• Wind and Structures
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• v.7 no.2
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• pp.107-130
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• 2004

This paper presents a time-domain approach for analyzing nonlinear random vibrations of long-span suspended cables under transversal wind. A consistent continuous model of the cable, fully accounting for geometrical nonlinearities inherent in cable behavior, is adopted. The effects of spatial correlation are properly included by modeling wind velocity fluctuation as a random function of time and of a single spatial variable ranging over cable span, namely as a one-variate bi-dimensional (1V-2D) random field. Within the context of a Galerkin's discretization of the equations governing cable motion, a very efficient Monte Carlo-based technique for second-order analysis of the response is proposed. This procedure starts by generating sample functions of the generalized aerodynamic loads by using the spectral decomposition of the cross-power spectral density function of wind turbulence field. Relying on the physical meaning of both the spectral properties of wind velocity fluctuation and the mode shapes of the vibrating cable, the computational efficiency is greatly enhanced by applying a truncation procedure according to which just the first few significant loading and structural modal contributions are retained.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.34 no.2
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• pp.90-98
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• 2021

Piezoelectric ceramic fiber composite (PCFC) was fabricated using a planar electrode printed piezoelectric ceramic fiber driven in transverse mode for small-scale wind energy harvester applications. The PCFC consisted of an epoxy matrix material and piezoelectric ceramic fibers sandwiched by interdigitated electrode (IDE) patterned polyimide films. The PCFC showed an excellent mechanical performance under a continuous stress. For the fabrication of PCB cantilever harvester, five -PCFCs were vertically attached onto a flexible printed circuit board (PCB) substrate, and then PCFCs were serially connected through a printed Cu circuit. The energy harvesting performance was evaluated applying an inverted structure, which imples its free leading edge located at an open end but the trailing edge at a clamped end, to enhance strain energy in a wind tunnel. The output voltage of the PCB cantilever harvester was increased as the wind speed increased. The maximum output power was 17.2 ㎼ at a resistance load of 200 ㏀ and wind speed of 9 m/s. It is considered that the PCB cantilever energy harvester reveals a potential use for wind energy harvester applications.

• Journal of Physiology & Pathology in Korean Medicine
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• v.16 no.6
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• pp.1100-1105
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• 2002

This thesis aims to provide an analytical basis for existing or new prescriptions based on the theory for properties and tastes of Korean oriental herbal medicines. To this end, prescriptions presented in 「the Various Changes in the Dominations of the Six Energies and their Relations with the Diseases」 of 『Plain Questions』 were analyzed based on the theory for properties and tastes of Korean oriental herbal medicines in 『Yellow Emperor's Canon Internal Medicine』. This thesis focused on symptoms and prescriptions based on the theory for properties and tastes of Korean oriental herbal medicines, which were described in 「the Various Changes in the Dominations of the Six Energies and their Relations with the Diseases」 of 『Plain Questions』 with regard to the year when Kweoleum is affecting the earth energy and the wind energy is partially over-abundant. Those symptoms and prescriptions originate from the theory of the five elements and six climates. The symptoms were analyzed from the perspective of physiology. The prescriptions were first analyzed based on the theory for properties and tastes of Korean oriental herbal medicines in 『Yellow Emperor's Canon Internal Medicine』. Then, a mix formula of oriental medicines pursuant to those prescriptions was studied. Lastly, proper prescriptions from 『Treatise of Cold-Induced Diseases』, which were in conformity with the above prescriptions, were selected. From the physiological point of view, symptoms with regard to the year when Kweoleum is affecting the earth energy and the wind energy is partially over-abundant can be, based on the theory of the five elements and six climates, diagnosed as the symptoms from impaired spleen and stomach due to excessive wind energy. Prescriptions from 『Treatise of Cold-Induced Diseases』pursuant to prescriptions based on the theory for properties and tastes of Korean oriental herbal medicines can be broken down into the following: pinellia decoction for reducing stomach-fire(Banhasasimtang); ginger decoction for reducing stomach-fire(Saenggangsasimtang); liquorice root decoction for reducing stomach-fire(Gamchosasimtang); and Chinese goldthread decoction(Hwangryentang). Therefore, symptoms of six kinds of weather presented in 「the Various Changes in the Dominations of the Six Energies and their Relations with the Diseases」 of 『Plain Questions』 can be analyzed from the physiological point of view. As a result, in addition to the methodology that analyzes existing prescriptions within the boundary of the theory for properties and tastes of Korean oriental herbal medicines in 『Yellow Emperor's Canon Internal Medicine』, it is expected that a theoretical basis for new prescriptions can be provided by analyzing prescriptions from 『Treatise of Cold-Induced Diseases』, based on prescriptions from the theory for properties and tastes of Korean oriental herbal medicines.

