• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.5
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• pp.552-567
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• 2017

The floating crane vessel in waves gives rise to the motion of the lifted object which is connected to the hoisting wire. The dynamic tension induced by the lifted object also affects the motion responses of the floating crane vessel in return. In this study, coupled motion responses of a floating crane vessel and a lifted subsea manifold during deep-water installation operations were investigated by both experiments and numerical calculations. A series of model tests for the deep-water lifting operation were performed at Ocean Engineering Basin of KRISO. For the model test, the vessel with a crane control system and a typical subsea manifold were examined. To validate the experimental results, a frequency-domain motion analysis method is applied. The coupled motion equations of the crane vessel and the lifted object are solved in the frequency domain with an additional linear stiffness matrix due to the hoisting wire. The hydrodynamic coefficients of the lifted object, which is a significant factor to affect the coupled dynamics, are estimated based on the perforation value of the structure and the CFD results. The discussions were made on three main points. First, the motion characteristics of the lifted object as well as the crane vessel were studied by comparing the calculation results. Second, the dynamic tension of the hoisting wire were evaluated under the various wave conditions. Final discussion was made on the effect of passive heave compensator on the motion and tension responses.

• Journal of the Society of Naval Architects of Korea
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• v.50 no.5
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• pp.282-290
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• 2013

The effects of the combination of blade number for forward and after propeller on the propeller shaft forces of a contra-rotating propeller (CRP) system are presented in the paper. The research is performed through the numerical simulations based on the Reynolds-Averaged Navier-Stokes equations (RANS). The simulation results of the present method in open water condition are validated comparing with the experimental data as well as the other numerical simulation results based on the potential method for 4-0-4 CRP (3686+3687A) and 4-0-5 CRP (3686+3849) of DTNSRDC. Two sets of CRP are designed and simulated to study the effect of the combination of blade number in behind-hull condition. One set consists of 3-blade and 4-blade, while the other is 4-blade and 4-blade. A full hull body submerged under the free surface is modeled in the computational domain to simulate directly the wake field of the ship at the propeller plane. From the simulation results, the fluctuations of axial force and moment are dominant in the case of same blade numbers for forward and after propellers, whereas the fluctuations of horizontal and vertical forces and moments are very large in the case of different blade numbers.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.10 s.241
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• pp.1289-1297
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• 2005

The flow in a microchannel is usually characterized as a low Reynolds number (Re) so that good mixing is quite difficult to be achieved. In this regard, we developed a novel chaotic micromixer, named Serpentine Laminating Micromixer (SLM) in the present study, Part 1. In the SLM, the higher level of chaotic mixing can be achieved by combining two general chaotic mixing mechanisms: splitting/recombination and chaotic advection. The splitting and recombination (in other term, lamination) mechanism is obtained by the successive arrangement of 'F'-shape mixing units in two layers. The chaotic advection is induced by the overall three-dimensional serpentine path of the microchannel. Chaotic mixing performance of the SLM was fully characterized numerically. To compare the mixing performance, a T-type micromixer which has the same width, height and length of the SLM was also designed. The three-dimensional numerical mixing simulations show the superiority of the SLM over the T-type micromixer. From the cross-sectional simulation results of mixing patterns, the chaotic advection effect from the serpentine channel path design acts favorably to realize the ideal lamination of fluid flow as Re increases. Chaotic mixing mechanism, proposed in this study, could be easily integrated in Micro-Total-Analysis-System, Lab-on-a-Chip and so on.

• Fire Science and Engineering
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• v.33 no.4
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• pp.77-82
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• 2019

Fire extinguishing systems are essential equipment in all indoor facilities to address unexpected fire scenarios, and appropriate fire extinguishing agent should be used depending on the place and object to protect. Among these, gaseous fire-extinguishing systems are used to protect electronic equipment. Therefore, inert gases that do not undergo chemical reactions are used mainly in those systems. On the other hand, recently, owing to the high integration of electronic equipment, there are some cases, in which large noise generated from gaseous systems damage the electronic equipment. In this study, numerical analysis of the discharge noise with various nozzle contraction angles was carried out to improve the gas fire extinguishing system. Numerical analysis was carried out using ANSYS FLUENT ver 18.1. The causes of the noise were elucidated using the swirl distribution. The noise level of the modified model was reduced by approximately 6 dB compared to the reference model, which is similar to the result of a previous study, confirming the validity of the method.

• Journal of the Korean Ceramic Society
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• v.48 no.3
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• pp.236-240
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• 2011

In order to deposit a homogeneous and uniform ${\beta}$-SiC films by chemical vapor deposition, we demonstrated the phase stability of ${\beta}$-SiC over graphite and silicon via computational thermodynamic calculation considering pressure, temperature and gas composition as variables. The ${\beta}$-SiC predominant region over other solid phases like carbon and silicon was changed gradually and consistently with temperature and pressure. Practically these maps provide necessary conditions for homogeneous ${\beta}$-SiC deposition of single phase. With the thermodynamic analyses, the CVD apparatus for uniform coating was modeled and simulated with computational fluid dynamics to obtain temperature and flow distribution in the CVD chamber. It gave an inspiration for the uniform temperature distribution and low local flow velocity over the deposition chamber. These calculation and model simulation could provide milestones for improving the thickness uniformity and phase homogeneity.

