• Title/Summary/Keyword: Frequency variation

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Evaluation of Mechanical Properties of Structural Ceramics ($Al_{2}O_{3}$) Using the High Frequency Ultrasonic C - Scan (초음파 C-Scan을 이용한 구조용 세라믹스의 기계적 특성평가)

  • Chang, Y.K.
    • Journal of the Korean Society for Nondestructive Testing
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    • v.9 no.2
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    • pp.18-24
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    • 1989
  • Computer-aided high frequency ultrasonic is applied to aluminum oxide(85w%, 94w%, 96w%, and 99w%) MOR(modulus of rupture) samples to evaluate mechanical properties such as density variation, pore content, elastic modulus, shear modulus, and poisson's ratio. Ultrasonic wave velocity and attenuation measurement techniques were used as an evaluator of such properties. Pulse-echo C-Scan images with different fate setting method using 50MHz center frequency 1 inch focal length transducer allows evaluation of density variation and pore content. Elastic modulus calculated with the relation of density and ultrasonic velocity. It shows good reliability as compared with resonance method. Sintered density variation of $0.025g/cm^{3}$, that is 0.6% of theoretical density in $Al_{2}O_{3}$ samples can be observed by ultrasonic velocity measurement. Attenuation measurement method qualitatively agree with 4-point fracture testing result concerning of porosity content.

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Variation in the Vibration Characteristics of a Piezoelectric Transducer due to Pre-pressure (예압에 따른 압전 변환기의 공진특성 변화)

  • Kim, Dae-Seung;Kim, Jin-Oh
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.16 no.1 s.106
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    • pp.89-100
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    • 2006
  • This paper presents an analytical approach to describe the variation in the vibration characteristics such as the natural frequency of a piezoelectric transducer under static pre-pressure. The transducer considered in this paper is a bolt-clamped Langevin-type transducer, which consists of a couple of piezoelectric discs, a couple of metal blocks for added mass effect, and a bolt to tighten them. A new analysis model for the transducer has been developed by taking into account the contact area between the piezoelectric ceramic disc and the metal block. The variation of the resonance frequency due to the pre-pressure has been calculated and compared with measured results reported earlier.

Interdecadal Variation of Wintertime Blocking Frequency over the Siberia

  • Lee, Hyun-Soo;Jhun, Jong-Ghap;Kang, In-Sik;Moon, Byung-Kwon
    • Journal of the Korean earth science society
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    • v.28 no.5
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    • pp.556-562
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    • 2007
  • The interdecadal variation of wintertime blocking frequency over the Siberia ($60^{\circ}E-140^{\circ}E$) is examined using the ECMWF/NCEP-NCAR re-analysis data for the period 1958-2006. The wintertime blocking frequency over the Siberia significantly decreased for the period 1986-2006, compared to the period 1958-1985, which is mainly due to the anomalous circulation of 500-hPa geopotential height field. During the period 1986-2006, there was enhancement in both the anomalous cyclonic flow over the western Siberia and the anomalous anticyclonic flow over the east Asia. These anomalous circulation patterns, which might be associated with changes in surface temperatures over the Asian continent, are suspected to playa possibly important role as an obstacle to the formation of blocking flow over the Siberia.

Design of Robust Convolution Input Shaper for Variation of Parameter (파라메터 변화에 강인한 Convolution 입력성형기 설계)

  • Park, Un-Hwan;Lee, Jae-Won;Lim, Byoung-Duk
    • Proceedings of the KSME Conference
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    • 2001.06b
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    • pp.127-133
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    • 2001
  • The flexibility of long reach manipulators presents a difficult control problem when accurate end-point position is required. Input shaping by convolving system commands with impulse sequences has been shown to be an effective method of reducing residual vibrations in flexible systems. However, existing shapers has been considered robustness for only frequency uncertainty. However, this paper presents new multi-hump convolution(CV) input shaper that could accommodate with the simultaneous variation of natural frequency and damping ratio. Comparisons with previously proposed input shapers are presented to illustrate the qualities of the new input shaper. These new shapers will be shown to have better robustness for the variation of frequency and damping ratio.

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Performance Verification of Anti-Islanding of Reactive Power Variation Method using Positive Feedback (정궤환을 이용한 무효전력 변동기반의 단독운전 방지 성능 검증)

  • Jo, Jongmin;Shin, Chang-Hoon;Cha, Hanju
    • The Transactions of the Korean Institute of Power Electronics
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    • v.24 no.2
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    • pp.105-110
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    • 2019
  • This study proposed a reactive power variation (RPV) method equipped with positive feedback (PF) for detecting the islanding operation of distributed generation systems. The proposed RPV consists of the constant reactive power component and a certain reactive power term and uses the frequency deviation between the rated and the measured frequencies. The constant reactive power is injected from distributed generation system and power factor is to 0.9975 in grid-connected operation. PF is activated from generation of the frequency deviation and the injected reactive power is continuously increased due to PF when islanding occurs. Consequently, the increasing reactive power causes the point of common coupling frequency to deviate from the maximum/minimum threshold level. Performance of the proposed RPV is verified in a 1.7 kW T-type inverter, and the detection times are 53 and 150 ms.

