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 Investigation of Water-Entry Process of a Trimaran Section Based on Model Test Results
Jianyu Liu, Wenyang Duan, Kangping Liao*, Ducheng Li
College of Shipbuilding Engineering, Harbin Engineering University
Harbin, Heilongjiang Province, CHINA

ABSTRACTTrimaran may suffer from large motion and strong bottom slammingwhen sailing under severe sea conditions, resulting in seriously local
structural damage. In this paper, the free fall water-entry process of atrimaran cross section was simulated based on a Cartesian grid CFD
code (CNT-CGCFD). The numerical simulation results of verticalacceleration, slamming load and evolution of free surface are comparedwith the model test data. Results show that the present method cansolve the water-entry of trimaran section accurately, and the slammingloads on cross deck are reduced by the air cushion in the water-entry
process.

KEY WORDS: Trimaran; water-entry; slamming; Cartesian grid;model test; air cushion

INTRODUCTION
As a new type of ship, trimaran gets more and more attention in recentyears. The trimaran will suffer from strong nonlinear action of waves
when sailing under severe sea conditions, resulting in large motion andstrong bottom slamming in the water entry process of the bow and stern.
The huge instantaneous slamming force is prone to cause the damage ofthe structure. Therefore, the accurate prediction of slamming load andacceleration is an important factor affecting the safety performance oftrimaran structure.
The water-entry slamming of ship is a complex nonlinear process
which contain the multiphase flow and structure motion. The
instantaneous slamming load and acceleration of structure are studied
during this process. The wedge structure and simplified mathematicalderivation were used to predict the slamming load in early research of
the water-entry problem, and some simplified slamming models areproposed (von Karman,1929; Wagner,1932). In the following study,
the Wagner’s theory is improved by using matched asymptotic
expansion method (Cointe and Armand,1987; Howison,1991), and Mei(1999) extended Wagner’s method applied to two-dimensional
structure with arbitrary shape in the study of water-entry slamming.
While the trimaran section structure is more complex, which composedof a main hull and two outriggers, and the main hull and outriggers are

2279

connected by cross deck. The slamming loads of the cross deck aresignificantly affected by the jet flow caused by the main hull and the air
cushion produced by the main hull and outriggers during the waterentry process. Therefore, it is difficult to study the water-entry processof trimaran cross section by using the slamming model. At present, theresearch on this is mainly based on model test and CFD numericalsimulation. Ogawa (2006) conducted a series of model tests to study
the relationship between ship motion and bow slamming load. Twowater-entry model tests have been carried out by Xie (2019) withdifferent bow shapes. It is considered that the bulbous bow has asignificant effect on the local slamming load, which should be paid
attention in the ship design stage. Swidan (2016) carried out a series ofdrop test of three-dimensional wave piercing catamaran and studied therelationship between the water entry velocity and the slamming load, as
well as pressure distribution. It is considered that the influence of thethree-dimensional effect in the water entry process of this structure
cannot be ignored. Zong (2020) studied the pressure and motion oftrimaran section with water-entry model test and observed the changeof flow field in the drop process by PIV technology. It is observed thatmany bubbles will be generated after the cross deck enter the water,while with the increase of the drop height, the position of the air-water
mixture trended towards the side hull. Compared with the modelexperiment, the numerical simulation method has higher repeatability,
and avoids the high cost in model test. The CFD method which
consider the viscosity can simulate the jet flow and free surface
evolution during the water-entry process of trimaran cross section. Sun(2019) proposed the modified MPS method to simulate the water-entry
process of trimaran cross section and analyzed the influence of flexible
cross section on reducing slamming load. Sun (2020) used thecomputational fluid dynamics software Star-CCM+ to simulate theslamming of trimaran section drop into water under different types(free fall, constant velocity, and harmonic motion), and compared theslamming loads under different water entry types. The unstructured
grid with moving mesh or overlapping grid are usually used to simulate
the movement of structure in the free drop process (Ghadimi, 2014;Neil, 2015; Wang, 2021). While the method based on moving mesh haslarge mesh deformation and low mesh quality, and needs a short time
step to ensure convergence, and the method based on overlapping gridneeds to interpolate the flow field variables in overlapping area andbackground area, which is inefficient. In this paper, the Cartesian gridand immersed boundary method are used to capture the boundary ofmoving structure. Compared with unstructured mesh, the mesh