• Journal of KSNVE
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• v.7 no.6
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• pp.909-918
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• 1997

Combustion oriented noise is a part of engine noise, which is mainly determined by the in-cylinder pressure profile and the structure attenuation of an engine. A numerical model for predicting the in-cylinder pressure profile and the resultant combustion noise developed by the use of a commercial code. The model is experimentally validated and updated based on the performance as well as the noise by considering the fuel injection timing, the fuel injection rate, Cetane number, intake temperature, and compression ratio. For providing a design guide of a fuel injector for a low combustion noise engine model, the optimal parameters of injection pressure profile, injection rate profile, and injection timing are determined, which gives the 5 dBA noise reduction.

• Journal of Power System Engineering
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• v.1 no.1
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• pp.42-51
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• 1997

In this study, in order to investigate the influence of cam profile on the injection rate, the characteristics of injection in PLN (pump - line - nozzle) diesel injection system were simulated. Six types of the profile of fuel cam were used for simulation. The maximum injection pressure and maximum injection rate of initial and end phase were analyzed to demonstrate the characteristics of injection. The mathematical model of the injection system and the computation results were verified by experimental results. Simulation results showed that the maximum injection pressure, maximum injection rate, injection quantity and pressure drop in the end phase were proportional to the velocity of fuel cam during the effective stroke.

• Tribology and Lubricants
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• v.31 no.5
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• pp.205-212
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• 2015

In this research, effects of profile changes of stem section of the plunger on the lubrication characteristics of a fuel injection pump (FIP) were evaluated by hydrodynamic lubrication analysis. The clearance between plunger and barrel was divided into two regions, head and stem. The head was not involved in preventing a decrease of fuel oil pressure. So, research efforts were focused on both edges of the plunger’s stem. The two -dimensional Reynolds equation was used to evaluate lubrication characteristics with variations in viscosity, clearance and profile for a laminar, incompressible, unsteady-state flow. Moreover, the equilibrium equation of moment and forces in the vertical and horizontal directions were used to determine the motion of the plunger. The equations were discretized using the finite difference method. Lubrication characteristics of the FIP were investigated by comparing the dimensionless minimum film thickness, or film parameter, which is the ratio of minimum film thickness to surface roughness. Through numerical analyses, we showed that the profile of the lower edge of the stem had no effect on lubrication characteristics, but the profile of the upper edge had a significant influence on lubrication characteristics. In addition, changes in the profile were more effective in improving lubrication characteristics under low viscosity conditions.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.320-329
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• 2008

The influence of thermodynamic transition associated with transcritical nitrogen injection upon the flow structure was investigated to explore numerical simulation of the injectant dynamics of oxygen/hydrogen coaxial jet in liquid rocket engines. Single and coaxial nitrogen jets were treated by comparing the transcritical and perfect-gaseous conditions, wherein the numerical model was accommodative to the real-fluid thermodynamics and transport properties at supercritical pressures. The model was in the first place validated by comparing the results of transcritical nitrogen injection between calculations and available experiments. For a single jet under the transcritical condition, the nitrogen kept a relatively high density up to its pseudo-critical temperature inside the mixing layer, since it remains less expanding until heated up to its pseudo-critical temperature. Numerical analysis revealed that cryogenic jets exhibit strong dependence of specific enthalpy profile upon the associated density profile that are both dominated by turbulent thermal diffusion. In the numerical model, therefore, exact evaluation of turbulent heat fluxes becomes very important for simulating turbulent cryogenic jets under supercritical pressures. Concerning the coaxial jets due to transcritical/gaseous nitrogen injections, the density profile inside the mixing layer was again affected by the thermodynamic transition of nitrogen. However, hydrodynamic instability modes of the inner jet did not show significant differences by this thermodynamic transition, so that further study is needed for the mixing process downstream of the near injection position.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.5
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• pp.1272-1290
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• 2013

Privacy-preserving collaborative filtering schemes are becoming increasingly popular because they handle the information overload problem without jeopardizing privacy. However, they may be susceptible to shilling or profile injection attacks, similar to traditional recommender systems without privacy measures. Although researchers have proposed various privacy-preserving recommendation frameworks, it has not been shown that such schemes are resistant to profile injection attacks. In this study, we investigate two memory-based privacy-preserving collaborative filtering algorithms and analyze their robustness against several shilling attack strategies. We first design and apply formerly proposed shilling attack techniques to privately collected databases. We analyze their effectiveness in manipulating predicted recommendations by experimenting on real data-based benchmark data sets. We show that it is still possible to manipulate the predictions significantly on databases consisting of masked preferences even though a few of the attack strategies are not effective in a privacy-preserving environment.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.5
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• pp.78-85
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• 2000

