• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.968-976
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• 2004

In the paper, deformation characteristics of fiber-mixed-soils, mixed polypropylene staple fibers of 0.3% fiber content with sands of various gradation, and their effectiveness of reinforcement were evaluated. A series of Resonant Column tests were performed with specimens prepared with varying Uniformity Coefficient and constant Curvature Coefficient. Maximum shear moduli 01 fiber-mixed-soils were increased by up to 30% and modulus reduction was also restrained in nonlinear range. Normalized shear modulus reduction curves of fiber-mixed-soils shift close to the upper limit of Seed curd Idriss's curves and are located within narrower band than those of unmixed soils, which proves the effectiveness on stiffness increment by reinforcing soils with fibers.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.177-180
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• 2008

The objective of this study is to get simulation data about pulsatile flow of a non-Newtonian fluid through a bifurcated tube. All the process was based on CFD method, with a commercial FVM code, SC/Tetra ver. 6.0 for solving, and with CATIA R16 for generating geometries. To define a non-Newtonian fluid, the following viscous models are used; the Powell-Eyring model, the modified Powell-Eyring model, the Cross model, the modified Cross model, the Carreau model, the Carreau-Yasuda model and the modified Power Law model. The flow calculation data using each model were compared with the other data of a existing paper. Finally, the Carreau model was recognized to give the best result with the SC/Tetra code, and the succeeding simulations are made with the model. For the pulsating flow condition, the sine wave type velocity profile is given as the inlet boundary condition. To investigate the effect of geometries and mesh, the pre-test is carried out with various curvature conditions of the bifurcated corner, and then with various mesh conditions. The final process is to calculate flow variables such as the wall shear stress (WSS) and the wall shear stress gradient (WSSG). To validate all the result, the simulation is compared with the existing data of the other papers. Generally speaking, there is a noticeable difference in the maximum and minimum value of WSS. It is not sure that the values in each data are on the exactly same location. However, the overall trend is similar. The next study needs to investigate the same situation by experimental method. Furthermore, if the flow is simulated with more pulsatile conditions, more data of flow field through a bifurcated tube could be achieved.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.12
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• pp.2636-2646
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• 2002

This research presents an analytical model to investigate vibration due to ball bearing waviness in a rotating system supported by two or more ball bearings, taking account of the centrifugal force and gyroscopic moment of the ball. The waviness of rolling elements is modeled by the sinusoidal function, and it is incorporated into the position vectors of the race curvature center. The Hertzian con tact theory is applied to calculate the elastic deflection and nonlinear contact force while the rotor has translational and angular motions. Both the centrifugal force and gyroscopic moment of the ball and the waviness of the rolling elements are included in the kinematic constraints and force equilibrium equations of a ball to derive the nonlinear governing equations of the rotor, which are solved by using the Runge-Kutta-Fehlberg algorithm to determine the new position of the rotor. The proposed model is validated by the comparison of the results of the prior researchers. This research shows that the centrifugal force and gyroscopic moment of the ball plays the important role in determining the bearing frequencies, i.e. the principal frequencies, their harmonics and the sideband frequencies resulting from the waviness of the rolling elements of ball bearing. It also shows that the bearing vibration frequencies are generated by the waviness interaction not only between the rolling elements of one ball bearing but also between those of two or more ball bearings constrained by the rotor.

• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.177-180
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• 2008

The objective of this study is to get simulation data about pulsatile flow of a non-Newtonian fluid through a bifurcated tube. All the process was based on CFD method, with a commercial FVM code, SC/Tetra ver. 6.0 for solving, and with CATIA R16 for generating geometries. To define a non-Newtonian fluid, the following viscous models are used; the Powell-Eyring model, the modified Powell-Eyring model, the Cross model, the modified Cross model, the Carreau model, the Carreau-Yasuda model and the modified Power Law model. The flow calculation data using each model were compared with the other data of a existing paper. Finally, the Carreau model was recognized to give the best result with the SC/Tetra code, and the succeeding simulations are made with the model. For the pulsating flow condition, the sine wave type velocity profile is given as the inlet boundary condition. To investigate the effect of geometries and mesh, the pre-test is carried out with various curvature conditions of the bifurcated corner, and then with various mesh conditions. The final process is to calculate flow variables such as the wall shear stress (WSS) and the wall shear stress gradient (WSSG). To validate all the result, the simulation is compared with the existing data of the other papers. Generally speaking, there is a noticeable difference in the maximum and minimum value of WSS. It is not sure that the values in each data are on the exactly same location. However, the overall trend is similar. The next study needs to investigate the same situation by experimental method. Furthermore, if the flow is simulated with more pulsatile conditions, more data of flow field through a bifurcated tube could be achieved.

