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<p>Robotic platforms have several characteristics such as speed and precision that make them enticing for use in medical procedures. Companies such as Intuitive Medical and Titan Medical have taken advantage of these features to introduce surgical robots for minimally invasive procedures. Such robots aim to reduce procedure and patient recovery times. Current technology requires platforms to be master-slave manipulators controlled by a surgeon, effectively converting the robot into an expensive surgical tool. Research into the interaction between robotic platforms and deformable objects such as human tissue is necessary in the development of autonomous and semi-autonomous surgical systems. This thesis investigates a class of robust linear controllers based on a worst case performance measure known as the $H_{\infty}$ norm, for the purpose of performing so called Indirect Deformable Object Manipulation (IDOM). This task allows positional regulation of regions of interest in a deformable object without directly interacting with them, enabling tasks such as stabilization of tumors during biopsies or automatic suturing. A complete approach to generating linear $H_{\infty}$ based controllers is presented, from derivation of a plant model to the actual synthesis of the controller. The introduction of model uncertainty requires $\mu$ synthesis techniques, which extend $H_{\infty}$ designs to produce highly robust controller solutions. In addition to $H_{\infty}$ and $\mu$ synthesis designs, the thesis presents an approach to design an optimal PID controller with gains that minimize the $H_{\infty}$ norm of a weighted plant. The three control approaches are simulated performing set point regulation in $\text{MATLAB}^{TM}$'s $simulink$. Simulations included disturbance inputs and noises to test stability and robustness of the approaches. $H_{\infty}$ controllers had the best robust performance of the controllers simulated, although all controllers simulated were stable. The $H_{\infty}$ and PID controllers were validated in an experimental setting, with experiments performed on two different deformable synthetic materials. It was found that $H_{\infty}$ techniques were highly robust and provided good tracking performance for a material that behaved in a relatively elastic manner, but failed to track well when applied to a highly nonlinear rubber compound. PID based control was outperformed by $H_{\infty}$ control in experiments performed on the elastic material, but proved to be superior when faced with the nonlinear material. These experimental findings are discussed and a linear $H_{\infty}$ control design approach is proposed.</p> / Master of Applied Science (MASc)

This research endeavor develops Isogeometric approach for analysis of composite structures and take advantage of higher order continuity, smoothness and variation diminishing property of Nurbs basis for stress analysis of composite and sandwich beams and plates. This research also computes stress concentration factor in a composite plate with a hole. Isogeometric nonlinear/linear finite element code is developed for static and dynamic analysis of laminated composite plates. Nurbs linear, quadratic, higher-order and k-refined elements are constructed using various refinement procedures and validated with numerical testing. Nurbs post-processor for in-plane and interlaminar stress calculation in laminated composite and sandwich plates is developed. Nurbs post-processor is found to be superior than regular finite element and in good agreement with the literature. Nurbs Isgoemetric analysis is used for stress analysis of laminated composite plate with open-hole. Stress concentration factor is computed along the hole edge and good agreement is obtained with the literature. Nurbs Isogeometric finite element code for free-vibration and linear dynamics analysis of laminated composite plates also obtain good agreement with the literature. Main highlights of the research are newly developed 9 control point linear Nurbs element, k-refined and higher-order Nurbs elements in isogeometric framework. Nurbs elements remove shear-locking and hourglass problems in thin plates in context of first-order shear deformation theory without the additional step and compute better stresses than Lagrange finite element and higher order shear deformation theory for comparatively thick plates i.e. a/h = 4. Also, Nurbs Isogeometric analysis perform well for vibration and dynamic problems and for straight and curved edge problems. / Ph. D.

The process of froth flotation relies on using air bubbles to collect desired mineral particles dispersed in aqueous media on the surface, while leaving undesirous mineral particles behind. For a particle to be collected on the surface of a bubble, the thin liquid films (or wetting films) of water formed in between must rupture. According to the Frumkin-Derjaguin isotherm, it is necessary that wetting films can rupture when the disjoining pressures are negative. However, the negative disjoining pressures are difficult to measure due to the instability and short lifetimes of the films. In the present work, two new methods of determining negative disjoining pressures have been developed. One is to use the modified thin film pressure balance (TFPB) technique, and the other is to directly determine the interaction forces using the force apparatus for deformable surfaces (FADS) developed in the present work. The former is designed to obtain spatiotemporal profiles of unstable wetting films by recording the optical interference patterns. The kinetic information derived from the spatiotemporal profiles were then used to determine the disjoining pressures using an analytical expression derived in the present work on the basis of the Reynolds lubrication theory. The technique has been used to study the effects of surface hydrophobicity, electrolyte (Al3+ ions) concentration, and bubble size on the stability of wetting films. Further, the geometric mean combining rule has been tested to see if the disjoining pressures of the wetting films can be predicted from the disjoining pressures of the colloid films formed between two hydrophobic surfaces and the disjoining pressures of the foam films formed between two air bubbles. The FADS is capable of directly measuring the interaction forces between air bubble and solid surface, and simultaneously monitoring the bubble deformation. The results were analyzed using the Reynolds lubrication theory and the extended DLVO theory to determine both the hydrodynamic and disjoining pressures. The FADS was used to study the effects of surface hydrophobicity and approach speeds. The results show that hydrophobic force is the major driving force for the bubble-particle interactions occurring in flotation. / Ph. D.

