• Journal of Mechanical Science and Technology
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• v.18 no.6
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• pp.1026-1035
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• 2004

An immersed boundary method for solving the Navier-Stokes and thermal energy equations is developed to compute the heat transfer over or inside the complex geometries in the Cartesian or cylindrical coordinates by introducing the momentum forcing, mass source/sink, and heat source/sink. The present method is based on the finite volume approach on a staggered mesh together with a fractional step method. The method of applying the momentum forcing and mass source/sink to satisfy the no-slip condition on the body surface is explained in detail in Kim, Kim and Choi (2001, Journal of Computational Physics). In this paper, the heat source/sink is introduced on the body surface or inside the body to satisfy the iso-thermal or iso-heat-flux condition on the immersed boundary. The present method is applied to three different problems : forced convection around a circular cylinder, mixed convection around a pair of circular cylinders, and forced convection around a main cylinder with a secondary small cylinder. The results show good agreements with those obtained by previous experiments and numerical simulations, verifying the accuracy of the present method.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.1
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• pp.167-174
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• 2005

The design for cold extrusion dies is very important, because the die insert is subjected to very high radial and hoop stresses. The design of cold extrusion dies has many constrained conditions. In this paper, the used assumptions are such that the yield strength of each ring is selected according to the allowable tensile or compressive hoop stress in each ring and the maximum allowable inner pressure, when yielding occurs in one ring of the dies, is obtained by the proposed equation. In order to obtain design variables, such as diameter ratios and interferences, using the maximum inner pressure, the flexible tolerance method was used for shrink-fitted thick-walled cylinders. ANSYS APDL was used to perform the repeated analysis of deformation of the dies due to the variation of the design variables. The response surface methodology is utilized to analyze the relationship between the design variables and the maximum radial displacement of the die insert during extrusion. From the results, it is found that outer diameter of the die insert has the largest effect on the minimization of maximum radial displacement at the inner surface of the dies.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.24-29
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• 2007

Low-speed Diesel Engine, 7K60MC-S, in Power Plant have been experienced high vibration frequently since these units were completed the construction works, but they did not have any fundamental vibration solutions up to date. Therefore, several vibration tests and analyses are conducted to identify the root cause of high vibration and to suggest the optimal countermeasures for diesel engine. The 9.25Hz & 25.4Hz vibrations have been observed on main body during operation. The magnitude of engine upper structural vibration is generally similar in horizontal transverse direction. However, differences in the 'Fore' and 'After' vibration magnitude at 9.25Hz occurs due to the inertia momentum added by SCR duct system with the same vibration phase angle. It is analyzed that the excess structural vibration be occurred when the natural frequency of engine body is accessed the exciting sources due to the explosion pressure and the discharge pulsation of 7 cylinders in resonance range.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.27 no.2
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• pp.168-174
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• 2017

In this work, a piezostack single-stage valve (PSSV) system is proposed and its control performance is experimentally evaluated at high temperature up to $150^{\circ}C$. In order to achieve this goal, a PSSV system is designed and operating principle and mechanical dimensions are discussed. A displacement amplifier and an adjust bolt are used to generate target displacement and to compensate thermal expansion. Then, an experimental apparatus is constructed to evaluate control performance of the PSSV system. The experimental apparatus consists of a heat chamber, a hydraulic circuit, a pneumatic circuit, pneumatic-hydraulic cylinders, thermal insulator, electronic devices, sensors, data acquisition (DAQ) board and a voltage amplifier. The flow rate and displacement control performance of the valve system are evaluated via experiment. The experimental results are evaluated and discussed at different temperatures and frequencies showing the controlled flow rate and spool displacement.

• Journal of Science Education
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• v.38 no.1
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• pp.78-95
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• 2014

Students' interest and motivation of a lesson can be deeply influenced by how their teacher starts his or her lesson. So the introduction part of math classes should be very carefully and thoughtfully designed. The goal of this study is to serve the foundation for developing the practical types of introduction part of math classes and to draw the implications for planning and teaching math classes. For these, 19 lesson plans titled by 'volume of cylinders' composed by elementary teachers and 2 lesson videos on the internet are analyzed. Finally, seven types of introduction parts of math class are probed and several implications are suggested.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2000.05a
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• pp.45-51
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• 2000

