• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2003.06a
• /
• pp.1022-1025
• /
• 2003

Although the globe is the most typical valve to control high pressure drop in piping system, it is very hard to figure out the characteristics of flow field in the globe valve caused by its complex geometry. So there is very few studies to find out flow characteristics of globe valve. In this study, numerical analysis for flow field in the globe valve is carried out using the Fluent code which is commercial CFD program. Pressure drop through the globe valve is also measured to verify the results come from numerical analysis. Comparing experiment with numerical analysis, two results are very close to each other. Also finite element method is employed to evaluate the safety of globe valve using the results coming from the flow analysis to make the boundary conditions for FEM analysis. Maximum stress appears on the inlet channel of valve where inlet flow runs against. Because the maximum stress between 11.7 MPa to 3.6 MPa is within 3.4% of yield stress. the structural safety of valve is considered to be very sound

• Journal of the Korean Society of Safety
• /
• v.17 no.4
• /
• pp.52-60
• /
• 2002

Failure criterion is a parameter to represent the resistance to failure of locally wall thinned pipe, and it depends on material characteristics, defect geometry, applied loading type, and failure mode. Therefore, accurate prediction of integrity of wall thinned pipe requires a failure criterion adequately reflected the characteristics of defect shape and loading in the piping system. In the present study, the finite element analysis was performed and the results were compared with those of pipe experiment to develop a sound criterion for failure of internally wall thinned pipe subjected to combined pressure and bending loads. By comparing the predictions of failure to actual failure load and displacement, an appropriate criterion was investigated. From this investigation, it is concluded that true ultimate stress criterion is the most accurate to predict failure of wall thinned pipe under combined loads, but it is not conservative under some conditions. Engineering ultimate stress estimates the failure load and displacement reasonably for al conditions, although the predictions are less accurate compared with the results predicted by true ultimate stress criterion.

• Structural Engineering and Mechanics
• /
• v.51 no.4
• /
• pp.627-641
• /
• 2014

Functionally graded steels (FGSs) are a family of functionally graded materials (FGMs) consisting of ferrite (${\alpha}$), austenite (${\gamma}$), bainite (${\beta}$) and martensite (M) phases placed on each other in different configurations and produced via electroslag remelting (ESR). In this research, the flow stress of dual layer austenitic-martensitic functionally graded steels under hot deformation loading has been modeled considering the constitutive equations which describe the continuous effect of temperature and strain rate on the flow stress. The mechanism-based strain gradient plasticity theory is used here to determine the position of each layer considering the relationship between the hardness of the layer and the composite dislocation density profile. Then, the released energy of each layer under a specified loading condition (temperature and strain rate) is related to the dislocation density utilizing the mechanism-based strain gradient plasticity theory. The flow stress of the considered FGS is obtained by using the appropriate coefficients in the constitutive equations of each layer. Finally, the theoretical model is compared with the experimental results measured in the temperature range $1000-1200^{\circ}C$ and strain rate 0.01-1 s-1 and a sound agreement is found.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.21 no.6
• /
• pp.556-561
• /
• 2008

This paper reports the characteristics of piezoelectric microspeakers that are audible in open air with high quality piezoelectric AlN thin film according to the materials properties. When we use a tensile-stressed silicon nitride diaphragm as a supporting layer, the Sound Pressure Level (SPL) is relatively small and constant at low frequency region and shows about 70 dB at 10 kHz. However, in case of a compressively stressed composite diaphragm, the SPL of the fabricated microspeakers shows higher output pressure than those of a tensile-stressed diaphragm. It produces more than 66 dB from 100 Hz to 15 kHz and the highest SPL is about 100 dB at 9.3 kHz with $20V_{peak-to-peak}$, sinusoidal input biases and at 10 mm distances from the fabricated microspeakers to the reference microphone. From the experimental results, it is superior to have a compressively composite diaphragm in order to produce a high SPL in piezoelectric microspeaker.

• Journal of Ocean Engineering and Technology
• /
• v.11 no.1
• /
• pp.10-15
• /
• 1997

Copper and its alloy had been used widely because of its pronouncing characteristics on their high thermal and electrical conductivity. Various fusion welding methods, such as SMAW, SAW, GTAW, GMAW, Electroslag welding amd so on are applied to weld copper and its alloy. But fusion welding of copper has so many welding problems. THe most serious problems were poor penetration amd high thermal contration stress due to its high thermal conductivity and porosity could be formed by rapid cooling rate of fusion welding. In order to avoid such fusion welding problems, preheating, peering and heat treatment must be applied to obtain sound weld joint of copper. But preheating induce another welding problem such as grain coarsening of weld heat affected zone. This grain coarsening reduces ductility and strength of weld joint. In this view of point, friction welding of copper is triedm to obtain sound weld joint of copper by reducing metallurgical problems. This study introduced new concept of heat input for evaluating the friction weldability of copper. As a result, weldability of copper could be evaluated by this new concept of heat input.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2007.11a
• /
• pp.37-38
• /
• 2007

This paper reports the characteristics of piezoelectric microspeakers that are audible in open air with high quality piezoelectric AlN thin film according to the materials properties. When we use a tensile-stressed silicon nitride diaphragm as a supporting layer, the Sound Pressure Level (SPL) is relatively small. However, the SPL of the fabricated microspeakers that have compressive-stressed composite diaphragm show higher output pressure than those of tensile-stressed diaphragm. It produces more than 60dB from 100Hz to 15kHz and the highest SPL is about 100dB at 9.3kHz with 20 Vpeak-to-peak sinusoidal input biases and at 10 mm distances from the fabricated microspeakers to the reference microphone.

