Wind oscillation analysis of a suspension bridge coupled with CFD

This study conducted a CFD-2D coupled analysis of a suspension bridge subjected to wind loads. Previous studies found that rotational oscillation was due to differences in the restoring force at hanger cables and could generate torsional oscillations. However, due to uncertain external force terms, the previous studies could not be applied to analyze actual structures. To enable application in a real design process, this study proposed a methodology for determining the external force terms. The external force terms were determined with CFD, and a moment force term was added to equations of motion derived from dynamic equilibrium conditions. All constants and properties were calculated from an assumed cross section of superstructure. This methodology can be used not only to avoid torsional resonance but also in preliminary analysis in the bridge design stage

Wind oscillation analysis of a suspension bridge coupled with CFD

This study conducted a CFD-2D coupled analysis of a suspension bridge subjected to wind loads. Previous studies found that rotational oscillation was due to differences in the restoring force at hanger cables and could generate torsional oscillations. However, due to uncertain external force terms, the previous studies could not be applied to analyze actual structures. To enable application in a real design process, this study proposed a methodology for determining the external force terms. The external force terms were determined with CFD, and a moment force term was added to equations of motion derived from dynamic equilibrium conditions. All constants and properties were calculated from an assumed cross section of superstructure. This methodology can be used not only to avoid torsional resonance but also in preliminary analysis in the bridge design stage

An Analysis of the Spatial and Temporal Evolution of the Urban Heat Island in the City of Zhengzhou Using MODIS Data

A rapid increase in urbanization has caused severe urban heat island (UHI) effects in China over the past few years. Zhengzhou is one of the emerging cities of China where residents are facing strong impact of UHI. By utilizing MODIS data on land surface temperature (LST) and employing 3S technology, this study investigates the UHI phenomenon in Zhengzhou over a 10-year period (2012–2021), aiming to analyze the spatio-temporal evolution characteristics of the UHI effect and the associated land cover changes. To the best of our knowledge, this study represents the first attempt to investigate annual and seasonal changes in different areas of Zhengzhou. It is noted that in the night-time, the intensity of the heat island is stronger than in daytime, which has moderate and weak heat island areas. Seasonal variation showed that in autumn, Zhengzhou has the strong heat island intensity, followed by summer, and the lowest is in winter and spring. The analysis reveals that built-up (construction) areas exhibit the highest LST, whereas forested land and water bodies have the lowest temperature levels. The findings of this study can serve as reference for reducing UHI and increasing thermal comfort in cities

Retrieval of Daily Reference Evapotranspiration for Croplands in South Korea Using Machine Learning with Satellite Images and Numerical Weather Prediction Data

Evapotranspiration (ET) is an important component of the Earth’s energy and water cycle via the interaction between the atmosphere and the land surface. The reference evapotranspiration (ET0) is particularly important in the croplands because it is a convenient and reasonable method for calculating the actual evapotranspiration (AET) that represents the loss of water in the croplands through the soil evaporation and vegetation transpiration. To date, many efforts have been made to retrieve ET0 on a spatially continuous grid. In particular, the Moderate Resolution Imaging Spectroradiometer (MODIS) product is provided with a reasonable spatial resolution of 500 m and a temporal resolution of 8 days. However, the applicability to the local-scale variabilities due to complex and heterogeneous land surfaces in countries like South Korea is not sufficiently validated. Meanwhile, the AI approaches showed a useful functionality for the ET0 retrieval on the local scale but have rarely demonstrated a substantial product for a spatially continuous grid. This paper presented a retrieval of the daily reference evapotranspiration (ET0) over a 500 m grid for croplands in South Korea using machine learning (ML) with satellite images and numerical weather prediction data. In a blind test for 2013–2019, the ML-based ET0 model produced the accuracy statistics with a root mean square error of 1.038 mm/day and a correlation coefficient of 0.870. The results of the blind test were stable irrespective of location, year, and month. This outcome is presumably because the input data of the ML-based ET0 model were suitably arranged spatially and temporally, and the optimization of the model was appropriate. We found that the relative humidity and land surface temperature were the most influential variables for the ML-based ET0 model, but the variables with lower importance were also necessary to consider the nonlinearity between the variables. Using the daily ET0 data produced over the 500 m grid, we conducted a case study to examine agrometeorological characteristics of the croplands in South Korea during the period when heatwave and drought events occurred. Through the experiments, the feasibility of the ML-based ET0 retrieval was validated, especially for local agrometeorological applications in regions with heterogeneous land surfaces, such as South Korea

Experimental evidence for interlayer decoupling distance of twisted bilayer graphene

Twisted bilayer graphene (tBLG) is two stacked single graphene sheets rotated at a specific angle. The twist angle plays an important role in the physical properties of the tBLG. In this study, we analyzed the interaction distance between two graphene layers in tBLG using Raman spectroscopy and atomic force microscopy. To confirm the interaction of the upper and bottom graphenes in the tBLG, we prepared two tBLGs with twist angles of 5° and 24°. The interlayer distance was controlled by depositing a gold bar between the two graphene layers. We found that the decoupling interlayer distance of the tBLG was different depending on the twist angle (0.74 nm for 5° and 1.66 nm for 24°). This indicates that the interaction between two graphene layers is strongly coupled with small twist angle, as expected

Spatio-spectral measurement of a surface plasmon polariton in a gold nano-slit array

