| 1. |
- Li, Peng, et al.
(författare)
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The effects of domain division types on the performance prediction of a rim-driven thruster
- 2023
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Ingår i: Ocean Engineering. - 0029-8018. ; 287
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Tidskriftsartikel (refereegranskat)abstract
- The rim-driven thruster (RDT) is an innovative propulsion thruster. The rotating subdomain can contain different assemblies with different domain division types (DDT). This paper tried to figure out the effects of DDT on the performance of RDT. This paper uses the Delayed Detached Eddy Simulation (DDES) turbulence model to conduct the simulations. Three DDTs are carefully analyzed to understand their effects on predictive performance. The convergence analysis is performed by taking a typical method: Grid Convergence Index (GCI). Some theoretical results and the experimental hydrodynamics of a popular combination of Ka 4–70 and MARIN 19 A are used to validate the numerical method. The numerical results demonstrate that the computational efficiency is influenced by the cell number on the interfaces between two subdomains and an inherent characteristic of DDT. Moreover, the torques acting on rim surfaces are closely accounting for the gap flow. Moreover, regarding the morphology and variables of the vortex system, the third type of DDT enhances vortices presenting in the hub region and vortex-instability region. Although the present analysis is performed for an RDT, the findings should be generally applicable for other RDT designs with similar structures and operational conditions.
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| 2. |
- Zhang, G. F., et al.
(författare)
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Rapid urbanization induced daily maximum wind speed decline in metropolitan areas: A case study in the Yangtze River Delta (China)
- 2022
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Ingår i: Urban Climate. - : Elsevier BV. - 2212-0955. ; 43
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Tidskriftsartikel (refereegranskat)abstract
- Wind extremes cause many environmental and natural hazard related problems globally, particularly in heavily populated metropolitan areas. However, the underlying causes of maximum wind speed variability in urbanized regions remain largely unknown. Here, we investigated how rapid urbanization in the Yangtze River Delta (YRD), China, impacted daily maximum wind speed (DMWS) between 1990 and 2015, based on near-surface (10 m height) DMWS observations, reanalysis datasets, and night-time lighting data (a proxy for urbanization). The station observation shows that annual DMWS in the YRD significantly (p < 0.05) declined during 1990-2015, by -0.209 m s(-1) decade(-1), while slightly (p > 0.1) positive trends were found in NCEP-NCAR1 (+0.048 m s(-1) decade(-1)) and ERA5 (+0.027 m s(-1) decade(-1)). An increasing divergence between the reanalysis output and the station observation since 2005 was found, and those stations located in areas with high rates of urbanization show the strongest negative annual DMWS trend, implying the key role of urbanization in weakening DMWS. This finding is supported by sensitivity experiments conducted using a regional climate model (RegCM4) forced with both 1990 and 2015 land-use and land-cover (LULC) data, where the simulated DMWS using the 2015 LULC data was lower than that simulated using the 1990 LULC data.
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| 3. |
- Deng, Kaiqiang, et al.
(författare)
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A dry-wet teleconnection between southwestern and northeastern China in winter and early spring
- 2024
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Ingår i: CLIMATE DYNAMICS. - 0930-7575 .- 1432-0894.
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Tidskriftsartikel (refereegranskat)abstract
- Global climate change has led to more frequent and intense dry and wet extremes, causing considerable socio-economic losses, but whether these extremes in distant regions are linked and what mechanisms are driving their changes remain unclear. Based on the standardized precipitation-evapotranspiration index and ERA5 reanalysis data, this study reveals a dry-wet teleconnection between southwestern China (SWC) and northeastern China (NEC) from January to April: when SWC was extremely dry, NEC tended to be anomalously wet, and vice versa. Although the seesawing teleconnection is most significant on interannual time scales, it also experienced interdecadal changes, with wet SWC and dry NEC in 1979-1998 and 2019-present and dry SWC and wet NEC in 1999-2018. Further investigations suggest that the pattern of dry SWC and wet NEC is related to anomalous anticyclones (cyclones) over SWC (NEC), which lead to significant changes in surface temperature and total precipitation in the respective regions. The dryness in western (eastern) SWC is mainly influenced by the changes in temperature (precipitation), while the NEC wetness is affected mainly by the changes in temperature. Observational and modeling studies further suggest that the pressure anomalies over SWC and NEC are caused by zonally and meridionally propagating Rossby wave trains, triggered by the North Atlantic Oscillation and the enhanced Indo-Pacific convection, respectively. These wave trains further lead to hydroclimatic extremes in North America, southern Europe, and the Middle East by regulating the atmospheric circulation anomalies over these regions.
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| 4. |
- Li, Peng, et al.
(författare)
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Improved efficiency with concave cavities on S3 surface of a rim-driven thruster
- 2023
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Ingår i: Physics of Fluids. - 1070-6631 .- 1089-7666. ; 35:10
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Tidskriftsartikel (refereegranskat)abstract
- Rim-driven thrusters (RDT) are of great interest for the development of integrated electric motors for underwater vehicles. Gap flow is one of the most prominent flow characteristics and plays an important role in the hydrodynamic performance of RDT. In this study, the rim in a carefully designed RDT was modified with several concave cavities defined by four parameters, and their influence on hydrodynamics was carefully calculated and analyzed. The simulations were performed using the k-ω shear stress transport turbulence model by solving the unsteady Reynolds-averaged Navier–Stokes equations. The numerical method was verified using a popular combination. The numerical results showed that the concave cavities on the rim improve the propulsive efficiency of RDT by a maximum of 3.52%. The increase in the propulsive efficiency is directly associated with the parameters of the concave cavities. Nevertheless, the flow in the gap has a negligible effect on the main flow field through the RDT. According to the numerical analysis, the different pressure integrals at the front and back surfaces of the concave cavities are the main reason for the improvement of the propulsive efficiency. The modification of the rim is helpful and practical for the hydrodynamic optimization of the RDT.
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