• Structural Engineering and Mechanics
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• v.51 no.5
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• pp.809-821
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• 2014

The truss based steel bridge structures usually consists of gusset plates which lose their load carrying capacity and rigidity under the effect of repeated and dynamics loads. This paper is focused on modeling the nonlinear material behavior of the gusset plates of the Truss Based Bridges subjected to dynamics loads. The nonlinear behavior of material is characterized by a damage coupled elsto-plastic material models. A truss bridge finite element model is established in Abaqus with the details of the gusset plates and their connections. The nonlinear finite element analyses are performed to calculate stress and strain states in the gusset plates under different loading conditions. The study indicates that damage initiation occurred in the plastic deformation localized region of the gusset plates where all, diagonal, horizontal and vertical, truss member met and are critical for shear type of failure due tension and compression interaction. These findings are agreed with the analytical and experimental results obtained for the stress distribution of this kind gusset plate.

• Wind and Structures
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• v.16 no.6
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• pp.629-660
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• 2013

This paper reviews the current state-of-the-art in the numerical evaluation of wind loads on buildings. Important aspects of numerical modeling including (i) turbulence modeling, (ii) inflow boundary conditions, (iii) ground surface roughness, (iv) near wall treatments, and (vi) quantification of wind loads using the techniques of computational fluid dynamics (CFD) are summarized. Relative advantages of Large Eddy Simulation (LES) over Reynolds Averaged Navier-Stokes (RANS) and hybrid RANS-LES over LES are discussed based on physical realism and ease of application for wind load evaluation. Overall LES based simulations seem suitable for wind load evaluation. A need for computational wind load validations in comparison with experimental or field data is emphasized. A comparative study among numerical and experimental wind load evaluation on buildings demonstrated generally good agreements on the mean values, but more work is imperative for accurate peak design wind load evaluations. Particularly more research is needed on transient inlet boundaries and near wall modeling related issues.

• Journal of Korean Society on Water Environment
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• v.31 no.2
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• pp.181-195
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• 2015

Algal blooms in lakes are one of major environmental issues in Korea. A three-dimensional, hydrodynamic and water quality model was developed and tested in Lake Euiam to assess the performance and limitations of numerical modeling with multiple algal groups using field data commonly collected for algal management. In this study, EFDC was adopted as the basic model framework. Simulated vertical profiles of water temperature, dissolved oxygen and nutrients monitored at five water quality monitoring stations from March to October 2013, which are closely related to algal dynamics simulation, showed good agreement with those of observed data. The overall spatio-temporal variations of three algal groups were reasonably simulated against the chlorophyll-a levels of those estimated from the limited monitoring data (chlorophyll-a level and cell numbers of algal species) with the RMSEs ranging from 2.6 to $17.5mg/m^3$. Also, note that $PO_4-P$ level in the water column was a key limiting factor controlling the growth of three algal groups during most of simulation period. However, the algal modeling results were not fully attainable to the levels of observation during short periods of time showing abrupt increase in algae throughout the lake. In particular, the green algae/cyanobacteria and diatom simulations were underestimated in late June to early July and early October, respectively. The results shows that better understanding of internal algal processes, neglected in most algal modeling studies, is necessary to predict the sudden algal blooms more accurately because the concentrations of external $PO_4-P$ and specific algal groups originated from the tributaries (mainly, dam water releases) during the periods were too low to fully capture the sharp rise of internal algal levels. In this respect, this study suggests that future modeling efforts should be focused on the quantification of internal cycling processes including vertical movement of algal species with respect to changes in environmental conditions to enhance the modeling performance on complex algal dynamics.

• Korean System Dynamics Review
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• v.9 no.2
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• pp.45-75
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• 2008

Roe Deer has been preserved for 25 years by the local government and the residents in Jejudo. However, the damage and harm of crops of the residents by Roe Deer are increasing as well. So, some experts worry about the unstability of ecosystem in Mt. Halla where Roe Deer live. This paper discuss the suitable number of Roe Deer population in Jejudo to protect the ecosystem in Mt. Halla and minimize the damage of residents in Jejudo. With system dynamics modeling and simulation, the population of Roe Deer at present is estimated about 2,300. However, the population of Roe Deer stays 'unstable balance'. So, a little change such as poaching and the increase of wild dogs may make the balance of ecosystem broken. According to the result of policy test simulation, we should keep on watching the poaching and maintain the number of wild dogs at about 100, so that the ecosystem in Jejudo can be stable. To reduce the moving of Roe Deer to low region, moreover, we should protect the Mt. Halla which is Roe Deer's habitat. If we are indifferent about these efforts, the ecosystem of Roe Deer in Mt. Halla will be ruined.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.6
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• pp.1882-1892
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• 1996

