• Corrosion Science and Technology
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• v.13 no.4
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• pp.130-138
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• 2014

Wall thinning can be classified into three types: flow-accelerated corrosion, cavitation erosion and solid particle erosion. This article presents a study of solid particle erosion, which frequently causes damages to power plants' pipe system. Unlike previous studies, this study uses a mechanism to make solid particles in a fluid flow collide with pipe materials in underwater condition. Experiment is conducted in three cases of velocity according to solid-water ratio using the three types of the materials of A106B, SS400, and A6061. The experiments were performed for 30 days, and the surface morphology and hardness of the materials were examined for every 7 days. Based on the velocity change of the solid particles in a fluid flow, the surface changes, the change in the amount of erosion, the erosion rate and the variation in the hardness of carbon steel and aluminum family pipe materials can all be determined. In addition, factor-based erosion rates are verified and a wall-thinning relation function is suggested for the pipe materials.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.3
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• pp.154-161
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• 2017

The purpose of this study was to investigate the change of length, opening width, and number of openings effecting on topography change around artificial reefs under erosive wave condition. Hydraulic model test was conducted to see sediment transport around the structures and the relation among the installation condition of the artificial reefs, generated velocity, wave deformation, and topographic change was reviewed. Experimental results show that the sediment transport rate was reduced; however, the scour around the structures was increased under the condition of having a single opening compared to the structures having a plurality of openings which shows inversely proportional to the size of Lr/W.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.10
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• pp.1-11
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• 2004

An experimental study was carried out to investigate the influence of flow conditions of a boundary layer on the near-wake of a flat plate. Various attaching positions of tripping wires were selected to change flow conditions on a boundary layer. Laminar, transitional, and turbulent boundary layer conditions at 0.98C from the leading edge are imposed to investigate the evolution of symmetric and asymmetric wake. An x-type hot-wire probe(55P61) is employed to measure at 8 stations of the near-wake region. Measured mean velocity distributions are presented in terms of similarity parameter. It is found that the symmetric wake collapses well to the universal profile in the central part of the wake. However, the universal profile is not suitable in describing an asymmetric wake.

• Journal of the Korean Ceramic Society
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• v.42 no.9 s.280
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• pp.607-612
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• 2005

The effect of MgO diluents in combustion synthesis of $TiB_2$ nano particles was investigated. The reaction $TiO_2\;+\;B_2O_3\;+\;xMg\;{\rightarrow}\;TiB_2\;+\;5MgO$ was used to synthesize $TiB_2$ nano particles. The combustion velocity was measured to examine the relation between the reaction temperature and the morphologies of particles. The diluent MgO did not react with the reactants and played a role to decrease combustion temperature. As the MgO diluents contents increased, the particles with the smaller size and the narrower size distribution were synthesized. At the condition of 6 mole of MgO, the combustion wave velocity was about 5 cm/see and the synthesized particles showed the size of 60 nm with narrow size distribution.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.13 no.4
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• pp.319-326
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• 2001

This paper reports on a recent investigation to determine criteria for the design of rubble-mound breakwaters. Existing theories and empirica] equations have been carefully reviewed and a new relation is proposed for the determination of optimum weight of armor unit of rubble-mound breakwater. A new parameter is introduced into the new semi-theoretical equation, which is closely related with the surface particle velocity of wave motion. The laboratory data reported by van der Meer(1987) were used for the determination of proper relations of empiricat parameters introduced into the new empirical equation.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.447-452
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• 2004

Vacuum interrupters in order to be used in various switch-gear components such as circuit breakers, distribution switches, contactors, etc. spread the arc uniformly over the surface of the contacts. The electrodes of vacuum interrupters are made of sinter-forged Cu-Cr materials for good electrical and mechanical characteristics. Since the closing velocity is 1-2m/s and impact deformation of the electrode depends on the strain rate at that velocity, the dynamic behavior of the sinter-forged Cu-Cr is a key to investigate the impact characteristics of the electrodes. The dynamic response of the material at intermediate strain rate is obtained from the high speed tensile test machine test and at the high strain rate is obtained from the split Hopkinson pressure bar test. Experimental results from both quasi-static and dynamic compressive tests are interpolated to construct the Johnson-Cook model as the constitutive relation that should be applied to simulation of the dynamic behavior of the electrodes. The impact characteristics of a vacuum interrupter are investigated with computer simulations by changing the amount of chromium content.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.5
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• pp.13-19
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• 2014

Urea-SCR system is the selective catalytic reduction to reduce nitrogen oxides ($NO_x$) emitted from diesel vehicles. The objective of this study is numerical analysis of 3-dimensional unsteady melting problems of frozen urea by using an electric heater. It can be applied to determine capacity of power with respect to time and the location of the urea suction pipe in urea storage tank. The study includes the change of liquid volume fraction, temperature profiles and a influence of natural convection by using the commercial software STAR-CCM+(v7.06). The accuracy of the numerical analysis is estimated by comparisons with experimental data. After validation, a numerical analysis for freezing urea is conducted with four different heating power. From the results, it was found that relation of velocity of phase interface and amount of melting urea by increasing heating power in a container. There is also a difference in trend between velocity of phase interface and amounts of melting urea because of effect of natural convection.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.6 no.2
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• pp.34-41
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• 1997

The objective of this study is to investigate experimentally the frequency characteristics of the hole tones generated by a circular jet of low speed impinging on a plate with a round hole. The experimental results about the sound spectrum and the time wave of the hole tone are presented and discussed in relation with the hole type, the jet velocity and the distance of the nozzle-to-plate with a round hole. From the sound spectrum and time wave measurements, it is found that the hole tone is generated not only by an interaction of convected vortices with a round hole but also by a series of vortex shedding from jets passing through a hole. The hole tones generated by a feedback mechanism consist of many frequency stages and also have a hysteresis phenomenon like an edge tone. But the hole tones generated by a series of vortex shedding have nothing with the stage characteristics. The frequencies of hole tones are influenced by the jet velocity, the distance of the nozzle-to-plate with a round hole and the hole type.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.242-245
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• 2009

The effect of fuel composition on flame length was studied in a non-premixed turbulent diluted hydrogen jet with coaxial air. The observed flame length was expressed as a function of the ratio of coaxial air to fuel jet velocity and compared with a theoretical prediction based on the velocity ratio. Four cases of fuel mixed by volume were determined. In the present study, we derived a scaling correlation for predicting the flame length in a simple jet with coaxial air using the effective jet diameter in the near-field concept. The experimental results showed that visible flame length had a good relation with the theoretical prediction. The scaling analysis is also valid for diluted hydrogen jet flames with varied fuel composition.

• Journal of the Korean Geosynthetics Society
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• v.15 no.1
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• pp.71-81
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• 2016

To evaluate the effects of magnetic force for transporting the dredged soil, magnetic energy inducing device was installed at the dredger. The whole length of transporting pipeline reaches more than 8.5km and the efficiency of the system and the characteristics of the flow are critical factors. The main parameters which govern the flow are flow-rate, velocity, concentration and slip-layer's condition, so in the field test monitoring system was applied to check the real time conditions of the closed circuit flow and the main parameters. From analyzing the relation between the dredged soil amounts and the pump power, it can be concluded that the magnetic forces effect on the transporting system, increase the transporting quantities of dredged soil and decrease power consumption of the pump.