• Fibers and Polymers
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• v.3 no.1
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• pp.8-13
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• 2002

The effect of block sequence on the self-assembly of ABC-type triblock copolymers in the ordered state is investigated using an isothermal-isobaric molecular dynamics simulation. The block sequence has an important effect ,on the ]norphology of ABC triblock copolymers. Different morphologies are observed depending on the block sequence as well as the block composition. The triblock copolymers with the volume fraction of 1 : 1 : 1 ($f_A$=$f_B$=$f_C$= 0.33) show the three phase and four layered lamellar structures irrespective of the block sequence. The $A_{32}$$B_{16}$$C_{32}$triblock copolymer with $f_B$=0.2 shows a morphology In which cylinders of midblock B are formed at the interface between A and C lamellae, whereas the morphology of triblock copolymer $B_{16}$$C_{32}$ $A_{32}$ and $C_{32}$ $A_{32}$ $B_{16}$ show a cylindrical core-shell structure and a lamellar type morphology, respectively. The $A_{20}$$B_{40}$$C_{20}$the triblock copolymer with the block B as a major component shows a tricontinuous structure, whereas both $B_{40}$$C_{20}$$A_{20}$ and $C_{20}$$A_{20}$$B_{40}$ triblock coolymers exhibit the lamellar structures. When the block B has larger volrome fraction with $f_B$=0.75, the matrix is composed of block B, and other two blocks A and C form spherical domains.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.10
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• pp.1042-1049
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• 2009

Design and optimization of a broadband waveguide magic-T was performed for X-Band tracking radars. A multi-stepped conducting cylinder was used to enhance the bandwidth performance of the conventional waveguide magic-Ts. Particles swarm optimization in conjunction with genetic algorithm was employed to obtain the optimized geometrical parameters. The optimized design exhibits low reflection coefficient below -20 dB at all waveguide ports with frequency bandwidth of 12%. The transmission loss and difference are within 0.2 dB and 0.1 dB, respectively. Measured results are also shown to be in good agreement with the simulated results. Finally, the bandwidth performances for five and seven-stepped conducting cylinders are also investigated.

• The Journal of the Korea institute of electronic communication sciences
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• v.12 no.5
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• pp.837-844
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• 2017

The weir to regulate water level in a tide generation tank is above and below carried by two electric cylinders which are mounted on right and left of weir itself. In this case, a movement difference between right and left cylinder causes unbalance of weir and friction between weir and guide. And then, the weir will not be sent to target point. In this study, a synchronous control system is developed to take accurate and quick equilibrium of the weir. The control system based on cross coupled structure consists of two I-PD controllers and a lead compensator. Each of the I-PD controllers is designed in order that the electric cylinder may exactly follow the reference signal without overshoot and input saturation. And the lead compensator is designed to achieve stable and accurate synchronization. Finally, the simulation result shows that the designed synchronous control system is effective for elimination of synchronous error.

• Transactions of the Korean hydrogen and new energy society
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• v.24 no.3
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• pp.206-215
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• 2013

A linear engine has advantages in terms of volume and weight, because there are no rotating parts. Thus, it is considered that linear engines might be suitable in hybrid vehicles. However, the linear engine has challenges in terms of the engine ignition timing and efficiency, so the engine has not been commercialized yet. In this study, the dynamic and combustion characteristics of the linear engine might be specified by various loads which are changed by conductance. The engine used in this experiment consists of two combustion chambers, four compressors, two linear alternators and a mover with a piston head and magnets. The way fuel is supplied in the experiment is by propane fuel being mixed with air in the carburetor, then being delivered into combustion cylinders via compressors. In the experiment, conductance is altered from 0.04 to 0.16mho, and the ignition timing is ahead by just 5.0mm from the maximum stroke. As a result of the experiment, frequency, stroke, input calories and maximum pressure are decreased when the conductance is increased. Meanwhile, IMEP, generation efficiency and electric power are increased when the conductance is increased. Therefore, it might confirm that high conductance generates more efficient electric power, but that thermal efficiency is the highest in the state of 0.08mho.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.1
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• pp.87-94
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• 2014

This study analyzes the characteristics of bond behavior of concrete, which is confined by external jackets such as shape memory alloy (SMA) and steel, according to confinement and stiffness ratios of the external jackets. For this purpose, SMA wires with 1.0 mm diameter and steel plates with 1.0 and 1.5 thickness are used to induce difference on confinement and stiffness ratios and, then, bond strength and behavior are analyzed considering the two factors. When external jakcets are used for the concrete cylinders, bond strengths of specimens increase and their bond failures are transferred from splitting failure to pull-out failure and, thus, the external jackets show confining effect. Bond strenght of concrete increase with increasing confinement and stiffness ratios of the external jackets. However, maximal circumferential strains decrease linearly with increasing the two values.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.3
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• pp.171-181
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• 2017

