A FIC-based stabilized finite element formulation for turbulent flows

We present a new stabilized finite element (FEM) formulation for incompressible flows based on the Finite Increment Calculus (FIC) framework. In comparison to existing FIC approaches for fluids, this formulation involves a new term in the momentum equation, which introduces non-isotropic dissipation in the direction of velocity gradients. We also follow a new approach to the derivation of the stabilized mass equation, inspired by recent developments for quasi-incompressible flows. The presented FIC-FEM formulation is used to simulate turbulent flows, using the dissipation introduced by the method to account for turbulent dissipation in the style of implicit large eddy simulation.Peer ReviewedPostprint (author's final draft

The higher the pitch the larger its crossmodal influence on visuospatial processing

High-pitched sounds generate larger neural responses than low-pitched sounds. We investigated whether this neural difference has implications, at cognitive level, for the 'vertical' representation of pitch. Participants performed a speeded detection of visual targets that could appear at one of four different spatial positions. Rising or falling frequency sweeps were randomly presented before the visual target. Faster reaction times to visual targets appearing above (but not below) a central fixation point were observed after the presentation of rising frequencies. No significant effects were found for falling frequency sweeps and visual targets presented below fixation point. These results suggest that the difference in the level of arousal between rising and falling frequencies influences their capacity for generating spatial representations. The fact that no difference was found, in terms of crossmodal effects, between the two upper positions may indicate that this 'spatial representation of pitch' is not specific for any particular spatial location but rather has a widespread influence over stimuli appearing in the upper visual field. The present findings are relevant for the study of music performance, the design of musical instruments, and research in areas where visual and auditory stimuli with certain complexity are combined (music in advertisements, movies, etc.)

Temporal Adaptation to Audiovisual Asynchrony Generalizes Across Different Sound Frequencies

The human brain exhibits a highly adaptive ability to reduce natural asynchronies between visual and auditory signals. Even though this mechanism robustly modulates the subsequent perception of sounds and visual stimuli, it is still unclear how such a temporal realignment is attained. In the present study, we investigated whether or not temporal adaptation generalizes across different auditory frequencies. In a first exposure phase, participants adapted to a fixed 220-ms audiovisual asynchrony or else to synchrony for 3 min. In a second phase, the participants performed simultaneity judgments (SJs) regarding pairs of audiovisual stimuli that were presented at different stimulus onset asynchronies (SOAs) and included either the same tone as in the exposure phase (a 250 Hz beep), another low-pitched beep (300 Hz), or a high-pitched beep (2500 Hz). Temporal realignment was always observed (when comparing SJ performance after exposure to asynchrony vs. synchrony), regardless of the frequency of the sound tested. This suggests that temporal recalibration influences the audiovisual perception of sounds in a frequency non-specific manner and may imply the participation of non-primary perceptual areas of the brain that are not constrained by certain physical features such as sound frequency

Applications of turbulence modeling in civil engineering

This work explores the use of stabilized finite element formulations for the incompressible Navier-Stokes equations to simulate turbulent flow problems. Turbulence is a challenging problem due to its complex and dynamic nature and its simulation if further complicated by the fact that it involves fluid motions at vastly different length and time scales, requiring fine meshes and long simulation times. A solution to this issue is turbulence modeling, in which only the large scale part of the solution is retained and the effect of smaller turbulent motions is represented by a model, which is generally dissipative in nature. In the context of finite element simulations for fluids, a second problem is the apparition of numerical instabilities. These can be avoided by the use of stabilized formulations, in which the problem is modified to ensure that it has a stable solution. Since stabilization methods typically introduce numerical dissipation, the relation between numerical and physical dissipation plays a crucial role in the accuracy of turbulent flow simulations. We investigate this issue by studying the behavior of stabilized finite element formulations based on the Variational Multiscale framework and on Finite Calculus, analyzing the results they provide for well-known turbulent problems, with the final goal of obtaining a method that both ensures numerical stability and introduces physically correct turbulent dissipation. Given that, even with the use of turbulence models, turbulent flow problems require significant computational resources, we also focused on programming and parallel implementation aspects of finite element codes, and in particular in ensuring that our solver can perform efficiently on distributed memory architectures and high-performance computing clusters. Finally, we have developed an adaptive mesh refinement technique to improve the quality of unstructured tetrahedral meshes, again with the goal of enabling the simulation of large turbulent flow problems. This technique combines an error estimator based on Variational Multiscale principles with a simple refinement procedure designed to work in a distributed memory context and we have applied it to the simulation of both turbulent and non-Newtonian flow problems.Postprint (published version

Vertical Mapping of Auditory Loudness: Loud is High, but Quiet is not Always Low

Although the perceptual association between verticality and pitch has been widely studied, the link between loudness and verticality is not fully understood yet. While loud and quiet sounds are assumed to be equally associated crossmodally with spatial elevation, there are perceptual differences between the two types of sounds that may suggest the contrary. For example, loud sounds tend to generate greater activity, both behaviourally and neurally, than quiet sounds. Here we investigated whether this difference percolates into the crossmodal correspondence between loudness and verticality. In an initial phase, participants learned one-to-one arbitrary associations between two tones differing in loudness (82dB vs. 56dB) and two coloured rectangles (blue vs. yellow). During the experimental phase, they were presented with the two-coloured stimuli (each one located above or below a central "departure" point) together with one of the two tones. Participants had to indicate which of the two-coloured rectangles corresponded to the previously-associated tone by moving a mouse cursor from the departure point towards the target. The results revealed that participants were significantly faster responding to the loud tone when the visual target was located above (congruent condition) than when the target was below the departure point (incongruent condition). For quiet tones, no differences were found between the congruent (quiet-down) and the incongruent (quiet-up) conditions. Overall, this pattern of results suggests that possible differences in the neural activity generated by loud and quiet sounds influence the extent to which loudness and spatial elevation share representational content

Does language influence the vertical representation of auditory pitch and loudness?

