• Journal of Institute of Control, Robotics and Systems
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• v.17 no.10
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• pp.1021-1028
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• 2011

The objective of this paper is to optimize the design parameters of a novel mechanism for a robotic knee orthosis. The feature of the proposed knee othosis is to drive a knee joint with independent actuation during swing and stance phases, which can allow an actuator with fast rotation to control swing motions and an actuator with high torque to control stance motions, respectively. The quadriceps device operates in five-bar links with 2-DOF motions during swing phase and is changed to six-bar links during stance phase by the contact motion to the patella device. The hamstring device operates in a slider-crank mechanism for entire gait cycle. The suggested kinematic model will allow a robotic knee orthosis to use compact and light actuators with full support during walking. However, the proposed orthosis must use additional linkages than a simple four-bar mechanism. To maximize the benefit of reducing the actuators power by using the developed kinematic design, it is necessary to minimize total weight of the device, while keeping necessary actuator performances of torques and angular velocities for support. In this paper, we use a SGA (Simple Genetic Algorithm) to minimize sum of total link lengths and motor power by reducing the weight of the novel knee orthosis. To find feasible parameters, kinematic constraints of the hamstring and quadriceps mechanisms have been applied to the algorithm. The proposed optimization scheme could reduce sum of total link lengths to half of the initial value. The proposed optimization scheme can be applied to reduce total weight of general multi-linkages while keeping necessary actuator specifications.

• Journal of the Korea Concrete Institute
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• v.23 no.6
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• pp.809-815
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• 2011

An experimental investigations on the bond-slip properties of the steel and Glass Fiber Reinforced Polymer(GFRP) bars in engineered cementitious composite (ECC) with Polyvinyl Alcohol (PVA) fibers are presented. Total of 8 beam specimens prepared according to the Rilem procedures with 2% of PVA and PE fiber volume percentage and steel and GFRP reinforcements significantly changed the failure mechanism and slightly improved bond strength. The main objective of the tests was to evaluate the load versus displacement and load versus slip behaviors and the bond strength for the following parameters: concrete type (normal and fiber concrete) and bar diameter (10 and 13 mm). The study results showed that ordinary concrete and ECC specimens showed similar behavior for steel reinforced specimen. However, GFRP reinforced specimen showed different behavior that the steel specimen. The code analytical results showed more accuracy compared to the experimental results as expected in conservative code provisions. Based on the obtained results, it is safe to conclude that the new parameters need to be adopted to ensure safe usage of ECC for construction applications.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.12 s.354
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• pp.83-88
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• 2006

In this paper, we propose a new cross bar embedded structure for improvement of attenuation characteristics along the different lossy media. A general characterization procedure based on the extraction of the characteristic impedance and propagation constant for analyzing a single MIS(Metal-Insulator-Semiconductor) transmission line used and an analysis for a new substrate shielding MIS structure consisting of grounded crossbars at the interface between Si and Sio2 layer using the Finite-Difference Time-Domain(FDTD) technique is used. In order to reduce the substrate effects on the transmission line characteristics, a shielding structure consisting of grounded cross bar lines over time-domain signal has been examined. The extracted, distributed frequency-dependent transmission line parameters as well as the line voltages and currents, and also corresponding equivalent circuit parameters have been examined as function of frequency. It is shown that the quality factor of the transmission line can be improved without significant changes in the characteristic impedance and effective dielectric constant.

• Journal of Mechanical Science and Technology
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• v.17 no.12
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• pp.1994-2003
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• 2003

The vibration of a flexible cantilever tube with nonlinear constraints when it is subjected to flow internally with fluids is examined by experimental and theoretical analysis. These kinds of studies have been performed to find the existence of chaotic motion. In this paper, the important parameters of the system leading to such a chaotic motion such as Young's modulus and the coefficient of viscoelastic damping are discussed. The parameters are investigated by means of system identification so that comparisons are made between numerical analysis using the design parameters and the experimental results. The chaotic region led by several period-doubling bifurcations beyond the Hopf bifurcation is also re-established with phase portraits, bifurcation diagram and Lyapunov exponent so that one can define optimal parameters for system design.

• International Journal of Concrete Structures and Materials
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• v.5 no.1
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• pp.29-33
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• 2011

This article employs Least Square Support Vector Machine (LSSVM) for determination of fracture parameters of concrete: critical stress intensity factor ($K_{Ic}^s$) and the critical crack tip opening displacement ($CTOD_c$). LSSVM that is firmly based on the theory of statistical learning theory uses regression technique. The results are compared with a widely used Artificial Neural Network (ANN) Models of LSSVM have been developed for prediction of $K_{Ic}^s$ and $CTOD_c$, and then a sensitivity analysis has been performed to investigate the importance of the input parameters. Equations have been also developed for determination of $K_{Ic}^s$ and $CTOD_c$. The developed LSSVM also gives error bar. The results show that the developed model of LSSVM is very predictable in order to determine fracture parameters of concrete.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.495-500
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• 2003

