• Journal of international Conference on Electrical Machines and Systems
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• 제3권4호
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• pp.389-393
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• 2014

This paper presents one of the methods for design to reduce the noise and vibration of 200kW motor for electric propulsion ship. One of the important factors affecting vibration of the motor is the resonance. The natural frequency and natural mode of the 200kW motor is analyzed by using FEM tool and impact test equipment to avoid the resonance. Also, compare FEM result with impact test result to make a reliable FE model of 200kW motor. In order to find out the effect of the noise and vibration of the motor by electromagnetic excitation force, conduct electromagnetic-structure coupled analysis. These characteristics are much useful to design 200kW motor for electric propulsion ship.

• 한국소음진동공학회논문집
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• 제23권12호
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• pp.1073-1081
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• 2013

The definition of the radiation efficiency is very important to estimated underwater radiated noise of a ship. Considering the structure of the ship, it can be found that the hull of a ship consists of a lot of plates supporting by longitudinal and transverse stiffener. Therefore, various modes of the hull vibration occur related to the combination of these plates including stiffeners. In this paper, the method to define the radiation efficiency is suggested considering the vibration mode of the hull based on Uchida's experimental equation of the radiation efficiency. The suggested method is verified by the experiments with various kinds of naval vessels.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 II
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• pp.1055-1060
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• 2001

Springing phenomena of ships is introduced with its concept, research history and approach methodology. Being a hydroelasticity problem, non-linear vibration and stochastic process, springing was formulated and modeled in vibration point of view separating hydrodynamic force into system properties and excitation force. Both RAO and response spectrum as well as wave spectrum were presented as a case study of springing analysis for a flexible vessel with wide breadth. The effect of advance speed, heading angle and loading condition were investigated as parametric study. The results and observations showed availability of analysis for the prediction of the ship springing behavior.

• 대한조선학회논문집
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• 제57권3호
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• pp.160-167
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• 2020

A two-stroke diesel engine and a propeller normally adopted in large merchant ships are regarded as major ship vibration sources. They are directly connected and generate various excitation components proportional to the rotating speed of diesel engine. Among the components, the magnitude of two excitation components with the same frequency generated by both engine and propeller can be compensated by the adjustment of their phase difference. It can be done by the optimization of propeller assembly angle but requires a number of burdensome trials to find the optimal angle. In this paper, the efficient estimation method to determine optimal propeller assembly angle is proposed. Its application requires the axial vibration measurement in sea trial and the numerical vibration analysis for propulsion shafting which can be substituted by additional vibration measurement after one-trial modification of propeller assembly angle. In order to verify the validity of the proposed method, the phase difference between two fifth order excitation components generated by both diesel engine and propeller of a real ship is calculated by the finite element analysis and its result is indirectly validated by the comparison of axial vibration responses at intermediate shaft obtained by the numerical analysis and the measurement in sea trial. Finally, it is numerically confirmed that axial vibration response at intermediate shaft at a resonant speed can be decreased more than 87 % if the optimal propeller assembly angle determined by the proposed method is applied.

• International Journal of Naval Architecture and Ocean Engineering
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• 제3권1호
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• pp.80-85
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• 2011

For the assessment of statistical characteristics of wave loads in the real sea state, the probability distribution of wave loads are computed based on the sufficient duration of computations in irregular waves. First of all, the estimation of wave impact loads is well modified applying the displacement potential formulation, which was proposed by one of authors, for solving Wagner's flow model. Consequently, the present computation method is also modified. Prior to the computation in irregular waves, preliminary computation to determine the adequate number of realization of irregular waves is examined. The effect of hull girder vibration on the statistical characteristics is examined by means of the computation with/without hull girder vibration. It is found that hull girder vibration has a certain effect on the probability of occurrence of wave loads. Furthermore, computations taking account of the effect of operation, that is the effects of ship speed and course change, is conducted for the rational evaluation of the effects of hull girder vibration. It is clarified that the effect of operation on the statistical characteristics of wave loads is significant. It is verified that the evaluation without the effect of operation may overestimate the effect of hull girder vibration.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 II
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• pp.1061-1066
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• 2001

