In situ colonization of marine biofilms on UNS S32760 duplex stainless steel coupons in areas with different water qualities: Implications for corrosion potential behavior

In the presence of biofilms, stainless steels （SS） exhibits an increase in corrosion potential, called ennoblement. In the present study, the corrosion potential （Eco,） behavior of the duplex SS UNS S32760 was recorded simultaneously with the in situ marine biofilm formation in two areas at Arraial do Cabo, Southeastern Brazil. The biofilm at Forno Harbor （an anthropogenically disturbed area） was characterized by higher relative abundances of Bacteria at day 2, followed by diatoms （especially Navicula sp.） on day 10 and dinoflagellates on day 18, whereas no clear trend was recorded at Cabo Frio Island （an undisturbed area）. The ennoblement of Ecor values was site-dependent. In a complementary laboratory assay, biofilms were removed and the Eco values registered in sterile conditions for the subsequent 10 days and corroborated in situ results. Understanding biofilms and SS interactions has important implications for materials science and engineering decisions as well as helping to fill in imnortant gaps in this knowledge.     

Mixing over the steep side of the Cycladic Plateau in the Aegean Sea

Intensive microstructure sampling over the southern slope of the Cycladic Plateau found very weak mixing in the pycnocline, centered on a thin minimum of diapycnal diffusivity with Kρ=1.5×¹⁰−6 m² s^− 1. Below the pycnocline, Kρ increased exponentially in the bottom 200 m, reaching 1 × 10^− 4 m² s^− 1 a few meters above the bottom. Near-bottom mixing was most intense where the bottom slope equaled the characteristic slope of the semi-diurnal internal tide. This suggests internal wave scattering and/or generation at the bottom, a conclusion supported by near-bottom dissipation rates increasing following rising winds and with intensifying internal waves. Several pinnacles on the slope were local mixing hotspots. Signatures included a vertical line of strong mixing in a pinnacle's wake, an hydraulic jump or lee wave over a downstream side of the summit, and a ‘beam’ sloping upward at the near-inertial characteristic slope. Because dissipation rate averages were dominated by strong turbulence, ?/νN² > 100, the effect on Kρ of alternate mixing efficiencies proposed for this range of turbulent intensity is explored.     

Impact of phytoplankton community size on a linked global ocean optical and ecosystem model

We isolated the effect phytoplankton cell size has on varying remote sensing reflectance spectra (R_rs(λ)) in the presence of optically active constituents by using optical and radiative transfer models linked in an offline diagnostic calculation to a global biogeochemical/ecosystem/circulation model with explicit phytoplankton size classes. Two case studies were carried out, each with several scenarios to isolate the effects of chlorophyll concentration, phytoplankton cell size, and size-varying phytoplankton absorption on R_rs(λ). The goal of the study was to determine the relative contribution of phytoplankton cell size and chlorophyll to overall R_rs(λ) and to understand where a standard band ratio algorithm (OC4) may under/overestimate chlorophyll due to R_rs(λ) being significantly affected by phytoplankton size. Phytoplankton cell size was found to contribute secondarily to R_rs(λ) variability and to amplify or dampen the seasonal cycle in R_rs(λ), driven by chlorophyll. Size and chlorophyll were found to change in phase at low to mid-latitudes, but were anti-correlated or poorly correlated at high latitudes. Phytoplankton size effects increased model calculated R_rs(443) in the subtropical ocean during local spring through early fall months in both hemispheres and decreased R_rs(443) in the Northern Hemisphere high latitude regions during local summer to fall months. This study attempts to tease apart when/where variability about the OC4 relationship may be associated with cell size variability. The OC4 algorithm may underestimate [Chl] when the fraction of microplankton is elevated, which occurs in the model simulations during local spring/summer months at high latitudes in both hemispheres.     

