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Traditional antifouling agents usually have a certain toxic effect on marine environments and non-target organisms. In this study, Dictyophora indusiata polysaccharide (DIP) was applied as a natural antifouling surface modifier to prepare the surface coating for marine antifouling. Three DIP coatings were prepared: D. indusiata spore polysaccharide (DISP), D. indusiata volva polysaccharide (DIVP), and D. indusiata embryonic body polysaccharide (DIEP). The antifouling, tribological, and anticorrosion behavior of the coatings were examined. Results revealed that the three kinds of DIP coatings had excellent antifouling properties, which could effectively prevent the adhesion of Chlorella and the attachment of water-based and oily stains on the surface. Additionally, the coatings showed great mechanical stability and could maintain an extremely low coefficient of friction (COF < 0.05) after continuous wear. The drag reduction rate of the coated surfaces reached 5%, showing a powerful lubrication performance. Furthermore, the DIP coatings presented an outstanding corrosion resistance, where the equivalent circuit impedances were 4–9 orders of magnitude higher than the control groups. This research showed a promising prospect of surface coating fabrication with DIP for marine devices to achieve the purpose of antifouling and drag reduction. [ABSTRACT FROM AUTHOR]

The transverse skin of dolphins exhibits a remarkable drag reduction effect. Although previous studies have identified the drag reduction effect of transverse grooves, no clear guidelines exist regarding the impact of groove parameters on turbulent drag reduction. Hence, this paper suggests a novel numerical study using the Reynolds-averaged Navier–Stokes method to investigate the influence of half-sine wave structure parameters on turbulent drag. The results showed that the aspect ratio of shape parameters significantly affected the drag reduction rate by altering the flow velocity and drag distribution near the wall and increasing the viscous sublayer thickness. Moreover, a novel index friction pressure ratio F P r was introduced to evaluate the drag reduction. It was revealed that the ratio F P r was stable at optimal drag reduction effect regardless of the velocity. By optimizing the F P r , a maximum drag reduction of 29.3% was achieved. These findings provide insight for optimizing transverse groove in drag-reducing surface applications. [ABSTRACT FROM AUTHOR]

Maintaining the long-term stability of water repellency and antifouling remains a challenge. This study presents the fabrication of a solid sharkskin-inspired surface exhibiting superhydrophobic and antifouling properties by polydimethylsiloxane (PDMS) and zinc oxide (ZnO) nanostructures through the simple microcasting and hydrothermal methods. The ZnO grown under optimal reaction parameters showed a remarkable contact angle of 151°, signifying the emergence of superhydrophobicity. Furthermore, the ZnO/PDMS sharkskin surface was found to reduce drag by up to 12.2%. Notably, the bacterial adhesion was decreased on the sharkskin-like PDMS surface with ZnO nanostructures by 96.5% compared to smooth PDMS. This resulted from the combined antifouling effects of ZnO photocatalytic property and the microstructure-induced hydrophobicity. Additionally, the ZnO nanostructures demonstrated exceptional mechanical stability and robustness. [ABSTRACT FROM AUTHOR]

Ship hulls and subsea equipment are plagued by current resistance, seawater particles impact, corrosion and other challenges in the ocean. Consequently, developing sustainable nontoxic antifouling coatings is highly urgent. Discoveries from nature have inspired us to design high-efficiency, environmentally friendly, and cost-effective antifouling coatings. In the study, a strategy of combining microstructures and Benzotriazole (BTA) was proposed through constructing shark skin shield scale structure, which improved drag reduction and increased abrasion resistance as well. On the synergistic effect of BTA as corrosion inhibitor, the friction coefficient of the coating was significantly reduced and the anti-corrosion performance was greatly improved. Compared to the smooth pure epoxy coating, the anti-corrosion performance and the drag reduction rate of Texture-BTA-3 % coating was improved by 30 % and about 10 %, respectively. Furthermore, the effect of coating structure on corrosion resistance was revealed. This investigation will broaden the applications in marine navigation with the favorable performance. [Display omitted] • A method for preparing epoxy resin with imitating sharkskin surface texture has been proposed. • Verified the influence of the coating texture on anti-corrosion performance. • Drag reduction rate of the designed coating in water is about 10 %. • The friction coefficient is reduced of 40 % during friction process. [ABSTRACT FROM AUTHOR]

