EFFICIENCY ANALYSIS OF SHALLOW WATER NUMERICAL SCHEMES

Analizirana su fizikalna svojstva strujanja sa slobodnom površinom i pripadni jednodimenzijski i dvodimenzijski modeli plitkih voda, na osnovu čega su definirani jednodimenzijski i dvodimenzijski numerički modeli. Predložen je niz poboljšanja u smislu povećanja efikasnosti provođenja numeričkih simulacija strujanja sa slobodnom površinom. U završnom poglavlju rada detaljno se opisuje postupak paralelizacije numeričkih simulacija plitkih voda te se opisuje način efikasne raspodjele proračunskog opterećenja. Razvijeni su i testirani serijski i paralelni računalni kodovi za provođenje jednodimenzijskih i dvodimenzijskih simulacija strujanja sa slobodnom površinom.Free surface flow problems and corresponding one-dimensional and two-dimensional shallow water models are analyzed and on that basis, effective one-dimensional and two-dimensional numerical models are defined. Some improvements concerning efficient free surface flow numerical simulations are introduced. In final chapter of the thesis parallelization strategy of shallow water numerical simulations is elaborated in detail, and also ways to conduct efficient load balance among processors are presented. Parallel and serial computer codes for one-dimensional and two-dimensional simulations are developed, documented and tested

Numerical Simulation of River Inflows in Rijeka Bay Coastal Area

In this paper, a model of water flow in the Porto Baroš has been developed, which is the part of the Rijeka coastal area, for the purpose of its renovation and conversion. For numerical simulation purposes, the depth of the seabed of Port was previously performed, based on which the geometry and numerical domain of Port were made. By conducting the flow simulation, the analysis was carried out, after which the analyses of the conceptual solutions with the introduction of the pipe discharge were performed with the aim of reducing the water pollution of the Porto Baroš area. Port geometry will be made in commercial SMS software and numerical domains and simulations in OpenFOAM open-source software

MPI Associated Scalability of Open-Source CFD Codes for Oil Spill Assessment

General-purpose CFD codes have recently become an increasingly discussed alternative to standardized, simplified and usually empirically calibrated specialized tools for pollution analyses. Commonly, CFD codes tend to provide physically more sensible results and can indicate the underlying cause for a given problem. Use for ecological problems, however, has usually been avoided due to the sizes of computational domains and inherent complexity of the calculations that need to be conducted. Adoption in recent years is mostly driven by significant improvements in computational capabilities and advancements related to code and communication optimizations. Unfortunately, due to substantial branching of codes and accompanying indispensable communication routines, especially in opensource community, performance and consequently applicability of codes, can vary significantly. This article aims to outline key limitations and quantify performance gains which can be obtained in a high-performance computing environment through the use of different communication protocols, when evaluating typical pollution problems such as oil spills. Obtained results indicate that savings of up to 40% in computational time can be achieved, depending on the code and message passing interface implementation for a problem in question, thus demonstrating the importance of communication protocols

Numerical Modeling of Inclined Buoyant Jets for Different Flow Conditions

The processes of discharge of higher density effluent into the recipient of lower density occur during the release of wastewater into the sea from desalination process, which is increasingly common today due to the shortage of drinking water. During such discharges, the goal is to achieve the best possible mixing, so that the impact of water with a high salt concentration on the environment is as small as possible. Since the jet returns to the bottom because of the influence of gravity, the use of nozzles at an angle increases the zone in which mixing occurs. In this paper, a numerical model of effluent discharge was made and buoyancy jets inclined at 45o were observed for different flow regimes. The influence of density and velocity on jet characteristics is shown. The numerical model was developed in OpenFOAM, and a comparison with experimental data from previous research is presented

Numerical Simulation of River Inflows in Rijeka Bay Coastal Area

In this paper, a model of water flow in the Porto Baroš has been developed, which is the part of the Rijeka coastal area, for the purpose of its renovation and conversion. For numerical simulation purposes, the depth of the seabed of Port was previously performed, based on which the geometry and numerical domain of Port were made. By conducting the flow simulation, the analysis was carried out, after which the analyses of the conceptual solutions with the introduction of the pipe discharge were performed with the aim of reducing the water pollution of the Porto Baroš area. Port geometry will be made in commercial SMS software and numerical domains and simulations in OpenFOAM open-source software

Rijeka Bay 3D VOF Costal Flow Model

3D multiphase flow was analyzed in the area of Rijeka bay in the Adriatic Sea. The necessary morphology data in the range of interest of the coastal bottom area were collected and the spatial surface was created. The functionality of the 3D model was studied in the large area of the realistic stochastic structure of the bottom and the shore. The probability of meteorological conditions and wind impact in the model has been shown. The obtained results give a detailed view of the velocity fields in the horizontal plane of different depths. Numerical simulation was performed in open source program OpenFOAM with Volume of Fluid (VOF) method using the Eulerian approach. For solving this problem interFOAM solver for two incompressible, isothermal, immiscible fluids was used. The resulting simulations showed dominant flow from the western coast of the Krk island to the eastern coast of the Istrian peninsula. Seawater enters the bay through the Srednja Vrata and Tihi Kanal and exits the bay through the Vela Vrata. This research has shown that using a VOF method can be successfully implemented for describing fluid motion in large areas such as bays and oceans

Numerical analysis of Wells turbine for wave power conversion

The sea wave energy is one of the high potential renewable energy sources. The Wells turbine as the main part of the Oscillalting Water Column energy plant is analyzed in this paper.  The Wells turbine uses air flow produced by the pressure change inside the oscillating water column. Efficient energy transformation is achieved with the use of self-rectifying Wells air turbine. Since the tangential force of the rotor acts only in one direction even though airflow is oscillating, turbine rotates always in the same direction. Series of numerical simulations are performed using software package FLUENT for the wide span of non-dimensional flow rate coefficient (fi) and employing three different turbulent models. Structured numerical mesh and application of the axisymmetric periodical boundary conditions raised the accuracy of the numerical model while reducing computational load three times compared to the model with the fully meshed domain. Finally, operation of the OWC plant consisting of the air chamber and the turbine was simulated for the Adriatic sea maritime conditions, giving satisfactory energy output considering compact dimension of the whole plant

An Iterative Algorithm for Optimizing Pipe Diameter in Pressurized System

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

Rijeka Bay 3D VOF Costal Flow Model

3D multiphase flow was analyzed in the area of Rijeka bay in the Adriatic Sea. The necessary morphology data in the range of interest of the coastal bottom area were collected and the spatial surface was created. The functionality of the 3D model was studied in the large area of the realistic stochastic structure of the bottom and the shore. The probability of meteorological conditions and wind impact in the model has been shown. The obtained results give a detailed view of the velocity fields in the horizontal plane of different depths. Numerical simulation was performed in open source program OpenFOAM with Volume of Fluid (VOF) method using the Eulerian approach. For solving this problem interFOAM solver for two incompressible, isothermal, immiscible fluids was used. The resulting simulations showed dominant flow from the western coast of the Krk island to the eastern coast of the Istrian peninsula. Seawater enters the bay through the Srednja Vrata and Tihi Kanal and exits the bay through the Vela Vrata. This research has shown that using a VOF method can be successfully implemented for describing fluid motion in large areas such as bays and oceans

Analysis of Microplastic Particle Transmission

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