Methods for prediction of wave kinematics
Author
Mercade Ruiz, Pau
Term
4. term
Education
Publication year
2014
Submitted on
2014-06-09
Pages
58
Abstract
Kystingeniører beregner ofte de belastninger, som bølger påfører offshore- og kystkonstruktioner. For at gøre det pålideligt skal man kunne forudsige bølgepartiklernes bevægelse (hastigheder og accelerationer), især ved den frie vandoverflade, hvor de er størst. For regelmæssige, gentagne bølger bruges Stream Function-bølgeteori bredt. For uregelmæssige bølger anvendes her en lokal Fourier-approksimationsmetode. Metoden er rettet mod at opfylde randbetingelserne ved den frie overflade helt præcist i et bevægeligt, lokalt vindue ved at approksimere hastighedspotentialet (en matematisk størrelse, hvis gradient giver strømningshastigheden) med lokale Fourier-komponenter. Metoden er implementeret i MATLAB og testet både mod stream function-bølger og mod laboratorieforsøg med uregelmæssige bølger. Resultaterne viser perfekt overensstemmelse med forudsigelser fra Stream Function-bølgeteori og med laboratoriemålinger.
Coastal engineers often need to estimate the forces that waves place on offshore and shoreline structures. To do this reliably, they must predict wave kinematics—the motion of water particles, including velocities and accelerations—especially at the free surface, where these are largest. For regular, repeating waves, the Stream Function Wave Theory is widely used. For irregular waves, this work applies a Local Fourier approximation method. The method focuses on exactly satisfying the free-surface boundary conditions in a moving local window by approximating the velocity potential (a mathematical function whose gradient gives the flow velocity) with local Fourier components. The approach is implemented in MATLAB and tested against both stream function waves and laboratory experiments of irregular waves. The results show perfect agreement with predictions from Stream Function Wave Theory and with laboratory measurements.
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