Effect of water depth on dynamic positioning capability
During operation,water depth is variable for offshore vessel,which poses effects on current and mean wave drift forces.For this reason,this work reveals the effect of water depth on dynamic positioning capability by comparing en-vironmental loads at five different water depth.The corresponding thruster maximum power percentages are solved by quad-ratic programming method.The results demonstrate that with the decreasing of water depth,both current and mean wave drift forces show rising trends.The differences in wave drift force are concentrated in the range from 0.5 to 1.5 rad/s,har-monic roll can enhance yaw moments to a large extent.The effect of dynamic loads can not be neglected at beams,total mo-ments are dominant by wind.The changes in environmental loads directly affects thruster power.Dynamic positioning capa-city is restricted by retractable thruster at fore,corresponding to 100 degree wave direction.When water depth is 15 m,the thruster is at full-loaded state.With water depth increasing to 50 m,the maximum power percentage is correspondingly de-creased to about 60％.In sum,for the given draft in this work,when water depth is less than 20 m,it has witnessed rapid in-creases in environmental loads and thruster maximum power percentage,posing great challenges to safe dynamic position-ing.On the other hand,water depth exceeding 40 m can be approximately regarded as infinite depth.
water depthdynamic positioningmean wave driftdynamic loads
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