• Journal of the Society of Naval Architects of Korea
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• v.57 no.2
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• pp.114-123
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• 2020

A high-order potential-based panel method based on Green's theorem, with piecewise-linear dipole strength on triangular panels, is formulated for the analysis of potential flow around a three-dimensional wing. Previous low-order panel methods adopt square panels with piecewise-constant dipole strength, which results in inherent errors. Square panels can not represent a high curvature lifting body, such as propellers, since the four vertices of the square panel do not locate at the same flat plane. Moreover the piecewise-constant dipole strength induces inevitable errors due to the steps in dipole strength between adjacent panels. In this paper a high-order panel method is formulated to improve accuracy by adopting a piecewise linear dipole strength on triangular panels. Firstly, the square panels are replaced by triangular panels in order to increase the geometric accuracy in representing the shape of the object with large curvature. Next, the step difference of the dipole strength between adjacent panels is removed by adopting piecewise-linear dipole strength on the triangular panels. The calculated results by the present method is compared with analytical ones for simple non-lifting geometries, such as ellipsoid. The results for an elliptic wing with zero thickness at finite angle of attack are compared with Jordan's results. The comparison shows reasonable agrements for the both lifting and non-lifting bodies.

• Journal of the Korean Electrochemical Society
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• v.7 no.4
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• pp.167-172
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• 2004

3,4-dihydroxybenzaldehyde(3,4-DHB) was oxidatively el electropolymerized on glassy carbon (GC) electrodes to prepare CC/p-3,4-DHB type electrodes, which were subsequently modified with 3,4-dihydroxybenzoic acid(3,4-DHBA) using 0.05M HCI as a catalyst. The esterification reactions were performed between -OH sites on the polymeric film surface of the p-3,4-DHB and the -COOH sites within the 3,4-DHBA molecules in solution. These reactions had a rate constant value of $1.1\times10^{-1}\;s^{-1}$ for the esterification step as obtained from the first-order rate constant in the solution. The electrochemical responses of the GC/p-3,4-DHB-3,4-DHBA electrodes exert an influence upon the buffer solution, its pH and applied potential ranges. The redox process of the electrode was more easily controlled by charge transfer kinetics than that of the CC/p-3,4-DHB. The modified electrodes had redox active sites that were 10 times more active than those present before modification. The electrical admittance of the modified electrodes was also three times higher than that of the unmodified electrodes. After being annealed in ethanol for 20 hrs the electrodes brought about a 3.3 times greater change of water molecules in the redox reaction. The modified electrodes are stable in the potential range of 0.4 to 0.55V.

• Journal of Ocean Engineering and Technology
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• v.1 no.2
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• pp.93-100
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• 1987

Corrosion fatigue cracking of the austenitic stainless steel(bese metal & heat affected zone by TIG weld) was studied experimentally under the environments of various specific resistance and air. The characteristics of corrosion fatigue crack growth rate and the environmental constants of paris' rule were investigated for SUS 304 weldments in the various specific resistance. The influences of stress intensity factor range and corrosion on the crack growth rate were compared. The characteristics of corrosion fatigue cracking for the weldments were inspected from mechanical, electrochemical and microstructural point of view. Main results obtained are as follows: 1) As the specific resistance decreases, the environmental constant C of paris'rule increases(hence the corrosion fatigue crack growth rate is rapid), but the environmental constant m decreases, so the effect of corrosion to the crack growth rate is more susceptible than thet of stress intensity factor range. 2) As the stress intensity factor range decreases, the corrosion fatigue crack growth rate of heat affected zone is more susceptible than that of the base metal. 3) The corrosion fatigue crack growth rate of the heat affected zone is more rapid than that of the base metal, because of the phenomenon of softening and the less noble potential coused by wedlding heat cycle. 4) The corrosion fatigue cracking of SUS 304 weldment appears transgranular fracture.

• 전기의세계
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• v.25 no.1
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• pp.95-100
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• 1976

The main purpose of this paper is to study on the transient current due to the change of environmental temperature under no external field in the arrangement of M$_{1}$(metal)-P(polyver)-M$_{2}$(metal). The specimer of polymeric insulator sandwiched by two metal electrodes composes a parallel-plate condenser represented by Maxwell-model. The behaviors of short circuit current flowing in M-P-M arrangement are very complex and the analysis of its conduction mechanism appears to be much complicated. In this paper we can suggest that a contact potential difference as an energetic state exists in the thin film specimen both sides of which are contacted by two different metals having different cook functions. Futhermore the contact potential difference appears to be constant through the course of temperature change, however, the dielectric constant and caparitance of the specimen must be temperature dependent. Accordingly the charge difference induced on both sides of electrodes may be a cause for the shory circuited transient current flowing through the external circuit. It is also suggestive that the results of the observation must be considered in cases of insulation design of electrical machines and D.C. cable for high voltage use.

