• Structural Engineering and Mechanics
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• 제78권4호
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• pp.497-518
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• 2021

In this study, a new method for treating the wall boundary in smoothed particle hydrodynamics (SPH) is proposed to simulate free surface flows effectively. Unlike conventional methods of wall boundary treatment through boundary particles, in the proposed method, the wall boundary condition is directly imposed by adding boundary truncation terms to the mass and momentum conservation equations. Thus, boundary particles are not used in boundary modeling. Doing so, the wall boundary condition is accurately imposed, boundary modeling is simplified, and computation is made efficient without losing stability in SPH. Performance of the proposed method is demonstrated through several numerical examples: dam break, dam break with a wedge, sloshing, inclined bed, cross-lever rotation, pulsating tank and sloshing with a flexible baffle. These results are compared with available experimental results, analytical solutions, and results obtained using the boundary particle method.

• Management Science and Financial Engineering
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• 제18권1호
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• pp.49-53
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• 2012

A novel method of transient stability analysis is presented in this paper. The proposed method extracts data points near the basin-of-attraction boundary and then builds a support vector machine (SVM) model learned from the generated data. The constructed SVM classifier has been shown to reduce dramatically the conservativeness of the estimated basin of attraction.

• Structural Engineering and Mechanics
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• 제85권6호
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• pp.809-823
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• 2023

In this work, dynamic stability analysis of the ball after contacting with the earth in the volleyball game is presented. Via spherical shell coordinate, the governing equations and general boundary conditions of the ball after contacting with the earth in the volleyball game is studied. Via Comsol multi-physics simulation, some results are presented and a verification between the outcomes is studied. Harmonic differential quadrature method (HDQM) is utilized to solve the dynamic equations with the aid of boundary nodes of the current spherical shell structure. Finally, the results demonstrated that thickness, mass of the ball and internal pressure of the ball alters the frequency response of the structure. One important results of this study is influence of the internal pressure. Higher internal pressure causes lower frequency and hence reduces the stability of the ball.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2014년도 추계 학술논문 발표대회
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• pp.167-168
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• 2014

Building destruction can be occurred by decreasing of structural stability and deformation according to fire. Especially, a structural behavior of beam can be shown a slightly difference by beam types. In this paper, an evaluation of the structural stability of beam made of ordinary structural steel designed by fixed and simple boundary condition was done by an analytic method using mechanical properties of SS 400 and an heat transfer theory.

• 대한수학회논문집
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• 제24권1호
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• pp.85-97
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• 2009

In this paper we study the existence of global weak solutions for a hyperbolic hemivariational inequalities with boundary source and damping terms, and then investigate the asymptotic stability of the solutions by using Nakao Lemma [8].

• 대한수학회지
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• 제49권4호
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• pp.715-731
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• 2012

This paper considers the stability of positive steady-state solutions bifurcating from the trivial solution in a delayed Lotka-Volterra two-species predator-prey diffusion system with a discrete delay and subject to the homogeneous Dirichlet boundary conditions on a general bounded open spatial domain with smooth boundary. The existence, uniqueness and asymptotic expressions of small positive steady-sate solutions bifurcating from the trivial solution are given by using the implicit function theorem. By regarding the time delay as the bifurcation parameter and analyzing in detail the eigenvalue problems of system at the positive steady-state solutions, the asymptotic stability of bifurcating steady-state solutions is studied. It is demonstrated that the bifurcating steady-state solutions are asymptotically stable when the delay is less than a certain critical value and is unstable when the delay is greater than this critical value and the system under consideration can undergo a Hopf bifurcation at the bifurcating steady-state solutions when the delay crosses through a sequence of critical values.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 추계 학술대회논문집
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• pp.134-140
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• 2007

Nonlinear parabolized stability equations for compressible flow in general curvilinear coordinate system are derived to deal with a broad range of transition prediction problems on complex geometry. A highly accurate finite difference PSE code has been developed using an implicit marching procedure. Blasius flow is tested. The results of the present computation show good agreement with DNS data. Nonlinear interaction can make the T-S fundamental wave more unstable and the onset of its amplitude decay is shifted downstream relative to linear case. For nonlinear calculations, rather small difference in initial amplitude can produce large change during nonlinear region. Compressible secondary instability at Mach number 1.6 is also simulated and showed that 1.1% initial amplitude for primary mode is enough to trigger the secondary growth.

