• Journal of the Korean Society of Visualization
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• v.9 no.2
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• pp.27-33
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• 2011

Supersonic liquid jet discharged from a nozzle has been investigated by using a ballistic range which is composed of high-pressure tube, pump tube, launch tube and liquid storage nozzle. High-speed Schlieren optical method was used to visualize the supersonic liquid jet flow field containing shock wave system, and spray droplet diameter was measured by the laser diffraction method. Experiment was performed with various types of nozzle to investigate the major characteristics of the supersonic liquid jet operating at the range of total pressure of 0.8 from 2.14 GPa. The results obtained shows that shock wave considerably affects the detailed atomization process of the liquid jet and as the nozzle diameter decreases, the shock wave angle and the averaged SMD of spray droplet tends to decrease.

• Journal of ILASS-Korea
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• v.2 no.2
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• pp.16-23
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• 1997

In this research a novel two-reference-beam double pulse holographic technique for the measurments of particle sizes and velocities was developed. This holographic method features the capability of separation of the first and second particle images by using two reference beams instead of one and the change of the polarization direction of laser light. The developed holographic system was tested through the measurements of droplet sizes and velocities in the spray created by two high speed impinging jets. The overall spray pattern clearly revealed the inherent wave nature. Smaller and faster droplets were generated with larger impingement angle, higher jet velocity. and smaller orifice diameter.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.4
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• pp.36-41
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• 2000

Mixing characteristics of unlike impinging streams double injectors have a great effect on combustion stability and combustion efficiency for liquid rocket engine. In this study a cold test was carried out, using water and TCE as simulants, in order to examine the effect of design parameters such as impingement angle, orifice diameter ratio and momentum ratio on the mass distribution and mixing quality.

• Journal of the Korean Society of Marine Environment & Safety
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• v.22 no.7
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• pp.884-891
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• 2016

A secondary injection system in a diesel engine has benefits: it can be controlled independently without interrupting engine control, it can be adapted to various layouts for exhaust systems, and it pose no reductant dilution problems compared to post injection systems in the combustion chamber or other supplemental reductant injections. In a secondary injection system, the efficiency of the catalyst depends on the method of reducing the supply. The reductant needs to be maintained and optimized with constant pressure, the positions and angles of injector is a very important factor. The concentration and amount of reductant can be changed by adjusting secondary injection conditions. However, secondary injection is highly dependent upon the type of injector, injection pressure, atomization, spray technology, etc. Therefore, it is necessary to establish injection conditions the spray characteristics must be well-understood, such as spray penetration, sauter mean diameter, spray angle, injection quantity, etc. Uniform distribution of the reductant corresponding to the maximum NOx reduction in the DeNOx catalyst system must also assured. With this goal in mind, the spray characteristics and impingement plate types of a secondary injector were analyzed using visualization and digital image processing techniques.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.2
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• pp.100-106
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• 2006

The behavior of spray impinging on the inclined constant temperature flat plate was experimentally investigated. To clarify the wall effect of a high pressure DISI injector, a relative angle of the inclined wall to a spray axis was varied. Spray penetration along the wall was observed optically and it was compared with that of a Fan spray type and Swirl type spray. To evaluate various spray motion quantitatively, a spray path penetration which describe the development of a spray tip along the wall was newly introduced. To observe the structure of an impinging spray, it was visualized by a controlled stroboscope light and its visualized image was captured on an CCD camera. Using the digital image of impinging spray $H_x$ and $R_x$ was extracted to clarify the structure of impinging spray. The main parameter of the relative position of the wall was the inclined angle which was defined as the angle was varied from $0^{\circ}$ (vertical impingement) to $60^{\circ}$ at the same condition.

• Hip & pelvis
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• v.35 no.4
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• pp.259-267
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• 2023

Purpose: Nondisplaced femoral neck fractures have traditionally been treated with in situ fixation. However, poor surgical and clinical outcomes have been reported for fractures with valgus deformity >15°, and the reduction of valgus impaction has recently been emphasized. In addition, early degenerative osteoarthritis can be caused by cam-type femoroacetabular impingement after healing of femoral neck fractures. This study was designed with the objective of confirming the difference in progression of radiographic osteoarthritis according to the severity of the valgus deformity. Materials and Methods: Patients who underwent internal fixation using multiple cannulateld screws for management of nondisplaced femoral neck fractures were divided into two groups: high valgus group (postoperative valgus angle ≥15°) and low valgus group (postoperative valgus angle <15°). Evaluation of demographic data and changes in the joint space width from the immediate postoperative period to the latest follow-up was performed. Results: A significant decrease in joint space width in both hip joints was observed in the high valgus group when compared with the low valgus group, including cases with an initial valgus angle less than 15° and those corrected to less than 15° of valgus by reduction. No complications requiring surgical treatment were observed in either group; however, two cases of avascular necrosis, one in each group, which developed in the low valgus group after reduction of the fracture, were followed for observation. Conclusion: Performing in situ fixation in cases involving a valgus deformity ≥15° in non-displaced femoral neck fractures may cause accelerated narrowing of the hip joint space.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.7
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• pp.445-454
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• 2022

