• 제어로봇시스템학회:학술대회논문집
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• 1991.10a
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• pp.601-605
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• 1991

In this paper an approximate solution method for the large-scale Traveling Salesman Problem(TSP) is presented. The method start with the subdivision of the problem domain into a number of clusters by considering their geometries. The clusters have limited number of nodes so as to get local solutions. They are linked to give the least path which covers the whole domain and become TSPs with start- and end-node. The approximate local solutions in each cluster are obtained by using geometrical property of the cluster, and combined to give an overall-approximate solution for the large-scale TSP.

• Journal of Korea Water Resources Association
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• v.41 no.8
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• pp.761-772
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• 2008

The object of this study is to develop the model that solves the numerically difficult problems in hydraulic engineering and to demonstrate the applicability of this model by means of various test examples, such as, verification in the gradually varied unsteady condition, three steady flow problems with the change of bottom slope with exact solution, and frictional bed with analytical solution. The governing equation of this model is the integral form of the Saint-Venant equation satisfying the conservation laws, and finite volume method with the Riemann solver is used. The evaluation of the mass and momentum flux with the HLL Riemann approximate solver is executed. MUSCL-Hancock scheme is used to achieve the second order accuracy in space and time. This study introduce the new and simple technique to discretize the source terms of gravity and hydrostatic pressure force due to longitudinal width variation for the balance of quantity between nonlinear flux and source terms. The results show that the developed model's implementation is accurate, robust and highly stable in various flow conditions with source terms, and this model is reliable for one-dimensional applications in hydraulic engineering.

• Computational Structural Engineering
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• v.11 no.1
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• pp.171-178
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• 1998

The added viscoelastic dampers increase damping and stiffness of buildings and results in so called non-classical or non-proportional damping problem. In this system the eigenvectors of the undamped system may not diagonalize the damping matrix, and the system is generally analyzed by converting the equation of motion into a 2n first order state-space form. As this approach is complex and time-consuming compared to the classically damped problem, the system is often analyzed by neglecting the off-diagonal terms in the damping matrix. In this paper the theoretical background of the approximate approach is studied, and the vibration characteristics of a three-story shear building with a viscoelastic damper are investigated using the exact and approximate method. It is found that the approximate method may produce good result when the additional damping is small, but as the damping increases the error also increase.

• Nuclear Engineering and Technology
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• v.21 no.1
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• pp.56-61
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• 1989

A simple, approximate method for determining the two-group adjoint flux based on the Borresen's coarse-mesh 1.5 group diffusion theory scheme is proposed. With the principle of the 1.5 group diffusion theory scheme, the method describes the thermal leakage term of the adjoint flux approximately by the geomerical buckling determined from the fast adjoint flux. The accuracy of the adjoint flux is investigated tv the comparison of the adjoint flux constructed from this method with a fine-mesh finite-difference KIDD computations. It is shown that the proposed method can predict the adjoint flux as good as the KIDD results. Possible applications of the present method are then suggested in conjunction with the application of the perturbation theory.

• Journal of the Korea Society of Computer and Information
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• v.14 no.12
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• pp.127-137
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• 2009

A practical algorithm of generating most probable states in decreasing order of probability of the network system state is suggested for approximating the performance of multi-mode network system using algebraic structure of the system states. Most complex system having network structure with multi-mode unit state is difficult to evaluate the performance or reliability due to exponentially increasing size of state space. Hence not an exact computing method but an approximated one is reasonable approach to solve the problem. To achieve the goal we should enumerate the network system states in order as a pre-processing step. In this paper, we suggest an improved algorithm of generating most probable multi-mode states to get the ordered system states efficiently. The method is compared with the previous algorithms in respective to memory requirement and empirical computing time. From the experiment proposed method has some advantages with regard to the criterion of algorithm performance. We investigate the advantages and disadvantage by illustrating experiment examples.

