• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.29 no.8 s.239
• /
• pp.948-955
• /
• 2005

A three-dimensional computation was conducted to understand effects of the inlet boundary layer thickness on the internal flow in a low-speed axial compressor operating at the design condition($\phi=85\%$) and near stall condition($\phi=65\%$). At the design condition, the flows in the axial compressor show, independent of the inlet boundary layer thickness, similar characteristics such as the pressure distribution, size of the hub comer-stall, tip leakage flow trajectory, limiting streamlines on the blade suction surface, etc. However, as the load is increased, the hub corner-stall grows to make a large separation region at the junction of the hub and suction surface for the inlet condition with thick boundary layers at the hub and casing. Moreover, the tip leakage flow is more vortical than that observed in case of the thin inlet boundary layer and has the critical point where the trajectory of the tip leakage flow is abruptly turned into the downstream. For the inlet condition with thin boundary layers, the hub corner-stall is diminished so it is indistinguishable from the wake. The tip leakage flow leans to the leading edge more than at the design condition but has no critical point. In addition to these, the severe reverse flow, induced by both boundary layer on the blade surface and the tip leakage flow, can be found to act as the blockage of flows near the casing, resulting in heavy loss.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
• /
• v.3B no.1
• /
• pp.16-22
• /
• 2003

This paper presents an application of an impedance boundary condition to 3D vector finite element analysis of a multi-port cylidrical microwave cavity using Snell's law. Computing memory benefits and computing time reduction are obtained from this method compared with the conventional finite element method(FEM). To verify the method, a high permittivity scatterer in free space is analyzed and compared with the results of conventional (FEM). In addition, this method has been analyzed several types of cavities, including water load, to demonstrate the validity and accuracy of the program.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.21 no.2
• /
• pp.186-193
• /
• 2011

The NDIF method(non-dimensional dynamic influence function method) for free vibration analysis of arbitrarily shaped plates with the simply supported edge is newly developed in the paper. In order to extract the system matrix that gives the natural frequencies and natural modes of the plate of interest, the difficulty of measuring higher differential terms involved in the simply supported boundary condition is successfully overcome. Finally, the excellence of the characteristics of convergence and accuracy of the proposed method is shown through two verification examples, which indicate that natural frequencies and natural modes obtained by the proposed method are very accurate and swiftly converged even though a small number of nodes are used compared with FEM.

• Composites Research
• /
• v.28 no.4
• /
• pp.176-181
• /
• 2015

In this study, the Z-shape fabric design is proposed as the way to enhance the ballistic performance of fabrics which are used as the intermediate layer of stuffed Whipple shield configurations. The Z-shape fabric employs a different boundary condition from those of conventional configurations of fabrics which include 4 edge fixed. Impact analysis on Z-shape aramid yarns and fabrics using LS-DYNA software was performed and the results were compared with 2 edge fixed and 4 edge fixed fabrics to identify the high velocity impact energy absorption characteristics of the Z-shape fabric. It was revealed that the Z-shape showed different impact behavior and higher energy absorption performance than 2 and 4 edge fixed fabrics.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.3
• /
• pp.584-590
• /
• 1994

A theoretical model has been developed to analyze the jet-edge interaction and the sound radiation. The edge responding to the sinuous impinging jet is regarded as an array of dipoles and their strength is determined by the boundary condition on the edge surface. The surface pressure distribution and the edgeforce are estimated using these dipoles. Then the pressure amplitude and directivity of the sound field is obtained by summing the radiating sounds from the dipole sources. It is found that the effective source is located a little distance downstream from the edge tip. And the directivity of the sound radiation is cardioid pattern near the edge but dipole pattern far from the edge. The theoretical model is confirmed by comparing the theoretical prediction of the edgeforce and sound pressure level with available experimental data.

• Geophysics and Geophysical Exploration
• /
• v.11 no.2
• /
• pp.153-160
• /
• 2008

Seismic modeling is used to simulate wave propagation in the earth. Although the earth's subsurface is usually semi-infinite, we cannot handle the semi-infinite model in seismic modeling because of limited computational resources. For this reason, we usually assume a finite-sized model in seismic modeling. In that case, we need to eliminate the edge reflections arising from the artificial boundaries introducing a proper boundary condition. In this study, we changed three kinds of boundary conditions (sponge boundary condition, Clayton and Engquist's absorbing boundary condition, and Higdon's transparent boundary condition) so that they can be applied in elastic wave modeling for anisotropic media. We then apply them to several models whose Poisson's ratios are different. Clayton and Engquist's absorbing boundary condition is unstable in both isotropic and anisotropic media, when Poisson's ratio is large. This indicates that the absorbing boundary condition can be applied in anisotropic media restrictively. Although the sponge boundary condition yields good results for both isotropic and anisotropic media, it requires too much computational memory and time. On the other hand, Higdon's transparent boundary condition is not only inexpensive, but also reduce reflections over a wide range of incident angles. We think that Higdon's transparent boundary condition can be a method of choice for anisotropic media, where Poisson's ratio is large.

