• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.224-227
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• 2007

This paper introduces the results of acoustic loads test conducted on the upper stage assembly of KSLV-I, which is the first Korea space launch vehicle. A launch vehicle and its payloads are subjected to severe acoustic pressure loading when they lift off and ascent during the transonic periods. Acoustic loadings are spreaded out broad frequncy-spectrum up to 10,000Hz. Acoustic loads are a primary source of structural random vibration of the upper stage and payloads. Therefore, in order to verify the structural integrity of the upper stage assembly of KSLV-I and the survivability of its components under severe random vibration environment, acoustic loads test is conducted in the high intensity acoustic chamber with 142dB (overall SPL). The results show the structural design and component random vibration specifications well meet with the environmental requirements.

• Journal of Korean Society of Environmental Engineers
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• v.34 no.4
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• pp.232-238
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• 2012

In this study, the noise mapping simulation is executed to design an effective barrier reducing noise levels of a school site. The geographical features of the ambient site and the school buildings are modelled in detail in order to consider sound propagation, deflection, and absorption phenomena etc. The main sound source, sound power level of expressway, is estimated on the basis of measured noise levels at several points of the site. The noise mapping simulation is performed by using ENPro, environmental noise prediction program based on ISO 9613 to analysis the effectiveness of noise barrier. Consequently, the noise barrier is designed to meet an environmental noise standard and satisfy low cost and safety conditions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.2
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• pp.127-134
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• 2020

High supersonic aircraft are exposed to high temperature environments by aerodynamic heating during supersonic flight. Thermal protection system structures such as double-panel structures are used on the skin of the fuselage and wings to prevent the transfer of high heat into the interior of an aircraft. The thin-walled double-panel skin can be exposed to acoustic loads by supersonic aircraft's high power engine noise and jet flow noise, which can cause sonic fatigue damage. Therefore, it is necessary to examine the behavior of supersonic aircraft skin structure under thermal-acoustic load and to predict fatigue life. In this paper, we designed and fabricated thermal-acoustic test equipment to simulate thermal-acoustic load. Thermal-acoustic testing of the titanium specimen under thermal-acoustic load was performed. The analytical model was verified by comparing the thermal-acoustic test results with the finite element analysis results.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.962-965
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• 2005

A high intensity progressive wave tube is installed at Korea Aerospace Research Institute (KARI) for acoustic environmental tests. The test facility has 700 mm x 800 mm cross-sectional area, and provides acoustic environment of 165 dB over the frequency range of $25Hz{\sim}10,000Hz$. The facility consists of a 6 m long acoustic wave tube, acoustic power generation systems, gases nitrogen supply systems, and acoustic control systems. This paper describes how the basic parameters of the facility and power generation systems are controlled to meet the requirement of the test. The shape and length of the tube has been designed by using the size of test objects and the wave propagation characteristics of the tube. The capacity of acoustic power generation systems is determined by the energy conversion of acoustic wave and the efficiency of acoustic modulators. Moreover, the paper introduces test run results of the tube. Overall of 163dB has been generated by using the test facility.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.867-872
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• 2002

A high intensity acoustic test facility is constructed at Korea Aerospace Research Institute (KARI) by 2003. The reverberant chamber of the facility has a volume of 1,228 cubic meters and shall provide an acoustic environment of 152 dB over the frequency range of 25 Hz to 10,000 Hz. The facility consists of a large scaled reverberant chamber, acoustic power generation systems, gases nitrogen supply systems, and acoustic control systems. This paper describes how the basic parameters of a chamber and power generation systems are controlled to meet the requirement of the test. The volume of a reverberant chamber is controlled by the size of test objects and the reverberant characteristics of a chamber. The capacity of acoustic power generation systems is determined by the energy absorption of a chamber and the efficiency of acoustic modulators. Simple math is employed to calculate the required power of acoustic modulators. Moreover, the paper explains how the distribution of sound pressure level at low frequency is checked by analytical and numerical methods.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.862-866
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• 2002

