Optical fiber sensor fusion for aerospace systems lifecycle management

Optical fiber is a material that can transport light signals, so resulting useful for data transmission and sensing applications. Fiber Bragg Gratings (FBG) are a specific type of optical sensors that can measure parameters like temperature, strain, and vibration. The PhD program focuses on developing a sensing and monitoring strategy for aerospace systems using FBG sensors networks. The study will include material selection, optical fiber manufacturing, sensors packaging and integration, calibration and interrogation techniques and smart logics development for acquiring and controlling phenomena affecting the equipment under test. Some experimental activities have already been conducted to analyse thermal and mechanical sensing and to define a reliable methodology for integrating sensors into various systems. During the tests, FBGs were found to have high accuracy and sensitivity for thermal variations, mechanical strain and shortterm thermal transients. The crucial role of bounding technique was also enhanced. Additionally, more complex tests have been conducted for sensor more realistic systems, both for space and aeronautic environments. The results gained in this first period are positive and encouraging, suggesting further developments during PhD progra

Innovative sensor networks for massive distributed thermal measurements in space applications under different environmental testing conditions

Optical fiber has seen significant development in the technical fields where it has been used in the last years. In the first place, obviously, for the Internet and, more broadly, to improve communication efficiency; but, more recently, for medicinal, structural, or lighting engineering applications. Furthermore, many optical solutions are beginning to be researched in the aerospace sector. The use of optical fiber, in particular, is strongly related to the employment of FBG type optical sensors, which may be particularly suitable for specific measurements of relevant physical parameters to be performed on specimens with typical aeronautical and/ or space employment. More specifically, the performance of several FBG sensors for temperature measurement in vacuum for validation tests of space products has been examined during this work. Unlike typical thermocouples, the adoption of this new type of sensor can provide substantial benefits, beginning with a significant gain in terms of the size of the fiber, which ensures a minimum disturbance on thermal data. Furthermore, if supplied with a suitable coating (in polyimide), the optical fiber may guarantee a very high operating temperature range, which is extensively compatible with the high-temperature range existent in space. The measurements were divided into two independent phases. First, a preliminary test was performed in the laboratory using a climatic chamber to evaluate several sensor network integration methodologies on the specimens and select the most effective one for the vacuum test. The test demonstrated that a simple adhesive bonding of the fiber to the specimens ensures a precise temperature measurement under vacuum and stable conditions. The following vacuum test program confirmed that FBGs could be used as temperature sensors even at very high temperatures. The good results of this test encourage us to consider FBG strategic for space applications and, particularly, for thermal characterizations, thanks to the high number of available sensors, combined with the minimal cable's size. However, further studies are required in cryogenic cases to validate the entire range of extreme temperatures that characterize the space environment

PROGNOSTICS OF AEROSPACE ELECTROMECHANICAL ACTUATORS USING THE FAILURE MAPS TECHNIQUE

The gradual deployment of Electro Mechanical Actuators (EMAs) as primary flight controls actuators, driven by the “more electric” approach, must be paired up with a solid prognostic background in order to overcome the limited experience and to support the system during his lifecycle. In fact, assessing EMAs actual states thanks to Prognostic and Health Monitoring (PHM) systems and detecting potential failures is crucial to guarantee the compliance to the relative safety requirements. The research activity described in this paper focuses on the development of a model-driven deterministic methodology based on Failure Modes Maps (FMMs). Thanks to data obtained through a Numerical Test Bench (NTB) and a Simplified Model (SM), the proposed prognostic algorithm is proved capable of detecting and identifying the source and magnitude of two different failures: rotor eccentricity and increased friction. After a short description of the implemented models and a general overview of typical EMA failure modes as well as FMMs development, the proposed algorithm is explained in detail. This is followed by a comprehensive study of the two simulated failures as well as the creation of the relative FMMs. Finally, the proposed prognostic algorithm is successfully applied on the obtained FMMs

Thermomechanical calibration of FBG sensors for aerospace applications

Optical fibers have found widespread use in engineering, from communication to sensors. Among them, Fiber Bragg Gratings are allowed to detect several parameters. Scope of this work is to assess their performances as temperature and mechanical strain sensors for aerospace: in this regard, an experimental calibration is discussed. Then, alternative approaches are tested in order to distinguish thermal from mechanical contributes. This is first addressed by using a hybrid system of digital and optical sensors, and then then with a fully optical system. Both the presented solutions reached the scope. A concept of a third, innovative approach, is also described

A genetic-based prognostic method for aerospace electromechanical actuators

Prior awareness of impending failures of primary flight command electromechanical actuators (EMAs) utilizing prognostic algorithms can be extremely useful. Indeed, early detection of the degradation pattern might signal the need to replace the servomechanism before the failure manifests itself. Furthermore, such algorithms frequently use a model-based approach based on a direct comparison of the real (High Fidelity) and monitor (Low Fidelity) systems to discover fault characteristics via optimization methods. The monitor model enables the gathering of accurate and exact data while requiring a minimal amount of processing. This work describes a novel simplified monitor model that accurately reproduces the dynamic response of a typical aerospace EMA. The task of fault detection and identification is carried out by comparing the output signal of the reference system (the high fidelity model) with that acquired from the monitor model. The Genetic Algorithm is then used to optimize the matching between the two signals by iteratively modifying the fault parameters, getting the global minimum of a quadratic error function. Once this is found, the optimization parameters are connected with the assumed progressive failures to assess the system's health. The high-fidelity reference model examined in this study is previously conceptualized, developed, implemented in MATLAB-Simulink and finally experimentally confirmed