• Journal of fish pathology
• /
• v.34 no.2
• /
• pp.243-248
• /
• 2021

Offshore wind power generation is an energy generation field that is rapidly developing owing to the increasing demand for clean energy. However, the physiological response of fish to the underwater noise generated during construction or operation of wind turbines is unclear. We confirmed the effects of sound pressures of 125, 135, 145, and 155 dB/µPa, including 140 dB/µPa (the standard sound pressure for noise damage recognition in South Korea), through serum analysis in rock bream (Oplegnathus fasciatus). High mortality induced by reduced immunity through artificial infection after stimulation was confirmed. These results suggest that rock bream is negatively affected by the noise generated during the construction of offshore wind power plants.

• The Journal of the Acoustical Society of Korea
• /
• v.22 no.8
• /
• pp.637-644
• /
• 2003

In this study, with the FEM we analyzed the variation of the resonance frequency, bandwidth, and sound pressure of the Tonpilz transducer in relation to its design variables. Through statistical multiple regression analysis of the results, we derived functional forms of the resonance frequency, bandwidth, and sound pressure in terms of the design variables. By applying the constrained optimization technique, SQP-PD, to the derived function, we determined the optimal structure of the transducer that could provide the highest sound pressure level at the resonance frequency of 30,000 Hz and having the -3 dB bandwidth more than 10%, The validity of the optimized results was confirmed through comparison of the optimal performance with that of the FEA. The optimal design method proposed could reflect all the cross-coupled effects of multiple structural variables, and could determine the detailed geometry of the transducer with great efficiency and rapidity.

• Journal of Environmental Science International
• /
• v.31 no.4
• /
• pp.365-368
• /
• 2022

The purpose of this study was to investigate the effects of desensitization and flooding on the behavior of dogs during grooming, focusing on their response to the sound and skin stimulation while using a clipper. A total of 20 adult dogs over two years of age with complete personality formation were included in the study. Ten dogs, of which three were Bichons (average weight 5 kg), four were Poodles (average weight 5 kg), and three were Malteses (average weight 4 kg), were subjected to the desensitization process. The remaining 10 adult dogs were subjected to the flooding experiment, and were of the same breed and average weight as the adult dogs used in the desensitization process. The desensitization and the flooding were performed three times a day (approximately 1 min per session) for 10 days. For desensitization, statistical significance was observed only on the fifth day, when compared by breed (p<0.05). Overall, when compared by measurement day, the results of desensitization for Bichon, Poodle and Maltese dogs were statistically significant (p<0.05). The results for the Bichon, Poodle, and Maltese dogs that were subjected to flooding were found to be statistically significant (p<0.05). There was a significant difference in the results of the flooding on the second and ninth days (p<0.05); however, flooding had no effect on the other days (p>0.05). Desensitization using the clipper, a beauty tool, was faster than flooding in achieving stabilization. In conclusion, desensitization and flooding showed positive results on the stress relief and emotions of dogs during grooming, with respect to cosmetic fear response.

• IEMEK Journal of Embedded Systems and Applications
• /
• v.17 no.1
• /
• pp.9-17
• /
• 2022

As the COVID-19 pandemic situation worsens, the time spent indoors increases, and the exposure to indoor environmental pollution such as indoor air pollution and noise also increases, causing problems such as deterioration of human health, stress, and discord between neighbors. This paper designs and implements a system that measures and monitors indoor air quality and noise, which are representative evaluation criteria of the indoor environment. The system proposed in this paper consists of a particulate matter measurement subsystem that measures and corrects the concentration of particulate matters to monitor indoor air quality, and a noise measurement subsystem that detects changes in sound and converts it to a sound pressure level. The concentration of indoor particulate matters is measured using a laser-based light scattering method, and an error caused by temperature and humidity is compensated in this paper. For indoor noise measurement, the voltage measured through a microphone is basically measured, Fourier transform is performed to classify it by frequency, and then A-weighting is performed to correct loudness equality. Then, the RMS value is obtained, high-frequency noise is removed by performing time-weighting, and then SPL is obtained. Finally, the equivalent noise level for 1 minute and 5 minutes are calculated to show the indoor noise level. In order to classify noise into direct impact sound and air transmission noise, a piezo vibration sensors is mounted to determine the presence or absence of direct impact transmitted through the wall. For performance evaluation, the error of particulate matter measurement is analyzed through TSI's AM510 instrument. and compare the noise error with CEM's noise measurement system.