High intensity vibro-acoustic testing is the appropriate method for flight qualification testing of space flight vehicle which must ensure the acoustic environment of launch. To qualify vibro-acoustic environment during its flight, High Intensity Acoustic Test was performed for KOMPSAT-2(Korea Multi-Purpose SATellite) STM(Structural Thermal Model). This paper presents the detailed description on the high intensity acoustic test for KOMPSAT-2. Additionally the test results was compared with the analysis ones, which were estimated with 3-D SEA(Statistical Energy Analysis) model.

• Korean Journal of Materials Research
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• v.3 no.4
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• pp.361-371
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• 1993

Among the various test methods for stress corrusiun cracking(SCC) susceptibility evaluatiun, the slow stram rate test(SSHT) method is a rapid and effective nwthod to evaluate the SCC susceptibility of metal in relatively short time. But it is very difficult to analyze the microfracture behaviors in SCC process by using the test(SSRT) method only. Up to now, it has been well known that the acoustic emission(AE) test is the effective technique to monitor the microcrack initiation and propagation in material fracture pmcess. Therefore. in this paper, we analyzed the correlation between the see process and the characteristics of AE signal by using the SSHT and the AE test. According to the test results. the AE signals produced from the material microfracture were clearly depended on the test environment. The AE signal characteristics generated during see process in synthetic sea water were comparatively greater than those. in air. In addition, the SCC behaviors could be definitely evaluated by the amplitude parameter of AE signals.

• Proceedings of the Korean Information Science Society Conference
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• 1998.10b
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• pp.268-270
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• 1998

수중에서 획득되는 대용량 데이터를 영구 보존하고 효율적으로 관리하기 위한 데이터베이스 시스템을 설계하고 구현하기 위해서는 대용량 데이터 관리, 다양한 저장장치 관리, 효율적 검색 기능, 융통성있는 데이터 타입 지원 등을 고려하여야 한다. 본 논문에서는 해상에서 획득되는 대용량 시험자료를 효율적으로 관리하기 위해 개발된 수주음향 데이터베이스 시스템에 대해서 논한다. 구축된 시스템은 각 시험별로 획득한 원시자료와 다양한 분석기법을 통하여 추출한 분석자료를 저장, 관리, 제공할 목적으로 개발되었으며, 속도를 고려한 효율적 저장방법, 보안 시험별 검색단어 변경 문제 및 분석자료의 다양한 그래픽 제공 등을 고려하여 대용량 CD-쥬크박스를 가진 유닉스 기반의 클라이언트/서버 환경에서 구현하였다.

• Aerospace Engineering and Technology
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• v.1 no.2
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• pp.91-104
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• 2002

Jet noise of propulsion systems is major source of acoustic loads of launch vehicles and sounding rockets. The investigation of characteristics of jet noise is inevitable for successful missions. In this paper, the mechanism of generation of acoustic loads due to jet noise was investigated. The major parameters that change the characteristics of acoustic loads were also suggested so that effects of the parameters could be investigated. The temporal and spatial characteristics of acoustic loads of KSR-III was demonstrated. The results show that the maximum value of the acoustic loads is found in the octave bands whose center frequencies are 250 Hz and 500 Hz. Finally, the methods and the facilities for the further investigation of acoustic loads were proposed.

• Journal of the Institute of Convergence Signal Processing
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• v.20 no.4
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• pp.177-185
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• 2019

In this paper, we propose and evaluate a FDE combined with STBC transmission structure to cancellation of ISI in underwater acoustic communication. To achieve this purpose, underwater acoustic channels are modeled and the simulation results are presented. In case of STBC-FDE, the transmission rate is less about 4% than STBC-OFDM, but the SER performance is better than STBC-OFDM that is larger from 4.4% to 16.8% at the SNR of 15dB than STBC-OFDM.