Alessandro Valiani | Università degli Studi di Ferrara (original) (raw)

Papers by Alessandro Valiani

Research paper thumbnail of Rapid transients in free-surface flows with movable bed: a 2-D numerical solution

Viene trattata la soluzione numerica, condotta con il metodo di MacCormack esplicito, del crollo ... more Viene trattata la soluzione numerica, condotta con il metodo di MacCormack esplicito, del crollo parziale di un muro verticale che separa due specchi d'acqua inizialmente in quiete. Il fondo alveo è ipotizzato erodibile sia a monte che a valle, e il lavoro ne analizza l'evoluzione topografica nel tempo. Questo aspetto è la sostanziale novità che contraddistingue la memoria da trattazioni analoghe presenti in letteratura. La trattazione numerica deve essere particolarmente accurata, in quanto la geometria della rottura qui ipotizzata è particolarmente 'severa': la chiamata allo sbocco dà luogo a velocità trasversali dello stesso ordine di quelle longitudinali, e la bidimensionalità del moto è pronunciata in gran parte del dominio di calcolo. Particolarmente interessante risulta l'effetto convettivo sui ricircoli a valle delle due porzioni di muro rimaste erette; tali ricircoli nascono in prossimità dei pennelli e vengono progressivamente allontanati dall'onda di sommersione. Le modalità di calcolo dell'erosione del letto alluvionale tengono conto delle pendenze locali del fondo, affinché non vengano superate pendenze dello stesso ordine di quella d'attrito statico. Ad una forte escavazione localizzata in corrispondenza della breccia segue una zona di deposito maggiormente sviluppata in direzione longitudinale. Viene inoltre evidenziato anche come, specie all'inizio del transitorio, la portata liquida e quella solida a valle della breccia non siano esattamente in fase

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Assessment of cardiac function by pulse wave analysis. A computational study

Research Square (Research Square), Feb 24, 2022

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Cardiac contractility is a key factor in determining pulse pressure and its peripheral amplification

Frontiers in Cardiovascular Medicine

BackgroundArterial stiffening and peripheral wave reflections have been considered the major dete... more BackgroundArterial stiffening and peripheral wave reflections have been considered the major determinants of raised pulse pressure (PP) and isolated systolic hypertension, but the importance of cardiac contractility and ventricular ejection dynamics is also recognised.MethodsWe examined the contributions of arterial compliance and ventricular contractility to variations in aortic flow and increased central (cPP) and peripheral (pPP) pulse pressure, and PP amplification (PPa) in normotensive subjects during pharmacological modulation of physiology, in hypertensive subjects, and in silico using a cardiovascular model accounting for ventricular–aortic coupling. Reflections at the aortic root and from downstream vessels were quantified using emission and reflection coefficients, respectively.ResultscPP was strongly associated with contractility and compliance, whereas pPP and PPa were strongly associated with contractility. Increased contractility by inotropic stimulation increased peak...

Bookmarks Related papers MentionsView impact

Research paper thumbnail of The effect of cardiac properties on arterial pulse waves: An in‐silico study

International Journal for Numerical Methods in Biomedical Engineering

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Alcuni schemi path-conservativi per l’integrazione delle acque basse su fondo mobile

XXXV CONVEGNO NAZIONALE DI IDRAULICA E COSTRUZIONI IDRAULICHE. Ambiente, Risorse, Energia: le Sfide dell’Ingegneria delle Acque in un Mondo che Cambia, 2016

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Riverbank Filtration” DI Acque Superficiali a Monte Della Potabilizzazione - Il Caso Della Città DI Ferrara

4° Convegno di Idraulica Urbana "Acqua e Città 2011- Pianificazione, Protezione e Gestione", 2012

