• Geomechanics and Engineering
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• v.8 no.1
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• pp.97-111
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• 2015

The kinematical approach of limit analysis is used to estimate the three dimensional stability analysis of rock slopes with nonlinear Hoek-Brown criterion under earthquake forces. The generalized tangential technique is introduced, which makes limit analysis apply to rock slope problem possible. This technique formulates the three dimensional stability problem as a classical nonlinear programming problem. A nonlinear programming algorithm is coded to search for the least upper bound solution. To prove the validity of the present approach, static stability factors are compared with the previous solutions, using a linear failure criterion. Three dimensional seismic and static stability factors are calculated for rock slopes. Numerical results of indicate that the factors increase with the ratio of slope width and height, and are presented for practical use in rock engineering.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 1993.06a
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• pp.873-876
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• 1993

A fuzzy controller designed by mini-max-gravity(MMG) method is essentially nonlinear with respect to the controller's input and output relationship, and stability analysis is thus needed to construct a stable control system. This paper deals with a design method of a position-type MMG fuzzy controller stable in a sense of Lyapunov when considered is a single-input-single-output linear, stable plant. We first introduce a method to construct a Laypunov function by using an eigen-value of A matrix of the linear, stable plant dynamics and then we derive an asymtotic stability condition in terms of scale factors for fuzzy state variables and controller gain. The stability condition is found reasonably practical through comparing the theoretical stability region with that obtained from simulations.

• Korean Chemical Engineering Research
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• v.57 no.5
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• pp.723-729
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• 2019

A theoretical analysis was conducted of convective instability driven by buoyancy forces under transient temperature fields in an annular porous medium bounded by coaxial vertical cylinders. Darcy's law and Boussinesq approximation are used to explain the characteristics of fluid motion and linear stability theory is employed to predict the onset of buoyancy-driven motion. The linear stability equations are derived in a global domain, and then cast into in a self-similar domain. Using a spectral expansion method, the stability equations are reformed as a system of ordinary differential equations and solved analytically and numerically. The critical Darcy-Rayleigh number is founded as a function of the radius ratio. Also, the onset time and corresponding wavelength are obtained for the various cases. The critical time becomes smaller with increasing the Darcy-Rayleigh number and follows the asymptotic relation derived in the infinite horizontal porous layer.

• Proceedings of the KIEE Conference
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• 1999.07c
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• pp.1054-1056
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• 1999

It is the most important in small signal stability analysis of large scale Power systems to compute only the dominant eigenvalues selectively with numerical stability and efficiency. In this Paper evoluted linear analysis program, transformed state matrix using Inverse transformation with complex shift and then Hessenberg process and iterative scheme are used to accelerate Hessenberg process, can calculate dominant eigenvalues. In this Paper, The accuracy of this Program has been validated against 4-machines 11-bus system and New England 10-machines 39-bus system. Also applied to KEPCO system - about 791-bus 250-machines 2500-branches, got 2568 order state matrix, and calculated two dominant modes. This analysis result equaled to result of EPRI's SSSP program to use commonly, and calculating time is faster.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.8 s.179
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• pp.1991-1999
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• 2000

This research has been performed to reveal the hysteresis phenomena of the hunting motion in a railway passenger car having a bolster. Since linear analysis can not explain them, bifurcation analysis is used to predict its outbreak velocities in this paper. However bifurcation analysis is attended with huge computing time, thus this research proposes more effective numerical algorithm to reduce it than previous researches. Stability of periodic solution is obtained by adapting of Floquet theory while stability of equilibrium solutions is obtained by eigen-value analysis. As a result, linear and nonlinear critical speed are acquired. Full scale roller rig test is carried out for the validation of the numerical result. Finally, it is certified that there are many similarities between numerical and test results.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.634-643
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• 2006

This study was intended to develop a high reliable technique by statistically processing on-site data with a general linear model, providing the basic data for construction, analysis of stability and establishment of maintenance measures for tunnel portal slopes in the future. This study evaluated the stability of a tunnel portal slope using a quantified technique, which is based on a general linear model. The important scores of each independent variable were allocated by using the ranges of the quantified values, based on the predicted coefficient of regression and the scores for categories of each independent variable were allocated so that those are equally spaced. The quantification model obtained from the results of evaluating the total data used for the quantification process provided precise results. In addition, it is expected that a more detail subdivision of response variables and sufficient data would produce a better stability evaluation standard.

• Structural Engineering and Mechanics
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• v.65 no.1
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• pp.121-128
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• 2018

Three structure-dependent integration methods with no numerical dissipation have been successfully developed for time integration. Although these three integration methods generally have the same numerical properties, such as unconditional stability, second-order accuracy, explicit formulation, no overshoot and no numerical damping, there still exist some different numerical properties. It is found that TLM can only have unconditional stability for linear elastic and stiffness softening systems for zero viscous damping while for nonzero viscous damping it only has unconditional stability for linear elastic systems. Whereas, both CEM and CRM can have unconditional stability for linear elastic and stiffness softening systems for both zero and nonzero viscous damping. However, the most significantly different property among the three integration methods is a weak instability. In fact, both CRM and TLM have a weak instability, which will lead to an adverse overshoot or even a numerical instability in the high frequency responses to nonzero initial conditions. Whereas, CEM possesses no such an adverse weak instability. As a result, the performance of CEM is much better than for CRM and TLM. Notice that a weak instability property of CRM and TLM might severely limit its practical applications.

• Steel and Composite Structures
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• v.14 no.6
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• pp.571-586
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• 2013

This paper focuses on the buckling capacity of a hybrid grid shell. The eigenvalue buckling, geometrical non-linear elastic buckling and elasto-plastic buckling analyses of the hybrid structure were carried out. Then the influences of the shape and scale of imperfections on the elasto-plastic buckling loads were discussed. Also, the effects of different structural parameters, such as the rise-to-span ratio, beam section, area and pre-stress of cables and boundary conditions, on the failure load were investigated. Based on the comparison between elastic and elasto-plastic buckling loads, the effect of material non-linearity on the stability of the hybrid barrel vault is found significant. Furthermore, the stability of a hybrid barrel vault is sensitive to the anti-symmetrical distribution of loads. It is also shown that the structures are highly imperfection sensitive which can greatly reduce their failure loads. The results also show that the support conditions pose significant effect on the elasto-plastic buckling load of a perfect hybrid structure.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.1
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• pp.181-186
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• 2009

In this paper, the stability analysis for uncertain dynamic systems with time-varying delays is considered. By constructing a new Lyapunov functional, a novel stability criterion is established in terms of linear matrix inequalities (LMIs). Two numerical examples are carried out to support the effectiveness of the proposed method.

• International Journal of Aeronautical and Space Sciences
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• v.12 no.1
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• pp.78-83
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• 2011

Traditional autopilot design requires an accurate aerodynamic model and relies on a gain schedule to account for system nonlinearities. This paper presents the control architecture applied to a dynamic model inversion at a single flight condition with an on-line neural network (NN) in order to regulate errors caused by approximate inversion. This eliminates the need for an extensive design process and accurate aerodynamic data. The simulation results using a developed full nonlinear 6 degree of freedom model are presented. This paper also presents the stability evaluation for control systems to which NNs were applied. Although feedback can accommodate uncertainty to meet system performance specifications, uncertainty can also affect the stability of the control system. The importance of robustness has long been recognized and stability margins were developed to quantify it. However, the traditional stability margin techniques based on linear control theory can not be applied to control systems upon which a representative non-linear control method, such as NNs, has been applied. This paper presents an alternative stability margin technique for NNs applied to control systems based on the system responses to an inserted gain multiplier or time delay element.