• Smart Structures and Systems
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• v.9 no.1
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• pp.71-104
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• 2012

In this research, a typical tension-leg type of floating platform incorporated with an innovative concept of underwater tuned liquid column damper system (UWTLCD) is studied. The purpose of this study is to improve the structural safety by means of mitigating the wave induced vibrations and stresses on the offshore floating Tension Leg Platform (TLP) system. Based on some encouraging results from a previous study, where a Tuned Liquid Column Damper (TLCD) system was employed in a floating platform system to reduce the vibration of the main structure, in this study, the traditional TLCD system was modified and tested. Firstly, the orifice-tube was replaced with a smaller horizontal tube and secondly, the TLCD system was combined into the pontoon system under the platform. The modification creates a multipurpose pontoon system associated with vibration mitigation function. On the other hand, the UWTLCD that is installed underwater instead would not occupy any additional space on the platform and yet provide buoyancy to the system. Experimental tests were performed for the mitigation effect and parameters besides the wave conditions, such as pontoon draught and liquid-length in the TLCD were taken into account in the test. It is found that the accurately tuned UWTLCD system could effectively reduce the dynamic response of the offshore platform system in terms of both the vibration amplitude and tensile forces measured in the mooring tethers.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2000.04a
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• pp.81-88
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• 2000

Unlike structures in the air, the vibration analysis of a submerged or floating structure such as offshore structures or ships is possible only when the fluid-structure interaction is understood, as the whole or part of the structure is in contact with water. Specially, the importance of the added mass is not necessary to say like the submerged vehicle, all of the hull body, is positioned in the water. This paper introduce two method to find natural frequency in consideration of fluid-structure modal coupled vibration analysis. The purpose of this study is to analyze of the vibration characteristic of submerged vehicle to obtain the anti-vibration design data, which could be used in the preliminary design stage data. Underwater pressure hull of submerged vehicle is used as the model of this study. The F.E.M model is meshed by shell and beam element. Also, considering of the inner hull weight, mass element is distributed in the direction of hull length. Numerical calculations are accomplished using the commercial B.E.M code. The characteristics of natural frequency(eigenvalues), mode shape(eigenvectors) and frequency-displacement response are analyzed. The results of this study will be used as the useful design data in preliminary anti-vibration design stage.

• Journal of Ocean Engineering and Technology
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• v.15 no.1
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• pp.19-25
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• 2001

Unlike structures in the air, the vibration analysis of a submerged or floating structure such as offshore structures or ships is possible only when the fluid-structure interaction is understood, as the whole or part of the structure is in contact with water. This paper introduces two methods to find natural frequency in consideration of fluid-structure interaction, direct coupled vibration analysis and fluid-structure modal coupled vibration analysis. The purpose of this study is to analyze the vibration characteristic of a submerged vehicle to obtain the anti-vibration design data, which could be used in the preliminary design stage. The underwater pressure hull of submerged vehicle is used as the model of this study. The F.E.M. model is meshed by shell and beam elements. Also, considering the inner hull weight, the mass element is distributed in the direction of hull length. Numerical calculations are accomplished by using the commercial B.E.M. code. The characteristics of natural frequency, mode shape and frequency-displacement response are analyzed.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.16 no.1
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• pp.30-36
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• 2020

In SMART, the flow mixing header assembly (FMHA) is used to mix the coolant flowing into the reactor core to maintain a uniform temperature. The FMHA is designed to have enough stiffness so the resonance with reactor internal structures does not occurs during the pipe break and the seismic accidents. Since the gap between the FMHA and the core support barrel assembly is very narrow compared with the diameter of FMHA, the hydrodynamic mass effect acting on the FMHA is not negligible. Therefore the hydrodynamic mass characteristics on the FMHA are investigated to consider the fluid and structure interaction effects. The result of modal analysis for the dry and underwater conditions, the natural frequency of primary vibration mode for the horizontal direction is reduced from 136.67 Hz to 43.76 Hz. Also the result of frequency response spectrum seismic analysis for the dry and underwater conditions, the maximum equivalent stress are increased from 13.89 MPa to 40.23 MPa. Therefore, reactor internal structures located in underwater condition shall consider carefully the hydrodynamic mass effects even though they have sufficient stiffness required for performing its functions under the dry condition.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1998.04a
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• pp.510-515
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• 1998

