• International Journal of Naval Architecture and Ocean Engineering
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• v.5 no.2
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• pp.313-323
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• 2013

Offshore floating structures have so-called moonpool in the centre area for the purpose of drilling, installation of subsea structures, recovery of Remotely-Operated Vehicle (ROV) and divers. However, this vertical opening has an effect on the operating performance of floating offshore structure in the vicinity of moonpool resonance frequency; piston mode and sloshing mode. Experimental study based on model test was carried out. Moonpool resonance of floating offshore structure on fixed condition and motion free condition were investigated. And, the effect of cofferdam which is representative inner structure inside moonpool was examined. Model test results showed that Molin's theoretical formula can predict moonpool resonance on fixed condition quite accurately. However, motion free condition has higher resonance frequency when it is compared with that of motion fixed. The installation of cofferdam moves resonance frequency to higher region and also generates secondary resonance at lower frequency. Furthermore, it was found that cofferdam was the cause of generating waves in the longitudinal direction when the vessel was in beam sea.

• The Journal of the Acoustical Society of Korea
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• v.30 no.4
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• pp.223-230
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• 2011

Korean bell is hung with some air gap between the bell bottom and the ground. In addition, it has a peculiar acoustic element, so called resonance cavity below the bell. A proper design of the air gap and cavity size dramatically amplifies the bell sound by resonance effect. Bell interior cavity, air gap and resonance cavity consist of an acoustic cavity system. When the acoustic cavity frequency coincides with the natural frequency of the bell body, the frequency component is significantly amplified. On the Sacred Bell of the Great King Seongdeok, this study proposes a resonance condition of the cavity system considering air gap effect for the first time. With the exact dimension of the bell, boundary element analysis is performed using SYSNOISE. Finally, this study reveals how the temperature in season influences the resonance condition and proposes a concept of variable type resonance cavity. By using the variable type resonance cavity, the cavity size is controlled on site and exact resonance is available regardless of temperature difference in season.

• 제어로봇시스템학회:학술대회논문집
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• 1992.10a
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• pp.1060-1066
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• 1992

One of the undesirable nonlinear phenomenon called 'wind up' occours when the integrator in the controller and the saturated actuator interact. Large overshoot, slow response, instability, limit cycle and jump resonance are the characteristics of wind up phenomenon. Several 'anti-windup' compensators have been developed to prevent some of the aforementioned nonlinear characteristics such as instabilituy and limit cycle, but none has studied the effect of antiwindup compensator on the jump resonance. In this paper, we developed an analyitcal method to design the compensator to prevent not only limit cycle but also jump resonance. An illustrative example is included to show the compensator eliminates jump resonance of effectively.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.1
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• pp.13-19
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• 2016

The flow-excited Helmholtz resonance phenomenon was investigated numerically using Reynolds averaged Navier-Stokes approach. The fundamental cause of the Helmholtz resonance phenomenon is known as shedding of a single discrete vortex from orifice edge that travels during one period of the oscillation. In this study, serrated deflector, which is biomimetic design of the owl's feather, is used to split a single vortex into small vortices. Rectangular deflector and serrated deflector are compared with numerical results of pressure and streamline inside the cavity. Consequently, the serration breaks the shedding period of vortex core and eliminates the resonance. Also, it changes the flow pattern in according to the location of different serration height. By making inflows and outflows occur simultaneously in spanwise direction in the cavity, the period of Helmholtz resonance disappears. Comparing between rectangular deflector and serrated deflector, the serrated deflector can deal with the Helmholtz resonance more effectively.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.882-887
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• 2001

This paper deals with the effect of mass-spring-mass resonance that is a characteristics of the multi-layered panels in order to enhance sound insulation performance. From theoretical and experimental investigation, it is evident that tuning mass-spring-mass resonance by controlling elastic modulus of the core materials is very important to improve the STC value without increasing the weight of panels, resulting in enhancing STC value more than 10 dB.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.2
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• pp.595-608
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• 2013

