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.
The infrastructures for oil and gas production and distribution need reliable monitoring systems. The risks for pipelines, in particular, are not only limited to natural disasters (landslides, earthquakes, extreme environmental conditions) and accidents, but involve also the damages related to criminal activities, such as oil theft. The existing monitoring systems are not adequate for detecting damages from oil theft, and in several occasion the illegal activities resulted in leakage of oil and catastrophic environmental pollution. Systems based on fiber optic FBG (Fiber Bragg Grating) sensors present a number of advantages for pipeline monitoring. FBG sensors can withstand harsh environment, are immune to interferences, and can be used to develop a smart system for monitoring at the same time several physical characteristics, such as strain, temperature, acceleration, pressure, and vibrations. The monitoring station can be positioned tens of kilometers away from the measuring points, lowering the costs and the complexity of the system. This paper describes tests on a sensor, based on FBG technology, developed specifically for detecting damages of pipeline due to illegal activities (drilling of the pipes), that can be integrated into a smart monitoring chain.
The concept “Disaster Mitigation and Sustainable Engineering” is introduced comprehensively and several examples are shown in this paper. It is emphasized that it can be effectively realized in the field “smart materials and structural systems.” As serious disasters may not occur for a long period of time, and the structures for disaster mitigation suffer from vast amount of maintenance cost etc., they are better to be used daily. Their compactness and deploying function are also very useful. In order to demonstrate the concept, two examples having been experimentally tried are introduced, that is, artificial forests and deployable structure based on honeycomb to be used against flooding. Other examples and products in the world are also introduced and future directions are discussed.
The Earth Orientation Parameters (EOP), i.e. the spin axis of the Earth, is influenced by the mass redistribution inside and
on the surface of the Earth. On the Earth surface, global ice melting, sea level change and atmospheric circulation are the
prime contributors. Recent studies have unraveled the majority of the mysteries behind the Chandler wobble, the annual
motion and the secular motion of the pole. The differences from the motion of a pole for a rigid Earth is indeed due to the
mass redistribution and transfer of angular momentum among the atmosphere, the oceans and solid Earth. The technique
of laser ranging and the use of laser ranged satellites such as LARES along with other techniques such Very Long Baseline
Interferometry (VLBI) allow to measure the EOP with accuracies at the level of ~200 μas which correspond to few
millimeters at the Earth’s surface, while the use of Global Navigation Satellite System (GNSS) data can reach an accuracy
even below 100 μas. At these unprecedented high levels of accuracy, even tiny anomalous behavior in EOP can be observed
and thus correlated to global environmental changes such as ice melting on Greenland and the polar caps, and extreme
events that involve strong ocean-atmosphere coupling interactions such as the El Niño. The contribution of Satellite Laser
Ranging (SLR) data such as from the LARES mission and similar satellites to this area is outlined in this paper.
The very low thermal expansion coefficient of silica at cryogenic temperature prevents the use of Fibre Bragg Grating
(FBG) sensors for high resolution temperature monitoring in cryogenic environments involving liquid gases or space
applications. To overcome such limitations sensors have been coated with different metals to improve the measurement
sensitivity in the very low temperature region, i.e. 4.2-35 K. Various coatings have been deposited by electrowinning on
the external fibre surface after aluminium pre-coating. Full characterization of this new type of sensor is described in the
paper.
An aluminum prototype of the AMICA (Astro Mapper for Instrument Check of Attitude) Star Tracker Support (ASTS) of the AMS_02 (Alpha Magnetic Spectrometer) space experiment has been instrumented with Fiber Bragg Gratings (FBGs). In this work the use of FBGs to perform dynamic tests on the ASTS prototype is reported. The excitation has been provided by an instrumented impact hammer, the mechanical response of the structure has been obtained by bonded FBGs and accelerometers. All time histories have been recorded, transformed in the frequency domain to retrieve Frequency Response Functions (FRFs)-accelerometer responses- and Strain Frequency Response Functions (SFRFs) -FBG responses-, both providing resonant frequencies and displacements (strain) shapes of the ASTS. Numerical simulations of this structure have been performed to predict its resonant frequencies and vibrational displacement (strain) shapes. Experimental results demonstrate the capability of FBGs to perform in situ experimental modal analysis as confirmed by the comparison of the optical response with the accelerometers one and the good agreement with the numerical analysis.
