• Journal of the Korean Wood Science and Technology
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• v.27 no.1
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• pp.50-55
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• 1999

Since ultrasonic stress wave velocity varies with wood temperature and moisture content, ultrasonic stress wave could be a tool to predict wood moisture content if temperature effect could be eliminated. This temperature effect was investigated by measuring the velocities of ultrasonic stress waves transmitting through air, a metal bar and a dimension lumber at various temperatures. For air the velocity and amplitude of the ultrasonic stress wave increase with temperature, while for a metal bar and a dimension lumber those decrease as temperature increases. However all three materials showed velocity hystereses with a temperature cycle. The effect of temperature and moisture content on stress wave velocity of a dimension lumber was depicted in the form of a three dimensional graph. The plot of stress wave velocity vs. wood moisture content was well fitted by two regression equations: a exponential equation below 46% and a linear equation above 46%.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.4
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• pp.101-107
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• 1998

A three-dimensional multi-phase flow is simulated around a smooth tire. This simulation is conducted by solving Navier-Stokes equation with a k-$\varepsilon$ turbulent model. The numerical calculations are carried out by modeling a multi-phase free surface flow mixed with air and water at the inlet. The numerical solutions show an intuitively resonable behavior of water around a moving tire. The calculated pressure around the tire surface along the moving direction is presented. The moving velocities of the tire are chosen to be 30, 40, 60, and 70 km/h. The numerically simulated pressures around the tire are compared with existing experimental data. The comparison shows a new possible tool of analyzing a hydroplaning phenomenon for an automobile tire by means of a computational fluid dynamics.

• Proceedings of the KIEE Conference
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• 2002.07d
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• pp.2076-2078
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• 2002

This paper presents an Intelligent Balance Beam Controller(IBBC) which can estimate the inertia of load automatically. Balance Beam controller is a kind of construction tool which can control the attitude of the load hanging in the air such as a beam carried by crane. In our previous work, Balance Beam had been built to control the object in air using a mechanical gyro system having a position controllable gimbal structure. In field application the load inertia for operation is not easy to figure out because the weight and shape which determines the inertia, varies depending on the object to be carried. Therefore it is difficult for a worker to operate a Balance Beam and an accident could be caused occasionally. We designed an automatic load estimator to measure the inertia of arbitrary load by using an angular velocity sensor that is installed on the Balance Beam. Simulation results and current status for implementation are presented.

• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.827-828
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• 2006

This paper proposes a new method for detecting broken rotor bars in a squirrel-cage induction motor. The air-gap flux variation analysis was done using search coils inserted in stator slots when broken rotor bar occurs. An accurate modeling and analysis of air-gap flux variation in the induction motor are developed using finite-element(FE) software packages, and measurement of the flux are made using search coils. The simulation was done for the induction motor with 380 [V]. 7.5 [kW], 4 Poles, 1,760 [rpm] ratings using the commercial FE analysis tool. The simulation and experiment results can be useful for detecting the broken rotor bar of an induction motor.

• Wind and Structures
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• v.3 no.2
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• pp.73-81
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• 2000

Snowdrifts around buildings can cause serious problems when formed on undesirable places. The formation of snowdrifts is highly connected to the wind pattern around the building, and the wind pattern is again dependent on the building design. The shear stress on the surface and snowdrifting around different buildings are investigated through CFD analysis and compared to measurements. The computations of shear stress shows local minima in the same areas as snowdrifts are formed. The snowdrifting computations utilises a drift-flux model where a fluid with snow properties is allowed to drift through a fluid with air properties. An apparent dynamic viscosity of the snow/air mixture is defined and used as a threshold criterion for snowdrifting. The results from the snowdrifting computations show increased snow density where snowdrifts are expected, and are in agreement with previous large-scale snowdrift measurements. The results show that computational fluid dynamics can be a tool for planning building design in snowdrifting areas.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.10
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• pp.854-862
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• 2002

In the previous research, a simplified correlation method was developed as an easy prediction tool for comparing energy use of cooling plants. The purpose of this paper is to test the applicability of this method for economic evaluation with two zones of a 20-story commercial building in Seoul. The results of this method were compared with the DOE-2 simulation and actual measured data. Then, Comparisons of life cycle cost were carried out for three types of cooling plants. Testing of one zone showed good agreement of within 10% error in cooling energy use and within 2% error in LCC. But testing of the other zone indicated that the use of this method were invalid when input variables were used beyond its valid range.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.6
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• pp.95-100
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• 2005

Since air pollution has become a globally critical issue and exhaust emissions from automobiles cause a major source of air pollution, many countries including advanced countries have stipulated stringent emission regulations. This research focused on engine performance characteristics with the application of a continuous regeneration diesel particulate filter and EGR together in a heavy duty vehicle, and gives some suggestions on the direction of designing points of view by comparing the experimental data with numerical results which were obtained through KIVA-3V.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.10 no.5
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• pp.53-59
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• 2001

A screw driver is widely used in assembling machine parts or electronic products such as the printed circuit board with a housing. As the parts to be assembled becomes small and precise, the higher precision of the controlling screw driver torque is required. However, because the operator controls the fastening torque based on experience, it must be inexact and the setting procedure will be time consuming job. Thus the screw driver which can exactly control the fastening torque is developed utilizing a bellows in this paper. The bellows is expanded by the inner air pressure and contracted by the spring operation. The bellows type driver is composed of a clutch mechanism with two solenoid valves and a pressure sensor. Those valves are controlled using the detected bellows pressure by the sensor. When the pressure reaches the setting value, the exit solenoid valve is opened to release the air pressure from the bellows so as not to deliver further torque. Through a series of experiments, the performance is examined and verified.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1999.05a
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• pp.263-268
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• 1999

With HAZ of A 106 Gr B steel weldment, fatigue test in air, electrochemical polarization test and corrosion fatigue test in 3.5wt.% NaCl solution were performed changing load ratio. Obtained results are as follows. 1) K$\sub$op/ was independent of K$\sub$max/ and load ratio in fatigue crack growth. 2) In variation of load ratio, the scatter band of crack growth curve was reduced by half considering crack closure 3) In the result of electrochemical polarization test, current density was increased abruptly when potential was larger than corrosion potential. 4) Fatigue crack growth rate in corrosive environment was markly higher than the rate in air because of corrosion characteristics of the material and anodization of inner surface crack.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.8
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• pp.664-670
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• 2002

A heat sink (HS) system using heat pipes for electronics systems was studied. The experimental results indicate that a cooling capacity of up to 150w at an overall temperature difference of $50^{\circ}C$ can be attainable. The heat sink design program also showed that a computer simulation can predict the most of the parameters involved. To do so, however, the interior temperature distribution had to be verified by experimental results. The current simulation results were close to the experimental results in acceptable range. The simulation study showed that the design program can be a good tool to predict the effects of various parameters involved in the optimum design of the heat sink.