During riserless drilling operations, which are carried out in some scientific drillings and in the initial stages of all drilling operations in oil and gas exploration, a lifting force is generated in addition to a drag forces in ocean current environment owing to the ocean current and the rotation of the drill pipe. This is called the Magnus effect, and it is a critical phenomenon during such operations. First, the lifting and drag forces are calculated using the computational fluid dynamic (CFD), and the lift and drag coefficients are calculated for several rotational velocities of the drill pipe and the velocities of the ocean current. It can be observed through the calculations that the lifting force increases as the rotational velocity of the drill pipe increases, and it reaches a level of approximately several times that of the drag force. The force reaches such a considerably high magnitude that it can induce the motions of the drill pipe, resulting in the generation of a high bending moment. An analytical model of a drill pipe has been established by applying an absolute nodal coordinate formulation (ANCF), which can express a relatively flexible and long pipe, such as a drill pipe. ANCF is a finite element method, and was basically developed to analyze deformable linear objects such as the cable. With ANCF, the absolute slopes of elements are defined based on the absolute nodal coordinate. Finally, the drill pipe motions are simulated using the established model by applying the results of CFD simulations for sample cases and referencing the operation of the Chikyu.

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We developed a new type of biologically inspired “flexible pipes” as a tsunami countermeasure to reduce tsunami risk on energy storage tanks located in coastal areas vulnerable to large-scale tsunamis. Flexible pipes for the reduction of tsunami wave load acting on oil and gas tanks are firehose-like pipes on a much larger scale that can be inflated with compressed air to form long vertical pipes when a tsunami occurs. These pipes can reduce the wave energy of the tsunami by energy dissipation similar to natural tsunami countermeasures such as mangroves and giant kelps. We developed flexible pipes by mimicking such biologically inspired tsunami protection mechanisms. The purpose of this paper is to provide an overview of the development of flexible pipes and present the effectiveness of our pipes through experimental results. We designed the dimensions of the full-scale pipes. Then, we carried out laboratory-scale experiments in the tsunami wave flume using 1:100 scale pipes and an oil tank model and long-period tsunami-like waves. We measured the reduction of momentum flux carried by this wave behind our flexible pipes and the hydrodynamic forces acting on the oil tank model reduced by the flexible pipes in a direct manner. The experimental results suggested that around 50% of maximum momentum flux could be reduced behind the flexible pipes whereas 40% of maximum hydrodynamic force in inflow direction could be reduced compared to the case without flexible pipes. The difference is attributed to overflow of water above the model oil tank in the no pipes case.<def-list> Nomenclature <def-item> <term> U </term> <def> flow velocity of full-scale tsunami in the inflow direction </def> </def-item> <def-item> <term> U </term> <def> flow velocity of model-scale tsunami in the inflow direction </def> </def-item> <def-item> <term> g </term> <def> gravitational constant </def> </def-item> <def-item> <term> H </term> <def> still water depth </def> </def-item> <def-item> <term> η </term> <def> wave elevation </def> </def-item> <def-item> <term> P </term> <def> porosity (or) void fraction </def> </def-item> <def-item> <term> V v </term> <def> volume of the void in a section </def> </def-item> <def-item> <term> V T </term> <def> total volume of the section </def> </def-item> <def-item> <term> C D </term> <def> drag coefficient </def> </def-item> <def-item> <term> C M </term> <def> inertia coefficient </def> </def-item> <def-item> <term> ρ w </term> <def> water density </def> </def-item> <def-item> <term> ρ pipe </term> <def> pipe density </def> </def-item> <def-item> <term> H </term> <def> flow depth of a tsunami flow </def> </def-item> <def-item> <term> B </term> <def> breadth of structure being attacked by tsunami wave </def> </def-item> <def-item> <term> F D </term> <def> drag force on the structure caused by the tsunami flow </def> </def-item> <def-item> <term> M </term> <def> momentum flux per breadth </def> </def-item> <def-item> <term> M average </term> <def> average value of maximum momentum fluxes from each test case </def> </def-item> <def-item> <term> M reduction </term> <def> reduced momentum flux </def> </def-item> <def-item> <term> D </term> <def> diameter of cylindrical oil tank </def> </def-item> <def-item> <term> Re </term> <def> Reynolds' number </def> </def-item> <def-item> <term> KC </term> <def> Keulegen-Carpenter number </def> </def-item> <def-item> <term> V </term> <def> viscosity of water </def> </def-item> <def-item> <term> T </term> <def> period of full-scale tsunami wave </def> </def-item> <def-item> <term> F x </term> <def> horizontal force by the tsunami-like wave on the model oil tank </def> </def-item> <def-item> <term> F z </term> <def> vertical force by the tsunami-like wave on the model oil tank </def> </def-item> <def-item> <term> F x_normalized </term> <def> normalized horizontal force </def> </def-item> <def-item> <term> F z_normalized </term> <def> normalized vertical force </def> </def-item> <def-item> <term> F x_max </term> <def> maximum horizontal force on the model tank </def> </def-item> <def-item> <term> F z_max </term> <def> maximum vertical force on the model tank </def> </def-item> <def-item> <term>EI</term> <def> bending stiffness </def> </def-item> <def-item> <term> I </term> <def> area moment of inertia </def> </def-item> <def-item> <term> E </term> <def> modulus of elasticity </def> </def-item> <def-item> <term> M </term> <def> mass matrix of the pipe in the finite element analysis </def> </def-item> <def-item> <term> K </term> <def> stiffness matrix of the pipe in the finite element analysis </def> </def-item> <def-item> <term> Q e </term> <def> external force vector of the pipe in the finite element analysis </def> </def-item> <def-item> <term> E </term> <def> position vector for a node in the finite element analysis </def> </def-item> <def-item> <term> ë </term> <def> acceleration vector for a node in the finite element analysis </def> </def-item> <def-item> <term>ΔT </term> <def> time step size </def> </def-item> <def-item> <term>Δx </term> <def> element size </def> </def-item> </def-list>

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