Inno Gatin | Faculty of mechanical engineering, univ. of Zagreb (original) (raw)
Papers by Inno Gatin
An extensive verification and validation of Finite Volume based CFD software Naval Hydro based on... more An extensive verification and validation of Finite Volume based CFD software Naval Hydro based on foam extend is presented in this paper for green water loads. Two— phase numerical model with advanced methods for treating the free surface is employed. Pressure loads on horizontal deck of a FPSO model are compared to experimental results from [1] for three incident regular waves. Pressure peaks and integrals of pressure in time are measured on ten different locations on deck for each case. Pressure peaks and integrals are evaluated as average values among the measured incident wave periods, where periodic uncertainty is assessed for both numerical and experimental results. Spatial and temporal discretization refinement study is performed providing numerical discretization uncertainties. Keywords— Green Water Loads, CFD, Regular Waves, VOF, Naval Hydro Pack
Tema ovog rada je primjena numerickih proracuna udarnih valnih opterecenja na nepomicne konstrukc... more Tema ovog rada je primjena numerickih proracuna udarnih valnih opterecenja na nepomicne konstrukcije pomorske tehnike. Koristen je programski paket Naval Hydro Pack u programu OpenFOAM. Koristen je model dvofaznog strujanja sa slobodnom povrsinom pomocu “Volume of Fluid” metode i “Level Set” metode. Jednadžbe su diskretizirane metodom kontrolnih volumena. Ukratko je prikazan nacin modeliranja valova pomocu relaksacijskih zona. Proveden je proracun opterecenja kvadratnog stupa uslijed udarnog vodenog vala te su rezultati uspoređeni s eksperimentalnim vrijednostima. Prikazan je nacin generiranja ekstremnog vala (engl. „freak wave“) pomocu fokusiranja valnih komponenti standardnog spektra energije valova. Provedena je simulacija ekstremnog vala te su prikazani rezultati proracuna.
In this paper a monolithic algorithm for coupling rigid body motion equations and pressure field ... more In this paper a monolithic algorithm for coupling rigid body motion equations and pressure field within a Finite Volume framework is presented. Monolithic coupling enables fewer number of pressure–velocity loops per time–step, thus reducing the required computational time. The presented method is compared to conventional partitioned coupling approach in terms of computational efficiency and accuracy. The results are compared to experimental data as well.
Provedena je numericka implementacija i validacija dvodimenzionalne nelinearne spektralne metode ... more Provedena je numericka implementacija i validacija dvodimenzionalne nelinearne spektralne metode visih redova (eng. "Higher Order Spectrum", skraceno HOS) za propagaciju trodimenzionalnih povrsinskih valova. Metoda je implementirana u programu otvorenog koda OpenFOAM, koji je specijaliziran za racunalnu dinamiku fluida (eng. "Computational Fluid Dynamics", CFD). Radi se o pseudo--spektralnoj metodi rjesavanja nelinearnih diferencijalnih jednadžbi koje opisuju problem povrsinskih valova u okviru modela potencijalnog strujanja. Pseudo-spektralni pristup omogucuje brzo rjesavanje problema povrsinskih valova s proizvoljnim brojem valnih komponenti, cime se može opisati realisticno stanje mora. Red nelinearnosti do kojeg se provodi HOS proracun je proizvoljan, sto cini metodu prilagodljivom specificnim primjenama. Problem se razlaže na nacin da se prostorni dio problema rjesava u spektralnoj domeni, dok se vremenski dio problema rjesava u fizickoj domeni. Pri tome se ...
