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Sea and ground

The Sea & Ground object allows you to define a number of environmental data, regarding the drawing and mechanical properties. The data to be defined is as follows :

Environment

Insertion environment

These are geometrical data to be used for the display in the 3D view window only :

  • Height above sea (m): This parameter is optional and is used only for graphical purposes in the 3D View window. Changing this parameter would alter the alignment of the view along the vertical Z axis when a side view is selected. This parameter does not impact the input data for the FE engine and has therefore no effect on the simulations.

  • Width (m): Width of the global insertion environment. This dictates the horizontal extent of the 2D seabeds. The width shall be set large enough to ensure that all line parts that should rest on the seabed could actually keep in contact with the surface that models the seabed.

Colours

These are data to be used for the display in the 3D view window only :

  • Sea color

  • Ground color

Physical parameters

Sea

The two next parameters will be used to compute the wave kinematics, the apparent weight and hydrostatic pressure.

  • Depth (m): this reference depth is used to determine the wave kinematics only and does not impact the location of the seabed surface used to model contact with the Line components.

Warning

The depth parameter would naturally be similar to the actual position of the seabed for horizontal seabeds. It is however still required to define the coordinates of such seabeds from the Seabed shape frame. You may for instance set the depth equal to 1000m, and define the Z coordinate of seabed as Z=-1000m.

Warning

Wave kinematics and hydrodynamic loadings are not accounted for anymore along line elements in case the mean line of the elements is located deeper than the depth parameter. Hydrodynamic loadings along lines are therefore calculated from the sea level down to a depth equal to the depth parameter.

  • Water density (kg/m3): the water density is constant over the water column.

  • Water kinematic viscosity (m2/s): the kinematic viscosity of seawater. This is used to determine the Reynold value of the flow past a Line. This parameter is useful when using Reynolds dependent drag or inertia loads and when modelling vortex induced vibrations.

  • Air density (kg/m3): the air density is constant above the sea surface. This parameter is used to derive the wind loads acting on line components.

  • Air kinematic viscosity (m2/s): The kinematic viscosity of air.

  • Gravity (m/s2): the acceleration caused by the gravitational attraction. The gravity is used to derive the weight in air of structural model components from the mass.

Seabed shape

Three different seabed shapes can be defined :

  • Horizontal : In this case, you just have to specify the XYZ coordinates of one point

  • Flat with slope: A point on the seabed (normally the origin) and the normal vector to the seabed plane has to be defined.

  • User defined: A 3D shape may be defined through an external text file with that has the following file format. Note that for complex bathymetry, the mesh can become quite large. With the option "Not used for post-treatment", the mesh data (nodes and triangles) are not translated in the .log file. The mesh file is directly provided to the solver that loads it dynamically. The nodes are then not saved in the output databases saving memory and time.

Ground connections

The connection point of any lines lying on the seabed (or penetrating it) must be defined in the Ground connection grid. Each connection point is defined by its name, X and Y coordinates expressed in the global coordinates system, and built-in angle parameters Azimuth and Elevation. The Z coordinate will be automatically set to the correct value.

You can add or remove any connection point from the grid by clicking the Add new connection or Remove selected connection buttons.