Spatial variability of the barotropic M2 constituent tidal current over the Rías Baixas Galician shelf (NW Spain)

Using current meters and systematically repeated vessel mounted ADCP data legs, we describe the role of the semidiurnal and diurnal constituents in the tidal currents and investigate the mesoscale variability of the M₂ tidal currents field along three cross-shelf legs over the Galician shelf. We found that the estimated values of the semi-major axes of the main semidiurnal tidal constituents are closely related to those obtained in previous research and that the tidal currents are predominantly semidiurnal. Amplitudes of the M₂ and S₂ semi-major axes constituents are comparable, and important fortnightly variability should thus be expected in the amplitude of the semidiurnal tidal currents. Vertical profiles of the semi-major axes of the main tidal constituents reveal that, in the absence of stratification, and far from the bottom frictional effects, the tidal currents are mostly barotropic. Over the slope, the tidal ellipses tilt from a north–south orientation toward the northeast–southwest direction and, as we go further into the shelf, their amplitude is increased, a feature that is reasonably explained by the transition from the dynamics of a Poincaré wave offshore to the dynamics of a northward alongshore propagating Kelvin wave over the shelf. The Ría de Vigo exerts a notable influence over the tidal currents, acting as an extension of the shelf and introducing a meridional variation in the orientation of the ellipses from the alongshore direction in the southern straight coast toward the northeast–southwest direction at the latitude of the Rías. Finally, the spatial fitting methods we tried have proved to be successful in VMADCP data detiding in this region.     

Hydrographic conditions affecting two fishing grounds of Mallorca island (Western Mediterranean): during the IDEA Project (2003–2004)

This paper describes the hydrographic conditions observed during six surveys carried out during 2003 and 2004, in the framework of the “IDEA Project” (acronym for “Influence of oceanographic structure and dynamics on demersal populations in waters of the Balearic Islands”). The surveys were developed on the shelf and slope of Mallorca Island, in particular in two fishing grounds at the north and south of the Mallorca channel. Periodic movements of the fishing fleet between these two areas have been regularly reported, suggesting a seasonal variability of the resources which could be in turn associated with the hydrodynamic variability. With this motivation, water masses affecting these grounds have been identified and their seasonal variability has been studied. Different oceanographic and environmental conditions have been found between the two fishing grounds. These differences are related to the presence of mesoscale structures, associated with the Western Mediterranean Intermediate Water (WIW) at the north of the Ibiza channel and big gyres detached from the Algerian Current. The former has been shown to have influence on the regional oceanic circulation and the latter could affect the progress of fresh Atlantic Water (AW) towards the channels and make possible the presence of high salinity values at intermediate waters at the south of Mallorca Island. Historical data from other oceanographic cruises carried out in the region are finally used to discuss the interannual variability of these mesoscale structures.     

Surf-riding and oscillations of a ship in quartering waves

The behavior of a ship encountering large regular waves from astern at low frequency is the object of investigation, with a parallel study of surf-riding and periodic motion paterns. First, the theoretical analysis of surf-riding is extended from purely following to quartering seas. Steady-state continuation is used to identify all possible surf-riding states for one wavelength. Examination of stability indicates the existence of stable and unstable states and predicts a new type of oscillatory surf-riding. Global analysis is also applied to determine the areas of state space which lead to surf-riding for a given ship and wave conditions. In the case of overtaking waves, the large rudder-yaw-surge oscillations of the vessel are examined, showing the mechanism and conditions responsible for loss of controllability at certain vessel headings.List of symbols c wave celerity (m/s) - C(p) roll damping moment (Ntm) - g acceleration of gravity (m/s²) - GM metacentric height (m) - H wave height (m) - I _x ,I _z roll and yaw ship moments of inertia (kg m²) - k wave number (m^–1) - K _H ,K _W ,K _R hull reaction, wave, rudder, and propeller - K _p forces in the roll direction (Ntm) - m ship mass (kg) - n propeller rate of rotation (rpm) - N _H ,N _W ,N _R hull reaction, wave, rudder, and propeller - N _P moments in the yaw direction (Ntm) - p roll angular velocity (rad/s) - r rate-of-turn (rad/s) - R(,x) restoring moment (Ntm) - Res(u) ship resistance (Nt) - t time (s) - u surge velocity (m/s) - U vessel speed (m/s) - v sway velocity (m/s) - W ship weight (Nt) - x longitudinal position of the ship measured from the wave system (m) - x _G ,z _G longitudinal and vertical center of gravity (m) - x _S longitudinal position of a ship section (S), in the ship-fixed system (m) - X _H ,X _W ,X _R hull reaction, wave, rudder, and propeller - X _P forces in the surge direction (Nt) - y transverse position of the ship, measured from the wave system (m) - Y _H ,Y _W ,Y _R hull reaction, wave, rudder, and propeller - Y _p forces in the sway direction (Nt) - z _Y vertical position of the point of action of the lateral reaction force during turn (m) - z _W vertical position of the point of action of the lateral wave force (m) Greek symbols angle of drift (rad) - rudder angle (rad) - wavelength (m) - position of the ship in the earth-fixed system (m) - water density (kg/m³) - angle of heel (rad) - heading angle (rad) - _e frequency of encounter (rad/s) Hydrodynamic coefficients K roll added mass - N _v ,N _r yaw acceleration coefficients - N _v N _r N _rr N _rrv ,N _vvr yaw velocity coefficients K. Spyrou: Ship behavior in quartering waves - X _u surge acceleration coefficient - X _u X _vr surge velocity coefficients - Y _v ,Y _r sway acceleration coefficients - Y _v ,Y _r ,Y _vv ,Y _rr ,Y _vr sway velocity coefficients European Union-nominated Fellow of the Science and Technology Agency of Japan, Visiting Researcher, National Research Institute of Fisheries Engineering of Japan     