Fibre Bragg Grating (FBG) sensors, can be used for temperature monitoring but the low thermal expansion coefficient of silica limits its sensitivity in cryogenic environment. However it will be shown that the use of a lead coating, electrodeposited on an aluminum pre-coated senosr, will enhance FBG sensing properties down to 5 K. Slight variations on the optical response of the coated FBG sensor are interpreted with the micrographic observation of the deposit.
In this paper, we present an application devoted to measure the dynamic response of a prototype of a support of a star tracker. Four different techniques have been used and compared with each other. Specifically Electronic Speckle Pattern Interferometry and Speckle Shearography have been used as full field modal appropriation techniques, impact hammer and accelerometer as a broad band conventional technique and finally broad band with impact hammer and FBG sensor as a newly proposed methodology. Modal parameters have been retrieved using all the four methodologies described above and compared. We have demonstrated that FBG sensors can be used to retrieve modal parameters useful as indicators of the state of health of a structural component. When embedded the FBG can be used actively also during the qualification process of the smart component as well as in service for shape monitoring. This latter purpose is important for precision pointing instruments such as the star tracker under investigation.
The aim of the present paper is to describe the tests performed on the zinc-aluminum specimens cast with optical fibers inserted in it. Aspect concerning the wettability of the fiber matrix interface and the buoyancy of the fiber into the melt are considered. Special care has been devoted to the realization of the chill for obtaining a slender specimen suitable for vibration tests. Metallographic studies have been carried out in order to obtain information on the state of the optical fiber. One arm of a Mach-Zehnder interferometer has been set with the specimen described above. Optimal correlation has been found between the excitation applied on the specimen and the response obtained by the fringe pattern variation.
Re-entry in planetary atmospheres is one of the most challenging environments to be faced by an aerospace structure. Presently space agencies are studying and developing programs to reduce launch costs by developing a new generation reusable launch vehicles. In fact a significant portion of the launch cost, for those vehicles, is represented by maintenance, non destructive testing and personnel involved in ground operations. For instance NASA and Lockeed Martin are leading the VentureStar program, where the real time health monitoring is considered an important aspect, while ESA has now finished a preliminary analysis for different reusable launch vehicle configurations. Fiber optic sensors which can be embedded into structural components can provide an efficient means for fast and reliable structural health monitoring. In this paper the possibility of embedding fiber optic sensors into materials subjected to particularly critical thermal treatments is verified. Several specimens of metal alloys and carbide based powders with embedded optical fibers have been prepared by the high pressure high velocity oxy fuel technique. The tests have proven the feasibility of the embedding with the above mentioned technology which exposes the fibers to quite a severe environment during the deposition. Micrographic analysis and optical transmission tests have been carried out on the sprayed specimens.
KEYWORDS: Resistors, 3D modeling, Finite element methods, Instrument modeling, MATLAB, Mathematical modeling, Control systems, Space operations, Capacitors, Matrices
Limiting structural response by increasing damping with passive devices it is attractive because these elements, even if they fail to work properly, will never introduce mechanical energy into the structure. Thus although active control results more efficient, nevertheless possible malfunction of the control system or the changed properties of mechanical components, during lifetime, may cause the control system itself to trouble the structure dynamics. That is especially true in space, where external operations are difficult or even impossible and the system must work for lifetimes of years in the space environment (radiations, space debris, etc.). In this paper piezoceramic materials, suitably loaded with either resistors or resistors and inductors, are considered. The similarity of the piezo device complex stiffness with the ones used for viscoelastic material models allows one to simulate, with relative ease, the behaviour of a structure equipped with passive piezo devices by the use of general purpose finite element codes. Finite element models of a beam and one model of a plate are considered as test cases. Estimations of the damping coefficients, introduced by the passive devices, are in excellent agreement in the different models of the beam considered and are consistent in the case of the plate.
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