• Title/Summary/Keyword: 반향음 감소

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Simulation of underwater echo reduction using miniaturized Helmholtz resonators (소형화된 헬름홀츠 공진기를 이용한 수중 반향음 감소해석 모의실험)

  • Park, SungJun;Kim, Jedo
    • The Journal of the Acoustical Society of Korea
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    • v.38 no.1
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    • pp.67-72
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    • 2019
  • In this study, we investigate the echo reduction performance of miniaturinzed Helmholtz resonators using smaller than wavelength acoustic metamaterial structures. The Helmholtz resonators are formed using air structures which exhibit large impedance mismatch with the surrounding underwater environment. Using the multi-physics software package, we find that significant reduction in the sonar signature is expected and frequency tailoring is possible by controlling the degree of space coiling and inner volume of the resonators. We find that for the basic Helmholtz resonators, up to 7 dB reduction in echo is expected at 10,000 Hz while when the miniaturized Helmoholtz resonators are used, up to 14 dB reduction in echo is expected at 5,000 Hz. In addition, frequency tailoring is demonstrated by varying the internal volume of the Helmholtz resonators and broadband characteristic is shown using superposition of various degree of space coiled structures. Through this study we investigate the effectiveness of the miniaturized Helmholtz resonators formed using air structures and the echo reduction results show promisses in the application of achieving underwater stealth.

A single sensor based active reflection control system using FxLMS algorithm (FxLMS를 이용한 단일 센서기반 능동 반향음 제어 시스템)

  • Kim, Jaepil;Ji, Youna;Park, Young cheol;Seo, Young soo
    • The Journal of the Acoustical Society of Korea
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    • v.36 no.1
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    • pp.57-63
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    • 2017
  • This paper presents an active acoustic-reflection control algorithm based on a single sensor. The proposed algorithm operates in a system comprising a single sensor located nearby the reflective surface and a control transducer mounted on the reflective surface. First, the incident and reflected acoustic signals are separated from the sensor signal, and a control signal is generated using the separated signals. For the signal separation, the proposed algorithm requires the response of the reflection path which is estimated from the acoustic response between an external sound source and the sensor. Finally, the control filter is adjusted using the FxLMS (Filtered-x Least Mean Square) algorithm. To verify the effectiveness of the proposed algorithm, it was implemented in real time using a DSP (Digital Signal Processing) board, and the experimental results obtained in one-dimensional air-acoustic environment show that the reflections of the 1 kHz burst can be reduced by 11.6 dB.

An Acoustic Reception Ability Analysis of SONAR Multilayer Structures by Using Elastic Theory (탄성이론을 이용한 소나 다층구조물의 음향 수신 성능해석)

  • Kwon, Hyun-Wung;Hong, Suk-Yoon;Song, Jee-Hun;Kim, Sung-Hee;Jeon, Jae-Jin;Seo, Young-Soo
    • The Journal of the Acoustical Society of Korea
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    • v.32 no.4
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    • pp.301-307
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    • 2013
  • SONAR detection performance is one of the key survivability factors in underwater weapon systems. In order to catch the acoustic ability of SONAR, multilayer SONAR structures are analyzed using the elastic theory. The applied results for the simple models are compared with those from commercial program, ANSYS, and the reliable results are obtained. The analysis of sound pressure level (SPL) and echo reduction (ER) by the thickness change of multilayer SONAR structures are performed using the verified elastic theory. As the thickness of anechoic layer is increased, SPL is distributed evenly and ER is increased slightly with the frequency. In decoupling layers and steel layers, SPL are hardly changed and ER is slightly decreased with the thickness increase of those layers. SPL and ER are not affected by the thickness change of the carbon reinforced plastic (CRP) layer. Therefore, to improve the acoustic ability of multilayer SONAR structures, the thickness increase of the anechoic layer and minimization of the decoupling layer, steel layer and CRP layer are desirable.

Low-Frequency Active Echo Reduction Using a Tile Projector (타일형 프로젝터를 이용한 저주파 능동 반향음 감소 기법)

  • Lee, Jae-Wan;Woo, Sangbeom;Jang, Hada;Lee, Keunsang;Kim, Wan-Gu;Kang, Hwi-Suk;Ohm, Won-Suk;Park, Youngcheol;Yoon, Suk Wang;Seo, Youngsoo
    • The Journal of the Acoustical Society of Korea
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    • v.33 no.6
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    • pp.366-374
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    • 2014
  • With the advent of submarine detection technology using low-frequency active sonar there is a call for a new submarine stealth device that can replace the existing passive anechoic tiles. Proposed in this study is a low-frequency echo reduction technique based on active impedance matching, which employs a tile projector designed to cover a wide area such as the surface of a ship. To judge the feasibility of the active impedance matching technique finite-element simulations of low-frequency echo reduction are performed. Based on the analysis, a tile projector is designed, fabricated, and tested in an acoustic tank for its low-frequency echo reduction performance.

A design of optimal filter for single sensor based acoustic reflection control (단일 센서 기반 반향음 제어를 위한 최적 필터 설계)

  • Jeon, Shin-Hyuk;Ji, Youna;Park, Young-cheol;Seo, Young-Soo
    • The Journal of the Acoustical Society of Korea
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    • v.36 no.5
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    • pp.353-360
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    • 2017
  • The single sensor based acoustic reflection control system separates the incident and reflected signals from the single sensor output, and reduces the reflected signal by generating an out-of-phase signal from the incident signal component. In this paper, we propose an optimal filter design method for a single sensor based reflection control system. In the proposed method, it is shown that the optimum control filter design is possible by using the measured impulse responses of the reflection and control paths. The reflection control algorithm based on the proposed optimal filter achieves better performance than the conventional adaptive filter-based algorithm and effectively controls the reflection without the initial convergence time. We performed computer simulations using the signals obtained in a 1-dimensional acoustic duct environment, and from the simulation results, it was confirmed that the proposed optimal filter has robust performance even in noisy environment.

