• 한국자동차공학회논문집
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• 제6권3호
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• pp.187-197
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• 1998

To investigate the spray behavior and atomization characteristics using an air-assist injector, spray visualization and PDPA measurements were carried out under the various assisted air pressures and the fixed fuel pressure. The air assist pintle type injector employed in this study is consisted of the air assist adaptor and an injector housing using the gasoline fuel and air as the working fluids. As results, increasing pressure of assisted air, the growth of spray tip penetration is gradually reduced at the end of spray and spray angle is steadily increased at the main spray region except from the early spray. For the air assist pressure of 25㎪ in a spray downstream, it is doncluded that droplet size distribution shows the peak of 10${\mu}{\textrm}{m}$ and most of the droplet sizes are less than 50${\mu}{\textrm}{m}$. Also, the air-assist injector extremely improves fuel atomization in order to produce much finer droplets, it shows that approximately, in this case, 50% decreade of SMD than without air assit.

• Maxillofacial Plastic and Reconstructive Surgery
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• 제23권4호
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• pp.348-356
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• 2001

The factors related to relapse in 20 skeletal class III patients who performed two-jaw surgery with Le Fort I maxillary osteotomy and bilateral sagittal split ramus osteotomy was investigated. All patients were fixed with miniplate on the maxilla and three screws at each mandible. Cephalograms taken at preoperative, immediate postoperative and 8 months postoperative after surgery were traced and digitized. 1.The horizontal and vertical relapse of maxilla and mandibular chin points was within 1mm postoperatively. Compare to the preceding report concerning the mandibular set-back surgery only group, this reveals two-jaw surgery for mandibular prognathism using rigid fixation is more stable. 2.Although there was no significant relapse tendancy was observed at chin points, the screw tip land-marks moves anterio-superiorly and each side of the screws moved as a one unit. The screw tip points moved similar direction to the masticatory force and this movements might be influenced by the muscular tension to the distal segment of the mandible. 3.According to the regression analysis, the amount of horizontal and vertical movement of mandibular set-back influenced the mandibular relapse. However, direction and amount of maxillary surgical movement did not inf1uenced the maxillary and mandibular relapse.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.447-450
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• 2002

The purpose of this 3-D numerical simulation is to calculate and examine a 500 kW Horizontal Axis Wind Turbine (HAWT) power performance and 3-D rotor flow characteristics, which are compared to calculation data from Delft University. The experimental approach, which has been the main method of investigation, appears to be reaching its limits, the cost increasing relate with the size of wind turbines. Hence, the use of Computational Fluid Dynamics (CFD) techniques and Navier-Stokes solvers is considered a very serious contender. We has used the CFD software package CFX-TASCflow as a modeling tool to predict the power performance and 3-D flow characteristics of a wind turbine on the basis of its geometry and operating data. The wind turbine with 40m diameters rotor, it was scaled to compare with the calculation data from delft university. The HAWT, which has eight-rpm variations are investigated respectively. The pitch angle is $+0.5^{\circ}$and wind speed is fixed at 5m/s. The tip speed ratio (TSR) of the HAWT ranging from 2.89 to 9.63.

• Structural Engineering and Mechanics
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• 제5권3호
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• pp.257-268
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• 1997

The elastic deflections and Euler buckling loads are investigated for a class of tapered and initially curved cantilevered beams subjected to loading at the tip. The beam's width increases linearly and its depth decreases linearly with the distance from the fixed end to the tip. Unloaded, the beam forms a circular are perpendicular to the axis of bending. The beam's deflection responses, obtained by solving the differential equations in closed form, are presented in terms of four nondimensional system parameters: taper ratio ${\kappa}$, initial shape ratio ${\Delta}_0$, end load ratio f, and load angle ${\theta}$. Laboratory measurements of the Euler buckling loads for scale models of tapered initially straight, corrugated beams compared favorably with those computed from the present analysis. The results are applicable to future designs of the end structures of highway guardrails, which can be designed to give the appropriate balance between the capacity to deflect a nearly head-on vehicle back to its right-of-way and the capacity to buckle sufficiently that penetration of the vehicle may be averted.

