43 research outputs found
Rad ne sadrži naslov na drugom jeziku.
A numerical model for simulating freshwater and seawater flow in highly stratified
estuaries was developed and validated. The governing equations for one-dimensional,
two-layer, and time-dependant shallow water flow were derived from the laws of
conservation of mass and linear momentum. The resulting equations are written
as a system of non-linear, hyperbolic, partial differential equations. To solve this
system, a finite volume method was used; specifically, a well-balanced Q-scheme for
two-layer shallow water flow in channels with irregular geometry was extended to
resolve additional friction and entrainment terms. Particular emphasis was placed on
the selection and validation of appropriate boundary conditions and the numerical
treatment of wet-dry transitions.
To assess the performance of the proposed model and examine the main physical
processes, a field sampling campaign was conducted during 2014-15 in the RjeÄina
River estuary. Entrainment rates were estimated from observed salinity profiles and
flow rates by a two-layer box model. Interfacial friction factors were determined by
fitting the numerical results to observed salt-wedge profiles. A steady arrested saltwedge
model, based on a finite difference method, was used for this purpose. When
the interfacial friction factor was calibrated, the numerical results agreed favourably
against field observations for both steady and variable flow conditions.
The combination of field observations and numerical experiments allowed for a
more detailed investigation of the main physical processes in microtidal estuaries.
The salt-wedge dynamics in the RjeÄina River estuary depends mainly on the river
flow rate, while the sea-level and channel geometry impose a second-order control.
Furthermore, a strong stratification persisted under all observed flow conditions.
Finally, none of the existing entrainment and interfacial friction laws proved adequate;
therefore, new empirical equations were proposed.IzraÄen je i validiran numeriÄki model za simuliranje teÄenja slane i slatke vode u
izrazito stratificiranim uÅ”Äima. VladajuÄe jednadžbe za jednodimenzijski, dvoslojni i
nestacionarni tok plitkih voda u koritima nepravilne geometrije, izvedene su iz zakona
oÄuvanja mase i koliÄine gibanja. RezultirajuÄe jednadžbe cine sustav nelinearnih,
hiperboliÄnih, parcijalnih diferencijalnih jednadžbi, a mogu se zapisati u vektorskom
obliku kao zakon održanja s izvornim Älanom.
Za rjeÅ”avanje navedenih jednadžbi koristila se metoda konaÄnih volumena, odnosno
dobro balansirana Q-shema za dvoslojno teÄenje u koritima nepravilne geometrije,
koja je modificirana kako bi se ukljuÄili dodatni Älanovi koji opisuju trenje i vertikalno
mijeÅ”anje. Posebna pozornost je posveÄena validiranju fizikalno relevantnog nizvodnog
rubnog uvjeta, definiranog dubinom gornjeg sloja na uÅ”Äu rijeke ili na mjestima
naglog suženja korita. TakoÄer je rijeÅ”en i problem pomicanja fronte donjeg sloja,
koji u numeriÄkom smislu predstavlja prijelaz izmeÄu suhog i mokrog dijela domene.
NumeriÄki model je verificiran za slucaj prizmatiÄnog korita s ravnim dnom, za
koji postoje analitiÄka rjeÅ”enja te za sluÄaj neprizmatiÄnog korita, usporedbom s
jednostavnijim stacionarnim numeriÄkim modelom temeljenim na metodi konaÄnih
razlika, odnosno implicitnoj trapeznoj metodi.
Terenska mjerenja na uÅ”Äu RjeÄine provedena su tijekom 2014. i 2015. godine pri
razliÄitim razinama mora i protocima rijeke, pri Äemu su mjerena fizikalna svojstva
vode na nekoliko profila duž uÅ”Äa. U tu svrhu, prvenstveno su se koristile CTD sonde
koje mjere tlak, temperaturu i elektriÄnu provodljivost po dubini vode. Iz navedenih
podataka izraÄunati su saliniteti i gustoÄa vode pomoÄu poznatih empirijskih izraza.
Ulazni protoci odreÄivali su se prema razini vode na pragu uzvodno od uÅ”Äa, za koji
je poznata protoÄna krivulja. AkustiÄni Dopplerov strujomjer se povremeno koristio
kako bi se validirali uzvodni protoci rijeke i izraÄunate brzine u pojedinim slojevima.
Intenziteti mijeÅ”anja meÄu slojevima odreÄeni su pomoÄu dvoslojnog Knudsenovog
modela na osnovu izmjerenih protoka i saliniteta vode u svakom sloju. Koeficijenti
trenja na razdjelnici slojeva dobiveni su metodom prilagodbe numeriÄkih rezultata
izmjerenim dubinama haloklina duž uÅ”ca RjeÄine. Uz kalibrirane koeficijente trenja,
poklapanja numeriÄkih rezultata i terenskih mjerenja su zadovoljavajuÄa, Å”to ukazuje
na vrlo dobru prognostiÄku moÄ predloženog modela u izrazito stratificiranim uvjetima.
Kombinacija terenskih mjerenja i numeriÄkih simulacija omoguÄila je detaljniji
uvid u relevantne fizikalne procese u izrazito stratificiranim uÅ”Äima. Pokazalo se
kako protok rijeke ima dominantni utjecaj na dinamiku slanog klina, dok u manjoj
mjeri utjecaj imaju razina mora i geometrija korita. Smanjenje protoka rijeke te
podizanje morske razine može uzrokovati jaÄi prodor slanog klina uzvodno. TakoÄer,
tijekom svih mjerenja zabilježena je kontinuirana stratifikacija stupca vode, neovisno
o mareografskim i hidroloŔkim uvjetima.
