• Tribology and Lubricants
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• v.38 no.2
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• pp.33-40
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• 2022

In this study, we present rotor dynamic analysis and operation test of a turbo expander for a hydrogen liquefaction plant. The turbo expander consists of a turbine and compressor wheel connected to a shaft supported by two hydrostatic radial and thrust bearings. In rotor dynamic analysis, the shaft is modeled as a rigid body, and the equations of motion for the shaft are solved using the unsteady Reynolds equation. Additionally, the operating test of the turbo expander has been performed in the test rig. Pressurized helium is supplied to the bearings at 8.5 bar. Furthermore, we monitor the shaft vibration and flow rate of the helium supplied to the bearings. The rotor dynamic analysis result shows that there are two critical speeds related with the rigid body mode under 40,000 rpm. At the first critical speed of 36,000 rpm, the vibration at the compressor side is maximum, whereas that of the turbine is maximum at the second critical speed of 40,000 rpm. The predicted maximum shaft vibration is 3 ㎛, whereas sub-synchronous vibration is not presented. The operation test results show that there are two critical speeds under the rated speed, and the measured vibration value agrees well with predicted value. The measured flow rate of the helium supplied to the bearing is 2.0 g/s, which also agrees well with the predicted data.

• Geomechanics and Engineering
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• v.28 no.5
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• pp.521-529
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• 2022

This research work deals with the development of air pluviation method for preparing uniform sand specimens for conducting large scale laboratory testing. Simulating real field conditions and to get reliable results, air pluviation method is highly desirable. This paper presents a special technique called air pluviation or sand raining technique for achieving uniform relative density. The apparatus is accompanied by a hopper, shutters with different orifice sizes and numbers and set of sieves. Before using this apparatus, calibration curves are drawn for relative density against different height of fall (H) and shutter sizes. From these calibration curves, corresponding to the desired relative density of 60%, the shutter size of 13mm and height of fall of 457.2 mm, are selected and maintained throughout the pluviation process. The density obtained from the mobile pluviator is then verified using the Dynamic Cone Penetrometer (DCP) test where the soil is poured in the box using defined shutter size and fall height. The results obtained from the DCP test are averaged as 60±0.5 which was desirable. The mobile pluviator used in this research is also capable of obtaining relative densities up to 90%. The instrument is validated using experimental and numerical approach. In numerical study, Plaxis 3D software is used in which the soil mass is defined by 10-Node tetrahedral elements and 6-Node plate is used to simulate plate behavior in the validation phase. The results obtained from numerical approach were compared with that of experimental one which showed very close correlation.

• The Journal of Korean Medicine Ophthalmology and Otolaryngology and Dermatology
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• v.35 no.3
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• pp.66-94
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• 2022

Objectives : Diabetic Foot Ulcer(DFU) is one of the common complications of diabetes. DFU is difficult to treat compared to other chronic wounds and clinically effective treatments are limited. The purpose of this study is to review the of external ointment treatment for DFU. Methods : 8 databases such as PubMed, EMBASE, CENTRAL, CNKI, NDSL, RISS, KISS, OASIS including English, Korean and Chinese were searched by structured search strategies that consist of terms as 'diabetic foot', 'diabetic foot ulcer(DFU)' and 'randomized' from January 2001 to January 2021. All randomized controlled trials(RCTs) involving treatment group as external ointment or in combination with conventional treatment were included. Results: A total of 20 RCTs was identified and analyzed. In treatment group, ointment was applied based on conventional treatment. A total of 16 different ointments were used, and the frequency of use was highest in the order of Heat-clearing drug, Blood-activating and stasis-dispelling drug, Tonifying and Replenishing drug and Orifice-opening drug. The most used herbs were in the order of Coptis chinensis Franch., Phellodendron chinense Schneid., Borneolum syntheticum., Angelica sinensis(Oliv.) Diels. In treatment group, a clinically effective effect was obtained compared to the contrast group. Conclusions : The result of this study suggest that external ointment treatment based on conventional treatment can be applied to DFU.

• Journal of Wetlands Research
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• v.25 no.3
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• pp.176-183
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• 2023

The aim of this paper is to understand the blade number effect on vortex turbine performance in the cylindrical vortex chamber below the free water surface. Using the same blade profile, the performance of gravitational vortex turbine is tested each with 2, 3, 4, 5 and 6 blades installed at the relative vortex height (y/h_v) ranging from 0.065 to 0.417. The obtained results indicate that the rotation, voltage, current and power increase in the relative vortex height of 0.065 and 0.111 when increasing the number of blades at flow velocity of less than 0.7 m/s. The average power of the 5-blade turbine is more than others. The performance of the 4-blade turbine with a 130 mm diameter installed near the orifice is higher than that of the same number of blades with a 220 mm diameter in the vortex chamber.

