The increasing size and mass of offshore wind monopiles are placing greater demands on installation vessels and crane capacity. Buoyancy-assisted upending has been proposed as a method to reduce lifting requirements by using controlled flooding and trapped air during the transition from horizontal to vertical configuration. However, the governing mechanisms and operational feasibility of this approach remain insufficiently understood.

This study investigates the upending behavior of monopiles using a coupled hydrostatic–dynamic model that accounts for flooding, trapped air compression, cable mechanics, and environmental loading. A numerical framework was developed to simulate the complete upending process and evaluate the influence of flooding opening diameter, reel speed, plug length, trunnion position, active air pumping, and monopile geometry. In addition, a geometry-dependent feasibility assessment was performed using 768 operational configurations for each investigated monopile geometry.

The results show that the global response is governed by hydrostatic moment balance and flooding-induced mass redistribution. The flooding opening diameter is the dominant operational parameter controlling internal water volume, while reel speed mainly affects the time scale of the operation. Due to the large internal volume, trapped air contributes only a limited fraction of the pressure difference driving flooding. Active pumping reduces flooding and draft but does not provide reductions in crane loading, indicating that air-pressure control alone is not an effective strategy for improving operational feasibility.

A global feasibility assessment demonstrates that buoyancy-assisted upending can reduce crane demand by approximately 35-58% relative to monopile mass. However, feasibility is governed by monopile geometry rather than by operational settings. Larger-diameter monopiles benefit from both increased buoyancy and reduced structural mass when designed for equivalent bending stiffness, resulting in substantially larger feasible operating envelopes. In contrast, increasing monopile length rapidly reduces feasibility due to increased structural mass and hydrostatic moment. Across the investigated design space, crane capacity is identified as the governing operational constraint, whereas seabed-clearance limitations are generally less restrictive.

The findings further indicate that controlled flooding remains an essential element of the concept. While trapped-air pressure itself is not the dominant mechanism, internal plug systems enable control of the active flooding volume and internal mass distribution. Removable inflatable plug concepts appear particularly attractive, as they minimize additional structural mass, can be installed and retrieved internally, and eliminate the need for additional seabed clearance during plug removal.

The study demonstrates that buoyancy-assisted upending can substantially expand the applicability of existing installation vessels by reducing crane load requirements. However, successful implementation depends on achieving a favorable balance between structural mass, buoyancy, and operational settings. The results, therefore, provide both a physical understanding of the governing mechanisms and a design-level assessment of the applicability of buoyancy-assisted upending for future offshore monopile installations.


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This dissertation investigates the mechanisms of ventilation inception on surface-piercing hydrofoils under quasi-static variations of the angle of attack (AoA). Two hydrofoil geometries, a Semi- Ogive profile with a blunt trailing edge and a streamlined NACA 0010-34, were tested in a towing tank across a range of Froude numbers (Fnh) and aspect ratios (AR). The study introduces a novel experimental methodology, quasi-static testing, which eliminates inertial effects associated with acceleration by maintaining constant Fnh while varying AoA. This approach contrasts with traditional ”static tests” found in the literature. A new flow regime map in the α−Fnh parametric space was developed, tracing distinct ventilation inception boundaries for the two hydrofoils and offering a more detailed representation of transitions between flow regimes. The findings challenge the validity of previous methodologies, which assumed that ventilation inception boundaries were dominated by stall angles and fixed AoA, overlooking the dynamics of ventilation inception. At low Fnh, leading-edge (LE) ventilation appears as the dominant mechanism, slightly enhancing lift by stabilizing flow on the suction surface. As Fnh increases, transitions to Rayleigh-Taylor (RT) instabilities become evident, particularly at moderate Reynolds numbers. At high Fnh (≥ 2.5), RT instabilities prevail, with trailing-edge (TE) effects becoming significant for the Semi-Ogive hydrofoil. In contrast, the streamlined NACA 0010-34 primarily exhibits RT-driven mechanisms. The results demonstrate that this new methodology yields precise and repeatable inception boundaries, representing a significant improvement over historical techniques. Notably, contrary to prior assumptions, the AoA at which ventilation inception occurs exceeds 15◦ and is no longer constant across various Fnh. Additionally, trailing-edge geometry was found to influence ventilation inception, particularly at higher AR, as evidenced by the diverging trends observed between the two hydrofoil profiles. Furthermore, the experimental results align well with semi-empirical models for lift and drag coefficients at Fnh ≥ 1.0, reinforcing the robustness of the findings. These contributions provide more in-depth insights into ventilation inception dynamics and offer valuable guidance for the design of hydrofoils in marine applications. ... Read more

