The interaction of a turbulent flow with the leading edge of a foil is one of the dominant noise sources for many engineering applications, including aircraft wings, (wind) turbine blades, and non-cavitating marine propellers such as those found on tidal turbines, naval vessels and submarines. Incorporating a better understanding of the turbulence intensity on the far-field radiated noise in the early design phases can help reduce low-frequency broadband noise that is harmful to humans and (marine) wildlife. A simple framework, such as that proposed by Amiet, can provide fast predictions once validated for more complex problems. The current work assesses numerical predictions on far-field radiated noise by the leading edge of a NACA0008 airfoil for varying turbulence intensities. The flow is simulated within ReFRESCO, a partially averaged Navier-Stokes solver in which turbulence is generated using a synthetic inflow turbulence generator. Inflow turbulence and predicted far-field noise by the Ffowcs Williams-Hawkings formulations are experimentally and numerically validated, showing that the proposed method can generate realistic turbulence, pressure data on the foil surface and associated far-field noise. Variation in the turbulence intensity shows an unwanted change in the integral length scale, which did not seem to affect the far-field radiated noise. In agreement with Amiet, a linear increase in turbulence intensity leads to a near quadratic increase of the radiated noise for a receiver directly above the foil. A rapid change in scaling is seen for receivers more closely aligned with the flow direction both up- and downstream of the foil, for which the far-field noise scales with the turbulence intensity to the sixth power. Variations in the turbulence intensity between 4 % and 16 % dominate over a change in the integral length scale from 30 mm to 65 mm.

In response to the leading narrative of increasing sustainability in the yachting sector, a research collaboration is started between the Delft University of Technology and Dykstra Naval Architects to examine the potential use of hydro generation on board sailing superyachts. By harvesting energy from the water flow when under sail, diesel generator use can be limited, reducing overall emissions. Currently, it is not yet possible to quantify the impact of a chosen hydro generation system on the overall design during the early stages of yacht design. To assess the correct balance between the inevitable increase in system weight and size relative to, for example, emission reduction. To allow for this, a novel method is developed, presenting the designer with the opportunity to explore various hydro generation systems quickly. With the ability to complete this in an early design stage, more opportunities for hydro generation remain, and the need for a feasibility study for hydro generation is removed. In this thesis, the developed method is described, and results are presented that provide insight into its applicability. The design method considers the impact of six variables that influence hydro generation. The first three variations concern size and include the propeller diameter, battery capacity, and sail area. The remaining considerations relate to operational and design choices and include decisions on energy consumption, fixed or controllable pitch propellers, and generation in the first or third quadrant. A scenario for an ocean crossing with a sailing yacht aiming to limit fuel consumption demonstrates the influence of these considerations. The results presented in the thesis show that the method provides the basis for a later detailed design stage when an actual hydro generation system is implemented.

Fiber-reinforced composite (FRC) marine propellers potentially outperform metallic propellers in terms of efficiency and underwater radiated noise (URN) by hydro-elastic tailoring of the blades. Several methods can assess the extent of these potentials. Research shows that embedded sensing methods can be used in dynamic measurements of composites. This thesis studies a full-scale application of a network of embedded piezoelectric sensors in an FRC marine propeller blade. The study prefers using piezoelectric sensors because of their ability to operate in a relatively wide frequency range. The focus of the thesis starts with designing the full-scale network of embedded piezoelectric sensors. Since no literature includes this application on FRC blades, this study holds a pioneering role in embedding piezoelectric sensors in an FRC marine propeller blade. Detailed analysis of material dimensions - including sensors, wiring, and fiber plies - leads to a successful sensor network design. Considerations regarding the location of 24 sensors included both the in-plane and the in-depth position within the FRC laminate. Fabrication of an FRC blade has been done using a resin transfer moulding (RTM) process. For the first time, an FRC marine propeller blade is embedded with piezoelectric sensors. Demoulding of the blade caused damage to some of the sensor wires. An amount of 54% of the embedded sensors survived the process with full connectivity. The performance of the intact sensors after fabrication is assessed. These sensors are exposed to free vibration tests of the FRC blade. An excitation is imposed on the blade with an impact hammer. A data acquisition (DAQ) system is used to capture the responses of the embedded piezo-sensors. The frequency response functions (FRFs) of multiple locations on the blade are computed. These FRFs provide more insight into the dynamic behavior of the blade. A frequency range of 1-1000Hz is used in the modal analysis. The first five natural frequencies are found between 240Hz and 840Hz. Natural frequencies measured by the embedded piezo-sensors and surface-mounted strain gauges differ up until 25% from natural frequencies computed by a finite element model (FEM) of the blade. The mode shape of the blade at the natural frequencies is computed for by the FEM and embedded piezo-sensors. Some difference in mode shapes is demonstrated between measurements computed by FEM and those measured by the embedded piezo-sensors and surface-mounted strain gauges. The piezo-sensors and strain gauges are in agreement regarding the measured natural frequencies. Therefore, it is expected that discrepancies exist between the physical blade and FEM. Several points for improvement of the results have been found. The study provides the first-time feasibility of dynamic measurements from embedded piezo-sensors in an FRC marine propeller blade. Additionally, a framework for reconstructing the full-field vibration response is provided, which can provide more accurate results when the agreement between piezo-sensor and FEM measurements has improved.

