Seminars 2013
Seminario
Martes 10 de Diciembre
The Janus family: a dedicated computer generation
BIFI, Universidad de Zaragoza
Abstract
Janus [1,2] is a special purpose computer designed as a
multipurpose reprogramable supercomputer. It is based
on a FieldProgrammableGateArray (FPGA) processor
architecture, which permits us reprogramming the
computer's hardware connections structure in order to
optimize its performance for each concrete problem to
solve. Encouraged by the good results obtained so far, the Janus Collaboration decided to go an step further developing and designing the new generation Janus dedicated computer, named JanusII [3]. In this talk I will introduce both supercomputers, Janus and JanusII, explaining their internal architectures and the way we profit by their resources and possibilities for the study of spin glasses, paradigm of complex systems. I will also discuss some of the last spin glass aims achieved with Janus. In addition, there is an international open call to the scientific community for the implementation on new applications on Janus (http://bifi.es/janus). [1] Janus Collaboration: F. Belletti et
al., Computer Physics Communications 178
(3), 208216, (2008).
El Seminario tendrá lugar a las 13:00 horas en la Sala
2.1.C19 (Edificio Sabatini) Universidad Carlos III
Seminario
Martes 12 de Noviembre
Corner waves downstream from a partially submerged
vertical plate
UC3M
Abstract
The highReynoldsnumber flow near the corner of a
vertical flat plate partially submerged across an
uniform stream has been studied using a combination of
experimental, numerical and analytical tools. In this
configuration, a three dimensional wave forms at the
corner of the plate which evolves downstream in a
similar way as a timeevolving two dimensional plunging
or spilling breaker (depending the occurrence of one or
the other type of breaker on the flow conditions).
Experiments have been performed submerging a flat plate
perpendicular to the free stream in the test section of
a recirculating water channel. Experimental results
show that the formation and the initial development of
the wave is nearly unaffected by the presence of the
channel walls and bottom even when their distance to
the corner, where the wave originates, is of the order
of the size of the wave itself. This is a remarkable
observation, that suggests that the formation of the
corner wave is a local process in a sense that it is
only influenced by the characteristics of the velocity
field very near the corner. Moreover, it has been
observed that the jet formed when the corner wave
adopts the plunging breaker configuration follows a
nearly ballistic trajectory, has is the case in
twodimensional unsteady plunging breakers. Theoretical
analysis shows that, taking advantage of the slender
nature of the flow, the 3D steady problem can be
transformed into a two dimensional unsteady one using
the so called 2D+T approximation. Together with the
high Reynolds number of the flow, the 2D+T
approximation makes the problem amenable to be
simulated numerically using a Boundary Element Method
(BEM). Moreover, a pressureimpulse asymptotic analysis
of the flow near the origin of the corner wave has been
performed in order to describe the initial evolution of
the wave and to clarify the physical mechanisms that
lead to its formation. The analysis shows that the flow
near the corner exhibits a self similar behavior at
short times, although the selfsimilar solution is
physically unattainable due to the existence of two
"jetlets" that impinge onto the base of the main jet
that causes the wave.
El Seminario tendrá lugar a las 13:00 horas en la Sala
2.1.C19 (Edificio Sabatini) Universidad Carlos III
Seminario
Martes 5 de Noviembre
A macroscopic particlewave system: Theoretical
investigation of walking droplets
MIT
Abstract
Yves Couder and his coworkers in Paris have discovered
a macroscopic particlewave system exhibiting many
features previously thought to be peculiar to the
microscopic quantum realm. A small liquid droplet
placed on the vibrating surface of a fluid bath, can be
made to bounce (essentially indefinitely) provided that
the amplitude and frequency of the oscillations is in
the "correct range". In particular: (1) The frequency
must be high enough that the "impact time" is too short
to allow the air layer between the drop and bath to
drain to the critical distance at which merger is
initiated by van der Waals forces, (2) The maximum
vertical acceleration of the free surface must exceed
gravity (so the drop can lift of after landing), (3)
The operational regime must be below the Faraday
instability threshold, so the liquid surface remains
(essentially) "flat". he experiments by Couder involve a millimeter sized droplet on a vibrating bath of silicone oil (viscosity 2050 times that of water). There, the drop may bounce indefinitely on the free surface, generating a localized field of surface waves that decays with distance from the drop. The drop interacts with this wave field, and undergoes several bifurcations in its behavior as the driving amplitude grows: from bouncing in place at the same frequency as the fluid bath, to a period doubling bifurcation, to spontaneous "walking" on the surface. Walking drops exhibit quantumlike effects in its behavior: diffraction, interference, orbit quantization in rotating frames, etc. Multiple bouncers communicate through their wave fields, and can orbit each other forming "atoms", or "crystal" lattices, etc. In this talk I will introduce an integral equation that describes the waveinduced force that acts on walking droplets. From this we can write a new guidance equation for walking droplets, that provides insight into their observed quantum behavior. In particular I will consider the behavior of a drop/particle in a rotating frame, and the myriad of patterns that this produces.
