Session: 04-03-03 Hydrodynamics

Paper Number: 104379

104379 - Hydrodynamic Forces Acting on Small-Diameter Pipelines Under Random Waves and Currents: A Case Study 

Small-diameter pipelines with the outer diameter ranging between 50 mm and 200 mm, such as umbilicals and power-transmission cables are commonly used in the oil & gas industry and the renewable-energy industry. The on-bottom stability design of pipelines requires both the amplitude and the time-history of the hydrodynamic forces. Comparing with oil & gas pipelines, the smaller diameter of umbilicals/cables leads to larger Keulegan-Carpenter numbers (KC) and smaller Reynolds numbers (Re). Since both the KC and Re numbers are governing parameters for the hydrodynamic forces, the prediction method for the forces on small-diameter pipelines may be different from those developed for oil & gas pipelines.

 

In this paper, the hydrodynamic forces induced by combined random waves and currents acting on a small-diameter pipeline are investigated, based on a few laboratory tests conducted in the large O-tube facility at the University of Western Australia. The diameter of the model pipe D is 50 mm, the peak-wave period T_p ranges from 9.1 s to 9.8 s, the significant wave-induced velocity U_p lays between 0.22 and 0.25 m/s, and the current to wave ratio α is in the range of 0 ~ 2. The resultant KC number ranges from 40 to 50 and the Re number is on the magnitude of 10⁴. The pipeline model is mounted on the smooth bottom of the O-tube.

 

Three methods for describing the time-history of the inline force are examined: 1) the conventional Morison equation, 2) the modified Fourier model (Jacobsen et al. 1988), and 3) the extended Wake II model (Aristodemo et al. 2011). The results show all the three methods perform equally well under the pure random wave condition, namely α = 0. However, the performances of these three methods under the combined random wave and current conditions (α > 0) need to be further investigated.

 

Reference:

Jacobsen V, Bryndum MB, Tsahalis DT (1988) Prediction of irregular wave forces on submarine pipelines. In: The seventh international conference on offshore mechanics and arctic engineering. ASME, Houston, Texas, pp 23–32.

Aristodemo F, Tomasicchio GR, Veltri P (2011) New model to determine forces at on-bottom slender pipelines. Coastal Engineering, 58 (3): 267-280.

Presenting Author: Yunfei Teng Guangzhou International Campus South China University of Technology

Presenting Author Biography: Dr. Yunfei TENG is doing his research work at South University of Technology (post doctoral position). His research focuses are 'on-bottom stability of pipelines/cables/umbilicals', 'wave boundary layer', 'turbulence modelling in coastal and ocean engieering'.

Authors:

Yunfei Teng South China University of Technology
Zhanjie Chen Dalian University of Technology
Terry Griffiths The University of Western Australia
Hongwei An The University of Western Australia
Scott Draper The University of Western Australia
Henning Mohr The University of Western Australia
Xin Cheng Dalian University of Technology
Xiaoyuan Hu South China University of Technology
Liang Cheng South China University of Technology