• Proceedings of the KSME Conference
• /
• 2004.11a
• /
• pp.1069-1074
• /
• 2004

This study investigated the effect of pressure variations on augmentation of heat transfer when the ultrasonic waves were applied. The augmentation ratio of heat transfer was experimentally investigated and was compared with the profiles of pressure distributions calculated applying a coupled finite element-boundary element method (coupled FE-BEM). As the ultrasonic intensities increase from 70W to 340W, the velocity of the liquid paraffin is found to increase as well as kinetic energy, This physical behavior known as quasi-Eckart streaming results from acoustic pressure variations in the liquid. Especially, the higher acoustic pressure distribution near two ultrasonic transducers develops more intensive flow (quasi-Eckart streaming), destroying the flow instability. Also, the profile of acoustic pressure variation is consistent with that of augmentation of heat transfer. This mechanism is believed to increase the ratio of hear transfer coefficient.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.9 no.4
• /
• pp.41-47
• /
• 2000

In this study, the purpose finds out the best welding conditions for bonding of electric wire by ultrasonic welding. The material was plastic-insulating low-voltage-cabels for automobiles. The experiment varied the values of welding time and welding pressure and fixed the values of amplitude and energy. With the facts, the best condition for ultrasonic welding to achieve bonding exactly is gained according to the size of the cross-sectional area of the cable, and the adhesive intensity is greatly influenced by the variables of welding time and welding pressure. Also when the welding time and welding time and welding pressure increase as the cross-sectional areas of the cable increase the welding result in gained exactly.

• Proceedings of the KSME Conference
• /
• 2003.04a
• /
• pp.678-683
• /
• 2003

Ultrasonic method using SH(shear horizontal) wave has been developed to determine the surface damage in fatigued material. Fatigue damages based on propagation energy were analyzed by multiregression analysis and phase measurement in interrupted fatigue test specimen including CrMoV and 12Cr alloy steel. From the test results, as the fatigue damage increased the propagation time of the launched waves increased and amplitude of wavelet decreased. Also, analysis for the waveform modulation showed a reliable estimation, with confidence limit of 97% for 12Cr steel and 95% for CrMoV steel, respectively. Therefore, It is thought that SH ultrasonic wave technique can be applied to determine fatigue damage of in-service component nondestructively.

• 한국가시화정보학회:학술대회논문집
• /
• 2004.11a
• /
• pp.22-25
• /
• 2004

The present paper investigated the correlation between acoustic pressure and heat transfer augmentation in acoustic fields. The acoustic pressure predicted by numerical work and compared with the augmentation ratio of heat transfer coefficient was experimentally measured. Also, particle image velocimetry(PIV) was used for the visualization of velocity vectors and kinetic energy distribution inside liquid region. For the numerical work, SVS programed with Fortran language and based on a coupled FE-BEM was used. Results of the present study, the acoustic pressure is increased by $60\%$ and the largest augmentation of heat transfer about $28\%$ was measured. Finally, the profiles of acoustic pressure is consistent with that of augmentation of heat transfer. It is concluded that a correlation exists between the acoustic pressure and the heat transfer augmentation.

• Journal of the Korean Society for Precision Engineering
• /
• v.26 no.6
• /
• pp.90-96
• /
• 2009

Ultrasonic method using SH(shear horizontal) wave has been developed to determine the surface damage in fatigued material. Fatigue damages based on propagation energy were analyzed by multi-regression analysis in interrupted fatigue test specimen including CrMoV and 12Cr alloy steel. From the test results, as the fatigue damage increased the propagation time of the launched waves increased and amplitude of wavelet decreased. Also, analysis for the waveform modulation showed a reliable estimation, with confidence limit of 97% for 12Cr steel and 95% for CrMoV steel, respectively. Therefore, It is thought that SH ultrasonic wave technique can be applied to determine fatigue damage of in-service component nondestructively.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2001.05a
• /
• pp.363-368
• /
• 2001

Because of rapid damping of light and electromagnetic wave, acoustic wave has been widely used for underwater communication. However, the propagation of the acoustic wave is highly dependent on the environment such as water properties(temperature, pressure, salinity), bottom and surface conditions, etc.. This paper deals with the surface reflection effect on the wave propagation in the underwater anechoic basin in KRISO. Both theortical and experimental approaches are performed and the results are compared.

• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.13 no.2
• /
• pp.104-111
• /
• 2004

Ultrasonic machining is a non-thermal, non-chemical, md non-electorial material removal process, and thus results in minimum modifications in mechanical properties of the brittle material during the process. Also, ultrasonic machining is a non-contact process that utilize ultrasonic vibration to impact a brittle material. In this research characteristics of micro-hole machining for brittle materials by ultrasonic machining(USM) process have been investigated. And the effect of ultrasonic vibration on the machining conditions is analyzed when machining fir non-conductive brittle materials using tungsten carbide tools with a view to improve form and machining accuracy.

• Journal of Welding and Joining
• /
• v.16 no.2
• /
• pp.48-56
• /
• 1998

This study was performed to find the best bonding conditions by comparing mechanical properties in thermoplastic resin of polyethylene (PE) and polyamide (PA) adhesion. Following results were obtained from the tests with varying welding time and welding pressure. Satisfactory adhesion was executed in ultrasonic welding for the same materials of PE and PA. The best welding conditions were found to be welding time of 1 second, welding pressure of 250kPa for PE-PE weding, 2 second and 350kPa for PA-PA welding. Welding time and welding pressure end to increase with the increase of materials strength. Dissimilar materials were adhered when adhesion and ultrasonc welding were performed simultaneously. The observation of the structure of ultrasonic welding area with microscope showed differenticated structures between well adhered region and badly adhered region.

• Laser Solutions
• /
• v.15 no.4
• /
• pp.1-5
• /
• 2012

We demonstrate that reduced graphene oxide (rGO) coated thin aluminum film is an effective optoacoustic transmitter for generating high pressure and high frequency ultrasound previously unattainable by other techniques. The rGO layer of different thickness is deposited between a 100 nm-thick aluminum film and a glass substrate. Under a pulsed laser excitation, the transmitter generates enhanced optoacoustic pressure of 64 times the aluminum-alone transmitter. A promising optoacoustic wave generation is possible by optimizing thermoelasticity of metal film and thermal conductivity of rGO in the proposed transmitter for laser-induced ultrasound (LIUS) applications.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2005.10a
• /
• pp.400-403
• /
• 2005

The sonar sensors can be divided into a piezo type and an electrostatic type according to a principle of an operating system. The electrostatic type of a sonar sensor is used for map building in this paper. If we know the characteristics of sonar sensor, we can derive the ultrasonic pressure equation from an acoustics theory. We, therefore, developed Ultrasonic Pressure Probabilistic Model (UPPM) to consider the sound pressure in the probability updating process. In this paper, we found that the quality of the resulting probability map is considerably improved, through combining the UPPM with the grid-based mapping algorithm.