Thesis (Ph.D.)--Michigan Technological University, 2007. / Includes bibliographical references. Also available on the World Wide Web.

Thesis (M.S.)--Michigan Technological University, 2006. / Includes bibliographical references. Also available on the World Wide Web.

Thesis (Ph.D.)--Michigan Technological University, 2006. / Includes bibliographical references. Also available on the World Wide Web.

In this paper the effects of inertia are explored for the case of a thermal excitation applied on the surface of an infinitely long, solid circular cylinder. The linear uncoupled field equations for a homogeneous, isotropic, thermoelastic medium are used to derive the desired field equations of stress and displacement. The solution procedure included, first, the determination of the thermal boundary value problem from the energy equation which is identically satisfied for the uncoupled condition. Secondly, substitution of the strain-displacement relationships and the previously obtained thermal relation into the equilibrium equation containing inertial effects. The equilibrium equation is the only nonidentically satisfied equation. Thirdly, a solution of this equation is then found in the S-domain by Laplace transformation. Finally, the desired displacement equation is transformed into the time-domain as a function of temperature, time and radius of the cylinder by using inverse Laplace transforms and the calculus of residues.

<p>A theoretical and experimental study of RHS joints is presented, with particular attention being devoted to RHS gap K joints due to their popularity and complex behaviour. The theoretical aspects include the derivation of a nine-node general shell element with six degrees of freedom per node, capable of modelling multiple intersections between plates and shells. The material behaviour is described using the Von Mises yield criterion and the Prandtl-Reuss flow equations. The plasticity algorithm allows a sampling point to yield within a load increment and traces both the elastic and inelastic stress increments accordingly. Refined numerical analyses allow for an accurate tracing of the yield surface in every iteration. Each sampling point within an element is capable of carrying individually specified material properties. This makes it possible to account for a strain-hardened zone near the corners of an RHS or for the material properties of the weldment. The experimental investigation included 26 isolated RHS joints which were subconfigurations of a gap K joint. The testing program made it feasible to assess the effects of the angle of branch inclination and the flexibility of the base. Numerous strain gauges and rosettes mounted on the branch walls near the weldment, provided load-strain characteristics at the toe, the heel and the sidewall for the entire history of loading. The effectiveness of the heel area and the type of failure mode were found to depend strongly on the angle of branch inclination. The rigid or flexible base conditions affected the stress distribution in the branch walls and the direction of the principal axes. The developed finite element model was used in the numerical simulation of the behaviour of RHS joints. All the joint configurations tested were subjects of the numerical simulation in three independent stages which allowed for the model to be thoroughly verified. A very good agreement between the experimental and numerical results was achieved in all stages. The numerical analysis provided complementary results towards better understanding of the behaviour of tested joints. The same numerical model was utilized in a parametric study of a gap K joint which included the effects of : the angle of branch inclination, the width ratio, the gap size and the chord width to thickness ratio. The results are presented by means of stresses in the branch member walls and the local deflections of the chord connecting face. A number of new observations are made which result in recommendations for the design of RHS joints.</p> / Doctor of Philosophy (PhD)

<p>The decoupled seismic analysis of Multi-Degree-Of-Freedom (MDOF) secondary system subjected to multiple-support excitations overestimates its response. It is recognized that the analysis overestimates the secondary system response because the dynamic characteristics of the combined Primary-Secondary (P-S) system are neglected. The problem that is addressed in this thesis is how to include the effects of these dynamic characteristics in decoupled seismic analyses of multiply-supported MDOF secondary systems. The objective is to estimate the secondary system response using a decoupled seismic analysis such that it approximates the response that would have been obtained using a coupled analysis. Three approaches are considered in addressing the problem. These are the conventional deterministic approach, the recently developed Cross-Cross-Floor-Spectrum (CCFS) approach, and the stochastic approach. Three major contributions are achieved. First, the complexity associated with the seismic analysis of multiply-supported MDOF secondary systems is highlighted. Second, an improved CCFS approach, that avoids the shortcomings of the original CCFS approach, is proposed. Third, a new stochastic approach, that accounts for the dynamic characteristics of the combined P-S system, is developed.</p> / Doctor of Philosophy (PhD)