• The Journal of Information Technology
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• v.3 no.2
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• pp.73-85
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• 2000

The efficient algorithms are suggested in this study for solving the multicommodity network flow problems applied to Communications Systems. These problems are typical NP-complete optimization problems that require integer solution and in which the computational complexity increases numerically in appropriate with the problem size. Although the suggested algorithms are not absolutely optimal, they are developed for computationally efficient and produce near-optimal and primal integral solutions. We supplement the traditional Lagrangian method with a price-directive decomposition. It proceeded as follows. First, A primal heuristic from which good initial feasible solutions can be obtained is developed. Second, the dual is initialized using marginal values from the primal heuristic. Generally, the Lagrangian optimization is conducted from a naive dual solution which is set as ${\lambda}=0$. The dual optimization converged very slowly because these values have sort of gaps from the optimum. Better dual solutions improve the primal solution, and better primal bounds improve the step size used by the dual optimization. Third, a limitation that the Lagrangian decomposition approach has Is dealt with. Because this method is dual based, the solution need not converge to the optimal solution in the multicommodity network problem. So as to adjust relaxed solution to a feasible one, we made efficient re-allocation heuristic. In addition, the computational performances of various versions of the developed algorithms are compared and evaluated. First, commercial LP software, LINGO 4.0 extended version for LINDO system is utilized for the purpose of implementation that is robust and efficient. Tested problem sets are generated randomly Numerical results on randomly generated examples demonstrate that our algorithm is near-optimal (< 2% from the optimum) and has a quite computational efficiency.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.4
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• pp.795-805
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• 1994

This paper presents the analytical results for the prediction of elastical local buckling stress of fiber reinforced plastic (orthotropic) structural shapes manufactured from pultrusion process. In the derivation, existing Bleich's approach which was originally derived for the isotropic structural shapes was extended and non-dimensionalized parameters which can simplify the numerical calculations were adopted. Analytical results were compared with reported closed-form solutions and experimental results. It is graphically shown that the results can be used effectively to predict the local buckling stress of pultruded fiber reinforced plastic structural shapes. Numerical results were presented graphically to estimate the local buckling stress of various cross-sectional dimensions and lengths of columns. In addition, limits of width to thickness ratio of flange and web of pultruded structural shapes were suggested in which material failure or overall buckling occurs prior to local buckling.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.1B
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• pp.21-27
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• 2012

The HLLL scheme, proposed by T. Linde, determines all the wave speeds from the initial states because the middle wave is evaluated by the introduction of a generalized entropy function. The scheme is considered a genuine successor to the original HLL scheme because it is completely separated form the Roe's linearization scheme unlike the HLLE scheme and does not rely on the exact solution unlike the HLLC scheme. In this study, a numerical model was configured by the HLLL scheme with the total energy as a generalized entropy function to solve governing equations, which are the one-dimensional shallow water equations without source terms and with an additional conserved variable relating a concentration. Despite the limitations of the first order solutions, results to three cases with the exact solutions were generally accurate. The HLLL scheme appeared to be superior in comparison with the other HLL-type schemes. In particular, the scheme gave fairly accurate results in capturing the front of wetting and drying. However, it revealed shortcomings of more time-consuming calculations compared to the other schemes.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.4
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• pp.25-33
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• 1990

The moment distribution method has been widely used for almost sixty years as an approximate method for the analysis of structural frames. The method is to calculate the end moments of structural members by iterative hand calculation. This study presents developements of closed form formulas which are derived basically from the moment distribution procedures. These formulas may provide simple forms and exact results which would overcome the disadvantages of the conventional moment distribution mothod, that is, approximation of the results and complexity of the procedures of the method. The proposed formulas may become one of the new procedures for analysis of statically indeterminate frames, and contribute specifically to the effective drawing of influence lines of continuous beams, which will provide a great deal of assistance in practical design of structures.

• Journal of Korean Society of Steel Construction
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• v.18 no.5
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• pp.597-606
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• 2006

Since FRP materials have various advantages over steel, many research activities to use them for the civil engineering applications are now in progress. The present paper deals with the local buckling behavior of FRP pultruded members as a first step toward the development of design criteria. In the design of compression members, it is very important to know not only if local buckling occurs or not but also which plate component governs local buckling, but it is not easy to perform this work in a rigorous manner. In the present paper, a simple and accurate equation which can compute the coefficients of buckling of orthotropic plates and local buckling of pultruded compression members is suggested by performing rigorous analysis, energy analysis, and parametric study. The local buckling strength and the plate component governing the local buckling behavior of thin-walled pultruded compression members can be easily determined by using the proposed equation.