• 한국소음진동공학회논문집
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• 제19권1호
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• pp.17-23
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• 2009

This paper proposes a new type of MR(magnetorheological) fluid based suspension system and applies it to military vehicle for vibration control. The suspension system consists of gas spring and MR damper. The nonlinear behavior of spring characteristics is evaluated with respect to the wheel travel and damping force model due to viscosity and yield stress of MR fluid is derived. Subsequently, a military vehicle of 6WD is adopted for the integration of the MR suspension system and its nonlinear dynamic model is established by considering vertical, pitch and roll motion. Then, a sky-hook controller associated with semi-active actuating condition is designed to reduce the imposed vibration. In order to demonstrate the effectiveness of the proposed MR suspension system, computer simulation is undertaken showing vibration control performance such as roll angle and pitch angle evaluated under bump and random road profiles.

• 국제초고층학회논문집
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• 제8권3호
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• pp.229-234
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• 2019

This report introduces the structural design of Hibiya Mitsui Tower built in Tokyo Midtown Hibiya. The upper part of this tower is used for offices and the lower portion is for commercial facilities and a cinema complex which need the large open spaces. The 192m-high building has 35 floors above ground and 4 below ground. The structure is a steel frame using CFT columns to feature the high-performance oil dampers and the buckling restrained braces for vibration control. First, an outline of the structural design of this building is presented. Second, we introduce the transfer frame adopted to realize the large open spaces in the lower part, and the long column supporting the corner part of the high-rise building to avoid making a shade on the adjacent Hibiya Park, which are the feature of this building. Finally, we present an outline of the latest highly efficient semi-active oil dampers adopted in this building, and the vibration responses of this tower.

• 한국산학기술학회논문지
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• 제19권5호
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• pp.160-166
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• 2018

본 연구에서는 주행하는 도로면의 단면 형상 정보를 이용하는 RPS 시스템과 다원형 감쇠 특성을 가지는 MSD 시스템을 기반으로 예견 제어 알고리즘을 적용한 지능형 현가 시스템을 제안하고, 그 결과를 제시하였다. 자동차의 과도한 진동과 조종 불안정성을 유발하는 대표적인 외란 입력은 주행하는 도로면에 돌출되거나 함몰된 불규칙한 주행 장애물이다. 이러한 장애물의 존재 유무만이 아니라 그 형상에 대한 정보를 안다면 이를 활용하여 제어 성능을 개선시킬 수 있다. 선행 연구 결과를 바탕으로 하여, 상용성을 고려한 구조화된 작동 시스템을 적용한 응용 연구를 수행하였다. 이를 위해 RPS 시스템과 예견 제어 기법을 기반으로 한 제어 알고리즘과 다차원화된 감쇠 특성을 가지는 MSD 시스템 간의 스위칭 알고리즘을 개발, 연계성을 제시하였다. 실차 적용성을 파악하기 위하여, 제안된 제어 프레임을 전차량 모델에 구현하여 시뮬레이션을 수행하였다. 구조적 간결성을 목표로 적용된 3-DS 작동기 시스템과 결합된 전자제어식 현가 시스템을 통하여 탑승자의 승차감과 차체의 조종 안정성을 효과적으로 개선할 수 있음과 제 시스템의 유용성을 확인하였다.

• Earthquakes and Structures
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• 제11권6호
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• pp.943-966
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• 2016

Recently, magnetorheological elastomer (MRE) material and its devices have been developed and attracted a good deal of attention for their potentials in vibration control. Among them, a highly adaptive base isolator based on MRE was designed, fabricated and tested for real-time adaptive control of base isolated structures against a suite of earthquakes. To perfectly take advantage of this new device, an accurate and robust model should be built to characterize its nonlinearity and hysteresis for its application in structural control. This paper first proposes a novel hysteresis model, in which a nonlinear hyperbolic sine function spring is used to portray the strain stiffening phenomenon and a Voigt component is incorporated in parallel to describe the solid-material behaviours. Then the fruit fly optimization algorithm (FFOA) is employed for model parameter identification using testing data of shear force, displacement and velocity obtained from different loading conditions. The relationships between model parameters and applied current are also explored to obtain a current-dependent generalized model for the control application. Based on the proposed model of MRE base isolator, a second-order sliding mode controller is designed and applied to the device to provide a real-time feedback control of smart structures. The performance of the proposed technique is evaluated in simulation through utilizing a three-storey benchmark building model under four benchmark earthquake excitations. The results verify the effectiveness of the proposed current-dependent model and corresponding controller for semi-active control of MRE base isolator incorporated smart structures.

