Stress analysis of a monopile foundation under the hammering loads
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- Institutt for marin teknikk 
The installation of monopile is a very important process in offshore wind turbine construction.Duringthemonopilebeingdrivendownbyhydraulichammer,hugeenergytransfersfromhammer to pile, which may cause monopile inclination. In order to keep the monopile steady inhorizontal direction, a gripper device is applied between the monopile and installation vessel.Thegrippercontactswithmonopilebyfourhydrauliccylinders. Inthemosttime,thehydrauliccylinder contacts with the smooth surface on the monopile, and it only bears axial load. While,the monopile is welded piece by piece, its surface is not perfectly smooth due to welds. Thewelds collide with the hydraulic cylinder and induce a vertical force on the hydraulic cylinder,whichmaydamagethehydrauliccylinder.This thesis analyzes the installation of monopile by HLV and hydraulic hammer. It presentsmodelling and calculation for the collision problem between welds and hydraulic cylinder. Aﬁniteelementmodelformonopile,weldsandgripperisbuiltinAbaqusCAE.Theexternalloadsincluding hammer load, soil resistance and cylinder force is obtained from hand calculation orpreviousthesisandthenappliedintotheﬁniteelementmodel. Theeffectsofchangingdifferentparameters (such as welds thickness, hammer energy, initial penetration depth etc.) is carriedoutforanalyzingthemethodforreducingthegripperstressduringcolliding.