Primjenom racunalne dinamike fluida (eng. „Computational Fluid Dynamics“, skraceno CFD) izvrsena ... more Primjenom racunalne dinamike fluida (eng. „Computational Fluid Dynamics“, skraceno CFD) izvrsena je analiza opterecenja nepomicnih konstrukcija izloženih dvofaznom strujanju sa slobodnom povrsinom i povrsinskim valovima. Rezultati su uspoređeni sa eksperimentalnim rezultatima radi potvrde tocnosti softverskog alata OpenFOAM. U radu se koriste metode simulacije viskoznog strujanja sa slobodnom povrsinom. Kroz rad se nastoji prikazati mogucnost primjene racunalne dinamike fluida na tipicne probleme proracuna opterecenja pomorskih objekata. \Najprije su prikazani matematicki modeli na temelju kojih se zasniva numericki proracun. Taj dio rada obuhvaca \Navier – Stokesove jednadžbe te njihove rubne uvjete, kao i formulaciju metode „Volume of Fluid“ (skraceno VOF) i „Level Set“ koje se koriste za definiciju slobodne povrsine kao granice dvaju medija. \Napravljen je proracun opterecenja nepomicnog stupa kvadratnog poprecnog presjeka prilikom nailaska udarnog vodenog vala (eng. „3D dam brea...
An overview of validation and verification studies of seakeeping simulations is given in this wor... more An overview of validation and verification studies of seakeeping simulations is given in this work. A detailed validation and verification study is performed for KRISO Container Ship (KCS) hull for design Froude number in head waves and oblique waves for various wave parameters and eading angles. Grid and periodic convergence tudies are performed for all cases, and the results are compared to experimental measurements. In addition, zero speed and low Froude number seakeeping results for regular and irregular head and oblique waves are presented for the Duisburg Test Case (DTC) container ship model. Enhanced body motion–fluid flow coupling is used in the latter simulations resulting in significant reduction of the required CPU time. Solution decomposition SWENSE (SpectralWave Explicit Navier–Stokes Equations) [1, 2] method is used for wave modelling with implicit relaxation zones, while embedded free surface model [3, 4] is employed for accurate interface representation. The methodol...
Harmonic Balance (HB) method is applied to the problems of surface gravity waves in the Naval Hyd... more Harmonic Balance (HB) method is applied to the problems of surface gravity waves in the Naval Hydro pack in foam–extend, which enables time–spectral simulations of wave diffraction. HB transforms a transient problem into a set of coupled steady state equations by assuming a temporally periodic flow.
Validation of the Naval Hydro CFD software pack for focused wave loading on a fixed FPSO is prese... more Validation of the Naval Hydro CFD software pack for focused wave loading on a fixed FPSO is presented in this paper. Naval Hydro is based on Finite Volume CFD software called foam–extend–4.0, and it is specialised for large–scale, two-phase surface flows encountered in naval hydrodynamics. Simulations are performed using SWENSE method (Spectral Wave Explicit Navier–Stokes Equations) for solution decomposition, while implicit relaxation zones are employed for wave initialisation and damping. Numerical results are submitted to a blind comparison with experimental results within the CCP–WSI Blind Test Workshop. Six cases are considered altogether where different incident waves and incident angles are considered. Pressure loads and free surface elevation are considered in this work.
Numerical framework for simulation of wave impact loads on ships and offshore structures in ocean... more Numerical framework for simulation of wave impact loads on ships and offshore structures in ocean environment is developed in this study, where fully
U ovom radu su prikazane mogucnosti brzih i tocnih simulacija pomorstvenosti broda u programskom ... more U ovom radu su prikazane mogucnosti brzih i tocnih simulacija pomorstvenosti broda u programskom paketu Naval Hydro u sklopu programa racunalne dinamike fluida (eng. “Computational Fluid Dynamics”, CFD) otvorenog koda foam-extend. Naval Hydro je programski paket specijaliziran za modeliranje dvofaznog, viskoznog i turbulentnog strujanja na velikim prostornim skalama. U programu se koristi eksplicitan tretman propagacije valova sto olaksava modeliranje valova uz smanjenje numericke greske difuzije i disperzije. Dodatnom spregom jednadžbe tlaka i jednadžbi gibanja krutog tijela omoguceno je koristenje manjeg broja iteracija algoritma, sto znatno smanjuje vrijeme proracuna. Da bi se prikazala brzina proracuna u odnosu na uobicajene CFD proracune pomorstvenosti, napravljena je komparativna studija između uobicajenih postavki simulacija broda na valovima i postavki za minimizaciju proracunskog vremena, te su rezultati uspoređeni sa eksperimentom. Smanjenje vremena proracuna umanjuje i to...
