• Computers and Concrete
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• v.12 no.2
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• pp.169-186
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• 2013

The aim of this paper is to determine the effect of soil-structure interaction and time dependent material properties on behavior of concrete box-girder highway bridges. Two different finite element analyses, one stage and construction stage, have been carried out on Komurhan Bridge between Elazi$\breve{g}$ and Malatya province of Turkey, over Fırat River. The one stage analysis assume that structure was built in a second and material properties of structure not change under different loads and site conditions during time. However, construction stage analysis considers that construction time and time dependent material properties. The main and side spans of bridge are 135 m and 76 m, respectively. The bridge had been constructed in 3 years between 1983 and 1986 by balanced cantilever construction method. The parameters of soil-structure interaction (SSI), time dependent material properties and construction method are taken into consideration in the construction stage analysis while SSI is single parameter taking into consideration in the one stage analysis. The 3D finite element model of bridge is created the commercial program of SAP2000. Time dependent material properties are elasticity modulus, creep and shrinkage for concrete and relaxation for steel. Soft, medium, and firm soils are selected for evaluating SSI in both analyses. The results of two different finite element analyses are compared with each other. It is seen that both construction stage and SSI have a remarkable effect on the structural behavior of the bridge.

• Journal of Magnetics
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• v.3 no.4
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• pp.127-133
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• 1998

I have overviewed the change in GMR on annealing, in conjunction with the change in microstructure. The Co46Al19O35 granular thin films were annealed at 30$0^{\circ}C$ for various annealing time to change the microstructure. The magnitude of GMR decreases considerably with increasing annealing time, although the size of Co granules estimated from TEM observation show a small change. Parameter fits of magnetization curves and magnetoresistance curves to the Langevin function suggest that large clusters consisting of several small Co granules, which are coupled ferromagnetically, are related with the decrease of GMR on annealing. The temperature dependence of electrical resistivity ($\rho$) shows the relationship of log $\rho$ versus $T^{-1/2}$ for the sample annealed for 10 min., 1 hr. and 6 hrs. However, the sample annealed for 38 hrs. shows the relationship of log $\rho$ versus$ T^{-1/4},$ which represents a significant change in the transport mechanism.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.3
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• pp.1040-1044
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• 2013

The present paper has been accomplished to elucidate the characteristics of temperature change in a car washer heater system for removal of frost formed at the surface of a car. The previous studies had used a simplified mathematical modeling to analyse the temperature change characteristics for a car washer heater system. In the present study, an unsteady computational fluid flow and heat transfer analysis for a washer heater system has been done by using computational fluid dynamic analysis method. From the present CFD analysis, the time dependent temperature change in a car washer heater system has been analysed and derived the heating time and ejection temperature of the washer liquid to establish the optimal design basis for a washer heater system.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.206-212
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• 2011

Hysteresis phenomena in fluid flow systems are frequently encountered in many industrial and engineering applications and mainly appear during the transient processes of change of the pressure ratio. Shock-containing flow field in supersonic nozzles is typically subject to such hysteresis phenomena, but associated flow physics is not yet understood well. In the present study, experimental work has been carried out to investigate supersonic nozzle flows during the transient processes of change in the nozzle pressure ratio. Time-dependent surface wall pressures were measured by a multiple of pressure transducers and the flow field was visualized using a nano-spark Schlieren optical method. The results obtained show that the hysteresis phenomenon is strongly dependent on the nozzle geometry as well as the time scale of the change of pressure ratio.

• Journal of the Ergonomics Society of Korea
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• v.30 no.6
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• pp.757-764
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• 2011

Objective: The aim of this study was to provide a method to improve the compliance and reduce the time by reducing the workload during the model change work. Background: The enterprises are constructing the small quantity batch production system by increasing the number of model change and reducing model-changing. However, the compliance is low because the work is strenuous and high skills are needed, so the system management is facing with many difficulties. Method: After classifying the model change work according to the purposes(preparation, change and adjustment) with the target of mascara filling machine, element tasks time were measured and the motion analysis(therblig symbol) and REBA analysis were performed. The study incorporated 3 independent variables as the number of motion, REBA score and the element time. The dependent variable is the type of element work as preparation, change and adjustment. The statistical test was performed by one-way ANOVA(${\alpha}$ < 0.05). Results: For the preparation, the number of motions appeared in the order of Use(U), Transport Loaded(TL), and Position(P). The order appeared in change is Use(U), Release Load(RL), and Grasp (G). The adjustment appeared in the order of Position(P) and Use(U). The results of average motion time as the element work times divided by the number of motion appeared in the order of adjustment(1.85sec/motion), preparation(1.11sec/motion), and change(0.62sec/motion). The results of REBA showed that the average risk level of change and adjustment were medium, but 53.1% of change and 42.9% of adjustment were evaluated as high. Conclusion: Reducing the avoidance and improving the compliance of work could be expected if the job autonomy were improved by improving the working postures with high risk level. Application: It is expected to solve the problem of reducing the time of model change work in the small quantity batch production system. The future work is to carry out the improvement directions found in the results and compare the results after improvement.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.147-148
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• 2010

Time-dependent deformation process of concrete was incrementally formulated to take account of the persistent change of creep-inducing stress as well as shrinkage and development of elastic modulus. Three types of experiments were performed including a set of experiments to derive three basic time-dependent equations regarding to shrinkage, creep and development of elastic modulus of concrete, cylindrical concrete specimen with axial reinforcements subjected to a sustained axial load, and RC beam subjected to uniformly distributed load as well as self-weight.

