• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.34 no.6
• /
• pp.643-651
• /
• 2001

Paddlewheel-driven circulation in a culture pond has been simulated based on the depth integrated 2 dimensional hydrodynamic model. Acceleration by paddlewheel is expressed as shaft force divided by water mass discharged by paddlewheel blades. The model has been calibrated and applied to culture ponds as following steps:- i) The model predicted velocities at every 10 m along longitudinal direction from the paddlewheel. The model was calibrated comparing the results with the measured values at mass correction factor $\alpha$ and dimensionless eddy viscosity constant $\gamma$, respectively, in a range $15\~20$ and 6. ii) Wind shear stress was simulated under conditions of direction $0^{\circ}C,\;90^{\circ}C\;and\;180^{\circ}C$ and speed 0.0, 2.5, 5.0 and 7.5 m/s. Change rate of current speed was <$1\%$ at wind in parallel or opposite direction to the paddlewheel-driven jet flow, while $4\%$ at orthogonal angle. iii) The model was then applied to 2 culture ponds located at the Western coast of Korea. The measured and predicted currents for the ponds were compared using the regression analysis. Analysis of flow direction and speed showed correlation coefficients 0.8928 and 0.6782 in pond A, 0.8539 and 0.7071 in pond B, respectively. Hence, the model is concluded to accurately predict circulation driven by paddlewheel such that it can be a useful tool to provide pond management strategy relating to paddlewheel operation and water quality.

• Journal of the Korean Institute of Landscape Architecture
• /
• v.42 no.6
• /
• pp.21-30
• /
• 2014

The purpose of this study was to evaluate human thermal comfort in summer by the type of greenery in parks and to explore planning solutions to supply a comfortable thermal environment in parks. The research was conducted in three different land cover types: a park with multi-wide-canopied trees(WOODLAND), park with grass(LAWN) and park with pavement(PAV) as reference sites in Hamyang-Gun SangrimPark. Field measurements of air temperature, relative humidity and wind velocity, short-wave and long-wave radiation from six directions(east, west, north, south, upward and downward) were carried out in the summer of 2014(August 21-23 and 29-30). Mean Radiant Temperature($T_{mrt}$) absorbed by a human-biometeorological reference person was estimated from integral radiation and the calculation of angular factors. The thermal comfort index PET was calculated by Rayman software, UTCI, OUT_SET$^*$ were calculated using the UTCI Calculator and the Thermal Comfort Calculator of Richard DeDear. The results showed that the WOODLAND has the maximum cooling effect during daytime, reduced air temperatures/$T_{mrt}$ by up to $5.9^{\circ}C/35^{\circ}C$ compared to PAV and lowered heat stress values despite increasing relative humidity values and decreasing wind velocity. While the LAWN had very slight cooling effects during daytime, reduced air temperatures/$T_{mrt}$ by up to $0.9^{\circ}C/3^{\circ}C$ compared to PAV, the improvement effects of the thermal comfort index was very slight. However, during nighttime the microclimatic and radiant conditions of WOODLAND, LAWN, and PAV were similar owing to the absence of solar radiation, reduction of wind velocity and an increase in relative humidity. Because the shading and evapotranspiration effects of the WOODLAND were much greater than the evapotranspiration effects of the LAWN, it can be said that the solutions for supplying comfortable thermal environment in parks are to amplify the green volumes rather than green areas. This study was undertaken to evaluate the human thermal comfort in summer of WOODLAND/LAWN parks and to determine the improvement effects of thermal comfort index. These results can contribute to the provision better thermal comfort for park users during park planning.

• Journal of Korea Water Resources Association
• /
• v.54 no.8
• /
• pp.577-587
• /
• 2021

Drought is generally considered to be a natural disaster caused by accumulated water shortages over a long period of time, taking months or years and slowly occurring. However, climate change has led to rapid changes in weather and environmental factors that directly affect agriculture, and extreme weather conditions have led to an increase in the frequency of rapidly developing droughts within weeks to months. This phenomenon is defined as 'Flash Drought', which is caused by an increase in surface temperature over a relatively short period of time and abnormally low and rapidly decreasing soil moisture. The detection and analysis of flash drought is essential because it has a significant impact on agriculture and natural ecosystems, and its impacts are associated with agricultural drought impacts. In South Korea, there is no clear definition of flash drought, so the purpose of this study is to identify and analyze its characteristics. In this study, flash drought detection condition was presented based on the satellite-derived drought index Evaporative Stress Index (ESI) from 2014 to 2018. ESI is used as an early warning indicator for rapidly-occurring flash drought a short period of time due to its similar relationship with reduced soil moisture content, lack of precipitation, increased evaporative demand due to low humidity, high temperature, and strong winds. The flash droughts were analyzed using hydrometeorological characteristics by comparing Standardized Precipitation Index (SPI), soil moisture, maximum temperature, relative humidity, wind speed, and precipitation. The correlation was analyzed based on the 8 weeks prior to the occurrence of the flash drought, and in most cases, a high correlation of 0.8(-0.8) or higher(lower) was expressed for ESI and SPI, soil moisture, and maximum temperature.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.15 no.2
• /
• pp.51-61
• /
• 2010

