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This study was performed to characterize and understand static loading capacities of the T-shaped, end-toace, mortise-and-tenon joints in pine plywood and oriented strandboard (OSB), and to develop mechanical models to predict its tensile, moment, and torsional resistance capacities. Results of the study indicated that the tensile resistance of a stapled-and-glued mortise-and-tenon joint in pine plywood and OSB ranges from 505 to 1933 lb. and 306 to 845 lb., respectively; the moment resistance ranges from 780 to 4428 lb.-in. and 612 to 2309 lb.-in., respectively; and the torsional resistance ranges from 598 to 2292 lb.-in. and 439 to 1260 lb.-in., respectively. The mechanical models proposed in this study were experimentally validated. The tensile, moment, and torsional resistances of a T-shaped, end-toace, stapled-and-glued, mortise-and-tenon joints can be estimated based on knowing basic material properties of single-staple tensile, lateral shear resistance, and material end-toace glue bonding tensile strength and shear strength.

<p>A mechanical model of an axial piston-type machine with a so-called wobble plate and Z-shaft mechanism is presented. The overall aim is to design and construct an oil-free piston expander demonstrator as a first step to realizing an advanced and compact small-scale steam engine system. The benefits of a small steam engine are negligible NOx emissions (due to continuous, low-temperature combustion), no gearbox needed, fuel flexibility (e.g., can run on biofuel and solar), high part-load efficiency, and low noise. Piston expanders, compared with turbines or clearance-sealed rotary displacement machines, have higher mechanical losses but lower leakage losses, much better part-load efficiency, and for many applications a more favourable (i.e., lower) speed. A piston expander is thus feasible for directly propelling small systems in the vehicular power range. An axial piston machine with minimized contact pressures and sliding velocities, and with properly selected construction materials for steam/water lubrication, should enable completely oil-free operation. An oil-free piston machine also has potential for other applications, for example, as a refrigerant (e.g., CO₂) expander in a low-temperature Rankine cycle or as a refrigerant compressor.</p><p> </p><p>An analytical rigid-body kinematics and inverse dynamics model of the machine is presented. The kinematical analysis generates the resulting motion of the integral parts of the machine, fully parameterized. Inverse dynamics is applied when the system motion is completely known, and the method yields required external and internal forces and torques. The analytical model made use of the “Sophia” plug-in developed by Lesser for the simple derivation of rotational matrices relating different coordinate systems and for vector differentiation. Numerical solutions were computed in MATLAB. The results indicate a large load bearing in the conical contact surface between the mechanism’s wobble plate and engine block. The lateral force between piston and cylinder is small compared with that of a comparable machine with a conventional crank mechanism.</p><p> </p><p>This study aims to predict contact loads and sliding velocities in the component interfaces. Such data are needed for bearing and component dimensioning and for selecting materials and coatings. Predicted contact loads together with contact geometries can also be used as input for tribological rig testing. Results from the model have been used to dimension the integral parts, bearings and materials of a physical demonstrator of the super-critical steam expander application as well as in component design and concept studies.</p>

Two fundamental questions in the investigation of any sensory system are what physical signals drive its primary sensory neurons and how such signals are encoded by the successive neural levels during natural behaviour. Due to the complexity of experiments with awake, actively sensing animals, most previous studies focused on anesthetized animals, where the motor component of sensation is abolished and therefore those questions are so far largely unanswered. The aim of this thesis is to exploit recent advance in electrophysiological, behavioural and computational techniques to address those questions in the sub-cortical whisker system of the mouse. To determine the input to the whisker system, in Chapter 2 I recorded from primary whisker afferents (PWAs) of awake, head-fixed mice as they explored a pole with their whiskers, and simultaneously measured both whisker motion and forces with high-speed videography. To predict PWA firing, I used Generalised Linear Models. I found that PWA responses were poorly predicted by whisker angle, but well predicted by rotational force (moment) acting on the whiskers. This concept of “moment encoding” could account for the activity of PWAs under diverse conditions - whisking in air, active whisker-mediated touch and passive whisker deflection. The discovery that PWAs encode moment raises the question of how mice employ moment to control their tactile behaviours. In Chapter 3 I therefore measured moment at the base of the whiskers of head-fixed mice, performing a novel behavioural task, which involved whisker-based object localisation. I then tested which features of moment during whiskerobject touch could predict mouse choice. By using probabilistic classifiers, I discovered that mouse choices could be accurately predicted from moment magnitude and direction during touch, combined with a non-sensory variable - the mouse choice in the previous trial. Finally, in Chapter 4 I asked how tactile coding generalized to whisker system sub-cortical brains regions during a natural active whisker-based behaviour. I therefore combined a naturalistic whisker-guided navigation task and extracellular recording with a novel generation of high density silicon probes (O3 Neuropixel probes) and studied how touch and locomotion were encoded by the whisker first (ventral posterior nucleus, VPM) and higher order thalamic relay (posterior complex, PO) and hypothalamic regions and (zona incerta, ZI). Using multiple linear regressions, I found that neurons in the relay nucleus VPM encoded not only touch, but also locomotion signals. Similarly, neurons in the higherorder regions PO and ZI were driven by both touch and locomotion. My study showed that in the awake animal, in the central part of the whisker system, peripheral signals were preserved, but were encoded concomitantly with motor variables, such as locomotion. In summary, in this thesis I identified the mechanical variable representing the major sensory input to the whisker system. I showed that mice are able to employ it to guide behaviour and found that correlate of this signal was encoded by central neurons of the whisker system in VPM, PO and ZI, concomitantly with locomotion.

