Wyniki wyszukiwania - BazTech

1

Numerical simulation of the seakeeping of a military trimaran hull by a novel overset mesh method in regular and irregular waves

Ghadimi Parviz, Karami Saeid, Nazemian Amin

Zeszyty Naukowe Akademii Morskiej w Szczecinie

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2021

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nr 65 (137)

38--50

EN

The hydrodynamic performance of trimaran hulls has been previously investigated for optimum performance in calm water, but there is still a limited understanding of its motion response; therefore, a CFD-based numerical approach was developed and applied on a trimaran hull in the presence of regular and irregular waves. To validate the CFD method, a comparison was conducted using both experimental and 3D panel method data. In this study, two different turbulence models were surveyed, and the SST Menter k-Omega (k-ω) turbulence model was shown to be a more accurate model than the realizable k-Epsilon (k-ε) model. The different features of the proposed numerical model include the implementation of an overset mesh method, unique mesh plan refinement, and wave-damping region. The discrepancy between the experimental data and the results of other seakeeping calculation methods have always been problematic, especially for low-speed strip theory and 3D panel methods, but good consistency was observed between the proposed CFD model and experimental data. Unlike potential-based or conformal mapping seakeeping analysis methods, the effect of nonlinear waves, hull shape above the waterline, and other ship dynamic phenomena were considered in this CFD application. The proposed CFD method reduces the simulation time and computational efforts for ship motion calculations.

2

Numerical and experimental study on seakeeping performance of a high-speed trimaran with T-foil in head waves

Li Ang, Li Yunbo

Polish Maritime Research

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2019

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nr 3

65--77

EN

The longitudinal motion characteristics of a slender trimaran equipped with and without a T-foil near the bow are investigated by experimental and numerical methods. Computational fluid dynamics ( CFD) method is used in this study. The seakeeping characteristics such as heave, pitch and vertical acceleration in head regular waves are analyzed in various wave conditions. Numerical simulations have been validated by comparisons with experimental tests. The influence of large wave amplitudes and size of T-foil on the longitudinal motion of trimaran are analyzed. The present systematic study demonstrates that the numerical results are in a reasonable agreement with the experimental data. The research implied that the longitudinal motion response values are greatly reduced with the use of T-foil.

3

A practical approach to the assessment of waterjet propulsion performance: the case of a waterjet-propelled trimaran

Zhang Lei, Zhang Jia-ning, Shang Yu-chen, Dong Guo-xiang, Chen Wei-min

Polish Maritime Research

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2019

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nr 4

27--38

EN

To obtain a reasonable evaluation of the performance of waterjet propulsion at the design stage, a semi-theoretical and semi-empirical method is used to calculate the fundamental parameters of waterjet propulsion performance using an iterative approach. To calculate the ship’s resistance, a boundary element method based on three-dimensional potential flow theory is used to solve the wave-making resistance, and an empirical approach is used to evaluate the viscous resistance. Finally, the velocity and pressure of the capture area of the waterjet propulsion control volume are solved based on turbulent boundary layer theory. The iteration equation is established based on the waterjet-hull force-balance equation, and the change in the ship’s attitude and the local loss of the intake duct are considered. The performance parameters of waterjet propulsion, such as resistance, waterjet thrust, thrust deduction, and the physical quantity of the control volume, are solved by iteration. In addition, a PID-controlled free-running ship model is simulated using the RANS CFD method as a comparison. We apply the proposed approach and the RANS CFD method to a waterjetpropelled trimaran model, and the simulation process and the results are presented and discussed. Although there are some differences between the two methods in terms of the local pressure distribution and thrust deduction, the relative error in the evaluation results for the waterjet propulsion performance is generally reasonable and acceptable. This indicates that the present method can be used at the early stages of ship design without partial information about the waterjet propulsion system, and especially in the absence of a physical model of the pump.

4

The research on characteristic parameters and resistance chart of operation and maintenance trimaran in the sea

Chen Y., Yang L., Xie Y., Yu S.

Polish Maritime Research

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2016

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S 1

20--24

EN

The paper determined the volume ratio of the main hull and side hull and their position characteristic parameter of operation and maintenance trimaran. Numerical simulation technology was used to do the analysis and calculation of trimarans which have different volume ratio of the main and side hull, and on this basis, the paper tried different positions of main and side hull, finally got the trimaran with optimum resistance performance and the chart of trimaran resistance estimation, so as to provide a new way in the selection of feature parameter of offshore wind farm maintenance trimaran and its resistance estimation.

5

Stochastic approach to movements of a multihull on waves

Królicka A.

Vibrations in Physical Systems

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2008

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Vol. 23

217--222

EN

Due to difficulties in determining precise initial conditions for the motion of sea waves and the nature of wind undulation, the dynamics of sea waves can be only modelled within the framework of a stochastic theory. The article presents a method for determining differential equations of motion for multihulls, such as catamaran or trimaran. The catamaran sails at constant translatory velocity and at an arbitrary angle to the undulation direction. The set of differential equations of motion presented in the article models anti-symmetric (lateral) movements of the catamaran. For those movements, stochastic differential equations ( Itô equations) are constructed in the form of the equation set (8). Using the state vector X and the excitation vector Y , the Itô equations take the form (9) and (10).

6

Hydrodynamic Analysis of Trimaran Vessels

Javanmardi M. R., Jahanbakhsh E., Seif M. S., Sayyaadi H.

Polish Maritime Research

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2008

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nr 1

11-18

EN

Trimaran vessels are developed for different applications and hydrodynamic behavior of such vessels is different than usual mono-hulls. In this paper hydrodynamic resistance and maneuvering of a trimaran with Wigley body form are investigated. The effects of outriggers position in four different longitudinal and two transverse locations are studied. For hydrodynamic simulations a CFD code has been developed and used. This code is capable for simulating three dimensional, time dependent, two phases, viscous flow coupled with rigid body motion. Formulation and solution algorithm are described in detail. Different case studies have been performance and numerical results have shown good agreement with experimental data. Based on resistance and maneuvering simulation of the trimaran vessels different conclusion are made. The results show that positions of outriggers have great effect on resistance and maneuverability of trimaran. The present method can be further employed to investigate other hydrodynamic qualities of trimaran vessels.