Stability And Dynamic Analysis Of Fluid-conveying Cryogenic Flexible Hose Under Multiple Excitation

At present,the offshore oil industry is facing the great challenge of deepwater development.A key question is how to avoid long distance transport in the development of offshore oil and gas fields.An innovative and more economical offshore development model is floating liquefied natural gas(FLNG)production.The model transport liquefied natural gas from the FLNG vessel to the LNG carrier through a flexible tail unloading system.But due to the relative movement between the two floating bodies,it may cause the fluid-conveying cryogenic flexible hose to produce excessive vibration.At the same time,the flow of liquid also has a great impact on the dynamic characteristics of the flexible hose.The analytical methods and results of this paper are as follows.(1)Based on the theory of three-dimensional potential flow,the hydrodynamic performance of FLNG ship and LNG ship is studied respectively.In the flexible tail unloading system,the multi-body coupling of the two floating bodies can be neglected since the distance between the FLNG vessel and the LNG ship is 60 m.According to their geometric parameters,the finite element models of two floating bodies are created using the commercial software ANSYS Aqwa.The ambient condition selects the sine waves with an effective wave height of 1 m.The RAO and the corresponding phases of the two floating bodies are investigated in the directions of heave,swing and pitch.(2)In order to better analyze the dynamic characteristics of the flexible hose,two coordinate systems,inertial coordinates and orthogonal coordinates,are used in this paper.The velocity and acceleration of the flexible hose and the conveying fluid are deduced according to the conversion relationship between the two coordinate systems.Then a small section of the flexible hose is taken for stress analysis and the equilibrium equation is established and simplified.The same process is made for the conveying fluid.Finally,the kinetic differential equation of the flexible hose is generated and the weak integral is used to obtain the standard vibration equation.The mass matrix,the unit damping matrix and the element stiffness matrix are obtained by solving the equation.(3)The vibration equation of the low-temperature hoses under the multi-point excitation is established.The left side is the reaction parameter,and the right side is the input of two floating bodies motion.By using the proposed formulation,the stability and dynamic response of a fluid-conveying cryogenic flexible hose are investigated.The parametric studies on the example flexible hose show that the natural frequencies of the flexible hose could be diminished to zero as the flow velocity increased and the flexible hose loses stability.Thus,the response of the flexible hose tends to infinity under multiple excitation.The conclusions drawn from this paper have guidance and reference value for engineering practices.