• Journal of the Korea Institute of Building Construction
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• v.19 no.1
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• pp.39-46
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• 2019

A three-dimensional flow simulation model for high flow concrete was developed using Incompressible Smoothed Particle Hydrodynamics (ISPH), which can solved Navier-Stokes equation with the assumption of a fluid to be incompressible. For the simulation, a computer program code for ISPH was implemented with MATALB programming code. A piecewise cubic spline function was used for the kernel function of ISPH. Projetion method was used to calculate the velocity and pressure of particles as a function of time. Fixed ghost particle was used for wall boundary condition. Free surface boundaries were determined by using virtual density of particles. In order to validate the model and the code, the simulation results of slump flow test, $T_{500}$ test and L-box test were compared with experimental ones. The simulation results were well matched with the experimental results. The simulation described successfully the characteristics of the flow phenomenon according to the change of the viscosity and yield stress of high flow concrete.

• Geotechnical Engineering
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• v.9 no.1
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• pp.45-58
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• 1993

Paper drain method is one of the methods used for the improvement of soft clay as hydraulic fill sites or the seaside industrial complex. This method adopts a card board as the drain materials instead of sand piles in sand drain method. In this paper 3 types of drain board are used to fond out the characteristics of consolidation by vacuum consolidation model test. So does the no drain board test. This test causes the reduction of pore water pressure to promote the settlement without change of ground water level. Conclusively, the vacuum consolidation shows 3-dimensional behaviors and pore water pressure reaches a negative value in a short time. In addition, it is expected to have a comparatively good consolidation effect using non -woven board, and vacuum loading results in increasing the shear strength at the bottom and top of call layers.

• Journal of Korean Society for Geospatial Information Science
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• v.14 no.4 s.38
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• pp.61-70
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• 2006

This paper presents photogrammetric processing to generate digital elevation models using SPOT-5 HRG stereo images and deals with the accuracy potential of HRG (High Resolution Geometry) supermode imagery for DEM generation. After bundle adjustment was preformed for sensor modelling, digital surface models were generated through the procedures of Epipolar image resampling and image matching. The DEM extracted from HRG imagery was compared along several test sections with the the refernce DEM which was obtained from the digital topographic maps of a scale of 1 to 5000. The ratio of the zone with DEM errors less than 5m to the whole zone was 53.8%, and about 2.5m RMSE was showed when assuming that the zones larger than 5m were affected by clouds, water bodies and buildings and excluding those zones from accuracy evaluation. In addition, the three-dimensional bird's eye view model and 3D building model were producted based on the DSM which was extracted from SPOT-5 HRG data.

• Geomechanics and Engineering
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• v.15 no.5
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• pp.1061-1070
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• 2018

The main purpose of retaining wall methods for deep excavation is to keep the construction site safe from the earth pressure acting on the backfill during the construction period. Currently used retaining wall methods include the common strut method, anchor method, slurry wall method, and raker method. However, these methods have drawbacks such as reduced workspace and intrusion into private property, and thus, efforts are being made to improve them. The most advanced retaining wall method is the prestressed wale system, so far, in which a load corresponding to the earth pressure is applied to the wale by using the tension of a prestressed (PS) strand wire. This system affords advantages such as providing sufficient workspace by lengthening the strut interval and minimizing intrusion into private properties adjacent to the site. However, this system cannot control the tension of the PS strand wire, and thus, it cannot actively cope with changes in the earth pressure due to excavation. This study conducts a preliminary numerical analysis of the field applicability of the controllable prestressed wale system (CPWS) which can adjust the tension of the PS strand wire. For the analysis, back analysis was conducted through two-dimensional (2D) and three-dimensional (3D) numerical analyses based on the field measurement data of the typical strut method, and then, the field applicability of CPWS was examined by comparing the lateral deflection of the wall and adjacent ground surface settlements under the same conditions. In addition, the displacement and settlement of the wall were predicted through numerical analysis while the prestress force of CPWS was varied, and the structural stability was analysed through load tests on model specimens.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.1
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• pp.1-7
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• 2014

