• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.16 no.4
• /
• pp.2415-2423
• /
• 2015

Experiments were conducted on sine wave fin-and-tube heat exchangers having oval tubes under wet condition. Oval tubes having an aspect ratio of 0.6 were made, by deforming 12.7mm round tubes. Twelve samples, having different fin pitch and tube row, were tested. Results showed that, for oval tube samples, the effect of fin pitch on j and f factor was not significant. As for the effect of tube row, the lowest j factor was obtained for one row configuration(81% of two row configuration), which is clear contrast to round tube samples, where the highest j factor was obtained for one row configuration. Possible reasoning is provided considering the flow and heat transfer characteristics of sine wave channel combined with connecting oval tubes. Comparison of $j/f^{1/3}$ with plain fin-and-tube heat exchanger having 15.9mm O.D. round tube reveals that present oval fin-and-tube heat exchanger shows superior thermal performance except for one row configuration. In other words, $j/f^{1/3}$ of the two row oval tube heat exchanger was 1.6~2.5 times larger than those of round tube heat exchanger, 1.4~2.4 times larger for three row configuration and 1.2~2.8 times for four row configuration.

• 재활복지
• /
• v.22 no.1
• /
• pp.157-168
• /
• 2018

The purpose of this study is to investigate the impact of semi-closed vocal training-based Vocal Aerobic Treatment on the voice improvement of soprano. Study subject was one soprano who appealed to the suffering of her voice problem due to vocal cord nodule. A study method of conducting pre/post acoustic evaluation and subjective voice evaluation to compare the measures was used; Vocal Aerobic Treatment was carried out twice a week for a total of 32 session. In the acoustic evaluation, MDVP (multi-dimensional voice program) and VRP (voice range profile) were used to evaluate the pitch, voice quality, and voice range; in the subjective voice evaluation, SVHI (singing voice handicap index) was used to assess voice satisfaction. As a result of the pitch evaluation, the soprano maintained a proper Fo. As a result of the voice quality evaluation, the jitter, shimmer, and the noise harmonic ratio numbers decreased compared to the numbers shown before the treatment. As a result of the voice range evaluation, the scope of the range was broadened, with the number of semitone increasing from 30 to 35. As for the subjective voice evaluation, the result of the total score obtained after the survey report divided by the number of questions showed a decrease from 3.6 to 0.6. The soprano herself reported of having a minor extent of a voice problem. The summary of the above results reflects that Vocal Aerobic Treatment is useful in the voice improvement of vocalists However, as this study is case research regarding the Vocal Aerobic Treatment effect on one soprano, further research on the treatment effect covering many other vocalists is necessary. Also, there is a need for follow-up studies regarding voice management and voice treatment program on not only the vocalists but also the voice users in many other professions.

• Applied Chemistry for Engineering
• /
• v.32 no.1
• /
• pp.83-90
• /
• 2021

In this study, effects of the physical and chemical properties of low temperature heated carbon on electrochemical behavior as a secondary battery anode material were investigated. A heat treatment at 600 ℃ was performed for coking of petroleum based pitch, and the manufactured coke was heat treated with different heat temperatures at 700~1,500 ℃ to prepare low temperature heated anode materials. The physical and chemical properties of carbon anode materials were studied through nitrogen adsorption and desorption, X-ray diffraction (XRD), Raman spectroscopy, elemental analysis. Also the anode properties of low temperature heated carbon were considered through electrochemical properties such as capacity, initial Coulomb efficiency (ICE), rate capability, and cycle performance. The crystal structure of low temperature (≤ 1500 ℃) heated carbon was improved by increasing the crystal size and true density, while the specific surface area decreased. Electrochemical properties of the anode material were changed with respect to the physical and chemical properties of low temperature heated carbon. The capacity and cycle performance were most affected by H/C atomic ratio. Also, the ICE was influenced by the specific surface area, whereas the rate performance was most affected by true density.

