• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.490-493
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• 2004

A 3-DOF actuator which has new principle and very simple structure is proposed. Its principle seems to be similar to conventional electromagnetic actuators, that is, to utilize the relation of control and bias fluxes produced by coils and permanent magnets, respectively, but the coils and permanent magnets of the proposed actuator are fixed in the stator. Such a structure helps to optimally design the actuator for its use. Some experimental and FEM analysis results show the feasibility of the proposed actuator and some characteristics of system that are useful lot structure design and control.

• Proceedings of the Acoustical Society of Korea Conference
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• 1994.06a
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• pp.770-774
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• 1994

The volume of an acoustic source is important in determining various acoustic parameters. One of the suggested techniques is the internal pressure method incorporating a loudspeaker attached to a chamber wall and a microphone inserted into the cavity. Although the method is easy to handle with a very simple measurement setup, the coupling effects between the dynamic system of the loudspeaker and acoustic field, and the effects of higher order modes introduced by the discontinuities in the acoustic field, and the effects of higher order modes introduced by the discontinuities in the acoustic field should be considered for precise result. In this study, higher order modes due to the discontinuities of loudspeaker and microphone boundaries are included and the electro-acoustic coupling effects are compensated for by using the results of two cylinders with different lengths. The volume velocity of a loudspeaker thus obtained agrees very with that measured by laser sensor.

• Wind and Structures
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• v.29 no.1
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• pp.33-41
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• 2019

The interaction of head waves with an infinite row of identical, equally spaced, rectangular breakwaters is investigated in the presence of uneven bottom topography. Using linear water wave theory and matched eigenfunction expansion method, the boundary value problem is transformed into a system of linear algebraic equations which are numerically solved to know the velocity potentials completely. Utilizing this method, reflected and transmitted wave energy are computed for different physical parameters along with the wave field in the vicinity of breakwaters. It is observed that the wave field becomes more complicated when the incoming wavelength becomes smaller than the channel width. A critical ratio of the gap width to the channel width, corresponding to the inflection point of the transmitted energy variation, is identified for which 1/3 of the total energy is transmitted. Similarly, depending on the incident wavelength, there is a critical breakwater width for which a minimum energy is transmitted. Further, the accuracy of the computed results is verified by using the derived energy relation.

• International Journal of High-Rise Buildings
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• v.10 no.2
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• pp.109-116
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• 2021

This paper explores the meaning and importance of tuning amongst other Tuned Mass Damper (TMD) parameters and describes processes to help ensure that an as-built TMD is properly tuned to the as-built high-rise building. A summary of key TMD components and TMD implementations will be presented as an introduction and review. Next, it will be shown that tuning is a means for optimizing TMD performance. A process using modal characterization tests during tower construction to estimate natural frequencies of the completed tower will be described. Finally, the use of a Frequency Response Function (FRF) as a means for verifying the frequency of a TMD will be proposed.

• Advances in aircraft and spacecraft science
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• v.11 no.2
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• pp.105-128
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• 2024

Vibrations in aerodynamic systems can lead to significant structural and performance issues. This paper presents a novel theorem for actively controlling aerodynamic vibrations through parametric stability analysis. The proposed approach models the aerodynamic system as a dynamic system with parametric excitation, allowing for the identification of stable and unstable regions in the parameter space. By strategically adjusting the system parameters, the vibrations can be effectively suppressed, enhancing the overall reliability and performance of the aerodynamic system. The theoretical underpinnings of the theorem are discussed, and the effectiveness of the approach is demonstrated through numerical simulations and experimental validation. The results show the potential of this method for practical implementation in various aerodynamic applications, such as aerospace engineering and wind turbine design.