This paper presents an efficient method for simulating extreme wave loads using Higher Order Spec... more This paper presents an efficient method for simulating extreme wave loads using Higher Order Spectral (HOS) method and Computational Fluid Dynamics (CFD) in OpenFOAM. HOS is capable of nonlinear propagation of arbitrary wave spectrum, while being computationally effective. CFD enables fully nonlinear two-phase, turbulent flow solution with vorticity effects at the cost of increased CPU time. In this work the coupling of HOS and CFD is briefly presented and numerical simulations depicting the capabilities of the coupling are shown.
Ovaj rad prikazuje mogucnosti primjene programskog paketa NavalHydro u programu OpenFOAM na probl... more Ovaj rad prikazuje mogucnosti primjene programskog paketa NavalHydro u programu OpenFOAM na probleme određivanja valnih opterecenja u brodogradnji. Diskretizacija Navier-Stokesovih jednadžbi se provodi metodom kontrolnih volumena, dok se za pracenje slobodne povrsine koristi „Volume of Fluid“ metoda. Paket NavalHydro prilagođen je provođenju proracuna gdje su prisutni znacajni utjecaji slobodne povrsine, sto ga cini pogodnim za određivanje valnih opterecenja. U ovom radu je prikazan proracun opterecenja vertikalnog cilindra uslijed nailaska harmonijskih valova. Rezultati su uspoređeni s eksperimentalnim podacima. Uz to je prikazana simulacija ekstremnog vala (eng. „freak wave“), koja pokazuje mogucnost određivanja opterecenja uslijed ovakvih pojava.
CFD simulation results for self propelled full scale ship are compared to sea trial measurements ... more CFD simulation results for self propelled full scale ship are compared to sea trial measurements in this work. Two–phase RANS based CFD numerical model used in this work is based on the Ghost Fluid Method for numerically robust treatment of discontinuities at the free surface and the algebraic Volume–of–Fluid method for interface capturing. The propeller is modelled as a pressure–jump based actuator disc, allowing CPU time efficient simulations while preserving the accuracy of integral results. The numerical model is implemented in foam–extend, a community driven fork of the OpenFOAM software. The comparison with sea trials includes achieved forward speed, thrust and torque for given shaft speed (in RPM) for a general cargo carrier.
U ovom radu su prikazane mogucnosti brzih i tocnih simulacija pomorstvenosti broda u programskom ... more U ovom radu su prikazane mogucnosti brzih i tocnih simulacija pomorstvenosti broda u programskom paketu Naval Hydro u sklopu programa racunalne dinamike fluida (eng. “Computational Fluid Dynamics”, CFD) otvorenog koda foam-extend. Naval Hydro je programski paket specijaliziran za modeliranje dvofaznog, viskoznog i turbulentnog strujanja na velikim prostornim skalama. U programu se koristi eksplicitan tretman propagacije valova sto olaksava modeliranje valova uz smanjenje numericke greske difuzije i disperzije. Dodatnom spregom jednadžbe tlaka i jednadžbi gibanja krutog tijela omoguceno je koristenje manjeg broja iteracija algoritma, sto znatno smanjuje vrijeme proracuna. Da bi se prikazala brzina proracuna u odnosu na uobicajene CFD proracune pomorstvenosti, napravljena je komparativna studija između uobicajenih postavki simulacija broda na valovima i postavki za minimizaciju proracunskog vremena, te su rezultati uspoređeni sa eksperimentom. Smanjenje vremena proracuna umanjuje i to...
