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Item type:Publication, Access status: with files , Manoeuvring in shallow water – a comprehensive and detailed analysis of shallow-water effects on the manoeuvring behaviour of modern seagoing vesselsShip manoeuvring in shallow water is critical for safe navigation and the design of waterways. This study investigates the manoeuvring behaviour of a container ship and a bulk carrier using free-running model tests (scale 1:60) across a wide range of speeds and water depths, complemented by verified and validated CFD simulations. The results reveal a strong dependence on under-keel clearance, including pronounced speed effects, directional asymmetries, and regime-dependent trend reversals.Publicationtype: Doctoral Thesis82 7 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Enhancement of an innovative current turbine based on magnetic restorationThis doctoral thesis investigates the stability, efficiency, and fatigue life of an innovative turbine designed to extract energy from renewable flow resources through theoretical, numerical, and experimental studies. The turbine is based on the phenomenon of torsional galloping with magnetic restoration, introduced here as a novel concept. Energy extraction is enabled by the unstable dynamic behaviour of the turbine; consequently, stabilisation of the oscillatory motion must be avoided. To exploit this instability efficiently, a magnetic restoring torque is incorporated into the system. This magnetic restoration allows the oscillation amplitude of the turbine to be controlled, thereby limiting excessive vortex shedding and reducing energy losses. A linearized and a non-linear mathematical model were developed and solved. Their predictions were compared with computational simulations and experimental measurements obtained in a current channel. The stability analysis classifies the system response into spiral sink, spiral source, source, and saddle-type solutions and demonstrates that the regions exhibiting the greatest instability coincide with those of highest efficiency. The damping associated with the power take-off system was identified as the dominant parameter, with an optimum value of 0.45. Under these conditions, a maximum efficiency of 56.8% was obtained for a blade limit angle of 30°, a/c = 0.75, and Re = 15 × 10⁴. This corresponds to 95.78% of the Betz limit of 59.3%, with an estimated fatigue life of approximately 21 years. The proposed turbine therefore represents a promising concept for energy generation in remote regions without access to conventional electricity infrastructure and may contribute to the diversification of renewable energy technologies. Finally, the applicability of the concept is investigated for a river in the Amazon Basin. The resulting plant configuration is shown to satisfy the local electricity demand using a relatively small number of turbines and at a lower cost than the alternative configurations considered. The numerical simulations were conducted at the Institute for Fluid Dynamics and Ship Theory (FDS) at Hamburg University of Technology (TUHH), while the experimental investigations were carried out at the Laboratory of Waves and Currents (LOC) at COPPE/UFRJ.Publicationtype: Doctoral Thesis78 14 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Performance of azimuth and bow thrusters during ship maneuvers(2025); Active maneuvering devices improve the maneuverability of a vessel during departure and arrival, reducing the need for tug assistance. However, their operation in significant oblique flow conditions leads to complex flow behaviors, posing challenges in predicting the ship's response within the port environment. This thesis develops an advanced maneuvering model that accounts for asymmetric flow interactions between the hull and maneuvering devices. An offshore supply vessel equipped with two stern azimuth thrusters and one bow thruster serves as the application case. The hydrodynamic performance of the vessel is evaluated using Reynolds-Averaged Navier-Stokes equations (RANS) simulations. Azimuth thrusters, being directly exposed to external flow, are highly sensitive to oblique inflow conditions. Under such conditions, the deformed propeller slipstream can result in the generation of thrust in excess of that observed under bollard pull conditions. This study identifies critical operating ranges to mitigate propulsion system failure through a systematic analysis of azimuth angles (from 0° bis +-180°), azimuth speeds, and ship speeds. The results of numerical simulation also support the development of an Artificial Neural Network (ANN) model for fast predicting the performance of thruster. In contrast, the bow tunnel propeller is shielded from external flow. As a result, the oblique flow may not have a significant effect on the performance of the propeller. However, the effects of the slipstream-hull interaction are taken into account. To evaluate these interactions, static simulations are performed on a vessel equipped with a single bow thruster at varying ship speeds and inflow angles. The transient effects of the slipstream are further analyzed by numerical Planar Motion Mechanism (PMM) tests. These tests not only capture transient phenomena, but also determine hydrodynamic derivatives which are subsequently