L’indagine, commissionata da HERA Ferrara assieme ad ATO 6 di Ferrara, é stata sviluppata da un G... more L’indagine, commissionata da HERA Ferrara assieme ad ATO 6 di Ferrara, é stata sviluppata da un Gruppo di Studio dell’Università di Ferrara (Dipartimento di Ingegneria e Dipartimento di Scienze delle Terre) per verificare, tecnicamente ed economicamente, l’opportunità di un intervento di “upgrading” delle opere di presa dal Po, con un sistema di prefiltrazione naturale, per una portata complessiva di 1.300 l/s. Dopo un esame delle varie tecniche di prelievo tramite “riverbank filtration”, vengono presentati i dettagli della tecnica giudicata più conveniente, quella dei pozzi orizzontali a raggiera. Sulla base anche delle indagini idrogeologiche, con sondaggi diretti eseguiti nell’alveo del Po, e di previsioni sul comportamento dell’acquifero tramite modellistica, lo Studio ha confermato gli aspetti positivi dell’intervento, con la garanzia di prelievo dell’acqua anche nei periodi di magra del Fiume, e con un efficace smorzamento delle punte di torbidità e dei rischi di inquinamenti della attuale presa diretta dal Fiume, pur efficacemente già controllati da uno degli impianti di potabilizzazione più moderni in Europa. L’indagine ha pure evidenziato zone di incertezza, connesse con la qualità dell’acqua in alveo, prelevata in condizioni statiche in occasione dei sondaggi, e che esigono una preventiva sperimentazione in condizioni dinamiche (pozzo “pilota” obliquo perforato in alveo). Lo Studio si conclude con un esame degli aspetti economici dell’intervento. I risparmi nella attuale gestione in termini di costi energetici, consumo di reagenti chimici, costi di smaltimento finale del fango, sono tali da compensare i costi di ammortamento dell’investimento iniziale, valutabile in circa 5 milioni di Euro. Dallo Studio é emersa anche l’opportunità di approfondimenti sulla realizzazione di drenaggi trasversali al Fiume, da attuare con tecniche di “directional drilling”, attualmente in pieno sviluppo, e con lavori che potrebbero comportare anche un collegamento fra gli acquedotti del Veneto e gli acquedotti dell’Emilia

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Numerical Solution of 1-D Shallow Water Equations at Junction for Sub-Critical and Super-Critical Flow

World Academy of Science, Engineering and Technology, International Journal of Mathematical and Computational Sciences, 2016

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Instability and kinematic for sand-water mixture or dry sand flowing past a circular cylinder

Proceedings of the International Conference on Fluvial Hydraulics, Lisbon, Portugal, 6-8 September 2006, 2006

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Discontinuità Del Fondo Nell’Ambito Delle Equazioni Alle Acque Basse

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Efficient analytical implementation of the DOT Riemann solver for the de Saint Venant–Exner morphodynamic model

Advances in Water Resources, Mar 1, 2018

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Modeling essential hypertension with a closed‐loop mathematical model for the entire human circulation

International Journal for Numerical Methods in Biomedical Engineering

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Comparison between different methods to compute the numerical fluctuations in path-conservative schemes for SWE-Exner model

We consider the Shallow Water Equations (SWE) coupled with the Exner equation. To solve these bal... more We consider the Shallow Water Equations (SWE) coupled with the Exner equation. To solve these balance laws, we implement a P0P2-ADER scheme using a path conservative method for handling the non-conservative terms of the system. In this framework we present a comparison between three different Dumbser-Osher-Toro (DOT) Riemann solvers. In particular, we focus on three different approaches to obtain the eigensystem of the Jacobian matrix needed to compute the fluctuations at the cell edges. For a general formulation of the bedload transport flux, we compute eigenvalues and eigenvectors numerically, analytically and using an approximate original solution for lowland rivers (i.e. with Froude number Fr) based on a perturbative analysis. To test these different approaches we use a suitable set of test cases. Three of them are presented here: a test with a smooth analytical solution, a Riemann problem with analytical solution and a test in which the Froude number approaches unity. Finally, a computational costs analysis shows that, even if the approximate DOT is the most computationally efficient, the analytical DOT is more robust with about 10% of additional cost. The numerical DOT is shown to be the heavier solution

Bookmarks Related papers MentionsView impact

Research paper thumbnail of An engineering approach to the source terms treatment in Shallow Water Equations

