• 한국정밀공학회지
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• 제32권6호
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• pp.577-585
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• 2015

We fabricated multi-scale such as macro-, micro-, and multi-scale wrinkles by using repetitive volume dividing (RVD) method and thermal curing process. Also wrinkle surface was modified with coating of a self-assembled monolayer (SAM). We measured the contact angle of each wrinkled surface, and observed the behavior of droplets on sloping surface. Through experimental study, we found out that the contact angle was much higher in case of multi-scale and SAM coated wrinkles. And micro-scale wrinkle showed a high contact angle comparing with that of macro-scale wrinkle. Dynamic behaviors of a water droplet like sliding velocity on diverse wrinkled surfaces were dependent on their static contact angles. These results showed that hydro-dynamic characteristics were changed depending on the wrinkle structure and the material forming the wrinkle. These dynamic characteristics can be utilized in bio-chip, microfluidics, and many others in order to control easily chemical reactivity.

• Physical Therapy Rehabilitation Science
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• 제10권4호
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• pp.406-413
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• 2021

Objective: The purpose of this study was to investigate effects of taping technique applied to knee instability. Design: Cross sectional study. Methods: Twenty-six participants with knee instabilityparticipated in this study. They were randomly assigned to the Kinesio taping (KT) group (n=13) and the dynamic taping (DT) group (n=13). Both groups applied knee stabilization taping techniques. In order to compare the effects of each taping technique, the change in the landing error scoring system (LESS) and lower extremity joint angle wasrecorded before and after the intervention. Results: Both groups significantly decreased in the change before and after the LESS (p<0.05). At the joint angle of the lower extremities, KT group significantly reduced the valgus angle at the max knee flexion (p<0.05). In DT group knee joint flexion and hip joint flexion angles were significantly increased at foot contact (p<0.05). In max knee flexion, the knee joint flexion angle was significantly increased (p<0.05). In foot contact, max knee flexion, the knee joint valgus angle was significantly increased (p<0.05). DT group showed more significant changes in knee joint flexion angle at foot contact and hip joint flexion angle at max knee flexion. Conclusions: Dynamic taping is a clinically applicable intervention method for lowering the risk of non-contact injury in participants with knee instability and for knee stability during rehabilitation exercises.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2003년도 학술대회지
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• pp.348-354
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• 2003

An analysis of the dynamic behavior between disk and roller has been performed when the torque is transmitted to toroidal IVT (Infinitely Variable Transmission). The contact area, shape and pressure with elliptical shapes between disk and roller are computed as the transmission ratios are changed. This study will give the information of contact shapes between roller-input dist and roller-output disk which are working under the most severe condition. The computed results are expected to guide the design criteria for the enhanced endurance li(e. Furthermore, the investigation of contact behaviors is very crucial to develop the traction oil that the efficiency of IVT system is most dependent on.

• Nuclear Engineering and Technology
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• 제55권4호
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• pp.1269-1279
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• 2023

Pool boiling experiments are performed within an isolated bubble regime at inclination angles of 0° and 45°. When a bubble grows and departs from the heating surface, the pressure, buoyancy, and surface tension force play important roles. The curvature and base diameter are required to calculate the pressure force, the bubble volume is required to calculate the buoyancy force, and the contact angle and base diameter are required to calculate the surface tension force. The contact angle, base diameter, and volume of the bubbles are evaluated using images captured via a high-speed camera. The surface tension force equation proposed by Fritz is modified with the contact angles obtained in this study. When the bubble grows, the contact angle decreases slowly. However, when the bubble departs, the contact angle rapidly increases owing to necking. At an inclination angle of 0°, the contact angle is calculated as 82.88° at departure. Additionally, the advancing and receding contact angles are calculated as 70.25° and 82.28° at departure, respectively, at an inclination angle of 45°. The dynamic behaviors of bubble growth and departure are discussed with forces by pressure, buoyancy, and surface tension.

• Korean Chemical Engineering Research
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• 제60권1호
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• pp.145-150
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• 2022

움직이는 접촉선에서의 계면 거동을 이해하기 위해 많은 연구자들은 동적접촉각에 대한 연구를 지속적으로 연구해 왔다. 하지만 가시화 기술의 한계로 선행연구에서의 동적접촉각에 대한 실험은 일반적으로 친수성 미세관에서 가시광선 기반으로 실험이 수행되었다. 하지만, 최근 다양한 연구 및 산업 분야에서 소수성 미세관에서의 동적접촉각에 대한 연구의 필요성이 대두되고 있다. 따라서, 본 연구에서는 높은 공간 및 시간 분해능을 갖는 방사광 X-선 영상법을 이용하여 소수성 마이크로 튜브 내 물-글리세롤 혼합물 슬러그의 동적접촉각을 측정하였으며, 이를 바탕으로 기존의 동적 접촉각 실험 상관식을 검증하였다.

