NUMERICAL PREDICTION OF HOTSPOT STRESS FOR DKK CHS JOINTS IN OFFSHORE JACKETS UNDER ARBITRARY LOADING
Ernest O. Oshogbunu 1*, Yong C. Wang 1 and Tim Stallard 1
1 School of Mechanical, Aerospace and Civil Engineering, Faculty of Science and Engineering,
University of Manchester, Manchester, UK
The design of jacket structures such as those widely used to support offshore wind turbines (OWT) is governed by fatigue criteria and this requires accurate prediction of the hotspot stress. 3D finite element analysis (FEA) models can be used for stress prediction, but the high computational cost makes this approach impractical for analysis of the multitude of realistic load combinations and geometric configurations that must be considered for day-to-day design. Consequently, design of such joints is reliant on semi-empirical methods which at present cannot fully describe the complex stress distribution within joints such as double K (DKK) common in OWT jackets. Thus, design optimization is limited. This paper identifies six basic brace load cases whose combinations can accurately represent force distributions in DKK joints under any realistic loading condition for calculating the azimuth stress of each brace weld toe. A set of 10 unique stress values is sufficient to predict the hotspot stress at the weld toe of all braces of a DKK joint under any arbitrary load case. Similar accuracy to full 3D FEA analysis and greater accuracy than existing parametric methods is shown.
Hotspot stresses; SCF profiles; Arbitrary load; DKK joint; Offshore wind turbine jacket