• The KSFM Journal of Fluid Machinery
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• v.16 no.1
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• pp.32-39
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• 2013

The multi-stage control valve is one of the devices which controls cavitation and high pressure drop. To attain the high pressure drop, the conventional control valves adopted the multi-stage trim to avoid the occurrence of local cavitation in valves. This work studied the effect of divergence angle on the characteristics of multi-stage trim. Pressure drop and flow characteristics was calculated for the 1 passage of multi-staged trim by using the FLUENT 6.3.26. The result showed that the pressure drop is significantly influenced by the divergence angle of multi-stage trim. In addition, the pressure drop increased consistently as the Reynolds number and divergence angle increases.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.4
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• pp.280-286
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• 2002

It has been long suspected that the transition region may give rise to local pressure fluctuations and radiated sound that are different from those created by the fully-developed turbulent boundary layer at equivalent Reynolds number. Experimental investigation described in this paper concerns the characteristics of pressure fluctuations at the transition. Flush-mounted microphones and hot wires are used to measure the pressure fluctuations and local flow velocities within the boundary layer in the low noise wind tunnel. From this experiment we could observe the spatial and temporal development process of T-S wave using Wigner-Ville method and find the relations between the characteristic frequency of T-S wave and free stream velocity and the boundary layer thickness based on nondimensional pressure spectra scaled on outer variables.

• Journal of The Korean Society of Integrative Medicine
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• v.5 no.4
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• pp.1-9
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• 2017

Purpose : This study was conducted among 195 adults in their 20s. To analyze the impact of the slope types of the scapulae on the plantar surface of the foot, the average pressure (AP), the maximum pressure (MP), the average of local distribution values, and the average movement of the center of pressure (COP) of the different slope types of the scapulae were compared. Method : The anterior-posterior slopes of the scapulae were measured by comparing the slopes of the left and right sides of the scapulae based on the differences in the height and the slope of the coracoid process and the angulus inferior scapulae. Those whose left side of the scapulae had an anterior slope were categorized as type 1, and those whose right side of the scapulae had an anterior slope, as type 2. The average plantar pressure, the center of plantar pressure, the maximum plantar pressure, and local distribution values were analyzed using a plantar pressure analyzer of the FSA. Result : In terms of the AP of the left and right feet, there was no statistically significant difference both in types 1 and 2 on the left and right feet. The comparison results of the MP and the average of local distribution values of the two slope types of the scapulae showed that there was no statistically significant difference on the X-axis both in types 1 and 2 on the left and right feet, but that there was a large statistically significant difference on the Y-axis both in types 1 and 2. That is, the MP of the right foot of the left anterior slope type was located more on the hindfoot than that of the right anterior slope type, and the MP of the left foot of the left anterior slope type was located more on the hindfoot than that of right anterior slope type. Conclusion : This study can be used as fundamental data to predict differences in the location and size of the COP and changes in plantar pressure distribution depending on the slope types of the scapulae, and control the distribution for therapeutic purposes.

• Journal of The Korean Dental Society of Anesthesiology
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• v.6 no.2 s.11
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• pp.98-102
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• 2006

The purpose of this study was to evaluate the difference on pain intensity and discomfort between pressure-controlled injection system and conventional syringe injection technique from the patients undergoing oral and maxillofacial surgery. In a prospective, randomized, case-controlled study, 60 patients were divided into two groups (n=30 in each). In experimental group, pressure-controlled injection system was applied. In control group, conventional syringe injection system was applied. Pain rating score (PRS) and visual analogue scale (VAS) were assessed. The average of VAS in experimental group ($16.67{\pm}15.07$) was smaller than that of control group ($25.63{\pm}22.21$), though there were no significant differences (P=0.072). In PRS, fifteen patients (50.0%) of experimental group answered that they experienced mild pain. However sixteen patients (53.3%) of control group answered that they experienced intermediate pain. From the results, pressure-controlled injection system may be an effective method to reduce pain during the dental local anesthetic procedure.