Surface particulate organic carbon (POC) concentration was measured in the Northeastern Gulf of Mexico on 9 cruises from November 1997 to August 2000 to investigate the seasonal and spatial variability related to synchronous remote sensing data (Sea-viewing Wide Field-of-view Sensor (SeaWiFS), sea surface temperature (SST), sea surface height anomaly (SSHA), and sea surface wind (SSW)) and recorded river discharge data. Surface POC concentrations have higher values (>100 $mg/m^3$) on the inner shelf and near the Mississippi Delta, and decrease across the shelf and slope. The inter-annual variations of surface POC concentrations are relatively higher during 1997 and 1998 (El Nino) than during 1999 and 2000 (La Nina) in the study area. This phenomenon is directly related to the output of Mississippi River and other major rivers, which associated with global climate change such as ENSO events. Although highest river runoff into the northern Gulf of Mexico Coast occurs in early spring and lowest flow in late summer and fall, wide-range POC plumes are observed during the summer cruises and lower concentrations and narrow dispersion of POC during the spring and fall cruises. During the summer seasons, the river discharge remarkably decreases compared to the spring, but increasing temperature causes strong stratification of the water column and increasing buoyancy in near-surface waters. Low-density plumes containing higher POC concentrations extend out over the shelf and slope with spatial patterns and controlled by the Loop Current and eddies, which dominate offshore circulation. Although river discharge is normal or abnormal during the spring and fall seasons, increasing wind stress and decreasing temperature cause vertical mixing, with higher surface POC concentrations confined to the inner shelf.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.9 no.4
• /
• pp.119-126
• /
• 2005

The objective of this paper is to evaluate the flexural tensile strength of unreinforced concrete masonry wall to ensure the structural safety in out-of-plane behaviors under the wind or earthquake loads. Flexural tensile strength of unreinforced concrete masonry wall has been obtained from the full scale tests of total 327 specimens and the statistical analysis are performed for each of the cases. The flexural tensile strength derived from experiments is classified as 13 groups according to masorny units, mortar ingredients, and the direction of tensile stresses and the mean tensile strength and the variable coefficient are obtained for each case. The uniform and concentrated transverse loads have been applied over the face of the wall specimens. The ultimate mean flexural tensile strengths are distributed from 1,564 kPa to 363 kPa according to masonry units, mortar ingredients, and other factors. The allowable flexural tension stress criteria will be established based on the mean flexural tensile strengths in the future.

• Journal of the Ergonomics Society of Korea
• /
• v.36 no.1
• /
• pp.23-36
• /
• 2017

Objective: This paper presents a study to evaluate the WBGT index for assessing the effects of a wide range of outdoor weather conditions on human responses. Background: The Wet Bulb Globe Temperature (WBGT) index was firstly developed for the assessment of hot outdoor conditions. It is a recognised index that is used world-wide. It may be useful over a range of outdoor conditions and not just for hot climates. Method: Four group experiments, involving people performing a light stepping activity, were conducted to determine human responses to outside conditions in the U.K. They were conducted in September 2007 (autumn), December 2007 (winter), March 2008 (spring) and June 2008 (summer). Environmental measurements included WBGT, air temperature, radiant temperature (including solar load), humidity and wind speed all measured at 1.2m above the ground, as well as weather data measured by a standard weather station at 3m to 4m above the ground. Participants' physiological and subjective responses were measured. When the overall results of the four seasons are considered, WBGT provided a strong prediction of physiological responses as well as subjective responses if aural temperature, heart rate and sweat production were measured. Results: WBGT is appropriate to predict thermal strain on a large group of ordinary people in moderate conditions. Consideration should be given to include the WBGT index in warning systems for a wide range of weather conditions. However, the WBGT overestimated physiological responses of subjects. In addition, tenfold Borg's RPE was significantly different with heart rate measured for the four conditions except autumn (p<0.05). Physiological and subjective responses over 60 minutes consistently showed a similar tendency in the relationships with the $WBGT_{head}$ and $WBGT_{abdomen}$. Conclusion: It was found that either $WBGT_{head}$ or $WBGT_{abdomen}$ could be measured if a measurement should be conducted at only one height. The relationship between the WBGT values and weather station data was also investigated. There was a significant relationship between WBGT values at the position of a person and weather station data. For UK daytime weather conditions ranging from an average air temperature of $6^{\circ}C$ to $21^{\circ}C$ with mean radiant temperatures of up to $57^{\circ}C$, the WBGT index could be used as a simple thermal index to indicate the effects of weather on people. Application: The result of evaluation of WBGT might help to develop the smart clothing for workers in industrial sites and improve the work environment in terms of considering workers' wellness.

