• Journal of the Earthquake Engineering Society of Korea
• /
• v.8 no.5 s.39
• /
• pp.55-64
• /
• 2004

In this paper, the preliminary design procedure of magnetorheological (MR) dampers is developed for controlling the building response induced by seismic excitation. The dynamic characteristics and control effects of the modeling methods of MR dampers such as Bingham, biviscous, hysteretic biviscous, simple Bouc?Wen, Bouc?Wen with mass element, and phenomenological models are investigated. Of these models, hysteretic biviscous model which is simple and capable describing the hysteretic characteristics, is used for numerical studies. The capacity of MR damper is determined as a portion of not the building weight but the lateral restoring force. A method is proposed for optimal placement and number of MR dampers, and its effectiveness is verified by comparing it with the simplified sequential search algorithm. Numerical results indicate that the capacity, number and the placement can be reasonably determined using the proposed design procedure.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2007.11a
• /
• pp.565-573
• /
• 2007

This paper is concerned with the dynamic modeling, active vibration controller design and experiments for a cylindrical shell equipped with MFC actuators. The dynamic model was derived by using Rayleigh-Ritz method based on Donnel-Mushtari shell theory. The actuator and sensors for the MFC actuator equations were derived based on pin-force model. The equations of motion were then reduced to modal equations of motion by considering the modes of interest. The sensor equations were also converted to a reduced form. An aluminum shell was fabricated to demonstrate the effectiveness of modeling and control techniques. The boundary conditions at both ends of the shell were assumed to be shear diaphragm. Theoretical natural frequencies were calculated and compared to experimental result. It was observed that the theoretical result is in good agreement with experimental result for the first two modes. The multi-input and multi-output positive position feedback controller, which can cope with first two modes, was then designed based on the blockinverse theory and implemented using DSP. It was found from experiment that vibrations can be successfully suppressed.

• Explosives and Blasting
• /
• v.26 no.2
• /
• pp.99-107
• /
• 2008

This study, to reduce a ground vibration damage of the structures in an area adjacent to housing structures located closely above the tunnel section, is the ground vibration reduction instance of a tunnel blasting selectively applied the ground vibration-controlled blasting method (delay time applied blasting method, large center hole cut method, Line Drilling method, etc) with an originally planned blasting method connected, but with it's workability and economic efficiency is satisfactory, so, the results says the ground vibration-controlled blasting method on a similar condition is very effective, even if the applicability is depend on the blasting method and ground condition of the work area.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2011.04a
• /
• pp.648-654
• /
• 2011

The feed-water piping system constitutes a complex flow impedance network incorporating dynamic transfer characteristics which will amplify some pulsation frequencies. Understanding pressure pulsation waves for the feed-water recirculation piping system with cavitation problem of flow control valve is very important to prevent acoustic resonance. Feed water recirculation piping system is excited by potential sources of the shock pulse waves by cavitation of flow control valve. The pulsation becomes the source of structural vibration at the piping system. If it coincides with the natural frequency of the pipe system, excessive vibration results. High-level vibration due to the pressure pulsation affects the reliability of the plant piping system. This paper discusses the piping vibration due to the effect of shock pulsation by the cavitation of the flow control valves for the recirculation piping of feed-water pump system in combined cycle power plants.

• Journal of Energy Engineering
• /
• v.15 no.3 s.47
• /
• pp.202-208
• /
• 2006

Although the importance of good conservation of historic sites including ancient royal tombs is well aware, still not much attention has been paid for the facilities and systems to preserve those historic sites, which includes precious artifacts as wall paints and carved works, etc. Even the general understanding about the environment of the underground space or tombs is not satisfactory. In the present study, vibration levels due to the operation of an HVAC system to maintain the desired indoor temperature and humidity are investigated experimentally. According to the measured data, the level of vibration inside the present model tomb with the indoor unit inside, showed order of magnitude less values than the Swiss Standards, but still higher than the value suggested by German standards, which is, zero. Further study will be pursued for cases including different ways of installation, because the vibration level depends not only on the system design, but also on the installation methods.

