Underwater explosion of cylindrical charge near plates: Analysis of pressure characteristics and cavitation effects

In this paper, a coupled scheme utilizing advantages of the Runge–Kutta discontinuous Galerkin (RKDG) method and finite elements is applied to investigate cavitation induced by rarefaction waves during a near-field underwater explosion of cylindrical charge. A high-order RKDG method has advantages of an accurate shock capturing. So, it was used to solve a governing Eulerian equation for a compressible fluid. A finite-element method (FEM) was suitable to deal with problems of a shock response of structures and, therefore, applied for structural analysis. The suggested method was used to study pressure characteristics and cavitation effects of underwater explosions of cylindrical charges near single/double plates. First, a cavitation model was introduced in the RKDG method, and a numerical model of a high-pressure bubble in a cylinder was developed. The obtained numerical results were compared with the known solution in order to verify the validity of the suggested method. Second, a RKDG-FEM model of underwater explosion of a spherical charge near a plate was developed; its results for maximum deflection at the centre of the plate were compared with experimental data to prove the effectiveness of the coupled algorithm. Then, this algorithm was employed to simulate the process of underwater explosions of cylindrical charges near a single plate. Here, effects of different parameters - thickness of the plate and a distance between the charge and the plate - on pressure and cavitation characteristics were studied. Finally, a numerical model of double plates subjected to a near-field underwater explosion was developed. Cavitation evolution and its effect on shock-wave loading were analysed. Additionally, the effect of the distance between two plates was studied. The suggested analysis and its results provide a reference for load characteristics of near-field underwater explosions and shock response of structures

SPH-BEM simulation of underwater explosion and bubble dynamics near rigid wall

A process of underwater explosion of a charge near a rigid wall includes three main stages: charge detonation, bubble pulsation and jet formation. A smoothed particle hydrodynamics (SPH) method has natural advantages in solving problems with large deformations and is suitable for simulation of processes of charge detonation and jet formation. On the other hand, a boundary element method (BEM) is highly efficient for modelling of the bubble pulsation process. In this paper, a hybrid algorithm, fully utilizing advantages of both SPH and BEM, was applied to simulate the entire process of free and near-field underwater explosions. First, a numerical model of the free-field underwater explosion was developed, and the entire explosion process– from the charge detonation to the jet formation–was analysed. Second, the obtained numerical results were compared with the original experimental data in order to verify the validity of the presented method. Third, a SPH model of underwater explosion for a column charge near a rigid wall was developed to simulate the detonation process. The results for propagation of a shock wave are in good accordance with the physical observations. After that, the SPH results were employed as initial conditions for the BEM to simulate the bubble pulsation. The obtained numerical results show that the bubble expanded at first and then shrunk due to a differences of pressure levels inside and outside it. Here, a good agreement between the numerical and experimental results for the shapes, the maximum radius and the movement of the bubble proved the effectiveness of the developed numerical model. Finally, the BEM results for a stage when an initial jet was formed were used as initial conditions for the SPH method to simulate the process of jet formation and its impact on the rigid wall. The numerical results agreed well with the experimental data, verifying the feasibility and suitability of the hybrid algorithm. Besides, the results show that, due to the effect of the Bjerknes force, a jet with a high speed was formed that may cause local damage to underwater structures

Die Wiederansiedlung von Flüchtlingen in der Schweiz: Eine Analyse der bisherigen Praxis und Diskussion von Handlungsoptionen

We report herein an iron-catalyzed azidotrifluoromethylation method for expedient vicinal trifluoromethyl primary-amine synthesis. This method is effective for a broad range of olefins and N-heterocycles, and it facilitates efficient synthesis of a wide variety of vicinal trifluoromethyl primary amines, including those that prove difficult to synthesize with existing approaches. Our preliminary mechanistic studies revealed that the catalyst-promoted azido-group transfer proceeds through a carbo-radical instead of a carbocation species. Characterization of an active iron catalyst through X-ray crystallographic studies suggests that in situ generated, structurally novel iron-azide complexes promote the oxidant activation and selective azido-group transfer

A sketch model of written production

<p>A sketch model of written production</p

Missing intentionality : the limitations of social media analysis for participatory urban design

This paper reflects upon some limitations of Urban Sensing, a EU-funded research project that explores the potential of social media analysis and data visualization as a source of knowledge for participatory urban planning processes. In Urban Sensing we did not only collect users’ contributions related to the context of their use and perception of the city, but all kinds of contributions, such as private comments or conversations with friends that are completely unrelated to urban issues. In most of the contributions collected in our platform, there is no intentionality from the users to post a tweet or check-in at Foursquare as actions to influence urban planning and management processes. Can this lack of intentionality undermine the potential of our platform as a bottom-up component for participatory processes

