• 제목/요약/키워드: Acoustic Space

검색결과 485건 처리시간 0.191초

A Performance Analysis of Active Mount with Moving-Coil type Electromagnetic Actuator Installed on the Elastic Foundation (탄성지지된 가동코일형 능동마운트의 성능 분석)

  • Jung, Woo-Jin;Bae, Soo-Ryong;Jeon, Jae-Jin
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 한국소음진동공학회 2014년도 추계학술대회 논문집
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    • pp.227-231
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    • 2014
  • Underwater radiated noise is one of the vital factors in underwater weapon systems like submarine. A passive elastic mount is an effective reduction method for the vibration from a ship-board machinery transmitted to the hull which is radiated as noise outside the hull. A passive elastic mount shows the limitation on the vibration reduction and needs multi stage mounting system including double stage one to meet the required underwater radiated noise criteria. It is necessary for the multi stage mounting system to consider the large displacement in the underwater shock explosion. So it is difficult to apply the multi stage mounting system in submarine because of space limitation. Also recent navy sonar system are trying to have the capability to detect the ship-borne acoustic signals in the low frequency range. An alternative to the passive mount is an active mount with moving-coil type electromagnetic actuator based on a conventional rubber mount in the low frequency range. In the previous paper, 4 active mounts with moving-coil type electromagnetic actuator based on the rubber mount were installed on the hard floor of the facility, which means no consideration on the elastic foundation effect for the control of the active mounts was taken into account. In this study, an experimental performance analysis on the active mount was carried out using 4 active mounts installed on the cylindrical structure to investigate the elastic foundation effect.

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Speech Quality Estimation Algorithm using a Harmonic Modeling of Reverberant Signals (반향 음성 신호의 하모닉 모델링을 이용한 음질 예측 알고리즘)

  • Yang, Jae-Mo;Kang, Hong-Goo
    • Journal of Broadcast Engineering
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    • 제18권6호
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    • pp.919-926
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    • 2013
  • The acoustic signal from a distance sound source in an enclosed space often produces reverberant sound that varies depending on room impulse response. The estimation of the level of reverberation or the quality of the observed signal is important because it provides valuable information on the condition of system operating environment. It is also useful for designing a dereverberation system. This paper proposes a speech quality estimation method based on the harmonicity of received signal, a unique characteristic of voiced speech. At first, we show that the harmonic signal modeling to a reverberant signal is reasonable. Then, the ratio between the harmonically modeled signal and the estimated non-harmonic signal is used as a measure of standard room acoustical parameter, which is related to speech clarity. Experimental results show that the proposed method successfully estimates speech quality when the reverberation time varies from 0.2s to 1.0s. Finally, we confirm the superiority of the proposed method in both background noise and reverberant environments.

Numerical Analysis of Rail Noise Regarding Surface Impedance of Ground by Using Wavenumber Domain Finite and Boundary Elements (지면 임피던스를 고려한 레일 방사 소음의 파수영역 유한요소/경계요소 해석)

  • Ryue, Jungsoo;Jang, Seungho
    • Journal of the Korean Society for Railway
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    • 제18권4호
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    • pp.289-300
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    • 2015
  • An important source of noise from railways is rolling noise caused by wheel and rail vibrations induced by acoustic roughness at the wheel-rail contact. In conventional approaches to predicting rail noise, the rail is regarded as placed in a free space so that the reflection from the ground is not included. However, in order to predict rail noise close to the rail, the effect of the ground should be contained in the analysis. In this study the rail noise reflected from the ground is investigated using the wavenumber domain finite element and boundary element methods. First, two rail models, one using rail attached to the rigid ground and one using rail located above rigid ground, are considered and examined to determine the rigid ground effect in terms of the radiation efficiency. From this analysis, it was found that the two models give considerably different results, so that the distance between the rail and the ground is an important factor. Second, an impedance condition was set for the ground and the effect of the ground impedance on the rail noise was evaluated for the two rail models.

