Performance analysis of polymer electrolyte membrane (PEM) fuel cell stack operated under marine environmental conditions

The marine environmental condition, especially NaCl, has been identified as one of the major sources of contamination on the performance of open cathode Proton Exchange Membrane Fuel Cells (PEMFC) system, when the power source is based on fuel cells for marine applications like submarines, navy ships etc., In the present paper, we have studied the performance of PEMFCs under the marine environment for a longer duration and also the recovery mechanism of the PEMFC power pack after contamination. It has been observed that the NaCl is a major contaminant for PEMFC, compared to NO _x and SO _x , which are major contaminants for fuel cells operating in the land regions. We have observed a performance loss of 60 % in PEMFC, when operated for 48 h, due to poisoning of PEMFC by NaCl vapours. The recovery of the stack is attempted by repeated water washing on the cathode side of the fuel cell, presuming that the salts get deposited only on the surface of the electrodes and the performance is easily recoverable. The recovery mechanisms are analysed by constant-current discharging operation and by modified experimental methods and are reported here. The performance vagaries in fuel cells due to sea water contamination is also analysed by linear fit and it is found that the rate of power increment after water wash is higher than the rate of power increment, around 11.5 W/10?h compared to normal environmental conditions, which is 4.1 W/10?h.     

Measurement of air–water CO2 transfer at four coastal sites using a chamber method

We measured the air–water CO₂ flux in four coastal regions (two coral reefs, one estuary, and one coastal brackish lake) using a chamber method, which has the highest spatial resolution of the methods available for measuring coastal air–water gas flux. Some of the measurements were considerably higher than expected from reported wind-dependent relationships. The average k₆₀₀ values for Shiraho Reef, Fukido Reef, Fukido River, and Lake Nakaumi were 1.5 ± 0.6, 3.2 ± 0.3, 0.69 ± 0.26, and 2.2 ± 0.9 (mean ± S.D.) times larger than the wind-dependent relationships. Results were compared with current-dependent relationships and vertical turbulence intensity (VTI). VTI is an index of water-surface stirring and is calculated from near-surface vertical velocity. Although some measurements from the reefs and river closely matched those expected from wind-dependent relationships, others were considerably higher. All data were correlated with VTI and were qualitatively explained by bottom macro-roughness enhancement. In Lake Nakaumi, results tended to differ from the wind-dependent relationships, and the difference between the measured and expected gas-transfer velocity was correlated with biological DO changes and/or the intensity of density stratification. We found these factors to have important effects on coastal gas flux. In addition, the chamber method was an effective tool for evaluating coastal gas flux.     

Fatigue life prediction of welded ship details

Ship structures are submitted to variable cyclic loading during navigation. The cyclic motion of waves induces variable and complex loadings in the structure, which could generate fatigue damage. Moreover, most of these metallic structures are welded assemblies. This technique generates local stress concentrations at the weld toe, which becomes a critical area regarding fatigue. In previous works, a methodology to predict fatigue life was developed and tested on butt-welded and cruciform joints. The present work focuses on other welded assemblies in order to extend fatigue crack initiation life evaluation to a wider range of ship details. The strategy could be split into two steps. First, a finite element calculation is performed under constant or variable amplitude loadings, in order to analyze the elastic shakedown of the structure. To characterize the material heterogeneity of the welded joint, experimental tests together with micro-hardness measurements, are performed on a simulated heat-affected zone. If there is a shakedown in the structure, a post-treatment is applied to predict the fatigue crack initiation. It is based on a two-scale damage model, initially developed by Lemaitre et al. and again includes the heterogeneity of fatigue properties. To validate this methodology, some experimental tests have been performed on welded assemblies which are typical of shipbuilding applications, using a fatigue machine. These comparisons between experimental and numerical fatigue lives are encouraging.     

Study of the seasonal cycle of the biogeochemical processes in the Ligurian Sea using a 1D interdisciplinary model

A one-dimensional coupled physical–biogeochemical model has been built to study the pelagic food web of the Ligurian Sea (NW Mediterranean Sea). The physical model is the turbulent closure model (version 1D) developed at the GeoHydrodynamics and Environmental Laboratory (GHER) of the University of Liège. The ecosystem model contains 19 state variables describing the carbon and nitrogen cycles of the pelagic food web. Phytoplankton and zooplankton are both divided in three size-based compartments and the model includes an explicit representation of the microbial loop including bacteria, dissolved organic matter, nano-, and microzooplankton. The internal carbon/nitrogen ratio is assumed variable for phytoplankton and detritus, and constant for zooplankton and bacteria. Silicate is considered as a potential limiting nutrient of phytoplankton's growth. The aggregation model described by Kriest and Evans in (Proc. Ind. Acad. Sci., Earth Planet. Sci. 109 (4) (2000) 453) is used to evaluate the sinking rate of particulate detritus. The model is forced at the air–sea interface by meteorological data coming from the “Côte d'Azur” Meteorological Buoy. The dynamics of atmospheric fluxes in the Mediterranean Sea (DYFAMED) time-series data obtained during the year 2000 are used to calibrate and validate the biological model. The comparison of model results within in situ DYFAMED data shows that although some processes are not represented by the model, such as horizontal and vertical advections, model results are overall in agreement with observations and differences observed can be explained with environmental conditions.     

