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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 Thesis59 80 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Advances toward Numerical Prediction of Noise Emitted by Yacht and Passenger Ship PropellersThe radiated underwater noise due to shipping activities raises considerably the natural underwater background noise level. With an estimated increase of about 3dB per decade, this development is extremely fast in comparison with evolutionary timescales for some of the affected sea fauna to adapt. Low frequency radiated noise covering the 63 Hz to 125 Hz 1/3 octave bands is dominated by propeller cavitation. At the same time, the highest levels of on-board noise are reportedly noted in the same lower-frequency bands, and they are thus also attributed to propeller cavitation. The present paper addresses the following main problems whose solution is critical for the adequate prediction of propeller acoustic performance using numerical approaches: 1) resolution of anisotropic fields of turbulence in the vicinity of propeller-induced vorticity; 2) prediction of dynamic behaviour of cavitation on propeller blades and in propeller-induced vortices; 3) solution of acoustic propagation in the ambient flow domain. Presenting the state-of-the-art in the field, the paper is further focused on the ongoing research and advances regarding the solution of the aforementioned problems in the R&D project ProNoVi. In particular, the aspects related to the use of scale resolving CFD simulations and implementation of acoustic analogy techniques with both the viscous flow and potential flow hydrodynamic solutions are discussed. The examples of validation studies are presented. The project ProNoVi (http://www.pronovi.eu/) is supported and funded by the MarTERA ERA-NET program, represented by BMWi-project (03SX461C) “ProNoVi” for the German partners (TUHH, Fr. Lürssen Werft GmbH & Co. KG, SCHOTTEL GmbH), the Research Council of Norway "Project 284501" for the Norwegian Partners (SINTEF Ocean, Helseth AS) and MIUR-project “ProNoVi” for the Italian partners (CNR-INM).Publicationtype: Conference Paper171 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Dynamic positioning with Voith Schneider Propeller: Experimental system validation with a model-scale offshore supply vessel(2017-09-19); ; ; ; Dynamic Positioning (DP) is an essential capability of marine vessels required for diverse scenarios. The retention of position by solely usage of thrusters requires an efficient and dynamic propulsion system. A Voith Schneider Propeller (VSP) features such qualities. In this paper a DP system is shown that utilizes the properties of a VSP in an enhanced way, especially in the thrust allocation. Parametrization of the DP system components was conducted by usage of hydrodynamic simulations. Experiments with a model-scale version of an offshore supply vessel were performed to validate the DP system, its components and the design and parametrization techniques. The trials show that thrusters with higher dynamic yield better DP quality. Furthermore, these were, to the knowledge of the authors, the first DP trials performed with a VSP-optimized allocation. 1Publicationtype: Conference Paper262 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Static and dynamic analysis methods of position-keeping capability for offshore supply vessels with voith-schneider propellers(American Society of Mechanical Engineers (ASME), 2017-06); ; This paper presents a static and a time-domain method to assess the position-keeping capability of monohull vessels. For the static analysis method, the equlibrium between mean environmental loads and available actuator forces is determined. In case of the dynamic assessment, the motions of the fully actuated ship in all degrees of freedom are simulated in time domain and evaluated by criteria regarding the position and heading of the ship. After first results from validation tests an exemplary application is shown by assessing the positioning capability of a Voith-Schneider propelled offshore supply vessel.Publicationtype: Conference Paper151 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Efficient simulation method to predict green water loads on superstructures(American Society of Mechanical Engineers (ASME), 2015-05); ; ; The numerical prediction of green water loads on superstructures is challenging due to the high number of required calculations to identify the critical operational conditions in the seaway which lead to overcoming seawater on deck. Further, the simulation of the non-linear behaviour of water on the deck and the prediction of impact loads require high computational effort. This paper presents an efficient three-step approach to simulate green water loads. The application of the developed procedure will be demonstrated on a mega yacht geometry.Publicationtype: Conference Paper71 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Time domain simulation of dynamic positioning manoeuvres based on impulse response functions(International Center for Numerical Methods in Engineering (CIMNE), 2015); ; The Paper focusses on the development of a numerical method to simulate ship motions under arbitrary external forces. Based on impulse response functions, the developed method benefits from the computational efficiency of boundary element methods in frequency domain to determine hydrodynamic forces acting on the vessel. Major nonlinear effects are captured directly in time domain. To capture the vessels drift motion, second-order wave excitation is considered. Wind and current induced forces complete the modelling of environmental loads. An interface to MATLAB/SIMULINK simplifies an efficient representation of the vessels control system and the dynamics of its propulsion plant. This finally allows time-domain simulations of complex dynamic positioning manoeuvres in natural seaways.Publicationtype: Conference Paper85