Estuarine Hydrodynamics Under Sea Level Rise

Estuaries provide a wide range of environmental, cultural, social, and economic services. However, sea level rise (SLR) is increasingly threatening these services in estuaries due to their low-lying topography and proximity to the open ocean. As such, the sustainable management of estuaries requires an evidence-based understanding of how different estuaries may respond to SLR over time and space. Assessing SLR impacts in estuaries can either be undertaken on an individual site basis or via broader approaches that may be relevant to many estuaries. This thesis utilises the latter approach and, to this aim, a large ensemble of idealised estuarine hydrodynamic simulations were developed and tested. The results are then analysed, (i) to present a systematic hydrodynamic understanding of different estuary types in present-day and future conditions, (ii) to detail the influence of SLR on tidal energy dynamics, (iii) to establish a framework for assessing SLR impacts on estuaries worldwide, and (iv) to guide decision-makers in establishing holistic, evidence-based management plans for estuaries. Initially, over 2000 idealised estuary models were simulated to determine how SLR influences the tidal dynamics of various systems with different boundary conditions (e.g., different estuary length, depth, convergence, entrance condition, roughness, river discharge). These results indicate that SLR can lead to tidal range amplification in some estuaries, although entrance restriction effects may offset this phenomenon. Further, SLR is likely to alter the distributions and magnitudes of tidal currents, tidal prism, tidal asymmetry, tidal energy, and the location of tidal energy harvesting sites. To link the idealised findings with real-world estuaries, 26 real-world estuaries were simulated and analysed under present-day and future sea level conditions. This information was used to identify sites that are most vulnerable to SLR-induced tidal variations. These results were consistent with the idealised findings and highlighted their transferability to certain estuaries worldwide without an existing, detailed hydrodynamic model. Long, weakly convergent estuaries with higher friction, river inflows and shallower water depths will likely experience significant changes in tidal dynamics due to SLR. The numerical approach and learnings presented in this thesis could be used to assess and predict cumulative SLR impacts on estuaries globally

A review of liquid droplet impacting onto solid spherical particles:A physical pathway to encapsulation mechanisms

Encapsulation has received a surge of interest in the biotechnological, chemical and pharmaceutical fields and other industrial processes, owing to numerous applications such as in fluidized catalytic cracking, antenna and wire fabrication, catalytic reactions, and process industries. For example, encapsulation is a technique used to entrap active agents within a carrier material and can be achieved through impact of droplets of encapsulating material on the solid particles of active agents. Considering the importance of dynamics of drop-particle collision, which directly affects the quality of film deposition during encapsulation, the current review is presented to investigate various aspects of drop impact on dry solid spherical surfaces, which is still lacking in the existing literature and aims at encouraging more researchers to study this topic. Also, this review covers frequent examples of droplet impingement onto curved surfaces, with a focus on the latest scientific findings in droplet impacting solid spherical surfaces

Optimal reservoir operation using Nash bargaining solution and evolutionary algorithms

Optimizing reservoir operation is critical to ongoing sustainable water resources management. However, different stakeholders in reservoir management often have different interests and resource competition may provoke conflicts. Resource competition warrants the use of bargaining solution approaches to develop an optimal operational scheme. In this study, the Nash bargaining solution method was used to formulate an objective function for water allocation in a reservoir. Additionally, the genetic and ant colony optimization algorithms were used to achieve optimal solutions of the objective function. The Mahabad Dam in West Azerbaijan, Iran, was used as a case study site due to its complex water allocation requirements for multiple stakeholders, including agricultural, domestic, industrial, and environmental sectors. The relative weights of different sectors in the objective function were determined using a discrete kernel based on the priorities stipulated by the government (the Lake Urmia National Restoration Program). According to the policies for the agricultural sector, water allocation optimization for different sectors was carried out using three scenarios: (1) the current situation, (2) optimization of the cultivation pattern, and (3) changes to the irrigation system. The results showed that the objective function and the Nash bargaining solution method led to a water utility for all stakeholders of 98%. Furthermore, the two optimization algorithms were used to achieve the global optimal solution of the objective function, and reduced the failure of the domestic sector by 10% while meeting the required objective in water-limited periods. As the conflicts among stakeholders may become more common with a changing climate and an increase in water demand, these results have implications for reservoir operation and associated policies

Large eddy simulation of pseudo shock structure in a convergent-long divergent duct

In this paper, the Pseudo shock structure in a convergent–long divergent duct is investigated using large eddy simulation on the basis of Smagorinsky–Lilly, Wall-Adapting Local Eddy-Viscosity and Algebraic Wall-Modeled LES subgrid models. The first objective of the study is to apply different subgrid models to predict the structure of Lambda form shocks system, while the ultimate aim is to obtain further control of the shock behavior. To achieve these goals, the dynamic grid adaption and hybrid initialization techniques are applied under the 3D investigation to reduce numerical errors and computational costs. The results are compared to the existing experimental data and it is found that the WMLES subgrid model results in more accurate predictions when compared to the other subgrid models. Subsequently, the influences of the divergent section length with the constant ratio of the outlet to throat area and, the effects of discontinuity of the wall temperature on the flow physics are investigated. The results indicate that the structure of compressible flow in the duct is affected by varying these parameters. This is then further discussed to provide a deeper physical understanding of the mechanism of Pseudo shock motion