This study is to develop the diesel engine which has 6 cylinder natural aspiration direct injection type of 7.4$\ell$ with high performance, low emissions and low fuel consumption Finally the developed engine meets Korean `98 exhaust emission regulation for the city bus of heavy duty diesel engine by optimizing the various combustion parameters affecting performance and exhaust emissions. Combustion parameters are the swirl ratio of intake ports, the profile of injection pump`s cam affecting injection pressure, the design features of piston bowl of injection pump`s cam affecting injection pressure, the design features of piston bowl of combustion chamber and injector`s hole size. Through experimental analysis, various combustion parameters are optimized and the results are as follows; the swirl ratio is 2.20, the profile of injection pump`s cam is concave and re-entrant ratio, inner diameter of piston bowl and hole diameter of injector is 0.88,$\psi$64.0mm and $\psi$0.25mm respectively.

• Journal of IKEEE
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• v.24 no.3
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• pp.828-837
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• 2020

This paper presents the optimal design of planar flyback transformer suitable for small-size and low-profile of AC to DC adapter for 10W tablet. This paper also proposes the injection winding transformer of Hybrid and Drum types capable of the winding method of automatic type and the reduction of transformer size and leakage inductance(L_k) compared to the conventional mass-production flyback transformer with the winding method of manual type. In particular, the injection winding transformer of Drum type proposed in this paper is constructed in a horizontal laying of its transformer to solve the connection problem of copper plate injection winding on the secondary side of the one of Hybrid type. The primary and secondary windings of the injection winding transformer of Hybrid and Drum types used the conventional winding and the copper plate injection winding, respectively. For the injection winding transformer of Hybrid and Drum types proposed in this paper, the optimal design of planar flyback transformer suitable for small-size and low-profile was carried out using Maxwell 2D and 3D tool.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.1
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• pp.1-8
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• 2000

A modified low-Reynolds-number Reynolds stress model is developed for the calculation of drag-reducing turbulent flows induced by polymer injection. The results without polymer injection are compared with the results of direct numerical simulation to ensure the validity of the basic model. In case of drag reduction, profiles of mean velocity and Reynolds stress components, in two-dimensional channel flow, obtained with a proper value of viscosity ratio are presented and discussed. Computed mean velocity profile is in very good agreement with experimental data. And, the qualitative behavior of Reynolds stress components with the viscosity ratio is also reasonable.

• Journal of the Korean Wood Science and Technology
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• v.30 no.2
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• pp.158-164
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• 2002

The properties of new porous carbon materials "Woodceramics" are affected by the characteristics of raw boards. To investigate of density profile and resin contents in impregnated boards, control board and 3 types of steam-injected boards were made by steam injection time, The wood species used for manufacturing boards was Sugi(Cryptomeria japonica). The results are as follows: 1) The density gradient of board after 10 minutes steam injection was the smallest and non-steamed board was largest. 2) The resin content and dimensional rise decreased with increase of board density, and were the largest in board after 10minutes steam injection but there was little difference between boards after 5 and 10 minutes steam injection.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.18 no.5
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• pp.1341-1368
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• 2024

The concept of privacy-preserving collaborative filtering (PPCF) has been gaining significant attention. Due to the fact that model-based recommendation methods with privacy are more efficient online, privacy-preserving memory-based scheme should be avoided in favor of model-based recommendation methods with privacy. Several studies in the current literature have examined ant colony clustering algorithms that are based on non-privacy collaborative filtering schemes. Nevertheless, the literature does not contain any studies that consider privacy in the context of ant colony clustering-based CF schema. This study employed the ant colony clustering model-based PPCF scheme. Attacks like shilling or profile injection could potentially be successful against privacy-preserving model-based collaborative filtering techniques. Afterwards, the scheme's robustness was assessed by conducting a shilling attack using six different attack models. We utilize masked data-based profile injection attacks against a privacy-preserving ant colony clustering-based prediction algorithm. Subsequently, we conduct extensive experiments utilizing authentic data to assess its robustness against profile injection attacks. In addition, we evaluate the resilience of the ant colony clustering model-based PPCF against shilling attacks by comparing it to established PPCF memory and model-based prediction techniques. The empirical findings indicate that push attack models exerted a substantial influence on the predictions, whereas nuke attack models demonstrated limited efficacy.