A finite volume model for two-layer shallow water flow in microtidal salt-wedge estuaries is presented in this work. The governing equations are a coupled system of shallow water equations with ...source terms accounting for irregular channel geometry and shear stress at the bed and interface between the layers. To solve this system we applied the Q-scheme of Roe with suitable treatment of source terms, coupling terms, and wet-dry fronts. The proposed numerical model is explicit in time, shock-capturing and it satisfies the extended conservation property for water at rest. The model was validated by comparing the steady-state solutions against a known arrested salt-wedge model and by comparing both steady-state and time-dependant solutions against field observations in Rjecina Estuary in Croatia. When the interfacial friction factor λi was chosen correctly, the agreement between numerical results and field observations was satisfactory.
Krvavica, N.; Travaš, V., and Ožanić, N., 2017. Salt-wedge response to variable river flow and sea-level rise in the microtidal Rječina River Estuary, Croatia. A finite-volume model for two-layer ...shallow-water flow is presented and applied to study the dynamic response of a salt wedge in a microtidal estuary to changes in river flow rate and sea-level rise (SLR). First, the shape of the arrested salt wedge was computed for different hydrographic conditions. Next, the response of the salt wedge to highly variable river flow was investigated. Finally, this model was applied to predict the impacts of the SLR on salinity intrusions in the Rječina River Estuary. To assess the model performance and to examine the salinity structure in the estuary, a field-sampling campaign was conducted during 2014 and 2015. Field observations revealed negligible longitudinal density variations in both freshwater and saltwater layers and highly stratified conditions for all considered river flow rates and sea levels. Furthermore, the maximum buoyancy frequency, computed as a measure of vertical stratification, was among the highest ever reported in field investigations. The behavior of the salt-wedge intrusion depends mainly on the river flow rate, although sea level and channel geometry become more influential under low-flow conditions. Computed salt-wedge shapes and propagation rates agreed well with field observations. The salinity structure in the Rječina River Estuary is not expected to change in the future for tested SLR scenarios, although stronger salt-wedge intrusion is predicted by the numerical model.
Coastal water quality management is a public health concern, as water of poor quality can potentially harbor dangerous pathogens. In this study, we employ routine monitoring data of EscherichiaColi ...and enterococci across 15 beaches in the city of Rijeka, Croatia, to build machine learning models for predicting E.Coli and enterococci based on environmental features. Cross-validation analysis showed that the Catboost algorithm performed best with R2 values of 0.71 and 0.69 for predicting E.Coli and enterococci, respectively, compared to other evaluated algorithms. SHapley Additive exPlanations technique showed that salinity is the most important feature for forecasting both E.Coli and enterococci levels. Furthermore, for low water quality sites, the spatial predictive models achieved R2 values of 0.85 and 0.83, while the temporal models achieved R2 values of 0.74 and 0.67. The temporal model achieved moderate R2 values of 0.44 and 0.46 at a site with high water quality.
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•Coastal water FIB measurements were used to train machine learning models.•Machine learning models trained with Catboost showed peak performance.•Strong R2 scores (0.85, 0.74) were achieved for spatial and temporal FIB prediction.•SHapley Additive exPlanations (SHAP) was used to analyze FIB environmental influences.•SHAP analysis showed salinity to be a major FIB stressor.
Microplastics (MPs) are found to be omnipresent in marine environments and their production and disposal are constantly increasing. In order to control and mitigate their negative effects on the ...environment, it is important to understand the processes involved in their transport and sinking. Most of the conducted experimental studies on MP in water have focused on exploring the settling behavior of MP particles under static flow conditions. This paper presents the results of an experimental study of MP particles in a horizontal stream of water. A series of laboratory experiments were carried out to measure the drag coefficient of quasi-radially-symmetric MP particles with different shapes (spheres, cubes, and crosses) and sizes (1.5 to 3.0 mm). In the study, the relationship between the drag coefficient and flow conditions represented by the local Reynolds number is investigated. The experimental procedure was validated, and a total of 400 measurements were performed. Values of the measured drag coefficient ranged from 0.8 to 2.5 for the values of Re from 40 to 300. The results show that the shape of MP particles in the water stream considerably influences the particle drag coefficient, with a rather complex relationship between the drag coefficient and flow conditions.
