• Journal of the Korea Institute of Military Science and Technology
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• v.4 no.2
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• pp.84-96
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• 2001

Test data for a naval vessel is massive, expensive and impossible to be retested in a underwater acoustic measurement on the same condition. So, it is very important. In this paper, I mention massive underwater acoustic multimedia database system that was developed to store a long time, manage systematically, supply raw data and analyze data to user in 2-tier structure. Also, I propose 3-tier structure to extend the current database system that can supply multimedia data.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2003.11a
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• pp.384-387
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• 2003

The object of the present work is the analysis of head/disk interaction during start/stop and constant speed operation using acoustic emission (AE). The frequency spectrum analysis is performed using the AE signal obtained during the head/disk interaction. The FFT (Fast Fourier Transform) analysis of the AE signals is used to understand the interaction between the AE signal and the state of contact.

• Journal of Welding and Joining
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• v.19 no.1
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• pp.40-48
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• 2001

An ultrasonic test method, as a nondestructive test is applied to ensure the clad interface quality assessment. According to the reference codes and standards, not only korea Industrial Standard(KS) but also American Society for Testing and Materials (ASTM) Standard, ultrasonic examination procedures use the pulse-echo, A-scan, back reflection signal drop method and/or side drilled reference hole used to establish the acceptance criteria of clad material test. But the variety of bonding materials and sizes makes it difficult to produce the reference blocks, or thus the criteria. In order to overcome these practical difficulties, new ultrasonic testing criterion is suggested. In this new method, the theoretical interface reflection signal amplitude level is calculated and suggested as an acceptance criteria with the back reflection signal set to 100% FSH(Full Screen Height) which is based on acoustic impedance mismatch at the clad interface for the explosive clad ultrasonic inspection. Applicability of suggested criterion, for the explosive clad Fe-Naval Brass with different bonding quality is confirmed to the pre-existed KS and ASTM specifications and verified by using SEM (Seanning Electron Microscope) micrograph. The results obtained by the suggested method is more conservative than the results according to the KS B 0234 and ASTM A 578 specifications The suggested method could be applicable to any other combination of explosive clad ultrasonic inspection.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.11a
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• pp.79-83
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• 2000

Interfacial and microfailure properties of carbon liber/bismaleimide (BMI) composites were evaluated using both tensile fragmentation and compressive Broutman tests with acoustic emission (AE). Since BMI is rather difficult matrix to apply for the conventional fragmentation test because of its too low elongation and too brittle and high modulus properties, dual matrix composite system was applied. After carbon fiber/BMI composite was prepared for rod shape by controlling differing curing stage, composites rod was embedded in toughened epoxy as outer matrix. The typical microfailure modes including fiber break, matrix cracking, and interlayer failure were observed during tensile testing, whereas the diagonal slippage in fiber ends was observed during compressive test. On the other hand, AE amplitudes of BMI matrix fracture were higher than carbon fiber tincture under tensile test because BMI matrix has very brittle and high modulus. The waveform of signals coming from BMI matrix fractures was consistent with AE amplitude result under tensile tests.

• Journal of the Society of Naval Architects of Korea
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• v.56 no.1
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• pp.94-101
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• 2019

Underwater acoustic power should be measured in a free field, but it is not easy to implement. In practice, the measurement could be performed in a reverberant field such as a water-filled steel tank and concrete tank. In this case, the structure and the acoustic field are strongly or weakly coupled according to material properties of the steel and water. So, characteristics of the water tank must be investigated in order to get the accurate underwater acoustic power. In detail, modal frequencies, mode shapes of the structure and frequency response functions of the acoustic field could represent the characteristics of the reverberant water tank. In this paper, the structure-acoustic coupling has been investigated on a reverberant water tank numerically and experimentally. The finite element analysis has been carried out to estimate the structural and acoustical modal parameters under the dry and water-filled conditions, respectively. In order to investigate the structure-acoustic coupling effect, the numerical analysis has been performed according to the structure stiffness change of the water tank. The acoustic frequency response functions were compared with the numerical analysis and acoustic exciting test. From the results, the structural modal frequencies of the water-filled condition have been decreased compared to those of the dry condition in the low frequency range. The acoustic frequency response functions under the coupled boundary conditions showed different patterns from those under the ideal boundary conditions such as the pressure release and rigid boundary condition, respectively.

