• KSCE Journal of Civil and Environmental Engineering Research
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• v.4 no.1
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• pp.49-58
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• 1984

This paper is to exhibit the numerical analysis of sediment transport in the slowly varing flow and the sediment transport relation between the steady and the unsteady flow in the alluvial stream. The gradually varied flow of alluvial stream and the sediment transport are very complicated physical phenomen. Therefore the mathematical modeling is needed to be established. Linear implicit means of modified indirect method are applied to sediment transport by numerical analysis instead of the conception of steady flow in order to decrease errors. Further more, this study has purpose on reasonable prediction of the river-bed variation by way of this numerical method.

• Journal of Mechanical Science and Technology
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• v.17 no.1
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• pp.129-138
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• 2003

A 1 : 20 laboratory scale test rig of a 200 MW tangentially fired boiler is built up with completely simulated structures such as platen heaters and burners. Iso-thermal turbulent flow in the boiler is mapped by 3-D PDA (Particle Dynamic Analyzer). The 3-D numerical models for the same case are proposed based on the solution of к-$\varepsilon$ model closed RANS (Reynolds time-Averaged Navier-Stokes) equations, which are written in the framework of general coordinates and discretized in the corresponding body-fitted meshes. Not only are the grid lines arranged to fit the inner/outer boundaries. but also to align with the streamlines to the best possibility in order to reduce the NDE (numerical diffusion errors). Extensive comparisons of profiles of mean velocities are carried out between experiment and calculation. Predicted velocities in burner region were quantitatively similar with measured ones, while those in other area have same tendency with experimental counterpart.

• Smart Structures and Systems
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• v.26 no.1
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• pp.63-75
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• 2020

Substructure pseudo-dynamic hybrid simulation (SPDHS) combining the advantages of physical experiments and numerical simulation has become an important testing method for evaluating the dynamic responses of structures. Various parameter identification methods have been proposed for online model updating. However, if there is large model gap between the assumed numerical models and the real models, the parameter identification methods will cause large prediction errors. This study presents an ANN (artificial neural network) method based on forgetting factor. During the SPDHS of model updating, a dynamic sample window is formed in each loading step with forgetting factor to keep balance between the new samples and historical ones. The effectiveness and anti-noise ability of this method are evaluated by numerical analysis of a six-story frame structure with BRBs (Buckling Restrained Brace). One BRB is simulated in OpenFresco as the experimental substructure, while the rest is modeled in MATLAB. The results show that ANN is able to present more hysteresis behaviors that do not exist in the initial assumed numerical models. It is demonstrated that the proposed method has good adaptability and prediction accuracy of restoring force even under different loading histories.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.5
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• pp.985-990
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• 2019

In subjects dealing with when historically important events took place, the application of memory laws can enhance the educational effectiveness. Methods to increase memory rate by applying additional information such as dots, lines, bars, etc. are being studied in numerical memory-based studies. This study proposes a method of applying the long-term memory mechanism that was lacking in the previous study. This is a mechanism that corrects the error data entered by user's mistake, and tries to increase the memory rate by giving a memorable effect. To this end, we propose the unique processes that are carried out in the mobile environments and we implement and evaluate the error correction numerical algorithms.

• Journal of the Society of Naval Architects of Korea
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• v.57 no.5
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• pp.278-286
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• 2020

Reynolds-averaged Navier-Stokes simulations have been performed to investigate an effect of numerical region with high resolution for Kelvin wave around KRISO container ship on its resistance. In the present study, 13 millions cells were used to describe wave profile along the ship hull and Kelvin wave patterns. In order to control a size of numerical region with high resolution for waves around the hull, we employed relaxation zones from a side boundary of numerical domain in which Kelvin wave was suppressed. When the far-field Kelvin wave was not precisely resolved due to the relaxation zone, the instantaneous history of ship resistance was affected although the time average of ship resistance showed -1.15~2.1 % errors. Especially, the damping characteristics of ship resistance in time history was significant when using a large relaxation zone in the side boundary.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.11
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• pp.17-23
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• 2021

A cyclone is a dust-separating mechanism that works on the principle of centrifugal force. The performance of a cyclone is evaluated using pressure loss and collection efficiency. A multi-cyclone arrangement is used to improve the collection efficiency within a limited area. In this study, experiments and numerical analyses were conducted on a dual arrangement of mini-hydrocyclone separators, which was fabricated using 3D printing. The experiment was performed at an inlet flow rate of 0.7 m/s, and alumina powder with a particle size of 0.5, 15, and 50 ㎛. ANSYS FLUENT, was used for the numerical analysis. The reliability of the numerical analysis was verified through a comparison with the experimental results. The errors in the experiment and numerical analysis were confirmed to be 2% at the outlet flow rate.