El Seminario tendrá lugar a las 13:00 horas en la Sala
2.1.C19 (Edificio Sabatini) Universidad Carlos III
Seminario
Martes 22 de Octubre
Capturing Nature's Creativity in Robotics & Tissue
Regeneration
Stanford University
Abstract
Throughout the years nature has inspired some of the
best inventions in engineering and medicine, from
building airplanes with movable wing surfaces like
those of birds to using viruses as a vehicle to deliver
genetic materials into cells. In this talk, I will
present our work aiming to solve problems in
engineering and medicine using natureinspired
approaches. In the first part, I will focus on
understanding the adhesive locomotion of gastropods for
the design of biomimetic robots. Specifically, some of
the critical questions we aim to address are: how do
softbodied creatures like slugs and snails propel
themselves through irregular terrains? Is the
rheological properties of the secreted mucus essential,
and what lessons can we learn from their crawling
mechanism for robotics design? In the second part, we
explore the possibility of manipulating cellcell
interactions as a strategy for cartilage regeneration
therapy. In particular, we explore the potential of
adiposederived stem cells as a catalyst to stimulate
cartilage regeneration by neonatal chondrocytes. The
questions we seek to answer are: how can we minimize
the number of neonatal chondrocytes, an extremely
scarce cell source, needed for cartilage repair? Can we
manipulate cellcell interactions by controlling cell
distribution and intercellular distance in 3D to
facilitate optimal synergy?
El Seminario tendrá lugar a las 13:00 horas en la Sala
2.1.C19 (Edificio Sabatini) Universidad Carlos III
Seminario
Lunes 14 de Octubre
On aerofoil tonal noise
Delft University of Technology
Abstract
Aerofoil tonal noise is an aeroacoustic phenomenon
peculiar of small wind turbines, compressors' blades
and UAVs, all applications where a laminar or at least
transitional flow can take place. Its investigation
spans a period of more than 40 years but up to date no
agreement between the researchers has been achieved.
The aspects object of research were linked to the flow
mechanism causing this acoustic emission and the
behaviour in terms of acoustic emission frequency with
respect to the free stream velocity. The aerofoil tonal noise is often referred to as aerofoil self noise. The reason for this appellation resides in the illuminating conjectures of Tam [1], who in 1974 proposed the occurrence of a feedback loop between the hydrodynamic fluctuations and the acoustic waves scattered by those fluctuations. The acoustic waves propagating in the whole field, were causing a forcing of the fluiddynamic field thus leading to the mutual interaction proper of a feedback loop. In the following years many researchers accepted this explanation introducing new findings and modifications. In one of the last works on the topic Desquesnes et al. [2] studied the flow mechanism causing tonal emission with a 2D DNS. They investigated the pressure signal in the far field finding a modulation of its amplitude. The period of this modulating envelope was equal to the invert of the separation, in terms of frequency, of the discrete peaks present in the acoustic power spectrum. The cause of this modulation was individuated in a varying phase shift between the disturbances of the boundary layers of the two sides of the aerofoil at the trailing edge. The results of a wind tunnel campaign by means of high speed PIV and simultaneous microphones measurements are here presented [3]. Furthermore linear stability theory LST in its spatial formulation has been applied to the timeaveraged flow fields. Some important confirmations about the reported flow features under which tonal noise is observed, are obtained. Moreover some new findings have been discovered thus leading to the rejection of some earlier conclusions as well as to the proposition of a new model of the feedback loop. [1] Tam, C.K.W. (1974). Discrete tones of isolated
airfoils. J. Acoust. Soc. Am., 55 (6):
11731177.