• Journal of Practical Engineering Education
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• v.7 no.2
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• pp.119-123
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• 2015

ABS material is easy to process, impact resistance and heat resistance is strong. ABS material is often used as a substitute for the interior and exterior metal material for an automobile. As the demand of ABS increases, fabricating education using ABS has also been increasing its importance. As part of its education, ABS material is used in the mold fabricating part of the regional and national skills competition. At this time, the force of the vise for fixing the ABS material in the processing using the ABS material can affect the final shape after machining. However, it has not been an accurate description of the notes and instructions of working in education. Therefore, in this study, we study the impact the force of vise affect structural shape in the fabricating education using ABS material and during fabricating education of ABS material, trying to present the notes of the appropriate it.

• Ocean Systems Engineering
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• v.10 no.1
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• pp.87-110
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• 2020

Catamaran has recently been a choice to support a typical vertical axis turbine in floating tidal current energy conversion system. However, motion responses associated with the catamaran can reduce the turbines efficiency. The possibility to overcome this problem isto change the catamaran parameter by varying and simulating the demi-hull separations to have lower motion responses. This simulation was undertaken by Computational Fluid Dynamic (CFD) using potential flow analysis. Cases of demi-hull separation were considered, with ratios of demi-hull separation (S) to the breadth of demi-hull (B), ^S/_B of 3.45, 4.95, 6.45, 7.2 and 7.95. In order to compare to the previous works in the literature, the regular wave was set with wave height of 0.8 m. Furthermore, the analysis was carried out by irregular waves with significant wave height, H_s, of about 0.09 to 1.5 m and the wave period, T, of about 1.5 to 6 s or corresponding to the wave frequency, ω, of about 1.1 to 4.2 rad/s. The wave spectrum was derived from the equation of the International Towing Tank Conference (ITTC). For the case of turbines-loaded catamaran under consideration, the new finding is that the least significant amplitude response can be satisfied at the ratio ^S/_B of 7.2. This study indicates that selecting a right choice of demi-hull separation ratio could contribute in reducing motion responses of the tidal current turbines-loaded catamaran.

• Journal of the Korea Safety Management & Science
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• v.17 no.2
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• pp.117-127
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• 2015

This study investigated the smoke blocking and control systems for the safety of residents evacuation and for the prevention of smoke spread through the central corridor in the event of central corridor type of intelligent building fire. We offered additional ways of utilizing smoke ventilators and intake ventilation equipment and utilized CFD-based fire simulation program(FDS Ver.5.5.3) in order to analyze the effect. As a result, many differences in the smoke block effect, depending on the application of smoke ventilator and location of installation, was found. In addition, the result was found that larger effect was showed not in the case of application of smoke ventilator in central corridor only but application in fire room. The reason is that the smoke leakage is blocked primarily as air is flowed in the fire room through open door by operation of intake smoke ventilator in the public corridor and secondarily, the smoke leakage to the public corridor could be blocked as fire and smoke were released to the opened smoke ventilator continuously. Especially, the effect was maximized through complex interactions by applying smoke ventilator and intake ventilation equipment in corridor together rather than applying smoke ventilator and intake ventilation equipment independently. The proposed measure through this study shall be considered from architectural plan as one of ways for blocking from smoke spread to the central corridor in the central corridor type of intelligent building. In addition, flaws on regulation shall be established and supplemented.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.8
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• pp.553-561
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• 2017

The main motivation for this study was to establish a CFD-based procedure for the analysis of heating characteristics, particularly in industrial furnaces. As certain open-source software packages have gained popularity in dealing with complex industrial problems, the OpenFOAM framework was selected for further development of advanced physical models to meet industrial requirements. In this study, the newly developed comprehensive model was applied to simulate physical processes in the full-scale horizontal furnace of a continuous galvanizing line (CGL). The numerical results obtained indicate that the current approach predicts heating characteristics reasonably well. It was also found that radiative heat transfer plays a dominant role in heating the moving strip. To improve the predictability of our method, further work is required to model the turbulence-chemistry interaction realistically, as well as to impose a physically correct thermal wall boundary condition.

• Journal of Energy Engineering
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• v.24 no.1
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• pp.88-96
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• 2015

Gear pump has a simple structure high reliability, easy operation and maintenance, widely used as a source of hydraulic system of hydraulic. In general, the gear pump was designed using variety of variables, the variables through the analysis of the mass flow rate and efficiency. In this paper, three-dimensional flow of the gear pump, in order to produce the optimal design of product, analysis was performed by using commercial software ANSYS v15.0 CFX. And then, combination of design parameters selected by ANSYS was carried out to confirm the simulation result. The efficiency and mass flow rate of the gear pump were studied by varying its rotational speed and the clearance between the gear tip and the housing. In the simulation results, as the rotational speed were increased, the average mass flow rate and efficiency increased. Furthermore, as the clearance between the gear tip and the housing was increased, the average mass flow rate and efficiency decreased.