• Clinical Endoscopy
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• v.56 no.4
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• pp.490-498
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• 2023

Background/Aims: Post-endoscopic retrograde cholangiopancreatography pancreatitis (PEP) is the most common and serious complication of endoscopic retrograde cholangiopancreatography. To prevent this event, a unique precutting method, termed opening window fistulotomy, was performed in patients with a large infundibulum as the primary procedure for biliary cannulation, whereby a suprapapillary laid-down H-shaped incision was made without touching the orifice. This study aimed to assess the safety and feasibility of this novel technique. Methods: One hundred and ten patients were prospectively enrolled in this study. Patients with a papillary roof size ≥10 mm underwent opening window fistulotomy for primary biliary access. In addition, the incidence of complications and success rate of biliary cannulation were evaluated. Results: The median size of the papillary roof was 6 mm (range, 3-20 mm). Opening window fistulotomy was performed in 30 patients (27.3%), none of whom displayed PEP. Duodenal perforation was recorded in one patient (3.3%), which was resolved by conservative treatment. The cannulation rate was high (96.7%, 29/30 patients). The median duration of biliary access was 8 minutes (range, 3-15 minutes). Conclusions: Opening window fistulotomy demonstrated its feasibility for primary biliary access by achieving great safety with no PEP complications and a high success rate for biliary cannulation.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.19 no.2
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• pp.155-162
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• 2023

In nuclear power plants, the flow rate information is a major indicator of the performance of rotating equipment such as pumps, and is a very important one required for facility operation and maintenance. To measure a flow rate, various types of methods have been developed and used. Among them, the differential pressure type using orifice and the direct doppler type using ultrasonic waves are the most commonly used. However, these flow rate measurement methods have limitations in installation, conditions and status of the measuring part, etc. To solve this problem, we have studied a new technique for measuring flow rate from scratch. In this paper, we have devised a technique to estimate the flow rate using an average moving velocity of large-scale eddy in turbulence that occurs in the piping flow field. The velocity of the large-scale eddy can be measured using the pressure fluctuation signals on the inner surface of the pipe. To estimate the flow rate, at first a cross-correlation function is applied to the two pressure fluctuation signals located at different positions in the down stream for calculating the time delay between the moving eddies. In order to validate the proposed flow rate estimation method, CFD analyses for the internal turbulence flow in pipe are conducted with a fixed flow condition, where the pressure fluctuation signals on the pipe inner surface are simulated. And then the average flow velocity of the large scale eddy is to be estimated. The estimated flow velocity is turned out to be similar to the fixed (known) flow rate.

• Journal of Wetlands Research
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• v.26 no.3
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• pp.236-244
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• 2024

This research was conducted to determine the performance of a two-stage vortex turbine with a free water surface. The performance of the two-stage runner was studied by varying the flow rate and the position of the runner in the cylindrical vortex chamber. The experimental results showed that the performance parameters such as torque, voltage, current, and rotational speed increased with increasing flow rate. The runner depth ratio has a significant impact on the performance of the two-stage vortex turbine. The highest power generated by the two-stage runner occurred in the range of 0.054 to 0.162 runner depth ratio near the orifice. The power output of the two-stage runner was higher than that of the single runner due to more vortex and blade contact area in the flow range of 7.2 to 7.7 L/s.

• Journal of Chest Surgery
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• v.32 no.7
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• pp.628-636
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• 1999

Background: Recent advances in understanding the anatomy of the complete atrioventricular septal defect(including right-dominant unbalanced atrioventricular septal defect) have led to alternative methods of repairing these defects. Material and Method: From May 1997 to July 1998, 8 consecutive infants(age range, 2 to 28 months, mean body weight 6.0$\pm$2.2 kg) received a single-stage intracardiac repair of the complete atrioventricular septal defect with modified surgical methods. Depending on the specific anatomic structure, the procedure was simplified in 3 patients by a direct closure of the ventricular element of the defect(Group I). Two patients judged unsuitable for direct closure due to a potential left ventricular outflow tract obstruction had received a standard two-patch repair(Group II). The remaining 3 patients with right-dominant unbalanced complete atrioventricular septal defect underwent biventricular repair; to enlarge the orifice of the left atrioventricular valve, the ventricular septal patch was placed slightly more to the right of the ventricular crest, a left sided bridging leaflet was augmented with an autologous pericardial patch, and the leaflet was repaired with a double- orifice(Group III . Result: In all 8 patients, the postoperative echocardiography demonstrated good hemodynamics. Seven patients were weaned from the ventilators after a mean 3$\pm$1 days, and 1 patient was weaned after 24 days due to a reoperation and emphysematous lung problem. A reoperation was performed in 1 patient for progressive left atrioventricular valve regurgitation due to leaflet tearing. There were no early and late mortalities. At the time of the latest review, judging from the echocardiographic criteria, left atrioventricular valve stenosis was mild in 1 patient(mean pressure gradient 6.5 mmHg, 13.5%), left atrioventricular valve regurgitation was absent or grade I in 7 patients(87.5%). The right atrioventricular valve regurgitation was absent or grade I in all 8 patients(100%). Conclusion: Infants with complete atrioventricular septal defect were treated with either a simplified approach with direct closure of the ventricular element of the defect or a modified surgical technique for a right-dominant unbalanced atrioventricular septal defect, depending on the anatomic structure. The results were no operative mortalities and low morbidity.

