• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.11 no.4
• /
• pp.22-30
• /
• 2001

In this paper, active control of vibrational intensity at a reference point in an infinite, elastic plate was discussed. The plate is excised harmonically by a vibrating source, which has a vertical point force. The optimal condition of controller was investigated to minimize the vibrational intensity being transmitted from the vibrating source to a reference point. Hence the method of feedforward control was employed for the control strategy and then the cost function was evaluated to find the optimal control force. Three types of control force (Vertical force, Moment, and Coupling force (a set of vertical force and moment) ) and controller's positions were examined to define the optimal condition of the controller. The vibrational intensity at a reference point was found to be reduced down to a zero level, compared with the uncontrolled case. Especially maximum reduction of vibrational intensity was achieved when the controller was collinearly positioned between a vibrating source and a reference point.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2004.05a
• /
• pp.410-415
• /
• 2004

The oscillation of the fluid caused by external forces is call ed sloshing, which occurs in moving vehicles with contained liquid masses, such as trucks, railroad cars, aircraft, and liquid rocket. This sloshing effect could be a severe problem in vehicle stability and control. In this study, the optimization design technique for reduction of the sloshing using evolutionary method is suggested. Two evolutionary methods are employed, respectively the artificial neural network(ANN) and genetic algorithm. An artificial neural network is used for the analysis of sloshing and genetic algorithm is adopted as optimization algorithm. As a result of optimization design, the optimized size and location of the baffle is presented

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1996.10a
• /
• pp.197-202
• /
• 1996

The dynamic interaction between a translating flexible arm and a trapezoidal velocity profile of a cart to which the flexible arm is attached is presented. Vibration of the flexible arm due to translation is analytically solved, and the conditions for suppressing vibration is derived in terms of velocity profiles. To prove the validity of the solution and the conditions, numerical computation and experiments are camed out. Only a natural frequency of vibrating plant is needed to obtain the conditions for vibration reduction. With this results, a passive vibration regulator as an open loop control scheme can be designed and direct application to industrial plants such as overhead crane can be made.

• Proceedings of the Korean Society Of Semiconductor Equipment Technology
• /
• 2002.11a
• /
• pp.94-96
• /
• 2002

• Structural Engineering and Mechanics
• /
• v.74 no.1
• /
• pp.129-143
• /
• 2020

This study proposes a new shape memory alloy-tuned mass damper (SMA-TMD) and investigates the effectiveness of this damper in reducing and controlling the vibrations of a transmission tower-line system under various seismic excitations. Based on a practical transmission line system and considering the geometric nonlinearity of this system, the finite element (FE) software ANSYS is used to create an FE model of the transmission tower-line system and simulate the proposed SMA-TMD. Additionally, the parameters of the SMA springs are optimized. The effectiveness of a conventional TMD and the proposed SMA-TMD in reducing and controlling the vibrations of the transmission tower-line system under seismic excitations is investigated. Moreover, the effects of the ground motion intensity and frequency ratio on the reduction ratio (η) of the SMA-TMD are studied. The vibration reduction effect of the SMA-TMD under various seismic excitations is superior to that of the conventional TMD. Changes in the ground motion intensity and frequency ratio have a significant impact on the η of the SMA-TMD. As the ground motion intensity and frequency ratio increase, the η values of the SMA-TMD first increase and then decrease. Studying the vibration reduction effects of the SMA-TMD can provide a reference for the practical engineering application of this damper.

• Journal of Power System Engineering
• /
• v.5 no.3
• /
• pp.64-72
• /
• 2001

This paper describes an optimal design technology in a segment type vertical guide bearing for vertical rotating machinery. Segment type vertical guide bearings have widely used for vertical rotating machinery, however bearing problems, such as excessive vibration and temperature rise, frequently take place in the actual machine. Such excessive vibration magnitude and/or abnormal bearing metal temperature rise result in serious damage and economic losses. Thus the segment type vertical guide bearing should be designed to get optimal characteristics in order to maintain stable operation without bearing failure due to abnormal vibration and/or abnormal bearing metal temperature. The preload ratio is the most important parameter in designing the segment type vertical guide bearing. Because adjustment of the bearing preload by changing the bearing clearance could easily control both the bearing stiffness and the cooling effect. In the paper, the influence of the preload effects on the bearing metal temperature and the bearing stiffness has been investigated both theoretically and experimentally in order to find out an optimum preload ratio. Results show that the segment type vertical guide bearing has an optimum preload ratio at which the bearing stiffness reaches a masimum value while the bearing metal temperature is minimized.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2003.11a
• /
• pp.47-55
• /
• 2003

