• Communications of the Korean Mathematical Society
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• v.36 no.1
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• pp.165-171
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• 2021

The purpose of this paper is to investigate the geometry of complete gradient Yamabe soliton (Mn, g, f, λ) with constant scalar curvature admitting a non-homothetic conformal vector field V leaving the potential vector field invariant. We show that in such manifolds the potential function f is constant and the scalar curvature of g is determined by its soliton scalar. Considering the locally conformally flat case and conformal vector field V, without constant scalar curvature assumption, we show that g has constant curvature and determines the potential function f explicitly.

• Kyungpook Mathematical Journal
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• v.61 no.4
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• pp.781-790
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• 2021

The goal of this paper is to characterize a class of almost Kenmotsu manifolds admitting *-conformal Ricci solitons. It is shown that if a (2n + 1)-dimensional (k, µ)'-almost Kenmotsu manifold M admits *-conformal Ricci soliton, then the manifold M is *-Ricci flat and locally isometric to ℍⁿ⁺¹(-4) × ℝⁿ. The result is also verified by an example.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.1
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• pp.96-107
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• 2001

An unsteady numerical simulation was performed to analyze flow structures behind a local suction/blowing in a flat-plate turbulent boundary layer. The local forcing was given to the boundary layer flow by means of sinusoidally oscillating jet. A version of the unsteady $\kappa$-$\xi$-f(sub)u model (Rhee and Sung 2000) was employed. The Reynolds number based on the momentum thickness was about Re(sub)$\theta$=1700. The forcing frequency was varied in the range 0.011$\leq$f(sup)+$\leq$0.044 with a fixed forcing amplitude A(sub)o=0.4. The predicted results were compared and validated with the experimental data. It was shown that the unsteady locally-forced boundary layer flow is predicted well by the $\kappa$-$\xi$-f(sub)u model. The effect of the pitch angle of local forcing on the reduction of skin friction was also examined.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.221-225
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• 2009

A solar thermal collector is a solar collector specifically intended to collect heat: that is, to absorb sunlight to provide heat. A flat plate is the most common type of solar thermal collector, and is usually used as a solar hot water panel to generate solar hot water. A flat plate collector consists basically of an insulated metal box with a glass or a plastic cover and a dark-colored copper absorber plate. Solar radiation is absorbed by the copper absorber plate and transferred to water that circulates through the collector in copper tubes. Ultrasonic welding is an industrial technique whereby high-frequency ultrasonic acoustic vibrations are locally applied to work pieces being held together under pressure to create a solid-state weld. In this study, we developed solar collector ultrasonic welding machine with digital controlled power supply and tested various welding conditions such as welding pressure, welding amplitude, welding speed. Welding speed was considered in 2~12m/min. The width of ultrasonic welds was increased with welding amplitude by 2.2~2.5mm. The fracture load of ultrasonic welds showed 20% higher than domestic products.

• Bulletin of the Korean Mathematical Society
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• v.53 no.6
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• pp.1715-1723
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• 2016

We study the characteristic Jacobi operator ${\ell}={\bar{R}({\cdot},{\xi}){\xi}$ (along the Reeb flow ${\xi}$) on the unit tangent sphere bundle $T_1M$ over a Riemannian manifold ($M^n$, g). We prove that if ${\ell}$ is pseudo-parallel, i.e., ${\bar{R}{\cdot}{\ell}=L{\mathcal{Q}}({\bar{g}},{\ell})$, by a non-positive function L, then M is locally flat. Moreover, when L is a constant and $n{\neq}16$, M is of constant curvature 0 or 1.

• Bulletin of the Korean Mathematical Society
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• v.42 no.1
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• pp.5-15
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• 2005

The conharmonic transformation is a conformal trans-formation which satisfies a specified differential equation. Such a transformation was defined by Y. Ishii and we have generalized his results. Twisted product space is a generalized warped product space with a warping function defined on a whole space. In this paper, we partially classified the twisted product space and obtain a sufficient condition for a twisted product space to be locally Riemannian products.

• Transactions of the Korean Society of Automotive Engineers
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• v.2 no.3
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• pp.1-12
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• 1994

A model engine having a flat cylinder head and a piston face and an off-center intake valve is investigated in this analysis. Calculation domain is confined to the half of the cylinder with swirl free inlet velocity condition. Due to the absence of measured inlet conditions, the inlet flowrates during induction period are calculated from overall mass and energy conservation requirements. Finite difference equation for velocity and pressure were solved by modified SIMPLER algorithm, standard k-$\varepsilon$turbulence model and hybrid scheme. From the result of prediction, dimensionless velocity distribution and turbulence intensities are investigated at each crank angle.

• Bulletin of the Korean Mathematical Society
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• v.33 no.3
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• pp.455-463
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• 1996

In [3] and [4], Kitahara, Pak and the author obtained the conformally invariant tensor $B_0$, which is an algebraic Hermitian analogue of the Weyl conformal curvature tensor W in the Riemannian geometry, by the decomposition of the curvature tensor H of the Hermitian connection and the notion of semi-curvature-like tensors of Tanno (see[7]). In [5], the author defined a conformally invariant tensor $B_0$ on a Hermitian manifold as a modification of $B_0$. Moreover he introduced the notion of local conformal Hermitian-flatness of Hermitian manifolds and proved that the vanishing of this tensor $B_0$ together with some condition for the scalar curvatures is a necessary and sufficient condition for a Hermitian manifold to be locally conformally Hermitian-flat.

• Communications of the Korean Mathematical Society
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• v.35 no.2
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• pp.639-651
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• 2020

Consider a gradient Einstein-type metric in the setting of K-contact manifolds and (κ, µ)-contact manifolds. First, it is proved that, if a complete K-contact manifold admits a gradient Einstein-type metric, then M is compact, Einstein, Sasakian and isometric to the unit sphere 𝕊²ⁿ⁺¹. Next, it is proved that, if a non-Sasakian (κ, µ)-contact manifolds admits a gradient Einstein-type metric, then it is flat in dimension 3, and for higher dimension, M is locally isometric to the product of a Euclidean space 𝔼ⁿ⁺¹ and a sphere 𝕊ⁿ(4) of constant curvature +4.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.567-570
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• 2010

With continuously increasing flat panel display size, uniformity of thin film deposition has been drawing more attentions and associated fabrication methodologies are being actively investigated. Since the convective flow field of mixture gas plays a significant role for deposition characteristics of thin film in an APCVD system, it is greatly important to maintain uniform distribution and consistent concentration of mixture gas species. In this paper, computational study has been performed for the improvement of flow uniformity of mixture gas in an APCVD reactor during thin film deposition process. A diffuser slit has bee designed to spread the locally concentrated gas flow exiting from the flow distributor. A uniform flow distributor has been developed which has less dependency on operating conditions for global flow uniformity