• Journal of Korean Society of Disaster and Security
• /
• v.14 no.1
• /
• pp.1-8
• /
• 2021

A corrugated pipe is widely used in firefighting equipment and sprinkler pipes because of its elasticity, which is less damaged by deformation and convenient facilities. However, the corrugated shape of the wall results in complex internal turbulent flow, and it is difficult to predict the pressure drop, which is an important design factor for pipe flow. The pressure drop in the corrugated tube is a function of the shape factors of the pipe wall, such as groove height, length, and pitch. Existing studies have only shown a study of pressure drop due to length changes in the case of D-shaped tubes with less than 5 pitch (P) and height (K) of the rectangular grooves in the tube. In this work, we conduct a numerical study of pressure drop for P/Ks with length and height changes of 2.8, 3.5 and 4.67 with Re Numbers of 55,000, 70,000 and 85,000. The pressure drop in the corrugated tube was interpreted to decrease with smaller P/K. We show that the pressure drop is affected by the change in the groove aspect ratio, and the increase in the height of the groove increases the recirculation area, and the larger the Reynolds number, the greater the pressure drop.

• Journal of Aerospace System Engineering
• /
• v.17 no.6
• /
• pp.54-62
• /
• 2023

Flapping-wing air vehicles, well known for their free vertical take-off and excellent flight capability, are currently under intensive development and research. While most of the studies have explored the effect of various parameters of synchronized motions on the unsteady aerodynamics of flapping wings, limited attention has been given to the effect of nonsynchronous motions on the unsteady aerodynamic characteristics of flapping wings. In the present study, we conducted a numerical analysis to investigate the unsteady aerodynamic characteristics of an airfoil flapping with different frequency ratios between pitch and heave oscillations. We identified the motions and angle of attacks due to nonsynchronous motions. It was found that the synchronous motion produced thrust with zero lift, but the nonsynchronous motion generated a large lift with little drag. The aerodynamic characteristics of the airfoil undergoing the non-synchronous motion were also analyzed using the vorticity distributions and the pressure coefficient around and on the airfoil. When r was equal to 0.5, larger leading and trailing edge vortices were observed compared to the case when r was equal to 1.0, and these vortices significantly affected the aerodynamic characteristics of the airfoil undergoing the nonsynchronous motion. In future, the effect of pitch amplitude on the unsteady aerodynamic characteristics of the airfoil will be studied.

• Journal of the Korean Society of Safety
• /
• v.33 no.1
• /
• pp.7-15
• /
• 2018

The friction factors according to the flow regimes in helical coil tubes depend on the coil diameter, the tube diameter, and the coil pitch. In previous studies, correlations for the laminar flow regime in helical coil tubes have been proposed. However, studies on the transition flow regime and the turbulent flow regime are insufficient and further researches are necessary. In this study, characteristics of the friction factors for the laminar, transition and turbulent flow regimes in helical coil tubes were experimentally investigated. The helical coil tubes used in the experiments were made of copper. The curvature ratios of the helical coil tubes, which means the ratio of helical coil diameter to inner diameter of the helical coil tube are 24.5 and 90.9. Experiments were carried out in the range of $529{\leq}Re{\leq}39,406$ to observe the flows from the laminar to the turbulent regime. The friction factors were obtained by measuring the differential pressures according to the flow rates in the helical coil tubes while varying the curvature ratios of the helical coil tubes. Experimental data show that the friction factors for the helical coil tube with 24.5 in the curvature ratio of the helical coil tube were larger than those in the straight tube in all flow regimes. As the curvature ratio of the helical coil tube increases, the friction factor in turbulent flow regime tends to be equal to that of the straight tube. In addition, it was confirmed that the transition flow regimes in the helical coil tubes were much wider than those in the straight tube, also the critical Reynolds numbers were larger than those in the straight tube. The results obtained in this experimental study can be used as basic data for studies on the water hammer phenomenon in helical coil tubes.

