The experiments presented here provided valuable information on a number of important issues. This result implies that the optically measured turbidity may represent not only suspended sediments due to the bed shear stresses, but also advective sediments suspended at other locations, for instance.
It should be noted that investigations of mooring loads in renewable energy Entropy analysis of spm patterns case study of liverpool bay are important not only in relation to the issues of reliability and power take off [ 11 ], but also in terms of minimizing the adverse effects of mooring lines on bottom sediments [ 12 ], as well as indirect effects of the eroded particles on a wide range of aquatic processes [ 13141516 ].
This interplay is particularly apparent in the surge XPOS motion, and in the loads in the leading mooring line.
Instruments deployed at three points on the flat included acoustic Doppler velocimeters ADVs for high-resolution velocity measurements, pressure-type wave gages PWGs for surface wave measurements, optical backscatter sensors OBSs for sediment concentration measurements, photoelectric sediment surface meters SSMs for bed elevation monitoring, and conductivity-temperature sensors CTs for temperature and density measurements.
In particular, the results from the tests in short crested sea conditions indicate that peak loads in a multi WEC array may be considerably higher than in a single WEC configuration Figure 7 but may be less frequent. Crosses and Blue Line: Conflicts of Interest The authors declare no conflict of interest.
An Agenda for the Future; Magoon, O. Tests on WEC 1 in regular and irregular waves and current - Tests on WECs in regular and irregular waves and current - Tests on WECs in regular and irregular waves and current - Tests on damping and mooring stiffness of WEC1 During the experiments the following instruments were deployed to collect measurement data: The topography of the tidal flat fluctuated by approximately 10 cm during the deployment with the significant wave height in excess of 0.
The experiments were conducted according to Froude scaling laws at 1: The results have implications for further studies related to the durability, design and installation of moored renewable energy devices, as well as the assessment of their ecological impact and environmental impact assessment. Near-bed velocity and turbidity measurements at an intertidal estuarine sand-flat influenced by fluvial discharges A day field observation was conducted at an intertidal estuarine sand-flat, on which fluvial sediments discharged from an adjacent river must be considered, to investigate hydrodynamics, suspension and transport of sediments, and It is reasonable to expect that the characteristics of WEC motions will depend on the number of WECs deployed in an array, as well as their positioning.
Therefore, it is concluded that the incohesive bed sediments, which were once suspended and transported offshore during rough wind wave conditions, were transported back to the shoreward direction during calm conditions, and this resulted in the gradual accretions of the topography of the flat.
Studies of Vickers and Johanningand Krivtsov et al. On the other hand, the turbidity due to the cohesive sediments was high when the river discharges fluvial sediment onto the flat.
A frequency domain approach. Five WEC array viewed along the Y axis towards the origin. An example of distributional fits to the mooring loads test It can be clearly seen Figure 6 that the trend line fitted to the data from a single WEC installations has the steepest slope and consequently lower values for extreme loads of all the configurations tested, whilst the 5 WEC configuration is characterized by the smallest slope of the trend line, and consequently higher values for extreme loads.
However, the results presented here indicate that higher energy efficiency may be accompanied by increased mooring loads.
The effect of sub-optimal control and the spectral wave climate on the performance of wave energy converter arrays. The five WEC array is shown in Figure 4. Analysis of the Trondheim dataset by Ashton et al. A series of bed level surveys was also carried out during spring tides.
The estimated sediment concentration due to the incohesive bed sediment suspension exactly varies with the bed shear stresses, and cohesive sediment concentrations are generally fluctuated in response to the river discharge.
Example results for WEC1 in short-crested seas test Whenever the seabed was eroded, appreciably high turbidity, which is calculated from the OBS outputs, was measured.
The results presented here will become particularly relevant in the future, as more wave energy devices are deployed at sea in open water conditions [ 17 ]. Complex effects involving low-frequency motions are known to be a matter of concern for commercial mooring installations [ 6 ].
Results reported here are at full scale. Near the seaward edge of the tidal flat, the bed shear stresses during the accretions are evaluated to be around 0.
Two mooring line load cells numbered n. During the tests, data were acquired synchronously using the Marintek CATMAN data acquisition system, filtered, scaled and output at 80 Hz real-time corresponding to Consequently, the suspension of the incohesive bed sediments occurred with the intense near-bed shear stresses induced by the combination of wind waves and tidal currents, resulting in rapid erosion.
The majority of loads on the mooring lines appeared to be broadly consistent with the logistic distribution, whilst the right tail appeared to conform to the extreme value distribution see Figure 6 and Figure 7. The extreme peak mooring loads in the leading mooring line were approximately doubled in similar environmental conditions in comparison to those in a single device.
The results presented here appear to be consistent with these findings, and show the corresponding increase in the mooring forces. The importance of mooring line dynamics for WECs has been addressed previously [ 5 ].
Comparison of extreme peak mooring tensions induced at different WEC array configurations in short crested seas. Including moorings in the assessment of a generic offshore wave energy converter:Entropy analysis of SPM patterns: case study of Liverpool Bay By V.
Krivtsov, O. A. Mikkelsen and S. E. Jones No static citation data No static citation data Cite. Abstract In Liverpool Bay (UK), suspended particulate matter (SPM) monitoring data and tidal data collected in the period September to February were analyzed by means of entropy analysis and factor analysis in order to identify the meteorological and oceanographic variables of importance for the characterisation of the shape of SPM size spectra.
Surface seawater samples were collected in the Irish Sea and Liverpool Bay area from the R.V. Prince Madog during the period of of March VOCs were purged with nitrogen, pre. Recent work in Liverpool Bay focused on the investigation of oceanographic and meteorological variables important for SPM characterisation using classification trees and.
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This paper describes the physical model testing of an array of wave energy devices undertaken in the NTNU (Norwegian University of Science and Technology) Trondheim basin between 8 and 20 October funded under the EU Hydralabs III initiative, and provides an analysis of the extreme mooring.Download