integrated into the maneuvering model. To fully extract the interaction effects, the PMM tests are performed separately for the ship with and without tunnel thruster. Finally, a maneuvering model is developed for ships equipped with two azimuth thrusters and one bow thruster. Using this model, turning circle simulations under various azimuth speeds, azimuth angles, and wake-field conditions demonstrate its effectiveness in predicting the ship's maneuvering performance.Publicationtype: Doctoral Thesis156 97 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Investigation of hydrodynamic effects on controllable-pitch propellers during crash stop maneuversPublicationtype: Doctoral Thesis95 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Einfluss von Maßstabseffekten auf die hydrodynamischen Eigenschaften von DüsenpropellernModel tests are carried out to test the hydrodynamic performance of ships, particularly for high-cost systems. However, these test are limited, as the test facilities and the test costs, which must be kept as low as possible, only permit comparatively large scales and consequently small models with low inflow velocities. In open water tests, the speeds must be adapted to the mechanical load limits of the measurement systems and propellers. Due to the resulting Reynolds number effects, a Reynolds number correction of the test results is necessary. When carrying out experimental investigations, the aim is to realize fully turbulent boundary layer flow on the test models. However, if the boundary layer is only partially turbulent in the model scale, new methods must be developed which allow the conversion of the hydrodynamic parameters as a function of the position of the laminar-turbulent boundary layer transition. Therefore, the development and further development of Reynolds number correction methods is of fundamental importance in model testing. The work presented here deals with the development of a Reynolds number correction method for open water test results of ducted propellers with accelerating nozzles. To isolate and better understand the physical effects, preliminary investigations were carried out using numerical flow calculations. Using a 2D- and a rotating 3D profile in a neutral, free-slip nozzle, the influence of the Reynolds number on the laminar/turbulent boundary layer and its effect on the drag and lift forces as well as the resulting relationships between lift and drag or propulsive force and torque were determined. CFD calculations of isolated propeller nozzles at different Reynolds numbers, in which the propeller effect was clearly defined by means of an actuator disk model, provided insights into the Reynolds number effects of the nozzles and their consequences for the propeller. It is shown that the formation of the boundary layer has a direct influence on the frictional and pressure forces. Four propellers were selected for systematic model tests and manufactured in two scales each (D = 200 mm and D = 350 mm) as controllable pitch propellers. The propeller hub was designed in such a way that different propeller diameters could be realized by means of spacer plates on the propeller blade feet and thus different gap dimensions between the propeller tip and the inside of the nozzle could be realized with a constant nozzle diameter. This made it possible to carry out extensive free-running and paint flow tests with the propellers with different pitch, gap dimensions and Reynolds numbers in the SVA-Potsdam towing tank. Since only a small Reynolds number range can be covered in model tests, comprehensive CFD calculations were carried out with ducted propellers for a wide Reynolds number range. The CFD calculations were validated on the basis of a large number of test results. Series calculations of geometrically different propellers in the Wag. 19A nozzle over a wide Reynolds number range generated a data basis for the development of an empirical Reynolds number correction model. This made it possible to determine the Reynolds number effects for 50 propellers with different area ratios, pitch settings, tip loads due to pitch and chord length, gap dimensions and skew distributions at different operating points. On the basis of this data, an empirical Reynolds number correction method for ducted propellers was developed for the most widely used Wag. 19A nozzle, in which both laminar-turbulent boundary layer effects and geometric propeller parameters are taken into account. The method makes it possible to determine the influence of the Reynolds number on the free running characteristics of ducted propellers as a function of geometric propeller parameters for the cavitation-free state.Publicationtype: Doctoral Thesis64 65 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Hydrodynamic aspects in the design of lift-based wave energy convertersPublicationtype: Doctoral Thesis90 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Numerical simulation of ship motion under consideration of design criterion for dynamic-positioning-systemsThe present thesis is concerned with the development and application of a simulation plattform called ”DPTool” for evaluating the Dynamic-Positioning (DP) capability of typical DP vessels with Voith-Schneider propellers in the time domain. The platform takes into account realistic environmental loads