Shipbuilders Design Pipeline Dredging Barge With FEA Software
- Tuesday, 26 December 2006
SIMA created finite element models of the general barge structure, as well as several components in high-load zones including the spud helmet, bulkheads, and spud leg structure. Linear static stress and critical buckling load analyses were performed to determine how the design would withstand the expected loading conditions. The goals of the analyses were to cut the design cost by making the barge in less time, ensuring safety, and reducing the steel quantity required by optimizing the design.
The model of the general barge structure consisted of four parts: the main platform (including the shell plate, deck plate, bottom, and bulkheads), modeled with 8-mm-thick plate elements; supports modeled with truss elements; spud legs modeled with beam elements; and spud helmets modeled with truss elements and used to apply loads to the spud legs.
One complicating factor in modeling the spud legs concerned the constraints. Not all of the spuds’ bearing points work simultaneously, so if all three spuds are driven into the sea bottom, the boundary conditions in the three bearing points are pinned — Tx, Ty and Tz constrained. There is a possibility of one of them slipping horizontally over a rock or stone on the ocean bottom. In this case, only two spuds would be pinned and the third would have only vertical translation constrained.
Static stress analyses with linear material models were performed for several different load combinations and constraints, which varied the number of spuds pinned, the excavator position, the wave position, the sea height, and the wind direction. In this simulation, the most important results were the beam and truss stresses and deflections. The critical load combination was determined, and SIMA found it could reduce the spud plate thickness from 19 to 12.5 mm for 9 meters of the spud length, while maintaining structural integrity. This significantly reduced the amount of steel required to manufacture the spud legs.
The detailed model of the spud leg structure was then modeled with 12.5-mm-thick plate elements and included transversal stiffeners (or diaphragms), which were omitted from the general structure model. A critical buckling load analysis was performed, which verified that the spud leg would not buckle.
Using FEA, the engineers learned how the behavior of a structure can vary regarding loads and constraints, and why it is necessary to understand the physical-mechanical phenomenon that controls the model in order to apply the correct loads and constraints. The company plans to use the software for future projects such as steel bridges, pressure vessels, fishing vessels, barges, and mechanical components.