A study of the nonlinear seismic response of free spanning submarine pipelines subject to a spatially varying earthquake ground motion is carried out. Firstly, an improved method for simulating multiple-station ground motions is proposed. Secondly, the motion equations of the pipeline under multiple-station excitation are derived. The hydrodynamic force applied on the pipeline is simplified as added masses. Thirdly, a nonlinear three-dimensional (3D) finite element model of free spanning submarine pipeline is established. The effects of different material constitutional relationships of steel pipe and soil as well as large displacement are discussed.
Submarine Pipelines are used to transport oil and gas from offshore oil fields to onshore terminal facilities or between offshore oil fields. Many offshore oil fields locate in the seismic regions. The seismic load has to be taken into account in the mechanical analysis of the submarine pipeline. Due to the anisotropy and inhomogeneity properties of soil, the seismic ground motions can vary significantly in magnitude, phase angle and frequency along pipeline routes. And the variation of the ground motions can influence the seismic response of the pipeline greatly. Thus, it is of great significance to study the response of the submarine pipeline subjected to multi-support excitation. In the recent few decades, many numerical simulations and experimental studies have been performed on the dynamic response of submarine pipelines under seismic excitation. Nath and Soh (1978) studied the harmonic and seismic responses of simplified pipeline models in proximity to the seabed using finite element method. Datta and Mashaly (1988, 1990) analyzed the transverse response of both buried and free spanning submarine pipelines under random earthquake excitation in the frequency domain using the spectral approach, which was based on the spatial discretization of the pipeline with nodal lumped masses.
