Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Numerical research on settlement characteristics of fine sediment in hopper of trailing suction hopper
dredger
Xiaodan Mao, Minhua Shu, Chen Zhang*, Jifu Yin

Key Laboratory, National Engineering Research Center of Dredging Technology and Equipment
Shanghai, China

ABSTRACT

structure of the energy dissipation tank, etc.) and loading technology(e.g. initial water level, loading time, etc.) (Camp, 1936; Camp, 1946;Cheng, 1997; Van, 2002). In addition, the inlet condition has asignificant influence in loading efficiency of TSHD (Baldock, 2003;
Braaksma, 2009; Pal, 2013; Zhao, 2018). Sedimentation model was
proposed and modified to illustrate the mechanism during the process
and accurately estimate the overflow loss. These sedimentation model
are generally divided into two types of process-based model andlearning-based model. The former one is focused on the movement
mechanism of mixture (Ferguson, 2004; Miedema, 1996; Ooijens,1999), and the other one employs monitoring data to estimateparameters such as loading mass and overflow loss (Braaksma, 2009;Xu, 2006).
The coast in China is dominated by fine sediment such as silt, whose
sedimentation mechanism is complex. The extremely low settling
velocity and immensely easily resuspension cost several hours to get
low capacity in hopper. Previous research did not cover the particle size
less than 100 μm (Saremi, 2014), and the sedimentation model did not
fit well for fine sediment. Thus this study focused on the inlet condition
under present hopper structure is aimed to investigate the settlement
characteristics of fine sediment in hopper, and explore the possible
method to improve loading capacity and efficiency based on thesimulation.

Settling characteristics of sediment in hopper are affected by many
parameters, such as particle size, hopper structure, energy dissipation ofinflow structure, overflow form, inlet flow and the inflow concentration,etc. Extremely low settling velocity and immensely easily resuspensionof silt is unfavorable for its sedimentation under the coupling driven by
gravity and turbulent flow. In order to study the settling characteristicsof the fine sediment in the loading-overflow process, a 3D hopper
model based on CFD method was established to simulate the influenceof particle size (50 μm, 80 μm and 115μm), inlet concentration (10%,20% and 30%) and inlet height (0.45 m, 0.65 m and 0.85 m) on
sedimentation performance of silt. The sediment volume curve presents
a two-segmented curve for silt sand and a three-segmented curve forsilt clay, and would reach equilibrium within 1 h with silt sand or underrelatively high concentration. High inlet concentration has a prominent
improvement of deposition mass and loading efficiency, but therelationship is positively nonlinear. 20% inlet concentration isrecommended. The primary driving force for silt in the hopper isadvection and diffusion rather than settling under gravity, therefore lowheight amplifying turbulence value and influence scope has a negative
influence on silt deposition under low inlet concentration. It would be abetter alternative measurement conducted in the context of proper inlet
concentration.

NUMERICAL METHOD
Governing Equation

KEY WORDS: Hopper; trailing suction hopper dredger; threedimensional numerical model; loading-overflow process; fine sediment.

The mixture model is a simplified Euler multiphase flow model, which
is widely used, such as sedimentation, cyclone separator, low-loadparticle flow and so on. The model can be used to simulate themultiphase flow under the conditions that the phases move at different
speeds, the particle phases are widely distributed, and the interphaselaw is unknown, etc. It can satisfy the solution of the multiphase flow
model with fewer variables, thus greatly reducing the solution time. Butthe mixture model does not allow inviscid flow. So, the mixture model
is employed to simulate unsteady flow multi-phase flow in the hopper.
The continuity equation of the mixture model is given as:

INTRODUCTION
The trailing suction hopper dredger (TSHD) has an important role indredging and reclamation due to its high adaptability and efficiency. It
is highly concentrated research on operation efficiency of TSHD, inwhich studies on loading-overflow process have been carried out for
decades (Braaksma, 2007, Hao, 2012, Li, 2005, Van, 2002). There areso many factors affecting the loading efficiency, including both designof hopper (e.g. ratio of length and width, relative position of inlet,

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