Cavitation Induction by Projectile Impacting on a Water Jet

The present paper focuses on the simulation of the high-velocity impact of a projectile impacting on a water-jet, causing the onset, development and collapse of cavitation. The simulation of the fluid motion is carried out using an explicit, compressible, density-based solver developed by the authors using the OpenFOAM library. It employs a barotropic two-phase flow model that simulates the phase-change due to cavitation and considers the co-existence of non-condensable and immiscible air. The projectile is considered to be rigid while its motion through the computational domain is modelled through a direct-forcing Immersed Boundary Method. Model validation is performed against the experiments of Field et al. [Field, J., Camus, J. J., Tinguely, M., Obreschkow, D., Farhat, M., 2012. Cavitation in impacted drops and jets and the effect on erosion damage thresholds. Wear 290–291, 154–160. doi:10.1016/j.wear.2012.03.006. URL http://www.sciencedirect.com/science/article/pii/S0043164812000968 ], who visualised cavity formation and shock propagation in liquid impacts at high velocities. Simulations unveil the shock structures and capture the high-speed jetting forming at the impact location, in addition to the subsequent cavitation induction and vapour formation due to refraction waves. Moreover, model predictions provide quantitative information and a better insight on the flow physics that has not been identified from the reported experimental data, such as shock-wave propagation, vapour formation quantity and induced pressures. Furthermore, evidence of the Richtmyer-Meshkov instability developing on the liquid-air interface are predicted when sufficient dense grid resolution is utilised

Immersed boundary method for cavitating and biological flows

The aim of the present work is the development of a computational tool to ease the numerical simulation of cavitating flows in domains of complex topology or with arbitrary moving boundaries. Within the framework of Computational Fluid Dynamics(CFD), an Immersed Boundary (IB) Method has been developed. According to the IB methodology, the grid that discretises the computational domain does not need to conform to the geometry and the solid boundaries are modelled on a fixed canonical grid by alternations of the governing equations in their vicinity. This modelling strategy is beneficial in terms of both computational cost and numerical solution. The grid generation, which is a complex and time consuming process, is simplified as a regular canonical grid, non-conformal to the boundaries, can be used. In addition, when moving boundaries are present, a conformal grid would need to adapt or deform following the motion of boundaries, which would increase the computational cost of the simulations in the first case and affect the solution in the latter case; the use of IB method alleviates these issues. The developed method follows the direct-forcing approach, which simply adds to the governing equations a source term to account for the body force acting on the fluid. The simplicity of the method makes it suitable for complex flow regimes, including phase change, strong shocks and compressibility effects, as well as Fluid Structure Interaction (FSI). Since cavitation dynamics regard a wide range of applications of engineering interest, from hydraulic machines to novel therapeutic techniques, the method is designed to be applicable in a wide range of flow regimes. Turbulent modelling and flow induced motion has been taken into account. The method has been successfully applied to cavitating and incompressible cases where conventional techniques are not easily or at all applicable. The shock-wave interaction with material interfaces is studied via the high-speed impact of a solid projectile on a water jet, which has been studied only experimentally before and only qualitative observations existed. The numerical investigation with the proposed methodology unveiled rich information regarding the physics of the impact, the resulting shock formation, cavitation development and interface instabilities initiation. Moreover, the methodology was applied on the thoroughly studied pulsatile flow through a bi leaflet Mechanical Heart Valve, to provide additional information regarding shear stress development. The methodology aids an experimental campaign employing novel shear stress measuring techniques, carried out by our collaborators. The research work and the developed method described in the present Thesis, intend to set the foundations for more elaborate numerical investigations of highly complex problems of Fluid Dynamics

Cavitation Induction by Projectile Impacting on a Water Jet

Following the work of Field et al. [4], who experimentally visualised cavity formation and shock propagation in impacted liquids at high velocities, the present study focuses on the simulation of the high velocity impact of a solid projectile on a water jet. The undeformable solid projectile is modelled through a direct forcing Immersed Boundary Method. The simulation is carried out using an explicit density based compressible solver, developed by Kyriazis et al. [6], which employs a two-phase flow model and includes phase change. This study gives a better insight on the phenomena following the impact of solids on liquids, including shock propagation and vapour formation, and demonstrates the capabilities of the presented Immersed Boundary Method to handle compressible cavitating flows

Children’s right to participate in early childhood care and education settings and relative innovatory supportive digital tools for ECCE professionals’ development

Young children’s participation is key to developing a culture of human rights, democracy, and rule of law and according to Council of Europe (2017) and United Nations (2005). In these terms, children’s right to participate is described as a key aspect in the framework of educational quality, and the positive relationship between children’s right to participate and early childhood care and education (ECCE) quality is already documented. Although this concept is not new to ECCE professionals, its application seems to remain a challenge within everyday activities. It is thus important for ECCE professionals to reflect on this right and on the practices towards its promotion, in order to be able to supply high quality education. The paper presents the innovatory attempts regarding the digital tools developed within the PARTICIPA Erasmus+ project (Professional development tools supporting participation rights in early childhood education) aiming to involve three target group -directors, teachers and teachers’ assistants- working in all types of early childhood care and education settings, so that have a digital space to reflect about children’s right to participate and its implementation. More specifically, the paper presents (a) a training program targeting the ECCE settings’ professionals provided through a massive open online course (MOOC) in 5 languages and disseminated in an online learning platform, focusing on the theoretical and practical aspects of children’s right to participate (i.e., state of the art, relevant pedagogical practices), (b) toolkits (i.e., validated self-assessment questionnaires) for ECCE directors and teachers and teacher assistants supported by discrete qualitative studies.info:eu-repo/semantics/publishedVersio

