Synthesis of electrical networks interconnecting PZT actuators to damp mechanical vibrations

This paper proves that it is possible to damp mechanical vibrations of some beam frames by means of piezoelectric actuators interconnected via passive networks. We create a kind of electromechanical wave guide where the electrical velocity group equals the mechanical one thus enabling an electromechanical energy transfer. Numerical simulations are presented which prove the technical feasibility of proposed deviceComment: International Symposium on Applied Electromagnetics and Mechanics in honor of Professor K.Miya, Tokyo: 2000. 9 page

Elastic interaction of interfacial spherical-cap cracks in hollow particle filled composites

AbstractThis work analyzes the elastic interaction between two spherical-cap cracks present along the outer surface of a hollow particle embedded in a dissimilar medium under remote uniaxial tensile loading. A semi-analytical approach based on an enriched Galerkin method is adopted to determine stress and deformation fields as functions of particle wall thickness and cracks’ configuration. The present analysis is limited to multiple interfacial spherical-cap cracks; that is, crack propagation is restrained to the particle-matrix interface and possibility of crack kinking in the matrix is not considered. Interfacial crack growth characteristics, conditions for stable crack propagation, equal crack growth, and shielding are established through energy release rate analysis. The study is relevant to the analysis of tensile and flexural failure of syntactic foams used in marine and aerospace applications. Results specialized to glass-vinyl ester syntactic foams demonstrate that particle wall thickness can be used to control crack stability and growth characteristics as well as tailoring the magnitude of the shielding phenomenon. Predictions are compared to finite element findings for validation and to results for penny-shaped cracks to elucidate the role of crack curvature

Analysis of hollow inclusion–matrix debonding in particulate composites

AbstractThis work aims at understanding the effect of particle–matrix interfacial debonding on the tensile response of syntactic foams. The problem of a single hollow inclusion with spherical-cap cracks embedded in a dissimilar matrix material is studied. Degradation of elastic modulus, cavity formation in the proximity of debonded regions, stress localization phenomena in the inclusion, debonding energetics, and crack kinking are studied for a broad range of inclusion wall thickness and debonding extent. A series solution based on the Galerkin method is proposed and validated through comparison with findings from boundary element and finite element methods. Results are specialized to glass particle-vinyl ester matrix systems widely used in marine structural applications. The insight gained into the role of particle–matrix debonding extent and inclusion wall thickness is useful in understanding the possible failure mechanisms of syntactic foams under tensile and flexural loading conditions and in tailoring their parameters for specific applications

Tritium transport in the vacuum vessel pressure suppression system for helium cooled pebble bed

In the frame of the safety studies for the EU-DEMO reactor, attention is paid to the hydrogen concentration in the vacuum vessel and connected volumes since it would lead to a possible hazard of releasing tritium and activated dust. The risk of explosion cannot be excluded a priori if H2 stockpiles. For this reason, in both water (WCLL) and helium (HCPB) cooled breeding blanket concepts of EU-DEMO, the problem is under investigation with a cross-reference between the available technologies in fission (such as the Passive Autocatalytic Recombiners – PAR) and fusion application. In particular, the recent analyses pointed out the implementation of the PARs into the Vacuum Vessel Pressure Suppression System or linked systems. This paper evaluates the Hydrogen behavior (main mobilized tritium source term) for the Helium-Cooled Pebble Bed (HCPB) VVPSS concept. The analyses preliminary investigate the stratification of the hydrogen mass inventory inside the PSS. In particular, a MELCOR 1.8.6 model of the PSS, based on past activities aimed at dust transport and thermohydraulic analyses, is adopted. The paper also introduces the applicability of PAR technology in the operation range of fusion devices, analyzing the problem of the recombination rate due to the dilution of Hydrogen after a Helium blowdown

Passive hydrogen recombination during a beyond design basis accident in a fusion DEMO plant

One of the most important environmental and safety concerns in nuclear fusion plants is the confinement of radioactive substances into the reactor buildings during both normal operations and accidental conditions. For this reason, hydrogen build-up and subsequent ignition must be avoided, since the pressure and energy generated may threaten the integrity of the confinement structures, causing the dispersion of radioactive and toxic products toward the public environment. Potentially dangerous sources of hydrogen are related to the exothermal oxidation reactions between steam and plasma-facing components or hot dust, which could occur during accidents such as the in-vessel loss of coolant or a wet bypass. The research of technical solutions to avoid the risk of a hydrogen explosion in large fusion power plants is still in progress. In the safety and environment work package of the EUROfusion consortium, activities are ongoing to study solutions to mitigate the hydrogen explosion risk. The main objective is to preclude the occurrence of flammable gas mixtures. One identified solution could deal with the installation of passive autocatalytic recombiners into the atmosphere of the vacuum vessel pressure suppression system tanks. A model to control the PARs recombination capacity as a function of thermal-hydraulic parameters of suppression tanks has been modeled in MELCOR. This paper aims to test the theoretical effectiveness of the PAR intervention during an in-vessel loss of coolant accident without the intervention of the decay heat removal system for the Water-Cooled LithiumLead concept of EU-DEMO

DEMO divertor cassette and plasma facing unit in vessel loss-of-coolant accident

As part of the pre-conceptual design activities for the European DEMOnstration plant, a carefully selected set of safety analyses have been performed to assess plant integrated performance and the capability to achieve expected targets while keeping it in a safe operation domain. The DEMO divertor is the in-vessel component in charge of exhausting the major part of the plasma ions' thermal power in a region far from the plasma core to control plasma pollution. The divertor system accomplishes this goal by means of assemblies of cassette and target plasma facing units modules, respectively cooled with two independentheat-transfer systems. A deterministic assessment of a divertor in-vessel Loss-of-Coolant Accident is here considered. Both Design Basis Accident case simulating the rupture of an in-vessel pipe for the divertor cassette cooling loop, and a Design Extension Conditions accident case considering the additional rupture of an independent divertor target cooling loop are assessed. The plant response to such accidents is investigated, a comparison of the transient evolution in the two cases is provided, and design robustness with respect to safety objectives is discussed

The role of noise and initial conditions in the asymptotic solution of a bounded confidence, continuous-opinion model

We study a model for continuous-opinion dynamics under bounded confidence. In particular, we analyze the importance of the initial distribution of opinions in determining the asymptotic configuration. Thus, we sketch the structure of attractors of the dynamical system, by means of the numerical computation of the time evolution of the agents density. We show that, for a given bound of confidence, a consensus can be encouraged or prevented by certain initial conditions. Furthermore, a noisy perturbation is added to the system with the purpose of modeling the free will of the agents. As a consequence, the importance of the initial condition is partially replaced by that of the statistical distribution of the noise. Nevertheless, we still find evidence of the influence of the initial state upon the final configuration for a short range of the bound of confidence parameter

Analysis of parameter mismatches in the master stability function for network synchronization

In this letter, we perform a sensitivity analysis on the master stability function approach for the synchronization of networks of coupled dynamical systems. More specifically, we analyze the linear stability of a nearly synchronized solution for a network of coupled dynamical systems, for which the individual dynamics and output functions of each unit are approximately identical and the sums of the entries in the rows of the coupling matrix slightly deviate from zero. The motivation for this parametric study comes from experimental instances of synchronization in human-made or natural settings, where ideal conditions are difficult to observe.Comment: Accepted for publication in EuroPhysics Letter