To predict vibrational energy density and intensity of beam-plate coupled complex structures in medium-to-high frequency ranges, Power Flow Finite Element Method(PFFEM) programs for plate, beam and some coupled structural elements are developed. The flexural, longitudinal and shear waves in plates are formulated and the joint element equations for multi-couped plates are fully developed. Also the wave transmission approach has been introduced to cover the energy transmission and reflection at the joint elements. Using the developed PFFEM program, vibration analysis for 2300TEU container ship model is performed and here the model data for this program are obtained by converting fonner FE model for structural analysis. This program predicts successfully the vibrational energy density and intensity upto 8,000 Hz for the ship model with over 50,000 DOF.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.791-796
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• 2000

The cavitation-induced fluctuating pressure of the container ship named "Sydney Express" is measured in Samsung Large Cavitation Tunnel(SCAT). In the measurements, a complete ship model is employed. The effects of thrust coefficient and cavitation number on cavity pattern and cavitation-induced fluctuating pressure were investigated experimentally. It is demonstrated that the fluctuating pressure coefficient is very sensitive to the cavitation number. The results of cavitation and pressure fluctuations are compared with those of ITTC and HSVA, which shows fairly good agreement. It is exhibited that the removal of rudder can significantly change the loading condition of a propeller, and can reduce the fluctuating pressure coefficient almost by half.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2012년도 춘계학술대회 논문집
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• pp.686-690
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• 2012

The modal test has been carried out using the exciter machine to investigate the vibration characteristics of the hull and super structure of the ship. The conventional exciter acts only one(1) direction and the exciter should be reinstalled for different direction test, which consumes additional expense. The 3 axes exciter has been designed of which force acts three directions without reinstallation for efficient modal test of the ship. It consists of rotatable base frame structure and the clutch mechanism for the unbalances to excite three directions. And the 3 axes exciter for the local structure has been made in advance and its performance test was carried out in the laboratory. The developed 3 axes exciter shows the ability of three-directions excitation with simple operation and modal test for the various local structure of the ship will be performed.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.550-555
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• 2007

This paper introduces the mechanical vibration-measurements of vibration on ships(ISO 20283). Regulations and guidelines for vibration of hull structures, propulsion machinery and onboard equipments on ship were established mainly by classification societies or International Association of Classification Societies(IACS). The initial draft of ISO 20283 was proposed by USA and based on US military standards. Though these are not suitable to passenger and merchant ships, many experts have felt the need of the ISO regulation for the vibration measurement on ship. Hence, these standards are re-drafted and reviewed by particulate ISO members. In this paper, authors introduce the important agendas and the controversial items during setup of ISO 20283.

• Structural Engineering and Mechanics
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• 제30권6호
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• pp.679-698
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• 2008

On marine vessels, delicate instruments such as navigation radars are normally mounted on ship masts. However the vibrations at the top of mast where the radar is mounted often cause serious deterioration in radar-tracking resolution. The most serious problem is caused by the rotational vibrations at the top of mast that may be due to wind loading, inertial loading from ship rolling and base excitations induced by the running propeller. This paper presents a method of semi-active vibration control using magneto-rheological (MR) dampers to reduce the rotational vibration of the mast. In the study, the classical optimal control algorithm, the independent modal space control algorithm and the double input - single output fuzzy control algorithm are employed for the vibration control. As the phenomenological model of an MR damper is highly nonlinear, which is difficult to analyse, a back- propagation neural network is trained to emulate the inverse dynamic characteristics of the MR damper in the analysis. The trained neural network gives the required voltage for each MR damper based on the displacement, velocity and control force of the MR damper quickly. Numerical simulations show that the proposed control methods can effectively suppress the rotational vibrations at the top of mast.