A numerical evaluation of stress concentrations of corroded plate surfaces of small-scale corroded steel specimens is compared with the experimentally estimated ones. Eleven specimens were cut from a steel box girder, which was initially corroded in real seawater conditions. The surface of all corroded specimens was analysed applying photogrammetry techniques, and a statistical description of an idealised corroded surface of each specimen was established. Fatigue lives of specimens are determined from the fatigue tests. Based on experimentally obtained fatigue lives, the stress concentration factors are calculated concerning the ideally smooth specimens. The correlation between the statistical parameters of the corroded specimen surfaces and the estimated stress concentration factors is analysed. Idealised corroded surfaces, converted in graphical format, are then used for the finite element modelling in ABAQUS software, and stress concentration factors are estimated from the finite element results. A convergence study is performed to determine the appropriate finite element mesh density. Comparison between experimentally obtained and numerically estimated stress concentration factors is performed as well as correlation analysis between actual and finite element predicted crack locations.

Microbiologically influenced corrosion is a global problem especially materials used in marine engineering. In that respect, inhibitors are widely used to control fouling and corrosion in marine systems. Most techniques used in inhibitor production are expensive and considered hazardous to the ecosystem. Therefore, scientists are motivated to explore natsural and green products as potent corrosion inhibitors especially in nano size. In this study, antibacterial and anticorrosive properties of green silver nanoparticles (AgNPs) were studied through weight loss, electrochemical characterization, and surface analysis techniques. The corrosion of copper (Cu) in artificial seawater (ASW), Halomonas variabilis (H. variabilis) NOSK, and H. variabilis + AgNPs was monitored using electrochemical measurements like open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization curves. AgNPs showed excellent antibacterial activity against pathogenic microorganisms. Electrochemical studies demonstrate a noticeable decrease in OCP and current density in ASW containing H. variabilis + AgNPs compared to both ASW and ASW inoculated with bacterium, which confirmed the decrease of corrosion rate of copper. Furthermore, the obtained voltammograms show that the silver nanoparticles were adsorbed on the copper electrode surface from the corrosion solution. Thus, the results prove that the novel idea of green silver nanoparticles acts as an anticorrosive film in the marine environment.

Subsea pipelines passing through the shallow area are physically protected against the environmental, accidental, and operational loads by trenching and backfilling. Depending on construction methodology, environmental loads, and seabed soil properties, the stiffness of backfilling material may become largely different from the native ground (softer than native ground in most of the cases). The different stiffness between the backfill and native ground affects the soil failure mechanisms and lateral soil resistance against large pipeline displacements that may happen due to ground movement, landslides, ice gouging, and drag embedment anchors. This important aspect is not considered by current design codes. In this paper, the effect of trench-backfill stiffness difference on lateral pipeline-backfill-trench interaction was investigated by performing centrifuge tests. The soil deformations and failure mechanisms were obtained by particle image velocimetry (PIV) analysis. Three experiments were conducted by using three different backfills including loose sand, slurry, and chunky clay that represent the purchased, natural in-fill, and preexcavated materials, respectively. The study shows that the current design codes underestimate the lateral soil resistance for small to moderate pipe displacements inside the trench and overestimate it for large lateral displacement, where the pipeline is penetrating into the trench wall.

A computational model is established to investigate the effects of a periodic gust flow on the wake structure of ventilated supercavities. The effectiveness of the computational model is validated by comparing with available experimental data. Benefited from this numerical model, the vertical velocity characteristics in the entire flow field can be easily monitored and analyzed under the action of a gust generator; further, the unsteady evolution of the flow parameters of the closed region of the supercavity can be captured in any location. To avoid the adverse effects of mounting struts in the experiments and to obtain more realistic results, the wake structure of a ventilated supercavity without mounting struts is investigated. Unsteady changes in the wake morphology and vorticity distribution pattern of the ventilated supercavity are determined. The results demonstrate that the periodic swing of the gust generator can generate a gust flow and, therefore, generate a periodic variation of the ventilated cavitation number σ. At the peak σ, a re-entrant jet closure appears in the wake of the ventilated supercavity. At the valley σ, a twin-vortex closure appears in the wake of the ventilated supercavity. For the forward facing model, the twin vortex appears as a pair of centrally rolled-up vortices, due to the closure of vortex is affected by the structure. For the backward facing model, however, the twin vortex appears alternately as a pair of centrally rolled-up vortices and a pair of centrally rolled-down vortices, against the periodic gust flow.