Marine equipment and ships operating in complex environments face high drag consumption and severe surface fouling. Non-smooth biomimetic surfaces with specific microstructures work to reduce surface drag and inhibit fouling. In this work, the biological sharkskin shield scale structure was simplified by the idea of segmented independence to construct a bionic non-smooth surface. Single-crystal lithography was used to create a negative template of the silicon substrate. We created a non-smooth bionic structure on the flexible polydimethylsiloxane (PDMS) surface through die casting and molding. Additionally, the bionic non-smooth surface was modified by decorating zeolitic imidazolate framework-67 (ZIF-67) particles to modulate the antifouling properties. Based on tests performed on a self-designed and processed circulating water bath laboratory bench (CWBLB), results showed the non-smooth surface effectively reduced drag by 7.3% compared to that of smooth surface. The contact angle (CA) measurement and anti-bio-adhesion experiment on the surface showed that PDMS surface CAs increased from 109.78° to 140.71°, and Chlorella vulgaris attachment was decreased by 65.3%. The non-smooth bionic surface effectively reduces drag and antifouling, and the effectiveness of the antifouling can be significantly enhanced by augmenting and regulating the particle surface modification method. Our results provide a feasible solution for ship drag reduction and antifouling, which is critical for industrial applications and sustainable development. • A method for processing single-crystal lithography of non-smooth hydrophobic surfaces has been developed. • A circulating water bath laboratory bench was designed, which can be used to measure axial resistance. • The ZIF-67 particle-modified surface possesses excellent resistance reduction and anti-fouling effects. [ABSTRACT FROM AUTHOR]

To improve the drag-reducing and antifouling performance of marine equipment, it is indispensable to learn from structures and materials that are found in nature. This is due to their excellent properties, such as intelligence, microminiaturization, hierarchical assembly, and adaptability. Considerable interest has arisen in fabricating surfaces with various types of biomimetic structures, which exhibit promising and synergistic performances similar to living organisms. In this study, a dual bio-inspired shark-skin and lotus-structure (BSLS) surface was developed for fabrication on commercial polyurethane (PU) polymer. Firstly, the shark-skin pattern was transferred on the PU by microcasting. Secondly, hierarchical micro- and nanostructures were introduced by spraying mesoporous silica nanospheres (MSNs). The dual biomimetic substrates were characterized by scanning electron microscopy, water contact angle characterization, antifouling, self-cleaning, and water flow impacting experiments. The results revealed that the BSLS surface exhibited dual biomimetic features. The micro- and nano-lotus-like structures were localized on a replicated shark dermal denticle. A contact angle of 147° was observed on the dual-treated surface and the contact angle hysteresis was decreased by 20% compared with that of the nontreated surface. Fluid drag was determined with shear stress measurements and a drag reduction of 36.7% was found for the biomimetic surface. With continuous impacting of high-speed water for up to 10 h, the biomimetic surface stayed superhydrophobic. Material properties such as inhibition of protein adsorption, mechanical robustness, and self-cleaning performances were evaluated, and the data indicated these behaviors were significantly improved. The mechanisms of drag reduction and self-cleaning are discussed. Our results indicate that this method is a potential strategy for efficient drag reduction and antifouling capabilities. [ABSTRACT FROM AUTHOR]

The biomimetic sharkskin riblet has attracted more attention in engineering and research owing to the economic benefit of drag-reducing and antifouling properties. Although several works have optimized the parameters for a number of riblet designs, there is not yet a study dedicated to optimizing for rectangular cuboidal riblet parameters. Hence, this work proposes a new numerical optimization of riblet orientations and arrangements of a three-dimensional rectangular cuboidal riblet. The shear-stress transport k-omega was adopted as an appropriate turbulence model for the simulation. The results showed that the riblets efficiently improved drag reduction regardless of the flow state. Riblets oriented perpendicularly to the flow direction showed the greatest performance of 11.3% and 6% in the laminar and turbulent flow, respectively. Moreover, the analysis of the flow field characteristics near the wall revealed a significant improvement in terms of reduction in near-wall velocity and shear stress. This work offers new perspectives on the role of the intricate multifunctional architecture of shark-scale structures in improving swimming speed and opening new doors for marine and underwater applications. • A numerical study of 3D shark riblets with different orientation and arrangement. • The SST k − ω model was adapted and laminar and turbulent conditions were discussed. • Simplified riblets greatly improved drag reduction regardless of the flow state. • Maximum performance was 11.3% and 6% in laminar and turbulent flow, respectively. • A significant reduction in near-wall velocity and shear stress was revealed. [ABSTRACT FROM AUTHOR]

The riblet structure on the surface of the shark skin provides significant drag reduction and fouling protection. Inspired by the structure of the shark skin, we present a direct ink writing protocol by modifying the rheological properties of polydimethylsiloxane to make it printable, and a series of flexible surfaces have been created with drag reduction and antifouling. The shear stress transport k–omega model was used as a suitable turbulence model for the numerical study to compare with results of drag reduction tests. Simulations and tests proved that printed non-smooth surfaces effectively reduced water drag, where the maximum drag reduction rate reached 18.16 % at 0.06 m/s. Through the analysis of the characteristics of the flow field near the wall, the drag reduction mechanism of the riblet surface was examined. Moreover, the antifouling tests revealed that the printed surface exhibited excellent fouling resistance and inhibited the spread of dirt on the surface. Our findings may provide a new surface skinning strategy for ships, underwater vehicles and wearable devices to reduce drag and contaminant adhesion and improve navigation efficiency and longevity. [Display omitted] • A convenient method for preparing commercial silicone rubber (PDMS) that can be used for direct ink writing is presented. • Preparation of large flexible skins with integrated drag reduction and antifouling design. • The maximum drag reduction for printed non-smooth surfaces is 18.17 %. [ABSTRACT FROM AUTHOR]