The interfacial friction and entrainment were investigated in a microtidal salt-wedge estuary. A detailed sampling campaign was conducted in the Rječina River estuary in Croatia from January 2014 to ...June 2015. The observed vertical profiles of salinity
s
and temperature
T
confirmed the presence of a highly stratified estuary, represented by an upper layer of freshwater separated from a lower salt-wedge by a sharp density interface. The entrainment rate
E
across the interface was estimated by a two-layer box-model, based on the observed freshwater flow rate
Q
and layer-averaged salinity. Interfacial friction factor
λ
i
was estimated by fitting the results of a numerical model to the observed interface depths. For this purpose we applied a numerical two-layer shallow water model extended to account for irregular non-prismatic cross sections of the channel. We found that in microtidal conditions, the strength of the stratification is reduced with increasing
Q
. Furthermore, we found that as
Q
increases, so does the shear velocity, the interfacial friction factor and the vertical mixing across the interface. More detail analysis showed that
E
may be parametrized by bulk non-dimensional parameters, in particular, a combination of bulk Richardson number
Ri
and average friction factor
λ
, which accounts for the channel bed friction and the interfacial friction. On the other hand,
λ
i
can be linked to a combination of Reynolds number
Re
and bulk Richardson
Ri
. Contrary to previous studies, we showed that in field conditions,
λ
i
may increase with
Re
.
In order to achieve optimal flow velocity in stationary flow condition in pressurized pipe systems, it is necessary to determine an optimal value of pipe diameter. It should be noted that even for a ...simple pipe network with pipes connected in only few numbers of loops, the determination of the optimal pipe diameter is an unintuitive problem and from the mathematical point of view a nonlinear problem that requires some iterative process with a relatively complicated update procedure between iterations. Usually, the optimization algorithms are based on stochastic methods. A deterministic approach is proposed that satisfies the prescribed constrains in terms of the specified flow velocity in the pressurized system of pipes. The presented iterative algorithm for optimizing the pipe diameter is implemented in computer code PIPENET3D (written in FORTRAN90) and used for hydraulic analysis of steady flow in an arbitrary pressured pipe system.
Analysis of Microplastic Particle Transmission Holjević, Toni; Travaš, Vanja; Kranjčević, Lado ...
Pomorski zbornik,
01/2022, Letnik:
Special edition 4, Številka:
4
Journal Article, Web Resource
Recenzirano
Odprti dostop
The progressive increase in the mass of microplastics in the ecosystem obliges us to urgently define measures to reduce its adverse effects, which primarily requires an understanding of the genesis ...of its presence and the dynamics of expansion through the biosphere. This paper aims to contribute to the understanding of the dynamics of microplastic particle motion, especially in the context of deposition rate with respect to microplastic material density, microplastic particle size and especially with respect to microplastic particle shape (which significantly affects shape resistance forces). For this purpose, an overview of existing works in the field of modeling the motion of microplastics is given, and a numerical model for modeling the transport of microplastic particles in an inhomogeneous fluid velocity field for laminar flow is formed. The proposed model is thus based on a system of two nonlinear ordinary differential equations.
A three-dimensional finite element model for nonlinear dynamic analysis of seismic site and structure response is proposed and discussed. A series of numerical examples are presented which include ...modelling of a reinforced concrete frame with a portion of the ground consisting of various horizontal layers resting on rigid bedrock. The theoretical framework of the numerical analysis is based on continuum mechanics and irreversible thermodynamics. The spatial discretisation is performed by a combination of linear tetrahedral (ground) and hexahedral (structure) finite elements. The time integration is carried out by the leap-frog method. Total Lagrange formulation is adopted to account for large rotations and large displacements. To account for cracking and damage of the concrete, the frame structure is modelled by the microplane model. Damage and cracking phenomena are modelled within the concept of smeared cracks. Plasticity model is used for the modelling the reinforcement and the ground adopting the Von Mises and Drucker-Prager yield criteria, respectively. The influence of the ground layer configurations on the structure response is investigated and discussed. Comparative analysis shows the importance of the soil-structure interaction effects and material nonlinearity. Furthermore, with the implemented microplane model, which is aimed to be used for fracture and damage analysis of concrete, it is possible do assess the sustained structural damage.
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