Papers by Keyword: Marine Riser

Abstract: Abstract: Many marine riser risk factors in service were analyzed and the riser risk factor hierarchical structure was modeled, the weight of each riser risk factor was evaluated by the improved fuzzy analytic hierarchy process (AHP) method. The simulation results and accident statistics from both home and abroad are in good agreement. It proves that the method has good practicability, more scientific, reasonable and simple than the traditional fuzzy AHP. The results provide theoretical reference for maintenance and management, danger elimination and reinforcement of marine riser.

Abstract: This paper attempts to explain the motion behaviour of the marine riser coupled to a drill string when the vortex induced vibration (VIV) is involved. Vibrations have been reported to have a major effect on the drilling performance, affecting the rate of penetration (ROP), causing severe damages to the drilling tools and also reduces the efficiency of the drilling process. There are two major components of drilling tools that are subjected to vibration, namely the marine riser and the drilling string. Analysis of vibration in the marine riser and drill string are two topical areas that have individually received considerable attention by researchers in the past. Though these two subjects are interrelated, borne by the fact that the marine riser encapsulates and protects the drill pipe, there have been few attempts to investigate them together as a unity. Due to the complexities of the models, simplified assumptions were made in order to undertake the investigation by using staggered approach. The results were compared with the experimental and simulation data from the open literature. It was found that the maximum displacement with negative damping occurs at low frequency and rotation speed.

Abstract: Gravity platform was widely used in marginal oilfield, so the strength and the stability of its marine riser under wave load became very important. By simplifying the Morison equation, the paper made the dynamic analysis of the riser come down to solving the fourth order non-homogeneous linear differential equation, thus got the analytical solution of its deflection, shear force and bending moment. And the comparison with Ansys simulation showed that this simplified method was feasible.

Abstract: Abstract: Both the method of engineering and nonlinear finite element method have been used to the analysis and optimum design of the 30 in. marine riser with the screw thread. Two load steps have been used in the finite element analysis including the processes of both assembling and applying the load of piling, and the nonlinear contact between marine risers has been considered in the simulation. Numerical results show that the stress in the marine riser increase rapidly when the magnitude of interference of the screw thread change slightly. By the way to change interferential magnitude of the screw thread, the maximum stress of Von Mises decrease from 681MPa to 381MPa and contact stress decrease from 238MPa to 122MPa. The engineering practice over 100 piles in offshore platform has shown that the numerical results are good.

Abstract: The tests on the vortex-induced vibration (VIV) of the cylinders with different helical strakes were carried out in a uniform current. Both in-line and cross-flow responses were measured and a comprehensive analysis was made in order to understand the phenomenon of VIV mitigation by helical strake and find optimal design parameters, which are more effective for VIV mitigation, of helical strakes. The results show that the cross flow response of the cylinders with helical strakes could be reduced significantly and its in-line response may be enhanced severely. Therefore, much attention should be paid to the design of helical strake.

Abstract: Riser vortex-induced vibration (VIV) has been the outstanding problem affecting the normal safe operation in offshore oil exploitation. In this paper, based on computational fluid dynamics, a three-dimensional large eddy simulation (LES) numerical model was used to calculate the flow fields of unsteady flow around marine riser with different approaching flow velocities. Then streamlines, velocity and vorticity contours, drag and lift coefficients in different conditions were obtained. Simulation results indicate that the flow properties in different depth display obvious difference, which present complex three dimensional characteristics with interacting. It is thus clear that flow around marine riser can not be regarded as plane potential flow simply. The results also show that with larger approaching flow velocity, lift coefficient amplitude is bigger and frequency is higher, which is easier to result in vibration. Our approach may provide some references for safe design and engineering practice of VIV controlling of marine riser.

Abstract: With the development of deep water drilling engineering, marine riser has become the important equipment. With the increase in water depth, the failure of marine riser is very serious, the vibration is the main reason. According to the actual situation, the model of marine is set up, the rule of lateral vibration is obtained. The result is helpful to avoid the phenomena of resonance of marine riser under wave loads.