• Journal of Ocean Engineering and Technology
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• v.25 no.5
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• pp.15-20
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• 2011

This study carried out a series of experiments involving impact tests (Drop Weight type & Charpy type with a standard specimen and newly designed I-type specimen), hardness tests, and fracture surface observations of French-made roll shell steel (F), abnormal roll shell steel (M), reheated roll shell steel (R), and S25C steel under heat treatment conditiAn experimental study was carried out to study the solid-liquid mixture upward hydraulic transport of solid particles in vertical and inclined annuli with a rotating inner cylinder. The lift forces acting on a fluidized particle play a central role in many important applications such as the removal of drill cuttings in horizontal drill holes, sand transport in fractured reservoirs, sediment transport, the cleaning of particles from surfaces, etc. In this study a clear acrylic pipe was used to observe the movement of solid particles. Annular velocities varied from 0.4 to 1.2 m/s. The effect of the annulus inclination and drill pipe rotation on the carrying capacity of a drilling fluid, particle rising velocity, and pressure drop in a slim hole annulus were measured for fully-developed flows of water and aqueous solutions of CMC (sodium carboxymethyl cellulose) and bentonite. The rotation of the inner cylinder was efficient at carrying particles to some degree. For a higher particle volume concentration, the hydraulic pressure loss of the mixture flow increased because of the friction between the wall and solids or between solids.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.6
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• pp.273-277
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• 2006

High velocity of oxy-fuel (HVOF) thermal spray coating is progressively replacing the other classical hard coatings such as chrome plating and ceramic coating by the classical methods, since the very toxic $Cr^{6+}$ ion is well known as carcinogen causing lung cancer, and the ceramic coatings are brittle. Co-alloy T800 powder is coated on the Inconel 718 substrates by the HVOF coating procesess developed by this laboratory. For the study of the possibility of replacing of chrome plating, the wear properties of HVOF Co-alloy T800 coatings are investigated using the reciprocating sliding tester with a counter sliding SUS 304 ball both at room and at an elevated temperature of $1000^{\circ}F\;(538^{\circ}C)$. The possibility as durability improvement coating is studied for the application to the high speed spindles vulnerable to frictional heat and wear. Wear mechanisms at the reciprocating sliding wear test are studied far the application to the systems similar to the sliding test such as high speed spindles. Wear debris and frictional coefficients of T800 coatings both at room and at an elevated temperature of $538^{\circ}C$ are drastically reduced compared to those of non-coated surface of Inconel 718 substrates. Wear traces and friction coefficients of both coated and non-coated surfaces are drastically reduced at a high temperature of $538^{\circ}C$ compared with those at room temperature. These show that the coating is highly recommendable far the durability Improvement coating on the surfaces vulnerable to frictional heat and wear.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.7
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• pp.957-966
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• 2000

The effect of rotation on the discharge coefficient of orifices with various length-to-diameter ratios and two different inlet corner radii was studied. Length-to-diameter ratios of the orifices range from 0.2 to 10, while the inlet shapes are square edged, or round edges of radius-to-diameter ratio of 0.5. From the experiment, we found that rotational discharge coefficient and Rotation number, when based on ideal exit velocity of the orifice considering momentum transfer from the rotor, describe the effect of rotation very well. In this study, the discharge coefficients of rotating orifices are shown to behave similar to those of the well-known non-rotating orifices. For both rotating and non-rotating orifices, the discharge coefficients increase with the length-to-diameter ratio until a maximum is reached. The flow reattachments in the relatively short orifices are responsible for the increase. The coefficient then decreases with the length-to-diameter ratio due to the friction loss along the orifice bore. The length-to-diameter ratio that yields maximum discharge coefficient, however, increases with the Rotation number because the increased flow-approaching angle requires larger length-to-diameter ratio for complete reattachment. The length-to-diameter ratio for complete reattachment is shorter for round edged orifices than that of square edged orifices by about a unit length-to-diameter ratio.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2465-2470
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• 2008

A new surface shape of an internal cooling passage which largely reduces the pressure drop and enhances the surface heat transfer is proposed in the present study. The surface shape of the cooling passage is consisted of the concave dimple and the riblet inside the dimple which is protruded along the stream-wise direction. Direct Numerical Simulation (DNS) for the fully developed turbulent flow and thermal fields in the cooling passage is conducted. The Numerical simulations for the 5 different surface shapes are conducted at the Reynolds number of 2800 based on the mean bulk velocity and channel height and Prandtl number of 0.71. The driving pressure gradient is adjusted to keep a constant mass flow rate in the x direction. The thermo-aerodynamic performance for the 5 different cases used in the present study was assessed in terms of the drag, Nusselt number, Fanning friction factor, Volume and Area goodness factor in the cooling passage. The value of maximum ratio of drag reduction is -22.86 [%], and the value of maximum ratio of Nusselt number augmentation is 7.05 [%] when the riblet angle is $60^{\circ}$ (Case5). The remarkable point is that the ratio of Nusselt number augmentation has the positive value for the surface shapes which have over $45^{\circ}$ of the riblet angle. The maximum Volume and Area goodness factor are obtained when the riblet angle is $60^{\circ}$ (Case5).