El Seminario tendrá lugar a las 13:00 horas en la Sala
2.1.C19 (Edificio Sabatini) Universidad Carlos III
Seminario
Martes 8 de Octubre
From Analogue Gravity to Elastic Cloaking
UC3M
Abstract
Analogue Gravity relies on the observation that certain
collective excitations in condensedmatter physics, for
example sound waves, have equations of motion that can
be written as a relativistic field in a curved
spacetime. I discuss several consequences, from
acoustic black holes in BoseEinstein condensates over
whitehole experiments in a kitchen sink, to the
possibility of arriving at acoustic and elastic
cloaking with composite metamaterials.
El Seminario tendrá lugar a las 13:00 horas en la Sala
2.1.C19 (Edificio Sabatini) Universidad Carlos III
Seminario
Viernes 19 de Julio
Modeling and simulation of bacterial biofilms
UC3M
Abstract
Bacterial biofilms may be seen as bacterial aggregates
embedded into a polysaccharide matrix with a high
resistance against removal processes, which results in
a recurrent source of problems in other disciplines
(medicine, engineering, etc). The behaviour of these
organisms is highly dependent of the physical system in
which they are present, thus showing a very high degree
of physical complexity. In this seminar we will focus
our efforts on describing a mathematical and
experimental modelization of biofilms by exposing a
different set of case studies. First the dynamics of
biofilms in straight ducts is studied. Experiments are
performed to obtain statistics about spreading
patterns, and a hybrid model (combining a discrete
approach for bacterial population with stochastical
behaviour rules and a continuum description of outer
fields ruling those probabilities) is presented to
simulate the biofilm dynamics, obtaining a successfully
prediction of the different patterns observed in real
experiments (at layers, ripples, streamers, mounds).
This part is completed by extending the scope of the
model to the formation of biofilm streamers inside a
corner flow, where biomass adhesion mechanism becomes
relevant. Streamers cross the channel joining both
corners as observed experimentally. Additionally we
perform a description of more complex dynamics observed
in biofilms. An experimental description of biofilm
dynamics under pulsatile flows at low Reynolds numbers
show spiral patterns not reported yet, supported by a
theoretical mechanism of formation based on the
competence between flow dynamics and nutrient
gradients.
El Seminario tendrá lugar a las 12:30 horas en la Sala
2.1.C19 (Edificio Sabatini) Universidad Carlos III
Seminario
Martes 2 de Julio
LeastSquares Finite Element Models of Flows of
Incompressible Fluids
Texas A & M University
Abstract
Finite element formulations based on the weakform
Galerkin method in solid and structural mechanics
resulted in enormous success. However, extension of
these concepts to fluid mechanics and other areas of
mechanics where the differential operators are either
nonself adjoint or nonlinear have met with mixed
success. Numerical schemes such as modified weight
functions, modified quadrature rule, optimal upwinding
etc. have been presented in the literature to alleviate
problems encountered with weak form Galerkin procedures
in solving nonself adjoint and nonlinear problems
outside of solid mechanics. The lecture presents the formulation and application of the leastsquares finite element formulations to the numerical solution of the NavierStokes equations governing twodimensional flows of viscous incompressible fluids. Finite element models of the vorticitybased or velocity gradientsbased NavierStokes equations are developed using the leastsquares technique. The use of leastsquares principles leads to a symmetric and positivedefinite system of algebraic equations that allow the use of iterative methods for the solution of resulting algebraic equations. Highorder nodal expansions are used to construct the discrete finite element models. The system of equations thus obtained is linearized by Newton's method and solved by the preconditioned conjugate gradient method. Exponentially fast decay of the leastsquares functional, which is constructed using the $L_2$ norms of the residuals in the governing equations, is verified for increasing order of the nodal expansions. Numerical results will be presented for several benchmark flow problems to demonstrate the predictive capability and robustness of the leastsquares based finite element models.
