• Journal of Korean Port Research
• /
• v.9 no.1
• /
• pp.57-63
• /
• 1995

In this paper we examine the mass transport within the boundary layer near the sea bottom. The fluid domain is seperated into inner and outer region of boundary layers. In outer region, the wave field is assumed to be inviscid and irrotational. When the incident waves enter the arrays of circular cylinders, the scattering of water waves by an array of N bottom mounted vertical circular cylinders is solved using the method proposed by Linton & Evans under the potential theory. In inner region, the Navier-Stokes equation must be satisfied with boundary conditions at the boundary later and bottom is to be represented by the sum of the Eulerian mean drift and the Stokes' drift.

• Journal of KIISE:Software and Applications
• /
• v.33 no.4
• /
• pp.427-439
• /
• 2006

The SBF (Simple Boundary Follower) is a boundary-following algorithm, and is used mainly for image recognition and presentation. The SBF is very popular because of its simplicity and efficiency in tracing the boundary of an object from an acquired binary image; however, it does have two drawbacks. First, the SBF cannot consistently process inner or inner-outer corners according to the follower's position and direction. Second, the SBF requires movement operations for the non-boundary pixels that are connected to boundary pixels. The MSBF (Modified Simple Boundary Follower) has a diagonal detour step for preventing inner-outer corner inconsistency, but is still inconsistent with inner-corners and still requires extra movement operations on non-boundary pixels. In this paper, we propose the ISBF (Improved Simple Boundary Follower), which solves the inconsistencies and reduces the extra operations. In addition, we have classified the tour maps by paths from a current boundary pixel to the next boundary pixel and have analyzed SBF, MSBF, and ISBF. We have determined that the ISBF has no inconsistency issues and reduces the overall number of operations.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.25 no.6
• /
• pp.786-798
• /
• 2001

This paper describes the phenomena of wake-induced transition of the boundary layers on a NACA0012 airfoil using measured phase-averaged data. Especially, the phase-averaged wall shear stresses are reasonably evaluated using the principle of Computational Preston Tube Method. Due to the passing wake, the turbulent patch is generated in the laminar boundary layer on the airfoil and the boundary layer becomes temporarily transitional. The patches propagate downstream with less speed than free-stream velocity and merge with each other at further down stream station, and the boundary layer becomes more transitional. The generation of turbulent patch at the leading edge of the airfoil mainly depends on velocity defects and turbulent intensity profiles of passing wakes. However, the growth and merging of turbulent patches depend on local streamwise pressure gradients as well as characteristics of turbulent patches. In this transition process, the present experimental data show very similar features to the previous numerical and experimental studies. It is confirmed that the two phase-averaged mean velocity dips appear in the outer region of transitional boundary layer for each passing cycle. Relatively high values of the phase-averaged turbulent fluctuations in the outer region indicate the possibility that breakdown occurs in the outer layer not near the wall.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2010.11a
• /
• pp.438-444
• /
• 2010

The spray characteristics of jet in crossflow (JICF) to improve the atomization and mixing characteristics of liquid Jet, while minimizing the impact on crossflow, were studied experimentally. By varying the temperature, velocity, pressure of crossflow and the speed, pressure of liquid Jet, the spray boundary (outer boundary, inner boundary) with the change of crossflow and liquid jet momentum ratio (q) were measured and led the experimental formula, compared with the results of previous work. Specifically, when the jet penetration with the shape of injector were measured, in the case of dual orifice Injector, under the influence of front orifice, the jet penetration of back orifice was improved approximately 18% ($L_h$ = 4 mm), compared with single orifice injector.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.32 no.7
• /
• pp.518-528
• /
• 2008

The effects of surface roughness on a turbulent boundary layer (TBL) were investigated using particle image velocimetry (PIV). The roughness elements used were periodically arranged two-dimensional spanwise rods, and the roughness height was ${\kappa}/{\delta}$. Introduction of the roughness elements increased the wake strength and the turbulent stress not only in the roughness sublayer but also in the outer layer. This indicates the existence of interaction between inner and outer layers for 2D rod-roughened wall. Roughness effects on a turbulence structure near the wall were obtained by PIV measurements. Iso-contours of mean velocities and Reynolds stresses in the roughness sublayer showed a very good agreement with previous DNS results.