• 센서학회지
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• 제18권6호
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• pp.461-466
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• 2009

This paper represents a piezoelectric ultrasonic linear actuator with flexural vibration mode. The actuator is composed of two piezo ceramics, the elastic body, and the connecting tip. It is driven by the frictional force between the connecting tip and the linear motion guide. Unimorph actuators have flexural vibration. Its middle point is fixed so that suitable to the flexural vibration of $3/2\lambda$. These vibrations contribute to elliptical motion by mixed mode between longitudinal and transverse mode. It was generated when the ultrasonic electrical signals with 90 degree phase difference are applied to two ceramics. A linear movement can be easily obtained using the elliptical motion. The ATILA, FEM simulator has been used to design actuator and verify the kinetic and dynamic analysis. We used the ceramics of $20\times10\times1$ mm size and confirmed the flexural vibration of the $3/2\lambda$ at the 79 kHz through the scanning of 3D-vibrometer. The maximum velocity of actuator was 221 mm/sec and the thrust force of actuator was 2.7 N in 200Vp-p of additional voltage.

• Geomechanics and Engineering
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• 제28권1호
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• pp.25-33
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• 2022

The energy transferred on drill rods by dynamic impact mainly determines the penetration depth for in-situ tests. In this study, the dynamic response and transferred energy of drill rods are determined from the frequency of the stress waves. AW-type drill rods of lengths 1 to 3 m are prepared, and strain gauges and an accelerometer are installed at the head and tip of the connected rods. The drill rods are hung on strings, allowing free vibration, and then impacted by a pendulum hammer with fixed potential energy. Increasing the rod length L increases the wave roundtrip time (2L/c, where c is the wave velocity), and hence the transferred energy at the rod head. At the rod tip, the first velocity peak is higher than the first force peak because a large and tensile stress wave is reflected, and the transferred energy converges to zero. The resonant frequency increases with rod length in the waveforms measured by the strain gauges, and fluctuates in the waveforms measured by the accelerometer. In addition, the dynamic response and transferred energy are perturbed when the cutoff frequency is lower than 2 kHz. This study implies that the resonant frequency should be considered for the interpretation of transferred energy on drill rods.

• 한국해양환경ㆍ에너지학회지
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• 제16권2호
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• pp.61-70
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• 2013

조류발전용 수직축터빈(VAT)의 3차원적인 유체동력학적 성능을 효과적으로 예측할 수 있는 연구를 진행하였다. 수치해석은 2차원과 3차원으로 수행하였으며 이를 통해 물리적 유동현상의 차이를 파악하였다. 3차원 효과는 주로 날개 끝단에서 발생하는 날개끝 보오텍스가 주된 원인으로서, 이로 인해 터빈 날개가 내어주는 양력이 손실되고 회전하는 터빈은 토크가 감소하였다. 이러한 현상은 본 연구에서 채택한 통상적인 수직축 터빈의 스팬-직경비 범위에서 상당한 수준으로 나타남을 확인하였다. 본 연구에서는 대상 터빈을 선정하고 2차원으로 성능해석 후 3차원 효과를 보정하는 비교적 간단하고 효과적인 방법을 제안하였다.