Brodovi i pucinski objekti izloženi su djelovanju vjetra i valova, pri cemu udarna valna opterece... more Brodovi i pucinski objekti izloženi su djelovanju vjetra i valova, pri cemu udarna valna opterecenja predstavljaju posebnu opasnost za sigurnost posade, opreme i broda. Relativno niska vjerojatnost pojave ekstremnih valnih udara cini ih teskim za opisati i predvidjeti, dok predstavljaju vrlo znacajan faktor prilikom projektiranja konstrukcija pomorskih objekata. Ekstremna valna opterecenja zbog toga predstavljaju važan izazov ne samo zbog sigurnosti konstrukcija vec i zbog potencijalnih usteda koje se mogu postici smanjenjem dimenzija konstruktivnih elemenata novogradnje uslijed boljeg poznavanja pojave valnog udara. Postoje razne pojave koje su vezane uz udarna valna opterecenja poput udaranja pramca (eng. "slamming") i opterecenja uslijed vode na palubi (eng. "green sea"). Karakteristike takvih pojava su komplicirana i brzo mijenjajuca geometrija slobodne povrsine, te visoki gradijenti tlaka tokom udara uz moguce utjecaje stlacivosti zarobljenih mjehura zraka. ...
arXiv: Fluid Dynamics, 2018
This paper presents a sharp free surface method for fully nonlinear flow of two immiscible phases... more This paper presents a sharp free surface method for fully nonlinear flow of two immiscible phases for wave propagation problems in the Finite Volume framework. The method resolves a sharp interface between two phases by combining the geometric reconstruction Volume-of-Fluid scheme isoAdvector for accurate advection of the free surface with the Ghost Fluid Method for the consistent treatment of density and pressure gradient discontinuities at the free surface. The method uses a compact computational stencil irrespective of cell shape and is formally second-order accurate in time and space. The primary focus of this work is to present the combined method and verify and validate it for wave-related problems in ocean sciences, marine and coastal engineering, by considering the following test cases: i) wave propagation of a two-dimensional wave with moderate steepness, ii) green water (water-on-deck) simulations for a ship model with violent free surface flow patterns. The method is impl...
This work presents various seakeeping sensitivity studies performed with a novel CFD model based ... more This work presents various seakeeping sensitivity studies performed with a novel CFD model based on solution and domain decomposition and the implicit treatment of free surface jump conditions via the Ghost Fluid Method (GFM). Solution decomposition via Spectral Wave Explicit Navier–Stokes Equations (SWENSE) allows us to efficiently simulate incident wave propagation, while domain decomposition via implicit relaxation zones prevents undesirable wave reflection off far field boundaries. The GFM discretises the pressure jump conditions, yielding interface–corrected interpolation schemes, which implicitly couple the two fluids at the free surface. In order to capture the interface, implicitly redistanced Level Set (LS) method derived from the Phase Field (PF) equation is used, rendering additional explicit redistancing unnecessary. The combined model is implemented in foam-extend-3.2, a community driven fork of the open source software OpenFOAM. Validation of the model is performed by ...
A numerical environment for efficient assessment of ship resistance using CFD is presented in thi... more A numerical environment for efficient assessment of ship resistance using CFD is presented in this paper. Predicting ship resistance in calm water with the Naval Hydro Pack can be performed within a few hours, including grid generation, computation and post–processing of results. Being able to rapidly predict ship resistance renders CFD a cost-effective design tool, since a hull form designer can evaluate multiple variants of hull geometry quickly. The process of setting up, running and post-processing is accelerated by automating the process to a high level, significantly decreasing the number of manual work effort. In this paper the capabilities of the Naval Hydro Pack are demonstrated by calculating steady resistance for three different benchmark hull forms, where time for pre-processing, processing and post-processing is reported. On average, it took two and a half hours to obtain steady state results per hull form, including set–up, computational time and data analysis. Results...