This report aims to investigate the dynamic simulation of an IMOCA 60 sailing yacht in big wave condi-tions. These yachts are equipped with hydrofoils, which significantly increases their speed. However, this increase in speed introduces a challenge: when encountering large waves, the yacht can experi-ence a ”crashing” behavior, where rapid acceleration leads to a collision with the wave ahead. These crashes can be severe enough to cause injuries to the crew onboard, making it essential to understand and mitigate these occurrences.
A Dynamic Velocity Prediction Program, DVPP, was developed to explore the yacht’s behavior in waves. This DVPP systematically models all the forces acting on the yacht, allowing them to be solved in the time domain. Particular attention was given to hydrodynamic forces, with a nonlinear Froude-Krylov force calculation to accurately represent the effect of waves on the yacht’s hull. Next to this, a correc-tion has been applied to the diffraction and radiation forces to take the effect of foiling into account. Furthermore, a correction has been applied to the aerodynamic forces to account for the flapping of sails due to changes in apparent wind angle.
To validate the DVPP’s accuracy regarding hydrodynamic and static forces, a heave decay test and RAOs of a Wigley hull were calculated. Based on these results, the DVPP agrees with the refer-ence data, which gives confidence in the DVPP. A qualitative validation was conducted to evaluate the DVPP’s ability to simulate an IMOCA 60 in wave conditions. These simulations demonstrated that the DVPP with the implemented corrections could accurately simulate an IMOCA 60 yacht in waves, as the results corresponded with those from a DVPP developed for an ocean-racing trimaran.
Further investigation was performed on the effect of the foils on the yacht. A parametric study revealed a clear correlation between the yacht’s behavior and sea state: higher sea states lead to more severe crashes. Further investigations into foil chord length and rake angle were also conducted. The analysis showed that a longer chord length tends to result in less influence of waves on the yachts speed, likely due to the increased drag associated with a longer chord, which limits the yacht’s speed.
Additionally, it was found that a lower rake angle leads to more severe slowdowns. This is attributed to the influence of wave orbital motion on the foils; at a lower rake angle, the increased angle of attack generated by the orbital movement increases lift as the wave approaches the stern of the yacht, leading to higher speeds and more significant impacts with the wave ahead. Furthermore, recovery from these crashes is slower with a lower rake angle, as the hydrofoil produces less lift overall. Based on this parametric study, it can be concluded that a larger chord length and a higher rake angle are preferred to minimize accelerations during slowdowns. However, further investigation is needed to understand how the yacht’s overall design influences its behavior in waves.
Lastly, a longer simulation, with challenging environmental conditions, was performed to investigate whether the DVPP could be used to simulate crashes in waves of an IMOCA 60. The results showed several slowdowns where the G force was above the threshold for a crash. This indicates that the DVPP can simulate these extreme events. Upon further analysis, it was concluded that the first part of the slowdown occurs due to the foil submergences, and a second slowdown occurs when the hull enters the water. Based on the results of the parametric study, the recommendations of a larger foil chord length and higher rake angle were applied to the simulation case; with these changes, the slowdowns were much lower, and the occurrence of crashes was reduced.
Furthermore, it is recommended that future research focus on enhancing the accuracy of the DVPP, particularly in the modeling of nonlinear hydrodynamic forces, radiation, and diffraction effects. Since an engineering solution was implemented, incorporating unsteady sail forces into the simulation to account for the effects of sail trimming on the yacht’s performance is also crucial for stable results in big waves. Further research is needed to present a method that is backed by further physics. ... Read more

Accurate modelling of ultimate or maximum hydrodynamic loads is crucial for the design of offshore wind turbines and ensure the survivability for its design life time. High fidelity direct Fluid-Structure Interaction models can provide accurate results but are too computationally expensive to deploy for the many environmental loading conditions that need to be evaluated during the design phase. Indirect numerical methods that separately obtain the wave kinematics and subsequently use those to calculate the hydrodynamic loads are widely used in the industry. Often extended linear wave theory is deployed to obtain the kinematics. However, for storm wave conditions and breaking wave events, this theory breaks down and requires engineering solutions such as separate slamming models to provide conservative force estimations. Fully nonlinear wave kinematics might directly represent steep and breaking waves, omitting the requirement of slamming models.
This study evaluates the performance of the non-hydrostatic wave model SWASH in simulating fully nonlinear wave kinematics that are subsequently used to obtain the hydrodynamic loads with the Morison equation. The project focuses on the extreme events of a typical 50 year return period storm in the North Sea. Deterministic comparison of the time series of the hydrodynamic loads of the nonlinear model with available experimental data and a linear model, that served as a benchmark representing the industry method, showed mixed results. Several large overshoots were observed in the nonlinear results for non extreme events, which were not present in the experimental data. Load estimates for extreme events were of mixed accuracy, both over and under estimations of the hydrodynamic load magnitudes were observed. The study concludes that while SWASH offers valuable insights into nonlinear wave dynamics, further refinement is needed to improve its reliability in load predictions.
Future research should initially focus on refining the implementation of SWASH, tackling the large overshoots by including a wave breaking turbulence model. ... Read more

In order to meet the shipping industry's emissions reduction goals, it is imperative to explore and adopt alternative marine fuels. Methanol (or methyl alcohol) is expected to play a large role in the future. However, current regulations limit the attractiveness of methanol as marine fuel due to the inability to use the space around a venting point on deck. Hazardous area zones are installed around fuel tank vapour outlets due to the flammability and toxicity of methanol vapour. Consequently, these areas become very impractical. This thesis investigates the ventilation of the fuel tank vapour below the waterline instead on deck in order to be able to limit/eliminate these areas. Therefore, the main research question is:

"What is the concentration of methanol at deck level when methanol is vented below the waterline?"

An Eulerian based CFD model and a simple integral model are used to predict the methanol concentration above the waterline. The integral model predicts the gas concentration above the waterline based on the gas flow rate reaching the surface and the radial inflow rate of air. The CFD model tracks parcels (group of bubbles with the same properties) using the force balance in the discrete phase model. Both of the models are successfully validated against experimental data from the "Rotvoll experiment" wherein methane was released at the bottom of a water basin. The CFD model showed strong superiority over the integral model, o.a. due to the lack of gas dissolution in the integral model.