Coastal wetlands can be saved from sea level rise by recreating past tidal regimes

Climate change driven Sea Level Rise (SLR) is creating a major global environmental crisis in coastal ecosystems, however, limited practical solutions are provided to prevent or mitigate the impacts. Here, we propose a novel eco-engineering solution to protect highly valued vegetated intertidal ecosystems. The new ‘Tidal Replicate Method’ involves the creation of a synthetic tidal regime that mimics the desired hydroperiod for intertidal wetlands. This synthetic tidal regime can then be applied via automated tidal control systems, “SmartGates”, at suitable locations. As a proof of concept study, this method was applied at an intertidal wetland with the aim of restabilising saltmarsh vegetation at a location representative of SLR. Results from aerial drone surveys and on-ground vegetation sampling indicated that the Tidal Replicate Method effectively established saltmarsh onsite over a 3-year period of post-restoration, showing the method is able to protect endangered intertidal ecosystems from submersion. If applied globally, this method can protect high value coastal wetlands with similar environmental settings, including over 1,184,000 ha of Ramsar coastal wetlands. This equates to a saving of US$230 billion in ecosystem services per year. This solution can play an important role in the global effort to conserve coastal wetlands under accelerating SLR

An investigation on the speed dependence of ice resistance using an advanced CFD+DEM approach based on pre-sawn ice tests

Over the past decades, the underlying mechanism of level ice resistance changing with ship speed has not been fully understood, particularly the resistance component due to ship interactions with broken ice pieces. Pre-sawn ice test can negate icebreaking component from the whole resistance of a ship in level ice, providing an effective approach to decompose ship-ice interactions and investigate the speed-dependent resistance from broken ice pieces. This work has built a computational model that can realistically simulate a ship advancing in a pre-sawn ice channel. The model applies Computational Fluid Dynamics (CFD) to solve the flow around an advancing ship, which is coupled with an enhanced Discrete Element Method (DEM) to model pre-sawn ice pieces. Model-scale experiments have also been conducted at the Aalto Ice Tank to validate the simulations, which shows the computational model can provide a reasonable estimation of the pre-sawn ice's resistance and movement around the ship. Upon validation, the dependence of ice resistance on ship speed was analysed. The simulations enable underwater monitoring of the ice motions, indicating that the speed dependence results from the mass of ice submerged underneath the ship and the displacement of broken ice induced by the ship. The identified relationships are more complex than the widely-used assumption that ice resistance linearly changes with ship speed in all cases, which provides a deeper understanding of ice resistance. As such, the findings from this study can potentially facilitate improvements in relevant empirical equations, useful for ship design, operational strategies and maritime management in polar regions

Offshore COVID-19 risk assessment based on a fishing vessel

Offshore crews often work near each other due to limited space, signifying a complex environment for the airborne transmission of the coronavirus (COVID-19). During offshore operations, a fishing vessel can be subjected to miscellaneous airflow conditions and will respond dynamically to ocean waves. To understand the risk of COVID-19 contagion, this research establishes a new computational model to analyse the airborne transmission of COVID-19 and develops effective mitigation strategies where possible. The concentration and coverage of coronavirus are scrutinised, considering typical airflows and wave-induced vessel motions. Furthermore, the COVID-19 infection risk is quantified using a probability index. The results show that the overall infection risk of a ship in tailwind is lower than in head or beam wind. Structural motions are for the first time coupled with the virus transmission, and it was found that the vessel’s oscillating movement in waves can reinforce the virus concentration in close proximity to the infected person and may help diffuse the virus outside the proximal region. The presented findings can inform the airborne contagion risks and corresponding hygienic measures for maritime and offshore operations, facilitating long-term human health in seas

The evolving landscape of sea-level rise science from 1990 to 2021

As sea-level rise (SLR) accelerates due to climate change, its multidisciplinary field of science has similarly expanded, from 41 articles published in 1990 to 1475 articles published in 2021, and nearly 15,000 articles published in the Web of Science over this 32-year period. Here, big-data bibliometric techniques are adopted to systematically analyse this large literature set. Four main research clusters (themes) emerge: (I) geological dimensions and sea-level indicators, (II) impacts, risks, and adaptation, (III) physical components of sea-level change, and (IV) coastal ecosystems and habitats, with 16 associated sub-themes. This analysis provides insights into the evolution of research agendas, the challenges and opportunities for future assessments (e.g. next IPCC reports), and growing focus on adaptation. For example, the relative importance of sub-themes evolves consistently with a relative decline in pure science analysis towards solution-focused topics associated with SLR risks such as high-end rises, declining ecosystem services, flood hazards, and coastal erosion/squeeze