• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.4 s.97
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• pp.429-436
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• 2005

In turbomachinery rotor, there are small differences in the structural and/or geometrical properties of individual blades, which are referred to as blade mistuning. Mistuning effect of the forced response of bladed disks can be extremely large as often reported in many studies. In this paper, the pattern optimization of intentional mistuning for bladed disks considering with damping and coupling effect is the focus of the present investigation. More specifically, the class of intentionally mistuned disks considered here is limited, for cost reasons, to arrangements of two types of blades (A and B, say) and Genetic Algorithm and steepest descent method are used to optimize the arrangement of these blades around the disk to reduce the forced response of blade with different damping and coupling stiffness. Examples of application involving both simple bladed disk models and a 17-blade industrial rotor clearly demonstrate the significant benefits of using this class of intentionally mistuned disks.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.1
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• pp.9-15
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• 2010

In this paper, dynamic modeling of hull structure including surface-bonded piezoelectric composite actuator was developed and structural vibration control performance was evaluated. Cylindrical shell structure with end-caps was considered as a host structure which could be used as a simple model of fuselage of aircraft and underwater vehicles. An advanced piezoelectric composite, macro-fiber composite(MFC), which has been developed in NASA Langley Research Center was applied for the effective structural vibration control. MFC has great flexibility by using piezoceramic fiber sheet and enhanced piezoelectric effect for in-plane motion by utilizing interdigitated electrode. Governing Equations were derived from the finite element model and modal characteristics were investigated. Modal test was conducted to verify the finite element model. Optimal controller was designed and implemented for the evaluation of vibration control performance. Structural vibration was controlled effectively by applying proper control input to the piezoelectric actuators.

• Explosives and Blasting
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• v.41 no.1
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• pp.32-45
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• 2023

Environmental regulations in Korea for blasting at industrial sites have conservative standards, which often result in reduced efficiency and cost-effectiveness due to the consideration of environmental regulations and public complaints. Therefore, there is a need for blasting methods that can reduce environmental damage while improving construction efficiency and cost-effectiveness. In this study, we analyzed the effects of the PA-Deck (Paraffin Air-Deck) blasting method, which is a kind of Air Decoupled Charge method in principle utilizing a paraffin-infused paper tube as an air gap, on reducing blasting hazards and improving blasting efficiency. The analysis also evaluated the effectiveness of newly applied equipment for collecting blasting vibration data, and derived the relationship between the explosion velocity and vibration velocity of explosives, and performed frequency analysis of the vertical component. The results of the blasting vibration velocity analysis showed that the Paraffin Waxed Paper Tube-based blasting method exhibited significantly lower vibration velocities compared to conventional blasting methods, and it was judged that more uniformly small-sized fragmented rocks were generated.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.2
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• pp.75-83
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• 2023

In this paper, we present the analysis results on the vibration serviceability of a pedestrian bridge considering the effect of pedestrian moving mass inertia. Using dynamic finite element analysis, we considered different walking scenarios, including pedestrian density, walking speed, random walking, and synchronized walking, to analyze the acceleration response of a 40m long single-span bridge with a steel composite box cross section. We showed that the equivalent fixed mass analysis method did not significantly differ from the moving mass analysis in the random walk scenario and a wider frequency excitation band may be useful to consider when evaluating vibration serviceability in a random walk scenario.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.4
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• pp.399-408
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• 2010

The characteristics of lifted laminar propane flames diluted with nitrogen have been investigated experimentally to elucidate self-excitation and the effects of flame curvature. Flame oscillation modes are classified as follows: oscillation induced by heat loss, a combination of oscillations induced by heat loss and buoyancy, and a combination of the oscillations induced by heat loss and diffusive thermal instability. It is shown that the oscillation induced only by heat loss is not relevant to the diffusive thermal instability and hydrodynamic instability caused by buoyancy; this oscillation is observed under all lift-off flame conditions irrespective of the fuel Lewis number. These experimental evidences are displayed through the analysis of the power spectrum for the temporal variation of lift-off height. The possible mechanism of the oscillation induced by heat loss is also discussed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.6
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• pp.440-447
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• 2013

In this paper, a higher harmonic control (HHC) methodology is applied to find the optimum input scenario for the vibratory hub loads reduction. A comprehensive aeroelastic analysis code, CAMRAD II, is used to model the HART (Higher-harmonic-control Aeroacoustic Rotor Test) II rotor, and parametric study is conducted for the best HHC inputs leading to a minimum vibration (MV) condition. The resulting outcomes are compared with the earlier HART II test results. It is indicated that the control input adopted in the MV condition showed less satisfactory results. The new MV condition obtained in the present investigation can achieve 45% lower vibration level than the baseline uncontrolled condition. The optimum HHC input results lead to 3/rev harmonic input having $0.8^{\circ}$ amplitude and $350^{\circ}$ phase angle. About 5% reduction in the required power is possible but accompanies with the increase of vibration level.

