Measurement and modelling of the vibration induced by working equipment on an offshore platform

For the vibration of long-served offshore platforms induced by working equipment, it is very difficult to determine the relevant parameters such as structural stiffness, mass and exciting loads accurately. In order to determine the parameters reasonably, a comprehensive vibration testing was carried out to learn the general vibrating features on the offshore platform by a total of 51 measured points distributed on different decks of a 15-year platform. The measurement showed that the induced vibration covers multiple modes with a range of frequencies because of the complexity of the platform structure. Therefore we introduced average amplitude of vibrating displacement at each measurement point to define its vibrating strength. With the measured results of the vibration, a finite element model of the platform with explicit solution was set up to simulate the vibration of the platform. The natural frequencies and average amplitudes at different locations were set as the target values to determine the unknown mass and exciting load in an updating procedure. The results of the modified model have a good agreement with the target values, which indicated that the modified model is reliable and the updating method for determining unknown parameters in a complex structure is feasible.

Automated summary

A comprehensive vibration testing of an offshore platform was conducted to understand its vibrating features and determine unknown parameters such as mass and exciting load through the establishment of a finite element model with explicit solution. The results showed good agreement between the modified model and target values, demonstrating the feasibility of determining unknown parameters in a complex structure through an updating method.