URANS simulations of static and dynamic maneuvering for surface combatant: part 1. Verification and validation for forces, moment, and hydrodynamic derivatives

Part 1 of this two-part paper presents the verification and validation results of forces and moment coefficients, hydrodynamic derivatives, and reconstructions of forces and moment coefficients from resultant hydrodynamic derivatives 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 regards to the computational fluid dynamics based maneuvering prediction method. In the current study, the ship is subjected to static drift, steady turn, pure sway, pure yaw, and combined yaw and drift motions at Froude number 0.28. The results are analyzed in view of: (1) the verification for iterative, grid, and time-step convergence along with assessment of overall numerical uncertainty; and (2) validations for forces and moment coefficients, hydrodynamic derivatives, and reconstruction of forces and moment coefficients from resultant hydrodynamic derivatives together with the available experimental data. Part 2 provides the validation for flow features with the experimental data as well as investigations for flow physics, e.g., flow separation, three dimensional vortical structure, and reconstructed local flows.     

Coastal Resources as an Engine of Economic Growth and Reduction of Poverty in West Africa: Policy Considerations

This article synthesizes lessons and outcomes from the second international Coastal Zone Asia-Pacific conference (CZAP) on “Improving the Quality of Life in Coastal Areas,” held in Brisbane in September 2004. The conference theme was chosen as a follow-up from the first CZAP that identified priority actions in response to the increasing recognition of social issues in coastal management, particularly those aiming to improve the state of the coastal areas in the Asia-Pacific region. The second CZAP explored the “quality of life” theme by placing emphasis on rectifying coastal poverty, sustaining livelihoods, and protecting cultural heritage. Mechanisms to address these issues were explored through international agreements, participatory research, capacity building, and education, as well as the continuing need for integrated planning, environmental management, and effective monitoring and evaluation. A post-conference survey showed that the second CZAP resulted in 122 initiatives (82 underway and another 40 planned) to progress the improvement of quality of life in coastal areas. These initiatives ranged from the establishment of a unit that is responsible for river basin and coastal zone management by the Thua Thien Hue provincial government in Vietnam, to a collaborative on-ground livelihoods project between NGOs, government, and financial institutions on coastal zone management facilitated by the Asian Development Bank. However, the authors argue that two key challenges for ICM in the Asia-Pacific region remain. These challenges relate to the effective monitoring and evaluation of ICM initiatives, as well as matching future ICM initiatives to emergent priority areas.     

Application of a validated primary production model (BLOOM) as a screening tool for marine, coastal and transitional waters

In order to manage aquatic systems, it is necessary to apply methods relating the environmental variables and system-state parameters with external factors that affect the system. External factors can be natural (i.e. the movement of water) or partly-anthropogenic (i.e. nutrient loads). In addition to the national authorities, who have been implementing environmental policies for several decades, the EU is presently implementing the Water Framework Directive (WFD) aimed at establishing a new set of standards for the ecological and water quality of water systems. Among these are the phytoplankton biomass and composition. Phytoplankton affects turbidity, oxygen depletion, total productivity of the system and the occurrence of (harmful) algal blooms. A range of methods is available to relate phytoplankton to the controlling environmental conditions. Among these are statistical relations for instance of the Vollenweider type as well as deterministic simulation models. At the end of the 1970s, a generic deterministic phytoplankton module called BLOOM was developed, which has since been applied to a wide range of fresh water and marine systems. Here we test the applicability of this model as a screening tool for coastal waters. We conclude that the model is able to reproduce observed chlorophyll levels adequately under a wide range of conditions. Subsequently the model is applied to demonstrate the potential impacts of reductions in nitrogen, phosphorus or both nutrients simultaneously. Depending on which factors are initially controlling, the impacts of these reductions vary considerably both between locations and during the season. While this type of application lacks explicit relations between nutrient concentrations and external loadings, it does consider a number of relevant conditions in a consistent way and requires remarkably little data and effort. It is therefore a valuable screening tool.     

Atmospheric CO2 measurements and error analysis on seasonal air–sea CO2 fluxes in the Bay of Biscay

Atmospheric molar fraction of CO₂ (xCO₂^atm) measurements obtained on board of ships of opportunity are used to parameterize the seasonal cycle of atmospheric xCO₂ (xCO₂^atm) in three regions of the eastern North Atlantic (Galician and French offshore and Bay of Biscay). Three selection criteria are established to eliminate spurious values and identify xCO₂^atm data representative of atmospheric background values. The filtered data set is fitted to seasonal curve, consisting of an annual trend plus a seasonal cycle. Although the fitted curves are consistent with the seasonal evolution of xCO₂^atm data series from land meteorological stations, only ship-board measurements can report the presence of winter xCO₂^atm minimum on Bay of Biscay. Weekly air–sea CO₂ flux differences (mmol C·m^− 2 day^− 1) produced by the several options of xCO₂^atm usually used (ship-board measurements, data from land meteorological stations and annually averaged values) were calculated in Bay of Biscay throughout 2003. Flux error using fitted seasonal curve relative to on board measurements was minimal, whereas land stations and annual means yielded random (− 0.2 ± 0.3 mmol C·m^− 2·day^− 1) and systematic (− 0.1 ± 0.4 mmol C·m^− 2 day^− 1), respectively. The effect of different available sources of sea level pressure, wind speed and transfer velocity were also evaluated. Wind speed and transfer velocity parameters are found as the most critical choice in the estimate of CO₂ fluxes reaching a flux uncertainty of 7 mmol C·m^− 2·day^− 1 during springtime. The atmospheric pressure shows a notable relative effect during summertime although its influence is quantitatively slight on annual scale (0.3 ± 0.2 mmol C·m^− 2·day^− 1). All results confirms the role of the Bay of Biscay as CO₂ sink for the 2003 with an annual mean CO₂ flux around − 5 ± 5 mmol C m^− 2 day^− 1.     

