• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.276-281
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• 2000

As the construction of the high-rise building increases worldwide, the effort has been exerted to improve the safety and serviceability if the structure against various types of external dynamic loads such as wind load, seismic load, etc. The mass damper, defined as dynamic absorber in mechanical engineering is known one of the effective methods to control the vibration of flexible large structures. The hybrid mass damper, HMD is known as the most appropriate type of the mass dampers. In this paper, the control force was designed for HMD by numerical simulations and the performance of HMD to control the flexible vibration of the steel tower induced by sinusoidal force excitation was evaluated, also TMD was designed for a 1-DOF lumped mass model.

• Ocean and Polar Research
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• v.26 no.2
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• pp.145-154
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• 2004

Surface energy and $CO_2$ fluxes have been measured over an ocean at Ieodo Ocean Research Station of KORDI since May 2003. Eddy covariance technique, which is a direct flux measurement, is used to quantitatively understand the interaction between the ocean surface and the atmospheric boundary layer. Although fluxes were continuously measured during the period from May 2003 to February 2004, the quality control of these data yielded <20% of data retrieval. The atmospheric stability did not show any distinct dirunal patterns and remained near-neutral to stable from May to June but mostly unstable during fall and winter in 2003. Sensible heat flux showed a good correlation with the difference between the sea water temperature and the air temperature. The maximum fluxes of sensible heat and latent heat were $120Wm^{-2}$ and $350Wm^{-2}$ respectively, with an averaged Bowen ratio of 0.2. The ocean around the tower absorbed $CO_2$ from the atmosphere and the uptake rates showed seasonal variations. Based our preliminary results, the daytime $CO_2$ flux was steady with an average of $-0.1 mgCO_2m^{-2}s^{-1}$ in summer and increased in winter. The nighttime $CO_2$ uptake was greater and fluctuating, reaching up to $-0.1 mgCO_2m^{-2}s^{-1}$ but these data require further examination due to weak turbulent mixing at nighttime. The magnitude of $CO_2$ flux was positively correlated with the half hourly changes in horizontal mean wind speed. Due to the paucity of quality data, further data collection is needed for more detailed analyses and interpretation.

• Steel and Composite Structures
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• v.41 no.5
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• pp.681-695
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• 2021

Many existing transmission or communication towers designed several decades ago have undergone nonreversible performance degradation, making it hardly meet the additional requirements from upgrades in wind load design codes and extra services of electricity and communication. Therefore, a new-type non-destructive reinforcement method was proposed to reduce the on-site operation of drilling and welding for improving the quality and efficiency of reinforcement. Six built-up steel angle members were tested under compression to examine the reinforcement performance. Subsequently, the cyclic loading test was conducted on a pair of steel angle tower sub-structures to investigate the reinforcement effect, and a simplified prediction method was finally established for calculating the buckling bearing capacity of those new-type retrofitted built-up steel angles. The results indicates that: no apparent difference exists in the initial stiffness for the built-up specimens compared to the unreinforced steel angles; retrofitting the steel angles by single-bolt clamps can guarantee a relatively reasonable reinforcement effect and is suggested for the reduced additional weight and higher construction efficiency; for the substructure test, the latticed substructure retrofitted by the proposed reinforcement method significantly improves the lateral stiffness, the non-deformability and energy dissipation capacity; moreover, an apparent pinching behavior exists in the hysteretic loops, and there is no obvious yield plateau in the skeleton curves; finally, the accuracy validation result indicates that the proposed theoretical model achieves a reasonable agreement with the test results. Accordingly, this study can provide valuable references for the design and application of the non-destructive upgrading project of steel angle towers.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.4
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• pp.329-335
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• 2007