Study of FBG-based optical sensors for thermal measurements in aerospace applications

Optical fibers have revolutionized several technological sectors in recent decades, above all that of communication, and have also found many applications in the medical, lighting engineering, and infrastructural fields. In the aerospace field, many studies investigated the adoption of fiber optics considering the planned transition from fly-by-wire to fly-by-light flight controls. A significant feature of optical fiber is its ability to be used not only as a transmission medium but also as a basis for fiber-embedded sensors; one of the most prominent types is based on Bragg gratings (FBGs). FBGs can replace several traditional sensors, providing measures of temperature, vibrations, and mechanical deformation. Optical sensors provide many advantages over traditional, electrical-based sensors, including EMI insensitivity, ease of multiplexing on a single line, resilience to harsh environments, very compact sizes and global weight saving. Furthermore, punctual knowledge of the temperature field is essential to perform the thermal compensation of the optical sensors used for strain measurements. In this work, the authors analyzed the performance of thermal sensors based on FBGs to verify their stability, accuracy, and sensitivity to operating conditions. Two different methods of FBGs surface application have been considered (gluing with pre-tensioning vs. non-tensioned bonding). The results were then compared to those acquired using typical temperature sensors to determine the relationship between the observed temperature and the Bragg wavelength variation (i.e. the proportionality coefficient Kt). The effects on the proportionality coefficient Kt, arising from fiber pre-tensioning and thermal expansion of the structural support, were then evaluated by comparing the results obtained with the two bonding approaches

Efficacy of Teduglutide for Parenteral Support Reduction in Patients with Short Bowel Syndrome: A Systematic Review and Meta-Analysis

Teduglutide has been described as an effective treatment for parenteral support (PS) reduction in patients with short bowel syndrome (SBS). However, a quantitative summary of the available evidence is still lacking. PubMed/Medline, EMBASE, Cochrane library, OVID, and CINAHL databases were systematically searched up to July 2021 for studies reporting the rate of response (defined as a ≥20% reduction in PS) to teduglutide among PS-dependent adult patients. The rate of weaning (defined as the achievement of PS independence) was also evaluated as a secondary end-point. Ten studies were finally considered in the meta-analysis. Pooled data show a response rate of 64% at 6 months, 77% at 1 year and, 82% at ≥2 years; on the other hand, the weaning rate could be estimated as 11% at 6 months, 17% at 1 year, and 21% at ≥2 years. The presence of colon in continuity reduced the response rate (−17%, 95%CI: (−31%, −3%)), but was associated with a higher weaning rate (+16%, 95%CI: (+6%, +25%)). SBS etiology, on the contrary, was not found to be a significant predictor of these outcomes, although a nonsignificant trend towards both higher response rates (+9%, 95%CI: (−8%, +27%)) and higher weaning rates (+7%, 95%CI: (−14%, +28%)) could be observed in patients with Crohn’s disease. This was the first meta-analysis that specifically assessed the efficacy of teduglutide in adult patients with SBS. Our results provide pooled estimates of response and weaning rates over time and identify intestinal anatomy as a significant predictor of these outcomes

Analysis of the fixing process of FBG optical sensors for thermomechanical monitoring of aerospace applications

In aerospace, lots of components can be defined as “safety critical”. As a result, it is crucial to early identify the failure precursors when the effects on the systems performances are still practically insignificant. For this reason, complex networks of sensors had been developed and integrated into different parts to monitor several operational parameters, useful for evaluating their health (such as such as temperatures, displacements, vibrations, etc). Clearly, due to the importance of data collected, the technology employed shall be very reliable, even while working in harsh environments. Sensors based on optical fiber Bragg grating (FBG) meet these requirements. However, the fiber’s integration process in the considered system is really crucial, from the moment that it could influence the sensors output. In this regard, gluing the optical sensors is really a critical activity, because the effects of the glue’s retire and its viscous assessment shall be analysed and quantified. In this work, it was done by comparing performances of two equal samples, each one with an FBG glued on it. The first sample was prepared about two months before the second one. Furthermore, data from both FBG have been collected from the gluing phase of the second sample and in the following days. The results showed that the assessment of the resin evolved in different phases, but all of them were united by the fact that the overall process makes sensors measures not reliable during this specific transitory phase. By observing the evolution of the linear fit gradients, it can be stated that the variations reached their maximum in the middle of the gluing process, when the fiber was detached from the tensioning device. Finally, at the end of the overall process, data output resulted stable, so making FBG employable for reliable thermal or strain measures