The Value of a Spillover Fishery for Spiny Lobsters Around a Marine Reserve in Northern New Zealand

The contribution that Leigh Marine Reserve in northern New Zealand makes to the local spiny lobster fishery was examined by comparing the catch characteristics of Jasus edwardsii around the reserve boundary with those from Coastal Leigh, 0.3-2 km from the reserve, and Little Barrier Island, 22-30 km from the reserve. Seasonal trends were apparent in the reserve catch characteristics, consistent with lobster movements into and out of offshore fishing areas adjacent to the boundary. No significant difference was detected in catch per unit effort (kg.trap haul -1 ) among locations. However, the catch around the marine reserve consisted of fewer but larger lobsters than at Little Barrier Island, while the size and number of lobsters caught per trap haul at Coastal Leigh was intermediate between the other two locations. Catch rates around the reserve were more variable than at the other sites, but on average, the amount of money made per trap haul was similar to Little Barrier Island and Coastal Leigh.     

The Decline of the Artisanal Fisheries in Mediterranean Coastal Areas: The Case of Cap de Creus (Cape Creus)

This article examines the sociocultural, economic, and environmental causes of the decline of the artisanal fisheries in the rocky coast of Cape Creus (NW Mediterranean) over the past decades. The changes that have occurred over time have favored trawlers, purse-seiners, shellfish fisheries, and tourism activities, to the detriment of artisanal fisheries. This article shows that the establishment of a marine reserve in 1998 could not reverse the observed decline in the artisanal fisheries. This raises the necessity of implementing a fishery management plan integrated into a coastal management plan, which should accompany the habitat protection. These plans could assist in the maintenance and the sustainable development of the artisanal fishing sector in Cape Creus as well as in other Mediterranean coastal areas where artisanal fisheries are also declining.     

Marine Protected Area Management Effectiveness: Progress and Lessons in the Philippines

Quantifying progress in management of marine protected areas (MPAs) is crucial to marine conservation and fisheries management in the Philippines. This study compiles data on the status, occurrence, and management gaps of MPAs through coordination with multiple organizations supporting and guiding MPAs in the Philippines. MPA management effectiveness was measured using a MPA Rating System. Since 2002 the modal MPA rating levels increased from level 1 (initiated) to level 4 (sustained) in 2008/9. This upward trend is attributed to factors that promoted both the establishment and improved management of MPAs. Analysis indicated that: (1) most MPAs struggle with budgetary constraints or lack of sustainable financing and (2) overall the MPAs are being maintained and progressing with notable improvement in management despite a range of difficulties encountered during the implementation process. For MPAs in the Visayan Region for which biophysical data were available, the MPA Rating System was used to assess the effectiveness of local government capacity building on MPA coral reef health. Our results suggest that MPAs with higher ratings are likely to have better reef health conditions.     

Analyzing the dispersion of cargo vapors around a ship’s superstructure by means of wind tunnel experiments

In a previous study, it was found that cargo tank operations like cleaning and venting, lead to higher cargo vapor concentrations around the ship’s superstructure. Can wind tunnel experiments confirm these findings? Is there an improvement when using higher outlets at high velocities compared to lower outlets with a low outlet velocity? Is there a relation between relative wind speed and measured concentration? These questions were investigated in the Peutz wind tunnel. By using a tracer gas for the wind tunnel experiments, concentration coefficients have been calculated for various settings. The study shows that using high-velocity outlets is an efficient way to keep concentrations as low as possible. The only exception is for relative wind directions from the bow. In this last case using a manhole as ventilation outlet leads to lower concentrations. With increasing wind speeds the building downwash effect resulted in higher concentration coefficients near the main deck. This study confirms our on-board measurements and suggests the lowering of the ventilation inlet of the accommodation, so that the high-velocity outlet can be used safely at all times.     

Two- and three-dimensional hydroelastic modelling of a bulker in regular waves

The relatively high rates of bulk carrier casualties in recent years, as well as structural features such as large deck openings, make this vessel type a suitable example for investigating the influence of hydroelastic modelling on predicting wave-induced loads and responses. Two- and three-dimensional fluid–flexible structure interaction models, due to their different degree of complexity and associated data requirements, can be used at different stages of the design process when estimating wave-induced loads, namely preliminary and detailed design stages, respectively.

In this paper, therefore, two- and three-dimensional hydroelasticity theories are applied to predict and compare the dynamic behaviour of a bulk carrier hull, based on OBO MV Derbyshire, in waves. Both symmetric and antisymmetric motions and distortions are incorporated in these investigations. The three-dimensional structural model consists entirely of shell finite elements, representing all major external and internal structural components, whilst the two-dimensional model is generated using Timoshenko beam finite element and finite difference discretisations. Issues relevant to the structural modelling stage, for both idealisations, are discussed. The in vacuo dynamic characteristics are compared for all models, with particular emphasis on the influence of hatch openings, shear centre and warping on the antisymmetric dynamics of the structure. For the wet analysis the fluid–flexible structure interaction is carried out using two-dimensional (Timoshenko beam and strip theory) and three-dimensional (beam and shell finite element idealisations combined with potential flow analysis based on pulsating source distribution over the mean wetted surface) analyses. Comparisons are made between steady-state responses predicted by two- and three-dimensional models in bow quartering regular waves.