The eye measurement to observe the sea surface condition and estimate the wave height has been used in the open sea or the ship. The experts in the eye estimation can measure the wave height very accurately. The Beaufort wind scale is most widely used as a standard index of the eye measurement. However, more definite reference data such as the representative images by each wave heights must be necessary because the appearances and explanations in the Beaufort wind scale are not enough to understand the sea surface condition far the researcher and the public. The modern field data acquisition technique has been developed to measure wave heights, ocean weather data and even images of the sea surface in real-time. In this study, the wireless field image transmitting system for wave heights and images is installed in the real-time ocean measurement system of Chodo light tower near Sokcho city in South Korea. The wave heights and surface images acquired from the real time system in the field are compared with explanations of the Beaufort wind scale. The wave heights and images measured with the precision ultrasonic wave sensor and the scientific sea surface image transmitting system should be helpful to obtain more precise and definite information than the data from the Beaufort wind scale.

• Wind and Structures
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• v.28 no.4
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• pp.255-270
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• 2019

Aerodynamic configurations of bridge decks have significant effects on the aerostatic torsional divergence and flutter forsuper long-span bridges, which are onset for selection of suitable bridge decksfor those bridges. Based on a cable-stayed bridge with double main spans of 1500 m, considering typical twin-box, stiffening truss and closed-box section, which are the most commonly used form of bridge decks and assumed that the rigidity of those section is completely equivalent, are utilized to investigate the effects of aerodynamic configurations of bridge decks on aerodynamic instability performance comprised of the aerostatic torsional divergence and flutter, by means of wind tunnel tests and numerical calculations, including three-dimensional (3D) multimode flutter analysis and nonlinear aerostatic analysis. Regarding the aerostatic torsional divergence, the results obtained in this study show twin-box section is the best, closed-box section the second-best, and the stiffening truss section the worst. Regarding the flutter, the flutter stability of the twin-box section is far better than that of the stiffening truss and closed-box section. Furthermore, wind-resistance design depends on the torsional divergence for the twin-box and stiffening truss section. However, there are obvious competitive relationships between the aerostatic torsional divergence and flutter for the closed-box section. Flutter occur before aerostatic instability at initial attack angle of $+3^{\circ}$ and $0^{\circ}$, while the aerostatic torsional divergence occur before flutter at initial attack angle of $-3^{\circ}$. The twin-box section is the best in terms of both aerostatic and flutter stability among those bridge decks. Then mechanisms of aerostatic torsional divergence are revealed by tracking the cable forces synchronous with deformation of the bridge decksin the instability process. It was also found that the onset wind velocities of these bridge decks are very similar at attack angle of $-3^{\circ}$. This indicatesthat a stable triangular structure made up of the cable planes, the tower, and the bridge deck greatly improves the aerostatic stability of the structure, while the aerodynamic effects associated with the aerodynamic configurations of the bridge decks have little effects on the aerostatic stability at initial attack angle of $-3^{\circ}$. In addition, instability patterns of the bridge depend on both the initial attack angles and aerodynamic configurations of the bridge decks. This study is helpful in determining bridge decksfor super long-span bridges in future.

• Journal of the Korean Association of Geographic Information Studies
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• v.18 no.1
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• pp.90-104
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• 2015

The purpose of this paper is to build a spatio-temporal evapotranspiration(ET) estimation model using Terra MODIS satellite image and by calibrating with the flux tower ET data from watershed. The fundamentals of spatial ET model, Surface Energy Balance Algorithm for Land(SEBAL) was adopted and modified to estimate the daily ET of Yongdam Dam watershed in South Korea. The daily Normalized Distribution Vegetation Index(NDVI), Albedo, and Land Surface Temperature(LST) from MODIS and the ground measured wind speed and solar radiation data were prepared for 2 years(2012-2013). The SEBAL was calibrated with the forest ET measured by Deokyusan flux tower in the study watershed. Among the model parameters, the important parameters were surface albedo, NDVI and surface roughness in order for momentum transport during calculation of sensible heat flux. As a result of the final calibration, the monthly averaged albedo and NDVI were used because the daily values showed big deviation with unrealistic change. The determination coefficient($R^2$) between SEBAL and flux data was 0.45. The spatial ET reflected the geographical characteristics showing the ET of lowland areas was higher than the highland ET.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.23 no.4
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• pp.153-178
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• 2018

