Combining H-Adaptivity with the Element Splitting Method for Crack Simulation in Large Structures

H-adaptivity is an effective tool to introduce local mesh refinement in the FEM-based numerical simulation of crack propagation. The implementation of h-adaptivity could benefit the numerical simulation of fatigue or accidental load scenarios involving large structures, such as ship hulls. Meanwhile, in engineering applications, the element deletion method is frequently used to represent cracks. However, the element deletion method has some drawbacks, such as strong mesh dependency and loss of mass or energy. In order to mitigate this problem, the element splitting method could be applied. In this study, a numerical method called ‘h-adaptive element splitting’ (h-AES) is introduced. The h-AES method is applied in FEM programs by combining h-adaptivity with the element splitting method. Two examples using the h-AES method to simulate cracks in large structures under linear-elastic fracture mechanics scenario are presented. The numerical results are verified against analytical solutions. Based on the examples, the h-AES method is proven to be able to introduce mesh refinement in large-scale numerical models that mostly consist of structured coarse meshes, which is also beneficial to the reduction of computational resources. By employing the h-AES method, very small cracks are well represented in large structures without any deletions of elements.

Impacts of UV-C irradiation on marine biofilm community succession

Marine biofilms are diverse microbial communities and important ecological habitats forming on surfaces submerged in the ocean. Biofilm communities resist environmental disturbance, making them a nuisance to some human activities (‘biofouling’). Anti-fouling solutions rarely address the underlying stability or compositional responses of these biofilms. Using bulk measurements and molecular analyses, we examined temporal and UV-C antifouling-based shifts in marine biofilms in the coastal Western North Atlantic Ocean during early fall. Over a 24-d period, bacterial communities shifted from early dominance of Gammaproteobacteria to increased proportions of Alphaproteobacteria, Bacteroidia and Acidimicrobiia. In a network analysis based on temporal covariance, Rhodobacteraceae (Alphaproteobacteria) nodes were abundant and densely connected with generally positive correlations. In the eukaryotic community, persistent algal, protistan, and invertebrate groups were observed, although consistent temporal succession was not detected. Biofilm UV-C treatment at 13 and 20 days resulted in losses of chlorophyll a and transparent exopolymer particles, indicating biomass disruption. Bacterial community shifts suggested that UV-C treatment decreased biofilm maturation rate and was associated with proportional shifts among diverse bacterial taxa. UV-C treatment was also associated with increased proportions of protists potentially involved in detritivory and parasitism. Older biofilm communities had increased resistance to UV-C, suggesting that early biofilms are more susceptible to UV-C based antifouling. The results suggest that UV-C irradiation is potentially an effective antifouling method in marine environments in terms of biomass removal and in slowing maturation. However, as they mature, biofilm communities may accumulate microbial members that are tolerant or resilient under UV-treatment. Importance Marine biofilms regulate processes from organic matter and pollutant turnover to eukaryotic settlement and growth. Biofilm growth and eukaryotic settlement interfering with human activities via growth on ship hulls, aquaculture operations, or other marine infrastructure are called ‘biofouling’. There is a need to develop sustainable anti-fouling techniques by minimizing impacts to surrounding biota. We use the biofouling-antifouling framework to test hypotheses about marine biofilm succession and stability in response to disturbance, using a novel UV-C LED device. We demonstrate strong bacterial biofilm successional patterns and detect taxa potentially contributing to stability under UV-C stress. Despite UV-C-associated biomass losses and varying UV susceptibility of microbial taxa, we detected high compositional resistance among biofilm bacterial communities, suggesting decoupling of disruption in biomass and community composition following UV-C irradiation. We also report microbial covariance patterns over 24 days of biofilm growth, pointing to areas for study of microbial interactions and targeted antifouling.

STATIC CONTROL OF DRAG-REDUCING AIR CAVITIES WITH VARIABLE CAVITATOR SHAPE

Air ventilation of submerged surfaces of ship hulls is a promising technique for drag reduction. To ensure high performance of air cavities in a broad range of operational conditions, the cavity properties can be controlled with help of compact hydrodynamic actuators. In this study, a potential flow theory is applied to model an air cavity formed behind a wedge-shaped cavitator under a horizontal wall imitating a ship bottom. By varying the wedge angle, it is possible to achieve states with maximum drag reduction at given operational conditions. The dependence of the optimal wedge angle on Froude number and hull trim is investigated. The air-cavity ability to reduce frictional drag is found to increase with rising flow speed and bow-down hull trim.