• Korean Journal of Environment and Ecology
• /
• v.21 no.4
• /
• pp.356-365
• /
• 2007

This study was conducted to evaluate the changed vegetational community structure according to vegetational succession in Chiaksan National Park of Korea by applying ordination and classification method of floristic composition along with the actual vegetation by correlation. As for the ratio of actual vegetation, Mongolian oak forest(33.1%) was the highest, followed by mixed forest(16.2%), Japanese larch forest(15.6%), deciduous broad-leaved forest(14.7%), red pine forest(11.1%), Korean pine forest(2.3%) and Pitch pine forest(0.1%), respectively. The vegetation was classified into Acer pseudosieboidianum-Quercus mongolica community, Cornus controversa-Carpinus cordata community, Quercus sonata community, Pinus densiflora community and afforestation. The Acer pseudosieboldianum-Quercus mongolica community-a subordinately ranked community-was divided into Carpinus laxiflora-Sassa borealis community, Fraxinus rhynchophylla community and Symplocos chinensis for. pilosa-Carex siderosticta community. The results of community classification using by ordination and classification method of floristic composition were similar to each other. The vegetational succession, with the combination of Quercus mongolica, Acer pseudosieboldianum and Rhododendron schlippenbachii, was predicted to form a climax forest from above the hillside.

• Journal of Physiology & Pathology in Korean Medicine
• /
• v.25 no.6
• /
• pp.1108-1112
• /
• 2011

Voice can be widely used to classify the four constitution types and to recognize one's health condition from extracting meaningful features as physical quantity in traditional Korean medicine or Western medicine. In this paper, we proposed the method to update the standard operating procedure (SOP) to acquire and record voices for extracting stable vocal features since they are sensitive to the variation of a subject's utterance. At first, we obtained pitch frequencies from vowels and the sentence and intensity form the sentence as features with voices acquired under subjects' utterance conditions and then the deviation ratios of features from median values according to the utterance conditions were obtained and the condition to minimize the ratio was selected as a new SOP. As a result, we decided the SOP for a subject to utter vowels with the length of 2s~1s and sentences with over 2s interval between them after practice, in consideration of the deviation and qualitative requirements. Stable voice features obtained from updated SOP produce accurate diagnosis, which will be developed and simplified for using in the u-Healthcare system of personalized medicine.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.14 no.4
• /
• pp.273-279
• /
• 2011

Turbulent flow analysis around a wind turbine blade was performed to evaluate the power performance of offshore wind turbine. Fluent package was utilized to solve the Reynolds-averaged Navier-Stokes equations in non-inertial rotating coordinates. The realizable k-$\varepsilon$ model was used for turbulence closure and the grid system combining structured and unstructured grids was generated. In the first, lift and drag forces of 2-D foil section were calculated and compared with existing experimental data for the validation. Then torque and thrust of the wind turbine blade having NACA 4-series sections were calculated with fixed pitch angle and rpm. Tip speed ratio was varied by changing wind speed. In the next, three kinds of end plate were attached at the tip of blade in order to increase the power of the wind turbine. Among them the end plate attached at the suction side of the blade was found to be most effective. Furthermore, performance analysis with tilt angle and rake was also performed.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.08a
• /
• pp.86-86
• /
• 2012

The new approaches for silicon solar cell of new concept have been actively conducted. Especially, solar cells with wire array structured radial p-n junctions has attracted considerable attention due to the unique advantages of orthogonalizing the direction of light absorption and charge separation while allowing for improved light scattering and trapping. One-dimenstional semiconductor nano/micro structures should be fabricated for radial p-n junction solar cell. Most of silicon wire and/or pillar arrays have been fabricated by vapour-liquid-solid (VLS) growth because of its simple and cheap process. In the case of the VLS method has some weak points, that is, the incorporation of heavy metal catalysts into the growing silicon wire, the high temperature procedure. We have tried new approaches; one is electrochemical etching, the other is noble metal catalytic etching method to overcome those problems. In this talk, the silicon pillar formation will be characterized by investigating the parameters of the electrochemical etching process such as HF concentration ratio of electrolyte, current density, back contact material, temperature of the solution, and large pre-pattern size and pitch. In the noble metal catalytic etching processes, the effect of solution composition and thickness of metal catalyst on the etching rate and morphologies of silicon was investigated. Finally, radial p-n junction wire arrays were fabricated by spin on doping (phosphor), starting from chemical etched p-Si wire arrays. In/Ga eutectic metal was used for contact metal. The energy conversion efficiency of radial p-n junction solar cell is discussed.