1,700 research outputs found
Third-order theory for the bending analysis of laminated thin and thick plates including the strain gradient effect
The aim of the paper is the development of a third-order theory for laminated composite plates that is able to accurately investigate their bending behavior in terms of displacements and stresses. The starting point is given by the corresponding Reddyâs Third-order Shear Deformation Theory (TSDT). This model is then generalized to consider simultaneously the Classical Laminated Plate Theory (CLPT), as well as the First-order Shear Deformation Theory (FSDT). The constitutive laws are modified according to the principles of the nonlocal strain gradient approach. The fundamental equations are solved analytically by means of the Navier methodology taking into account cross-ply and angle-ply lamination schemes. The numerical applications are presented to highlight the nonlocal effects on static behavior
Pre-test analysis of protected loss of primary pump transients in CIRCE-HERO facility
In the frame of LEADER project (Lead-cooled European Advanced Demonstration Reactor), a new configuration of the steam generator for ALFRED (Advanced Lead Fast Reactor European Demonstrator) was proposed. The new concept is a super-heated steam generator, double wall bayonet tube type with leakage monitoring [1]. In order to support the new steam generator concept, in the framework of Horizon 2020 SESAME project (thermal hydraulics Simulations and Experiments for the Safety Assessment of MEtal cooled reactors), the ENEA CIRCE pool facility will be refurbished to host the HERO (Heavy liquid mEtal pRessurized water cOoled tubes) test section to investigate a bundle of seven full scale bayonet tubes in ALFRED-like thermal hydraulics conditions. The aim of this work is to verify thermofluid dynamic performance of HERO during the transition from nominal to natural circulation condition. The simulations have been performed with RELAP5-3D© by using the validated geometrical model of the previous CIRCE-ICE test section [2], in which the preceding heat exchanger has been replaced by the new bayonet bundle model. Several calculations have been carried out to identify thermal hydraulics performance in different steady state conditions. The previous calculations represent the starting points of transient tests aimed at investigating the operation in natural circulation. The transient tests consist of the protected loss of primary pump, obtained by reducing feed-water mass flow to simulate the activation of DHR (Decay
Heat Removal) system, and of the loss of DHR function in hot conditions, where feed-water mass flow rate is absent. According to simulations, in nominal conditions, HERO bayonet bundle offers excellent thermal hydraulic behavior and, moreover, it allows the operation in natural circulation
Post-test simulation of a PLOFA transient test in the CIRCE-HERO facility
CIRCE is a leadâbismuth eutectic alloy (LBE) pool facility aimed to simulate the primary system of a heavy liquid metal (HLM) cooled pool-type fast reactor. The experimental facility was implemented with a new test section, called HERO (Heavy liquid mEtal pRessurized water cOoled tubes), which consists of a steam generator composed of seven double-wall bayonet tubes (DWBT) with an active length of six meters. The experimental campaign aims to investigate HERO behavior, which is representative of the tubes that will compose ALFRED SG. In the framework of the Horizon 2020 SESAME project, a transient test was selected for the realization of a validation benchmark. The test consists of a protected loss of flow accident (PLOFA) simulating the shutdown of primary pumps, the reactor scram and the activation of the DHR system. A RELAP5-3D© nodalization scheme was developed in the pre-test phase at DIAEE of âSapienzaâ University of Rome, providing useful information to the experimentalists. The model consisted to a mono-dimensional scheme of the primary flow path and the SG secondary side, and a multi-dimensional component simulating the large LBE pool. The analysis of experimental data, provided by ENEA, has suggested to improve the thermalâhydraulic model with a more detailed nodalization scheme of the secondary loop, looking to reproduce the asymmetries observed on the DWBTs operation. The paper summarizes the post-test activity performed in the frame of the H2020 SESAME project as a contribution of the benchmark activity, highlighting a global agreement between simulations and experiment for all the primary circuit physical quantities monitored. Then, the attention is focused on the secondary system operation, where uncertainties related to the boundary conditions affect the computational results
An experimental investigation of the independent effect of suction and degree of saturation on very small-strain stiffness of unsaturated sand
The paper presents an experimental investigation of very small strain stiffness of unsaturated sand. A triaxial test apparatus was equipped with bender elements and compression discs in order to assess the stiffness at very small strains by measuring the velocity of propagation of shear and compression waves through an unsaturated sample. The negative water column method was adopted to apply suction at the base of the sample. The experiments were designed to investigate the independent effect of suction and degree of saturation on the wave propagation velocities. This was achieved by testing the sand sample on both the drying and wetting path
Analytical pressureâdeflection curves for the inflation of pre-stretched circular membranes
Analytical, numerical and experimental study of the finite inflation of circular membranes
In the present work we derive an analytical expression for the pressureâdeflection curve of circular membranes subjected to inflation. This problem has been studied mostly from a numerical point of view and there is still a lack of accurate closed-form solutions in nonlinear elasticity. The analytical formulation is developed with a semi-inverse method by setting a priori the kinematics of deformation of the membrane. A compressible MooneyâRivlin material model is considered and a pressureâdeflection relation is derived from the equilibrium. The kinematics is approximated and therefore the obtained solution is not exact. Consequently, the formulation is adjusted by introducing an additional polynomial function in the pressureâdeflection equation. The polynomial is calibrated by fitting numerical solutions of the exact system of differential equilibrium equations. The calibration is done over a wide range of constitutive parameters that covers the response of all rubber materials for technological applications. As a result, a definitive and accurate expression of the applied pressure as a function of the deflection of the membrane is obtained. The formula is validated with finite element (FE) simulations and compared with other solutions available in the literature. The comparison shows that the present model is more accurate. In addition, unlike the other models, it can be applied to compressible materials. Experimental uniaxial and bulge tests are carried out on rubber materials and the model proposed is used to characterize the MooneyâRivlin constitutive parameters. Since the pressureâdeflection formula is accurate and easy-to-use, it is an innovative tool in engineering applications of inflated membranes
Effective thermal properties of fibre reinforced materials
The thermal behaviour of an elastic matrix reinforced with synthetic micro or macro fibres subjected to a constant heat flow is investigated in the present work. Steady-state condition for the heat flux is considered and isotropic thermal conductivity for both the matrix and fibres is assumed. Owing to the geometry of the system, reference is made to bipolar cylindrical coordinates.