High operation speeds and thin coating films are desirable in many industrial applications. But the quality of the product, which is primarily determined by an optimum process window, is affected by non-uniformities and instabilities originating at higher operation speeds. Unlike other academic works, because of associated industrial relevance, particular attention was given towards the use of industrially relevant coating systems or generation of model fluids, which replicate the real coating solutions. One of the novelties of the research proposed lie in an integrated approach, utilising a range of comparative rheometrical techniques, with a focus on measurement of: (i) high strain rate shear viscosity [η], (ii) high strain rate uniaxial extensional viscosity [ηE] (iii) high strain rate elasticity (N1). Deformable roll coating, in terms of classification, is the ultimate metered coating flow. The flow is controlled by the combination of hydrodynamic force and elastic deformation effect, which could be complicated by the presence of non-Newtonian fluid. This study necessitated the design and construction of a sophisticated deformable coating rig with the ability to operate over a wide range of conditions. Although the irregularities and instabilities associated with the roller coating process has been studied previously, the concerned speeds of operation in this study is around three times higher. The main objectives of this study was to carry out a comprehensive experimental programme establishing relationship exist between film thickness, film quality and operating parameters. Main identified operating parameters are roll speeds, roll gaps or applied load between the rolls, the elasticity with thickness of elastomeric layer and different rheological properties of the coating fluids. Surface instabilities and air entrainment are identified as the major limitations to being able to coat at higher speeds. / Tata Steel Europe / The full text was made available at the end of the embargo, 1st July 2020

The objective of a coating operation is to transfer a defect free liquid film onto a continuous substrate in order to meet the requirements of the final products. Mainly two concerns govern the process. The first concern is the economics of the process and the second concern is the quality of the coated film. The economics of the process are dictated by the speed of coating and the film thickness. Clearly, higher speeds mean better productivity hence less cost of operation and thinner films are desirable because less material is being used. Quality is governed by film uniformity and integrity, indicating that the film will perform as designed. Film defects such as streaks or tiny air bubbles are indication that the film properties are not uniform rendering it unacceptable to customers. One of the most versatile coating systems to achieve thin films at high speeds is reverse roll coating which has been used for a long time all over the world. At low speed, typically 1m/s, this coating operation is inherently stable and with small gaps of order 100 microns can ii lead to film thickness of order 30-50 microns. Much research, theoretical and experimental, has been devoted to this coating flow but only at low speeds and for large gaps (>100 microns). There are no comprehensive data how very thin films, 20 microns and less (particularly lower limits in the region of 5 microns) can be achieved at high speeds, of 2 or more metres per second. This study is concerned precisely with this aim, that of investigating the effect of large speeds and small roller gaps (rollers nearly touching or in elastohydrodynamic contact) to achieve the very thin films desired by modern applications (electronics, medical and others). In order to achieve this aim, a rig was designed and built to enable to understand the effect of various coating conditions and liquid properties on the metered film thickness and coating instability. To achieve thin films at high speeds, small roll gap and low viscosity are needed, however flow instabilities will develop under these conditions. To achieve stable coating window at high speeds high surface tension is needed. It was found that the roll gap and the viscosity have complicated effect on the coating window. In the case of low viscosity liquid (7mPa.s), small roll gaps are needed, whereas in the case of high viscosity liquid (more than 30mPa.s), large gaps are needed. It was found that Weber number is better describer for ribbing instability in rigid reverse roll coating unlike in rigid forward roll coating in which capillary number is the one. In addition the potential of reverse deformable roll coating (rolls in elastohydrodynamic contact) was investigated in order to achieve much thinner films at higher speeds. As a result of the investigation of reverse deformable roll coating, it was found that there is a possibility to get much thinner stable films at much higher speeds compared to reverse rigid roll coating. The liquid transfer from an applicator roller to a PET film was investigated in this study. It was found that air stagnation at downstream meniscus and air entrainment at upstream meniscus depend on the liquid properties such as viscosity and surface tension and coating conditions such as web tension and wrap angle of web. As a result, wet film instability also depends on liquid properties and coating conditions. It was found that air stagnation causes streaks on the wet film and air entrainment caused bubbles on the wet film. To get a stable wet film, it was found that suitable viscosity and high surface tension were needed. / TOYOBO

No / Axially loaded rubber blocks of long, thin rectangular and circular cross section whose ends are bonded to rigid plates are studied. Closed-form expressions, which satisfy exactly the governing equations and conditions based upon the classical theory of elasticity, are derived for the total axial deflection and stress distribution using a superposition approach. The corresponding relations are presented for readily calculating the apparent Young's modulus, Ea, the modified modulus, E'a, and the deformed lateral profiles of the blocks. From these, improved approximate elementary expressions for evaluating Ea and E'a are deduced. These estimates, and the precisely found values, agree for large values of the shape factor S, with those previously suggested, but also fit the experimental data more closely for small values of S. Confirmation is provided that the assumption of a parabolic lateral profile is invalid for small values of S.

