• Journal of the Korean Wood Science and Technology
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• v.51 no.6
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• pp.470-480
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• 2023

This study aimed to develop a sound-absorbing composite using sugarcane bagasse (SB) and coffee silver skin (CS) as raw materials. The composite boards were manufactured by bonding the fibers with Melamine Urea-Formaldehyde adhesive, ensuring a consistent thickness of 30 mm. Various densities were employed, namely 380, 450, and 520 kg/m³. The samples were fabricated with different fiber ratios, including SB100%, SB75% with CS25%, and SB50% with CS50%. The sound absorption coefficient (SAC) and noise reduction coefficient (NRC) were measured using the impedance tube method within a frequency range of 63-6,300 Hz. The experimental results revealed that the mixing ratio of CS exerted a notable influence on enhancing the SAC, while the density of the composite board exhibited a significant impact on increasing both the SAC and NRC. Among the densities tested, the optimal value was observed at 520 kg/m³, yielding a SAC value of 0.65 at a frequency of 1,000 Hz and an NRC value of 0.55 for the SB50-CS50 composite plate. These findings underscore the importance of considering the CS mixing ratio and composite board density when aiming to optimize sound absorption properties.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.5
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• pp.833-839
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• 2003

The effects of stiffeners on the modal characteristics of rectangular plates are investigated. A modeling method for the modal analysis of rectangular plates with stiffeners is presented. A mass density Dirac's delta function is used to idealize the stiffeners mathematically. The equations of motion for the plates are derived and transformed into a dimensionless form. To confirm the accuracy of the method presented in this study, numerical result are obtained and compared to those of a commercial program. The mode shape variations due to some parameter variations are also exhibited.

• Structural Engineering and Mechanics
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• v.65 no.4
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• pp.491-504
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• 2018

Because of sandwich structures with low weight and high stiffness have much usage in various industries such as civil and aerospace engineering, in this article, buckling and free vibration analyses of coupled micro composite sandwich plates are investigated based on sinusoidal shear deformation (SSDT) and most general strain gradient theories (MGSGT). It is assumed that the sandwich structure rested on an orthotropic elastic foundation and make of four composite face sheets with temperature-dependent material properties that they reinforced by carbon and boron nitride nanotubes and two flexible transversely orthotropic cores. Mathematical formulation is presented using Hamilton's principle and governing equations of motions are derived based on energy approach and applying variation method for simply supported edges under electro-magneto-thermo-mechanical, axial buckling and pre-stresses loadings. In order to predict the effects of various parameters such as material length scale parameter, length to width ratio, length to thickness ratio, thickness of face sheets to core thickness ratio, nanotubes volume fraction, pre-stress load and orthotropic elastic medium on the natural frequencies and critical buckling load of double-bonded micro composite sandwich plates. It is found that orthotropic elastic medium has a special role on the system stability and increasing Winkler and Pasternak constants lead to enhance the natural frequency and critical buckling load of micro plates, while decrease natural frequency and critical buckling load with increasing temperature changes. Also, it is showed that pre-stresses due to help the axial buckling load causes that delay the buckling phenomenon. Moreover, it is concluded that the sandwich structures with orthotropic cores have high stiffness, but because they are not economical, thus it is necessary the sandwich plates reinforce by carbon or boron nitride nanotubes specially, because these nanotubes have important thermal and mechanical properties in comparison of the other reinforcement.

• Journal of Ocean Engineering and Technology
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• v.24 no.6
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• pp.61-70
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• 2010

This study presents free vibration analyses of perforates steel plates with various cutouts. Four different parameters (shape, size, curvature radius ratio, and rotation of cutouts) were considered to investigate the effects of those parameters on the free vibration characteristics, such as natural frequencies of the perforated steel plates. Three different shapes of cutouts are circle, square, and triangle, and the considered sizes are 5, 10, 15, 20, and 25 mm. For the triangular and square cutouts, the characteristic radii of the inscribed circles of those cutouts were defined. In addition, the curvature radius ratio was defined as the ratio of curvature radius of bluntness and the characteristic radius. Then, total seven different curvature radius ratios (0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1) were considered. To investigate the rotation effect of the cutouts, it was considered four rotations ($0^{\circ}$, $15^{\circ}$, $30^{\circ}$, and $45^{\circ}$) for the square cutouts and three rotations (0, 15, and 30) for the triangular cutouts. All the free vibration analyses were conducted using a general purpose finite element program. From the analyses we found that the most influential parameter for the free vibration response of the perforated plates is the size of cutout. The other factors such as the shape, curvature radius ratio, and rotation are minors; they mainly change the natural frequency as long as the size effect is accompanied.

• Journal of Industrial Technology
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• v.20 no.B
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• pp.125-130
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• 2000

Heat dissipation technology using flow resonant phenomenon is a kind of new concept in heat transfer area. A vibration exciter is needed to generate air turbulence which has the natural shedding frequency of heat system. A mechanical vibrating device for the air flow oscillation is introduced, which is driven by a moving coil actuator. An analytical dynamic model for this mechanical vibration exciter is presented and its validity is verified by the comparison with experimental data. Values of some unknown system parameters in the analytic model are estimated through the system identification approach. Based on this mathematical model, a high bandwidth vibration phase, it turns out the high modal resonant characteristics of vibrating plate are the major barrier against obtaining a high bandwidth vibration exciter.