The human crystalline lens is a complex, inhomogeneous and dynamic optical element which enables the eye to adjust focus in a process known as accommodation. Age related changes in the optical and mechanical properties of the lens cause a loss in accommodative ability leading to a condition known as presbyopia. Several experimental surgical techniques are under development for the correction of presbyopia. The goal of this dissertation is to better understand the relationship between the crystalline lens shape, its non-uniform refractive index gradient and its optical power and their changes with age and accommodation. In this study direct lens power and shape measurements were acquired on isolated lenses, and on lenses mounted in a lens stretching system designed to simulate accommodation. Several lens shape and power measurement techniques were developed for this study including a Scheimpflug camera system optimized for imaging the crystalline lens. Direct measurements of lens shape and power were used to develop an age-dependent optical-mechanical model of the lens during accommodation. The study shows that the normal growth of the lens is a major contributor to the progressive loss of accommodation amplitude, independent of changes in the elastic properties of the lens. These findings suggest that accommodation can be restored by refilling the lens with a material having a uniform refractive index.

The physiological energy requirements of prosthetic gait in lower-limb amputees have been observed to be significantly greater than those for able-bodied subjects. However, existing models of energy flow in walking have not been very successful in explaining the reasons for this additional energy cost. Existing mechanical models fail to capture all of the components of energy cost involved in human walking. In this thesis, a new model is developed that estimates the physiological cost of walking for an able-bodied individual; the same cost of walking is then computed using a variation of the model that represents a bi-lateral below-knee amputee. The results indicate a higher physiological cost for the amputee model, suggesting that the model more accurately represents the relative metabolic costs of able-bodied and amputee walking gait. The model is based on a two-dimensional multi-body mechanical model that computes the joint torques required for a specified pattern of joint kinematics. In contrast to other models, the mechanical model includes a balance controller component that dynamically maintains the stability of the model during the walking simulation. This allows for analysis of many consecutive steps, and includes in the metabolic cost estimation the energy required to maintain balance. A muscle stress based calculation is used to determine the optimal muscle force distribution required to achieve the joint torques computed by the mechanical model. This calculation is also used as a measure of the metabolic energy cost of the walking simulation. Finally, an optimization algorithm is applied to the joint kinematic patterns to find the optimal walking motion for the model. This approach allows the simulation to find the most energy efficient gait for the model, mimicking the natural human tendency to walk with the most efficient stride length and speed.

The physiological energy requirements of prosthetic gait in lower-limb amputees have been observed to be significantly greater than those for able-bodied subjects. However, existing models of energy flow in walking have not been very successful in explaining the reasons for this additional energy cost. Existing mechanical models fail to capture all of the components of energy cost involved in human walking. In this thesis, a new model is developed that estimates the physiological cost of walking for an able-bodied individual; the same cost of walking is then computed using a variation of the model that represents a bi-lateral below-knee amputee. The results indicate a higher physiological cost for the amputee model, suggesting that the model more accurately represents the relative metabolic costs of able-bodied and amputee walking gait. The model is based on a two-dimensional multi-body mechanical model that computes the joint torques required for a specified pattern of joint kinematics. In contrast to other models, the mechanical model includes a balance controller component that dynamically maintains the stability of the model during the walking simulation. This allows for analysis of many consecutive steps, and includes in the metabolic cost estimation the energy required to maintain balance. A muscle stress based calculation is used to determine the optimal muscle force distribution required to achieve the joint torques computed by the mechanical model. This calculation is also used as a measure of the metabolic energy cost of the walking simulation. Finally, an optimization algorithm is applied to the joint kinematic patterns to find the optimal walking motion for the model. This approach allows the simulation to find the most energy efficient gait for the model, mimicking the natural human tendency to walk with the most efficient stride length and speed.

To get an improved understanding and knowledge of the processes and phenomena during the late phase of a core melt down accident the FOREVER-experiments (Failure of Reactor Vessel Retention) are currently underway. These experiments are simulating the lower head of a reactor pressure vessel under the load of a melt pool with internal heat sources. The geometrical scale of the experiments is 1:10 compared to a common Light Water Reactor. During the first series of experiments the Creep behaviour of the vessel is investigated. Due to the multi-axial creep deformation of the three-dimensional vessel with a non-uniform temperature field these experiments are on the one hand an excellent possibility to validate numerical creep models which are developed on the basis of uniaxial creep tests. On the other hand the results of pre-test calculations can be used for an optimized experimental procedure. Therefore a Finite Element model is developed on the basis of the multi-purpose commercial code ANSYS/Multiphysics®. Using the Computational Fluid Dynamic module the temperature field within the vessel wall is evaluated. The transient structural mechanical calculations are performed applying a creep model which is able to take into account great temperature, stress and strain variations within the model domain. The new numerical approach avoids the use of a single creep law with constants evaluated for a limited stress and temperature range. Instead of this a three-dimensional array is developed where the creep strain rate is evaluated according to the actual total strain, temperature and equivalent stress for each element. Performing post-test calculations for the FOREVER-C2 experiment it was found that the assessment of the experimental data and of the numerical results has to be done very carefully. A slight temperature increase during the creep deformation stage of the experiment for example could explain the creep behaviour which appears to be tertiary because of the accelerating creep strain rate. Taking into account both - experimental and numerical results - gives a good opportunity to improve the simulation and understanding of real accident scenarios.

