• The Journal of the Acoustical Society of Korea
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• v.40 no.4
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• pp.270-277
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• 2021

In the power ultrasound fields, the flange position for fixing the transducer is an important factor influencing on electro-mechanical efficiency of the transducer. We suggested a practical method that can determine the installation position of the flange for different resonance modes of the bolt-clamped type Langevin ultrasonic transducer. A semicircular wedge-shaped jig was manufactured and moved along the lateral surface of the transducer. The vibration characteristics were examined after a constant pressure was applied to the semicircular wedge-shaped jig. By observing the change of the input admittance of the transducer depending on the position of the pressure application, the optimum position for the flange installation could be determined. The resonant modes of the transducer were calculated by a Mason's equivalent circuit, and the particle velocity distribution for each resonance mode was calculated by a transmission line model. Since the optimum positions determined from an experimental result show a good correspondence with the node positions of the vibration modes calculated by the transmission line model, the validity of the suggested method was verified.

• Journal of the Semiconductor & Display Technology
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• v.16 no.2
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• pp.32-38
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• 2017

This paper is about the analysis on the vibration characteristic of tooling units on the precision bed in high-speed automatic lathe for precision machining. An automatic lathe operating at about 25,000 RPM is a critical factor in the self-weight stress and deformation of the bed. Especially, the resonance frequency should be grasped in advance to prevent abnormal vibration that may occur during processing. If the wrong bed is used, the resonant frequency can have a fatal influence on the precision machining and increase the defective rate of precision machined parts such as semiconductor parts. In this paper, vibration characteristics were evaluated through static load and resonance frequency analysis of automatic lathe bed. As a result, the maximum stress was 0.14MPa, the maximum deformation amount was $17.9{\mu}m$, and the natural frequency was 364.72Hz. The resonance frequency was calculated as 718Hz, and the stability was confirmed by being in the range of 400Hz or more, which is the processing condition.

• Journal of the Semiconductor & Display Technology
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• v.17 no.1
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• pp.66-70
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• 2018

This paper is about the analysis on the vibration characteristic of tooling units on the precision bed in turning and hobbing automatic lathe for precision machining. An automatic lathe operating at about 12,000 RPM is a critical factor in the self-weight stress and deformation of the bed. Especially, the resonance frequency should be grasped in advance to prevent abnormal vibration that may occur during processing. If the wrong bed is used, the resonant frequency can have a fatal influence on the precision machining and increase the defective rate of precision machined parts such as semiconductor parts. In this paper, vibration characteristics were evaluated through static load and resonance frequency analysis of automatic lathe bed. As a result, the maximum stress was 14.52 MPa, the maximum deformation amount was $12.15{\mu}m$, and the natural frequency was 189.43 Hz. The resonance frequency was calculated as 500 Hz, and the stability was confirmed by being in the range of 200 Hz or more, which is the processing condition.

• Steel and Composite Structures
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• v.50 no.2
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• pp.201-216
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• 2024

This paper is motivated by the lack of studies relating to vibration and nonlinear resonance of fluid-conveying cantilever porous GPLR pipes with fractional viscoelastic model resting on nonlinear foundations. A dynamical model of cantilever porous Graphene Platelet Reinforced (GPLR) pipes conveying fluid and resting on nonlinear foundation is proposed, and the vibration, natural frequencies and primary resonant of such system are explored. The pipe body is considered to be composed of GPLR viscoelastic polymeric pipe with porosity in which Halpin-Tsai scheme in conjunction with fractional viscoelastic model is used to govern the construction relation of the nanocomposite pipe. Three different porosity distributions through the pipe thickness are introduced. The harmonic concentrated force is also applied on pipe and excitation frequency is close to the first natural frequency. The governing equation for transverse motion of the pipe is derived by the Hamilton principle and then discretized by the Galerkin procedure. In order to obtain the frequency-response equation, the differential equation is solved with the assumption of small displacement, damping coefficient, and excitation amplitude by the multiple scale method. A parametric sensitivity analysis is carried out to reveal the influence of different parameters, such as nanocomposite pipe properties, fluid velocity and nonlinear viscoelastic foundation coefficients, on the primary resonance and linear natural frequency. Results indicate that the GPLs weight fraction porosity coefficient, fractional derivative order and the retardation time have substantial influences on the dynamic response of the system.

• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.1169-1171
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• 2002

In this paper, RFRPP(Random Frequency Randomized Pulse Position ) PWM for three-phase voltage-controlled inverters is proposed. The LLPWM(Lead-Lag PWM) techinquc is that three switching pulses are located randomly back and forth in each switching interval. But with the restriction of random distribution, the harmonic spectrum cannot be dispersedly and continuously distributed. This paper calculates the duty ratio of the switching pulse firstly. Second, the switching pulses are located randomly in the switching interval. Third, the fixed switching frequency of the space vector modulation is randomly varied. To verify the validity of the proposed technique, simulation study is tried using Matlab/Simulink. When a proposed techniquc is employed, the harmonic spectrum of the inverter output voltagc varies from one cycle to the next and the EMI(Electromagnetic Interference) and resonant vibration are greatly alleviated.

• Proceedings of the IEEK Conference
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• 2003.07c
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• pp.2585-2588
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• 2003

2 관성 공진계는 마른 응답을 위해 제어이득을 크게 하면 공진에 의해 축비틀림 진동이 일어나는 경우가 많다. 본 논문에서는 반복 학습 제어기법을 활용하여 불확실한 모델 계수를 포함하는 2 관성 공진계의 진동억제를 시도한다. 2관성 공진계의 경우 제어 대상이 되는 부하측 속도는 학습 제어로 직접 적용하기가 힘들고 또한 측정 또한 어렵다. 본 논문에서는 부하측 속도와 전동기측 속도간의 관계를 이용하여 직접 부하측 속도를 제어하는 대신 전동기측 속도를 제어하여 간접적으로 부하측 속도를 제어하였다. 제안된 방식은 전형적인 2 관성 공진계에 모의 실험을 통해 적용되었고, 정확한 모델이 없이도 진동 없는 마른 응답특성을 보여준다.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.193-196
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• 2002

The thermoacoustic refrigerator has not only considerable possibility but also commercial usability, because it has high reliability, lower vibration, no moving part, and can easily be constructed. In order to determine the optimum resonant tube length and the frequency, the open-tube-type(3$\lambda$/4) and close- tube - type (2$\lambda$/2) thermoacoustic refrigerator were constructed. In third harmonic, the temperature difference of 3$\lambda$/4 refrigerator was $53^{\circ}C$(resonator length :400mm). In second harmonic, the temperature difference of 2$\lambda$/2 refrigerator was $51^{\circ}C$(resonator length :400mm).

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.988-992
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• 2002

Ultrasonic machining technology has been developed over recent years for the manufacture of and quality-assured precision parts for several industrial application such as optics, semiconductors, aerospace, and automobile application. The past decade has seen a tremendous in the use of ceramics in structural application. The excellent thermal, chemical and wear resistance of these material can be realized because of recent improvements in the overall strength and uniformity of advanced ceramics. Ultrasonic machining, in which abrasive particles in slurry with water are presented to the work surface in the presence of an ultrasonic-vibrating tool, is process which should be of considerable interest, as its potential is not limited by the electrical or chemical characteristics of the work material, making it suitable for application to ceramics. This paper intends to further the understanding of the basic mechanism of ultrasonic machining for brittle material and ultrasonic machining of ceramics based in the fracture-mechanic concept has been analyzed.

• Journal of KSNVE
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• v.8 no.6
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• pp.1113-1120
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• 1998

For an analysis of some Helmholtz resonators, it is likely to be more appropriate to consider acoustic field within cavity than just the 1-DOF analogous model. However, a design method that considers increased parameters than the lumped model. is not a trivial process due to the trade-off effect among the parameters. In this paper. the genetic algorithm. one of the optimization technique that rapidly converges to global fittest solution and robust convergence. is applied to the design process of Helmholtz resonators. Results show that the genetic algorithm can be successfully and efficiently used to find the resonant frequencies for both lumped model and distributed model.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.6
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• pp.434-440
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• 2013

With polymer properties and ceramic volume fraction as design variables, the optimal structure of 1-3 piezocomposites has been determined to maximize the thickness mode electromechanical coupling factor. When the piezocomposite vibrates in a thickness mode, inter-pillar resonant modes are likely to occur between lattice-structured piezoceramic pillars and polymer matrix, which significantly deteriorates the performance of the piezocomposite. In this work, a new method to design the structure of the 1-3 type piezocomposite is proposed to maximize the thickness mode electromechanical coupling factor while preventing the occurrence of the inter-pillar modes. Genetic algorithm was used for the optimal design, and the finite element analysis method was used for the analysis of the inter-pillar mode.