• The Bulletin of The Korean Astronomical Society
• /
• v.35 no.1
• /
• pp.72.2-72.2
• /
• 2010

We use three-dimensional hydrodynamic simulations to investigate nonlinear gravitational responses of gas to, and the resulting drag force on, a massive perturber moving on a circular orbit through a uniform gaseous medium. We assume that the background medium is non-rotating and adiabatic with index 5/3, and represent the perturber using a Plummer potential with softening radius a. This work extends our previous study where we showed that the drag force on a straight-line trajectory is proportional to a0.45 if the perturber is massive enough. This indicates that the orbital decay of supermassive black holes (SMBHs) near galaxy centers may take much longer than the prediction of the linear force formula applicable for low-mass perturbers. For the circular orbits are considered, however, we find that the nonlinear drag force becomes independent of a, but dependent instead on the orbital radius R as $\varpropto$ R0.5. This suggests not only that the choices of large values of a, for resolution issues, in recent numerical experiments for mergers of SMBH, are marginally acceptable, but also that the gaseous drag indeed provides an efficient mean for the orbtial decay of SMBHs.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2003.05a
• /
• pp.921-925
• /
• 2003

An analytical method for the free vibration of single circular plate submerged in a fluid-filled rigid cylindrical vessel was developed by the Rayleigh-Ritz method based on the Fourier-Bessel series expansion. It was assumed that the plate is clamped at an offcentered location of the cylinder, and the non-viscous incompressible fluid contained in the cylinder is bisected by the plate. It was found that the theoretical results can predict well the fluid-coupled natural frequencies with excellent accuracy comparing with the finite element analysis results. The offcentered distance effect on the natural frequencies was also observed.

• Solar Energy
• /
• v.19 no.1
• /
• pp.67-75
• /
• 1999

The effect of radiation heat transfer was investigated under various operating conditions in a circular tube with circumferential fins and circular disks. Using a finite volume technique(FVM) for steady laminar flow, the governing equations were derived in order to simulate the flow and temperature fields. In addition, the P-1 approximation and the Weighted Sum of Gray Gas Model(WSGGM) were used for the radiation transport equation(RTE). From the results, radiation heat transfer was significant compared to convection heat transfer. These results will be applied to the design of the heat exchanger for a condensing bolier, which were developed for domestic heating.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2001.11b
• /
• pp.1254-1259
• /
• 2001

This paper deals with the free vibrations of circular arches with variable cross-section. The differential equations governing free, in-plane vibrations of tapered circular arches, including the effects of rotatory inertia, shear deformation and axial deformation, are derived and solved numerically to obtain frequencies and mode shapes. Numerical results are calculated for the quadratic arches with hinged-hinged and clamped-clamped end constraints. Three general taper types for a rectangular section are considered. The lowest four natural frequencies and mode shapes are presented over a range of non-dimensional system parameters： the subtended angle, the slenderness ratio and the section ratio.

• Smart Structures and Systems
• /
• v.16 no.1
• /
• pp.81-100
• /
• 2015

This paper presents nonlinear analysis of an arbitrary functionally graded circular plate integrated with two functionally graded piezoelectric layers resting on the Winkler-Pasternak foundation. Geometric nonlinearity is considered in the strain-displacement relation based on the Von-Karman assumption. All the mechanical and electrical properties except Poisson's ratio can vary continuously along the thickness of the plate based on a power function. Electric potential is assumed as a quadratic function along the thickness direction. After derivation of general nonlinear equations, as an instance, numerical results of a functionally graded material integrated with functionally graded piezoelectric material obeying two different functionalities is investigated. The effect of different parameters such as parameters of foundation, non homogenous index and boundary conditions can be investigated on the mechanical and electrical results of the system. A comprehensive comparison between linear and nonlinear responses of the system presents necessity of this study. Furthermore, the obtained results can be validated by using previous linear and nonlinear analyses after removing the effect of foundation.

