No description available.

No description available.

This project aims to develop efficient and robust tools for optimal design of wind turbine adaptive blades. In general, wind turbine adaptive blade design is an aero-structure coupled design process, in which, the evaluation of aerodynamic performance cannot be carried out precisely without structural deformation analysis of the adaptive blade. However, employing finite element analysis (FEA) based structural analysis commercial packages as part of the aerodynamic objective evaluation process has been proven time consuming and it results in inefficient and redundant design optimisation of adaptive blades caused by elastic-coupled (bend-twist or stretch-twist) iteration. In order to achieve the goal of wind turbine adaptive blade integrated design and analysis, this project is carried out from three aspects. Firstly, a general geometrically linear model for thin-walled composite beams with multi-cell, non-uniform cross-section and arbitrary lay-ups under various types of loadings is developed for implementing structural deformation analysis. After that, this model is validated by a simple box-beam, single- and multi-cell wind turbine blades. Through validation, it denotes that this thin-walled composite beam model is efficient and accurate for predicting the structural deformations compared to FEA based commercial packages (ANSYS). This developed beam model thus provides more probabilities for further investigations of dynamic performance of adaptive blades. Secondly in order to investigate the effects of aero elastic tailoring and implanting elastic coupling on aerodynamic performance of adaptive blades, auxiliary software tools with graphical interfaces are developed via MATLAB codes. Structural/material characteristics and configurations of adaptive blades (i.e. elastic coupling topology, layup configuration and material properties of blade) are defined by these auxiliary software tools. By interfacing these software tools to the structural analysers based on the developed thin-walled composite beam model to an aerodynamic performance evaluator, an integrated design environment is developed. Lastly, by using the developed thin-walled composite beam model as a search platform, the application of the decoupled design method, a method of design of smart aero-structures based on the concept of variable state design parameter, is also extended.

Metal loss due to corrosion is a serious threat to the integrity of pressurised oil and gas transmission pipes. Pipe metal loss defects are found in either single form or in groups (clusters). One of the critical situations arises when two or more defects are spaced close enough to act as a single lengthier defect, causing major impact on the pressure containing capacity of a pipe and leading to rupture rather than localised leak at the centre of defects. There have been many studies conducted to determine the distance needed for defects to interact leading to a failure pressure lower than that when the defects are treated as single and not interacting. Despite such efforts, there is no universally agreed defect interaction rule and pipe operators around the world have various rules to pick and choose from. In this work, the effects of defect shapes and orientations on closely spaced defects are tested experimentally and further analysed using finite element analysis. Burst pressures of commonly used ductile steel pipes in the oil and gas industries, namely X52 and X60, are measured under internal pressure loading. The pipes were machined with circular and curved boxed defects at different orientations to simulate actual metal loss defects. The burst pressure results were compared with those obtained using existing analytical methods. Comparison of the results showed conservatism in the existing analytical methods which may potentially lead to unnecessary plant shutdowns and pipe repairs. A failure criterion for both single and interacting defects was proposed and validated numerically using the experimental data obtained in this research work. The numerical results when using the proposed failure criterion showed that defect shapes and orientations have a great influence on the failure pressure of pipes containing interacting defects. A simplified mathematical model based on the parametric results and relevant to the cases studied is proposed with the objective of reducing the known conservatism in the existing pipe standards when it comes to the assessment of defect interaction.

The piston-cylinder liner interface comprises more than half of the total engine rubbing friction. With current demand being for internal combustion engines with better fuel economy, lower exhaust emissions and higher performance, reducing this form of friction is the subject of much study. The research reported in this thesis is concerned with the development of an existing floating liner rig to measure the friction in this region. The performance features of the modified setup have also been assessed. Parametric studies have been undertaken with the modified setup to identify the potential means of friction reduction. Modifications undertaken in the sealing method and driveline assembly has facilitated friction measurement at higher gas loading of up to 80 barg. The modified sealing assembly with a sealing ring overcame the problem of arbitrary force interruption through irregular liner and seal contacts. Addition of five times higher inertia flywheel aided the motor to support the rig with adequate torque during high gas loading operations. Calibrations have been performed at each different build of piston-liner combination to reduce build to build variability in measurement. Experimental studies have been undertaken to assess the friction characteristics for different factors such as operating pressure, temperature and speed, lubricant oil formulation, piston-liner clearance, piston material etc. Tests have been undertaken at a range of operating conditions; peak pressure of 0 to 80 barg, speed of 1000 to 2000 rpm and average mid-liner temperature of 40 to 90 ˚C. Peak cylinder pressure has been observed to be dominating the friction followed by temperature and speed. Friction spikes were observed near the top dead centre for pressurised operations; where normal load on the rings are highest in a cycle. Higher speed generally results in a higher total frictional loss. However at higher temperature and peak pressure, contrasting effect of speed on total friction has been reported. The study further identified that piston motion play important roles in determining mixed/boundary friction along with the local gas pressure, velocity and oil film temperature. Friction reductions have been obtained by using a lower viscosity oil and higher piston-liner clearance. Maximum friction reduction of 18% has been reported in this study by using SAE 0W-30 oil in place of SAE 5W-30. Diametric clearance of 80 μm obtained a maximum reduction of 12% compared to a lower clearance of 20 μm. The use of steel piston has shown potential in reducing friction over aluminium piston but the design and weight of piston played a dominant role in the frictional loss.

