• Journal of Ecology and Environment
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• v.37 no.2
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• pp.91-97
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• 2014

Little is known about how the increased porosity of a deciduous windbreak, which results from loss of leaves, influences wind speed reduction. We hypothesized that, with loss of foliage, the wind speed reduction effectiveness of a deciduous windbreak decreases on near leeward side but not on further leeward side and that wind speed recovers faster in the full foliage season than in other seasons. During summer, autumn, and winter (full, medium, and non-foliage season, respectively), we observed wind speed and direction around a deciduous windbreak in a traditional Korean village on windward and near and further leeward sides (at -8H, 2H, and 6H; H = 20 m, a windbreak height). We used a linear mixed effects model to determine that the relative wind speed reduction at 2H significantly decreased from 83% to 48% ($F_{2,111.97}=73.6$, P < 0.0001) with the loss of foliage. However, the relative wind speed reduction at 6H significantly increased from 26% to 43% ($F_{2,98.54}=18.5$, P < 0.0001). Consequently, wind speed recovery rate between 2H and 6H in summer was two times higher than in autumn and ten times higher than in winter ($F_{2,102.93}=223.1$, P < 0.0001). These results indicate that deciduous windbreaks with full foliage seem to induce large turbulence and increase wind speed recovery rate on leeward side. Our study suggests that further research is needed to find the optimal foliage density of a deciduous windbreak for maximizing windbreak effectiveness regardless of seasonal foliage changes.

• Wind and Structures
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• v.22 no.1
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• pp.17-41
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• 2016

To address the uncertainty of the flight trajectories caused by the turbulence and gustiness of the wind field over the roof and in the wake of a building, a 3-D probabilistic trajectory model of flat-type wind-borne debris is developed in this study. The core of this methodology is a 6 degree-of-freedom deterministic model, derived from the governing equations of motion of the debris, and a Monte Carlo simulation engine used to account for the uncertainty resulting from vertical and lateral gust wind velocity components. The influence of several parameters, including initial wind speed, time step, gust sampling frequency, number of Monte Carlo simulations, and the extreme gust factor, on the accuracy of the proposed model is examined. For the purpose of validation and calibration, the simulated results from the 3-D probabilistic trajectory model are compared against the available wind tunnel test data. Results show that the maximum relative error between the simulated and wind tunnel test results of the average longitudinal position is about 20%, implying that the probabilistic model provides a reliable and effective means to predict the 3-D flight of the plate-type wind-borne debris.

• Journal of Forest and Environmental Science
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• v.32 no.2
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• pp.212-218
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• 2016

The research was conducted windward of an irrigated Acacia amplicips Maslin windbreak established to protect As Salam Cement Plant from winds and moving sands. Two belts with approximate optical porosities of 50% and 20% were studied in River Nile State, Sudan. The research aimed at assessing the efficiency of the two belts in wind speed reduction and sand deposition. Research methods included: (i) estimation of optical porosity, (ii) measurements of windward wind speeds at a control and at distances of 0.5 h (h stands for windbreak height), 1 h and 2 h at two vertical levels of 0.25 h and 0.5 h, (iii) estimation of relative wind speeds at the three positions (distance and height) at windward and (iv) estimation of wind erosive forces and prediction of zones of sand deposition. Results show that while the two belts reduced windward wind speeds at the two levels for the three distances, belt II was more effective. Nearest sand deposition occurred at 2 h and 1h windward of belt II and belt I, respectively, at level 0.25 h. At level 0.5 h, sand was deposited only at 2 h windward of belt II and no sand deposition occurred windward of belt I. The study concludes that less porous windbreaks are more effective in reducing wind speed and in depositing sand in windward direction at a distance of not less than twice the belt height.

