• Journal of Advanced Marine Engineering and Technology
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• v.12 no.2
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• pp.21-34
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• 1988

Machinery enclosures are widely adopted to reduce the noise emission in various fields of application. Emitted noise, which is due to the vibration of enclosure's outer surface, is composed of two kinds of sound with different path of propagation. One is the "structure-borne sound", while the other is "air-borne sound". In order to get a most efficient machinery enclouser a prudent consideration upon the above structure-borne and air-borne sound is required, as the guiding principle of contermeasure for each noise is quite different. The controlling of input vibration and its isolation are major subjects for the structure-borne sound, and the specifications of absorbing members and damping panels are the major related matters for the air-borne sound. Hence, it seems very efficient to separate the total sounds into two categories with a great accuracy when one think of further reduction of noise from the existing enclosure, although its separating methods have not been made clear for many years. Author proposes an application method of experimental modal analysis to extract the structure-borne sound from the measured total radiation sound, as the air-borne sound is deduced by the vectorial difference between the measured total radiation sound and the calculated structure-borne sound. In order to calculate the correct structure-borne sound by the excitation at an arbitrary point on the enclosure structure, it is important to decide 1) how to estimate the enclosure's surface vibration velocity and 2) how to compute the radiation sound which is considered as the effect of vibration modes of enclosure surface. The former can be solved with total frequency response function calculated by the application of experimental modal analysis. The latter is to be solved by the author's new approaches for radiation sound computation by means of the Rayleigh's integral equation and the boundary-element method applied complex surface vibration velocity. As a first step, structure-borne sound by the excitation at an arbitry point on the rectangular plate with fixed edges, has been calculated to verified the reliability of the developed computation methods. The results of calculation show good agreements with those of the actual measurements.actual measurements.

• Transactions of the Korean Society of Automotive Engineers
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• v.2 no.3
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• pp.21-32
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• 1994

The Problem of mechanical vibration is investigated for an automotive exhaust system. The vibrational reduction effect is systematically evaluated according to the attachment of the exhaust system. Moreover, the optimal attachment position of bellows is determined from the viewpoint of vibration isolation. The structure is analysed by the finite element technique where the geometry, the mass, the stiffness and the damping properties of the exhaust pipe are modeled. The validity of the developed model is verified by comparing with the experimental results. An optimization is carried out by the quadratic approximation algorithm. The reaction transferred to an automobile body by the hanger is considered ad the objective function. It is shown that the exhaust system which has the bellows at the optimal position is more effective for the vibrational characteristics than the others. It is also proved that this analytical method is quite useful in the design stage of the exhaust system.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.5
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• pp.414-422
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• 2013

As structure-borne sound, the floor impact sound is one of the serious noises in residential building. Most of heating system applied to the typical Korean residential building is floor heating system which is called ondol. The ondol usually consists of finishing material, mortar with heating coil, light-weight aerated concrete and reinforced concrete. This study focused on the isolation of heavy-weight impact sound and modification of mortar and light-weight aerated concrete. Specifically the glass foam aggregate was added on light-weight aerated concrete. Also, water-cement ratio and amount of cement on mortar were revised. The sound pressure level of heavy-weight impact was measured in reverberation chamber using both bang-machine and impact ball. The size of specimen was 1 m by 1 m. Substitution ratio of glass foam aggregate on light-weight aerated concrete shows relationship with heavy-weight impact sound pressure level. In addition, heavy-weight impact sound pressure level was decreased with increment of water-cement ratio and amount of cement on mortar.

• Earthquakes and Structures
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• v.6 no.2
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• pp.127-140
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• 2014

Laminated rubber bearing is very popular base isolation of earthquake engineering pertaining to the passive structural vibration control technologies. Rubber used in fabricating NRB and LRB can be easily attacked by various environmental factors such as oxygen, heat, light, dynamic strain, and organic liquids. Among these factors, this study carried out thermal aging test to investigate the effect of thermal aging on the mechanical properties of laminated rubber bearings in accelerated exposure condition of $70^{\circ}C$ temperature for 168 hours. The compressive-shear test was carried out to identify the variation of compressive and shear properties of the rubber bearings before and after thermal aging. In contrast to tensile strength and elongation tests, the hardness of rubber materials showed the increasing tendency dependent on exposure temperature and period. Based on the test results, the property changes of rubber bearing mainly aged by heat are quantitatively presented.