This paper is proposed the computation method of moored ship motion considering harbor resonance, and estimated that the harbor resonance have an effect on moored ship motion. The computation of harbor resonance was used CGWAVE model and the computation of moored sip motion was used the Green function method expressed by three dimensions. This method was verified with the field observation data of moored ship motion, and the application of actual harbor was investigated with wave field data and down time record data in Pohang New Harbor. The resonance periods in Pohang New Harbor that obtained from wave field data were 80, 33, 23, 8 minute, which are the long waves, and 42, 54, 60 second, which are the infra-gravity waves inside harbor slip. The simulated results of harbor resonance were corresponded with the wave field data. This study was investigated on 5,000 ton, 10,000 ton and 30,000 ton ship sized in Pier 8 of Pohang New Harbor that the harbor resonance has effect on moored ship motion from simulated results of ship motion in case of included resonance and excluded resonance. In case of included resonance, the ship motion have increased by 12~400 percent when compared with results of excluded resonance. We could find that the harbor resonance have still more an effect on the surge and heave motions of a large size ship and the roll and yaw motions of a small size ship.

• Proceedings of the Korean Magnetic Resonance Society Conference
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• 2001.02a
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• pp.9-9
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• 2001

• Journal of the Korean Society of Safety
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• v.33 no.5
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• pp.9-14
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• 2018

The piping system of a nuclear power plant plays a role of transferring high energy fluid to equipment and various devices. The safety and soundness of these piping systems are very closely related to the operability of the power plant. In the case of a welded part of a small diameter pipe, it may grow as a microcrack due to a lack of penetration, and it may grow to a size that affects the safety of the pipe due to the influence of mechanical vibration and fatigue load. Resonance refers to an increase in energy as the natural frequency of an object coincides with the frequency applied to the external force. When this resonance occurs, the frequency is the resonance frequency. In this study, when defects exist in the welds of small diameter pipe, the natural frequency of the pipe changes and resonance may occur. Since these resonances are likely to cause fatigue damage to the piping, resonance frequency changes due to the size and shape of the defects are analyzed and evaluated. As a result of the vibration test, the resonance frequency tended to decrease as the depth of the defect deepened, and the influence was larger when the defect existed at the bottom of the top of the trough. Also, it was confirmed that the Transverse cracks had an effect on the resonance frequency in the presence of the cracks in the weld bead, compared to the longitudinal cracks. As a result of this study, it is expected that the cause of the defect and the condition of the pipe can be monitored because the resonance frequency tendency according to the shape of the crack is analyzed.

• Journal of Mechanical Science and Technology
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• v.14 no.7
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• pp.744-751
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• 2000

To achieve lower flying height for high areal recording density, the laser zone texturing of the disk needs to be designed to reduce glide height. One problem of the laser bump design is that the regular laser bump pattern often produces glide resonance phenomenon, which leads to failure of the glide height test. However, it was found in this study that glide resonance is an intrinsic problem of the glide head used and resonance phenomenon depends on the type of the head slider, that is, the natural frequency of the slider body. Therefore, higher glide height or glide failure caused by glide resonance does not lead to head/media interface problem in the real drive operating conditions in which the data head is used. Pseudo-random bump pattern greatly reduces the glide resonance. Smaller bump pitch will also help to reduce the glide resonance. However, as bump spacing becomes smaller, glide height will be increased due to increased air pressure developed around the bumps. Lowering bump height is the most effect way to reduce glide avalanche.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.98-103
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• 2003

This paper presents phenomena of vibration and noise due to acoustic resonance in tube bank of a HRSG. Acoustic resonance is may arise when the vortex shedding frequency coincides with the acoustic natural frequency. At this tube bank, dominant frequencies of vibration in this system were 43.5, 67.5㎐. The 3$\^$rd/ acoustic natural frequency calculated was 68.5㎐. When the difference of vortex shedding frequency and acoustic natural frequency is within ${\pm}$20%, acoustic resonance could occur. In this system, in order to prevent acoustic resonance, acoustic baffle was installed in the tube bank before operating. But acoustic resonance occurred. So, we evaluate the effect of acoustic mode due to baffle extension length. After investigating, we did revise acoustic baffle to eliminate acoustic resonance effectively.