• Title/Summary/Keyword: Acoustic Waves

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Determination of magneto-hydrodynamic quantities in umbrae and bright points using MHD seismology

  • Cho, Il-Hyun;Moon, Yong-Jae
    • The Bulletin of The Korean Astronomical Society
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    • v.43 no.1
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    • pp.53.2-53.2
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    • 2018
  • We perform seismological diagnostics of the physical parameters in umbral photospheres and G-band bright points. The technique is based on the theory of slow magneto-acoustic waves in a non-isothermally stratified photosphere with uniform vertical magnetic fields. For the seismology of sunspot umbrae, we calculate the weighted frequency of three-minute oscillations observed by SDO/HMI continuum and use it to estimate the Alfvn speed and plasma-beta, which range 7.5-10.5 km/s and 0.65-1.15, respectively. We identify and track bright points in the G-band movie by using a 3D region growing method. Then we apply the seismological diagnostics to the bright points in the Hinode/BFI Blue continuum. We will present the Alfvn speed and plasma-beta in the bright points.

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Polarization and Charge Transport in Unfilled Epoxy (비충전 에폭시의 분극 및 전하 이동)

  • Gwak, Hyun-Woo;Choi, Yong-Sung;Lee, Kyung-Sup
    • Proceedings of the KIEE Conference
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    • 2008.07a
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    • pp.2311-2312
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    • 2008
  • The investigations included the measurements of volume currents and also internal space charges on epoxy samples of mm thicknesses. The current versus time relations were shown to correspond well with classical forms of dielectric response such as the Curie-von Schweidler model. After the time transient, near steady currents were extremely small and exhibited a significant temperature dependence, similar in relation to the Poole-Frenkel hoping transport model. Equivalent resistances were on the order of 1019 ohms and represent very weak charge transport. Electrically stimulated acoustic waves were used to quantify the small internal charges that would accumulate within the epoxy. There was a notable homocharge near both anode and cathode. The dielectric response and the internal charge were related to show a consistent model for charge transport within unfilled epoxy.

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A PWM Strategy for Noise Reduction of Inverter-Induction Motor Drive System (인버터-유도전동기 구동시스템의 소음 저감을 위한 PWM 방식)

  • Seo, Young-Min;Lee, Ju-Hoon;Yoon, In-Sik;Park, Young-Jeen;Hong, Soon-Chan
    • Proceedings of the KIEE Conference
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    • 1999.11b
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    • pp.398-402
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    • 1999
  • In PWM inverter fed traction motor drive systems, the switching frequency is restricted and thus the electromagnetic acoustic noise is generated. To reduce such an audible noise, we propose the modified RSF(Randomized Switching Frequency)-PWM method. In the proposed RSF-PWM method, both triangular wave and sawtooth wave are used in one period as carrier waves. Because the proposed method has inherently the same property as sinusoidal PWM method, there is no problem of linearity. To verify the validity of the modified RSF-PWM method, computer simulations are carried out.

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Paleoenvironments and Volcanism of the Ulleung Basin : Sedimentary Environment (울릉분지의 고환경과 화산활동 특성에 관한 연구 : 퇴적환경)

  • PARK Maeng-Eon;LEE Gwang-Hoon;SONG Yong-Sun
    • Korean Journal of Fisheries and Aquatic Sciences
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    • v.29 no.4
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    • pp.481-496
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    • 1996
  • The last Sea is a typical bark-arc basin consisting of basins, plateaus, ridges, and seamounts. The Ulleng Basin, located in the southwestern corner of the last Sea, contains thick Neogene sedimentary sequence. Analysis of over 2,500 km of single-channel seismic reflection data suggests that hemipelagic sedimentation prevailed over much of the basin during the late Miocene and pelagic sedimentation became more dominant during the Pliocene. During the Pleistocene terrigeneous sediments transported by turbidity currents and other gravity flows, together with continuous hemipelagic settling, resulted in well-stratified sedimentary layers. Influx of terrigenous sediments during the Pleistocene formed depocenters in the western and southern parts of the basins. In the Ulleung Interplain Gap, where the Ulleung Basin joins the deeper Japan Basin, sediment waves suggesting bottom current activities are seen.

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Study of Sound Transmission Characteristics of using a Scale Reverberation Chamber and vibro acoustic FEM (투과손실 예측을 위한 유한요소 해석과 소형 잔향실 실험의 비교에 검증에 관한 연구)

  • Lee, Jun-Heon;Kim, Bum-Soo;Kim, Kwan-Ju
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2011.10a
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    • pp.92-95
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    • 2011
  • The walls of modern train cars are required to have higher transmission loss since modern train have had high speed and light weight. The method based on Reverberation Chamber like KS F 2808 could be used to measure transmission loss. However, this method has difficulty in that constrained Standard of it requires extremely large facilities. Recently, the method based on Scale Reverberation Chamber is used as an alternative to Reverberation Chamber. The method of Scale Reverberation Chamber is known to be small and economical but it provides standing wave that directly influences measurement error. Therefore, this research is focus on predicting standing waves based on method of FFM and reducing measurement error by changing shape of chamber.

