Numerical simulation of dynamic positioning (DP) in ice is a novel research topic that has potential in many industrial and scientific applications. This paper reviews some challenges associated with numerical ice modeling and presents a classification of approaches for modeling the ice loads in DP simulations. The approaches are classified into three groups: empirical and statistical models, experimental data series methods, and physically based modeling. The strengths and weaknesses of the approaches are summarized, and recommended uses are outlined in this paper. In addition, a novel, nonsmooth, discrete element model of a DP vessel in managed ice is presented. The model was used to perform a numerical multibody simulation of a series of model tests with a conceptual Arctic drillship on DP in managed ice using the commercial physics engine Vortex. The numerical model simulated the ice basin, the DP vessel, the managed ice, the surrounding fluid, and their interactions. Comparison of the simulation results with experimental data showed that for head-on ice drift, the numerical model reproduced the experimental results reasonably well. However, for higher ice drift angles, discrepancies between the simulation results and the model testing data increased considerably. Possible reasons for the discrepancies are discussed in the paper, along with suggestions for future research. To the best of the authors’ knowledge, both the classification of various approaches for simulating DP in ice and the high-fidelity numerical DP model are novel and have not been published previously.
DYPIC -Dynamic Positioning in ICE -is an international research and development project partially financed by the national research agencies of Germany, Norway and France. This 3-years initiative (2010-2012) focused on the development of Dynamic Positioning (DP) technology for the Arctic environment. The projects' backbone was formed by two extensive experimental campaigns performed in 2011 and 2012. This paper summarizes the work performed within the project and spotlights the technical and scientific findings emerged from it. Special attention is payed to two facets of the project: the design of experimental devices, systems and setups for ice tank testing including the development of a dynamic positioning system for model basin facility, and the development of an ice basin numerical simulator. Finally, the opened perspectives are discussed with a special focus on the operational matters.
Offshore operations in ice-covered waters are drawing considerable interest from both the public and private sectors. Such operations may require vessels to keep position during various activities, such as lifting, installation, crew change, evacuation, and possibly drilling. In deep waters, mooring solutions become uneconomical and, therefore, dynamic positioning (DP) systems are attractive. However, global loads from drifting sea ice can be challenging for stationkeeping operations of DP vessels. To address this challenge, the current paper investigates DP in level ice conditions using experimental and numerical approaches. The experimental part describes a set of ice model tests which were performed at the large ice tank of the Hamburg Ship Model Basin (HSVA) in the summer and autumn of 2012. Experimental design, instrumentation, methods, and results are presented and discussed. The numerical part presents a novel model for simulating DP operations in level ice, which treats both the vessel and the ice floes as separate independent bodies with six degrees-of-freedom. The fracture of level ice is calculated on-the-fly based on numerical solution of the ice material failure equations, i.e., the breaking patterns of the ice are not precalculated. The numerical model is connected to a DP controller and the two systems interchange data dynamically and work in a closed-loop. The structures of the models, as well as the physical and mathematical assumptions, are discussed in the paper. Finally, several ice basin experiments are reproduced in the numerical simulator, and the results of the physical and numerical tests are compared and discussed.
Dynamic Positioning (DP) systems are intensely used in a large range of ship operations nowadays. The growing interest of Arctic exploration and exploitation may introduce a new application area for those systems. The very few full scale DP operations in the Arctic have demonstrated the need for improvements in DP systems for ice-covered waters. External forces due to the ice environment are very different from open water forces and especially the dynamic component of the loads is much higher. This paper firstly reviews DP in open water and spotlights the needs for adaptations to ice-covered regions. The architecture of a controller answering ice requirements is then presented. This system has been successfully tested at the large ice tank of the Hamburg Ship Model Basin (HSVA) in 2012 within the European R&D project DYPIC [1]. The designs of open water and ice control laws are then compared in two simulation frameworks. The first framework involves only the current, wind and waves, while the second framework deals with the ice conditions. The numerical ice simulator, utilized in this paper, is a novel high-fidelity modelling tool developed by the Norwegian University of Science and Technology (NTNU).
Offshore operations in ice-covered waters are drawing considerable interest from both the public and private sectors. Such operations may involve a requirement for vessels to keep position during various activities, e.g. lifting, installation, crew change, evacuation, and possibly drilling. In deep waters, mooring solutions become uneconomical and therefore dynamic positioning (DP) systems are attractive. However, the ice environment is highly variable with ice features ranging from mild pack ice to pressure ridges and icebergs. This paper focuses on level ice as one of the primary ice types for DP operations in cold waters. The paper presents two major contributions: experimental and numerical. The experimental part is devoted to the description of ice model tests performed at the large ice tank of the Hamburg Ship Model Basin (HSVA) in the summer and autumn of 2012. Experimental design, instrumentation, methods and results are presented and discussed. The numerical part presents a novel model for simulating DP operations in level ice. In the modelling, the vessel and the ice floes are treated as separate independent bodies with 6DOF. The fracture of level ice is calculated on-the-fly based on numerical solution of the ice material failure equations, i.e. the breaking pattern is not pre-calculated. The numerical model is connected to the DP controller and the two systems interchange data dynamically and work in a closed loop. The structures of the models as well as the physical and mathematical assumptions are discussed in the paper. Furthermore, several ice basin experiments are reproduced in the numerical simulation and the results of the physical and numerical tests are compared. To the best of the authors’ knowledge, both accurate ice basin tests of DP in level ice and high fidelity simulations of such experiments are novel and have not been published previously.
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