• Wind and Structures
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• v.36 no.4
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• pp.249-261
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• 2023

Aerodynamic force coefficients are generally prescribed by an ensemble average of ten and/or twenty 10-minute samples. However, this makes it difficult to identify the exact probability distribution and exceedance probability of the prescribed values. In this study, 12,600 10-minute samples on three tall buildings were measured, and the probability distributions were first identified and the aerodynamic force coefficients corresponding to the specific non-exceedance probabilities (cumulative probabilities) of wind load were then evaluated. It was found that the probability distributions of the mean and fluctuating aerodynamic force coefficients followed a normal distribution. The ratios of aerodynamic force coefficients corresponding to the specific non-exceedance probabilities (C_f,Non) to the ensemble average of 12,600 samples (C_f,Ens), which was defined as an adjusting factor (C_f,Non/C_f,Ens), were less than 2%. The effect of coefficient of variation of wind speed on the adjusting factor is larger than that of the annual non-exceedance probability of wind load. The non-exceedance probabilities of the aerodynamic force coefficient is between P_C,nonex = 50% and 60% regardless of force components and aspect ratios. The adjusting factors from the Gumbel distribution were larger than those from the normal distribution.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.30 no.2
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• pp.185-195
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• 2020

Objectives: The purpose of this study was to analyze noise exposure levels and the rate of exceedance of exposure limits in workplaces from a 2015 measurement of working environments according to area, industry, and scale of workplace and to determine changes compared to the past. Methods: Among the 408,875 measurements of noise in working environments from 27,030 workplaces in 2015, 16,359 workplaces that were linked to special health examination data were selected as the subjects of this study. The eight-hour corrected measurements and geometric mean values of the individual noise measurements of the workplaces were used to calculate noise exposure levels and the exceedance rate of exposure limits. Results: The average noise exposure level of the overall workplaces making up the subjects of this study was 83.6 dBA, and the exceedance rate of exposure limits was 15.1%. At least half of the noise measurements exceeded the exposure limits in 13.7% of the workplaces. Noise exposure levels were higher in the manufacturing industry and in smaller-scale workplaces. The exceedance rate of noise exposure limits was higher in the mining and manufacturing industries and in smaller-scale workplaces. Conclusions: Noise exposure has shown improvements compared to the past, but the exceedance rate of exposure limits was still high, and more than half of the workers were being exposed to noise of 85 dBA or higher. Therefore, it is necessary to make more active improvements in working environments in terms of noise exposure.

• Communications for Statistical Applications and Methods
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• v.15 no.5
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• pp.793-798
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• 2008

Extreme value inference deals with fitting the generalized extreme value distribution model and the generalized Pareto distribution model, which are recently combined to give a single model, namely a two-dimensional non-homogeneous Poisson exceedance point process model. In this paper, we extend the two-dimensional non-homogeneous Poisson process model to include non-stationary effect or dependence on covariates and then derive the likelihood for the extended model.

• Magazine of the Korean Society of Agricultural Engineers
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• v.28 no.3
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• pp.69-78
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• 1986

This studies were established to find out the characteristics of frequency distributiom for the number of occurrence and magnitude, probable flood flows according to the return periods, design floods, and design frequency factors for the studying basins in relation to the risk levels which can be correlated with design return period and the life of structure in the non-annual exceedance series. Eight watersheds along Han, Geum, Nak Dong and Seom Jin river basin were selected as studying basins. The results were analyzed and summarized as follows. 1. Poisson distribution and Exponential distribution were tested as a good fitted distributions for the number of occurrence and magnitude for exceedance event, respectively,at selected watersheds along Han, Geum, Nak Dong and Seom Jin river basin. 2.Formulas for the probable flood flows and probable flood flows according to the return periods were derivated for the exponential distribution at the selected watersheds along Han, Geum, Nak Dong, and Seom Jin river basin. 3.Analysis for the risk of failure was connected return period with design life of structure in the non-annual exceedance series. 4.Empirical formulas for the design frequency factors were derivated from under the condition of the return periods identify with the life of structure in relation to the different risk levels in the non-annual exceedance series. 5.Design freguency factors were appeared to be increased in proportion to the return periods while those are in inverse proportion to the levels of the risk of failure. Numerical values for the design frequency factors for the non-annual exceedance series ware appeared generally higher than those of annual maximum series already published by the first report. 6. Design floods according to the different risk levels could be derivated by using of formulas of the design frequency factors for all studying watersheds in the nor-annual exceedance series.

• Wind and Structures
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• v.11 no.6
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• pp.455-478
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• 2008

The present study aims to estimate the wind ventilation performance for pedestrian level domains from the air quality point of view. Three typical models of a dense urban area were considered and numerically simulated in order to examine the effects of the geometry of such models on wind flow characteristics, which in turn affect the air quality, within the pedestrian domain of a street canyon located within this area. The calculated flow fields were employed to estimate the exceedance probabilities within the study domain using a new approach: air exchange rate within the domain. The study has been applied to nine cities in Japan: Tokyo, Osaka, Sapporo, Niigata, Fukuoka, Nagoya, Sendai, Yokohama, and Kyoto, based on their mean wind velocity data. The results demonstrated that the exceedance probability analysis of the pedestrian wind environment could be a valuable tool during the design stage of inhabited areas for the evaluation of pollutant-removal efficiency by the applied wind. Also, the calculated probabilities demonstrated substantial dependence on both the geometry of building arrays and the wind conditions of the nine cities.

