• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.3
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• pp.252-261
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• 2016

A spar-type floating substructure that is being widely used for offshore wind power generation is vulnerable to resonance in the heave direction because of its small water plane area. For this reason, the stable dynamic response of this floating structure should be ensured by accurately identifying the resonance characteristics. The purpose of this study is to analyze the characteristics of the combination resonance between the excitation frequency of a regular wave and natural frequencies of the floating substructure. First, the nonlinear equations of motion with two degrees of freedom are derived by assuming that the floating substructure is a rigid body, where the heaving motion and pitching motions are coupled. Moreover, to identify the characteristics of the combination resonance, the nonlinear term in the nonlinear equations is approximated up to the second order using the Taylor series expansion. Furthermore, the validity of the approximate model is confirmed through a comparison with the results of a numerical analysis which is made by applying the commercial software ANSYS AQWA to the full model. The result indicates that the combination resonance occurs at the frequencies of ${\omega}{\pm}{\omega}_5$ and $2{\omega}_{n5}$ between the excitation frequency (${\omega}$) of a regular wave and the natural frequency of the pitching motion (${\omega}_{n5}$) of the floating substructure.

• Journal of the Korean Society of Visualization
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• v.18 no.1
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• pp.26-37
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• 2020

Magnetic resonance thermometry (MRT) is a technique capable of measuring three-dimensional mean temperature fields by utilizing temperature-dependent shifts in proton resonance frequency. In this study, experimental verification of the technique is obtained by measuring 3D temperature fields within fully developed turbulent pipe flow, using 3T and 7T MRI scanners. The effect of the proton resonance frequency (PRF) thermal constant is examined in detail.

• Journal of ILASS-Korea
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• v.29 no.1
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• pp.23-31
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• 2024

This study conducted a 3D thermo-acoustic analysis based on the helmholtz solver to analyze the major resonance modes causing combustion instability in a single-can combustor. The experimental investigations were carried out on a test rig designed by the Korea Institute of Machinery & Materials (KIMM) under various conditions of hydrogen co-firing and fuel staging. Through these experiments, two primary unstable frequencies were identified. To determine the resonance modes of these frequencies, a 3D thermo-acoustic analysis was conducted using temperature information from the test rig. The results confirmed that the unstable frequencies observed in the experiments were all longitudinal modes. Additionally, the mode shapes identified in the analysis facilitated a simplification of the exit geometry for the low-order network model, confirming that this did not significantly affect the fundamental resonance modes.

• The Journal of Korean Academy of Prosthodontics
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• v.43 no.4
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• pp.487-497
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• 2005

Purpose: Resonance frequency analysis (RFA) , a non-invasive technique for the clinical measurement of implant stability, was investigated. Peri-implant bony defect may contribute to implant failure. This in vitro study evaluated the resonance frequencies according to various bony defects and determined whether the directional bone defect can affect the value of frequency analysis. Material and Method: Fifteen 3.75 mm in diameter and 10 mm in length, machined self-tapping implant future were used. Twelve types of bone defects that have different horizontal and vertical dimensions were simulated. Embedded implants were attached to the dental surveyor. Then, the transducer was connected with the implant fixture and the ISQ value was measured at four different directions. Two-way analysis of variance and post hoc $Sch\`{e}ffe'$ test were performed at the 95% significance level. Results: The control group showed the highest ISQ value and 5 thread-$360^{\circ}$ group had the lowest one. As the vertical exposure of implants in each angle was increased, the ISQ value was decreased. Although the horizontal exposure in each thread was increased, the ISQ value was not significantly decreased. Conclusion : Although the simulated defect type was different from each other, the ISQ value was similar among groups.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.8
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• pp.720-725
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• 2011

Most ultrasonic vibration cutting tools are operated at the resonance condition of the longitudinal vibration of the structure consisting of booster, horn and bite. In this study, a transverse vibration tool with beam shape is designed to utilize the vibration characteristics of the beam. Design point of the transverse vibration tool is to match the resonance frequency of the bite to the frequency of the signal to excite the piezoelectric element in the booster. The design process to match the natural frequency of the longitudinal vibration mode of the horn and that of the transverse vibration mode of the bite is presented. Dimensions of the horn and bite are searched by trend analysis through which the standard shapes of the horn and bite are determined. After the dimensions of each component of the cutting tool consisting of booster, horn and bite are determined, the assembled structure was experimentally tested to verify that true resonant condition is achieved and proper vibrational displacement are obtained to ensure that enough cutting force is generated.

