Numerical simulation of deep-towed streamer cable in ocean current by ALE finite element method

High frequency seismic reflection surveys using deep-towed streamers are now of interest to explore sub-seafloor structures bearing hydrothermal deposit with adequate resolution. One of the problems arose with the utilization of the deep-towed streamer is the navigation or the location estimation of seismic sources and streamers to assure the necessary resolution. The estimation errors in the positioning come from the inaccurate acoustic positioning and from cable feathering, i.e., waving of the towed streamer cable in the ocean current. It is inevitable to minimize the positioning error of the location of the sources and the streamers to enhance the resolution of deep-towed surveys. Since a streamer waves due to the interaction of the streamer cable with the drag force in the seawater, it is necessary to estimate the behavior of the streamer when towed. For simulating the behavior of the streamer cable in a kinematic way, we employed a finite element method using arbitrary Lagrangian Eulerian (ALE) finite element formulation in the fluid domain, and total Lagrangian formulation for the cable. The geometrical compatibility conditions and the equilibrium conditions on the interface are automatically established by equating the displacement, velocity and acceleration on the interface common to the fluid and the cable. Finally, we confirmed that our numerical simulations reproduce the cable feathering behavior. Our results demonstrate that the drag force and the positioning error are strongly dependent not only on the speed of the ocean current but also the angle between the towed direction and the ocean current. We think that the present research would surely be applicable to the estimation of the streamer behavior when towed in deep water and can be extendable to the problem of positioning.