• Journal of Advanced Research in Ocean Engineering
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• v.3 no.4
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• pp.193-203
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• 2017

This study investigated the steady-flow effects present in the numerical computation of the resistance added to a ship in waves. For a ship advancing in the forward direction, a time-domain 3D Rankine panel method is applied to solve the ship motion problem, and the added resistance due to waves is calculated using a near-field method, with the direct integration of the second-order pressure on the hull surface. In the linear potential theory, the steady flow is approximated by the basis potential of a uniform flow or double-body flow in order to linearize the boundary conditions. By applying these two different linearization schemes, the coupling effects between steady and unsteady solutions were examined. Furthermore, in order to analyze the steady-flow effects on the hull geometry, the computation results for two realistic hull forms, a KVLCC2 tanker and DTC containership, were compared. In particular, the mj term, which represents the coupling effects under the body boundary condition, was evaluated considering the geometry of a non-wall-sided ship. Lastly, the characteristics of the linearization schemes were examined in relation to the disturbed waves around a ship and the components of added resistance.

• Journal of KSNVE
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• v.7 no.1
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• pp.43-53
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• 1997

This paper investigated the practical use for measuring the structural intensity (power flow per width of cross section) in a uniform semi-infinite beam in flexural vibration. The structural intensity is obtained as a vector at a measurement point, One-dimensional structural intensity can be obtained from 4-point cross spectral measurement, or 2-point measurement on the assumption of far field. The measurement errors due to finite difference approximation and phase mismatch of accelerometers are examined. For precise measurements, it would be better to make the value of k$\delta$(wave number x space between accelerometers) between 0.5 and 1.0. Formulation of the relation between bending waves in structures and structural intensity makes it possible to separate the wave components by which one can get a state of the vibration field. Experimental results are obtained from 2- and 4-point measurement performed at 200mm (near field) and 400mm (far field) apart from excitation point in random excitation. the results are compared with the theoretical values and measured values of input power spectrum in order to verify the accuracy of structural intensity method, 2-point method is suggested as the practical structural intensity method.

• Journal of the Korean Mathematical Society
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• v.51 no.1
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• pp.87-98
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• 2014

Let R be a commutative ring with identity and M an R-module. In this paper, we associate a graph to M, say ${\Gamma}(M)$, such that when M = R, ${\Gamma}(M)$ is exactly the classic zero-divisor graph. Many well-known results by D. F. Anderson and P. S. Livingston, in [5], and by D. F. Anderson and S. B. Mulay, in [6], have been generalized for ${\Gamma}(M)$ in the present article. We show that ${\Gamma}(M)$ is connected with $diam({\Gamma}(M)){\leq}3$. We also show that for a reduced module M with $Z(M)^*{\neq}M{\backslash}\{0\}$, $gr({\Gamma}(M))={\infty}$ if and only if ${\Gamma}(M)$ is a star graph. Furthermore, we show that for a finitely generated semisimple R-module M such that its homogeneous components are simple, $x,y{\in}M{\backslash}\{0\}$ are adjacent if and only if $xR{\cap}yR=(0)$. Among other things, it is also observed that ${\Gamma}(M)={\emptyset}$ if and only if M is uniform, ann(M) is a radical ideal, and $Z(M)^*{\neq}M{\backslash}\{0\}$, if and only if ann(M) is prime and $Z(M)^*{\neq}M{\backslash}\{0\}$.

• Journal of Institute of Convergence Technology
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• v.5 no.2
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• pp.27-32
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• 2015

Air intakes are an essential component of aircraft engines. They are mainly used to offer uniform airflows to engine faces. Fighter aircraft have to mask the engine face inside the fuselage in order to reduce the Radar Cross Section(RCS). Therefore, offset intakes like a S-Duct are one of promising components for this purpose. During a fight, it is unavoidable that the flow will enter the intakes at some face angles other than zero. In this case, the performance of the aircraft engine will be influenced to the angle of incidence. In this study, the CFD analysis of the semi-circular S-Duct with AR(0.5,0) is performed to investigate the influence of the angle of incidence on the performance of the S-Duct using a distortion coefficient. To consider the adverse pressure gradient, a $k-{\omega}$ SST turbulence model is employed. The secondary flow and flow separation are observed for all computational cases. It is found that the positive incidence angle produces the best performances.

• Journal of Electrical Engineering and Technology
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• v.3 no.1
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• pp.36-42
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• 2008

In a gas insulated substation (GIS), Very Fast Transient Over-voltages (VFTOs) are generated due to switching operations and ground faults. These fast transients are associated with high frequency components of the order of a few hundreds of MHz. These transients may cause internal faults i.e., layer-to-layer faults or minor faults in a capacitively graded bushing, which is one of the important pieces of terminal equipment for GIS. In the present study, the PSPICE model has been developed to calculate the voltage distribution across the layers of 420kV graded bushing for high frequency pulses of rise time 1 to 50ns, which simulate the VFTO. For this simulation, an equivalent electrical network of bushing with different equivalent layers has been considered. The effect of different equivalent layers modeling circuits on the non-uniform voltage factor has been analysed. The influence of copper strip inductance on voltage distribution across layers has also been analysed for various rise times of high frequency transients. Finally, the leakage current of the bushing is calculated for evaluating the bushing condition under these transients.