Effects of Ambient Environmental Factors on the Stereotypic Behaviors of Giant Pandas <i>(Ailuropoda melanoleuca)</i>

<div><p>Stereotypies are commonly observed in zoo animals, and it is necessary to better understand whether ambient environmental factors contribute to stereotypy and how to affect animal welfare in zoo settings. This study investigated the relationships between stereotypic behaviors and environmental factors including ambient temperatures, humidity, light intensity, sound intensity and number of visitors. Seven giant pandas were observed in three indoor enclosures and three outdoor enclosures. Environmental factors were measured for both indoor and outdoor enclosures and the effect they had on stereotypical behaviors was investigated. Our research found that light intensity significantly correlated with all stereotypies behaviors. Higher environmental temperature reduced the duration of pacing but increased the frequency of pacing, the duration and frequency of door-directed, meanwhile the duration of head-toss. However, we found no noticeable effect of humidity on stereotypic behaviors except for the frequency of head-toss. We also found that sound intensity was not correlated with stereotypies. Finally, the growth of visitors was negatively associated with the duration of door-directed. These results demonstrated that various environmental factors can have significant effects on stereotypic behaviors causing the expression of various stereotypies. Thus, stereotypies in zoo animals may not simply represent suboptimal welfare, but rather might be adopted as a means of coping with an aversive environment.</p></div

Elucidating Molecular Iridium Water Oxidation Catalysts Using Metal–Organic Frameworks: A Comprehensive Structural, Catalytic, Spectroscopic, and Kinetic Study

As a new class of porous, crystalline, molecular materials, metal–organic frameworks (MOFs) have shown great promise as recyclable and reusable single-site solid catalysts. Periodic order and site isolation of the catalytic struts in MOFs facilitate the studies of their activities and reaction mechanisms. Herein we report the construction of two highly stable MOFs (<b>1</b> and <b>2</b>) using elongated dicarboxylate bridging ligands derived from Cp*Ir­(<b>L</b>)­Cl complexes (<b>L</b> = dibenzoate-substituted 2,2′-bipyridine, <b>bpy-dc</b>, or dibenzoate-substituted 2-phenylpyridine, <b>ppy-dc</b>) and Zr₆O₄(OH)₄(carboxylate)₁₂ cuboctahedral secondary building units (SBUs) and the elucidation of water oxidation pathways of the Cp*Ir­(<b>L</b>)Cl catalysts using these MOFs. We carried out detailed kinetic studies of Ce⁴⁺-driven water oxidation reactions (WORs) catalyzed by the MOFs using UV–vis spectroscopy, phosphorescent oxygen detection, and gas chromatographic analysis. These results confirmed not only water oxidation activity of the MOFs but also indicated oxidative degradation of the Cp* rings during the WOR. The (<b>bpy-dc</b>)­Ir­(H₂O)₂XCl (X is likely a formate or acetate group) complex resulted from the oxidative degradation process was identified as a competent catalyst responsible for the water oxidation activity of <b>1</b>. Further characterization of the MOFs recovered from WORs using X-ray photoelectron, diffuse-reflectance UV–vis absorption, luminescence, and infrared spectroscopies supported the identity of (<b>bpy-dc</b>)­Ir­(H₂O)₂XCl as an active water oxidation catalyst. Kinetics of MOF-catalyzed WORs were monitored by Ce⁴⁺ consumptions and fitted with a reaction–diffusion model, revealing an intricate relationship between reaction and diffusion rates. Our work underscores the opportunity in using MOFs as well-defined single-site solid catalytic systems to reveal mechanistic details that are difficult to obtain for their homogeneous counterparts

Asymmetric [4 + 2]-Cycloaddition of Copper–Allenylidenes with Hexahydro-1,3,5-triazines: Access to Chiral Tetrahydroquinazolines

A copper-catalyzed asymmetric formal [4 + 2]-cycloaddition of copper–allenylidenes and hexahydro-1,3,5-triazines has been developed, providing chiral tetrahydroquinazolines in moderate to good yields and with high enantioselectivities for most cases (up to 88% yield and 98% ee)

Environmental Factors between Outdoor and Indoor Enclosures.

<p>Environmental Factors between Outdoor and Indoor Enclosures.</p

Key Differences in Enclosure Characteristics for Outdoor and Indoor.

<p>Key Differences in Enclosure Characteristics for Outdoor and Indoor.</p