SummaryThis paper numerically discusses how the performance of a NACA marine propeller is affected by the number of blades, which is one of the most crucial geometrical parameters determining the performance of a propeller. Results are presented in terms of the hydrodynamic and structural parameters. The results show that changing the number of blades changes the hydrodynamic efficiency, torque, thrust, cavitation behaviour and structural stiffness of the propeller nonlinearly. Furthermore, it is shown that the propellers structural lifetime is shortened by increasing the number of blades. Hence, the propeller's number of blades is a multi-objective function and will be discussed in this research. The applied tool which is used to study the hydrodynamic performance of the propellers is a RANS-based CFD one and the FEM is considered to study the structural behaviour of the propellers.
This paper assessed the antifouling activities of a superhydrophobic surface with a contact angle of 161.6°and a sliding angle of 4.1°which can be employed on large scales. The preparation of PDMS/silica nanoparticles composite was first described for the production of superhydrophobic surfaces with different contents of silica nanoparticles. Then, the surface roughness of the produced samples was investigated. Subsequently, the surface reaction against the algae was evaluated at different immersion times. The samples coated with PDMS-to-Silica ratio of 100% exhibited higher stability against algal growth for more than 10 h while samples with a coating ratio of 25% withstood algae for less than 2 h, indicating the influence of surface roughness. Although the withstanding time of this coating cannot compete with the commercial antifouling coatings, it becomes vital when it comes to the use of this coating as a drag-reducing surface in which fouling worsens the effectiveness.
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