Development of Biologically Inspired Flexible Pipes for Tsunami Attenuation

Abstract

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>