NUMERICAL INVESTIGATIONS OF FLUSHING TIME IN SMALL MARINAS

This paper presents the results of 2D and 3D numerical simulations of sea circulation and water mass exchange for a marina with hypothetical dimensions (L/B=2 and L/B=0.5) to calculate the return flow factor. The return flow factor b was analyzed in relation to the marina entrance width, sea current velocity outside the marina (0, 1, 2, and 5 cm/s) and the sea surface level oscillation dynamics. The basic comparative parameter is the e-flushing time, Tf. The intensity of forced circulation is calculated to achieve time Tf of less than 10 days. The impact of the wind field on the e-flushing time for different marina widths was analyzed using a 3D numerical model. The numerical simulation results indicate that the e-flushing time Tf depends on the amplitude of the tidal signal, secondary to the width of the marina inlet, and the smallest amount on the velocity field in the outer region. Conversely, the return flow factor b depends on the width of the marina entrance, less on the tidal signal amplitude, and least on the current velocity outside the marina if currents are ≥ 1 cm/s. Forced circulation of 1 m3/s is only required for the marina with a smaller tidal amplitude (position Dubrovnik) to achieve Tf<10 days. If at the observed location wind is a dominant sea circulation generator, a wider marina entrance will allow faster sea exchange

NUMERICAL MODELLING OF THE MORPHODYNAMICS OF THE PLOČE GRAVEL BEACH IN RIJEKA

The morphodynamics of an artificial gravel beach in the Bay of Rijeka (Ploče Beach) was analyzed. The morphological changes of the beach face were monitored through an intense situation of gravitational surface wind waves from the incident SSW direction. A numerical modeling technique was applied, after initially establishing a numerical model for wave deformation. A model for sediment transport was established based on its results. Both models were based on the finite volume method. In addition, the partial contribution of the longshore component of sediment transport was analyzed based on empirical formulae. The modeling results were verified by comparing the positions and amounts of eroded/accumulated material along the beach with the processing of terrain images in the form of point clouds. The erosion and accumulation positions of the beach sediment material, obtained by numerical model simulations, corresponded to the surveyed positions. The total volume of eroded and accumulated material based on terrain image processing corresponded to the model values

Hindcast of Significant Wave Heights in Sheltered Basins Using Machine Learning and the Copernicus Database

Long-term time series of wave parameters play a critical role in coastal structure design and maritime activities. At sites with limited buoy measurements, methods are used to extend the available time series data. To date, wave hindcasting research using machine learning methods has mainly focused on filling in missing buoy measurements or finding a mapping function between two nearshore buoy locations. This work aims to implement machine learning methods for hindcasting wave parameters using only publicly available Copernicus data. Ensemble regression and artificial neural networks were used as machine learning methods and the optimal hyperparameters were determined by the Bayesian optimization algorithm. As inputs, data from the MEDSEA reanalysis wave model were used for the wave parameters and data from the ERA5 atmospheric reanalysis model were used for the wind parameters. The results of this study show that the normalized RMSE of the test data improved by 29% for Rijeka and 12% for Split compared to the original MEDSEA wave hindcast at buoy locations. The proposed method was extremely efficient in removing bias in the original MEDSEA hindcasts (e.g., NBIAS = -0.35 for Rijeka) to negligible values for both Split and Rijeka (NBIAS < 0.03)

Contribution of Wind and Waves in Exchange of Seawater through Flushing Culverts in Marinas

In this work contribution of wind and waves on the water exchange through flushing culverts between the marina and surrounding water body have been investigated. The hybrid modelling technique was used. Results of culvert discharge, produced by waves on physical model, were implemented in 3D circulation model. Using circulation model, the optimum flushing culverts position in body of breakwater was defined for marinas with hypothetical geometry, characteristic for Croatian Adriatic Sea. The model was forced by wind from 8 directions and velocities 1-5 Bf. Furthermore, numerical simulations were also done for a real - world marina – the Ičići marina. The real breakwater geometry and hydrographic conditions (depths, tides, sea temperatures and salinity) were included. The analysis results show that the flushing culverts may have important contribution to seawater exchange in marina, even in summertime situations with significant wave heights of 0.5 m and duration of 6 hours

