Predicting plastic deformation and localization band around a wellbore drilled through a porous rock is a challenging task that could have important implications for the prediction of instability and ...sand production. This study focuses on analyzing stress field, plastic zones, and localized deformations around a horizontal borehole drilled at a great depth through a highly porous rock formation. Several laboratory studies demonstrate that, depending on the loading path, highly porous rocks are susceptible to different failure mechanisms, but most of these mechanisms are mainly due to shear-induced dilation and shear-enhanced compaction. Plasticity models, in conjunction with bifurcation analysis, represent an extremely useful framework for describing such detailed constitutive responses. This paper presents a new elastoplastic constitutive model characterized by two yield surfaces intersecting smoothly, that is able to capture the different failure modes. The model is validated against experimental data for several different porous rocks, and it is then used to determine the stress and strain distributions around a horizontal wellbore using nonlinear finite element analysis. Particular interest is devoted to predicting the condition for the formation of a localized band of intense deformation, elucidating the factors that either prevent or enhance the band initiation. Results of simulations show the key role played by the elastoplastic constitutive model and the effects of the mud pressure, the in-situ stress condition and geometric imperfections in the development and propagation of plastic zone, as well as in the initiation of localization zone.
•An elastoplastic constitutive model has been proposed to describe high porous rocks.•The model has been validated against experimental data.•The model has been used to predict plasticity and localization around a wellbore.•Depending on stress conditions, dilatant and compactant mechanism take place.•In situ conditions affect significantly the plasticity and the initiation of bands.
Two serious obstacles in constructing terrestrial gravitational wave (GW) detectors that can resolve low-frequency signals (≤ 10 Hz) are seismic and Newtonian noises. Here we describe a new detector ...concept by adopting new measurement techniques and configurations to overcome the present low-frequency barrier due to these noises. Six magnetically levitated superconducting test masses, widely separated along three orthogonal axes, each with three degrees of freedom, constitute a tensor GW detector. The tensor outputs could be combined to better reject the Newtonian noise. Unlike current two-dimensional detectors, a single tensor detector is able to determine the polarization of GWs and the direction to sources on its own.
In this paper, we summarize the present state-of-the-art on the proof-of-principle experiment of frequency-dependent squeezing implemented through EPR entanglement for Virgo gravitational-wave ...detector and we introduce Virgo subsystem proposal for frequency-dependent squeezing, obtained with a compact apparatus and without the costs required by the infrastructure for the filter cavity.
AbstractThe problem of dynamic instability of rectangular plates with complex constraints at the edges is here solved starting from a theory in the literature; the suggested approach allows for the ...definition of generic, nonperfect constraint configurations for the regions of instability due to in-plane compression loads as diagrams that are expressed in function of the applied dynamic force and its frequency. The novelty of the work stands in (1) the study of viscoelasticity, combined with damage, at the constraints, which allows for the discussion of the performance of a rectangular plate with regards to dynamic instability at varying degrees of damping and damage, and (2) the analytical approach developed to solve the associated eigenvalue problem for rectangular plates with generic viscoelasto-damaged constraints at two opposite edges and simply supported at the other edges. Regarding the second point, the differential equation of motion of such a system is derived and, via the variable separation method, a solution for the transverse displacements is sought among those satisfying the generic boundary conditions at the four edges. Namely, the constraints are assigned in a homogeneous way, which has particularly convenient results for computational purposes. By imposing that the determinant of the resulting system vanishes, a closed-form solution is found for the free-vibration problem. The associated boundaries of the unstable regions for specific constraint configurations are discussed.
