• Proceedings of the KSME Conference
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• 2002.08a
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• pp.245-248
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• 2002

Vortex lock-on or resonance in the flow behind a circular cylinder is visualized by a time-resolved PIV when a single frequency oscillation is superimposed on the mean incident velocity. Measurements are made of the $K{\'{a}}rm{\'{a}}n$ vortices in the wake-transition regime at the Reynolds number 360. Basically, natural shedding state is observed to compare with lock-on state. Wake motion by the change of the shedding frequency of lock-on state is investigated. When lock-on occurs, the vortex shedding frequency is found to be half the oscillation frequency as expected from previous experiments. The physical flow phenomena of natural shedding and lock-on states are analyzed with physical parameters of recirculation and vortex formation region. Consequently, it is found that the change of wake bubble plays an important role in the flow at the lock-on state. Vortex formation region is also actively changed like recirculation region as the lock-on occurs. Therefore, it is deduced that the recirculation region is closely related with the vortex formation region.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.101-106
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• 2011

In the present paper, the phenomena of abnormal noise and vibration due to acoustic resonance of CFBC(Circulating Fluidized Bed Combustion) boiler was presented. The acoustic resonance which occurred in the gas path of CFBC boiler system was caused by coincidence of vortex shedding frequency of tube bank and acoustic natural frequency of duct and hopper. And, the phenomena of beating arose from the interference of two closed resonant waves at 66.4Hz and 70.8Hz. There are two control methods for acoustic resonance in this system. The first method is to change the vortex shedding frequency from the structural alterations on the tube bank. And the second method is to change the acoustic natural frequency of the gas path with the installation of anti-noise baffles. The second one which is relatively easy to apply, was adapted in this study. As a result, the noise and vibration level have been decreased by 41dB and 94% at 66.4Hz, respectively. And the improvement of noise and vibration at 70.8Hz was identified by sensory evaluation.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.1155-1160
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• 2008

In the present study investigated the heat dissipation characteristics of the natural convection type radiator by using the latent heat from a solid-liquid PCM(Phase Change Material). Total radiator volume size is $423{\times}295{\times}83\;mm$ and PCM tank size is $398{\times}270{\times}26\;mm$. The objective was elapsed time lower than maximum operating temperature. Experimental condition, in order to study the effects of the phase-change phenomenon, carried out the various mass flow rate, input electric power, and heat of fusion temperature of two type PCMs. For the above experimental conditions, the cooling performance by using the latent heat showed that heat absorption rate performs for about 3 hours from using PCM $38^{\circ}C$. However, cooling performance by using PCM $50^{\circ}C$ showed higher than surface temperature of heater block because of heat of fusion.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.10
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• pp.922-928
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• 2016

Bearing in mind that global climate change is a rising issue, the coastal community of Prek Thnaot, Cambodia has been put on severe effects about natural disasters caused from poor infrastructure and agriculture dependence. This paper proposes to provide and guide a strategic action for the sustainable development path of coastal community in a more continuous manner including a robust resilience to impacts of climate change, natural disasters, and other risks. In doing so, this paper will help environmentally sound management and coastal resources sustainability being sound for socially and economically inclusive development. Proposed fourteen strategic actions for the research should be accompanying with the participation of and cooperation from the local coastal community. Based on the proposed strategic actions, it is critical that the local authorities and other key stakeholders need to accomplish. Providing a good insight for the central government, the strategic action is expected to integrate and prepare a management strategy plan for the local coastal community level. Therefore, this information can be applied to other coastal areas to promote and ensure sustainable protection and management of coastal resources.

• The Journal of Natural Sciences
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• v.10 no.1
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• pp.1-7
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• 1998

A Lennard-Jones fluid layer adsorbed on a smooth solid surface was studied at coverages $\theta$ ~ 0.8 to 1.8 on an isotherm by performing intensive grand canonical Monte Carlo simulations. The results clearly show a picture of two-step melting process which used to be observed in recent thermodynamic measurements of argon monolayer melting on graphite. The observed melting process consist of an abrupt density change followed by a gradual transition. Snapshots of monolayer configurations indicate that the creation and dissociation of a dislocation pair are involved in the melting mechanism. Taking the effect of system size into account, it is suggested that, while the abrupt density change may be not related to the theory of Kosterlitz, Thouless, Halperin, Nelson, and Young (KTHNY), the second gradual transition is probably a KTHNY-type melting transition.

• Journal of the Korean Institute of Landscape Architecture
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• v.26 no.3
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• pp.288-296
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• 1998

Natural or human disturbances cause landscape changes, which may be measured by the degree of heterogeneity. In a 16km$\times$19km area, divided into 100m$\times$100m cells, of Seoul city and its suburb, land covers are classified into 6 groups in aerial photos and land use maps. The degree of heterogeneity is defined as the number of cells that surround a central cell but have different land cover from the central cell divided by 8. The value of the degree of heterogeneity is between 0 and 1. Major findings are 1) Both urban and natural areas have low degree of heterogeneity, about 0.15~0.17. 2) Suburban area under heavy pressure of development and urbanization has highest degree of heterogeneity, about 0.25. 3) The peak of the degree of heterogeneity moved about 4.5km outward in 22 years. 4) Outer suburban area has lower degree of heterogeneity as the area is a greenbelt or forest. 5) The results show the areas with higher degree of heterogeneity which may need landscape management plans, and natural areas with lower degree of heterogeneity which may need landscape conservation plans. A landscape change model may be built for a specific city when this technique is applied to multiple sectors of the city, and the model may predict future landscape changes of the city.

