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2 Polish Maritime Research

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Bao Guozhi, Liu Bolong, Yang Ruitao, Si Xiaodong

Polish Maritime Research

2025

nr 2

4--16

To achieve dynamic similarity with the experimental characteristics of structural flow, experimental models are often designed to stimulate turbulence that mimics high Reynolds number conditions. However, the size, shape, and placement of the trip wires play a crucial role in effectively exciting turbulence. This paper focuses on the SUBOFF scaling model as the subject of investigation. The RANS method was employed to analyse the flow field characteristics of a rotating body model with different excitation filaments, and the flow field properties of the model under trip wire perturbation were compared with those of a full-scale model at a 1:17.5 scaling ratio, to ensure similarity in terms of the Froude number. The goal was to identify the trip wire installation solution that most closely resembled the flow field characteristics of the full-scale model. The study found that the trip wire altered the boundary layer structure. Different installation positions of the trip wire led to varying effects on the boundary layer and local pressure gradient, which in turn affected the recovery of the boundary layer and modified the local flow field structure. By satisfying the condition for Froude number similarity, an experimental model subjected to surge filament perturbation can accurately simulate a pressure gradient, turbulence intensity, and vortex core structure that are comparable to those of a full-scale model. This finding offers a new approach for experiments focused on achieving high Reynolds number similarity.

Study of predictive control model for cooling process of mark III LNG bunker

Bao Guozhi, Qin Weiguang, Jiang Qingfeng, Pu Chunrong

Polish Maritime Research

2024

nr 3

102--112

When loading liquefied natural gas (LNG) onto a dual-fuel LNG container ship fuelled by LNG, there is a considerable temperature difference between LNG and the fuel tank at room temperature. The current solution is to pre-cool the tank with LNG through a spray line but the cooling process, if not correctly handled, can result in excessive cooling rates and Boil-Off Gas (BOG), which can expose the tank to increased temperature stress and gas pressure. Therefore, this paper takes the Mark III fuel tank of a specific type of LNG container ship as the object and realises a real-time predictive control system by writing a UDF (User Defined Function) to simulate and analyse the influence of LNG spray rate on the change of cooling effect, cooling time and cooling cost under the unidirectional LNG spray cooling mode. Compared with the results of the fuel tank gas experiment, the deviation of numerical model simulation results is less than 5%. Under the same cooling rate, the real-time control scheme can achieve a more uniform cooling rate and reduce the total LNG consumption by 25%. With the increase in LNG cooling rate, the cooling time, LNG usage, and the total BOG exhaust volume all decrease; however, the decreased range gradually decreases as well. The results of this paper provide parameters and suggestions for optimising and improving the LNG fuel tank cooling monitoring and control system.