Previous seminars - Page 5
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
The problem of the long wave runup on a beach is discussed in the framework of the rigorous solutions of the nonlinear shallow-water theory. The key and novel moment here is the analysis of the runup of a certain class of asymmetric waves, the face slope steepness of which exceeds the back slope steepness. Shown is that the runup height increases when the relative face slope steepness increases whereas the rundown weakly depends on the steepness. The results partially explain why the tsunami waves with the steep front (as it was for the 2004 tsunami in the Indian Ocean) penetrate deeper into inland compared with symmetric waves of the same height and length.
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
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
Flow induced vibration (FIV) is a recent discipline in Flow Assurance which focuses on the piping and equipment vibrations caused by the internal flow of gas, oil and/or water in subsea production systems (SPS). Those vibrations may cause fatigue failure at weak spots in the piping such as welds and tees. Due to recent incidents and ever-increasing production rates and velocities, FIV is now considered as a major limiting factor in the design and operation of SPS. Based on real cases and ongoing projects, this presentation provides an introduction to the following aspects: fluid-structure interaction mechanism, fatigue mechanism, design requirements for SPS, analysis tools and vibration monitoring techniques.
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-Väisälä 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
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.
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.
In order to secure the safety of ships travelling along the Norwegian coast, several fine-scale wave models have been applied for the most dangerous wave areas, such as the Steady State Irregular Wave Model (STwave) and a refraction model (www.met.no: kyst_og_hav). Lately, the model Simulating Waves Nearshore (SWAN) from TUDelft, The Netherlands, was employed to forecast waves in Trondheim ship lane. SWAN is a spectral wave model, similar to WAM, developed for shallow water or coastal areas by including depth-induced wave breaking, triad wave-wave interaction and an implicit numerical scheme that allows SWAN to run efficiently on high horizontal resolution. At met.no, SWAN was set up with 418x150 grid points and a 500mx500m grid cell size. It receives spectra on the outer boundaries from met.no's operational version of WAM and is driven by winds from a 4 km x 4 km atmospheric model. The model has furthermore the option to include varying current fields (refraction, blocking, and frequency shift) which we would like to test. Current fields can be obtained from an ocean or tidal model. We will present our experience with SWAN and results so far of comparing the forecasted wave parameters with those from a buoy located at Stor-Fosna in the ship lane. Acknowledgements: The work is performed in collaboration with the Norwegian Coastal Authorities (Kystverket).
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
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
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
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
Stratified flow phenomena are prevalent throughout the oceans. We present the results of laboratory experiments that study several ocean inspired problems, including: the settling of marine snow, spontaneous propulsion of asymmetric objects and the generation of internal wave beams by topography. These experiments cover a large range of physical scales, from as small as 100 microns for the settling of marine snow to several meters for internal wave generation, emphasizing the richness of interesting and important research problems is stratified flow
Dr. Tom Peacock of Dept. of Mechanical Engineering, MIT is a visitor at the BILAT-program. He is an expert on theoretical physics, and does currently theoretical, experimental and field work on internal waves in the ocean.
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
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
Air-sea interaction plays a vital role in modulating weather and climate from global scales down to scales of the smallest surface waves. Ultimately, the bulk parameterization of air-sea fluxes in coupled atmosphere-ocean models depends on small scale processes. In this talk I will present results of ongoing air-sea interaction research at Scripps that uses both traditional atmospheric measurements of heat flux along with infrared imaging of the sea surface to study wave-modulated heat flux and surface turbulence. These measurements were made off the Scripps Pier and from R/P FLIP off the coast of California. A second set of experiments was undertaken in the Gulf of Tehuantepec, on the Pacific coast of Mexico, which is well known for the regular occurrence of high winds in winter which blow through the mountain gap at the head of the gulf out over the Pacific. In February 2004, we conducted a 4-week campaign of airborne measurements of the development of the wave field and wind field with fetch out to approximately 500 km offshore. The primary aim of the experiment was to measure the coupled development of the wave field and wind field, including the statistics of surface wave breaking for an improved understanding of the dissipation of surface waves and their role in air-sea fluxes. We used the NSF/NCAR C130 with its standard suite of meteorological measurements, GPS dropsondes and AXBTs, along with the NASA Airborne Terrain Mapper (ATM) used as a scanning LIDAR for surface wave measurement, and a video imaging package for measuring whitecaps. I will present an overview of the experiment and the results so far pertaining to the evolution of the surface wave field, wave breaking and extreme wave statistics.
Ken Melville is professor at the Scripps Institution of Oceanography, University of California and is an international expert on air-sea interaction.
In a recent Ph.D. project the possibility of applying the Discontinuous Galerkin spectral/hp element method for the next generation of Boussinesq-type models has been investigated. These numerical methods have reached a level of maturity that turns them into an attractive alternative to the existing Boussinesq-type models, which traditionally have been based on finite difference methods in structured domains. In particular, we seek to take advantage of the geometrical flexibility of spectral/hp finite element methods to enable us to solve wave problems in increasingly complex environments. A nodal discontinuous Galerkin finite element method (DG-FEM) is used for the spatial discretization to solve a recently derived set of high-order Boussinesq-type equations [1] in complex and curvilinear geometries, and thereby amends the application range of previous numerical models. The new Boussinesq method allows for the accurate description of fully nonlinear and dispersive water waves in both shallow and deep waters, and to demonstrate and investigate the applicability of the model both linear and nonlinear test cases have been considered where water waves interact with bottom-mounted fully reflecting structures. References [1] Madsen, P. A., Bingham, H. B. and Liu, H. 2002 A new Boussinesq method for fully nonlinear waves from shallow to deep water. J. Fluid Mech. 462, pp. 1-30.
Dr. Allan Engsig-Karup is at Coastal, Maritime and Structural Engineering Technical University of Denmark (DTU) Lyngby, Denmark.
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