1,721,026 research outputs found
Advances in Environmental Hydraulics
Full text linkIn lieu of an abstract, this is an excerpt from the first page.Environmental Hydraulics (EH) is the scientific study of environmental water flows and their related transport and transformation processes affecting the environmental quality of natural water systems, such as rivers, lakes, and aquifers, on our planet Earth
Tidal range energy resource assessment of the Gulf of California, Mexico
Full text linkThere is growing interest in harnessing renewable energy resources in Latin America. Converting the energy of the tides into electricity has the distinct advantage of being predictable, yet the tidal range resource of Latin America is largely unquantified. The northern part of the Gulf of California (GC) in Mexico has a relatively large mean tidal range (4m–5m), and so could be a potential site for tidal range energy exploitation. A detailed quantification of the theoretical tidal range energy resource was performed using tidal level predictions from a depth-averaged barotropic hydrodynamic model. In addition, a 0-D operation modelling approach was applied to determine the power that can be technically extracted at four key sites. The results show that the annual energy yield ranges from 20 to 50 kWh/m2, while the maximum values are between 45 and 50 kWh/m2 in the vicinity of the Gulf of Santa Clara. Within the region, the Gulf of Santa Clara is one of the most promising, delivering a technical annual energy output of 125 GWh (ebb-only generation), 159 GWh (two-way) and 174 GWh (two-way with pumping) within an impoundment area of 10 km2. This equates to 50%, 40% and 33% of the absolute energy conversion relative to a much-studied reference site (Swansea Bay, UK) that has been under consideration as the world’s first tidal lagoon power plant. This study provides the basis for more detailed analysis of the GC to guide selection of suitable sites for tidal range energy exploitation in the region
Tidal range structure operation assessment and optimisation
Full text linkThe construction and operation of tidal range structures has been in the spotlight since the UK Government-commissioned Hendry Review advised that tidal power can play a significant role in the future energy mix. Tidal range proposals undergo rigorous scrutiny over their feasibility and environmental implications, despite presenting opportunities to deliver sustainable large-scale electricity supplies to the national grid. Preceding efforts to harness UK's untapped tidal energy resource through barrages were dismissed on the grounds of feasibility and environmental uncertainties. There is now a need to develop reliable engineering tools that can be used to improve designs under consideration. In this case a novel coastal ocean finite-element model is coupled with tidal power plant operation algorithms. This is applied to assess the performance of tidal range structures such as the Swansea bay and Cardiff tidal lagoons. The analysis takes into account an adaptive operation that aims to maximise the electricity output over variable spring–neap tidal conditions. It is demonstrated that such hydrodynamic models, when informed regarding the design of the constituent turbines and sluice gates, can simulate the power plant operation to provide insights to the energy output and hydro-environmental impacts of such schemes
Numerical and Experimental Modelling of Flow and Kinetic Processes in Serpentine Disinfection Tanks
Full text linkNew water directives impose strict regulations to reduce the footprint of treatment operations and contaminant levels, which suggest a performance review of water treatment facilities, including disinfection contact tanks. Serpentine contact tank units suggest plug flow to be the optimal hydrodynamic condition at which disinfection performance is maximized. However, previous studies indicate that flow exhibits a residence time distribution (RTD) which can be significantly distorted from what is dictated by plug flow. Over the years, there has been rising concern over the impact of such digressions from optimal hydraulic conditions on microbe inactivation and the regulation of potentially carcinogenic Disinfection By-Products (DBPs). With the growth of computing power and the advancement of computational models, the potential of contact tank water disinfection optimization by means of numerical modelling techniques can be assessed. In this study, Acoustic Doppler Velocity (ADV) and fluorescent tracer dye measurement campaigns are carried out to assess the hydraulic efficiency of a serpentine contact tank physical model and evaluating appropriate indicators. Then, three-dimensional Computational Fluid Dynamics (CFD) models are set up to simulate the hydrodynamic and solute transport processes for a variety of contact tank geometries examining the effects of inlet design, baffling configuration and tank scale. The simulation capability to reproduce the actual conditions is attested through comparisons against available laboratory results. The CFD approach is subsequently refined with appropriately selected kinetic models, describing the processes of disinfectant decay, pathogen inactivation and DBP formation. Results highlight that computational models can become invaluable tools for the simulation of disinfection processes as they can reproduce the conditions encountered experimentally to a satisfactory extent. Moreover, the optimization of hydraulic efficiency, as studied numerically, facilitates more uniform disinfectant contact time which corresponds to greater levels of pathogen inactivation and a more controlled by-product accumulation
Numerical and experimental modelling of flow and kinetic processes in serpentine disinfection tanks
Full text linkNew water directives impose strict regulations to reduce the footprint of treatment operations and contaminant levels, which suggest a performance review of water treatment facilities, including disinfection contact tanks. Serpentine contact tank units suggest plug flow to be the optimal hydrodynamic condition at which disinfection performance is maximized. However, previous studies indicate that flow exhibits a residence time distribution (RTD) which can be significantly distorted from what is dictated by plug flow. Over the years, there has been rising concern over the impact of such digressions from optimal hydraulic conditions on microbe inactivation and the regulation of potentially carcinogenic Disinfection By-Products (DBPs).
