• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.10a
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• pp.301-306
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• 2002

The characteristics of parameters for the probability distribution of fatigue crack growth lives by the non-Gaussian random process simulation method is investigated. In this paper, the material resistance to fatigue crack growth is treated as a spatial random process, which varies randomly on the crack surface. Using the previous experimental data, the crack length - the number of cycles curves are simulated. The results are obtained for constant stress intensity factor range conditions with stress ratio of R=0.2, three specimen thickness of 6, 12 and 18mm, and the four stress intensity level. The probability distribution function of fatigue crack growth lives seems to follow the 3-parameter Wiubull and shows a slight dependence on specimen thickness and stress intensity level. The shape parameter, ${\alpha}$, does not show the dependency of thickness and stress intensity level, but the scale parameter, ${\beta}$, and location parameter, ${\upsilon}$, are decreased by increasing the specimen thickness and stress intensity level. The slope for the stress intensity level is larger than the specimen thickness.

• Journal of the Korean Society of Systems Engineering
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• v.14 no.1
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• pp.44-51
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• 2018

The purpose of RAM analysis in weapon systems is to reduce life cycle costs, along with improving combat readiness by meeting RAM target value. We analyzed the sensitivity of the RAM analysis parameters to the use of the operating system by using the Markov Process based model (MPS, Markov Process Simulation) developed for RAM analysis. A Markov process-based RAM analysis model was developed to analyze the sensitivity of parameters (MTBF, MTTR and ALDT) to the utility of the 81mm mortar. The time required for the application to reach the steady state is about 15,000H, which is about 2 years, and the sensitivity of the parameter is highest for ALDT. In order to improve combat readiness, there is a need for continuous improvement in ALDT.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.9 no.2
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• pp.80-86
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• 2000

Although polishing process take 30-50% of whole process of manufacturing die and mold it has not been fully automat-ed yet. Considering current trend of manufacturing it is necessary to study on polishing automation. To accomplish automation reliable database must be developed. For developing it polishing mechanism should be defined and a general empirical formula that can be applied widely should be created. In this paper it is found that polishing process must be separated into 2 process such as removing cusp and getting fine surface process and the polishing parameter which is com-posed of major machining parameters and normalization of data can be applied efficiently in making reliable database.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.4
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• pp.625-632
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• 2012

Optimization of process parameters in polymer extrusion is an important task to reduce manufacturing cost. To determine the optimum values of the process parameters, it is essential to find their influence on the strength of polymer breathable thin film. The significance of six important process parameters namely, extruder cylinder temperature, extruder speed, extruder dies temperature, cooling roll temperature, stretching ratio, stretching roll temperature on breathable film strength of polymer extrusion was determined. Moreover, this paper presents the application of Taguchi method and analysis of variance (ANOVA) for maximization of the breathable film strength influenced by extrusion parameters. The optimum parameter combination of extrusion process was obtained by using the analysis of signal-to-noise ratio. The conclusion revealed that extruder speed and stretching ratio were the most influential factor on the film strength, respectively. The best results of film strength were obtained at higher extruder speed and stretching ratio.

• Transactions of Materials Processing
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• v.19 no.4
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• pp.203-209
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• 2010

In the hot press forming process (HPF), a martensitic structure is obtained by controlling the cooling rate when cooling a boron sheet that is heated up to over $900^{\circ}C$. The HPF process has various advantages such as the improvement in formability and material properties and minimal spring back of the deformed materials. The factors related to the cooling rate depend on the heat transfer characteristics between heated materials and dies. Therefore, in this study, the cooling rate is controlled by adjusting the heat transfer coefficient of the material at the pressing process. And, the mechanical properties and microstructure of the deformed material is demonstrated during the HPF process where cold dies are used to form the heated steel plate. This is achieved by varying the major forming conditions that control the cooling rate regarded as the most important process parameter.

