With the shift to renewable energy becoming more important than ever before and offshore wind farms being one of the sustainable energy resources available, many offshore wind farms are currently being built.
One of the difficulties of these wind farms built with monopiles is that the monopiles and electricity cables must be protected from scouring and falling objects. The protection is usually performed by placing a layer of rocks around and over these objects. For deep water up to 400 meters, vertical fall pipes are used to place the rocks directly under the rock placement vessel. This is impossible when placing rocks around monopiles, as the monopile stands in the way of where the vessel would have to lie during the rock placement procedure.
The inclined fall pipe (IFP) was introduced recently to combat this issue. The IFP, which hangs diagonally next to the vessel, can place rocks a couple of meters to the vessel's side, leaving a safe distance between the vessel and the monopile. Rocks tend to form clusters inside the pipe during placement with an IFP. This means the rocks exit the pipe in bursts of clusters, resulting in uneven rock layers if the rocks are placed during the movement of the vessel. Another result is less accurate placement of the rocks as the rocks at the outer layer of a cluster, during the free fall, are pushed further out, away from the intended placement location.

This thesis investigates the processes of rocks moving inside an inclined fall pipe and simulates this process numerically. This is achieved with a Finite-Volume solver for the fluid coupled with a Discrete Element model for the particles. The results are compared to existing experimental data.

The simulation results show the same rock behavior as in the lab tests for angles up to 60 degrees. The clusters start forming from the small volume concentration differences within the rock layer. The higher densities concentrate and become clusters, while the lower densities become gaps. In the simulations, this process is caused by the differences in the flow velocity of the fluid and the resulting drag differences of the particles. This knowledge is a first step towards finding solutions to lower the formation of clusters and thus, the more accurate placement of the rocks on the sea floor.

Furthermore, multiple points of improvement for the solver have been found. For angles of 75 degrees and steeper, the rock movements of the simulations miss a certain chaoticness, which may be attributed to missing turbulent drag forces in the solver. The velocities predicted by the solver are too high; multiple possible causes are speculated. The simulation results follow the same trends as the lab results, meaning they could be used for qualitative comparisons. Various additions to enhance the solver are proposed.
The influence of a system parameter, the distance factor was noticed to be stronger in shear flows than in homogeneous flows during a system parameter variation. This distance factor relates the fluid-particle interaction radius to the particle diameter. Finding limits for this parameter in shear flow could enhance the solver's prediction capability.

With the shift to renewable energy, more monopiles will be placed. The simulations show which forces cause the cluster formations and can be used to investigate ways of reducing them. This can reduce the spillage of rocks during operation, making the entire rock placement more efficient and will reduce costs.
The solver with the enhancements for better prediction capabilities could be used to further optimize the rock placement accuracy and efficiency. This would reduce wind farm costs and help the shift to renewable energy.

There is a growing demand of various metals originating from the sustainable energy transition. The current supply and investments plans for these critical minerals are insufficient to enable this green energy transition. Other problems are the dependency of third countries and multiple drawbacks of land-mining. Deep-sea mining could be a great outcome, by collection of nodules on the seabed in the CCZ area. Different mining trials have been executed, but large-scale mining has not started yet. So far, there is no design guideline for a polymetallic nodule dry bulk (transshipment) terminal. The design and construction phase for a dry bulk terminal takes several years, therefore, the design of such a terminal should be investigated. This thesis will focus on the design of a transshipment terminal to accommodate these large-scale mining activities in the future. The logistics and location determination of this terminal are also taken into account. The thesis contains a case-study which is formed in collaboration with Allseas. For this case-study, the simulation-based approach is chosen to design the transshipment terminal. This approach integrates many stochastic variations, identifies bottlenecks, and allows for sensitivity analysis or ’what if’ scenarios. This method was compared to traditional design methods that rely on rules of thumb and practical experiences.

