• Structural Engineering and Mechanics
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• v.70 no.4
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• pp.479-497
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• 2019

In the current code design, the use of a uniform internal pressure coefficient of cooling towers as internal suction cannot reflect the 3D characteristics of flow field inside the tower body with different ventilation rate of shutters. Moreover, extreme weather such as heavy rain also has a direct impact on aerodynamic force on the internal surface and changes the turbulence effect of pulsating wind. In this study, the world's tallest cooling tower under construction, which stands 210m, is taken as the research object. The algorithm for two-way coupling between wind and rain is adopted. Simulation of wind field and raindrops is performed iteratively using continuous phase and discrete phase models, respectively, under the general principles of computational fluid dynamics (CFD). Firstly, the rule of influence of 9 combinations of wind speed and rainfall intensity on the volume of wind-driven rain, additional action force of raindrops and equivalent internal pressure coefficient of the tower body is analyzed. The combination of wind velocity and rainfall intensity that is most unfavorable to the cooling tower in terms of distribution of internal pressure coefficient is identified. On this basis, the wind/rain loads, distribution of aerodynamic force and working mechanism of internal pressures of the cooling tower under the most unfavorable working condition are compared between the four ventilation rates of shutters (0%, 15%, 30% and 100%). The results show that the amount of raindrops captured by the internal surface of the tower decreases as the wind velocity increases, and increases along with the rainfall intensity and ventilation rate of the shutters. The maximum value of rain-induced pressure coefficient is 0.013. The research findings lay the basis for determining the precise values of internal surface loads of cooling tower under extreme weather conditions.

• Wind and Structures
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• v.27 no.1
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• pp.11-27
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• 2018

The straight-cone steel cooling tower is a novel type of structure, which has a distinct aerodynamic distribution on the internal surface of the tower cylinder compared with conventional hyperbolic concrete cooling towers. Especially in the extreme weather conditions of strong wind and heavy rain, heavy rain also has a direct impact on aerodynamic force on the internal surface and changes the turbulence effect of pulsating wind, but existing studies mainly focus on the impact effect brought by wind-driven rain to structure surface. In addition, for the indirect air cooled cooling tower, different additional ventilation rate of shutters produces a considerable interference to air movement inside the tower and also to the action mechanism of loads. To solve the problem, a straight-cone steel cooling towerstanding 189 m high and currently being constructed is taken as the research object in this study. The algorithm for two-way coupling between wind and rain is adopted. Simulation of wind field and raindrops is performed with continuous phase and discrete phase models, respectively, under the general principles of computational fluid dynamics (CFD). Firstly, the rule of influence of 9 combinations of wind sped and rainfall intensity on flow field mechanism, the volume of wind-driven rain, additional action force of raindrops and equivalent internal pressure coefficient of the tower cylinder is analyzed. On this basis, the internal pressures of the cooling tower under the most unfavorable working condition are compared between four ventilation rates of shutters (0%, 15%, 30% and 100%). The results show that the 3D effect of equivalent internal pressure coefficient is the most significant when considering two-way coupling between wind and rain. Additional load imposed by raindrops on the internal surface of the tower accounts for an extremely small proportion of total wind load, the maximum being only 0.245%. This occurs under the combination of 20 m/s wind velocity and 200 mm/h rainfall intensity. Ventilation rate of shutters not only changes the air movement inside the tower, but also affects the accumulated amount and distribution of raindrops on the internal surface.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.151-151
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• 2022

The impact of raindrops on the soil surface causes soil detachment, which may be estimated by measuring the kinetic energy (KE) of the raindrops. Since direct measurements of rainfall force on ground surfaces are not generally available, empirical equations are an alternative option to estimate KE from rainfall intensity (I), which has the greatest influence over soil erosion and is easily accessible. Establishing the optimal formulation for the relationship between kinetic energy and rainfall intensity has proven to be difficult. Thus, this research considered thirty-seven rainfall events observed from June 2020 to December 2021 using a laster optical disdrometer erected in Kyungpook National University to examine the characteristics of KE-I relationships. We concentrated our discussion on the formation of two different expressions of the KE, including KE expenditure (KE_exp) and KE content (KE_con). The following conclusions were drawn: (1) We employed statistical analysis to demonstrate that the KE_exp is more suitable expression for establishing an empirical rule between KE and I than the KE_con. (2) A power-law model was used to find the best correlation between KE_exp-I relationship, whereas the best match between KE_con and I were found using an exponential equation.

• Journal of The Geomorphological Association of Korea
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• v.19 no.2
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• pp.133-143
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• 2012

To evaluate the kinetic energy of the raindrops, the drop size distribution and the terminal velocity of the raindrops had been measured from January to September 2010 using the laser-optical disdrometer in KIGAM, Daejeon, Korea. The relationship between kinetic energy (KE) and rainfall intensity (I) was computed as logarithmic and exponential model, respectively, under the rainfall intensity of about 142mm/h. The exponential model is more suitable for the relationship of KE-I than the logarithmic model, because the exponential model presented better fit for KE over 50mm/h of rainfall intensity. Meanwhile, the differences of the total kinetic energy existed in rainfall events with almost same total rainfall depth, and KE values of Daejeon at high rainfall intensity underestimated rather than the others under temperate climate. Therefore, these differences of KE in rainfall events and geographical regions imply the result from the variations of rainfall intensity within a rainfall event.