<p> Wave propagation analysis in 1-D and 2-D composite structures is performed efficiently and accurately through the formulation of a User-Defined Element (UEL) based on the wavelet spectral finite element (WSFE) method. The WSFE method is based on the first order shear deformation theory which yields accurate results for wave motion at high frequencies. The wave equations are reduced to ordinary differential equations using Daubechies compactly supported, orthonormal, wavelet scaling functions for approximations in time and one spatial dimension. The 1-D and 2-D WSFE models are highly efficient computationally and provide a direct relationship between system input and output in the frequency domain. The UEL is formulated and implemented in Abaqus for wave propagation analysis in composite structures with complexities. Frequency domain formulation of WSFE leads to complex valued parameters, which are decoupled into real and imaginary parts and presented to Abaqus as real values. The final solution is obtained by forming a complex value using the real number solutions given by Abaqus. Several numerical examples are presented here for 1-D and 2-D composite waveguides. Wave motions predicted by the developed UEL correlate very well with Abaqus simulations using shear flexible elements. The results also show that the UEL largely retains computational efficiency of the WSFE method and extends its ability to model complex features.</p><p> An enhanced cross-correlation method (ECCM) is developed in order to accurately predict damage location in plates. Three major modifications are proposed to the widely used cross-correlation method (CCM) to improve damage localization capabilities, namely actuator-sensor configuration, signal pre-processing method, and signal post-processing method. The ECCM is investigated numerically (FEM simulation) and experimentally. Experimental investigations for damage detection employ a PZT transducer as actuator and laser Doppler vibrometer as sensor. Both numerical and experimental results show that the developed method is capable of damage localization with high precision. Further, ECCM is used to detect and localize debonding in a composite material skin-stiffener joint. The UEL is used to represent the healthy case whereas the damaged case is simulated using Abaqus. It is shown that the ECCM successfully detects the location of the debond in the skin-stiffener joint.</p>

<p> The structure-property relationships of Ultra-High Performance Concrete (UHPC) were quantified using imaging techniques to characterize the multiscale hierarchical heterogeneities and the mechanical properties. Through image analysis the average size, percent area, nearest neighbor distance, and relative number density of each inclusion type was determined and then used to create Representative Volume Element (RVE) cubes for use in Finite Element (FE) analysis. Three different size scale RVEs at the mesoscale were found to best represent the material: the largest length scale (35 mm side length) included steel fibers, the middle length scale (0.54 mm side length) included large voids and silica sand grains, and the smallest length scale (0.04 mm side length) included small voids and unhydrated cement grains. By using three length scales of mesoscale FE modeling, the bridge of information to the macroscale cementitious material model is more physically based.</p>

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering and Dept. of Mechanical Engineering, 1987. / Bibliography: leaves 85-86. / by Nitindra R. Joglekar. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering and Dept. of Mechanical Engineering, 1987. / Bibliography: leaves 58-59. / by Lawrence J. Bowling. / M.S.

Ceria and zirconia ceramics are well known for their ability to conduct oxygen ions, making them useful in constructing devices such as oxygen sensors and solid-oxide fuel cells. Increasing the ionic conductivity of these materials is a major point of interest, because this increases the efficiency and decreases the operating temperature of such fuel cells. Recent experimental results have shown that superlattices of alternating CeO2 and ZrO2 thin films that are alloyed with Gd2O3 exhibit ionic conductivity that is superior to the individual monolithic materials. The enhanced ionic conductivity in these structures is attributed to the interfacial effects. Analytical modeling has shown that there are two possible mechanisms that lead to changes in the ionic conductivity: (a) an enhanced equilibrium concentration of oxygen vacancies in the layered structure arising as a part of the thermodynamic equilibrium across the interfaces, and (b) change in the defect formation energies and kinetic barriers due to interaction of defects with the epitaxial strain field in the heterogeneous system. The extent of this interaction is determined by the layer thickness and interfacial dislocation structure. Aiming to understand these mechanisms, a molecular dynamics (MD) study is performed to determine the interfacial and defect structures in pure and Gd-doped CeO2/ZrO2 superlattices, and the results are compared with the recent experimental observations. / A Thesis submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Degree Awarded: Spring Semester, 2006. / Date of Defense: March 31, 2006. / Computer Simulation, Nanostructured Materials, Interfaces / Includes bibliographical references. / Anter El-Azab, Professor Directing Thesis; Chiang Shih, Committee Member; Peter N. Kalu, Committee Member; Namas Chandra, Committee Member.