• Advances in nano research
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• v.10 no.1
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• pp.25-42
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• 2021

In this article, the vibration behavior of embedded Functionally Graded Nanoplate (FGNP) employing nonlocal Kirchhoff's plate theory has been investigated under hygrothermal environment. The FGNP is considered to be supported by Winkler-Pasternak foundation. The Eringen's differential theory is used for size effect on the vibration of the FGNP. Rayleigh-Ritz method with orthogonal polynomials are employed for the governing equations and edge constraints. The advantage of this method is that it overcomes all the drawbacks of edge constraints and can easily handle any combinations of mixed edge constraints. The coefficients viz. moisture expansion, thermal expansion and elastic coefficients are considered to be transversely graded across the FGNP. The similarity of the calculated natural frequencies is examined with the previous research, and a good concurrency is seen. The objective of this article is to analyze the parameters' effect on the nondimensionalized frequency of embedded FGNP under hygrothermal environment subjected to all possible edge constraints. For this, uniform and linear rise of temperature and moisture concentration are considered. The study highlights that the nonlocal effect is pronounced for higher modes. Moreover, the effect of the Pasternak modulus is seen to be prominent compared to the Winkler modulus on non dimensionalized frequencies of FGNP.

• Journal of Industrial Technology
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• v.21 no.B
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• pp.125-132
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• 2001

Heat dissipation technology using flow resonant phenomenon is a kind of new concept in heat transfer area. A vibration exciter is needed to generate air turbulence which has the natural shedding frequency of heat system. A mechanical vibrating device for the air flow oscillation is introduced, which is driven by a moving coil actuator. An analytical dynamic model for this mechanical vibration exciter is presented and its' validity is verified by the comparison with experimental data. Values of some unknown system parameters in the analytic model are estimated through the system identification approach. Based on this mathematical model, the vibration exciter using strain displacement estimator is developed. And in the experiment, the feedback control is used. During the experimental verification phase, it turns out the high modal resonant characteristics of vibrating plate are the major barrier against obtaining a high bandwidth vibration exciter.

• Smart Structures and Systems
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• v.26 no.5
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• pp.619-629
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• 2020

Solar towers, which often has a large aspect ratio and low fundamental natural frequency, were extremely prone to large amplitude of wind-induced vibrations, especially Vortex-Induced Vibration (VIV). A tiny Tuned Mass Damper (TMD) with conveniently adjustable eddy current damping was specially designed and manufactured for elastic wind tunnel tests of a solar tower. A series of numerical simulations by using the COMSOL software were conducted to determine three key parameters, including the thickness of the back iron plate and the conductive plate (T_b and T_c), the distance between the magnet and the conductive plate (T_d). Based on the results of numerical simulations, a tiny TMD was manufactured and its structural parameters were experimentally identified. The optimized values of the tiny TMD can be conveniently realized. The tiny TMD was installed at the top of the elastic test model of a 243-meter-high solar tower, and a series of wind tunnel tests were carried out to examine the effectiveness of the TMD in suppressing wind-induced responses of the test model. The results showed that the wind-induced responses could be obviously reduced by the TMD, especially in the cross-wind direction. The cross-wind RMS and peak responses at the critical wind velocity can be reduced by about 86% and 75%, respectively. However, the maximum reduction of the responses at the design wind velocity is about 45%, obviously less than that at the critical wind velocity.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.1A
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• pp.191-203
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• 2006

The vibration characteristics of composite stiffened laminated plates with stiffener is presented using the assumed natural strain 9-node shell element. To compare with previous research, the stiffened plates are composed of carbon-epoxy composite laminate with a symmetric stacking sequence. Also, the result of the present shell model for the stiffener made of composite material is compared with that of the beam model. In the case of torsionally weak stiffener, a local buckling occurs in the stiffener. In this case, the stiffener should be idealized by using the shell elements. The current investigation concentrates upon the vibration analysis of rectangular stiffened and unstiffened composite plates when subjected to the in-plane compression and shear loads. The in-plane compression affect the natural frequencies and mode shapes of the stiffened laminated composite plates and the increase in magnitude of the in-plane compressive load reduces the natural frequencies, which will become zero when the in-plane load is equal to the critical buckling load of the plate. The natural frequencies of composite stiffened plates with shear loads exhibit the higher values than the case of without shear loads. Also, the intersection, between the curves of frequencies against in-plane loads, interchanges the sequence of some of the mode shapes as a result of the increase in the inplane compressive load. The results are compared with those available in the literature and this result shows that the present shell model for the stiffened plate gives more accurate results. Therefore, the magnitude, direction type of the in-plane shear and compressive loads in laminated composite stiffened plates should be selected properly to control the specific frequency and mode shape. The Lanczos method is employed to solve the eigenvalue problems.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.63-68
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• 2001

An experimental study was carried out to identify the various regimes of natural convective boiling and to determine the Critical Heat Flux(CHF) on a 70mm square surface which is inclined at $180^{\circ}$(upward), $90^{\circ}, \;45^{\circ}$. The heater block made of copper with cartridge heaters is submerged in a water tank with windows for visualization. As the heat flux increases from $100kW/m^2$ to $1.1MW/m^2$, the heat transfer regime migrates from the nucleate boiling to film boiling and results in a rapid heat up of the heater block. An explosive vapor generation on the heated surface, whose size and frequency are characterized by the heat flux, is visualized by using a digital camcorder with $512{\times}512$ pixel size at 30fps.