The numerical models are applied to the case wherein a mixture of methanol and nitrogen is vented due to an overpressure. The overpressure could be caused by for example the failure of the vapour return line when bunkering or a fire. The bunker tanks are protected by a pressure relief valve, which reduces the overpressure by directing the gases in the bunker tank towards the venting location below the waterline. The flow rate characteristic (pressure - flow rate) of the pressure relief valve determines the rate at which the gases are injected in the water. The gas dissolution showed strong dependence on the departure bubble diameter and the venting depth. Different cases with different initial bubble sizes and different venting depths were simulated. The CFD model showed that in the most critical case (lowest venting depth 0.5m and largest initial bubble size 0.08m) the gas dissolution is large enough such that no methanol vapour reaches the deck of the ship and barge. The subsea venting of methanol-nitrogen vapour proved to be a safe alternative compared to the venting above deck. ... Read more

Internal combustion engine (ICE) emissions cause numerous social, environmental, health, and economic issues, including extreme weather or harm to public health. These effects are also experienced in the Chinese Pearl River Delta, where a high-speed, 200-passenger ferry named the Coastal Cruiser 200 (CC-200) uses ICEs to operate. The CC-200's designer, CoCo Yachts, is interested in the technical and economic feasibility of a zero-emission CC-200 variant to negate its contribution to the total ICE emissions. Investigating this interest is this study's purpose, as no currently-operating zero-emission ferries were identified that, at minimum, sail at 30 knots and carry 200 passengers. To reach the study's conclusions, primary and secondary quantitative data were collected, analyzed, and integrated into a parametric model developed to assess the ferry's technical feasibility. Moreover, this data were used to perform an economic assessment. Results showed that a 200-passenger, 30- to 40-knot, emission-free ferry is technically feasible and may or may not be economically feasible when implementing a battery-, compressed hydrogen-, or liquid hydrogen energy carrier system, hydrofoils, and all identified weight-saving measures. It was concluded that for these configurations, the 30-knot, battery-powered hydrofoil ferry has the highest likelihood of being both technically and economically feasible. ... Read more

The electricity demand increases globally and requires a shift toward renewable sources to prevent the exhaustion of the planet. The shipping industry is responsible for 2-3 % of the global Greenhouse Gas emissions and Heerema Marine Contractors (HMC) identified floating solar as a promising solution to reduce the emissions, of their crane vessel Sleipnir, during operations. This study is the starting point of a technical feasibility study as a temporary energy supply for Sleipnir. The design is strongly focused on the temporary deployment and limited occupied deckspace during transit. Current floating solar systems are commonly designed for permanent deployment as supporting structure for rigid glass photovoltaic (PV) panels. Furthermore, modular constructions are used to limit the transportation costs however they are not designed for temporary deployment. A new PV innovation is flexible lightweight films which allow a more flexible supporting structure. A flexible thin sheet can be spooled on a drum to make temporary deployment possible. The influence of the wave loading on the coupled hydrodynamic behaviour is evaluated since wind and current loading are predictable based on previous research.

The structural design parameters of the thin sheet and drum are designed to mimic the excitation motion since wave structure interaction has been minimized to reduce the mooring force. Therefore, the draft must be low and the characteristic length related to the bending stiffness of the sheet should be smaller than the excitation wavelength. The draft of the drum should be low to have a natural heave frequency higher than the excitation frequency.

The coupled hydrodynamic response for head loading is evaluated with model tests in a towing tank. The concept is scaled according to Froude to ensure the surface waves, which are gravity-driven, are properly scaled. Regular waves are chosen based on the workability wave spectrum of Sleipnir. The roll and heave response over the frequency domain is indicated by analyzing the stable response at certain frequencies. The motions of the drum are obtained with the use of object tracking based on video recordings. The force within the connection of the system was measured with a force transducer whereas the mooring force was measured with a newly developed 3D-sensor.

It turns out that the heave motion of the system mimics the excitation motion over the wavelengths resulting in small drift forces. Significant rotations of the drum were observed for the longer wavelengths leading to water pumping over the sheet. The overturning moment is driven by the dynamic pressure over the drum diameter and the measured force in the connection generates a counteracting moment. The connection force is proportional to the buoyancy required to submerge the sheet and the acceleration of the free-floating sheet.

The feasibility of an OFPV concept for Sleipnir is demonstrated but the rotations have to be reduced by lowering the natural roll frequency. The drum dominates the coupled hydrodynamic behaviour compared to the sheet. Either the dimensions of the drum should be lowered or the thickness of the sheet must be increased. Decreasing the drum diameter is favourable over a thicker sheet since that would increase the characteristic length. Another option is to adjust the geometry of the drum to a shape where increased water displacement is required for the roll motion.
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Deterministic predictions of wave induced ship motion are increasingly often used to enlarge the oper- ational envelope of ships that perform complex operations at open sea. The large amount of complex operations performed nowadays, motivates the relevance of motion predictions. The company Next Ocean provides these forecasts, based on linear seakeeping theory. While highly linear degrees of freedom are predicted accurately, roll motion predictions prove to be more demanding and are less accurate. This research aims to improve roll prediction accuracy by adding (non)linear damping to the equations of motion. The prediction optimization is performed on data of the platform supply vessel Acta Auriga.