CNRS (France), 2011

The efficient numerical treatment of the shallow water source terms for applications of engineeri... more The efficient numerical treatment of the shallow water source terms for applications of engineering interest is analyzed. Both fixed and movable bed problems were considered. The developed approaches are often based on physically reasoning rather than on a more formal mathematical approach: The well-balanced DFB technique (Divergence Form for Bed Slope Source Term) is based on the idea that the bed slope source term corresponds to the static force due to the non-horizontality of the bottom, and therefore may be computed, in any cell, for a constant value of the free surface elevation; the method for managing the bed discontinuities here presented is based on a suitable reconstruction of the conservative variables at the cell interfaces, coupled with a correction of the numerical flux, based on the local conservation of the total energy. The need of a greater computational efficiency has prompted the use of high-order schemes. For this reason, the topic of the well-balancing was addressed in the context of the central WENO schemes, on fixed and movable bed, respectively. In these works suitable procedures are used to achieve the evaluation of the point-values of the flux derivative coupled with the bed slope source term and the spatial integration of the source term itself, analytically manipulated to take advantage from the regularity of the free-surface elevation. Further difficulties usually arising in the practical applications are due to the necessity of a correct boundary condition modeling. This aspect is challenging in the high-order models also because of the large extension of the computational support (i.e. the stencil) and therefore the suitability of the compact WENO family of Hermitian type is explored. For the first time this kind of scheme was used to integrate the shallow water equations. The Hermitian WENO scheme, which is interesting for one dimensional problems, becomes too cumbersome in a two dimensional contest, so the very recent activity is finally shifted to the study of third-order 2D RKDG schemes

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Thermal Instability of a Power-Law Fluid Flowing in a Horizontal Porous Layer with an Open Boundary: A Two-Dimensional Analysis

Transport in Porous Media, 2017

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Uncertainty quantification of viscoelastic parameters in arterial hemodynamics with the a-FSI blood flow model

This work aims at identifying and quantifying uncertainties related to elastic and viscoelastic p... more This work aims at identifying and quantifying uncertainties related to elastic and viscoelastic parameters, which characterize the arterial wall behavior, in one-dimensional modeling of the human arterial hemodynamics. The chosen uncertain parameters are modeled as random Gaussian-distributed variables, making stochastic the system of governing equations. The proposed methodology is initially discussed for a model equation, presenting a thorough convergence study which confirms the spectral accuracy of the stochastic collocation method and the second-order of accuracy of the IMEX finite volume scheme chosen to solve the mathematical model. Then, univariate and multivariate uncertain quantification analyses are applied to the a-FSI blood flow model, concerning baseline and patient-specific single-artery test cases. A different sensitivity is depicted when comparing the variability of flow rate and velocity waveforms to the variability of pressure and area, the latter ones resulting m...

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Numerical methods for hydraulic transients in visco-elastic pipes

A wide and critical comparison of the capability of Method of Characteristics, Explicit Path-Cons... more A wide and critical comparison of the capability of Method of Characteristics, Explicit Path-Conservative Finite Volume Method and Semi-Implicit Staggered Finite Volume Method is presented and discussed, in terms of accuracy and efficiency. The viscoelastic behaviour of the pipe wall, the effects of the unsteadiness of the flow on the friction losses, cavitation and cross-sectional changes are considered. The analyses are performed comparing numerical solutions obtained using the three models against experimental data and analytical solutions. Water hammer studies in high density polyethylene pipes, for which laboratory data have been provided, are used as test cases. Considering the viscoelastic mechanical behaviour of plastic materials, a 3-parameter and a multi-parameter linear viscoelastic rheological model are adopted and implemented in each numerical scheme. Original extensions of existing techniques for the numerical treatment of such viscoelastic models are introduced in thi...

