Potential Impact of Sudden Change of Wind Condition on Offshore Operation

The emphasis in this paper is to investigate the potential impact on offshore operation caused by the sudden change of wind condition. First, a questionnaire survey was conducted on experienced operation workers in Japan. The results show 74% respondents have experienced the danger of sudden change of wind condition in offshore operation. It is found that both the operation on board and the motion of ship can be affected by sudden change of wind condition. One-dimensional time-domain simulations are done to understand the performance of dynamic positioning system (DPS) when suffering from sudden change of wind condition. Squall models are determined on the basis of real cases on the sea near Japan. The results show an operation ship with PD control cannot keep its positioning in the allowable operation zone if the peak of wind speed exceeds more than a certain degree of the designed value. Wind feedforward can decrease the ship’s maximum displacement only with a short measurement interval. Adding integral control to the DPS can also achieve the ship staying in its allowable zone but bring severe destabilization. The jointed effects of unbefitting wind feedforward and PID control may make the ship more difficult in dealing with the squall in a short time. By using the Davenport spectrum, squall models are turned into fluctuating wind form. The gust with higher speed than the mean wind speed appears. However, it does not affect the performance of the DPS. It also illustrates that squall, a sudden change of wind condition in a relatively long time, can bring effects on DPS with motion outside its control. This will result in negative effects on offshore operation.