Απόκριση παραμετρικού διατοιχισμού σε τυχαίους κυματισμούς

Φανουράκη, Αλεξάνδρα; Fanouraki, Alexandra

dc.contributor.author	Φανουράκη, Αλεξάνδρα	el
dc.contributor.author	Fanouraki, Alexandra	en
dc.date.accessioned	2022-11-07T10:57:44Z
dc.date.available	2022-11-07T10:57:44Z
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/56108
dc.identifier.uri	http://dx.doi.org/10.26240/heal.ntua.23806
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	Random Waves	en
dc.subject	Διατοιχισμός	el
dc.subject	Παραμετρικος	el
dc.subject	Spectral analysis	en
dc.subject	Random Phase Model	en
dc.subject	Parametric roll	en
dc.title	Απόκριση παραμετρικού διατοιχισμού σε τυχαίους κυματισμούς	el
heal.type	bachelorThesis
heal.classification	Μαθηματικά,Μηχανική	el
heal.language	en
heal.access	free
heal.recordProvider	ntua	el
heal.publicationDate	2022-07-15
heal.abstract	This work deals with parametric resonance which poses a great danger especially for container ships sailing in following or head seas. As a parametric resonance phenomenon, parametric roll is characterized by a periodical alteration of one of its characteristics, in this case the restoring ability of the ship. In this diploma thesis, important parameters that affect the instability of the ship are discussed. Also, the way in which the problem is modeled to find the ship’s response to roll is presented. The ship used for this study, as a sample ship, is a large containership, with Loa = 250 meters. The response of the ship is found by solving the one degree of freedom differential equation of rolling motion. The value of the righting arm, hence the restoring term, is derived from the equilibrium of the ship in the pitch and heave motions (pseudo-static model or else called 1.5 D.O.F.), for each specific time instant and position of the ship on the wave. After constructing the numerical model and selecting the appropriate discretization of the hull geometry to solve the hydrostatic equilibrium at each position, the information on the form of the free surface is selected. The waves are irregular one-directional following waves. The free surface elevation is approximated by the random phase model. The different harmonic frequencies are correlated with the corresponding wave heights by a specific energy spectrum (in particular the Jonswap spectrum). Specific cases were selected for consideration in order to construct a stability diagram, with the values of the significant height and the ratio a = 4 ω0 2 ωep 2 with the encounter frequency corresponding to the peak period. The diagrams were constructed for a different range of ship’s forward speed and sea states. The results showed that, there are regions of instability, of which a few are cases of capsizing. These regions are narrower and generally shorter than those found in regular waves. From the data extracted we could say that the areas of instability correspond to lower ship speeds. In addition, for speeds over 12 knots there was no parametric roll observed at all. Parametric resonance is a dangerous phenomenon that can lead to large roll angles, and cause severe container losses and economic damage. From the results of this thesis it is obvious that in irregular waves parametric roll occurs at a lower frequency. However, in cases where it occurs it can cause large roll angles and even capsizing. As the phenomenon of wave randomness in combination with dynamic stability is a complex one, further studies are needed to provide a more complete picture of the occurrence of parametric roll in random waves.	en
heal.advisorName	Σπύρου, Κώστας	el
heal.committeeMemberName	Ζαραφωνίτης, Γεώργιος	el
heal.committeeMemberName	Γρηγορόπουλος, Γρηγόρης	el
heal.academicPublisher	Εθνικό Μετσόβιο Πολυτεχνείο. Σχολή Ναυπηγών Μηχανολόγων Μηχανικών. Τομέας Μελέτης Πλοίου και Θαλάσσιων Μεταφορών	el
heal.academicPublisherID	ntua
heal.numberOfPages	123 σ.	el
heal.fullTextAvailability	false