• Journal of the Korean Society of Radiology
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• v.14 no.3
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• pp.235-243
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• 2020

Lumbar Lordosis Angle (LLA) is an index that can be used to evaluate the curvature of the lumbar vertebrae. It can measure the structural stability of the lumbar spine and the stability of each segment of the vertebral column at the intervertebral disc angle (IDA). Especially, our data shows it is found to be a strong positive correlation between obesity and the angle of lordosis for lumbar vertebrae. Also, the reason for the large IDA in the case of obesity seems to be the result of the weakening of anatomical structure as well as the gravity effect. And, the obesity interferes with normal sagittal balance and fails to maintain a straight posture with minimal energy. Therefore, the obesity can be an important factor in causing back pain by changing the lumbar lordosis.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.1
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• pp.9-19
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• 2017

In this study, stator shroud injection in a single-stage transonic axial compressor is proposed. A parametric study of the effect of stator shroud injection on aerodynamic performances was conducted using the three-dimensional Reynolds-averaged Navier-Stokes equations. The curvature, length, width, and circumferential angle of the stator shroud injector and the air injection mass flow rate were selected as the test parameters. The results of the parametric study show that the aerodynamic performances of the single-stage transonic axial compressor were improved by stator shroud injection. The aerodynamic performances were the most sensitive to the injection mass flow rate. Further, the total pressure ratio and adiabatic efficiency were the maximum when the ratio of circumferential angle was 10％.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.1
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• pp.1-7
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• 2016

Most of the work has been done till now focused on flows over wall mounted cavities in a straight wall where the incoming flow is uniform. However, the investigation on such kind of flow over a cavity mounted on the curved walls has been seldom reported in the existing literatures. In the present study, the numerical analysis was performed to investigate the cavity flow mounted on the curved walls. The effects of wall shape, the curvature radius and the flow Mach number, were investigated for high-subsonic flows. The results show that the static pressure of cavity floor increases as the L/R increases. This effect is found to be more significant when the flow Mach number is higher. The cavity drag for the curved walls are higher as compared with that of straight wall.

• Bulletin of the Korean Chemical Society
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• v.31 no.9
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• pp.2483-2487
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• 2010

Pseudo-first-order rate constants ($k_{obsd}$) were measured spectrophotometrically for nucleophilic substitution reactions of 4-nitrophenyl picolinate (6) with alkali metal ethoxides (EtOM, $M^+\;=\;K^+$, $Na^+$ and $Li^+$) in anhydrous ethanol at $25.0{\pm}0.1^{\circ}C$. The plot of $k_{obsd}$ vs. [EtOM] exhibits upward curvature regardless of the nature of $M^+$ ions. However, the plot for the reaction of 6 with EtOK is linear with significantly decreased $k_{obsd}$ values when 18-crown-6-ether (18C6, a complexing agent for $K^+$ ion) is added in the reaction medium. Dissection of $k_{obsd}$ into $k_{EtO^-}$ and $k_{EtOM}$ (i.e., the second-order rate constant for the reaction with dissociated $EtO^-$ and ion-paired EtOM, respectively) has revealed that ion-paired EtOM is 3~17 times more reactive than dissociated $EtO^-$. The reaction has been proposed to proceed through a 5-membered cyclic transition state, in which $M^+$ ion increases the electrophilicity of the reaction site. Interestingly, $Na^+$ ion exhibits the largest catalytic effect. The presence of a nitrogen atom in the pyridine moiety of 6 has been suggested to be responsible for the high $Na^+$ ion selectivity.

• Journal of the Korean Society of Clothing and Textiles
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• v.18 no.3
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• pp.387-394
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• 1994

Journal of the Korean Society of Clothing and Textiles Vol. 18, No. 3 (1994) p. 387∼394 In this study, the restriction of slacks (blue jean) versus box pleats skirt was investigated, from the view point of peripheral blood flow at the toe according to motion variation and E.M.G. analysis of leg muscles after walking on the flat or going up and down stairways. Besides, the pressure of slacks on the lower extrimity was measured statically and dynamically. The main results were summerized as follows; 1. The clothing pressure applied by slacks was; each one of thigh and lower leg was 18.2 g/ cm2 and 22.1 g/cm2 in upright, 63.4 g/cm2 and 26.6 g/cm2 in sitting on the chair, on both sides of thigh and lower leg 272.0 g/cm2 over in squatting. 2. When the motion starts from upright, the dynamic clothing pressure reach their peak before the motions end. When the motion ends and the body comes to a still condition, the clothing pressure grow lower and indicate a constant value. but when the body starts moving again to return to upright, the pressures once grow higher and go to zero value after reaching the peak. The pressure on the knee show much greater than those on the hip. This can be because these pressures depend on the degree of skin stretching motion and of its curvature. 3. The surface E.M.G. in leg muscles M. rectus femoris and M. gastrocnemius were recoreded. In the case of wearing slacks, two muscles were activated much more than wearing skirt. 4. The peripheral blood flow at the toe by wearing slacks was lower than wearing skirt. Also the case when squatting, the peripheral blood flow at the toe was low.

• Journal of the Korean Society for Precision Engineering
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• v.30 no.4
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• pp.368-374
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• 2013

Maintenance works for current high-rise buildings significantly depend on human labor, unlike other construction processes that are gradually being automated. Herein, this paper proposes robotic building maintenance system using motion control, in specific, reducing a system jerk which is directly subjected to improve the process performance and economic feasibility. The sensor for detecting straight and curvature section of the building facade, moreover rail-joint segment can be detected and be utilized for reducing jerk of the system. Analysis of the proposed system error caused by excessive vibration, e.g. jerk motion is introduced. To enhance the stability and safety of the system, herein, the strategy is proposed for enhancing the performance of the system based on anti-jerk motion control algorithm which comes out increasing the stability and sustainability of the integrated system, as well.