• Journal of the Korean GEO-environmental Society
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• v.19 no.12
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• pp.15-23
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• 2018

The occurrence of soil erosions in Korea is mostly driven by flowing water which has a close relationship with rainfalls. The soil eroded by rainfalls flows into and deposits in the river and it polluted the water resources and making the rivers become difficult to be managed. Recently, the frequency of heavy rainfall events that are more than 30 mm/hr has been increasing in Korea due to the influence of climate change, which creating a favourable condition for the occurrence of soil erosion within a short time. In this study, we proposed a method to estimate the distribution of rainfall intensity and to calculate the energy produced by a single rainfall event using the cumulative distribution function that take into account of the physical characteristics of rainfall. The raindrops kinetic energy estimated by the proposed method are compared with the measured data from the previous studies and it is noticed that the raindrops kinetic energy estimated by the rainfall intensity variation is very similar to the results concluded from the previous studies. In order to develop an equation for estimating rainfall kinetic energy, rainfall particle size data measured at a rainfall intensity of 0.254~152.4 mm/hr were used. The rainfall kinetic energy estimated by applying the cumulative distribution function tended to increase in the form of a power function in the relation of rainfall intensity. Based on the equation obtained from this relationship, the rainfall kinetic energy of 1~80 mm/hr rainfall intensity was estimated to be $0.03{\sim}48.26Jm^{-2}mm^{-1}$. Based on the relationship between rainfall intensity and rainfall energy, rainfall kinetic energy equation is proposed as a power function form and it is expected that it can be used in the design of short-term operated facility such as the sizing of sedimentation basin that requires prediction of soil loss by a single rainfall event.

• 보존과학연구
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• s.35
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• pp.73-86
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• 2014

The Seosanmaaesamjonbulsang (national treasure 84) is carved has a quite developed tectonic line in a precipitous wall of stratified rock to the vertical and horizontal directions. The main buddha and the left part of it have got the biological weathering and the efflorescence has been detected on the shoulder part of the right buddha. It has been caused by the raindrops from upper rock after the dismantling of the protection shelter in 2007. Two proper measures have been taken in order to reduce the weathering and protect it from some damages. The one is removing the contaminant by dry/wet cleaning not to get any damage on the rock. The other is the isolation by the construction of a new waterway used L-30 on the upper part of the rock not to contaminate the surface of Rock-carved triad buddha with the raindrops from upper rock. Moreover, the sunlight for buddha has been increased and good ventilation has been made by cutting down the trees around the Rock-carved triad buddha.

• Journal of The Geomorphological Association of Korea
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• v.23 no.3
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• pp.105-122
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• 2016

To evaluate the changes in the physical characteristics of open rainfall related to canopy effects and rainfall intensity in Korea, the terminal velocity of raindrops and drop size distributions(DSD) were continuously measured by an optical-laser disdrometer in an open site(Op) and in two forest stands(Th1: Larix leptolepis, Th2: Pinus koraiensis) during five rainfall events in 2008. The terminal velocity, DSD and two forms of kinetic energy(KE, $Jm^{-2}$ $mm^{-1}$; KER, $Jm^{-2}$ $h^{-1}$) of open rainfall drops were determined and were compared with those of throughfall drops under two different canopy heights. The effects of the canopy and rainfall intensity, together with wind speed, on the changes in drop size and kinetic energy of throughfall were evaluated. Throughfall drops were larger than open rainfall drops. The distribution of terminal velocities for the drop sizes measured at Th2 was lower than that at Op; however, at Th1 the distribution was similar to that at Op. The total kinetic energy of throughfall at Th1 and Th2 was higher than the total kinetic energy of open rainfall, and the kinetic energy distribution for the drop sizes wassimilar to the drop size distribution. The observed throughfall-KER at Th1 was lower than an estimate previously produced using a model. The overestimation from the modeled value at Th1 was likely to be due to overestimated values of a square root transformation of fall height and its coefficient in the model because the distributions of terminal velocity for the drop size measured at Th1 were similar to those of open rainfall.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2005.11a
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• pp.67-74
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• 2005

Microbeam PIXE, often called micro-PIXE, is a powerful tool tot analyzing a wide range of elements for various samples, as well as, it has important applications of interest to the atmospheric science. In this study, qualitative elemental imagination for various atmospheric environmental species was attempted using micro-PIXE. Here, we present the results of an application of micro-PIXE to the study of atmospheric environment. The detailed spatial resolution of multiple elements lot various samples like individual ambient particles, individual raindrops, individual fog droplets, and individual snow crystals could be successfully achieved by scanning 2.6 MeV H+ micro beam (1-2 ${\mu}m$) accelerated by 3 MV single-end accelerator.

• Journal of Korean Society for Atmospheric Environment
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• v.24 no.E1
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• pp.54-62
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• 2008

Microbeam PIXE, often called micro-PIXE, is one of powerful tools for analyzing a wide range of elements for various samples. Moreover, it has important applications of interest to the atmospheric science. In the present study, a qualitative elemental imagination for various atmospheric environmental species was attempted using micro-PIXE. Especially, in combination with a novel individual droplet collection method and the micro-PIXE analytical technique, the chemical specification of various individual atmospheric samples could be carried out. Here, we briefly introduce the results of an application of micro-PIXE to the study of atmospheric environment. The detailed spatial resolution of multiple elements for various samples like individual ambient particles, individual raindrops, individual fog droplets, and individual snow crystals could be successfully achieved by scanning 2.6 MeV $H^+$ micro beam ($1{\sim}2{\mu}m$) accelerated by 3 MeV single-end accelerator.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.5
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• pp.701-710
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• 1999

To predict rain attenuation accurately, we must know scattering characteristics of rain-drops for real drop shapes. In this paper, the scattering characteristics of rain-drops are analyzed by an analytical model, and the differences in the characteristics of the forward scattering amplitudes for three different rain-drop shapes are compared. Using the results for the Pruppacher-Pitter's real rain-drop shaper, the specific rain attenuation in domestic environment is predicted, and the difference from the ITU-R model is compared and analyzed.