• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.4
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• pp.381-387
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• 2016

In this paper, the methodology applied to the improvement of stress analyses is extended to free vibration and buckling analyses. The essence of the methodology is the Saint-Venant's principle that is applicable to beam and plate models. The principle allows one to dimensionally reduce three-dimensional elasticity problems. Thus the methodology can be employed to vibration and buckling as well as stress analysis. First, the principle is briefly revisited, and then the formations of classical beam theories are presented. To improve the predictions, the perturbed terms (unknowns) are introduced together with the warping functions that are calculated by stress equilibrium equations. The unknowns are then calculated by applying the equivalence of stress resultants (i.e., Saint-Venant's principle). As numerical examples, cantilever and simply supported beams are analytically solved. The results obtained are compared with those of the classical beam theories. It is shown that the methodology can be used to improve the predictions without introducing shear correction factors.

• Journal of Energy Engineering
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• v.21 no.1
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• pp.1-17
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• 2012

In Korea, there are increasing concerns on nuclear manpower demand and supply due to construction of domestic nuclear power plants and exporting nuclear power plant. In addition, aging of nuclear manpower is another important concern for stable nuclear manpower demand and supply. A shortage of skilled high-quality human resources resulted in massive retirements of senior workers may seriously undermine Korean nuclear competitiveness. This paper analyzed current state of aging of nuclear manpower based on statistical analysis on Korean nuclear organizations. The data used in this paper is manpower statistics of domestic nuclear organizations surveyed in 2001 and 2010. This paper analyzed trends of manpower change for 10 years and based on these analyses, has reviewed the level of the aging nuclear manpower by surveyed organization and integrated. Finally, this paper suggested to direction of manpower recruitment to cope with aging nuclear manpower and alternatives to find a solution to problems of nuclear manpower demand and supply.

• Journal of Korean Society of Steel Construction
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• v.17 no.6 s.79
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• pp.661-672
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• 2005

For the efficient stochastic optimization of steel structures for which a large number of analyses is required, artificial neural networks,which have emerged as a powerful tool that could have been used to replace time-consuming procedures in many scientific or engineering applications, are applied. They are utilized for the solution of the equilibrium equations resulting from the application of the finite element method in connection with the reanalysis type of problem, for which a large number of finite element analyses are required in this study. As such, the use of artificial neural networks to predict finite element analysis outputs simplifies and facilitates the performance of the stochastic optimal design of structural systems where a trained neural network is used to replace the structural reanalysis phase. Moreover, to improve efficiency of used artificial neural networks, genetic algorithm is utilized. The stochastic optimizer used in this study is an algorithm based on the evolution theory. The efficiency of the proposed procedure is examined in problems with both volume (weight) functions and real-world cost functions

• Computational Structural Engineering
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• v.3 no.3
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• pp.113-123
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• 1990

The paper is concerned with the elasto-plastic and geometrically nonlinear analysis of shell structures using an improved degenerated shell element. In the formulation of the element stiffness, the combined use of three different techniques was made. They are; 1) an enhanced interpolation of transverse shear strains in the natural coordinate system to overcome the shear locking problem ; 2) the reduced integration technique in in-plane strains to avoid the membrane locking behavior ; and 3) selective addition of the nonconforming displacement modes to improve the element performances. This element is free of serious shear/membrane locking problems and undesirable compatible/commutable spurious kinematic deformation modes. In the formulation for plastic deformation, the concept of a layered element model is used and the material is assumed von Mises yield criterion. An incremental total Lagrangian formulation is presented which allows the calculation of arbitrarily large displacements and rotations. The resulting non-linear equilibrium equations are solved by the Netwon-Raphson method combined with load or displacement increment. The versatility and accuracy of this improved degenerated shell element are demonstrated by solving several numerical examples.

• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.6
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• pp.530-539
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• 2013

In large vessels, proper water level must be maintained with a balance for right and left equilibrium by absorbing or draining sea water in ballast water tank. However, this ship's ballast-water can be drained marine organisms to local sea area by world trade and this can be a source of ecological disturb. In order to solve these problems, marine organisms must be removed in accordance with the international covenant for the emission of microorganisms. By this reason, the seawater electrolysis rectifier of low-voltage high-current rectifiers with excellent ability for microbial treatment is required. In this paper, PSFB converter will be discussed for the seawater electrolysis rectifier. Furthermore, a new output control method with the power limit operation under the limited maximum voltage condition is proposed for this rectifier. The simulation for the proposed current control method for PSFB Converter is shown using MATLAB/SIMULINK. Finally the usefulness of the proposed control method is presented by the experimental results.

