• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.1C
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• pp.72-80
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• 2003

This paper proposed the method of finding optimal weight vectors for enhancing the performance of an adaptive array antenna system by adopting a novel beam-forming algorithm in CDMA (code division multiple access) channel. This algorithm is a liberalized power method, based on power method, with the total computational load, O(4N). Where, N denotes the number of antenna elements. The performance of the proposed algorithm is shown in terms of SER (symbol error rates), allowable capacity, and the convergence characteristic in IS2000 1X CDMA channel. As a result of simulations, the adaptive way antenna system allows 6-10 times more users than the conventional one in a cell of a base station. Furthermore, the proposed algorithm shows superior performance to the conventional one regarding symbol error rates, converging characteristics, and computational load.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.457-462
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• 2002

Generally speaking, durability, load carrying capacity and the life of structure becomes to be shortened in all structures as time passed. Also, we have to repair and reinforce because of tile decrease of the traffic volume and overloaded vehicles in the bridge. External prestressing method is most popular and effective strengthening method which can be used for the prestressed concrete-girders. When strengthening with external prestressing method, there are many ways to install anchorage system. But, These methods have many faults. For example, the achorage force is so small or an anchorage system installation damages an existing structure. So, this paper suggested a new anchorage system to strengthen without any damage to the structure and then confirm the increase of durability and the properties of behavior with experimentation.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.03a
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• pp.211-219
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• 2002

This study is performed to investigate the behavior of multi-column piers and to evaluate the seismic performance. In this study, 3 types of scale model piers with 2-column are designed and tested by quasi-static load in both longitudinal and transverse directions. Each type of model consisting of 2 specimens has different reinforcement details in the lap splice of longitudinal bars and amount of transverse reinforcements. This paper reports that the ductility of the model in transverse direction is rather higher than in longitudinal direction because of formation of several plastic hinges and that the ultimate displacement and the energy absorbtion capacity are enhanced by using continuous longitudinal bars instead of lap-splice ones. And it is confirmed that relatively large amount of ductility can be achieved by providing sufficient lap-splice length and transverse reinforcements with end hook even if longitudinal bars are lap spliced in the base of pier.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.04b
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• pp.427-432
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• 1998

The objective of this research is to observe the actual response of low-rise nonseismic moment-resisting reinforced frame subjected to varied levels of earthquake ground motions. First of all, the reduction scale for the model was determined as 1 : 5 considering the capacity of the shaking table to be used. This model was, then, subjected to the shaking table motions simulating Taft N21E component earthquake ground motions, whose peak ground accelerations(PGA's) were modified to 0.12g, 0.2g, 0.3g, and 0.4g. The global behavior and failure mode were observed. The lateral accelerations and displacements at each story and local deformations at the critical portions of structure were measured. The base shear was measured by using specially made load cells. Before and after each earthquake simulation test, free vibration tests were performed to find the changes in the natural period and damping ratio of the model.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.8
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• pp.2039-2052
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• 1994

In this study, an expert system for multi-stage cold forging process design of axisymmetric parts is developed. The available geometries are axisymmetric shape and cylinder with a hold in one end. The overall system is composed of knowledge-based system for process sequence design, output module interfaced with CAD system and material data-base. In the developed system, designed process can be modified in order to reduce the number of processes and make the distribution of forming load be almost equal at various deforming stages within the machine capacity. After process sequence design is completed, results can be stored as a text file or a commercial CAD system file. The capabilities of the developed system are illustrated through various examples of process design.

• Tribology and Lubricants
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• v.26 no.5
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• pp.283-290
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• 2010

In this study, the stiffness and damping coefficients of herringbone grooved air journal bearings are studied. A generalized coordinate transformation method to handle the complex geometry of incompressible fluid bearing is modified for compressible fluid. The modified equations are discretized by the base of finite difference method. A new computer program using Visual C++ language is developed. The load carrying capacity and stiffness and damping coefficients are calculated according to the design parameters like groove depth or the number of grooves and compared to that of plain air journal bearings.

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.2
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• pp.238-245
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• 2003

To overcome the weakness in the load capacity of conventional robot manipulators actuated by motors with the speed reducer such as the harmonic driver, we proposed a new closed-chain type of the robot actuator which is composed of the four-bar-link mechanism driven by the ball screw. The robot manipulator is revolute-jointed and composed of four axes. The base axis is actuated by the lineal actuator such as the ball screw, and the others are actuated by the proposed actuator. We analyzed the mechanism of the actuators of the robot joints, and developed the dynamics model. The dynamics are expressed in the joint coordinates and then they are mapped into the sliding coordinates of the ball screw. We performed fundamental tests on the structure of the robot.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.8 s.197
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• pp.89-96
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• 2007

In this paper, a new air bearing stage with magnetic preload and a linear motor has been developed for the small precision machine systems. The new air bearing stage is unique in the sense that permanent magnets attached bottom of the iron core of table are used not only for preloading air bearings in vertical direction but also for generating thrust force by current of the coil at base. The characteristics of air bearings using porous pads were analyzed with numerical method, and the magnetic circuit model was derived for linear motor for calculating required preload force and thrust force. A prototype of single axis miniature stage with size of $120(W){\times}120(L){\times}50(H)\;mm^3$ was designed and fabricated and examined its performances, vertical stiffness, load capacity, thrust force and positioning resolution.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.540-543
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• 2002

Conventional robot manipulators actuated by motors with the speed reducer such as the harmonic drive have weakness in the load capacity, since the speed reducer does not have enough strength. To overcome this, we proposed and constructed a new type of the robot actuator which is four-bar-link mechanism driven by the ball screw. We developed a new type of a revolute-jointed robot manipulator composed of four axes. The base axis is actuated with conventional speed reducer, but the others are actuated by the proposed actuators. We analyzed the mechanism of the actuators of the robot joints, and developed the dynamics model. The dynamics are expressed in the joint coordinates, and then they are mapped into the sliding coordinates of the ball screw. The structure specifications of the manipulator shown.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.11A
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• pp.822-830
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• 2009

The spectrum efficiency of mobile communication networks can be improved dramatically adopting multiple antennas technologies. In order to guarantee the licensed rights of primary user (PU), the cognitive radio system should perform in a relatively low interference manner when it gets access to the spectrum of licensed networks. In this paper, we explore a uniformly distributed circular antenna array to implement beamforming algorithm that is accomplished by optimization method at the base station of cognitive radio networks, and therefore we can suppress the interference to PU by steering quite low transmission power toward PU and constructing a narrow beam toward cognitive user (CU). By reducing the constraint number of the optimization problem, we also propose a null steering algorithm that steers rather low radiation power toward PU, while the other areas in the same cell are covered by radiation power except the local area around PU. It is pursued to reduce the computation load and enlarge the capacity of cognitive radio networks extremely. The simulation results demonstrate that the proposed algorithms process superior performance.