• 한국자동차공학회논문집
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• 제14권2호
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• pp.194-201
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• 2006

Roof-fairing and deflector system have been used on heavy-duty trucks to minimize aerodynamic drag force not only for driving stability of the truck but also for energy saving by reducing the required driving power of the vehicle. In this study, a numerical simulation was carried out to see aerodynamic effect of the drag reducing device on the model vehicle. Drag and lift force generated on the five different models of the drag reducing system were calculated and compared them each other to see which type of device is efficient on the reduction of driving power of the vehicles quantitatively. An experiment has been done to see airflow characteristics on the model vehicles. Airflow patterns around the model vehicles were visualized by smoke generation method to compare the complexity of airflow around drag reducing device. From the results, the deflector systems(Model 5,6) were revealed as a better device for reduction of aerodynamic drag than the roof-fairing systems(Model 2,3,4) on the heavy-duty truck and it can be expected that over 10% of brake power of an engine can be saved on a tractor-trailer by the aerodynamic drag reducing device at normal speed range($80km/h{\sim}$).

• Journal of Biosystems Engineering
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• 제14권4호
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• pp.242-250
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• 1989

The performance of a vertical type centrifugal distributor of granular materials was studied by means of mathematical models and experimental investigations. To develop the mathematical description of particle motion, some assumptions were made. The distribution process consisted of three stages: the entrance of a particle to the blade, the motion of the particle on the blade, and the motion of the particle in the air. The physical properties of fertilizer, which affected the particle motion, were investigated: bluk density, coefficient of friction, coefficient of restitution, and particle size distribution. The particle motion were simulated by using a computer. A prototype distributor was designed and constructed for experimental tests. The following conclusions were drawn from the computer simulation and experiment results. 1. The fertilizer may slide or roll at the point of contact when they impact on the blade and move along the blade. 2. The interaction among fertilizers may prevent them from bouncing. 3. When fertilizers roll on the blade, rolling resistance is one of the factors affecting the particle's motion. 4. The trajectory angle and position of fertilizers from a disc depend on the blade position and particle shape, but the rotating speed of the disc affected them only slightly.

• Journal of Welding and Joining
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• 제35권2호
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• pp.6-12
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• 2017

Ti-alloys have high specific strength and are widely used for the filed of space aeronautics plant. However, it is difficult to process Ti-Alloys due to its high yield strength and it cannot raise the machining speed because it has a possibility of catching fire while processing. In order to reduce the number of processes for the Ti-alloys, the researches related to Additive Manufacturing(AM) have been actively carried out at the moment. As for the initial stage of AM market related to Ti-alloys, it started to use the raw material of powder metal, and it is currently being developed based on welding. In this study, Interpass peening reduced the size of the primary ${\beta}$ grain in the z-axis direction, increased the nucleation site of ${\alpha}-colony$, and decreased the length and width of ${\alpha}$ laths as though interpass rolling. Interpass peening leads to an increase in yield/ultimate tensile strength without decrease elongation, resulting decrease in anisotropy of the material.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2006년도 추계학술대회 논문집
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• pp.447-453
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• 2006

The major objective of this study is to investigate the fatigue behavior evaluation of immovability crossing for railway turnout by the field test. In railway engineering, an appliance is necessary to allow a vehicle to move from one track to another. This appliance came to be known technically as turnout. So, turnout is required very complex railway technologies such as rolling stock, track. Due to the plan under the application of high speed train, turnout are needed more stable for fatigue behaviors. It analyzed the mechanical behaviors of turnout crossing with propose its advanced technical type on the field test and fatigue evaluation for the dynamic fatigue characteristics. As a result, the advanced type crossing are obviously effective for the fatigue damage ratio and dynamic response which is non-modified type. The analytical and experimental study are carried out to investigate the passing path of contact surface and fatigue damage trend decrease dynamic stresses and deflections on advanced crossing type. And the advanced type reduce dynamic fatigue damage ratio and increase fatigue life(about each 38%)more than non-modified type. From the field test results of the servicing turnout crossing, it is evaluated that the modification of contact angle, weight, material and sectional properties is very effective for ensure against fatigue risks.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 춘계학술대회 및 창립 30주년 심포지엄(논문집)
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• pp.185-190
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• 2006

항주파에 의해 해안침식, 호안 결괴, 하역곤란 및 어선 등을 포함한 소형선박의 동요가 발생하며, 심지어 최근에는 수상오토바이, 모터보트 및 여객선의 고속주행은 해수욕장의 수영객 및 낚시꾼 등 어로작업중인 어민에게 위협이 되고 있다. 특히, 천해역에서 발생한 항주파는 심해역에서 발생한 항주파보다 연안시설 또는 작업인원의 안전에 더 큰 영향을 미칠 수 있으며, 파고는 천해역에서 발생하여 극천해역으로 진행하는 경우, 천해역 파고의 1.8배정도로 커진다. 또한 극천해역에 약간의 흐름이 존재하여도 파는 진행하지 못한다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.786-789
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• 2005

