Ocean Engineering

A Three-Dimensional Coupled Fluid-Sediment Interaction Model With Bed-Load/Suspended-Load Transport for Scour Analysis Around a Fixed Structure

[+] Author and Article Information
Tomoaki Nakamura

School of Civil and Construction Engineering, Oregon State University, 220 Owen Hall, Corvallis, OR 97331tnakamura@nagoya-u.jp

Norimi Mizutani

Department of Civil Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japanmizutani@civil.nagoya-u.ac.jp

Solomon C. Yim

School of Civil and Construction Engineering, Oregon State University, 220 Owen Hall, Corvallis, OR 97331solomon.yim@oregonstate.edu

J. Offshore Mech. Arct. Eng 131(3), 031104 (Jun 03, 2009) (9 pages) doi:10.1115/1.3124132 History: Received July 07, 2008; Revised January 27, 2009; Published June 03, 2009

The predictive capability of a three-dimensional (3D) numerical model for sediment transport and resulting scour around a structure is investigated in this study. Starting with the bed-load and suspended-load sediment transport (reference) model developed by Takahashi (2000, “Modeling Sediment Transport Due to Tsunamis With Exchange Rate Between Bed Load Layer and Suspended Load Layer,” Proceedings of the 27th International Conference on Coastal Engineering, ASCE, Sydney, Australia, pp. 1508–1519), we first introduce an extension to incorporate Nielsen’s modified Shields parameter to account for the effects of infiltration/exfiltration flow velocity across the fluid-sand interface on the sediment transport (the modified Shields-parameter model). We then propose a new model to include the influence of the effective stress to account for the stress fluctuations inside the surface layer of the sand bed (the effective-stress model). The three analytical models are incorporated into a 3D numerical solver developed by Nakamura (2008, “Tsunami Scour Around a Square Structure,” Coast. Eng. Japan, 50(2), pp. 209–246) to analyze the dynamics of fluid-sediment interaction and scour. Their solver is composed of two modules, namely, a finite-difference numerical wave tank and a finite-element coupled sand-skeleton pore-water module. The predictive capability of the three alternative coupled models is calibrated against hydraulic experiments on sediment transport and resulting scour around a fixed rigid structure due to the run-up of a single large wave in terms of the sediment transport process and the final scour profile after the wave run-up. It is found that, among the three models considered, the proposed effective-stress model most accurately predicts the scouring process around the seaward corner of the structure. The results also reveal that the deposition and erosion patterns predicted using the effective-stress model are in good agreement with measured results, while a scour hole at the seaward corner of the structure cannot be always predicted by the other two models.

Copyright © 2009 by American Society of Mechanical Engineers
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Figure 1

Computational procedure of the coupling technique among the NWT, the SWM, and one of the sediment transport models, i.e., the STM, the MSM, and the ESM

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Figure 2

Experimental setup: (a) schematic figure of a wave flume and the positions of gauges; (b) typical profile of a single long wave with the wave period T of 6.0 s; and (c) miniature video camera installed inside the structure

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Figure 3

Comparison between measured (left) and computed (right) wave run-up around the structure for Case 1: (a) 6.9 s after the incident wave begins to be generated in the numerical simulation, (b) 7.5 s, and (c) 8.8 s

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Figure 4

Comparison between measured and computed (a) water surface fluctuation η in front of the seawall and (b) excess pore-water pressure pe inside the sand for Case 3

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Figure 5

Maximum value of the computed relative mean effective-stress ratio γ during wave run-up in a cross-sectional view of y=0 for Case 3

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Figure 6

Comparison between measured and predicted time series of the nondimensional maximum scour depth zsmax/B around the seaward corner of the structure: (a) Case 2, (b) Case 3, and (c) Case 5

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Figure 7

Final scour depth zsf after wave run-up: (a) the hydraulic experiments, (b) the STM, (c) the MSM, and (d) the ESM (left: Case 1, center: Case 3, and right: Case 4)




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