• Journal of Mechanical Science and Technology
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• v.16 no.3
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• pp.320-326
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• 2002

A modeling method for the vibration analysis of rotating composite cantilever plates is presented in this paper. The coupling effects between inplane motions and the bending motion are considered and explicit mass and stiffness matrices are derived for the modal analysis. Numerical results are obtained and some of them are compared to those of a commercial program to confirm the accuracy of the present method. Numerical results show that the coupling effects become important only when laminates are stacked up unsymmetrically. Incidentally, natural frequencies loci veering, loci crossing, and associated mode shape variations are observed.

• Journal of Fisheries and Marine Sciences Education
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• v.19 no.3
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• pp.383-389
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• 2007

To evaluate the performance of heat exchanger with rotating porous plates, the experimental investigation was carried out under various conditions. With an equal interval of 18 mm inside the heat exchanger, the rotating porous plates are mounted. The hot and cold airs enter at opposite ends of heat exchanger and exchange heat each other. In order to measure the temperature distribution of the hot air side inside heat exchanger, the thermocouples are inserted between the plates. The first location of thermocouple is 10 mm downstream from the inlet of heat exchanger, and succeeding ten locations are aligned at an equal interval of 18 mm. As a result of the measurement, the temperature distribution inside heat exchanger was constant as the hot air temperature of inlet is low. It was found that the heat transfer rate does not depend on the variation of RPM at the lower temperature of inlet. The heat transfer rate at the higher temperature of inlet increased a little with the increase in RPM.

• Wind and Structures
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• v.13 no.2
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• pp.127-144
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• 2010

Pressure measurements on static and autorotating flat plates have been recently reported by Lin et al. (2006), Holmes, et al. (2006), and Richards, et al. (2008), amongst others. In general, the variation of the normal force with respect to the angle of attack appears to stall in the mid attack angle range with a large scale separation in the wake. To date however, no surface pressures have been measured on auto-rotating plates that are typical of a certain class of debris. This paper presents the results of an experiment to measure the aerodynamic forces on a flat plate held stationary at different angles to the flow and allowing the plate to auto-rotate. The forces were determined through the measurement of differential pressures on either side of the plate with internally mounted pressure transducers and data logging systems. Results are presented for surface pressure distributions and overall integrated forces and moments on the plates in coefficient form. Computed static force coefficients show the stall effect at the mid range angle of attack and some variation for different Reynolds numbers. Normal forces determined from autorotational experiments are higher than the static values at most pitch angles over a cycle. The resulting moment coefficient does not compare well with current analytical formulations which suggest the existence of a flow mechanism that cannot be completely described through static tests.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.10a
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• pp.173-176
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• 1997

A refined plate theory including the effects of transverse shearing is used to predict the free vibration frequencies, mode shapes and stress distributions in spinning laminated composite plates. In this theory, the displacements are expressed by trigonometric series representation through the thickness. In the series for the displacements only the first few terms are retained. The model is validated by comparing the results for isotropic plates with those available in the literature.

• Journal of the Korean Society for Precision Engineering
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• v.32 no.3
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• pp.243-251
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• 2015

In order to develop an automatic system for welding thin steel plates with curvature such as the corrugated membranes of an LNG storage tank, a rotating mechanism should be firstly designed for the torch to easily follow the weld seam with a constant distance and angle. In this study, a torch rotating mechanism consisting of three circular links, two square-type links and a torch link was proposed for automation of the welding process. A weld-seam tracking system with two axis slides and the proposed rotating mechanism was successfully simulated with a dynamic simulation software. A prototype tracking system was manufactured and a tracking test with the system was then carried out. The test results with tracking system showed that the rotating mechanism could be implemented and it was feasible to be used in automatic tracking of weld seam with curvature.

• Journal of the Korea Institute of Military Science and Technology
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• v.10 no.3
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• pp.16-24
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• 2007

The high-frequency analysis method of back-scattering cross section spectrum of rotating targets is established. The time history of the back-scattering cross section is calculated using a quasi-stationary approach, based on a physical optics and a physical theory of diffraction, combining an adaptive triangular beam method to consider the shadow effect. And the spectra of back-scattering cross section by the Doppler effect are analyzed applying a simple fast Fourier transform method to its time history. The numerical calculation for rotating targets, such as rotating metal plates and underwater propeller, are carried out. The time history appears to be periodic with respect to the number of wings. The backscattering cross section spectrum level and its frequency shift are dependent on the rotating speed, direction, and the shape of the targets.