• Journal of Astronomy and Space Sciences
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• v.41 no.1
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• pp.25-33
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• 2024

This paper evaluates the influence of rainfall on propagated signal at different time exceedance percentages of an average year, over the climate zones of the country. Specifically, it demonstrates critical and non critical signal fade or signal outage time exceedance (0.001% to 1%) for Ku, K, and Ka-band systems in an average year. The study was carried out using meteorological data made available by the Nigerian Meteorological Agency (NiMet) over a period of 10 years (2009-2018). The four climate zones in the country were represented by five (5) locations; Maidugiri (warm desert climate), Sokoto (tropical dry climate), Port Harcourt (tropical monsoon climate), Abuja and Enugu (tropical savanna climate). The parameters were simulated into the International Telecommunications Union Recommended (ITU-R) models for rain attenuation over the tropics and results presented using MatLab and Origin Lab. Results of Ku band propagations showed that only locations in the tropical savanna and tropical monsoon climates experienced total signal outage for time percentage exceedance equal to or below 0.01% for both horizontal and vertical polarizations. At K band propagations, the five locations showed to have experienced signal outage at time exceedance equal to and below 0.01%, almost same was recorded for the Ka-band propagation. It was also observed that horizontal and vertical polarization of signal had slightly different rain attenuation values for the studied bands at the five locations, with horizontal polarization having higher values than vertical polarization.

• Computational Structural Engineering
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• v.4 no.3
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• pp.107-115
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• 1991

A probabilistic-Fuzzy model for seismic hazard analysis is developed. The proposed model is able to reproduce both the randomness and the imprecision in conjunction with earthquake occurrences. Results-of this research are (a) membership functions of both peak ground accelerations associated with a given probability of exceedance and probabilities of exceedance associated with a given peak ground acceleration, and (b) characteristic values of membership functions at each location of interest. The proposed probabilistic-fuzzy model for assessment of seismic hazard is successfully applied to the Wasatch Front Range in Utah in order to obtain the seismic maps for different annual probabilities of exceedance, different peak ground accelerations, and different time periods.

• Journal of the Korean earth science society
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• v.23 no.8
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• pp.683-696
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• 2002

In this work. we investigated the ozone data sets that exceeded ambient air quality standards from 31 air quality monitoring stations dispersed across the Seoul metropolitan city during the period covering 1990 and 2000. To specifically describe spatial dependency of high level O$_3$ occurrence, we grouped our data into four different geographical ozone exceedance is much longer in SW than the other three sectors. When we compared the exceedance data in terms of occurrence frequency, the month of maximum frequency differed slightly among different sectors. Examination of long-term exceedance trend indicated that its frequency increased continuously from all sectors over the past years, although slightly opposite patterns existed in their absolute values. Most importantly, its peak occurrence frequency seemed to center in very recent years such as 1998 (NE sector) and 2000 (ail pattern sectors except NE). Consequently, we were able to describe the existence of certain patterns of ozone exceedance data sets in terms of both temporal and spatial scales.

• Journal of Wetlands Research
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• v.20 no.2
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• pp.136-144
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• 2018

The Ministry of the Environment conducts a water environment management plan and TMDL(Total Maximum Daily Load) for integrated watershed management, and determines whether the target water quality is achieved using water quality monitoring data. The concentration of monitoring points located in the downstream of the watershed is the outcome of complicated mechanisms such as influx of pollutants from the tributaries of the watershed and self-purification of river water. The purpose of this study is to analyze the effect of main stream and tributary water quality on the target water quality point using the water pollution source tracking and exceedance rate of watershed. In this study, FDC and exceedance rate analysis were performed on six water quality items including BOD and T-P, which are the targets of TMDL. Water quality items and points affecting the target water quality point were derived from flow rate. In this study, the pollution source tracking through FDC analysis and exceedance rate analysis will be able to establish more efficiently the water quality management strategy for each branch to achieve the target water quality.

• Journal of Korean Society on Water Environment
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• v.21 no.5
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• pp.516-519
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• 2005

An useful protocol coiled load duration curve methodology to estimate contaminant loading to a river on an exceedance probability scale was developed in this research. The technique was further applied to estimate total coliform loading to the Geum River, using the daily mean flow rate and total coliform concentration data during January, 1996 and July, 2004 for the Gongju where an automated monitoring station is located. Drought flow of the Gongju (=50.3 cms) was equivalent to 40% on an exceedance probability scale. Load duration curve for total coliform loading at the Gongju was constructed. Standard duration curve was constructed with the water quality criteria for the class 2 (total coliform concentration = 1000 MPN/100 mL). By plotting load duration curve with standard duration curve, it could be revealed that water quality do not meet the desired water quality for 47% on an exceedance probability scale. If linearity between flow rate and coliform concentration is assumed, it can be interpretated that water quality exceeds desired criteria when average mean flow rate is over 51 cms.