### Abstract

Numerical simulations were carried out to investigate hydrodynamic forces on submarine pipelines in oscillatory flows, with a focus on the conditions under which the pipeline diameter D is of a similar order of magnitude to the boundary-layer thickness δ i.e., δ/D ∼ O(1). Two-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with shear stress transport (SST) k-ω turbulence closure were solved using a Petrov–Galerkin finite element method (PG-FEM). The effects of the seabed roughness k_{s}/D and the Keulegan-Carpenter number KC = U_{m}T/D on the hydrodynamic force coefficients were investigated, where k_{s} is the Nikuradse's equivalent roughness, T is the period of oscillatory flow and U_{m} is the amplitude of the oscillatory velocity. The diameter of the submarine pipeline is fixed at D = 0.1 m. The Reynolds number, defined as Re = U_{m}D/υ (where ν is the kinetic fluid viscosity), ranges from 1 × 10^{4} to 4.5 × 10^{4}. The numerical results show that the boundary-layer thickness increases with k_{s}. Hydrodynamic force coefficients are significantly affected by δ/D in the range of δ/D ∼ O(1), while δ/D depends on k_{s}/D and KC number. The negligence of velocity reductions in the wave boundary layer leads to overestimations of the submerged weight required for achieving on-bottom stability.

Original language | English |
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Pages (from-to) | 114-123 |

Number of pages | 10 |

Journal | Coastal Engineering |

Volume | 140 |

DOIs | |

Publication status | Published - 1 Oct 2018 |

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### Cite this

*Coastal Engineering*,

*140*, 114-123. https://doi.org/10.1016/j.coastaleng.2018.06.006

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*Coastal Engineering*, vol. 140, pp. 114-123. https://doi.org/10.1016/j.coastaleng.2018.06.006

**Effect of oscillatory boundary layer on hydrodynamic forces on pipelines.** / Tang, Guoqiang; Cheng, Liang; Lu, Lin; Teng, Yunfei; Zhao, Ming; An, Hongwei.

Research output: Contribution to journal › Article

TY - JOUR

T1 - Effect of oscillatory boundary layer on hydrodynamic forces on pipelines

AU - Tang, Guoqiang

AU - Cheng, Liang

AU - Lu, Lin

AU - Teng, Yunfei

AU - Zhao, Ming

AU - An, Hongwei

PY - 2018/10/1

Y1 - 2018/10/1

N2 - Numerical simulations were carried out to investigate hydrodynamic forces on submarine pipelines in oscillatory flows, with a focus on the conditions under which the pipeline diameter D is of a similar order of magnitude to the boundary-layer thickness δ i.e., δ/D ∼ O(1). Two-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with shear stress transport (SST) k-ω turbulence closure were solved using a Petrov–Galerkin finite element method (PG-FEM). The effects of the seabed roughness ks/D and the Keulegan-Carpenter number KC = UmT/D on the hydrodynamic force coefficients were investigated, where ks is the Nikuradse's equivalent roughness, T is the period of oscillatory flow and Um is the amplitude of the oscillatory velocity. The diameter of the submarine pipeline is fixed at D = 0.1 m. The Reynolds number, defined as Re = UmD/υ (where ν is the kinetic fluid viscosity), ranges from 1 × 104 to 4.5 × 104. The numerical results show that the boundary-layer thickness increases with ks. Hydrodynamic force coefficients are significantly affected by δ/D in the range of δ/D ∼ O(1), while δ/D depends on ks/D and KC number. The negligence of velocity reductions in the wave boundary layer leads to overestimations of the submerged weight required for achieving on-bottom stability.

AB - Numerical simulations were carried out to investigate hydrodynamic forces on submarine pipelines in oscillatory flows, with a focus on the conditions under which the pipeline diameter D is of a similar order of magnitude to the boundary-layer thickness δ i.e., δ/D ∼ O(1). Two-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with shear stress transport (SST) k-ω turbulence closure were solved using a Petrov–Galerkin finite element method (PG-FEM). The effects of the seabed roughness ks/D and the Keulegan-Carpenter number KC = UmT/D on the hydrodynamic force coefficients were investigated, where ks is the Nikuradse's equivalent roughness, T is the period of oscillatory flow and Um is the amplitude of the oscillatory velocity. The diameter of the submarine pipeline is fixed at D = 0.1 m. The Reynolds number, defined as Re = UmD/υ (where ν is the kinetic fluid viscosity), ranges from 1 × 104 to 4.5 × 104. The numerical results show that the boundary-layer thickness increases with ks. Hydrodynamic force coefficients are significantly affected by δ/D in the range of δ/D ∼ O(1), while δ/D depends on ks/D and KC number. The negligence of velocity reductions in the wave boundary layer leads to overestimations of the submerged weight required for achieving on-bottom stability.

KW - fluid force coefficients

KW - numerical simulation

KW - On-bottom stability

KW - small-diameter submarine pipeline

KW - wave boundary layer

UR - http://www.scopus.com/inward/record.url?scp=85053189109&partnerID=8YFLogxK

U2 - 10.1016/j.coastaleng.2018.06.006

DO - 10.1016/j.coastaleng.2018.06.006

M3 - Article

VL - 140

SP - 114

EP - 123

JO - Coastal Engineering

JF - Coastal Engineering

SN - 0378-3839

ER -