## Visiting address

Ullevål StadionSognsveien 77B

0855 OSLO

Norway

Time and place:
Mar. 28, 2011 12:15 PM,
fellesområdet 9.etasje

Turbulence is complex flow phenomenon with a wide range of scales of motion. Even though there is advancements in measurement technologies, the tools we use in the laboratories are often not adequate to extract all the information necessary for understanding and characterizing this flow. How-wire anemometry has been used by researcher for many decades due to its high temporal resolution. Even though it has good temporal resolution, it can only provide single point data. One also needs to be careful while using hot-wires because it has its own limitations given different flow configurations. In this talk, we will see some examples of hot-wire measurements in shear flow turbulence. Namely we will look at axisymmetric wake, turbulent boundary layers, and wake boundary layer interactions. Each of these measurements requires different setups and different adjustments. We will discuss what we can measure, how we can measure, how we can calibrate and how we should interpret the results.

Murat Tutkun is at the Defense Research Establishment (FFI) and Ecole Centrale de Lille, France

Time and place:
Mar. 11, 2011 1:15 PM,
fellesområdet 9.etasje

Recent findings show that moderate mixing levels typical of mid-latitude can erode or even remove the Arctic cold halocline layer and that internal wave induced mixing is enhanced in the absence of sea ice. In a seasonally ice-free Arctic Ocean increased levels of mixing, sufficient to remove the cold halocline layer, can be expected as a result of wind energy input over large areas of open water. The ice is then easily exposed to the relatively warm Atlantic water, possibly leading to a strong positive feedback. I will report on insight gained from field work conducted during the International Polar Year. Detailed finescale and turbulence measurements were made from drifting ice in the central Arctic and in the southern Yermak Plateau located in the Marginal Ice Zone northwest of Svalbard. Observations are analyzed to describe the characteristics of internal waves and turbulent mixing in the Arctic Ocean. The role of diapycnal mixing away from abyssal plains is discussed for the Arctic Ocean and regional heat budget and ice cover.

Ilker Fer is at the Department of Geophysics at UiB

Time and place:
Mar. 7, 2011 12:15 PM,
fellesområdet 9.etasje

This paper presents a Bayesian hierarchical space-time stochastic model for significant wave height. The model has been fitted by data for an area in the North Atlantic ocean and aims at describing the temporal and spatial variability of significant wave height in this area. It could also serve as foundation for further extensions used for long-term prediction of significant wave height and future return periods of extreme significant wave heights. The main model and preliminary simulation results will be presented. Furthermore, a discussion of possible model extensions and future work will be included.

Erik Vanem is at the Statistics division of the Department of Mathematics at UiO

Time and place:
Dec. 6, 2010 1:15 PM,
B91

We present a fast marching level set method for reservoir simulation based on a fractional flow formulation of two-phase, incompressible, immiscible flow in two or three space dimensions. The method uses a fast marching approach and is therefore considerably faster than conventional finite difference methods. The fast marching approach compares favorably with a front tracking method as regards both efficiency and accuracy. In addition, it maintains the advantage of being able to handle changing topologies of the front structure.

Co-authored with Knut-Andreas Lie and Kenneth Karlsen

Nils Henrik Risebro is professor at CMA

Time and place:
Nov. 29, 2010 1:15 PM,
B91

Morten Haug Emilsen is at VP Software and Technology, Add Wellflow AS

Time and place:
Oct. 18, 2010 1:15 PM,
B91

This talk deals with the capability or conventional ship radars to be used as a microwave remote sensing tool to study the spatio-temporal evolution of ocean waves. The first part of the talk is focussed on the "state of the art" of this technique, showing some results obtained from different sea state conditions. The second part of the talk is going to describe the new developments on the measuring of ocean waves using radar sensors, as well as open questions that concern some of the future research works on this field.

José Carlos Nieto Borge is professor at the University of Alcalá, Spain

Time and place:
Aug. 16, 2010 1:15 PM,
B91

Aleksey Marchenko is professor and departemental leader for the UNIS Arctic Technology department

Time and place:
Apr. 28, 2010 3:15 PM,
Seminarrom 231, Helga Engs hus

Time and place:
Mar. 1, 2010 1:00 PM,
lounge area, 9th floor, Abel bld

Main advantages and challenges of using Domain-Decomposition (DD) strategies for marine applications are examined. Splitting algorithms are discussed with emphasis on the spatial DD. Examples are given for platform and ship problems in connection with bottom-slamming and green-water occurrence. Features of the involved DD strategies are described and relevant verification and validation studies reported.