Most operational uses of wind speed data require measurements at, or estimates generated for, the reference height of 10 m above mean sea level (AMSL). On the Ieodo Ocean Research Station (IORS), wind speed is measured by instruments installed on the lighthouse tower of the roof deck at 42.3 m AMSL. This preliminary study indicates how these data can best be converted into synthetic 10 m wind speed data for operational uses via the Korea Hydrographic and Oceanographic Agency (KHOA) website. We tested three well-known conventional empirical neutral wind profile formulas (a power law (PL); a drag coefficient based logarithmic law (DCLL); and a roughness height based logarithmic law (RHLL)), and compared their results to those generated using a well-known, highly tested and validated logarithmic model (LMS) with a stability function (${\psi}_{\nu}$), to assess the potential use of each method for accurately synthesizing reference level wind speeds. From these experiments, we conclude that the reliable LMS technique and the RHLL technique are both useful for generating reference wind speed data from IORS observations, since these methods produced very similar results: comparisons between the RHLL and the LMS results showed relatively small bias values ($-0.001m\;s^{-1}$) and Root Mean Square Deviations (RMSD, $0.122m\;s^{-1}$). We also compared the synthetic wind speed data generated using each of the four neutral wind profile formulas under examination with Advanced SCATterometer (ASCAT) data. Comparisons revealed that the 'LMS without ${\psi}_{\nu}^{\prime}$ produced the best results, with only $0.191m\;s^{-1}$ of bias and $1.111m\;s^{-1}$ of RMSD. As well as comparing these four different approaches, we also explored potential refinements that could be applied within or through each approach. Firstly, we tested the effect of tidal variations in sea level height on wind speed calculations, through comparison of results generated with and without the adjustment of sea level heights for tidal effects. Tidal adjustment of the sea levels used in reference wind speed calculations resulted in remarkably small bias (<$0.0001m\;s^{-1}$) and RMSD (<$0.012m\;s^{-1}$) values when compared to calculations performed without adjustment, indicating that this tidal effect can be ignored for the purposes of IORS reference wind speed estimates. We also estimated surface roughness heights ($z_0$) based on RHLL and LMS calculations in order to explore the best parameterization of this factor, with results leading to our recommendation of a new $z_0$ parameterization derived from observed wind speed data. Lastly, we suggest the necessity of including a suitable, experimentally derived, surface drag coefficient and $z_0$ formulas within conventional wind profile formulas for situations characterized by strong wind (${\geq}33m\;s^{-1}$) conditions, since without this inclusion the wind adjustment approaches used in this study are only optimal for wind speeds ${\leq}25m\;s^{-1}$.

• THE INTERNATIONAL COMMERCE & LAW REVIEW
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• v.55
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• pp.265-290
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• 2012

CEPA (Comprehensive Economic Partnership Agreement) between India and Korea may vitalize Korean economy more and more. Currently most of Korean firms have entered into manufacturing industries like electronics and automobiles. But only a few Korean companies are trying to penetrate into Indian green industry so this paper suggest how to enter into Indian green industry, especially renewable energy sectors. First, Exporting main shaft, tower-flange and polysilicon products can be considered, as a first step of entry mode. Second, entry mode based on contract like technology licensing, strategic alliance and joint venture establishment can be also one of options. For example, Korean solar energy industry which show more competitiveness than that of Indians should try to make technological licensing on PV modules. In addition to this, they should also try to make joint ventures with right Indian partners and build up 'Solar City' nearby regions like Gurgaon in India where many Korean firms are located. Korean shipbuilding firms like Hyundai Engineering which keep on developing wind turbo engines can also try to make strategic alliance with Indian firms like Suzlon which has strong competitiveness. After that, they should explore Korean and Indian wind sector markets together. Third, brownfield investment can be last and final option as a entry mode as we consider the peculiar characteristics of renewable energy industry. Lastly, Korean government which are rush to indulge into green business should formulate more proper and realistic policies to give big incentives the concerned firms which are trying to open international green market so government should make Korean green firms not to lose good market opportunities related to green industry like renewable energy sectors. Renewable energy sectors are basically regarded as infrastructures so close contact to Indian central government as well as state government will be also required.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.719-720
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• 2007

