Now showing 1 - 7 of 7
  • Publication
    The Dynamics Effects of Marine Growth on a Point Absorbing Wave Energy Converter
    (University of Malta, 2016-01-01) ; ;
    Wave energy convertors have the potential to generate a sizeable proportion of Ireland’s energy needs. 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 two torus shaped point absorbers moving against a monopile in operational conditions using combined potential flow boundary element method and Morison equation viscous drag. Marine growth thickness and surface roughness have a notable effect on the platform hydrodynamic forces. However, the power matrix remains generally similar. The smaller WEC shows the greatest change with a 20 % increase in draft and 5 % increase in power.
  • Publication
    Numerical Modelling of a Combined Tension Moored Wind and Wave Energy Convertor System
    (European Wave and Tidal Energy Conference, 2017-01-01) ; ;
    The offshore wind industry is moving to deeper water sites which generally have more severe environmental conditions. This presents not only a challenge to deploying devices in such conditions but also an opportunity for developing combined hybrid platforms that harvest both wind and wave energy. This paper introduces the novel tension moored combined wind and wave energy converter (WEC): TWindWave. Numerical modelling of the system in power production and novel survival modes is undertaken. Hydrodynamic interaction is analysed and shown to reduce the overall WEC power production. The addition of the WECs onto platform characteristics is described. Novel survival modes which involve ballasting the WEC floats and sinking them along the platform columns, before they rotate around the column and pontoon connecting bends are described and analysed. Future work incorporating these results and more advanced techniques are proposed.
  • Publication
    Reliability of extreme wave prediction methods
    Extreme wave parameters are used for engineering design in our seas and oceans, yet the methods used to determine them are non-standardized and can give highly variable output. With increased commercial activity in the marine sector, the importance of accurate extreme wave parameter determination has become increasingly apparent. This is particularly the case for marine renewable structures where even small over-predictions in design parameters can affect the whole feasibility of the project. This paper addresses the methods of extreme wave prediction currently in use, with a view to selecting the optimal method for the prediction of extreme wave conditions (Hs, Hmax and Tz) in coastal Irish waters. The paper identifies pitfalls and drawbacks of current extreme prediction methods, with particular attention given to the use of limited in time buoy data from coastal locations where development is to take place. In addition a new methodology of determining extreme wave periods, that is the wave periods occurring coincidentally with the most extreme wave heights, is established. This is important as the destructive energy of a wave is dependent on the wave period. By estimating the extreme wave energy and significant wave height, it is possible to formulate a method of reliably approximating the likely coincident wave period.
  • Publication
    Visual inspection and bridge management
    This paper estimates visual inspection quantitatively prior to its implementation in a Bridge Management System using a Value of Information (VoI) approach employing a Bayesian pre-posterior analysis. Information from a significant number of real bridges from Ireland and Portugal are considered in this regard following existing commercial practices. The variation of different parameters on the estimated VoI is investigated including the assumed probabilistic models of the prior bridge state, the likelihood of inspector assigned condition ratings and the economic setting surrounding the cost matrix for maintenance decision alternatives. The values of no information, perfect information and imperfect information are presented and the change in the optimal strategy based on such information is assessed. The effect of human imperfections in assessment and difference in condition rating scale are also estimated. The studies and findings of this paper are expected to allow a better insight for practising engineers and researchers working in bridge management.
      463Scopus© Citations 35
  • Publication
    Sensor measurement strategies for monitoring offshore wind and wave energy devices
    While the potential of offshore wind and wave energy devices is well established and accepted, operations and maintenance issues are still not very well researched or understood. In this regard, scaled model testing has gained popularity over time for such devices at various technological readiness levels. The dynamic response of these devices are typically measured by different instruments during such scaled tests but agreed sensor choice, measurement and placement guidelines are still not in place. This paper compared the dynamic responses of some of these sensors from a scaled ocean wave testing to highlight the importance of sensor measurement strategies. The possibility of using multiple, cheaper sensors of seemingly inferior performance as opposed to the deployment of a small number of expensive and accurate sensors are also explored. An energy aware adaptive sampling theory is applied to highlight the possibility of more efficient computing when large volumes of data are available from the tested structures. Efficient sensor measurement strategies are expected to have a positive impact on the development of an device at different technological readiness levels while it is expected to be helpful in reducing operation and maintenance costs if such an approach is considered for the devices when they are in operation.
      202Scopus© Citations 13
  • Publication
    The Hurst exponent as an indicator of the behaviour of a model monopile in an ocean wave testing basin
    With the importance of renewable energy well-established worldwide, and targets of such energy quantified in many cases, there exists a considerable interest in the assessment of wind and wave devices. While the individual components of these devices are often relatively well understood and the aspects of energy generation well researched, there seems to be a gap in the understanding of these devices as a whole and especially in the field of their dynamic responses under operational conditions. The mathematical modelling and estimation of their dynamic responses are more evolved but research directed towards testing of these devices still requires significant attention. Model-free indicators of the dynamic responses of these devices are important since it reflects the as-deployed behaviour of the devices when the exposure conditions are scaled reasonably correctly, along with the structural dimensions. This paper demonstrates how the Hurst exponent of the dynamic responses of a monopile exposed to different exposure conditions in an ocean wave basin can be used as a model-free indicator of various responses. The scaled model is exposed to Froude scaled waves and tested under different exposure conditions. The analysis and interpretation is carried out in a model-free and output-only environment, with only some preliminary ideas regarding the input of the system. The analysis indicates how the Hurst exponent can be an interesting descriptor to compare and contrast various scenarios of dynamic response conditions.
      186Scopus© Citations 5
  • Publication
    Dynamic Effects of Anchor Positional Tolerance on Tension Moored Floating Wind Turbine
    For water depths greater than 60m floating wind turbines will become the most economical option for generating offshore wind energy. Tension mooring stabilised units are one type of platform being considered by the offshore wind energy industry. The complex mooring arrangement used by this type of platform means that the dynamics are greatly effected by offsets in the positioning of the anchors. This paper examines the issue of tendon anchor position tolerances. The dynamic effects of three positional tolerances are analysed in survival state using the time domain FASTLink. The severe impact of worst case anchor positional offsets on platform and turbine survivability is shown. The worst anchor misposition combinations are highlighted and should be strongly avoided. Novel methods to mitigate this issue are presented.
      196Scopus© Citations 2