Dynamic Simulation of Ships

Study of dynamic draught of ships under constant environmental conditions







The company i4sea wanted to improve its port consultancy tool called i4cast by offering its clients useful information with the aim of making port operations safer, more efficient and, therefore, more profitable. For that, out partner ITMATI developed a software tool that allows the calculation of the dynamic draught of ships under constant environmental conditions in shallow waters, such as port areas. Under certain known conditions of bottom sea, bathymetry, wind, etc., the dynamic draught has been obtained as a result by calculating the RAOs (“Response Amplitude Operators”) for a whole range of frequencies of interest. In this way, in certain points of interest of the vessel, such as the bow perpendicular and the stern perpendicular, its maximum vertical displacement has been calculated, as well as the critical draught, which indicates the height of the minimum water column for the vessel to navigate without being obstructed by the sea floor.


In this software tool two calculation stages can be identified that can be used independently, the calculation of the equilibrium position, and the calculation of the hydrodynamic behavior of the vessel. In order to perform these calculations in a robust and efficient way for any type of ship hull, a robust methodology has also been designed to mesh the hull part of the submerged ship and the surrounding fluid where the waves propagate around it. This pre-processing stage of the hull geometries and their corresponding meshing has been implemented using the free software codes Gmsh (http://gmsh.info/ ) and Salome (https://www.salome-platform.org/ ). Equilibrium position In this part, the ship’s equilibrium position is calculated without taking into account the interaction of the water surface waves with the ship. This calculation can be done without taking into account the environmental conditions (hydrostatic equilibrium), or by introducing the effect of wind and squat effect produced by the speed of the sea current and that due to the speed of the ship itself. Hydrodynamic behavior Taking as a reference the previously calculated equilibrium position, the wave is added with a determined frequency spectrum and assumed as data. In this way, translation and rotation movements are calculated with respect to the vessel’s initial axes. From the dynamic characterization of the ship (through the calculation of RAOs), the dynamic draught of the ship is obtained taking into account the frequency and the amplitude of the incident waves that configure the background sea on which the ship sails. The two stages of calculation of the equilibrium position and dynamic behavior of the ship are developed under the paradigm of intensive use of free software, based on its implementation in an object-oriented programming using Python (https://www.python.org/), and using the finite element library (FEniCS https://fenicsproject.org/).

Impact and results

Thanks to these developments, the platform i4cast has improved its capacity and allowed it to position itself advantageously over its competitors, offering its clients useful information with the aim of making port operations safer, more efficient and, therefore, more profitable.

Results in figures

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