Search Results (3)

This experimental study investigates the effect of changes in the arrangement of horizontal pipelines on changes in the velocity pattern in three dimensions and the scouring process around these submarine pipelines. Experiments have been carried out in four cases: single pipe, two pipes with a distance of 0.5 D, two pipes with a distance of D, and three pipes with a distance of 0.5 D (D is the diameter of the pipes). The velocity upstream, downstream, and on the pipes have been measured by the Acoustic Doppler Velocimeter (ADV). The results show that a single pipe’s scouring depth in the first case is more significant than in the other cases. In the second case, the presence of the second pipe at a distance of 0.5 D from the first pipe significantly reduced the scour depth (28.6%) compared to the single pipe condition by changing the velocity pattern around the pipelines. By increasing the number of pipes to 3 with a distance of 0.5 D, this reduction in scouring depth has reached 47.6% compared to the single pipe condition. However, in the case of two pipes with a distance of D, the reduction of scouring depth was 21.4% compared to the case of a single pipe, and compared to the case of two pipes with a distance of 0.5 D, it increased by 10%. Full article

The Bay of Bengal and Arabian Sea are annually exposed to severe tropical cyclones, which impose massive infrastructure damages and cause the loss of life in coastal regions. Cyclone Shaheen originally generated in the Bay of Bengal in 2021 and translated a rare east-to-west path toward the Arabian Sea. Although the cyclone’s wind field can be obtained from reanalysis datasets such as ERA5 (fifth generation European Centre for Medium-Range Weather Forecasts), the wind speed cannot be reproduced with realistic details in the regions close to the center of cyclone due to spatial resolution. In this study, to address this problem, the high-resolution advanced Weather Research and Forecasting (WRF) model is used for simulation of Shaheen’s wind field. As a critical part of the study, the sensitivity of the results to the planetary boundary layer (PBL) parameterization in terms of the track, intensity, strength and structure of the cyclone Shaheen is investigated. Five experiments are considered with five PBL schemes: Yonsei University (YSU); Mellor–Yamada–Janjić (MYJ); Mellor–Yamada–Nakanishi–Niino level 2.5 (MYNN); Asymmetric Convective Model version 2 (ACM2); Quasi-Normal Scale Elimination (QNSE). The track, intensity, and strength of the experiments are compared with the wind fields obtained from the Joint Typhoon Warning Centre (JTWC) dataset. The results imply the high dependency of the track, intensity, and strength of the cyclone to the PBL parameterization. Simulated tracks with non-local PBL schemes (YSU and ACM2) outperformed those of the local PBL schemes (MYJ, MYNN, and QNSE), especially during the rapid intensification phase of Shaheen before landfall. The YSU produced highly intensified storm, while the ACM2 results are in better agreement with the JTWC data. The most accurate track was obtained from the ERA5 data; however, this dataset overestimated the spatial size and underestimated the wind speed. The WRF model using either YSU or ACM2 overestimated the wind speed compared to that of the altimeter data. The YSU and ACM2 schemes were able to reproduce the observed increase in wind speed and pressure drop at in situ stations. The wind data from EAR5 and cyclone parametric model were applied to the SWAN model to simulate the wave regime in the Arabian Sea during the time that Shaheen was translating across the region. Janssen formulation for wind input and whitecapping dissipation source terms in combination with both ERA5 and hybrid wind were used and the minimum combined error in the prediction of significant wave height ($H_s$) and zero up-crossing wave period ($T_z$) was examined. The maximum significant wave height for hybrid wind is higher than that of ERA5, while the cyclone development was successfully inferred from the wave field of the hybrid data. Full article

Excess sludge production is one of the limitations of the biological activated sludge process. Therefore, the study’s objective is to upgrade the MBBR process to an integrated fixed film-activated sludge (IFAS) process to reduce excess sludge production. Two scenarios were followed in this study to eliminate sludge production in the biological activated sludge process: first, modifying the moving bed biofilm reactor (MBBR) system by increasing the solid retention time (SRT) from 5 to 15 days; and second, upgrading the MBBR process to the integrated fixed-film activated sludge (IFAS) process by applying return activated sludge (RAS) of 50, 100 and 150% with operating hydraulic retention time (HRT) of 6, 12, 14 and 20 h. The results revealed that the first scenario reduced sludge production from 750 to 150 g/day, whereas the second scenario eliminated sludge generation. In the second scenario, operating the system as an IFAS process with complete SRT has eliminated sludge due to sludge decay and cell lysis. In part 3 of the second scenario, the results also showed that the system achieved low effluent pollutants concentrations of 3, 12, 8 and 45 mg/L for BOD, COD, TSS and NO₃, respectively. Operating at complete SRT may eliminate sludge production but also result in higher NO₃ effluent concentration due to the production of NH₃ from sludge decay and cell lysis. To conclude, sludge elimination in an activated sludge system is possible by carefully controlling the process and applying RAS without additional treatment. Full article