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Mathematical study of linear morphodynamic acceleration and derivation of the MASSPEED approach

Morphological accelerators, such as the MORFAC (MORphological acceleration FACtor) approach, are ... more Morphological accelerators, such as the MORFAC (MORphological acceleration FACtor) approach, are widely adopted techniques for the acceleration of the bed evolution, which reduces the computational cost of morphodynamic numerical simulations. In this work we apply a non-uniform acceleration to the one-dimensional morphodynamic problem described by the de Saint Venant-Exner model by multiplying all the spatial derivatives by an individual constant (>1) acceleration factor. The final goal is to identify the best combination of the three accelerating factors for which i) the bed responds linearly to hydrodynamic changes; ii) a consistent decrease of the computational cost is obtained. The sought combination is obtained by studying the behaviour of an approximate solution of the three eigenvalues associated with the flux matrix of the accelerated system. This approach allows to derive a new linear morphodynamic acceleration technique, the MASSPEED (MASs equations SPEEDup) approach, a...

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Data for: Modeling blood flow in viscoelastic vessels: the 1D augmented fluid-structure interaction system

Model implementation in MATLAB language and scripts to reproduce test cases described in the pape... more Model implementation in MATLAB language and scripts to reproduce test cases described in the paper MODELING BLOOD FLOW IN VISCOELASTIC VESSELS: THE 1D AUGMENTED FLUID-STRUCTURE INTERACTION SYSTEM.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of The Numerical Simulation of Steady and Unsteady Flows in Channel Networks Using an Extended Riemann Problem at the Junctions

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Modeling blood flow in networks of viscoelastic vessels with the 1D augmented fluid-structure interaction system

A noteworthy aspect in blood flow modeling is the definition of the mechanical interaction betwee... more A noteworthy aspect in blood flow modeling is the definition of the mechanical interaction between the fluid flow and the biological structure that contains it, namely the vessel wall. Particularly, it has been demonstrated that the addition of a viscous contribution to the mechanical characterization of vessels brings positive results when compared to in-vivo measurements. In this context, the implementation of boundary conditions able to keep memory of the viscoelastic contribution of vessel walls assumes an important role, especially when dealing with large circulatory systems. In this work, viscoelasticity is taken into account in entire networks via the Standard Linear Solid Model. The implementation of the viscoelastic contribution at boundaries, namely inlet, outlet and junction, is carried out considering the natively hyperbolic nature of the mathematical model. Specifically, a non-linear system is established based on the definition of the Riemann Problem at junctions, char...

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Rapid transients in free-surface flows with movable bed: a 2-D numerical solution

Viene trattata la soluzione numerica, condotta con il metodo di MacCormack esplicito, del crollo ... more Viene trattata la soluzione numerica, condotta con il metodo di MacCormack esplicito, del crollo parziale di un muro verticale che separa due specchi d'acqua inizialmente in quiete. Il fondo alveo è ipotizzato erodibile sia a monte che a valle, e il lavoro ne analizza l'evoluzione topografica nel tempo. Questo aspetto è la sostanziale novità che contraddistingue la memoria da trattazioni analoghe presenti in letteratura. La trattazione numerica deve essere particolarmente accurata, in quanto la geometria della rottura qui ipotizzata è particolarmente 'severa': la chiamata allo sbocco dà luogo a velocità trasversali dello stesso ordine di quelle longitudinali, e la bidimensionalità del moto è pronunciata in gran parte del dominio di calcolo. Particolarmente interessante risulta l'effetto convettivo sui ricircoli a valle delle due porzioni di muro rimaste erette; tali ricircoli nascono in prossimità dei pennelli e vengono progressivamente allontanati dall'onda di sommersione. Le modalità di calcolo dell'erosione del letto alluvionale tengono conto delle pendenze locali del fondo, affinché non vengano superate pendenze dello stesso ordine di quella d'attrito statico. Ad una forte escavazione localizzata in corrispondenza della breccia segue una zona di deposito maggiormente sviluppata in direzione longitudinale. Viene inoltre evidenziato anche come, specie all'inizio del transitorio, la portata liquida e quella solida a valle della breccia non siano esattamente in fase

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Assessment of cardiac function by pulse wave analysis. A computational study

Research Square (Research Square), Feb 24, 2022

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Cardiac contractility is a key factor in determining pulse pressure and its peripheral amplification

