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.

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.

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.

Currently, there is no infrastructure between the two Indonesian islands Flores and Adonara. The islands are separated by the Larantuka Strait, which has a width varying between 600 and 1000 meters. The local government would like a bridge between the two islands. However, as the water in the 18 meter deep strait is heavily subjected to tidal forces - creating a tidal amplitude of about 1.5 m and tidal flow velocities ranging up to 4.5 m/s - structural design is challenging. As traditional bridges were deemed too expensive, a new type of bridge was introduced: the `Tidal Bridge'. The pendulum founded floating bridge, which is proposed to span the deepest 400 meters of the cross-section, is designed with tidal turbines attached to the bottom of the structure. The energy production mitigates the financial burden that the 225 million US dollar Palmerah Tidal Bridge will bring. At the time of writing, a pre-feasibility study has been performed by Antea, proposing initial structural dimensions. BAM took over the design process, which lead to questions regarding the dynamic stability of the design. The objective of this report is to answer the following two research questions: 1. How can the dynamic response due to two-dimensional forcing of a Tidal Bridge be determined? 2. What design choices can further optimise the dynamic behaviour of a Tidal Bridge? A numeric tool has been created to predict the dynamics of the proposed design as function of an input of wind, waves, and current. Based on (experimental) literature, hydrodynamic coefficients determining the fluid-structure interaction were determined. The complex shape of the floaters did not allow appropriate validation of the accompanying added mass and radiation damping coefficients. Comparison with a model constructed in Ansys Aqwa showed values of similar magnitude, but precise magnitudes could not be determined. In order to find these important coefficients, a set of experiments has been performed to determine the added mass (moment of inertia) and radiation damping (moment of inertia) for heave and roll motion. The experiments showed that the added mass equations for heave were well defined, while the added mass moment of inertia equations for roll motion deviated up to 250 per cent. The acquired data was used to find better relations between the added mass (moment of inertia) and the floater dimensions. Please note, the empirical relations are based on limited data and with little mathematical background. Hence, the relations should be used with care. The radiation damping coefficients that were also extracted from the experiments showed no clear trend, but did confirm that the hand-calculations were of correct magnitude. Using the constructed model, forcing characteristics of the Tidal Bridges are investigated. In these computations, the Palmerah Tidal Bridge dimensions are used as a case study. It was noted that the extreme non-linearity of different elements of the problem (changing pendulum angle, hydrodynamic pressure field, and particle velocity/acceleration field) do not allow for linear approximation. While a linear mass-spring system predicts that the natural period is about 6.7 seconds, the maximum dynamic amplitude is found for wave periods of 9 seconds. This coincides with the largest expected waves for the Palmerah Tidal Bridge location. Reducing the natural period of the design is recommended. Additionally, research was done into the contribution of the various types of forcing, where it was found that traffic weight has negligible effect on the dynamics. Wind forces add only a few percent to the pendulum forces, but do have a significant contribution to the displacements. Furthermore, research into the impact of an approaching wave field showed that accelerations during first impact may overshoot the maximum steady state acceleration by more than 200 per cent. A parametric study on the dynamics of Tidal Bridges was performed, which did research into the the forcing combinations that lead to most amplification of the dynamics. It shows that different loading combinations are governing for accelerations in the three different degrees of freedom present in a two-dimensional system. In here, difference was found for the dynamic behaviour induced by waves from the two different wave directions, leading to two sets of three forcing combinations. This data was used to investigate the effect of three design parameters: the angle of the pendulum, the hinge location of the pendulum and the depth of the strait. Moreover, a sensitivity study is performed on a set of parameters defining the Tidal Bridge. It shows that the mass of the segment, the added mass, the floater length, the design turbine force, and the pendulum angle are most important if it comes to design optimisation. Based on the parametric study and the forcing characteristics, conclusions and recommendations are made for improvements of Tidal Bridge designs in general and more specifically: the Palmerah Tidal Bridge.

The Ampelmann system occasionally starts vibrating unexpectedly, especially while the system is placed on a pedestal. These vibrations are believed to be caused by the eigenfrequencies of the system and/or amplification caused by the motion control algorithm. In this research an investigation in this phenomenon was done. This investigation was done via an analysis of the eigenfrequencies of the active controlled hexapod. A finite element method model was created to determine the eigenfrequencies of the system. This model was made using MATLAB and the toolbox StaBIL 2.0, created by the university of Leuven. All the elements of the system are modeled as beams except the hydraulic actuators. The properties of the elements which represent the hydraulic actuators are calculated separately using a modelling study on stiffness characteristics of hydraulic cylinder under multi-factors.
Possible causes for the unexpected vibrations have been investigated via measurements performed on Ampelmann systems. Data which was readily available is analyzed. Based on this data three possible causes have been determined. These are: the influence of the pedestal, residual motions due to limitations of the Ampelmann system and vibrations in the bottom frame due to compensating for gangway motions. To investigate the influence of the pedestal and the vibrations in the bottom frame two experiments have been performed. The residual motions have been investigated via calculations based on data already available. The amplitude of the response in the results from the first experiment performed to investigate the vibrations in the bottom frame due to gangway motions is negligible over the entire test period. The data from the calculations done to investigate the effect of the residual motions show no amplification. The results of the experiment and the calculations lead to the conclusion that these do not cause unwanted behavior. The second experiment to determine the influence of the pedestal shows four peaks in the frequency domain of both the signals. The first is directly caused by vessel motions. The other three have a cause which is not directly related to vessel motions. The data from the sensor on the Ampelmann system, at the top of the pedestal, does not contain a peak which is not present at the ship deck. From this it can be concluded that the eigenfrequencies of the pedestal do not have a relevant influence. For one of these peaks the amplitude of the graph related to the top of the pedestal is higher than the one corresponding to the ship deck. A possible explanation for this phenomenon could be the eigenfrequencies and corresponding eigenmodes of the ship deck. The pedestal functions as a leaver arm amplifying the rotations related to eigenmodes of the ship deck. This may cause the unexpected vibrations.