• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.383-389
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• 2013

Rotor system is a very important part which produces lift, thrust and control force in helicopter. Component of rotor system must endure various flight load for the required life. In helicopter rotor system, bearingless rotor system is the highest technology rotor system compare with articulated and hingeless rotor system. Baaringless rotor system is not include mechanical flap hinge, lag hinge and pitch bearing. Bearingless rotor component flexbeam which made by composite material has conduct hinge and bearing role instead of mechanical flap hinge, lag hinge and pitch bearing. These characteristics has less part number and lass weight than others. In this paper, conduct safe life analysis of bearingless composite component flexbeam and torque tube applying to utility helicopter load condition.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.97-99
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• 2013

We introduced an earthquake-resistant design using acoustic rnetamaterials. There are two way in that field: one is a cloaking method and the other is a shadow zone method of seismic waves. Cloaking is a general property of a wave that changes the direction depending on the refractive index. Metamaterials control the propagation and transmission of specified parts of the wave and demonstrate the potential to render an object seemingly invisible. The shadow zone is a method of negative modulus using many huge resonators and it attenuates the amplitude of the wave exponentially. We compared and explained the fimdarnental principles of the two methods.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.1
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• pp.67-73
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• 2002

The flexibility of long reach manipulators presents a difficult control problem when accurate end-point position is required. Input shaping by convolving system commands with impulse sequences has been shown to be an effective method of reducing residual vibrations in flexible systems. However, existing shapers have been considered robustness fur only frequency uncertainty. However, this paper presents new multi-hump convolution(CV) input shaper that could accommodate with the simultaneous variation of natural frequency and damping ratio. Comparisons with previously proposed input shapers are presented to illustrate the qualities of the new input shaper. These new shapers will be shown to have better robustness fur the variation of frequency and damping ratio.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.324-329
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• 2003

An air-conditioner has various noise sources such as cooling fan noise, pumping noise, flow noise and impact noise. Among these, impact noise is the most unpleasant source. This is because the noise is produced in indoor unit of air-conditioner. To control the noise source effectively, first we must identify the noise sources. When we identify impact noise source, the measurement have to be carried out simultaneously. So we use beamforming method that requires less measurement points than intensity method and acoustic holography. The objective of this paper is to estimate the location of impact source. This objective can be achieved by using minimum variance cepstrum that is able to detect impulse embedded in noise. In this study, modified beamforming method based on cepstrum domain is proposed. Then this method applied to air-conditioner noise sources which produce impact noise.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.543-548
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• 2002

Nowadays since the customers of HDD's are interested in their noise levels in addition to their primary performances such as their average access time, capacity, HDD manufacturers make efforts on reducing the noise. The works to reduce noise are usually based on the measurable physical quantities such as SPL or acoustic intensity level. However, since the HDD noise is Judged by human beings, the basis of noise reduction should be human sensations. In this paper, the noise levels of various HDD's are evaluated by the human jury test to find a relationship between the physical quantities used for noise control and the human sensations of noise. Discrepancies are found in the judgments by the human beings and by the physical quantities. The loudness level, a psychoacoustic variable, is used to solve the discrepancy.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.134-139
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• 2002

We have made known the study of shape development of interference device for vehicle noise control. It's primary object greatly attenuate the noise due to transport vehicle by small products installed on the noise barrier edge. Also, it is able to improve the insertion loss of a noise barrier without increasing the height. The present time, we set up a newly manufactured products on the noise barrier edge and testify to it's the performance make use of an experiment and evaluation for the reduction of highway traffic noise. In this paper the frequency characteristic of interference device of noise barriers with attached newly developed products in terms of shape, absorptive material and split panel, are examined using field test at highway.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.10
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• pp.975-982
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• 2004

Helmholtz resonator is used to reduce noise of the narrow frequency band. It has high transmission loss at its resonance frequency. The silencer that combines many resonators could control broadband noise at low frequency. To convey this rather simple idea, serial and parallel arrangement of resonators have been tested to obtain high transmission loss characteristics in the band of which are selects. Theoretical and experimental results explain these characteristics in the absence of mean flow. The change of acoustic characteristics by the resonance frequencies and resonators arrangement are explained by using the equivalent Impedance analysis that is defined in this paper. It shows that the transmission loss has a maximum value when the separation distance between each resonator is λ/4 of its wavelength.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.10
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• pp.955-961
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• 2004

A novel concept of feedback loop design for modal test and model updating is proposed. This method uses the closed-loop natural frequency information for parameter modification to overcome the problems associated with the conventional method employing the modal sensitivity matrix. To obtain new modal information from closed-loop system, controllers should be effective in changing modal data while guaranteeing the stability of closed-loop system. But it is very hard to guarantee the stability of the closed-loop system with non-collocated sensor and actuator set. In this research, we proposed a controller called mode-decoupling controller that can change a target mode as much as the designer wants guaranteeing the stability of closed-loop system. This controller can be computed Just using measured open-loop modeshape matrix. A simulation based on time domain input/output data is performed to check the feasibility of proposed control method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.365-367
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• 2002

A parallelized topology optimization is applied to the design of a DVD-pickup bobbin, for which the design objective is to maximize the fundamental frequency within a given mass limit. Unlike the existing serial topology optimization, the present method can deal with a large number of design variables, and thus can yield practical and realistic results. The structural member-sizing filter is also employed to control the topological complexity of the optimized bobbin structure.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.226-233
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• 2003

There are many researches going on to develop the information storage devices using Blue-ray disc and DVD as a demand for high-density information storage devices is highly increasing. This high-density information storage device requires a short-wave laser and objective lens of high numerical aperture set in fer its operation. And, that brings out rapid decrease of tilt tolerance. Therefore, it is necessary that an actuator should control tilt motions to get a stable signal. In this paper, a new mathematical form of 3-D.O.F coupled model is formulated and magnetic circuit in constraints is most effectively designed with the use of the moving coil type actuator in higher sensitivity. Further, this paper presents a tilt coil whose rotational center point is put on that of the lens through the variation of tilt coil and proposes a 3-axis actuator with high sensitivity improved in its dynamic property through its structure analysis.