In this work, the laminar-to-turbulent transition phenomenon around the two- and three-dimensional ellipsoid at different Reynolds numbers is numerically investigated. In the present paper, Reynolds Averaged Navier Stokes (RANS) equations with the Spalart-Allmaras, SST k - ω, and SST-Trans models are used for numerical simulations. The possibility of laminar-toturbulent boundary layer transition is summarized in phase diagrams in terms of skin friction coefficient and Reynolds number. The numerical results show that SST-Trans method can detect different aspects of flow such as adverse pressure gradient and laminar-to-turbulent transition onset. Our numerical results indicate that the laminar-to-turbulent transition location on the 6:1 prolate spheroid is in a good agreement with the experimental data at high Reynolds numbers.

A steady-state roll motion of ships with nonlinear damping and restoring moments for all times is modeled by a second-order nonlinear differential equation. Analytical expressions for the roll angle, velocity, acceleration, and damping and restoring moments are derived using a modified approach of homotopy perturbation method (HPM). Also, the operational matrix of derivatives of ultraspherical wavelets is used to obtain a numerical solution of the governing equation. Illustrative examples are provided to examine the applicability and accuracy of the proposed methods when compared with a highly accurate numerical scheme.

In the present paper, the hydrodynamic performance of stepped planing craft is investigated by computational fluid dynamics (CFD) analysis. For this purpose, the hydrodynamic resistances of without step, one-step, and two-step hulls of Cougar planing craft are evaluated under different distances of the second step and LCG from aft, weight loadings, and Froude numbers (Fr). Our CFD results are appropriately validated against our conducted experimental test in National Iranians Marine Laboratory (NIMALA), Tehran, Iran. Then, the hydrodynamic resistance of intended planing crafts under various geometrical and physical conditions is predicted using artificial neural networks (ANNs). CFD analysis shows two different trends in the growth rate of resistance to weight ratio. So that, using steps for planing craft increases the resistance to weight ratio at lower Fr and decreases it at higher Fr. Additionally, by the increase of the distance between two steps, the resistance to weight ratio is decreased and the porpoising phenomenon is delayed. Furthermore, we obtained the maximum mean square error of ANNs output in the prediction of resistance to weight ratio equal to 0.0027. Finally, the predictive equation is suggested for the resistance to weight ratio of stepped planing craft according to weights and bias of designed ANNs.

Temporal evolutions of scour at submerged circular cylinders were investigated. Flow visualization was carried out around the cylinders over plane, under developed and equilibrium scour holes. Video analysis technique was used to formulate the equations for determining the diameter of the horseshoe vortex around the submerged cylinders, which is also verified from the vector diagrams drawn using the velocity measurements. The scour process similar to live bed scour was noticed around the downstream cylinder. The diameter of the horseshoe vortex is found to depend on the diameter of respective cylinder, submergence ratio, spacing between the cylinders and skew angle. This formulation along with the dislodgement and transportation of a single sediment particle is further incorporated in the proposed model for determining the time variation of scour around the submerged cylinders. It is evident from the results that the upstream cylinder shelters the downstream cylinder and thereby reduces the scour at the downstream cylinder. Proposed model is further extended to incorporate the effect of non-uniformity of the sediment particles on the time variation of scour depth. The results indicate significant reduction of scour depth of around 6% and 35% for upstream and downstream cylinders respectively due to the formation of the armor layer. The model is also compared with the local scour component of field data around cylindrical bridge piers to establish the differences in the scour process around a partially submerged cylinder and fully submerged tandem and skewed cylinders.

The model-driven architecture (MDA)/model-based systems engineering (MBSE) approach, in combination with the real-time Unified Modeling Language (UML)/Systems Modeling Language (SysML), unscented Kalman filter (UKF) algorithm, and hybrid automata, are specialized to conveniently analyze, design, and implement controllers of autonomous underwater vehicles (AUVs). The dynamics and control structure of AUVs are adapted and integrated with the specialized features of the MDA/ MBSE approach as follows. The computation-independent model is defined by the specification of a use case model together with the UKF algorithm and hybrid automata and is used in intensive requirement analysis. The platform-independent model (PIM) is then built by specializing the real-time UML/SysML’s features, such as the main control capsules and their dynamic evolutions, which reflect the structures and behaviors of controllers. The detailed PIM is subsequently converted into the platform-specific model by using open-source platforms to quickly implement and deploy AUV controllers. The study ends with a trial trip and deployment results for a planar trajectory-tracking controller of a miniature AUV with a torpedo shape.

