• 한국소음진동공학회논문집
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• 제13권8호
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• pp.651-657
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• 2003

A new mechanical-electrical hybrid passive damping treatment is proposed to improve the performance of structural vibration control. The proposed hybrid passive damping system consists of a constrained layer damping treatment and a shunt circuit. In a passive mechanical constrained layer damping, a viscoelastic material damping layer is used to control the structural vibration modes in high frequency range. The passive electrical damping is designed for targeting the nitration amplitude in the low frequency range. The governing equations of motion are derived through the Hamilton's principle. The obtained mathematical model Is validated experimentally. The presented theoretical and experimental techniques provide invaluable tools for controlling the multiple modes of a vibrating structure over a wide frequency band.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2003년도 추계학술대회
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• pp.227-232
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• 2003

As the most precision equipment requiring very strict vibration environment are vulnerable to the surrounding vibration condition, they adapt the passive or active vibration isolation system. When it comes to the passive isolation system, the resonance of the isolation system causes excessive resonance response, and finally results in the degrade the equipment performance. This paper deals with the active control method to control this resonance induced response, and includes the experiment on the active control for controlling the resonance response on the table against the excitation of the same frequency with the natural frequency of the isolation system. The electromagnetic actuator was designed and the control effect was verified by the experiment. The experiment showed that the electromagnetic actuator is effective for controlling the low frequency isolation resonance response of the precision equipment.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 춘계학술대회논문집
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• pp.623-627
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• 2001

Suppression of very low-frequency noise from an automobile exhaust system is difficult due mainly to its large wave length. Therefore, the configuration of total exhaust system, i,e., piping and muffler layout, is important at low frequencies. In this paper, an optimal layout technique of exhaust systems has been developed for reducing low-frequency exhaust noise. For this purpose, system insertion loss and virtual attenuation coefficient have been defined by considering the effects of mean flow and temperature gradient in the pipe. The applicability of present method is investigated with an actual automobile exhaust system and an optimized layout of pipes and mufflers is suggested.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1998년도 유체기계 연구개발 발표회 논문집
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• pp.166-172
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• 1998

This paper describes the shaft vibration phenomena measured on a pump-turbine ofa pumped storage power plant. The pump-turbine runs at a rotational speed of 450 rpm (7.5 Hz). The power output (load) of the pump-turbine was varied from 100 to 300 MW in the generating mode. It was found that the magnitude of the shaft vibration was highly dependent upon the power load. The vibration magnitude of the shaft vibration is very high in the middle load zone from 170 to 210 MW, elsewhere the vibration low. From vibration spectra, it was found that the frequency of major vibration in that load zone was 2.5 Hz which is approximately $34\%$ of the shaft rotating speed in Hz. This frequency component disappeared below and above that load zone. This subsynchronous vibration is caused by the flow induced disturbance due to spiral vortex flow downstream of the pump-turbine runner. Furthermore, it was found that shaft vibration was highly decreased due to the increase of bearing preload.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.606-611
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• 2000

It has been noted that the low frequency absorption coefficient of a porous sample placed in a standing wave tube is affected by the nature of the sample's edge constraint. The edge constraint has the effect of stiffening the solid phase of the sample, which itself can be strongly coupled to the material's fluid phase, and hence the incident sound field, by viscous means at low frequencies. In recent work it has also been shown that such a circumferential constraint causes the low frequency transmission loss of a layer of fibrous material to approach a finite low frequency limit that is proportional to the flow resistance of the layer and which is substantially higher than that of an unconstrained sample of the same material. However, it was also found that the benefit of the circumferential edge constraint was reduced in a transitional frequency range by a shearing resonance of the sample. Here it will be shown that the effect of that resonance can be mitigated or eliminated by adding additional axial and radial constraints running through the sample. It will also be shown that the constraint effect can be modeled closely by using a finite element procedure based on the Biot poroelastic theory. Implications for low frequency barrier design are also discussed.

• 센서학회지
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• 제21권4호
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• pp.298-302
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• 2012

This paper describes the design and fabrication of a low frequency vibration driven high-efficiency electromagnetic energy harvester based on FR(Flame Resistance)-4 spring which converts mechanical energy into useful electrical power. The fabricated generator consists of a vertically polarized NdFeB permanent magnet attached to the center of spring and a planar type copper coil which has higher efficiency compare with cylindrical type coil. ANSYS finite analysis and Matlab were used to determine the resonance frequency and output power. The generator is capable of producing up to 1.36 $V_{pp}$ at 9 Hz, which has the maximum power of 639 ${\mu}W$ with a load resistance of $3.25k{\Omega}$.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.234-237
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• 2007

To protect a satellite and electronic equipment from the acoustic load generated by rocket propulsion system, many launch vehicle use acoustic blanket. Acoustic load is main source of random vibration working on the payload. Most high frequency region of the acoustic loads is reduced by payload fairing skins and acoustic blanket, but low frequency region is not. In order to reduce acoustic load of low frequency region, we designed array resonator panel which was made of composite materials. Insertion loss capacity of the payload fairing with acoustic blanket was verified from PLF acoustic test in the acoustic chamber.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2009년도 춘계학술대회 논문집
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• pp.394-402
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• 2009

To investigate the heavy-weight impact noise of apartment houses, numerical analysis was performed. The analysis acoustic pressure consider acoustic mode by finite element method. The variables considered effecting on the acoustic pressure are the Acoustic mode, acoustic damping, and the impulse load. The heavy-weight impact noise is a changeable value in the room. Since the most part of the frequency component of heavy-weight impact noise has low frequency. The noise in low frequency is related to the vibration of structure, the reflection of acoustic wave caused by wall and the standing wave called by acoustic mode. The prediction by the numerical analysis was verified with test result of the heavy weight-impact noise at apartment houses.

• Transactions on Electrical and Electronic Materials
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• 제13권3호
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• pp.125-128
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• 2012

This paper describes the design, simulation and characterization of an AA size electromagnetic energy harvester that is capable of converting environmental vibration into electrical energy. A magnetic spring technique is used to scavenge energy from low frequency external vibrations. The generator is characterized by ANSYS 2D finite element analysis, and optimized in terms of moving mass, fixed magnet size, coil width and load resistance. The optimized energy harvester is able to generate 53.5 mW of average power at 8.1 Hz resonance frequency, with a displacement of 0.5 mm.

• 로봇학회논문지
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• 제11권2호
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• pp.73-82
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• 2016

This paper focuses on the vibration analysis of planar cable-driven parallel robots on their configurations. Despite of many advantages of the cable robots, elasticity of the cables may cause the vibration at the existence of external disturbance, resulting in deterioration of positioning accuracy. According to the vibration theory, having high first order natural frequency can prevent resonance with low frequency disturbance from the surrounding environment. A series of simulations showed that choosing frame / end-effector shape and cable connection method affects robots' natural frequency. For the precise simulation, the cables are modeled as linear springs and axial vibration of cables is mainly considered. Aspect ratios of the frame and end-effector are defined as non-dimensional parameters while their areas are fixed. It was shown that vibration analysis guides to design a planar cable robot in terms of high capacity to reduce vibration.