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refraction due to the base structure and interaction effects between the members in the lattice structure.
- Small-scale tests of the lattice tower only. These test excluded the effect of the GBS, which is in fact the conventional way the wave loads on the tower are considered in the Morison approach in the FE model- ling.
- Large-scale oscillation tests of a section of the lattice tower. These tests in the MARIN Shallow Water Basin at scale 1:5 give insight into shielding effects in the loading (neglected in the FE modelling) and provide results of drag and added mass effects (CD and CM values) for se- lected parts of the lattice structure with minimum scale effects.
- Small-scale oscillation tests of the same section of the lattice tower. These tests with the section at scale 1:63.2 in a scale model of the Shallow Water Basin at scale 1:12.64 are used as a way to quantify the scale effects between the tests in general. They are a bridge between the small- scale tests and the large-scale tests.
The related simulations carried out consist of two components: - Finite Element modelling by Ramboll in Denmark. FE modelling with the Ramboll
Offshore Structural Analysis (ROSA) soft- ware is carried out at a number of stages: from the overall structural evaluation of the complete platform to detailed analysis of the wave loads on specific parts that were used during the testing. This FE analysis provides detailed structural response and stresses but does not in- clude shielding, makes use of empirical drag and inertia coefficients and assumes a simplified (undisturbed) wave field.
- Diffraction modelling by MARIN. Linear diffraction modelling of the GBS only with the DIFFRAC code is used to determine the disturbed wave field and wave kinematics.
The Structural Monitoring System (SMS) for the South Arne platform was provided by Fugro Structural Monitoring. The purpose of the SMS is to monitor the topside displacements and rotations, the strains in selected parts of the lattice tower and the wave height.
The OTC paper alongside presents the details of this integrated methodology of model tests, simulations and offshore measurements and it also marks an important first step towards multi-scale testing.
“Evaluating the Loading and Structural Response of an Offshore Platform Using Integrated Large and Small Scale Testing Combined With Diffraction and Finite Element Analysis and Offshore Measurements”, Bas Buchner, Robert Heerink and Jaap de Wilde (MARIN), Joel Witz (Hess) and Karen la Cour Hjelholt (Ramboll), OTC 19978, OTC 2009, Houston.
report 25
1 and 2: South Arne Platform with its small scale (1:63.2) model of GBS and lattice tower
3: Lattice tower alone tests at small scale (1:63.2)
4: The section of the lattice tower at large scale (1:5) in the Shallow Water Basin (with the Hess, Ramboll and MARIN project team)
5: The oscillation set-up in the scale 1:12.64 scale model of the Shallow Water Basin with the section of the lattice tower at scale 1:63.2 (at the background the full size Shallow Water Basin used for the 1:5 scale tests).
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