• The Journal of the Acoustical Society of Korea
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• v.33 no.4
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• pp.238-247
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• 2014

In this paper, rail vibration and its sound radiation are investigated, then the rail noise measurement by using microphone array is explored theoretically. A concrete slab track for domestic high speed trains is modeled as a Timoshenko beam on elastic support, regarding the moving of the excitation force on the rail. From the radiation characteristics of rail noise generated by a line source, the effect of moving load on sound radiation is obtained. Also it is found that the beam angle of the microphone array is a prominent factor to measure the rail noise level reliably because the rail noise propagates as a plane wave. In this investigation, a proper beam angle for the rail noise measurement by microphone array is suggested.

• The Journal of the Acoustical Society of Korea
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• v.37 no.4
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• pp.233-241
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• 2018

In this paper, we develop a durability test method that can verify the noise caused by the repeated load on the door trim grip handle. The test method was developed in consideration of the load mode and durability test cycle applied to the grip handle. In order to verify the validity of the method, we demonstrated the door trim grip handle noise that occurred in the field claim with the product in the early stage of mass production through the developed test method. Finally, It is used to detect and improve the noise of subsequent development products through the currently developed test method.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.2
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• pp.125-131
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• 2002

we analyzed acoustic emission signals obtained from three kinds of brittle materials under compression load by Vickers hardness tester. The results obtained can be summarized as follows; The signal in each material could be divided into three signal based on the properties of load. All specimens were not detected acoustic emission signals in stage II which was load constant region., and were detected in stage I and stage III. Glass was detected high amplitude signals in stage III. $Al_2O_3\;and\;Al_2O_3/Sic$ were detected high amplitude signals in stage I.

• The Journal of the Acoustical Society of Korea
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• v.26 no.6
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• pp.235-242
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• 2007

The test and evaluation of floor impact sound is mainly conducted before move in the residence. Floor impact sound generating is actually the conditions in which a heavy load like a curtain and furniture is installed, the situation before and after move in the residence is different. In this study, we investigate the floor impact sound variations according to the live load installation like furniture in the source room. The vibration acceleration level and floor impact sound level variation were measured before and after live load ($200kg/m^2$) installation in the floor impact sound test building and the field. The difference was not large although the vibration acceleration level and the floor impact sound level were reduced through measurement result of load installation. Resonance frequency was not changed by load installation.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.12
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• pp.1146-1151
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• 2011

Acoustic load from rocket propulsion system is main source of random vibration working on the payload. To protect payload from this acoustic load, additional APS(acoustic protection system) is generally applied. Noise reduction capacity of APS can be verified through acoustic test and vibro-acoustic coupled analysis. This paper compared the results of acoustic test and vibro-acoustic coupled analysis about KSLV-I payload fairing with APS.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.244-249
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• 2011

The potential hazards resulting from a low-velocity impact (bird-strike, tool drop, runway debris, etc.) on aircraft structures, such as engine nacelle or a leading edges, has been a long-term concern to the aircraft industry. Certification authorities require that exposed aircraft components must be tested to prove their capability to withstand low-velocity impact without suffering critical damage. In most of the past research studies unloaded specimens have been used for impact tests, however, in reality it is much more likely that a composite structure is exposed to a certain stress state when it is being impacted, which can have a significant effect on the impact performance. And the radiated impact sound induced by impact is analyzed for the damage detection evaluation. In this study, an investigation was undertaken to evaluate the effect in-plane loading on the impact force and sound of composite laminates numerically.

• Journal of the Korean Society for Nondestructive Testing
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• v.18 no.5
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• pp.365-372
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• 1998

The method of measuring the nonlinear effect of ultrasonic waves is suggested as a new approach for the effective evaluation of material degradation. In sonic wave propagation, the existence of nonlinear effect can be demonstrated by the generation of higher order harmonic waves. So, at first, the mechanism of generating higher order harmonic components due to nonlinear effect was explained by using nonlinear elasticity. Next, we attempted to measure how much of the higher order harmonic component was generated in the degraded material. For this purpose, a measurement system mainly based on a high-powered nonlinear ultrasonic signal analysis system was constructed, and SS41 and SS45 specimen intentionally degraded by tensile load and fatigue load were tested. From the results, we confirmed that the measurement of nonlinear acoustic effect may be useful for the evaluation of material degradation.

• Transactions of the KSME C: Technology and Education
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• v.5 no.2
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• pp.127-134
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• 2017

The reactor internals shall be secured in safety and structural integrity under various vibrational loading conditions. Thus, U.S. NRC, Regulatory Guide 1.20 requires the evaluation for the reactor internals due to acoustic induced vibration including the response to the reactor coolant pump pressure pulsation. This paper suggests a methodology to develop an analytical model of the core support barrel accounting for the fluid around the structure and to analyze the responses to the pump pulsation loads using acoustic structure interaction analysis. The analysis results were compared with those of US Palo Verde 1 CVAP and showed a good agreement. Thus, it is expected that the suggested methodology could be an efficient way to evaluate the response of the core support barrel to the pump pulsation loads.

• Composites Research
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• v.14 no.5
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• pp.46-53
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• 2001

In this research, damage behavior of singly oriented ply (SOP) fiber metal laminate (FML) subjected to concentrated load was studied. The static indentation tests were conducted to study fiber orientation effect on damage behavior of FML. During the static indentation tests, acoustic emission technique (AE) was adopted to study damage characteristics of FML. AE signals were obtained by using AE sensor with 150kHz resonance frequency and the signals were compared with indentation curves of FML. The damage process of SOP FML was divided by three parts, i.e., crack initiation, crack propagation, and penetration. The AE characteristics during crack initiation show that the micro crack is initiated at lower ply of the plate, then propagate along the thickness of the plate with creating tiber debonding. The crack grow along the fiber direction with occurring 60∼80dB AE signal. During the penetration, the fiber breakage was observed. As fiber orientation increases, talc fiber breakage occurs more frequently. The AE signal behaviors support these results. Cumulative AE counts could well predict crack initiation and crack propagation and AE amplitude were useful for the prediction of damage failure mode.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.234-237
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• 2007

To protect a satellite and electronic equipment from the acoustic load generated by rocket propulsion system, many launch vehicle use acoustic blanket. Acoustic load is main source of random vibration working on the payload. Most high frequency region of the acoustic loads is reduced by payload fairing skins and acoustic blanket, but low frequency region is not. In order to reduce acoustic load of low frequency region, we designed array resonator panel which was made of composite materials. Insertion loss capacity of the payload fairing with acoustic blanket was verified from PLF acoustic test in the acoustic chamber.