OrcaFlex examples

Payload handling

Below is a list of links to OrcaFlex example topics. Within each topic are a number of examples which each comprise one or more simulation files, a description pdf file, workspace files and sometimes other supporting files. The files for each example are zipped for easy download. The simulation files can be opened and viewed with the demonstration version of OrcaFlex.

Payload handling

F01 Lowering hydrodynamics

In these three example models, we consider a number of effects that often need to be accounted for when performing a lifting or lowering analysis through the sea surface in OrcaFlex.

The examples illustrate:

  • The effect of object size on the selected modelling method.
  • How multiple model objects can be connected together to form a complex structure (structure discretisation).
  • Modelling of slam loads.
  • Modelling of trapped water.

F02 Passive compensation

When lowering a structure into the water, from an offshore construction vessel, the heave of the vessel can result in severe motions of the payload and / or high loads on the crane.

To reduce these effects, heave compensation devices are often used. These can be active systems that adjust winch payout to keep the payload at a constant depth (see the example F03), or passive systems where the payload is allowed to move but there is additional compliance, with damping, to reduce the loads on the crane when the vessel heaves upwards.

This example considers the passive system, using a generic passive heave compensation (PHC) device as an example.

F03 PID controlled active winch

This package-lowering example uses a winch to model an active heave compensation (AHC) device. An external function, written in Python, is used to control the length of the winch, thereby holding an object at a particular depth.

F04 Payload transfer

This example shows a large payload being transferred from the deck of one vessel to the deck of another. Constraint objects are used to model the movements of the crane. The response of both vessels is fully calculated and therefore captures the effect of the shifting payload.

F06 Spool piece manoeuvring

This example demonstrates how to use the pre-bend facility in OrcaFlex to model a spool piece. This feature facilitates the modelling of lines which are not straight when in the unstressed state. The analysis considers the scenario where the spool piece is lowered through the splash zone, capturing slamming effects. Constant and variable slam data is applied to both the spool piece (modelled as a line object) and the spreader bar (modelled as a 6D buoy). Line feeding is utilised to lower the spool into the water.

F07 Suction anchor lowering

In this example we show how to model a suction anchor lowering operation.

Lowering of a suction anchor vertically through the sea surface requires careful consideration of the change in axial added mass and inertial loads encountered as the suction anchor cap hits the sea surface, trapping a volume of water inside.