• Journal of the Korean Society of Safety
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• v.11 no.3
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• pp.126-136
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• 1996

Synthesis of perfluoromethanesulfonyl fluoride(PFMSF) which is a valuable precursor of perfluoro-chemicals such as surface modifier and fine chemicals was studied by electrochemical fluorination (ECF). In order to determine the termination of preelectrolysis, it was carried to monitor the variation of current during preelectrolysis by means of constant cell voltage operation. In a batch cell, chronopotentiometric electrolysis and various chemical analysis such as GC, GC/MS and If were used to understand the potential change of electrode and synthesis and control of hazardous gases products. Termination of preelectrolysis was determinated by measurement the current and/or detection of $F_2$ gas generation. And during the preelectrolysis, an amount of generated $OF_2$ was shown that a lot of moisture was absorbed from air when a cell was filled with anhydrous hydrogen fluoride( AHF ). Above 4V cell voltage, $F_2$ gas was generated and acted on any form of fluorinating agents. In the ECF of MSC (methane sulfonyl chloride) by constant current operation, the potential of anode was intimately relation with generation of $SO_2F_2$. Exchange of Cl to F was dominatly occured in a initial stage. There were various gaseous products including PFMSF as main product and $C_4$ compounds.

• Journal of Korean Port Research
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• v.14 no.4
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• pp.475-479
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• 2000

A possibility of the implementation of a quartz crystal sensor to the determination of chemical oxygen demand is examined by checking the electrochemical behavior of the sensor in a glucose solution. Since the surface of a quartz crystal has to be oxidized, a relatively active metal is coated on the surface of a usual 9 MHz AT-cut crystal. The electrochemical behavior is investigated by measuring the changes of current, resonant frequency and resonant resistance while a constant potential is applied. The crystal is installed in a specially designed container, and a quartz crystal analyzer is utilized to measure the frequency and resistance simultaneously. The variations of the measurements are examined at different concentrations of glucose solution, and a proper relation between the concentrations of glucose solution, and a proper relation between the concentration and the measurements is analyzed. As a result, it is found that a linear relation between the concentration of less than 900 ppm and the peak current when a constant potential of -180 mV (SSCE) is applied. The relation can be utilized for the determination of glucose concentration in sea water, and considering a direct relation between gluose concentration and chemical oxygen demand tells a possibility of the measurement of chemical oxygen demand using quartz crystal oscillators.

• Journal of the Korean Mathematical Society
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• v.37 no.5
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• pp.779-791
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• 2000

The nonlinear stage of the evolution of free boundary between a light fluid and a heavy fluid driven by an external force is studied by a potential flow model with a source singlarity. The potential flow model is applied to a bubble and spije evolution for constantly accelerated interface (Rayleigh-Taylor instability) and impulsively accelerated interface (Richtmyer-Meshkow instability). The numerical results of the model show that, in constantly accelerated intergace, bubble grows with constant velocity and the spike falls with gravitational acceleration at later times, while the velocity of the bubble in impulsively accelerated interface decay to zero asymp flow model for the bubble and spike for constantly accelerated interface and impulsively accelerated interface.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.6
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• pp.832-839
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• 1998

The potential work is defined as the maximum available work extractable from a composite system. It is important concept to understand the behavior of a composite system because it is a property of the composite system and shows the possible room for the system to change its state by itself. To explain this concept quantitatively, the behavior of a composite system composed of two simple ideal gas systems is analyzed. The potential work of the composite system is estimated, the various reversible processes from a given state to the equilibrium state and the processes on which potential works are constant are shown on the T-P and S-V planes. Such an effort will be necessary to understand and characteristics of composite systems as well as helpful for a deeper comprehension of the energy conversion principles.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.1
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• pp.41-46
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• 2007

Surface potential properties at the interface of pentacene thin films on gold (Au) and aluminum (Al) surfaces were investigated by using a near-field scanning microwave microprobe (NSMM). The surface potential formed across the pentacene film was observed by measuring the microwave reflection coefficient $S_{11}$ and compared with the result of a Kelvin-probe method. The obtained reflection coefficient ${\Delta}S_{11}$ of the pentacene thin films on Al was decreased as the pentacene film thickness increased due to the increased accumulation of negative space charges, while for Au ${\Delta}S_{11}$ was essentially constant.

• Journal of Korean Society of Water and Wastewater
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• v.12 no.2
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• pp.115-126
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• 1998

In use of anaerobic bioconversion shellfish wastes present special problems, since the chitinous structures in the shell faction degrade very slowly in an anaerobic environment. Enzymatic pretreatment method was evaluated for improving the anaerobic bioconversion potential of blue crab processing wastes. An enzymatic pretreatment using chitinase enhanced the ultimate methane yield and biodergradation rate constant for total crab solid wastes by 15% and 19% respectively, above those of the untreated wastes. When the enzymatic pretreatment applied to the shell fraction alone, it resulted in increase of 34% in the ultimate methane yield and 38% in the reaction rate. The results indicate that anaerobic bioconversion of these wastes is technically feasible and enzymatic pretreatment will improve the efficiency of the process.