An extensive verification and validation of Finite Volume based CFD software Naval Hydro based on... more An extensive verification and validation of Finite Volume based CFD software Naval Hydro based on foam extend is presented in this paper for green water loads. Two— phase numerical model with advanced methods for treating the free surface is employed. Pressure loads on horizontal deck of a FPSO model are compared to experimental results from [1] for three incident regular waves. Pressure peaks and integrals of pressure in time are measured on ten different locations on deck for each case. Pressure peaks and integrals are evaluated as average values among the measured incident wave periods, where periodic uncertainty is assessed for both numerical and experimental results. Spatial and temporal discretization refinement study is performed providing numerical discretization uncertainties. Keywords— Green Water Loads, CFD, Regular Waves, VOF, Naval Hydro Pack
Tema ovog rada je primjena numerickih proracuna udarnih valnih opterecenja na nepomicne konstrukc... more Tema ovog rada je primjena numerickih proracuna udarnih valnih opterecenja na nepomicne konstrukcije pomorske tehnike. Koristen je programski paket Naval Hydro Pack u programu OpenFOAM. Koristen je model dvofaznog strujanja sa slobodnom povrsinom pomocu “Volume of Fluid” metode i “Level Set” metode. Jednadžbe su diskretizirane metodom kontrolnih volumena. Ukratko je prikazan nacin modeliranja valova pomocu relaksacijskih zona. Proveden je proracun opterecenja kvadratnog stupa uslijed udarnog vodenog vala te su rezultati uspoređeni s eksperimentalnim vrijednostima. Prikazan je nacin generiranja ekstremnog vala (engl. „freak wave“) pomocu fokusiranja valnih komponenti standardnog spektra energije valova. Provedena je simulacija ekstremnog vala te su prikazani rezultati proracuna.
In this paper a monolithic algorithm for coupling rigid body motion equations and pressure field ... more In this paper a monolithic algorithm for coupling rigid body motion equations and pressure field within a Finite Volume framework is presented. Monolithic coupling enables fewer number of pressure–velocity loops per time–step, thus reducing the required computational time. The presented method is compared to conventional partitioned coupling approach in terms of computational efficiency and accuracy. The results are compared to experimental data as well.
Provedena je numericka implementacija i validacija dvodimenzionalne nelinearne spektralne metode ... more Provedena je numericka implementacija i validacija dvodimenzionalne nelinearne spektralne metode visih redova (eng. "Higher Order Spectrum", skraceno HOS) za propagaciju trodimenzionalnih povrsinskih valova. Metoda je implementirana u programu otvorenog koda OpenFOAM, koji je specijaliziran za racunalnu dinamiku fluida (eng. "Computational Fluid Dynamics", CFD). Radi se o pseudo--spektralnoj metodi rjesavanja nelinearnih diferencijalnih jednadžbi koje opisuju problem povrsinskih valova u okviru modela potencijalnog strujanja. Pseudo-spektralni pristup omogucuje brzo rjesavanje problema povrsinskih valova s proizvoljnim brojem valnih komponenti, cime se može opisati realisticno stanje mora. Red nelinearnosti do kojeg se provodi HOS proracun je proizvoljan, sto cini metodu prilagodljivom specificnim primjenama. Problem se razlaže na nacin da se prostorni dio problema rjesava u spektralnoj domeni, dok se vremenski dio problema rjesava u fizickoj domeni. Pri tome se ...
