Abstract
Smart isolation devices (SIDs) are commonly used in pressurized subsea pipelines that need to be maintained or repaired. The sudden stoppage of the SID may cause large water hammer pressures, which may threaten both the pipeline and the SID. This paper proposes a simulation method by using a coupled dynamic mesh technique to simulate water hammer pressures in the pipeline. Unlike other water hammer simulations, this method is the first to be used in the simulation in pipelines with a moving object. The implicit method is applied to model the moving SID since it has the mutual independence between the space step and the time step. The movement of the SID is achieved by updating the size of the computational meshes close to the SID at each time step. To improve the efficiency of the simulation and the ability of handling complex boundary conditions, the pipe sections far away from the SID can also be simulated by using the explicit Method of Characteristics (MOC). Verifications were conducted using the simulated results from the Computational Fluid Dynamics (CFD) numerical simulation. Two scenarios have been studied and the comparisons between the simulated results by using the dynamic meshes in 1D methods and those by the CFD simulation show a high correlation, thus validating the new method proposed in this paper.
Highlights
Corrosions and cracks are common in aged water, oil and gas subsea pipelines
Tion, Wang and Yang [12] combined the explicit Method of Characteristics (MOC) with the Preissmann four-poin the implicit method is predicted to have the potential to be used with dynamic meshes finite-difference implicit method [13] to simulate the unsteady flow in pipelines and th, which is essential to simulate a moving transient processes in hydropower systems
S1 and S5 (LE1 = LE2 = 270 m, as shown in Figure 3, the lengths of S2 and S4 should be longer than the moving distance of the smart isolation devices (SIDs) during the deceleration process) modeled by the MOC method and other sections modeled by the implicit method
Summary
Corrosions and cracks are common in aged water, oil and gas subsea pipelines. Strategically targeted pipeline maintenance, replacement and rehabilitation are of critical importance in these pipelines. When it approaches the targeted section and is allowed to stop, it starts to decelerate suddenly by extending some external slips to press against the pipeline internal wall (Figure 1b). By opening the valve (SID valve) in the middle of the SID, the SID becomes hollow to keep the water flowing in the pipe (Figure 1c) Another SID can be injected into the pipeline with the same procedure to be stopped at a location upstream of the original SID (Figure 1d).
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