• Journal of the Korean Society for Precision Engineering
• /
• v.22 no.9 s.174
• /
• pp.27-33
• /
• 2005

This study deals with the truing of diamond wheel fur the manufacture of micro v-shaped grooves with fine sharp edges in the grinding. Fine micro v-shaped grooves are key components to fabricate LGP(light guide plate), optical fiber connector and so on. Conventional v-shaped groove methods such as etching and lithography are difficult to make grooves with accuracy and cutting by lathe is difficult to select target materials. Therefore, as a preliminary stage to developing the grinding technology that will be expected fabrications for micro 3-dimensional structure of high effectivity and accuracy and freed up the restrictions of machinability to the materials for micro v-shaped grooves, truing is carried out with resin bond diamond wheel and electroforming diamond wheel using a cup-type truer. From the experimental results, it is found that the effects according to working direction of the cup-type truer and the restrainable methods of plastic deformation that is generated at wheel edge are examined. As a result, fine micro v-shaped diamond wheel was obtained, which are applicable to micro grinding for optical devices.

• Proceedings of the KSME Conference
• /
• 2008.11b
• /
• pp.2448-2453
• /
• 2008

The present study numerically investigates the flow and heat transfer characteristics of rib-induced secondary flow in a cooling channel with staggered V-shaped ribs, extruded on both walls. The rib-height-to-hydraulic diameter ration (h/$D_h$) is 0.17; the rib pitch-to-height ratio (p/h) equals 2.8; the Reynolds number is 50,000. Shear stress transport (SST) turbulence model is used as a turbulence closure. The present results are compared with those for a continuous V-shaped rib. Computational results show that, for average heat transfer rate the staggered V-shaped rib gives about 2.5 times higher values than the continuous V-shaped rib, while, for the streamwise pressure drop the former gives about 5 times higher values than the latter. Consequently, for the thermal performances, based on the equal pumping power condition, the staggered one gives about 2 times higher values than the continuous one. Also, for the staggered V-shaped rib, complex secondary flow patterns are generated in the duct due to the snaking flow in the streamwise direction, and more uniform heat transfer distributions are obtained.

• Proceedings of the KSME Conference
• /
• 2003.04a
• /
• pp.1453-1460
• /
• 2003

The present study investigates the effects of rib arrangements and aspect ratios of a rectangular duct simulating the cooling passage of a gas turbine blade. Two different V-shaped rib configurations are tested with the aspect ratios (W/H) of 3 to 6.82. One is the continuous V-shaped rib configuration with $60^{\circ}$ attack angle, and the other is the discrete V-shaped rib configuration with $45^{\circ}$ attack angle. The square ribs with the pitch to height ratio of 10.0 are installed on the test section in a parallel arrangement for both rib configurations. Reynolds numbers based on the hydraulic diameter are changed from 10,000 to 30,000. A naphthalene sublimation method is used to measure local heat/mass transfer coefficients. For the continuous V-shaped rib configuration, two pairs of counter-rotating vortices are generated in a duct, and high transfer region is formed at the center of the ribbed walls of the duct. However, for the discrete V-shaped rib configuration with $45^{\circ}$ attack angle, complex secondary flow patterns are generated in the duct due to its geometric feature, and more uniform heat/mass transfer distributions are obtained for all tested cases

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.22 no.2
• /
• pp.263-267
• /
• 2013

The continuing demand for increasingly slimmer and brighter liquid crystal display (LCD) panels has led to an increased focus on the role of light guide panels (LGPs) or optical films that are used to obtain diffuse, uniform light from the backlight unit (BLU). The most basic process in the production of such BLU components is the micromachining of V-shaped grooves. Thus, given the current trend, micromachining of V-shaped grooves is expected to play increasingly important roles in today's manufacturing technology. LCD BLUs comprise various optical elements such as a LGP, diffuser sheet, prism sheet, and protector sheet with V-shaped grooves. High-aspect-ratio patterns are required to reduce the number of sheets and enhance light efficiency, but there is a limit to the aspect ratio achievable for a given material and cutting tool. Therefore, this study comprised a series of experimental evaluations conducted to determine the machining limit in microcutting V-shaped grooves on electroless nickel plated die materials when using single-crystal diamond tools with point angles of $20^{\circ}-80^{\circ}$. Cutting performance was evaluated at various cutting speeds and depths of cut using different machining methods and machine tools. The experimental results are that V-shaped patterns with angles of $80^{\circ}$ or up can be realized regardless of the machining conditions and equipment. Moreover, the feed rate has little effect on machinability, and it is thought that the fly-cut method is more efficient for shallow patterns.

• The Journal of Asian Finance, Economics and Business
• /
• v.7 no.11
• /
• pp.55-65
• /
• 2020

The objective of this study is to investigate how investors in the Stock Exchange of Thailand practically trade in response to a magnitude of profits and losses, given a discussion of the widely well-known behavioral explanation, so called as the disposition effect. We provide empirical evidence of an existence of the V-shaped disposition effect, which has been recently found in several advanced equity markets. By adopting the methodology suggested by An's (2016) and Fama and Macbeth (1973), we document that stock return patterns in relation to aggregate unrealized gains and losses of investors are consistent with the V-shaped selling schedule, given an increase in unrealized gains and losses over the period of January 1996 to December 2015. The effect of unrealized gains is stronger than that of unrealized losses and this asymmetry underlies the existence of the V-shaped disposition effect in the Thai equity market. Interestingly, the effect of the V-shaped selling schedule is strongest over the short-term holding time horizon. Last but not the least, stocks for which investors have large unrealized gains and losses outperform in the following month and the long-short trading strategy, based on this premise, generates the average 1.7% monthly (equivalent to 20.0% per year) abnormal return.