To enable the use of nonlinear forces, the equations of motions are first implemented in the time domain using Cummins’ equations. The linear coefficients in this equation are determined from the frequency dependent coefficients in Acta Auriga’s hydrodynamic database. To ensure the correctness and investigate the limitations of the implemented Cummins equation, the results from the time and frequency domain are extensively compared. Both monochromatic excitations, as well as spectrum (JONSWAP) excitations are considered. In contrast to linear force coefficients, nonlinear force coefficients are generally not known for a given vessel. Implementing these forces into the equations of motion imposes the need for an approximation of these coefficients. Estimates for the linear, quadratic and cubic viscous damping forces are made, using both the measured motions of a vessel operating at sea and the predictions of the corresponding excitation force, made by Next Ocean. A multivariate regression algorithm is used for the identification.

The Cummins equation was successfully implemented. However, the translation from frequency to time domain was more error prone than anticipated; the frequency dependent coefficients need to meet requirements that are typically not met by databases meant for frequency domain calculations only. Furthermore, degrees of freedom without a restoring force showed running away behaviour that could not be negated without adding extra damping. The roll motion was susceptible to instabilities. The exact origin of this instability was looked for, but could not be found. Adding damping resolved the instability. Furthermore, the interpolation in the roll response amplitude operator introduced errors in the initialisation of time domain calculations, which led to inaccurate results when spectrum excitations corresponding to more severe sea states were used. Only under specific conditions, these high energy spectra led to accurate roll predictions. Adding damping made for a close match between frequency and time domain calculation for all degrees of freedom. The complexities mentioned made that an easily scalable algorithm could not be obtained using time domain calculations. Easy scalability be- ing important to Next Ocean means that running time domain simulations in Next Ocean’s product is deemed unrealistic. This also means that no nonlinear forces can be used in real time applications.

In an attempt to improve linear predictions, coefficients in the linear seakeeping model, including the linear damping coefficient, are identified and vessel motions are re-predicted with the added damping and updated linear force coefficients, using the Cummins equation. None of the identified parameters led to better predictions than were obtained by Next Ocean. Identifying and updating parameters was therefore concluded to be not beneficial to the quality of the motion predictions. Adding a fixed amount of linear roll damping, which was not identified from the field data, did lead to improved prediction quality; correlations between predictions and measurements increased by 9.6%.

While the motion prediction could not be improved using the Cummins equation, valuable information on the time domain simulations was obtained. The finding that better predictions were consistently obtained by adding a fixed amount of damping, sparks an opportunity for further research into the ideal amount of damping. This, and more elaborate identification schemes could provide meaningful insight to improve motion predictions. ... Read more

In the port of Ostend a discharge sluice is going to be constructed as part of an enforced dike ring. The proposed location of this discharge sluice is close to an already existing marina, the Royal Yachtclub Oostende (RYCO), and hindrance is expected regarding the outflow of the sluice in marina direction. When designing the sluice, an optimal balance has to be found between acceptable flow velocities in the downstream area and the capacity of the discharge sluice. It is therefore very important to be able to determine resulting flow patterns.

Formulas and rules of thumb found in literature are not sufficient to determine the resulting flow pattern of this system due to the complex geometry, including a pile row for flow velocity reduction. Other studies have shown that numerical models could simulate flow patterns of discharge sluices with much detail. However, a lot of detail in the results also requires much computational time. An example of a detailed numerical software program that is able to simulate the complete three-dimensional flow field is COMSOL Multiphysics 5.6 (COMSOL). Although it provides the most detail, simulating the flow in the entire area of interest (including the RYCO) for a complete tidal cycle in COMSOL would take too much computational time.

The objective of the present study is therefore to investigate the possibilities of determining the flow pattern downstream of a discharge sluice using a numerical method that requires less computational time but has sufficient accuracy to determine the potential impact of a discharge sluice on nautical activities.

In the present study, two options are considered to determine the flow field downstream of a discharge sluice. Method COMSOL-D3D is a coupled numerical method of a COMSOL and a coarser Delft3D-FLOW 4 (D3D) model. The other option, method D3D, uses only a D3D model and the sluice outflow is schematized by means of the general discharge relation.

As validation of the results is not possible due to a lack of measurement data, the methods are applied to a simplified case. The flow pattern resulting from each method is compared to the results obtained with a so-called baseline method. This method consists of modelling the entire domain with only a detailed numerical model, COMSOL. This is possible since, for validation purpose, the domain of the simplified case is relatively small and only stationary conditions are considered.

In conclusion, there is a lot of potential in the use of both methods in predicting the flow pattern downstream of a discharge sluice. They produce for the simplified case flow patterns similar to those obtained with the detailed method. Moreover, both methods require relatively little computational time compared to a full 3D simulation, method D3D requires the least amount. However, there are a number of conditions for the application of both methods.

The methods cannot be applied in the direct vicinity of the discharge sluice where the flow is highly three-dimensional. If one is interested in the flow in the first meters after the outflow opening or around the pile row, for example for designing the bottom protection, the two considered options are not sufficiently accurate. The flow in this area is too complex to simulate in a D3D model. In this case it is recommended to model the situation completely in COMSOL or a model similar to COMSOL. Furthermore, method D3D can only be applied if the sluice system is simple enough to correctly determine the discharge coefficient analytically/empirically and to simulate the effect of the pile row with a simplification in D3D. It is possible to accurately determine the effect of the pile row on the flow in this study with a schematized porous plate in D3D. Further research must show whether this applies to all types of pile rows.