Korea, for the first time in the world, constructed 765 kV double circuits transmission lines, which has 3 phases and 6 bundles with vertical arrangement using steel pipes in 1998. Also in 2002, we developed 765kV outdoor full GIS substation with self-developed technology. KEPCO accumulated a wealth of technologies for 765kV system construction and operation, and are listed 5th in technology field in the world. With this advanced technologies, we are developing oversea business. We started with a projects, 'Development Study on the Power System Network Analysis in Myanmar' in 2001, and continued the project to transmission design, consulting for transmission technology including the education of foreign trainees in south-east and middle east asia. Currently, 12 overseas businesses including 330kV transmission system consulting in Ghana, are in progress. In 2007, beginning with 750 kV transmission consulting in China, we are operating ATT(Advanced Transmission Technology) training program, which educate engineers of government and utilities company from China, Myanmar, Cambodia, Laos and Cambodia. However, for the successful development study on the power system, design of the power system and the training service, it is essential to standardize load design criteria in consideration of temperature, wind speed, air pressure and density, etc. of the other countries. Therefore, in this paper, standardized load design criteria for Cambodia, Laos, Myanmar is explained.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.291-291
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• 2023

증발량을 산정하는 방법 중 증발접시를 활용한 방법은 하천의 증발량을 직접적으로 측정할 수 있는 장점이 있는 반면, 장기간의 증발접시를 활용한 증발량 추정은 현실적으로 쉽지 않다. 대표적인 증발량 산정식으로는 에너지 수지 및 공기동역학적 원리의 혼합적용 방법(PCE, Penman combination equation)과 경험적 바람공식(PWF, Penman wind function)이 있다. PCE로 산정된 증발량의 경우 하천 내 바닥열(bed heat flux)과 물기둥의 열저장 변화율이 장기간 규모의 순 복사량에 비해 작은 값을 가져 식에서 제외되므로 전반적으로 증발량이 과대 추정되는 문제가 발생한다. 반면, PWF로 산정한 증발량에서는 광범위한 매개변수 범위와 기상자료의 부족으로 모형의 불확실성을 증대시키는 요인으로 작용한다. 본 연구의 최종적인 목표는 하천 수로의 수면증발량을 추정하는 것이지만, 실제 하천 중심에서 증발량을 추정하기 위한 수문학적 자료는 매우 부족한 실정이다. 따라서, 본 연구에서는 유역단위에서의 증발량을 전이하는 방안을 모색하고자 하며, 구체적인 연구과정은 다음과 같다. 첫째, 유역단위 수문학적 자료를 수집하여(flux tower 자료 활용) 유역단위의 증발량을 산정한다. 둘째, PCE와 PWF으로 산정한 증발량과 관측된 증발량을 이용하여 각 식의 매개변수를 최적화한다. 마지막으로 최적화된 매개변수를 적용한 증발량과 관측값의 유사성을 분석한다. 본 연구에서는 하천단위의 증발량을 산정하기 위해 PWF을 적용하였으며 용담댐 내의 기상자료를 활용하여 산정한 증발량과 실제 용담댐 내의 수면증발량의 상관성을 분석한 결과 높은 상관성 확인할 수 있었다. 따라서 하천 주변에 증발량 추정을 위한 최소한의 기상정보가 존재하는 지역에서, 하천단위의 증발량을 산정할 수 있으며 장기간의 증발량도 산정할 수 있을 것으로 판단된다.