• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.9
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• pp.773-779
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• 2014

A qualitative and quantitative analysis on flame dynamics is required to model combustion instability characteristics in gas turbine lean premixed combustors. The current paper shows the flame transfer function modeling results using CFD(Computational Fluid Dynamics) techniques for the flame dynamics study. It is generally known that flame shapes determine the basic characteristics of the flame transfer function. The comparisons of the modeled flame shapes with the measured ones were made using the optimized heat transfer conditions. Modeling results of the flame transfer function show the close behaviors to the measured data with a reasonable accuracy if the flame geometry can be exactly captured.

• Korean Journal of Computational Design and Engineering
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• v.19 no.4
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• pp.316-323
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• 2014

This paper proposes the 3D modeling and simulation technique for predicting the integrated performance of combat vehicle. To consider the practical driving and firing condition of a combat vehicle, the full vehicle model, which can define the six degrees-of-freedom of vehicle motion and various firing angles, is developed. The critical design parameters such as the stiffness and damping coefficient of suspension system are applied to construct the analysis model of vehicle. A simple ballistic model, which incorporates the empirical interior ballistic model and the point mass trajectory model, is built to estimate the firing range and the firing recoil force. To predict the integrated performance and analyze the effect of system parameters, MATLAB/SIM-ULINK model of a combat vehicle for performing the real time simulation is also developed. Several simulation tests incorporating the road bump and the firing recoil force are presented to confirm the effectiveness of the proposed vehicle model.

• Coupled systems mechanics
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• v.7 no.6
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• pp.731-753
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• 2018

The recent seismic events have led to concerns on safety and vulnerability of Reinforced Concrete Moment Resisting Frame "RC-MRF" buildings. The seismic design demands are greatly dependent on the computational tools, the inherent assumptions and approximations introduced in the modeling process. Thus, it is essential to assess the relative importance of implementing different modeling approaches and investigate the computed response sensitivity to the corresponding modeling assumptions. Many parameters and assumptions are to be justified for generation effective and accurate structural models of RC-MRF buildings to simulate the lateral response and evaluate seismic design demands. So, the present study aims to develop reliable finite element model through many refinements in modeling the various structural components. The effect of finite element modeling assumptions, analysis methods and code provisions on seismic response demands for the structural design of RC-MRF buildings are investigated. where, a series of three-dimensional finite element models were created to study various approaches to quantitatively improve the accuracy of FE models of symmetric buildings located in active seismic zones. It is shown from results of the comparative analyses that the use of a calibrated frame model which was made up of line elements featuring rigid offsets manages to provide estimates that match best with estimates obtained from a much more rigorous modeling approach involving the use of shell elements.

• Journal of the Korean Society of Safety
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• v.33 no.5
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• pp.28-34
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• 2018

Recently, various engineering approaches have been widely used in the accident investigation field to identify the cause of the accident and to predict damage by accident. Computational analysis is the most commonly used method of accident investigation technique. This technique is mainly used to identify the mechanism of the accident generation and to determine the cause when it is difficult to reproduce the situation at the time of the accident or when it is impossible to perform a reproduction experiment. In this study, The computational fluid dynamics analysis for nitrogen asphyxiation accident generated by defect of building structural between diffusion outlet and cooling tower was performed to determine the inflow path of the suffocation gas, death possibility by concentration of suffocation gas and predicted the time of death due to the accident using 3D modeling and FLACS program. We can quantify diffusion concentration of asphyxiation gas and predict mechanism of death occurrence by accident and evaluate the consequence Analysis through this study. In the future, This method can be widely used in the field of gas safety by improving the reliability and validity of the analysis.

• Steel and Composite Structures
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• v.29 no.2
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• pp.175-186
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• 2018

The plastic hinge method and the plastic zone method are extensively adopted in displacement-based elements and force-based elements respectively for second-order inelastic analysis. The former enhances the computational efficiency with relatively less accurate results while the latter precisely predicts the structural behavior but generally requires more computer time. The displacement-based elements receive criticism mainly on plasticity dominated problems not only in accuracy but also in longer computer time to redistribute the forces due to formation of plastic hinges. The multi-element-per-member model relieves this problem to some extent but will induce a new problem in modeling of member initial imperfections required in design codes for direct analysis. On the contrary, a force-based element with several integration points is sufficient for material yielding. However, use of more integration points or elements associated with fiber section reduces computational efficiency. In this paper, a new force-based element equipped with stress-resultant plasticity model with minimal computational cost is proposed for second-order inelastic analysis. This element is able to take the member initial bowing into account such that one-element-per-member model is adequate and complied with the codified requirements of direct analysis. This innovative solution is new and practical for routine design. Finally, several examples demonstrate the validity and accuracy of the proposed method.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.3
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• pp.237-248
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• 2011