Investigators who study on combustion in the cylinders of reciprocating piston type internal combustion engines have been encountered embarrassments due to the difficulties of adjusting specific parameter without interfacing other parameters such as cylinder wall temperature composition of gas in the cylinder existence of cylinder lubricant etc. Rapid compression-expansion machine the position and speed of piston of which are able to be controlled by means of a system controlled electrically and speed of piston of which are able to be controlled by means of a system controlled electrically and actuated hydraulically could be utilized as one of the most preferable countermeasures against those difficulties. Several units of rapid compression-expansion machines were developed but the speed up of frequency of piston movement still is the problem to be improved to cope with actual speed of internal combustion engines. Authors designed and manufactured a new rapid compression-expansion machine electrically controlled hydraulically actuated and computer programed and then examined the performance of one. Results of a set of experiments revealed acquirements of certain improvement of frequency of piston movement preserving the stability of system response and reproducing accurate compression ratio of cylinder those are the key function for the in-cylinder combustion experiments of internal combustion engines.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.687-687
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• 2013

In rearpoint contact solar cell and the PERC (passivated emitter rear contact) type cell, surfaces were passivated by SiO2 or Al2O3 to increase solar cell efficiency. Therefore, we have investigated the effect of surface passivation for crystalline silicon solarcell using mass-production atomic layer deposited (ALD) Al2O3. The patttern which consists of cylinders with 100um diameter and 5um height was formed by PR patterning on Si (100) substrate and then Al2O3 of about 10nm and 20nm thickness was deposited by ALD. The pattern in 10 nm Al2O3 film was removed by dipping in aceton solution for about 10 min but the pattern in 20 nm Al2O3 film was not. The influences of process temperature and heat treatment were investigated using microwave photoconductance decay (PCD) and Quasi-Steady-State photoconductance (QSSPC). The solar cell process used in this work combines the advantage of using the applicability of a selective deposition associated with a ALD passivation and the use of low-cost screen print for the contacts formation.

• Journal of the Korean Society of Industry Convergence
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• v.2 no.1
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• pp.45-52
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• 1999

It is difficult to keep the balance of supply and demand for natural aggregates in recent years, because natural resources have become to be almost exhausted. Crushed stone is already used for coarse aggregate instead of river gravel at present. Now, crushed sand or sea sand should be used for fine aggregate, because natural sand also has been exhausted with a few exceptions around Nakdong River. The sea sand has a lot of problems which are the corrosion of reinforcement bars, the investment of facility for cleansing salt and the cost increase due to the insufficiency of industrial water. Therefore, it is necessary to produce and to utilize the crushed sand very actively, but some material properties which are related to water absorption, strength and chemical durability, prevent from determining the generalized criteria because its rocks make much differences in its physical and chemical characteristics. In this paper, fundamental physical properties of crushed sand, which comes from Daegu Subway construction fields, have been investigated for the usability on basic material of concrete. The optimum replacement ratio and the strength estimation method of crushed sand replacing natural sand also have been presented here through the compressive strength test of ready-mixed concrete cylinders.

• Ocean Systems Engineering
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• v.4 no.3
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• pp.169-183
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• 2014

For the reliable design of substructure supporting offshore wind turbines it is very important to reduce the effects of wave forces. Since the substructure is strongly influenced by the effects of wave forces as the size of substructure increases. In the present study, the hybrid substructure with multi-cylinder is newly suggested to reduce the effects of wave forces. Using diffraction theory the scattering waves in a fluid region are expressed by an Eigenfunction expansion method with three dimensional potential theory to calculate the wave force acting on the hybrid substructure. The wave force and wave run-up acting on the hybrid substructure is presented to examine the water wave interaction according to the variation of cylindrical size and the distance among cylinders. It is found that the suggested hybrid substructure with multi-cylinder is very useful to reduce the effects of wave forces acting on the substructure for offshore wind turbines.

• Computers and Concrete
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• v.26 no.3
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• pp.293-307
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• 2020

The aim of this paper is to develop design-oriented models for the prediction of the ultimate strength and ultimate axial strain for concrete confined with glass fiber-reinforced polymer (GFRP) wraps. Twenty of most used and recent design-oriented models developed to predict the strength and strain of GFRP-confined concrete in circular sections are selected and evaluated basing on a database of 163 test results of concrete cylinders confined with GFRP wraps subjected to uniaxial compression. The evaluation of these models is performed using three statistical indices namely the coefficient of the determination (R²), the root mean square error (RMSE), and the average absolute error (AAE). Based on this study, new strength and strain models for GFRP-wrapped concrete are developed using regression analysis. The obtained results show that the proposed models exhibit better performance and provide accurate predictions over the existing models.