Improving pollutant emissions in diesel engines for heavy-duty transportation using retarded intake valve closing strategies

A combined theoretical and experimental study has been carried out to determine the real potential of reducing pollutant emissions in a HD diesel engine by means of retarding the intake valve closing. The effects produced by this alteration of the basic operation cycle have been examined by a preliminary modelling study, and from the obtained results, a modified camshaft was manufactured with a delayed intake valve closing of 60 crank angle degrees. Single-cylinder engine tests were carried out with this modified camshaft, and the emissions and fuel consumption were recorded. The results showed that the retarded intake valve closing can enhance the premixed combustion phase, and thus simultaneously reduce soot and NOx emissions. Moreover, the combustion process attained is extremely tolerant to exhaust gas recirculation, and by adoption of this measure, Euro-5 emissions limits can be achieved at the tested conditions without after-treatment.     

Estimates of vertical mixing during a Lagrangian experiment off the Galician coast

An adjoint 1-D model was used to determine vertical diffusivity coefficients from temperature profiles collected within a filament escaping from the Galician coast following an upwelling event. The optimisation scheme ended with relatively high diffusivity values within the thermocline (9×10⁻⁵ m² s⁻¹). Such high values are relevant for biogeochemical exchanges between surface and deep waters in stratified areas.The optimised values were several orders of magnitude higher than the bulk of diffusivity measurements recorded with a free-falling device; however, the optimisation solution was consistent with the arithmetic mean of the measurements in the thermocline (7.7×10⁻⁵ m² s⁻¹), giving more weight to the few largest values. Below the thermocline, the data assimilation method failed because of the three-dimensional nature of the advective field of the upwelling system. Ignoring this advective forcing in the model led to estimates that were two orders of magnitude too high.The results suggest that turbulent mixing is a random process where a few intense events determine the average mixing that drives the long-term evolution of the water column structure. This statistical property is very important when one wants to use instantaneous diffusivity measurements for modelling purposes.     

Adapting without Retreating: Responses to Shoreline Change on an Inlet-Associated Coastal Beach

Coastal barrier systems around the world are experiencing higher rates of flooding and shoreline erosion. Property owners on barriers have made significant financial investments in physical protections that shield their nearby properties from these hazards, constituting a type of adaptation to shoreline change. Factors that contribute to adaptation on Plum Island, a developed beach and dune system on the North Shore of Massachusetts, are investigated here. Plum Island experiences patterns of shoreline change that may be representative of many inlet-associated beaches, encompassing an equivocal and dynamically shifting mix of erosion and accretion. In the face of episodic floods and fleeting erosive events, and driven by a combination of strong northeast storms and cycles of erosion and accretion, the value of the average Plum Island residence increases by 34% for properties on the oceanfront where protection comprises a publicly constructed soft structure. Even in the face of state policies that ostensibly discourage physical protection as a means of adaptation, coastal communities face significant political and financial pressures to maintain existing protective structures or to allow contiguous groups of property owners to build new ones through collective action. These factors mitigate against adapting to shoreline change by retreating from the coast, thereby potentially increasing the adverse effects of coastal hazards.     

