• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.158-158
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• 2018

Drought is a recurrent natural hazard in Bangladesh. It has significant impacts on agriculture, environment, and society. Well-timed information on the onset, extent, intensity, duration, and impacts of drought can mitigate the potential drought-related losses. Thus, drought characteristics need to be explained in terms of frequency, severity, and duration. This paper aims to characterize the spatial and temporal pattern of meteorological drought using EDI and illustrated drought severity over Bangladesh. Twenty-seven (27) station-based daily rainfall data for the study period of 1981-2015 were used to calculate the EDI values over Bangladesh. The evaluation of EDI is conducted for 4 sub-regions over the country to confirm the historical drought record-developed at the regional scale. The finding shows that on average, the frequency of severe to extreme drought is approximately 0.7 events per year. As a result of the regional analysis, most of the recorded historical drought events were successfully detected during the study period. Additionally, the seasonal analysis showed that the extreme droughts were frequently hit in northwestern, middle portion of the eastern and small portion of central parts of Bangladesh during the Kharif(wet) and Rabi(dry) seasons. The severe drought was affected recurrently in the central and northern regions of the country during all cropping seasons. The study also points out that the northern, south-western and central regions in Bangladesh are comparatively vulnerable to both extreme and severe drought event. The study showed that EDI would be a useful tool to identify the drought-prone area and time and potentially applicable to the climate change-induced drought evolution monitoring at regional to the national level in Bangladesh. The outcome of the present study can be used in taking anticipatory strategies to mitigate the drought damages on agricultural production as well as human sufferings in drought-prone areas of Bangladesh.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.153-153
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• 2019

Evapotranspiration (ET) is an important component of hydrological processes. Accurate estimates of ET variation are of vital importance for natural hazard adaptation and water resource management. This study first developed a soil water index (SWI)-based Priestley-Taylor algorithm (SWI-PT) based on the enhanced vegetation index (EVI), SWI, net radiation, and temperature. The algorithm was then compared with a modified satellite-based Priestley-Taylor ET model (MS-PT). After examining the performance of the two models at 10 flux tower sites in different land cover types over East Asia and Australia, the daily estimates from the SWI-PT model were closer to observations than those of the MS-PT model in each land cover type. The average correlation coefficient of the SWI-PT model was 0.81, compared with 0.66 in the original MS-PT model. The average value of the root mean square error decreased from $36.46W/m^2$ to $23.37W/m^2$ in the SWI-PT model, which used different variables of soil moisture and vegetation indices to capture soil evaporation and vegetative transpiration, respectively. By using the EVI and SWI, uncertainties involved in optimizing vegetation and water constraints were reduced. The estimated ET from the MS-PT model was most sensitive (to the normalized difference vegetation index (NDVI) in forests) to net radiation ($R_n$) in grassland and cropland. The estimated ET from the SWI-PT model was most sensitive to $R_n$, followed by SWI, air temperature ($T_a$), and the EVI in each land cover type. Overall, the results showed that the MS-PT model estimates of ET in forest and cropland were weak. By replacing the fraction of soil moisture ($f_{sm}$) with the SWI and the NDVI with the EVI, the newly developed SWI-PT model captured soil evaporation and vegetation transpiration more accurately than the MS-PT model.

• Journal of the Korea Convergence Society
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• v.10 no.11
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• pp.303-308
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• 2019

This study suggests a method for deriving earthquake response based on log-normal distribution in order to obtain realistic and reliable probability and statistical seismic response of structures. The development of three earthquake suites were presented, with a brief description of 2%, 10%, and 50% in 50 years probability of exceedance according the USGS Los Angeles probabilistic seismic hazard maps. In order to analyze the basic dynamic behavior, a Single-Degree-of-Freedom (SDOF) structure was selected and the seismic response spectrum representing the response of each natural period was plotted. Overall, the mean response values presented through the log-normal distribution is lower than the standard normal distribution. Thus, it is considered that the former method can be provided as the effective cost on performance-based seismic design more than the latter one.