• Current Optics and Photonics
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• v.6 no.5
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• pp.445-452
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• 2022

We developed an adaptive optics test bench using an optical simulator and two rotating phase plates that mimicked the atmospheric turbulence at Bohyunsan Observatory. The observatory was reported to have a Fried parameter with a mean value of 85 mm and standard deviation of 13 mm, often expressed as 85 ± 13 mm. First, we fabricated several phase plates to generate realistic atmospheric-like turbulence. Then, we selected a pair from among the fabricated phase plates to emulate the atmospheric turbulence at the site. The result was 83 ± 11 mm. To address dynamic behavior, we emulated the atmospheric disturbance produced by a wind flow of 8.3 m/s by controlling the rotational speed of the phase plates. Finally, we investigated how closely the atmospheric disturbance simulation emulated reality with an investigation of the measurements on the optical table. The verification confirmed that the simulator showed a Fried parameter of 87 ± 15 mm as designed, but a little slower wind velocity (7.5 ± 2.5 m/s) than expected. This was because of the nonlinear motion of the phase plates. In conclusion, we successfully mimicked the atmospheric disturbance of Bohyunsan Observatory with an error of less than 10% in terms of Fried parameter and wind velocity.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.11
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• pp.1-7
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• 1995

The problem of amplitude-and frequency-modulated waveforms is analyzed when a linearly polarized electromagnetic wave is scattered by a slowly rotating rotor with metal plates. ECM in conjunction with a quasi-stationary method is used to analyze the modulated waveforms. The modulated waveforms depend on the orientation and dimension of the object. its rotation speed, and very strongly on the incident and scattering directions. The modulate waveforms of a rotating non-skewed metal plate and a rotor with two blades are functions of twice the rotating frequency of those. Similar results are discussed for a rotating skewed metal plate, but the modulated waveforms is a function of the rotating frequency. Numerical results based on our ECM are presented and compared with those of Sikta's and PO solution.

• Wind and Structures
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• v.13 no.2
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• pp.169-189
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• 2010

This paper describes the use of coupled Computational Fluid Dynamics (CFD) and Rigid Body Dynamics (RBD) in modelling the aerodynamic behaviour of wind-borne plate type objects. Unsteady 2D and 3D Reynolds Averaged Navier-Stokes (RANS) CFD models are used to simulate the unsteady and non-uniform flow field surrounding static, forced rotating, auto-rotating and free-flying plates. The auto-rotation phenomenon itself is strongly influenced by vortex shedding, and the realisable k-epsilon turbulence modelling approach is used, with a second order implicit time advancement scheme and equal or higher order advection schemes for the flow variables. Sequentially coupling the CFD code with a RBD solver allows a more detailed modelling of the Fluid-Structure Interaction (FSI) behaviour of the plate and how this influences plate motion. The results are compared against wind tunnel experiments on auto-rotating plates and an existing 3D analytical model.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.9
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• pp.2082-2088
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• 1995

In this paper, we designed and fabricated the magnetic bearings and built-in type cylindrical capacitive transducers for improving the vibration characteristics of rotating shaft. The eddy current and magnetic field from the electromagnet of the bearing don't affect the measuring signal of the capacitive type transducers so that it is possible to locate the capacitive sensor plates around the magnetic bearing poles and can improve the spillover problem which is induced by the noncollocation of the sensors and actuators. According to the sensitivity calibration schemes using a X-Y table, the cylindrical capacitive transducers have a good linearities in the .+-.70.mu.m range from the geometric center of the sensor plates. The measured results also show high displacement sensitivities of the sensors. According to the performance test of the magnetic bearing which is controlled by the analog PD controllers, we found that the built-in capacitive transducer system successfully measures the journal displacement in the magnetic field and therefore the magnetic bearing system supports the rotating shaft up to 12,000 rpm.