For method COMSOL-D3D it is important that a correct coupling is made between both models. Here it is important to gradually impose the flow rates in the D3D model. Furthermore, the coupling should be made before the predicted point at which the jets starts deflecting towards the side but downstream of the area at which three-dimensional flows caused by the pile row are present.

It is important to note that due to a lack of validation data there is an uncertainty in the results following from the model approaches. Further research and the use of validation data must show how accurate the results of the considered methods are.

In this research method D3D is applied to the Ostend case. It becomes clear that flow rates exceed predetermined limits for safe operation in the marina. This applies to the entire marina and a large part of the time that the discharge sluice is discharging in marina direction. Measures will therefore have to be taken to prevent this. It is recommended to use method COMSOL-D3D to investigate the optimization between flow velocities in the marina and the discharge capacity. This is due to the fact that the design of the discharge sluice is expected to become much more complex and as a result the discharge coefficient is no longer easy to determine using formulas from literature. ... Read more

Liner shipping companies engage in strategic cooperation to deal with the market’s overcapacity, capital intensiveness and volatile freight rates. However, these partnerships do not reach their full potential and have lowered the level of service in the industry. To identify how carriers would be able to realise further synergies, this study has investigated the current performance of liner shipping companies and developed a model to identify and assess potential partnership opportunities. This model supports liner shipping companies in their decision of who to partner with and what kind of partnership to pursue. The study has been confined to a single transpacific route. On the basis is an overview of vessels that sail this route over a period of several years. This overview includes information on arrival dates, number of containers on board, capacity and operator for each vessel. This is used to examine local demand and deployed capacity, vessel utilisation and competition. The analysis confirms trends found in literature, such as the growing size of vessels that are enabled by strategic cooperation. Most importantly, it indicates flexibility on the side of vessel operators in their decision of which vessels they deploy per route during the year. A synergy model has been developed based on the findings in literature and the results of this analysis. This model uses the identified flexibility in vessel deployment and builds on the notion that liner shipping companies should pursue more integrated partnerships to realise further synergies. The model was also applied to the case of CMA CGM’s acquisition of APL in 2016. After calculating the costs for sailing each of the available vessels, potential partnerships were identified for the analysed route. This was done by optimising vessel deployment for the cargoes to be transported at minimum cost and with a limited number of partners. A strategic-level assessment was then performed to determine whether a partnership would be feasible among the identified companies and to what extent integration should take place. By including both the companies’ motivations (drivers) and factors that facilitate a positive environment (facilitators) for the partnership, this assessment brings multiple perspectives to the table. The conclusion is that carriers can adjust which vessels they deploy to match transport demand and that they can use this to realise further synergies. By using a model with both a quantitative and a qualitative component, it is possible to identify potential partnerships that result in cost reduction, maintain high vessel utilisation and allow for improvements in the level of service that companies offer to their customers. It is recommended to extend the coverage of the model to include more routes, ports and vessels for a more comprehensive analysis. Furthermore, using variable transit times in the model to determine when vessels are available would make the model more realistic and would also allow changes in vessel speed to be included in the analysis. It is also advised to explore opportunities for regulatory bodies to apply this model for monitoring and assessment of the effects partnerships have on competition per route. ... Read more

The negative effects of global warming can already be noticed. The burning of fossil fuel not only contributes to global warming, but also to the reduction of air quality, especially in urban areas. In order to limit the climate change, as well as to improve the air quality, more and more vehicles are replaced by emission free versions. This thesis is a case study in which the feasibility of replacing a fast passenger ferry (300 passengers, 30 knots) by an emission free vessel was investigated. Two options remained after analysing different methods of emission free propulsion: battery powered and hydrogen fuel cell powered, both in combination with an electric motor. So in this report, the emission free ferry is an electric vessel. Without additional design changes, a battery powered version is not possible. So a reduction in energy consumption is required. A hydrogen powered ferry is feasible, but more expensive, thus a reduction in energy consumption is desirable as well. It must be mentioned that costs is not the most important aspect, because the reduction in emissions might be worth it. Furthermore, a lot of indirect costs are related to pollution. The effect on energy consumption was analysed for three design related changes: elongating the hull, using carbon composite instead of aluminium, and applying expected future battery and fuel cell systems. Currently, a battery powered ferry is only feasible with an elongated hull, but future technology significantly increases feasibility, also for the original hull length. A reduction of structural weight also increases feasibility, which effectively means a reduction in costs. The hydrogen powered ferry was already feasible, but the above mentioned changes in design improve feasibility, i.e. reduce the costs. Two operational changes were analysed as well: operating at a lower design speed and operating on a shorter crossing. The first has a limited effect on energy consumption, but the latter significantly increases feasibility of the battery powered ferry. Both changes do not have much effect on the feasibility of the hydrogen powered concept. The final concept that was analysed is the hydrofoil supported catamaran, because hydrofoils can significantly reduce resistance. Compared to existing hydrofoil vessels, there are two major differences: the electric concept has relatively more weight, and its design speed is significantly lower. Therefore, the hydrofoil must be relatively large to generate the required lift, and a larger hydrofoil suffers from larger 3D and interference effects. This drastically lowers the efficiency, and as a result, the hydrofoil concept is not a feasible solution. It can be concluded that an emission free fast ferry is feasible. A battery powered ferry is best suited for short crossings and the hydrogen fuel cell powered ferry can operate at longer crossings. The direct costs are likely to be higher, but this might be worth it, as it leads to a reduction of emissions, and thus to a reduction of indirect costs related to pollution. So the remaining question is: do we want to invest now, or pay for the damage afterwards? ... Read more

The international maritime sector accounts for about 2% of all global carbon dioxide (CO2) emissions, the main greenhouse gas that causes global warming. Nations meeting at the United Nations International Maritime Organization (IMO) in London have proposed an initial strategy for the reduction of greenhouse gas (GHG) emissions from ships, setting out to reduce GHG emissions from international shipping by phasing them out as soon as possible with the aim to achieve zero emission by the end of this century. Heerema Marine Contractors (HMC) is a world leading marine contractor in the international offshore energy industry and aims to be a role model in environmental responsibility through carbon emission reductions.

