• Journal of Korean Society of Steel Construction
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• v.14 no.1
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• pp.1-12
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• 2002

To obtain more accurate responses of laminated composite structures, the effect of transverse shear deformation, transverse normal strain/stress and a nonlinear variation of in-plane displacements with respect to the thickness coordinate need to be considered in the analysis. The improved higher-order theory is used to determine the deflections and natural frequencies of laminated composite structures. A quasi-elastic method is used for the solution of viscoelastic analysis of the laminated composite plates and sandwiches. Solutions of simply-supported laminated composite plates and sandwiches are obtained and the results are compared with those by the 3D elasticity theory and other theories. The improved theory proposed in this paper is shown to predict the deflections and natural frequencies more accurately than all other theories.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.2 no.3
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• pp.75-86
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• 1982

The degeneration of two classes of thick beam elements has been conducted, one (DB6) based on the conventional Timoshenko beam assumptions whereas the other (DB7) based on the assumed cubic axial displacement profile. While an adjustable shear correction factor is required for the DB 6 element to compensate for the unrealistic distribution of shear strain across the thickness, the DB 7 element assumes the more realistic quadratic profile of shear strain at the outset. With the plane-stress continuum solution as reference, solutions obtained by these two element models are compared with the analytical Timoshenko solution, the analytical thin beam solution and several available solutions of other existing beam elements. The result indicates that the performance of the higher order beam element DB 7 is consistently superior to any others. This is true for the whole range of aspect ratios of beam, in both static and free vibration analyses.

• The Journal of the Acoustical Society of Korea
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• v.35 no.4
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• pp.253-260
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• 2016

In this paper, derivation of the STL (Sound Transmission Loss) of the double plates installed in an impedance tube is discussed using an analytic method, where an air cavity exists between the plates. Vibration of the plates and sound pressure field inside the tube are expressed in terms of infinite series of modal functions. Under the plane wave assumption, it is shown that consideration of the first few modes yields sufficiently accurate results, and locations of peaks and dips are investigated. It is determined that the peak frequencies of the double plates coincide with those of each single plate. When the two plates are identical, the STL of the double plates as well as that of the single plate become zero at the natural frequencies of the single plate. The location and amplitude of the dips are investigated using an approximation solution when the cavity depth is very small.

• Journal of Korean Society of Steel Construction
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• v.9 no.4 s.33
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• pp.601-609
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• 1997

Bending and vibration results for a laminated plate base on a simplified higher-order plate theory with four variables are presented. Assuming a constant in-plane rotation tensor through the thickness in Reddy's higher-order shear deformation theory it is shown that a simpler higher-order theory can be obtained with the reduction of one variable without significant loss in the accuracy. This simple higher-order shear deformation theory is then used for predicting the natural frequencies and deflection of simply-supported laminated composite plates. The results obtained for antisymmetrical laminated composite plates compare favorably with third-order and first-order shear deformation theory. The information presented should be useful to composite-structure designers, to researchers seeking to obtain better correlation between theory and experiment and to numerical analysts in checking out their programs.

• Structural Engineering and Mechanics
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• v.25 no.4
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• pp.481-500
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• 2007

The dynamic instability of doubly curved panels, subjected to non-uniform tensile in-plane harmonic edge loading $P(t)=P_s+P_d\;{\cos}{\Omega}t$ is investigated. The present work deals with the problem of the occurrence of combination resonances in contrast to simple resonances in parametrically excited doubly curved panels. Analytical expressions for the instability regions are obtained at ${\Omega}={\omega}_m+{\omega}_n$, (${\Omega}$ is the excitation frequency and ${\omega}_m$ and ${\omega}_n$ are the natural frequencies of the system) by using the method of multiple scales. It is shown that, besides the principal instability region at ${\Omega}=2{\omega}_1$, where ${\omega}_1$ is the fundamental frequency, other cases of ${\Omega}={\omega}_m+{\omega}_n$, related to other modes, can be of major importance and yield a significantly enlarged instability region. The effects of edge loading, curvature, damping and the static load factor on dynamic instability behavior of simply supported doubly curved panels are studied. The results show that under localized edge loading, combination resonance zones are as important as simple resonance zones. The effects of damping show that there is a finite critical value of the dynamic load factor for each instability region below which the curved panels cannot become dynamically unstable. This example of simultaneous excitation of two modes, each oscillating steadily at its own natural frequency, may be of considerable interest in vibration testing of actual structures.