• Steel and Composite Structures
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• v.29 no.1
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• pp.53-66
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• 2018

A high-order nonlocal strain gradient model is developed for wave propagation analysis of porous FG nanoplates resting on a gradient hybrid foundation in thermal environment, for the first time. Material properties are assumed to be temperature-dependent and graded in the nanoplate thickness direction. To consider the thermal effects, uniform, linear, nonlinear, exponential, and sinusoidal temperature distributions are considered for temperature-dependent FG material properties. On the basis of the refined-higher order shear deformation plate theory (R-HSDT) in conjunction with the bi-Helmholtz nonlocal strain gradient theory (B-H NSGT), Hamilton's principle is used to derive the equations of wave motion. Then the dispersion relation between frequency and wave number is solved analytically. The influences of various parameters (such as temperature rise, volume fraction index, porosity volume fraction, lower and higher order nonlocal parameters, material characteristic parameter, foundations components, and wave number) on the wave propagation behaviors of porous FG nanoplates are investigated in detail.

• International Journal of Aeronautical and Space Sciences
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• v.12 no.1
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• pp.1-15
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• 2011

This paper reviews most of the research done in the field of tensile buckling characteristics pertaining to aerospace structural elements with special attention to local buckling and parametric excitation due to periodic loading on plate and shell elements. The concepts of buckling in aerospace structures appear as the result of the application of a global compressive applied load or shear load. A less usual situation is the case, in which a global tensile stress creates buckling instability and the formation of complex spatial buckling pattern. In contrast to the case of a pure compression or shear load, here the applied macroscopic load has no compressive component and is thus globally stabilizing. The instability stems from a local compressive stress induced by the presence of a defect, such as a crack or a hole, due to partial or non-uniform applied load at the far end. This is referred to as tensile buckling. This paper discusses all aspects of tensile buckling, theoretical and experimental. Its far reaching applications causing local instability in aerospace structural components are discussed. The important effects on dynamic stability behaviour under locally induced periodic compression have been identified and influences of various parameters are discussed. Experimental results on simple and combination resonance characteristics on plate structures due to tensile buckling effects are elaborated.

• The Journal of the Korea Contents Association
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• v.4 no.4
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• pp.79-87
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• 2004

In this paper, we propose a probability map based genetic algorithm to detect lips from portrait image. The existing genetic algorithm used to get an optimal solution is modified in order to get multiple optimal solutions for lips detection. Each individual consists of two chromosomes to represent coordinates x, y in space. Also the algorithm introduce a preserving zone in the population, a modified uniform crossover, a selection without individual duplication. Using probability map of H, 5 components, the proposed algorithm has adaptability in the segmentation of objects with similar colors. In experiments, we analyzed relationships of primary parameters and found that the algorithm can apply to the detection of other ROIs easily

• Korean Journal of Materials Research
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• v.22 no.1
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• pp.8-15
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• 2012

Silicon-based thin film was prepared at room temperature by an electrochemical deposition method and a feasibility study was conducted for its use as an anode material in a rechargeable lithium battery. The growth of the electrodeposits was mainly concentrated on the surface defects of the Cu substrate while that growth was trivial on the defect-free surface region. Intentional formation of random defects on the substrate by chemical etching led to uniform formation of deposits throughout the surface. The morphology of the electrodeposits reflected first the roughened surface of the substrate, but it became flattened as the deposition time increased, due primarily to the concentration of reduction current on the convex region of the deposits. The electrodeposits proved to be amorphous and to contain chlorine and carbon, together with silicon, indicating that the electrolyte is captured in the deposits during the fabrication process. The silicon in the deposits readily reacted with lithium, but thick deposits resulted in significant reaction overvoltage. The charge efficiency of oxidation (lithiation) to reduction (delithiation) was higher in the relatively thick deposit. This abnormal behavior needs to clarified in view of the thickness dependence of the internal residual stress and the relaxation tendency of the reaction-induced stress due to the porous structure of the deposits and the deposit components other than silicon.

• Water for future
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• v.16 no.4
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• pp.221-236
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• 1983

In semi-enclosed shallow sea areas typified by the Yellow sea and the East China Sea, currents and sea surface variations are predominantly tidal. During the recent years two-dimensional numerical hydrodynamic model of the Yellow Sea and the East China Sea has been developed, based on the vertically-integrated equations of motion and continuity, capable of reproducing amplitudes and phases of the principal components of tides to satisfiable accuracy. As a subsequent development a three-dimensional hydrodynamical nymerical model covering the Yellow Sea and the East China Sea has been formulated to investigate the vertical distribution of horizontal tidal current and the response of the continented to investigate the vertical distribution of horizontal tidal current and the response of the continental shelf sea to steady uniform wind stress field imposed over the surface. Features of the M2 tidal current and the wind-induced three-dimensional current structure determined from the computation have been examined and discussed.