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.10 no.3
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• pp.109-119
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• 1998

A horizontal tow-dimensional version of POM (Princeton Ocean Model) was modified in representing the bottom friction and the open boundary conditions. To simulate the flooding and drying of intertidal flats, a wetting-and-drying scheme was incorporated into the model. The model then was applied to the Chunsu Bay and its adjacent coastal water. Only the water movement due to tides, the dominant forcing in the study area, was considered. This presents the procedure and the results of model calibration and verification for the Chunsu Bay system. The model was calibrated, using the average tidal characteristics in Tide Tables, for the amplitudes and the phases of tidal waves throughout the modeling domain. Calibration results showed that the model gave a good reproduction of tidal waves. The calibrated model was verified using the time-series measurements of surface elevation and current velocity in the summer of 1995. The model reproduced the tides currents very well. calibration and verification results demonstrated that the model is capable of reproducing the tidal dynamics in the Chunsu Bay system.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.6
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• pp.401-408
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• 2019

The objective of this study is to develop a new type of buried sensor module that can directly assess pre-stressed concrete by measuring strain using a hetero-core optical fiber sensor. In this regard, experiments were conducted to evaluate the performance of the sensor using an exposure sensor module. Based on the experimental results, when the values of the displacement control velocity were 0.12 mm/min and 1.80 mm/min, the corresponding delays in the measurement were 52.1 s and 2.6 s respectively, which indicated that the maximum delay between the two measurements was a factor of 19. Due to the measurement delay phenomena, the sensor module used in the experiments cannot be employed to check the real-time state of the structure. Thus, additional experiments were needed to develop a new sensor module that can measure the real-time state of the structure. To investigate the cause of the measurement delay phenomena, three experiments were conducted. It was confirmed that measurement delay is mainly attributed to frictional resistance. The measurement delay phenomena were not observed in the experiments using the friction-removed device.

• Korean Journal of Materials Research
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• v.24 no.1
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• pp.60-65
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• 2014

Fe-based amorphous coatings were fabricated on a soda-lime glass substrate by the vacuum kinetic spray method. The effect of the gas flow rate, which determines particle velocity, on the deposition behavior of the particle and microstructure of the resultant films was investigated. The as-fabricated microstructure of the film was studied by field emission scanning electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HR-TEM). Although the activation energy for transformation from the amorphous phase to crystalline phase was lowered by severe plastic deformation and particle fracturing under a high strain rate, the crystalline phases could not be found in the coating layer. Incompletely fractured and small fragments 100~300 nm in size, which are smaller than initial feedstock material, were found on the coating surface and inside of the coating. Also, some pores and voids occurred between particle-particle interfaces. In the case of brittle Fe-based amorphous alloy, particles fail in fragmentation fracture mode through initiation and propagation of the numerous small cracks rather than shear fracture mode under compressive stress. It could be deduced that amorphous alloy underwent particle fracturing in a vacuum kinetic spray process. Also, it is considered that surface energy caused by the formation of new surfaces and friction energy contributed to the bonding of fragments.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.12
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• pp.805-814
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• 2011

In the present study, the detailed flow structure and heat transfer characteristics in the newly-designed heat transfer surface geometry were investigated. The surface geometry proposed in the present study is a traditional dimple structure combining with a protrusion inside the dimple, which is named a protrusion-in-dimple in this study. The basic idea underlying the present surface geometry is to enhance the flow mixing and the corresponding heat transfer in the flow re-circulating region generated by a conventional dimple cavity. The present study was performed by the direct numerical simulation at a Reynolds number of 2800 based on mean velocity and channel height and Prandtl number of 0.71. Three different protrusion heights for protrusion-in-dimples were considered as the main design parameter of the present study. The calculated pressure drop and heat transfer capacity were assessed in terms of the Fanning friction factor and Colburn j factor. The overall performances estimated in terms of the volume and area goodness factor for protrusion-in-dimple cases were higher than the conventional dimple case.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.5
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• pp.829-837
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• 1992

This paper presents a new approach for the analysis of hot strip rolling processes. The approach is based on the finite element method and capable of predicting velocity field in the strip, temperature field in the strip, temperature field in the roll, and roll pressure. Basic finite element formulations for heat transfer analysis are described with emphasis on the treatment of numerical instability resulting from a standard Galerkin formulation. Comparison with the theoretical solutions found in the literature is made for the evaluation of the accuracy of the temperature solutions. An iterative scheme is developed for dealing with strong correlations between the metal flow characteristics and the thermal behavior of the roll-strip system. A series of process simulations are carried out to investigate the effect of various process parameters including interface friction, interface heat transfer coefficient, roll speed, reduction in thickness, and spray zone. The results are shown and discussed.

• Journal of Powder Materials
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• v.12 no.2 s.49
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• pp.136-145
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• 2005

Graphite-Ni composite powders were synthesized by mechanical alloying(MA) and spray drying(SD). Fabricated powders as well as commercial graphite-Ni powders were thermally sprayed on mild steel substrates using high velocity oxygen fuel (HVOF) thermal spray process and flame thermal spray process. The effects of several process parameters on related properties in thermally sprayed coatings have been investigated and correlated with microstructures in this study. The results indicated that the desired properties can be obtained when commercial powders were applied using HVOF process, while coating properties in case of MA powder application were inferior to those in HVOF process in so far. However, it is suggested that property enhancement can be obtained if the fraction of hexagonal graphite phase can be increased in mechanically alloyed powders.