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The great challenge of the 21st century to mitigate climate change requires generation of green electricity to be an achievable goal. One way of producing green electricity is through usage of wave energy converters which are devices that use the energy of the ocean waves to produce electricity.   W4P Waves4Power AB is a company from Sweden, devoted to commercializing their wave energy converter called the WaveEl buoy. The WaveEl buoy is a point absorber that produces electricity by using the energy of the waves to run a hydraulic motor connected to a generator. The working principle of the buoy is to let a water piston oscillate in a tube with a water column. The water column exerts flow resistance forces on the piston as it oscillates, and these forces create a frame of reference upon which the hydraulic motor system may operate. There are leakage clearances at the sides of the water piston that allow for flow of water past the piston and associated with this flow are parts of the flow resistance forces. The flow resistance forces that are present due to water flow in the leakage clearances are calculated with the use of a flow resistance parameter and, in the literature, there is little investigation conducted as to the importance of this parameter.  The goal of present thesis work was to investigate the effect on 4 parameters of the WaveEl buoy system (power captured from the waves, flow resistance force acting on the piston, mean piston position, and number of bumper hits) due to adoption of 3 different values of the flow resistance parameter. One of these values was the currently assigned value by Waves4Power at the time when this study was conducted. The value was the constant 0.75 and was a guess by Waves4Power. The other two values were received from a parallel thesis work done at Karlstad University by Linnéa Tebelius where, with the use of CFD, Tebelius calculated the flow resistance parameter with different levels of accuracy.  The results of present thesis work were generated from simulations in a MATLAB Simulink model describing the dynamics of the WaveEl buoy system. Simulated time varied from 5.5 to 8.5 minutes per simulation. Generated results were compared to the results from using 0.75 as the value for the flow resistance parameter and showed that the energy captured from the waves was, at most, overestimated by approximately 13 % and underestimated by 6 %, depending on applied level of accuracy for description of the dynamic flow resistance parameter and simulated wave state. Furthermore, it was found that number of bumper hits varied extensively, in some cases from 0 to 47, between simulations where the only difference was applied value of the flow resistance parameter – further indicating that assigning a more accurate value on the dynamic flow resistance parameter may be of great importance when modelling the dynamics of the WaveEl buoy system.

Few aircraft engine manufacturers are able to consistently achieve high levels of performance reliability in newly manufactured engines. Much of the variation in performance reliability is due to the combined effect of tolerances of key engine components, including tip clearances of rotating components and flow areas in turbine nozzles. This research presents system analysis methods for determining the maximum possible tolerances of these key components that will allow a turbine engine to pass a number of specified performance constraints at a selected level of reliability. Through the combined use of a state-of-the-art engine performance code, component clearance loss models, and stochastic simulations, regions of feasible design space can be explored that allow for a pre-determined level of engine reliability. As expected, constraints such as spool speed and fuel consumption that are highly sensitive to certain component tolerances can significantly limit the feasible design space of the component in question. Discussed are methods for determining the bounds of any components feasible design space and for selecting the most economical combinations of component tolerances. Unique to this research is the method that determines the tolerances of engine components as a system while maintaining the geometric constraints of individual components. The methods presented in this work allow for any number of component tolerances to be varied or held fixed while providing solutions that satisfy all performance criteria. The algorithms presented in this research also allow for an individual specification of reliability on any number of performance parameters and geometric constraints. This work also serves as a foundation for an even larger algorithm that can include stochastic simulations and reliability prediction of an engine over its entire life cycle. By incorporating information such as time dependent performance data, known mission profiles, and the influence of maintenance into the component models, it would be possible to predict the reliability of an engine over time. Ultimately, a time-variant simulation such as this could help predict the timing and levels of maintenance that will maximize the life of an engine for a minimum cost. / Master of Science

Yes / Background: When trans-tibial amputees cross obstacles leading with their prosthesis, foot clearance is achieved using compensatory swing-phase kinematics. Such compensation would suggest able-bodied individuals normally use swing-phase ankle dorsiflexion to attain adequate obstacle clearance, however, direct evidence of such contribution is equivocal. The present study determined the contribution of sagittal plane ankle motion in achieving lead-limb clearance during obstacle negotiation. Methods: 12 male able-bodied individuals (ages 18-30) completed obstacle crossing trials while walking on a flat surface. Lead-limb (right) ankle motion was manipulated using a knee-ankle-foot orthosis. Trials were completed with the ankle restricted at a neutral angle or unrestricted (allowing ~ ±15  plantar/dorsiflexion). Findings: Restricted ankle motion caused significant increase in trail-limb foot placement distance before the obstacle (p=0.005); significant decrease in vertical toe clearance (p<0.003), vertical heel clearance (p=0.045) and lead-limb foot placement distance after the obstacle (p=0.045); but no significant changes in knee angle at instant of crossing or in average walking speed. Interpretation: The shifts in foot placements altered the part of swing that the lead-limb was in when the foot crossed the obstacle, which led to a decrease in clearance. These adaptations may have been due to being unable to dorsiflex the ankle to ‘lift’ the toes in mid-swing or to being unable to plantarflex the ankle during initial contact following crossing, which changed how the lead-limb was to be loaded. These findings suggest individuals using ankle bracing or those with ankle arthrodesis, will have reduced gait safety when negotiating obstacles.

