This thesis presents a) a scheme for selecting the most suitable flexure hinge compliance equations, and b) a simple methodology of deriving kinetostatic models of micro-motion stages by incorporating the scheme mentioned above. There were various flexure hinge equations previously derived using different methods to predict the compliances of circular flexure hinges. However, some of the analytical/empirical compliance equations provide better accuracies than others depending on the t/R ratios of circular flexure hinges. Flexure hinge compliance equations derived previously using any particular method may not be accurate for a large range of t/R ratios. There was no proper scheme developed on how to select the most suitable and accurate hinge equation from the previously derived formulations. Therefore, the accuracies and limitations of the previously derived compliance equations of circular flexure hinges were investigated, and a scheme to guide designers for selecting the most suitable hinge equation based on the t/R ratios of circular flexure hinges is presented in this thesis. This thesis also presents the derivation of kinetostatic models of planar micromotion stages. Kinetostatic models allow the fulfillment of both the kinematics and the statics design criteria of micro-motion stages. A precise kinetostatic model of compliant micro-motion stages will benefit researchers in at least the design and optimisation phases where a good estimation of kinematics, workspace or stiffness of micro-motion stages could be realised. The kinetostatic model is also an alternative method to the finite-element approach which uses commercially available software. The modelling and meshing procedures using finite-element software could be time consuming. The kinetostatic model of micro-motion stages wasdeveloped based on the theory of the connection of serial and parallel springs. developed based on the theory of the connection of serial and parallel springs. The derivation of the kinetostatic model is simple and the model is expressed in closed-form equations. Material properties and link parameters are variables in this model. Compliances of flexure hinges are also one of the variables in the model. Therefore the most suitable flexure hinge equation can be selected based on the scheme aforementioned in order to calculate the kinetostatics of micro-motion stages accurately. Planar micro-motion stages with topologies of a four-bar linkage and a 3-RRR (revolute-revolute-revolute) structure were studied in this thesis. These micromotion stages are monolithic compliant mechanisms which consist of circular flexure hinges. Circular flexure hinges are used in most of the micro-motion stages which require high positioning accuracies. This is because circular flexure hinges provide predominantly rotational motions about one axis and they have small parasitic motions about the other axes. The 3-RRR micro-motion stage studied in this thesis has three-degrees-of-freedom (DOF). The 3-RRR stage consists of three RRR linkages and each RRR linkage has three circular flexure hinges. A Pseudo-Rigid-Body-Model (PRBM), a kinetostatic model and a two-dimensional finite-elementanalysis (FEA) model generated using ANSYS of micro-motion stages are presented and the results of these models were compared. Advantages of the kinetostatic model was highlighted through this comparison. Finally, experiments are presented to verify the accuracy of the kinetostatic model of the 3-RRR micromotion stage. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1289361 / Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 2007

This thesis explores the design of flexible pipes, buried in shallow trenches with dry sand backfill. The thesis reports the comprehensive analysis of twenty-two full-scale load tests conducted between 1989 and 1991 on pipe installations, mainly within a laboratory facility, at the University of South Australia. The pipes were highly flexible, spirally-wound, uPVC pipes, ranging in diameter from 300 to 450 mm. Guidelines were required by industry for safe cover heights for these pipes when subjected to construction traffic. The tests were designed by, and conducted under the supervision of, the author, prior to the author undertaking this thesis. As current design approaches for pipes could not anticipate the large loading settlements and hence, soil plasticity, experienced in these tests, finite element analyses were attempted. Extensive investigations of the materials in the installations were undertaken to permit finite element modelling of the buried pipe installations. In particular, a series of large strain triaxial tests were conducted on the sand backfill in the buried pipe installations, to provide an understanding of the sand behaviour in terms of critical state theory. Subsequently a constitutive model for the soil was developed. The soil model was validated before implementation in an element of finite element program, AFENA (Carter and Balaam, 1995). Single element modelling of the triaxial tests proved invaluable in obtaining material constants for the soil model. The new element was applied successfully to the analysis of a side-constrained, plate loading test on the sand. The simulation of the buried pipe tests was shown to require three-dimensional finite element analysis to approach the observed pipe-soil behaviour. Non-compliant side boundary conditions were ultimately adjudged chiefly responsible for the difficulty in matching the experimental data. The value of numerical analyses performed in tandem with physical testing was apparent, albeit in hindsight. The research has identified the prediction of vertical soil pressure above the pipe due to external loading as being the major difficulty for designers. Based on the finite element analyses of the field tests, a preliminary simple expression was developed for estimation of these pressures, which could be used with currently available design approaches to reasonably predict pipe deflections.

Thesis (M.S.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains xii, 86 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 80-82).

The intrinsic flexibility of unstructured meshes is compelling for numerical ocean modeling. Complex topographic features, such as coastlines, islands and narrow straits, can faithfully be represented by locally increasing the mesh resolution and because there is no constraint on the mesh topology. In that respect, the finite element method is particularly promising. Not only does it allow for naturally handling unstructured meshes but it also offers additional flexibility in the choice of interpolation and is sustained by a rich and rigorous mathematical framework. This doctoral research was carried out under the auspices of the SLIM (Second-generation Louvain-la-Neuve Ice-ocean Model) project, the objective of which is to develop an ocean general circulation model using the finite element method. This PhD dissertation deals with one-, two- and three-dimensional finite element ocean modeling. We chiefly focus on the accurate representation of some selected oceanic processes and we devote much effort toward using a consistent finite element method to solve the underlying equations. We first concentrate on the finite element solution to a one-dimensional benchmark for the propagation of Poincaré waves with particular emphasis on the discontinuous Galerkin method and a physical justification for computing the numerical fluxes. We then compare three finite element formulations (vorticity - streamfunction, velocity - pressure and free-surface) for the solution to geophysical fluid flow instabilities problems. The prominent -- and remaining -- part of this work deals with three-dimensional ocean modeling on moving meshes. It covers the selection of the right elements for the vertical velocity and tracers through achieving strict tracer conservation and local consistency between the elevation, continuity and tracer equations. The ensuing three-dimensional model is successfully validated against a realistic tidal flow around a shallow-water island. New physical insights are proposed as to the physical processes encountered in such flows.