• Composites Research
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• v.35 no.3
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• pp.134-138
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• 2022

In this study, Ti powder/Polymer concrete composites were processed by adding the PZT powder, one of the piezoelectric materials, to improve the vibration damping effect of Polymer concrete. Ti powder was added at a constant ratio in order to maximize the vibration damping effect using the piezoelectric effect. Three types of composite material specimens were prepared: a specimen without PZT powder, specimens with 2.5 wt% and 5 wt% of PZT powder. The vibration characteristics and compression properties were analyzed for all specimens. As a result, it was confirmed that as the addition ratio of PZT powder increased, the Inertance value at the resonant frequency decreased due to the piezoelectric effect when the vibration generated from Ti powder/polymer concrete was transmitted. Especially, the Inertance value was decreased by about 19.3% compared to the specimen without PZT at the resonant frequency. The change in acceleration with time also significantly decreased as PZT powder was added, confirming the effect of PZT addition. In addition, through the compression strength test, it was found that the degree of deterioration in compression properties due to the addition of PZT up to 5 wt% was insignificant, and it was confirmed that the powder was evenly dispersed in the composites through the cross-sectional analysis of the specimen.

• The Journal of the Acoustical Society of Korea
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• v.22 no.3
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• pp.217-223
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• 2003

A novel cooling method induced by acoustic streaming generated by ultrasonic vibration at 30㎑ is presented. Ultrasonic vibration is obtained by piezoelectric devices and the maximum vibration amplitude of 50 m is achieved by including a horn, mechanical vibration amplifier in the system and making the complete system resonate. To investigate the enhancement of heat transfer capability of acoustic streaming, the temperature variations of heat source and air in the vicinity of heat source are measured in real-time. It is observed that acoustic streaming is instantly induced by ultrasonic vibration, resulting in the significant temperature drop due to the bulk air flow caused by acoustic streaming. In addition, it is observed that the cooling effect on the heat source is maximized when the gap between the ultrasonic vibrator and heat source coincides with the multiples of half-wavelength of the ultrasonic wave. This fact results from the resonance of the sound wave. The theoretical analysis of the dependence on the gap is also accomplished and verified by experiment. The advantage of the proposed cooling method by acoustic streaming is noise-free due to the ultrasonic vibration and maintenance-free because of the absence of moving parts. Moreover. This cooling method can be utilized to the nano and micro-electro mechanical systems, where the fan-based conventional cooling method can not be employed.

• Journal of Bio-Environment Control
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• v.21 no.4
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• pp.437-444
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• 2012

This study was aimed to minimized the impact force and vibration transmitted to transporting agricultural product from the power tiller trailer by installing vibration absorption device. The vibration absorbable trailer (I) mounted with leaf spring suspension and shock absorber was developed and compared on vibration absorption performance with the existing trailer (E) equipped no vibration absorption device. In order to identify the vibration absorption effect of the trailer developed in this study, the vibration accelerations, occurred during driving on paved road with loading 360 kg of pear, were measured and analyzed using FFT analyzer. The magnitude of average vibration acceleration was decreased highly for the improved trailer mounted with vibration absorption device in comparing with existing trailer in the frequency range under 60 Hz and under 80 Hz. And similar vibration absorption effect was represented for the improved trailer in all frequency range. Especially, in the frequency range between 40 Hz and 80 Hz, the magnitude of vibration acceleration for the improved trailer was decreased with 1/3 times in comparing with existing trailer. So, the transporting loss including damage of agricultural product could be decreased highly by using the improved vibration absorbable trailer mounted with leaf spring suspension and shock absorber simultaneously, designed in this study.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.2
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• pp.1109-1117
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• 2014

We study free vibration analysis of sigmoid functionally graded materials(S-FGM) nano-scale plates, using a nonlocal elasticity theory of Eringen in this paper. This theory has ability to capture the both small scale effects and sigmoid function in terms of the volume fraction of the constituents for material properties through the plate thickness. Numerical solutions of S-FGM nano-scale plate are presented using this theory to illustrate the effect of nonlocal theory on natural frequency of the S-FGM nano-scale plates. The relations between nonlocal and local theories are discussed by numerical results. Further, effects of (i) power law index (ii) nonlocal parameters, (iii) elastic modulus ratio and (iv) thickness and aspect ratios on nondimensional frequencies are investigated. In order to validate the present solutions, the reference solutions are compared and discussed. The results of S-FGM nano-scale plates using the nonlocal theory may be the benchmark test for the free vibration analysis.