• Explosives and Blasting
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• v.32 no.2
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• pp.1-8
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• 2014

In this study, 16 test blastings had been carried out with different spacings, burdens, drilling lengths, and charges per delay for investigating the characteristics of ground vibration propagation, which depends on the delay time. From the tests, it was possible to derive a ground vibration equation. Using the equation, the characteristics of ground vibration could be investigated by analyzing the nomogram and predicting the Peak Particle Velocity (PPV), which are influenced by the delay time and the priming location. The trend of ground vibration change depending on the delay time was analyzed for the standards charges of 0.5, 1.6, 5, and 15 kg, which were suggested in "Blasting design and construction guidelines to road construction" by the Ministry of Land, Infrastructure and Transport. From the study, it would be possible to suggest a favorable vibration control method, which depends on the charge.

• Journal of the Earthquake Engineering Society of Korea
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• v.3 no.1
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• pp.103-112
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• 1999

This is study to estimate the pump induced vibration in time and frequency domain by frequency response function between two points in case of 20Hp and 50Hp centrifugal pumps. The frequency response function has real and imaginary information of signals, and response function has also real and imaginary information. So the vibration force can be obtained from the response function and frequency response function by complex calculation. And it is compared with the theoretically estimated values and it is suggested that the amplitude of vibration with main frequency is about 10~25% of pump and motor weight, and the magnitude of unbalanced mass is about 30~60% of pump and motor weight to estimated vibration force in time domain. There are the other kinds of vibration components with different frequency values of 2~3 times of its main frequency, and these kinds of information are used to control the tuning ratio between operating frequency of pump and structural frequency of concrete slab.

• Journal of the Korean Society for Precision Engineering
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• v.30 no.7
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• pp.762-768
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• 2013

This study investigated the effect of whole-body vibration on muscle function and muscular reaction in the knee joint. We recruited thirty healthy subjects and divided them into a training group, who experienced whole-body vibration, and a control group, who did not. The training group performed whole-body vibration exercises for 30 min per day, 3 days a week, for 8 weeks. We measured knee joint torque to estimate muscle strength and reaction, using BIODEX System 3. Knee joint peak torque and total work performed increased significantly in the training group, and muscle acceleration time decreased. These results suggest that stimulation by whole-body vibration can improve muscle strength and reaction by improving muscle tone and increasing blood temperature and flow speed in muscular fiber. Our results also indicate that 4 weeks of exercise with whole-body vibration is required to improve the reaction response, and six weeks to improve strength.

• Tunnel and Underground Space
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• v.24 no.1
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• pp.97-109
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• 2014

In order to identify the characteristics of the propagation depending on delay time (20, 25 ms) and priming location (top priming, middle priming, bottom priming), test blasts were carried out a total of 4 times using different spacing, burden, drilling length, charge per delay and was derived the formula to predict blast vibration. This study investigated the characteristics of vibration by analysis of the nomogram and prediction of Peak Particle Velocity (PPV) from delay time and priming location by the formula to predict ground vibration. And it analyzed the trends of vibration increase by standards charge 0.5, 1.6, 5, 15 kg. Standards charge is "Blasting design and construction guidelines to road construction" by the Ministry of Land, Infrastructure and Transport. Depending on the charge in favor of vibration control method is proposed. Thus, when the design was to be used as a variable.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.5
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• pp.385-393
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• 2013

In this paper, the mechanism identification and the avoidance measures on the phenomena of transient acoustic vibration amplified at the water-supply piping system to regulate the steam temperature of the boiler reheater in 500MW class supercritical power plant are presented. The pressure pulsation waves induced by the impeller passing of two feed-water pumps with five blades are coincident with the local acoustic modes of boiler reheater water-supply piping system. There are the phenomena amplified at the peaks of 5X, 10X, 15X and 20X in spectrums of piping vibration, sound pressure, and the feed-water's pressure pulsation waves. The shut-off device is installed in the piping system for the interception of pressure pulsation waves transmitted from two feed-water pumps and the modified design change of the piping layout is applied for the acoustic resonance avoidance. The acoustic natural frequencies are separated from the harmonics of pressure pulsation waves induced by the pump impellers passing through the design change of the span length. The acoustic vibration is gone by resonance avoidance measures. As a result, more than 20 dBA reduction is achieved from 100 dBA to 80 dBA.