• Title/Summary/Keyword: Acoustic Test

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Full-Frequency Band Acoustic Analysis of Sandwich Composite Structure Using FE-BEM and SEA Method (FE-BEM 및 SEA 해석 기법을 활용한 샌드위치 복합재 구조물의 전 주파수 대역 음향 해석)

  • Lee, Dae-Oen;Lee, Yoon-Kyu;Kim, Hong-Il;Kim, Jae-Young
    • Journal of the Korea Institute of Military Science and Technology
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    • v.21 no.4
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    • pp.422-428
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    • 2018
  • Increase in use of lightweight structures, coupled with the increased acoustic loads resulting from larger and longer range guided missiles, has made missile more susceptible to failures caused by acoustic loads. Thus, accurate prediction of acoustic environment and the response is becoming ever more important for mission success. In this paper, the acoustic response of a sandwich composite skin structure to diffuse acoustic excitation is predicted over a broad frequency range. For the low frequency acoustic analysis, coupled FE-BEM method is used where the structure is modeled using FEM and the interior and exterior fluid is modeled using BEM. For the high frequency region, statistical energy analysis is applied. The predicted acoustic level inside the structure is compared with the result from acoustic test conducted in reverberation chamber, which shows very good agreement.

Evaluation of Acoustic Performance about Dome-typed Gymnastics Training Floor Using Auralization (가청화를 이용한 돔형 체조연습장의 음향 성능평가에 관한 연구)

  • Yun, Jae-Hyun;Ju, Duck-Hoon;Kim, Jae-Soo
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.17 no.8
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    • pp.708-719
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    • 2007
  • In case of indoor gymnastics training floor, in view of its characteristics, since it is simultaneously required the related smooth communication between the coach and the player, also the acoustic performance regarding to the clearness of music, besides the sport activity, the consideration about the acoustic character has entered the stage as an indispensable element. On such viewpoint, recently constructed dome-typed gymnastic training floor was optimized acoustic design with remodeling through acoustic simulation test. And acoustic satisfaction degree and reaction was attempted to investigate about the gymnastics training floor estimating value of human's psychological(sensual) degree using auralization that enables to experience the virtual sound field at the stage of design. As the result of investigation about the research on the space of object, it could be known that the valuation regarding to the acoustic performance of 'after-improvement' was distinctly more refined than that of 'before-improvement'. It is now considering that such result of the study can be utilized as the useful data which enables to improve the retrenchment effect of the construction cost as well as the acoustic capability, by means of the prediction control on the acoustic problem from the stage of design, for the occasion when the similar indoor sport gymnasium is planning to build for the near future.

An Experimental Study on the Friction of CrN Coated Specimen using the Acoustic Emission Sensor (AE 센서를 이용한 CrN 코팅의 마찰특성에 관한 연구)

  • 조정우;이영제
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 1999.06a
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    • pp.215-219
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    • 1999
  • One of the innovative physical methods that provide insight into the basic processes which determine friction and wear behavior of coated machine tools is acoustic emission (AE). In this study, an investigation of the relation between AE and friction signal produced during repeated sliding test is presented. The material of test specimens is CrN coated 0.2% plain carbon steel with 1 Um thickness. The obtained results demonstrate that AE signal is very related with friction, and AE signal is more sensitive than friction when CrN coated film come off the substrate.

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A Study on the Performance Prediction and Evaluation of Scale Down Noise Reducing Device on the Top of Noise Barrier (축소모형 방음벽 상단장치의 성능예측 및 평가에 관한 연구)

  • Yoon, Je-Won;Kim, Young-Chan;Jang, Kang-Seok;Hong, Byung-Kook
    • Proceedings of the KSR Conference
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    • 2011.10a
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    • pp.2844-2851
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    • 2011
  • The purpose of this study is to set up an acoustic prediction technique and to perform the IL test of scale down noise reducing device for the development of the noise reducing device as the development of 400km/h class high speed train. First of all, the IL prediction of noise reducing device was performed with the 2D BEM method. And the noise test of scale down noise reducing device in anechoic chamber was performed for the verification of acoustic prediction technique and IL performance evaluation. As the results, the acoustic prediction technique for the development of noise reducing device was verified because the averaged IL difference between prediction and test is in 2dB(A). And the measured IL value of noise reducing device is less than 2dB(A), and additional IL with polyester absorption material is increased about 0.5dB(A).

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Acoustic Emmision Characteristics according to Failure Modes of Pipes with Local Wall Thinning (감육배관의 손상모드에 따른 음향방출 특성)

  • 안석환;남기우;김선진;김진환;김현수;박인덕
    • Journal of Ocean Engineering and Technology
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    • v.16 no.5
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    • pp.66-72
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    • 2002
  • Fracture behaviors of pipes with local wall thinning are very important for the integrity of nuclear power plant. However, effects of local wall thinning on strength and fracture behaviors of piping system were not well studied. Acoustic emission(AE) has been widely used in various fields because of its extreme sensitivity, dynamic detection ability and location of growing defects. In this study, we investigated failure modes of locally wall thinned pipes and AE signals by bending test. From test results, we could be divided four types of failure modes of ovalization, crack initiation after ovalization, local buckling and crack initiation after local buckling. And fracture behaviors such as elastic region, yielding region, plastic deformation region and crack progress region could be evaluated by AE counts, accumulative counts and time-frequency analysis during bending test. The result of the frequency range is expected to be basic data that can inspect plants in real-time.