Analysis of beach nourishment and construction in Croatia

Plaže istočne obale Jadrana čine temelj turističke ponude Hrvatske, ali su pod iznimnim pritiskom turizma i klimatskih promjena. Za upravljanje obalom potrebni su podatci, a zasad izostaje i nacionalna strategija. Podatci o plažama prikupljeni su iz regionalnih programa svake županije, potom su prikupljeni podatci o postupku dohranjivanja obale putem ankete jedinica lokalne samouprave, a posebno su i analizirane snimke iz zraka za podatke o nasipavanju (tj. izgradnji) obale. Hrvatska ima 1904 pretežito male šljunčane plaže, provodi dohranu svake druge godine u malim količinama, a ujedno je i nasipala 27 % nove površine, sve pretežito za potrebe plaža, luka i turizma.Beaches on the eastern Adriatic coast are the basis of Croatia’s tourism offering while also being under pressure from climate change. Data is necessary to manage beaches effectively, but data is lacking as well as the long awaited national strategy for coastal management. This paper collected data about beaches from regional documents, nourishment data was obtained by survey from local municipalities while beach construction data was obtained from aerial photogrammetry. Croatia has more than 1904 small gravel beaches and nourishment is performed in small increments beinnaly, while more than 27 % of existing beach area has been constructed all primarily for the needs of beaches, marines and tourism

Use of culverts for improving exchange of seawater in ports

Kakvoća mora unutar ograđenih akvatorija može biti ugrožena nezadovoljavajućom količinom izmjene mora. Ovim radom se prikazuju propusti (cijevni, pločasti i kanalski) kao efikasno rješenje u svrhu izbjegavanja stagnacije mora. Uz pozitivan utjecaj povećane cirkulacije morske vode kroz akvatorij prisutnošću propusta, valna energija koja tijekom olujnog vremena penetrira kroz propust u zaštićeno područje može biti ograničavajući čimbenik. Pregledom prethodnih istraživanja i konstrukcijskih rješenja propusta na hrvatskoj obali, u ovom radu se predlažu osnovne preporuke za oblikovanje propusta.The quality of seawater in enclosed water basins can be negatively affected by inadequate exchange of seawater. Various culverts (pipe culverts, box culverts, and duct culverts) are presented in the paper as an efficient solution for preventing stagnation of seawater. In addition to positive influence of culvert-induced higher circulation of seawater in the basin, the wave energy penetrating during stormy weather into the protected area via culverts may be a limiting factor. Basic culvert shaping recommendations, relying on the study of previous research and structural solutions for culverts used on Croatian coast, are also presented in the paper

A numerical analysis of pollutant dispersion from the chimney of the medical waste incinerator in the urban environment