The present study numerically investigated the effect of the advance ratio on the wake characteristics of the marine propeller in the propeller open water test. Therefore, a wide range of the advance ratio(0.2${\kappa}-{\omega}$SST Model are considered. The three-dimensional vortical structures of tip vortices are visualized by the swirl strength, resulting in fast decay of the tip vortices with increasing the advance ratio. Furthermore, to better understanding of the wake evolution, the contraction ratio of the slip stream for different advance ratios is extracted from the velocity fields. Consequently, the slip stream contraction ratio decreases with increasing the advance ratio and successively the difference of the slip stream contraction ratio between J=0.2 and J=0.8 is about 0.1R.

• Korean Journal of Metals and Materials
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• v.48 no.5
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• pp.469-475
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• 2010

In this study, the interfacial bond strength of a squeeze infiltrated $Al_{18}B_{4}O_{33}$/AS52 Mg composite was investigated by using a finite element method. Three types of Mg composites with volume fractions of 15, 25 and 35% were fabricated. Three-dimensional models of the composite were developed by using a unit cell model in order to determine the effective elastic modulus of the metal matrix composite and the interfacial bond strength between the whisker and magnesium matrix. After modeling, numerical results were compared with the experimental tensile test results of $Al_{18}B_{4}O_{33}$/AS52 Mg composites. The results showed that the effective modulus of the composite strongly depended on the interfacial strength between the matrix and reinforcement. Based on the numerical and experimental findings, it was found that the strong interfacial bond was achieved by the interfacial reaction product of 30 nm thick MgO, which led to an improvement in the mechanical properties of the $Al_{18}B_{4}O_{33}$/AS52 Mg composites.

• Nuclear Engineering and Technology
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• v.56 no.6
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• pp.1950-1958
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• 2024

For the pressurized water reactor two-step calculation, the traditional assembly homogenization and two-group neutron diffusion calculation have been widely used. When it comes to the core pin-by-pin simulation, many models and techniques are different and unsettled. In this paper, the homogenization methods based on the pin discontinuity factors and super homogenization factors are used to get the pin-cell homogenized parameters. The heterogeneous leakage model is applied to modify the infinite flux spectrum of the single assembly with reflective boundary condition and to determine the diffusion coefficients for the SP3 solver which is used in the core simulation. To reduce the environment effect of the single-assembly reflective boundary condition, the online method for the SPH factors updating is applied in this paper, and the functionalization of SPH factors based on the least-squares method will be pre-made alone with the table of the group constants. The fitting function will be used to update the thermal-group SPH factors with a whole-core pin-by-pin homogeneous solution online. The three-dimensional Watts Bar Nuclear Unit 1 (WBN1) problem was utilized to test the performance of pin-by-pin calculation. And numerical results have demonstrated that PWR pin-by-pin core calculation has more accurate results compared with the traditional assembly-homogenization scheme.

• Water Engineering Research
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• v.3 no.1
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• pp.57-62
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• 2002

This research is intended to integrate long-term operation rules and real time operation policy for conservation & flood control in a reservoir. The familiar Yield model has been modified and used to provide long-term rule curves. The model employs linear programming technique under given physical conditions, i.e., total capacity, dead storage, spillways, outlet capacity and their respective elevations to find required and desired minimum storage fur different demands. To investigate the system behavior resulting from the above-mentioned operating policy, i.e., the rule curves, the simulation model was used. Results of the simulation model show that the results of the optimization model are indeed valid. After confirmation of the above mentioned rule curves by the simulation models, gate operation procedure was merged with the long term operation rules to determine the optimum reservoir operating policy. In the gate operation procedure, operating policy in downstream flood plain, i.e., determination of damaging and non-damaging discharges in flood plain, peak floods, which could be routed by reservoir, are determined. Also outflow hydrograph and variations of water surface levels for two known hydrographs are determined. To examine efficiency of the above-mentioned models and their ability in determining the optimum operation policy, Esteghlal reservoir in Iran was analyzed as a case study. A numerical model fur the solution of two-dimensional dam break problems using fractional step method is developed on unstructured grid. The model is based on second-order Weighted Averaged Flux(WAF) scheme with HLLC approximate Riemann solver. To control the nonphysical oscillations associated with second-order accuracy, TVD scheme with SUPERBEE limiter is used. The developed model is verified by comparing the computational solutions with analytic solutions in idealized test cases. Very good agreements have been achieved in the verifications.