<p>Traditionally, textiles were dried outdoors with the wind and the sun enhancing the drying process. Tumble dryers offer a fast and convenient way of drying textiles independent of weather conditions. Tumble dryers, however, consume large amounts of electrical energy. Over 4 million tumble dryers are sold each year in Europe and a considerable amount of energy is used for drying of clothes. Increasing energy costs and the awareness about environmental problems related to a large energy use has increased the demand for dryers with better energy efficiency. The aim with this thesis is to show how to improve the energy efficiency of domestic tumble dryers.</p><p>Two types of tumble dryers are available on the market today: the open cycle dryer and the closed cycle dryer. In the open cycle dryer room air is heated and led into the drying drum. The exhaust air leaves the dryer and is often evacuated outside the building. In the closed cycle dryer an internal airflow is recirculated inside the dryer. When the hot air has passed through the drying drum it is led through a heat exchanger where the water vapour is condensed before the air is heated again and led to the drum. The heat exchanger is cooled with room air.</p><p>Drying at low temperature has been shown to reduce the specific energy use for an open cycle tumble dryer. In Paper I a correlation between the specific energy use, the drying time and the heat supply was established for a specific load by using the exhaust air temperature. It was shown that the total drying time and specific energy use could be predicted from data during the first hour of the process. This result indicated a possibility to create a control system that makes it possible for the user to choose between low energy use or short drying time.</p><p>The focus of Paper II is to reduce the energy use for a closed cycle tumble dryer. Energy and mass balances were established in order to determine feasible improvements. Energy and mass flows in the dryer indicated that reducing leakage from the internal system of the dryer gave the largest reduction of specific energy use. Insulation of the back cover of the dryer and opening the internal system during the falling drying rate period also gave positive results on the energy use. In total a feasible reduction of the energy use of approximately 17% was calculated.</p>

<p>Both optimal disturbances and optimal control are studied by means of numerical simulations for the case of the flat-plate boundary-layer flow. The optimisation method is the Lagrange multiplier technique where the objective function is the kinetic energy of the flow perturbations and the constraints involve the linearised Navier–Stokes equations. We consider both the optimal initial condition leading to the largest growth at finite times and the optimal time-periodic forcing leading to the largest asymptotic response. The optimal disturbances for spanwise wavelengths of the order of the boundary layer thickness are streamwise vortices exploiting the lift-up mechanism to create streaks. For long spanwise wavelengths it is the Orr mechanism combined with the amplification of oblique wave packets that is responsible for the disturbance growth. Control is applied to the bypass-transition scenario with high levels of free-stream turbulence. In this scenario low frequency perturbations enter the boundary layer and streamwise elongated disturbances emerge due to the non-modal growth. These so-called streaks are growing in amplitude until they reach high enough energy levels and breakdown into turbulent spots via their secondary instability. When control is applied in the form of wall blowing and suction, within the region that it is active, the growth of the streaks is delayed, which implies a delay of the whole transition process. Additionally, a comparison with experimental work is performed demonstrating a remarkable agreement in the disturbance attenuation once the differences between the numerical and experimental setup are reduced.</p><p> </p><p> </p>

<p>Constrained optimization is used to derive human postures and movements. In the first study a static 3D model with 30 muscle groups is used to analyse postures. The activation levels of these muscles are minimized in order to represent the individual's choice of posture. Subject specific data in terms of anthropometry, strength and orthopedic aids serve as input. The aim is to study effects from orthopedic treatment and altered abilities of the subject. Initial validation shows qualitative agreement of posture strategies but further details about passive stiffness and anthropometry are needed, especially to predict pelvis orientation. In the second application, the athletic long jump, a problem formulation is developed to find optimal movements of a multibody system when subjected to contact. The model was based on rigid links, joint actuators and a wobbling mass. The contact to the ground was modelled as a spring-damper system with tuned properties. The movement in the degrees of freedom representing physical joints was described over contact time through two fifth-order polynomials, with a variable transition time, while the motion in the degrees of freedom of contact and wobbling mass was integrated forwards in time, as a consequence. Muscle activation variables were then optimized in order to maximize ballistic flight distance. The optimization determined contact time, end configuration, activation and interaction with the ground from an initial configuration. The results from optimization show a reasonable agreement with experimentally recorded jumps, but individual recordings and measurements are needed for more precise conclusions.</p><p> </p>

<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>