• Tribology and Lubricants
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• 제34권1호
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• pp.23-32
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• 2018

Coupling is a mechanical component that transmits rotational force by connecting two shafts. Curvic coupling is widely used in high-performance systems because of its excellent power transmission efficiency and easy machining. However, coupling applications change dynamic behavior by reducing the stiffness of an entire system. Contact surface stiffness is an important parameter that determines the dynamic behavior of a system. In addition, the roughness profile of a contact surface is the most important parameter for obtaining contact stiffness. In this study, we theoretically establish the process of contact and bending stiffness analysis by considering the rough surface contact at Curvic coupling. Surface roughness parameters are obtained from Nayak's random process, and the normal contact stiffness of a contact surface is calculated using the Greenwood and Williamson model in the elastic region and the Jackson and Green model in the elastic-plastic region. The shape of the Curvic coupling contact surface is obtained by modeling a machined shape through an actual machining tool. Based on this modeling, we find the maximum number of gear teeth that can be machined according to the contact angle. Curvic coupling stiffness is calculated by considering the contact angle, and the calculation process is divided into stick and slip conditions. Based on this process, we investigate the stiffness characteristics according to the contact angle.

• Tribology and Lubricants
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• 제16권4호
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• pp.289-294
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• 2000

This paper present the contact stresses, which considers the shear stress at the cam and follower interface in the direct acting type valve train system of a high speed engine. To determine the contact condition, the normal contact forces are calculated by using the lumped mass dynamic modeling. The line contact is considered between the cam and follower interface. The variations of dynamic stresses are presented as a function of camshaft rotational angle. Also the effects of various design parameters are investigated.

• 설비공학논문집
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• 제30권1호
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• pp.33-43
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• 2018

This study numerically investigated statistic and dynamic behaviors of the water droplet on plate with or without various structured-pillars at nano-scale by molecular dynamics simulation. This study considered smooth plate, plate with the rectangular-structured pillar, and the plate with dual-structured pillar under various characteristic energy conditions. The static behavior of water droplet depending on the plate shape, plate surface energy, and the pillar characteristics were examined. After the water droplet reaches its steady state, this study investigated the dynamic behavior of the water droplet by applying a constant force. Finally, this study investigated the static and dynamic behaviors of the water droplet by measuring its contact angle and contact angle hysteresis. As a result, we found that the structure was more hydrophobic.

• 한국표면공학회지
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• 제35권2호
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• pp.129-137
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• 2002

The purpose of solderability assessment is to predict the effectiveness of soldering process. It is important for companies pursuing zero defects manufacturing because poor solderability is the major cause of two third of soldering failures. The most versatile solderability method is wetting balance method. However, there exist so many indices for wettability in the wetting balance test e.g. time to reach 2/3 values of maximum wetting force, tine to reach zero wetting force, maximum withdrawal force. In this study, three solderability assessment methods, which were the maximum withdrawal force, the wetting balance and the dynamic contact angle (DCA), were evaluated by comparing each other. The wetting balance technique measures the solderability by recording the forces exerted from the specimen after being dipped into the molten solder. Then the force at equilibrium state can be used to calculate a contact angle, which is known as static contact angles. The DCA measures contact angles occurred during advancing and withdrawing of the specimen and the contact angles are known as dynamic contact angles. The maximum withdrawal force uses the maximum force during withdrawal movement and then a contact angle can be calculated. In this study, the maximum withdrawal force method was found to be an objective index for measuring the solderability and the experiment results indicated good agreement between the maximum withdrawal force and the wetting balance method.

• 한국가시화정보학회지
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• 제22권1호
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• pp.28-33
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• 2024

We visualized the rupturing of liquid films flowing over a disk rotating with large angular velocity. A setup of high speed imaging for liquid flows on dark and reflective surfaces are suggested. From the result, rivulet structures are revealed to be strongly governed by three-dimensional surface structures developed in the film flow. Additionally, unique flow structures including the rivulet sliding and internal meandering are investigated. Generation mechanism of such structures are discussed in terms of the dynamic contact angle theory.