• Journal of Environmental Science International
• /
• v.25 no.8
• /
• pp.1115-1129
• /
• 2016

To analyze human thermal environments in protected horticultural houses (plastic houses), human thermal sensations estimated using measured microclimatic data (air temperature, humidity, wind speed, and solar and terrestrial radiation) were compared between an outdoor area and two indoor plastic houses, a polyethylene (PE) house and a polycarbonate (PC) house. Measurements were carried out during the daytime in autumn, a transient season that exhibits human thermal environments ranging from neutral to very hot. The mean air temperature and absolute humidity of the houses were $14.6-16.8^{\circ}C$ (max. 22. $3^{\circ}C$) and $7.0-12.0g{\cdot}m^{-3}$ higher than those of the outdoor area, respectively. Solar (K) and terrestrial (L) radiation were compared directionally from the sky hemisphere (${\downarrow}$) and the ground hemisphere (${\uparrow}$). The mean $K{\downarrow}$ and $K{\uparrow}$ values for the houses were respectively $232.5-367.8W{\cdot}m^{-2}$ and $44.9-55.7W;{\cdot}m^{-2}$ lower than those in the outdoor area; the mean $L{\downarrow}$ and $L{\uparrow}$ values were respectively $150.4-182.3W{\cdot}m^{-2}$ and $30.5-33.9W{\cdot}m^{-2}$ higher than those in the outdoor area. Thus, L was revealed to be more influential on the greenhouse effect in the houses than K. Consequently, mean radiant temperature in the houses was higher than the outdoor area during the daytime from 10:45 to 14:15. As a result, mean human thermal sensation values in the PMV, PET, and UTCI of the houses were respectively $3.2-3.4^{\circ}C$ (max. $4.7^{\circ}C$), $15.2-16.4^{\circ}C$ (max. $23.7^{\circ}C$) and $13.6-15.4^{\circ}C$ (max. $22.3^{\circ}C$) higher than those in the outdoor area. The heat stress levels that were influenced by human thermal sensation were much higher in the houses (between hot and very hot) than in the outdoor (between neutral and warm). Further, the microclimatic component that most affected the human thermal sensation in the houses was air temperature that was primarily influenced by $L{\downarrow}$. Therefore, workers in the plastic houses could experience strong heat stresses, equal to hot or higher, when air temperature rose over $22^{\circ}C$ on clear autumn days.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.11a
• /
• pp.741-744
• /
• 2008

Quality control of early age concrete significantly influences the long term performance. Primary factors for early age concrete quality control should include the relative humidity and temperature variation, and these are more important as structures become massive and huge. Temperature raise due to cement hydration causes stress, which can develop to cracking with internal and/or external restraints. Exposure conditions including ambient temperature, humidity and wind also significantly affect the cracking behavior of early age concrete. Among many of studies on the early age concrete behavior, investigation on the variation of temperature and relative humidity internal of concrete is not common. That is in part because the difficulties in measuring the relative humidity and temperature inside the concrete. This study used a digital sensor with an appropriate logger to measure internal temperature and relative humidity. This direct measuring method is expected to provide more reliable and comprehensive data acquisition on the early age behavior of concrete.

• Spatial Information Research
• /
• v.21 no.2
• /
• pp.55-71
• /
• 2013

This study assessed the thermal comfort of new towns in the Seoul Metropolitan Area (Ilsan, Bundang, Dongtan1) using PET (Physiologically Equivalent Temperature) which refers to real human heat stress. The relationship between PET and urban spatial elements was also analyzed using multiple regression analysis. The study results show that the thermal comfort of Dongtan 1, which is considering a reduction of the urban heat island effect in the planning phase, is higher than other cities. In addition, through regression results, the impervious ratio, floor area ratio, commercial area ratio, and residential area ratio were found to be major factors increasing PET. Moreover, the river area ratio and NDVI were found to be major factors decreasing PET. This study has scientific significance as research that focuses on the assessment of thermal comfort scientifically and definitely, by estimating PET for an entire urban area using GIS analysis that included remote sense analysis and the wind field model. The results of this study can be used in preparing more effective urban plans for the promotion of citizen thermal comfort.

• Composites Research
• /
• v.29 no.2
• /
• pp.79-84
• /
• 2016

An adhesive can be used to connect two different materials in structures. In comparing with other connecting methods, such as bolt, rivet, and hot melting, the adhesive does not need to use them. It leads to reduce the weight and decrease the stress concentration along the connecting line. This work studied the comparison of mechanical and interfacial properties of commonly-used two adhesives, acrylic type and bisphenol-A epoxy type. Tensile and flexural strength of neat adhesives were also compared. Lap shear test of two adhesives was deduced from the measurement of tensile and fatigue tests. After testing, the failure patterns of adhesive surfaces were observed by a microscope. Tensile strength and mechanical fatigue resistance at using bisphenol-A epoxy adhesive were better than acrylic adhesive. Also adding CNT reinforcement in epoxy adhesive can anticipate mechanical improvement.