• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2704-2707
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• 2008

We perform an active control on flow over a circular cylinder using a synthetic jet at Re=3900. The synthetic jet is issued from a cavity located inside the cylinder, generating a train of vortices near the surface. These vortices interact with and weaken the main vortices, resulting in drag reduction at a high frequency.

• Journal of Magnetics
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• v.12 no.3
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• pp.113-117
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• 2007

Here we report a theoretical description of ferromagnetic vortex dynamics. Based on Thiele's formulation of the Landau-Lifshitz-Gilbert equation, the motion of the vortex core could be described by a function of the vortex core position. Under a parabolic potential generated in the circular magnetic patterns, the vortex core showed a circular rotation-namely the gyrotropic motion, which could be described by a 2-dimensional simple harmonic oscillator. The gyrotropic frequency and apparent damping constant were predicted and compared with the values obtained micromagnetic calculation.

• Journal of Ocean Engineering and Technology
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• v.15 no.1
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• pp.12-18
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• 2001

This study concentrates on the second-order diffraction problem around circular cylinders in multi-frequency waves. The method of solution is a time-domain Rankine panel method which adopts a higher-order approximation for the velocity potential and wave elevation. In the present study, the multiple second-order quadratic transfer functions are extracted from the second-order time signal generated in random waves, and the comparison with other bench-mark test results shows a good agreement. This approach is directly applicable to prediction of nonlinear forces on offshore structures in random ocean.

• Journal of electromagnetic engineering and science
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• v.10 no.1
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• pp.39-44
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• 2010

In this paper, a compact wideband antenna with a band-notch function is proposed. It operates over the UWB band with a band-stop characteristic. To increase the impedance bandwidth, a ring-shaped radiator is used. By attaching a circular stub to the ring-shaped radiator, the band-notch performance is obtained. The proposed antenna operates over a frequency range from 2.7 GHz to 11 GHz to satisfy the 10-dB return-loss requirement and provides band-stop performance in the frequency band from 5.15 GHz to 6.1 GHz. Experimental results reveal that the proposed antenna exhibits good radiation performance and is suitable for UWB applications.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.11 no.2
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• pp.34-38
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• 2012

In this paper, the particle swarm optimization (PSO) algorithm is adopted to design a modified ring-slot type patch rectenna with a resonance frequency of 2.45GHz. In order to accomplish minimization of dimensions and circular polarization (CP) and harmonic suppression, axial direction slits and side-cuts are added to the patch of the ring. The PSO manipulated this kind of multi-dimensional problem very well, and as a result, the designed rectenna shows a desirable performance of return loss of 21.36dB and axial ratio of 2.92dB at the frequency of 2.45GHz with compact sizing.

• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.75-80
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• 2009

The present paper focuses on the analysis of aero-acoustics characteristic by several boundary conditions. In this simulation, a high-order and high-resolution numerical schemes are used for the accurate computation of compressible flow with several boundary conditions including characteristic boundary conditions as well as extrapolation and zonal characteristic boundary condition. These boundary conditions are applied to the computation of two dimensional circular cylinder flows with Mach number of 0.3 and Reynolds number of 400. The computation results are validated with measurement datum and other computation results for the Strouhal frequency of vortex shedding, the mean drag coefficient and root-mean-square lift for the unsteady periodic flow regime. Secondary frequency is predicted by three kinds of boundary conditions characteristic.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.5
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• pp.468-474
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• 2002

In this paper a novel two-arm microstrip spiral antenna with a circular slot on the ground plane is presented. The proposed antenna structure is constructed in a planar form without a balun circuit and the radiation characteristics of conventional and eccentric spiral antennas are obtained simultaneously. The main beam direction is normal to the plane of the spiral for characteristic frequency band and the direction of the main beam moves linearly into $\theta$ and $\phi$ direction as the frequency increases.

• Journal of electromagnetic engineering and science
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• v.13 no.1
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• pp.34-37
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• 2013

This paper presents a novel ultra-wideband (UWB) antenna that rejects narrow and broad bands and is suitable for wireless communications. The base of the proposed antenna has a circular patch that can cover the UWB frequency range (3.1~10.6 GHz). The interference issues caused by co-existence within the UWB operation frequency are overcome by a design that uses a parallel-coupled asymmetric dual-line with a circular monopole antenna. The proposed antenna showed a stable radiation pattern, realized gain and reflection coefficient lower than -10 dB across the UWB operation bandwidth except for 5.15~5.85 GHz and 7.25~8.4 GHz. The fabrication, simulation, and measurement results obtained for the proposed antenna were in good agreement with the expected values.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.3
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• pp.230-235
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• 2004

This paper deals with the free vibration analysis of circular strip foundations with the variable breadth. Taking into account effects of both rotatory inertia and shear deformation, differential equations governing free vibrations of such foundations are derived. The Winkler foundation is chosen as the model of soil foundation. The breadth of strip foundation is assumed to be a linear function. The differential equations are solved numerically to calculate natural frequencies. In numerical examples, the strip foundations with the hinged-hinged, hinged-clamped. clamped-hinged and clamped-clamped end constraints are considered. The parametric studies are conducted and the lowest four frequency parameters are reported in figures as the non-dimensional forms.

• Steel and Composite Structures
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• v.14 no.4
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• pp.397-408
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• 2013

This paper deals with multiobjective optimization of symmetrically laminated composite truncated circular conical shells subjected to external uniform pressure load and thermal load. The design objective is the maximization of the weighted sum of the critical buckling load and fundamental frequency. The design variable is the fibre orientations in the layers. The performance index is formulated as the weighted sum of individual objectives in order to obtain optimal solutions of the design problem. The first-order shear deformation theory (FSDT) is used in the mathematical formulation of laminated truncated conical shells. Finally, the effect of different weighting factors, length-to-radius ratio, semi-cone angle and boundary conditions on the optimal design is investigated and the results are compared.