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Foredragene høsten 2007 vil normalt finne sted på mandager kl. 14.15-15.00
i seminarrom B91, 9. etg. i matematikkbygningen. Rommet er reservert for
mekanikkseminar fram til 16.00.
Programmet annonseres her og per epost til avdeling for mekanikk etterhvert
som det blir klart.
MEKANIKKSEMINARER HØST 2007:
- Mandag 5/11 kl. 14:15-15:00 i B91:
Didier Clamond
Lagrangian description of steady waves
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 tehUniversity of Nice, Sophia-Antipolis.
- Mandag 27/8 kl. 14:15-15:00 i B91:
Hermann M. Fritz
Tsunami research
Part I: Tsunami field reconnaissance
On 26 December 2004, a great earthquake occurred off the North tip of Sumatra,
Indonesia. A transoceanic tsunami was generated resulting in a tsunami death toll in excess of
200,000. The author covered most diverse coastlines impacted by the mega tsunami from the
near to the far field encompassing Sumatra (Indonesia), Sri Lanka, The Maldives, Oman,
Yemen, Somalia, The Comoros, Madagascar. A variety of standard tsunami field survey
techniques were used. Numerous eyewitness interviews were recorded on video to estimate the
number of waves, their height and period as well as the tsunami arrival time. In addition overland
flow velocities were determined from eyewitness video recordings based on in-situ image
rectification and Particle Image Velocimetry (PIV). The author also led tsunami survey teams in
the immediate aftermath of the 17 July 2006 South Java tsunami and the 1 April 2007 Solomon
Islands tsunami. The tsunami impact is compared against Hurricane Katrina's storm surge.
Part II: Landslide generated tsunami
Landslides may pose perceptible tsunami hazards to areas commonly regarded as immune.
Tsunamis are commonly associated with submarine earthquakes. However more than 10% of
all tsunamis are generated by landslides or landslide like volcano collapses with subaerial,
partially submerged or submarine origins. In recorded history landslide generated tsunamis have
attained local wave heights and runup heights of more than 100m and 500m, respectively,
thereby locally exceeding maximum wave and runup heights of tectonic tsunamis by more than
an order of magnitude. The coupling between the landslide motion and the generated tsunami
waves is of critical importance given the characteristic trans-critical landslide versus tsunami
velocity Froude numbers. Landslide generated tsunamis were investigated most recently in the
three-dimensional tsunami basin at Oregon State University (OSU) based on the generalized
Froude similarity. The landslide emplacement characteristics were controlled by means of a
novel pneumatic landslide generator. Deformable landslides of subaerial and submarine origin
were modeled with granular materials. State-of-the-art measurement techniques such as particle
image velocimetry (PIV) were applied. Landslide generated tsunamis were investigated
previously in a two-dimensional physical laboratory at the Swiss Federal Institute of Technology
(ETH). The physical model results were compared to the giant rockslide generated tsunami
which struck the shores of the Lituya Bay, Alaska, in 1958. Further the experimental results
were used as a benchmark for numerical flow simulations.
Hermann Fritz is
Assistant Professor at the
School of Civil and Environmental Engineering,
Georgia Institute of Technology.
His Research interests include:
Tsunamis; Hurricane storm surges; non-linear and breaking water waves; mass flows (subaerial
and submarine landslides, avalanches, debris flows, turbidity currents, pyroclastic flows);
oceanic volcano island collapses; hydraulic, coastal, marine and offshore structures;
hydropower and wave energy; river engineering; sediment transport and morphologic
processes; advanced whole field multi-dimensional measurement techniques (laser-based PIV,
LSV and LIF); numerical simulations of multiphase flows; natural hazard mitigation and risk
analysis;
- Tirsdag 14/8 kl. 11:15-12:00 i B91:
Michael Stiassnie
Viscous Effects on Wave-Generation by Strong Winds
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.
Foredrag vår 2007
Foredrag høst 2006
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