• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.220-223
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• 2007

Acoustic test of the payload fairing of Korea satellite launch vehicle was conducted to verify the performance of acoustic protection system installed inside the payload fairing. This paper briefly introduces the acoustic test procedures and its results. Overall 148 dB acoustic loads were exerted on the payload fairing structures which mated with the upper stage structure of the launch vehicle. In order to verify the increase of insertion loss by the acoustic protection system, two kinds of test were performed. One is conducted with acoustic protection system and the other without acoustic protection system. Internal acoustic loads as well as external ones were measured and the measured insertion losses were compared with the requirement. The results showed that the acoustic protection system increases the insertion loss by more than 6 dB above 125 Hz. They also indicated that some design modification of Helmholtz resonator array is required to increase the insertion loss at a cavity resonant frequency.

• Aerospace Engineering and Technology
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• v.7 no.2
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• pp.117-122
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• 2008

Acoustic test was performed to verify the ability of KSLV-I PLF acoustic protection system (Acoustic blanket) to reduce the acoustic load. The test results showed that the acoustic protection system has +3 dB safety margin compared with design requirement. This paper also illustrates the increase of insertion loss by the acoustic protection system by comparing that of the bare PLF structure.

• 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.196-201
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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.

• Journal of Sensor Science and Technology
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• v.13 no.6
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• pp.479-487
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• 2004

The prevention of noise induced hearing loss is very important, because there is no treatment for it. There are some kinds of devices for hearing protection, and those are effective in preventing a noise induced hearing loss. However, people often resist the use of hearing protection devices because it is difficult to have a conversation. Therefore, a hearing protection device is must effective not only in hearing protection but also in preserving communication ability. In this paper, we proposed a small acoustic filter for ITE type noise protector to solving the problem about the difficulties of conversation. That is applied a principle of acoustic filters that have been used for a muffler of automobiles, guns, and etc. To find out the sound transmission characteristic at the eardrum, we regarded an acoustic filter and external ear canal as a coupled system. So, we simulated the coupled system with OrCad, and experimented with a designed acoustic filter and a 2 cc coupler which has the same transmission characteristic as the external ear canal has. We confirmed that it is possible to adjustment acoustic transmission characteristics through simulation of electrical model for acoustic filter and external ear and experiments using designed small acoustic filters.

• Journal of Sensor Science and Technology
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• v.28 no.5
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• pp.318-322
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• 2019

In shooting training, an impact point identification system that uses the impact wave of the bullet to check the impact point in the target plate has been recently used. Acoustic sensors used in these systems must be able to detect shock waves of high sound pressure levels and be both waterproof and dustproof for rainy weather and dusty environments, respectively. In this study, membranes with excellent waterproof, dustproof, and sound transmitting characteristics were selected through a characteristics test; a protection cap was installed to install the selected materials. After coupling the produced protection cap to the acoustic sensor housing, the sensitivity and phase characteristics of the acoustic sensor were checked. Through the waterproof and dustproof test, the performances of its sensitivity and phase characteristics were confirmed. Finally, the normal shockwave of a 5.56 mm diameter bullet was measured using a shockwave detection signal collecting plate equipped with a prototype of the acoustic sensor at a 100 m firing range.

• Smart Structures and Systems
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• v.32 no.4
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• pp.195-205
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• 2023

The contact acoustic emission (AE) monitoring system is time-consuming and costly for monitoring concrete structures in large scope, in addition, the great difference in acoustic impedance between air and concrete makes the detection process inconvenient. In this work, we broaden the conventional AE source localization method for concrete to the non-contact (air-coupled) micro-electromechanical system (MEMS) microphones array, which collects the energy-rich leaky Rayleigh waves, instead of the relatively weak P-wave. Finite element method was used for the numerical simulations, it is shown that the propagation velocity of leaky Rayleigh waves traveling along the air-concrete interface agrees with the corresponding theoretical properties of Lamb wave modes in an infinite concrete slab. This structures the basis for implementing a non-contact AE source location approach. Based on the experience gained from numerical studies, experimental studies on the proposed air-coupled AE source location in concrete slabs are carried out. Finally, it is shown that the locating map of AE source can be determined using the proposed system, and the accuracy is sufficient for most field monitoring applications on large plate-like concrete structures, such as tunnel lining and bridge deck.

