• Title, Summary, Keyword: Transfer stability

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Effect of Si on Spatter Generation and Droplet Transfer Phenomena of MAG Wwlding (MAG 용접의 스패터 발생 및 용적이행현상에 미치는 Si의 영향)

  • 안영호;이종봉;엄동석
    • Journal of Welding and Joining
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    • v.17 no.3
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    • pp.36-43
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    • 1999
  • The effect of Si content in welding wires on spattering characteristics and droplet transfer phenomena was studied. In MAG welding using 80% Ar-20% $CO_2$ shielding gas, spattering characteristics and droplet transfer phenomena were varied with Si content of wire. With increasing Si content, the spattering ratio and the ratio of large size spatter $(d\geq1.0mm)$ were increased. The increase of Si content in molten metal made surface tension increase due to reduction of oxygen content, which resulted from deoxidizing action of silicon. The increase of surface tension resulted in unstable transfer phenomena and arc instability in both short circuit and spray region. With changing Si content of wire, spattering characteristics and droplet transfer phenomena was directly influenced by the variation of surface tension, compared with the effect of arc stability.

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Development of Fuzzy Controller for Stabilizing the Arc State in Gas Metal Arc Welding (GMA 용접에 있어서 아크 안정화를 위한 퍼지제어기 개발에 관한 연구)

  • Kang, Moon-Jin;Lee, Se-Hun
    • Journal of the Korean Society for Precision Engineering
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    • v.16 no.12
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    • pp.152-160
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    • 1999
  • The weld quality of $CO_2$ arc welding is closely related to the arc stability. As the characteristics of the arc are excessively complex and nonlinear, it is not easy to make the arc model as mathematical form and to control the arc state to be stabilized. This paper was aimed to estimate the arc stability and to control for stabilizing the arc state in short circuit metal transfer mode of $CO_2$ arc welding. For these purposes, the behaviors of arc stability was investigated at different welding conditions using Mita's arc stability index, and the fuzzy control algorithm which uses the arc stability index as control imput and the arc voltage as control output was developed. In the control of the arc stability, the experiments of two cases were performed; the case of setting an initial welding voltage arbitrarily, the case of the step change in workpiece shape. Obtained results were as follows; Mita's arc stability index was able to be estimated qualitatively in the case of using the inverter type welding power source and the control performance for stabilizing the arc status was excellent in the case of existing step change disturbance.

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Instability of the IncFII-Type Plasmid Carrying blaNDM-5 in a Klebsiella pneumoniae Isolate

  • Shin, Juyoun;Baek, Jin Yang;Chung, Doo Ryeon;Ko, Kwan Soo
    • Journal of Microbiology and Biotechnology
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    • v.27 no.9
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    • pp.1711-1715
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    • 2017
  • In this study, we characterized the $bla_{NDM-5}$-bearing plasmid in a Klebsiella pneumoniae isolate that had lost the plasmid during serial passage. We determined the complete sequences of the plasmid pCC1410-2, which was extracted from a K. pneumoniae ST709 isolate collected at a Korean hospital from which two NDM-5-producing K. pneumoniae isolates were subsequently isolated. As a result, the pCC1410-2 plasmid had a backbone structure that was similar to those of two plasmids previously reported from the same hospital, but lacked some antibiotic resistance genes ($bla_{TEM-1}$, rmtB, mphR(A), mrx(A), and mph(A)). A 9-bp repeating unit encoding three amino acids (Gln-Gln-Pro) was inserted in TraD in pCC1410-2. Thus, the pCC1410-2 plasmid might be transferred from the previously identified carbapenem-resistant K. pneumoniae, but some delections and inversions might have occurred during the process. We compared the transfer frequency and stability of the plasmids. The relative frequency of conjugative transfer and stability in the host were significantly lower in pCC1410-2 than in previously reported $bla_{NDM-5}$-bearing plasmids in Korea. A low transfer frequency and instability in the host may cause underestimation of carbapenemase-producing Enterobacteriaceae in the clinical setting and in surveillance studies.

Reduced Order Identification and Stability Analysis of DC-DC Converters

  • Ali, Husan;Zheng, Xiancheng;Wu, Xiaohua;Zaman, Haider;Khan, Shahbaz
    • Journal of Power Electronics
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    • v.17 no.2
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    • pp.453-463
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    • 2017
  • This paper discusses the measurement of frequency response functions for various dc-dc converters. The frequency domain identification procedure is applied to the measured frequency responses. The identified transfer functions are primarily used in developing behavioral models for dc-dc converters. Distributed power systems are based upon such converters in cascade, parallel and several other configurations. The system level analysis of a complete system becomes complex when the identified transfer functions are of high order. Therefore, a certain technique needs to be applied for order reduction of the identified transfer functions. During the process of order reduction, it has to be ensured that the system retains the dynamics of the full order system. The technique used here is based on the Hankel singular values of a system. A systematic procedure is given to retain the maximum energy states for the reduced order model. A dynamic analysis is performed for behavioral models based on full and reduced order frequency responses. The close agreement of results validates the effectiveness of the model order reduction. Stability is the key design objective for any system designer. Therefore, the measured frequency responses at the interface of the source and load are also used to predict stability of the system.