• Progress in Superconductivity
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• 제10권1호
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• pp.60-67
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• 2008

We present domestic efforts for superconducting fault current limiter (SFCL) application in the Korea Electric Power Corporation (KEPCO) grid and pending points at issue. KEPCO's decision to upgrade the 154 kV/22.9 kV main transformer from 60 MVA to 100 MVA cast a problem of high fault current in the 22.9 kV distribution lines. The grid planners supported adopting an SFCL to control the fault current. This environment friendly to SFCL application must be highly dependent upon the successful development of SFCL having specifications that domestic utility required. The required conditions are (1) small size of not greater than twice of 22.9 kV gas insulated switch-gear (GIS), (2) sustainability of current limitation without the line breaking by circuit breakers (CB) for maximum 1.5 seconds. Also, optionally, recommended is (3) the reclosing capability. Conventional resistive SFCLs do not meet (1) $\sim$ (3) all together. A hybrid SFCL is an excellent solution to meet the conditions. The hybrid SFCL consists of HTS SFCL components for fault detection and line commutation, a fast switch (FS) to break the primary path, and a limiter. This characteristic structure not only enables excellent current limiting performances and the reclosing capability, but also allows drastic reduction of HTS volume and small size of the cryostat, resulting in economic feasibility and compactness of the equipment. External current limiter also enables long term limitation since it is far less sensitive to heat generation than HTS. Semi-active operation is another advantage of the hybrid structure. We will discuss more pending points at issues such as maintenance-free long term operation, small size to accommodate the in-house substation, passive and active control, back-up plans, diagnosis, and so on.

• Smart Structures and Systems
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• 제21권3호
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• pp.359-371
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• 2018

Strong seismic events commonly cause large drift and deformation, and functionality failures in the superstructures. One way to prevent functionality failures is to design structures which are ductile and flexible through yielding when subjected to strong ground excitations. By developing forces that assist motion as "negative stiffness forces", yielding can be achieved. In this paper, we adopt the weakening and damping method to achieve a new approach to reduce all of the structural responses by further adjusting damping phase. A semi-active control system is adopted to perform the experiments. In this adaptation, negative stiffness forces through certain devices are used in weakening phase to reduce structural strength. Magneto-rheological (MR) dampers are then added to preserve stability of the structure. To adjust the voltage in MR dampers, an inverse model is employed in the control system to command MR dampers and generate the desired control forces, where a velocity control algorithm produces initial required control force. An extensive numerical study is conducted to evaluate proposed methodology by using the smart base-isolated benchmark building. Totally, nine control systems are examined to study proposed strategy. Based on the numerical results of seven earthquakes, the use of proposed strategy not only reduces base displacements, base accelerations and base shear but also leads to reduction of accelerations and inter story drifts of the superstructure. Numerical results shows that the usage of inverse model produces the desired regulated damping, thus improving the stability of the structure.

• Wind and Structures
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• 제21권5호
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• pp.565-595
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• 2015

In recent years, high-rise buildings received a renewed interest as a means by which technical and economic advantages can be achieved, especially in areas of high population density. Taller and taller buildings are being built worldwide. These types of buildings present an asset and typically are built not to fail under wind loadings. The increase in a building's height results in increased flexibility, which can lead to significant vibrations, especially at top floors. Such oscillations can magnify the overall loads and can be annoying to the top floors' occupants. This paper shows that increased stiffness in high-rise buildings may not be a feasible solution and may not be used for the design for comfort and serviceability. High-rise buildings are unique, and a vibration control system for a certain building may not be suitable for another. Even for the same building, its behavior in the two lateral directions can be different. For this reason, the current study addresses the application of hybrid tuned mass and magneto-rheological (TM/MR) dampers that can work for such types of buildings. The proposed control scheme shows its effectiveness in reducing floors' accelerations for both comfort and serviceability concerns. Also, a dissipative analysis carried out shows that the MR dampers are working within the possible range of optimum performance. In addition, the design loads are dramatically reduced, creating more resilient and sustainable buildings. The purpose of this paper is to stimulate, shape, and communicate ideas for emerging control technologies that are essential for solving wind related problems in high-rise buildings, with the objective to build the more resilient and sustainable infrastructure and to optimally retrofit existing structures.

