The Simulation Of Riser’s Vortex Induced Vibration And Suppression By Affiliated Risers Using Discrete Vortex Method

Marine riser is the key structure of marine oil and gas exploration andproduction system as the connection with well and floating platform. In thecomplex ocean environment, vortex induced vibration(VIV) has detrimentalside effects on riser’s properly working and safety, it can even causeproduction and environmental accidents. This paper researchs the problem ofriser’s VIV with discrete vortex method(DVM) simplifying the problem totwo dimensional model. To control the VIV axial-rod shrouds are attached.And the effects of number of affliated riser and flow angle have beendiscussed.Useing stream function method and image method respectively verify DVMin different Reynold numbers. The result shows a good computationalefficiency and agrees well with experiment result. Compared with imagemethod, stream function method has better expansibility. The result of1DOFshows initial branch, locking area and lower branch well but there is an errorat the maximum value compared with experiment. The result of2DOFindicates that the stream wise vibration strengthens the lateral vibration.Riser with different numbers of afflicted risers have been investigated,whose results have a good agreement with experiments. At differentnumbers, the result shows that shrouds can suppress the drag and liftcoefficients, and vortex shedding, except for the situation of4rods withinflow. The more number of rods achieves better suppression effect.Moreover the10rods shroud is less sensitive to the inflow direction than4rods shroud. For10afflicted risers, it is concluded that both time-averageddrag coefficient and fluctuating lift coefficient are less than that of thecorresponding bare cylinder with a reduction up to about26%and79%respectively. The vibrating model results about the suppression of VIV arebasically identical with fixed ones about the decrease of drag force and lift force. In locking area the maximum amplitude reduces15%at most fornumber is4and in the same situation the decrement is42%for8whichshows a great suppression effect to VIV.In a word, this paper attempt to research the riser’s VIV and the control withattached axial-rods shrouds using DVM which has good computationalefficiency, to provide fast and accurate reference.