El Seminario tendrá lugar a las 12:30 horas en la Sala
2.1.C17 (Edificio Sabatini) Universidad Carlos III
Seminario
Lunes 24 de junio
The RBFFD Method: Developments and Applications
UC3M
Abstract
Radial Basis Function (RBF) methods have become a truly
meshless alternative for the interpolation of
multidimensional scattered data and the solution of
PDEs on irregular domains. Its dependence on the
distance between centers makes RBF methods conceptually
simple and easy to implement in any dimension or shape
of the domain. There are two different formulations for
the solution of PDEs: the global RBF method and the
local RBF method. The global RBF formulation yields dense differentiation matrices which are spectrally convergent independently of the node distribution. Its principal drawback is that, as the overall number of centers increases, the condition number of the collocation matrices increases, and this fact restricts the applicability of the method in practical problems. To overcome some of the drawbacks of the global RBF method, the local RBF method was independently proposed by several authors (also known as RBFFD). Unlike the global RBF method, the RBFFD method lacks spectral accuracy. However, the main feature of the method is the hability for handling irregular domains using highly sparse differentiation matrices while approximating the differential operators to high order. In this thesis we focus on the RBFFD method. In the first part we analyze the convergence properties of the method obtaining novel analytical formulas for the local truncation error as a function of the shape parameter, internodal distance and stencil size. This result proof the existance of a range of values of the shape parameter for which RBFFD methods are more accurated than FD. Indeed, it usually exists an optimal shape parameter for which the local truncation error cancel outs and the approximation is exact. To leading order, such a value is independent of the internodal distance and only relies on the function and its derivatives. These results allow us to develop novel algorithms for the selection of the shape parameter in the solution of PDEs. In this line, two different strategies are proposed: a nodeindependent shape parameter, which minimizes the norm of the global error, and a nodedependent shape parameter, which minimizes the local truncation error at each node of the domain. Applications of the present methods have been studied in the solution of classical elastostatic problems, for which it is shown that the accuracy can significantly increased one or two orders of magnitude with respect to finite differences by efficiently tuning the values of shape parameters. The applicability of the method is explored in the second part of this thesis. In this way, a threedimensional problem for the propagation of a premixed laminar flame through a duct is solved. The good performance of the method inspires us to implement an RBFFD method for the numerical study of an idealized Wankel microcombustor, for which the geometry is more complex. The combustible flow field and the combustion process are respectively modeled through the steady NavierStokes equations and the combustion model above.
El Seminario tendrá lugar a las 12:30 horas en la Sala
2.1.C19 (Edificio Sabatini) Universidad Carlos III
Seminario
Viernes 14 de junio
Models for largescale turbulent structures on jets and
their radiated noise
California Institute of Technology/UPM
Abstract
Turbulent jet noise is a technological problem of great
importance that has received continuous attention for
decades. While stateoftheart numerical simulations
are today capable of simultaneously predicting
turbulence and its radiated sound, a theoretical
framework enabling fast prediction in order to guide
noisecontrol efforts is incomplete. In this direction,
the peak noise radiation in the aft direction of
highspeed jets has been linked to the dynamics of the
largescale wavepackets existing in the flow:
intermittent, advecting disturbances that are
correlated over distances far exceeding the integral
scales of turbulence, the signatures of which can be
distinguished in the vortical turbulent region and in
the acoustic near and far fields. The present research uses parabolized stability equations (PSE) in order to model the statistical wavepackets as instability waves of the turbulent mean flow for subsonic and ideallyexpanded supersonic round jets. The theoretical framework and algorithmic details will be discussed. Extensive comparisons and validations are performed against experimental measurements and data from large eddy simulations, demonstrating the utility of PSE in modeling (i) the largescale structures in the velocity field, (ii) the pressure signature in the acoustic nearfield and (iii) the highly directional peak noise in the acoustic farfield.
El Seminario tendrá lugar a las 12:30 horas en la Sala
2.1.C19 (Edificio Sabatini) Universidad Carlos III
Conferencia del Programa de Cátedras de Excelencia
Jueves, 16 de mayo
Multiple Scales and Coupled Phenomena in Nature and
Mathematical Models
Wilfrid Laurier University/Visiting Professor at UC3M
Abstract
Interacting time and space scales are universal. They
frequently go hand in hand with coupled phenomena which
can be observed in nature and manmade systems. Such
mutiscale coupled phenomena are fundamental to our
knowledge about all the systems surrounding us, ranging
from such global systems as the climate of our planet,
to such tiny ones as quantum dots, and all the way down
to the building blocks of life such as nucleic acid
biological molecules. In this talk I will provide an overview of some coupled multiscale problems that we face in studying physical, engineering, and biological systems. I will start from considering tiny objects, known as low dimensional nanostructures, and will give examples on why the nanoscale is becoming increasingly important in the applications affecting our everyday lives. By using fully coupled mathematical models, I will show how to build on the previous results in developing a new theory, while analyzing the influence of coupled multiscale effects on properties of these tiny objects. The remaining part of the talk I will devote to coupled multiscale problems in studying biological structures constructed from ribonucleic acid (RNA). As compared to deoxyribonucleic acid (DNA) and some other biomolecules, RNA offers not only a much greater variety of interactions but also great conformational flexibility, making it an important functional material in many bioengineering and medical applications. Examples of numerical simulations of such biological structures will be shown, based on our developed coarsegrained methodologies.
