3,316 research outputs found
Test of FBG sensors for monitoring high pressure pipes
Fibre Bragg Grating (FBG) sensors are increasingly being used on a wide range of civil, industrial and aerospace structures. The sensors are created inside optical fibres (usually standard telecommunication fibres); the optical fibres technology allows to install the sensors on structures working in harsh environments, since the materials are almost insensitive to corrosion, the monitoring system can be positioned far away from the sensors without sensible signal losses, and there is no risk of electric discharge. FBG sensors can be used to create strain gages, thermometers or accelerometers, depending on the coating on the grating, on the way the grating is fixed to the structure, and on the presence of a specifically designed interface that can act as a transducer. This paper describes a test of several different FBG sensors to monitor an high pressure pipe that feeds the hydraulic actuators of a 6 degrees-of-freedom shaking table at the ENEA Casaccia research centre. A bare FBG sensor and a copper coated FBG sensor have been glued on the pipe. A third sensor has been mounted on a special interface to amplify the vibrations; this last sensor can be placed on the steel pipe by a magnetic mounting system, that also allows the its removal. All the sensor are placed parallel to the axis of the pipe. The analysis of the data recorded when the shaking table is operated will allow to determine which kind of sensor is best suited for structural monitoring of high pressure pipelines
Global minimizers of coexistence for competing species
A class of variational models describing ecological systems of k species
competing for the same resources is investigated. The occurrence of coexistence
in minimal energy solutions is discussed and positive results are proven for
suitably differentiated internal dynamics
Almgren-type monotonicity methods for the classification of behavior at corners of solutions to semilinear elliptic equations
A monotonicity approach to the study of the asymptotic behavior near corners
of solutions to semilinear elliptic equations in domains with a conical
boundary point is discussed. The presence of logarithms in the first term of
the asymptotic expansion is excluded for boundary profiles sufficiently close
to straight conical surfaces
Sharp asymptotic estimates for eigenvalues of Aharonov-Bohm operators with varying poles
We investigate the behavior of eigenvalues for a magnetic Aharonov-Bohm
operator with half-integer circulation and Dirichlet boundary conditions in a
planar domain. We provide sharp asymptotics for eigenvalues as the pole is
moving in the interior of the domain, approaching a zero of an eigenfunction of
the limiting problem along a nodal line. As a consequence, we verify
theoretically some conjectures arising from numerical evidences in preexisting
literature. The proof relies on an Almgren-type monotonicity argument for
magnetic operators together with a sharp blow-up analysis
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