scholarly journals Numerical Study of Hydrodynamic Derivatives and Course Stability under Ship-Bank Interaction

Author(s):  
Han Liu ◽  
Ning Ma ◽  
Xiechong Gu
Author(s):  
Chengqian Ma ◽  
Ning Ma ◽  
Xiechong Gu ◽  
Peiyuan Feng

Abstract The theoretical method, or named the potential flow method, is most widely used in the research of maneuvering in waves. However, this approach used in previous studies is based on the assumption that maneuvering hydrodynamic derivatives in waves are the same as those in calm water. However, this assumption can be inaccurate, which makes the simulations inexact sometimes. Meanwhile, there are few experiments performed to investigate the hydrodynamic derivatives in waves considering the complexities of the experimental setup and data processing. There is even no systematic numerical simulation in this field. Considering the importance of the wave effect on the hydrodynamic derivatives and the advantages of the CFD method, in this study, the numerical simulations of the PMM tests on a containership S175 in regular waves are performed for the first time. The hydrodynamic derivatives in waves are obtained by simulations in the following waves, to be specific, the surf-riding condition. The surf-riding condition is chosen for separating the wave-induced component easily and researching the reason for the broaching-to phenomenon. The simulation results are validated by experimental data with satisfactory accuracy, which indicates the effectiveness of the numerical setup. The results reveal that the wave has a significant effect on hydrodynamic derivatives. The detailed changing trends and simulation methods of all hydrodynamic derivatives are proposed in this paper. Moreover, the course stability in waves is evaluated by the hydrodynamic derivatives in waves, which verifies the reason for the occurrence of the broaching-to phenomenon.


Author(s):  
Chengqian Ma ◽  
Ning Ma ◽  
Xiechong Gu

Abstract Maneuvering in waves is a complex and critical issue that confuses researchers for the last several decades. Among the existing methods for predicting the maneuverability in waves, the widely-used mathematical model approach (MMG model) is considered to be efficient and accurate in large wavelength and small wave steepness conditions. However, based on the assumption that the maneuvering forces in waves are the same as those in calm water, the wave effect on the hydrodynamic derivatives is neglected in most mathematical model approaches. According to the previous theoretical analysis and experimental data, this assumption is flawed. Therefore, several experiments and some numerical simulations have conducted to research the wave effect on hydrodynamic derivatives. In the present study, oblique towing tests and pure yaw tests will be simulated using the state-of-the-art CFD techniques to obtain the linear hydrodynamic derivatives in waves. The simulation cases in the present study are set according to previous PMM tests of S175 containership in surf-riding conditions. And the simulation results are in good agreement with experimental ones. Based on that, the wave effect on hydrodynamic derivatives is obtained and some discussions are made. Finally, the course stability of the containership on the different relative position of the wave are calculated to analyze the preliminary reason for the broaching-to phenomenon.


1998 ◽  
Vol 77 (2) ◽  
pp. 473-484 ◽  
Author(s):  
M. Sampoli, P. Benassi, R. Dell'Anna,

2020 ◽  
pp. 57-65
Author(s):  
Eusébio Conceiçã ◽  
João Gomes ◽  
Maria Manuela Lúcio ◽  
Jorge Raposo ◽  
Domingos Xavier Viegas ◽  
...  

This paper refers to a numerical study of the hypo-thermal behaviour of a pine tree in a forest fire environment. The pine tree thermal response numerical model is based on energy balance integral equations for the tree elements and mass balance integral equation for the water in the tree. The simulation performed considers the heat conduction through the tree elements, heat exchanges by convection between the external tree surfaces and the environment, heat exchanges by radiation between the flame and the external tree surfaces and water heat loss by evaporation from the tree to the environment. The virtual three-dimensional tree model has a height of 7.5 m and is constituted by 8863 cylindrical elements representative of its trunks, branches and leaves. The fire front has 10 m long and a 2 m high. The study was conducted taking into account that the pine tree is located 5, 10 or 15 m from the fire front. For these three analyzed distances, the numerical results obtained regarding to the distribution of the view factors, mean radiant temperature and surface temperatures of the pine tree are presented. As main conclusion, it can be stated that the values of the view factor, MRT and surface temperatures of the pine tree decrease with increasing distance from the pine tree in front of fire.


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