In the modern world, environmental concerns arise due to an increase in the green house gas (GHG) emissions of the shipping industry; in 2015, 2,5% of global GHG emissions came from the shipping industry alone. Measures must be set in place to reduce the future emissions. One way to reduce emissions is by imposing the Energy Efficiency Design Index (EEDI). This is a measure to define the ratio between the CO2-production and the cargo capacity and speed of a ship. In other words, this ratio defines the environmental cost over societal benefit of a ship. The International Maritime Organisation wants to have a set requirement on the EEDI of new ships and preferably reduce this for existing ships. One way to reduce the EEDI is by reducing the installed engine power of the ship. One risk is that the ship might then become underpowered when it sails in adverse weather. The underpowering of ships could lead to safety hazards for the passengers and crew. For that matter, this thesis will investigate whether the ocean-going chemical tanker 'Castillo de Tebra' is underpowered when sailing in large waves. Specifically, the effect of the waves on the inflow velocity of the propeller will be looked at and how this affects the propulsive performance of the vessel.
An extensive literature review was carried out in order to find out what the state-of-the-art is within the determination of ship propulsion in waves. This has been divided into three separate subjects, namely wave excitation, propeller and engine operating in waves and finally manoeuvring and seakeeping. When determining the forces that occur on a ship when it advances in waves, most methods use potential flow as the results are reliable and have low time effort. Determining propeller performance when the full wake distribution is known can also be done using potential flow methods. Basic open-water characteristics are a valid alternative as well. CFD can be used for both wave excitation and propeller performance calculations, but this is time consuming and computationally complex. When simulating manoeuvring and seakeeping behaviour of ships, two-time scale methods or unified methods are mainly used.
For the research part of this thesis, numerical simulations were performed to determine the change of inflow velocity at the propeller plane for a large range of wave frequencies and wave directions, for a vessel having a forward speed. This velocity change was used to determine what the thrust and torque generation of the propeller is in waves. The engine operating envelope and ship thrust envelope were used to check whether the engine has enough power to provide the torque that the propeller generates and whether the ship has enough thrust availability. Frequency-domain results were transformed into time records for irregular waves using the JONSWAP wave spectrum and a cosine funtion. It was concluded that the ship was underpowered in adverse weather conditions, when an instant control system was assumed that inject enough fuel instantly to keep the engine at the rated speed when it needs to deliver more power. It was also assumed that the ship speed was kept at the design speed. In reality, voluntary and involuntary speed loss will occur when a ship sails in bad weather. Voluntary in the form of manual speed decrease by the captain and involuntary in the form of added resistance causing the ship to reduce in speed. A number of solutions are finally presented in this thesis to omit engine overloading in adverse weather.