The thermodynamic (energy and exergy) analysis of a condensate heating system, its segments, and components from a marine steam propulsion plant with steam reheating is performed in this paper. It is found that energy analysis of any condensate heating system should be avoided because it is highly influenced by the measuring equipment accuracy and precision. All the components from the observed marine condensate heating system have energy destructions lower than 3 kW, while the energy efficiencies of this system are higher than 99%. The exergy efficiency of closed condensate heaters continuously increases from the lowest to the highest steam pressures (from 70.10% to 92.29%). The ambient temperature variation between 5 ℃ and 45 ℃ notably influences the exergy efficiency change of both low pressure heaters and the low pressure segment equal to 31.61%, 12.37%, and 18.35%, respectively.

Human error, an important factor, may lead to serious results in various operational fields. The human factor plays a critical role in the risks and hazards of the maritime industry. A ship can achieve safe navigation when all operations in the engine room are conducted vigilantly. This paper presents a systematic evaluation of 20 failures in auxiliary systems of marine diesel engines that may be caused by human error. The Cognitive Reliability Error Analysis Method (CREAM) is used to determine the potentiality of human errors in the failures implied thanks to the answers of experts. Using this method, the probabilities of human error on failures were evaluated and the critical ones were emphasized. The measures to be taken for these results will make significant contributions not only to the seafarers but also to the ship owners.

Emissions of exhaust gases and particulate matter from a dual fuel marine engine using methanol as fuel with marine gasoil as pilot fuel have been examined for a ferry during operation. The emission factor for nitrogen oxides is lower than what is typically found for marine gasoil but does not reach the tier III limit. The emissions of particulate matter are significantly lower than for fuel oils and similar to what is found for LNG engines. The main part of the particles can be found in the ultrafine range with the peak being at around 18 nm. About 93% of the particles are evaporated and absorbed when using a thermodenuder, and thus a large majority of the particles are volatile. Methanol is a potential future marine fuel that will reduce emissions of air pollutants and can be made as a biofuel to meet emission targets for greenhouse gases.

The development of microchannels with open flow for use in irrigation and rainy areas is challenged by electricity generation via hydrokinetic devices in shallow and low velocity flows. Conventional hydrokinetic turbines are known to be highly dependent on current speed and water depth. Another drawback of conventional turbines is their low efficiency. These shortcomings lead to the need to accelerate the flow in the channel system to enhance the extracted power. The method of deploying a novel turbine configuration in irrigation channels can help overcome the low performance of conventional hydrokinetic turbines. Therefore, this study experimentally presents a bidirectional diffuser-augmented channel that includes dual cross flow/Banki turbines. Results show that the maximum efficiency of the overall system with two turbines is nearly 55.7%. The efficiency is low relative to that of hydraulic turbines. Nevertheless, the result can be considered satisfactory given the low head of the present system. The use of this system will contribute to a highly efficient utilization of flows in rivers and channels for electrical energy generation in rural areas.

This paper discusses the damage identification in the mooring line system of a floating wind turbine (FWT) exposed to various environmental loads. The proposed method incorporates a non-probabilistic method into artificial neural networks (ANNs). The non-probabilistic method is used to overcome the problem of uncertainties. For this purpose, the interval analysis method is used to calculate the lower and upper bounds of ANNs input data. This data contains some of the natural frequencies utilized to train two different ANNs and predict the output data which is the interval bounds of mooring line stiffness. Additionally, in order to reduce computational time and more importantly, identify damage in various conditions, the proposed method is trained using constant loads (CL) case (deterministic loads, including constant wind speed and airy wave model) and is tested using random loads (RL) case (including Kaimal wind model and JONSWAP wave theory). The superiority of this method is assessed by applying the deterministic method for damage identification. The results demonstrate that the proposed non-probabilistic method identifies the location and severity of damage more accurately compared to a deterministic one. This superiority is getting more remarkable as the difference in uncertainty levels between training and testing data is increasing.

Monitoring the ecology and physiology of corals, sediments, planktons, and microplastic at a suitable spatial resolution is of great importance in oceanic scientific research. To meet this requirement, an underwater microscope with an electrically controlled variable lens was designed and tested. The captured microscopic images of corals, sediments, planktons, and microplastic revealed their physical, biological, and morphological characteristics. Further studies of the images also revealed the growth, degradation, and bleaching patterns of corals; the presence of plankton communities; and the types of microplastics. The imaging performance is majorly influenced by the choice of lenses, camera selection, and lighting method. Image dehazing, global saturation masks, and image histograms were used to extract the image features. Fundamental experimental proof was obtained with micro-scale images of corals, sediments, planktons, and microplastic at different magnifications. The designed underwater microscope can provide relevant new insights into the observation and detection of the future conditions of aquatic ecosystems.