Experimental Study on Coupling Dynamics of a High Dimensional Nonlinear Riser Structure and Floating Platform by Truncated Equivalent Method

This paper represents an experimental and theoretical study of dynamic characteristics of coupling resonance between a deep-water riser (DR) and a floating platform. The super long DR used for transporting offshore oil & gas is a high dimensional nonlinear pipeline, and the complex characteristics of coupling response is clarified when the heave amplitude or frequency of the floating platform changes. By using the method of reverse combination of test data (RCTD), a fluid-structure coupling model of DR acted by internal fluid, wave flow and floating platform is constructed. Truncated equivalent method and frequency search method are both adopted to deal with the 1300 m DR during the experimental study on mechanism of coupling resonance. Results of the scaled model tests show that higher order resonance is easy to occur when the DR transports high-density fluid, and amplitude jump phenomenon appears in the resonance region at the DR top, which is closely related to the internal fluid transported. According to the transformation of similarity relationship, the results of scaled model test and numerical calculation are consistent, and equivalent truncation method is convenient to study the large-scale nonlinear DR structures.