• Journal of Mechanical Science and Technology
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• v.14 no.2
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• pp.177-187
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• 2000

Dilution is an important factor which influences the properties of clad layer. In this paper the change of dilution during laser cladding and the control of dilution are simulated by a finite element method. The adaptive mesh method is adopted for the time-dependent finite element method computation so that the shape of melt pool can be well represented. The situation of the width control of melt pool is also simulated, which indicates that the dilution can be controlled if the width of melt pool is controlled. Computational results indicate that if a line energy (input energy per unit distance) remains constant the dilution will increase with time, especially at the beginning. Simulation results show that it is possible to control dilution in a certain range if the line energy decreases with time. Experiment of Nd: YAG laser cladding with wire feeding is performed. Experiment results coincide well with the FEM results.

• Water for future
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• v.25 no.2
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• pp.67-78
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• 1992

Several field surveys were conducted to investigate changes of water quality with time in a tidal river. Results indicated that nitrification process were dependent on the change of salinity and suspended solids concenttration. Therefore laboratory batch experiments were conducted, using suspended solids and sediment taken from a tidal river, to study the effect of salinity on nitrification and to estimate kinetic parameters of it in the tidal river. suspended solids and sediment were sampled at a point in the middle stream. Sediments were collect from the aerobic layer of mud. The change of nitrogen concentration with time was clearly explained with Monod groth model and kinetic parameters were obtained by curve fitting method. Changes in NH4-N, NO2-N, and NO3-N concentrations in the river ROKKAU with time were simulated well using Lagrangian reference frame and parameter values obtained in the laboratory tests. T도 mechanism of nitrification by suspended solids and sediment in a tidal river is shown to depend on tidal effects.

• KIEAE Journal
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• v.5 no.1
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• pp.51-57
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• 2005

In this study, time-dependent concentration variations of VOCs from fixed furniture and Ondol floor widely used as finishing material of the floor were measured, and prediction equations were developed based on the measured results. VOCs were measured and analyzed based on EPA TO-17 and NIOSH 1500, 1501 method respectively, and GC/FID were used for the analysis of VOCs concentration. Measurements were carried out for 10 days after the installation of furniture and for 40 days after the installation of the floor in the residence constructed more than 10 years ago. In both case of floor and furniture installation, time-dependent concentration decay of VOCs can be properly converted into logarithmic scale. Especially in case of furniture, toluene showed the highest concentration and took longest time to decay. As a result of the prediction of VOCs concentration decay under different air change rate using estimated equations, concentration decay rate of indoor VOCs increased rapidly as the air change rate also increased.

• Proceedings of the Korean Geotechical Society Conference
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• 2003.03a
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• pp.257-264
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• 2003

Tunnelling in water bearing soils influences the ground water regime. It has been indicated in the literature that the existence of ground water above a tunnel influences tunnel stability and the settlement profile. Only limited research, however, has been done on ground water movements around tunnels and their influence on tunnel performance. Time dependent soil behaviour can be caused by the changes of pore water pressure and/or the viscous properties of soil(creep) under the stress change resulting from the advance of the tunnel face. De Moor(1989) demonstrated that the time dependent deformations due to tunnelling are mainly the results of pore pressure dissipation and should be interpreted in terms of effective stress changes. Drainage into tunnels is governed by the permeability of the soil, the length of the drainage path and the hydraulic boundary conditions. The potential effect of lime dependent settlement in a shallow tunnel is likely to occur rapidly due to the short drainage path and possibly high coefficient of consolidation. Existing 2D modelling methods are not applicable to these tunnelling problems, as it is difficult to define empirical parameters. In this paper the time-based 2D modelling method is adopted to account for the three dimensional effect and time dependent behaviour during tunnel construction. The effect of coupling between the unloading procedure and consolidation during excavation is profoundly investigated with the method. It is pointed out that realistic modelling can be achieved by defining a proper permeability at the excavation boundary and prescribing appropriate time for excavation Some guidelines for the numerical modelling of drained and undrained excavation has been suggested using characteristic time factor. It is highlighted that certain range of the factor shows combined effect between the unloading procedure due to excavation and consolidation during construction.