Optimization of the skidded load-out process

Abstract

The structures which HMC installs offshore are fabricated onshore and subsequently moved onto a barge or ship, seafastened and then transported to the offshore location. The process of moving a structure from the onshore quayside to the barge or ship is called the load-out. This load-out can be performed by lifting, skidding or using a trailer (SPMT). This thesis research focused only on a skidded load-out onto a barge.
During the load-out the weight of the jacket or topside is gradually transferred from the quay to the barge. The barge gradually takes more of the load so ballast water needs to be continuously pumped or discharged depending on the location of the structure and the location of the ballast tank concerned. Improper ballasting during this process will cause the alignment between the quay and the barge to be disrupted which in turn causes peak loads in the topside or jacket and the barge. It is questioned if there are more suitable ballasting methods or a structural solution in order to lower these peak loads? It is also modeled what the effects are of quayside stiffness and the best method to model this stiffness.
Therefore a 2-D representation of the entire load-out is made. This model will be made using the finite element method, via a numerical model, in MATLAB. A base case load-out of a topside will be applied to this model. Using this model, optimizing the ballast configuration will be researched. Several different criteria for the optimization were tested and its different effects on the forces during the load-out were researched and quantified. The structural solution of relocating the skidbeams to an area of lower deck stiffness was also tested and the results studied. The effects of the quayside stiffness and modelling methods were also quantified using the 2-D MATLAB model.
The conclusion derived from the optimizations is that there are other ballast configurations which perform better in reducing the peak forces experienced during the load-out. The key to these optimizations is that they keep the barge-quay alignment as perfect as possible. If a critical element is present in the load-out the ballast configuration can be adjusted to lower the forces in this specific element. The results of the simulation in which the skidbeams were relocated show that this approach has no beneficial effects in reducing the forces during the load-out, mainly due to the presence of the transverse bulkheads in het barge. Furthermore for the modelling of the quayside it was proven that especially when using a low stiffness quayside, modelling the quayside without taking into account the foundation layer stiffness is inaccurate and can lead to lower forces in the model than which occur in reality.