Adaptation of the Artificial Compressibility Formulation
for Free Surface Flows with Applications in Ship & Marine
Hydrodynamics

Ντούρας, Δημήτρης; Ntouras, Dimitris

dc.contributor.author	Ντούρας, Δημήτρης	el
dc.contributor.author	Ntouras, Dimitris	en
dc.date.accessioned	2024-05-29T10:01:44Z
dc.date.available	2024-05-29T10:01:44Z
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/59564
dc.identifier.uri	http://dx.doi.org/10.26240/heal.ntua.27260
dc.rights	Αναφορά Δημιουργού-Μη Εμπορική Χρήση-Όχι Παράγωγα Έργα 3.0 Ελλάδα	*
dc.rights.uri	http://creativecommons.org/licenses/by-nc-nd/3.0/gr/	*
dc.subject	CFD	en
dc.subject	Two-phase flows	en
dc.subject	Artificial compressibility	en
dc.subject	Rigid body dynamics	el
dc.subject	FSI	el
dc.subject	Υδροδυναμικής	el
dc.subject	Τεχνητής Συμπιεστότητας	el
dc.title	Adaptation of the Artificial Compressibility Formulation for Free Surface Flows with Applications in Ship & Marine Hydrodynamics	en
dc.title	Προσαρμογή της μεθόδου της Τεχνητής Συμπιεστότητας σε ροές με ελεύθερη επιφάνεια και εφαρμογή της σε προβλήματα Ναυτικής και Θαλάσσιας Υδροδυναμικής	el
heal.type	doctoralThesis
heal.classification	Computational Fluid Dynamics	en
heal.language	en
heal.access	free
heal.recordProvider	ntua	el
heal.publicationDate	2023-10
heal.abstract	Computational Fluid Dynamics (CFD) has enabled the design process in many engineering applications. Advancements in computing power have allowed for the extension of CFD methodsin multi–phase flows. This category of methods can be directly applied in the field of Ship & Marine Hydrodynamics. Multi–phase modeling can be used to study the interaction of the two–immiscible fluids (air/water). A methodology can be formulated to address problems such as wave propagation, viscous effects close to surface piercing boundaries and wave–structure interaction. This thesis investigates the extension of the Artificial Compressibility (AC) method in free surface flows in conjunction with the Volume of Fluid (VoF) approach. The objective is to formulate a complete CFD methodology for the hydrodynamic analysis of ship hulls and offshore platforms. A thorough validation and verification process is followed. Carefully designed numerical experiments are conducted and results are compared against analytical, experimental and other numerical results. The capabilities, limitations and potential enhancements of the method are outlined. The methodology is implemented as an extension to the compressible URANS solver MaPFlow, developed at NTUA. In the following chapters, initially, the theoretical background of the coupled AC/VoF methodology is discussed. Afterwards, the numerical formulation of the Unsteady Reynolds Averaged Navier Stokes (URANS) equations for free surface flows is given in detail. The equations are discretized using the finite volume method in unstructured polyhedral grids. Since the structure can move in space, cell can motion and deformation is also consider in the discretization process. Focus is further given on introducing waves in a computational domain. Waves are introduced and absorbed using source terms that drive the flowfield to a target solution. The linear theory of Airy and the Stream Function theory of Fenton are used as basis for the numerical wave generation. Additionally, the problem of turbulence overproduction near the free surface is faced. Existing options are examined and further guidelines are given. Fluid–Structure Interaction (FSI) problems are at the core of the validation test cases. For these purposes, a 6 Degrees of Freedom (DoFs) rigid body solver is developed and coupled with the URANS solver. In order to effectively move the rigid body inside the computational mesh, deformation algorithms are utilized. A series of validation test cases are conducted inspired from the domain of Ship & Marine Hydrodynamics. Firstly, simplified 2–dimensional (2D) flows are considered. The specifics of generation and propagation, wave interaction with variable bathymetry and wave–induced motion of floating platforms are examined. Taken advantage of the simplifications arising from the 2D approximation, parametric studies are conducted regarding the influence of the AC parameter –β–, as well as, the parameters for wave generation and absorption. The method is generalized in the 3–dimensional space (3D). Comments are made on the challenge of maintaining the hydrostatic equilibrium in 3D applications, especially for polyhedral cell elements. The validation process continues by considering more realistic applications. The developed numerical methodology is used as a tool to assess the efficiency of a propeller in deep water, the resistance and the dynamic trim of two ship hulls and the response of floating structures in regular and irregular head waves conditions. As indicated by the comparisons, the method performs well in all cases. A fine agreement between the results is found, proving that the developed coupled AC/VoF numerical methodology can compete against already existing State––of–the–Art numerical tools and contribute to the further advancement of the CFD tools	en
heal.advisorName	Παπαδάκης, Γεώργιος	el
heal.advisorName	Papadakis, Georgios	en
heal.committeeMemberName	Voutsinas, Spyros	en
heal.committeeMemberName	Belibassakis, Konstantinos	en
heal.committeeMemberName	Spyrou, Konstantinos	en
heal.committeeMemberName	Papadopoulos, Christos	en
heal.committeeMemberName	Tzabiras, George	en
heal.committeeMemberName	Giannakoglou, Kyriakos	en
heal.academicPublisher	Εθνικό Μετσόβιο Πολυτεχνείο. Σχολή Ναυπηγών Μηχανολόγων Μηχανικών. Τομέας Ναυτικής και Θαλάσσιας Υδροδυναμικής	el
heal.academicPublisherID	ntua
heal.fullTextAvailability	false