• Journal of KSNVE
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• v.9 no.3
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• pp.472-476
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• 1999

The effect of static preload on the dynamic properties of rubber materials is rather important, especially when good isolation characteristics are required at high frequencies. However, there are still few papers for dynamic characteristics of compressed rubber components. It was demonstrated in reference (4) that for bonded rubber material of a cylindrical shape, a simplified theory equation between linear dynamic and nonlinear static behavior of rubber material was useful to predict their combined effects. This paper presents the second part of the study. It is confirmed that for the compressed rubber material, the stress can be factored into a function of frequency and a function of strain(stretch). The finite element methodis applied to analyze non-linear large deformation of rubber material and its results are compared with those of a simplified theory equation. The predicted dynamic material properties based on non-linear static finite element analyses have a good agreement of experimental results and those based on simplified theory equation.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1151-1156
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• 2003

The dynamic properties of short-fiber reinforced Chloroprene rubber for vibration isolators have been studied as functions of interphase conditions and fiber content. The loss factor showed the maximum at strain amplitude 2%, and increased 0.09 for matrix, 0.05 for reinforced rubber with increasing frequency respectively. The dynamic ratio rapidly decreased with increasing strain amplitude, and some increased with increasing frequency. The better interphase condition showed the lower dynamic ratio. Therefore, the short-fiber reinforced rubber could have the better isolation in frequency ratio(${\sqrt{2}}min$.) compared to frequency ratio(${\sqrt{2}}max$.). And we have investigate the possibility of applying short-fiber reinforced rubber to automotive engine mount.

• Earthquakes and Structures
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• v.8 no.4
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• pp.889-913
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• 2015

Structural vibration characteristics of a semi-active base-isolated building were investigated using seismic observation records including those of the 2011 Great East Japan earthquake (Tohoku earthquake). Three different types of analyses were conducted. First, we investigated the long-term changes in the natural frequencies and damping factors by using an ARX model and confirmed that the natural frequency of the superstructure decreased slightly after the main shock of the Tohoku earthquake. Second, we investigated short-term changes in the natural frequencies and damping factors during the main shock by using the N4SID method and observed different transition characteristics between the first and second modes. In the second mode, in which the superstructure response is most significant, the natural frequency changed depending on the response amplitude. In addition, at the beginning of the ground motion, the identified first natural frequency was high possibly as a result of sliding friction. Third, we compared the natural frequencies and damping factors between the conditions of a properly functional semi-active control system and a nonfunctional system, by using the records of the aftershocks of the Tohoku earthquake. However, we could not detect major differences because the response was probably influenced by sliding friction, which had a more significant effect on damping characteristics than did the semi-active dampers.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.5
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• pp.41-48
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• 2005

The Rotating transmission is made up of belts, mass disks and gears. This transmission is controlled electro-mechanically by the motor and operation program. The control strategy of the system can be to change belts' stiffness and the masses of mass disk and gear. This system can be modeled as a rigid body, and also finds broad application in such diverse fields as machine tools, the cruise control system In automobiles, and control in the attitude and gimbals of spacecraft. This Transmission proves the necessity and effect of a closed loop control. The study of the Rotating Transmission excited by its base motion is able not only to predict the rotational performance, but to obtain the fundamental data for vibration isolation. In this research, we compared the response characteristics of the two controllers by means of the experiments on PD controller and PID controller added on integral action. Furthermore, we studied the response abilities such as steady state error, overshoot, and ect. and the response velocities such as rising time, settling time, and ect. in the rotating transmission.

• Earthquakes and Structures
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• v.24 no.5
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• pp.333-343
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• 2023

Various seismic isolation and reduction devices have been applied to suppress the longitudinal vibration of continuous girder bridges. As representative devices, lead rubber bearing (LRB) and fluid viscous damper (FVD) might suffer from deterioration during the long-term service. This study aims to evaluate the impact of device deterioration on the seismic responses of continuous girder bridges and investigate the seismic behavior of deteriorated LRBs and FVDs. Seismic performance of a simplified bridge model was investigated, and the influence of device deterioration was evaluated by the coefficient of variation method. The contribution of LRB and FVD was assessed by the Sobol global sensitivity analysis method. Finally, the seismic behaviors of deteriorated LRBs and FVDs were discussed. The result shows that (i) the girder-pier relative displacement is the most sensitive to the changes in the deterioration level, (ii) the deterioration of FVD has a greater effect on the structural responses than that of LRB, (iii) FVD plays a major role in energy dissipation with a low degradation level while LRB is more essential in dissipating energy when suffering from high degradation level, (iv) the deteriorated devices are more likely to reach the ultimate state and thus be damaged.

• Journal of Drive and Control
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• v.13 no.3
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• pp.8-14
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• 2016

This study describes the effect of the critical pressure ratio of a control valve on the performance of an air spring system composed of an air spring, auxiliary chamber, control valve and mass in order to suggest a more efficient design for an air spring system. The critical pressure ratio of the control valve is assumed to have a fixed value, but the critical pressure ratio of the control valve is known to have various values between 0.05 and 0.6, and the effect of the variation of the critical pressure ratio on the performance of the air spring system has not yet been reported. The analysis derives nonlinear and linear governing equations of the air spring system, including the critical pressure ratio of the control valve. This simulation study is presented to show that the impedance and transmissibility characteristics of the air spring system change due to variations in the critical pressure ratio of the control valve as well as its sonic conductance. As a result, the critical pressure ratio of the control valve should be maintained as large as possible to improve the vibration isolation characteristics of the air spring system.