As a result of HMC’s global activities, their fleet covers a considerable distance through transit across the globe. Their large semi-submersible crane vessels are conventionally transported through towing by a tug. The great amounts of fuel required for these transits provides a significant opportunity for the reduction of HMC’s carbon footprint. One such initiative proposed within HMC is the application of wind-assisted ship propulsion on the tow configuration.

This report presents an initial investigation of the feasibility of wind-assisted towing of the HMC’s Thialf, a semi-submersible crane vessel. Previous internal research at HMC showed the feasibility of using a discarded Panamax vessel as a floating breakwater. While operationally the discarded Panamax was found to be feasible, economically this was not the case. In this research, using the Panamax as a wind-assisted tug for towing the Thialf is investigated. As such the Panamax vessel can be employed for multiple purposes; for wind-assisted towing and as a floating breakwater, improving the financial feasibility.

To test the performance of a wind-assisted tow operation, a comprehensive 2D model is developed in this research to be able to check configuration variations in a wind-assisted tow setup. A conceptual design of a Panamax vessel converted into a sailing tug is implemented in a 2D model simulation. The performance in combination with the Thialf is assessed under the common environmental conditions experienced by the Thialf for various transit routes.

Results showed that the use of a wind-assisted tow configuration based on a Panamax, without using the Thialf propulsion is not feasible. The main point of failure is the required force balance transverse to the sailing direction. The Panamax basis used for the preliminary wind- assisted tug design proved to be not the optimal base case due to the limited leeward force generation under a drift angle and the large sensitivity to environmental loading. Although implemented measures improved the systems performance, it is debatable whether a wind- assisted tow configuration with the associated uncertainties is the most promising area to accomplish significant CO2 reductions.


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When propellers are operating near the free surface,  phenomenon called ventilation might occur. Due to insufficient immersion and high thrust loading, the propeller draws air, resulting in a reduced thrust. Reduced thrust may have consequences such as loss of propulsive power, control and steerability, and may therefore be leading to safety issues. Long time exposure to ventilation’s unsteady torque loading can also lead to propulsive unit malfunctioning. As propeller diameters tend to grow bigger, free surface clearance decreases and room is left for air to be drawn. To increase understanding of the phenomenon, current experimental and numerical research was executed.  The used propeller was a Wageningen C4.55-propeller, an in design condition lightly-loaded propeller with low blade area, fitting to the trend of increasing diameters. The research was bound by perfect conditions to capture ventilation in the purest form; no influences of wake, waves and ship motion were taken into account. Experimental research showed that free surface ventilation appeared to be the most stable and predictable ventilation regime. Inception through free surface breaking mainly depends on the pressure gradient between the propeller tip and free surface, the tip immersion rate and the ability to draw the free surface. Increased ventilation thrust breakdown showed to be influenced by the local velocity on the blade, which mainly depends on the propeller rotation rate. Vortex ventilation was the most unstable regime in the experiments. Inception seems to be independent of the propeller loading, but influenced by local flow phenomena in the area above the propeller and propeller characteristics . It is believed that vortex inception, shape and wash-out resembles the appearance of the cavitating propeller-hull vortex. Vortex ventilation showed a bistability effect. Experimental results were obtained using a statistical research planning/Design of Experiments, such that polynomial models could be constructed. The model fitted the data well, demonstrated by the fitting coefficient r2 exceeding 0.9. Structural shortcomings were found in capturing the highly unsteady vortex ventilation, variations in mixed ventilation and increased thrust breakdown in free surface ventilating. Numerically, ventilation was simulated using the incompressible VoF-solver ReFRESCO. Vortex ventilation inception was not found, even when a scale resolving simulation was conducted. This is ascribed to insufficient application of the SRS-model in the near blade area, due to insufficient convergence of the omega-equation. Also application of Boussinesqs assumption in the k-equation might be stringent. Free surface ventilation inception was accurately found, both in simulations with a for ventilation adapted actuator disk model and with the propeller. Thrust breakdown was underestimated by CFD. Only breakdown due to surface piercing was found. Underestimation is ascribed to the absence of air entrainment. Application of TNT-EARSM-model (which is not using Boussinesqs assumption) and application of free-slip boundary conditions did not improve the shortcoming. As in literature, other free surface discretization schemes showed the same lack of air engtrainment, the origin might be in the VoF-assumption, being the increased interpolated density used in the momentum equation which prevents air to be convected.     ... Read more