The proper parameters in a twin roll strip casting are important to obtain the stabilization of the Mg sheet. What is examined in this paper is the quantitative relationships of the important control parameters such as the roll speed, height of pool region, outlet size of nozzle, solidification profile and the final point of solidification in a twin roll strip casting Unsteady conservation equations were used for transport phenomena in the pool region of a twin roll strip casting in order to predict a velocity, temperature distributions of fields and a solidification process of molten magnesium. The energy equation of cooling roll Is solved simultaneously with the conservation equations of molten magnesium In order to consider the heat transfer through the cooling roil. The finite difference method (2-D) and the finite element method (2-D) are used in the analysis of pool region and cooling roil to reduce computing time and to improve the accuracy of calculation respectively.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.1005-1011
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• 2004

Squeeze film dampers (SFDs) have been commonly used to effectively enhance the dynamic behavior of the rotating shaft supported by rolling element bearings. However, due to the recent trends of high operating speed, high load capacity and light weight in rotating machinery, it is becoming increasingly important to change the dynamic characteristics of rotating machines in operation so that the excessive vibrations, which may occur particularly when passing through critical speeds or unstable regions, can be avoided. Semi-active type SFDs using magneto-rheological fluid (MR fluid), which responds to an applied magnetic field with a change in rheoloaical behavior, are introduced in order to find its applications to rotating machinery as an effective device attenuating unbalance responses. In this paper, a semi-active SFD using MR fluid is designed, tested and identified by means of linear analysis to investigate the capability of changing its dynamic properties such as damping and stiffness. Furthermore, the proposed device is applied to a rotor system to investigate its potential capability for vibration attenuation: an efficient method for selecting the optimal location of the proposed damper is introduced and control algorithm that could improve the unbalance response properties of a flexible rotor is also proposed.

• 드라이브 ㆍ 컨트롤
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• 제10권4호
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• pp.14-21
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• 2013

The numerical analysis of the automatic ship mooring system which was equipped in the ship for trying to berth at the pier was performed in this study. The automatic ship mooring using hydraulic winch was a new method that had not need to change the existing devices and to help a pilot ship of outside. The numerical results of the proposed mooring system including ship motion were that the speed and rolling phenomenon of ship was affected by changing in the ship weight and affected the slope maintenance and yaw degree of ship if there has a trim of stern. Also, a static force of ship at the initial movement was important to calculate the mooring power. The moving force and inertial force of ship on the vertical direction was confirmed for the mooring stability. Therefore, the power and velocity of hydraulic mooring winch should be determined by considering the significant characteristics such as weight, velocity, inertial force and moving force of ship.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 추계학술대회 논문집
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• pp.666-672
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• 2008

Train wheels are the most important part of the high-speed rail system with supporting body, running stably and safely. Wheel exchange and fix plan is computed by the worker who managing entire Train Maintenance Process based on his know-how so that this system is losing its reliability and accuracy. And predicting of the wheel's lifetime is absolutely difficult matter because of uncertainty between trains like mileage of the type of trains, condition of operation, curve section and wheel's cutting pattern. Therefore workers always used to hold many wheels. For this reason, the cost of stock is soar when the level of stock was normal. If the stock is sufficient, the cost of stock will rise. On the other hand, If the stock is deficient, we would have trouble that the plan of the train maintenance process will be failed. Thus this paper aimed at application that "Wheel Managing System" which is able to predict wheel's life-cycle and demands under the RIMS(Rolling-Stock Information Maintenance System) with analysing wheel exchanging and cutting status considering economical or stable aspects.

• Tribology and Lubricants
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• 제39권4호
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• pp.123-132
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• 2023

In this study, the expansion, stress, and operating clearance of bearing elements during operation are observed using the inner/outer ring temperature test data of a 3.0×10⁶ DN-class roller bearing. The operating clearance characteristics of inner-/outer-ring cooling (IORC) bearings are compared to those of inner-ring cooling (IRC) bearings. For IRC bearings, the thermal expansion of the outer ring is the most important factor in clearance variation. As a result, the operating clearance is less than the initial clearance of 61 ㎛, and the operating clearance decreases to 0.5 ㎛ at 25,500 rpm. Conversely, the temperature of the outer ring of IORC bearings is lower than that of IRC bearings, so the operating clearance is kept smaller. When the coolant flow rate to the outer ring is approximately 1.5 to 2.0 L/min, the temperature difference between the inner and outer rings is minimized and the operating clearance is maintained at a significantly lower level than IRC bearings. Small operating clearances are expected to be effective in reducing cage slip and skid damage in roller bearings. The results and analysis procedures of this study can be utilized to design of bearing clearance, lubricant flow rate, and assembled interference in the early design stage of aerospace roller bearings.