Five-Sided Semi-Submersible Columns for VIM Reduction
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Solution Overview
Problem
Conventional semi-submersible vessels with rectangular columns face challenges in load distribution and vortex-induced motion (VIM) due to the rectangular shape and orientation of their columns, which can lead to complications in mooring and increased motion amplitudes.
Innovation Solution
The use of five-sided columns with four perpendicular faces and one outermost face oriented at a 45-degree angle to the longitudinal axis of the pontoon, providing improved hydrodynamic properties and allowing for easier load distribution and reduced VIM by varying the projected width of the columns depending on the current direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If rectangular columns are used with faces at 45 degrees to the pontoon axis, then the column configuration is simple and easy to manufacture, but the vortex-induced motion amplitudes increase and load distribution becomes complicated
Solution Approach 1:
The patent applies asymmetry by changing from a symmetric rectangular column cross-section to an asymmetric five-sided column where one face is oriented at 45 degrees to the pontoon axis while the other faces are at different angles. This asymmetric configuration disrupts the symmetry of vortex shedding and reduces VIM amplitudes, directly addressing the harmful vortex-induced motion effect while maintaining manufacturing feasibility
Solution Approach 2:
The patent applies local quality by varying the orientation of specific column faces relative to the pontoon axis. The five-sided column has faces at different angles (with one face at 45 degrees), creating locally optimized hydrodynamic properties at different positions around the column circumference. This local variation in face orientation reduces VIM while maintaining overall structural simplicity
2Device complexity
If rectangular columns are used, then the column structure is simple, but the mooring line installation becomes difficult and load distribution is complicated
Solution Approach 1:
The asymmetric five-sided column configuration with one face at 45 degrees to the pontoon axis creates favorable geometric relationships for mooring line attachment. This asymmetric orientation allows mooring lines to attach more directly to the column structure, simplifying installation procedures and improving load distribution compared to conventional rectangular columns
Solution Approach 2:
The five-sided column provides locally optimized attachment surfaces at different orientations. The specific 45-degree face orientation creates favorable local geometry for mooring line connection, making installation easier while the varied face angles throughout the column structure enable better load distribution pathways
3Object-affected harmful factors
If the column width is increased to reduce VIM, then the buoyancy is maintained, but the column dimensions increase
Solution Approach 1:
The asymmetric five-sided column configuration reduces VIM amplitudes without requiring increased column width by disrupting vortex shedding symmetry through angular variation. The 45-degree face orientation and varied angular distribution of faces create hydrodynamic conditions that reduce VIM while maintaining compact column dimensions and preserving buoyancy characteristics
Data Source
AI summary
A semi-submersible vessel comprises pontoons having a generally five-sided transverse cross section. In the case of a 4-sided semi-submersible, the columns may be arranged in a generally rectangular form with a column at each corner of the rectangular form, each column having with four sides disposed at a right angle to at least one adjacent side and a fifth side on the exterior of the generally rectangular form disposed at 45 degrees to each adjacent side.