• Proceedings of the KSME Conference
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• 2000.04a
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• pp.433-439
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• 2000

Lots of semi-active control devices have been developed in recent years because they have the best features of passive and active system. Especially, controllable magneto-rheological(MR) fluid devices have received significant attention in these area of research. The MR fluid is the material that reversibly changes from a free-flowing, linear viscous fluid to a semisolid with a controllable yield strength in milliseconds when exposed to a magnetic field. If the magnetic field is induced by moving a permanent magnet instead of applying current to a solenoid, it is possible to design a MR damper consuming low power because the power consumption is reduced at steady state. This paper proposes valve mode MR damper using permanent magnetic circuit that has wide range of operation with low power consumption and small size. To design a MR damper that has a large maximum dissipating torque and a low damping coefficient, a design parameter is adopted. The magnetic circuit, material of choke and choke type are selected experimentally with the design parameter. The behaviors of the damper are examined and torque tracking control using PID feedback controller is performed for step, ramp and sinusoidal trajectories.

• Ocean Systems Engineering
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• v.7 no.3
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• pp.225-246
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• 2017

Excessive dynamic-tension variations on the top-tensioned risers (TTRs) deteriorate the structural integrity and cause potential safety hazards. This phenomenon has become more remarkable in the development of deep-water fields with harsher environmental loads. The conventional prediction method of tension variations in hydro-pneumatic tensioner (HPT) has the disadvantage to underestimate the magnitude of cyclic loads. The actual excessive dynamic tension variations are larger when considering the viscous frictional fluid effects. In this paper, a suppression method of tension variations in HPT is modeled by incorporating the magneto-rheological (MR) damper and linear-force actuator. The mathematical models of the combined HPT and MR damper are developed and a force-control scheme is introduced to compensate the excessive tension variations on the riser tensioner ring. Numerical simulations and analyses are conducted to evaluate the suppression of tension variations in HPT under both regular- and irregular-wave conditions for a drilling riser of a tensioned-leg platform (TLP). The results show that significant reduction of tension variations can be achieved by introducing the proposed system. This research has provided a theoretical foundation for the HPT tension control and related structural protection.

• Journal of Mechanical Science and Technology
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• v.19 no.10
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• pp.1835-1845
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• 2005

In this paper a safe arm with passive compliant joints and visco-elastic covering is designed for human-friendly service robots. The passive compliant joint (PCJ) is composed of a magneto-rheological (MR) damper and a rotary spring. In addition to a spring component, a damper is introduced for damping effect and works as a rotary viscous damper by controlling the electric current according to the angular velocity of spring displacement. When a manipulator interacts with human or environment, the joints and cover passively operate and attenuate the applied collision force. The force attenuation property is verified through collision experiments showing that the proposed passive arm is safe in view of some evaluation measures.

• Structural Engineering and Mechanics
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• v.82 no.4
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• pp.445-458
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• 2022

Some of the control systems used in engineering structures that use sensors and decision systems have some time delay reducing efficiency of the control system or even might make it unstable. In this research, in addition to considering the effect of the time delay in vibration control process, predictive control is used to compensate the time delay. A semi-active vibration control approach with the help of magneto-rheological dampers is implemented. In addition to using fuzzy inference system to determine the appropriate control voltage for MR damper, structural behavior prediction system and specifying future responses are also used such that the time delays occurring within control process are overcome. For this purpose, determination of prediction horizon is conducted for one, five, and ten steps ahead for single degree of freedom structures with periods ranging from 0.1 to 4 seconds, subjected to twenty earthquake excitations. The amount of time delay applied to the control system is 0.1 seconds. The obtained results indicate that for 0.1 second time delay, average prediction error values compared to the case without time delay is 3.47 percent. Having 0.1 second time delay in a semi-active control system reduces its efficiency by 11.46 percent; while after providing the control system with structure behavior prediction, the difference in the results for the control system without time delay is just 1.35 percent on average; indicating a 10.11 percent performance improvement for the control system.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.5 s.248
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• pp.550-559
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• 2006

This paper presents designs and performance investigations of two bypass-type MR (magneto-rheological) shock dampers for high impulsive force systems, one of which is with single rod and the other with double rod. First of all, on the basis of the Bingham properties of the MR fluid and the magnetic field analysis of the magnetic circuit, the MR shock dampers are designed and manufactured. After experimental investigations on their magnetic field-dependent damping forces and responses characteristics, dynamic models of the proposed dampers are formulated and compared. Then, a simple 1 degree-of-freedom mass-drop system is constructed, and the effective and practical control algorithm is designed by considering dynamic characteristics of the shock control system. The shock control performances of the proposed MR shock dampers are verified through the comparison study of experiment results with simulation ones.