The shipping industry is forced to reduce its emissions and underwater radiated noise in order to decrease the impact on the environment and limit global warming. Moreover, a low acoustic signature can be lifesaving for a navy ship, especially during submarine on mine threats. To be able to operate as flexible as possible under these threats, a flexible propulsion plant is required. A diesel engine with a controllable pitch propeller (CPP) is contributing to this. A method to reduce the emissions and noise of such a plant is to improve the control strategy. Often this is tested with numerical models. However, frequently they contain many simplifications of reality, for example, the neglection of several hydrodynamic effects. Hardware In the Loop (HIL) takes these effects into account by replacing a software part of the model with a hardware component. In this research, the CPP is the scaled hardware part. A feasibility study is performed to determine whether a propeller open water HIL setup can be used to simulate the dynamic behaviour of the propulsion plant. Therefore, a comparison is made between full and model scale numerical simulation of a diesel engine with a CPP controlled by adaptive pitch control (APC). To reduce the pitch actuations with the APC strategy a Kalman filterwith deadband is implemented. Full-scale simulations with irregular waves demonstrated that the pitch actuations could be reduced during acceleration and at a constant speed. The validated full-scale model is Froude scaled and implemented in a model of the open water HIL setup. The results of the full and model scale simulations are very similar. Thus, the HIL setup can be used to simulate the dynamic behaviour of a propulsion plant. However, the hardware limitations such as the backlash in the CPP blades, the low sample rate of the actual pitch and the Froude dissimilarity of the acceleration of the towing tank need to be resolved to ensure the scaled simulations are representative for the actual, full scale, vessel. Due to these limitations, it is not possible to use the setup at this moment to perform experiments and improve novel control strategies. If these physical limitations of the current HIL setup are overcome, the effect of the propeller and the pitch control strategy during turns can be investigated by performing experiments with oblique inflow.

Tip vortex cavitation was previously identified as a source of the broadband noise emitted by ships underwater. This leads to unwanted noise and vibrations on board, which reduces passenger comfort, and increases the underwater signature of naval ships. The influence of different cavitation regimes on propellers and boundary layer transition on wings, has led to studies that isolate the cavitating tip vortex. This is done by using a converging-diverging nozzle (Venturi tube) geometry, combined with a suitable inflow condition to simulate a cavitating line vortex. The currently available computational power allowed for a comparative study of SRS methods (i.e. the IDDES model) and RANS models (i.e. the k − ω SST and EARSM) in wetted and cavitating vortex conditions. Both the general flow field, as well as the dynamics of the cavity deformations in the vortex were analyzed in this thesis. The geometry was selected based on the available experimental validation data for the wetted flow case, whereby preliminary studies determined the inflow and outflow lengths of the domain. A Lamb-Oseen tangential velocity profile was specified at the inlet. The vortex strength and viscous core size were tuned to obtain similar inflow conditions as in the experimental measurements, which used a fixed-blade swirl generator to generate the line vortex. The flow field in the wetted vortex case demonstrated an excessive amount of viscous diffusion of the vortex for both RANS models.This was caused by the overproduction of modeled turbulent kinetic energy at the viscous core edge. EARSM resuls were verified in a grid- and time step refinement study, however the large modeling error in the viscous core prevented the validation of the results. The IDDES model results were closer to the experimental reference, but were obtained with an almost laminar flow field. Modeled turbulence was mostly dissipated and no resolved velocity fluctuations were present in the flow at the measurement section. In the cavitating vortex simulations, numerical diffusion of the EARSM led to a more diffuse vapor core interface and a more downstream development of the vortex cavity compared to IDDES, where the flow field remained predominantly laminar at the measurement section. Both EARSM and IDDES predicted a solid-body rotation of the vapor core, combined with an increase of radial velocity towards the vapor core edge. The non-negligible radial velocity resulted in a conical cavity shape. The velocity profile of the simulated line vortex therefore did not correspond to that of a cavitating Lamb-Oseen vortex (which assumes no radial velocity components), such that the simulated line vortex was not representative of a cavitating tip vortex. he sheet cavities originating from sharp edges at the front and end of the Venturi throat strongly influenced the flow field and cavity dynamics. The developed front sheet cavity determined the streamwise inception of the vapor core of the vortex. Periodic shedding and collapse of the irregular downstream sheet cavity caused axial and radial contractions of the vapor core
as well as a noncircular deformation of the cavity cross-section. No traveling or standing Kelvin waves could be identified on the cavity interface using the developed post-processing and spectral analysis tool. The identified cross-sectional deformation did not correspond to cavity deformation modes defined in previous research and none of the other deformation modes were found to occur. Grid-dependent solutions, numerical noise and large wavenumber resolution indicated that a finer grid is required and that the analyzed length of the cavity should increase to improve the quality of numerical analyses of simulated cavity dynamics.

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.