• Proceedings of the KSR Conference
• /
• 2000.11a
• /
• pp.374-381
• /
• 2000

본 논문에서는 지진 발생시, LRB가 설치된 교량의 시간이력 해석을 수행하였다 이를 위해 LRB의 비선형 거동특성을 Bi-linear로 모형화 하였으며, 기존의 방법인 등가선형으로 모형화된 해석결과와 비교하였다. 또한 LRB받침만 설치된 경우와, LRB받침과 일반탄성받침이 함께 사용된 경우를 해석하여, 받침이 혼합된 경우, 상시하중과 지진하중시 발생할 수 있는 문제점을 검토하였다. 4경간 연속교량에 적용된 해석결과를 보면, LRB만을 설치한 경우, Pot-Bearing만 설치된 경우에 .비해, 고유주기 상승과 이력감쇠에 의한 지진력의 감소와 함께, 지진력의 효과적인 분배를 볼 수 있었으며, 일반탄성받침과의 적절한 조합에 의해서도, 충분한 면진성능을 얻을 수 있었다. 또한 LRB의 등가선형 모델이 Bi-linear 모델에 비해 보수적인 해석결과를 나타내었다.

• Journal of the Korean Geotechnical Society
• /
• v.24 no.12
• /
• pp.113-120
• /
• 2008

One-dimensional site response analysis is widely used to simulate the seismic site effects. The equivalent linear analysis, which is the most widely used type of site response analysis, is essentially a linear method. The method applies constant shear modulus and damping throughout the frequency range of the input motion, ignoring the dependence of the soil response on the loading frequency. A new type of equivalent linear analysis method that can simulate the frequency dependence of the soil behavior via frequency-strain curve was developed. Various forms of frequency-strain curves were proposed, and all curves were asserted to increase the accuracy of the solution. However, its validity has not been extensively proven and the effect of the shape of the frequency-strain curve is not known. This paper used two previously proposed frequency-strain curves and three additional curves developed in this study to evaluate the accuracy of the frequency-dependent equivalent linear method and the influence of the shape of the frequency-strain curves. In the evaluation, six recordings from three case histories were used. The results of the case study indicated that the shape of the frequency-strain curve has a dominant influence on the calculated response, and that the frequency dependent analysis can enhance the accuracy of the solution. However, a curve that results in the best match for all case histories did not exist and the optimum curve varied for each case. Since the optimum frequency-strain curve can not be defined, it is recommended that a suite of curves be used in the analysis.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.8 no.3
• /
• pp.33-42
• /
• 2004

While transforming the inelastic system into the equivalent elastic one gives an advantage of simpler analysis, the actual inelastic behavior of the system is hardly modeled in the capacity spectrum method (CSM). Therefore, the accuracy of CSM depends on the precise estimation of equivalent period and damping ratio as well as the modification of the elastic response spectrum and the corresponding demand spectrum. In this paper, the effect of demand spectrums on the accuracy of CSM is evaluated. First, the response reduction factors provided in ATC-40 and Euro Code are evaluated. Numerical analysis results indicated that the acceleration responses obtained using the factor of Euro Code are closer to the actual response than those obtained using the factors of ATC-40. Next, the accuracy of CSM is evaluated constructing the demand spectrum using the absolute acceleration responses and pseudo acceleration responses. The results obtained using the absolute acceleration responses were found to be generally larger than those obtained using the pseudo ones. Since CSM often underestimates the response, the use of absolute acceleration response gives the response relatively closer to the exact ones. However, the difference becomes negligible as the hardening ratio and the yield strength ratio become larger.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2002.10a
• /
• pp.459-466
• /
• 2002

The purpose of this study is to propose a new method for evaluating equivalent damping ratios of a structure with supplemental damping devices to assess their control effect quantitatively. A MDOF system is transformed to an equivalent SDOF system based on the assumption that the first mode dominates structural response. Approximate closed-form formulas for the evaluation of the first damping ratio are presented for various damping devices. Through numerical analysis of a ten-story building equipped with damping devices, the effectiveness of equivalent SDOF model and closed form formulas are verified.

• Journal of Power System Engineering
• /
• v.1 no.1
• /
• pp.98-105
• /
• 1997

In general, crankshafts which are used in internal combustion reciprocating engines are subjects to high torsional vibration. Therefore, a damper is often used to minimize the torsional vibration in reciprocating engines. In this paper, in order to investigate damping performance of viscous damper, the real effective viscosity and complex damping coefficient of silicone oil, and the effective inertia moment of inertia ring are calculated considering the relative motion between damper casing and inertia ring. Based on these results multi-cylinder shaft is modeled into equivalent 2-degree of freedom system and optimum condition is estimated by calculating the amplification factor of viscous damper. Also the test damper was manufactured according to the result of theoretical investigation, the performance and durability was ascertained through experimental examination.