URANS simulations of static and dynamic maneuvering for surface combatant: part 2. Analysis and validation for local flow characteristics

Part 2 of this two-part paper presents the analysis and validation results of local flow characteristics for a surface combatant Model 5415 bare hull under static and dynamic planar motion mechanism simulations. Unsteady Reynolds averaged Navier–Stokes (URANS) computations are carried out by a general-purpose URANS/detached eddy simulation research code CFDShip-Iowa Ver. 4. The objective of this research is to investigate the capability of the code in relation to the computational fluid dynamics-based maneuvering prediction method. In the current study, the ship is subjected to static drift, steady turn, pure sway and pure yaw motions at Froude number 0.28. The free surface, three dimensional vortical structure and, the validation of two dimensional local flow quantities together with the available experimental data are of the interest in the current study. Part 1 provides the verification and validation results of forces and moment coefficients, hydrodynamic derivatives, and reconstructions of forces and moment coefficients from resultant hydrodynamic derivatives.     

自主水下航行器发展概述

自主水下航行器（AUVs）因其应用于海洋勘探而逐渐成为一个有趣的研究对象。波浪滑翔机是一种行驶于波浪表面的无人滑行器（SUV）,它借助海洋能来推动自己,这对于典型的AUVs所采用的电机供能以及昂贵的锚链系统浮标供
　　能来说,是一种技术上的重大跨越。该文讨论了最有效率的AUVs类型。第一部分为每一种类型的发展历程,第二部分为它们各自的技术特点。此外,波浪滑翔机作为应用于海洋部门的一种新型水下机器人,文中简要地给出它的过去,现在以及未来的发展概述。研究波浪滑翔机的意义在于证明它的效率以及实用性,进而取代诸多的AUVs来实现各种实际应用。而研究结果也表明波浪滑翔机确实可以应用于众多领域。对于海洋检测而言,相比于其他AUVs,波浪滑翔机提供了更廉价,更经济,更环保的作业模式,同时也不需要缆绳、船舶等海上作业服务。     

Enabling a viable technique for the optimization of LNG carrier cargo operations

In this study, we optimize the loading and discharging operations of the Liquefied Natural Gas (LNG) carrier. First, we identify the required precautions for LNG carrier cargo operations. Next, we prioritize these precautions using the analytic hierarchy process (AHP) and experts’ judgments, in order to optimize the operational loading and discharging exercises of the LNG carrier, prevent system failure and human error, and reduce the risk of marine accidents. Thus, the objective of our study is to increase the level of safety during cargo operations.     

Biogeography-based combinatorial strategy for efficient autonomous underwater vehicle motion planning and task-time management

Autonomous Underwater Vehicles (AUVs) are capable of spending long periods of time for carrying out various underwater missions and marine tasks. In this paper, a novel conflict-free motion planning framework is introduced to enhance underwater vehicle’s mission performance by completing maximum number of highest priority tasks in a limited time through a large scale waypoint cluttered operating field, and ensuring safe deployment during the mission. The proposed combinatorial route-path planner model takes the advantages of the Biogeography-Based Optimization (BBO) algorithm toward satisfying objectives of both higher-lower level motion planners and guarantees maximization of the mission productivity for a single vehicle operation. The performance of the model is investigated under different scenarios including the particular cost constraints in time-varying operating fields. To show the reliability of the proposed model, performance of each motion planner assessed separately and then statistical analysis is undertaken to evaluate the total performance of the entire model. The simulation results indicate the stability of the contributed model and its feasible application for real experiments.     

Effect of fatigue strain range on properties of high-strength structural steel

Ship hulls are built with stiffened steel plates and experience continuous fatigue load cycles when in service. Mechanical properties of the steel are expected to change due to the application of these cyclic loads. Therefore, the mechanical properties of the material at various levels of fatigue damage need to be understood. This paper presents two test series that were conducted to determine the effect of two different strain ranges (2000 and 3000 micro strains) of fatigue cycles on the mechanical properties of high-strength structural steel. The test results indicate that the cycle-dependent behaviours of the material can cause a slight increase or a significant decrease in the yield strength when compared to its virgin state. However, the ductility of the steel does not change much as the strain cycle increases.     

Further study on the ultimate strength analysis of spherical pressure hulls

From a comparative study it is concluded that current design rules for the spherical pressure hull of manned submersible need to be updated and unified. In this paper, a series of spherical pressure hulls are calculated by nonlinear FEM. Based on these numerical results, the influence of critical arch length and the relationship of ultimate strength with t/R and structural imperfection are studied. Finally, empirical formulae for the ultimate strength of the titanium alloy spherical pressure hull of deep manned submersible based on numerical computations are given. The formulae can be used as the core equations to update current design rules.