This paper Presents active control algorithm using probability density function of structural energy. It is assumed that the structural energy under excitation has Rayleigh probability distribution. This assumption is based on the fact that Rayleigh distribution satisfies the condition that the structural energy is always positive and the occurrence probability of minimum energy is zero. The magnitude of control force is determined by the probability that the structural energy exceeds the specified target critical energy, and the sign of control force is determined by Lyapunov controller design method. Proposed control algorithm shows much reduction of peak responses under seismic excitation compared to LQR controller, and it can consider control force limit in the controller design. Also, chattering problem which sometimes occurs in Lyapunov controller can be avoided.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.15 no.5 s.98
• /
• pp.595-603
• /
• 2005

In this work, the multiple dynamic absorber( MDA ) is introduced to reduce several vibration modes of shadow mask simultaneously and its design method is developed from the theory of the simple dynamic absorber. When designing the dynamic absorber, there are three significant design parameters such as mass, damping ratio and tuning frequency. Therefore the sensitivity analysis for those parameters has been executed in order to find out the design criteria of multiple dynamic absorber using the finite element model of shadow mask. The multiple dynamic absorber(MDA) designed by the proposed method is tested theoretically and experimentally to estimate the efficiency of vibration reduction. From the results, it is verified that the method is feasible to apply the system having the multiple nitration modes and more efficient than the thin wire-type damper used commercially to reduce the vibration of shadow mask.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.24 no.5
• /
• pp.545-557
• /
• 2021

Engine is the main source of vibration that generates unwanted noise and vibration of vehicle chassis. Especially, in submarine applications, radiation of noise signatures can be detected at some distance away from the submarine using a sonar array. Thus quiet operation is crucial for submarine's survivability. This study addresses reduction of the force transmissibility originating from engines and transmitted to hull through engine mounts. An inertial damper, as an actuator of hybrid mount system, is addressed to reduce even further the level of vibration. Narrow band FxLMS algorithms are broadly used to cancel the vibration of engine mount because of its excellent performance of canceling narrow band noise. However, in real active dampers, the maximum displacement of damper mass is kinematically restricted. When the control input signal from the FxLMS algorithm exceeds this limitation, the damper mass will collide with the mechanical stops and results in many problems. Originated from these, a modified narrow band FxLMS algorithm based on the equalizer technique with the maximum allowable displacement of active damper mass is proposed in this study. Some simulation results showed that the propose algorithm is effective to suppress vibration of engine mount while ensuring given displacement constraint.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.12 no.5
• /
• pp.374-379
• /
• 2002

A new active muffler system has been developed and its superior performance on both noise reduction and engine torque increase is demonstrated with experiment. Main characteristic of the proposed muffler system is the use of destructive interference by transmission path difference of divided exhaust pipes to reduce major exhaust noise components thereby overcoming problems of other active exhaust noise control methods. The exhaust pipe is divided into two sections and joined again downstream. One divided pipe has a sliding mechanism to vary its length, which is controlled to make half wavelength transmission path difference for the major engine rpm frequency. In this system one divided pipe is used to control major rpm frequency and its Harmonics and another pipe is used to control noise component double the frequency of rpm. An after-market tuning muffler, which has very simple internal structure and minimal back pressure, is also installed to remove remaining wideband noise. To make the system to be small enough to be practical, conventional muffler is also installed and used in low rpm range and active muffler is only employed in high rpm range. Noise reduction of the proposed system is comparable to conventional passive muffler. The engine dynamo test has proved the proposed system can recover almost all the torque lost by conventional muffler.