Frontiers in Cardiovascular Medicine

BackgroundArterial stiffening and peripheral wave reflections have been considered the major dete... more BackgroundArterial stiffening and peripheral wave reflections have been considered the major determinants of raised pulse pressure (PP) and isolated systolic hypertension, but the importance of cardiac contractility and ventricular ejection dynamics is also recognised.MethodsWe examined the contributions of arterial compliance and ventricular contractility to variations in aortic flow and increased central (cPP) and peripheral (pPP) pulse pressure, and PP amplification (PPa) in normotensive subjects during pharmacological modulation of physiology, in hypertensive subjects, and in silico using a cardiovascular model accounting for ventricular–aortic coupling. Reflections at the aortic root and from downstream vessels were quantified using emission and reflection coefficients, respectively.ResultscPP was strongly associated with contractility and compliance, whereas pPP and PPa were strongly associated with contractility. Increased contractility by inotropic stimulation increased peak...

Bookmarks Related papers MentionsView impact

Research paper thumbnail of The effect of cardiac properties on arterial pulse waves: An in‐silico study

International Journal for Numerical Methods in Biomedical Engineering

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Alcuni schemi path-conservativi per l’integrazione delle acque basse su fondo mobile

XXXV CONVEGNO NAZIONALE DI IDRAULICA E COSTRUZIONI IDRAULICHE. Ambiente, Risorse, Energia: le Sfide dell’Ingegneria delle Acque in un Mondo che Cambia, 2016

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Riverbank Filtration” DI Acque Superficiali a Monte Della Potabilizzazione - Il Caso Della Città DI Ferrara

4° Convegno di Idraulica Urbana "Acqua e Città 2011- Pianificazione, Protezione e Gestione", 2012

L’indagine, commissionata da HERA Ferrara assieme ad ATO 6 di Ferrara, é stata sviluppata da un G... more L’indagine, commissionata da HERA Ferrara assieme ad ATO 6 di Ferrara, é stata sviluppata da un Gruppo di Studio dell’Università di Ferrara (Dipartimento di Ingegneria e Dipartimento di Scienze delle Terre) per verificare, tecnicamente ed economicamente, l’opportunità di un intervento di “upgrading” delle opere di presa dal Po, con un sistema di prefiltrazione naturale, per una portata complessiva di 1.300 l/s. Dopo un esame delle varie tecniche di prelievo tramite “riverbank filtration”, vengono presentati i dettagli della tecnica giudicata più conveniente, quella dei pozzi orizzontali a raggiera. Sulla base anche delle indagini idrogeologiche, con sondaggi diretti eseguiti nell’alveo del Po, e di previsioni sul comportamento dell’acquifero tramite modellistica, lo Studio ha confermato gli aspetti positivi dell’intervento, con la garanzia di prelievo dell’acqua anche nei periodi di magra del Fiume, e con un efficace smorzamento delle punte di torbidità e dei rischi di inquinamenti della attuale presa diretta dal Fiume, pur efficacemente già controllati da uno degli impianti di potabilizzazione più moderni in Europa. L’indagine ha pure evidenziato zone di incertezza, connesse con la qualità dell’acqua in alveo, prelevata in condizioni statiche in occasione dei sondaggi, e che esigono una preventiva sperimentazione in condizioni dinamiche (pozzo “pilota” obliquo perforato in alveo). Lo Studio si conclude con un esame degli aspetti economici dell’intervento. I risparmi nella attuale gestione in termini di costi energetici, consumo di reagenti chimici, costi di smaltimento finale del fango, sono tali da compensare i costi di ammortamento dell’investimento iniziale, valutabile in circa 5 milioni di Euro. Dallo Studio é emersa anche l’opportunità di approfondimenti sulla realizzazione di drenaggi trasversali al Fiume, da attuare con tecniche di “directional drilling”, attualmente in pieno sviluppo, e con lavori che potrebbero comportare anche un collegamento fra gli acquedotti del Veneto e gli acquedotti dell’Emilia

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Numerical Solution of 1-D Shallow Water Equations at Junction for Sub-Critical and Super-Critical Flow

World Academy of Science, Engineering and Technology, International Journal of Mathematical and Computational Sciences, 2016

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Instability and kinematic for sand-water mixture or dry sand flowing past a circular cylinder

