Transverse response of offshore pipelines to random ground motion

Abstract

SUMMARYA method is presented for the determination of the transverse response of the idealized suspended span of an offshore pipeline to random seismic input. The method is based on spatial discretization of the pipe with nodal lumped masses. The earthquake is assumed to be a stationary random process characterized by a power spectral density function. The cross spectral density function between two random seismic excitations along the pipe length is defined with the help of a local earthquake power special density function, which is assumed to be the same for the two end supports of the pipeline, and a frequency dependent weighted function which decays exponentially with distance from the pipe supports. The solution is obtained in the frequency domain using the spectral approach and is presented in terms of r.m.s. displacements and stresses. The formulation adequately includes the pressure drag effect which tends to dampen the pipe motions. Utilizing this method of analysis, several idealized pipe sea bed configurations, in which the pipe is anchored between two end blocks and subjected to horizontal ground excitations normal to the pipe axis, have been analysed to predict the influence of certain important parameters on the response.

Using pipe-in-pipe systems for subsea pipeline vibration control

“…For the free span of the pipeline, the interaction between the free span and the surrounding water should be taken into account. The effective mass of the free span can be calculated as [11,13] = + −…”

“…The damping of the outer pipe is normally considered to comprise hydrodynamic damping, soil damping and structural damping, which account for the contributions of the surrounding water, supporting soil and structure itself to the overall damping ratio. In the present study, a total damping ratio of = 5% is assumed [11,13] and modelled by COMBIN14 elements in ANSYS.…”

“…Nath and Soh [11] investigated the harmonic and seismic responses of offshore oil pipelines in proximity to the seabed using finite element method. Datta and Mashaly analysed the transverse seismic responses of buried [12] and free-spanning [13] submarine pipelines under random seismic excitation in the frequency domain based on the spectral approach.…”

“…According to Eqs (12). and(13), and , can be calculated as 0.215 and 4.08 × 10 5 Ns/m. thus equals , /138 = 2956 Ns/m.…”

Seismic Dynamics of Pipeline Buried in Dense Seabed Foundation

“…Actually, researchers mainly focused on the seismic dynamics and the stability of submarine pipeline from about 1980s. At the early stage, the seismic performance of free-spanning pipelines supported by a number of upholders was the focus of engineers and scientists [24,25]. To the authors' best knowledge, Wang and Cheng [26] first investigated the axial seismic dynamics of a buried pipeline adopting a simplified quasi-static method, in which the soil-pipeline interaction was modelled by some virtual springs.…”