ACA Engineering Consultants have undertaken the Structural Analysis of a number of high load capacity Drag Chains for offshore and land-based oil rigs for
Metreel Ltd., Nottinghamshire. |
| A structural model of the drag chain is generated in the ANSYS finite element program, version 12.0, from arrangement and detail drawings provided by the client. |
| The analysis would be performed using a combination of SHELL, BEAM, MASS, CONTACT and LINK element types for the structural model, to accurately represent the various components of the structure. |
| In order to accurately identify any potential structural failure, a typical analysis of the drag chain structure would be performed for a number of load cases; e.g. for dead load only, for dead load with snow and ice load and for dead load with an operational wind speed. |
| Example Load Case 1 – Dead Load Only |
| For this load case a gravitational acceleration of 9.81 m/s2 would be applied to the chain structure (including the mass of the plates, beams and hoses), based on the material density. In addition to this equivalent pressures would be applied to the cross bars of the inner chain to simulate the distribution of the cable mass along the chain.
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| Example Load Case 2 – Dead Load plus Snow Load plus Ice Load |
| For this load case the loads described for load case 1 would be applied. Additionally pressures would be applied to the cross bars which are situated on the upper surface of the top strand of the chain. Also vertical forces would be applied to the top internal bars of the upper stand of the chain, to simulate snow load. Finally nodal forces would be applied to all external nodes, to simulate the existence of ice spread uniformly over the exterior surface of the chain..
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| Example Load Case 3 – Dead Load plus Wind Load |
| For this load case the loads described for load case 1 would be applied. Additionally pressures would be applied to the windward and leeward link side plates, to simulate a specific wind speed applied laterally to the complete chain structure.
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