such as wind, waves, and currents, which have been investigated both numerically and experimentally. The numerical methods include simulating ship motion in waves, parameterizing control using system identification, and an allocation module for de termining control inputs to maneuvering devices. These methods are integrated into a holistic MATLAB/Simulink model as a ”Software-in-the-Loop” (SIL) and can be operated through a graphical interface. Ship motion is simulated using the ”IMPRES” method based on impulse response functions in potential theory. The DP system control is achieved through a nonlinear PID controller with a Kalman filter for ship motion in waves. An optimization algorithm is used for the allocation module to generate the required maneuvering forces realistically and efficiently within a short time. In the scope of this work, wind, current, and wave forces on two models, an offshore supply vessel and a tugboat, have been investigated and measured through experiments. Wind force measurements were conducted in the wind tunnel of the Hamburg University of Technology. The influence of the wind tunnel’s boundary layer was examined prior to the measurements. Flow forces were measured in the towing tank of SVA-Potsdam. For this purpose, the offshore supply vessel model was towed through the tank at various encounter angles and speeds using a force measurement carriage. A comparison of the evaluated experiments with three different numerical methods - a steady-state and a transient Reynolds-Averaged Navier-Stokes (RANS) simulation, as well as a hybrid Detached Eddy Simulation (DES) approach - quantifies the discrepancies between the various methods and the experiments. Determination of wave forces was achieved by restraining the model with springs, allowing for full first-order motion. The measurements were compared with three different numerical methods: a two-dimensional strip method PDStrip, a three-dimensional panel method in the frequency domain, and a transient RANS method. The impacts of deviations between experimental and numerically simulated forces on DP simulations are presented in the work through comparative simulations. The functionalities of the ”DPTool” are demonstrated in a use case, comparing a static method with the dynamic method developed in this work in the time domain.Publicationtype: Doctoral Thesis52 78 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Quantification of the cavitating propulsor-induced underwater sound pressure in the far-field as well as on the ship hull based on turbulence resolved flow simulations and acoustic analogyThe simulation of underwater radiated noise is previously studied with well-defined single acoustic sources or propellers in open water condition. In this work the finite volume method is explored to capture the acoustic sources by resolving turbulent length scales, specifically in the propeller slipstream, applying a Volume-of-Fluid two-phase treatment with the OpenFOAM Schnerr-Sauer model and combining it with the permeable surface Ffowcs-Williams-Hawkings acoustic analogy. Beginning with advanced test cases the noise of propulsor-hull combinations is evaluated and leads to good agreement with measurements.Publicationtype: Doctoral Thesis74 321 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Development of a numerical approach for the simulation of boatlanding maneuversThe thesis is about the development of a numerical method for the simulation of boat-landing maneuver at offshore platforms. The approach is based on a boundary panel method, and it computes the boat-landing maneuver in the time domain considering the non-linear free water surface. A fender contact model is applied to describe the friction forces between fender and boat-landing struts and to detect whether the fender slips or not during the landing maneuver. Furthermore, model tests are conducted in waves. The experimental data is used to validate the developed method. It is demonstrated that the approach is able to simulate the boat-landing maneuver and that it is able to forecast the occurrence of slip during the maneuver.Publicationtype: Doctoral Thesis147 459 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Entwicklung von Methoden zum KI-gestützten Propellerentwurf im frühen Entwurfsstadium(2022-08-10); The aim of the work is to develop an AI-based design method for the creation of a propeller geometry that serves as a starting point for the design process. It should be possible to consider boundary conditions such as the maximum diameter, the required thrust or the available power. Based on a literature review regarding possible AI approaches or methods, these are evaluated in terms of their suitability for supporting propeller design. They range from simple regressions to artificial neural networks. Subsequently, the AI approaches suitable for the task are to be selected and corresponding models are to be implemented from them under consideration of the mentioned boundary conditions. The models are to be trained on the basis of available data from propeller series. In order to assess their quality, the calculated and available free-running characteristics are to be compared for an example propeller. Based on the comparison, neural networks are best suited for this application.Publicationtype: Master Thesis169 569