Tensile softening characteristics play an important role in the structural behavior of steel fiber-reinforced ultra high performance concrete. Tension softening modeling and numerical analysis method are necessary for the prediction of structural performance of steel fiber-reinforced concrete. The numerical method to predict the flexural behavior is proposed in this study. Tension softening modeling is carried out by using crack equation based on fictitious crack and inverse analysis in which load-crack opening displacement relationship is considered. Thereafter material modeling is performed considering tension softening. The comparison of moment-curvature curves of the numerical analysis results with the test results indicates a reasonable agreement. Therefore, the present numerical results prove that good prediction of flexural behavior of steel fiber-reinforced ultra high performance concrete beams can be achieved by employing the proposed method.

• Journal of Broadcast Engineering
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• v.18 no.1
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• pp.1-9
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• 2013

Accuracy of the 3-D model is essential in model-based camera tracking. However, 3-D object modeling requires dedicated and complicated procedures for precise modeling without any errors. Even if a 3-D model contains a certain level of errors, on the other hand, the tracking errors cause by the modeling errors can be different from its perceptual errors; thus, it is an important aspect that the camera tracking can be successful without precise 3-D modeling if the modeling errors are within the user's permissible range. In this paper, we analyze the tolerance of 3-D object modeling errors by comparing computational matching errors with perceptual matching errors through user evaluations, and also discuss permissible ranges of 3-D object modeling errors.

• Korean Journal of Computational Design and Engineering
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• v.12 no.2
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• pp.137-145
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• 2007

This paper concerns about residential environment analysis program implementation for design and analysis on public housing complexes such that view and daylight analysis processes are automated and integrated into existing design routine to achieve better design efficiency. Considering the architectural design trends this paper chooses ArchiCAD as a platform for a CAD system, which contains the concepts such as integrated object-oriented CAD, virtual building and BIM. Residential environment analysis system consists of three components. The first component is the 3D modeling part defining 3D form information for external geographic contour models, site models and interior/exterior of apartment buildings. The second is the parametric library part handling the design parameters for view and daylight analysis. The last is the user interface for the input/output and integration of data for the environment analysis. Daylight analysis shows rendered images as well as results of daylight reports and grades per time and performs the calculations for floor shadow. It separates the site-only analysis from the analysis of site and exterior environmental parameters. View analysis considers horizontal and vertical view angles to produce view image from each unit and uses the bitmap analysis method to determine opening ratio, scenery ratio and void ratio. We could expect better performance and precision from this residential environment analysis system than the existing 2D drawing based view and daylight analysis methods and overcome the existing one-way flow of design information from 3D form to analysis reports so that site design modifications are automatically reflected on analysis results. Each part is developed in a module so that further integration and extension into other related estimation and construction management systems are made possible.

• Nuclear Engineering and Technology
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• v.44 no.1
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• pp.33-42
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• 2012

In the present study, CFD is employed to investigate phenomena occurring during a process of thermal stratification in U-bent pipes at transitional Reynolds number. URANS evaluation had been chosen for its low computational costs during transient analysis and for the evaluation of modeling performance in these conditions. Application of CFD at transitional Reynolds number and buoyancy driven flows indeed contains deeper uncertainties in relation to the range of applicability for hydrodynamic and thermal models. The methodology applied in the work points out, through validations with the basic problems constituting the complex stratified phenomenon, the applicability of the current turbulence modeling. Accurate predictions have been found in relation to transitional Reynolds number in bent pipes and region of stability induced by the gravitational field. On the other hand the defects introduced in the unstable region of the U bent pipe, are discussed in relation to the adopted modeling.

• Journal of ILASS-Korea
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• v.21 no.2
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• pp.104-110
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• 2016

Main purpose of the current paper is to show results of time lag analysis using phase information of flame transfer function in order to predict combustion instabilities in a gas turbine combustor. The flame transfer function (FTF) is modeled using a commercial Computational Fluid Dynamics (CFD) code (Fluent). Comparisons of the modeled flame shapes with the measured ones were made using the optimized heat transfer conditions and combustion models. The FTF modeling results show a quite good agreement with the measurement data in predicting the phase delay (i.e. time lag). Time lag analysis results using the phase of FTF shows better combustion instability prediction accuracy than using time lag calculated from the steady state flame length.