Previous events - Page 169
Fredagskollokvium
Fredagskollokvium
Fredagskollokvium
Fredagskollokvium
Fredagskollokvium
Fredagskollokvium
Leif Are Klevan ved Farmasøytisk institutt vil forsvare sin avhandling for graden ph.d. (philosophiae doctor): Evolutionary aspects of the DNA repeat bcrl from the B. cereus group and plasmids related to the pX01 plasmid from B. anthracis
Fredagskollokvium
Fredagskollokvium
Fredagskollokvium
Fredagskollokvium
This presentation concerns the mathematical formulation of steady surface gravity waves in a Lagrangian description of motion. It will be demonstrated that classical second-order Lagrangian Stokes-like approximations do not represent a steady wave motion in the presence of net mass transport (Stokes drift). A general mathematically correct formulation is then derived. This derivation leads naturally to a Lagrangian Stokes-like perturbation scheme that is uniformly valid for all time, i.e. without secular terms. This scheme is illustrated, both for irrotational waves, with seventh-order and third-order approximations in deep water and finite depth, respectively, and for rotational waves with a third-order approximation of the Gerstner-like wave on finite depth. It is also shown that the Lagrangian approximations are more accurate than their Eulerian counterparts of same order.
Didier Clamond has been a post.-doc. at the Department at Mathematics, UiO. He is now faculty member at the University of Nice, Sophia-Antipolis.
Fredagskollokvium
Fredagskollokvium
Fredagskollokvium
Fredagskollokvium
Fredagskollokvium
Fredagskollokvium
Fredagskollokvium
Fredagskollokvium
Ekstra fredagskollokvium
Fredagskollokvium
The talk deals with the stability of water waves in a shear flow. A carefully designed numerical solver enables to extend the range of previous calculations, and to obtain results for larger wavelengths (up to 20 cm) and stronger winds (up to a shear-velocity of 1 m/s). The main finding is the appearance of a second unstable mode which quite often turns out to be the dominant one. A comparison between results from the viscous model (Orr-Sommerfeld equations), and those of the inviscid model (Rayleigh equations), for 18cm long waves, reveals some similarity in the structure of the eigenfunctions, but a significant difference in the imaginary part of the eigenvalues (i.e. the growth-rate). It is found that the growth-rate for the viscous model is 10 fold larger than that of the inviscid one.
Michael Stiassnie er professor ved Technion, Israel