A spatio-spectral measurement of transmitted near field distribution from a nano optic structure is demonstrated by near field scanning optical miscroscopy (NSOM) with the point spectroscopic approach. This method provides spectral information of nano-optic system with sub-diffraction limit spatial resolution. The gold nano slit array is a good model system where analytical calculation is possible by the modal expansion method for all diffraction orders with surface impedance boundary conditions. The point spectroscopic analysis of near field distribution shows a good agreement with theoretical model calculation

Analysis of Long-Term Prestress Loss in Prestressed Concrete (PC) Structures Using Fiber Bragg Grating (FBG) Sensor-Embedded PC Strands

This study aims to develop a prestressed concrete steel (PC) strand with an embedded optical Fiber Bragg Grating (FBG) sensor, which has been developed by the Korea Institute of Civil Engineering and Building Technology since 2013. This new strand is manufactured by replacing the steel core of the normal PC strand with a carbon-fiber-reinforced polymer (CFRP) rod with excellent tensile strength and durability. Because this new strand is manufactured using the pultrusion method, which is a composite material manufacturing process, with an optical fiber sensor embedded in the inner center of the CFRP Rod, it ensures full composite action as well as proper function of the sensor. In this study, a creep test for maintaining a constant load and a relaxation test for maintaining a constant displacement were performed on the proposed sensor-type PC strand. Each of the two tests was conducted for more than 1000 h, and the long-term performance verification of the sensor-type PC strand was only completed by comparing the performance with that of a normal PC strand. The test specimens were fabricated by applying an optical fiber sensor-embedded PC strand, which had undergone long-term performance verification tests, to a reinforced concrete beam. Depending on whether grout was injected in the duct, the specimens were classified into composite and non-composite specimens. A hydraulic jack was used to prestress the fabricated beam specimens, and the long-term change in the prestress force was observed for more than 1600 days using the embedded optical fiber sensor. The experimental results were compared with the analytical results to determine the long-term prestress loss obtained through finite-element analysis based on various international standards

Analysis of Long-Term Prestress Loss in Prestressed Concrete (PC) Structures Using Fiber Bragg Grating (FBG) Sensor-Embedded PC Strands

This study aims to develop a prestressed concrete steel (PC) strand with an embedded optical Fiber Bragg Grating (FBG) sensor, which has been developed by the Korea Institute of Civil Engineering and Building Technology since 2013. This new strand is manufactured by replacing the steel core of the normal PC strand with a carbon-fiber-reinforced polymer (CFRP) rod with excellent tensile strength and durability. Because this new strand is manufactured using the pultrusion method, which is a composite material manufacturing process, with an optical fiber sensor embedded in the inner center of the CFRP Rod, it ensures full composite action as well as proper function of the sensor. In this study, a creep test for maintaining a constant load and a relaxation test for maintaining a constant displacement were performed on the proposed sensor-type PC strand. Each of the two tests was conducted for more than 1000 h, and the long-term performance verification of the sensor-type PC strand was only completed by comparing the performance with that of a normal PC strand. The test specimens were fabricated by applying an optical fiber sensor-embedded PC strand, which had undergone long-term performance verification tests, to a reinforced concrete beam. Depending on whether grout was injected in the duct, the specimens were classified into composite and non-composite specimens. A hydraulic jack was used to prestress the fabricated beam specimens, and the long-term change in the prestress force was observed for more than 1600 days using the embedded optical fiber sensor. The experimental results were compared with the analytical results to determine the long-term prestress loss obtained through finite-element analysis based on various international standards

The Outcomes of Selection in a Closed Herd on a Farm in Operation

A herd of Berkshire pigs was established in 2003 and subjected to selection without introduction of any genetic resources until 2007. The complete pedigree, including 410 boars and 916 sows, as well as the records from 5,845 pigs and 822 litters were used to investigate the results obtained from the selections. The index of selection for breeding values included days to 90 kg (D90kg), backfat thickness (BF) and number of piglets born alive (NBA). The average inbreeding coefficients of pigs were found to be 0.023, 0.008, 0.013, 0.025, 0.026, and 0.005 from 2003 to 2007, respectively. The genetic gains per year were 12.1 g, −0.04 mm, −3.13 days, and 0.181 head for average daily gain (ADG), BF, D90kg, and NBA, respectively. Breeding values of ADG, BF and D90kg were not significantly correlated with inbreeding coefficients of individuals, except for NBA (−0.21). The response per additional 1% of inbreeding was 0.0278 head reduction in NBA. The annual increase of inbreeding was 0.23% and the annual decrease in NBA due to inbreeding was 0.0064 head. This magnitude could be disregarded when compared with the annual gain in NBA (0.181 head). These results suggest that inbreeding and inbreeding depression on ordinary farms can be controlled with a proper breeding scheme and that breeding programs are economical and safe relative to the risks associated with importation of pigs

Copper-based etalon filter using antioxidant graphene layer

Copper is a low-cost material compared to silver and gold, having high reflectivity in the near infrared spectral range as well as good electrical and thermal conductivity. Its properties make it a good candidate for metal-based low-cost multilayer thin-film devices and optical components. However, its high reflectance in the devices is reduced because copper is easily oxidized. Here, we suggest a copper-based Fabry-Perot optical filter consisting of a thin dielectric layer stacked between two copper films, which can realize low-cost production compared to a conventional silver-based etalon filter. The reduced performance due to the inherent oxidation of the copper surface can be overcome by passivating the copper films with monolayer graphene. The anti-oxidation of copper film is investigated by optical microscopy, x-ray photoelectron spectroscopy, and transmission measurement in UV-vi spectral ranges. Our results show that the graphene coating can be expanded for various metal-based optical devices in terms of anti-corrosion