In response to the sharp decline of seagrass globally, various restoration techniques have been developed and applied; many at limited scale and with limited success. This research focuses on the fluid mechanics and behaviour of seagrass seeds in a sand mixture through physical laboratory experiments. The objective is to establish a technique that incorporates seagrass seeds with sand-capping to develop seagrass restoration methods suitable for upscaling. Due to the limited amount of available seeds, laboratory experiments were conducted to find a suitable proxy for seeds from both intertidal and subtidal Zostera marina populations by tracking and analysing the particle's terminal settling velocity. The average terminal settling velocity of the seeds was 5.97 cm/s, slightly larger than that of sand particles with a diameter of 0.35 mm with a settling velocity of around 5.2 cm/s. Subsequently, the distribution of proxy seeds in the settled sediment of the "sand-capped layer" was determined after dispersal in five sediment-water mixtures with a volumetric concentration ranging from 5 % to 30 %. Mixtures with three-grain sizes grain sizes were released (d_{50} = 0.175, 0.35, and 0.52 mm) in a column of 1m and subsequently in a column of 1.5 m, where only the top 0.5m had a sediment-water mixture, while the area below consisted of a column of still water. Results show a general trend: seeds segregate to the top of the settled layer, further enhanced by larger grain sizes and higher sediment concentrations. Tests using the lowest concentrations (5-10 %) showed the best result, for which the largest number of proxies were located at an optimal depth (1 cm-5.5 cm) for protection and germination when using medium coarse and fine-sized sand grains. The results provide valuable insights into the dynamics of seed segregation in sediment mixtures and the hindered settling effect of a bimodal mixture, showing that seeds move differently to sand in a mixture, experiencing more rotation and drifting within a mixture not observed when following trajectories in a still water column. The larger seed particles segregated to the top of the settled layer due to the difference in behaviour with the sediment mixture. Even though the terminal velocity of the seeds in a still water column was larger.

When waves break, air and water mix and small air bubbles are formed in the water, creating aeration. The mixture of air and water alters the behavior of the fluid. Traditionally, it has been assumed that aeration has a damping effect on impact, as exemplified by the use of air bubbles in the swimming pool below the Olympic 10m platform and during synchronized 10m platform jumps to reduce the force exerted on the swimmer's body.

However, in recent years, it has been found that this assumption does not hold true in all situations involving aeration. When treating aerated water as a non-compressible fluid, it does exhibit a damping effect on impact. However, when treating aerated water as a compressible fluid, the speed of sound of the mixture can actually change with implications for the propagation of density waves. This means that an aerated water impact can feature pressure oscillations that increase the force instead of reducing it. Consequently, hydraulic structures that have been or will be constructed with the assumption that aeration only has a damping effect, may be affected.

Understanding the effect of wave-induced aeration on a horizontal platform is crucial for the design of new hydraulic structures in a more efficient and cost-effective manner. This research aims to determine the maximum force experienced by a horizontal surface during an aerated wave impact. The investigation involves using a numerical method, followed by a series of self-conducted small-scale sloshing experiments. The simulations contribute in two ways: they aid in understanding the problem and the magnitude of forces acting on the experimental setup, and they assist in verifying the experimental results once the experiments are completed. For the experiments, a new tank layout has been designed to facilitate the creation of aerated water inside the tank. The tank is used for conducting experiments where aerated wave impacts are compared to non-aerated wave impacts for different wave impacts. The experimental results confirm both the effect of pressure reduction due to aeration when the aeration level is near to 4%, as well the effect that the maximum pressure can increase for aeration levels between 1 and 2%.

The electric pulse fishing technique is no longer an option for fishermen. Therefore, they have to fall back on beam trawl fishing. This method has several disadvantages such as high fuel consumption and much soil disturbance. This system therefore deserves an investigation into improvement.
There is various literature on interaction of offshore structures with the soil. Processes in which a structure is also towed through the seabed are ploughing and cutting. Experiments with tickler chains are done and also numerical models are created.
Experiments were performed to acquire the required information that could not be retrieved from literature. In these experiments a chain element is towed through a sand layer in various configurations in a controlled way. Parameters that are varied are: velocity, chain link diameter, angle of attack, density, grain size.
A decrease of the angle of attack leads to a decrease of the tow force. The force per unit length is defined by dividing the tow force by the projected length. The projected length perpendicular to the towing direction, decreases for a decrease of angle of attack. However, the force per unit length also decreases for a decrease of the angle of attack. That means that the projected length is not the only explanation for the decrease in force.
The experiments indicate that the forces for higher penetration depths and higher chain link diameters are very high. An increase of density leads to a significant increase of the internal friction angle for low confining pressures. The increase of the internal friction angle leads to a higher passive soil pressure coefficient. The increase of this coefficient can certify the high forces.
Two dimensionless parameters are defined: the dimensionless force and the Froude number. An estimate for the increase of the passive pressure coefficient is integrated in the dimensionless force to clarify the high values for dense soil. After plotting the experimental results expressed in these dimensionless parameters, a linear trend line representing the data with reasonable accuracy of R2 = 0.611.