Purpose - The purpose of this paper is to show how to find the regions of dynamic instability of a beam axially loaded and visco-elastically constrained at its ends by Kelvin-Voigt translational and ...rotational units variously arranged according to different configurations, by using the equation of boundary frequencies.Design methodology approach - With respect to visco-elasticity the time variable is present as a parameter so that the above-mentioned exact approach is exploited to draw three-dimensional diagrams of the dynamic component of the periodic load and its frequency, varying with time and with the viscosity parameter μ characterizing the restraints.Findings - For not rigidly constrained configurations a peculiar asymptotic tendency is recognizable in both cases.Research limitations implications - The study allows for identifying the influence of visco-elastic restraints in the response of a beam under a dynamic axial load. Dynamic excitation occurs in several fields of mechanics: dynamic loads are encountered in structural systems subjected to seismic action, aircraft structures under the load of a turbulent flow and industrial machines whose components transmit time-dependant forces.Practical implications - Visco-elasticity accounts for possible vibration control solutions planned to improve the dynamic response of the rod; they can consist of layers of visco-elastic material within the body of the modelled element or local viscous instruments affecting the boundary conditions; the latter is the application this paper focuses on.Originality value - With this paper a calculation procedure to get an exact solution for particular static configurations of the beam is followed in order to define the influence of visco-elastic restraints under a dynamic axial load; the responses are given in terms of boundary frequencies domains and are supposed to be useful to learn the behaviour in time and in dependence of the intrinsic viscosity of the restraints.
A viable technique for the preparation of highly thermal conductive joints between sapphire components in gravitational wave detectors is presented. The mechanical loss of such a joint was determined ...to be as low as 2 × 10−3 at 20 K and 2 × 10−2 at 300 K. The thermal noise performance of a typical joint is compared to the requirements of the Japanese gravitational wave detector, KAGRA. It is shown that using such an indium joint in the suspension system allows it to operate with low thermal noise. Additionally, results on the maximum amount of heat which can be extracted via indium joints are presented. It is found that sapphire parts, joined by means of indium, are able to remove the residual heat load in the mirrors of KAGRA.
In this paper a new procedure for structural assessment of tunnel constructions during fire is presented. In particular, it consists of two steps: the first one deals with a realistic evaluation of ...thermal fluxes, both convective and radiative, for the whole tunnel. In the fires recently occurred in some European tunnels, the duration of the fire was longer than expected and the produced temperature fields were much more severe than those considered in standard codes. Therefore, such a kind of evaluation is of great importance. As second step, a simulation of the hygro-thermo-mechanical behaviour of concrete structure will be carried out using thermal fluxes previously calculated as thermal input for a fully coupled code, which considers concrete as a multiphase porous material.
•Three-stage study on the behaviour of storage plants.•Concrete with upgraded thermo-mechanical characteristics.•SolTeCa experimental system considered.•Thermal cycling of storage elements up to ...400°C.•Thermo-mechanical analyses.
A three-stage study on the behaviour of storage plants employing concrete with upgraded thermo-mechanical characteristics is here developed. The first stage defines the experimental campaign on a mixing at improved conductivity, via the SolTeCa experimental system, with review of the storage elements geometry, location of thermocouples and cycling procedures. The experimental results, obtained by ENEA via a comparison with appropriately performed numerical calculations, are interpreted during the second stage. Finally, a first design of a new equipment for the thermal cycling of storage elements up to 400°C is proposed, based on Joule-effect heating. The numerical results are reported, in order to understand the thermal dynamics as well as the induced thermo-mechanical effects on concrete elements.
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In this paper we study the behavior of the Casimir energy of a “multi-cavity” across the transition from the metallic to the superconducting phase of the constituting plates. Our analysis is ...carried out in the framework of the ARCHIMEDES experiment, aiming at measuring the interaction of the electromagnetic vacuum energy with a gravitational field. For this purpose it is foreseen to modulate the Casimir energy of a layered structure composing a multy-cavity coupled system by inducing a transition from the metallic to the superconducting phase. This implies a thorough study of the behavior of the cavity, in which normal metallic layers are alternated with superconducting layers, across the transition. Our study finds that, because of the coupling between the cavities, mainly mediated by the transverse magnetic modes of the radiation field, the variation of energy across the transition can be very large.
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