An analysis method of the vortex-induced vibrations of a tethered sphere

AbstractVortex-induced vibrations (VIV) in systems with more than one degree of freedom often present complex synchronization among the motion components, also hidden by the randomness that characterizes the motion itself. A phase average method has been here developed and applied to the displacements of a tethered sphere, at low mass and damping, to analyze its xy trajectories over a wide range of reduced velocities, 5 ≤ U* ≤ 25 (Reynolds numbers, 5.1 × 103 ≤ Re ≤ 2.67 × 104). This method has allowed the identification of both the periodic and chaotic contribution of each motion component, accurately reconstructing the underlying trajectory periodic pattern. The two classical vibration modes, I and II, have been also observed. The method developed here was able to better rebuild the experimental data compared to other methods found in the relevant literature, providing useful insights into the study of the dynamic response of a freely-oscillating tethered sphere immersed in a steady flow

Wave Energy Harnessing in Shallow Water through Oscillating Bodies

This paper deals with wave energy conversion in shallow water, analyzing the performance of two different oscillating-body systems. The first one is a heaving float, which is a system known in the literature. The second one is obtained by coupling the heaving float with a surging paddle. In order to check the different behaviors of the multibody system and the single-body heaving float, physical models of the two systems have been tested in a wave flume, by placing them at various water depths along a sloping bottom. The systems have been tested with monochromatic waves. For each water depth, several tests have been performed varying the geometrical and mechanical parameters of the two systems, in order to find their best configurations. It has been found that the multibody system is more energetic when the float and the paddle are close to each other. Capture width ratio has been found to significantly vary with water depth for both systems: in particular, capture width ratio of the heaving float (also within the multibody system) increases as water depth increases, while capture width ratio of the paddle (within the multibody system) increases as water depth decreases. At the end, the capture width ratio of the multibody system is almost always higher than that of the heaving float, and it increases as water depth increases on average; however, the multibody advantage over single body is significant for water depth less than the characteristic dimension of the system, and decreases as water depth increases

Tecniche di modellazione di reattori di disinfezione con agenti chimici: dall’IDDF alla CFD

Il processo di disinfezione ricopre un ruolo fondamentale negli impianti di potabilizzazione e depurazione. Un importante strumento di supporto alla progettazione e all’ottimizzazione di questa fase è la modellazione del processo, basata su un approccio convenzionale, come l’Integrated Disinfection Design Framework (IDDF), o su un approccio avanzato, come la fluidodinamica computazionale (Computational Fluid Dynamics, CFD). Nel presente lavoro, le due tecniche modellistiche, IDDF e CFD, sono state applicate per la modellazione a scala pilota di un reattore di contatto aperto a setti, confrontando le loro prestazioni nella descrizione del processo di disinfezione e svolgendo un’analisi di sensitività sui principali parametri operativi e cinetici. Una prima parte del lavoro si è concentrata sulla corretta applicazione delle due tecniche modellistiche, utilizzando i dati sperimentali disponibili per scopi di calibrazione, mentre nella seconda parte le due tecniche modellistiche sono state confrontate. Entrambi gli approcci sono risultati strumenti efficaci nel caso si disponga di dati sperimentali affidabili, indispensabili per la messa a punto e la corretta applicazione dei modelli. La scelta dell’approccio più idoneo non è univoca, ma dipende fondamentalmente dell’obiettivo del lavoro e dalle risorse computazionali disponibili. Per quanto un approccio semplificato come l’IDDF abbia dimostrato di essere uno strumento efficace per la stima dei fenomeni coinvolti nei processi di decadimento dell’ipoclorito di sodio, inattivazione batterica e formazione di sottoprodotti, questo tralascia qualsiasi informazione circa gli effetti locali, a differenza della CFD che ha invece evidenziato come la loro identificazione sia indispensabile per determinare e quantificare possibili fonti di non idealità