It is known that the Dutch North Sea coast consists mostly of sand, which creates the need for continuous maintenance.
For the time being, these maintenance activities are carried out with the aid of trailing suction hopper dredgers (TSHDs), which emit greenhouse gases during dredging operations.
As the world continues to prioritize sustainability, the field of marine engineering is no exception.
The Dutch Rijkswaterstaat goal is to reduce these emissions to zero by 2030 at the latest.
For this reason, C-Job Naval Architects has designed the Autonomous Low Energy Replenishment Dredger (ALERD) to meet the anticipated increase in Dutch coastal maintenance while simultaneously providing sustainable and cost-effective solutions for such maintenance work.
The development of autonomous replenishment dredgers has to be further investigated in order to determine the energy requirements and if it is a worthy future investment.

Regarding the research’s approach, first, the environmental conditions need to be determined in order to identify the environment in which these submarines will operate and the relevant destabilizing forces that they create. Ocean currents, ocean waves, as well as seabed interaction with submarines and generally underwater vehicles will be reviewed with respect to modelling, as they can have a significant impact on stability and manoeuvrability.
In order to counteract the developed forces, forward thrusters, vertical tunnel thrusters, and the trim tanks will be modelled.
Investigating the aforementioned topics, the simultaneous research about the modelling of the environmental forces and the seabed interaction on underwater vehicles and the existence of a model that can estimate the energy consumption is recognized as a “gap” in the literature.
As a result, a simulation model for an underwater vehicle, especially a submarine that operates in shallow water, that takes into account all the previously mentioned destabilizing factors and counteracting forces, will contribute to the advancement of a model that effectively estimates the required energy, using Matlab, Simulink.

In the developed model, three PID controllers in the three different degrees of freedom, surge, heave and pitch, are applied.
They control the rpm for the forward thrusters and the vertical tunnel thrusters in surge and heave respectively.
The PID controller in pitch direction adjusts the water mass that needs to be transferred from one trim tank to another in order to handle the pitch motion.
The ALERD is used as a case study for the generated model.

At the present phase of the ALERD concept, detailed hydrodynamic characteristics remain unavailable. The undertaking of CFD simulations or scale-model tests is deemed undesirable due to their perceived expense and time-consuming nature, particularly given the incomplete status of the ALERD's key parameters.
The mathematical equations that describe the former are modelled in Matlab, Simulink to perform time-domain simulations.
The ALERD has an unique operational profile in which it operates underwater in all three of its operational modes: transit, dredging, and discharge. This operational profile for the ALERD is based on conventional dredgers working in coastal replenishment along the Dutch coastline. Each operating mode has its own set of criteria, such as the goal depth, desired speed, and operational time.

It is worth noting that given the operational profiles for the velocity in surge, the depth and the pitch, the ALERD follows them successfully.
Nevertheless, the presence of the waves cause an oscillating behavior of the ALERD in heave and pitch directions which cannot be eliminated if only PID controllers are utilised.
The PID controllers fail to cancel out the oscillations by themselves.
Since the implementation of a different control strategy is not in the scope of this project, a different solution needs to be explored to estimate the required energy.
For this reason, a low-pass filter is applied at the resultant rpm of the PID controller in heave direction in order to make the oscillating behaviour of the rpm converge to a value, and calculate the required thrust.
As a result, the consumed energy for a full dredging cycle is determined per actuator.