• Proceedings of the KIEE Conference
• /
• 2001.07b
• /
• pp.780-782
• /
• 2001

SRM은 회전자의 구조가 간단하고 간단한 제어장치로 구동이 가능한 장점이 있지만 Cogging Torque로 인한 소음, 진동, 토크리플 등으로 인해 SRM의 안정화 운전에 장애가 되는 단점이 있다. 이를 제거하기 위한 방법으로는 외부회로에 제어기를 도입하여 전류파형을 조절하는 방법이 있으나 이 경우 고가의 복잡한 정밀제어기를 부착해야한다. 본 연구에서는 회전자의 형상을 조절하여 Cogging Torque를 감소시키는 방법을 연구한다. 이를 위하여 유한요소법을 이용하여 설계변수의 민감도를 계산하고 최적화 기법을 사용하여 형상변경 실시를 반복하여 최적설계를 하고자 한다.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.12
• /
• pp.3127-3135
• /
• 1994

An approach to the simultaneous optimal design of structure and control system for large free-free flexible beam is presented. The flexible beam is modeled by the finite element method. And the reduced model of small degree of freedom is constructed by use of modal analysis. The tapered beam is considered so that the number of design variables is not dependent on the increasing number of finite elements. The width of several points of tapered beam and control gain are taken as design variables. The shape of beam and control gain are optimized simultaneously for the minimum weight of total structure including control system subject to the constraints of the magnitude of displacement of beam. It is shown that the simultaneous optimal design of structure and control systems is indeed useful.

• Proceedings of the Optical Society of Korea Conference
• /
• 2001.02a
• /
• pp.22-23
• /
• 2001

광결정(Photonic crystals)은 유전체를 주기적으로 배치한 구조인데, 이런 구조에 의해 1차원, 2차원, 또는 3차원적으로 빛을 제어할 수 있다. [1] 이런 주기적인 구조로 인해 광결정 내에서는 특정에너지와 특정 방향을 가진 빛이 진행하지 못하는 광밴드 갭(photonic band gap)뿐만 아니라 밴드구조와 밀접한 관계가 있는 비정상적인 광분산이 나타나기도 한다. 이러한 비정상적인 광분산에는 입사빔의 미세한 파장변화에 따른 PC내에서의 급격한 빛의 꺾임이나, 단일 파장의 입사빔이 두갈래로 갈라지는 현상, 또는 negative나 1보다 작은 굴절효과 등이 있는데, 이러한 현상을 해석하기 위한 것으로 광결정내의 고정된 진동수에 해당하는 점들을 2차원 k공간에서 표시한 분산곡선(dispersion surface)이 도입되었다. [2] (중략)

• Journal of the Earthquake Engineering Society of Korea
• /
• v.4 no.2
• /
• pp.47-56
• /
• 2000

지반-구조물 상호작용 시스템 구조물의 진동제어 시스템 복합재료 구조물과 같은 비비례 감쇠 구조물의 경우 정확한 동적응답을 얻기 위해서는 감쇠행렬을 고려한 고유치 문제를 계산하는 것이 필수적이다 그러나 대부분의 고유치 해법에서는 구하고자 하는 고유치 중 일부를 누락시킬 수 있기 때문에 어떤 고유치 해법이 실제문제에 응용 가능한 방법이 되기 위해서는 누락된 고유치의 존재 여부를 검사하는 기법을 포함하고 있어야만 한다. 비감쇠나 비례감쇠 시스템의 경우에는 널리 알려진 Sturm 수열성질을 이용하여 누락된 고유치를 쉽게 검사할 수 있는 반면에 비비례 감쇠 시스템의 경우에는 널리 알려진 Sturm 수열 성질을 이용하여 누락된 고유치를 쉽게 검사할 수 있는 반면에 비비례 감쇠 시스템의 경우에는 아직까지 검사 기법이 개발되어 있지않다 본 논문에서는 편각의 원리를 이용하여 감쇠행렬을 고려한 고유치 문제의 누락된 고유치의 존재여부를 검사하는 기법을 제안하였다 제안방법의 효용성을 검증하기 위하여 두가지 수치예제를 고려하였다.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.15 no.3 s.96
• /
• pp.354-363
• /
• 2005

Squeeze film dampers (SFDs) have been commonly used to effectively enhance the dynamic behavior of the rotating shaft supported by rolling element bearings. However, due to the recent trends of high operating speed, high load capacity and light weight in rotating machinery, it is becoming increasingly important to change the dynamic characteristics of rotating machines in operation so that the excessive vibrations, which may occurparticularly when passing through critical speeds or unstable regions, can be avoided. Semi-active type SFDs using magneto-rheological fluid (MR fluid), which responds to an applied magnetic field with a change in rheological behavior, are introduced in order to find its applications to rotating machinery as an effective device attenuating unbalance responses. In this paper, a semi-active SFD using MR fluid is designed, tested, and identified to investigate the capability of changing its dynamic properties such as damping and stiffness.In order to apply the MR-SFD to the vibration attenuation of a rotor, a systematic approach for determining the damper's optimal location is investigated, and also, a control algorithm that could improve the unbalance response characteristics of a flexible rotor is proposed and its control performance is validated with a numerical example.