This paper is concerned with the position control of the ond degree-of freedom manipulator using pneumatic artificial muscle actuator which is built to have a proper compliance. For t his pneumatic artificial muscle actuator though, it is difficult to make an effective control scheme due to the nonlinearity and uncertainties on the dynamics of the actuator. In this paper, a third-order equation of motion is derived for the actuator including the dynamics of the pneumatic servovalve. Later, various modeling uncertainties due to the nonlinearity and unmodeled dynamics of the servo vlave and the actuator are taken care of, as a trade-off between the closed-loop performance of the controlled system and its robustness to uncertainties. A controller using .mu. synthesis thchnique is designed, and robust performance against measurement noise, various modeling uncertainties due to the dynamics of the servo valve and actuator is achieved. The effectiveness of the proposed control methods is illustrated through simulations and experiments.

• Korean System Dynamics Review
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• v.16 no.1
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• pp.5-23
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• 2015

The purpose of this study is to analyze the land-use changes in the coastal areas using system dynamics modeling and to provide directions for effective management to maintain coastal dune areas. This research process consists of four steps: First, we built the basic model based on the causal loop diagram which was analyzed the land-use change of Sindu-ri Coastal Dune. Second, a time series land-use change map using Arc Map was established. Third, the validity of the basic model was tested. Finally, three simulations were performed for the cut over area($100,000m^2/y$, $150,000m^2/y$, $200,000m^2/y$) of windbreak for maintaining the coastal dune areas. Simulation of the basic model showed that the area of the coastal dune will be consistently decreased. Based on the simulation, if windbreak were cut down $150,000m^2/y$, windbreak area will be restored to the target area in 2019. This study has the limitation which the simulation is progressed with a limited variable: area. Therefore, the modeling of coastal dune should be reflected various variables in the further study.

• Proceedings of the KSME Conference
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• 2001.06b
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• pp.241-246
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• 2001

This paper introduces modeling and solution for the dynamics of pipeline inspection gauge (PIG) flow in natural gas pipeline. Without of bypass flow, the dynamic behavior of the PIG depends on the different pressure between the rear and nose parts, which is generated by injected gas flow behind the tail of the PIG and expelled gas flow in front of its nose. With bypass flow, the PIG dynamics also depends on the amount of bypass flow across its body. The mathematical model are derived for unsteady compressible flow of the PIG driving and expelled gas, and for dynamics of the PIG. The bypass flow is assumed to be incompressible with the condition of its Mach number smaller than 0.45. The method of characteristic (MOC) and the Runge-Kutta method are used to solve the system governing equations. The simulation is performed with a pipeline segment in the Korea Gas Corporation (KOGAS) low pressure system, Ueijungboo-Sangye line. The simulation results show that the derived mathematical model and the proposed solution are effective for estimation the dynamics of the PIG with and without bypass flow under given operational condition.

• Korean System Dynamics Review
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• v.8 no.1
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• pp.187-209
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• 2007

This paper deals with the policy failure in housing markets. In order to understand basic mechanism leading to policy failure, systems thinking and system dynamics modeling is applied to housing markets and housing policy. This paper will show different set of causal maps on housing policy, and compare causal reasons of housing policy and its critics.

• Management Science and Financial Engineering
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• v.19 no.1
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• pp.37-41
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• 2013

This study presents an application of stochastic model for limit order book (LOB) dynamics to Korean Stock Index Futures (KOSPI 200 Futures). Since KOSPI 200 futures market is widely known as one of the most liquid markets in the world, direct application of an existing model is hardly possible. Therefore, we modified an existing model to successfully model and predict the dynamics of extremely liquid KOSPI 200 futures market.

• Journal of the Korea Society for Simulation
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• v.12 no.1
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• pp.49-58
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• 2003

There have been growing recognition on the needs of coordination of diverse activities across cross-functional business areas necessarily involving group decision-making processes. Although many group decision-making support tools and methods have been introduced to enable the collaborative processes of group decision-making, they often lack features supporting the dynamic complexity issues. This study proposes system dynamics modeling approach based on simulation techniques to deal with the group decision-making tasks having properties of dynamic complexity.