Evidence of large-scale amplitude modulation on the near-wall turbulence

The relationship between large- and small-scale motions remains a poorly understood process in wall-bounded turbulence. Such misunderstanding is perhaps, in part, due to the limited scale separation typical of many laboratory-scale facilities. A recent investigation performed by Hutchins and Marusic [11] in a high Reynolds number turbulent boundary layer has qualitatively shown the existence of a modulating influence of the large-scale log region motions on the small-scale near-wall cycle. For this study we build upon these observations, using the Hilbert transformation applied to the spectrally filtered smallscale component of fluctuating velocity signals, in order to quantitatively determine the degree of amplitude modulation imparted by the large-scale structures onto the near-wall cycle

Analysis of scale energy budgets in wall turbulence using dual plane PIV

The scale energy budget in the near wall region is a subject of great interest in turbulent flows since it combines concepts from independent analysis in physical space and scale space. Earlier, this energy budget was studied numerically using Direct Numerical Simulation (DNS) data and experimentally using low resolution dual plane Particle Image Velocimetry (PIV) data. It was observed that the low resolution PIV data were not sufficient to accurately capture the dynamics of the energy balance and hence high resolution experiments were conducted in similar experimental conditions. The results from these high resolution data conducted in two locations of the logarithmic layer of the boundary layer indicate that the resolution of these experiments is sufficient to capture the scale energy budget in the near wall region. Predictions of the cross-over scale, which is related to the relative importance of production and transfer of turbulent kinetic energy, are found to match expected trends, and illustrate that the experimental technique provides a powerful tool for the scale energy budget analysis

The Influence of Spatial Resolution due to Hot-Wire Sensors on Measurements in Wall-Bounded Turbulence.

Reassessment of compiled data reveal that recorded scatter in the hot-wire measured near-wall peak in viscous-scaled streamwise turbulence intensity is due in large part to the simultaneous competing effects of Reynolds number and viscous-scaled wire-length l ( lUt n, where l is the wirelength, Ut is friction velocity and n is kinematic viscosity). These competing factors can explain much of the disparity in existing literature, in particular explaining how previous studies have incorrectly concluded that the inner-scaled near-wall peak is independent of Re. We also investigate the appearance of the, so-called, ‘outerpeak’ in the broadband streamwise intensity, found by some researchers to occur within the log-region of high Reynolds number boundary layers. We show that this ‘outer-peak’ is most likely a symptom of attenuation of small-scales due to large l . Fully mapped energy spectra, obtained with two different l , are presented to demonstrate this phenomena. The spatial attenuation resulting from wires with large l effectively filters small-scale fluctuations from the recorded signal

Oil film interferometry in high Reynolds number turbulent boundary layers

There is continuing debate regarding the validity of skin friction measurements that are dependent on the functional form of the mean velocity profile, for example, the Clauser chart method. This has brought about the need for independent and direct measures of wall shear stress, tw. Of the independent methods to measure tw, oil film interferometry is the most promising, and it has been extensively used recently at low and moderately high Reynolds number. The technique uses interferometry to measure the thinning rate of an oil film, which is linearly related to the level of shear stress acting on the oil film. In this paper we report on the use of this technique in a high Reynolds number boundary layer up to Rq = 50,000. Being an independent measure of tw, the oil film measurement can be used as a means to validate more conventional techniques, such as the Preston tube and Clauser chart at these high Reynolds numbers. The oil-film measurement is validated by making comparative measurements of tw in a large-scale fully-developed channel flow facility where the skin friction is known from the pressure gradient along the channe

Numerical modelling for earthquake engineering: the case of lightly RC structural walls

Different types of numerical models exist to describe the non‐linear behaviour of reinforced concrete structures. Based on the level of discretization they are often classified as refined or simplified ones. The efficiency of two simplified models using beam elements and damage mechanics in describing the global and local behaviour of lightly reinforced concrete structural walls subjected to seismic loadings is investigated in this paper. The first model uses an implicit and the second an explicit numerical scheme. For each case, the results of the CAMUS 2000 experimental programme are used to validate the approaches

When the optimal is not the best: parameter estimation in complex biological models

Background: The vast computational resources that became available during the past decade enabled the development and simulation of increasingly complex mathematical models of cancer growth. These models typically involve many free parameters whose determination is a substantial obstacle to model development. Direct measurement of biochemical parameters in vivo is often difficult and sometimes impracticable, while fitting them under data-poor conditions may result in biologically implausible values. Results: We discuss different methodological approaches to estimate parameters in complex biological models. We make use of the high computational power of the Blue Gene technology to perform an extensive study of the parameter space in a model of avascular tumor growth. We explicitly show that the landscape of the cost function used to optimize the model to the data has a very rugged surface in parameter space. This cost function has many local minima with unrealistic solutions, including the global minimum corresponding to the best fit. Conclusions: The case studied in this paper shows one example in which model parameters that optimally fit the data are not necessarily the best ones from a biological point of view. To avoid force-fitting a model to a dataset, we propose that the best model parameters should be found by choosing, among suboptimal parameters, those that match criteria other than the ones used to fit the model. We also conclude that the model, data and optimization approach form a new complex system, and point to the need of a theory that addresses this problem more generally

When linearity prevails over hierarchy in syntax

Hierarchical structure has been cherished as a grammatical universal. We use experimental methods to show where linear order is also a relevant syntactic relation. An identical methodology and design were used across six research sites on South Slavic languages. Experimental results show that in certain configurations, grammatical production can in fact favor linear order over hierarchical structure. However, these findings are limited to coordinate structures and distinct from the kind of production errors found with comparable configurations such as “attraction” errors. The results demonstrate that agreement morphology may be computed in a series of steps, one of which is partly independent from syntactic hierarchy

The coupling between inner and outer scales in a zero pressure boundary layer evaluated using a Hölder exponent framework

This work considers the connectivity between large and small scales in boundary-layer turbulence by formalizing the modulation effect of the small scales by the large in terms of the pointwise Hölder condition for the small scales. We re-investigate a previously published dataset from this perspective and are able to characterize the coupling effectively using the (cross-)correlative relations between the large scale velocity and the small scale Hölder exponents. The nature of this coupling varies as a function of dimensionless distance from the wall based on inner-scaling, ${y}^{+}$, as well as on the boundary-layer height, δ. In terms of the fundamental change in the sign of the coupling between large and small scales, the critical height appears to be ${y}^{+}\sim 1000$. Below this height, small scale structures are associated with (and occur earlier than) maxima in the large scale velocity. Above this height, while the lag is similar in magnitude, the small scale structures are associated with minima in the large scale velocity. To consider these results further, we introduce a modified quadrant analysis and show that it is the coupling to the large scale low velocity state that is critical for the dynamics

Методическая работа в дошкольной образовательной организации как условие повышения информационно-коммуникационной компетентности педагогов

Тема работы актуальна. В ВКР представлены условия, способствующие развитию компонентов ИКК педагогов. Работа имеет практическую значимост