Acoustic Noise Measurement for the Wind Turbine Blade by Using Time-domain Beamforming (시간영역 빔포밍을 사용한 풍력터빈 축소모델 소음원 측정)

  • Cho, Tae-Hwan;Kim, Cheol-Wan
    • New & Renewable Energy
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    • v.5 no.2
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    • pp.25-30
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    • 2009
  • The wind tunnel test to identify the acoustic noise source position of the wind turbine blade was conducted in KARI low speed wind tunnel. Microphone array and time-domain beamforming methodology was applied to this study. To reduce the data processing time, a modified beamforming method with a criteria between calculation time step and grid size for rotating angle in the cylinderical coordinate system was proposed. The test results shows that the data processing time to identify the noise source position was reduced to 20% compared with conventional method. And the dominant noise source of the blade moves from inboard to blade tip as the frequency increases.

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Tendency of Calibration and Test for Acoustic Field in KRISS (KRISS 에서 수행된 음향관련 교정 및 시험 검사 동향)

  • Suh, Jae-Gap;Jung, Sung-Soo;Jho, Moon-Jae;Suh, Sang-Joon
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2000.06a
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    • pp.1767-1771
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    • 2000
  • We report the number of calibration and test for acoustic field which were conducted in KRISS between the year of 1990 and 1999. The items contain sound level meter and calibrator for calibration and sound absorption coefficient, transmission loss, sound pressure level of siren, sound pressure level and power of acoustic instrument and relative accessories for test. The data show that the number of them have been increased continuously.

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Acoustical Similarity for Small Cooling Fans Revisited (소형 송풍기 소음의 음향학적 상사성에 관한 연구)

  • 김용철;진성훈;이승배
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 1995.04a
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    • pp.196-201
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    • 1995
  • The broadband and discrete sources of sound in small cooling fans of propeller type and centrifugal type were investigated to understand the turbulent vortex structures from many bladed fans using ANSI test plenum for small air-moving devices (AMDs). The noise measurement method uses the plenum as a test apparatus to determine the acoustic source spectral density function at each operating conditions similar to real engineering applications based on acoustic similarity laws. The characteristics of fans including the head rise vs. volumetric flow rate performance were measured using a performance test facility. The sound power spectrum is decomposed into two non-dimensional functions: an acoustic source spectral distribution function F(St,.phi.) and an acoustic system response function G(He,.phi.) where St, He, and .phi. are the Strouhal number, the Helmholtz number, and the volumetric flow rate coefficient, respectively. The autospectra of radiated noise measurements for the fan operating at several volumetric flow rates,.phi., are analyzed using acoustical similarity. The rotating stall in the small propeller fan with a bell-mouth guided is mainly due to a leading edge separation. It creates a blockage in the passage and the reduction in the flow rate. The sound power levels with respect to the rotational speeds were measured to reveal the mechanisms of stall and/or surge for different loading conditions and geometries, for example, fans installed with a impinging plate. Lee and Meecham (1993) studied the effect of the large-scale motions like impinging normally on a flat plate using Large-Eddy Simulation(LES) and Lighthill's analogy.[ASME Winter Annual Meeting 1993, 93-WA/NCA-22]. The dipole and quadrupole sources in the fans tested are shown closely related to the vortex structures involved using cross-correlations of the hot-wire and microphone signals.

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Pressure Characteristics on Korean High-Speed Railway Acoustic Screen Using 1/61 Scaled-Down Moving Model Rig

  • Jang, Yong-Jun;Kim, Hag-Beom;Jung, Woo-Sung;Kim, Dong-Hyeon
    • International Journal of Railway
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    • v.2 no.2
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    • pp.93-97
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    • 2009
  • The experiments for aerodynamic characteristics of railway acoustic screen are performed using 1/61 scaled-down moving model rig facility which employs an axis symmetry and one wire guidance method. The launching mechanism is an air-gun type. The train model for the experiment is the high speed train (Korea Train Express: KTX) and the tested speed is about 300 km/h. The tested train length is 61 em which is corresponding to two units of KTX train. The cross sectional area and weight of train model are 0.00264 $m^2$ and 287 g, respectively. The Reynolds number based on the model train length is $1.2{\times}10^7$. The strength of pressure wave is measured using piezo typed pressure sensor. The measured pick value of pressure was as high as 365 Pa in the shortest gap between the acoustic screen and model train. The measured pressure is well compared with the field test data of mc 779-1 [2] values. However, the experimental data were slightly lower than the mc 779-1 values. The results show the model test can be used as a substitute for the field test.

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Study on Real-Time Weld Quality Evaluation by Acoustic Emission for Production of Drills by Friction Weldiing (마찰용접에 의한 드릴 생산에서의 AE에 의한 실시간 품질평가에 관한 연구)

  • 오세규;윤인진;오정환;오명석
    • Journal of Ocean Engineering and Technology
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    • v.7 no.2
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    • pp.121-130
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    • 1993
  • A study off riction welding of high speed steel(SKH 51) bar for blade side to carbon steel(STC 3)bar for shank side was carried out experimentally through tensile test, hardness test, microstructure, and acoustic emission (AE) test. So, this paper deals with optimizing the welding conditions and the real-time quality (strength) evaluation of friction weleded joints by acoustic emission technique. The results obtained are summarized as follows: (1) For friction welded joints of SKH 51to STC 3 steel bars, the total upset (U) increases linearly with an increase of heating time (t sub(1)). (2) The determined optimum welding conditions are heating time (t sub(1)) 7-9 sec, upsetting time (t sub(2)) 5 sec, heating pressure(P sub(1)) 12 kg sub(f)mm supper(2), upsetting pressure (P sub(2)) 15 kg sub(f) mm supper(2) and rotating speed (n) 2, 000 rpm, resulting in a computed relationship between the tensile strength of the joint .sigma. (kg sub(f) mm supper(2)) and the heating time t sub(1) (sec) as the following. sigma.=2.39t sub(1)

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