Primjenom racunalne dinamike fluida (eng. „Computational Fluid Dynamics“, skraceno CFD) izvrsena ... more Primjenom racunalne dinamike fluida (eng. „Computational Fluid Dynamics“, skraceno CFD) izvrsena je analiza opterecenja nepomicnih konstrukcija izloženih dvofaznom strujanju sa slobodnom povrsinom i povrsinskim valovima. Rezultati su uspoređeni sa eksperimentalnim rezultatima radi potvrde tocnosti softverskog alata OpenFOAM. U radu se koriste metode simulacije viskoznog strujanja sa slobodnom povrsinom. Kroz rad se nastoji prikazati mogucnost primjene racunalne dinamike fluida na tipicne probleme proracuna opterecenja pomorskih objekata. \Najprije su prikazani matematicki modeli na temelju kojih se zasniva numericki proracun. Taj dio rada obuhvaca \Navier – Stokesove jednadžbe te njihove rubne uvjete, kao i formulaciju metode „Volume of Fluid“ (skraceno VOF) i „Level Set“ koje se koriste za definiciju slobodne povrsine kao granice dvaju medija. \Napravljen je proracun opterecenja nepomicnog stupa kvadratnog poprecnog presjeka prilikom nailaska udarnog vodenog vala (eng. „3D dam brea...
An overview of validation and verification studies of seakeeping simulations is given in this wor... more An overview of validation and verification studies of seakeeping simulations is given in this work. A detailed validation and verification study is performed for KRISO Container Ship (KCS) hull for design Froude number in head waves and oblique waves for various wave parameters and eading angles. Grid and periodic convergence tudies are performed for all cases, and the results are compared to experimental measurements. In addition, zero speed and low Froude number seakeeping results for regular and irregular head and oblique waves are presented for the Duisburg Test Case (DTC) container ship model. Enhanced body motion–fluid flow coupling is used in the latter simulations resulting in significant reduction of the required CPU time. Solution decomposition SWENSE (SpectralWave Explicit Navier–Stokes Equations) [1, 2] method is used for wave modelling with implicit relaxation zones, while embedded free surface model [3, 4] is employed for accurate interface representation. The methodol...
Harmonic Balance (HB) method is applied to the problems of surface gravity waves in the Naval Hyd... more Harmonic Balance (HB) method is applied to the problems of surface gravity waves in the Naval Hydro pack in foam–extend, which enables time–spectral simulations of wave diffraction. HB transforms a transient problem into a set of coupled steady state equations by assuming a temporally periodic flow.
Validation of the Naval Hydro CFD software pack for focused wave loading on a fixed FPSO is prese... more Validation of the Naval Hydro CFD software pack for focused wave loading on a fixed FPSO is presented in this paper. Naval Hydro is based on Finite Volume CFD software called foam–extend–4.0, and it is specialised for large–scale, two-phase surface flows encountered in naval hydrodynamics. Simulations are performed using SWENSE method (Spectral Wave Explicit Navier–Stokes Equations) for solution decomposition, while implicit relaxation zones are employed for wave initialisation and damping. Numerical results are submitted to a blind comparison with experimental results within the CCP–WSI Blind Test Workshop. Six cases are considered altogether where different incident waves and incident angles are considered. Pressure loads and free surface elevation are considered in this work.
Numerical framework for simulation of wave impact loads on ships and offshore structures in ocean... more Numerical framework for simulation of wave impact loads on ships and offshore structures in ocean environment is developed in this study, where fully
U ovom radu su prikazane mogucnosti brzih i tocnih simulacija pomorstvenosti broda u programskom ... more U ovom radu su prikazane mogucnosti brzih i tocnih simulacija pomorstvenosti broda u programskom paketu Naval Hydro u sklopu programa racunalne dinamike fluida (eng. “Computational Fluid Dynamics”, CFD) otvorenog koda foam-extend. Naval Hydro je programski paket specijaliziran za modeliranje dvofaznog, viskoznog i turbulentnog strujanja na velikim prostornim skalama. U programu se koristi eksplicitan tretman propagacije valova sto olaksava modeliranje valova uz smanjenje numericke greske difuzije i disperzije. Dodatnom spregom jednadžbe tlaka i jednadžbi gibanja krutog tijela omoguceno je koristenje manjeg broja iteracija algoritma, sto znatno smanjuje vrijeme proracuna. Da bi se prikazala brzina proracuna u odnosu na uobicajene CFD proracune pomorstvenosti, napravljena je komparativna studija između uobicajenih postavki simulacija broda na valovima i postavki za minimizaciju proracunskog vremena, te su rezultati uspoređeni sa eksperimentom. Smanjenje vremena proracuna umanjuje i to...