Various boundary conditions can be considered on the contours of the fibres. In particular, for a matrix reinforced with two fibres taken as insulated inclusions, a vanishing heat flow across the contour of the fibres must be imposed.
After the temperature field has benn determined analytically, a homogeneization procedure is performed in order to find the equivalent thermal properties of the fibre reinforced composite material
The impact of SuperB on flavour physics
This report provides a succinct summary of the physics programme of SuperB,
and describes that potential in the context of experiments making measurements
in flavour physics over the next 10 to 20 years. Detailed comparisons are made
with Belle II and LHCb, the other B physics experiments that will run in this
decade. SuperB will play a crucial role in defining the landscape of flavour
physics over the next 20 years.Comment: 20 pages, 6 figure
Cooperative JahnâTeller effect and the role of strain in the tetragonal-to-cubic phase transition in MgxCu1
Temperature and composition dependences of the I41/amd â [Fd\bar 3m] phase transition in the MgxCu1âââxCr2O4 spinel solid solution, due to the melting of the cooperative JahnâTeller distortion, have been studied by means of single-crystal X-ray diffraction. Crystals with x = 0, 0.10, 0.18, 0.43, 0.46, 0.53, 1 were grown by flux decomposition methods. All crystals have been refined in the tetragonal I41/amd space group except for the Mg end-member, which has cubic symmetry. In MgxCu1âââxCr2O4 the progressive substitution of the JahnâTeller, d9 Cu2+ cation with spherical and closed-shell Mg2+ has a substantial effect on the crystal structure, such that there is a gradual reduction of the splitting of a and c unit-cell parameters and flattening of the tetrahedra. Single-crystal diffraction data collected in situ up to T = 1173â
K show that the tetragonal-to-cubic transition temperature decreases with increasing Mg content. The strength of the CuâCu interaction is, in effect, modulated by varying the Cu/Mg ratio. Structure refinements of diffraction data collected at different temperatures reveal that heating results in a gradual reduction in the tetrahedron compression, which remains significant until near the transition temperature, however, at which point the distortion of the tetrahedra rapidly vanishes. The spontaneous strain arising in the tetragonal phase is large, amounting to 10% shear strain, et, and âŒâ
1% volume strain, Vs, in the copper chromite end-member at room temperature. Observed strain relationships are consistent with pseudoproper ferroelastic behaviour ([e_{\rm t}^2] â Vs â [q_{\rm JT}^2], where qJT is the order parameter). The I41/amd â [Fd\bar 3m] phase transition is first order in character for Cu-rich samples and then evolves towards second-order character. Although a third order term is permitted by symmetry in the Landau expansion, this behaviour appears to be more accurately represented by a 246 expansion with a change from negative to positive values of the fourth-order coefficient with progressive dilution of the JahnâTeller cation
On the edge-wave of a thin elastic plate supported by an elastic half-space
In this contribution, we consider edge-wave propagating in a thin elastic semiinfinite
plate which is bilaterally supported by a homogenenous isotropic elastic half-space. The
problem is formulated in terms of a eigenproblem constituted by a system of five linear PDEs
in the plate transverse displacement and in the scalar and vector elastic potentials subject
to mixed boundary conditions accounting for plate-fundation displacement continuity under
the plate and zero normal stress outside. Zero tangential stress is envisaged throughout. The
problem could be reduced to an inhomogenenous Wiener-Hopf functional equation in terms of
the half-space surface displacement and of the plate-to-fundation contact pressure only. The
kernel function is analyzed and the Rayleigh wave speed is obtained together with a novel
dispersion equation. Finally, kernel factorization is performed
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