VIM Testing of a Paired Column Semi Submersible

Abstract

This paper summarizes VIM towing test results of Houston Offshore Engineering’s Paired-Column Semisubmersible (PC Semi) platform that was performed at the UC Berkeley towing tank. The PC semi configuration is different from a conventional Deep Draft Semi (DD Semi) in three aspects, 1) 8 columns vs. 4 columns; 2) rectangle column vs. square column; 3) larger column slenderness ratio. Typically, a larger column slenderness ratio may result in more pronounced VIM. Since VIM significantly affects mooring and riser strength and fatigue, it is crucial to explore the VIM response characteristics of the PC Semi configuration. VIM has been characterized as a difficult subject with a complicated structural-hydrodynamic interaction. The physical mechanics is generally less well understood and numerical prediction is generally less reliable. Model testing has become an important and widely accepted design tool to derive reliable A/D envelops and drag coefficients. This project builds on the VIM testing experiences obtained in Finnigan and Roddier (2007), which showed that VIM testing at small scale is only slightly conservative. A scale factor of 1:160 was used in the present tests. The Reynolds Number for the tests varied from 15,000 to 30,000 depending on the towing speeds. This manuscript provides some details on the test setup and overall program, and highlights the key results of the tests.

Wave induced stress profile on a paired column semisubmersible hull formation for column reinforcement

“…The uniqueness of its dynamic behaviour has been observed in its wave influenced and vortex-induced motions. Different reports have been presented as an attestation to that fact [ [1][2][3][4]]. However, the influence of the wave behaviour on the deformation and stress distribution on the hull has not been studied.…”

“…After solving the equation (2), [13] expressed the velocity potential from linear wave theory in its complex form as;…”

“…The wave is considered to progressively change from a steady to an unsteady state. Its unsteady nature is computed using perturbation formulation and expressed in Taylor's series as = (0) + (1) + (2)…”

“…The results for hull deformations at various wave headings were computed, and a contrast for the effect of current heading on the motion response recorded in [2] was observed. Maximum hull deformation occurred between 30 0 and 45 0 flow incidence around the cut-water-plane.…”

VIM Model Testing and VIM Induced Mooring Fatigue of a Dry Paired-Column Semisubmersible Platform

“…Detailed descriptions of the test facilities, model scales, test setups, instrumentation and test programs at the UC Berkeley towing tank and Marin's Depressurized Wave Basin are given in Zou et al (2013), and the Marin test report, Ref [8] respectively. In this paper, only the VIM model test program at MARIN is outlined.…”