A public domain code "Object Oriented Finite element analysis for materials science" (OOF) has been extended to include tools for analysis of viscoelastic materials. Utility of these tools has been discussed along with possible applications in this publication. Added features in OOF include means to quantitatively analyze the spatiotemporal response of a composite polymeric material in dynamic as well as in static deformation conditions. These coupled with the existing features of OOF, in particular, the complete analysis of mechanical characteristics of materials provide a comprehensive tool for the studies of time dependent behavior of variety of materials including polymeric solid composites, polymer nanocomposites, polymer blends, block copolymers, and so on. The viscoelastic module draws its strength from the underlying OOF architecture to provide a macroscopic evaluation of mechanical properties using microstructural details. An application of this module for deformation analysis is the characterization of mechanical behavior a polymer nanocomposites. The deformation behaviour of polymer composite depends on the combined characteristic relaxation times of its constituents as well as its microstructural details. Results of analysis are expected to provide better insight into the role of microstructure as well as the role of interphase on the average mechanical / Singapore-MIT Alliance (SMA)

We present a method for Poisson’s equation that computes guaranteed upper and lower bounds for the values of linear functional outputs of the exact weak solution of the infinite dimensional continuum problem using traditional finite element approximations. The guarantee holds uniformly for any level of refinement, not just in the asymptotic limit of refinement. Given a finite element solution and its output adjoint solution, the method can be used to provide a certificate of precision for the output with an asymptotic complexity which is linear in the number of elements in the finite element discretization. / Singapore-MIT Alliance (SMA)

Silicon in single crystal form has been the material of choice for the first demonstration of the MIT microengine project. However, because it has a relatively low melting temperature, silicon is not an ideal material for the intended operational environment of high temperature and stress. In addition, preliminary work indicates that single crystal silicon has a tendency to undergo localized deformation by slip band formation. Thus it is critical to obtain a better understanding of the mechanical behavior of this material at elevated temperatures in order to properly exploit its capabilities as a structural material. Creep tests in simple compression with n-type single crystal silicon, with low initial dislocation density, were conducted over a temperature range of 900 K to 1200 K and a stress range of 10 MPa to 120 MPa. The compression specimens were machined such that the multi-slip <100> or <111> orientations were coincident with the compression axis. The creep tests reveal that response can be delineated into two broad regimes: (a) in the first regime rapid dislocation multiplication is responsible for accelerating creep rates, and (b) in the second regime an increasing resistance to dislocation motion is responsible for the decelerating creep rates, as is typically observed for creep in metals. An isotropic elasto-viscoplastic constitutive model that accounts for these two mechanisms has been developed in support of the design of the high temperature turbine structure of the MIT microengine. / Singapore-MIT Alliance (SMA)

We introduce a new method for computing a posteriori bounds on engineering outputs from finite element discretizations of the incompressible Stokes equations. The method results from recasting the output problem as a minimization statement without resorting to an error formulation. The minimization statement engenders a duality relationship which we solve approximately by Lagrangian relaxation. We demonstrate the method for a stabilized equal-order approximation of Stokes flow, a problem to which previous output bounding methods do not apply. The conceptual framework for the method is quite general and shows promise for application to stabilized nonlinear problems, such as Burger's equation and the incompressible Navier-Stokes equations, as well as potential for compressible flow problems. / Singapore-MIT Alliance (SMA)

This thesis investigates stray losses in AC machines using the time-stepped finite element technique. Two aspects of this topic are involved in this thesis. The first aspect is to construct a finite element model for AC machine systems and develop an efficient numerical solution for the system equation; as the emphasis of this thesis, the second aspect is use the above model to analyze stray losses in AC machines under a variety of operation, design and manufacturing conditions. The thesis modifies the traditional 2-D finite element technique to account for the variations in electromagnetic field along the machines axis resulting from skewed structures, rotor interbar currents and ventilation ducts. Domain decomposition and parallel computation are incorporated to efficiently give a numerical solution to the system equation. The factors affecting harmonic stray losses in AC machines including pulse width modulation (PWM) supply, interbar resistance and slot shape are investigated using the above efficient analysis tool. Simulations and tests under different load conditions are carried out for an induction motor to investigate the additional harmonic stray loss caused by the PWM supply. For a large synchronous generator, simulations and tests are performed to study the effect of different amortisseur interbar resistances on the slot harmonic contents and the resulting harmonic stray loss in the amorisseur cage. As a factor influential to magnet stray loss in permanent magnet synchronous machines, various slot shape designs are assessed by simulations. An optimization based on an evolutionary strategy is implemented to find the best slot shape design with minimum machine loss. The conclusions in the thesis provide valued information to direct the future design and manufacture of efficient AC machines. / Power Engineering and Power Electronics

Thesis (Ph.D.)--State University of New York at Buffalo, 2006. / Includes bibliographical references. Also available online from ProQuest (http://proquest.umi.com/).