• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.3
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• pp.178-185
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• 2005

Crack tip displacement is originated by tensile stress component, s and shear stress component, t on pure Mode I and pure Mode II. The crack tip displacement(CTD) depends on combined types of different two stress components under mixed-mode loading conditions (MMLC). Thus, the analysis of crack tip displacement must be CTD vector, dv which is composition of ds and dt under MMLC. In this paper, various effects of MMLC on the crack closure are studied experimentally. The crack closure magnitude is calculated from the information of crack tip displacement under MMLC. This information has been obtained from the high resolution optical microscope in direct observations of crack displacement behavior at the crack tip. Observed crack tip displacement is analyzed by using CTD vector to determine crack opening load. The various effects of MMLC on the crack closure are explained using crack opening ratio with crack length and mode mixture. The effective stress intensity factor considering crack closure is also discussed.

• Journal of Power System Engineering
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• v.5 no.3
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• pp.73-79
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• 2001

The purpose of this investigation is experimentally to clarify the machinability and tool wear of STS 304 steel pipe material for piping. In order to determine the effects of cutting parameters and tool wear on thrust, torque, AE RMS, drilling is conducted on CNC milling machine. In this experiment, it is measured that thrust, torque, tool wear length, tool wear area and AE RMS during drilling using Hss tool. It has been found that a) During the drilling, the thrust and the torque of the STS 304 pipe are received more the effect of the feed than the spindle speed and the thrust increase with the increase of feed, b) The value of the AE RMS is been larger the effect of the cutting speed than the feed rate, and the value of the AE RMS increase with the increase of spindle speed, c) It has been found that the suitable feed in feed condition of 0.03, 0.05, 0.1, 0.15mm/rev is below 0.05mm/rev, d) The value of the AE RMS was shown a characteristic of the jump value during it was a sudden inrcrease of the tool wear. The increased character of the AE RMS value can be known an effective factor of the tool wear detection, and e) It can be quantitatively evaluated the condition of the tool according to calculate a area of the drill wear image which is obtained by a vision system.

• Journal of The Korean Astronomical Society
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• v.46 no.4
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• pp.161-172
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• 2013

A focal reducer is developed for CQUEAN (Camera for QUasars in EArly uNiverse), which is a CCD imaging system on the 2.1 m Otto Struve telescope at the McDonald observatory. It allows CQUEAN to secure a wider field of view by reducing the effective focal length by a factor of three. The optical point spread function without seeing effects is designed to be within one pixel ($0.283^{\prime\prime}$) over the field of view of $4.82^{\prime}{\times}4.82^{\prime}$ in optimum wavelength ranges of 0.8-1.1 ${\mu}m$. In this paper, we describe and discuss the characteristics of optical design, the lens and barrel fabrications and the alignment processes. The observation results show that the image quality of the focal reducer confirms the expectations from the design.

• Journal of Korean Society of Water and Wastewater
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• v.11 no.1
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• pp.109-118
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• 1997

In this study, we examined the structural analysis of water demand fluctuation for water distribution control of water supply network. In order to analyze for the length of stationary time series, we calculate autocorrelation coefficient of each case equally divided data size. As a result, it was found that, with the data size of around three months, any case could be used as stationary time series. we analyze cross-correlation coefficient between the daily water consumption's data and primary influence factors. As a result, we have decided to use weather conditions and maximum temperature as natural primary factors and holidays as a social factor. Applying the multiple ARIMA model, we obtains an effective model to describe the daily water demand prediction. From the forecasting result, even though we forecast water distribution quantity of the following year, estimated values well express the flctuations of measurements. Thus, the suitability of the model for practical use can be confirmed. When this model is used for practical water distribution control, water distribution quantity for the following day should be found by inputting maximum temperature and weather conditions obtained from weather forecast, and water purification plants and service reservoirs should be operated based on this information while operation of pumps and valves should be set up. Consequently, we will be able to devise a rational water management system.

• Journal of the Korean Society of Safety
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• v.9 no.3
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• pp.13-21
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• 1994

Effects of tensile and compression residual stresses in the welded SS41 and A17075-76 on fatigue crack propagation behavior are investigated when a crack propagates from residual stresses region. We propose the fatigue crack growth equation on tensile and compression residual stresses in welded metal. The results obtained in this experimental study are summarized as follows . 1 ) A fatigue crack growth equation which applied fatigue fracture behavior of the welded metal is proposed. (equation omitted) where, $\alpha$, $\beta$, ${\gamma}$ and $\delta$ are constants, and R$_{eff}$ is effective stress ratio [R$_{eff}$=(Kmin+Kres)/(Kmax+Kres)], Kcf is critical fatigue stress intensity factor. The constants are obtained from nonlinear least square method. The relation between crack length and number of cycles obtained by integrating the fatigue crack growth rate equation is in agreement with the experimental data. 2) The experimental results confirmed that the cause of crack extension and retardation by residual stresses has relation to the phenomenon of crack closure. 3) The relaxing trend of residual stresses by the crack propagation was greater In case of compressive residual stress than that of tensile residual stress in the welded metal.tal.

