Finding the Optimum Methodology for Fatigue Assessment of an Internal Lifting Tool During Offshore Transport

Finding the Optimum Methodology for Fatigue Assessment of an Internal Lifting Tool During Offshore Transport

Afshan Naseem Ansari, Afshan (TU Delft Aerospace Engineering)

Alderliesten, Rene (mentor)
He, Luke (graduation committee)
Hees, Wouter van (graduation committee)

Delft University of Technology

Aerospace Engineering

2020-01-22

Royal IHC B.V. is recognized in the dredging and offshore industry. It’s head office is situated in the Netherlands and with more than 3000 employees working from sites and offices all around the world, it is able to ensure its local presence on every continent. Nowadays a subsidiary company of Royal IHC, IHC IQIP is expanding the scope of its Internal Lifting Tool (ILT), by using it for lifting as well as for transportation of jackets and topsides from offshore to onshore. The ILT is a tool used for lifting and upending of tubular offshore structures. Furthermore, it is designed for static lifting load acting on it for a short duration of time and not designed against multiple constraints like impact of wave load, current load, wind load etc. Using the same ILT for transportation of the tubular structures requires additional analysis for certifying the tool. During the transportation of tubular structures, the ILT is subjected to periodic wave-induced inertial load, which may induce a fatigue issue in it. The impact of this loading condition is unknown to the ILT’s structural integrity, which is designed for single lifting purposes. Therefore, the possible damage during transportation should be evaluated in accordance to offshore standards. The main objective of this thesis is to determine and demonstrate the procedure required for calculating the fatigue damage and fatigue life of the ILT. This research was performed considering that fatigue is critical during the transportation process. A step-by-step approach was adopted to complete this research. The first step was to understand the fatigue phenomena, based on different loading conditions, different methods to evaluate the stresses were studied. From the study it was determined that the stress based fatigue approach best suits the loading condition applied on the tool. This was followed by determining the method to evaluate the random environmental loads and finding a method to incorporate these loads to find the fatigue damage. Fatigue damage is generally determined in time domain. Cyclic loads varying with time is used for this assessment and the damage is computed on the basis of stress and strain. This analysis is advantageous when the load or the structural response is not linear. Random cyclic loads, when being assessed in time domain require large amount of data. This is not feasible and therefore, spectral fatigue analysis is preferred. In this approach power spectral density (PSD) functions are used for modelling the load and response of the structure. Lastly, spectral fatigue analysis of the ILT requires input from FEA analysis. There are various software packages generally used for FEA analysis. It was found that limited study has been conducted for determining which software package gives more accurate results of the stresses. The findings of the this thesis include the methodology for computing fatigue life for an ILT, determining fatigue life of an ILT using this methodology and to find which FEA software provides better results for stresses used to compute fatigue damage.

FEM analysis
Spectral fatigue analysis
Internal lifting tool

http://resolver.tudelft.nl/uuid:70318b26-4b72-4d04-9bff-1aad2b693e2f

2025-01-22

Student theses

master thesis

© 2020 Afshan Afshan Naseem Ansari