With the growth of computing power and the advancement of computational models, the potential of contact tank water disinfection optimization by means of numerical modelling techniques can be assessed. In this study, Acoustic Doppler Velocity (ADV) and fluorescent tracer dye measurement campaigns are carried out to assess the hydraulic efficiency of a serpentine contact tank physical model and evaluating appropriate indicators. Then, three-dimensional Computational Fluid Dynamics (CFD) models are set up to simulate the hydrodynamic and solute transport processes for a variety of contact tank geometries examining the effects of inlet design, baffling configuration and tank scale. The simulation capability to reproduce the actual conditions is attested through comparisons against available laboratory results. The CFD approach is subsequently refined with appropriately selected kinetic models, describing the processes of disinfectant decay, pathogen inactivation and DBP formation.
Results highlight that computational models can become invaluable tools for the simulation of disinfection processes as they can reproduce the conditions encountered experimentally to a satisfactory extent. Moreover, the optimization of hydraulic efficiency, as studied numerically, facilitates more uniform disinfectant contact time which corresponds to greater levels of pathogen inactivation and a more controlled by-product accumulation
On the association between Real and Accrual-based earnings management and corporate ownership in Greece
Full text linkGoing Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The impact of real-world constraints on tidal stream energy resource assessments
Full text linkThe potential of tidal stream energy in the UK is widely acknowledged to be significant, however, real-world constraints greatly limit the viable extraction of energy. Multiple lease sites for development have been withdrawn or remain in testing phases since their agreement, due to financial and technical challenges. This evidences the need to strategically define new areas for development based on refined assessments and inform the development of arrays at sites by identifying and overcoming the challenges and constraints.
To investigate the challenges of quantifying the tidal stream energy resource and examine a range of parameters affecting the resource, a low order idealised channel model is adopted. Different channel characteristics are applied to consider multiple case studies and blockage-corrected blade element momentum theory is used to represent turbine performance, also adopted in higher order modelling. The investigation highlights the inter-dependence of key parameters affecting tidal stream energy resource assessments, much like the constraints limiting the resource. Findings from the low order model inform the impact of modelling assumptions necessary for higher order modelling.
The use of a 2-D model enabled the investigation of bathymetry as a limiting practical constraint and the implication of the spatial variability of tidal stream energy at a site, which informed the development of a novel framework for designing arrays of homogeneous and heterogeneous turbine specifications (diameter and rated speed). Comparison of homogeneous and heterogeneous arrays in the Inner Sound highlights that adopting heterogeneous designs (with diameters of 5 - 20 m and rated speeds of 1.5 - 2.5 m/s) can increase power per turbine, while deploying significantly fewer turbines. The approach maximises usage of a site, whilst allowing the maximum allowable diameter of turbine to be deployed in areas, and exploits the spatial variation of the resource across a site by tailoring turbines to operate at appropriate rated speeds for a target capacity factor.
