Underwater radiated noise (URN) from ship propellers has attracted increasing interest in recent years due to its adverse environmental effects on marine life and their communication channels. The environmental concern to reduce shipping noise and the industrial requirements for faster computational tools are driving factors that promote research in the specialized domain of hydroacoustics. This thesis deals with the development of such a computationally efficient numerical tool, which can be used in the prediction of underwater radiated noise in the early design phase of propellers.
The numerical model is developed with two major objectives – versatility in assessing the relative contributions from the major propeller-noise generating mechanisms, and rapidity in prediction of overall noise behaviour. It uses the Farassat-1A solid-FWH formulation of the Ffowcs-Williams- Hawkings equation by defining equivalent acoustic sources on the propeller blade, sheet cavity and tip vortex cavity surfaces. In particular, the application of the solid-FWH formulation to the tip vortex cavity model is the major novelty in this thesis.
The hydrodynamic flow solution is obtained from a potential flow based solver ESPPRO, which includes analytical models of sheet cavitation and tip vortex cavitation. The hydroacoustic numerical model developed within this thesis, DoLPHiN, is a Python-based code that is primarily designed to accept input from ESPPRO; but during the research, the code has also been adapted to read input from the commercial, finite-volume-based Navier-Stokes solver, STAR-CCM+.
The numerical model implementations are verified through analytical case studies for simple geometrical shapes, such as a pulsating sphere and an oscillating cylindrical cavity. The verification study is further extended for propeller geometries by identifying approximate reference solutions in simplified operating conditions. The numerical tool is validated for industrial application through comparison of its noise prediction with model-scale and full-scale noise measurements. Specific characteristics of the propeller noise spectrum are identified in order to evaluate its noise prediction capabilities. The uncertainty factors involved when validating with experimental measurements are also explored in detail. Furthermore, a design study is presented, which shows potential use of the numerical tool in practical propeller design and optimization applications.
Plastic litter is introduced into the oceans from land-based sources located in many countries around the world. Marine plastic pollution may therefore be attributable to multiple states, resulting in shared state responsibility. This article discusses the issue of shared state responsibility for land-based marine plastic pollution by examining (i) primary rules of international law concerning the prevention of land-based marine plastic pollution; (ii) secondary rules of international law on this subject; and (iii) possible ways of strengthening the primary rules. It concludes that the barrier for the invocation of state responsibility may become higher in cases of shared state responsibility. Three cumulative solutions to this problem are proposed: elaborating the obligation of due diligence, strengthening compliance procedures, and interlinking regimes governing the marine environment and international watercourses.
This paper presents experimental measurements of beaching times for buoyant microplastic particles released, both in the pre-breaking region and within the surf zone. The beaching times are used to quantify cross-shore Lagrangian transport velocities of the microplastics. Prior to breaking the particles travel onshore with a velocity close to the Lagrangian fluid particle velocity, regardless of particle characteristics. In the surf zone the Lagrangian velocities of the microplastics increase and become closer to the wave celerity. Furthermore, it is demonstrated that particles having low Dean numbers (dimensionless fall velocity) are transported at higher mean velocities, as they have a larger tendency to be at the free-surface relative to particles with higher Dean numbers. An empirical relation is formulated for predicting the cross-shore Lagrangian transport velocities of buoyant microplastic particles, valid for both non-breaking and breaking irregular waves. The expression matches the present experiments well, in addition to two prior studies.
Despite the relatively rich literature on the omnipresence of microplastics in marine environments, the current status and ecological impacts of microplastics on global Marine Protected Areas (MPAs) are still unknown. Their ubiquitous occurrence, increasing volume, and ecotoxicological effects have made microplastic an emerging marine pollutant. Given the critical conservation roles of MPAs that aim to protect vulnerable marine species, biodiversity, and resources, it is essential to have a comprehensive overview of the occurrence, abundance, distribution, and characteristics of microplastics in MPAs including their buffer zones. Here, extensive data were collected and screened based on 1565 peer-reviewed literature from 2017 to 2020, and a GIS-based approach was applied to improve the outcomes by considering boundary limits. Microplastics in seawater samples were verified within the boundaries of 52 MPAs; after including the buffer zones, 1/3 more (68 MPAs) were identified as contaminated by microplastics. A large range of microplastic levels in MPAs was summarized based on water volume (0–809,000 items/m 3) or surface water area (21.3–1,650,000,000 items/km 2), which was likely due to discrepancy in sampling and analytical methods. Fragment was the most frequently observed shape and fiber was the most abundant shape. PE and PP were the most common and also most abundant polymer types. Overall, 2/3 of available data reported that seawater microplastic levels in MPAs were higher than 12,429 items/km 2, indicating that global MPAs alone cannot protect against microplastic pollution. The current limitations and future directions were also discussed toward the post-2020 Global Biodiversity Framework goals.
The impact of the growing cruise ship industry on air quality levels was investigated at the port of Copenhagen, Denmark. In 2018, 345 cruise ships visited Copenhagen, emitting 291 tons of NOx near the city centre. A spatiotemporal cruise ship emission inventory was developed for 2018 based on port list information, engine data, main and auxiliary engine power functions, and NOx emission factors, and was implemented in the OML-Multi atmospheric dispersion model. Evident plume effects from the cruise ships, which were traced by introducing the concept of likely concentration contribution, were obtained in the modelled and measured concentrations at Langelinie Quay, which is the busiest cruise ship terminal in Copenhagen port. Hourly peak values of NOx well above 200 μg m−3 were obtained at the top of a residential building at Langelinie Quay. The emissions from cruise ships were increasing the annual concentration of NO2 in the port area by up to 31% at ground level, and 86% 50 m above the ground in comparison to the urban background level. No exceedance of the European annual limit value of NO2 was obtained. The short-term impact of cruise ships was more pronounced with local exceedances of the hourly European limit value for NO2. Increasing cruise ship activity in Copenhagen port leads to air quality deterioration on short time scales with implications for human health.
Taking offspring in a problem of ship emission reduction by exhaust gas recirculation control for large diesel engines, an underlying generic estimation challenge is formulated as a problem of joint state and parameter estimation for a class of multiple-input single-output Hammerstein systems with first-order dynamics, sensor delay, and a bounded time-varying parameter in the nonlinear part. This brief suggests a novel scheme for this estimation problem that guarantees exponential convergence to an interval that depends on the sensitivity of the system. The system is allowed to be nonlinear, parameterized, and time dependent, which are characteristics of the industrial problem we study. The approach requires the input nonlinearity to be a sector nonlinearity in the time-varying parameter. Salient features of the approach include simplicity of design and implementation. The efficacy of the adaptive observer is shown on simulated cases, on tests with a large diesel engine on test bed, and on tests with a container vessel.