• Proceedings of the KWS Conference
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• 2009.11a
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• pp.48-48
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• 2009

Conventionally in pulsed gas metal arc welding (GMAW-P), drop transfer is analyzed with simplest square pulse waveform. While the pulse current is described by four parameters (peak current magnitude and time plus base current magnitude and time), it deviates the real pulse shape. Real pulse can be better idealized by the trapezoidal pulse waveform described by two additional parameters, i.e., current rise and fall rate (dI/dt). Power source response rate is described by these parameters. In this work, the effect of these parameters on drop transfer is predicted by the force displacement model (FDM). While peak current has significant effects on drop detachment, drop transfer is also influenced by the current rise rate. Predictions indicate that the current rise rate can have considerable effects on the size of the detached drop if other pulse parameters are kept constant. FDM is applied to determine peak time for one drop one pulse condition (ODOP) when rests of the pulse parameters are given. The predicted range of ODOP shows good agreement with experimental data.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.2B
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• pp.203-209
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• 2004

In OBS networks, the burst dropping due to contention significantly affects the performance of TCP, but existing drop policies have not considered this problem and researches related to TCP have been mainly studied on burst assembling. We propose the drop policy considering retransmission of TCP to improve the performance of TCP in OBS networks. The proposed drop policy is the Retransmission Count-based DP that regards retransmission count of bursts as priority when it selects dropping burst. This paper evaluates the performance of RC-based DP model and general DP model using ns-2. The metrics of performance evaluation are TCP throughput, maximum sequence number of received TCP packets and drop rate of packet as simulation time increases.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.7B
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• pp.528-537
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• 2008

This paper proposes a dynamic job distribution algorithm in a hybrid NoC structure which can improve system network performance by reducing deadlock and packet drop rate for various multimedia applications. The proposed job distribution algorithm schedules every job to the sub-cluster where packet drop rate can be minimized for each multimedia application program. The proposed Job distribution algorithm and network topology targets multimedia applications frequently used in modern embedded systems, such as MPEG4 and MP3 decoder, GPS positioning system, and OFDM demodulator. Experimental results show that packet drop rate was reduced by about 13.0%, and chip area was increased by about 2.7% compared to the APSRA algorithm. When compared to the XY algorithm popularly used for benchmarking, the packet drop rate was reduced by about 23.9%, while chip area was increased by about 3.0%.

• Journal of the Korean Society of Tobacco Science
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• v.26 no.2 s.52
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• pp.117-125
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• 2004

In this study, we have investigated the natural and puffing combustibility of cigarette brands and the compulsory ash-drop, and analysed factors related to the materials. Cigarette combustibility was greatly affected by the tobacco weight in cigarettes rod. Combustion rate of 4AOR cigarette made by flue-cured tobacco was 5.02 $^{mm}/_{min}\;and\;10\%$ faster than 1BO cigarette. Combustion pattern has interrelation with sugars, chlorine and ash contents among tobacco components. Combustion rate of 4DL, flue-cured tobacco was 55 seconds faster than 1CL tobacco extremely much in sugars contents, and ash drop was maintained at $21\%$ longer. Combustion time and burning rate were fast in cigarette made by expanded tobacco slice and tobacco stem and the formation of ash was poor. The length of puffed ash drop of expanded tobacco slice and tobacco stem were 18.6 mm and 25.2 mm and these forced ash drop length were 3.8 mm and 4.9 mm respectively. Puffed burning rate of general cigarette was $14.3\%$ faster than static burning rate and super slim type cigarettes was $21.3\%$ faster. Combustion rate and ash drop of domestic and foreign cigarette brands were quite different depending on tar level and cigarette types. The lower tar level, the faster combustion rate and the shorter ash drop.

• Journal of Korean Society for Atmospheric Environment
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• v.11 no.4
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• pp.361-367
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• 1995

This study has been carried out to investigate the filteration performance of Electrostatically Stimulated Fabric Filter(ESFF) at high temperature condition. The electric field was maintained parallel to the fabric surface. The benefits of ESFF are lower residual pressure drop, improvement of fine particle removal efficiency and increasing reduced rate of pressure drop during a filteration cycle, stable operation at higher filtering velocities. According to the variance of filtering velocities and dust loadings, the results are summarized as follows; By imposing an electric field on the filter, the reduced rate of pressure drop was 7.sim.18% at room temperature, and when filtering velocity was 1.8m/min and dust loading was 1g/m$^{3}$, the value of reduced rate of pressure drop was shown the highest. Under the electric field around the filter, the reduced rate of pressure drop was 10.sim.35% at high temperature, and when filtering velocity was 1.8m/min and dust loading was 1g/m$^{3}$, the value of reduced rate of pressure drop was shown the highest. Most of all, at high temperature, the value of reduced rate of pressure drop was resulted to 25%. Also the collecting efficiency was shown clearly improved. By the SEM photo analysis, the number of penetrated particles at the Conventional Fabric Filter was approximately two times that of Electrostatically Stimulated Fabric Filter.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.5
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• pp.391-397
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• 2002