Marilena Greco is professor at Department of Marine hydrodynamics at NTNU

Time and place:
Feb. 22, 2010 12:15 PM,
B91

Time and place:
Jan. 25, 2010 12:15 PM,
B91

Oscillating boundary layers in the ocean are of fundamental interest as they are important in phenomena such as mixing, sediment transport and drift mechanisms. These boundary layers occur on different time and length scales. The waves induce a thin layer near the surface, and, for intermediate and shallow water depths, an oscillatory bottom boundary layer. The gravity forces from the moon and the sun, in conjunction with the Earths rotation, induces tidal boundary layers. Oscillatory boundary layers often result from an interaction between the oscillatory motion and a current, for example induced by wind at the ocean surface. In general these boundary layers are turbulent in the ocean, and it will be shown how these boundary layers can be calculated using a relative simple two-equation turbulence model. Results from an ongoing work considering the entire water column for a tidal flow with wind at the surface will be given. Finally a few preliminary LES test results from channel flow, from our development of LES codes, will be presented, and a brief discussion of some problems which we expect to face when using these models on geophysical flows will be given.

Lars Erik Holmedal is researcher at Department of Marine Technology, NTNU

Time and place:
Nov. 25, 2009 3:15 PM,
Aud. 2, Georg Sverdrups hus

Computer simulation is a powerful tool, which utilizes the power of computers in order to support and enforce the creativity of structural engineers. Although it is frequently used in research and development its potential for civil engineering practice has not yet been fully exploited. This is in part due to a lack of appropriate software tools well suited for this purpose. The author is involved in development of the software ATENA, which is aimed to bridge this gap. Theoretical background, solution methods and algorithmic solutions will be briefly described and validations of the models by experiments will be shown. The presentation will focus on numerous examples form engineering practice ranging from small (fastenings to concrete) to large structures (highway bridge, nuclear power plant containment). It will be shown that numerical simulation is becoming a powerful tool for solution of demanding problems of existing as well as new constructions.

Dr. Cervenka is the founder of the company Cervenka Consulting in Prague, Czech Republic. He is an internationally recognized expert in the field of mechanics of concrete structures and author of many scientific publications. His PhD thesis (University of Colorado, USA, 1970) on the topic of "Inelastic Finite Element Analysis of Reinforced Concrete Panels under In-Plane Loads", was a major contribution to the development of numerical models of concrete structures. He is recipient of numerous awards: Alexander von Humboldt research fellowship in Germany, Kajima foundation in Japan, Fellow of the Czech Engineering Academy, University of Colorado Distinguished Engineering Alumnus, and others. At present his main activity is in research and consulting in the field of concrete structures.

Time and place:
Oct. 29, 2009 12:00 PM,
fellesareal utenfor B91

Environmental challenges related to hydrocarbon-based energy sources as well as resource constraints are the driving forces behind the R&D focus of StatoilHydro. In this presentation we will discuss availability of hydrocarbon energy sources and global energy demand. We will show how this motivates the research focus of StatoilHydro.

Ruben Schulkes is Chief Researcher Production Technology at StatoilHydro, Research Centre Porsgrunn, and is Professor II at the Mechanics Division

Time and place:
Oct. 15, 2009 2:15 PM,
B91

The mixing of temperature and pollutants in the ocean can be studied by examining how pairs of particles, deployed together, separate in time and space. Here we consider a recent field experiment in which 120 satellite-tracked surface drifters were deployed in pairs and triplets off the Norwegian coast. We discuss the observed dispersion, and how this can be rationalized within the framework of the theory of two-dimensional turbulence.

Joseph Lacasce is professor at the Department of Geosciences

Time and place:
Oct. 8, 2009 2:15 PM,
B91

Recent efforts to investigate a possible increased lifetime of old platforms have brought attention to some challenging hydrodynamic problems. Due to higher extreme waves and subsidence of seabed some of these platforms have become vulnerable to wave crests hitting the deck of the platform. Higher estimates of extreme wave crests may be due to better understanding of non-linear wave effects as well as including the uncertainty related to possible climate change effects. Due to complexity of deck geometry, CFD has been found necessary to predict wave impact loads. Numerical procedures to estimate extreme wave crests, obtain corresponding fluid particle kinematics and calculate impact loads will be presented.

Jørn Birknes is scientist at Det Norske Veritas

Time and place:
Sep. 24, 2009 2:15 PM,
B91

The word seismology is often associated with earthquakes. However, the tightly related term ``seismic'' comprises a valuable technology used extensively by the oil and gas industry in its exploration, development, and reservoir management operations. This talk will explain how marine seismic operations are carried out, and highlight some technological challenges that are faced. Special attention will be given to a factors like wave motion and turbulence, that add complexities to the operational environment. Such factors are challenging to handle from both a fluid dynamical and a signal-processing perspective.

