• Journal of Advanced Marine Engineering and Technology
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• v.39 no.4
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• pp.418-424
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• 2015

Marine Environment Protection Committee of the International Maritime Organization has decided to reinforce the NOx emission standards for ships passing an ECA(Emission Control Area) with Tier III standards from January 1, 2016. In this study, real-time measurements of the exhaust gas, cylinder pressure and fuel consumption were conducted at each load of a T/S Hanbada main engine of Korea Maritime and Ocean University, which is controlled by single injection and double post injection for reducing NOx emissions. The results showed that the quantity of CO2 and NOx increased in proportion to the engine load, whereas the CO concentration was inversely proportional to the engine load. In addition, double post injection decreased 10 % of P-max and reduced 25~30 % of the NOx emissions compared to single injection, whereas there was a trade-off relation, such as increase 3~5 % of SFOC (Specific Fuel Oil Consumption).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.12
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• pp.1035-1042
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• 2010

The thermal stratification effect has been thought as one of the way to avoid dramatically generating the heat from HCCI combustion. We investigate the effect of thermal stratification on HCCI combustion fueled by DME and n-Butane. The thermal stratification occurs in a combustion chamber of a rapid compression machine with premixture by buoyancy effect that is made of fuel and air. The premixture is then adiabatically compressed, and during the process, the in-cylinder gas pressure is measured and two-dimensional chemiluminescence images are prepared and analyzed. Under the thermal stratification, the LTR starting time and the HTR starting time are advanced than that of homogeneous case. Further, the LTR period and the luminosity duration under homogeneous conditions are shorter than the corresponding quantities under stratified conditions. Additionally, under stratified conditions, the brightest luminosity intensity is delayed longer than that of homogeneous condition.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.11
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• pp.1183-1189
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• 2015

This study focuses on the design of the tapered joints of a wind power turbine. The main variables of the tapered joint are the transmitted torque, shaft diameter, contact area of the tapered ring, and tightening torque of the bolts, which applies a compressive pressure from the hub to the shaft. The stress distribution of the taper fit was calculated under axisymmetric plane strain conditions because of the small taper angle. The axial displacement of the clamp can be calculated from the radial elastic deformation and the taper angle. The stress field of each ring is obtained from the cylinder stress equation. To verify the accuracy of the calculation, finite element (FE) analysis was performed, and the results of the calculation and FE analysis were compared. The hoop stress of the tapered surface showed a discrepancy of approximately 10, but the trends of the stress distributions of each component and the relative movement obtained by FE analysis were in good agreement with the analytical calculation results.

• Journal of the Semiconductor & Display Technology
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• v.10 no.1
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• pp.43-49
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• 2011

In this study, the dynamic characteristics of an air spring connected with an external chamber through a flexible tube are examined. The uncoupled dynamic parameters of the air spring are identified through experiments, followed by the suggestion of a model-based approach to obtain the remaining coupled dynamic parameters using the various frequency response functions derived in PART I paper [1]. To improve or control the damping characteristics of the air spring, this vibration isolation air spring system is physically established in laboratory scale. And we attempt to identify various parameters used to describe to air spring system by both theoretically [1] and experimentally, which is performed in this report. The damping parameter of the tube system is identified through experiments on the system incorporated with the air cylinder, and a nonlinear regression procedure is employed to find solutions. The resulting value is used to expect the frequency response function of dynamic pressure in the top chamber (air spring) with respect to that in the bottom chamber (external chamber). Comparison with the experimental data supports the validity of the present estimation procedures. Also, the dynamic mechanism of the damping effects particularly in a low frequency range is investigated through this experimental endeavor.

• Journal of Industrial Technology
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• v.18
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• pp.249-258
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• 1998

In this paper, we investigated the post-combustion removal of nitrogen oxide($NO_x$) and sulfur oxide($SO_x$) which is based on the gas to particle conversion process by the pulsed corona discharge. Under normal pressure, the pulsed corona discharge produces the energetic free electrons which dissociate gas molecules to form the active radicals. These radicals cause the chemical reactions that convert $SO_x$ and $NO_x$ into acid mists and these mists react with $NH_3$ to form solid particles. Those particles can be removed from the gas stream by conventional devices such as electrostatic precipitator or bag filter. The reactor geometry was coaxial with an inner wire discharge electrode and an outer ground electrode wrapped on a glass tube. The simulated flue gas with $SO_x$ and $NO_x$ was used in the experiment. The corona discharge reactor was more efficient in removing $SO_x$ and $NO_x$ by adding $NH_3$ and $H_2O$ in the gas stream. We also measured the removal efficiency of $SO_x$ and $NO_x$ in a cylinder type corona discharge reactor and obtained more than 90 % of removal efficiency in these experimental conditions. The effects of process variables such as the inlet concentrations of $SO_x$, $NH_3$ and $H_2O$, residence time, pulse frequencies and applied voltages were investigated.