• Plant Journal
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• v.4 no.3
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• pp.54-59
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• 2008

The resonance of boiler is caused by exciting force in the gas path and it generates the vibration by the harmony of boiler's dimensional factor. According to trending toward the boiler of increasing capacity and a bigger size, it has a problem of the vibration at back-pass heating surfaces. We can predict such vibrations as comparison between vortex frequency and gas column's natural frequency. We can't rely on the method for the past decades because of changing parameters, such as an allowable error, gas temperature, gas velocity, Strouhal number. We can reduce the vibration to use the seasoning effect and change the operating condition in coal fired boiler but it's not essential solution. When the vibration occurred in the model boiler, we must measures the acoustic pressure and frequency of places for considering the means. So far, we confirmed the problem from field measures and theoretical analysis about the acoustic vibration of boiler. We installed anti-acoustic baffle in a existing boiler to change the acoustic natural frequency at the cavity, which results in reducing the acoustic vibration. The first, we prove that the acoustic resonance is caused by harmonizing vortex shedding frequency of tube heat surface with acoustic natural frequency of cavity in the range of 650~750 MW loads. The second, the acoustic resonance at the back-pass heating surface has the third order of acoustic natural frequency at the second economizer. We install five anti-acoustic baffles at the second economizer to reducing the resonance. We confirm considerably reducing the acoustic vibration of boiler during the commercial boiler.

• The Journal of the Acoustical Society of Korea
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• v.18 no.7
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• pp.67-73
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• 1999

We constructed a class Ⅳ Flextensional transducer, and analyzed the effects of the variation in its material properties and structure on the resonance frequency of the transducer. We used the FEM for the analysis. Major axis length, minor axis length, thickness and material properties of the shell turned out to have large effects, while volume of the insert material, material properties and thickness of the ceramic bar have little. Thickness of the nodal-plate has no effect on the resonance frequency. Results of the present work can be utilized to design Class W Flextensional transducers of various resonance frequency.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.226-227
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• 2008

We constructed a class I Flextensional transducer, and analyzed the variation of the resonance frequency of the transducer in relation to its design variables. We used the FEM for the analysis. Major axis length, minor axis length, thickness and material properties of the shell have large effects on the resonance frequency. In addition, the validation of the FE model was verified by manufacturing and comparison of the impedance analysis.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.919-922
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• 2003

The correlation between noise and vibration by a heavy-weight floor impact was studied. The triggering technique was used for increasing the reliability and stability to measure the level of sound pressure, sound intensity and vibration acceleration. The simple finite element and rigid body analysis method were suggested to calculate the natural frequencies of the multi-layer floor system. The result show that the isolation material adapted to reduce the light-weight floor impact noise, causing the natural frequency lower, make resonance with dominant driving frequency, and increase the noise level very sharply. Therefore the noise level Peak in the region of low frequency, below 63Hz, would be related with the natural frequencies of the floor system.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.8
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• pp.661-667
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• 2004

The characteristics of noise and vibration by a heavy impact source was studied. The triggering method was used for increasing the reliability and stability to measure the level of sound pressure. sound intensity and vibration acceleration. A simple finite element model and a rigid body analysis method were suggested to calculate the natural frequencies of the multi-layer floor system. The results show that the resilient materials decrease the natural frequency of the reinforced concrete slab, make a resonance with dominant driving frequency in the low frequency region, and increase the vibration and noise level. A simple finite element model and rigid body models was suggested to calculate the natural frequencies of the floor systems.