Skip to content

Home > Model Components > Rigid Bodies > Drawing

Rigid bodies drawings

The geometry of rigid bodies must be explicitly defined as a meshed surface or as an assembly of bar elements, may be either read from a simple text file or defined by using predefined surfaces shapes.

Mesh Data File

Type in the address for the file that contains surface meshing data or browse to the file to import meshing data. Click here for more details about the file format.

The center of imported mesh - i.e. node with (0,0,0) coordinates - can be located either at the reference point of the Rigid Body or at any selected fairlead or hang-off point. The center of mesh located at the reference point of the Rigid Body by default.

Rigid bodies may also be used to model series of lines such as bar elements connected together.

Predefined Shapes

An alternative to using the mesh data files is to define the rigid body surface as a predefined shape. Meshing and distribution of triangle elements required for display in the 3D View window or to handle contact with lines is done automatically by the GUI in this case. Select the Mesh option and then choose the type of shape from the drop-down list as illustrated below :

Box

Boxes are simple rectangular shapes as illustrated below and defined by the following parameters :

  • Length (m) : dimension in the local X direction

  • Width (m) : dimension in the local Y direction

  • Height (m) : dimension in the local Z direction

  • Segmentation : number of elements in the X, Y and Z directions. All default to 1.

  • Orientation : default orientation of normal vector used to handle contact with lines is outwards the box. The orientation can be changed by selecting the Inverse normal vector option.

Cylinder

Cylinders are simple shapes as illustrated below and defined by the following parameters :

  • Radius (m) : this is the distance between the surface and the main axis.

  • Length (m) : Length of the cylinder.

  • Number of elements along length : The number of elements along the axis must be set so as to be compatible with the number of line elements likely to contact the cylinder. A single element can however be enough for a wide range of situations.

  • Starting angle (deg.) : Starting and ending angles used to generate the cylinder from the radius and main axis can be defined to model complete revolution or partial revolution. Setting these values to 0 degree and 360 degrees respectively correspond to a complete revolution about the axis.

  • Ending angle (deg.) : Starting and ending angles used to generate the cylinder from the radius and main axis can be defined to model complete revolution or partial revolution. Setting these values to 0 degree and 360 degrees respectively correspond to a complete revolution about the axis.

  • Number of elements along circumference : This defines the number of elements to be placed on the circumference. The number of elements must high enough to ensure smooth description of the curved part. Using for instance 36 elements will correspond to one element every 10 degrees. Recommended minimum value for 360 degrees is 12 elements.

Rectangle

Rectangles shapes are simple two-dimensional planes as illustrated below and defined by the following parameters :

  • Length (m) : dimension in the local X direction

  • Number of elements along length

  • Width (m) : dimension in the local Y direction

  • Number of elements along width

  • Orientation of normal vector is upwards by default, so that (U,V,N) coordinates system is direct.

Surface of revolution

Surfaces of revolution can be used to model any surface of revolution such as bellmouths. The surface is defined trough its main axis and radius as a function of position along the axis.

  • Number of points along main axis : the number of points must be set depending on the curvature of the shape so that the size of elements allows to properly describe the geometry. Linear interpolation is used between user-defined points.

  • Position of points along main axis (m) : defines the positions of the nodes along the main axis at which radii will be specified.

  • Radius profile (m): This is the distance between the surface and the main axis as a function of the position along the axis.

  • Starting angle (deg.) : Starting and ending angles used to generate the surface of revolution from the radius profile and main axis can be defined to model complete revolution or partial revolution. Setting these values to 0 degree and 360 degrees respectively correspond to a complete revolution about the axis.

  • Ending angle (deg.) : Starting and ending angles used to generate the surface of revolution from the radius profile and main axis can be defined to model complete revolution or partial revolution. Setting these values to 0 degree and 360 degrees respectively correspond to a complete revolution about the axis.

  • Number of elements along circumference : This defines the number of elements to be placed on the circumference. The number of elements must high enough to ensure smooth description of the curved part. Using for instance 36 elements will correspond to one element every 10 degrees. Recommended minimum value for 360 degrees is 12 elements.

Arch

Arches are surface defined as curved plates that can be sued to model mid- water arches surface used with flexible risers for configurations like lazy-S or steep-S. The surface includes two curved parts and a portion of plane in- between. The surface is illustrated below and can be defined through the following parameters :

  • Length (m) : dimension in the local Y direction

  • Number of elements along length

  • Width (m) : dimension in the local X direction.

  • Number of elements along the middle plane part. Recommended minimum value is 2.

  • Radius (m) : The radius used to define the curved parts.

  • Number of elements along curved part : The number of elements must be set so as to get a smooth description of the curved part and avoid sharp edges. Recommended value is 7 as a starting point.

Note

The width must be higher than two times the radius to preserve the shape.

User defined surface

User-defined surfaces are similar to surfaces defined in Mesh Text files except that the definition of nodes and triangles is done directly from the window. The parameters used to defined these surfaces are as follows :

  • Number of nodes

  • List of X,Y and Z coordinates for all nodes

  • Number of triangle elements

  • List of nodes identification numbers defining the triangle elements

Note

Similar conventions to those used within mesh text files apply as regards the orientation of the surface, as detailed here.

Not used in calculation

Activating this option results in the Rigid Body mesh being used for display purpose only in the DSS files. The Rigid Body is therefore not considered in the analysis (as the nodes and mesh elements are not translated in the LOG file anymore) which allows speeding up the calculation and saving hard drive space.

Warning

This option may be activated only in case the Rigid Body component is not used to model contact with line components. Contact modelling requires that is option is disabled.