The vibration of a flexible cantilever tube with nonlinear constraints when it is subjected to flow internally with fluids is examined by experiment and theoretical analysis. These kind of studies have often been performed that finds the existence of chaotic motion. In this paper, the important parameters of the system leading to such a chaotic motion such as Young's modulus and coefficient of viscoelasticity in tube material are discussed. The parameters are investigated by means of a system identification so that comparisons are made between numerical analysis using the parameters of a handbook and the experimental results. The chaotic region led by several period-doubling bifurcations beyond the Hopf bifurcation is also re-established with phase portraits and bifurcation diagram so that one can define optimal parameters for system design.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.7
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• pp.745-752
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• 2012

Diesel engines are most suitable for biodiesel fuel because diesel fuel has a higher cetane number compared to gasoline and diesel engines have no spark ignition system; hence, engine conversion is easy and cost effective. For these reasons, in this study, the spray behavior characteristics of vegetable palm oil were analyzed by using a common-rail injection system of a commercial diesel engine, and the results were compared with those obtained for the diesel fuel. The injection pressures and blend ratios of palm oil and diesel fuel (BD3, BD5, BD20, BD30, BD50, and BD100) were the main parameters. The experiments were conducted for different injection pressures-500 bar, 1000 bar, 1500 bar, and 1600 bar-by setting the injection duration at $500{\mu}s$. We determined there is no significant difference in the macro characteristics of the spray behavior (spray penetration and spray angle) in response to any change in the blend ratio of palm oil and diesel fuel at a fixed injection pressure. In particular, all experiments showed a spray angle of approximately $15^{\circ}$.

• Journal of the Korean Geophysical Society
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• v.2 no.2
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• pp.135-142
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• 1999

Interpretations of 3-component magnetic logging data obtained for a reinforced bar as a model of the line of the magnetic dipoles are conducted using a least squared inversion technique. The length of the bar is 1.12 m, sampling interval is 0.05 m, the distance between the bar and the borehole is 0.3 m, and the top of the bar is fixed at 0 m of depth. The bar is set to be approximately vertical. Magnetic anomalies smoothed with FFT are used as input data for the inversion. For the interpretation of magnetic logging data the depth to the top, the length, the magnetic moment per unit length, the direction of the magnetization (declination and inclination), and the bearing and plunge of the line of magnetic dipoles are left as unknown parameters. The comparison of the results obtained from the individual inversion of the horizontal component or the vertical component of the magnetic anomalies, and those from the simultaneous inversion of horizontal and vertical component of the magnetic anomalies shows that there exist some disagreements between each inversion result. The depth to the bottom of the bar, which is actually 1.12 m, is estimated as 1.18 m, and the inclination of the magnetization is estimated as -76°by simultaneous inversion. The negative value of the inclination indicates that the strength of the remnant magnetization is much greater than that of the induced magnetization, so that the direction of the resultant magnetization points to the top of the bar.

• Journal of the Korea Concrete Institute
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• v.23 no.3
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• pp.273-280
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• 2011

Ten high-strength concrete beam specimens, which have various combinations of different types of flexural reinforcement and short fibers were constructed and tested. Six beams were reinforced with two layers of steel, CFRP, and GFRP bar combinations. The other four beams were reinforced with two layers of single type CFRP and GFRP bars, with steel and synthetic short fibers. An investigation was performed on the influence of the parameters on the load-carrying capacity, post cracking stiffness, cracking pattern, deflection behavior, and ductility. The low post cracking stiffness, large deflection, deep crack propagation, large crack width, and low ductility of FRP bar-reinforced beams were controlled and improved by positioning steel bars in the inner layer of the FRP bar layer. In addition, the addition of fibers increased the first-cracking load, ultimate flexural strength, and ductility as well as the deep propagating cracks were controlled in the FRP bar-reinforced concrete beams. The increased ultimate concrete strain of fiber-reinforced concrete should be determined and considered when FRP bar-reinforced concrete members with fibers are designed.

• Steel and Composite Structures
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• v.21 no.1
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• pp.73-91
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• 2016

The use of box columns has been increased due to the rigidity in rigid orthogonal moment resisting frames. On the other hand, the installation and welding of necessary horizontal continuity plates inside the columns are both labor-consuming and costly tasks. Accordingly, in this paper, a new beam-to-box column connection by trapezoidal external stiffeners and horizontal bar mats is presented to provide seismic parameters. The proposed connection consists of eight external stiffeners in the level of beam flanges and five horizontal bar mats in Concrete Filled Tube (CFT) columns. The new connection effectively alleviates the stress concentration and moves the plastic hinge away from the column face by horizontal external stiffeners. In addition, the result shows that proposed connection has provided the required strength and rigidity of connection, so that the increased strength, 8.08% and rigidity, 3.01% are compared to connection with internal continuity plates, also the results indicate that this connection can offer appropriate ductility and energy dissipation capacity for its potential application in moment resisting frames in seismic region. As a result, the proposed connection can be a good alternative for connection with continuity plates.