Evaluating air emission inventories and indicators from cruise vessels at ports

This paper provides an estimation of air emissions (CO₂, NO_X, SO_X and PM) released by cruise vessels at the port level. The methodology is based on the “full bottom-up” approach and starts by evaluating the fuel consumed by each vessel on the basis of its individual port activities (manoeuvring, berthing and hoteling). The Port of Barcelona was selected as the site at which to perform the analysis, in which 125 calls of 30 cruise vessels were monitored. Real-time data from the automatic identification system (AIS), factor emissions from engine certificates and vessel characteristics from IHS Sea-web database were also collected for the analysis. The research findings show that the most appropriate indicators are inventory emissions per “port-time gross tonnage”, “port-time passenger” and “port time”. These emission indicators improve our understanding of cruise emissions and will facilitate the work that aims to estimate reliably and quickly the in-port ship emission inventories of cruise ports.     

Unsteady finite-depth effects during resistance tests on a ship model in a towing tank

This paper covers an extension of the study of Doctors et al. (J Ship Res 52(4):263–273, 2008) on oscillations in wave resistance during the constant-velocity phase of a towing-tank resistance test on a ship model to the case of relatively shallow water. We demonstrate here that the unsteady effects are very prominent and that it is essentially impossible to achieve a steady-state resistance curve in a towing tank of typical proportions for a water-depth-to-model-length ratio of 0.25. This statement is particularly true in the speed region near a depth Froude number of unity. However, on the positive side, we show here that an application of unsteady linearized wave-resistance theory provides an excellent prediction of the measured total resistance, when one accounts for the form factor in the usual manner. Finally, a simple application of the results to the planning and analysis of towing-tank tests is presented.     

Benthic sediment composition and nutrient cycling in an Intermittently Closed and Open Lake Lagoon

Surfical sediments within Corunna Lake, a moderate size Intermittently Closed and Open Lake Lagoon (ICOLL), were examined for solid phase nutrient concentrations (TN, TP, TOC,) and solute exchange rates between the sediment and water column (O₂, NO₃–N, NH₄–N, FRP, and N₂). The surfical sediments in Corunna Lake contained high concentrations of TN (5 mg/g dry mass), total phosphorus (0.6 mg/g dry mass), and TOC (~ 5% dry mass). The carbon stable isotope ratio (δ¹³C) and TOC:TN ratios (δ¹³C ~ ? 24, TOC:TN ~ 11–14) demonstrated that the composition of the organic matter in the sediment was a mixture derived primarily of degraded planktonic matter. The close association between TP and Fe concentrations highlighted the potential role Fe plays in mediating Filterable Reactive Phosphorus (FRP) concentrations in the water column of Corunna Lake. In situ benthic chamber incubations were used to measure benthic fluxes. Solute exchange rates between the sediment and water column in Corunna Lake were similar to other reported studies (O₂ = ? 469 to ? 1765 µmol m^? 2 h^? 1, NH₄–N = 0.1–63 µmol m^? 2 h^? 1, NO₂/NO₃–N = 0 µmol m^? 2 h^? 1, FRP = ? 4–1.6 µmol m^? 2 h^? 1and N₂ = 12–356 µmol m^? 2 h^? 1). As more carbon was deposited and mineralized the efficiency of the bacterial population to denitrify nitrogen in the sediment decreases. The linkage between land use and benthic biogeochemistry was also explored. A dairy farm exists in the middle catchment of Corunna Lake, and the receiving bay sediment consistently demonstrated the highest oxygen consumption rates in winter and spring (? 1408 µmol m^? 2 h^? 1 in winter, ? 1691 µmol m^? 2 h^? 1 in spring) and lowest denitrification efficiencies during summer (~ 3%). Nitrate/nitrite fluxes were not observed during any of the chamber incubations, with the concentrations of nitrate/nitrite being below detection limits (< 10 μg/L). Seasonal changes influenced the rates of solute exchange between the sediment and water column. Critical measures of solute exchange for NH₄–N and biogenic N₂ indicated that seasonal temperature changes play a significant role in mediating the reaction rates of sedimentary based biogeochemical processes. Measurable FRP fluxes were small but greater in the benthic sediments which received higher carbon inputs. Sediments have a high capacity to adsorb P which is released as sediment oxygen demand increases as a result of increases in labile carbon loads.