El Seminario tendrá lugar a las 12:30 horas en el
Auditorio Padre Soler, Universidad Carlos III
Seminario
Miércoles, 15 de mayo
Flammability of Materials in Spacecrafts
University of California at Berkeley
Abstract
Space exploration vehicles frequently employ cabin
environments that are not at standard sea level
atmospheric conditions. NASA's Constellation Program
considers a human space exploration cabin environment
of reduced ambient pressure and increased oxygen
concentration. This enhanced oxygen and reduced
pressure atmosphere (approximately 56 kPa and 32 the
Space Exploration Atmosphere, SEA, and while it reduces
preparation time for EVAs by reducing the risk of
decompression sickness it may have a significant impact
on the flammability of materials. In this presentation
the work being conducted at the University of
California Berkeley regarding the flammability of
materials in environments similar to those expected in
those future space based facilities, i.e.,
microgravity, low velocity flow, elevated oxygen
concentrations, and reduced pressures, is reviewed. A
description of the equipment and facilities used in
those studies and a summary of the results will be
presented.
El Seminario tendrá lugar a las 12:30 horas en la Sala
2.1.C17 (Edificio Sabatini) Universidad Carlos III
Seminario
Viernes, 10 de mayo de 2013
Vibrated fluids: Faraday waves, crosswaves, and
vibroequilibria
UPM
Abstract
The behavior of vibrated fluids and, in particular, the
surface or interfacial instabilities that commonly
arise in these systems have been the subject of
continued experimental and theoretical attention since
Faraday's seminal experiments in 1831. Both orientation
and frequency are critical in determining the response
of the fluid to excitation. Low frequencies are
associated with sloshing while higher frequencies may
generate Faraday waves or crosswaves, depending on
whether the axis of vibration is perpendicular or
parallel to the interface. In addition, high frequency
vibrations are known to produce large scale
reorientation of the fluid (vibroequilibria), an effect
that becomes especially pronounced in the absence of
gravity. We describe the results of experimental and
theoretical investigations into the effect of
vibrations on fluid interfaces, particularly the
interaction between Faraday waves and crosswaves. Experiments utilize a dualaxis shaker configuration that permits two independent forcing frequencies, amplitudes, and phases to be varied. Theoretical results, based on the analysis of reduced models, and on numerical simulations, are described and compared to experiment. In particular, the nonlinear Schrodinger equation models used to study crosswaves since Jones (JFM 138, 1984) are extended to include surface tension and to allow the inhomogeneous forcing term to vary on the same lengthscale as the crosswave modulation, an assumption that is needed for high frequency (large aspect ratio) experiments such as ours.
El Seminario tendrá lugar a las 12:30 horas en la Sala
2.1.C19 (Edificio Sabatini) Universidad Carlos III
Seminario
Viernes, 5 de abril de 2013
Wellposed and illposed regimes in μ(I)rheology for
granular materials
Duke University
Abstract
Progress in understanding granular flow has been
greatly hampered by the lack of satisfactory
constitutive equations. Historically, the concept of a
Coulomb material, based on rateindependent plasticity,
was introduced to describe granular materials. On
substitution into the equations for conservation of
mass and momentum, this constitutive relation leads to
a system of evolution equations loosely analogous to
the NavierStokes equations; friction gives rise to a
term that formally resembles viscosity. However, it
turns out that this system is illposed. Numerous
higherorder, nonlocal theories have been introduced
in an attempt to resolve this difficulty; while many of
these are wellposed, they are invariably quite
complicated, perhaps unnecessarily so. In the last decade the French school (GDR MIDI) proposed a natural modification of the Coulomb constitutive equation. In this theory the coefficient of friction varies with the shear rate (which is measured by a nondimensional inertial number $I$); this property leads to the name $\mu(I)$rheology. Their equation, which is based on experiments of flow down inclined planes and on dimensional analysis, retains a level of simplicity comparable to Coulomb material. In this talk we analyze the wellposedness of the governing equations using $\mu(I)$rheology. Specifically, we show that these evolution equations are wellposed for a large range of deformation rates but become illposed at extremes of slow or fast deformation. It is known that additional effects, not represented in $\mu(I)$rheology, become important in these two extremes. Thus, the present mathematical result and physical understanding of granular materials support one another. On the numerical side, several authors have adapted a recently proposed finite volume method for solving the NavierStokes equations to problems with $\mu(I)$rheology. In this method, the pressure viscosity contribution is evaluated explicitly; this is appropriate for viscosity in the NavierStokes equations (where the viscosity operator is elliptic) but questionable for the notnecessarilyelliptic operator that occurs in $\mu(I)$rheology. Reflecting this mismatch, numerical results using this method show no indication of illposedness: i.e., they do not reproduce the stability properties of the PDE derived assuming $\mu(I)$rheology. To better capture the behavior of the PDE, we propose a PISOlike method that evaluates implicitly the viscous pressure contributions, and we derive a new pressure equation based on the Schur complement. We present numerical simulations to illustrate that our method does capture illposedness as predicted by theory.
