• Proceedings of the Korea Concrete Institute Conference
• /
• 1992.10a
• /
• pp.167-172
• /
• 1992

To analyze the effects compressive strength of concrete and longitudinal steel ratio on second-order moment of columns, 30tied rein reinforced concrete columns with hinged ends were tested. The 80mm square cross section was used and the amount of eccentricity was 24mm. The compressive strengths of column specimens with slenderness ratios of 10, 60, and 100were 250, 648 and 880kg/$\textrm{cm}^2$, and the longitudinal steel ratios were 1.98%(4-D6) and 3.95%(8-D6). The ratio of ultimate load capacity to that of short column with the same eccentricity (Pu/Pn) was much decreased at high slenderness ratio with increasing the compressive strength of concrete. And the lateral displacement of slender column at the ultimate load was decreased as the strength was increased. These are due to that at high slenderness ratio the load capacity and behavior of column are affected by flexural rigidity. And, it was also found that with increasing steel ratio, the value of Pu/Pn and the lateral displacement at the ultimate load were larger for the same slenderness ratio.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1998.10a
• /
• pp.462-467
• /
• 1998

A rational method for prediction of long-term deflections of reinforced concrete beams under sustained loads was proposed. Strain and stress distributions of uncracked and fully cracked sections after creep and shrinkage were determined from the requirements of strain compatibility and force equilibrium of a section, and then long-term deflections were calculated from the section analysis results. In fully cracked section analysis, noncoincidence of the neutral axis of strain and the neutral axis of stress after creep and shrinkage was taken into account. The accuracy of the proposed method was verified by comparison with several experimental measurements of beam deflections. The proposed approximate procedure gave the better predictions than the existing approximate methods. At the same time, the proposed method also retained simplicity of the calculation, since maximum long-term deflection could be obtained without tedious integration of the curvatures.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.30 no.4
• /
• pp.320-328
• /
• 1994

In 1980 s to 1990 s the marine propulsion diesel engines have been developed into lower speed and longer stroke for the enegy saving (small S.F.O.C). As these new trends the conventional mechanical-hydraulic governors were not adapted to the new requirements and the digital governors have been adopted in the marine use. The digital governors usually use the control algorithms such as the PID control, optimal control, adaptive control and etc. While the engine has delay time and parameter variations these control algorithms have difficulty in considering the stability and the robustness for the model uncertainty. In this study, the $H_{\infty}$ controller design method are applied in order to design the feedback controller K(s) to the speed control of the low speed marine diesel engine, and the two-degree-of-freedom control system is constituted with $H_{\infty}$controller. By comparison of responses of the two-degree-of-freedom control system under the delay time and parameter variations is confirmed.

• Magazine of the Korea Concrete Institute
• /
• v.10 no.3
• /
• pp.153-164
• /
• 1998

본 연구는 양생온도의 영향에 따른 콘크리트의 장기강도 예측식을 개발하고, 기존에 보고된 데이터를 이용하여 제안식의 신뢰성을 검증하기 위한 것이다. 제안식은 반응률상수 모델을 이용하였으며, 콘크리트의 장기강도에 영향을 미치는 인자로 양생온도에 따른 확산장벽의 효과를 고려하였다. 제안식을 검증하기위하여 각각의 데이터를 28일 상대강도의비로바꾸어 -0.6~59.7$^{\circ}C$ 범위의 8개의 평균 양생온도에 대해서 회귀분석하였다. 회귀분석을통해 제안식의 온도 영향계수인 반응율상수, 한계강도, 반응지수를 양생온도에 따른 함수식으로 표현하였다. 제안식은 기존의모델식에 비해 신뢰성이 높았으며, 초기재령에서는 기존의 모델식등과 큰 차이를나타내지 않았으나 장기재령으로 갈수록 제안식의 정확도가 크게 높아짐을 알 수 있었다.

• Progress in Superconductivity and Cryogenics
• /
• v.6 no.1
• /
• pp.1-5
• /
• 2004

Long length of Bi-2223/Ag superconducting wives were fabricated by stacking and drawing process with advanced heat-treatment schedules. Intermediate annealing was carried out to increase the homogeneity and uniformity of the superconducting filaments embedded in the silver matrix. Phase modification from tetragonal to orthorhombic Bi-2212 by pre heat treatment(PHT) was executed to improve the texture and phase transformation of Bi-2223. Drawing stress was measured to predict the sausaging and stress limit. Rolling Parameters such as thickness. width and winding tension were investigated to roll the tape with uniformity. 1 km length of Bi-2223/Ag superconducting wires were fabricated without any breakage. Critical current (Je) of 270 m length of superconducting tapes was measured over than $70 A/cm^2$ continuously after final sintering.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.33 no.2
• /
• pp.141-148
• /
• 1997

This paper is concerned with the vibration control of multi-layer structure for ultra-tall buildings and main tower of large bridge etc. We have modeled the multi-layer structure with the distributed mass system as the lumped mass system of two-degree-of-freedom structure and made experimental equipment. The LQ optimal control theory is applied to the design of the control system. The designed control system is simulated by computer. As a result, the LQ regulator showed good vibration control performance with impact excitation.

• Journal of KSNVE
• /
• v.6 no.3
• /
• pp.357-362
• /
• 1996

The magnetic levitation system has great advantages, such as little friction, no lubrication, no noise and so on. But the magnetic levitation system need a stabilizing controller because it is a unstable, system in natural and it need a sensor for displacement measurement to control the system. In this paper, we proposed a sensorless method to measure the gap between the magnetic pole and the levitated object with application the inductance characteristic which vary according to gap. We made a driving circuit which supply simultaneously the control input PWM(Pulse Width Modulation) signal and the carrier PWM signal to estimate the gap. Because the inductance is a function of gap, and the current of the carrier signal is a function of the inductance, we could estimate the gap from the measurement of the current of the carrier signal. Finally, we investigated the validity of the proposed method through the experimental results.

• Journal of Power System Engineering
• /
• v.3 no.4
• /
• pp.79-85
• /
• 1999

The magnetic levitation system is utilized in the magnetic bearing of high-speed rotor system because of little friction, no lubrication, no noise and so on. The magnetic levitation system needs the feedback controller for the stabilization of system, and gap sensors are generally used to measure the gap. The use of sensor easily goes into troublesome caused by sensor failure discord between the measurement point and the control point etc. This paper gives a controller design method of magnetic levitation system which satisfies the given $H_{\infty}$ control performance and the robust stability of the presence of physical parameter perturbations. To the end, we investigated the validity of the designed controller through results of simulation.

• Journal of Power System Engineering
• /
• v.2 no.2
• /
• pp.41-46
• /
• 1998

This paper presents the vibration control for the two degree-of-freedom which is a reduced model of multi-layer structure. This reduced model is designed for the first and second order resonance in the low frequency domain where the disturbance such as the earth quake has the large energy. And a designed controller using the LQ type $H_{\infty}$ control theory shows the good performance for the impulse disturbance through the experimental results and the simulation results respectively.

• Journal of Power System Engineering
• /
• v.7 no.1
• /
• pp.60-67
• /
• 2003

This paper introduces basic study how to restrain the vibration of a four story shear structure. We have modeled a four story shear structure mathematically and have identified each parameters by experiment. We have gotten a reduced nominal model through modal analyzing method and the $H_{\infty}$ control theory is used in the control system design to get the robust controller. It's shown that the desirable performances is confirmed through the mathematical simulation. And a designed controller applying the $H_{\infty}$ control theory shows the good performance for the impulse disturbance through the simulation results. That is, the robustness of this control system is confirmed for the ability of disturbance rejection and modeling error.