• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.527-532
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• 2011

Whirling vibration in severe cases may result in shaft cracking and typically gap sensors are utilized to confirm its values under the outside underwater of ship. The bending stress value causing whirling vibration on the propulsion shafting system of a 40-ton small vessel was verified by theoretical analysis and its vibration measurement. However, because of underwater condition, the accuracy for this measurement method is presumed low. In this study, the strain gauge basic principle and the bending stress calculation method are considered. The relationships are then applied for obtaining the whirling vibration of the 40-ton small vessel. As a result, a new method in estimation of whirling vibration is reached and suggested.

• Journal of Ocean Engineering and Technology
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• v.26 no.4
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• pp.30-36
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• 2012

Recently, the underwater radiated noises generated from large commercial ships have become a globally important issue. Countries with large ports and environmental protection organizations demand strict safety guidelines in relation to underwater radiated noise. In this paper, the coupled PFFE/PFBE method is used to investigate the vibration and underwater radiated noise of a commercial ship. PFFEM is employed to analyze the vibrational responses of the commercial ship, and PFBEM is applied to analyze the underwater radiation noise. The vibrational energy of the structure is treated as an acoustic intensity boundary condition of PFBEM to calculate the underwater radiation noise. Numerical simulations are presented for the commercial ship under various frequencies, and reliable results are obtained.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.04a
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• pp.498-503
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• 2009

This paper presents the vibration problem of the Engine Casing (E/C) "B" deck in the handymax vessel and describes a method to avoid resonance. The first ship of the series did not have any vibration issue on the "B" deck. However, resonance condition occurred when additional machine was installed to the following vessels. To understand the dynamic characteristics of the deck, the normal mode analysis and impact test have been performed. Within the normal operating range of the vessel, the $1^{st}$ natural frequency of the E/C "B" deck is close to the main engine's $6^{th}$ order. Based on these analysis, a reinforcement on the deck was suggested and it proved to be effective. Since actual impact test after the reinforcement also confirmed the resonance avoidance.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1054-1059
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• 2007

This paper summarized a solution procedure for a large cylindrical structure mounted underneath a ship as a sonar. Vibration analysis of the water loaded structure is required to enhance the structural reliability as well as acoustic performance of the sonar. It is, however, often very difficult to solve such structures since they have many DOFs, considering the frequency of interest and the waterloading. The cyclic symmetric method is firstly reviewed to show how the eigen properties of the full model can be obtained from the representative segment model. The mode mapping method is then proposed and verified to take into account the waterloading with the minimum DOF for the analysis. The solution procedure is finally proposed and applied for a waterloaded cylindrical array structure.

• Special Issue of the Society of Naval Architects of Korea
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• 2005.06a
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• pp.134-137
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• 2005

Recently, in VLCC, shafting system is stiffer due to large engine power whereas hull structure is more flexible due to scantling optimization, which can be suffered from alignment damage by incompatibility between shafting and hull, In this study, shafting system without stern tube forward bush was adapted for less sensitive system against external factors. Also, shaft alignment analysis was considered with hull deflection at various ship loading conditions and stern tube after bush of long journal bearing was evaluated by static squeezing pressure and dynamic oil film pressure with sloping control. Whirling vibration was also reviewed to avoid resonance with propeller blade order. So, reliable shafting design for VLCC could be achieved through optimized alignment analysis for the system without stern tube forward bush.

• Journal of Ship and Ocean Technology
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• v.6 no.2
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• pp.1-11
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• 2002

For the analysis of vibrational energy density and intensity of partitioned complex system structures in medium-to-high frequency ranges, A software based on the Power Flow Analysis(PFA) has been developed for the plate elements. The flexural, longitudinal and shear waves in plates are formulated and the joint element equations for multi-coupled plates are fully developed. Also, the wave transmission approach has been introduced to cover the energy transmission and reflection at the joint plate elements. To confirm the validity of the developed PFA software, the submarine-shaped complex structures are used for the analysis of vibration intensity and energy density.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.294-297
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• 2014

A Shipboard power system consists of three or four diesel generator sets connected to a grid. In case of dual fuel diesel generator sets employed LNG ship as a prime mover, large amounts of electricity are required for electric propulsion, auxiliary machinery and accommodation facilities. The electrical connection between generators through a network, torsional vibration can lead power swings. In this paper, the influence on the network by the torsional vibration of diesel generator sets in grid operation were studied. The torsional vibration characteristics were investigated and analyzed through theoretical analysis and the vibration measurement and the results were presented.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.12
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• pp.992-998
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• 2014

Acoustic radiation efficiency is one of the important factors in the prediction of underwater radiated noise of ships. A ship has much equipment to operate successful mission in a ship. Most of equipment is running simultaneously as multi-excitation and becomes the source of underwater radiated noise. In many cases of multi-excitation, phase difference between multi-excitation is not considered. Because vibration response under multi-excitation is the vector sum of each single excitation, acoustic radiation efficiency based on surface velocity field can be affected by phase of excitation. In this study, acoustic radiation efficiency of a plate on air and a stiffened cylindrical model in water under multi-excitation with phase difference is investigated.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.7 s.124
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• pp.572-578
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• 2007

Two stroke low speed diesel engines are widely used for marine propulsion or as power plant prime mover. These engines have many merits which includes higher thermal efficiency, mobility and durability. Yet various annoying vibrations occur sometimes in ships or at the plant itself. Of these vibrations, torsional vibration is very important and dictates a careful investigation during the engme's initial design stage for safe operation. With the rule and limit on torsional vibration in place, shaft strength fatigue due to torsional vibration however demands further analysis which possibly can be incorporated in the classification societies' rule and limit. In addition, the shaft's torsional vibration stresses can be calculated equivalently from accumulated fatigue cycles number due to transient torsional vibration in time domain. In this paper, authors suggest a new estimation method combined with Palmgren-Miner equation. A 6S70MC-C ($25,320ps{\times}91rpm$) engine for ship propulsion was selected as a case study. Angular velocity was measured, instead of shaft's strain, for simplified measurement and it was converted to torsional vibration stress for accumulated fatigue cycle numbers in shafting life time. Likewise, the accumulated fatigue calculation was compared with shaft fatigue strength limit. This new method can be further realized and confirmed in ship with two stroke low speed diesel engine.

• The KIPS Transactions:PartA
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• v.17A no.2
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• pp.81-92
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• 2010

There has been some research in the equipment defect detection based on vibration information. Most research of them is based on vibration monitoring to determine the equipment defect or not. In this paper, we introduce more accurate system for engine defect detection based on vibration information and we focus on detection of engine defect for boat and system control. First, it uses the duplicated-checking method for vibration information to determine the engine defect or not. If there is a defect happened, we use the method using error part of vibration information basis with error range to determine which kind of error is happened. On the other hand, we use the engine trend analysis and standard of safety engine to implement the vibration information database. Our simulation results show that the probability of engine defect determination is 100% and the probability of engine defect classification and detection is 96%.