• Earthquakes and Structures
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• v.17 no.5
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• pp.511-519
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• 2019

The concrete gravity dam is one of the most important parts of the nation's infrastructure. Besides the benefits, the dam also has some potentially catastrophic disasters related to the life of citizens directly. During the lifetime of service, some degradations in a dam may occur as consequences of operating conditions, environmental aspects and deterioration in materials from natural causes, especially from dynamic loads. Cumulative Absolute Velocity (CAV) plays a key role to assess the operational condition of a structure under seismic hazard. In previous researches, CAV is normally used in Nuclear Power Plant (NPP) fields, but there are no particular criteria or studies that have been made on dam structure. This paper presents a method to calculate the limitation of CAV for the Bohyeonsan Dam in Korea, where the critical Peak Ground Acceleration (PGA) is estimated from twelve sets of selected earthquakes based on High Confidence of Low Probability of Failure (HCLPF). HCLPF point denotes 5% damage probability with 95% confidence level in the fragility curve, and the corresponding PGA expresses the crucial acceleration of this dam. For determining the status of the dam, a 2D finite element model is simulated by ABAQUS. At first, the dam's parameters are optimized by the Minitab tool using the method of Central Composite Design (CCD) for increasing model reliability. Then the Response Surface Methodology (RSM) is used for updating the model and the optimization is implemented from the selected model parameters. Finally, the recorded response of the concrete gravity dam is compared against the results obtained from solving the numerical model for identifying the physical condition of the structure.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.191-191
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• 2017

Floods have become more widespread and frequent among natural disasters and consisted significant losses of lives and properties worldwide. Flood's impacts are threatening socio-economic and people's lives in the Mekong River Basin every year. The objective of this study is to identify the flood hazard areas and inundation depth in the Mekong River Basin. A rainfall-runoff and flood inundation model is necessary to enhance understanding of characteristic of flooding. Rainfall-Runoff-Inundation (RRI) model, a two-dimensional model capable of simulating rainfall-runoff and flood inundation simultaneously, was applied in this study. HydoSHEDS Topographical data, APPRODITE precipitation, MODIS land use, and river cross section were used as input data for the simulation. The Shuffled Complex Evolution (SCE-UA) global optimization method was integrated with RRI model to calibrate the sensitive parameters. In the present study, we selected flood event in 2000 which was considered as 50-year return period flood in term of discharge volume of 500 km3. The simulated results were compared with observed discharge at the stations along the mainstream and inundation map produced by Dartmouth Flood Observatory and Landsat 7. The results indicated good agreement between observed and simulated discharge with NSE = 0.86 at Stung Treng Station. The model predicted inundation extent with success rate SR = 67.50% and modified success rate MSR = 74.53%. In conclusion, the RRI model was successfully used to simulate rainfall runoff and inundation processes in the large scale Mekong River Basin with a good performance. It is recommended to improve the quality of the input data in order to increase the accuracy of the simulation result.

• Journal of Nutrition and Health
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• v.54 no.4
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• pp.342-354
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• 2021

Purpose: Obesity is a serious public health issue for the modern society and is considered a chronic health hazard. There are many surgical and pharmacological approaches to treat obesity. However, various potentially hazardous side effects remain the biggest challenge. Therefore, diets based on foods derived from natural products have gained increasing attention compared to anti-obesity drugs. Recently, research on edible insects as a food source has been a topic of considerable interest in the scientific communities. This study examined the anti-obesity effects of ingesting an edible insect by feeding a high-fat diet (HFD)-induced obese mouse models with a diet containing Tenebrio molitor larvae powder (TMLP). Methods: Six-week-old female C57BL/6J mice were divided into 4 groups according to treatment: 100% normal diet (ND), 100% HFD (HFD), HFD 99% + TMLP 1% (TMLP), and HFD 97% + TMLP 3% (TMLP 3%). TMLP was added to the HFD for 6 weeks for the latter two groups. Results: Compared to the HFD group, mice in the TMLP group showed weight loss, and micro-computed tomographic imaging revealed that the volume of the adipose tissue in the abdominal area also showed significant reduction. After an autopsy, the fat weight was found to be significantly reduced in the TMLP group compared to the HFD group. In addition, the degree of fat cell deposition in the liver tissue and the size of the adipocytes significantly decreased in the TMLP group. Reverse transcription polymerase chain reaction analysis for the mRNA expression of adipogenesis-related genes namely CCAAT-enhancer-binding proteins (C/EBP-β, C/EBP-δ), and fatty acid-binding protein 4 (FABP4) showed that the expression levels of these genes were significantly reduced in the TMLP group compared to the HFD group. Serum leptin level also decreased significantly in the TMLP group in the comparison with the HFD group. In addition, total cholesterol, triglyceride, and glucose levels in mouse serum also decreased in the TMLP group. Conclusion: Taken together, our results showed that TMLP effectively inhibited adipocyte growth and reduced body weight in obese mice.