It needs to be mentioned that when factoring in all environmental conditions and seabed interactions, the ALERD exhibits a maximum overshoot of 6.25\% when descending to a depth of 8 meters. This deviation is not considered critical, as it poses no risk of grounding.
In the case of operation at a depth of 15 meters during dredging conditions, the combined maximum overshoot, which accounts for both the depth controller and pitch controller, is estimated at 7.3\% (0.58m). This level of overshoot is considered safe, given that the ALERD has a clearance of 2 meters.
Regarding the energy results, it is concluded that the forward thrusters consume 4192kWh, the vertical tunnel thrusters 340kWh and the pump for the trim tank system 0.2kWh.
These results cannot be verified since the ALERD is a unique concept design and there are no available data of similar submarine dredgers.
However the developed model can be used for the estimation of the required energy of similar designs that are in a preliminary design phase.
Furthermore, the maximum demanded power for the thrusters and the pump can be determined using the model, in order to define the size of the necessary machinery.

The concluding recommendations mostly revolve around the functionality improvement of the tool, in order to increase its quality and generate models of higher accuracy.
An adaptive PID controller is recommended to be implemented, since the gains for the PIDs can change dynamically. By using adaptive coefficients, a PID controller can be made more robust and versatile, able to handle nonlinearities, and changes in system dynamics.
Furthermore, a state-observed is suggested to be applied in combination with the already existed PID controllers in order to estimate and compensate for unknown environmental forces in real-time and eliminate the oscillating behaviour.
Last but not least, the hydrodynamic coefficients should be improved to the actual hull shape of the submarine in further investigation.

Due to the constant growth of global maritime shipping, the optimization of grabs used for unloading bulk carriers is more and more relevant. Especially for a coarse material like limestone, the average payload can be improved, by altering the grab design. It is suggested that the penetration and cutting depth of a grab can be improved, which will have a positive effect on the payload. This research is limited to the contact surface of the grab with the bulk material, the knife. Subsequently, the following research question is answered in this research:

How to enhance the penetration and cutting depth considering coarse cohesionless material?

This is done, by implementing a DEM model using the bulk calibration approach [1], several in situ
and laboratory experiments are performed to measure certain macro properties. The experiment is numerically replicated, and micro parameters are changed iteratively until the predicted macro response matches the desired results. A comprehensive study of similar papers considering the penetration resistance using a DEM model is executed, which resulted in selecting the penetration resistance and porosity as target variables. The particle shape of a DEM model has a significant influence on the bulk material behavior. The novelty of this research consists of doing a preliminary analysis before the final calibration process, in which several polyhedral and (multi)-spherical particle shapes are compared. For investigating the penetration resistance, a new test setup for in situ use is developed and constructed. The implementation of this setup proved to be successful, eleven data samples were collected. For the bulk density, an in situ and laboratory setup are compared, of which the laboratory setup proved to be more reliable. Several additional laboratory experiments are executed for the particle density, Particle Size Distribution (PSD) and wall friction. Using the results of the experiments, a DEM model is created, with which a preliminary analysis is done using extreme values of the calibration variables. Four spherical and four polyhedral shapes are compared, which resulted in the two-spherical shape begin the most optimal option. All the polyhedral shapes proved to be not fitting, especially due to their underestimation of the penetration resistance. Due to the high variance of the experimental penetration tests, two parameter sets with identical porosity are calibrated: one with a low resistance target, and one with a high resistance target. Using Design of Experiments (DoE) in combination with surrogate modelling with a linear regression, several optimal parameters sets are created, in which the uncertainty is considered as well. After selecting two optimal parameter sets, the simulations are verified by comparing the experiments and simulations qualitatively. Additionally, a quantitative verification using the stiffness of the force data of each time-step is performed as well. Using the calibrated models, an additional DEM model is created with a bigger particle bed, to investigate the penetration and cutting resistance. By altering the geometry of the knife, a decrease in resistance was achieved, mainly in the cutting phase. It is recommended to consider the flowing behavior of limestone as well, with which a complete material model can be calibrated and validated, and full-scale simulations can be performed.

The objective of this research is to evaluate what is required to make the operation of multiple robots feasible for large scale seafloor imaging campaigns. Three blocking issues were identified; high cost of subsea robots, limited handling efficiency and insufficiently performant localization technology. These are solved by applying, in order: novel engineering solutions, automation, and solutions from literature. A proof of concept system design and a model are developed to analyze how the physical parameters of the subsea robots relate to the performance of the subsea mapping system. A case study shows that for large areas, the proposed solution is 80 times faster and less costly than conventional approaches. In conclusion, there is a technically feasible approach that can be used photograph the seafloor in a more cost-effective manner on a large scale.