• 한국HCI학회:학술대회논문집
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• 2006.02a
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• pp.33-39
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• 2006

Home modification has come to be recognized as an important intervention strategy to manage health care conditions, maintain or improve functioning, ensure safety, and reduce the wheelchair user's dependency on others. However, the availability of skilled professionals with experience in home modifications for accessibility is limited. A system that enables accurate remote assessments would be an important tool to improve our ability to perform home assessments more easily and at decreased cost. A Remote Wheelchair Accessibility Assessment System (RWAAS) using Virtualized Reality(VR) technology was developed that enabled clinicians to assess the wheelchair accessibility of users' built environments from a remote location. Characteristics of the camera and 3D reconstruction program chosen for the system significantly affect its overall reliability. In this study, we performed two reliability analyses on the hardware and software components: 1) Verification that commercial software can construct sufficiently accurate 3D models by analyzing the accuracy of dimensional measurements in a virtualized environment; 2) comparison of dimensional measurements with four camera settings. Based on these two analyses, we were able to specify a consumer level digital camera and the Photomodeler Pro software for this system. And we then tested the feasibility of the selected software and hardware in an actual environment. Lastly, A field evaluation was performed to test whether this new system is comparable to the traditional method of accessibility assessment to evaluate its ability to assess the accessibility of a wheelchair user's typical built environment. The results of field trials showed high congruence between the assessments by two methods. Findings suggested that the RWAAS assessments have the potential to enable specialists to assess potential accessibility problems in built environments regardless of the location of the client, home, or specialist.

• Journal of Oral Medicine and Pain
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• v.41 no.3
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• pp.85-90
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• 2016

Purpose: The aim of this study was to develop an automated software to extract tooth and pulpal area from sectional cone-beam computed tomography (CBCT) images, which can guarantee more reproducible, objective and time-saving way to measure pulp/tooth volume ratio. Methods: The software program was developed using MATLAB (MathWorks). To determine the optimal threshold for the region of interest (ROI) extraction, user interface to adjust the threshold for extraction algorithm was added. Default threshold was determined after several trials to make the outline of extracted ROI fitting to the tooth and pulpal outlines. To test the effect of starting point location selected initially in the pulpal area on the final result, pulp/tooth volume ratio was calculated 5 times with different 5 starting points. Results: Navigation interface is composed of image loading, zoom-in, zoom-out, and move tool. ROI extraction process can be shown by check in the option box. Default threshold is adjusted for the extracted tooth area to cover whole tooth including dentin, cementum, and enamel. Of course, the result can be corrected, if necessary, by the examiner as well as by changing the threshold of density of hard tissue. Extracted tooth and pulp area are reconstructed three-dimensional (3D) and pulp/tooth volume ratio is calculated by voxel counting on reconstructed model. The difference between the pulp/tooth volume ratio results from the 5 different extraction starting points was not significant. Conclusions: In further studies based on a large-scale sample, the most proper threshold to present the most significant relationship between age and pulp/tooth volume ratio and the tooth correlated with age the most will be explored. If the software can be improved to use whole CBCT data set rather than just sectional images and to detect pulp canal in the original 3D images generated by CBCT software itself, it will be more promising in practical uses.