SHIP-SHIP HYDRODYNAMIC INTERACTION IN CONFINED WATERS WITH COMPLEX BOUNDARIES BY A PANELLED MOVING PATCH METHOD

This paper presents a potential flow solution for online estimation of hydrodynamic interaction between ships moving in restricted waters with complex boundaries. Each ship in concern is linked with a moving patch representing the arbitrary bathymetry beneath it. The wetted surfaces of ship hulls are meshed and loaded prior to the simulation, while the moving patches are dynamically discretized by a fast and robust mesh generator. The proposed method is validated for the ship- ship interaction case in the shallow water case with a flat and horizontal seabed where the mirror image technique is applicable, and satisfactory agreement is obtained. The method is further applied to simulate two interaction scenarios involving arbitrary seabed topography, and the numerical results are obtained and discussed.

Selective Metal Coordination in Antifouling Coatings

<p>Marine biofouling is the accumulation of biological material (e.g. microorganisms, soft- and hard-fouling organisms) on the surface of an object submerged in seawater, and it remains a worldwide problem for shipping industries. The fouling of ship hulls results in a reduction of speed and manoeuvrability due to frictional drag, as well as increased fuel consumption and accelerated corrosion, and the exorbitant expenses and losses of efficiency attributed to biofouling have prompted the development of antifouling coatings. Current antifouling paints use copper as a biocidal agent, but copper-based paints are increasingly being banned due to environmental concerns about the non-target effects of leached copper. This project aims to circumvent these concerns and tightening regulations via a revolutionary concept: the development of marine antifouling paints that incorporate Cu(II)-selective ligands to draw the biocidal ingredient (i.e. Cu(II)) from seawater. A multistage strategy emerged for the development of this technology. First, criteria were established for the project’s ideal ligand, and ligands were synthesised or selected based on these criteria. Second, the ligands were incorporated in coatings through covalent modification of the paint binder or additives. Third, methodology was developed and implemented to test each coating’s ability to coordinate and retain Cu(II), as well as its subsequent ability to prevent microfouling by marine bacteria. The suitability of two ligand classes was assessed: acylhydrazones and tetraaza macrocycles, specifically cyclen. Unlike the acylhydrazones, cyclen met the established criteria and was initially evaluated as a curing agent and/or surface-modifier in a two-pack epoxy system with resin Epikote™ 235. However, the Cu(II)-loading by these coatings was relatively low, being at most ~0.05% w/w, and the modification of silica, a common paint additive, with cyclen was explored as an alternative formulation route. The method for the functionalisation of silica with cyclen was optimised, and the maximum Cu(II)-loading achieved by the product was 2.60% w/w. The cyclen-functionalised silica was incorporated on the surface of an epoxy coating, and a bacterial adherence assay was developed to assess the cellular attachment of marine bacterium Vibrio harveyi to this coating, which was found to be undeterred. Yet, the development of the strategy and testing methodology by which the project’s goals may be achieved provides a solid foundation for future work.</p>

Selective Metal Coordination in Antifouling Coatings

<p>Marine biofouling is the accumulation of biological material (e.g. microorganisms, soft- and hard-fouling organisms) on the surface of an object submerged in seawater, and it remains a worldwide problem for shipping industries. The fouling of ship hulls results in a reduction of speed and manoeuvrability due to frictional drag, as well as increased fuel consumption and accelerated corrosion, and the exorbitant expenses and losses of efficiency attributed to biofouling have prompted the development of antifouling coatings. Current antifouling paints use copper as a biocidal agent, but copper-based paints are increasingly being banned due to environmental concerns about the non-target effects of leached copper. This project aims to circumvent these concerns and tightening regulations via a revolutionary concept: the development of marine antifouling paints that incorporate Cu(II)-selective ligands to draw the biocidal ingredient (i.e. Cu(II)) from seawater. A multistage strategy emerged for the development of this technology. First, criteria were established for the project’s ideal ligand, and ligands were synthesised or selected based on these criteria. Second, the ligands were incorporated in coatings through covalent modification of the paint binder or additives. Third, methodology was developed and implemented to test each coating’s ability to coordinate and retain Cu(II), as well as its subsequent ability to prevent microfouling by marine bacteria. The suitability of two ligand classes was assessed: acylhydrazones and tetraaza macrocycles, specifically cyclen. Unlike the acylhydrazones, cyclen met the established criteria and was initially evaluated as a curing agent and/or surface-modifier in a two-pack epoxy system with resin Epikote™ 235. However, the Cu(II)-loading by these coatings was relatively low, being at most ~0.05% w/w, and the modification of silica, a common paint additive, with cyclen was explored as an alternative formulation route. The method for the functionalisation of silica with cyclen was optimised, and the maximum Cu(II)-loading achieved by the product was 2.60% w/w. The cyclen-functionalised silica was incorporated on the surface of an epoxy coating, and a bacterial adherence assay was developed to assess the cellular attachment of marine bacterium Vibrio harveyi to this coating, which was found to be undeterred. Yet, the development of the strategy and testing methodology by which the project’s goals may be achieved provides a solid foundation for future work.</p>