• Journal of Digital Convergence
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• v.16 no.5
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• pp.231-237
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• 2018

This paper investigates the impact of the channel variations and channel estimation errors on the error performance of convolutional coded STBC systems. We consider the orthogonal Almouti STBC and the quasi-orthogonal Jafarkhani STBC, and the error performance of the convolutional coded STBC system is investigated according to the channel variation and channel estimation error via numerical simulations. Simulation results show that, if the channel variation speed is slow, time diversity effects improve the error performance compared to the static-channel cases. However, if the channel variation speed is fast, unlike ZF or MMSE detection, the conventional STBC detection has the significant performance degradation especially with the quasi-orthogonal Jafarkhani STBC. Further, the error performance of the system is significantly degraded as the channel estimation errors become stronger, regardless of the detection scheme and channel variation speed.

• Smart Structures and Systems
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• v.18 no.6
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• pp.1169-1188
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• 2016

Real-time substructuring techniques are currently an advanced experimental method for testing large size specimens in the laboratory. In dynamic substructuring, the whole tested system is split into two linked parts, the part of particular interest or nonlinearity, which is tested physically, and the remanding part which is tested numerically. To achieve near-perfect synchronization of the interface response between the physical specimen and the numerical model, a good controller is needed to compensate for transfer system dynamics, nonlinearities, uncertainties and time-varying parameters within the physical substructures. This paper presents the substructuring approach and control performance of the linear and the adaptive controllers for testing the dynamic characteristics of soil-structure-interaction system (SSI). This is difficult to emulate as an entire system in the laboratory because of the size and power supply limitations of the experimental facilities. A modified linear substructuring controller (MLSC) is proposed to replace the linear substructuring controller (LSC).The MLSC doesn't require the accurate mathematical model of the physical structure that is required by the LSC. The effects of parameter identification errors of physical structure and the shaking table on the control performance of the MLSC are analysed. An adaptive controller was designed to compensate for the errors from the simplification of the physical model in the MLSC, and from parameter identification errors. Comparative simulation and experimental tests were then performed to evaluate the performance of the MLSC and the adaptive controller.

• Journal of Korean Society of Transportation
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• v.23 no.8 s.86
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• pp.153-162
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• 2005

This study is carried out to evaluate the sight distance change due to construction errors of vertical crest curves. Various design speeds and grades as well as various size of construction errors are incorporated in this study. After showing theoretical methodology numerical results are compared and analysed for the given ranges of parameters. New vertical curve change rate(m/%) is suggested to guarantee minimum sight distance under construction errors. As to the results, the reduction of sight distance are $2.8{\sim}21.3m$ at 120km/h, $2.0{\sim}15.1m$ at 100km/h, $1.4{\sim}10.6m$ at 80km/h, $1.0{\sim}7.5m$ at 60km/h $0.5{\sim}3.9m$ at 40km/h. Vortical curve change rates need to be increased about $6{\sim}25%$ to provide minimum stopping sight distance according to design speed.

• Korean Journal of Geomatics
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• v.3 no.1
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• pp.15-22
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• 2003

This study aims to construct a management system of road position information as part of the build-up to a maintenance and management system of highways. First, information on the positions of the roads were obtained by a real-time kinematic satellite surveying, and then the degree of accuracy was analyzed in comparison with the data of the existing design drawings. The linear coordinates of road center line obtained by using RTK GPS showed about 7.6-13.2cm errors in X and Y directions in the case of the national road No.2 section, and about 8.4-9.2cm errors in the case of local road No.1045 section. These errors were within the tolerance scope regulated by the TS survey, and could be practically used. In the case of vertical alignment, there were about 6.2cm errors in the Z direction in local road No.1045 section. Aerial photographs are normally used in producing numerical maps, and it can be practically used because the tolerance scope of the elevation control point is l0cm when the scale of aerial photographs is 1/1000. The management system of road position information, utilizing Object-Oriented Programming(OOP), was built having the data acquired in this way as the attribute data. The system developed in this way can enable us to spot the positions of road facilities, the target of management with ease, to easily update the data in case of changes in the positions of roads and road facilities, and to manage the positions of roads and road facilities more effectively.