• The KSFM Journal of Fluid Machinery
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• v.15 no.4
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• pp.5-11
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• 2012

To identify the flow characteristics of the SMART reactor, a flow distribution model test and a numerical simulation are performed in KAERI. Among several part of the SMART reactor, the fuel assemblies are simulated using simulators because of the complexity. The geometries of the core in the SMART reactor and simulator are different, but some similarities are maintained such as the ratio of pressure drop in the vertical and cross directions. There are cross flow holes in each core simulator to reproduce the cross flow of SMART fuel assemblies. To know the flow characteristics of the cross flow, numerical analysis is performed. As the cross flow area is decreased, the pressure drop between inlet and outlet is decreased. Also, when the flow imbalance between two core simulators is constant, the cross flow area does not significantly affect the cross flow.

• Korean Journal of Applied Biomechanics
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• v.21 no.4
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• pp.429-436
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• 2011

In this study, we have experimented with 9 players at the national delegate level. Although there were some differences in the average effects of 3 types of one-two straight movements after the application of wheel axle, there were no statistical differences in the case of surface reacting forces, electromyograms, and impact forces. When the right fist was impacted using the one-two straight movements and the wheel axle was applied with 3 segmentations, high impact forces were obtained for the pronation in the following order-72.01 $m/s^2$ (type 2), 70.93 $m/s^2$ (type 3), and 58.19 $m/s^2$ (type 1). Higher values of the surface reacting force were found for type 1 that did not exhibit pronation in the left foot, whereas in the case of the vertical direction of the right foot, type 2 with pronation exhibited higher values and impact forces. In the right electromyogram, high impact forces due to the activation of the muscular electric potential were obtained for lumbar erector (LE) spinae and triceps brachii (TB) with type 1; LE spina, latissimus dosi (LD), and upper trapezius (UT) with type 2; and brachioradialis (BR), UT, and rectus abdominal (RA) with type 3. Due to pronation and complex motions of the 3 pronation segmentations, the efficiency was higher for impacts due to one-two straight movements.

• ETRI Journal
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• v.34 no.6
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• pp.962-965
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• 2012

In this letter, we propose a new RESURF stepped oxide (RSO) process to make a semi-superjunction (semi-SJ) trench double-diffused MOSFET (TDMOS). In this new process, the thick single insulation layer ($SiO_2$) of a conventional device is replaced by a multilayered insulator ($SiO_2/SiN_x/TEOS$) to improve the process and electrical properties. To compare the electrical properties of the conventional RSO TDMOS to those of the proposed TDMOS, that is, the nitride_RSO TDMOS, simulation studies are performed using a TCAD simulator. The nitride_RSO TDMOS has superior properties compared to those of the RSO TDMOS, in terms of drain current and on-resistance, owing to a high nitride permittivity. Moreover, variations in the electrical properties of the nitride_RSO TDMOS are investigated using various devices, pitch sizes, and thicknesses of the insulator. Along with an increase of the device pitch size and the thickness of the insulator, the breakdown voltage slowly improves due to a vertical field plate effect; however, the drain current and on-resistance degenerate, owing to a shrinking of the drift width. The nitride_RSO TDMOS is successfully fabricated, and the blocking voltage and specific on-resistance are 108 V and $1.1m{\Omega}cm^2$, respectively.

• Structural Engineering and Mechanics
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• v.48 no.4
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• pp.455-466
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• 2013

In recent years, many countries have added railway noise to the issues covered by noise regulations. It is known that the rail is the dominant source of rolling noise at frequency range of 500Hz-2000Hz for the conventional speeds (<160km/h). One of the effective ways to reduce noise from railway track is using a rail vibration absorber. To study the acoustic performance of rail absorber, the decay rates of vibration have long been used by researcher. In this paper, A FE model of a periodic supported rail with infinite element in ABAQUS is developed to study the acoustic performance of the rail absorber. To compute the decay rates, acceleration responses along the rail transferred to MATLAB to obtain response levels in frequency domain and then by processing the response levels, the decay rates obtained for each1/3octav band. Continous rail absorber is represented by a steel layer and an elastomer layer. The decay rates for conventional rail and rail with one-side absorber and also, the rail with two side absorber are obtained and compared. Then, to improve the system of rail absorber, a steel plate with elastomer layer is added to bottom of the rail foot. The vertical decay rate results show that the decay rate of rail vibration along the track is significantly increased around the tuned frequency of the absorber and thus the rail vibration energy is substantially reduced in the corresponding frequency region and also effective in rail noise reduction.