A tip-vortex in the wake of a finite length lift generating surface has a low pressure region near the axis of the tip-vortex. This low pressure region can trigger tip-vortex cavitation especially in ship propellers which has adverse effects by causing vibration and underwater noise production. One way of minimising the tip-vortex cavitation is by reducing the propeller blade loading but at a cost of lower operating efficiency of the propeller. An alternative passive approach, to delay the onset of cavitation, by increasing the minimum pressure in the core of the tip-vortex through modification of the tangential velocity profile of the tip-vortex is investigated in this thesis. In this thesis, the effect of upstream turbulence on the peak tangential velocity of the tip-vortex from a NACA 662-415 hydrofoil is investigated through stereo-Particle Image Velocimetry measurements. The turbulence is produced by a passive grid placed in the upstream of the hydrofoil. The tangential velocity profile at three different turbulent intensities were compared with measurements from a baseline no grid case that had nearly uniform and steady inflow to the hydrofoil. The tangential velocity profile of the vortex exhibits a reduction in the average peak tangential velocity under the influence of the grid generated turbulence compared to the no grid case. The measurements taken at two downstream locations, 0.5 and 1.3 chord length downstream from tip of the hydrofoil, showed that a significant reduction in the magnitude of the average peak tangential velocity of the tip-vortex is observed only at the latter position. Also, on examining the axial velocity profiles, a significant reduction in the magnitude of the average peak axial velocity in the core of the tip-vortex was observed under the influence of grid generated turbulence. An apparent effect of the upstream turbulence on the tangential velocity of the tipvortex is seen to appear only when sufficient time is given for a secondary vortex structure, from the upstream turbulence, to form around and be intensified by the primary tip-vortex. At 1.3 chord length downstream from the tip of the hydrofoil, the reduction in the magnitude of the peak tangential velocity is accompanied by increase core radius of the tip-vortex. ... Read more

In the early 00 of this century, Keuning et al. (2007) looked into the hydrodynamic forces on the rudder and the influence of the hull and keel on these forces. Among others, they have assessed the lift and drag forces on the rudder. One of the outcomes of this study was an asymmetric lift curve; for negative rudder angles the rudder seems to stall at angles more than five degrees smaller than for the positive rudder angles.
The goal for this research is to find and clarify the physical phenomenon which induces the rudder to stall at smaller rudder angles when subjected to a negative rudder angle (during bearing away). The main question to be answered in this report is: What physical phenomenon is at the basis of the asymmetric stalling behaviour on the rudder of a sailing yacht?
Towing tank tests are used to validate the data from Keuning et al. (2007). After which RANS CFD simulations are conducted in NUMECA to compare the towing tank tests to and to visualise the wake of the yacht in attempt to clarify the phenomena found.

A number of conclusions were found in this study. Firstly, the results of the towing tank experiments showed similarities to the previous experiments by Keuning et al. (2007). Differences are found in stall angles for positive rudder angles. These differences raise questions on the correctness of either of the experiments.
Secondly, no reasonable explanation is found for the negative drag forces found in the towing tank experiments. It is expected that these originate from the set-up of the rudder.
Thirdly, the lift curve found in the experiments is confirmed by the CFD data for the test cases. The physical effect behind the early stall behaviour of the rudder is still unknown. It is indicated that a part of the decrease in stall angle, a couple of degrees, is caused by the influence of the keel, when the disturbance passes on the low pressure side of the rudder. The hull is responsible for the remaining decrease. The CFD data indicates an influence of the vorticity of the keel and the boundary of the hull to cause a disturbance on the rudder.
Further research in necessary to clarify the results found in this study.
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In this thesis the differences between the monohull and semi-submersible are investigated. For a general heavy lift crane operation and its operational profile, the difference is performance and total cost are calculated. These are used to determine the turning point, the point where the semi-submersible is more favourable for a heavy lift crane operation. The monohull has relatively low capital and operational costs, but also a lower workability. There is thus a balance that has to be investigated and compared between the two vessel types. This is done for the North Sea and West Africa, which have significantly different sea conditions. ... Read more

Currently there are three methods of calculating the Dynamic Positioning capability of a vessel namely: static calculations, real-time time domain simulations and fast-time time domain simulations, although the outcome of the last two should be identical. In each of these methods a set of input variables is required to perform the calculations. These inputs are not always exactly known and are therefore sometimes estimated or taken from databases. It is not always clear how big the uncertainty in these estimated inputs is, and on top of that: how big the effect on the predicted DP capability is. To be able to quantify how certain a DP capability calculation is and which input data contribute most to the output uncertainty, in this thesis the input uncertainties for both static and fast-time dynamic calculations are investigated. Each method is subdivided in three different design stages which are: conceptual design, preliminary design and as built design. For the static calculations all three design stages are evaluated but for the fast-time dynamic simulations only the as built stage is considered.

The static calculation part of the analysis consists of determining the input uncertainties, the input sensitivities to the output and finally calculating the output uncertainty. The method used for this calculation assumes that either the relation between input and output is linear or can be linearised at the point of interest. The input uncertainties are calculated using historical data of the Bibby Wavemaster 1 which is the vessel used as case study throughout this thesis and is specifically designed for the purpose of servicing offshore wind farms. It is observed that the input uncertainties of the main dimensions of the vessel are clearly reducing when moving through the design stages. Furthermore it is concluded that the environmental coefficients of wind, waves and current are the most uncertain, even in the conceptual design stage where input parameters of the main dimensions of the vessel vary the most. When considering the sensitivity in the three design stages no big changes were observed, meaning that in all design stages the main dimensions of the vessel are most sensitive to the output. Finally the uncertainty in the output was evaluated were it was observed that for the as built stage still a standard deviation of 4% uncertainty of the output is present, resulting in a calculated 99.7% confidence interval of either 12% too high or too low.