This paper presents an efficient method for simulating extreme wave loads using Higher Order Spec... more This paper presents an efficient method for simulating extreme wave loads using Higher Order Spectral (HOS) method and Computational Fluid Dynamics (CFD) in OpenFOAM. HOS is capable of nonlinear propagation of arbitrary wave spectrum, while being computationally effective. CFD enables fully nonlinear two-phase, turbulent flow solution with vorticity effects at the cost of increased CPU time. In this work the coupling of HOS and CFD is briefly presented and numerical simulations depicting the capabilities of the coupling are shown.
Ovaj rad prikazuje mogucnosti primjene programskog paketa NavalHydro u programu OpenFOAM na probl... more Ovaj rad prikazuje mogucnosti primjene programskog paketa NavalHydro u programu OpenFOAM na probleme određivanja valnih opterecenja u brodogradnji. Diskretizacija Navier-Stokesovih jednadžbi se provodi metodom kontrolnih volumena, dok se za pracenje slobodne povrsine koristi „Volume of Fluid“ metoda. Paket NavalHydro prilagođen je provođenju proracuna gdje su prisutni znacajni utjecaji slobodne povrsine, sto ga cini pogodnim za određivanje valnih opterecenja. U ovom radu je prikazan proracun opterecenja vertikalnog cilindra uslijed nailaska harmonijskih valova. Rezultati su uspoređeni s eksperimentalnim podacima. Uz to je prikazana simulacija ekstremnog vala (eng. „freak wave“), koja pokazuje mogucnost određivanja opterecenja uslijed ovakvih pojava.
CFD simulation results for self propelled full scale ship are compared to sea trial measurements ... more CFD simulation results for self propelled full scale ship are compared to sea trial measurements in this work. Two–phase RANS based CFD numerical model used in this work is based on the Ghost Fluid Method for numerically robust treatment of discontinuities at the free surface and the algebraic Volume–of–Fluid method for interface capturing. The propeller is modelled as a pressure–jump based actuator disc, allowing CPU time efficient simulations while preserving the accuracy of integral results. The numerical model is implemented in foam–extend, a community driven fork of the OpenFOAM software. The comparison with sea trials includes achieved forward speed, thrust and torque for given shaft speed (in RPM) for a general cargo carrier.
U ovom radu su prikazane mogucnosti brzih i tocnih simulacija pomorstvenosti broda u programskom ... more U ovom radu su prikazane mogucnosti brzih i tocnih simulacija pomorstvenosti broda u programskom paketu Naval Hydro u sklopu programa racunalne dinamike fluida (eng. “Computational Fluid Dynamics”, CFD) otvorenog koda foam-extend. Naval Hydro je programski paket specijaliziran za modeliranje dvofaznog, viskoznog i turbulentnog strujanja na velikim prostornim skalama. U programu se koristi eksplicitan tretman propagacije valova sto olaksava modeliranje valova uz smanjenje numericke greske difuzije i disperzije. Dodatnom spregom jednadžbe tlaka i jednadžbi gibanja krutog tijela omoguceno je koristenje manjeg broja iteracija algoritma, sto znatno smanjuje vrijeme proracuna. Da bi se prikazala brzina proracuna u odnosu na uobicajene CFD proracune pomorstvenosti, napravljena je komparativna studija između uobicajenih postavki simulacija broda na valovima i postavki za minimizaciju proracunskog vremena, te su rezultati uspoređeni sa eksperimentom. Smanjenje vremena proracuna umanjuje i to...
