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Publications (14)2.18 Total impact

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    ABSTRACT: Evaluation of the heart work is starting to emerge as a new diagnostic tool for arterial diseases. The aim of this study is to develop a mathematical model for the estimation of heart work utilizing the pulse waves between two points of a vessel. In order to calculate heart work, medical data such as blood pressure waveforms (which are measured using a cuff) are utilized. The heart work is calculated by employing the modified Windkessel model together with the viscosity models of Casson or Herschel-Bulkely (H-B). The results indicate that the compliance values at the proximal and distal locations differ for the Casson and H-B models.
    Transactions of the Korean Society of Mechanical Engineers B 01/2012; 36(2).
  • Transactions of the Korean Society of Mechanical Engineers B 10/2010; 34(10):893-899.
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    ABSTRACT: Recently, Korean Government is encouraging to propagate the small hydro-electric power in renewable energy development policy as the “Low CO2 Green Growth” policy. However, turbines in the Korea Water Resources Corporation (below K-water) operated at an average of 10% less than well-designed turbines due to the design weakness or the inferior manufacturing techniques for the small hydropower facilities. Thus, maintenance fees increased because the cavitations had excessively occurred on the main parts of turbines such as the runner, guide vane and Stator, the life cycles of turbines were reduced and the frequency breakdowns were increased. In order to improve the efficiency the CFD-based design system is applied to the Francis turbine replacement project with Korea Fluid Machinery Association (below KFMA) and K-water. Therefore, the inversed design technique and the fully turbulent 3-dimensional flow simulations are performed for both the existing and new turbines at design and off design conditions. As a result, the runner is optimized to the greatest extent with a possible minimum cost under the geometrical constraints of the existing machine. The performances of the new design are verified by extensive model tests and the guarantees have all been successfully met.
    ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting collocated with 8th International Conference on Nanochannels, Microchannels, and Minichannels; 01/2010
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    ABSTRACT: While recent advances in percutaneous coronary interventions, treatment of coronary bifurcation lesions is a challenging area. For increasing the success rate of complicated angioplasty and minimizing complication, micro-robot angioplasty which has the benefits of precision and miniaturization is emerging as one of treatment modalities. Atherosclerosis might be affected by the vascular geometry such as diameter, curved angle, bifurcation angle, and by the hemodynamic factor, such as oscillatory shear stress. The purpose of this study is investigating the flow characteristics and distributions of the hemodynamic wall parameters (HWP) and comparing atheroma volume (AV) according as bifurcation angle (BA). Coronary bifurcation model between left anterior descending artery and first diagonal branch according as different angle from computed tomogram data. HWP, such as time averaged wall shear stress (TAWSS), oscillating shear index (OSI), and wall shear stress (WSS) distributions in coronary bifurcation model were calculated under different bifurcation angle (30, 45, 60, and 90°). AV was analyzed quantitatively with CT and intravascular ultrasound (IVUS) from patients with stable angina (n = 89). AV was compared according as BA. The bigger the BA, the lower TAWSS and the higher OSI at SB [TAWSS (Pa): 0.133, 0.020, 0.045, 0.060, OSI: 0.309, 0.472, 0.442, 0.469 at 30, 45, 60, and 90°, respectively]. The low shear zone was widening when the BA increasing. The mean AV of side branch in small BA (n = 40,
    01/2010;
  • Sang-Ho Suh, Hyung-Woon Roh, Jong-Youn Byun
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    ABSTRACT: Sedimentation phenomenon of suspended solids occurs by the gravitational force. Pollution particles are separated from slowly flowing waste water in clarifier. Recently, the sludge suction collector is Preferred rather than the scraper type sludge collector due to the enhancement of the clarifier efficiency. The sludge suction collector is usually operated by the user's experiences without any scientific and/or technical consideration. To evaluate the performance of sludge suction collector, the three dimensional numerical simulation was conducted by the finite volume method. To analyze the performance, the velocity vectors and the suction flow rates of the orifices were investigated. The result showed that each suction flow rate through out the collector was equivalent in the sludge suction collector and the efficiency of suction collector was good to remove high concentrated sludge in clarifier.
    Journal of Fluid Machinery. 01/2006; 9(5).