Provedene su numeričke analize širenja onečišćenja iz dimnjaka spalionice medicinskog otpada u urbaniziranom okruženju. Istraživanje je usmjereno na iznalaženje pozicije i visine dimnjaka čime se osigurava da poniranje oblaka onečišćenja prema tlu pri opstrujavanju zgrade s dimnjakom (tzv. downwashing) posljedično ne ugrožava zdravlje ljudi u neposrednoj blizini dimnjaka. Analiziran je slučaj prisutnosti objekta-zgrade idealizirane geometrije (uz varijaciju visine i duljine zgrade) ispred objekta tipske spalionice s dimnjakom (fiksnih dimenzija), te slučaj izvedbe dimnjaka na vrhu zgrade idealizirane geometrije (uz varijaciju pozicije i visine dimnjaka) bez zasebnog objekta spalionice. Praćene su koncentracije onečišćenja na dva metra iznad tla. Rezultati provedenog istraživanja pokazali su da u realnim uvjetima izgradnje (prisutnost zgrada uokolo objekta spalionice) i okoliša (brzina i smjer vjetra) dimnjak treba biti viši za 20 metra od obližnjeg objekta-zgrade ili izveden na sredini krovne konstrukcije u visini 20 metra, a ne uz tehnološku zgradu za postupanje s otpadom (spalionica) sa visinom 2,5 puta većom od same spalionice.Numerical analyses were carried out on the dispersion of pollution from the chimney of a medical waste incinerator in an urban environment. The research focused on determining the location and height of the chimney to ensure that the descent of pollution plumes towards the ground, known as “downwashing”, does not pose a health risk to people in the immediate vicinity of the chimney. Two scenarios were investigated in the study: the presence of a building with idealized geometry (with height and length variations) in front of a typical waste incinerator with a fixed size chimney and the case of a chimney on top of a building with idealized geometry (with position and height variations) without a separate waste incinerator. The pollutant concentrations were monitored at a height of 2 meters above the ground. The results of the study show that under realistic design conditions (presence of surrounding buildings) and environmental factors (wind speed and direction), the chimney should be positioned 20 meters higher than the adjacent building or in the middle of the roof structure at a height of 20 meters. This is better than a chimney next to the waste disposal facility (incinerator) that is 2.5 times higher than the incinerator itself

Nomogramme zur Berechnung der Funktionalität von Fischwegen an kleinen Wehren

Izgradnja bioloških staza (u inženjerskoj praksi uobičajeno ribljih staza) u određenoj mjeri umanjuje negativne ekološke utjecaje gospodarskog razvoja i omogućuje ostvarivanje uzdužne povezanosti vodotoka koja je ključna za zadovoljenje migracijskih potreba vodnih organizama. Tehničke riblje staze su od najčešće korištenih tipova ribljih staza za uzvodnu migraciju riba. Cilj ovog rada bio je izvesti nomograme za provedbu direktnog proračuna funkcionalnosti u postupku projektiranja tehničkih ribljih staza. S obzirom na riblje vrste na području RH u ovom radu su analizirana dva tipa: bazenske riblje staze i riblje staze s vertikalnim otvorima. Za funkcioniranje tehničkih ribljih staza najvažniji parametri su: dubina vode, kritična brzina tečenja u prolazima, osiguranje minimalnog protoka i volumetrijska disipacija snage u definiranim granicama. Za potrebe provedbe istraživanja izrađeni su fizički model u laboratoriju i numerički model u OpenFOAM-u. Na temelju provedenih istraživanja definirane su osnovne preporuke za projektiranje geometrije ribljih staza u hidrauličkim uvjetima određenim ribljim vrstama na području Republike Hrvatske.The construction of biological passes (usually fish passes in engineering practice) reduces, to a certain degree, negative ecological impacts of economic development and enables the achievement of longitudinal watercourse connectivity that is vital for meeting migratory needs of water organisms. Technical fish passes are one of the most used types of fish passes for upstream fish migration. The goal of the paper was to derive nomograms for implementing direct calculations of functionality in the technical fish pass design procedure. Considering fish species in the area of the Republic of Croatia, the paper analysed two types: basin fish passes and fish passes with vertical openings. The most important parameters for technical fish pass functionality are water depth, critical flow velocity, ensuring minimum flow and volumetric energy dissipation within defined limits. For investigation purposes, a physical model in the lab and a numerical model in OpenFOAM were developed. Based on the conducted investigation, basic recommendations for designing fish pass geometry in hydraulic conditions determined by fish species in the area of the Republic of Croatia were defined.Der Bau von Wanderhilfen (in der Praxis meistens von Fischwegen) verringert in gewissem Maße ökologisch negative Auswirkungen der wirtschaftlichen Entwicklung und ermöglicht die Längsverbindung von Fließgewässern, was für die Befriedigung der Wanderungsbedürfnisse von Wasserorganismen entscheidend ist. Die Fischtreppe ist der am meisten gebaute Typ der Fischaufstiege. Das Ziel dieses Beitrags war, Nomogramme zur Berechnung der Funktionalität bei der Planung von Fischwegen zu erstellen. Die heimischen Fischarten in Kroatien berücksichtigend, wurden zwei Fischpasstypen analysiert: Beckenpässe und Schlitzpässe. Damit die Fischwege ihrer Funktion gerecht werden, müssen die wichtigsten Parameter, d.h. die Wassertiefe, die kritische Strömungsgeschwindigkeit in den Pässen, Sicherstellung eines minimalen Durchflusses und volumetrische Kraftdissipation in definierten Grenzen in Betracht gezogen werden. In dieser Untersuchung wurden ein physisches Modell im Laboratorium und ein numerisches Modell in OpenFOAM erstellt. Auf Grund der durchgeführten Untersuchungen konnten Grundempfehlungen zur Projektierung der Geometrie von Fischwegen in hydraulischen, durch bestimmte Fischarten festgestellten Bedingungen auf dem Gebiet der Republik Kroatien gegeben werden