• Journal of the Earthquake Engineering Society of Korea
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• v.25 no.2
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• pp.59-69
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• 2021

Historical records of earthquakes are generally used as a basis to extrapolate the instrumental earthquake catalog in time and space during the probabilistic seismic hazard analysis (PSHA). However, the historical catalogs' input parameters determined through historical descriptions rather than any quantitative measurements are accompanied by considerable uncertainty in PSHA. Therefore, quantitative assessment to verify the historical earthquake parameters is essential for refining the reliability of PSHA. This study presents an approach and its application to constrain reliable ranges of the magnitude and corresponding epicenter of historical earthquakes. First, ranges rather than specific values of ground motion intensities are estimated at multiple locations with distances between each other for selected historical earthquakes by reviewing observed co-seismic natural phenomena, structural damage levels, or felt areas described in their historical records. Based on specific objective criteria, this study selects only one earthquake (July 24, 1643), which is potentially one of the largest historical earthquakes. Then, ground motion simulations are performed for sufficiently broadly distributed epicenters, with a regular grid to prevent one from relying on strong assumptions. Calculated peak ground accelerations and velocities in areas with the historical descriptions on corresponding earthquakes are converted to intensities with an empirical ground motion-intensity conversion equation to compare them with historical descriptions. For the ground motion simulation, ground motion prediction equations and a frequency-wavenumber method are used to consider the effects of possible source mechanisms and stress drop. From these quantitative calculations, reliable ranges of epicenters and magnitudes and the trade-off between them are inferred for the earthquake that can conservatively match the upper and lower boundaries of intensity values from historical descriptions.

• Journal of the Korean Geotechnical Society
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• v.38 no.8
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• pp.17-27
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• 2022

To characterize the dynamic properties of Gimhae Plains sediments, we calculated natural frequencies using microtremor horizontal-to-vertical spectral ratios and derived shear wave velocity profiles by inversion of Rayleigh-wave dispersion curves obtained by the high frequency-wavenumber and modified spatial autocorrelation methods. Our results suggest that in this region, strong amplification of ground motion is expected in the vibration frequency (f ≥ 1 Hz). Additionally, obtained velocity profiles show that shear wave velocities are ~200 and 400 m/s for the shallow marine and old fluvial sediments, respectively. Bedrock is possibly encountered at depths of 60-100 m at most sites. We developed a simplified shear wave velocity model of shallow sediments based on the obtained profiles. Our results suggest that a large area in the Gimhae Plains could be categorized as an S6 site based on the Korean seismic design code (KDS 17 10 00).

• Journal of Korean Association for Spatial Structures
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• v.23 no.2
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• pp.19-28
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• 2023

Timber structures are susceptible to moisture, contamination, and pest infestation, which can compromise their integrity and pose a significant fire hazard. Despite these drawbacks, timber's lightweight properties, eco-friendliness, and alignment with current architectural trends emphasizing sustainability make it an attractive option for construction. Moreover, timber structures offer economic benefits and provide a natural aesthetic that regulates building temperature and humidity. In recent years, timber domes have gained popularity due to their high recyclability, lightness, and improved fire resistance. Researchers are exploring hybrid timber and steel domes to enhance stability and rigidity. However, shallow dome structures still face challenges related to structural instability. This study investigates stability problems associated with timber domes, the behavior of timber and steel hybrid domes, and the impact of timber member positioning on dome stability and critical load levels. The paper analyzes unstable buckling in single-layer lattice domes using an incremental analysis method. The critical buckling load of the domes is examined based on the arrangement of timber members in the inclined and horizontal directions. The analysis shows that nodal snapping is observed in the case of a concentrated load, whereas snap-back is also observed in the case of a uniform load. Furthermore, the use of inclined timber and horizontal steel members in the lattice dome design provides adequate stability.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.5B
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• pp.511-517
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• 2006

Flood damage is one of the most important and influential natural disaster which has an effect on human beings. Local concentrated heavy rainfall in urban area yields flood damage increase due to insufficient capacity of drainage system. When the excessive flood occurs in urban area, it yields huge property losses of public facilities involving roadway inundation to paralyze industrial and transportation system of the city. To prevent such flood damages in urban area, it is necessary to develop adequate inundation analysis model which can consider complicated geometry of urban area and artificial drainage system simultaneously. In this study, an urban flood analysis model adopting the unstructured computational grid was developed to simulate the urban flood characteristics such as inundation area, depth and integrated with subsurface drainage network systems. By the result, we can make use of these presented method to find a flood hazard area and to make a flodd evacuation map. The model can also establish flood-mitigation measures as a part of the decision support system for flood control authority.