Thomas Elboth is geophysicist at Fugro-Geoteam AS

Time and place:
Sep. 17, 2009 12:00 PM,
fellesareal utenfor B91

The slow growth of a crack in windshield represents a mechano-chemical process: The stress at the tip of the fracture is not high enough to cause rapid fracture motion. Instead, fracture motion is determined by the diffusion of hydrogen to the crack tip, where it weakens the material, leading to crack tip propagation. The velocity of the fracture depends on the coupling between deformation, transport, and reactions. Similar coupled processes determine the rate of many reaction processes of geological relevance, such as weathering and carbonation during mineralogical CO2 sequestration. We have developed numerical model that allow us to address mechano-chemical processes during fluid infiltration. The model demonstrates that fracturing assisted reaction fronts in shrinking materials propagate with a constant velocity and width, and that the reaction rate in volume increasing reactions may be accelerated by feedback processes between fluid flow, mechanical deformation, and reactions.

Anders Malthe-Sørenssen is professor at the Department of Physics, working at the center for Physics of Geological Processes

Time and place:
Sep. 10, 2009 2:15 PM,
B91

Jan Erik H. Weber, Department of Geosciences, University of Oslo Göran Broström, Norwegian Meteorological Institute, Oslo Nonlinear density-driven convection in a conditionally unstable fluid is studied theoretically. The novelty here is that the destabilizing basic density gradient is expressed in terms of the vertical perturbation velocity through a unit step function. This is done by introducing a one-way source step function due to phase transitions in the equation for the perturbation density. Then we can model the fact that the density-gradient is unstable when the perturbation vertical velocity is upward (positive), and stable when the vertical perturbation velocity is downward (negative), characterizing conditional stability. Linear analytical solutions as well as numerical results for nonlinear two-dimensional steady convection are presented.

Jan Erik Weber is professor at Department of Geosciences

Time and place:
Mar. 3, 2008 2:45 PM,
B91

A theoretical model for propagation of internal waves under an ice cover is developed. The sea water is considered to be inviscid, non-rotating, and incompressible and the Brunt-VÃ¤isÃ¤lÃ¤ frequency is supposed to be constant. The ice is considered of uniform thickness, with constant values of Young's modulus, Poisson's ratio, density and compressive stress in the ice. The boundary conditions are such that the normal velocity at the bottom is zero and, at the undersurface of the ice, the linearized kinematical and dynamic boundary conditions are satisfied. We present and analyze explicit solutions for the internal waves under the ice cover and the dispersion equations. It is shown that when the frequency is near, but smaller than the Brunt-Vaisela frequency the ice deflections can be considerable. The theoretical results are compared with experimental data for the Arctic regions.

Sergey Muzylev is at the Shirsov Institute of Oceanology, Moscow

Time and place:
Mar. 3, 2008 2:15 PM,
B91

The study is based on field measurements since 2002. We analyze the transport of Antarctic Bottom Water in Deep Channels of the Atlantic: Vema Channel (31deg S), Romanche Fracture Zone (0 deg) and Vema Fracture Zone (11 deg N). The flow of bottom water in the Vema Channel can reach 4 mln. sq. m per second and the velocity is as high as 60 cm/s. The transport and velocities in the Romanche Fracture Zone and Vema Fracture Zone are smaller and do not exceed 500 th. sq. m per sec. The major penetration of bottom waters to the Northeastern Atlantic basins occurs through the Vema FZ but not through the Romanche FZ because strong tidal internal waves on the slopes of the Mid-Atlantic Ridge near Romanche FZ exceed 50 m, while at the Vema FZ they are approximately 20 m. Such difference in mixing of bottom waters with the overlying North Atlantic Deep water results in the fact the deep Northeastern Atlantic basins are filled with the bottom water transported through the Vema FZ.

Eugene Morozov is proessor at the Shirshov Institute of Oceanology, Moscow

Time and place:
Nov. 15, 2007 2:15 PM,
B91

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.

Time and place:
Aug. 14, 2007 11:15 AM,
B91

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

Time and place:
May 21, 2007 12:15 PM,
B91

M. Stiassnie , A. Regev, and Y. Agnon: The stability and long-time evolution of narrow spectra homogeneous seas subject to inhomogeneous disturbances is studied. Specifically, we study unidirectional spectra, where according to classical homogeneous theory (i.e. the Kinetic equation), no spectral evolution is expected. In the region of instability , recurrent evolution is discovered. This behavior is qualitatively different from recent work on discrete spectra that exhibited irreversible widening of narrow spectra. The inhomogeneous structure of the unstable modes that leads to the recurrent evolution is revealed.

Time and place:
Apr. 23, 2007 12:15 PM,
B91