• Magazine of the Korean Society of Agricultural Engineers
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• v.15 no.3
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• pp.3096-3106
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• 1973

As a link in the chain of antidrought measure, our attempt is made to obtain basic informations on the construction of an infiltration gallary which can be supplied with irrigation water by catching of underground water in small river beds, which is economical, permanent and efficient. The experiment was made, concerning the structure of catchment conduits, by constructing a model sand tank $1.5m{\times}5m{\times}1.5m$ in dimension made of reinforced concrete. Various kinds of measuring equipment were attached to the model tank which contains a set of catchment conduits, each of them was made 30cm in diameter and 60cm in length with the ratio of sectional area to total area of influx holes 10:1, 20:1, 30:1. The average size of influx holes was fixed from 0mm to 10mm, 20mm and 30mm in diameter respectively. Obtained results are as follow; (a) In view of the water catchment capacity, manufacturing cost and the antipressure strength of the catchment conduits, it is the best method to decide the total number of influx holes 20 per sq. meter of each tile surface, and the size of influx holes 20mm in diameter, when the conduits have diameter less than 1m. (b) The greatest factor of safety against external load is to arrange the influx holes in a zigzag manner on the tile surface. The most effective formula of arrangement is $S{\geqq}\sqrt{2gd}$ where: s : spacing of opening row. g : spacing of opening line. d : diameter of influs hole.

• Journal of Microbiology and Biotechnology
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• v.13 no.5
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• pp.680-686
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• 2003

This study was carried out to characterize the antilisterial substances produced by Leuconostoc sp. W65 and to evaluate the effects of pH, temperature, and time on inhibitory activity using response surface methodology. Leucocin W65, an antilisterial substance produced by Leuconostoc sp. W65, markedly inhibited the growth of Listeria monocytogenes, L. innocua, and L. ivanovii, whereas other pathogens including Gram-negative bacteria were not susceptible. The pH was the most effective factor with regard to bacteriocin activity, while temperature and time of heat treatment had no significant effect. Fifty percent of inhibitory activity remained after 22.8 min at pH 4.2 and $121^{\circ}C$. Leucocin W65 was purified by ammonium sulfate precipitation, hydrophobic interaction chromatography, and tricine-SDS-PAGE. Compositional analysis originally estimated the peptide to be 56 amino acids in length without asparagine, glutamine, and tryptophane. The sequence of partial N-terminal amino acid residues of purified bacteriocin was identified as follows: $NH_{2}-XGXAGVXPXGGQQPXVPLXYP$.

• Journal of Welding and Joining
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• v.15 no.1
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• pp.66-80
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• 1997

This paper describes a newly developed arc-sensing algorithm of seam-tracking for FCA W (flux-cored arc welding) horizontal fillet welding. In this algorithm, arc current and the Weighted-Are-Current (WAC) are used to adjust the position of a weld torch in directions of bead throat and weaving, respectively. The WAC, which is newly devised in this study, means that arc current in the vicinity of weaving end is more emphasized than that in the center of weaving. The reason of this is because there usually exists much noise in the center of weaving due to abrupt change of arc length in case some empty gaps exist in a fillet joint Variance analysis was performed in order to check the effect of weld parameters on arc current and the WAC. As a result, the relationships between tip-to-workpiece distance and arc current, and between weaving offset and the WAC were established.To check "the validity of the algorithm, seam-tracking experiments were performed ;mder various welding condition. The result of experiments showed a satisfactory tracking performance in the presence of empty gaps in a horizontal fillet joint.et joint.

• Computers and Concrete
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• v.3 no.1
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• pp.43-64
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• 2006

A tendon model that can effectively be used in finite element analyses of prestressed concrete (PSC) structures with bonded tendons is proposed on the basis of the bond characteristics between a tendon and its surrounding concrete. Since tensile forces between adjacent cracks are transmitted from a tendon to concrete by bond forces, the constitutive law of a bonded tendon stiffened by grouting is different from that of a bare tendon. Accordingly, the apparent yield stress of an embedded tendon is determined from the bond-slip relationship. The definition of the multi-linear average stress-strain relationship is then obtained through a linear interpolation of the stress difference at the post-yielding stage. Unlike in the case of a bonded tendon, on the other hand, a stress increase beyond the effective prestress in an unbonded tendon is not section-dependent but member-dependent. The tendon stress unequivocally represents a uniform distribution along the length when the friction loss is excluded. Thus, using a strain reduction factor, the modified stress-strain curve of an unbonded tendon is derived by successive iterations. The validity of the proposed two tendon models is verified through correlation studies between analytical and experimental results for PSC beams and slabs.

• Nuclear Engineering and Technology
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• v.52 no.4
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• pp.734-741
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• 2020

A new air-cooled waste heat removal system with a direct contact heat exchanger was designed for SMRs requiring 200 MW of waste heat removal. Conventional air-cooled systems use fin structure causing high thermal resistance; therefore, a large cooling tower is required. The new design replaces the fin structure with a vertical string type direct contact heat exchanger which has the most effective performance among tested heat exchangers in a previous study. The design results showed that the new system requires a cooling tower 50% smaller than that of the conventional system. However, droplet formation on a falling film along a string caused by Rayleigh-Plateau instability decreases heat removal performance of the new system. Analysis of Rayleigh-Plateau instability considering drag force on the falling film surface was developed. The analysis results showed that the instability can be prevented by providing thick string. The instability is prevented when the string radius exceeds the capillary length of liquid by a factor of 0.257 under stagnant air and 0.260 under 5 m/s air velocity.