Proceedings of the International Conference on Fluvial Hydraulics, Lisbon, Portugal, 6-8 September 2006, 2006

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Discontinuità Del Fondo Nell’Ambito Delle Equazioni Alle Acque Basse

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Efficient analytical implementation of the DOT Riemann solver for the de Saint Venant–Exner morphodynamic model

Advances in Water Resources, Mar 1, 2018

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Modeling essential hypertension with a closed‐loop mathematical model for the entire human circulation

International Journal for Numerical Methods in Biomedical Engineering

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Comparison between different methods to compute the numerical fluctuations in path-conservative schemes for SWE-Exner model

We consider the Shallow Water Equations (SWE) coupled with the Exner equation. To solve these bal... more We consider the Shallow Water Equations (SWE) coupled with the Exner equation. To solve these balance laws, we implement a P0P2-ADER scheme using a path conservative method for handling the non-conservative terms of the system. In this framework we present a comparison between three different Dumbser-Osher-Toro (DOT) Riemann solvers. In particular, we focus on three different approaches to obtain the eigensystem of the Jacobian matrix needed to compute the fluctuations at the cell edges. For a general formulation of the bedload transport flux, we compute eigenvalues and eigenvectors numerically, analytically and using an approximate original solution for lowland rivers (i.e. with Froude number Fr) based on a perturbative analysis. To test these different approaches we use a suitable set of test cases. Three of them are presented here: a test with a smooth analytical solution, a Riemann problem with analytical solution and a test in which the Froude number approaches unity. Finally, a computational costs analysis shows that, even if the approximate DOT is the most computationally efficient, the analytical DOT is more robust with about 10% of additional cost. The numerical DOT is shown to be the heavier solution

Bookmarks Related papers MentionsView impact

Research paper thumbnail of An engineering approach to the source terms treatment in Shallow Water Equations

CNRS (France), 2011

The efficient numerical treatment of the shallow water source terms for applications of engineeri... more The efficient numerical treatment of the shallow water source terms for applications of engineering interest is analyzed. Both fixed and movable bed problems were considered. The developed approaches are often based on physically reasoning rather than on a more formal mathematical approach: The well-balanced DFB technique (Divergence Form for Bed Slope Source Term) is based on the idea that the bed slope source term corresponds to the static force due to the non-horizontality of the bottom, and therefore may be computed, in any cell, for a constant value of the free surface elevation; the method for managing the bed discontinuities here presented is based on a suitable reconstruction of the conservative variables at the cell interfaces, coupled with a correction of the numerical flux, based on the local conservation of the total energy. The need of a greater computational efficiency has prompted the use of high-order schemes. For this reason, the topic of the well-balancing was addressed in the context of the central WENO schemes, on fixed and movable bed, respectively. In these works suitable procedures are used to achieve the evaluation of the point-values of the flux derivative coupled with the bed slope source term and the spatial integration of the source term itself, analytically manipulated to take advantage from the regularity of the free-surface elevation. Further difficulties usually arising in the practical applications are due to the necessity of a correct boundary condition modeling. This aspect is challenging in the high-order models also because of the large extension of the computational support (i.e. the stencil) and therefore the suitability of the compact WENO family of Hermitian type is explored. For the first time this kind of scheme was used to integrate the shallow water equations. The Hermitian WENO scheme, which is interesting for one dimensional problems, becomes too cumbersome in a two dimensional contest, so the very recent activity is finally shifted to the study of third-order 2D RKDG schemes

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Thermal Instability of a Power-Law Fluid Flowing in a Horizontal Porous Layer with an Open Boundary: A Two-Dimensional Analysis

Transport in Porous Media, 2017

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Uncertainty quantification of viscoelastic parameters in arterial hemodynamics with the a-FSI blood flow model

This work aims at identifying and quantifying uncertainties related to elastic and viscoelastic p... more This work aims at identifying and quantifying uncertainties related to elastic and viscoelastic parameters, which characterize the arterial wall behavior, in one-dimensional modeling of the human arterial hemodynamics. The chosen uncertain parameters are modeled as random Gaussian-distributed variables, making stochastic the system of governing equations. The proposed methodology is initially discussed for a model equation, presenting a thorough convergence study which confirms the spectral accuracy of the stochastic collocation method and the second-order of accuracy of the IMEX finite volume scheme chosen to solve the mathematical model. Then, univariate and multivariate uncertain quantification analyses are applied to the a-FSI blood flow model, concerning baseline and patient-specific single-artery test cases. A different sensitivity is depicted when comparing the variability of flow rate and velocity waveforms to the variability of pressure and area, the latter ones resulting m...