• English Language & Literature Teaching
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• no.5
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• pp.219-247
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• 1999

The purpose of this paper is to examine how Korean learners of English reset the "prodrop" parameter of Korean into "non-prodrop" parameter of English in the process of English acquisition. An experiment was conducted to 45 Korean learners of English on the prodrop phenomenon, namely on the null referential or null nonreferential subject, and subject-verb agreement by way of grammatical judgment. The results of the experiment are as follows: First, L2 learners follow the parameter of L1, and then reset the parameter of L2 regardless of the parameter of L1 as their L2 abilities advance. Thus, this study provides further support for the hypothesis that universal grammar is available via L1. Second, the referential subject is, at first, easier to acquire than nonreferential subject, and the triggering fact for the switch from [+prodrop] to [-prodrop] was the use of nonreferential subjects. Third, 3rd person agreement has no connection with the acquisition of the prodrop parameter as a result of subject-verb agreement. Therefore, these results indicate that verb agreement is not a trigger for the recognition of the obligatory subject.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 1996.06c
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• pp.559-568
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• 1996

• Transactions of the Korean hydrogen and new energy society
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• v.29 no.1
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• pp.71-80
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• 2018

Electrospinning is a versatile technique that utilizes electrostatic forces to produce very thin and fine fibers of polymer ranging from submicron to nanometer scale. The technique can be applied to fibers of a various polymer types. Working parameters in the electrospinning are very important to understand not only the nature of electrospinning but also the conversion of polymer solutions into nanofibers through electrospinning. Those parameters in the electrospinning can be broadly divided into three parts. The first parameter is solution parameters such as molecular weight of polymer, concentration, viscosity, surface tension and conductivity/surface charge density of solution. The second parameter is process such as voltage, distance between the collector and the tip of the syringe, shape of collectors, flow rate. The third parameter is ambient parameters such as humidity and temperature. Fibers which made by electrospinning with working parameters are applied for various fields according to shape such as medical, cloth, photodiode, a sensor technology, catalyst, filtration, battery etc.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.7 s.166
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• pp.1139-1146
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• 1999

Reliability analysis of structures based on fracture mechanics requires knowledge on statistical characteristics of the parameter C and m in the fatigue crack growth law, $da/dN=C({\Delta}K)^m$. The purpose of the present study is to investigate if it is possible to predict fatigue crack growth rate by only the fluctuation of the parameter C. In this study, Paris-Erdogan law is adopted, where the author treat the parameter C as random and m as constant. The fluctuation of crack growth rate is assumed only due to the parameter C. The growth resistance coefficient of material to fatigue crack growth (Z=1/C) was treated as a spatial stochastic process, which varies randomly on the crack path. The theoretical crack growth rates at various stress intensity factor range are discussed. Constant ${\Delta}K$ fatigue crack growth tests were performed on the structural steel, SM45C. The experimental data were analyzed to determine the autocorrelation function and Weibull distributions of the fatigue crack growth resistance. And also, the effect of the parameter m of Paris' law due to variation of fatigue crack growth resistance was discussed.

• 제어로봇시스템학회:학술대회논문집
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• 1999.10a
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• pp.288-291
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• 1999

The PID (Proportional-Integral-Derivative) controller is widely used in the industries for more than fifty years with the well known Ziegler-Nichols tuning method and others varieties. However, most of the PID controller being used in the real practice still require trial and error adjustment for each process after the tuning method is done, which is consuming of time and needs the operator experiences to obtain the best results for the controller parameter. In order to reduce the inconvenience in the controller tuning, this paper presents a design of an automatic PID controller parameter analyzer being used as a support instrument in the industrial process control. This analyzer is designed based on the tuning formula of Dahlin to synthesize the PID controller parameter. Using this analyzer, the time to be spent in the trial and error procedures and its complexity can be neglected. Experimental results using PID controller parameter synthesized from this analyzer to the liquid level control plant model and the fluid flow control plant model show that the responses of the controlled systems can be efficiently controlled without any difficulty in mathemathical computation.