Within this report, an analytical research will be performed on the effectivity of Tuned Mass Dampers (TMDs) and Viscoelastic Dampers (VEDs), and a conclusion will be drawn as to which is most effective in damping the oscillations of an earthquake. First of all, a simple model of second-order differential equations describing the oscillations of each floor within a building of n floors is derived, in which no frictional forces are taken into account. The solution to this model is derived for a building of two floors, which demonstrates the characteristics of oscillations in this model and which shows how resonance is represented mathematically, and what patterns of oscillations look like. Then, a TMD and VED are added to the model of one floor to expose what their working principles are. Subsequently, the methods of adding these dampers to the models for two, five and ten floors are given. For varying earthquake-frequencies, the maximum displacement within 5 seconds is determined, which shows the effect of TMDs and VEDs for different positions within the building. The conclusion from these results is that the effect of the TMDs is always that at the eigenfrequencies, the oscillations of the building are no longer resonating. However, the building will start resonating for other eigenfrequencies due to the TMD. The VED is more consistent, though its damping-effect on resonating frequencies is smaller than for the TMDs. The conclusion is that VEDs are most effective, though more dampers have to be added to improve its effectiveness. After this, a new model is introduced, which does contain a friction force: air resistance. Based on the new model, it is concluded that even oscillations for resonating frequencies are eventually damped out, though they do still grow large. Again, TMDs and VEDs are added to the model, and similar conclusions about the effectivity of the dampers as for the first model were drawn.

Humans are efficient at moving due to their exceptional mastery of bipedal locomotion. Several models have been made that attempt to model the motion of the centre of mass with a spring-mass system with various degree of success. For example, a two dimensional model tracks the height of the centre of mass well and a three dimensional model explains the normal force exerted on the ground.

In this report a three dimensional model is constructed to describe the motion of the centre of mass, with the purpose to determine the spring constant and the rest length in a simple prosthetic leg. The research question is: can a three dimensional spring-mass model accurately track the centre of mass and can this be used to determine the optimal properties of the spring of a simple prosthetic leg?

The spring mass model consists of two springs connected to the ground and the centre of mass. The springs do not exert a force on the centre of mass if they are extended. The model incorporates steps by moving the ground connection points instantaneously over fixed points on a rail. The model can be used in two distinct ways. The first generates a periodic trajectory by finding the optimal initial positions y₀ and z₀ (PPFA) and the second finds the optimal spring parameters k and u to fit a data set (DFA). The optimal conditions are found by discretizing the parameter space and using an iterative process. The space around the best parameters becomes the parameter space for the next iteration.

The PPFA shows that the initial lateral displacement is nearly constant with respect to the spring constant when the rest length is chosen such that the centre of mass is at constant height if the model is stationary. The PPFA also shows that there are two distinct y-trajectories possible for walking. Running, however, has only one trajectory. Several versions of the model are fit to the data: only discretised step widths, discretised step widths and a x₀-offset, and distinct legs. There is not much difference between these models. The x₀-offset is only Δs = -0.02m confirming that the position of the feet does align with the extreme values of the y- and z-position. The model fits the general characteristics well but fine details in the motion are lost. Future research should investigate how cumbersome these deviations of the data are perceived by people using a simple prosthetic.

The world faces an increasing energy problem, forcing people to search for sustainable energy sources. Offshore wind energy has shown great potential to financially compete with traditional energy sources. Recent developments like the slip-joint connection increase this potential. However, for further optimization of the design of a slip-joint, the location of the contact areas between the two cones must be known. Previous attempts to detect these contact areas based on techniques such as heat transfer or ultrasonic measurements have proven insufficient. A possible new way of detecting contact areas, is through the behaviour of Energy Flux. Energy Flux methods have shown great potential as a damping identification tool in other applications. Therefore, in this study the relation between Energy Flux behaviour and the presence of a contact point in the time-, frequency- and time-frequency-domain is studied. To this end, a numerical analysis of a vibrating simply supported Euler Bernoulli beam is conducted, simulating a contact area with a point load. The analysis in the frequency-domain showed the most promising results. Presence of a contact point (i) introduces peaks at twice the first and twice the second eigenfrequencies, and (ii) increases peak height at the location of the contact point. The pressure of the simulated contact point increased these effects. In the time-domain the presence of a contact point increased the amplitude of the cumulative energy flux. This change was most significant at the antinode of the first eigenmode. The location of the contact point was of little influence on this effect. These results show that the presence of a contact area influences the behaviour of the energy flux. The results are encouraging for a later implementation of the energy flux method for the detection of contact areas in a slip-joint. As a validation of these results, an experiment has been proposed. After execution of this experiment, further research is needed in (i) the behaviour of Energy Flux in a conical shape, and (ii) Energy Flux measurements of higher frequencies.

One of the challenges associated with offshore wind turbine installations is the mating phase. Aligning a transition piece onto its substructure under offshore conditions is a complicated and time-consuming procedure. Another issue found in a number of commissioned offshore wind turbines is related to the sustainability of the connection between the transition piece and the substructure. With wind turbines increasing in size and wind farms being built further from shore in deeper waters, the current bolted- and grouted connections are seemingly not the most suitable future proof options. This is where the Double Slip Joint steps in. A simple plug- and go connection device provided by KCI The Engineers. The Double Slip Joint’s innovative solution takes away the time-consuming phases like manually fastening a number of bolts or the buffer period of waiting for grout material to fully solidify before commissioning a wind turbine. This study aims to gain more useful insights on the installation behavior of the Double Slip Joint during the mating phase under various offshore environmental conditions. The chosen system for this study consists of a hoisted wind turbine tower which is lowered onto a monopile. A numerical model for this tower-monopile system is developed in Excel where the user is able to manipulate input parameters such as mean wind velocity, tower lowering velocity, crane motions etc. After a series of validation using Ansys Finite Element models, simulations from the developed Excel model were carried out to study the Double Slip Joint’s behavior during the mating phase from both a jack-up - and a floating vessel. A key finding from this study is the necessity to round off the sharp edges of the Double Slip Joints conical rings in order to avoid contact stresses that might lead to unwanted damage. The simulation results indicate that installations carried out from a jack-up vessel can be optimised to perfectly tolerate a mean wind velocity of 15 m/s, whereas that of a floating vessel can be optimised up to 13 m/s. The possibility of achieving higher mean wind velocities indicate that the weather window for offshore installations can have a greater range. The results obtained from this study confirm the potential of the Double Slip Joint for future offshore wind turbine installations.