• Proceedings of the KSPS conference
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• 2002.11a
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• pp.145-149
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• 2002

This study was performed to find out changes in acoustic measurements of voice after eating egg, apple and pear. Ten college students vocalized /a/ before and after eating egg, apple and pear. Dr. Speech was utilized to obtain changes of subjects's acoustic measurements. A t-test was peformed to determine acoustic changes of voice before and after eating egg, apple and pear. No significant difference was observed in acoustic measurements before and after eating egg, apple and pear. However, the subjects seemed to show some improvements in Jitter, HNR, and NNE in the order of egg, apple, and pear even though they did not reach a statistical significance. It was concluded that a more systematic research paradigm is needed in order to objectively reject or substantiate a variety of conceptions on food items and their effects on voice.

• Phonetics and Speech Sciences
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• v.10 no.3
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• pp.41-48
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• 2018

This study examined the acoustic characteristics of Korean alveolar fricatives of normal children. Developing children aged 3 and 7, typically produced 2 types of nonsense syllables containing alveolar fricative /sV/ and /VsV/ sequences where V was any one of three corner vowels (/i, a, and u/). Stimuli containing the speech materials used in a production experiment were presented randomly to 12 speech language pathologists (SLPs) for a perception test. The SLPs responded by selecting one of seven alternative sounds. Acoustic measures such as duration of frication noise, normalized intensity, skewness, and center of gravity were examined. There was significant difference in acoustic measures when comparing vowels. Comparison of syllable structures indicated statistically significant differences in duration of frication noise and normalized intensity. Acoustic parameters could account for the perceptual data. Relating the acoustic and perception data by means of logistic regression suggests that duration of frication noise and normalized intensity are the primary cues to perceiving Korean fricatives.

• Journal of the Korea Institute of Military Science and Technology
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• v.21 no.4
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• pp.481-488
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• 2018

This study suggest the improvement of the CFRP adhesive mixing ratio about acoustic window to enhance SONAR performance. The CFRP of submarine is produced by allocation an acoustic window zone by the beam width of SONAR sensors. During the sea trial, SONAR system's bearing and range accuracy data is not in tolerance due to debonding phenomenon on CFRP. The inappropriate mixing ratio of adhesives caused that peeling phenomenon occurred in the acoustic window part, which is the reason for the deterioration of SONAR sensors performance. The report includes explanation of test procedure of SONAR, root cause analysis, CFRP manufacturing procedure, laboratory tests results, and proof of the performance at the sea trial.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.259-262
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• 2002

Application of combustion stabilization devices such as baffle and acoustic cavity to liquid propellant rocket engine is investigated to suppress high-frequency combustion instability, i.e., acoustic instability. First, these damping devices are designed based on linear damping theory. As a principal design parameter, damping factor is considered and calculated numerically in the chambers with various specifications of these devices. Next, the unbaffled chambers with/without acoustic cavities are tested experimentally for several operating conditions. The unbaffled chamber shows the specific stability characteristics depending on the operating condition and has small dynamic stability margin. The most hazardous frequency is clearly identified through Fast Fourier Transform. As a result, the acoustic cavity with the present design has little stabilization effect in this specific chamber. Finally, stability rating tests are conducted with the baffled chamber, where evident combustion stabilization is observed, which indicates sufficient damping effect. Thrust loss caused by baffle installation is about $2{\%}$.

• Journal of KSNVE
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• v.6 no.4
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• pp.447-456
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• 1996

Dynamic characteristics of the bell-type structure including acoustic effects and transient dynamic problems were analyzed numerically. Natural frequencies, mode shapes and transient dynamic analysis used the finite element method with 3-D general shell element. Mode shapes and stress distributions of transient dynamic analysis were expressed by computer graphics. The method using this study was evaluated by comparision of theoretical results at reference papers(14), (15) and the experimental test using Fast Fourier Transform analyzer. Vibrational modes governing acoustic characteristics of the typical bell-type structure depended on the first flexural mode(4-0 mode) and the second flexural mode(6-0 mode). Asymmetric effects by Dangiwas, acoustic holes gave rise to beat frequencies, and the Dangjwa was found to be most effective. When impact load acted on the bell, stress concentration occured at the rim part of bell. It was found that the bell type structure should be designed thickly at the rim part in order to prevent impact load from stress concentration.