• Korea-Australia Rheology Journal
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• 제19권4호
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• pp.211-219
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• 2007

Here we demonstrate complex transient behavior of viscoelastic liquid described numerically with the Leonov model in straight and contraction channel flow domains. Finite element and implicit Euler time integration methods are employed for spatial discretization and time marching. In order to stabilize the computational procedure, the tensor-logarithmic formulation of the constitutive equation with SUPG and DEVSS algorithms is implemented. For completeness of numerical formulation, the so called traction boundaries are assigned for flow inlet and outlet boundaries. At the inlet, finite traction force in the flow direction with stress free condition is allocated whereas the traction free boundary is assigned at the outlet. The numerical result has illustrated severe forward-backward fluctuations of overall flow rate in inertial straight channel flow ultimately followed by steady state of forward flow. When the flow reversal occurs, the flow patterns exhibit quite complicated time variation of streamlines. In the inertialess flow, it takes much more time to reach the steady state in the contraction flow than in the straight pipe flow. Even in the inertialess case during startup contraction flow, quite distinctly altering flow patterns with the lapse of time have been observed such as appearing and vanishing of lip vortices, coexistence of multiple vortices at the contraction comer and their merging into one.

• 한국경영과학회지
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• 제41권1호
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• pp.87-98
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• 2016

A single machine scheduling problem for jobs with stochastic processing time is considered in this study. Shortest processing time (SPT) sequencing according to the expected processing times of jobs is optimal for schedules with minimal expected mean flow time when all the jobs arrive to be scheduled and their expected processing times are known. However, SPT sequencing according to the expected processing time may not be optimal for the minimization of the mean flow time when the actual processing times of jobs are known. This study evaluates the complexity of SPT sequencing through a comparison of the mean flow times of schedules based on the expected processing times and actual processing times of randomly generated jobs. Evaluation results show that SPT sequencing according to the expected flow time exhibits chaotic variation to the optimal mean flow time. The relative deviation from the optimal mean flow time increases as the number of jobs, processing time, or coefficient of variation increases.

• 한국전산유체공학회지
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• 제13권2호
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• pp.27-41
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• 2008

An unstructured hybrid mesh flow solver has been developed for the simulation of three-dimensional steady and unsteady incompressible flow fields. The incompressible Navier-Stokes equations with an artificial compressibility method were discretized by using a node-based finite-volume method. For the unsteady time-accurate computation, a dual-time stepping method was adopted to satisfy a divergence-free flow field at each physical time step. An implicit time integration method with local time stepping was implemented to accelerate the convergence in the pseudo-time sub-iteration procedure. The one-equation Spalart-Allmaras turbulence model has been adopted to solve high-Reynolds number flow fields. The flow solver was parallelized to minimize the CPU time and to overcome the computational overhead. This method has been applied to calculate steady and unsteady flow fields around submarine configurations and a 3-D infinite cylinder. Validations were made by comparing the predicted results with those of experiments or other numerical results. It was demonstrated that the present method is efficient and robust for the prediction of steady and unsteady incompressible flow fields.

• 대한산업공학회지
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• 제37권4호
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• pp.367-381
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• 2011

Reducing waste for the efficiency of production is becoming more important because of the rapidly changing market circumstances and the rising material and oil prices. The dispatching also has to consider the characteristic of production circumstance for the efficiency. The production circumstance has the non-identical parallel machines with rework rate since machines have different capabilities and deterioration levels in the real manufacturing field. This paper proposes a dispatching method, FTLR (Flow Time Loss Index with Rework Rate) for production efficiency. The goal of FTLR is to minimize flow time based on such production environments. FTLR predicts the flow time with rework rate. After assessing dominant position of expected flow time per each machine, FTLR performs dispatching to minimize flow time. Experiments compare various dispatch methods for evaluating FTLR with mean flow time, mean tardiness and max tardiness in queue.

• 한국도로학회논문집
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• 제14권6호
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• pp.131-138
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• 2012

PURPOSES : Two-lane highways have one lane in each direction, and lane changing and passing maneuvers take place in the opposing lane depending on the availability of passing sight distance. 2001 Korea Highway Capacity Manual (KHCM) is classified into two classes of two-lane highways (Type I, II), and average travel speed and time-delayed rate are used as measures of effectiveness (MOEs). However, since existing two-lane highways have both uninterrupted and interrupted traffic flow-system elements, a variety of free-flow speeds exhibits in two-lane highways. In addition, it is necessary to check if the linear-relationship between volumes and time-delayed rate is appropriate. Then, this study is to reestablish the relationship between average travel speed, time-delayed rate, and flow. METHODS : TWOPAS model was selected to conduct this study, and the free-flow speeds of passenger cars and the percentage of following vehicles observed in two-lane highways were applied to the model as the input. The revised relationships were developed from the computer simulation. RESULTS : In the revised average travel speed vs. flow relationship, the free-flow speed of 90km/h and 70km/h were added. It shows that the relationship between time delayed-rate and flow appeared to be appropriate with the log-function form and that there was no difference in time-delayed rate between the free flow speeds. In addition to revise the relationships, the speed prediction model and the time-delayed rate prediction model were also developed. CONCLUSIONS : The revised relationships between average travel speed, time-delayed rate, and flow would be useful in estimating the Level of Service(LOS) of a two-lane highway.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 가을 학술발표회 논문집
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• pp.91-96
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• 2002