The deployability, regarding mobility, of Boskalis trenchers, is currently determined by practical knowledge. The lack of theoretical knowledge means that risk assessments in the tender phase are less accurate. This reduced accuracy has two negative consequences. First, the trencher may fail. Secondly, the safety margins can be too large. Both consequences result in additional duration and costs. This research considers two ways of failure. The first one is slipping; as a result of this, the track does not have enough traction, which causes the tracks to turn while the trencher does not move forward. The slipping can happen in two ways. The first way is due to soil failure with the grousers fully penetrated. This results in the trencher digging itself in. The other way is that the grousers are not penetrated and the trenchers slips due to the tracksoil interaction. In order to prevent the trencher from slipping, horizontal stability between the soil and tracks should be obtained. The second way of failure is that the trencher sinks into the soil. Vertical stability between the applied pressure and the bearing capacity should be achieved to prevent this kind of failure. In this research a model has been developed that can approximate the operating range of different trenchers. With the help of these operating ranges, the model can make risk assessments in an early phase of the project. There will be little knowledge about the soilspecific parameters and the exact external conditions in this phase. Should there be a risk in the area of mobility along with the project, the model is also able to provide a more indepth analysis. In addition, the model aims to apply to different types and sizes of trenchers. The research answers the following question: ”Which different operational environments and soil conditions have a critical influence on the deployability of a subsea tracked trencher regarding the vertical stability and horizontal stability of the soil¬track interaction system? The model considers the trencher’s mobility in terms of vertical and horizontal stability, where the axes rotate with the slope. Meyerhof’s effective area method approximates the vertical stability. This method is used to take into account the eccentric loads. A traction calculation model approaches horizontal stability. Based on the penetration depth of the individual elements of a track, a shear mode is determined. The available traction force per element can be calculated using these shear modes using the Mohrcoulomb shearing theory. With a case study for the CBT2400, the research question is answered. In this case study, we first look at the different external processes that influence mobility. In addition, the various soil parameters and trencher dimensions are examined. Finally, the results of this study will be compared with two reallife projects. The results show that the mobility of the trencher is better in granular soils than in cohesive soils. In cohesive soils, the trencher’s mobility depends on the external factors that change in the driving direction, like pitch slopes and currents that have a frontal impact. In cohesive soils, the sensitivity is a vital soil parameter besides the undrained shear strength. Since the sensitivity is not included in the soil research, it is recommended to do it in future projects. In granular soils, external factors from all angles must be taken into account, like pitch and roll angles and currents from all directions. With granular soils, especially the relative density and internal friction angle are essential; in addition, the grain size must be taken into account. The grain size influences the permeability of the soil. The permeability, together with the relative density, determine if contractancy and dilatancy will take place in the soil. It could be interesting to change the grouser and track dimensions to improve the trencher’s mobility. However, this depends on the circumstances in which the trencher would have to operate. The model was validated using two cases involving the Borssele and Moray East projects. An important conclusion is that the model can be used to estimate the potential risk areas reasonably. However, it is recommended to test the model in predefined circumstances and soil parameters.

