Bacterial biofilms are complex surface attached communities of bacteria held together by self-produced polymer matrixs mainly composed of polysaccharides, secreted proteins, and extracellular DNAs. Bacterial biofilm formation is a complex process and can be described in five main phases: (i) reversible attachment phase, where bacteria non-specifically attach to surfaces; (ii) irreversible attachment phase, which involves interaction between bacterial cells and a surface using bacterial adhesins such as fimbriae and lipopolysaccharide (LPS); (iii) production of extracellular polymeric substances (EPS) by the resident bacterial cells; (iv) biofilm maturation phase, in which bacterial cells synthesize and release signaling molecules to sense the presence of each other, conducing to the formation of microcolony and maturation of biofilms; and (v) dispersal/detachment phase, where the bacterial cells depart biofilms and comeback to independent planktonic lifestyle. Biofilm formation is detrimental in healthcare, drinking water distribution systems, food, and marine industries, etc. As a result, current studies have been focused toward control and prevention of biofilms. In an effort to get rid of harmful biofilms, various techniques and approaches have been employed that interfere with bacterial attachment, bacterial communication systems (quorum sensing, QS), and biofilm matrixs. Biofilms, however, also offer beneficial roles in a variety of fields including applications in plant protection, bioremediation, wastewater treatment, and corrosion inhibition amongst others. Development of beneficial biofilms can be promoted through manipulation of adhesion surfaces, QS and environmental conditions. This review describes the events involved in bacterial biofilm formation, lists the negative and positive aspects associated with bacterial biofilms, elaborates the main strategies currently used to regulate establishment of harmful bacterial biofilms as well as certain strategies employed to encourage formation of beneficial bacterial biofilms, and highlights the future perspectives of bacterial biofilms.

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Beyond Risk: Bacterial Biofilms and Their Regulating Approaches.

Full-scale unsteady RANS CFD simulations of ship behaviour and performance in head seas due to slow steaming

Predicting the effect of biofouling on ship resistance using CFD

There has been mounting concerns over energy consumption and environmental impacts due to an increase in worldwide shipping activities. The International Maritime Organization has adopted regulations to impose limits on greenhouse gas emissions originated from fuel combustion of marine vessels. Such regulations are introduced in terms of energy efficiency design index and energy efficiency operational indicator. Extensive electrification of ship propulsion and shipboard power systems has been vastly proposed in the literature to make onboard energy systems more efficient. However, energy efficiency in the context of maritime transport is becoming even more stringent. Various technologies and operational practices therefore are being proposed to ensure full compliance with the tightening restrictions. The methods to increase energy efficiency and environmental performance of all-electric ships to satisfy such requirements involve integration of energy storage with a contribution of intelligent power management to optimize power split between various power generation sources; a tendency toward DC power distribution due to eliminating the need of all generators to be synchronized at a specific frequency; installation of unconventional propulsors for greater maneuverability requirements while keeping fuel consumption low; adoption of low carbon content fuel like liquefied natural gas for dual fuel diesel electric propulsion; establishment of onboard renewable energy systems for alternative clean power options; fuel cell integration in complementary operation with conventional diesel generators. This paper identifies promising technologies and practices that are applicable to onboard energy systems of all-electric ships and also reveals energy efficiency sensitivity of all-electric ships to different applications. The proposed strategies should be eventually combined with alternative technology-based and operational-based measures as implemented on conventional propulsion ships in order to realize full potential for energy efficient operation.

Energy efficiency of integrated electric propulsion for ships – A review

Experimental and numerical hydrodynamic analysis of a stepped planing hull

Predictions of added resistance and the effective power of ships were made for varying barnacle fouling conditions. A series of towing tests was carried out using flat plates covered with artificial barnacles. The tests were designed to allow the examination of the effects of barnacle height and percentage coverage on the resistance and effective power of ships. The drag coefficients and roughness function values were evaluated for the flat plates. The roughness effects of the fouling conditions on the ships’ frictional resistances were predicted. Added resistance diagrams were then plotted using these predictions, and powering penalties for these ships were calculated using the diagrams generated. The results indicate that the effect of barnacle size is significant, since a 10% coverage of barnacles each 5 mm in height caused a similar level of added power requirements to a 50% coverage of barnacles each 1.25 mm in height.

https://tandfonline.com/doi/pdf/10.1080/08927014.2017.1373279

Effect of barnacle fouling on ship resistance and powering

A CFD model for the frictional resistance prediction of antifouling coatings

https://cyberleninka.org/article/n/142032.pdf

Yigit Kemal Demirel

Papers

Full-scale unsteady RANS CFD simulations of ship behaviour and performance in head seas due to slow steaming

Predicting the effect of biofouling on ship resistance using CFD

Effect of barnacle fouling on ship resistance and powering

A CFD model for the frictional resistance prediction of antifouling coatings

Design optimisation of Propeller Boss Cap Fins for enhanced propeller performance