Numerical modelling of fish eggs dispersion at the Patos Lagoon estuary — Brazil

The Patos Lagoon estuary is the most important nursery ground for commercially relevant species of fish and crustaceans in the South of Brazil, maintaining fisheries that sustain 3500 fisher families throughout the Rio Grande do Sul State coastline. Around 80% of the interior estuarine area is very shallow (< 2 m), and recruitment of fish eggs and larvae to the inner parts of the Patos Lagoon estuary is directly related to the circulation pattern in the area, which is controlled by local and non-local wind effects and freshwater discharge. The objective of this study is to investigate the processes controlling the transport of estuarine dependent fish eggs between the Atlantic Ocean and the Patos Lagoon estuary.An integrated numerical system based on a bi-dimensional hydrodynamic model and a Lagrangean transport model of passive particles is applied to a selection of scenarios representing the passage of weather fronts over the area. At this stage, fish eggs are represented as buoyant passive particles. Modelling results are compared against field data for the period under investigation (September/October 1999) and historical records. Short term results are analysed in terms of the meteorological conditions (wind direction, intensity and duration) controlling the transport of eggs to the inner parts of the estuary and the extension of their excursion. This experiment is the first attempt to couple biological and physical information to study fish eggs transport, and to enhance the current knowledge about recruitment of important fisheries resources in southern Brazil.     

Ballast Water Risk Indication for the North Sea

The ballast water from ships carries marine organisms that have invasive potential. The International Maritime Organization Ballast Water Management Convention (2004) requires ballast water exchange or ballast water management (BWM) systems either onboard or ashore. Ships can be exempted on the basis of risk assessment, when exclusively sailing between specific ports or in an enclosed area. In reply to our questionnaire, the shipping sector argues that the North Sea is ecologically homogeneous and exemptions could therefore be granted. This paper proposes that the North Sea area is, in fact, not homogeneous in terms of hydrographical and biological conditions; therefore, ballast water is a relevant transport mechanism for organisms. Within the North Sea, the short shipping routes indicate a high risk for survival. We examined actual simulation models for ballast water risk assessment in the North Sea, and we have identified the major parameters that need to be included in such models. These models provided a basis; they further need to be combined and adapted for the purpose of evaluating the rationale for an exemption. We concluded that exemptions from BWM are not recommended for the North Sea area. Anticipating the Ballast Water Management Convention, ship owners might do well to study possibilities for installing BWM systems onboard.     

通过形状差异修正模式方法进行的损伤识别试验(英文)

An experimental program was undertaken to test the feasibility to detect the occurrence of structural damage using a modified mode shape difference technique. The vibration response of a steel beam fixed at one end and hinged at the other was obtained for the intact and damage conditions. Modal analysis was performed to extract the frequencies and mode shapes. The method shows a good potential in detection of occurrence and location of damage.     

Comparison of the stress distributions of liquid gas road tankers with various configurations during braking, cornering, and vertical bump maneuvers

This paper compares the stress and displacement distributions of different head-shell junction configurations in LPG road tankers during different vehicle design maneuvers, such as braking, cornering, and vertical bumps, for the first time. Various combinations of heads (e.g., spherical and toroidal) and shell cross sections (circular and elliptical) are considered. The ABAQUS finite element software is used to model and analyze the fluid-filled tankers. The results show that the most critical maneuver affecting the fluid-filled tankers is cornering and the safest maneuver is braking. Moreover, the results reveal that the outer surface of the tanker generally behaves the most critically in all maneuvers, and cylindrical tankers with smaller cross-sections behave more acceptably compared to those with larger cross-sections. Among fluid-filled vehicle tankers with identical platform areas, tankers with elliptical cross-sections behave the most acceptably.     

Vibration path analysis and optimal design of the suspension for brake judder reduction

Brake judder is abnormal vibration, which is mainly generated by uneven contact between the brake disc and pad. The abnormal vibration from BTV (Brake Torque Variation) is transferred to the suspension and the steering system during braking. In this paper, judder simulation is carried out using a multi-body dynamic analysis program to analyze the relationship between judder and the transfer mechanism, which consists of the suspension and the steering system. In order to verify the analytical model, test results are compared with the simulation results. A sensitivity analysis is also carried out. In addition, an optimization method is presented for judder reduction, using the design of experiments.     

Optimising a Car Chassis

This paper presents a method to optimise a car chassis fitted either with passive or active suspensions. Provided that a full vehicle model is available for accurate simulations of many different driving situations (J-turn, lane-change, power-on/power-off on even/rough, dry/wet roads), the method allows to tune the parameters of the chassis system (suspension elastokinematics, stiffnesses, dampings, actuator gains, tyre pressures...) in order to achieve the desired dynamic behaviour of the car in all of the considered driving situations. According with the Global Approximation approach, the original physical car model is substituted by another purely numerical mathematical model (backpropagating Artificial Neural Network). This reduces the simulation time dramatically and enables the optimisation process to come to successful results. The computation of the Pareto-optimal set is performed by using Genetic Algorithms. The method is validated by optimising the parameters of the suspension system of an actual car.