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    Dong-Joo Kim, Hyung-Woon Roh, Sang-Ho Suh
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    ABSTRACT: In this study the effects of fluid viscosity on the pump performances for a conventional centrifugal pump were experimentally investigated. The study aimed to compare the pump characteristics between water and viscosity fluids. In order to measure the flow rate and pressure, v-notch welt and bourdon pressure gauges were used for the codes of KS B6301 and KS B6302. The working fluids were water, aqueous sugar and glycerin solutions. The results were summarized as follows : The experimental results were summarized as follows : the pump characteristics of the total head, shaft power, and efficiency with high viscosity fluids were different from those of water. When the viscosity of the applied fluid was increased, the total head and efficiency were more decreased than those of water. The decreasing gradients of the total head and the efficiency were larger than water due to the increased disk friction losses at the duty operation point. However, the shut-off head was almost constant regardless the viscosity of applied fluids. Each efficiency curves for the sugar and glycerin solutions was decreased up to and than that of water, respectively.
    Journal of Fluid Machinery. 01/2004; 7(2).
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    Sun-Kyung Sung, Sang-Ho Suh, Hyung-Woon Roh
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    ABSTRACT: When the water flowing inside of the heat transfer equipments such as heat exchangers, condensers, and boilers is heated, calcium, magnesium sulfate, and other minerals in the water are deposited and built up for scales on the heat transfer surfaces. When those scales accumulate on the heat transfer surfaces, their performance of the heat transfer become progressively reduced due to the increase of the heat transfer resistance. The mechanism of this reduced heat transfer is called fouling. This study investigated the formation of the fouling in a heat exchanger with river and tap water flowed inside of it as a coolant. In order to visualize the formation of the fouling and to measure the fouling coefficients, a lab-scale heat exchanging system was used. Based on the experimental results, it was found that the formation of fouling for river water was quite different with the formation for tap water. ??? ??뼀 ?????G?
    Transactions of the Korean Society of Mechanical Engineers B 01/2004; 28(6).
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    Hyung-Woon Roh, Jae-Soo Kim, Sang-Ho Suh
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    ABSTRACT: The periodicity of the physiological flow has been the major interest of analytic research in this field up to now. Among the mechanical forces stimulating the biochemical reaction of endothelial cells on the wall, the wall shear stresses show the strongest effect to the biochemical product. The objective of present study is to find the effects of velocity waveform on the wall shear stresses and pressure distribution along the artery and to present some correlation of the velocity waveform with the clinical observations. In order to investigate the complex flow phenomena in the bifurcated tube, constitutive equations, which are suitable to describe the rheological properties of the non-Newtonian fluids, are determined, and pulsatile momemtum equations are solved by the finite volume prediction. The results show that pressure and wall shear stresses are related to the velocity waveform of the physiological flow and the blood viscosity. And the variational tendency of the wall shear stresses along the flow direction is very similar to the applied sinusoidal and physiological velocity waveforms, but the stress values are quite different depending on the local region. Under the sinusoidal velocity waveform, a Newtonian fluid and blood show big differences in velocity, pressure, and wall shear stress as a function of time, but the differences under the physiological velocity waveform are negligibly small.
    Journal of Mechanical Science and Technology 01/2003; 17(2):296-309. · 1.09 Impact Factor
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    Min-Tae Cho, Hyung-Woon Roh, Sang-Ho Suh, Jae-Soo Kim
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    ABSTRACT: The objectives of the present study are to numerically and experimentally investigate the steady and pulsatile flow phenomena in the circular tubes, to quantitatively compare the flow characteristics of Newtonian and non-Newtonian fluids, and to find meaningful hemodynamic information through the flow analysis in the human blood vessels. The particle image velocimetry is adopted to visualize the flow fields in the circular tube. and the results from the particle image velocimetry are used to validate the results of the numerical analysis. In order to investigate the blood flow phenomena in the circular tube. constitutive equations, which are suitable to describe the rheological properties of the non-Newtonian fluids. are determined, and the steady and pulsatile momentum equations are solved by the finite volume prediction. The velocity vectors of the steady and pulsatile flow in the circular tube obtained by the particle image velocimetry arc in good agreement with those by the numerical analysis. For the given mass flow rate. the axial velocity profiles of the Newtonian and the non-Newtonian fluids appear differently. The pulsatile flow phenomena of the Newtonian and the non-Newtonian fluids are quite different from those of the steady flow.
    Transactions of the Korean Society of Mechanical Engineers B 01/2002; 26(11).
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    ABSTRACT: The pump/motor selection program for optimized selection of regional water supply facilities was developed based on a flowchart compiled from basic operational data, total head requirement, initial pump/motor specification selection etc. This program was developed in Visual Basic. The program accepts, as in the flowchart, operational requirements of pumps and other system requirements, and calculates specific speed based on flow rate, total head and rotational speed. Then the calculated specific speed is used to select pump types and speed prior to determining likelihood of cavitation occurring at the calculated NPSH. Power requirement is then calculated for safe operation of pump to assist final pump selection. Test results of the program match very closely to the design values of Paldang intake pump station(3rd stage) proving that the program can be used as an effective and practical aid for designing new regional water supply systems.