• Structural Engineering and Mechanics
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• v.49 no.5
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• pp.619-629
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• 2014

As hyperboloidal cooling towers (HCTs) growing larger and slender, they become more sensitive to gust wind. To improve the dynamic properties of HCTs and to improve the wind resistance capability, stiffening rings have been studied and applied. Although there have been some findings, the influence mechanism of stiffening rings on the dynamic properties is still not fully understood. Based on some fundamental perceptions on the dynamic properties of HCTs and free ring structures, a concept named "participation degree" of stiffening rings was proposed and the influence mechanism on the dynamic properties was illustrated. The "participation degree" is determined by the modal deform amplitude and latitude wave number of stiffening rings. Larger modal deform amplitude and more latitude waves can both result in higher participation degree and more improvement to eigenfrequencies. Also, this concept can explain and associate the pre-existing independent findings.

• Journal of the Korean Society for Heat Treatment
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• v.24 no.1
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• pp.10-15
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• 2011

Recently, renewable energy sources such as wind turbine, solar cell are interested in preventing global warming which is caused by the consumption of fossil fuel. SCM440(H) and SNCM439 have been used in the major components of the wind turbine gear because of excellent mechanical properties. In the present study, the heat treated mechanical properties of SCM440(H) and SNCM439 with 150 mm diameter were compared with those with 25 mm diameter which is generally accepted material for structural application. Heat treated SCM440(H) showed better mechanical properties such as tensile strength, hardness and impact absorbed energy compared with those in SNCM439. Hardenss value between as-quenched and as-quenched followed by tempering showed big difference in SNCM439, however the difference in SCM440(H) was relatively small. Heat treated mechanical properties of the alloys with 25 mm diameter were more uniform value than those with 150 mm diameter.

• Atmosphere
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• v.33 no.4
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• pp.413-422
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• 2023

Urban Air Mobility (UAM) is promising, sustainable and efficient air transportation in a metropolitan area. Korean government has recently announced operation demonstration plans as a step toward commercialization of UAM. However, there is lack of understanding on the potential impact of weather on UAM operation. We collected weather observations from Gimpo International Airport and 5 automatic weather stations (AWS) along UAM corridor of the Han-River to assess weather barriers such as low visibility, wind gust and wind shear. The results show the frequency of low visibility near the corridor fluctuated significantly from year to year depending on the concentration of fine particulate matter (PM_2.5) in Seoul. The frequency of high wind speed-shift calculated using 1-minute wind observations was increased not only during the spring season (March, April, and May) but also the beginning of rainy season (Jun). In addition, a chance of high wind shear from 1-minute wind observations varied by the stations, suggesting that the condition is largely affected by topography including a river and high-rise buildings. These basic weather properties suggest that there are substantial weather barriers to UAM operations along the Han-River Corridor, while they cannot properly surveil micro-scale weather conditions in detail such as wind gust and wind shear over the corridor. Thus, this study suggests that potential barriers related to adverse weather need to be evaluated, building high-density weather observations infrastructure prior to UAM demonstration and commercialization.

• Composites Research
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• v.29 no.6
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• pp.336-341
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• 2016

This paper conducted the study on the electromagnetic and mechanical applicability of CNT-coated glass fiber for wind blades. Large-size wind blade has the serious pending problems to meet the target, such as interfering radar signals, increasing weights, and increasing repair costs. In this paper, we are suggesting the CNT-coated glass fiber in order to overcome these problems. First, the CNTs were strongly coated on the surfaces of glass fiber by suggested coating process, and the CNT-coated glass fiber/epoxy composites were fabricated by Va-RTM process. We designed and fabricated a radar absorbing structure using the CNT-coated glass fiber, which showed over 90% radar absorbing performance between 8.3 and 12.1 GHz frequency. In addition, we confirmed the improvement of mechanical properties on the strength and modulus of tensile, compressive, and in-plane shear.

