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| 2. |
- Jianfeng, Lin, 1994, et al.
(author)
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Angle of attack impact on flow characteristics around finite-length rotating columns
- 2024
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In: Physics of Fluids. - 1089-7666 .- 1070-6631. ; 36:6
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Journal article (peer-reviewed)abstract
- The finite-length rotating column has been extensively studied because of its importance in various fields, such as marine and aerospace. In this study, the hydrodynamic performance of a finite-length rotating column with two free ends at different angles of attack is investigated using a large eddy simulation method. The effects of various geometries (including an equal-section cylinder and a variable-section truncated cone), incoming flow velocities, column rotation speeds, and angles of attack on the lift and drag characteristics and wake field of the rotating column are analyzed. The results reveal that a free end creates a concentrated tip vortex, which shortens the effective length that can generate the Magnus effect. Across different geometries and computational conditions, a relatively consistent lift coefficient is found for angles of attack from 60° to 120°, with the cone design significantly reducing the drag by approximately 10% for angles of attack from 120° to 150°. These findings provide valuable insights into the practical application of finite-length rotating columns. Specific recommendations for optimizing the design of these columns are suggested, including choosing appropriate geometries and considering the effects of incoming flow velocities and column rotation speeds.
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| 3. |
- Jianfeng, Lin, 1994, et al.
(author)
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Comprehensive Investigation of Flow Dynamics around Rotating Cylinders
- 2024
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In: 2024 EFDC1.
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Conference paper (peer-reviewed)abstract
- The study addresses the intricate dynamics of flow around rotating cylinders, a classic problem in fluid mechanics known for the Magnus effect. This research delves into unconventional yet compelling aspects of rotating cylinders, investigating the influence of rotational speed, incoming flow velocity, geometric shape, free surface, and angle of attack on lift-drag characteristics and wake flow fields. To begin with, fully parametric three-dimensional modelling of rotating cylinders was carried out using the Sobol design optimisation method coupled with computational fluid dynamics. The Sobol method efficiently explored the design space, focusing on critical parameters such as cylinder end diameters and lengths. The results revealed several local optimum values for lift and drag, showing the effect of the Magnus effect on vortex separation points and leading to significant variations in pressure and velocity distributions. Furthermore, the investigation was extended to the mode change of rotating cylinders in twophase flows through large eddy simulation. The findings showed that increasing the submergence depth generally improves lift generation, especially for rotations with higher speeds. At low submergence depths of less than one cylinder diameter, the pattern of vortices in the single-phase flow is altered under the same operating conditions. Surprisingly, the effectiveness of the Magnus effect diminishes at a depth of half the cylinder diameter. This study represents the first exploration of the mode change in rotating cylinders induced by two-phase flows. Additionally, the hydrodynamic performance of rotating cylinders at different angles of attack was investigated using an improved delayed detached eddy simulation method. The focus here is on the end effect of the rotating cylinder. The study identified an optimal spin ratio that maximised the lift-drag ratio while emphasising the profound influence of the angle of attack and spin ratio on the streamwise and crosswise vortex structures. In conclusion, this study not only sheds light on the intricate dynamics of flow around rotating cylinders and provides new insights into Magnus effect-induced phenomena, but also paves the way for future advances in engineering applications, such as optimising the performance of rotating structures in various fluid environments. Further exploration of these findings may contribute to the development of more efficient and robust engineering solutions in the fields of energy harvesting, aquatic robotics, and fluid transport systems.
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| 4. |
- Jianfeng, Lin, 1994, et al.
(author)
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Hydrodynamic performance of a rim-driven thruster improved with gap geometry adjustment
- 2023
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In: Engineering Applications of Computational Fluid Mechanics. - : Informa UK Limited. - 1994-2060 .- 1997-003X. ; 17:1
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Journal article (peer-reviewed)abstract
- The hubless rim-driven thruster (RDT) has become increasingly interesting for ship propulsion. Gap flow has been proven as the main feature of RDT that cannot be simply neglected. In this study, based on a classical hubless RDT, the effects of the gap geometry are studied by adjusting its axial passage length, and inlet and outlet oblique angles. The hydrodynamic characteristics of the RDT were simulated with OpenFOAM based on the k – ω shear stress transport turbulence model. Due to the pressure increase after the main flow passes through the rotating blades, the flow inside gap is driven upstream, which is opposite to the main flow direction. It is found that the hydrodynamic efficiency is increased as the gap axial passage length is shortened, which is realized by increasing the oblique angle with the fixed inlet and outlet positions. Moving the inlet and outlet to further downstream and upstream positions has negligible effects on the hydrodynamic efficiency and leads to recirculating flow within the gap near its inlet. These findings shed light on the design of the gap geometry to improve the RDT hydrodynamic performance.
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| 5. |
- Jianfeng, Lin, 1994, et al.