• Wind and Structures
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• v.26 no.3
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• pp.179-190
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• 2018

Translation of tornadoes is an important feature in replicating the near-ground tornado flow field which has been simulated in previous studies based on Ward-type tornado simulators using relative motion of the ground plane. In this laboratory investigation, effects of translation on the near-ground tornado flow field were studied using the ISU Tornado Simulator that can physically translate over a ground plane. Two translation speeds, 0.15 m/s and 0.50 m/s, that scale up to those corresponding to slowly-moving tornadoes in the field were selected for this study. Compared with the flow field of a stationary tornado, the simulated tornado with translation had an influence on the spatial distribution and magnitude of the horizontal velocities, early reversal of the radial inflow, and expansion of the core radius. Maximum horizontal velocities were observed to occur behind the center of the translating tornado and on the right side of its mean path. An increase in translation speed, resulted in reduction of maximum horizontal velocities at all heights. Comparison of the results with previous studies that used relative motion of the ground plane for simulating translating tornadoes, showed that translation has similar effects on the flow field at smaller radial distances (~2 core radius), but different effects at larger radial distances (~4 core radius). Further, it showed that the effect of translation on velocity profiles is noticeable at and above an elevation of ~0.6 core radius, unlike those in studies based on the relative motion of the ground plane.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.658-663
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• 2011

The purpose of this study is to develop an air-passing soundproofing panel with more improved structure to reduce the $CO_2$ emission and installation cost. To reduce the emission of $CO_2$ ; it is suggested to choose low $CO_2$ emission material relative to the aluminum and to reduce the materials by developing a specially designed air-passing soundproofing panel structure. First of all, we performed the flow analysis to predict the wind pressure according to the open angle of the air-passing soundproofing panel and the noise level analysis at the receiver point. To verify the simulation, a prototype of the soundproofing panel was made. The flow test in the wind tunnel and load test were performed. The economic evaluation for the installation of the air-passing soundproofing panel was performed and specifications of the installation was prepared. As the results of this research, it was verified that the wind load was reduced about 40% to that of the conventional one at 25m/s wind speed in the wind tunnel test. By applying the 4m span soundproofing wall with air-passing soundproofing panel and under the cost of 250 thousand $won/m^2$ instead of the conventional 2m span panel, the installation cost will always be lowered than the conventional one in the combination of (60:40~50:50) conventional to air-passing soundproofing panel from the economic evaluation. The 20% reduction of $CO_2$ was found by changing the 50% of aluminum soundproof panel to air-passing soundproofing panel.

• Smart Structures and Systems
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• v.17 no.2
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• pp.209-230
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• 2016

The Canton Tower is a high-rise slender structure with a height of 610 m. A structural health monitoring system has been instrumented on the structure, by which data is continuously monitored. This paper presents an investigation on the identified modal properties of the Canton Tower using ambient vibration data collected during a whole day (24 hours). A recently developed Fast Bayesian FFT method is utilized for operational modal analysis on the basis of the measured acceleration data. The approach views modal identification as an inference problem where probability is used as a measure for the relative plausibility of outcomes given a model of the structure and measured data. Focusing on the first several modes, the modal properties of this supertall slender structure are identified on non-overlapping time windows during the whole day under normal wind speed. With the identified modal parameters and the associated posterior uncertainty, the distribution of the modal parameters in the future is predicted and assessed. By defining the modal root-mean-square value in terms of the power spectral density of modal force identified, the identified natural frequencies and damping ratios versus the vibration amplitude are investigated with the associated posterior uncertainty considered. Meanwhile, the correlations between modal parameters and temperature, modal parameters and wind speed are studied. For comparison purpose, the frequency domain decomposition (FDD) method is also utilized to identify the modal parameters. The identified results obtained by the Bayesian method, the FDD method and a finite element model are compared and discussed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.65-70
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• 2000

Flying an aircraft is not like driving a train along a railway track. There are many factors that may affect an aircraft's course, including the wind speed and direction relative to the aircraft's intended flight path. This paper investigates noise exposed area by using INM. Especially, effect on aircraft route to minimise the number of people overflown by departing aircraft is evaluate. The result shows that track keeping scheme is effective to reduce the noise area. On the other track at 4000ft is negligible to the noise contour.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.297-302
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• 2011