Finally, the framework is extended to identify multiple, independent, heterogeneous arrays across the Pentland Firth. The successive identification of arrays presents a feasible incremental development strategy for the Pentland Firth and minimises interference between arrays by accounting for how the resource responds to presence of arrays. A range of development options are proposed, based on different priorities. The tidal stream energy resource is assessed to be within 1 - 1.8 GW in the Pentland Firth with the consideration of real-world constraints, based on different development strategies and priorities
Developing a multi-scale parallelised coupled system for wave-current interactions at regional scales
Full text linkAt coastal areas, the interplay between waves and currents is crucial. This interaction impacts many phenomena and applications, highlighting the necessity for accuracy and speed
in the numerical representation of Wave-Current Interactions (WCI). These applications
encompass a wide spectrum, including coastal morphology, sediment transport, offshore
structure scouring, pollutant mixing, infrastructure design, marine energy projects, and
storm surges. The complexity in representing WCI stems from incorporating multi-scale
processes with diverse temporal and spatial scales. For example, wind wave periods range
from seconds to hours, while the wavelengths span from centimetres to kilometres. In
contrast, tides showcase much larger scales with periods in the order of hours and wave-lengths in the order of thousands of kilometres. Practically, reconciling all these processes
and scales within a single model is improbable, leading to the need for coupled systems
to address this challenge.
This study presents the development of a Python-interfaced multi-scale parallelised coupled modelling system for WCI. It is formed by coupling the spectral wave model Simulat ing WAves Nearshore (SWAN) with the 2-D shallow-water equation hydrodynamics model
Thetis. The coupling is facilitated by the Basic Model Interface (BMI), a lightweight
generic coupling interface. The impact of waves on current is introduced via the radiation
stress formulation, accompanied by the integration of wave-roller effects. Two coupling
options are offered: online and offline. The online choice supports both one-way and
two-way coupling, while the offline alternative is focused on one-way coupling.
Considering that only few existing WCI models report on validation in controlled environments, a suite of benchmarking scenarios is established consisting of analytical and
experimental scenarios in quasi 1-D and 2-D configurations. In these cases, sensitivity
analyses are performed spanning various parameters in both models. The results underscore the importance of customising each coupled configuration when WCI are prominent,
rather than solely relying on recommended or “default” values. Calibrated results align
well with the data and often showcase the same level of accuracy as other 3-D WCI. This
efficiency means less computational cost, as the developed model converges faster and
requires less CPU time compared to alternative options.
A month-long numerical representation of the field configuration located in Duck, North
Carolina, investigates the coupled system’s performance under moderate wind conditions.
This scenario serves to assess the influence of various coupling approaches on its predictions. Since this area is primarily influenced by waves and features low current speeds, the
coupling modes have minor impact on wave predictions. However, with coupling modes
transitioning from no to two-way coupling, the hydrodynamics predictions exhibit substantial improvement in regions where WCI are evident. The improved accuracy does not
encompass areas characterised by rip currents or other processes that require a vertical
discretisation for their hydrodynamics. Discrepancies between online and offline one-way
coupling configurations are evident, with the most pronounced differences observed in the
SWAN-to-Thetis coupling. They can be attributed to different interpolation methodologies.
Ultimately, the WCI system is applied in a regional configuration within the Orkney
archipelagos, UK. Specifically, the model simulates the waters of Westray Firth, a region
known for its energetic tidal conditions, to assess its capacity for effectively depicting
WCI phenomena in regional scales. Our predictions correlate well with the observations,
accurately mirroring the sinusoidal pattern of the measured wave parameters, usually
attributed to tidal effects. Furthermore, our model showcases similar precision to a 3-D
WCI coupled system implemented in the same region at lower computational cost.
The coupled system developed during this thesis presents an efficient tool for incorporating WCI phenomena across various scales, exhibiting performance comparable to its 3-D
counterparts. Its efficiency is highlighted by: (a) minimising computational resource usage, as evidenced by a 38% reduction in the number of cores employed during the Westray
Firth application; (b) reducing elapsed real times; and (c) accelerating convergence, such
as achieving convergence 1.4 to 18 times faster in benchmarking scenarios. It provides
a crucial foundation for researchers and stakeholders that seek to adopt a precise and
efficient solution, independent of the 3-D nature of WCI. This unlocks new opportunities for its versatile employment in a range of applications spanning from initial research
and decision-making stages to optimisation studies and to the development of forecasting
systems
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