• 센서학회지
• /
• 제24권1호
• /
• pp.1-5
• /
• 2015

The V-grooved single-mode fiber in which a surface part of the core was removed was investigated as a quasi-distributed water detection sensor. In the normal state, the V-grooved region is filled and covered with a specific RI (Refractive Index)-matched medium, and the sensor experiences minimal optical loss. As water invades the V-grooved region, the material is dissolved and removed, and a considerable optical loss occurs owing to the large RI difference between the fiber core and water. The experimental results showed the feasibility of the device as a sensor element of the quasi-distributed water detection sensor system based on general optical time domain reflectometry (OTDR).

• Tribology and Lubricants
• /
• 제18권2호
• /
• pp.105-108
• /
• 2002

Specially designed grooved journal bearings are installed in the main coolant pump for SMART (System-integrated Modular Advanced ReacTor) to support radial load on the rotating shaft. The canned motor type main coolant pumps are arranged vertically on the reactor vessel and filled with circulating primary coolant which is pure water. The main coolant pump bearings are lubricated with this coolant without any other external lubricant supply. Because lubricating condition is too severe for this bearing to generate proper hydrodynamic film, investigation of lubrication characteristics of the journal bearing is important to satisfy life constraint of whole pump system, and the results will be applied to the analysis of dynamic characteristics of the shaft system. The bearing is made of silicon graphite which has self$.$lubricating effect. A lubrication analysis method is proposed for this vertically grooved journal bearing in the main coolant pump of SMART, and lubricational characteristics of the bearings are examined in this paper.

• 한국정밀공학회지
• /
• 제21권3호
• /
• pp.117-123
• /
• 2004

A brake disc with helical grooved vent in radial direction is proposed for the improvement of thermal dissipation. The heat transfer phenomenon is analyzed far both the proposed disc and the conventional one using finite element method. The thermal dissipation is considerably influenced by the geometrical differences of the brake discs. The results of the analysis show that the proposed brake disc with helical grooved vent has the improved performance to dissipate the thermal energy more effectively.

• Wind and Structures
• /
• 제30권6호
• /
• pp.617-631
• /
• 2020

Wake-induced aerodynamics of yawed circular cylinders with smooth and grooved surfaces in a tandem arrangement was studied. This pair of cylinders represent sections of stay-cables with smooth surfaces and high-voltage power conductors with grooved surfaces that are vulnerable to flow-induced structural failure. The study provides some insight for a better understanding of wake-induced loads and galloping problem of bundled cables. All experiments in this study were conducted using a pair of stationary section models of circular cylinders in a wind tunnel subjected to uniform and smooth flow. The aerodynamic force coefficients and vortex-shedding frequency of the downstream model were extracted from the surface pressure distribution. For measurement, polished aluminum tubes were used as smooth cables; and hollow tubes with a helically grooved surface were used as power conductors. The aerodynamic properties of the downstream model were captured at wind speeds of about 6-23 m/s (Reynolds number of 5×10⁴ to 2.67×10⁵ for smooth cable and 2×10⁴ to 1.01×10⁵ for grooved cable) and yaw angles ranging from 0° to 45° while the upstream model was fixed at the various spacing between the two model cylinders. The results showed that the Strouhal number of yawed cable is less than the non-yawed case at a given Reynolds number, and its value is smaller than the Strouhal number of a single cable. Additionally, compared to the single smooth cable, it was observed that there was a reduction of drag coefficient of the downstream model, but no change in a drag coefficient of the downstream grooved case in the range of Reynolds number in this study.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2007년도 추계학술대회 논문집
• /
• pp.141-142
• /
• 2007

• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 2003년도 추계학술발표대회 개요집
• /
• pp.204-206
• /
• 2003

The purpose of this study is to investigate the characteristics of X-grooved butt weldments of SM 490 A. The flank angles and toe radii of weld beads are measured and analysed statistically. In addition, other properties are also studied.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2007년도 춘계학술대회 논문집
• /
• pp.199-200
• /
• 2007

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 추계학술대회
• /
• pp.622-627
• /
• 2003

A numerical study is made of a flow in a cylinder with a rotating grooved endwall disk. The aim is to describe differences in the flow fields when there is concentrically-grooved obstacle characterized by amplitude(a) and wave number(N). The Reynolds number(Re) is varied from $10^{3}$ to $10^{4}$ and the aspect ratio(Ar) fixed to 1.0 for the most part of the simulation. For the various cases of amplitude(a) and wave number(N), numerical results are acquired. As the endwall groove roughness increases until certain limit, the interior azimuthal velocity component(v) increases drastically. But over the limit, the swirl motion chararcterized by velocity v decreases and finally it approaches much alike Ar=1.0-a case. The reason of activating swirl motion is based on increasing of torque transported by endwall disk. Torque coefficients($C_{T}$) are aquired for the various (a,N,Re) combinations and the limiting phenomena of swirl motion activation is explained.

• 한국생산제조학회지
• /
• 제22권3_1spc호
• /
• pp.544-550
• /
• 2013

A grooved surface with anisotropic wettability was fabricated on a silicon substrate using photolithography, reactive ion etching, and a KOH etching process. The contact angles (CAs) of water droplets were measured and compared with the theoretical values in the Cassie state and Wenzel state. The experimental results showed that the contact area between a water droplet and a solid surface was important to determine the wettability of the water. The specimens with native oxide layers presented CAs ranging from $71.6^{\circ}$ to $86.4^{\circ}$. The droplets on the specimens with a native oxide layer could be in the Cassie state because they had relatively smooth surfaces. However, the CAs of the specimens with thick oxide layers ranged from $33.4^{\circ}$ to $59.1^{\circ}$. This indicated that the surface roughness for a specimen with a relatively thick oxide layer was higher, and the water droplet was in the Wenzel state. From the CA measurement results, it was observed that the wetting on the grooved surface was anisotropic for all of the specimens.

• Journal of Mechanical Science and Technology
• /
• 제19권12호
• /
• pp.2296-2302
• /
• 2005

This study is focused on the comparison of heat transfer performance of two thermosyphons having 60 straight and helical internal grooves. Distilled water has been used as working fluid. Liquid fill charge ratio defined by the ratio of working fluid volume to total internal volume of thermosyphon, the inclination angle and operating temperature were used as experimental parameters. The heat flux and heat transfer coefficient are estimated from experimental results. The conclusions of this study may be summarized as follows; Liquid fill charge ratio, inclination angle and geometric shape of grooves were very important factors for the operation of thermosyphon. The optimum liquid fill charge ratio for the best heat flux were $30\%$. The heat transfer performance of helically grooved tube was higher than that of straight grooved tube in low inclination angle (less than $30^{\circ}$), but the results were opposite in high inclination angle (more than $30^{\circ}$). As far as optimum inclination angle concerns, range of $25^{\circ}\~30^{\circ}$ for a helically grooved tube and about $40^{\circ}$ for a straight grooved tube are suggested angles for the best results.