Analysis of the impact of winds, tide oscillations and density distribution on the sea exchange through culverts in the marinas as exemplified by the Ičići marina

Prikazani su rezultati provedenih 3D numeričkih simulacija cirkulacije i izmjene mora s ciljem kvantifikacije doprinosa cijevnih propusta u izmjeni mora iz akvatorija marine s morem iz okolnog područja. Osim djelovanja vjetra i plimnih oscilacija u numeričkom modelu uvažena je i prostorno/vremenska promjenjivost temperature i saliniteta u profilima otvorenih granica modela, propusta i ulaza u marinu. Prvotno je analizirana marina hipotetskih geometrijskih obilježja: duljina 300m, širina 150m, varijabilne dubine od 3 do 7m. Varirana je širina ulaza u marinu (25m i 50m), pozicije cijevnih propusta (4 pozicije), smjer i brzina vjetra (N, NE, E, SE, S, SW, W, NW ; 1, 3, 5 Bf), geografska lokacija (sjeverni jadran – Rovinj ; južni jadran – Dubrovnik), doprinos gradijenta gustoće mora. Nastavno su provedene numeričke simulacije za marinu Ičići, uzimajući u obzir stvarnu geometriju zaštitnih građevina (lukobrana), realistične oceanografske uvjete (dubine, dinamika morskih razi, temperatura i salinitet mora) i djelovanje vjetra. Temeljem dobivenih rezultata predložena je i praktična metodologija za izbor pozicije cijevnih propusta u tijelu zaštitne građevine marine.The paper presents the results of the conducted 3D numerical simulations of the sea circulation and exchange with the aim to quantify the contribution of pipe culverts to the sea exchange from the marina area and the surrounding sea. In addition to wind action and tide oscillations, the numerical model also takes into account the spatial/temporal changes in temperature and salinity in the profiles of open boundaries of the model, culverts and the marina entrance. Initially, a marine of hypothetical geometric characteristics was analyzed – with a length of 300m, width of 150m and variable depth of 3 - 7m. The following elements were varied: the width of the marine entrance (25m and 50m), positions of pipe culverts (4 positions), wind direction and velocity (N, NE, E, SE, S, SW, W, NW; 1, 3, 5 Bf), geographical location (northern Adriatic – Rovinj; southern Adriatic – Dubrovnik) and the contribution of the sea density gradient. Following this, numerical simulations were conducted for the Ičići marina by taking into consideration the actual geometry of the protection facilities (breakwater), realistic oceanographic conditions (depth, sea level dynamics, sea s temperature and salinity) and wind action. Based on the obtained results, a practical methodology for selecting the positions of pipe culverts in the structure of the marina protective facility was also proposed