Formation of Denmark Strait overflow water and its hydro-chemical composition

The dense overflow across the Denmark Strait is investigated with hydrographic and hydro-chemical data and the water mass composition of the Denmark Strait Overflow Water (DSOW) is determined by multivariate analysis. Hydrographical properties, the transient tracers CFC-11 and CFC-12, oxygen and nutrients are utilized for the water mass definitions. Distribution and characteristics of water masses north of Denmark Strait are described, the important water masses at the sill and the variability on weekly time-scales are discussed, and the entrainment and mixing of water into the overflow plume in the northern Irminger Basin is calculated. The analysis indicates that water masses both from the Nordic Seas and the Arctic Ocean are important for the formation of DSOW. It is found that water masses transported with the East Greenland Current make up about 75% of the overflow at the sill. The overflow at, and shortly south of, the sill is inhomogeneous with a low-salinity component dominated by Polar Intermediate Water. The high-salinity component of the overflow is mainly of Arctic origin. The water mass composition, and the short-term variability for 7 repeats of sections close to the sill are described, and these illustrate that the overflow is in fact a composite of a number of water masses with different formation and transport histories. This indicate that the overflow is a robust feature, but that it responds to variations in the circulation or atmospheric forcing that influences the formation of intermediate and deep water masses within the Arctic Mediterranean and the North Atlantic. At a section about 400 km south of the sill the overflow is well mixed and modified by entrainment of, mainly, Iceland–Scotland Overflow Water and Labrador Sea Water, together constituting 30% of the overflow plume. The entrainment of Middle Irminger Water dominates shortly downstream of the sill, before the overflow plume reaches too deep but the entrainment seems to be intermittent in time.     

Technology application and development trend of intelligent unmanned system北大核心CSCD

Intelligent unmanned system combat is moving from concepts to actual combat applications. The military applications of intelligent unmanned systems are emphasized by focusing on the needs of the combat missions that they will undertake on future battlefields and summarizing the development statuses of land, air and maritime unmanned systems. Aiming at the key problems faced by intelligent unmanned systems and the practical difficulties that will be faced on the battlefield in the future, we analyze the key technologies required for intelligent unmanned systems, including autonomous perception and understanding in complex environments, behavioral decision-making and trajectory planning, autonomous navigation and positioning, multi-scenario autonomous skill learning and intelligent control, unmanned cluster cooperative control, natural human-computer interaction, etc. At the same time, aiming at the problems that will be encountered in the further development of intelligent unmanned systems on the battlefield in the future, we start with individual enhancement and cluster enhancement, and conduct a detailed analysis of the development trends of intelligent unmanned systems. © 2022 Palaeobulgarica. All rights reserved.     

Measuring the thicknesses of the freshwater-layer plume and sea ice in the land-fast ice region of the Mackenzie Delta using helicopter-borne sensors

Helicopter-borne sensors have been used since the early 1990s to monitor ice properties in support of winter marine transportation along the east coast of Canada. The observations are used in ice chart production and to validate ice hazard identification algorithms using satellite advanced synthetic aperture radar (ASAR) imagery. In this study we evaluated the sensors' additional capability to monitor the freshwater plume characteristic beneath land-fast ice. During the Canadian Arctic Shelf Exchange Study (CASES) data were collected over the Mackenzie Delta in the southern Beaufort Sea where a buoyant river plume exists. Results showed that the electromagnetic–laser system could describe not only the ice properties but also the horizontal distribution of the freshwater plume depths that decreased in depth stepwise offshore as the flow of the buoyant plume was restricted by a series of ridge-rubble fields running parallel to the coast. Relative to the 2 m mean ice thickness, the plume layer depth varied from zero under mobile offshore pack ice to 3 m inshore of the third set of ridge-rubble fields.     

Torque control of a vehicle with electronic throttle control using an input shaping method

The shock-jerk phenomenon is usually observed in vehicles with manual transmission systems that are rapidly accelerating, and this phenomenon makes the passenger feel uncomfortable. This phenomenon can be minimized using torque control of the vehicle with throttle-by-wire or an ETC (Electronic Throttle Control) system. In this paper, the drivetrain of the vehicle is modeled to simulate the vehicle behavior, and the control strategy of ETC is studied to reduce shock and jerk characteristics using an input shaping method. The control logic is verified by using vehicle modeling and simulations.     

A European perspective on bond finance for the maritime industry

The European Shipping Industry faces a huge capital requirement over the next decade as a result of increasing trade and ageing fleets. This growth in demand is juxtaposed with a contraction in the number of banks willing to support the industry and a general tightening of credit facilities. Consequently, companies have been forced to access the capital markets for equity and debt. The difficulties experienced particularly in the bond markets have lead to premature dismissal of this relatively new form of finance. This paper seeks to explore the suitability of bond finance and finds that it is largely dependent on the perception of the maritime industry by the investment community.