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Numerical methods for hydraulic transients in visco-elastic pipes

A wide and critical comparison of the capability of Method of Characteristics, Explicit Path-Cons... more A wide and critical comparison of the capability of Method of Characteristics, Explicit Path-Conservative Finite Volume Method and Semi-Implicit Staggered Finite Volume Method is presented and discussed, in terms of accuracy and efficiency. The viscoelastic behaviour of the pipe wall, the effects of the unsteadiness of the flow on the friction losses, cavitation and cross-sectional changes are considered. The analyses are performed comparing numerical solutions obtained using the three models against experimental data and analytical solutions. Water hammer studies in high density polyethylene pipes, for which laboratory data have been provided, are used as test cases. Considering the viscoelastic mechanical behaviour of plastic materials, a 3-parameter and a multi-parameter linear viscoelastic rheological model are adopted and implemented in each numerical scheme. Original extensions of existing techniques for the numerical treatment of such viscoelastic models are introduced in thi...

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Mathematical study of linear morphodynamic acceleration and derivation of the MASSPEED approach

Morphological accelerators, such as the MORFAC (MORphological acceleration FACtor) approach, are ... more Morphological accelerators, such as the MORFAC (MORphological acceleration FACtor) approach, are widely adopted techniques for the acceleration of the bed evolution, which reduces the computational cost of morphodynamic numerical simulations. In this work we apply a non-uniform acceleration to the one-dimensional morphodynamic problem described by the de Saint Venant-Exner model by multiplying all the spatial derivatives by an individual constant (>1) acceleration factor. The final goal is to identify the best combination of the three accelerating factors for which i) the bed responds linearly to hydrodynamic changes; ii) a consistent decrease of the computational cost is obtained. The sought combination is obtained by studying the behaviour of an approximate solution of the three eigenvalues associated with the flux matrix of the accelerated system. This approach allows to derive a new linear morphodynamic acceleration technique, the MASSPEED (MASs equations SPEEDup) approach, a...

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Data for: Modeling blood flow in viscoelastic vessels: the 1D augmented fluid-structure interaction system

Model implementation in MATLAB language and scripts to reproduce test cases described in the pape... more Model implementation in MATLAB language and scripts to reproduce test cases described in the paper MODELING BLOOD FLOW IN VISCOELASTIC VESSELS: THE 1D AUGMENTED FLUID-STRUCTURE INTERACTION SYSTEM.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of The Numerical Simulation of Steady and Unsteady Flows in Channel Networks Using an Extended Riemann Problem at the Junctions

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Modeling blood flow in networks of viscoelastic vessels with the 1D augmented fluid-structure interaction system

A noteworthy aspect in blood flow modeling is the definition of the mechanical interaction betwee... more A noteworthy aspect in blood flow modeling is the definition of the mechanical interaction between the fluid flow and the biological structure that contains it, namely the vessel wall. Particularly, it has been demonstrated that the addition of a viscous contribution to the mechanical characterization of vessels brings positive results when compared to in-vivo measurements. In this context, the implementation of boundary conditions able to keep memory of the viscoelastic contribution of vessel walls assumes an important role, especially when dealing with large circulatory systems. In this work, viscoelasticity is taken into account in entire networks via the Standard Linear Solid Model. The implementation of the viscoelastic contribution at boundaries, namely inlet, outlet and junction, is carried out considering the natively hyperbolic nature of the mathematical model. Specifically, a non-linear system is established based on the definition of the Riemann Problem at junctions, char...

Bookmarks Related papers MentionsView impact