• 유체기계공업학회:학술대회논문집
• /
• 2005.12a
• /
• pp.169-172
• /
• 2005

Numerical analysis of turbulent flow in three-dimensional channel with V-shaped ribs extruded on both walls has been carried out. Reynolds-averaged Navier-Stokes are calculated for analysis of fluid flow and heat transfer. Shear stress transport (SST) turbulence model is used as a turbulence closure. Computational results for heat transfer rate show good agreements with experimental data.

• Journal of Korea Water Resources Association
• /
• v.36 no.3 s.134
• /
• pp.507-520
• /
• 2003

A V-shaped riffle is an artificial hydraulic structure haying two wings from the streamside with a narrow opening in between. It is usually made of crushed stones or large boulders. It limits channel width and accelerates the flow through the constricted section causing a local scour just downstream. The V-shaped riffle provides with a unique aquatic habitat by forming a pool and sandbars around the pool edge, increasing local morphologic, hydraulic and sedimentological diversity. This study investigates experimentally the scour characteristics of the V-shaped riffle in the sandbed stream and proposes a predictive equation for the scour. Total 45 cases of experiments were conducted to examine the effect of hydraulic factors and configuration of V-shaped riffle on the geometry of scour holes. From the comparison of the experimental results of this study with the predictive equation of spur dike by Breusers and Raudkivi(1991), it is found that their predictive equation of spur dike underestimates the maximum scour depth downstream of the V-shaped riffle. h new predictive equation for the maximum scour depth was developed using the non-dimensional hydraulic and geometrical variables. The parameters used in the proposed equations were determined using the experimental data. The analysis reveals that the scour depth is dependent dominantly on the Froude number at the opening of the V-shaped riffle, while the angle of riffle and the opening width also affect the scour depth. The proposed equation for the scour of V-shaped riffle well agrees with the experimental data. It can be used for estimating the scour of the V-shaped riffle in sandbed streams.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.25 no.5
• /
• pp.337-344
• /
• 2015

As many of armored vehicles are seriously exposed to threat of IEDs(Improvised Explosive Devices) in the Afghanistan war and the Iraq war. V-shaped military vehicles are deeply studied in order to protect crews and mounted soldiers against land mines. Generally the experiment on full-scaled V-shaped structure needs excessively high cost, which becomes a huge barrier to study. In this paper, we explore the possibility to make a half-scaled model of the V-shaped structure by using the geometric similarity scaling. We demonstrate the geometric similarity scaling between the original model and the half-scaled model is established on the momentum and deflections of structure via computer simulations and experiments. At this stage, we conduct only numerical analysis of predicting vibration of V-shaped structure because measuring vibration of structure is difficult in the mass-explosion experiment, which is remained as future work.

• Proceedings of the KSR Conference
• /
• 2009.05a
• /
• pp.574-580
• /
• 2009

This study is investigate the bending behavior of real size RC beams strengthened with carbon fiber sheets. For experimental study, 1 control beam and 8 strengthened beams of real size(4 NU-beams and 4 U-beams) are tested and compared. NU-beam has not a V-shaped band and V-beam has a V-shaped band. The variables of experiment are composed of the number of carbon fiber sheets, the existence of U-shaped band, and four point loading, etc. The experimental results showed that the strengthening system with U-shaped band controls the premature debonding and provides a more ductile failure mode than the strengthening system without V-shaped band. It can be found from the load-deflection curves that as the number of fiber sheets is increased, the maximum strength and the flexural rigidity is increased. For the strengthening method with carbon fiber sheets of the real size RC beams, it is required the finding a solution to the bonding problem.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.26 no.11
• /
• pp.1542-1551
• /
• 2002

The present study investigates the convective heat/mass transfer characteristics and pressure drop inside the rib-roughened cooling passage of gas turbine blades. The internal cooling passage is simulated using a square duct with h- and V-shaped rectangular ribs which have a 60。attack angle. A naphthalene sublimation technique is employed to determine the detailed local heat/mass transfer coefficients using the heat and mass transfer analogy. The ribs disturb the main flow resulting in the recirculation and secondary flows near the ribbed wail. The secondary flow patterns and the local heat transfer in the duct are changed significantly according to the rib orientation. A square duct with ∧ - and V-shaped ribs have two pairs of secondary flow due to the rib arrangement. Therefore, the average heat/mass transfer coefficients and pressure drop of ∧ - and V-shaped ribs are higher than those of the continuous ribs with 90$^{\circ}$ and 60$^{\circ}$attack angles. The ∧-shaped ribs have higher heat/mass transfer coefficients than the V-shaped ribs, and the uniformity of heat/mass transfer coefficient are increased with the discrete ribs due to the flow leakage and acceleration near the surface.