(author)
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Intelligent ship anti-rolling control system based on a deep deterministic policy gradient algorithm and the Magnus effect
- 2022
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In: Physics of Fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 34:5
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Journal article (peer-reviewed)abstract
- Anti-rolling devices are widely used in modern shipboard components. In particular, ship anti-rolling control systems are developed to achieve a wide range of ship speeds and efficient anti-rolling capabilities. However, factors that are challenging to solve accurately, such as strong nonlinearities, a complex working environment, and hydrodynamic system parameters, limit the investigation of the rolling motion of ships at sea. Moreover, current anti-rolling control systems still face several challenges, such as poor nonlinear adaptability and manual parameter adjustment. In this regard, this study developed a dynamic model for a ship anti-rolling system. In addition, based on deep reinforcement learning (DRL), an efficient anti-rolling controller was developed using a deep deterministic policy gradient (DDPG) algorithm. Finally, the developed system was applied to a ship anti-rolling device based on the Magnus effect. The advantages of reinforcement learning adaptive control enable controlling an anti-rolling system under various wave angles, ship speeds, and wavelengths. The results revealed that the anti-rolling efficiency of the intelligent ship anti-rolling control method using the DDPG algorithm surpassed 95% and had fast convergence. This study lays the foundation for developing a DRL anti-rolling controller for full-scale ships.
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| 6. |
- Jianfeng, Lin, 1994, et al.
(author)
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Shape optimization and hydrodynamic simulation of a Magnus anti-rolling device based on fully parametric modeling
- 2023
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In: Physics of Fluids. - 1070-6631 .- 1089-7666. ; 35:5
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Journal article (peer-reviewed)abstract
- Ship anti-rolling devices are an essential component of modern vessels. The core component of the Magnus effect-based ship anti-rolling device is a rotating cylinder, hereinafter referred to as the Magnus cylinders. In this paper, fully parametric three-dimensional modeling of Magnus cylinders was performed, and the design space dimension was reduced using the Sobol design optimization method while still providing accurate and reliable results. The Sobol method generates quasi-random sequences that are more uniformly spaced in the search space and can more efficiently cover the entire solution space. The shape optimization study of the Magnus cylinder was carried out in conjunction with the computational fluid dynamics method to find the geometry of the Magnus cylinder with excellent hydrodynamic performance. Critical design parameters include the diameters of the cylinder ends and the length of the cylinder. The hydrodynamic and flow field characteristics of Magnus cylinders before and after the optimization were compared. The results show that there can be multiple local optimal values for lift and drag of Magnus cylinders within the design space to increase the lift and decrease the drag. The Magnus effect primarily influences the position of the vortex-shedding separation point at the surface of Magnus cylinders and deflects the wake to one side. For the optimized Magnus cylinder, the distribution of pressure and velocity in the flow field is significantly different. This research forms the basis for improving the practical application of Magnus anti-rolling devices.
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| 7. |
- Lin, Jianfeng, et al.
(author)
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Experimental investigation and intelligent control of the magnus anti-rolling device for ship stability at zero speed
- 2024
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In: Ocean Engineering. - 0029-8018. ; 308
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Journal article (peer-reviewed)abstract
- Under zero-speed conditions, ships are particularly susceptible to the effects of waves, which directly impact the safety of the vessel. A ship anti-rolling device based on the Magnus effect is designed to mitigate rolling motions across a full range of speeds, thereby enhancing the vessel's stability. This study presents an experimental investigation and intelligent control of Magnus anti-rolling devices aimed at enhancing ship stability at zero speed. The test setup, intelligent control algorithm, and experimental procedures specifically tailored for evaluating the Magnus anti-rolling device were designed. Following this, a comprehensive analysis was conducted to assess the effects of different cylinder geometries, swinging speeds, initial roll angles, and control methods on the anti-rolling characteristics of the device. Results demonstrate that the intelligent control method achieves an average anti-rolling efficiency of 89%. Additionally, the optimised geometric model of the Magnus anti-rolling device exhibits improved anti-rolling efficiency relative to the original model. The study confirms the stability and robustness of the intelligent Magnus anti-rolling device and suggests future research directions for practical applications aboard full-scale vessels in complex marine environments.
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| 8. |
- Sun, Huiliang, et al.
(author)
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A monothiophene unit incorporating both fluoro and ester substitution enabling high-performance donor polymers for non-fullerene solar cells with 16.4% efficiency
- 2019
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In: Energy & Environmental Science. - : ROYAL SOC CHEMISTRY. - 1754-5692 .- 1754-5706. ; 12:11, s. 3328-3337
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Journal article (peer-reviewed)abstract
- Thiophene and its derivatives have been extensively used in organic electronics, particularly in the field of polymer solar cells (PSCs). Significant research efforts have been dedicated to modifying thiophene-based units by attaching electron-donating or withdrawing groups to tune the energy levels of conjugated materials. Herein, we report the design and synthesis of a novel thiophene derivative, FE-T, featuring a monothiophene functionalized with both an electron-withdrawing fluorine atom (F) and an ester group (E). The FE-T unit possesses distinctive advantages of both F and E groups, the synergistic effects of which enable significant downshifting of the energy levels and enhanced aggregation/crystallinity of the resulting organic materials. Shown in this work are a series of polymers obtained by incorporating the FE-T unit into a PM6 polymer to fine-tune the energetics and morphology of this high-performance PSC material. The optimal polymer in the series shows a downshifted HOMO and an improved morphology, leading to a high PCE of 16.4% with a small energy loss (0.53 eV) enabled by the reduced non-radiative energy loss (0.23 eV), which are among the best values reported for non-fullerene PSCs to date. This work shows that the FE-T unit is a promising building block to construct donor polymers for high-performance organic photovoltaic cells.
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