El Seminario tendrá lugar a las 12:30 horas en la Sala
2.1.C19 (Edificio Sabatini) Universidad Carlos III
Seminario
Miércoles, 20 de marzo de 2013
Coupled Mathematical Models for MultiPhase Materials:
Nonlinear Dynamics and Numerical Approximations
Wilfrid Laurier University/Visiting Professor at UC3M
Abstract
Coupled nonlinear mathematical models are essential in
describing most natural phenomena, processes, and
manmade systems. From large scale mathematical models
of climate to modelling of quantum mechanical effects
coupling and nonlinearity go often hand and hand.
Coupled dynamic systems of partial differential
equations (PDEs) provide a foundation for the
description of many such systems, processes, and
phenomena. In majority of cases, however, their
solutions are not amenable to analytical treatments and
the development, analysis, and applications of
effective numerical approximations for such models
become a core element in their studies. In this talk we will focus on mathematical models that are based on the Landau framework of phase transformations based on nonmonotone free energy functions. Phase transformations are universal phenomena, and one specific example that we will consider in this talk is motivated by mesoscopic mathematical models for the description of multiphase solid materials. Such models provide an intermediate length scale description between the atomistic level and the level that is usually used for bulk materials. In particular, we will discuss several classes of problems where nonequilibrium phenomena such as phase transformations are important, focusing on the dynamics of materials with shape memory. The talk will provide further insight into their application areas, the development of computationally efficient reduction procedures for their 3D modelling, and the construction of fully conservative schemes for solving the associated problems.
El Seminario tendrá lugar a las 12:30 horas en la Sala
2.1.D03 (Edificio Sabatini) Universidad Carlos III
Seminario
Jueves, 7 de marzo de 2013
ElastoInertial Turbulence
Monash University
Abstract
Direct numerical simulations of channel flow with
Reynolds numbers ranging from 1,000 to 10,000 (based on
the bulk and the channel height) have been used to
study the formation and dynamics of elastic
instabilities and their effects on a polymeric flow.
The dynamics of turbulence generated and controlled by
polymer additives has been investigated from the
perspective of the coupling between polymer dynamics
and flow structures.
El Seminario tendrá lugar a las 16:00 horas en la Sala
7.1.H03 (Edificio Juan Benet) Universidad Carlos III
Seminario
Miércoles, 27 de febrero de 2013
Unsteady characteristics of a shallow porous cylinder
wake
Sheffield Fluid Mechanics Group, University of
Sheffield
Abstract
In this work the result of laboratory flow
visualisations and Large Scale Particle Image
Velocimetry measurements of the wake developed after
three emerged square arrays of rigid cylinders in a
shallow water flow are presented. It is observed that
for all cases a steady wake is developed downstream the
array and it is followed by a vortex street pattern. It
is shown that not always higher porosities produce a
more extended steady wake and reduced turbulent
intensities. It is also shown that in two cases the
dominant wake frequency remain constant, and indication
that the solid volume fractions do not affect the wake
frequency. It is also observed that this frequency was
also present within the slow steady wake in one of the
measured cases, which could be evidence of an
instability initiated within the cylinder array. Based
on a Dynamic Mode Decomposition and Wavelet analysis of
two and onedimensional time series a description of
the dominant coherent structures in the near and far
field is presented. A discussion regarding the use of
fractal arrays will be also presented.
El Seminario tendrá lugar a las 12:30 horas en la Sala
7.1.H01 (Edificio Juan Benet) Universidad Carlos III


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