• Journal of the Korean association of regional geographers
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• v.10 no.2
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• pp.341-355
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• 2004

This thesis is to analyze characteristic of sustainable development in the Nak-dong River. The results are summarized in the followings. 1) The principles which did not consider the equilibrium between development and environment, ecosystem, security. precautionary measure, equity could devise a plan, changes of economic land area, sand & gravel extractions from the riverbed, the river contamination cleanup, dam build 2) The rules which disregard polluter pay and opening participation in public affairs could input of too much province budget and manpower, project team. The measures to solve these problems could be proposed expansion of environmental infrastructure, sustainable sand & gravel extractions from the riverbed, fortifying the assistance of the residents who live in Dam construction site and the peripheral area of Dam, lower local fund rates in national projects, and the creation of management organization.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.3
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• pp.2178-2184
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• 2015

With the development of wireless network technologies, mobile users may use various networks easily and expect more advanced services. On the other hand, it may bring on some problems with network resource management that should lead the service provider to improve the current service quality and manage the network resource efficiently. This paper proposes the optimized radio resource management (RRM) scheme that integrates the Grey Relational Analysis (GRA) and game theory. The first applies the GRA to determine the Grey Relation Coefficient (GRC) factors that represent the network preference, and the network provider then selects the requested service that provide maximum payoff through Nash Equilibrium. Six requested services that have one application service among four different types of service classes were considered and the game was played repeatedly. In WiMAX, WLAN 1 and WLAN 2 game, the maximum payoff of each players was 93, 90.6 and 92.8 respectively. The experimental results show that every requested service can be selected by the network provider. Consequently, the proposed radio resource management mechanism is more effective in heterogeneous wireless networks.

• Journal of Navigation and Port Research
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• v.36 no.6
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• pp.513-519
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• 2012

Understanding the behavior of pollutants in the marine environment is essential for coping with the marine pollution problems such as eutrophication. In this study, the effects of environmental parameters on phosphorus release from marine sediment to sea water were investigated. The environmental parameters such as pH in the range of 7 to 9, temperature from 10 to 20C and dissolved oxygen levels (DO) renging 0.7 to 7.0mg/L were examined. Phosphorus release data were taken from batch tests excluding biotic effects, and analyzed using a first-order kinetic model. The effects of environmental parameters were quantified using a statistical methodology. High pH, high temperature, and low DO increased phosphorus release from the sediment to sea water. pH from 7 to 9, temperature from 10 to $20^{\circ}C$, or DO from 7.0 to 0.7 mg/L magnified the equilibrium phosphorus concentration up to 2~3 times.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.3
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• pp.237-244
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• 2016

This paper presents a nonlinear Moving Least Squares(MLS) difference method for material nonlinearity problem. The MLS difference method, which employs strong formulation involving the fast derivative approximation, discretizes governing partial differential equation based on a node model. However, the conventional MLS difference method cannot explicitly handle constitutive equation since it solves solid mechanics problems by using the Navier's equation that unifies unknowns into one variable, displacement. In this study, a double derivative approximation is devised to treat the constitutive equation of inelastic material in the framework of strong formulation; in fact, it manipulates the first order derivative approximation two times. The equilibrium equation described by the divergence of stress tensor is directly discretized and is linearized by the Newton method; as a result, an iterative procedure is developed to find convergent solution. Stresses and internal variables are calculated and updated by the return mapping algorithm. Effectiveness and stability of the iterative procedure is improved by using algorithmic tangent modulus. The consistency of the double derivative approximation was shown by the reproducing property test. Also, accuracy and stability of the procedure were verified by analyzing inelastic beam under incremental tensile loading.

• Journal of Radiation Protection and Research
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• v.11 no.1
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• pp.77-82
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• 1986

Determination of the relation between the kerma(Kinetic Energy Released in Material) and the absorbed dose is one of the basic problems of dosimetry. Kerma and absorbed dose were measured for 6 MV X-ray from the high energy medical linear accelerator and $^{60}Co$ gamma-ray. The experimental results show that the absorbed dose in the transient equilibrium region practically coincide with the kerma in water and Al for $^{60}Co$. The maximum dose depths were $1.45g/cm^2$ for 6MV X-ray and $0.48g/cm^2\;for\;^{60}Co$ gamma-ray. The ratios of the absorbed dose at maximum build-up to the collision kerma at the surface, ($K^{att}$), were 0.949 for 6MV X-ray and 0.992 for $^{60}Co$ gamma-ray. No difference was found between water and Al when the standard field size was used. This results show that the dependence of $K^{att}$ on the material is very small.