• Smart Structures and Systems
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• v.25 no.1
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• pp.111-122
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• 2020

Researchers up to date have introduced several Structural Health Monitoring (SHM) techniques with varying advantages and drawbacks for each. Satellite positioning systems (GPS, GLONASS and GALILEO) based techniques proved to be promising, especially for high natural period structures. Particularly, the GPS has proved sufficient performance and reasonable accuracy in tracking real time dynamic displacements of flexible structures independent of atmospheric conditions, temperature variations and visibility of the monitored object. Tall structures are particularly sensitive to oscillations produced by different sources of dynamic actions; such as typhoons. Wind forces induce in the structure both longitudinal and perpendicular displacements with respect to the wind direction, resulting in torsional effects, which are usually more complex to be detected. To efficiently track the horizontal rotations of the in-plane sections of such flexible structures, two main issues have to be considered: a suitable sensor topology (i.e., location, installation, and combination of sensors), and the methodology used to process the data recorded by sensors. This paper reports the contributions of the measurements recorded from dual frequency GPS receivers and uni-axial accelerometers in a full-scale experimental campaign. The Canton tower in Guangzhou-China is the case study of this research, which is instrumented with a long-term structural health monitoring system deploying both accelerometers and GPS receivers. The elaboration of combining the obtained rather long records provided by these two types of sensors in detecting the torsional behavior of the tower under ambient vibration condition and during strong wind events is discussed in this paper. Results confirmed the reliability of GPS receivers in obtaining the dynamic characteristics of the system, and its ability to capture the torsional response of the tower when used alone or when they are combined with accelerometers integrated data.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.6
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• pp.569-574
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• 2011

In research vessels or naval ships, airborne noise from machineries such as diesel engine is the major source of underwater noise at low speed. In this paper, effect of engine noise on underwater noise is studied by considering two paths; sound radiation from hull plate and direct airborne noise transmission through hull plate. SEA (Statistical energy analysis) is used to predict hull plate vibration induced by engine noise, where SEA model consists of only two subsystems; engine room air space and hull plate. The pressure level in water is calculated from sound radiation by plate. Engine noise transmission through hull plate is obtained by assuming plane wave propagation in air-limp plate-water system. Two effects are combined and compared to the measurement, where speaker is used as a source in engine room and sound pressure levels in engine room and water are measured. The hydrophone is located 1 m away from the hull plate. It is found below 1000 Hz, prediction overestimates underwater sound pressure level by 5 to 12 dB.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.64.1-64.1
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• 2011

MIRIS (Multipurpose Infra-Red Imaging System), is a small infrared space telescope which is being developed by KASI, as the main payload of Science and Technology Satellite 3 (STSAT-3). Two wideband filters (I and H) of the MIRIS enables us to study the cosmic infrared background by detecting the absolute background brightness. The narrow band filter for Paschen ${\alpha}$ emission line observation will be employed to survey the Galactic plane for the study of warm ionized medium and interstellar turbulence. The opto-mechanical design of the MIRIS is optimized to operate around 200K for the telescope, and the cryogenic temperature around 90K for the sensor in the orbit, by using passive and active cooling technique, respectively. The engineering and qualification model of the MIRIS has been fabricated and successfully passed various environmental tests, including thermal, vacuum, vibration and shock tests. The flight model was also assembled and is in the process of system optimization to be launched in 2012 by a Russian rocket. The mission operation scenario and the data reduction software is now being developed. After the successful mission of FIMS (the main payload of STSAT-1), MIRIS is the second Korean space telescope, and will be an important step towards the future of Korean space astronomy.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.1
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• pp.225-234
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• 2019

By using the Triboelectric nanogenerators, known as TENG, we can take advantages of high conversion efficiency and continuous power output even with small vibrating energy sources. Nonlinear energy extraction techniques for Triboelectric vibration energy harvesting usually requires synchronized active electronic switches in most electronic interface circuits. This study presents a nonlinear energy harvesting with high energy conversion efficiency to harvest and save energies from human active motions. Moreover, the proposed design can harvest and store energy from sway motions around different directions on a horizontal plane efficiently. Finally, we conducted a comparative analysis of a multi-mode energy storage board developed by a silicon-based piezoelectricity and a transparent TENG cell. As a result, the experiment showed power generation of about 49.2mW/count from theses multi-fully harvesting source with provision of stable energy storages.

• International Journal of Clinical Preventive Dentistry
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• v.14 no.4
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• pp.228-234
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• 2018

Objective: The authors have experimented for the artificial plaque removal effect of several kinds of 360 degree rotating head typed tooth-brushes with sonic vibratory actioned by using of automatic machine for horizontal scrub method in order to find the better toothbrush type for plaque removal. Methods: The experiment was conducted on three medium to 360 degree rotating head toothbrushes, a medium sized toothbrush and a medium sized toothbrush, and a flat toothbrush consisting of 30 ordinary toothbrushes. A brushing machine with horizontal scrubbing was manufactured and had variations of the end of the bristle attached to or near the surface of the teeth, a vibrating wave action force of 16,000 or 18,000 cycles per minute, and a working time of 2 or 3 minutes. The tooth removal effect was confirmed by scanning and analyzing images with a computer program after automatic brushing with the machine. The elimination rate results for each group were analyzed using the independent t-test and one-way ANOVA test. Results: It revealed the most in removal effect for the artificial plaque in such conditions as action at near the tooth surface with 18,000 cycle for 3 minutes in case of using A, B, and C tooth-brush. And it has more removal effect rate than for using the plane tooth-brush (p<0.05). Conclusion: It was recommended to develop the 360 degree rotating head and vibratory toothbrush focusing to use near the tooth surface with 18,000 cycles of vibration for 3 minutes at one site of the teeth area.