An Objective Performance Analysis of Crosstalk Cancellation Scheme for Sound Rendering Systems Based on Listener Position Tracking (청취자 위치정보 기반 Sound Rendering 시스템 상호간섭 제거기법의 객관적 성능분석)

  • Lee, Jung-Hyuck;Kim, Yeong-Moon;Yoo, Seung-Soo;Kim, Sun-Yong
    • The Journal of Korean Institute of Communications and Information Sciences
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    • 제36권2C호
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    • pp.112-118
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    • 2011
  • In this paper, we conduct an objective performance analysis of the crosstalk cancellation scheme studied in [11]. While the conventional scheme is only applicable to a listener on the optimal listenable region (sweetspot), the space skew/crosstalk cancellation (SS/CC) scheme in [11] can mitigate crosstalk regardless of the listener's position by using listener position tracking (LPT) system. The SS/CC scheme is composed of two parts: LPT-based SS and CC parts. In this paper, the SS/CC scheme is evaluated by some criteria such as follows: condition number, and the balance characteristic, its root mean square error, and running average.

Error analysis of acoustic target detection and localization using Cramer Rao lower bound (크래머 라오 하한을 이용한 음향 표적 탐지 및 위치추정 오차 분석)

  • Park, Ji Sung;Cho, Sungho;Kang, Donhyug
    • The Journal of the Acoustical Society of Korea
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    • 제36권3호
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    • pp.218-227
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    • 2017
  • In this paper, an algorithm to calculate both bearing and distance error for target detection and localization is proposed using the Cramer Rao lower bound to estimate the minium variance of their error in DOA (Direction Of Arrival) estimation. The performance of arrays in detection and localization depends on the accuracy of DOA, which is affected by a variation of SNR (Signal to Noise Ratio). The SNR is determined by sonar parameters such as a SL (Source Level), TL (Transmission Loss), NL (Noise Level), array shape and beam steering angle. For verification of the suggested method, a Monte Carlo simulation was performed to probabilistically calculate the bearing and distance error according to the SNR which varies with the relative position of the target in space and noise level.

Wave Generation and Its Effect on Lesion Detection in Sonoelastography: Theory and Simulation Study (음향 탄성영상법에서 연조직 내 파동 발생과 병변 검출의 특성: 이론 및 시뮬레이션 연구)

  • 박정만;권성재;정목근
    • The Journal of the Acoustical Society of Korea
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    • 제24권5호
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    • pp.282-293
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    • 2005
  • Sonoelastography is an ultrasound-based technique that visualizes the elastic properties of soft tissues by measuring the tissue motion generated by an externally applied vibration. In this paper. the characteristics of wave generation in soft tissues due to an acoustic vibrator are studied. The effects of modal patterns on the detectability of lesions such as tumors in senoelastography are also investigated These are accomplished by analyzing the vibration patterns calculated using theoretical equations and finite element methods in halt space, infinite plate. and finite-sized tissue. A finite-width source generates shear waves with large amplitude Propagating in specific directions. and the generation characteristics depend both on the width and frequency of the vibrator. as well as the distance from it. It is shown in a finite-sized tissue that the lesion detection in displacement images is quit dependent on the modal patterns inside tissue. In contrast it Is also found that the lesion detectability in strain images is less dependent on the modal Patterns and is much better than that in displacement images.

Dynamic Characteristics of Coaxial Swirl-Jet Injector with Acoustic Excitation (동축형 스월-제트 인젝터의 음향가진에 따른 동특성)

  • Bae, Jinhyun;Kim, Taesung;Jeong, Seokgyu;Jeong, Chanyeong;Choi, Jeong Yeol;Yoon, Youngbin
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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    • pp.691-698
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    • 2017
  • In this study, the injector transfer function (ITF) of a gas-gas coaxial jet-swirl injector is measured by applying excitation to jet or swirl flow using a loudspeaker. As a result of measuring the ITF according to the variation of feed system length, the ITF peak occurs at the resonance frequency of the space where the perturbed flow passes. When applying the excitation to the jet flow, as the jet flow increases up to 56 slpm, the magnitude of ITF decreases, and ITF increases thereafter. Therefore the larger the velocity difference between the jet and the swirl flow, the larger the ITF. In the case of the swirl excitation, the ITF decreases as the jet flow increases because of the decrease of the energy with respect to the constant flow at the downstream. This difference is caused by the location of the hot wire anemometer on the downstream of the injector center axis.