• Earthquakes and Structures
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• 제20권1호
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• pp.39-53
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• 2021

By means of installing sloped rolling-type seismic isolators (SRI), the horizontal acceleration transmitted to the to-be-protected object above can be effectively and significantly reduced under external disturbance. To prevent the maximum horizontal displacement response of SRI from reaching a threshold, designing large and conservative damping force for SRI might be required, which will also enlarge the transmitted acceleration response. In a word, when adopting seismic isolation, minimizing acceleration or displacement responses is always a trade-off. Therefore, this paper proposes that by exploiting the possible information provided by an earthquake early warning system, the damping force applied to SRI which can better control both acceleration and displacement responses might be determined in advance and accordingly adjusted in a semi-active control manner. By using a large number of ground motion records with peak ground acceleration not less than 80 gal, the numerical results present that the maximum horizontal displacement response of SRI is highly correlated with and proportional to some important parameters of input excitations, the velocity pulse energy rate and peak velocity in particular. A control law employing the basic form of hyperbolic tangent function and two objective functions are considered in this study for conceptually developing suitable control algorithms. Compared with the numerical results of simply designing a constant, large damping factor to prevent SRI from pounding, adopting the recommended control algorithms can have more than 60% reduction of acceleration responses in average under the excitations. More importantly, it is effective in reducing acceleration responses under approximately 98% of the excitations.

• Smart Structures and Systems
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• 제9권4호
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• pp.373-392
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• 2012

Tracking control of systems with variable stiffness hysteresis using a gain-scheduled (GS) controller is developed in this paper. Variable stiffness hysteretic system is represented as quasi linear parameter dependent system with known bounds on parameters. Assuming that the parameters can be measured or estimated in real-time, a GS controller that ensures the performance and the stability of the closed-loop system over the entire range of parameter variation is designed. The proposed method is implemented on a spring-mass system which consists of a semi-active independently variable stiffness (SAIVS) device that exhibits hysteresis and precisely controllable stiffness change in real-time. The SAIVS system with variable stiffness hysteresis is represented as quasi linear parameter varying (LPV) system with two parameters: linear time-varying stiffness (parameter with slow variation rate) and stiffness of the friction-hysteresis (parameter with high variation rate). The proposed LPV-GS controller can accommodate both slow and fast varying parameter, which was not possible with the controllers proposed in the prior studies. Effectiveness of the proposed controller is demonstrated by comparing the results with a fixed robust $\mathcal{H}_{\infty}$ controller that assumes the parameter variation as an uncertainty. Superior performance of the LPV-GS over the robust $\mathcal{H}_{\infty}$ controller is demonstrated for varying stiffness hysteresis of SAIVS device and for different ranges of tracking displacements. The LPV-GS controller is capable of adapting to any parameter changes whereas the $\mathcal{H}_{\infty}$ controller is effective only when the system parameters are in the vicinity of the nominal plant parameters for which the controller is designed. The robust $\mathcal{H}_{\infty}$ controller becomes unstable under large parameter variations but the LPV-GS will ensure stability and guarantee the desired closed-loop performance.

• Structural Engineering and Mechanics
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• 제17권3_4호
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• pp.539-556
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• 2004

In this paper, the design, fabrication and characterization of a piezoelectric friction damper are presented. It was sized with the proposed practical procedure to minimize the story drift and floor acceleration of an existing 1/4-scale, three-story frame structure under both near-fault and far-field earthquakes. The design operation friction force in kip was numerically determined to range from 2.2 to 3.3 times the value of the peak ground acceleration in g (gravitational acceleration). Experimental results indicated that the load-displacement loop of the damper is nearly rectangular in shape and independent of the excitation frequency. The coefficient of friction of the damper is approximately 0.85 when the clamping force on the damper is above 400 lbs. It was found that the friction force variation of the damper generated by piezoelectric actuators with 1000 Volts is approximately 90% of the expected value. The properties of the damper are insensitive to its ambient temperature and remain almost the same after being tested for more than 12,000 cycles.