• Archives of Plastic Surgery
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• 제36권1호
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• pp.66-74
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• 2009

Purpose: The importance of the deformities in alar - columellar complex has been underestimated in Asian ethnic groups for the last decades. Fortunately, with increasing familiarity of the open rhinoplasty techniques, the anatomic details of the nasal tip have been pointed up. Definitely, having an interest and demand for improving the sub - normal relationship between the alar rim and columella are indebted for such growing of knowledge about nasal tip anatomy. However, it is true that any single procedure is not settled as versatile and fully confident modality to correct the retracted notching of the alar rim. With this article, I should like to propose another useful option for treating retracted ala. Methods: The author has tried to correct alar rim retraction by means of: (1) Triangular onlay septal cartilage graft on the lower lateral cartilage with the medial end fixed to the anterior surface of the lateral crus(Alar extension graft), (2) Inserting lateral end of the alar extension graft to the vestibular skin pocket in the form of a finger - in - groove, (3) using the vestibular skin in the form of an advancement flap, and (4) using the soft shield graft to prevent possible visible step - off of the alar margin. Results: The author applied an alar extension graft to 16 patients in order to correct a retracted ala for the last 27 months (August, 2003 - October, 2005). The distances from alar rim to long axis of nostril were improved to be within 2 mm in all of the cases, and also the shape of the alar rim changed to a round form. Nostril asymmetry (6%) in one case, temporary palpable step - off (18%) in three cases, temporary visible step - off (6%) in one case, and temporary paresthesia of the tip (25%) in four cases were observed. Conclusion: The alar extension graft is simple and efficacious. It does not need donor sites other than the operative field, and its results are predictable. In particular, since it may give structural intensity to a weak lower lateral cartilage, it may be preferentially used for the correction of a retracted ala that arises from hypoplastic lower lateral cartilage. Moreover intensified lower lateral cartilage also improves the esthetic shape of lobule.

• Restorative Dentistry and Endodontics
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• 제37권2호
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• pp.68-73
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• 2012

Objectives: The purpose of this study was to assess the accuracy of Root ZX (J. Morita Corp.) according to the location of major foramen and open apex. Materials and Methods: 81 mandibular premolars with mature apices were selected. After access preparation, 27 teeth were instrumented to simulate open apices. 54 teeth were classified according to location of major foramen under surgical microscope (${\times}16$). The file was fixed at the location of apical constriction by Root ZX using glass ionomer cement .The apical 4 mm of the apex was exposed and photo was taken and the distance from file tip to the major foramen was measured by calibrating metal ruler on graph paper. The results were statistically analyzed using ANOVA and Scheffe test at p < 0.05 level. Results: Mean distance from file tip to major foramen was 0.308 mm in Tip foramen group (I), 0.519 mm in Lateral foramen group (II) and 0.932 mm in open apex group (III). Root ZX located apical constriction accurately within ${\pm}0.5mm$ in group I of 85.71%, in group II of 59.09%, and in group III of 33.33%. There was a statistically significant difference between group I and III (p < 0.05). Conclusion: Root ZX located apical constriction accurately regardless of location of major foramen. However, Root ZX couldn't find it in open apex. Clinicians have to use a combination of methods to determine an appropriate working length at open apex. It may be more successful than relying on just electronic apex locator.

• Archives of Plastic Surgery
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• 제33권6호
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• pp.681-687
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• 2006

Purpose: The nose of most Koreans is characterized as a low nasal dorsum, retracted columella, and an acute columella-labial angle. For the surgical correction of the tip and columella, a modified septal extension graft, along with augmentation rhinoplasty has been developed. Methods: With this technique, a septal extension graft is fixed on the entire caudal margin of the septum (the cephalic-caudal axis) and at the same time, it is placed above the anterior nasal spine, in the membranous portion of the septum and at the base of the columella(the anterior-posterior axis). The present report describes the results obtained in 13 patients and offers an analysis of the results as judged by the columella-labial angle and 4 proportional indices(nose height index, nasal bridge length index, nasal tip projection index, columella length index), measured by photogrammetry. Results: The postoperative values obtained in these 5 categories increased significantly compared to the preoperative ones, thus confirming that the projection of tip was augmented, the nose was lengthened, and the columella was advanced caudally and lengthened. Moreover, these positive outcomes were still maintained during the follow-up period, and no side effects, such as saddle nose deformity, were reported. Conclusion: A modified septal extension graft can be considered as an effective method for the surgical correction of the nasal tip and columella in Koreans.