Most of large structures such as ship, airplane, and so on have internal structure home noise sources. The operation of the machineries results in vibration and noise of the structure. Particularly, the vibration of the machineries is transmitted to the far place from the sources and emits noise into the water or outdoor as well as the inner space of the structure. In the case of warships this emission into the water induces noise to reduce the performance of its underwater acoustic equipment. Therefore the structure home noise levels of the installed machineries are strictly limited. This paper shows examples of structure home noise reduction from machineries including pumps.

• 한국태양에너지학회:학술대회논문집
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• 2008.04a
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• pp.348-358
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• 2008

Unlike structures in the air, the vibration analysis of a submerged or floating structure such as offshore structures is possibly only when the fluid-structures is understood, as the whole or part of the structure is in contact with water. Through the comparision between the experimental result and the finite element analysis result for a simple cylindrical model, it was verified that an added mass effects on the cylindrical structure. Using the commercial FEA program ANSYS(v.11.0), underwater added mass was superposed on the mass matrix of the structure. A frequency response analysis of forced vibration in the frequency considered the dynamic load was also performed. It was proposed to find the several important modes of resonance peak for these fixed cylindrical type structures. Furthermore, it is expected that the analysis method and the data in this study can be applied to a dynamic structural design and dynamic performance evaluation for the ground and marine purpose of power generator by wind.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.4
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• pp.449-457
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• 2016

Cylindrical array sensor of a surface ship to detect an enemy is normally installed in the sonar dome. Reflected signals by some structures inside the sonar dome make unwanted signals. To minimize unwanted signals, acoustic baffles are used. Acoustic baffles are hard to install and replace, so the durability of acoustic baffles is an important design parameter. To verify the durability of acoustic baffle, accelerated aging tests according to temperature and pressure were performed. Acoustic baffle specimens were made and they are tested the visual and the performance (echo reduction and transmission loss) inspection before and after aging. After the inspection, the effect of accelerated aging of the acoustic baffles were discussed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.612-618
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• 2000

The underwater explosion which has the high energy brings about the shock wave and the pulsating gas bubble. In general, structural vibration from the shock wave is more serious than the pulsating gas bubble. This shock wave may damage the important fragile structures and equipment in ship. This paper demonstrates that the shock wave propagating the structure can be reduced by ER inserts. The wave transmission of ER inserted beam is theoretically derived using Mead & Markus model, and the theoretical results are composed with the finite element analysis results. To experimentally verify the ER insert, ER insert in an aluminum plate is made and two piezoceramic disks are used as transmitter and receiver. Details of the experiment are addressed.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.11
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• pp.876-882
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• 2014

This study investigates an efficient method to estimate the total acoustic radiation power of submerged circular cylindrical structures. Since the acoustic radiation power of submerged vehicles can be changed during the operation, the estimation for its monitoring onboard is required to accomplish the missions. The total acoustic radiation power is estimated using the measured velocity and the calculated radiation efficiency of the surface which consists of submerged rectangular plate elements. Experiments are carried out to validate the estimation approach. Comparisons of the estimation results with the measurements show that they are in a good agreement for the mid-high frequency range and match well for the cases of different excitation locations which correspond to the different operation modes of underwater vehicles as well. Therefore, this estimation method can be applied effectively to the development of the radiated noise monitoring-system.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.5
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• pp.528-535
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• 2016

The vibration of a ship gives a significant effect on the noise radiated into the water. This paper focused on the vibration of ship hull due to the sub-generator located on the deck in the anchored condition. The contributions of the transfer paths between sub-generator and ship hull were analyzed using the TPA and the OTPA method. While the sub-generator was operation and the main engine was turned off, the vibrations were measured simultaneously at the 38 locations of the ship and the one hydrophone was arranged to measure the underwater radiated noise at the overside ship. The results of the transfer path by applying TPA and OTPA were compared and discussed. As a result of these methods, the top of stovepipe and valve are contributive. Reinforcing these structures is the most effective to reduce the vibration of ship hull.