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

Operation Safety of Trailing Suction Hopper Dredger (TSHD) under Medium-long Period Wave
Jianzhang Qi*, Yuchi Hao*Jianzhang Qi
National Engineering Research Center of Dredging Technology and Equipment, Shanghai, China

is strong, and the energy in the waves is high, which often leads to thesevere six-degree-of-freedom (6-DOF) motion of the TSHD under theforce of wave. During the operation, the drag arm and the drag head ofthe TSHD are connected to the hull through hoses. The wave
compensator can play some effect on the seakeeping in order to resist
the large ship oscillation of the TSHD under severe sea conditions, but
the wave compensator have limits in the maximum travel. During theoperation, if the motion of the drag head and the drag arm exceeds thesafety limit of the wave compensator, it will pose a serious threat to theoperation safety of the TSHD.

ABSTRACTDuring the dredging construction process, the trailing suction hopper
dredger (TSHD) working in medium-long period waves often has asevere 6-DOF motion, which will generate force on the drag head anddrag arm, then endangers the safety of the operation. Combined withthe actual engineering situation, based on the CFD method, a series ofnumerical simulations were carried out on the motion of a 10,000cubic-meter TSHD under the medium-long period waves. Themotion(roll, pitch, pitch) under the sailing state and the dredging state
was analyzed. Considering the influence of the drag arm and the travelof the wave compensator, the operation safety of the TSHD under
medium and long period waves is discussed. The results show that themotion amplitude of TSHD is increased in medium-long period wave,
and the motion of drag head may exceed the maximum travel of thewave compensator, which possibly cause danger.

Some practitioners in the dredging industry had discovered thisproblem. Among them, Hannot from MTI and Krijger from IHC (2013)combined Ship hydrodynamics, Multibody dynamics and Soil
dynamics to write a modeling software 'Dynamic Operations inDredging and Offshore' (DODO), which can help designer analysis thesafety of TSHD and CSD. But the hydrodynamics solution in DODO
uses the potential flow method, the accuracy is limited. Zhou (2020)
used the hydrodynamic software workbench AQWA to calculate themotion of a 10,000-cubic-meter TSHD under transverse waves andhead waves with long period, but did not consider the multi-bodycoupling between the drag arm and the ship hull, the selection of wave
directions was also limited. Mao (2019) used the hydrodynamic
software ADAMS to simplify the model of the ship hull and the wave
compensator, considered the motion response of the TSHD model inwaves under the coupling effect of wind, wave and current. Wang andLu (2011) considered the effects of wind, wave, current, wave
compensator, and soil, constructed the motion equation of the TSHD,and solved its 6-DOF motion. Chen (2014) formulated the motion
equations of ship and numerically solved coupling the effect of draghead.

KEY WORDS: TSHD; medium-long period; drag arm; CFD;
operation safety.
INTRODUCTION
Trailing suction hopper dredger (TSHD) is one of the two mostmainstream ship types in the dredging industry today, and is widelyused in dredging and remediation, channel excavation and maintenance,
submarine tunnels and other projects. During the operation, the main
working tools of the TSHD are the drag head and the drag arm. The
drag arm is connected to the hull while the drag head is grounded. The
drag head sucks the sediment into the suction pipe, enters the mudpump through the elbow, and finally discharges it into the spoil hopperof the TSHD through the mud pump.

The existing research generally adopts the potential flow method,which ignores the fluid viscosity and vortex, and also lacks theconsideration of the motion coupling of the drag arm. In the calculationof sea state, the short-period waves in the offshore area are mainlyconsidered. But, during the engineering construction at Nigeria,
medium-long period waves are relatively common, and the TSHD’s

Medium and long period waves, defined as waves with periods betweentides and swells. In the near-port dredging engineering, it is inevitable
for the TSHD to operate under medium-long period wave, such as theseas of Nigeria, Mauritania Friendship Port, Indonesia's Java Island,and Chile, etc. In these sea areas, the waves have these characteristics:
the period is long, the wave height is not high but the penetrating power

880