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Earthquakeproof Engineering by Metamaterials (메타물질을 이용한 내진설계)

  • Kim, Sang-Hoon
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2013.04a
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    • pp.97-99
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    • 2013
  • We introduced an earthquake-resistant design using acoustic rnetamaterials. There are two way in that field: one is a cloaking method and the other is a shadow zone method of seismic waves. Cloaking is a general property of a wave that changes the direction depending on the refractive index. Metamaterials control the propagation and transmission of specified parts of the wave and demonstrate the potential to render an object seemingly invisible. The shadow zone is a method of negative modulus using many huge resonators and it attenuates the amplitude of the wave exponentially. We compared and explained the fimdarnental principles of the two methods.

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Comparison of track vibration characteristics for domestic railway tracks in the aspect of rolling noise (철도 전동 소음의 관점에서 해석한 국내 철도의 진동 특성 비교)

  • Ryue, Jungsoo;Jang, Seungho
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2013.04a
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    • pp.644-647
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    • 2013
  • The important source of noise from railways is rolling noise caused by wheel and rail vibrations induced by acoustic roughness at the wheel-rail contact. The main contributors for rolling noise are the sleepers, rail and wheels. In order to analyze and predict rolling noise, it is necessary to understand the vibrating behaviors of railway tracks, as well as the wheels. In the present paper, theoretical modelings of the railway track are reviewed in terms of the rolling noise, and they are applied for the three representative types of domestic railway tracks operated: the conventional ballasted track, KTX ballasted track and KTX concrete track. The characteristics of waves propagating along rails were investigated and compared between the tracks. The tracks were modeled as discretely supported Timoshenko beams and compared in terms of the averaged squared amplitude of velocity which is directly related to the sound radiation from the rails.

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Measurement of plastic anisotropy of cold rolled steel sheets using electromagnetic acoustic transducer (EMAT를 이용한 냉연강판의 소성이방성 측정)

  • 황의찬;장경영;안봉영;이승석;김수광;김상영
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1994.10a
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    • pp.383-388
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    • 1994
  • Ultrasonic sensor for evaluating plastic anisotropy was developed. Magnetostrictive type EMAT is sensor to transmit and receive the Lamb wave using magnetostriction. It is suitable for on line processing because of transmitting and receiving ultrasonic without contact ODCs(orientation distribution coefficients), W $_{400}$. W $_{420}$. W $_{440}$. were respectively calculated using zeroth order Lamb wave velocities, the calculated ODCs was used for evaluating plastic anisotropy, the results was compared for mean values of destructive tests. Besides, the Lorentz EMAT for generating longitudinal wave and two shear waves simultaneously and the Lorentz type EMAT for measuring SH wave velocities were made. ODCs were calculated using the measured resonant modes and velocities. the results of two methods show possibility of an line processing measurement.

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Recent Ultrasonic Guided Wave Inspection Development Efforts

  • Rose, Joseph L.;Tittmann, Bernhard R.
    • Journal of the Korean Society for Nondestructive Testing
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    • v.21 no.4
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    • pp.371-382
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    • 2001
  • The recognition of such natural wave guides as plates, rods, hollow cylinders, multi-layer structures or simply an interface between two materials combined with an increased understanding of the physics and wave mechanics of guided wave propagation has led to a significant increase in the number of guided wave inspection applications being developed each year. Of primary attention Is the ability to inspect partially hidden structures, hard to access areas, and teated or insulated structures. An introduction to some physical consideration of guided waves followed by some sample problem descriptions in pipe, ice detection, fouling detection in the foods industry, aircraft, tar coated structures and acoustic microscopy is presented in this paper. A sample problem in Boundary Element Modeling is also presented to illustrate the move in guided wave analysis beyond detection and location analysis to quantification.

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Impact Localization of a Composite Plate Using a Single Transducer and Spatial Focusing Signal Processing Techniques (단일 센서와 공간집속 신호처리 기술을 이용한 복합재 판에서의 충격위치 결정)

  • Cho, Sungjong;Jeong, Hyunjo
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2012.10a
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    • pp.715-722
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    • 2012
  • A structural health monitoring (SHM) technique for locating impact position in a composite plate is presented in this paper. The technique employs a single sensor and spatial focusing properties of time reversal (TR) and inverse filtering (IF). We first examine the focusing effect of back-propagated signal at the impact position and its surroundings through simulation. Impact experiments are then carried out and the localization images are found using the TR and IF signal processing, respectively. Both techniques provide accurate impact location results. Compared to existing techniques for locating impact or acoustic emission source, the proposed methods have the benefits of using a single sensor and not requiring knowledge of material properties and geometry of structures. Furthermore, it does not depend on a particular mode of dispersive Lamb waves that is frequently used in the SHM of plate-like structures.

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