• Journal of Mechanical Science and Technology
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• v.18 no.8
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• pp.1479-1489
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• 2004

The effect of fluctuation of Equivalence Ratio (ER) in a turbulent reactive field has been studied in order to check the global combustion characteristics induced by the local fluctuation. When the flow is premixed on a large scale, closer examination on a small scale reveals that local fluctuations of ER exist in an imperfectly premixed mixture, and that these fluctuations must be considered to correctly estimate the mean reaction rate. The fluctuation effect is analyzed with DNS by considering the joint PDF of reactive scalar and ER, followed by modeling study where an extension of stochastic mixing models accounting for the ER fluctuation is reviewed and tested. It was found that models prediction capability as well as its potential is in favor to this case accounting the local ER fluctuation. However, the effect of local fluctuation did not show any notable changes on the mean global characteristics of combustion when statistical independence between the reactive scalar and ER field is imposed, though it greatly influenced the joint PDF distribution. The importance of taking into account the statistical dependency between ER and combustible at the initial phase is demonstrated by testing the modeled reaction rate.

• Journal of Astronomy and Space Sciences
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• v.35 no.2
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• pp.55-66
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• 2018

The solar magnetic field plays a central role in the field of solar research, both theoretically and practically. Sunspots are an important observational constraint since they are considered a discernable tracer of emerged magnetic flux tubes, providing the longest running records of solar magnetic activity. In this presentation, we first review the statistical properties of the latitudinal distribution of sunspots and discuss their implications. The phase difference between paired wings of the butterfly diagram has been revealed. Sunspots seem to emerge with the exponential distribution on top of slowly varying trends by periods of ~11 years, which is considered multiplicative rather than additive. We also present a concept for the center-of-latitude (COL) and its use. With this, one may sort out a traditional butterfly diagram and find new features. It is found that the centroid of the COL does not migrate monotonically toward the equator, appearing to form an 'active latitude'. Furthermore, distributions of the COL as a function of latitude depend on solar activity and the solar North-South asymmetry. We believe that these findings serve as crucial diagnostic tools for any potential model of the solar dynamo. Finally, we find that as the Sun modulates the amount of observed galactic cosmic ray influx, the solar North-South asymmetry seems to contribute to the relationship between the solar variability and terrestrial climate change.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.1
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• pp.75-79
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• 2007

The cathode design is one of the most important parts in order to enhance the performance of fuel cells. A 3-D model of the porous oxygen reducing cathode with perforated current collectors is analysed for the enhanced design in fuel cells. Simulation is performed using equations of electric potential balance, momentum balance, and mass balance. The gas concentrations are quite large and are significantly affected by the reactions that take place. The weight fraction of oxygen, velocity field for the gas phase, and local overvoltage are illustrated in the porous reactive cathode layer. The current density is also analysed and the result shows the distribution and variation are stated in a wide range. It is found that the rate of reaction and the current production is higher beneath the orifice, and decreases as the distance to the gas inlet increases. The significance of the results is discussed in the viewpoint of the mass transportation phenomena, which is inferred that the mass transport of reactants dictates the efficiency of the electrode in this design and at these conditions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.7
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• pp.552-558
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• 2009

An experimental study using the combustor with branch tube was conducted in order to model the industry combustor with FGR (flue gas recirculation) system and to study a thermo-acoustic instability generated by a branch tube. The branch tube is a structure used to modify a system geometry and then to change its pressure field, and the thermo-acoustic instability, usually occurs in a confined geometry, can result in serious problems on industrial combustors. Thus understanding of the instability created by modifying geometry of combustor is necessary to design and operate combustor with FGR system. Pressure fluctuation in the combustion chamber was observed according to diameter and length of branch and it was compared with the solution of 1-D wave equation. It was found that branch tube affects the pressure field in the combustion chamber, and the pressure fluctuation in the combustion chamber was reduced to almost zero when phase difference between an incipient wave in the combustion chamber and a reflected wave in the branch tube is $\pi$ at the branch point. Also, the reduction of pressure fluctuation is irrespective of the installed height of branch tube if it is below $h^*=0.9$ in the close-open tube and open-open tube.

• Journal of the Korea Institute of Military Science and Technology
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• v.12 no.1
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• pp.37-43
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• 2009

Fluctuations in the ocean are closely related with the underwater acoustic propagation. Internal waves are generated by fluctuation of isopycnal layer in the upper part of the stratified ocean, which are propagated from offshore to coastal area. Physical characteristics of the internal waves existed in the East Sea were derived from the five field experimental data and the ocean monitoring buoy nearshore the mid-east coast of Korea. The dominant periods are appeared in the near-inertial period about $17{\sim}20hours$ and the short period about a few minutes. The wavelengths of them are $10{\sim}50km$ and $300{\sim}1000m$, and the phase speeds are $20{\sim}100cm/s$ and $30{\sim}70cm/s$, respectively The maximum amplitudes are about $20{\sim}25m$. Under the environment of short depression internal wave propagation, the variations of transmission loss field were investigated using an range-dependent acoustic transmission loss model(RAM). The result shows that the large irregular variations of transmission loss caused by progressing the internal wave from offshore toward coast.