    Journal of Fluid Machinery. 01/2001; 4(4).
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    ABSTRACT: In this study the effects of nozzle diameter on the performance characteristics for the tangential impeller-type water meter are studied experimentally. The nozzle is cut along the tangential direction of the inner case in the water meter. The nozzle shape is round and the number of nozzles used for the experimental study are 8. The performance characteristics are discussed for various nozzle diameters such as 3.1, 3.3, 3.5, 4.0, 4.5 and 5.0 mm. Among the tangential impeller-type water meters, the water meter with the nozzle diameter of 5.0 mm shows the least pressure loss and the instrumental error compared to the Korean Standards.
    Journal of Fluid Machinery. 01/1999; 2(3).
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    Sang-Ho Suh, Sang-Sin Yoo, Hyung-Woon Roh
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    ABSTRACT: The three-dimensional flow analysis using the finite volume method is presented to compare the steady flow characteristics of blood with those of blood substitutes such as water and aqueous polymer solution in an idealized double branching model. The model is used to simlllate the region of the abdominal aorta near the celiac and superior mesenteric branches. Apparent viscosities of blood and the aqueous Separan solution are represented as a function of shear rate by the Carreau model, Water and aqueoiu Separan AP-273 500wppm solution are frequently used as blood substitutes in vitro experiments. Water is a typical Newtonian fluid and blood and Separan solution are non-Newtonian fluids. Flow phenomena such as velocity distribution, pressure variation and wall shear stress distribution of water, blood and polymer solution are quite different due to differences of the rheological characteristics of fluids. Flow phenomena of polymer solution are qualitatively similar to those of blood but the phenomena of water are quite different from those of blood and polymer solution. It is recommended that a lion-Newtonian fluid which exhibits very similar rheological behavior to blood be used in vitro experiments. A non-Newtonian fluid whose rheological characteristics are very similar to those of blood should be used to obtain the meaninylll hemodynamic data for blood flow in vitro experiment and by numerical analysis
    Journal of Biomedical Engineering Research. 01/1997; 18(2).
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    ABSTRACT: Most studies on wind flows around buildings are focused on the flow fields of buildings with prismatic shapes. Only a few works on wind flows around odd-geometrical buildings are reported. Comprehensive studies for the flow phenomena in odd-geometrical buildings are of significance for practical building construction and heating-ventilating-air conditioning applications. Characteristics of approaching wind are determined by the climate data based on the history of typhoons that have passed through Korea. The wind characteristics obtained by the statistical data are used for numerical simulations. Three-dimensional wind flows around the model of odd-geometrical building are simulated using the finite volume method. Velocity vectors and average-wind-pressure coefficients for equivalent static load are calculated by numerical results. The magnitudes of the wind pressure coefficients for the model building are relatively small compared with those of prismatic-shaped buildings. The largest average-wind-pressure coefficient for southwestern wind of 1.04 can be found near the top on the south wall for an odd-geometrical building with wind openings, the average-wind-pressure coefficients are decreased by approximately 19–27% on the windward surfaces and 32–53% on the leeward surfaces compared with those for buildings with prismatic shapes.
    Journal of Wind Engineering and Industrial Aerodynamics - J WIND ENG IND AERODYN. 01/1997; 67:659-670.
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    ABSTRACT: Atherosclerosis, which is a degenerative vascular disease, is believed to occur in the blood vessels due to deposition of cholesterol or low density hpoprotein (LDL) Atherosclerotic lumen narrowing causes reduction of blood flow due to hemodynamic features Several hypothetical theories related to the hemodynamic effects have been reported. high shear stress theory, low shear stress theory, high shear stress gradient theory, flow separation and turbulence theory, and high pressure theory However, no one theory clearly explains the causes of atherosclerosis The objective of the present study was to investigate the mechanism of the generation of atherosclerosis In the study, the database of Korean carotid and coronary arteries for geometrical and hemodynamic clinical data was established The atherosclerotic sites were predicted by the computer simulations. The results of the computer simulation were compared with the in vivo experimental results, and then the pathogenesis of atherosclerosis by using the clinical data and several hypothetical theories were investigated From the investigation, it was concluded carefully that the mechanism of the generation of atherosclerosis was related to the hemodynamic effects such as flow separation and oscillatory wall shear stress on the vessel walls
    Journal of Mechanical Science and Technology 19(3):836-845. · 1.09 Impact Factor