• Structural Engineering and Mechanics
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• v.36 no.6
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• pp.759-783
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• 2010

In this paper, compressive strength of carbon fiber reinforced polymer (CFRP) confined concrete cylinders is formulated using a hybrid method coupling genetic programming (GP) and simulated annealing (SA), called GP/SA, and a robust variant of GP, namely multi expression programming (MEP). Straightforward GP/SA and MEP-based prediction equations are derived for the compressive strength of CFRP-wrapped concrete cylinders. The models are constructed using two sets of predictor variables. The first set comprises diameter of concrete cylinder, unconfined concrete strength, tensile strength of CFRP laminate, and total thickness of CFRP layer. The most widely used parameters of unconfined concrete strength and ultimate confinement pressure are included in the second set. The models are developed based on the experimental results obtained from the literature. To verify the applicability of the proposed models, they are employed to estimate the compressive strength of parts of test results that were not included in the modeling process. A sensitivity analysis is carried out to determine the contributions of the parameters affecting the compressive strength. For more verification, a parametric study is carried out and the trends of the results are confirmed via some previous studies. The GP/SA and MEP models are able to predict the ultimate compressive strength with an acceptable level of accuracy. The proposed models perform superior than several CFRP confinement models found in the literature. The derived models are particularly valuable for pre-design purposes.

• Journal of the Korean Institute of Gas
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• v.19 no.5
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• pp.7-12
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• 2015

Hydrogen is usually produced by using syngas generated by the fuel reforming for natural gas so far. The further process is needed for increasing the hydrogen yield of syngas. However, the process for upgrading the hydrogen yield is accompanied by additional energy sources and economic costs. Thus related studies on the method for using as a mixture in itself have been conducted in order to utilize more efficiently syngas. The effect on the engine performance for methane/syngas mixture of 30kW spark ignition gas engine for power generation has been investigated in this study. As a result, it was found that the combustion phenomena such as the maximum in-cylinder pressure and crank angle at that time have been improved by methane/syngas mixture. Through these, fuel conversion efficiency could be enhanced by about 98% of methane/hydrogen mixture and $NO_x$ emissions could be reduced by about 12% of methane-hydrogen mixture.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.1
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• pp.23-32
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• 2016

Various studies have been conducted for drag reduction of a high-speed vehicle by injecting counterflow jet from its nose cone. In this study, in order to obtain baseline data and key parameters for drag reduction method, the counterflow jet study of the USA is reviewed and summarized. The nose cone shapes of each study are hemisphere cylinder, truncated cone, and reentry capsule, and their test conditions are summarized accordingly. Key parameters for drag reduction are jet mach number, mass flow rate, and pressure ratio. Even though drag reduction effects show various results according to given test conditions, it is found that the drag reduction effect reaches up to 40~50%.

• Journal of the Korean Institute of Gas
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• v.19 no.6
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• pp.28-33
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• 2015

In this study, a dual fuel engine fueled with natural gas and diesel was tested to investigate the effects of heating value variation of CNG fuel. CNG substitution rate which is defined as the ratio of CNG and diesel supplied in a heating value basis was fixed at 80%. The higher heating value was varied from $10,400kcal/Nm^3$ to $9,400kcal/Nm^3$ by mixing nitrogen gas with pure CNG and diesel fuel was injected at a fixed injection timing. The engine test results showed that thermal efficiency and power output were decreased as the heating value of mixed CNG fuel was decreased. And the peak cylinder pressure was also decreased but the ignition delay time and the combustion duration and timing were almost same.

• Ocean Systems Engineering
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• v.8 no.4
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• pp.381-407
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• 2018

This paper presents a hybrid numerical approach, which combines a two-phase Navier-Stokes model (NS) and the fully nonlinear potential theory (FNPT), for modelling wave-structure interaction. The former governs the computational domain near the structure, where the viscous and turbulent effects are significant, and is solved by OpenFOAM/InterDyMFoam which utilising the finite volume method (FVM) with a Volume of Fluid (VOF) for the phase identification. The latter covers the rest of the domain, where the fluid may be considered as incompressible, inviscid and irrotational, and solved by using the Quasi Arbitrary Lagrangian-Eulerian finite element method (QALE-FEM). These two models are weakly coupled using a zonal (spatially hierarchical) approach. Considering the inconsistence of the solutions at the boundaries between two different sub-domains governed by two fundamentally different models, a relaxation (transitional) zone is introduced, where the velocity, pressure and surface elevations are taken as the weighted summation of the solutions by two models. In order to tackle the challenges associated and maximise the computational efficiency, further developments of the QALE-FEM have been made. These include the derivation of an arbitrary Lagrangian-Eulerian FNPT and application of a robust gradient calculation scheme for estimating the velocity. The present hybrid model is applied to the numerical simulation of a fixed horizontal cylinder subjected to a unidirectional wave with or without following current. The convergence property, the optimisation of the relaxation zone, the accuracy and the computational efficiency are discussed. Although the idea of the weakly coupling using the zonal approach is not new, the present hybrid model is the first one to couple the QALE-FEM with OpenFOAM solver and/or to be applied to numerical simulate the wave-structure interaction with presence of current.