• International Journal of Aeronautical and Space Sciences
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• 제13권1호
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• pp.43-57
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• 2012

In a modern aircraft, there are many variations in its mass, stiffness, and aerodynamic characteristics. Recently, an analytical approach was proposed, and this approach uses the idea of uncertainty to find out the most critical flight flutter boundary due to the variations in such aerodynamic characteristics. An analytical method that has been suggested to predict robust stability is the mu method. We previously analyzed the robust flutter boundary by using the mu method, and in that study, aerodynamic variations in the Mach number, atmospheric density, and flight speed were taken into consideration. The authors' previous attempt and the results are currently quoted as varying Mach number mu analysis. In the author's previous method, when the initial flight conditions were located far from the nominal flutter boundary, conservative predictions were obtained. However, relationships among those aerodynamic parameters were not applied. Thus, the varying Mach number mu analysis results required validation. Using an optimization approach, the varying Mach number mu analysis was found out to be capable of capturing a reasonable robust flutter boundary, i.e., with a low percentage difference from boundaries that were obtained by optimization. Regarding the optimization approach, a discrete nominal flutter boundary is to be obtained in advance, and based on that boundary, an interpolated function was established. Thus, the optimization approach required more computational effort for a larger number of uncertainty variables. And, this produced results similar to those from the mu method which had lower computational complexity. Thus, during the estimation of robust aeroelastic stability, the mu method was regarded as more efficient than the optimization method was. The mu method predicts reasonable results when an initial condition is located near the nominal flutter boundary, but it does not consider the relationships that are among the aerodynamic parameters, and its predictions are not very accurate when the initial condition is located far from the nominal flutter boundary. In order to provide predictions that are more accurate, the relationships among the uncertainties should also be included in the mu method.

• 터널과지하공간
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• 제8권2호
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• pp.118-129
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• 1998

A three dimensional boundary element method-BEAP3D was applied to the stability analysis of the mine openings not only to improve the stability during mining operations but also to serve the evaluation of the mine openings for further utilization. Stability analysis on the stability of the room-and-pillar stopes underneath of the old mine openings and the openings to be created by the newly proposed sublevel stoping method at the Nowhado Pyrophyllite Mine, showed that rock mass around the old and new stopes would be stable. Six stopes of a sublevel stoping designed for the Choongmu Limestone Quarry would be stable, too. A sublevel stoping method consisting of six stopes was similarly suggested for the Keumpyung Quartzite Mine. The stability can be guaranteed through out six stopes. Since mining starts from the bottom 1st sublevel to the uppermost sublevel, the safety of the stopes will improve together with the mining process. It would highly be recommended to investigate in-situ rock properties and the rock stresses for future studies. Even though the rock around the uppermost part and bottom of all the stopes have a very high factor of safety, spot reinforcements such as rock bolting would be recommended to mitigate the intermediate and minor principal stresses acting in a tensile mode.

• International Journal of Aeronautical and Space Sciences
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• 제12권4호
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• pp.305-317
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• 2011

This paper presents an overview on flutter boundary prediction in tests which is principally based on a system stability measure, named Jury's stability criterion, defined in the discrete-time domain, accompanied with the use of autoregressive moving-average (AR-MA) representation of a sampled sequence of wing responses excited by continuous air turbulences. Stability parameters applicable to two-, three- and multi-mode systems, that is, the flutter margin for discrete-time systems derived from Jury's criterion are also described. Actual applications of these measures to flutter tests performed in subsonic, transonic and supersonic wind tunnels, not only stationary flutter tests but also a nonstationary one in which the dynamic pressure increased in a fixed rate, are presented. An extension of the concept of nonstationary process approach to an analysis of flutter prediction of a morphing wing for which the instability takes place during the process of structural morphing will also be mentioned. Another extension of analytical approach to a multi-mode aeroelastic system is presented, too. Comparisons between the prediction based on the digital techniques mentioned above and the traditional damping method are given. A future possible application of the system stability approach to flight test will be finally discussed.