• Geomechanics and Engineering
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• v.28 no.4
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• pp.359-374
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• 2022

Geology conditions are crucial in decision-making during the planning and design phase of a tunnel project. Estimation of the geology conditions of road tunnels is subject to significant uncertainties. In this work, the effectiveness of a novel regression method in estimating geological or geotechnical parameters of road tunnel projects was explored. This method, called Gaussian process regression (GPR), formulates the learning of the regressor within a Bayesian framework. The GPR model was trained with data of old tunnel projects. To verify its feasibility, the GPR technique was applied to a road tunnel to predict the state of three geological/geomechanical parameters of Rock Mass Rating (RMR), Rock Structure Rating (RSR) and Q-value. Finally, in order to validate the GPR approach, the forecasted results were compared to the field-observed results. From this comparison, it was concluded that, the GPR is presented very good predictions. The R-squared values between the predicted results of the GPR vs. field-observed results for the RMR, RSR and Q-value were obtained equal to 0.8581, 0.8148 and 0.8788, respectively.

• The Journal of Korean Institute for Practical Engineering Education
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• v.3 no.2
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• pp.136-141
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• 2011

The current tendency on development and change of equipment system in the factory are overlapped with the specific field of the existing systems such as PLC, DCS and SCADA, and the limited portion of the systems in the specific field stands in their own field. Specially, systematic integration, inspection control system and manufacturing management system, management information system are getting closely linked and therefore we increasingly need the open system. Meeting the needs, manufacturing automated equipments in the factory overcoming the shortcomings of unlinked unit equipment recently are getting changed to the phase closely linking with other systems. The training systems for the university, however, have not kept up with the needs from the industry, in spite that fused complex function and performance are asked in the field. To solve the problems, we suggest that the training courses and the equipment designed for the undergraduate education.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.28 no.6
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• pp.1463-1474
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• 2018

Fuzzing is one of the software testing techniques that find security flaws by inputting invalid values or arbitrary values into the program and various methods have been suggested to increase the efficiency of such fuzzing. In this paper, focusing on the existence of field with high relevance to coverage and software crash, we propose a new method for intensively fuzzing corresponding field part while performing field based fuzzing. In this case, we use a deep learning model called Variational Autoencoder(VAE) to learn the statistical characteristic of input values measured in high coverage and it showed that the coverage of the regenerated files are uniformly higher than that of simple variation. It also showed that new crash could be found by learning the statistical characteristic of the files in which the crash occurred and applying the dropout during the regeneration. Experimental results showed that the coverage is about 10% higher than the files in the queue of the AFL fuzzing tool and in the Hwpviewer binary, we found two new crashes using two crashes that found at the initial fuzzing phase.

• Korean Journal of Construction Engineering and Management
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• v.11 no.2
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• pp.74-82
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• 2010

A government agency has been announced to increase 23,663 hundred million wons by cost of design change which occurred in the pre-construction and construction phase. As design change is a phenomenon to occur by means of a characteristic of the building design that standardization is difficult, even if it is said that a perfect design is done in design phase, design change is prevented, and it is going to decrease, and there is a limit. Because there are some causes in all of the construction project, it is change order of client, relative system, unfit design and field condition, etc. In this study, we are suggested logic and basic model of the decision making support process model that it should selecting the optimal alternative through complex and quantitative analyzed: that is cost, performance and constructability as respect Owner or CMr is executing project under the CM delivery system construction project which it occurred design change.

• Korean Journal of Social Welfare
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• v.59 no.4
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• pp.245-272
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• 2007

The purpose of this study was to create and validate Scale of Resilience to Burnout and Scale of Burnout Risk for social workers in medical settings. For the purpose, instrument development model, a kind of mixed methods research was used. In the first phase, six dimensions of resilience(: professional competency, accomplishment and worthwhileness, firm belief and value about their profession, good teamwork, support by their agency, and individual resources) and six dimensions of risk to burnout(: dissatisfaction with organizational condition, interpersonal stress among team members, organizational conflict, work related stress, deficiency of professionalism, and individual stress) were suggested thorough the preceding papers with qualitative approaches. The second phase involved analysis of a survey of 185 participants that appeared to validate the dimensions of the measures. The construct validity and reliability of each measure were tested. And it was founded that there were its own factors in each concept, although resilience to burnout related negatively to burnout risk. The results of this study suggest mixed methods research is useful to develop measures reflecting voices in the social work field.