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How FEA/CFD Can Validate Structural Integrity on Offshore Oil Platforms

Numerical simulation on offshore platform

Hyco Canada Ltd., a division of WEBER-HYDRAULIK group has been a leading hydraulic cylinder manufacturer for more than 50 years. The company specializes in rod and telescopic cylinders for various industries and a large spectrum of applications including marine cranes, oil rigs skidding systems, drill floor raising systems and more.

Working on an offshore oil platform has its challenges. The demanding operational conditions in the area of oil extraction require reliable hydraulic systems regardless of the environment. One of the challenges includes having to compensate for the instabilities induced by waves and water currents which can have a significant impact on the machinery used in oil drilling.

The project

Creaform’s 3D Engineering Services was contracted to validate the structural integrity of the piston of an hydraulic cylinder. To do so, Creaform’s numerical simulation (FEA/CFD) team performed the structural analysis of a piston undergoing an impact at a two foot per second velocity and a scenario intended to simulate the displacement of an oil platform induced by waves. This project required finite element modeling, non-linear implicit transient analysis for impact scenario and margins of safety calculations for metallic components and interface joints (fasteners).

A non-linear transient simulation under an implicit calculation scheme was used in order to assess the strength of the assembly. Non-linear boundary conditions have been used to represent the impact scenario. Initial velocity and contact algorithms between moving part and cylinder as well as tuned structural damping to represent viscosity of surrounding fluid have been used to represent impact dynamic. Material behavior has been represented with linear properties (elastic) for all components. Metallic components and welds have been represented with a 3D hexahedral and tetrahedral elements fine mesh to allow extraction of Von-Mises stresses. These stresses have been used to assess structural integrity of components and welds during impact scenario. Bolts have been represented by 1D elements in order to allow extraction of loads, used to compute safety margins against fastener tensile, shear, slip and thread failure of the fasteners and locally interfacing components. Structural integrity of structure, based on computed margins of safety on structural components, welds and joints has been demonstrated for 2 foot per second impact scenario, according to customer specifications.

Technical challenges

The project required knowledge and techniques within the field of dynamic transient analyses in order to choose proper parameters such as contact algorithms and damping values. Given the nature of the problem, both implicit and explicit dynamics could have been used; each with a careful choice of related parameters. Implicit non-linear transient analysis of a quarter of the symmetric geometry with time step choice based on a preliminary modal analysis of impacting components were chosen to simulate the impact.