This study is to analyze the influence of paste flow, compaction time and compaction thickness on the fundamental properties of porous concrete. Results of this study were shown as follows; 1) As paste flow increase, compaction time according to paste flow and compaction thickness decrease. Also, though paste flow is same, as compaction thickness increase, compaction time Increase. So It must be considered that the influence of compaction time according to paste flow and compaction thickness. 2) In the range of this study, compressive strength is the highest value at paste flow 190mm. 3) Occasion of manufactured compactor in this study compaction thickness 10, 15cm is influenced heavily but compaction thickness 20cm is influenced slightly.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.682-687
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• 2003

The variations of temperature and velocity fields in a Hele-Shaw convection cell (HSC) were investigated using a holographic interferometry and 2-D PIV system with varying Rayleigh number. To measure quasisteady changes of temperature field, two different measurement methods of holographic interferometry; double-exposure method and real-time method, were employed. In the double-exposure method, unwanted waves can be eliminated effectively using digital image processing technique and the reconstruction images are clear, but transient flow structure cannot be reconstructed clearly. On the other hand, transient convective flow can be reconstructed well using the real-time method. However, the fringe patterns reconstructed by the real-time method contain more noises, compared with the double-exposure method. Experimental results show a steady flow pattern at low Rayleigh numbers and a time-dependent periodic flow structure at high Rayleigh numbers. The periodic flow pattern at high Rayleigh numbers obtained by the real-time holographic interferometer method is in a good agreement with the PIV results.

• 한국가스학회지
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• 제16권4호
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• pp.8-15
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• 2012

GO-FLOW기법은 시스템이 정상적으로 작동할 가능성을 평가할 수 있는 기법으로써 신호선과 연산자를 사용하여 시스템을 GO-FLOW Chart로 모델화하고, 이 GO-FLOW Chart를 순차적으로 해석하여 시스템의 신뢰도를 평가하는 기법이다. 그러나 GO-FLOW기법은 1개의 시스템 구성요소를 여러 개의 연산자로 모델링하므로 시스템 흐름도와 상이한 GO-FLOW Chart가 작성될 수 있고, 시간점을 지정하여 시간을 모델링하므로 실제 운전시간에 따른 신뢰도 변화를 평가하기 어렵다. 따라서 본 연구에서는 구성요소의 기능(정상/고장)을 기준으로 시스템의 신뢰도를 평가하는 기법을 개발하였다. 본 기법은 구성요소의 운전상태와 상관없이 그 기능을 유지할 가능성을 기준으로 시스템의 신뢰도를 평가하며, 1개의 구성요소는 1개의 연산자로 모델링하므로 시스템 흐름도와 거의 유사한 모델도를 작성할 수 있고, 실제시간을 반영한 연산자를 사용하여 실제시간에 따른 시스템의 신뢰도를 쉽게 평가할 수 있다.

• Journal of Mechanical Science and Technology
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• 제15권3호
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• pp.300-308
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• 2001

Tracking of moving objects within video streams is a complex and time-consuming process. Large number of moving objects increases the time for computation of tracking the moving objects. Because of large computations, there are real-time processing problems in tracking of moving objects. Also, the change of environment causes errors in estimation of tracking information. In this paper, we present a new method for tracking of moving objects using optical flow motion analysis. Optical flow represents an important family of visual information processing techniques in computer vision. Segmenting an optical flow field into coherent motion groups and estimating each underlying motion are very challenging tasks when the optical flow field is projected from a scene of several moving objects independently. The problem is further complicated if the optical flow data are noisy and partially incorrect. Optical flow estimation based on regulation method is an iterative method, which is very sensitive to the noisy data. So we used the Combinatorial Hough Transform (CHT) and Voting Accumulation for finding the optimal constraint lines. To decrease the operation time, we used logical operations. Optical flow vectors of moving objects are extracted, and the moving information of objects is computed from the extracted optical flow vectors. The simulation results on the noisy test images show that the proposed method finds better flow vectors and more correctly estimates the moving information of objects in the real time video streams.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2023년도 봄 학술논문 발표대회
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• pp.197-198
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• 2023

This study was conducted as part of research and development of high-strength grout. Accordingly, dolomite aggregate was used as a filler incorporated into the high-strength grout. Dolomite aggregate has a disadvantage of increasing the viscosity of the grout due to higher generation of fine powder than other aggregates. Accordingly, in this experiment, it was confirmed that the viscosity, flow time, and flow of high-strength grout change according to the volume composition ratio of dolomite aggregate and cement-based material. All experiments were conducted based on the Korean Industrial Standard KS F 4044, and the mixing factor was applied according to the composition ratio of the binder and the filler. In the experiment, the amount of fine powder contained in the dolomite aggregate rather than the silica sand used in the past is grasped, and after mixing with the grout accordingly, the mixture is proceeded to measure the viscosity in an unhardened state. In addition, the flow and flow time of the grout are evaluated according to the viscosity. As a result of the experiment, it was confirmed that the viscosity and flow time decreased and the flow increased as the volume composition ratio of the dolomite aggregate to the cement-based material increased.