Drag Chains |
 
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Drag Chains |
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A drag chain is used to simulate the presence of a chain connected to a structure, where a portion of the chain lies along the seabed. The chain itself is not modelled physically using standard elements, rather gravity and lift forces for the drag chain are computed and applied as point loads at the specified node of the structure. The gravity load is calculated from the length of drag chain not lying on the seabed. This length is calculated from the elevation above the seabed of the chain node (the chain is assumed to hang vertically) and the chain length, which is a user input. The lift force on each chain is calculated from the relative fluid/structure velocity at the chain node and the specified lift coefficient. The lift force is computed as follows:
(1)
where 
is the total lift force, 
is the specified drag chain lift coefficient, 
is the mass density of seawater, 
is the magnitude of the horizontal component of relative fluid/structure velocity at the drag chain node, and is the length of drag chain not lying on the seabed.
•*DRAG CHAIN is used to include drag chains in the structural model.