• Proceedings of the KIEE Conference
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• 1999.07g
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• pp.3289-3291
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• 1999

The vibration and impact hinders the movement of micro dynamic system. The controllable micro damper is a solution for this problem. In this paper, the controllable micro damper for MR(Magneto - Rheological) Fluid is designed and fabricated using bulk micromachining process and organic bonding technique. The damping constant of micro MR damper changes according to input magnetic field. The response of the micro MR damper is measured and the experimental results are compared.

• Proceedings of the KIEE Conference
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• 2008.10b
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• pp.163-164
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• 2008

본 논문에서는 MR(Magneto-rheological)댐퍼의 특성을 파악하고 모델링하기 위해 실험 장치를 설계 및 제작을 하였다. 그리고 MR댐퍼의 특성 중 전항복(pre-yieid) 영역에서의 속도가 증가하거나 및 감소할 때의 감쇠력의 차이를 보이는 이력현상을 모델링하기 위해 개선된 Bouc-Wen 모델을 이용하였다. 다양한 실험을 통해 Bouc-Wen 모델의 변수들을 이용하여 구하였다.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.10
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• pp.69-76
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• 2000

Lots of semi-active control devices have been developed in recent years because they have the best features of passive and active system. Especially, controllable magneto-rheological(MR) fluid devices have received significant attention in these area of research. The MR fluid is the material that reversibly changes from a free-flowing, linear viscous fluid to a semisolid with a controllable yield strength in milliseconds when exposed to a magnetic field. If the magnetic field is induced by moving a permanent magnet instead of applying current to a solenoid, it is possible to design a MR damper consuming low power because the power consumption is reduced at steady state. This paper proposes valve mode MR damper using permanent magnetic circuit that has wide range of operation with low power consumption, a design parameter is adopted. The magnetic circuit, material of choke and choke type are selected experimentally with the design parameter. The behaviors of the damper are examined and torque tracking control using PID feedback controller is performed for step, ramp and sinusoidal trajectiories.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.9 s.180
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• pp.2274-2282
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• 2000

An MR(Magneto-Rheological) fluid damper is designed and applied to the semi-active suspension system of a 1/4 car model. The damping constant of the MR damper changes according to input current and the time delay of the damper is included in the system dynamics. The passive method, LQ control and Frequency shaped LQ control are compared in experiments. The advantage of the proposed frequency shaped LQ control is that the ride comfort improves in frequency range from 4 to 8Hz where human body is most sensitive and the driving safety improves around the resonance frequency of unsprung mass, 11Hz. The experiments using a 1/4 car model show the effectiveness of the algorithm.

• Structural Engineering and Mechanics
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• v.31 no.1
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• pp.39-56
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• 2009

Vibration is an undesirable phenomenon in a dynamic system like lightly damped aerospace structures and active vibration control has gradually been employed to suppress vibration. The objective of the current investigation is to introduce an active torsional magneto-rheological (MR) fluid based damper for vibration control of a typical nose landing gear. They offer the adaptability of active control devices without requiring the associated large power sources. A torsional damper is designed and developed based on Bingham plastic shear flow model. The numerical analysis is carried out to estimate the damping coefficient and damping force. The designed damper is fabricated and an experimental setup is also established to characterize the damper and these results are compared with the analytical results. A typical FE model of Nose landing gear is developed to study the effectiveness of the damper. Open loop response analysis has been carried out and response levels are monitored at the piston tip of a nose landing gear for various loading conditions without damper and with MR-damper as semi-active device. The closed-loop full state feedback control scheme by the pole-placement technique is also applied to control the landing gear instability of an aircraft.