<p>The surface of cell membranes can display a high degree of lateral heterogeneity. This non-uniform distribution of constituents is characterized by mobile nanodomain clusters called rafts. Enriched by saturated phospholipids, cholesterol and proteins, rafts are considered to be vital for several important cellular functions such as signalling and trafficking, morphological transformations associated with exocytosis and endocytosis and even as sites for the replication of viruses. Understanding the evolving distribution of these domains can provide significant insight into the regulation of cell function. Giant vesicles are simple prototypes of cell membranes. Microdomains on vesicles can be considered as simple analogues of rafts on cell membranes and offer a means to study various features of cellular processes in isolation. </p><p>In this work, we employ a continuum approach to model the evolution of microdomains on the surface of Giant Unilamellar Vesicles (GUVs). The interplay of species transport on the vesicle surface and the mechanics of vesicle shape change is captured using a chemo-mechanical model. Specifically, the approach focuses on the regime of vesicle dynamics where shape change occurs on a much faster time scale in comparison to species transport, as has been observed in several experimental studies on GUVs. In this study, shape changes are assumed to be instantaneous, while species transport, which is modeled by phase separation and domain coarsening, follows a natural time scale described by the Cahn--Hilliard dynamics.</p><p>The curvature energy of the vesicle membrane is defined by the classical Canham--Helfrich--Evans model. Dependence of flexural rigidity and spontaneous curvature on the lipid species is built into the energy functional. The chemical energy is characterized by a Cahn--Hilliard type density function that intrinsically captures the line energy of interfaces between two phases. Both curvature and chemical contributions to the vesicle energetics are consistently non-dimensionalized.</p><p>The coupled model is cast in a diffuse-interface form using the phase-field framework. The phase-field form of the governing equations describing shape equilibrium and species transport are both fourth-order and nonlinear. The system of equations is discretized using the finite element method with a uniform cubic-spline basis that satisfies global higher-order continuity. For shape equilibrium, geometric constraints of constant internal volume and constant surface area of the vesicle are imposed weakly using the penalty approach. A time-stepping scheme based on the unconditionally gradient-stable convexity-splitting technique is employed for explicit time integration of nonlocal integrals arising from the geometric constraints.</p><p>Numerical examples of axisymmetric stationary shapes of uniform vesicles are presented. Further, two- and three-dimensional numerical examples of domain formation and growth coupled to vesicle shape changes are discussed. Simulations qualitatively depicting curvature-dependent domain sorting and shape changes to minimize line tension are presented. The effect of capturing the difference in time scales is also brought out in a few numerical simulations that predict a starkly different pathway to equilibrium.</p> / Dissertation

This thesis identified key mix design variables that influence the mechanical properties and behaviour of shockpads and developed a mechanical model to describe this behaviour. This investigation was undertaken to address the lack of scientific understanding of shockpad layers used in synthetic sports pitches. Shockpads play a crucial role in the player and ball interaction properties of synthetic pitches. However, the current poor state of knowledge regarding shockpad mix design effects and the implications for site practice during construction was developed through constructor experience and basic testing. This lack of comprehensive knowledge was reflected in the barelyexistent standards for design specification and testing requirements stipulated by sporting governing bodies at the time of this project inception. Further scientific investigation of the effects of shockpad mix design on mechanical properties and behaviour was required to develop guidelines to optimise shockpad design, construction and testing and also to build more knowledge on sport surface behaviour due to growing interest among the industry and other stakeholders such as governing bodies and sport shoe manufacturers for example. A method to construct small-scale cast in-situ shockpads in the laboratory was developed to produce reliable and repeatable samples for investigation, including a benchmark shockpad and shockpads with carefully controlled mix design variations. Shockpad thickness, binder content, binder type, rubber size, rubber size distribution and bulk density were varied through a range of appropriate values in the laboratory constructed shockpads. Shockpads and shockpad-carpet systems (using water based and 3'1 generation carpets) were subjected to Berlin Artificial Athlete and 2.25 kg Clegg Hammer impacts to measure player-surface interaction properties and vertical hockey ball impacts to measure ball interaction properties. Tensile measurements and cyclic fatigue testing were used to determine shockpad durability. Impact testing was repeated on shockpads and shockpad-carpet systems with thickness variations to determine shockpad behaviour using a force plate. Behaviour measurements were used to develop a mechanical model to describe shockpad behaviour. (Continues...).