# Seminars - Page 4

Patrick J. Lynett is from the University of Southern California.

Randall J. LeVeque, Applied Mathematics Department University of Washington

Lateral-torsional buckling of elastic structures under combined loading will be considered in this seminar. This problem has been first reported in the habilitation thesis of Prandtl dated 1899. Closed-form solutions based on Bessel's functions are available for some speciﬁc types of loading. However, numerical methods such as the Finite Element Methods (FEM) or other approximate methods are needed in the general case. More generally, approximation of the buckling curve (limit of the stable domain in the loading parameters space) is investigated from the stationary property of the Rayleigh’s quotient. The approximation is then compared to a numerical approach, namely the iterative method of Vianello and Stodola. Closed-form solutions give upper bounds with relative error less than 0.2%. It is shown that the stable domain of the loading parameter space is convex. The Papkovitch–Schaefer theorem proven in 1934 is extended for this specific problem, despite the nonlinear dependence of the equilibrium equations on the loading parameters for the one-dimensional system. The boundary of the stable domain is clearly nonlinear, but this nonlinearity is weak. It is shown that Dunkerley’s lower bound is relevant for the two structural cases considered, and the maximum relative error induced by such a lower bound is lower than 2%. Prandtl's linear approximation is then validated approximately one century later the pioneer works of Prandtl devoted to elastic instability.

Noël Challamel is Professor at the Department of Civil Engineering (LIMATB), University of South-Brittany, Lorient, France, and Marie Curie fellow at the Department of Mathematics, University of Oslo, Oslo, Norway.

The fundamental mechanisms of plasticity in inorganic glasses are distinctly different from those in crystalline metals. Whereas dislocations and their mobility require plasticity in metals, mechanisms responsible for permanent deformation in glasses are to be looked at the atomistic scale. The lecture will deal with this and will involve topics such as for instance constitutive material laws, plasticity theory, dislocation theory, computational mechanics, multiscale analysis, finite element methods, crack modelling, etc.

Vincent Keryvin is professor at Department of Materials Engineering (LIMATB), University of South-Brittany, Lorient, France.

This seminar will be focused on some elementary structural systems such as the cantilever beam. The cantilever is an old problem in structural mechanics already investigated by Galileo (1638) from equilibrium and strength arguments. This structural paradigm will be reconsidered here using buckling, post-buckling and inelastic theory. We will first present some fundamental buckling results for axially loaded columns. This model covers the case of a tree under its own weight or gives an answer to Babel mythology, at least from the stability theory point of view. This in-plane buckling problem in presence of distributed and concentrated axial forces has been recently exactly solved using hypergeometric functions. The post-buckling behavior associated with a nonlinear boundaryvalue problem will be also discussed using some asymptotic and numerical methods. The out-of-plane buckling problem of this cantilever beam will be further investigated. The lateral-torsiona l buckling problem of Prandtl (1899) dealing with the stability boundary of a beam loaded by its own weight and a concentrated force will be also solved. The convexity theorem of Papkovitch and Schaefer (1934) will be shown for these structural problems. The seminar will be concluded by the inelastic analysis of the beam in bending. We will show the need to develop a nonlocal plasticity law to describe the post-failure behavior of a beam in presence of softening. Wood’s paradox (1968) is overcome by using a nonlocal plasticity model. The Galileo problem is then revisited in the light of nonlocal mechanics. Applications of such theoretical studies can be found in the field of civil engineering at the macro scale (reinforced concrete design, timber beams, steel or composite beams…), but also at micro- or nano-scales including for instance nanostructures.

Challamel is Professor of Civil Engineering, University of South Brittany, Lorient, France, and Marie Curie Fellow in solid mechanics (faststoffmekanikk) at UiO (2011/2012).

Volume tracking is a popular method for the computation of two phase flow problems. In this talk we present a reformulation of volume tracking in two dimensions in terms of an explicit tracking of the interface between the two immiscible phases. This allows for a higher order accurate representation of the interface with respect to the spatial discretization while conserving the mass up to roundoff precision.

Joris Verschaeve is postdoc at the Mechanics Division, Department of Mathematics, University of Oslo.

Ocean Engineering (OE) is considered by many to be a matured field which is mainly controlled by the oil industries. However, due to the growing interdiciplinary nature of OE, it presents new exciting challenges for scientists and engineers with a solid background in topics like hydrodynamics, acoustics, physio-chemistry as well as electro-kinetics, electromagnetics and control theory. Some practical examples will be discussed.

Touvia Miloh is professor at Tel Aviv University.

An idealized mathematical model of tsunami evolution in deep sea and across the continental shelf is proposed. The initial value problem in deep sea is related to the well known Cauchy- Poisson problem, and the tsunami propagation across the continental shelf is derived using the linearized shallow water equations.

When analyzing different cases of tsunamis in deep sea it was found that tsunamis evolve into two basic wave types. One resembles a single wave and the other a wave packet. The analysis of different cases of tsunamis at the shoreline reveals that the continental shelf, due to its geometrical properties, serves as a tsunami amplifier, producing tsunami amplitudes up to 20 times larger than those at the edge of the continental shelf.

A comparison with tsunami measurements suggests that the idealized model may be used for a reliable assessment of the principle hydrodynamic properties of the tsunami, such as the tsunami amplitude and its half- period.

The new mathematical model for tsunami evolution is used to derive a synthetic tsunami database for the southern part of the Eastern Mediterranean coast. Information about coastal tsunami amplitudes, half-periods, currents, and inundation levels is presented.

Michael Stiassnie is professor at the Department of Civil and Environmental Engineering, Technion – Israel Institute of Technology.

Simulations of Fluid-Solid interactions (FSI) are becoming more common as faster computers enables the study of larger models including both fluids and solids. In many applications it is of significant importance to determine the impact that a flowing fluid has on the mechanical structure surrounding it. Vortex-induced vibrations can give structural failure due to fatigue, but it can also produce undesired acoustic noise. During the seminar, several examples of FSI problems and solutions will be demonstrated. The examples include the study of flow induced vibrations in a compressor exhaust, the dynamic flow of oil through a filter, the impact of water waves on a submerged object, etc.

Large-eddy simulations are also advancing in the industrial CFD society. RANS modeling has shown to be insufficient in many complex flow situations, and LES has proven to provide answers to many fundamental questions in turbulent flows. A brief demonstration of an example with flow over a wing profile is presented. Using LES, it is possible to extract valuable information regarding lift, drag, etc., but it is also possible to visualize the turbulent structures evolving from the boundary layer on the wing.

Love Håkansson is at EDR - Engineering Data Resources

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

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

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

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

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

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

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

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

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

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.

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