• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.77-78
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• 2002

A regression formula including the inlet film thickness as the parameter for the starvation factor in EHL condition is obtained by numerical analysis with Elord‘s cavitation algorithm. In addition, an apparatus for starved film thickness measurement by use of the white light interferometry is developed in order to verify the proposed regression formula. From observation results by this apparatus, the proposed regression formula can predict the reduction of central film thickness caused by starvation in a ball-plate contact with an uncertainty up to 10%

• The Journal of the Acoustical Society of Korea
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• v.31 no.6
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• pp.384-390
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• 2012

Passive sonars employ DEMON(Detection of Envelope Modulation on Noise) processing to extract propeller information from the radiated noise of underwater targets. However, the conventional DEMON processing suffers from the interference of tonal signals because it extracts propeller signals and some types of tonal signals as well. If there are some tonals in the frequency band for DEMON processing, the conventional DEMON processing may additionally extract frequency informations originated from the interaction between different tonals. In this paper, we propose a modified DEMON processing, which can eliminate the interference of the tonals. The proposed algorithm removes tonals in DEMON processing band before demodulation processing, hence results the robustness to the interference of the tonals. Some numerical simulations demonstrate the improved performance of the proposed algorithm against the conventional algorithm.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.4
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• pp.403-410
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• 2008

This paper describes the optimization of the rudder section by the genetic algorism based on VLM(Vortex Lattice Method) and panel method. The developed propeller-rudder analysis program has been validated by comparing with experimental data. The research extends to optimize the anti-erosion rudder section of the large container ship. The object function is the amount of pressure at leading edge of rudder which is closely related with erosion phenomena. The optimized rudder has been compared with conventional rudder with NACA 0021 section by analyzing with the developed program. The finally optimized section has low and mild pressure distribution in comparison with the NACA rudder. The experiments is expected to be carried out for the validation of the present optimization and more parametric study of section geometry is also expected to be conducted in the near future.

• KSTLE International Journal
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• v.1 no.2
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• pp.76-82
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• 2000

Turbulence in journal bearing operation is examined and the thermal variability is studied for isothermal, convective and adiabatic conditions on the walls under aligned and misaligned conditions. Also, the effects of a contraction ratio at the cavitation region and the mixing between re-circulating oil and inlet oil on the fluid field of oil film are included. An algorithm for the solution of the coupled turbulent Reynolds and energy equations is used to examine the effects of the various factors. Heat convection is found to play only a small role in determining friction and load under no mixing condition. However, under realistic mixing condition, the heat convection cannot be ignored. The wall temperature and heat transfer have been found to be of secondary important factors to the mixing effectiveness at the groove and the final mixture temperature.

• Journal of ILASS-Korea
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• v.1 no.1
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• pp.76-84
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• 1996

The nozzle geometry and up-stream inject ion condition affect the characteristics of flow inside the nozzle. such as turbulence and cavitation bubbles. Flow details in fuel nozzle orifice with sudden contraction of cross sectional area have been investigated both experimentally and numerically. The measurements of velocities of internal flow in a scaled-up nozzle with different length to diameter rat io(L/d) were made by laser Doppler velocimetry in order to clarify the effect of internal flow on the characteristics of fuel spray. Mean and fluctuating velocities and discharge coefficients were obtained at various Reynolds numbers. The turbulent intensity and turbulence kinetic energy in a sharp inlet nozzle were higher than that in a round inlet nozzle. Calculations were also performed for the same nozzles as scaled-up experimental nozzles using the SIMPLE algorithm. External spray behavior under different nozzle geometry and up-stream flow conditions using Doppler technique and visualization technique were also observed.

• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.3
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• pp.246-255
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• 2017

The proposed design methodology represents a new approach to optimize the propeller-hull system simultaneously. In this paper, two objective functions are considered, the first objective function is Lifetime Fuel Consumption (LFC) and the other one is cost function including thrust, torque, open water and skew efficiencies. The variables of the propeller geometries (Z, EAR, P/D and D) and ship hull parameters (L/B, B/T, T and $C_B$) are considered to be optimized with cavitation, blades stress of propeller. The well-known evolutionary algorithm based on NSGA-II is employed to optimize a multi-objective problem, where the main propeller and hull dimensions are considered as design variables. The results are presented for a series 60 ship with B-series propeller. The results showed that the proposed method is an appropriate and effective approach for simultaneously propeller-hull system design and is able to minimize both of the objective functions significantly.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.2
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• pp.278-287
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• 2002

The objective of the paper was to calculate the pressure drop and to investigate the recirculation region of the conical orifices used in Kwang-yang Iron & Steel Company. The flow field with water used as a working fluid was the turbulent flow for Reynolds number of 2$\times$10$^4$. The effective parameters fur the pressure drop and the recirculation region were the conical orifice\`s inclined angle ($\theta$) against the wall, the interval(S) between orifices, the relative angle of rotation($\alpha$) of the orifices, the shape of the orifice's hole(circle, rectangle, triangle) having the same area, the number(N) of the orifice's holes having the same mass flow rate, and the thickness(t) of the orifices. It was fecund that the shape of the orifice's hole, the number of the orifice's holes and the thickness of the orifice affected the total pressure drop a lot and that the conical orifice's inclined angle against the wall, the relative angle of rotation of the orifices, the number of the orifice's holes and the thickness of the orifices affected the center location of the recirculation region. The PISO algorithm with FLUENT code was employed to analyze the flow field.

• Tribology and Lubricants
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• v.32 no.1
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• pp.24-31
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• 2016

In this paper hydrodynamic lubrication analysis is carried out to investigate the effects of groove location on the lubrication performance of a piston and cylinder system in a linear compressor. The rectangle shaped grooves having a constant groove depth and width are applied on the lubrication area of the piston. The Universal Reynolds equation is used to calculate the oil film pressure, and the Elrod algorithm with the finite different method is used to solve the governing equation. The JFO boundary condition is applied to predict cavitation regions. Transient analysis for different locations of the grooves on the piston is carried out using the typical operating condition of the linear compressor in order to estimate the variations of frictional power losses and minimum film thicknesses. When the grooves are applied on the lubrication area, both the frictional power loss and the minimum film thickness decrease. The frictional power loss can be reduced effectively, while maintaining a minimum film thickness to enable the piston operation without direct contact with the cylinder surface, by means of choosing a proper location of the grooves. The optimum location of the grooves to improve a lubrication performance depends on the operation condition or the system requirements specification.