• Journal of the Earthquake Engineering Society of Korea
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• v.24 no.2
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• pp.95-102
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• 2020

Electrical instruments and devices contained in cabinets for controlling nuclear power plants require seismic qualification; likewise, in-cabinet response spectrum (ICRS) is necessary. Gupta et al. (1999) suggested the Ritz method, where rocking, frame bending, and plate bending behaviors of cabinets are considered, as a method for determining ICRS. This research proposes a method to determine the rocking stiffness of cabinets, which represents its rocking behavior. The cabinet is fixed on mounting frames and is connected to the base concrete by anchors. When horizontal excitation is applied to the cabinet, the mounting frames at anchors are locally deformed, the mounting frames are bent, and then rocking in the cabinet becomes evident. A method to determine equivalent vertical spring stiffness representing the local deformation of the mounting frames at anchors is then proposed. Subsequently, the rocking stiffness of this mounting frame is calculated upon assumption of the mounting frame as an indeterminate beam.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.1 s.173
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• pp.52-61
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• 2000

The role of quantitative nondestructive evaluation of defects is becoming more important to assure the reliability and the safety of structure, which can eventually be used for residual life evaluation of structure on the basis of fracture mechanics approach. Although ultrasonic technique is one of the most widely used techniques for application of practical field test among the various nondestructive evaluation technique, there are still some problems to be solved in effective extraction and classification of ultrasonic signal from their noisy ultrasonic waveforms. Therefore, crack size determination through a neural network based on the back-propagation algorithm using back-scattered ultrasonic signals is established in this study. For this purpose, aluminum plate containing vertical or inclined surface breaking crack with different crack length was used to receive the back-scattered ultrasonic signals by pulse echo method. Some features extracted from these signals and sizes of cracks were used to train neural network and the neural network's output of the crack size are compared with the true answer.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.433-439
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• 2001

An experimental study was carried out on the characteristics of the mixed-convection heat transfer from a protruding heat source module which had uniform heat flux and was located on a flat plate in the inclined channel. The effects of the inclined channel(${\varphi}=0{\sim}90^{\circ}$) was studied for the input power($Q=3,\;7W$) and inlet air velocities($V_{i}=0.1{\sim}0.9m/s$). Experimental results indicate that the input power was most effective parameter on the temperature differences between inlet air and module. The effects of the inclined angle was negligible when the inlet velocities were above 0.5m/s and 0.9m/s at Q = 3W, 7W respectively. As the inclined angle of the channel increases, the temperatures of the module are decreased. So we obtained the best condition on the adiabatic board at the vertical channel.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.8
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• pp.2101-2112
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• 1994

A two-dimensional biomechanical model was developed in order to calculated the lower extremity kinematics and kinetics during level walking. This model consists of three segments : the thigh, calf, and foot. Each segment was assumed to be a rigid body ; its motion to be planar in the sagittal plane. Five young males were involved in the gait experiment and their anthropometric data were measured for the calculation of segmental masses and moments of inertial. Six markers were used to obtain the kinematic data of the right lower extremity for at least three trials of walking at 1.0m/s, and simultaneously a Kistler force plate was used to obtain the foot-floor reaction data. Based on the experimental data acquired for the stance phase of the right foot, calculated vertical joint forces reached up to 0.91, 1.05, and 1.11 BW(body weight) at the hip, the knee, the ankle joints, respectively. The flexion-extension moments reached up to 69.7, 52.3, and 98.8 Nm in magnitude at the corresponding three joints. It was found that the calculated joint loadings of a subject were statistically the same for all his three trials, but not the same for all five subjects involved in the gait study.

• Korean Journal of Applied Biomechanics
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• v.15 no.1
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• pp.259-274
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• 2005

The purpose of this study was to compare the kinematic and kinetic parameters of lower extremity joints between novice and experienced sports aerobic dancers during two heights of depth jumps. Four male dancers were participated in this study and they performed 40cm and 60cm height depth jump three times, respectively. Four ProReflex MCU cameras (100frame/sec) and a Kistler force plate (1000Hz) were used for data collection. The results indicated that the duration of contact phase of experienced group was shorter than that of novice group regardless of jump height. For minimum angle of hip, knee, and ankle joints, the novice group had tendency to decrease the angle but the experienced group had increased the joint angle with jump height. There was no difference of total ground reaction force between the groups but the reaction force had tendency to increase with jump height. Thus, this study implied that repetition of jump and landing may induce joint related injury and further study such as. EMG analysis of lower extremity can be needed to verify the relationship between injury and ground reaction force.

• The KSFM Journal of Fluid Machinery
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• v.9 no.2 s.35
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• pp.7-12
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• 2006

This study is to develop a system of electric power generation utilizing the wind resources available in the domestic wind environment. We tested drag-type vortical wind turbine models, which have two different types of blades: a flat plate and circular arc shape. Through a performance test, conditions of maximum rotational speed were found by measuring the rpm of wind turbine. The rotational speed was measured by a tachometer in a wind tunnel and the tunnel wind speed was by using a pilot-static tube and a micro manometer. The performance test for a prototype was accomplished by calculating power, power coefficient, torque coefficient from the measurement of torque and rpm by a dynamometer controller From the measurements for miniature turbine models with two different blades, the circular arc shape was found to Produce a maximum rotational speed for the same wind velocity condition. Based on this result, the prototype with the circular arc blade was made and tested. We found that it produces 500W at the wind velocity of 10.8 m/s and the power coefficient was 20%.