of the laminate, causing failures, such as intraply cracks and delaminations, that are similar to those caused by low-velocity impact. Stress distributions in the laminate can be calculated using a potential energy approach, and these stress distributions can be correlated with failure locations in the five-point bending …

Theoretical And Experimental Study Of Inlet Manifold Pressure Profiles Using Compensated Transducers, P Mtui

Tanzania Journal of Engineering and Technology (TJET)

Computer simulation and experimental findings on single cylinder four-stroke cycle engine were done with a view of getting more realistic inlet manifold pressures. Since there is a direct relationship between the inlet pressure profiles and the volumetric efficiency of the engine, then there is a possibility of utilizing the knowledge of these profiles to enhance better engine air flow characteristics and hence improvement of engine performance.

The simulation program is based on hometropic process with constant specific heats where the results were validated using experimental findings of the engine with varying engine speeds.

Experimental results are obtained by measuring manifold …

Modal Analysis Of Gyroscopically Coupled Sound-Structure Interaction Problems, Vijay B. Bokil

Mechanical & Aerospace Engineering Theses & Dissertations

In many practical situations we encounter sound-structure interaction between the fluid in a cavity and the flexible wall on the boundary. The aircraft cabin interacting with its fuselage and double-leaf partition walls interacting with the enclosed cavity are some of the typical examples. The vibratory behavior of the structure and the acoustical pressure inside the cavity are affected by this interaction.

In most of the cases, the governing differential equations for the coupled system can be shown to involve gyroscopic coupling. A special method has been applied to decouple the equations in terms of pairs of generalized coordinates and the …

Transfer Function Models And Control Of A Flexible Structure Using Piezoelectric Laminates, Joseph A. Colvin

Mechanical & Aerospace Engineering Theses & Dissertations

The development of piezoelectric polymer films has generated a great deal of excitement in the structural controls community because they are lightweight, durable, distributed in nature and have broad band frequency characteristics. The flurry of research inspired by piezoelectric films has primarily been dedicated to using them as distributed sensors, and to a lesser extent, as distributed actuators.

Active damping of structural vibrations using piezoelectric polymer films as sensors and actuators has primarily been directed toward taking advantage of their distributed nature and employing various types of distributed control theory. This approach does not easily yield insight into the dynamics …

Hierarchical Flux-Based Thermal-Structural Finite Element Analysis Method, Sandra P. Polesky

Mechanical & Aerospace Engineering Theses & Dissertations

A hierarchical flux-based finite element method is developed for both one- and two-dimensional thermal-structural analyses. Derivation of the finite element equations is presented. The resulting finite element matrices associated with the flux-based formulation are evaluated in closed-form. The hierarchical finite elements include additional degrees of freedom in the approximation of the element variable distributions by the use of nodeless variables. The nodeless variables offer increased solution accuracy without the need for defining actual nodes and rediscretizing the finite element model. Thermal and structural responses obtained using the hierarchical flux-based method are compared with results obtained from a conventional linear finite …

Development Of A Model Updating Technique For Controls-Structures Integrated Design Optimization, Angela Georges

Mechanical & Aerospace Engineering Theses & Dissertations

A model updating technique is developed with the intent of providing an efficient means of improving the accuracy of the modelling of the vibrational qualities of a large, flexible structure as it undergoes an integrated controls-structures design optimization. The proposed technique utilizes eigenvalue/eigenvector sensitivity information, two different model reduction methods which assign weights of importance to the vibrational modes of the structure, and modal switching based upon the modal weights determined by the model reduction methods. Issues associated with the numerical implementation of the proposed technique, such as discontinuities induced by modal switching, are also addressed.

The proposed model updating …