A Combustion Instability Analysis of a Model Gas Turbine Combustor by the Transfer Matrix Method

  • Cha, Dong-Jin;Kim, Jay-H.;Joo, Yong-Jin
    • Proceedings of the KSME Conference
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    • pp.2946-2951
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    • 2008
  • Combustion instability is a major issue in design of gas turbine combustors for efficient operation with low emissions. Combustion instability is induced by the interaction of the unsteady heat release of the combustion process and the change in the acoustic pressure in the combustion chamber. In an effort to develop a technique to predict self-excited combustion instability of gas turbine combustors, a new stability analysis method based on the transfer matrix method is developed. The method views the combustion system as a one-dimensional acoustic system with a side branch and describes the heat source as the input to the system. This approach makes it possible to use the advantages of not only the transfer matrix method but also well-established classic control theories. The approach is applied to a simple gas turbine combustion system to demonstrate the validity and effectiveness of the approach.

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Characteristics of Stability and Intensity of Vertical Transfer in the Western Channel of the Korea Strait

  • Chung, Jong Yul
    • 한국해양학회지
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    • v.10 no.2
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    • pp.57-66
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    • 1975
  • Structure of thermocline, characteristics of stability and intensity of vertical transfer have been studied with hourly oceanographic data in each layers on Line 207 from 1968 to 1969. It is found that a typical thermocline is formed at depths of 10 to 50 meters in summer and early autumn and its core is located near depths of 25 meters. The maximum diffusion coefficient of vertical turbulent is found to be 140$\textrm{cm}^2$/sec at the surface layer(i.e., 0-10 meters), while the minimum is 5$\textrm{cm}^2$/sec at depths of 25 meters, consistent with characteristics of stability and structure of thermocline layers. Our computed diffusion coefficient and stability indicate that the mixing hardly takes place below depths of 80 meters during summer and early autumn, but for the rest of the season mixing could move up to the depth of 50 meters. It appears that the Western Channel of the Korea Strait consist of three different water masses during summer and autumn, and for the rest of the season, two kinds are present.

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Transient Stability in Dry-winding Superconducting Magnets (비함침 초전도마그네트의 과도안정성)

  • Kim, Seok-Beom;Ishiyama, Atsushi;Han, Kyung-Hee
    • Proceedings of the KIEE Conference
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    • pp.89-91
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    • 1996
  • In dry-winding(unfilled) superconducting magnets, the behavior of liquid helium occupying the extremely small void space within the winding is contributed as a primary factor for transient stability of magnets. Therefore, numerical experiments have been carried out concerning the influences of transient heat transfer of liquid helium ocupying the void space in the winding and thermal properties of insulation at the conductor surface on the transient stability of magnets, by using three-dimensional finite element method(FEM). In this paper, we are going to consider three different cases for heat transfer characteristics of liquid helium to observe the influences of the rest of liquid helium in void space within the winding on the transient stability.

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Stability of the Cable-in-Conduit Conductors (CIC 초전도 도체의 안정성)

  • 류경우
    • Electrical & Electronic Materials
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    • v.10 no.9
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    • pp.895-900
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    • 1997
  • A Quench in cable-in-conduit (CIC) conductors is often initiated by a disturbance such as strand motion that generates a highly localized normal zone in a strand or a few strands of the CIC conductors. The localized normal zone causes current and heat transfer between a disturbed strand and neighboring strands. Electrical and thermal contact characteristics between strands thus have an effect on the transient stability of the CIC conductors. In this paper the effect of contact characteristics between strands on the CIC conductor stability is presented based on the measured heat transfer characteristics of supercritical helium (SHe) for the local heating. The quench and recovery processes of the strands for the abrupt and highly localized disturbance are analyzed at the boundary between quench and recovery.

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Natural Convective Flow and Heat Transfer in a Square Enclosure with a Horizontal Partition (수평격판을 갖는 정사각형 밀폐공간내에서 자연대류 유동 및 열전달)

  • 정인기;김점수;송동주
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.9
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    • pp.2304-2314
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    • 1993
  • Natural convective flow and heat transfer in a two-dimensional square enclosure fitted with a horizontal partition are investigated numerically. The enclosure was composed of the lower hot and the upper cold horizontal walls and the adiabatic vertical walls, and a partition was situated perpendicularly at the one vertical insulated wall. The governing equations are solved by using the finite element method with Galerkin method. The computations were carried out with the variations of length, position and thermal conductivity of the partition, and Rayleigh number based on the temperature difference between two horizontal walls and the enclosure height with water(Pr=4.95). As the results, an oscillatory motion of natural convection is resulted in a sudden rise of overall heat transfer, but the increase of length of partition is significantly restrained the increase of Nusselt number. The maximum heat transfer was shown just before the transition of the direction of oscillating flow. An oscillatory motion of flow was perfectly shown the stability with the decrease of the length of partition and Rayleigh number. Also, the heat transfer was raised with the increase of the thermal conductivity in proportion to the increase of the length of partition. The stability and oscillation of flow are affected by the position of partition.