Two-phase cross flow exists in many shell-and-tube heat exchangers such as condensers, evaporators, and nuclear steam generators. The drag force acting on a tube bundle subjected to air/water flow is evaluated experimentally. The cylinders subjected to two-phase flow are arranged in a normal square array. The ratio of pitch to diameter is 1.35, and the diameter of the cylinder is 18 mm. The drag force along the flow direction on the tube bundles is measured to calculate the drag coefficient and the two-phase damping ratio. The two-phase damping ratios, given by the analytical model for a homogeneous two-phase flow, are compared with experimental results. The correlation factor between the frictional pressure drop and the hydraulic drag coefficient is determined from the experimental results. The factor is used to calculate the drag force analytically. It is found that with an increase in the mass flux, the drag force, and the drag coefficients are close to the results given by the homogeneous model. The result shows that the damping ratio can be calculated using the homogeneous model for bubbly flow of sufficiently large mass flux.

• Journal of Energy Engineering
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• v.8 no.2
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• pp.272-278
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• 1999

In the present study, measurements of thermal contact resistance (TCR) were conducted for joints of brass and aluminium cylinders of 30 mm in diameter, 45 mm in length, when their interfaces were; ⅰ) under vacuum, ⅱ) charged with a pure silicone grease and ⅲ) charged with a mixture of silicone grease and powder of aluminium (#325). Also the data were compared with analytical calculations using Fouche's model. The data of TCR for joints under vacuum state varied in the range of (2∼100)${\times}$10$\^$-5/(㎡$^{\circ}C$/W) depending on their surface roughness. When the contact surfaces were carefully ground, a reduction of 30∼50% in TCR was obtained. But the surface treatment with silicone grease gave rise to a reduction of about 5∼10 times more than that of vacuum state. The analytical prediction by Fouche's model showed a good agreement within 10~30%, for the case of contact surface charged with silicone grease.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.33 no.1
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• pp.46-58
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• 1997

The energy saving is one of the most important factors for profit in marine transportation. In order to reduce the fuel oil consumtion the ship's propulsion efficiency must be increased as possible. The propulsion efficiency depends upon a combination of an engine and a propeller. The propeller has better efficiency as lower rotational speed. This situation led the engine manufacturers to design the engine that has low speed, long stroke and a small number of cylinders. Consequently, the variation of rotational torque became larger than before because of the longer delay-time in fuel oil injection process and an increased output per cylinder. As this new trends the conventional mechanical-hydrualic governors for engine speed control have been replaced by digital speed controllers which adopted the PID control or the optimal control algorithm. But these control algorithms have not enough robustness to suppress the variation of the delay-time and the parameter perturbation. In this paper we consider the delay-time and the perturbation of engine parameters as the modeling uncetainties. Next we design the robust servo controller which has zero offset in steady state engine speed, based on H sub($\infty$) control theory. The validity of the controller was investigated through the response simulation. We used a personal computer and an analog computer as the digital controller and the engine (plant) part respectively. And, we could certify that the designed controller maintains its robust servo performance even though the engine parameters may vary.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.1
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• pp.48-55
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• 2011

Hydraulic excavator is one of the most widely used heavy machines in construction sites including dismantling. In the dismantling sites, the excavators equipped with crusher or breaker carry out dangerous operations, so drivers are always exposed to unexpected danger. For safety operation, remote control of the hydraulic excavator has been studied using proportional control valve, which requires an appropriate motion control of its bucket tip. In this case, kinematics and dynamics analysis have to be preceded through modeling of excavator. However, it is difficult to acquire reasonable results from the analysis due to insufficient information of physical parameters such as mass of each links and locations of mass centers, etc. This study deals with the trajectory control of bucket tip, which is based on experimental estimation of cylinder output force. The estimated forces are fed into the control of each cylinder in order to compensate gravitational and frictional effects in the cylinders. The control was applied to horizontal trajectories that are for flattening work.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.776-785
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• 2006

Ship builder's requirement for a higher power output rating has lead to the development of super large two stroke low speed diesel engines. Usually a large-sized bore ranging from 8-14 cylinders, this engine group is capable of delivering power output of more than 100,000 bhp at maximum continuous rating. Other positive aspects of this engine type include higher thermal efficiency, reliability, durability and mobility. This all playa vital role in meeting the propulsion requirement of vessels, specifically for large container ships, of which speed is a primary concern to become more competitive. Consequently, this also resulted in the modification of engine parameters and new component designs to meet the consequential higher mean effective pressure and higher maximum combustion pressure. Even though the fundamental excitation mechanism unchanged, torsional vibration stresses in the propulsion shafting are subsequently perceived to be higher. As such, one important viewpoint in the initial engine design is the resulting vibration characteristic expected to prevail on the propulsion shafting system(PSS). This paper investigated the torsional vibration characteristics of these super large engines. For the two node torsional vibration with a nodal point on the crankshaft, a tuning damper is necessary to reduce the torsional stresses on the crankshaft. Hence, the tuning torsional vibration damper design and compatibility to the shafting system was similarly reviewed and analyzed.