The offshore wind market experiences large growth over the last decade. There is a clear trend to installation in deeper waters and to larger wind turbines, to maximize the energy output. The majority of offshore windmills use a monopile foundation, which due to the current trends are getting larger. Seaway Heavy Lifting (SHL) is a company that installs these monopile foundations, with their Heavy Lift Vessels (HLV). The largest HLV of Seaway can transport and install three monopiles at a time. However, with larger monopiles it is expected to be reduced to two monopiles or even less. In order to be competitive in the monopile installation market, SHL is looking for a method to transport the monopiles to the HLV, instead of using the HLV for transportation. A previous comparative study showed that floating transport of monopiles to the HLV is the most favorable method. However, SHL is unexperienced with this method and therefore requires a study on developing the best method to install the monopiles within the workability of the HLV. Therefore, the thesis goal is:
"Design of a method for installation of large floating monopiles in heavy weather conditions".
To design such a method, it will first be determined what steps are necessary and which options can used to fulfill these steps. With a multi criteria analysis will be determined what combination will lead to the best method. The best two methods will be subjected to a sensitivity analysis to determine its feasibility.
The method consists of five steps: floatation, towing, mooring, hook-in and lifting. A multicriteria analysis shows that using airbags is the most favorable method of making the monopile float, while using a flange clamp for towing and lifting. In order to reduce motions, the mooring can be either on the side of the vessel in a gripper frame, or by sinking one end of the monopile to the seabed. When the monopile is in moored position the pre-rigged rigging can be taken over by the main hook of the crane.
Both methods are modelled in the simulation software package Ansys AQWA. A soil model has been made to assess the influence of the grounding on the motion behaviour of the monopile. Due to the soil properties it is faster and relatively accurate to model the connection between the soil and the monopile as a hinge instead of applying the soil model. The system is subjected to different waveheights and wavelengths, while varying the direction of the environmental forces, the trim of the monopile on the seabed and the orientation of the monopile to the vessel.
The installation of a grounded monopile in heavy weather is a feasible option. The simulations have shown that installation is possible up till a significant waveheigth of two meters with a peak period of 8s. The least trimmed position has the best performance over different environmental forces directions. The best option for installation is in a configuration where the vessel and the monopile are facing the environmental conditions head-on, with a 42 degrees monopile trim. However, it has to be noted that other monopile orientations with respect to the HLV are performing good as well, as long as the trim of the monopile is 42 degrees. Using other trim options is possible, but limited to specific orientations.
The installation of monopiles with a gripper attached to the vessel seems to be a viable option, but only once the soil model is improved. The simplification of the soil model by replacing it with a hinge gives uncertainties in the real force acting on the interface between the vessel and the grounded monopile. However, when considering the RMS force of 30 minute simulations without taking lateral forces into account, the results are well within the set boundaries.
Thus can be concluded that installation of a floating monopile is feasible, when using the grounding method. It is recommended to improve the soil model for both methods, to improve the accuracy of the results. To ensure a safe installation and a safe operation during its lifetime, the structural integrity of the monopile should be investigated. Small deformations can drastically reduce the fatigue life of the structure. An end-plug to lower the monopile to the seabed and reinforce the structure could be an option to ensure the structural integrity. Furthermore, it should be investigated if a gripperframe is a realistic option due to its size. The dimension could turn out impossible for catching and releasing extra large monopiles in heavy weather conditions. Lastly, it turns out that grounding a monopile is more time consuming and difficult than anticipated. Therefore it is recommended to research the installation of a free floating monopile or mooring a floating monopile alongside the HLV.

This thesis report proposes a framework to implement Navigation, Guidance and Control (GNC) systems, that enable point-to-point autonomy for displacement vessels. A model-based control approach is chosen as the basis of the GNC systems. The resulting algorithms are implemented for verification in a 1:25 scale model of a Azimuth Stern Drive (ASD) 3111 Damen tug named "Damen Autonomous Ship", aka DASh.

First, a compact maneuvering model that captures relevant dynamics of displacement vessel is formulated and identified using system identification.

Secondly,the guidance system is automated such that it connects an initial state to a goal state with a collision
free path that satisfies all input and differential constraints of the vessel model. To this end, the kinodynamic
Rapidly-exploring Random Tree (RRT) algorithm is extended to use a maneuver automaton and optimal motion primitives in its steering function. A learned cost-to-go distance metric for the state space is formulatedto efficiently calculate distance between states, which is used to search for nearest neighbors in the kino-
dynamic RRT algorithm. The performance of the planner using the learned cost-to-go distance metric is compared to a minimal curve length distance metric based on
Dubins Curves and the commonly used straight-line Euclidean distance metric. It is shown that the learned cost-to-go and the minimal curve length distance metric result in paths of similar performance while the Euclidean metric performs severely worse.

