The Pilot Study On Responses Of Submerged Floating Tunnel Subjected To The Steady Current

Submerged Floating Tunnel(SFT) has much more comprehensive advantages than the traditional cross-traffic structures. The cable-SFT should have wide expansive prospects in virtue of its flexible forms, which call for its in-depth study.In this paper, the author has conducted a number of preliminary theoretical studies on dynamic responses of the cylindrical cable-SFT subjected to the steady flow, and in the end, gets some preliminary theory results.Firstly, a SFT mechanical model is established according to the force characteristics of the cylindrical cable-SFT subjected to the steady flow. In the model, the practical assumptions are given below: the single segment of SFT is simplified as a solid body, then linear spring and damper are set up on the solid body to simulate restriction inflicted by other segments, and the natural frequency of the solid body is equivalent to the natural frequency of the SFT which simplified as a elastic simple beam; the cables are simplified as tension strings, every four of which are located on a segment and are symmetric about the vertical plane of the segment axis; according to the axis of the segment and the vibration engendered in the plane formed by cables; the steady flow is horizontal and perpendicular to the segment axis; the vibration is symmetric about the cable plane.Secondly, on the basis of the revised Morison formula and Newton's mechanics laws, a group of differential dynamical equations for the mechanical model are deduced, namely a mathematics model of a single segment in the SFT subjected to the steady flow. Then simplify the group of differential equations and solve it by numerical analysis theory; the solving process is run by "Circular 4Cables_SFT Calculator", a small value calculator programmed by the author.Finally, in the paper, referring to the railway one-lane tunnel, related parameters are set. After taking the velocity of steady flow and the angle between cable and flowθ_k as discrete variables, and calculating the model for 145 times and every time for 3000s, whenθ_k∈(30°,70°) and V∈[0.0015m/s,0.45m/s], some primary conclusions are educed by analyzing the calculation results : with the increase ofθ_k ,the displacement of the segment decreases while its lateral component decreases and its component along the direction of flow increases. What's more, the tension at the end of the cables reduces and the displacement of the cables decreases firstly, then increases, and the cables keep down state basically while librating; with the increase of V, the displacement of the segment increases while its lateral component decreases and its component along the direction of flow increases. The tensions at the end of the cables whose sides are against the flow increase and the tensions at the end of the cables whose sides are back on the flow decrease, meanwhile, the displacement of the cables increase and the cables also keep down state almost while librating; When V is less than a certain value, a resonance may happen among the cables and the resonance within 1:1 may happen between the segment and the cables when givingθ_k a suitable value. The resonance among the cables has much less effectthan that between the cables and the segment.