Three-Phase AC-to-DC Resonant Converter Operating in High Power Factor Mode in High-Voltage Applications

  • Chaudhari, Madhuri A.;Suryawanshi, Hiralal M.;Kulwal, Abhishek;Mishra, Mahesh K.
    • Journal of Power Electronics
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    • v.8 no.1
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    • pp.60-73
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    • 2008
  • In this paper a three-phase ac-to-dc resonant converter with high input power factor and isolated output is proposed. To improve the input power factor of the converter, high frequency current is injected into the input of the three-phase diode bridge rectifier. It is injected through an impedance network consisting of a series of L-C branches from the output of the high frequency three-phase inverter. A narrow switching frequency variation is required to regulate the output voltage. A design example with different design curves is illustrated along with the component ratings. Experimental verification of the converter is performed on a prototype of 3 kW, 1000 V output, operating above 300 kHz. Experimental results confirm the concept of the proposed converter. Narrow switching frequency variation is required to regulate the output voltage.

A Study on Temperature Features of Broadband Ultrasonic Attenuation (초음파 광역 감쇠의 온도 특성에 관한 연구)

  • 신정식;안중환;한승무;김형준
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1997.10a
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    • pp.245-248
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    • 1997
  • The distilled water is used for the ultrasonic wave propagating material in the measurements of broadband ultrasonic attenuation (BUA) that is applied in industrial and medical applications, The acoustic impedance of water is significantly changed with its temperature. Therefore, the quantitative evaluation of BUA with temperature and the ultrasonic wave propagating distance is highly needed. In this study, we evaluated the variation of attenuation with change in temperature. To measure the variation of BUA in the low frequency region at the temperatures, 27$^{\circ}C$, 29$^{\circ}C$, and 31$^{\circ}C$, we tested the Plyethylene, Teflon, MC-Nylon, Urethane specimens and analyzed the center frequency, frequency bandwidth, spectral peak amplitude. The results showed that BUA value appeared to be lower with increasing temperature. This may be due to the fact that the frequency feature of ultrasonic wave is affected by not only the specific gravity, acoustic impedence, but material crystalline, porosity, the distance of ultrasonic wave propagation in water.

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A Study on Characteristics According to the Parameter Variation for Hybrid Shaft Design (하이브리드 샤프트 설계 파라미터 변화에 따른 특성 연구)

  • Hong, Yong;Kim, Hyun-Sik;Hong, Dong-Pyo
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.19 no.3
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    • pp.274-281
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    • 2009
  • The carbon fiber epoxy composite material and aluminum have many advantages over other materials because of their high specific stiffness and good fatigue characteristics. Basically, the propeller shaft of automobile requires bending frequency of higher than 2,700 Nm and high natural frequency of higher than 9,200 rpm occurred by fast revolution. For this reason, natural frequency and torsion torque characteristics of hybrid shaft was studied in variation of its outer-diameter and thickness. Vibration and torque characteristics of hybrid shaft were compared by torsion tester, natural frequency experiments and FE analysis. Designed hybrid shaft satisfied its vibration and torque characteristics when its outer-diameter was 60 mm and thickness was 5 mm. Therefore, hybrid material enables to manufacture one piece structure hybrid propeller shaft rather than current two piece structure.

Effects of Seismic Isolated Frequency in Structural Responses of Cylindrical Tanks (면진주파수가 원통형탱크의 구조응답에 미치는 영향)

  • Koo, Gyeong-Hoi;Lee, Jae-Han;Yoo, Bong
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 1995.10a
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    • pp.258-265
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    • 1995
  • For design of seismic isolated system the determination of isolated frequency is very important. In this paper the effects of seismic isolated frequency for cylindrical tank are investigated using the 1940 EL Centre earthquake(NS). From the results of analysis the seismic isolated frequencies significantly depend on input acceleration and displacement components in lower frequency regions. Therefore, the seismic isolated frequency should be determined by consideration of input ground motion characteristics. For the seismic analysis the modified hysteretic hi-linear model of seismic isolators which can consider the yield load variation, shape of hysterisis loop variation and hardening effects of isolators is proposed. The analyses using the proposed model give similar displacement responses but higher maximum acceleration responses than those using the simple hysteretic hi-linear model.

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Dynamic Voltage and Frequency Scaling for Power-Constrained Design using Process Voltage and Temperature Sensor Circuits

  • Nan, Haiqing;Kim, Kyung-Ki;Wang, Wei;Choi, Ken
    • Journal of Information Processing Systems
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    • v.7 no.1
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    • pp.93-102
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    • 2011
  • In deeply scaled CMOS technologies, two major non-ideal factors are threatening the survival of the CMOS; i) PVT (process, voltage, and temperature) variations and ii) leakage power consumption. In this paper, we propose a novel post-silicon tuning methodology to scale optimum voltage and frequency "dynamically". The proposed design technique will use our PVT sensor circuits to monitor the variations and based on the monitored variation data, voltage and frequency will be compensated "automatically". During the compensation process, supply voltage is dynamically adjusted to guarantee the minimum total power consumption without violating the frequency requirement. The simulation results show that the proposed technique can reduce the total power by 85% and the static power by 53% on average for the selected ISCAS'85 benchmark circuits with 45 nm CMOS technology compared to the results of the traditional PVT compensation method.