Measurement System for Performance Evaluation of Acoustic Materials in a Small Water Tank (소형수조에서 음향재료의 반향음감소와 투과손실 측정시스템 구성)

  • Shin, Mi-Ru;Cho, Jung-Hong;Lee, Kyung-Teak;Kim, Jea-Soo;Jeon, Jae-Jin;Ham, Il-Bea;Kang, Chang-Gi
    • The Journal of the Acoustical Society of Korea
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    • v.30 no.2
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    • pp.63-72
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    • 2011
  • Since the detection probability is critically dependent on the target strength (TS) in active sonar and on the radiated noise level (RNL) in passive sonar, the acoustic materials for echo reduction (ER) and transmission loss (TL) are widely used for the stealth of underwater targets. In this paper, a measurement system based on the small water tank, for the frequency range of greater than 30 kHz, is developed and verified using reference targets. In order to design the water tank and the geometry of test samples, a program is developed to calculate the arrival time of interfering signals due to the reflection from water tank walls and also due to the diffraction from the edge of the test samples. Considering all the interfering signals, an optimal experimental configuration for water tank and test samples is designed and used throughout the experiment. Next, the signal processing algorithms to estimate ER and TL are developed based on the measured propagation loss reflecting the geometric spreading characteristics of the transducer. Finally, a set of reference targets such as aluminium plate and perfectly reflecting plate are used in a small water tank to verify the developed measurement system.

A Study of Echo Reduction of Underwater Acoustic Material Considering Ocean Condition (수중환경을 고려한 수중 음향재료의 반향음 감소성능 연구)

  • Seo, Young Soo;Ham, Il Bae;Jung, Woo Jin
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2014.10a
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    • pp.377-384
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    • 2014
  • The requirement of acoustic material which is used in underwater environment more increases. The material is used to reduce acoustic signature and radiate noise for underwater vehicle. Underwater acoustic material was made by viscoelastic material such as a rubber and a polyurethane etc. The mechanical and acoustic characteristics of these material change with hydrostatic pressure. In order to increase an acoustic performance according to hydrostatic pressure, several kinds of scatterers were added to viscoelastic material. In this paper, acoustic modelling and analysis techniques of underwater acoustic material with hydrostatic pressure were introduced and proposed. The specimens for pulse tube test were made and echo reductions were calculated and measured with hydrostatic pressure. Also the characteristics of echo reduction of the specimens with hydrostatic pressure were obtained and discussed.

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A Study on the Echo Reduction Performance of Underwater Acoustic Material (수중 음향재료의 반향음 감소성능 연구)

  • Seo, Young Soo;Ham, Il Bae;Jung, Woo Jin
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.24 no.11
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    • pp.868-875
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    • 2014
  • The requirement of acoustic material which is used in underwater environment more increases. The material is used to reduce acoustic signature and radiate noise for underwater vehicle. Underwater acoustic material was made by viscoelastic material such as rubber and polyurethane etc. The mechanical and acoustic characteristics of these material change with hydrostatic pressure. In order to improve an acoustic performance according to hydrostatic pressure, several kinds of scatterers were added to viscoelastic material. In this paper, acoustic modelling and analysis techniques of underwater acoustic material with hydrostatic pressure were introduced and proposed. The specimens for pulse tube test were made and echo reductions were calculated and measured with hydrostatic pressure. Also the characteristics of echo reduction of the specimens with hydrostatic pressure were obtained and discussed.

A Study on the Low-frequency Active Echo Reduction Technology for Reducing Underwater Target Echo Signal (수중 표적 신호 방해를 위한 저주파 능동 반향음 감소 기술 연구)

  • Kim, Jaepil;Ji, Youna;Park, Young-cheol;Noh, Eunghwy;Ohm, Won-Suk;Choi, Yonggyu;Kim, Daeup;Seo, Youngsoo
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.27 no.1
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    • pp.43-50
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    • 2017
  • Acoustic tiles are typically installed on the surface of pressure vessels in submarines to minimize echoes based on the ship's own noise and active sonar. In this study, we studied low frequency active echo reduction techniques to reduce underwater target echo signals. Active control algorithms using tile type projectors and FxLMS logic have been developed and the projectors have been installed in the assumed hull structure. The effectiveness of projectors and control algorithms has been evaluated in time and frequency domain analysis through experiments in the tank.

A Study on the Acoustic Performance Design Technique of Underwater Acoustic Material (수중 음향재료의 음향성능 설계기법 연구)

  • Seo, Youngsoo;Ham, Ilbae;Jeon, Jaejin
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.23 no.10
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    • pp.920-927
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    • 2013
  • The requirement of acoustic performance about underwater acoustic material which is used in underwater environment more increases. Underwater acoustic material was made by viscoelastic material such as a rubber and a polyurethane etc. In order to increase an acoustic performance, several kinds of inclusions were added to viscoelastic material. In this paper, acoustic modelling and analysis techniques were introduced and the acoustic characteristics of underwater acoustic material were studied. Echo reduction and transmission loss were calculated with volume fraction of inclusion in the material. Also the characteristic impedance and the input impedance of underwater acoustic material were obtained and effects on the echo reduction and transmission loss of material were discussed.