• Journal of Chest Surgery
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• v.40 no.3 s.272
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• pp.200-208
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• 2007

Background: The effect of patient-prosthesis mismatch (PPM) on the clinical outcome following aortic valve replacement (AVR) remains controversial. This study compared the surgical outcomes of AVR between patients with a patient-prosthesis mismatch and those having undergone an aortic annular enlargement. Material and Method: Six hundred and twenty seven adult patients, who underwent AVR with stented bioprosthetic or mechanical valves, between January 1996 and February 2006, were evaluated. PPM was defined as an indexed effective orifice area (iEOA) ${\leq}0.85cm^2/m^2$, and Severe if the iEOA${\leq}0.65cm^2/m^2$ PPM was present in 103 (16.4%, PPM group) patients, and severe in 11 (1.8%, SPPM group). During the period of the study, 21 patients underwent an AVR with annular enlargement (AE group). Result: The mean iEOA of the AE group was larger than that of the PPM group ($0.95\;vs.\;0.76cm^2/m^2,\;p=0.00$). The AE group had longer CPB, ACC and operation times than the PPM group, and showed a tendency toward higher operative mortality (14.3% vs. 2.9%, p=0.06). The SPPM group had higher AV pressure gradients (peak/mean) than the AE group (72/45 mmHg vs. 38/25 mmHg, p=0.02/0.06) and suffered more AV related events (AV reoperation or severe aortic stenosis)(45.5% vs. 9.5%, p=0.03). LV masses were not regressed in the patients who experienced an AV related event. Conclusion: During AVR in patients with a small aortic annulus, annular enlargement should be carefully applied taking into account the high risk of operative mortality due to annular enlargement and co-morbidities of patients. Aortic annular enlargement; however, should be considered as an alternative method in patients expected to have a severe PPM after an AVR.

• Journal of Biomedical Engineering Research
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• v.25 no.5
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• pp.421-430
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• 2004

Clinically, it is almost impossible for a physician to distinguish subtle changes of frequency spectrum by using a stethoscope alone especially in the early stage of thrombus formation. Considering that reliability of mechanical valve is paramount because the failure might end up with patient death, early detection of valve thrombus using noninvasive technique is important. Thus the study was designed to provide a tool for early noninvasive detection of valve thrombus by observing shift of frequency spectrum of acoustic signals with computer aid diagnosis system. A thrombus model was constructed on commercialized mechanical valves using polyurethane or silicon. Polyurethane coating was made on the valve surface, and silicon coating on the sewing ring of the valve. To simulate pannus formation, which is fibrous tissue overgrowth obstructing the valve orifice, the degree of silicone coating on the sewing ring varied from 20％, 40％, 60％ of orifice obstruction. In experiment system, acoustic signals from the valve were measured using microphone and amplifier. The microphone was attached to a coupler to remove environmental noise. Acoustic signals were sampled by an AID converter, frequency spectrum was obtained by the algorithm of spectral analysis. To quantitatively distinguish the frequency peak of the normal valve from that of the thrombosed valves, analysis using a neural network was employed. A return map was applied to evaluate continuous monitoring of valve motion cycle. The in-vivo data also obtained from animals with mechanical valves in circulatory devices as well as patients with mechanical valve replacement for 1 year or longer before. Each spectrum wave showed a primary and secondary peak. The secondary peak showed changes according to the thrombus model. In the mock as well as the animal study, both spectral analysis and 3-layer neural network could differentiate the normal valves from thrombosed valves. In the human study, one of 10 patients showed shift of frequency spectrum, however the presence of valve thrombus was yet to be determined. Conclusively, acoustic signal measurement can be of suggestive as a noninvasive diagnostic tool in early detection of mechanical valve thrombosis.