• International Journal of Aeronautical and Space Sciences
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• v.4 no.1
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• pp.9-18
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• 2003

In this work, a closed-form analysis is performed for the structural response of coupled composite blades with multi-cell sections. The analytical model includes the effects of shell wall thickness, transverse shear, torsion warping and constrained warping. The mixed beam approach based on Reissner's semi-complementary energy functional is used to derive the beam force-displacement relations. The theory is validated against experimental test data and other analytical results for coupled composite beams and blades with single-cell box-sections and two-cell airfoils. Correlation of the present method with experimental results and detailed finite element results is found to be very good.

• Journal of Communications and Networks
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• v.9 no.4
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• pp.466-472
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• 2007

Single carrier block transmission with frequency domain equalization(SC-FDE) has been shown to be a promising candidate in ultra-wideband(UWB) communications. In this paper, we analyze the performance of SC-FDE over UWB communications with channel estimation error. The probability density functions of the frequency domain minimum mean-squared error(MMSE) equalizer taps are derived in closed form. The error probabilities of single carrier block transmission with frequency domain MMSE equalization under imperfect channel estimation are presented and evaluated numerically. Compared with the simulation results, our semi-analytical analysis yields fairly accurate bit error rate performance, thus validating the use of the Gaussian approximation method in the performance analysis of the SC-FDE system with channel estimation error.

• Structural Engineering and Mechanics
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• v.53 no.6
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• pp.1167-1182
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• 2015

In this study, the stresses and electric potential redistributions of a cylinder made from functionally graded piezoelectric material (FGPM) are investigated. All the mechanical, thermal and piezoelectric properties are modeled as power-law distribution of volume fraction. Using the coupled electro-thermo-mechanical relations, strain-displacement relations, Maxwell and equilibrium equations are obtained including the time dependent creep strains. Creep strains are time, temperature and stress dependent, the closed form solution cannot be found for this constitutive differential equation. A semi-analytical method in conjunction with the Mendelson method of successive approximation is therefore proposed for this analysis. Similar to the radial stress histories, electric potentials increase with time, because the latter is induced by the former during creep deformation of the cylinder, justifying industrial application of such a material as efficient actuators and sensors.

• Proceedings of the KSR Conference
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• 2004.10a
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• pp.1407-1412
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• 2004

Impedance calculations of electric railway traction systems is essential to define characteristics and to design it. The self impedance is defined voltage drop rate per unit length, the mutual impedance is represented as a voltage induced to transmission line from transmission line. The self and the mutual impedance are influenced by ground return currents. The earth is considered as a semi-infinitely extended non-ideal conductor. The current of transmission line produces earth current induced magnetically and it flow through a path having minimum impedance. Carson proposed the impedance calculation formula using wave equations and magnetic field equations. Though the formula have an improper equation, that is still used as a standard impedance calculation method. This paper introduced an impedance calculation method that the complex depth of earth return method assumes that the current in conductor returns through an imagined earth depth path located directly under original conductor at a depth of. In this paper, we showed that this proposed method has a closed form and is easier than Carson's.

• Proceedings of the KIPE Conference
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• 2005.07a
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• pp.697-700
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• 2005

An adaptive fuzzy sliding-mode controller (SMC) for uncertain or ill-defined single-input single-output (SISO) nonaffine nonlinear systems is proposed. By using the universal approximation property of the fuzzy logic system (FLS), it is tuned on-line to cancel the unknown system nonlinearity. We adopt a self-structuring FLS to guarantee global stability of the closed-loop system rather than semi=global boundedness. The control and adaptive laws are derived so that the estimated fuzzy parameters are bounded and the sliding condition is satisfied.

• Journal of Power Electronics
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• v.9 no.4
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• pp.526-534
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• 2009

This paper introduces the electronic ballast for high pressure sodium (HPS) lamps which provides power regulation during the whole lamp life without using a closed-loop power control system, in spite of large variations of lamp characteristics resulting from lamp aging. The structure of the electronic ballast and the parameters of HPS lamps are described. A mathematical model for the ballast is developed and used for the design and analysis of the ballast. A design procedure is presented to design the ballast which provides intrinsic power regulation over the whole lamp life. To improve the technical specifications of the ballast, the practical and standard constraints are considered in the design. According to the design procedure, an electronic ballast for 250-W HPS lamps is designed. All theoretical analyses are verified with the help of a semi-industrial experimental setup. The results validate that the designed ballast provides power regulation during the whole lamp life.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.11a
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• pp.161-164
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• 2000

In this paper, a finite element structural analysis for thin-walled open-section composite beams with elastic couplings has been performed. The analysis includes the effects of transverse shear across beam sections, torsion warping and constrained warping. Reissner's semi-complementary energy functional is used to obtain the beam st illness coefficients The bending and torsion related warpings and the shear correct ion factors are obtained as part of the analysis. The resulting theory describes the beam kinematics in terms of the axial, flap and lag bending, flap and lag shear, torsion and torsion-warping deformations. The static response has been validated against finite element predict ions, closed form solutions, and experimental data for rectangular sol id and I-beams with elastic couplings. The free vibration results are also compared with available literature.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.3142-3147
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• 2008

A simple transient simulation of ground source heat pump system was carried out to investigate the effects of ground thermal conductivity on its performance. The TRNSYS code with a simple water to water heat pump model was used to compare the COP variation of the system. A new ground heat exchanger called by semi-closed loop was proposed and constructed in the real site. The effective thermal conductivity was measured using the test equipment developed by according to the line source model. The simulation results showed that highly efficient thermal conductivity of the grout material could increase the performance of the heat pump system very well. And the new ground heat exchanger showed the increased effective thermal conductivity as the penetration water flow rate(PWFR) was increased. Therefore, the performance improvement of the heat pump system using the proposed ground heat exchanger can be expected.

• Structural Engineering and Mechanics
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• v.54 no.4
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• pp.649-664
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• 2015

In this study, the authors present an analytical approach to find the axisymmetric buckling load of two joined isotropic conical shells under axial compression. The problem of two joined conical shells may be considered as the generalized form of joined cylindrical and conical shells with constant or stepped thicknesses. Thickness of each cone is constant; however it may be different from the thickness of the other cone. The boundary conditions are assumed to be simply supported with rigid rings. The governing equations for the conical shells are obtained and solved with an analytical approach. A simple closed-form expression is obtained for the buckling load of two joined truncated conical shells. Results are compared and validated with the numerical results of finite element method. The variation of buckling load with changes in the thickness and semi-vertex angles of the two cones is studied. Finally, application of the results in practical design and range of engineering validity are investigated.

• East Asian mathematical journal
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• v.37 no.5
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• pp.577-584
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• 2021

Let p : X → D be a proper surjective holomorphic submersion where X is a Kähler manifold and D is the unit disc in ℂ. Let Ω be a d-closed semi-positive real (1, 1)-form on X. If each X_s := p^-1(s) for s ∈ D satisfies $-c_1(X_s)+{\Omega}{\mid}_{X_s}$ is Kähler, then the Kähler-Ricci flow twisted by ${\Omega}{\mid}_{X_s}$ has a long time solution by Cao's theorem. This family of twisted Kähler-Ricci flows induces a relative Kähler form ω(t) on the total space X. In this paper, we prove that the positivity of ω(t) is preserved along the twisted Kähler-Ricci flow.