Now showing 1 - 5 of 5
  • 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
    Analysis of End-Stop Parameters on the Performance of Heaving Point Absorber Wave Energy Convertors
    Wave energy converters (WEC) have the potential to generate a sizeable proportion of Ireland’s energy needs. Although there has been a great deal of research into WEC technology, no commercial devices exist at this time. One reason for this, has been underestimating the forces involved in the marine environment, and thus under designing components, especially power take off (PTO) systems. End stops are a crucial component of all moving body converters, which have rigid connections to PTOs. They are designed to protect the PTO mechanism by restricting the allowable travel distance. End stops, although vital components of WEC technology limit energy generation and thus must be taken into account in initial design. In this paper, a torus shaped point absorber moving against a monopile is numerically modelled in operational conditions using combined potential flow boundary element method and modified Morison's equation viscous drag. Two torus geometries are modelled, varying the radius and draft. The effect of various end-stop parameters on PTO forces and average annual energy generation are analysed. These parameters being; WEC travel distance, end stop distance and stiffness. Two separate Irish sites are analysed, a high energy site off the west coast and a medium energy site off the south coast. This paper aids WEC development by describing the performance effects of end stop design.
  • 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.
      299Scopus© Citations 45
  • Publication
    Predicted tunnel-induced settlement and damage to Findlaters church with respect to freefield and constructed side considerations
    Dublin, Ireland is scheduled to constructing its first metro in 2010, with a pair of tunnels connecting the city center to the airport. This study presents first-order predictions of the anticipated soil settlement and related building damage for a single structure on the route. The structure is a 19th century, stone church on glacial till situated almost directly above the shallowest portion of one of the tunnel crowns and immediately adjacent to a station box. To assess potential damage, a settlement trough is predicted based on another recent Dublin tunnel and the anticipated settlement is applied to the church. Damage predictions based on these freefield predictions are made and then revised as to the anticipated impact of the structure itself based on building stiffness, which significantly reduces the maximum differential settlement from 63mm to 36mm resulting in minimal predicted damage.
      5565Scopus© Citations 2
  • Publication
    Experimental comparison of dynamic responses of a tension moored floating wind turbine platform with and without spring dampers
    The offshore wind industry is rapidly maturing and is now expanding to more extreme environments in deeper water and farther from shore. To date fixed foundation types (i.e. monopoles, jackets) have been primarily used but become uneconomical in water depths greater than 50m. Floating foundations have more complex dynamics but at the moment no design has reached commercialization, although a number of devices are being tested at prototype stage. The development of concepts is carried out through physical model testing of scaled devices such that to better understand the dynamics of the system and validate numerical models. This paper investigates the testing of a scale model of a tension moored wind turbine at two different scales and in the presence and absence of a spring damper controlling its dynamic response. The models were tested under combined wave and wind thrust loading conditions. The analysis compares the motions of the platform at different scales and structural conditions through RAO, testing a mooring spring damper for load reductions.
      248Scopus© Citations 11