Higher frequency and louder sounds are associated with higher positions whereas lower frequency and quieter sounds are associated with lower locations. In English, ''high'' and ''low'' are used to label pitch, loudness, and spatial verticality. By contrast, different words are preferentially used, in Catalan and Spanish, for pitch (high: ''agut/agudo''; low: ''greu/grave'') and for loudness/verticality (high: ''alt/alto''; low: ''baix/bajo''). Thus, English and Catalan/Spanish differ in the spatial connotations for pitch. To analyze the influence of language on these crossmodal associations, a task was conducted in which English and Spanish/Catalan speakers had to judge whether a tone was higher or lower (in pitch or loudness) than a reference tone. The response buttons were located at crossmodally congruent or incongruent positions with respect to the probe tone. Crossmodal correspondences were evidenced in both language groups. However, English speakers showed greater effects for pitch, suggesting an influence of linguistic background

Robust Design Optimization applied to aeronautics combining stochastic calculus with evolutionary algoritms

Las incertidumbres son un problema cotidiano en la ingeniería aeroespacial y en sus aplicaciones. Los métodos de optimización robusta utilizan, normalmente, y para asegurar la robustez de las soluciones, la generación aleatoria de los valores con incertidumbres así como criterios de selección multi-punto para la determinación del óptimo. Desde un punto de vista computacional, la aplicación a problemas de fluido-dinámica (CFD) o interacción fluido-estructura (FSI) puede ser extremadamente cara. Este trabajo presenta el acoplamiento entre el cálculo estocástico y los algoritmos evolutivos para la definición de un procedimiento de optimización robusta. Se propone, en primer lugar, una metodología para el cálculo estocástico, que a continuación se aplica a la solución de problemas de optimización. Estos métodos propuestos se han aplicado a dos tipos de problemas; un problema de CFD y otro de FSI orientados a la reducción de la resistencia aerodinámica y del fenómeno de estabilidad estructural conocido por «flutter», respectivamente.Uncertainties are a daily issue to deal with in aerospace engineering and applications. Robust optimization methods commonly use a random generation of the inputs and take advantage of multi-point criteria to look for robust solutions accounting with uncertainty definition. From the computational point of view, the application to coupled problems, like fluid-dynamics (CFD) or fluid-structure interaction (FSI), can be extremely expensive. This work presents a coupling between stochastic analysis techniques and evolutionary optimization algorithms for the definition of a stochastic robust optimization procedure. At first, a stochastic procedure is proposed to be applied into optimization problems. The proposed method has been applied to both CFD and FSI problems for the reduction of drag and flutter, respectively.Peer Reviewe

Scalable system for large unstructured mesh simulation

Dealing with large simulation is a growing challenge. Ideally for the wellparallelized software prepared for high performance, the problem solving capability depends on the available hardware resources. But in practice there are several technical details which reduce the scalability of the system and prevent the effective use of such a software for large problems. In this work we describe solutions implemented in order to obtain a scalable system to solve and visualize large scale problems. The present work is based on Kratos MutliPhysics [1] framework in combination with GiD [2] pre and post processor. The applied techniques are verified by CFD simulation and visualization of a wind tunnel problem with more than 100 millions of elements in our in-hose cluster in CIMNE.Postprint (published version

Improving a strongly coupled method for FSI by a simple approximation of the pressure tangent matrix

La interacción de los fluidos con las estructuras de su entorno es un desafío clásico para las técnicas numéricas. El objetivo de este trabajo es doble: en primer lugar se proporciona una explicación teórica simple de los principales problemas que se deben superar cuando se trata con un fluido incompresible. A continuación se introduce y justifica un nuevo procedimiento para la solución de problemas complejos de interacción fluido-estructura. Dicha estrategia se basa en la introducción de un «laplaciano de interfase» en el contorno común entre ambos medios. La idea es considerar la dependencia entre la presión del fluido y la velocidad de la estructura como un problema no lineal, que se va a resolver mediante un esquema cuasi-Newton. Se demuestra que el término de interfase resultante es una aproximación de la matriz tangente de dicho problema no lineal, usando exclusivamente álgebra lineal discreta. Finalmente, se verifica la validez de la técnica propuesta mediante su aplicación a algunos ejemplos.The interaction of fluids with surrounding structures constitutes a classical challenge for the different numerical techniques. The aim of current work is twofold: first we provide a simple theoretical explanation of the problems to be faced in incompressible FSI. Then we introduce and justify a new procedure for the solution of complex fluid-structure interaction problems. Such a new strategy is based on the introduction of an «interface Laplacian» at the coupling boundary. The idea is to consider the dependence between fluid pressure and structural velocity as a non linear problem for which a Quasi-Newton scheme is sought. The new interface term is then proved to be an approximation of the tangent matrix for such non-linear problem. In the derivation of this result we make use exclusively of discrete linear algebra. Finally, we prove the efficiency of the new approach showing its ability to tackle standard benchmark problems.Peer Reviewe