yes / Background Unilateral trans-tibial amputees have bilaterally reduced toe clearance, and an increased risk of foot contact, while crossing obstacles compared to the able-bodied. While the able-bodied tend to lead with a ‘preferred’ limb it is equivocal whether amputees prefer to lead with the intact or prosthetic limb. This study determined the effects of laterality, compared to side of amputation, on amputees' obstacle crossing performance. To help understand why laterality could affect performance we also assessed knee proprioception for both limbs. Methods Foot placement and toe clearance parameters were recorded while nine amputees crossed obstacles of varying heights leading with both their intact and prosthetic limbs. Joint-position sense was also assessed. Participants self-reported which limb was their preferred (dominant) limb. Findings There were no significant differences in foot placements or toe clearance variability across lead-limb conditions. There were no significant differences in toe clearance between intact and prosthetic lead-limbs (p = 0.28) but toe clearance was significantly higher when amputees led with their preferred compared to non-preferred limb (p = 0.025). There was no difference in joint-position sense between the intact and residual knees (p = 0.34) but joint-position sense tended to be more accurate for the preferred, compared to non-preferred limb (p = 0.08). Interpretation Findings suggest that, despite the mechanical constraints imposed by use of a prosthesis, laterality may be as important in lower-limb amputees as it is in the able bodied. This suggests that amputees should be encouraged to cross obstacles leading with their preferred limb. / Engineering and Physical Sciences Research Council

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No / A 2D finite element model of frictional heating in a pad-disc brake system is proposed for analyzing the heat partition and heat flux at the pad/disc interface during braking. And further find out how long the model can reach a thermal stable situation. The temperature on the friction surfaces of automotive brake is an influential factor of the brake performance. A formulation of friction heat generation during braking with constant velocity is presented, and the effects of thermal contact resistance on a contact surface are simulated by ABAQUS with different thermal contact conductance/clearance settings. The heat partition at contact surface with different time instants are analyzed. Results show that the heat partition along the interface is affected by the interface contact pressure and the thermal contact conductance. Additionally, results based upon the proposed model show that at normal thermal contact conductance conditions, typically 104 W/m2K for friction brake applications, the heat partition and the interface temperature become sensitive to the interface pressure variation, in comparison with that under ideal high thermal contact conductance condition (or low thermal contact resistance condition), typically 106 W/m2K. The comparison between results from simulations with different interface thermal conductance values indicate the parameters are sensitive in normal thermal conductance applications and how thermal conductance affect brake performance. And it is worthy to try control interface thermal conductance by using different pad/disc materials to make interface thermal conductance at a proper value.

The present study focuses on local heat transfer characteristics on the tip and near-tip regions of a turbine blade with a flat tip, tested under transonic conditions in a stationary, 2-D linear cascade consisting of seven blades, the three center blades having a variable tip clearance gap. The effects of tip clearance and exit Mach number on heat transfer distribution were investigated on the tip surface using a transient infrared thermography technique. In addition, thin film gages were used to study similar effects on the near-tip regions at 94% based on engine blade span of the pressure and suction sides. The experiments were conducted at the Virginia Tech transonic blow-down wind tunnel facility with a seven-blade linear cascade. Surface oil flow visualizations on the blade tip region were carried-out to shed some light on the leakage flow structure. Experiments were performed at three exit Mach numbers of 0.7, 0.85, and 1.05 for two different tip clearances of 0.9% and 1.8% based on engine blade span. The exit Mach numbers tested correspond to exit Reynolds numbers of 7.6 x 105, 9.0 x 105, and 1.1 x 106 based on blade true chord. The tests were performed with a freestream turbulence intensity of 12%. Results at 0.85 exit Mach showed that an increase in the tip gap clearance translates into a 12% increase in the heat transfer coefficients on the blade tip surface. Similarly, at 0.9% tip clearance, an increase in exit Mach number from 0.85 to 1.05 also led to a 24% increase in heat transfer on the tip. High heat transfer was obtained at the leading edge area of the blade tip, and an increase in the tip clearance gap and exit Mach number augmented this leading edge heat transfer. At 94% of engine blade span on the suction side near the tip, a peak in heat transfer was observed in all test cases at an s/C of 0.66 due to the onset of a downstream leakage vortex. At the design condition, this peak represents an increase of a factor of 2.5 from the immediate preceding s/C location. An increase in both the tip gap and exit Mach number resulted in an increase, followed by a decrease in the near-tip suction side heat transfer. On the near-tip pressure side, a slight increase in heat transfer was observed with increased tip gap and exit Mach number. In general, the suction side heat transfer is greater than the pressure side heat transfer as a result of the suction side leakage vortices. / Master of Science