As climate change escalates and the demands for energy resources increase, modern geotechnical engineering must tackle critical challenges to ensure sustainable development and enhance the resilience of infrastructure in society. The coupled chemo-hydro-mechanical processes in multiphase materials present significant challenges in geotechnical engineering, particularly for applications like carbon sequestration, geological disposal of nuclear waste, and hydraulic fracturing with reactive fluids, all of which involve highly heterogeneous and strongly anisotropic multiphysics environments. This dissertation introduces a multiphysical computational framework specifically designed to address the challenges associated with these unconventional applications. In this dissertation, we consider not only the local multiphysical coupling effects in the constitutive model but also the nonlocal effects arising from pore fluid flow, chemical species convection and diffusion, chemical reactions occurring in both solid and fluid constituents, and damage due to fluid pressure acting on fractures in the solid. We have integrated all these physical processes and developed a single unified model capable of handling the complex hydro-chemo-mechanical responses of geomaterials under varying geochemical conditions, confining pressures, and external loading scenarios. This computational framework offers a comprehensive simulation tool to investigate the long-term stability of geomaterials, which is determined by the intensity of chemical reactions under specific temperature and pressure conditions (assuming an isothermal condition in this dissertation), as well as the sustainability of geotechnical infrastructure in erosive environments driven by both mechanical and chemical processes. Three key aspects of engineering applications related to the effects of chemical reactions in geotechnical engineering are addressed. Firstly, we have integrated a complete calcite reaction system into poromechanics to couple pore geochemistry with poroelasticity theory. This integration is capable of predicting the geomechanical response essential for long-term stability analysis in \ch{CO2} sequestration engineering. Key features of this model include a multi-field finite element approach, local-equilibrium explicit geochemistry characterization of the calcite dissolution/precipitation reaction system, a robust algorithm for sequentially coupling pore geochemistry with poromechanics, and strategies to enhance the computational efficiency of solvers. Secondly, for applications involving acid working fluids in hydraulic fracturing, we have extended and adapted previous models within the phase field method framework. This extended integration effectively addresses the effects of chemically assisted fracturing in hydraulic fracturing operations. The key innovations of this model are the implementation of the phase field method to capture crack behaviors with poromechanics, the modeling of acid fluid transport in porous media and fractures, and its application to multiple mineral reaction systems. Thirdly, we have proposed a constitutive model that incorporates pore geochemistry and the pressure dissolution effect into internal variables, effectively capturing the chemical reactions contributing to softening in geomaterials. This model effectively illustrates and predicts chemically induced weathering or damage in granular porous media, such as sinkholes and subsidence. Derivations of a thermodynamically-based degradation index consider the influences of pore geochemistry and contact forces between grains and bonds. The model also proposes cross-scale relationships that consider reaction effects from individual particle sizes to particle aggregates. Furthermore, these relationships are incorporated into classical Cam-Clay-type models, along with the derivation of a consistent tangent modulus. / Dissertation / Doctor of Philosophy (PhD) / This thesis presents the comprehensive behaviors of geomaterials under mechanical, fluid, and chemical interactions, which result in displacement and cracking. Since there is no existing software or simulation tool that includes all the physical behaviors considered in this dissertation, the development and implementation of these physical mechanisms, followed by testing and analysis for engineering problems, constitutes the main contribution of this work. The newly developed simulation tool ranges from simulating the mechanical behavior of porous media saturated with water and reactive fluid to modeling the seepage of water/reactive fluid that triggers damage (cracks) in the porous media. This simulation tool can effectively analyze engineering problems that focus on the interactions between the working fluid and the host solid matrix under complex solution conditions. Examples include modeling carbon sequestration in saline aquifers and the storage of nuclear waste in subsurface repositories etc. The simulation tool proposed in this thesis incorporates rigorous mathematical derivations, efficient and accurate multiscale discretization techniques, robust non-iterative and iterative numerical coupling strategies, and thorough comparisons between numerical results and experimental/laboratory data. Simultaneously, it is important to recognize the model's limitations. Although the model assumes local equilibrium and interactions between physical mechanisms, it cannot fully capture all behaviors under these assumptions due to the restrictions in our understanding and potential constraints of numerical methods.