Subjective well-being and the 2008 recession in European regions

How can we explain why some regions experienced large decreases in subjective well-being during the 2008 recession, while in other regions, the changes were only very modest? Building on the literature on resilience in subjective well-being during periods of crisis, this article explores a related but undervalued factor that moderates the localized relationship between macroeconomic developments and life evaluation: regional quality of governance. We use individual-level data on life satisfaction and personal information taken from Eurobarometer for 89 European regions in the EU-28 for the period of 2005–2014, combined with macroeconomic variables and regional quality of governance data to test for the hypothesized moderating effect of quality of governance. The results demonstrate that increased regional unemployment and financial stress have a less aggravating effect on subjective well-being in regions characterized by a high quality of governance. These results support the capacity of quality of governance to buffer the negative effects of adverse macroeconomic conditions, most likely through generating trust and providing a safety net

Internet use and Problematic Internet Use: a systematic review of longitudinal research trends in adolescence and emergent adulthood

The aim of this systematic literature review is to map the longitudinal research in the field of Internet Use (IU) and Problematic Internet Use (PIU) in adolescents and emergent adults. Further, this study endeavours to examine the terminology and instruments utilized in longitudinal IU and PIU research and investigate whether statistically significant results have arisen from the areas of research focus. In a total of 29 studies, trends in the research of adolescent/emergent adult IU and PIU were discovered. These trends were conceptualized into individual, contextual and activity-related factors. Findings suggested that individual factors are the most researched and have demonstrated significant relationships with adolescent/young adult PIU. However, more research on contextual and activity-related factors is needed in order to achieve a clearer understanding of young people’s IU and PIU behaviours, and to incorporate into a comprehensive model that will guide future research in this growing field

Hematuria Secondary to an Internal Iliac Artery Aneurysm

We report a case of macroscopic hematuria secondary to an aneurysm of the internal iliac artery. An 84-year-old male presented to our department with a 12-hour history of painless gross hematuria. Cystoscopy showed decreased expansion suggesting compression from outside the bladder. At the point of compression, increased vascularization was noted in the bladder mucosa without evidence of active bleeding. No trace of blood was identified coming from the ureteric orifices, the bladder neck, or the prostate. There was no evidence of intra-vesicular masses or other inflammatory changes. The abdominal computed tomography scan revealed left-sided hydronephrosis and an abdominal aortic aneurysm involving the aortic bifurcation and both internal iliac arteries. There was no evidence of rupture. An aneurysm of the internal iliac artery is a rare cause of macroscopic hematuria that can be fatal. Awareness of this as a possible cause of hematuria may assist in immediate diagnosis and appropriate treatment

Need fulfilment and internet gaming disorder: a preliminary integrative model

Background: The need for a better understanding of the risk factors underpinning disordered gaming has been consistently emphasized. Although, gaming may offer a simple and straightforward means of alleviating distress, relying on gaming to address one's unmet psychological needs could invite problematic usage. Self-determination theory highlights the significance of three universally inherent psychological needs for relatedness, competency, and autonomy. A motivation to engage in gaming may be to address unmet needs and may become problematic. Objective: This study aimed to assess whether experienced levels of loneliness, depression and self-esteem mediate the association between Internet Gaming Disorder (IGD) behaviours and Need-Fulfilment deficits. Method: The participants comprised of 149 adults (83 males, 66 females), aged between 18 and 62 years. A series of self-reported questionaries assessing their levels of IGD behaviours, depression, loneliness, self-esteem and need-fulfilment were completed. Results: Need-fulfilment deficits were linked to higher IGD behaviours. Interestingly, this association was mediated by the reported levels of self-esteem and depression and not loneliness. Conclusions: The findings lend further empirical support for the mediating role of psychological distress between need fulfilment deficits and IGD behaviours. Keywords: Internet gaming disorder, Self-determination, Need-fulfilment, Psychological distres

A Gas Leak Rate Measurement System for the ATLAS MUON BIS-Monitored Drift Tubes

A low-cost, reliable and precise system developed for the gas leak rate measurement of the BIS-Monitored Drift Tubes (MDTs) for the ATLAS Muon Spectrometer is presented. In order to meet the BIS-MDT mass production rate, a total number of 100 tubes are tested simultaneously in this setup. The pressure drop of each one of the MDT is measured, within a typical time interval of 48 hours, via a differential manometer comparing with the pressure of a gas tight reference tube. The precision of the method implemented is based on the system temperature homogeneity, with accuracy of ÄT = 0.3 oC. For this reason, two thermally isolated boxes are used testing 50 tubes each of them, to achieve high degree of temperature uniformity and stability. After measuring several thousands of the MDTs, the developed system is confirmed to be appropriate within the specifications for testing the MDTs during the mass production