Railway construction in the random vibration natural phenomena, as well as a relatively regular train loads for dynamic loads, such as a usability and safety should be ensured. Vibration due to train loads and seismic vibrations caused by wind compared to the typically very small in size, rather than the safety of the structure affects the usability. Recently in the downtown area, ground and underground facilities, such as a permanent facility that may cause excessive vibration increases, associated with the construction of these transportation facilities on ground vibrations of structures has been increasing concern and complaint. More recently, high-speed train vibration and noise due to furnace is increasing. In order to solve this problem, such as soundproof considering several feet, but by applying the vibration and noise reduction measures insufficient for the study is Free. In this study, track structure, track, and the inside of the building to support the system, the different forms of neurological history and share about the history cheonanahsan high-speed rail, if passed by the bus stop on the train loads of noise, and the history of interior noise and vibration measurement / analysis of measurement results to assess the relative comparison with the relevant provisions were reviewed. Based on this history, future plans for the design of the bridge to reflect the results of a study is intended to provide information. Waiting for the analysis of vibration and noise reduction, cheonanahsan history passed quietly in the train, on average, appeared to 67.53dB and 65.41dB nervous week on average, were measured with the history. Nervous week waiting room of history and the history cheonanahsan radically different shapes and sizes, so a direct comparison is impossible, but the vibration caused by the disc on the base of the polyurethane elastomer disk is not supported by GERB SYSTEM Waiting more effective in reducing the noise level considered in The main materials for railway and for the localization will help to ensure affordability is considered.

• Journal of Environmental Science International
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• v.9 no.5
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• pp.385-388
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• 2000

Visibility reduction is a barometer of air pollution which people can notice easily. First of all we need to measure quantified visibility continuously in order to examine visibility reduction. Prevailing visibility is not practical to measure visibility depending on observer's expertness. Scattering visibility using Forward Scattering Meter(Belfort Visibility Sensor 6230) has been measured at Kwangan-Dong in Pusan and analysed since July 1998. According to the analysis the correlation coefficient(R) between prevailing visibility and scattering visibility was 0.7235. The visibility appeared that each frequency of poor visibility(under 6km) and good visibility(over 25km) was 10.6%, 9.7% on summertime in Pusan and the visibility range from 10km to 20km ranked high frequency as a half of whole ranges. The order of correlation coefficients between visibility an air pollutants are ranking CO. PM10 and NO2 that values are 0.5878, 0.5369,l 0.5284 respectively. In meteorolgical factor the case of poor visibility presented more weakly wind speed and higher relative humidity than the case of good visibility. The correlation coefficient between calculated visibility of multiple linear regression model and observed visibility was 0.7215. But the trend of calculated and observed visibility variation was similar with the exception of several good visibility cases.

• Journal of the Korean Institute of Landscape Architecture
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• v.50 no.1
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• pp.68-77
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• 2022

The human thermal environment in an apartment complex located in Seoul was quantitatively analyzed to devise methods to modify human heat-related stresses in landscape and urban planning. Microclimatic data (air temperature, relative humidity, wind speed, and short- and long-wave radiation) were collected at 6 locations [Apt-center, roof (cement), roof (grass), ground, playground, and a tree-lined road] in the late spring and summer, and the data were used to estimate the human thermal sensation, physiological equivalent temperature (PET) and universal thermal climate index (UTCI). As a result, the playground location had the highest thermal environment, and the roof (grass) location had the lowest. The mean difference between the two locations was 0.8-1.1℃ in air temperature, 1.8-4.0% in relative humidity, and 7.5-8.0℃ in mean radiant temperature. In open space locations, the wind speed was 0.4-0.5 ms-1 higher than others. Also, a wind tunnel effect happened at the Apt-center location during the afternoon. For the human thermal sensation, PET and UTCI, the mean differences between the playground and roof (grass) locations were: 5.2℃ (Max. 11.7℃) in late spring and 5.4℃ (Max. 18.1℃) in summer in PET; and 3.0℃ (Max. 6.1℃) in late spring and 2.6℃ (Max. 9.8℃) in summer in UTCI. The mean differences indicated a level change in PET and 1/2 level in UTCI, and the maximum differences showed greater changes, 2-3 levels in PET, and 1-1.5 levels in UTCI. Moreover, the roof (grass) location gave 4.6℃ PET reduction and a 2.5℃ UTCI reduction in late spring, and a 4.4℃ PET reduction and a 2.0℃ UTCI reduction in the summer when compared with the roof (cement) location, which results in a 2/3 level change in PET and a 1/3 level in UTCI. Green infrastructure locations [roof (grass), ground, and a tree-lined road] were not statistically significant in the reduction of PET and UTCI in thermal environment modifying effects. The implementation of green infrastructure, such as rooftop gardens, grass pavement, and street tree planting, should be adopted in landscape planning and be employed for human thermal environment modification.