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Compressible Simulation of Rotor-Stator Interaction in Pump-Turbines

  • Yan, Jianping;Koutnik, Jiri;Seidel, Ulrich;Hubner, Bjorn
    • International Journal of Fluid Machinery and Systems
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    • 제3권4호
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    • pp.315-323
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    • 2010
  • This work investigates the influence of water compressibility on pressure pulsations induced by rotor-stator interaction (RSI) in hydraulic machinery, using the commercial CFD solver ANSYS-CFX. A pipe flow example with harmonic velocity excitation at the inlet plane is simulated using different grid densities and time step sizes. Results are compared with a validated code for hydraulic networks (SIMSEN). Subsequently, the solution procedure is applied to a simplified 2.5-dimensional pump-turbine configuration in prototype with different speeds of sound as well as in model scale with an adapted speed of sound. Pressure fluctuations are compared with numerical and experimental data based on prototype scale. The good agreement indicates that the scaling of acoustic effects with an adapted speed of sound works well. With respect to pressure fluctuation amplitudes along the centerline of runner channels, incompressible solutions exhibit a linear decrease while compressible solutions exhibit sinusoidal distributions with maximum values at half the channel length, coinciding with analytical solutions of one-dimensional acoustics. Furthermore, in compressible simulation the amplification of pressure fluctuations is observed from the inlet of stay vane channels to the spiral case wall. Finally, the procedure is applied to a three-dimensional pump configuration in model scale with adapted speed of sound. Normalized Pressure fluctuations are compared with results from prototype measurements. Compared to incompressible computations, compressible simulations provide similar pressure fluctuations in vaneless space, but pressure fluctuations in spiral case and penstock may be much higher.

A New Current Control Algorithm for Torque Ripple Reduction of BLDC Motors (BLDC 전동기의 토크리플 저감을 위한 새로운 전류제어 알고리즘에 대한 연구)

  • 김태성;안성찬;현동석
    • The Transactions of the Korean Institute of Power Electronics
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    • 제6권5호
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    • pp.416-422
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    • 2001
  • The BLDC(Brushless DC) Motor is characterized by linear torque to current and speed to voltage. It has low acoustic noise and fast dynamic response. Moreover, it has high power density with high proportion of torque to inertia in spite of small size drive. However, when armature current is commutated, the current ripple is generated by the motor inductance components in stator windings and back-EMF. This current ripple caused to torque ripple. Therefore, it is difficult to apply the BLDC motor to a precision servo drive system. In this paper, a new current control algorithm using fourier series coefficients is proposed. This proposed algorithm can minimize torque ripple due to the phase current commutation of BLDC motor. Simulation and Experimental results prove the effectiveness at the Proposed algorithm through comparison with the conventional unipolar PWM method.

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A Study on the Simulator for the fabrication of bandpass filter for the Wide-band Codeless Division Multiple Access (광 대역 통과 필터 제작을 위한 모의 실험기)

  • 유일현
    • Journal of the Korea Institute of Information and Communication Engineering
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    • 제8권3호
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    • pp.686-693
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    • 2004
  • We have studied a method to fabricated a Surface Acoustic Waves (SAW) filter for Wide band Codeless Division Multiple Access(WCDMA) was formed on the Langasite substrate and was evaporated by Aluminum-Copper alloy and then we developed a simulator using the mathematica package. And, we can design and fabricate the Slanted finger Inter-digital Transducer (SFIT) for the purpose to decreased the ultimate rejections on side of the electrodes, and performed computer-simulation by simulator. Also, we have employed that the block weighted type Inter-digital Transduce(IDT) as input transduce of the filter and the withdrawal weighted type IDT as an output transducer of the filter in order to minimize effect of diffractions. We have employed that the number of pairs of the input and output IDT are 50 pairs and the thickness and the width of reflector are $5000\AA$, and $1\lambda/4(\cong3.6{\mu}m)$, respectively. Also the width of IDT' finger and the space between IDT' finger and reflector are $1\lambda$/16 and 1\lambda$/8, respectively. Frequency response of the fabricated SAW bandpass filter has the property that center frequency is about 190MHz, bandwidth at the 3dB is probably 4MHz and out-band attenuation is -60dB approximately.