• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.4
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• pp.1975-1988
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• 2019

Short-term traffic flow prediction plays an important role in intelligent transportation systems (ITS) in areas such as transportation management, traffic control and guidance. For short-term traffic flow regression predictions, the main challenge stems from the non-stationary property of traffic flow data. In this paper, we design an ensemble cascading prediction framework based on extremely randomized trees (extra-trees) using a boosting technique called EET to predict the short-term traffic flow under non-stationary environments. Extra-trees is a tree-based ensemble method. It essentially consists of strongly randomizing both the attribute and cut-point choices while splitting a tree node. This mechanism reduces the variance of the model and is, therefore, more suitable for traffic flow regression prediction in non-stationary environments. Moreover, the extra-trees algorithm uses boosting ensemble technique averaging to improve the predictive accuracy and control overfitting. To the best of our knowledge, this is the first time that extra-trees have been used as fundamental building blocks in boosting committee machines. The proposed approach involves predicting 5 min in advance using real-time traffic flow data in the context of inherently considering temporal and spatial correlations. Experiments demonstrate that the proposed method achieves higher accuracy and lower variance and computational complexity when compared to the existing methods.

• Journal of Mechanical Science and Technology
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• v.16 no.7
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• pp.959-965
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• 2002

Effective hydraulic conductivity of a statistically anisotropic heterogeneous medium is obtained for steady two-dimensional flows employing stochastic analysis. Flow equations are solved up to second order and the effective conductivity is obtained in a semi-analytic form depending only on the spatial correlation function and the anisotropy ratio of the hydraulic conductivity field, hence becoming a true intrinsic property independent of the flow field. Results are obtained using a statistically anisotropic Gaussian correlation function where the anisotropy is defined as the ratio of integral scales normal and parallel to the mean flow direction. Second order results indicate that the effective conductivity of an anisotropic medium is greater than that of an isotropic one when the anisotropy ratio is less than one and vice versa. It is also found that the effective conductivity has upper and lower bounds of the arithmetic and the harmonic mean conductivities.

• Geomechanics and Engineering
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• v.16 no.4
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• pp.423-433
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• 2018

A three-dimensional model is constructed to simulate water infiltration in an unsaturated slope from a leaking pipe. Adaptive mesh refinement and time stepping are used, assisted by an automatic procedure for progressive steepening of the hydraulic property function for better convergence. The model is justified by comparing the simulated results with experimental data. Steady-state flow is investigated considering various pipe water pressures, locations and sizes of the opening, and soil layering. The opening size significantly affects the soaked zone around the pipe. Preferential flow dominates along the pipe longitudinal direction in the presence of a loose backfill around the pipe.

• Design & Manufacturing
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• v.6 no.2
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• pp.1-5
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• 2012

Weld line in injection molded part is one of the defects in injection molding process. Weld line deteriorates not only appearance quality but mechanical property. In this study, ABS and PP were used as experimental materials. And weld line length, depth and strength have been examined according to the injection molding conditions. As the results of experimental studies, weld line length increased as flow rate increases for all materials. And the flow rate is most influenced to the creation of weld line length. Also weld line strength increased, as flow rate and melt temperature increase for all materials. The whole experiment results was similar to CAE analysis results.

• 유체기계공업학회:학술대회논문집
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• 1998.12a
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• pp.223-232
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• 1998

To investigate the flow inside the centrifugal impeller, computer program which can solve Three-dimensional compressible turbulent flow has been developed. The Navier-Stokes equations were chosen as the governing equation for viscous flow while Euler equations for inviscid case. Time marching method was incorporated with the Flux Difference Splitting method suggested by Roe to capture the steep gradients such as a shock. For high order of accuracy, MUSCL approach was adopted while differentiable limiter to ensure TVD property. For turbulence closure, Baldwin- Lomax model was applied due to its simplicity. To demonstrate the capabilities of present program, several validation problems have been solved and compared with experiments and other available data. From the above calculations generally good agreements were obtained. Finally, the developed code was applied to Eckardt's impeller and the performance prediction was carried out. Some important aspects on boundary condition for successful simulation were discussed and the remedy was also introduced.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.178-181
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• 2004

Heat treatment is one of important manufacturing process that determine the quality of the products. Because of a difference of mechanical property by heat treatment, It is necessary to This papers presents flow stress and yield point through tensile test. The goal of this study is to obtain the data of flow stress and yield point at martensite, bainite, ferrite/pearlite phase structure using SCM420, SCr420. The result of tensile test is satisfied and is expected to develop an available FEM analysis.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.1735-1740
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• 2005

In this paper, ways of improving the performances of roundabouts under the assumption that the Advanced Vehicle System is proposed. The situation on a road contains uncertainty and complexity caused by different vehicles having different directions and time-varying traffic flow. This sort of system with high uncertainty is called Multi Agent System (MAS). The MAS is a collective system, including numbers of agents and performs high diversity of the configuration as well as it has nonlinear property and complexity. Hence it is difficult to analyze and control the multi-agent system. A roundabout can be considered as an MAS with numbers of moving vehicles. So it must be difficult to use a centralized control technique to all vehicles in an intersection. Therefore, to improve the performances of roundabouts, multi-agents flow control algorithm for vehicles in Roundabouts using 'self-organization' technique is proposed.

• Journal of Advanced Marine Engineering and Technology
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• v.18 no.3
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• pp.63-67
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• 1994

A main property for fiber reinforced thermoplastic composite material in compression molding is the flow of fibers. This flow is so effective a long direction of acting force that this study examined for the inclined angel of 30$^{\circ}$, 45$^{\circ}$ and 6$^{\circ}$. Below the near softing temperature of plastic, the fiber has been fractured at a point so that the fiber strength is smaller then the local hydrostatic stress in the mold. It has been found that the position of fracture is changing accrding to the incling angle. In case of the above softing temperature, the larger the inclined is, the farther the flow of fiber move. Also the plastic flow has been progresed with the cicular are type.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.737-738
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• 2002

To develop and improve a GIS(Gas Insulated Switchgear), the prediction of the pressure in puffer cylinder and the flow between the nozzle and the moving electrode within GIS is very important.The leading companies in GIS business issue the results of the study of flow within GIS including arc plasma. In this study, the characteristics of the flow of the GIS developed by HHI(Hyundai Heavy Industries Co. Ltd.) was investigated. To simulate the compressible flow of GIS, the CFX, a commercial CFD code, was used. With moving grid method, the movement of piston and electrode was simulated. The moving grid method was superior to the method of varying the property of cells to move an obsticle, in stability and convergencce of solution. The calculated maximum pressure within the puffer cylinder was matched with experimental data within $5{\%}$ error. The oscilation of pressure in GIS after the movement of electrode was well predicted.

• Journal of computational fluids engineering
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• v.4 no.2
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• pp.9-16
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• 1999

The present study investigates flow character and heat transfer behaviors of viscoelastic non-Newtonian fluid in a 2:1 rectangular duct. An axially-constant heat flux on bottom wall and peripherally constant temperature boundary condition(H1) was adopted. The Reiner-Rivlin fluid model is used as the normal stress model for the viscoelastic fluid and temperature-dependent viscosity model is adopted. The present results show a signifiant change of the main flow field which causes a large heat transfer enhancement. This phenomena can be explained by the combined effect of buoyancy, temperature-dependent viscosity and viscoelastic property on the flow.