Research On The Drag Reduction Performance Of The Riser On The Typical Grooved Surface

The ocean contains more than 70%of the world's oil and gas resources,and which is the main battleground of the future oil and gas development.In view of the abundant oil and gas resources in the South China Sea,the sea conditions are extremely bad,and the severe typhoons and internal waves are rare in the world.Reliable equipment and system is a powerful guarantee for the safe exploitation of deep-sea oil and gas,and the riser is the key equipment,which is the only channel connecting the drilling platform and subsea BOP.Under the interaction of complex sea conditions,riser will withstand tremendous drag force,which leads to riser bending deformation and wear,top tension increase,and the service life decline,even seriously threat to deep-sea oil and gas exploitation.Based on above,this paper introduces bionic texture on the riser surface,and explores the design method and feasibility of bionic texture to reduce the drag force,so as to achieve the purpose of improving the safety and stability of the riser system.The main work is as follows:(1)The research progress of vortex induced vibration suppression device and bionic texture reduction at home and abroad was reviewed.The research on the working condition of the riser and the determination of the biomimetic texture parameters are carried out,and the riser mechanical model was established.It is clear that to achieve the purpose of drag reduction with the method of bionic texture parameter optimization by changing the fluid distribution law in the boundary layer.(2)The research on the flow around riser with the the numerical simulation method of LES is carried out.By using Fluent software to simulate and analyze the distribution rule of flow field variables,such as drag force,pressure coefficient,pressure,velocity,separation point,vortex discharge frequency and vorticity.(3)Based on 6 kinds of Reynolds number,it has been carried out drag reduction research about smooth riser and V-grooved riser which contains 5 kinds of roughness coefficient(Ks)and 3 kinds of groove number.The drag force,pressure,velocity,vorticity,Strouhal(St)and the width of the wake region are compared with the different texture parameters and non texture parameter risers,and the principle of drag reduction is analyzed.And then the texture parameters with better drag reduction effect have been screened out,which provides a new idea and method for the drag reduction and the mechanical behavior control of the riser system.(4)Based on the better drag reduction effect of V-grooved parameters(Ks =0.007,n=32),the ANSYS Mechanical APDL module was used to analyze the drag force,deflection,bending moment and top tension of the riser when the sea water flow around it.And the result shows that the top tension decreased 5.33%with texture riser,which helps to reduce the energy consumption of the riser tensioner and the local mechanical performance is optimized.(5)According to the Reynolds similarity criterion,an experimental platform which is similar to the riser condition of ocean has been designed and built,and the experiment of flow around riser could be performed under multiple Reynolds number,which can get rid of the dependence of the flow test on the water tunnel and wind tunnel.Based on this experimental bench,a new study on the flow around a riser based on 4 operating conditions,3 grooves roughness and 3 kinds of grooves was carried out,and then the relationship between the drag reduction rate of the bionic textured riser and the groove roughness and the number of grooves is analyzed.The experimental data shows that the appropriate V-grooved texture of riser has a better drag reduction effect,and the experimental results are basically consistent with the simulation results,which verifies the reliability of the simulation method and the feasibility of drag reduction with bionic texture.In summary,this paper carried out the unit experiment and the numerical simulation of drag reduction of riser with the bionic texture.And find the influence of texture types,the number of texture roughness and groove numbers on the riser 's drag reduction performance,and the top tension is well controlled.The results of this paper are of great significance to the further research and final application of the biomimetic texture in the field of deep-sea oil and gas development.