PostojeÄi parametrizacijski modeli za intenzitet mijeÅ”anja u stratificiranim sredinama
nisu se pokazali dovoljno pouzdanima na uÅ”Äu RjeÄine. Detaljnije analize
sugeriraju kako je intenzitet mijeÅ”anja moguÄe zadovoljavajuÄe prognozirati tek
na osnovu kombinacije poznatih bezdimenzionalnih parametara toka i koeficijenta
trenja. Parametrizacijski modeli za koeficijent trenja na razdjelnici pokazali su se joÅ”
manje pouzdanima. Analize izmjerenih podataka sugeriraju kako se koeficijent trenja
poveÄava s protokom rijeke, Å”to je u suprotnosti s postojeÄim saznanjima. ZakljuÄno,
predloženi su novi empirijski izrazi za prognoziranje intenziteta mijeŔanja i koeficijenta
trenja na razdjelnici u izrazito stratificiranim uÅ”Äima
Numerical analysis of hysteresis in rating curves for open channel flow
For the purpose of studying the hysteresis in rating curves for unsteady flow regime in open channels, a numerical analysis of water wave propagation is performed by a numerical integration of one-dimensional (1D) Saint Venant differential equations. By applying two different boundary conditions, which are specified as the time change in water level h at the upstream boundary of the flow domain, it is shown that the downstream rating curves can obtain the same shapes in the Q-h plane. However, to emphasize the expected difference in rating curves, a third, time axis, is added. Accordingly, the rating curves obtain a spatial shape from which the dynamics of evolution in the relation between the stage h and related discharge Q can be evidenced. Apart from the description of the used numerical formulation (based on the method of characteristics), a numerical example is also presented in the support of the given statements
ESTIMATON OF MAXIMUM SHORT-TERM PRECIPITATION OVER THE RIJEKA REGION
In this paper, we considered the occurrence of extreme short-term rainfall in the region of Rijeka city, analyzed the extreme values, and commented on application of the results. We estimated the maximum precipitation amounts for different occurrence probabilities (return periods) for time intervals of 5, 10, 20, 30, 40, and 60 minutes, as well as 2, 4, 8, 12 and 24 hours, using data taken at the Rijeka meteorological station over periods of 1958ā2011 and 1958ā2012. Additionally, we evaluated the extremity of a heavy rainfall event that affected the city of Rijeka on September 12th, 2012. Using absolute extremes recorded for time intervals of 20 minutes to 2 hours, we accounted for precipitation peaks to calculate new intensityādurationāreturn period curves for Rijeka. In this way, we revised the precipitation input parameters used to plan and design urban drainage systems. This revision included significant changes for durations of 20, 30, and 40 minutes, for which the amounts recorded on September 12th, 2012 had return periods of longer than 100 years
STREAM 1D: Numerical model for predicting the salt-water intrusion in highly stratified estuaries
STREAM 1D je raÄunalni model za prognoziranje hidrodinamiÄkih procesa u izrazito uslojenim uvjetima. Procesne jednadžbe izvedene su iz zakona oÄuvanja mase i koliÄine gibanja za jednodimenzionalno i nestacionarno teÄenje dva sloja plitkih voda razliÄitih gustoÄa u koritima proizvoljne geometrije. NumeriÄki algoritam implementiran je u Python 3.6 programskom jeziku, a temelji se na metodi konaÄnih volumena, odnosno dobro uravnoteženoj Roevoj Q-shemi. Model je detaljno validiran usporedbom s terenskim mjerenjima za sluÄaj dvoslojnog teÄenja na uÅ”Äu RjeÄine. U ovome su radu prikazane moguÄnosti modela u prognoziranju duljine prodora slane vode uslijed konstantnog protoka rijeke. Uz kalibrirani koeficijent trenja na razdjelnicu meÄu slojevima, poklapanja numeriÄkih rezultata i izmjerenih vrijednosti su zadovoljavajuÄa.STREAM 1D is a computational model for simulating hydrodynamic processes in highly stratified conditions. Governing equations are derived from the conservation laws for mass and linear momentum, for one-dimensional and time-dependent shallow water flow of two-layer of different densities and in channels with irregular geometry. The numerical algorithm is implemented in Python 3.6, and is based on the finite volume method, or more precisely on a well-balanced Q-scheme of Roe. This model was thoroughly validated by comparing the results with field measurements of two-layer flow in the RjeÄina River Estuary. In this work, we present the modelās capability to predict the salt-water intrusion length under constant river flow. When the interfacial friction factor between the layers is calibrated, the agreement between the numerical results and measured values is satisfactory
A Simplified Computational Model of the Sea Organ in Zadar
U ovom su radu analizirane graÄevinske karakteristike te hidrauliÄki i akustiÄki aspekti Morskih orgulja u Zadru. U tu svrhu razvijen je pojednostavnjeni raÄunalni model koji se sastoji od dvodimenzijskog modela gibanja morske povrÅ”ine te algoritma za transformaciju vremenske serije oscilacija morske povrÅ”ine u zvuÄni MIDI zapis s tonovima odgovarajuÄe frekvencije, trajanja i jakosti. Usto je analizirana i vjetrovalna klima zadarskog akvatorija te su definirani relevantni valni parametri. Kako bi se procijenile moguÄnosti raÄunalnog modela Morskih orgulja, prikazana su dva primjera za razliÄite smjerove i visine valova.This paper analyses the construction characteristics as well as the hydraulic and acoustical aspects of the Sea Organ in Zadar. A simplified computational model was developed for this purpose, by combining a two-dimensional model for generating surface waves and an algorithm for transforming the time series of sea-surface oscillations into a MIDI sound of a corresponding frequency, duration and intensity. Furthermore, the wind-wave climate in the Zadar channel was analysed to define the relevant wave parameters. Two examples for different wave directions and heights are presented to assess the performance of the proposed computational model