• International Journal of Railway
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• v.1 no.4
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• pp.149-156
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• 2008

During maintenance or construction works in or at the tracks of railways, high risks for passengers and railway staff, especially for the workers on the construction site exist. The high risks result out of the movement of rail vehicles, like trains or construction vehicles, which must be faced by using any available technical and operational technologies for securing them against the environment. Therefore, it is necessary to evaluate the level of protection continuously and to identify new and innovative methods and technologies for the protection of the gang (construction worker, machines and material). Especially on construction sites at line sections with two or more parallel tracks but also with single tracks, there are still a lot of incidents and accidents mostly with seriously injured persons or fatalities. These were mainly gang members that breach the railway-loading gage. By using proper warning or protection systems, the avoidance of such accidents must be achieved. The latest developments. in gang protection systems concern on the one hand fixed barriers in the middle between the construction site and the operated track and on the other hand construction vehicles equipped with automatic warning systems. The disadvantage of such protection methods is that the gang can be warned against an approaching train but a monitoring of the gang members cannot be performed. Only one part of a potential dangerous situation will be detected. If the gang members will overhear the acoustic warning signal of the security staff and the workers will not leave the danger zone in the track, the driver of the approaching train had no chance to react to the dangerous situation. An accident is often inevitable. While the detection of acoustic warning signals by the gang members working on a construction site is very difficult, the acoustical planning of an automatic warning system has to be designed for an acoustic short range level of one meter besides the construction vehicle. The decision about the use of today's technical warning system (fixed systems, automatic warning systems, etc.) must be geared to the technical feasibility and the level of safety which is needed. Criteria for decision guidance to block a track should be developed by danger estimation and economical variables. To realize the actual jurisdiction and to minimize the hazards of railway operations by the use of construction vehicles near the tracks further developments are needed. This means, that the warning systems have to be enhanced to systems for protection, which monitor the realization of the warning signal as a precondition for giving a movement authority to a train. This method can protect against accidents caused by predictable wrongdoing. The actual state of the art technique of using a collective warning combined with additional security staff is no longer acceptable. Therefore, the Institute of Transportation System of the German Aerospace Center in Braunschweig (Germany) will develop a gang warning and protection system based upon imaging methods, with optical sensors such as video in visible and invisible ranges, radar, laser, and other. The advantage of such a system based on the possibility to monitor both the gang itself and the railway-loading gauge either of the parallel track or of the same track still in use. By monitoring both situations, the system will be able to generate a warning message for the approaching train, that there are obstacles in the track, so that the train can be stopped to prevent an accident. And also the gang workers will be warned, while they breach their area.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.11
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• pp.1059-1066
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• 2011

The micro-perforated panel absorber(MPPA) is one of promising noise control elements because of its applicability to extreme environments where general porous materials cannot be used. Since the MPPA is inherently non-porous sound absorber, it can be a good candidate of acoustic protection system of a space launcher. The overall sound pressure level inside payload fairings of commercial launch vehicles is so high(around 140 dB OASPL) that the conventional linear impedance model cannot be directly applied to the design of the acoustic protection systems. In this paper an acoustic impedance models of a micro-perforated panel absorber at high sound pressure environment were reviewed and the use of the impedance on the practical design of MPPAs was addressed. The variation of absorption characteristics of MPPA was discussed according to the design parameters, e.g., perforation ratio, the minute hole diameter, the thickness of MPP and the incident sound pressure level.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.178-185
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• 2011

The micro-perforated panel absorber (MPPA) is one of promising noise control elements because of its applicability to extreme environments where general porous materials cannot be used. Since the MPPA is inherently non-porous sound absorber, it can be a good candidate of acoustic protection system of a space launcher. The overall sound pressure level inside payload fairings of commercial launch vehicles is so high (around 140 dB OASPL) that the conventional linear impedance model cannot be directly applied to the design of the acoustic protection systems. In this paper an acoustic impedance models of a micro-perforated panel absorber at high sound pressure environment were reviewed and the use of the impedance on the practical design of MPPAs was addressed. The variation of absorption characteristics of MPPA was discussed according to the design parameters, e.g., perforation ratio, the minute hole diameter, the thickness of MPP and the incident sound pressure level.