• The Journal of the Acoustical Society of Korea
• /
• v.12 no.4
• /
• pp.39-46
• /
• 1993

조화집중이동하중을 받는 무한보에서의 음향방사에 대한 연구는 선박, 비행기, 타이어 트레드 밴느 등과 같은 계의 설계시 계의 구조물로부터 발생하는 소음에 대한 해결방안을 제시해 준다. 구조물 표면에 발생하는 음향파워는 svktnqusghks방법을 이용하여 보의 전길이에 분포된 음향 인텐시티를 적분하여 구한다. 보의 표면에서 발생하는 음향파원는 미하수, 장력, 감쇠계수, 기초강성계수, 그리고 파수비에 의해서 결정된다. 각 인자에 따른 음향파워에 대한 정성적인 분석을 수행하기 위해 심프슨 적분방법을 이용하여 수치적분을 하였다. 무한보에 작용하는 유체하중에 3다라 진동에너지가 음향에너지로 변환되는 비율이 달라진다. 밀도가 큰 유체는 등가감쇠로 작용하여 보로부터 방사된 음향에너지는 빠르게 감소된다. 하중의 이동에 의하여 도플러이동효과가 발생하여 무한보의 공진부근에서의 음향파워 파크가 분리되고 보의 기초감쇠의 영향으로 음향에너지는 감소된다.

• Journal of KSNVE
• /
• v.9 no.2
• /
• pp.258-264
• /
• 1999

The purpose of this paper is to investigate the damping behavior of a flexible joint. The slip at a structrual joint is selected at the tips of two identical cantilever beams adjoining each other. Both the direction of normal force and its magnitude varies due to the global deformation of the structure from mode to mode in the friction model. The friction dependent on vibration displacements resultsin the same functional behavior of the hysteretic material damping. Linearized energy loss factors are obtained as functions of both linear and torsional spring stiffness for their groups of symmetric and anti-symmetric modes, respectively. Experimental measurements as made for comparisons with analytical estimations by controlling the magnitude of fastening torque in the fastener, Hi-Lite. Trends on damping levelsmeasured in a very common vibration test method make an excellent agreement on the estimated damping levels.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.34 no.4
• /
• pp.25-32
• /
• 2006

An advanced method of Relaxed Static Stability (RSS) is utilized for improving the aerodynamic performance of modern version supersonic jet fighter aircraft. The flight control system utilize RSS criteria in both longitudinal and lateral-directional axes to achieve performance enhancements and improve stability. The T-50 advanced trainer employs the RSS concept in order to improve the aerodynamic performance and the flight control law in order to guarantee aircraft stability. The longitudinal two modes are the short period with high frequency and the phugoid mode with low frequency. The design goals of longitudinal control laws is concerned with the short period damping and frequency optimization using lower order equivalent system and utilizing the requirement of MIL-F-8785C. Analysis of short period mode has been and continues to be performed This paper addresses the analysis of aircraft phugoid node characteristics such as damping, natural frequency, and analysis of aircraft pitch motion that impacted by angle of attack limiter and auto pitch attitude control law.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2004.10a
• /
• pp.492-499
• /
• 2004

The purpose of this paper is to present a design procedure of coulomb friction dampers for controlling elastic and inelastic responses of building structures. The equivalent damping and frequency increased by the friction damper are estimated using ATC-40 and ATC-55 procedures which provide equivalent linear system for bilinear one, and then a design formula to achieve target performance response level by friction damper is presented. It is identified that there exists error between the responses obtained by this formula and by performing nonlinear analysis and the features of the error vary according to the hardening ratio, yield strength ratio, and structural period. Equations for compensating this er개r are reposed based on the least square method, and the results from numerical analyses indicate that the error is significantly reduced, and the proposed formula can be used without much error for designing coulomb friction damper for retrofitting a structure showing elastic or inelastic behavior.

• Journal of Navigation and Port Research
• /
• v.26 no.3
• /
• pp.281-288
• /
• 2002

It might be true that both experimental and analytic techniques have been developed in the vibration analysis end engineering. It could not be said, however, that the experimental method has been also developed as much as analytic method, such as Finite Element Method One of the reason is that computation time becomes longer and that the solution often diverges depending on the choice of initial value in solving nonlinear equation. The equation in experimental modal analysis is usually composed of the nonlinear term of natural frequency and modal damping ratio, and the linear one of equivalent stiffness. In this study, the nonlinear terms were solved first, and then the linear term was obtained. The experimental modal parameters were estimated, applying the developed experimental modal analysis curve-fitting method to the super-structure model. In addition, the number of modes and modal damping ratio could be easily determined by the developed program with the application of graphical techniques and with easy handling button.