• Journal of ILASS-Korea
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• v.27 no.2
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• pp.84-93
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• 2022

To implement carbon-neutrality in transportation sectors until 2050, hydrogen is considered a promising fuel for internal combustion engines because hydrogen does not contain carbon itself. Although hydrogen does not emit CO₂ emission from its combustion process, the low energy density in a volume unit hinders the adoption of hydrogen. Therefore, the understanding of hydrogen jet behavior and measurement of equivalence ratio must be conducted to completely implement the high-pressure hydrogen direct injection. The main objective of this research is feasibility test of hydrogen local equivalence ratio measurement by laser-induced breakdown spectroscopy (LIBs). To visualize the macroscopic structure of hydrogen jet, high-speed schlieren imaging was conducted. Moreover, LIBs has been adopted to validate the feasibility of hydrogen local equivalence ratio measurement. The hydrogen injection pressure was varied from 4 MPa to 8 MPa and injected in a constant volume chamber where the ambient pressure was 0.5 MPa. The increased injection pressure extends the vertical penetration of hydrogen jet. Due to the higher momentum supply when the injection pressure is high, the hydrogen has easily diffused in all directions. As the laser trigger timing has delayed, the low hydrogen atomic emission was detected due to the longer mixture formation time. Based on equivalence ratio measurement results, LIBs could be applied as a methodology for hydrogen local equivalence ratio measurement.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.210-213
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• 2004

Based on plastic instability, analytical prediction of bursting failure on tube hydroforming processes under combined internal pressure and independent axial feeding is carried out. Bursting is irrecoverable phenomenon due to local instability under excessive tensile stresses. In order to predict the bursting failure, three different classical necking criteria such as diffuse necking criterion for sheet and tube, local necking criterion for sheet are introduced. The incremental theory of plasticity fur anisotropic material is adopted and then the hydroforming limit and bursting failure diagram with respect to axial feeding and hydraulic pressure are presented. In addition, the influences of the material properties such as anisotropy parameter, strain hardening exponent on bursting pressure are investigated. As results of the above approach, the hydroforming limit in view of bursting failure is verified with experimental results.

• Journal of Ocean Engineering and Technology
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• v.28 no.3
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• pp.209-217
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• 2014

In the present study, the water impact loads on two-dimensional symmetric and asymmetric wedges were mainly studied. The impact pressure and force were measured during a vertical drop of the symmetric and asymmetric wedges. The measured pressure was compared with analytic solutions. The measured force at a local area of the wedge was compared with the integrated pressures and analytic solutions. Some findings on symmetric and asymmetrical wedge drops are presented, and the reliability of the force sensor used for the measurement of the local impact force is discussed.

• Transactions of Materials Processing
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• v.13 no.7
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• pp.629-634
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• 2004

Based on plastic instability, analytical prediction of bursting failure on tube hydroforming processes under combined infernal pressure and independent axial feeding is carried out. Bursting is irrecoverable phenomenon due to local instability under excessive tensile stresses. In order to predict the bursting failure, three different classical necking criteria such as diffuse necking criterion for sheet and tube, local necking criterion for sheet are introduced. The incremental theory of plasticity for anisotropic material is adopted and then the hydroforming limit and bursting failure diagram with respect to axial feeding and hydraulic pressure are presented. In addition, the influences of the material properties such as anisotropy Parameter, strain hardening exponent and strength coefficient on bursting Pressure are investigated. As results of the above approach, the hydroforming limit in view of bursting failure is verified with experimental results.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.811-816
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• 2000

It has been long suspected that the transition region may give rise to local pressure fluctuations and radiated sound that are different from those created by the fully-developed turbulent boundary layer at equivalent Reynolds number. Experimental investigation described in this paper concerns the characteristics of pressure fluctuations at the transition. Flush-mounted microphones and hot wires are used to measure the pressure fluctuations and local flow velocities within the boudary layer in the low noise wind tunnel. From this experimental we could observe the spatial and temporal development process of T-S wave using Wigner-Ville method and found the possibility of relation between the characteristic frequency of T-S wave and free stream velocity and the boundary layer thickness based on nondimensional pressure spectra scaled on outer variables.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2723-2728
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• 2008

The present study is numerically and experimentally performed to reveal the pumping characteristics of a helical-type molecular drag pump (HTDP) in the molecular transition flow region. In the experimental study, the pressures are measured simultaneously at the 5 positions along the helical channel of rotor under various conditions of outlet pressure and throughputs, and nitrogen is used as test gas. The outlet pressure is in the range of 26-533 Pa. As results, the local pressure changes are checked corresponding to the various outlet pressure and throughput of HTDP. In the numerical study, Navier-Stokes equations with slip boundary conditions are employed (Re< 1000, Kn< 0.1). The local pressure distribution and the pumping speed are calculated. The numerical results are compared with the experimental results. The numerically computed value agrees with the experimental data within an error of approximately 5%.