Ice accretion on the aircraft components, such as wings, fuselage, and empennage, can occur when the aircraft encounters a cloud zone with high humidity and low temperature. The prevention of ice accretion is important because it causes a decrease in the aerodynamic performance and flight stability, thus leading to fatal safety problems. In this study, a shape design optimization of a multi-element airfoil is performed to minimize the amount of ice accretion on the high-lift device including leading-edge slat, main element, and trailing-edge flap. The design optimization framework proposed in this paper consists of four major parts: air flow, droplet impingement and ice accretion simulations and gradient-free optimization algorithm. Reynolds-averaged Navier-Stokes (RANS) simulation is used to predict the aerodynamic performance and flow field around the multi-element airfoil at the angle of attack 8°. Droplet impingement and ice accretion simulations are conducted using the multi-physics computational analysis tool. The objective function is to minimize the total mass of ice accretion and the design variables are the deflection angle, gap, and overhang of the flap and slat. Kriging surrogate model is used to construct the response surface, providing rapid approximations of time-consuming function evaluation, and genetic algorithm is employed to find the optimal solution. As a result of optimization, the total mass of ice accretion on the optimized multielement airfoil is reduced by about 8% compared to the baseline configuration.

• Clinics in Shoulder and Elbow
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• v.20 no.4
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• pp.217-221
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• 2017

Background: The purpose of this study was to evaluate the clinical and radiographic outcomes of internal fixation with locking T-plates for osteoporotic fractures of the proximal humerus in patients aged 65 years and older. Methods: From January 2007 through to December 2015, we recruited 47 patients aged 65 years and older with osteoporotic fractures of the proximal humerus. All fractures had been treated using open reduction and internal fixation with a locking T-plate. We classified the fractures in accordance to the Neer classification system; At the final follow-up, the indicators of clinical outcome-the range of motion of the shoulder (flexion, internal rotation, and external rotation) and the presence of postoperative complications-and the indicators of radiographic outcome-the time-to-union and the neck-shaft angle of the proximal humerus-were evaluated. The Paavolainen method was used to grade the level of radiological outcome in the patients. Results: The mean flexion was $155.0^{\circ}$ (range, $90^{\circ}-180^{\circ}$), the mean internal rotation was T8 (range, T6-L2), and the mean external rotation was $66.8^{\circ}$ (range, $30^{\circ}-80^{\circ}$). Postoperative complications, such as plate impingement, screw loosening, and varus malunion were observed in five patient. We found that all patients achieved bone union, and the mean time-to-union was 13.5 weeks of the treatment. The mean neck-shaft angle was $131.4^{\circ}$ at the 6-month follow-up. According to the Paavolainen method, "good" and "fair" radiographic results each accounted for 38 and 9 of the total patients, respectively. Conclusions: We concluded that locking T-plate fixation leads to satisfactory clinical and radiological outcomes in elderly patients with proximal humeral fractures by providing a larger surface area of contact with the fracture and a more rigid fixation.

• Journal of ILASS-Korea
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• v.11 no.4
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• pp.251-265
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• 2006

To prevent the ozonosphere from being destroyed by Halon, it is an urgent task to find out Halon replacement. As one of the replacements water mist have showed broad applications by its advantages: little pollution to environment (not destroying the ozone layer or bring green house effect), extinguishing fire quickly, consuming a small quantity of water and having little damage to the protected objects. The methods of generating water mist strongly influence fire suppression effectiveness, which determine the cone angle, drop size distribution, flux uniformity, and momentum of the generating spray. The traditional water mist nozzle included pressure jet nozzles, impingement nozzles and twin-fluid nozzles. All of them have more or less disadvantages for fire suppression. Therefore, many research institutes and corporations are taking up with innovations in mist generation. This article provided some recent studies in State Key Laboratory of Fire Science (SKLFS) of University of Science and Technology of China. SKLFS have investigated new methods of generating water mist (i.e. effervescent atomization and ultrasonic atomization). and self developed a series of nozzles and developed advanced DPIVS (Digital Particle Image Velocimetry and Sizing) technique. Characteristics of water mist (the distribution of droplet sizes, flux density, spray dynamics and cone angle) produced by these nozzles were measured under different conditions (work pressure, nozzle geometry, etc.) using LDV/APV and DPTVS systems. A series of experiments were performed to study the fire suppression effectiveness in different fire scenario (different kindsof the fuel, fire size and ventilation conditions). The fire extinguishing mechanisms of water mist was also discussed.

• The Journal of Engineering Geology
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• v.6 no.2
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• pp.53-58
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• 1996

In order to investigate the source mechanism of micro cracks through acoustic emission measurement induced by rock fracture, careful calibration of the entire linkage of the detecting system, from the transducers to transient recorder, is an essential requirement prior to testing. Transducers and digitiging system are generally the weakest links in the measurement system because they must translate mechanical motions into digital electric signals. In this study, PAC piezoelectric pressure transducers are calibrated with a standard NBS conical shaped displacement transducer and a DG piezoelectric displacement transducer. The NBS and PAC transducers are insensitive to changes in horizontal impingement angle but sensitive to changes in incident angle. The ray path along the logitudinal axis of the tranducer produced a maximum response while the ray path perpendicular to the transducer axis gave a minimum. And a difference in individual transducers factor for a peak-to-peak amplitude of PAC transducers was within 40%. An average PAC transducer coefficient was determined as 77mv/pm by an absolute calibration test using NBS transducer.