Laser Scanning Ship Hulls to Support Hydrodynamic Simulations

Terrestrial laser scanning is an effective technology to capture high density and accurate point clouds about objects with complex geometry. Ship industry requires 3D hull models for multiple reverse engineering purposes; renovation, as-built analysis, simulations etc. The paper discusses how terrestrial laser scanning can be applied to capture ship hull geometry to support hydrodynamic simulations. It presents recommendations of survey geometry and methods considering scanner locations, reflectivity issues. Hydrodynamic simulations require specific types of surface models as inputs; data processing procedure is discussed how the point clouds are effectively transformed to models to be applied. Resource analysis is also included, such as duration of survey and processing, equipment to be used.

Assessment of the technical condition of ship hulls using mobile magnetic devices

Оценку технического состояния корпуса судна проводят с применением диагностических датчиков. С помощью них замеряются, например, толщина обшивки, параметры бухтин, вмятин, гофрировки. Процессы эти трудоемкие и достаточно сложные. Проблемой автоматизации таких операций является удержание измерительной аппаратуры на криволинейной поверхности корпуса судна и перемещение аппаратуры по ней. Одним из вариантов решения проблемы является применение подвижных тележек с установленными на них магнитными устройствами. В данной работе исследуются вопросы влияния кривизны обшивки корпуса судна на параметры подвижной магнитной системы. Представлены расчетные схемы для различных компоновок, физические и математические модели. Анализ полученных математических выражений позволил сделать выводы по вариантам размещения, по зазору и скорости его изменения, клиренсу транспортного устройства, углу между опорной поверхностью и торцевой плоскостью магнита, который приводит к уменьшению силы притяжения. Учтен начальный зазор. Проведены расчеты зависимостей изменения радиуса кривизны корпуса судна от колеи и конструктивной схемы мобильных устройств. The assessment of the technical condition of the vessel's hull is carried out using diagnostic sensors. They are used to measure, for example, the thickness of the skin, the parameters of camber, dents, corrugations. These processes are time-consuming and quite complex. The problem of automation of such operations is the retention of measuring equipment on the curved surface of the hull of the vessel and the movement of equipment along it. One of the solutions to the problem is the use of movable trolleys with magnetic devices installed on them. In this paper, the issues of the influence of the curvature of the hull covering on the parameters of the mobile magnetic system are investigated. Calculation schemes for various layouts, physical and mathematical models are presented. The analysis of the obtained mathematical expressions allowed us to draw conclusions on the placement options, on the gap and the speed of its change, the clearance of the transport device, the angle between the support surface and the end plane of the magnet, which leads to a decrease in the force of attraction. The initial gap is taken into account. Calculations of the dependences of changes in the radius of curvature of the hull of the vessel on the track and the design scheme of mobile devices are carried out.

Analysis of the use of paint coatings to protect the hull from corrosion

The most common and reliable method of protecting a ship’s hull from corrosion is paint coatings. Paint coatings can be used to paint products of any size. In case of complete or partial destruction, the paintwork can be easily restored by tinting or completely repainting the surface. Paints and varnishes are easily combined with other methods of corrosion protection. The use of paint coatings is more economical in comparison with other types of corrosion protection. Therefore, it is currently the most common method of protecting ship hulls. In order to determine the quality, the experimental studies of various paints and varnishes were carried out. Experimental prototypes were made. The effect of low temperatures and the effect of an impending water flow on paint and coatings were considered. The main conclusions were drawn from the results of the experiments. For long-term protection from the external environment, it is necessary that the coating film should maintain high adhesion to the surface maintain continuous, have minimal water absorption, devoid of pores and be solid. Samples with a two-layer and three-layer coating of Jotun paint have the best adhesion. Satisfactory results were also obtained on samples with a three-layer coating of XC-436 enamel and with a two-layer coating of stone red.