It is shown that whereas the predicted symmetric dynamic responses obtained from two- and three-dimensional models are in good agreement, differences are observed for the antisymmetric dynamic characteristics. It is thought that this may be due to inadequacies in the beam models employed when simulating the global dynamic behaviour of this highly non-prismatic hull girder whilst allowing for the effects of warping.     

Hydrodynamic characteristics of slotted breakwaters under regular waves

The performance of a slotted breakwater consisting of one row of vertical slots was investigated theoretically and experimentally under normal regular waves. A simple theoretical model based on an eigenfunction was developed. The wave transmission, reflection, energy loss, and hydrodynamic force exerted on the breakwater were calculated for different values of the wave and structure parameters. The validity of the theoretical model was examined by comparing its results with theoretical and experimental results obtained from different studies. It was found that the transmission coefficient decreases with increasing dimensionless wavenumber (kh), increasing wave steepness (H _i/L), and decreasing breakwater porosity (ε). The reflection coefficient showed the opposite trend to the transmission coefficient. Also, about 20–50% of incident wave energy was lost due to the effect of the breakwater. In addition, the proposed theoretical model can be used for predicting the performance of slotted breakwaters and the hydrodynamic forces exerted on these structures using the friction coefficient f = 1.5.     

A finite element model for flexible pipe armor wire instability

The constructive disposition of metallic and plastic layers confers flexible pipes with high and low axial stiffness respectively when tensile and compressive loads are applied. Under certain conditions typically found during deepwater installation or operation, flexible pipes may be subjected to high axial compression, sometimes accompanied by bending. If not properly designed, the structure may not be able to withstand this loading and fails. From practical experience observed offshore and in laboratory tests two principal mechanisms, which will be discussed in this paper, have been identified regarding the configuration of the armor wires. When the pipe fails by compression the armor wires may exhibit localized lateral or radial deflections, consequently permanent damage is observed in the armor wires with a sudden reduction of the structure’s axial stiffness. The pressure armor may also unlock, thus causing potential fluid leakage.In this work a finite element model is developed to estimate the critical instability load and failure modes. An axi-symmetric model is constructed employing a complex combination of beam and spring elements. For each armor layer only one wire needs to be modeled, hence the computational cost is minimized without compromising the phenomenon characterization. A parametric case study is performed for a typical flexible pipe structure, where the friction coefficient between the wire armors and the external pressure are varied, and the critical instability loads and failure modes are obtained and results are discussed.     

Numerical analysis of cavitating propeller and pressure fluctuation on ship stern using a simple surface panel method “SQCM”

This paper presents a calculation method for the pressure fluctuation induced by a cavitating propeller. This method consists of two steps: the first step is the calculation of propeller sheet cavitation, and the second step is the calculation of pressure fluctuation on the ship stern. It is for practicality that we divide the method into two steps but do not calculate these steps simultaneously. This method is based on a simple surface panel method “SQCM” which satisfies the Kutta condition easily. The SQCM consists of Hess and Smith type source panels on the propeller or cavity surface and discrete vortices on the camber surface according to Lan’s QCM (quasi-continuous vortex lattice method). In the first step, the cavity shape is solved by the boundary condition based on the free streamline theory. In order to get the accurate cavity shape near the tip of the propeller blade, the cross flow component is taken into consideration on the boundary condition. In the second step, we calculate the cavitating propeller and the hull surface flow simultaneously so as to calculate the pressure fluctuation including the interaction between the propeller and the hull. At that time, the cavity shape is changed at each time step using the calculated cavity shape gotten by the first step. Qualitative agreements are obtained between the calculated results and the experimental data regarding cavity shape, cavity volume and low order frequency components of the pressure fluctuation induced by the cavitating propeller.     

耦合非线性三维海洋立管的边界控制(英文)

This paper presents a design of boundary controllers implemented at the top end for global stabilization of a marine riser in a three dimensional space under environmental loadings. Based on the energy approach, nonlinear partial differential equations of motion, including bending-bending and longitudinal-bending couplings for the risers are derived. The couplings cause mutual effects between the three independent directions in the riser’s motions, and make it difficult to minimize its vibrations. The Lyapunov direct method is employed to design the boundary controller. It is shown that the proposed boundary controllers can effectively reduce the riser’s vibration. Stability analysis of the closed-loop system is performed using the Lyapunov direct method. Numerical simulations illustrate the results.     

Experimental assessment of the ultimate strength of a box girder subjected to severe corrosion

The objective of this paper is to describe the experimental assessment of the ultimate strength of a severely corroded box girder subjected to a uniform bending moment resulting from four-point loading. Three box girders that could simulate the behaviour of midship sections have been deteriorated in corrosive seawater environment to simulate different levels of corrosion degradation of ageing ship structures. During the deterioration process, various parameters have been controlled and the total weight lost was registered. Corroded plate thicknesses have been measured in 212 points and a statistical analysis has been performed. The resulting corrosion wastage has been fitted by a non-linear time variant degradation model. The experimental results of the ultimate strength test of a severely corroded box girder subjected to a four-point loading have been analysed. The load-displacement and moment-curvature relationship is discussed, different failure modes are identified, and the strain gauges readings are analysed.