Dynamic Loads

This section contains information about change of static loads and various dynamic loads including boundary change

1. Static load condition

This may be used to scale the static loads at the start of the dynamic analysis

  • volume : Scaling of volume loads

  • specified nodal loads : Scaling of specified forces

  • current velocity : Scaling of current velocities

2. Segment length variation

This may be used to change the stress-free segment length of specified segments during a simulation. The rate of segment length change is specified.

The functionality may be used for simplified analyses of operations such as tie-in or winching.

Lengthening segments can be more numerically challenging than shortening as lengthening may lead to compression.

3. Temperature variation

This may be used to change the temperature of selected parts of the Slender System. The stress-free length of the elements will be changed if the specified temperature is different than the initial temperature.

The initial temperature and the thermal expansion coefficient are given in the cross-section specification. This load will not have any effect if the thermal expansion coefficients have their default value of zero.

4. Pressure variation

This may be used to change the internal pressure in selected Main Riser Lines in the Slender System. The change of internal pressure will have two effects:

  1. stress-free element lengths will be changed f the pressure expansion coefficient is not zero

  2. wall tension and calculated stresses will be changes

The initial internal pressure is specified in the Main Riser Line specification.

The pressure expansion coefficient is given in the cross-section specification.

5. Winch variation

This may be used to winch in or out a line attached to a Winch. The winch is defined in AR Winch in the Slender System.

The specified velocity of the winch run will be modified so that it complies to the specified maximum velocity and the time required to reach the maximum velocity of the winch. These parameters are given in the winch specification.

6. Boundary change

This may be used to change the boundary conditions of selected modes in the Slender System.

The following types of boundary changes are available

  • Free: the node is changed to a free node

  • Fixed: Fix all or some of the degrees-of-freedom of the node

  • Prescribed: Fix all or some of the degrees-of-freedom of the node to a Support Vessel.

  • Slave: the node is changed to a slave of another node in the the system, the so-called master node. This results in a rigid connection between the nodes.

The node may be specified by

  • a supernode id

  • line id, segment number and node number

Use Prescribed to attach a node to a Support Vessel.

Use Slave to attach a node to a SIMO body node.

7. Dynamic nodal force

This may be used to apply a specified load at a specified node in the Slender System. The loads may be specified in

The global coordinate system in one of the following degrees-of-freedom

  • 1: force in global X-direction

  • 2: force in global Y-direction

  • 3: force in global Z-direction

  • 4: moment about global X-direction

  • 5: moment about global Y-direction

  • 6: moment about global Z-direction

The local element coordinate system (of local element number Node) in one of the following degrees-of-freedom

  • 1: force in local X-direction at end 1 of element

  • 2: force in local Y-direction at end 1 of element

  • 3: force in local Z-direction at end 1 of element

  • 4: moment about local X-direction at end 1 of element

  • 5: moment about local Y-direction at end 1 of element

  • 6: moment about local Z-direction at end 1 of element

  • 7: force in local X-direction at end 2 of element

  • 8: force in local Y-direction at end 2 of element

  • 9: force in local Z-direction at end 2 of element

  • 10: moment about local X-direction at end 2 of element

  • 11: moment about local Y-direction at end 2 of element

  • 12: moment about local Z-direction at end 2 of element

The loads may be defined as

  • Constant value of P1

  • Harmonic with amplitude P1, Period and Phase

  • Ramp with rate of change P1

  • Read from specified file with formats

8. Dynamic current variation

Time series of the direction and velocity of the current may be read from a ile with format.

Not available for analyses with SIMO bodies.

9. Rigid moonpool column

This may be used to modify the wave kinematics for part of the system.

10. Dynamic wind change

This may be used to specify an IEC 2005 wind event. The following types are available

  • Extreme coherent gust with direction change

  • Extreme vertical wind shear

  • Extreme horizontal wind shear

  • Extreme operating gust

  • Extreme direction change

Only available for some wind types.

11. Wind turbine fault

This may be used to specify a wind turbine fault condition. The following types are available

  • Wind turbine shutdown

  • Wind turbine blade pitch fault

12. Wind velocity ramping

The wind velocity can be ramped using a predefined clutch. The wind will be gradually scaled from an initial scaling value up to the full value at specified Ramp Duration.

The clutch options are shown in Ramping of Wind Velocity

um windload ramp
Figure 1. Wind ramp clutch options