OFFSHORE STRUCTURES Q


The selection of suitable construction sites is based primarily upon adequate quay area for onshore fabrication, a dredged depth to at least 8m at LAT, and sufficient wet area for the necessary winter storage of units


the USA, amongst many other possible locations. The attraction of many of the above locations is the relative closeness to shore (approximately 25 km) for deep water. Around the UK such opportunities exist in


the following areas: the Celtic Array around Anglesey; Northumberland offshore Blyth; South of the currently planned Moray Firth field; offshore Pembrokeshire; and in the Celtic Deep. One example of a possible towing route


would be from a fabrication site in Belfast to areas in and around the Celtic Array near Anglesey. This location is particularly suitable with possible electrical connection to the power station at Wylfa and the pumped storage scheme of Dynorwic, with further onward connection to the main grid. Another example would be the extensive


area of deep water close to shore offshore Southern Ireland nearest to Cork.


Model testing Model testing formed a key part of the design process for the in-place conditions. The particular offshore site chosen for purposes of the study was the Celtic Array offshore the coast of Anglesey. The preliminary sizing of the column is


based upon the allowable tilt criteria for the operating conditions, which in this case provided a diameter of the column of 17m.


The maximum tilt of the column under operating conditions had to comply with the criteria of a maximum inclination of 8 degrees provided by the wind turbine manufacturer. Looking at the inclination data


statistically it was concluded that: a tilt of 6 degrees or more does not occur for more than 0.002% of the time; a tilt of 4degrees or more does not occur for more than 16% of the time. Following on from the model testing


which confirmed the size of the column for 90m of water, a sensitivity study was performed for the same turbine size and weight, but with the water depth increased from 90m to 130m. For this sensitivity study it was possible to reduce the diameter of the column from 17m to 13m in order to achieve comparable results in terms of column inclination. In this case the column inclination for the operating conditions increased slightly to 7 degrees, which is still below the 8 degrees considered to be acceptable.


Onshore fabrication Several sites around the UK exist for the possible fabrication of the AWC. These include Belfast, Milford Haven Inchgreen/ Greenock on the Clyde, Seaton on Teesside. The current philosophy is to build the column and base units on a suitable quay area. The selection of suitable construction sites is based upon: adequate quay area for onshore fabrication; a dredged depth to at least 8m at LAT; sufficient wet area for the necessary winter storage of units. The target


! SCALEMODELOFTHE!RTICULATED7IND#OLUMNWASTESTEDFOR TWOWEEKSINABASININ4OULON &RANCE


fabrication production rate is to produce 50


$IAGRAMSHOWINGTHEPLACEMENTOFHEAVYIRON OREBALLASTINTOTHEBASEANDTHEDEBALLASTING OFTHECOLUMN


Articulated Wind Column advantages


s4HE!7#ISALOW-COST CONSTRUCTION  INSTALLATIONANDOPERATION WINDTURBINE


SUBSTRUCTUREFORDEEPWATERS


s3UITABLEFORWATERDEPTHSINTHERANGE70m TO


MFORLARGETOEXTRA LARGETURBINES


s!PPLICABLETODEEPWATERSCLOSERTOSHORE  REDUCINGTHEGRIDCONNECTIONCOSTSANDGRID ELECTRICALLOSSES


s)TSSIZEISDESIGNEDACCORDINGTOTHEALLOWABLE MOTIONCRITERIAOFTHEWINDTURBINE


s4HE!7#ISBASEDUPONAROBUSTDESIGN CONCEPTWHICHHASBEENPROVENTORESISTHARSH .ORTH3EACONDITIONS


s1UICKANDSAFEINSTALLATIONPROCESS ASWELLAN EQUALLYQUICK SAFEANDENVIRONMENTALFRIENDLY DECOMMISSIONINGPROCESS


s!RTICULATIONATTHEBASEPROVIDESFORA COMPLIANTCOLUMNWITHREDUCEDFORCESON THECOLUMNANDBASE


s"UOYANCYANDHYDRODYNAMICINERTIAPROVIDE STABILITY


s)MPROVEDBEHAVIOUR PERFORMANCEOFTHE COLUMNISACHIEVEDWITHEITHERINCREASED DIAMETER ORTHEADDITIONOFBUOYANCY ELEMENTSBELOWTHEWAVEZONE


23


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