• Journal of the Korean Wood Science and Technology
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• v.49 no.5
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• pp.471-481
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• 2021

This study investigated the hygroscopicity and UV deterioration characteristics of 3 domestic and 4 imported woods using natural oil, stain, and varnish paints. In terms of hygroscopicity, it was found that the hygroscopicity of the painted wood was lower than that of the unpainted wood, and that as the number of coatings increased, the hygroscopicity decreased. In terms of anti-absorption, oil-based chemical paints showed higher resistance than water-based paints, and natural oils showed results comparable to oil-based paints. As for the UV deterioration, the amount of color change of the painted wood was lower than that of the unpainted wood, and there was no significant difference according to the number of times of painting. The amount of color change was found to be low in oil-based paints and hardwoods. Through this study, we confirmed effective moisture blocking and small color changes during painting using paints, and it is believed that wood can be protected from internal and external defects through selective and efficient painting based on data for excellent painting performance.

• Smart Structures and Systems
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• v.29 no.5
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• pp.705-714
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• 2022

In this paper, the effect of magnetic field on the vibration behavior of a Magnetorheological elastomer (MRE) sandwich MEMS actuated by electrostatic actuation with conductive skins are examined within the multiple scales (MMS) perturbation method. Magnetorheological smart materials have been widely used in vibration control of various systems due to their mechanical properties change under the influence of different magnetic fields. To investigate the vibrational behavior of the movable electrode, the Euler-Bernoulli beam theory, as well as Hamilton's principle is used to derive the equations and the related boundary conditions governing the dynamic behavior of the system are applied. The results of this study show that by placing the Magnetorheological elastomer core in the movable electrode and applying different magnetic fields on it, its natural vibrational frequency can be affected so that by increasing the applied magnetic field, the system's natural frequency increases. Also, the effect of various factors such as the electric potential difference between two electrodes, changes in the thickness of the core and the skins, electrode length, the distance between two electrodes and also change in vibration modes of the system on natural frequencies have been investigated.

• Journal of Environmental Impact Assessment
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• v.18 no.6
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• pp.347-357
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• 2009

This study conducted a vulnerability assessment on Korea's physical infrastructure to provide base data for developing strategies to strengthen Korea's ability to adapt to climate change. The assessment was conducted by surveying professionals in the field of infrastructure and climate change science. A vulnerability assessment was carried out for seven climate change events: average temperature increases, sea level rise, typhoons and storm surges, floods and heavy rain, drought, severe cold, and heat waves. The survey asked respondents questions with respect to the consequences of each climate change event, the urgency of adaptation to climate change, and the scale of investment for adaptation to each climate change event. Thereafter, management priorities for infrastructure were devised and implications for policy development were suggested. The results showed that respondents expected the possibility of "typhoons and storm surges" and "floods and heavy rain" to be the most high. Respondents indicated that infrastructure related to water, transportation, and the built environment were more vulnerable to climate change. The most vulnerable facilities included river related facilities such as dams and riverbanks in the "water" category and seaports and roads in the "transport and communication" category. The results found were consistent with the history of natural disasters in Korea.

• Journal of environmental and Sanitary engineering
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• v.8 no.2
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• pp.49-64
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• 1993

The present waste problems require a change of thinking with regard to conventional economics. It has been generally believed that competitive markets maximize social welfare. But, the other hand, a few economists argue that "the competitive markets cannot always be relied on to provide all goods in the efficient amount." One of the best examples of the latter contention is the environmental problem. What is the basic thinking of the conventional economics that causes this problems \ulcorner What is the present problem that requires the change of conventional economic thinking \ulcorner The environmental problem result from the conventional economic thinking such as pursuing the limitless of the Gross National Product(GNP), believing the increasing returns in economics of scale and the efficiency of competitive market. This economic principles, howe- ver, does not apply currently to public goods, especially environmental amenity and natural resource because the price of markets does not reflect the natural goods of services. We call this eternality. Externalizes are no considered by either buyers or sellers of goods of which production or use results in an eternality. This leads to market failure are causes an waste problem in the economic activities. Today, it is almost impossible to say in a word what the solution for waste problems is because they are by-products complicated and entangled human activities. In this paper, I have introduced the causes of environmental problems only from the economic point of view. I have also described the needs of conversion of conventional economic thinking. Firstly, sustainable development, maintaining the natural resources, should be the basis of the economic growth rather that pursuing the limitless growth of GNP. Secondly, an appropriate scale of human's production activity should be taken into account to reduce the impact to the natural environment. Thirdly, internalization of eternality is asked to correct the market failure. This requires the public policy such as imposing a talsubsidy, assigning a property right or implement a more detailed environmental quality standard through, because use of the natural resources can be. allocated optimally by the intervention of government or social associations.