Design of paired column semisubmersible hull
Creators: name: Odijie, Charles
Publisher: name: Lancaster University
Year: 2016
Subjects: Semisubmersible hull

description: There is a constant effort to reconfigure column stabilized
      semisubmersible unit to meet the challenging demands associated with deep
      water exploration. Paired column semisubmersible platform is one of the
      recent column stabilized semisubmersible hull configured to allow top-deck
      well head compatibility for oil reserves in deep waters. Its unique
      ability to maintain reduced vertical motion in extreme weather conditions
      despite its hull size and payload create a high payload to motion ratio,
      as compare to conventional semisubmersible hulls. This unique feature
      makes it recommendable for other hull applications in ocean engineering. A
      study has been carried out to harness this high payload to motion ratio
      offered by this new hull concept in the development of drilling and
      production platforms in deep waters, support and foundation systems.
      
      Numerical models were developed to understand the semisubmersible hull
      (dynamics of the reduced vertical motion and its ability to withstand
      bending and twisting behaviour from extreme wave conditions). Prior to
      this, a preliminary CFD model was developed in to understand the vortex
      shedding effect on the arrayed columns. An experimental setup was also put
      together to understand this motion behaviour, alongside a detailed review
      of the first model. The motion response of a scaled hull model was studied
      in a wave tank with a Digital Image Correlation (DIC) system known as
      Imetrum. To further investigate its application for other ocean depths and
      support systems, series of hydrodynamic models were developed in ANSYS
      AQWA with weather conditions as recommended by API, DNV, and ABS. The AQWA
      model was validated with results recorded by Imetrum system from the wave
      tank experimental test. The wave forces and moments were studied for
      different draft sizes and ocean conditions, and their response where
      checked in ORCAFLEX. A finite element model was finally developed in APDL
      to understand the nature and effect of stresses from wave, current and
      wind loads, alongside topside integration.
      
      The results obtained from the FE model was use to postulate reinforcement
      during scantling, for different hull applications. The results for motion
      response showed favourable heeling moment for smaller draft sizes as
      recommended by regulatory bodies, but a reconfiguration for heave
      displacement might be required for smaller draft size. In such case, an
      increase in pontoon area or an additional heave plate attachment has been
      recommended. Furthermore, the effect of wavecurrent interactions was
      observed to create unique motion behaviour for all draft sizes at
      resonance frequency range. A fluid-structure interaction model of
      multi-phase flow will be required to understand this behaviour. The stress
      concentration on the columns generated from hydrodynamic loads was
      observed to be higher on the inner columns, relative to the outer ones.