About the link between biodiversity and spectral variation

Aim: The spectral variability hypothesis (SVH) suggests a link between spectral varia -tion and plant biodiversity. The underlying assumptions are that higher spectral vari-ation in canopy reflectance (depending on scale) is caused by either (1) variation in habitats or linked vegetation types or plant communities with their specific optical community traits or (2) variation in the species themselves and their specific optical traits.Methods: The SVH was examined in several empirical remote-sensing case studies, which often report some correlation between spectral variation and biodiversity- related variables (mostly plant species counts); however, the strength of the observed correlations varies between studies. In contrast, studies focussing on understanding the causal relationship between (plant) species counts and spectral variation remain scarce. Here, we discuss these causal relationships and support our perspectives through simulations and experimental data.Results: We reveal that in many situations the spectral variation caused by species or functional traits is subtle in comparison to other factors such as seasonality and physiological status. Moreover, the degree of contrast in reflectance has little to do with the number but rather with the identity of the species or communities involved. Hence, spectral variability should not be expressed based on contrast but rather based on metrics expressing manifoldness. While we describe cases where a certain link between spectral variation and plant species diversity can be expected, we be -lieve that as a scientific hypothesis (which suggests a general validity of this assumed relationship) the SVH is flawed and requires refinement.Conclusions: To this end we call for more research examining the drivers of spectral variation in vegetation canopies and their link to plant species diversity and biodiver-sity in general. Such research will allow critically assessing under which conditions spectral variation is a useful indicator for biodiversity monitoring and how it could be integrated into monitoring network

A novel lumped parameter model for Loop Heat Pipes – validation and parametric analysis

A one dimensional lumped parameter model has been developed within the general framework of the open source software Octave, in order to describe the physical behaviour of a Loop Heat Pipe. By means of the electro-thermal-hydraulic analogy, this model gives the values of temperature and pressure for every part of the device, in response to varying boundary conditions. Furthermore, a novel approach in describing the phase change at the condenser has been adopted, differentiating the vapour quality variation over time. The code is initially validated against both simulation and experimental data found in literature. Since the present work aims to produce a design tool for the automotive industry, a parametric analysis on the geometrical characteristics of a Loop Heat Pipe is then performed, identifying and quantifying the most influential design parameters

Strength in numbers:combining multi-source remotely sensed data to model plant invasions in coastal dune ecosystems

International audienceA common feature of most theories of invasion ecology is that the extent and intensity of invasions is driven by a combination of drivers, which can be grouped into three main factors propagule pressure (P), abiotic drivers (A) and biotic interactions (B). However, teasing apart the relative contribution of P, A and B on Invasive Alien Species (IAS) distributions is typically hampered by a lack of data. We focused on Mediterranean coastal dunes as a model system to test the ability of a combination of multi-source Remote Sensing (RS) data to characterize the distribution of five IAS. Using generalized linear models, we explored and ranked correlates of P, A and B derived from high-resolution optical imagery and three-dimensional (3D) topographic models obtained from LiDAR, along two coastal systems in Central Italy (Lazio and Molise Regions). Predictors from all three factors contributed significantly to explaining the presence of IAS, but their relative importance varied among the two Regions, supporting previous studies suggesting that invasion is a context-dependent process. The use of RS data allowed us to characterize the distribution of IAS across broad, regional scales and to identify coastal sectors that are most likely to be invaded in the future. © 2019 by the authors

Reference standard to read the air-driven calloric reflex test results

Universidade Federal de São Paulo (UNIFESP) Escola Paulista de MedicinaUniversidade Bandeirante de São Paulo Programa de Mestrado Profissional em Reabilitação Vestibular e Inclusão SocialFMUSP Hospital das Clínicas Setor de OtoneurologiaUniversidade Federal de São Paulo (UNIFESP) Escola Paulista de Medicina Disciplina de Otologia e OtoneurologiaUNIFESP, EPM, Disciplina de Otologia e OtoneurologiaSciEL

Appearance of a low superheat "quasi-Leidenfrost" regime for boiling on superhydrophobic surfaces

Pool boiling experiments were performed with degassed water on stainless steel substrates with different surface topographies and wettabilities. Boiling curves and visual observations of the boiling process have been carried out. The onset of nucleate boiling (ONB) has been measured and the influence of roughness and wettability has been quantified. Boiling curve shape is different between the hydrophilic and the superhydrophobic cases; superhydrophobic surfaces reaching the ONB heat flux at a lower superheat and presenting a "quasi-Leidenfrost" regime, without showing the typical boiling curve. Bubbles are easier to form on superhydrophobic surfaces, therefore the nucleation temperature is smaller, and bubbles are larger and stable. The ONB appears after less than 5 K of superheat on superhydrophobic surfaces, while on hydrophilic surfaces, with the same surface roughness, the superheat is above 7 K. Furthermore, superhydrophobic samples with a different roughness present the same boiling curve, meaning that, when the contact angle exceeds a certain value, the wettability has a predominant role on the surface roughness