• Korean Journal of Acupuncture
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• v.31 no.3
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• pp.117-124
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• 2014

Objectives : The purpose of this study is to understand the meaning and the yin-yang properties of the six qi and the three yin and three yang as well as to understand the relationship between the six qi and the three yin and three yang. Methods : As the concept of six qi is the six climatic influences after all, I tried to grasp the yin and yang properties of the six qi on the basis of the meteorology and Yun Qi theory. Based on this I studied the concept and properties of the three yin and three yang. Results and Conclusions: (1) Among the six qi, cold and heat refer to temperature, dryness and dampness to humidity, and wind and ministerial fire to atmospheric pressure. Wind is an ascending air current while ministerial fire is a descending air current. Therefore, wind, heat, and dampness are the yang, and ministerial fire, dryness, and cold are the yin. (2) Three yin and three yang represent changes of ying and yang of all things following six qi changes. Simple deviation of qi can be described by yin and yang, but consequent changes in form required further developed concepts of three yin and three yang. In other words, the changes of the form caused by wind, heat, and dampness are namely reverting yin, lesser yin, and greater yin respectively, while the changes of the form caused by ministerial fire, dryness, and cold are expressed as lesser yang, yang brightness, and greater yang respectively.

• Proceedings of the KSRS Conference
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• 1998.09a
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• pp.286-291
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• 1998

SAR has provided weather independent images on land and sea surface, which can be used for extracting various useful informations. Recently attempts to estimate wind field parameters from SAR images over the oceans have been made by various groups over the world. Although scatterometer loaded in ERS-1 and ERS-2 observes the global wind vector field at spatial resolution of 50 Km with accuracies of $\pm$2m/s in speed, the spatial resolution may not be good enough for applications in coastal regions. It is weil known the sea surface roughness is closely correlated to the wind field, but the wind retrieval algorithms from SAR images are yet in developing stage. Since the radar backscattering properties of the SAR images are principally the same as that of scatterometer, some previous studies conducted by other groups report the success in mesoscale coastal wind field retrievals using ERS SAR images. We have tested SWA (SAR Wind Algorithm) and CMOD4 model for estimation of wind speed using an ERS-1 SAR image acquired near Cheju Island, Korea, in October 11, 1994. The precise estimation of sigma nought and the direction of wind are required for applying the CMOD4 model to estimate wind speed. The wind speed in the test sub-image is estimated to be about 10.5m/s, which relatively well agrees to the observed wind speed about 9.0m/s at Seoguipo station. The wind speed estimation through the SWA is slightly higher than that of CMOD4 model. The sea surface condition may be favorable to SWA on the specific date. Since the CMOD4 model requires either wind direction or wind speed to retrieve the wind field, we should estimate the wind speed first using other algorithm including SWA. So far, it is not conclusive if the SWA can be used to provide input wind speed data for CMOD4 model or not. Since it is only initial stage of implementing the wind field retrieval algorithms and no in-situ observed data is currently avaliable, we are not able to evaluate the accuracy of the results at the moment. Therefore verification studies should be followed in the future to extract reliable wind field information in the coastal region using ERS SAR images.

• Wind and Structures
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• v.12 no.5
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• pp.413-424
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• 2009

A series of wind tunnel free-decay sectional model dynamic tests were conducted to examine the effects of torsional-to-vertical natural frequency ratio of 2DOF bridge dynamic systems on the aerodynamic and dynamic properties of bridge decks. The natural frequency ratios tested were around 2.2:1 and 1.2:1 respectively, with the fundamental vertical natural frequency of the system held constant for all the tests. Three 2.9 m long twin-deck bridge sectional models, with a zero, 16% (intermediate gap) and 35% (large gap) gap-to-width ratio, respectively, were tested to determine whether the effects of frequency ratio are dependent on bridge deck cross-section shapes. The results of wind tunnel tests suggest that for the model with a zero gap-width, a model to approximate a thin flat plate, the flutter derivatives, and consequently the aerodynamic forces, are relatively independent of the torsional-to-vertical frequency ratio for a relatively large range of reduced wind velocities, while for the models with an intermediate gap-width (around 16%) and a large gap-width (around 35%), some of the flutter derivatives, and therefore the aerodynamic forces, are evidently dependent on the frequency ratio for most of the tested reduced velocities. A comparison of the modal damping ratios also suggests that the torsional damping ratio is much more sensitive to the frequency ratio, especially for the two models with nonzero gap (16% and 35% gap-width). The test results clearly show that the effects of the frequency ratio on the flutter derivatives and the aerodynamic forces were dependent on the aerodynamic cross-section shape of the bridge deck.