Now showing 1 - 3 of 3
  • Publication
    The dynamic effects of marine growth on a tension moored floating wind turbine
    (Taylor & Francis, 2016-01-01) ; ;
    As the offshore wind industry moves to water depths greater that 50m floating platforms will become the only cost effective solution for mounting turbines. Such platforms will be susceptible to bio fouling over their design life with marine growth capable of altering the hydrodynamic loading. Marine growth causes member effective diameter, mass, drag coefficients, force and hydrodynamic added mass to increase. In this paper, marine growth of various thickness and surface roughness is numerically modelled on a tension moored floating wind turbine under survival conditions using combined potential flow boundary element method and Morison equation viscous drag. The influence of time variant Reynolds number dependant drag coefficients is compared against time invariant drag coefficients. Marine growth thickness and surface roughness have a notable effect on the platform hydrodynamic forces. Surge, pitch motions, and nacelle accelerations decrease as surface roughness increases. Maximum tendon forces increase and minimum tendon forces decrease. This increases the probability of a catastrophic tendon snap or slack event. The authors calculate the increase in displacement required to avoid this loss in tension. Detailed limits on the quantity of marine growth are suggested by the authors, above which the platform must be cleaned. The time invariant drag coefficient method has been found to give sufficiently consistent results to the time variant Reynolds number drag coefficient method
  • Publication
    Dynamic response mitigation of floating wind turbine platforms using tuned liquid column dampers
    In this paper, we experimentally study and compare the effects of three combinations of multiple tuned liquid column dampers (MTLCDs) on the dynamic performance of a model floating tension-leg platform (TLP) structure in a wave basin. The structural stability and safety of the floating structure during operation and maintenance is of concern for the performance of a renewable energy device that it might be supporting. The dynamic responses of the structure should thus be limited for these renewable energy devices to perform as intended. This issue is particularly important during the operation of a TLP in extreme weather conditions. Tuned liquid column dampers (TLCDs) can use the power of sloshing water to reduce surge motions of a floating TLP exposed to wind and waves. This paper demonstrates the potential of MTLCDs in reducing dynamic responses of a scaled TLP model through an experimental study. The potential of using output-only statistical markers for monitoring changes in structural conditions is also investigated through the application of a delay vector variance (DVV) marker for different conditions of control for the experiments.
      360Scopus© Citations 50
  • Publication
    A Delay Vector Variance based Marker for an Output-Only Assessment of Structural Changes in Tension Leg Platforms
    Although aspects of power generation of many offshore renewable devices are well understood, their dynamic responses under high wind and wave conditions are still to be investigated to a great detail. Output only statistical markers are important for these offshore devices, since access to the device is limited and information about the exposure conditions and the true behaviour of the devices are generally partial, limited, and vague or even absent. The markers can summarise and characterise the behaviour of these devices from their dynamic response available as time series data. The behaviour may be linear or nonlinear and consequently a marker that can track the changes in structural situations can be quite important. These markers can then be helpful in assessing the current condition of the structure and can indicate possible intervention, monitoring or assessment. This paper considers a Delay Vector Variance based marker for changes in a tension leg platform tested in an ocean wave basin for structural changes brought about by single column dampers. The approach is based on dynamic outputs of the device alone and is based on the estimation of the nonlinearity of the output signal. The advantages of the selected marker and its response with changing structural properties are discussed. The marker is observed to be important for monitoring the as- deployed structural condition and is sensitive to changes in such conditions. Influence of exposure conditions of wave loading is also discussed in this study based only on experimental data.
      267Scopus© Citations 2