Brodovi i pucinski objekti izloženi su djelovanju vjetra i valova, pri cemu udarna valna opterece... more Brodovi i pucinski objekti izloženi su djelovanju vjetra i valova, pri cemu udarna valna opterecenja predstavljaju posebnu opasnost za sigurnost posade, opreme i broda. Relativno niska vjerojatnost pojave ekstremnih valnih udara cini ih teskim za opisati i predvidjeti, dok predstavljaju vrlo znacajan faktor prilikom projektiranja konstrukcija pomorskih objekata. Ekstremna valna opterecenja zbog toga predstavljaju važan izazov ne samo zbog sigurnosti konstrukcija vec i zbog potencijalnih usteda koje se mogu postici smanjenjem dimenzija konstruktivnih elemenata novogradnje uslijed boljeg poznavanja pojave valnog udara. Postoje razne pojave koje su vezane uz udarna valna opterecenja poput udaranja pramca (eng. "slamming") i opterecenja uslijed vode na palubi (eng. "green sea"). Karakteristike takvih pojava su komplicirana i brzo mijenjajuca geometrija slobodne povrsine, te visoki gradijenti tlaka tokom udara uz moguce utjecaje stlacivosti zarobljenih mjehura zraka. ...
arXiv: Fluid Dynamics, 2018
This paper presents a sharp free surface method for fully nonlinear flow of two immiscible phases... more This paper presents a sharp free surface method for fully nonlinear flow of two immiscible phases for wave propagation problems in the Finite Volume framework. The method resolves a sharp interface between two phases by combining the geometric reconstruction Volume-of-Fluid scheme isoAdvector for accurate advection of the free surface with the Ghost Fluid Method for the consistent treatment of density and pressure gradient discontinuities at the free surface. The method uses a compact computational stencil irrespective of cell shape and is formally second-order accurate in time and space. The primary focus of this work is to present the combined method and verify and validate it for wave-related problems in ocean sciences, marine and coastal engineering, by considering the following test cases: i) wave propagation of a two-dimensional wave with moderate steepness, ii) green water (water-on-deck) simulations for a ship model with violent free surface flow patterns. The method is impl...
This work presents various seakeeping sensitivity studies performed with a novel CFD model based ... more This work presents various seakeeping sensitivity studies performed with a novel CFD model based on solution and domain decomposition and the implicit treatment of free surface jump conditions via the Ghost Fluid Method (GFM). Solution decomposition via Spectral Wave Explicit Navier–Stokes Equations (SWENSE) allows us to efficiently simulate incident wave propagation, while domain decomposition via implicit relaxation zones prevents undesirable wave reflection off far field boundaries. The GFM discretises the pressure jump conditions, yielding interface–corrected interpolation schemes, which implicitly couple the two fluids at the free surface. In order to capture the interface, implicitly redistanced Level Set (LS) method derived from the Phase Field (PF) equation is used, rendering additional explicit redistancing unnecessary. The combined model is implemented in foam-extend-3.2, a community driven fork of the open source software OpenFOAM. Validation of the model is performed by ...
A numerical environment for efficient assessment of ship resistance using CFD is presented in thi... more A numerical environment for efficient assessment of ship resistance using CFD is presented in this paper. Predicting ship resistance in calm water with the Naval Hydro Pack can be performed within a few hours, including grid generation, computation and post–processing of results. Being able to rapidly predict ship resistance renders CFD a cost-effective design tool, since a hull form designer can evaluate multiple variants of hull geometry quickly. The process of setting up, running and post-processing is accelerated by automating the process to a high level, significantly decreasing the number of manual work effort. In this paper the capabilities of the Naval Hydro Pack are demonstrated by calculating steady resistance for three different benchmark hull forms, where time for pre-processing, processing and post-processing is reported. On average, it took two and a half hours to obtain steady state results per hull form, including set–up, computational time and data analysis. Results...