In the dynamic calculation part only the as built stage is considered. Again the uncertain parameters are defined but due to the PID controller in the dynamic model some new input parameters are now present. The gains of this PID controller are assumed to be uncertain and are therefore taken into account during the dynamic uncertainty analysis. Due to a limitation in the aNySIM licence bought by Damen it is impossible to change the wave coefficients which causes their uncertainty not to be taken into account. Since the dynamic simulations are considered to have strong non linearities and possibly even discontinuities due to thruster saturation, the calculation method used for the static part is not applicable anymore. Therefore it is decided to use Monte Carlo simulations to quantify the uncertainty in dynamic DP calculations. Due to the large computational time required to perform large amounts of Monte Carlo simulations with aNySIM, a machine learning method is used to capture the dynamic behaviour of the vessel. A small number of simulations performed by aNySIM is required to train the model which are selected using the Sobol design of experiments technique. This technique optimises the choice of the simulation points to make sure the complete space of possible inputs is covered. By using the machine learning model to obtain an output of a dynamic simulation only a fraction of a second is required instead of 17 minutes when using aNySIM. By running the Monte Carlo simulation on the created machine learning model it was observed that the 97.7% confidence interval for offset can either be calculated up to 8.7% too low or too high whereas the prediction for heading up to 23.1% too low or too high when compared to the base case. It is concluded that using DP for the purpose of people transferring by means of a "Walk To Work" bridge, uncertainties should be taken into account to reduce both safety and contractual requirements risks.
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Dykstra Naval Architects are regularly designing large classic sailing yachts or motor-sailors, of which the draft is an important design restriction.The sailing performance is increased by adding lift-generating appendages,without increasing the draft. An example is a retractable centre board, havinga big influence on the sailing properties. Predicting the performance of the centre board contribution in a hull-keel-centre board configuration is the subject of this research. When predicting the performance of large sailing yachts, Dykstra wants to keep the ability to superpose an appendage to the data of a hull-keel configuration obtained from towing tank experiments or CFD simulations. This means that a method must be developed to estimate the contribution of the centre board, in terms of side force, resistance and centre of effort. Both towing tank experiments and CFD simulations are conducted for this research. The Maltese Falcon is used as the 'case ship'. A towing tank model of the Maltese Falcon was already made and tested at the TU delft in 2002. This model is again subjected to towing tank experiments, with a new keel and two new centre boards, resulting in 9 different hull-keel-centre board configurations. The main focus was on the towing tank experiments, executed in the Delft Hydromechanics Laboratory. CFD simulations were done to validate the results of the towing tank experiments and to gain visual insight in the flow around the vessel. The lift-carry-over on the keel and hull above the centre board can clearly be seen, as well as the influence of the centre board on the circulation in the flow around the underwater body of the yacht. After post-processing all experimental data, the results of the towing tank experiments are used to develop formulations to predict the performance contribution of the centre board. The measured lift of the centre board contribution was roughly a factor 2 higher than the centre would generate according to Wicker & Fehlner theory. Additionally, it was found that the lift-carry-over does not only have a positive effect on the generated side force, but also on the resistance. Furthermore, it was found that heeling the Maltese Falcon model by 15 degrees, yields the same magnitude oflift-carry-over as for the upright conditions. This resulted in the conclusion that heeling the yacht has no influence on the lift-carry-over from centre board to keel-hull. The new prediction methods, derived from the towing tank experiment data, are validated on YACHT1 and Adela. These are existing yachts with hull-keel-centre board configurations, but both very different. This enabled an interesting examination on the influence of certain aspects of the configuration on the performance of the centre board contribution. All in all, it was found that the predicted centre board contribution corresponded really well to the measured data of YACHT1 and Adela. This provides enough trust to implement the new centre board performance prediction methods in the Dykstra performance prediction tool. Every new design cycle of a yacht with hull-keel-centre board configuration will serve as a validation of the derived performance prediction methods. ... Read more

During the early stages of ship design exploration, design freedom is abundant but problem knowledge is scarce and most costs are already committed. This amounts to an incentive to look at the influences of the requirements on a design, to better understand how a concept is defined. This thesis investigates the operational architecture concerning how systems are used (often in a temporal fashion). A way to quantify the operational architecture is with operability, which describes the ability of a ship to perform its mission. This thesis identified the system performance consisting of availability and vulnerability part of operability as its main topic. Markov theory was selected to assess the availability of systems in order to maximize the operability of a naval vessel. Transition rates of systems are a key element of Markov theory but are hard to obtain during Early Stage Ship Design. A network-theory-based approach allocated nonquantifiable focus points to each system to determine their importance within a network. These were then linked to transition rates, which are required for a Markov chain to calculate the availability of a system. Four case studies were performed to test the model: several configurations were compared, two different focus points approaches were used, different ranges of rates were applied, and systems were added or subtracted. The model proved to behave according to educated guesses beforehand but also gave new insights in connections between nodes. The eigenvector centrality approach used to allocate focus points was found to be better than the combined connectivity approach. The scale of the ranges of rates should not result in very high values for system availability since they do not provide data which makes comparisons between network configurations possible. Very low values of system availability were deemed too far off from real-life values. This thesis paves the road towards a total assessment of operability. It has focused on the availability of systems, and delivered a method to make preliminary decisions for systems design in the early stages. ... Read more