Amplitude, frequency and synchronization analysis of tension-leg platforms under vortex-induced vibration

• Autores: Jerónimo Domingo Guijarro
• Directores de la Tesis: Luis Perez Rojas (dir. tes.)
• Lectura: En la Universidad Politécnica de Madrid ( España ) en 2021
• Idioma: español
• Materias:
  • Ciencias tecnológicas
    • Tecnología naval
      • Arquitectura naval
• Enlaces
  • Tesis en acceso abierto en: Archivo Digital UPM
• Resumen

  • Offshore wind energy has become an important energy source that is reducing the fossil fuel energy consumption and many nations oil dependence. One of the most promising solutions for installations on medium depths seas is the Tension Leg (TLEG) platform. These platforms are provided with tension-legs, cylinders under tensile stress, as their mooring system. The tension legs must be calculated to withstand Vortex-Induced Vibrations.

    Vortex-Induced Vibrations are a high hazard phenomenon for these platform structures that can lead to their failure and destruction. It is an extremely complicated phenomenon that links both flow and structure behavior as, at every instant, the results of flow feedback the structure behavior as well as this last one does it with the flow. A special case of VIV is that called synchronization. Synchronization, or lock in, is a VIV case where the vortex spreading frequency and the structure oscillation frequency are equal.

    This interaction between flow and structure makes the VIV to depend on several direct parameters: geometric as leg length and diameter, fluid dynamic as the flow velocity and structural as the leg material density and Young´s modulus.

    Computational simulation has become the tool, out of towing tanks, to analyze legs or risers since commercial computational links between the commercial fluid dynamic codes and their respective commercial structure calculus codes were developed back in 2006.

    Several works have been developed, still limited in comparison to the required ones to analyze such multi-parameter phenomenon. In fact, currently, all the works have focused on vary the Reynolds number, for a certain riser, in low value ranges and without analyzing the rest of parameters, not allowing the generalization of such results to other risers.

    The present work has focused on analyzing VIV by computational methods in a higher Reynolds number range of a larger riser, moving all parameters closer to the ones experienced by real facilities, analyzing the occurrence of synchronization and the effect of Reynolds number and the Young modulus.

    A summary of the main results is: The results point out the dependence of the oscillation amplitude with the Reynolds number and flow direction, the relationship between the flow and oscillation frequency and the action of the induced tension and the significant synchronization in the rigid cylinder case. A energy balance and a preliminary qualitative analysis of similar risers are also presented.