Pressure drop were experimentally investigated for ice slurry flowing in the acrylic pipes with inner diameter of 24 mm. Ice slurry was made from 6.5% ethylene glycol-water solution, and the pipes is consisted of horizontal, vertical (upward and downward) and $90^{\circ}$ elbow pipe. The ice Packing factor (IPF) and the flow rate of the experiments were varied from 0 to 30% and from 5 to 70kg/min respectively The measured pressure drop in various pipe positions were compared with those for the solution flow (IPF=0). The pressure drop was larder than that for solution flows as the IPF increased when the flow rate was low or very high. Sharp increases in pressure drop were observed for the cases when IPF is more than 70% in horizontal and vertical pipes, whereas the pressure drop increased with the IPF simultaneously in an elbow pipe.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.6
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• pp.781-788
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• 2003

In the present study, the heat and flow characteristics of a parallel-flow heat exchanger are numerically analyzed by using three-dimensional turbulent modeling. Heat transfer rate and pressure drop are evaluated using the concept of the efficiency index by varying the locations, the shapes and angles of inlet/outlet, and the protrusion height of flat tube. It is found that negative angle of the inlet improves the heat transfer rate and pressure drop. Results show that the locations of the inlet and outlet should be toward the right side and the left side to the reference model, respectively, in order to enhance the heat transfer rate and pressure drop. Increasing the height of the lower header causes pressure drop to decrease and yields the good flow characteristics. The lower protrusion height of flat tube shows the improvement of the heat transfer rate and pressure drop. The heat transfer rate is greatly affected by the parameters of outlet side such as the location and angle of the outlet. However, the pressure drop is influenced by the parameters of inlet side such as the location and angle of inlet and the height of the header.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.3
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• pp.72-78
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• 2007

A diesel particulate filter causes progressive increase in back pressure of an exhaust system due to the loading of soot particles. To maintain the pressure drop caused by DPF under proper level, a regeneration process is mandatory when excessive loading of soot is detected in the filter. It is a major reason why the relation between the amount of soot and the pressure drop in a DPF becomes crucial. On the other hand, pressure drop varies with not only the soot loading but also conditions of exhaust gas such as mass flow rate. Therefore, the relation among them becomes complicated. Furthermore, the characteristics of heat transfer in a DPF is another crucial parameter in order for the filter to avoid thermal crack during regeneration period. This study presents characteristics of pressure drop under various conditions of soot loading and mass flow rate in catalyzed diesel particulate filter. This study also shows characteristics of heat transfer in DPF when high temperature gas flows into the filter. Experiments reveal that the soot loading and mass flow rate affect characteristics pressure drop independently. Experiments also indicate that the amount of coating material has little influence on pressure drop with changes in soot loading and mass flow rate. However, increased catalyst coating may lead to the improved heat transfer which is efficiency to reduce thermal stress of the filter.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.12 no.6
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• pp.29-35
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• 2003

In this research 4 plate type ER-Valves which have same surface but different width and length are designed and an experimental apparatus is constructed. With this experimental apparatus, flow rate and pressure drop of ER fluid flowing in ER-valves are measured with varying electric field strength of ER-valve, and relation between valve types and pressure drop is also experimented. ER fluid is made silicon oil mixed with 40wt% starch having hydrous particles. If we allow the same electric field in the ER-Valve, we came to how that the pressure drop is effected by the electrode length and electrode width. When the strength of the electric field increased, the pressure drop happened big and the flow rate decreased.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.13 no.1
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• pp.63-68
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• 2004

Recently ER fluids are put to practical use in fluid power industry field. As only with electrical signal change to the valve in which ER fluid flowing, ER fluid flow is controlled, so devepment of simple ER valves have been tried. In this case a technical problem is to check the pressure drop caused from flow rate change in valves because the pressure drop is very small. In this study ER valves are designed and manufactured, and small pressure drop induced from flow rate change is checked by pressure transducer which is made with appling strain gage. The ER valves and pressure drop check method are considered to be applied to the fluid power industry.