1. Additional Features

This group gives a description of special features that normally are not used in analysis of flexible riser system.

1.1. Local element axis definition

Additional to Arbitrary system AR.

This data group may be used to specify a reference vector that is used to determine the initial orientation of the local y- and z-axes of beam elements.

If a local element axis is not specified for an element, the default procedure described in Line, line type and supernode connectivity is used.

This data group must be given for all cross sections with hydrodynamic loads model: Net properties and hydrodynamic added mass coefficients for net (HNET) as the reference vector and the element’s x-axis define the net plane during static and dynamic analysis.

1.1.1. Data group identifier, one input line

LOCAl ELEMent AXIS

1.1.2. Number of input lines for special axis definition, one input line

NAXDEF

  • NAXDEF: integer: Number of input lines for special axis definition

1.1.3. Specification of reference vector for definition of the local axes in the initial configuration, NAXDEF input lines

LINE-ID ISEG IEL RNX RNY RNZ

  • LINE-ID: character(8): Line identifier.

  • ISEG: character/integer: Local segment number within line LINE-ID

    • = ``0’ or `ALL' means all segments in specified line

  • IEL: character/integer: Local element number within segment ISEG

    • = `0’ or `ALL' means all elements in specified segment `ISEG

  • RNX: real: X-component of the reference vector

  • RNY: real: Y-component of the reference vector

  • RNZ: real: Z-component of the reference vector

The reference vector is to be given in global system.

The element’s local x-axis goes from end 1 to end 2 of the element.

The element’s local z-axis is given by the cross product between the element’s local x-axis and the reference vector.

The element’s local y-axis is given by the cross product of the local z-axis and the local x-axis.

The reference vector must not be parallel with the element’s initial x-axis. For cross sections with hydrodynamic load type: Net properties and hydrodynamic added mass coefficients for net cross sections, the reference vector must be chosen so that it is not parallel to the element’s x-axis during the static and dynamic analyses.

For beam elements, the element axes are found at the stress-free configuration and will subsequently follow the element.