Lastly, the navigation and control systems are implemented on DASh. Due to disturbances present in real
world environments, the paths must be tracked using feedback control. State estimation for navigation,
based on position and heading measurements is performed by implementing an observer using a Extended
Kalman Filter (EKF). Non-linear model predictive control (NMPC) in combination with thrust allocation is used to control the vessel during path execution. Due to real time requirements of DASh, the EKF, NMPC and the thrust allocation algorithm are directly implemented inefficient C ++, on the on-board computer of DASh.
It is shown that NMPC converges to static reference positions faster and with less control inputs compared to
traditional non-linear PD control. It is also shown that time-varying trajectories created by the kinodynamic RRT can be executed successfully. This shows that the identified model is suitable for use in model-based
control and that the planned paths indeed satisfy the input and differential constraints of the vessel.

In the offshore industry, there is a growing demand for designing efficient, sustainable and competitive products. In order to fulfil the component requirements, a method named topology optimization can be applied. This is a mathematical design method which can be used in the early phases of the design process.At IHC there is an interest of applying topology optimization for their equipment development process. Therefore the possibilities and limitations of the method should be investigated thoroughly.

The research covers the optimization process of a motion compensated gangway. A motion compensated gangway is a walkway which can be used to provide access from the transport vessel to the offshore structure. Its function is to transport people and cargo safely from the ship to the offshore structure or vice
versa. The goal of this research was to determine to what extent topology optimization can be used in the design of a motion compensated gangway. Finding an optimized result in terms of weight and stiffness by using this mathematical method which satisfies all the requirements. The structural optimization is carried out with several commercial software packages which are compared by using a multi-criteria analysis.

During the optimization process it has been found that there are essentially two stages in the optimization process. In the first stage, the topology or beam orientation of the structure is defined by the topology optimization process. In this part the concept of the design is generated. Variation of the optimization parameters was used in order to develop an efficient structure. The objective for the optimizer was to minimize the compliance of the structure for a certain volume fraction.

In the second stage, the dimensions of all the beams and elements are defined by performing a size optimization. A line model is generated which represents the orientation of the members in the structure. During the size optimization the shape and the dimensions of the members are defined in order to fulfill the
objective. The objective is to minimize the mass of the structure while constraints are defined for the maximum allowable stresses in the members and the maximum vertical deflection of the structure. This post-processing step is required in order to obtain a feasible design. The structural stability of the gangway was improved by performing a linear buckling analysis and by adapting the structure in order to reduce the buckling behaviour.

In the final step of the optimization process, a CAD drawing is generated. This model is analysed by performing a finite element analysis. This showed that the new optimized design satisfies all the requirements which are stated by the DNV for designing a motion compensated gangway. The combination of the topology and size optimization resulted in a new design which yielded a weight reduction of 36,4% compared to the current design. The weight was reduced from 13,08 ton to 8,31 ton, while still satisfying all the constraints. Therefore it can be concluded that this methodology can be used in the optimization of a motion compensated gangway structure

Estimators at the production department of Great Lakes Dredge & Dock Company use a number of models to make production estimates for a job. These models require the slurry concentration in the suction arm of a trailing suction hopper dredge (TSHD) as an input. Currently this concentration is estimated based on results of previous projects. To aid in the estimation of the slurry concentration a model that calculates the in situ production and slurry concentration has to be developed.

During this research a model was developed that calculates in situ production by iteratively finding equilibrium between the actuator moments and the cutting moments around a draghead visor hinge. The slurry concentration is then calculated using the in situ production and a function describing the relationship between slurry concentration and dredge pump flow based on data of an existing TSHD.An extension to existing cutting theory was made to model the effects of the presence of water jets in the cutting teeth of the draghead. In this extension water jets were modeled as a pressure source which provides water to reduce the pore under pressures that cause cutting forces.The production model was evaluated by performing sensitivity analyses. In general the course of the production as a function of the trailing speed that was found could be described as a linear increase followed by a steep drop in production after which production started increasing again at a lower rate. It was found that it was mainly the geometry of the draghead that caused this steep drop. Another finding is that the production at operational trailing speeds (1 to 2 knots) is only of a realistic order of magnitude (between 36 and 125 m^3/min in this case) when still in the linear increase.

The conclusions that were drawn during the development of the model and the sensitivity analyses are that the TSHD draghead production might actually be best described as a linear function of the trailing speed and that the angle of internal friction of the sand is the parameter with the largest influence on the production. Of controllable parameters the pressure in the actuator had the largest influence on the production. That the results of the tooth jet extension correspond sufficiently well with an energy-based type of approach.