• 한국해양학회지
• /
• v.16 no.1
• /
• pp.12-23
• /
• 1981

A numerical experiment is made in order to clarify the mechanism of the upwelling phenomenon along the coast near the poleward edge of the western boundary current. The possibility of the upwelling is suggested from the analysis of the observational data in the east of Honshu, Japan, and in the south eastern coast of Korean Peninsula. This upwelling phenomenon is very deep and can be traced to the bottom layer. The upwelling phenomenon seems to be a general oceanic feature which characterizes the region along the west coast near the poleward edge of the western boundary current. This experiment is simulating the oceanic condition of the transition region between Kuroshio front and the Oyashio front in the east of Honshu, Japan. The possible explanations of the causes of the upwelling are as follows;In the interior of the modeled ocean the cold heavy water supplied from the north and the warm light water from the south make the north-south gradient of the pressure field and accelerate the eastward current to produce the h-orizontal divergence feld near the west coast. The divergence is compensated by the upwelling near the separation region. Another one is that the upwell-ed cold water strengthen constantly the pressure gradient which is balanced by the northward current and is weakened by the horizontal diffusion.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.25 no.8
• /
• pp.1183-1188
• /
• 2001

This paper reports on the starved lubrication for the piston ring. In this analysis, two types of inlet boundary conditions, fully flooded and starved condition, are considered at the leading edge. The inlet position of effective lubrication and squeeze term are obtained by numerically iterative method. The effective lubricated region is reduced due to the starved condition at the inlet. The starved condition at the inlet significantly reduced the minimum oil film thickness(MOFT) at the midstroke of piston, and the friction force is also increased due to the thin oil film thickness. In the starved conditions, the power loss is significantly increased.

• The Journal of Information Technology
• /
• v.8 no.2
• /
• pp.77-84
• /
• 2005

In this paper, electromagnetic scattering problems by a resistive strip grating with tapered resistivity on a grounded dielectric plane according to strip width and spacing, relative permittivity and thickness of dielectric layers, and incident angles of a electric wave are analyzed by applying the Fourier-Galerkin Moment Method known as a numerical procedure. The boundary conditions are applied to obtain the unknown field coefficients and the resistive boundary condition is used for the relationship between the tangential electric field and the electric current density on the strip. The resistivity of resistive strips in this paper varies from zeroes at one edge to infinite at the other edge, then the induced surface current density on the resistive strip is expanded in a series of Jacobi polynomials of the order ${\alpha}=0.2,\;{\beta}=-0.2$ as a orthogonal polynomials. The numerical results of the geometrically normalized reflected power in this paper are compared with those for the existing perfectly conducting strip. The numerical results of the normalized reflected power for conductive strips case with zero resistivity in this paper show in good agreement with those of existing papers.

• Structural Engineering and Mechanics
• /
• v.83 no.4
• /
• pp.451-463
• /
• 2022

The present study deals with forced vibrations of an elastic circular plate supported along its circular edge by unilateral elastic springs. The plate is assumed to be subjected to a uniformly distributed and a concentrated load. Under the combination of these loads, equations of motion are explicitly derived for static and dynamic response analyses by assuming a series of the displacement functions of time and other unknown parameters which are to be determined by employing Lagrangian functional. The approximate solution is sought by applying the Lagrange equations of motions by using the potential energy of the external forces that includes the contributions of the edge forces and the external moments, i.e., those of the effects of the boundary condition to the analysis. For the numerical treatment of the problem in the time domain, the linear acceleration procedure is adopted. The tensionless character of the support is taken into account by using an iterative process and, the coordinate functions for the displacement field are selected to partially fulfill the boundary conditions so that an acceptable approximation can be achieved faster. Numerical results are presented in the figures focusing on the nonlinearity of the problem due to the plate lift-off from the unilateral springs at the edge support.