• Steel and Composite Structures
• /
• v.50 no.5
• /
• pp.499-513
• /
• 2024

This paper describes the experimental and numerical investigations of octagonal Concrete-Filled Double Skinned Steel Tube (CFDST) short columns under the influence of various internal sizes of the circular and square steel tubes, with constant cross-sectional dimensions of the external octagonal steel tube under concentric loading. The non-linear finite element analysis of octagonal CFDST columns was executed using the ABAQUS to forecast and compare the axial compression behavior influenced by the various sizes of internal circular and square steel tubes. The study shows that the axial compressive strength and ductility of octagonal CFDST columns were significantly influenced by various internal dimensions of the circular and square steel tubes with the strengths of constituent materials.

• The Journal of The Korea Institute of Intelligent Transport Systems
• /
• v.19 no.3
• /
• pp.116-128
• /
• 2020

This study compared the delays of scramble crosswalks and general crosswalks, considering the pedestrian and vehicle traffic at intersections. Based on the signal theory, this study used traffic delays as a measure of feasibility of installing scramble crosswalks. The road structure and length of signal lights were assumed to be specific numbers to calculate the delays in vehicles and pedestrians. With the computed delays, this study compared general crosswalks and scramble crosswalks, and evaluated the feasibility sections on the installation of scramble crosswalks using circular and non-circular signal phases, respectively. The analysis confirmed that the introduction of scramble crosswalks might be more appropriate when the traffic ratio on the main roads is high. In addition, the application of non-circular signal phases is more proper for the operation of scramble crosswalks than circular signal phases. In the non-circular signaling system, however, it was shown that diagonal crosswalks might not be practical if the demand for diagonal crossing is too low. These results are expected to contribute to the development of basic guidelines for assessing the installment feasibility of scramble crosswalks in terms of traffic operation and efficiency.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.2 no.2
• /
• pp.87-94
• /
• 1998

Behavioral characteristics of shallow circular arches with dynamic loading and different end conditions are analysed. Geometric nonlinearity is modelled using Lagrangian description of the motion. The finite element analysis procedure is used to solve the dynamic equation of motion, and the Newmark method is adopted in the approximation of time integration. The behavior of arches is analysed using the buckling criterion and non-dimensional time, load and shape parameters which Humphreys suggested. But a new deflection-ratio formula including the effect of horizontal displacement plus vertical displacement is presented to apply for the non-symmetric buckling problems. Through the model analysis, it's confirmed that fix-ended arches have higher buckling stability than hinge-ended arches, and arches with the same shape parameter have the same deflection ratio at the same time parameter when loaded with the same parametric load.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.24 no.1
• /
• pp.36-46
• /
• 2013

This paper proposes the design of broadband spiral antenna for a potable non-linear junction detector (NLJD) system. To realize the broadband antenna design, it was considered optimization of the number of spiral turns by iteration calculation. Ground plane with the Archimedean spiral slit to keep the same current distribution between radiating plane and ground is considered for circular polarization design. In order to realize high directivity and high gain of the proposed antenna, the cavity wall and the metal cap which is located on back of ground plane were also considered in design. Measurement results of return loss were agreed well with VSWR 2:1 at interested frequency band among 2.4 to 2.44 GHz, 4.84 to 4.92 GHz and 7.28 to 7.36 GHz. Measured axial ratio was observed 3 dB below and showed reasonable agreement with simulation results. Characteristics of the RHCP(Right Hand Circular Polarization) with the measured gain of 6.8 dBi above at interested frequency band were also observed.

• Structural Engineering and Mechanics
• /
• v.52 no.2
• /
• pp.221-238
• /
• 2014

A four-noded curved shell finite element for the geometrically non-linear analysis of beams curved in plan is introduced. The structure is conceived as a sequence of macro-elements (ME) having the form of transversal segments of identical topology where each slice is formed using a number of the curved shell elements which have 7 degrees of freedom (DOF) per node. A curved box-girder beam example is modelled using various meshes and linear analysis results are compared to the solutions of a well-known computer program SAP2000. Linear and non-linear analyses of the beam under increasing uniformly distributed loads are also carried out. In addition to box-girder beams, the proposed element can also be used in modelling open-section beams with curved or straight axes and circular plates under radial compression. Buckling loads of a circular plate example are obtained for coarse and successively refined meshes and results are compared with each other. The advantage of this element is that curved systems can be realistically modelled and satisfactory results can be obtained even by using coarse meshes.