• Journal of KSNVE
• /
• v.6 no.5
• /
• pp.671-677
• /
• 1996

This paper presents the analytical method for predicting turbulence- induced noise in the multilayered cylinder composed of an outer hose, an inner fluid and an internal core. It is assumed that an infinite axisymmetric cylinder is located horizontally in water with free stream velocity and the turbulent boundary layer (TBL) surrounding the outer hose is fully developed and homogeneous. The transfer function at the core surface due to the propagation of the pressure fluctuation within the TBL is formulated using the linearized Navier-Stockes equation for solid and fluid. In the estimation of the energy spectrum of wall pressure fluctuation, the empirical formula proposed by Strawderman based on the Corcos model is used. A general algorithm for the calculation of the pressure level at the surface of a core, that is, turbulence- induced noise, is presented. Through the detailed numerical simulation, it is found that the major noise mechanism is the propagation of the bulge wave along hose.

• Proceedings of the KSME Conference
• /
• 2003.11a
• /
• pp.610-615
• /
• 2003

This experiment has been carried out to find the structure of turbulent boundary layer with instantaneous velocity fields obtained in stream-wall-normal planes using a stereo-PIV (Particle Image Velocimetry) method. And it has been measured perpendicular plane and horizontal plane with hairpin vortex structure by Reynolds number change and made third dimension shape for section of horizontal plane through stereo-PIV. In the outer layer hairpin vortices occur in streamwise-aligned packets that propagate with small velocity dispersion. A streaky structure is composed of counter-rotating vortex. According as y+ increases, streaky structure's interval space decrease, and it shows that hairpin shape of prior research is vertified. The objective of the present research is to gain a better understanding of coherent structures in the outer of wall turbulence by experimentally examining coherent structures.

• Journal of Power System Engineering
• /
• v.5 no.1
• /
• pp.104-109
• /
• 2001

The stress distributions of hydranlic actuator cylinder tube acting in uniform inner pressure were analysed by the boundary element method(BEM). STKM13C tube was utilized for machine structural purposes model, its inner radius was 100 mm and outer radius was 140 mm. Axial length was semi-infinite and the isoparametric element of BEM was used. Radial and tangential stresses are maximum(-20.3 MPa and 52 MPa) at the inner radius and the minimum at the outer radius of the hydraulic actuator cylinders for an industrial systems. Stress diminution ratio was about 0.6 MPa/mm. And then coincidence between the simulation techniques as exact results(Lame' equation) and finite element method(FEM) is found to be fairly good, showing that the proposed analysis by BEM is reliable.

• The Bulletin of The Korean Astronomical Society
• /
• v.37 no.2
• /
• pp.134.1-134.1
• /
• 2012

The radiation belt structure can be approximately reproduced by a form of diffusion equation, which takes into account the radial diffusion process as well as those in pitch angle and energy. The solution of the equation depends on several factors including initial and boundary conditions, diffusion coefficients, and plasmapause location. In this paper, we have attempted to determine a set of approximate functions for the energetic electron fluxes near the outer edge of the outer belt in terms of solar wind variable. We used the electron flux data from SST onboard the THEMIS spacecraft and determined its correlation with solar wind conditions in a systematic way. The functions were determined separately for different energy channels from ~30 keV up to 719 keV. Our determination of these functions allows us to predict the radial boundary condition for the electron flux, which can be implemented in a forecast model.

• Journal of the Korean Society of Visualization
• /
• v.20 no.1
• /
• pp.38-44
• /
• 2022

An interscale transport of the turbulent kinetic energy (TKE) and Reynolds shear stress (RSS) is examined in an adverse pressure gradient (APG) turbulent boundary layer (TBL). The direct numerical simulation data of an APG TBL at Re_τ = 834 and β = 1.45 is employed. The TKE and RSS transport equations are divided into large and small scales, leading to the introduction of interscale transport. The TKE mainly transfers from large scales to small ones in the outer region, and vice versa for the RSS. An interscale transport of TKE and inverse interscale transport of RSS are amplified by APG, and the latter results in the increase in large scales of TKE production. Some of outer large scales of enhanced TKE transfer to small scales and then dissipate by viscosity, and the remains dissipate turbulent-non-turbulent interfaces by turbulent transport.