• Title/Summary/Keyword: Resonance Frequency Analysis

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Combination resonances in forced vibration of spar-type floating substructure with nonlinear coupled system in heave and pitch motion

  • Choi, Eung-Young;Jeong, Weui-Bong;Cho, Jin-Rae
    • 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.

Application of Magnetic Resonance Thermometry (MRT) on Fully Developed Turbulent Pipe Flow using 3T and 7T MRI (완전발달 난류 원관 유동에서의 3T 및 7T MRI를 이용한 자기공명온도계의 적용)

  • You, Hyung Woo;Baek, Seungchan;Kim, Dong-Hyun;Lee, Whal;Oh, Sukhoon;Hwang, Wontae
    • 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.

Resonance Mode Anlaysis in a Single Can-type Combustor through 3D Thermo-acoustic Analysis based on Helmholtz Solver (헬름홀츠 솔버 기반의 3차원 열음향해석을 통한 발전용 단일 캔 연소기에서의 공진 모드 분석)

  • Junwoo Jung;Daesik Kim
    • 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.

A COMPARATIVE ANALYSIS WITH RESONANCE FREQUENCY ACCORDING TO VARIOUS SIMULATED BONE DEFECTS (다양한 가상 골 결함에 따른 공진 주파수의 비교 분석)

  • Kim Sang-Mi;Park Chan-Jin;Yi Yang-Jin;Chang Beom-Seok;Cho Lee-Ra
    • 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.

Design of a Ultrasonic Cutting-tool Utilizing Resonance Condition of Transverse Vibration of Beam Type Structure (보의 횡진동 공진특성을 이용한 초음파 진동절삭공구 설계)

  • Byun, Jin-Woo;Han, Sang-Bo
    • 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.

A Case Study on the Reduction of Noise and Vibration at the Backpass Heat Surface in the Power Plant Boiler (발전용 보일러 후부 전열면 소음진동 저감에 관한 연구)

  • Lee, Gyong-Soon;Lee, Tae-Gu;Moon, Seung-Jae;Lee, Jae-Heon
    • 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.

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A Study on the Frequency Characteristics of a Class I Flextensional Transducer (Class I Flextensional 변환기의 주파수 특성에 관한 연구)

  • Kang, Kook-Jin;Lee, Young-Jin;Paik, Jong-Hoo
    • 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.

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Noise and Vibration Characteristics by Heavy-weight Floor Impact (중량바닥충격에 의한 소음 및 진동 특성)

  • 서상호;송희수;전진용
    • 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.

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Noise and Vibration Characteristics of Concrete Floor Structures Using Resilient Materials Driven by Standard Heavy Impact Source (완충재 유무에 따른 표준중량충격원에 의한 콘크리트 바닥 구조의 소음 및 진동 특성)

  • 송희수;전진용;서상호
    • 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.

A Study on the Frequency Characteristics of a Class IV Flextensional Transducer (Class IV Flextensional 트랜스듀서의 주파수 특성 변화에 관한 연구)

  • 강국진;노용래
    • 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.

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