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This article presents a novel algorithm for vibration suppression with inertial actuators. This algorithm is designed to cancel out harmonic disturbances and finds application in rotating machines like helicopters and, more in general, in structures connected to rotors, which generate a single-harmonic disturbance with a frequency far from any natural frequency of the structure. The existing control algorithms for inertial actuators are mainly designed to cancel out vibrations arising from slightly damped structural modes, so they are not suitable for this specific application, whereas the proposed control algorithm is based on the Enhanced Phase Locked Loop (EPLL), a non-linear adaptive bandpass filter originally designed to stabilize electrical systems. In this work, the use of the EPLL is extended to the vibration control of a mechanical system as it is used to track frequency and amplitude variations of the vibration acceleration and calculate the required control force to suppress it. In this article, the algorithm is described, and the parameters of the EPLL are tuned, analyzing their influence on the actuators' performances. Numerical simulations are performed to discuss its stability, analyze its performance, and compare this novel algorithm to other existing control strategies. Finally, the proposed control algorithm is applied to a helicopter tailplane using two identical inertial actuators. The experiments have shown that the EPLL-based control can effectively cancel out single-harmonic vibrations far from the resonance and that it is robust to amplitude and frequency variations. [ABSTRACT FROM AUTHOR]

In 2018 a collaborative project between Politecnico di Milano (PoliMI) and Regione Lombardia (RL) was launched to join forces and expertise toward the improvement of the regional transport infrastructures maintenance management. One of the project goals was the development of regional guidelines aimed to support the design and implementation of monitoring systems for bridges. The focus of this paper is on the illustration of the Monitoring Regional (MoRe) guidelines and of their implementation on nine pilot monitoring systems designed and deployed within the project. The (MoRe) guidelines tackle the entire monitoring process from the analyses of the monitoring goals and the preliminary investigations needed to the identification of the phenomena and relevant indicators to monitor, up to the selection of monitoring devices and the presentation of results. A short illustration of the permanent monitoring systems installed on nine exemplary bridges in the Lombardia region concludes the paper. [ABSTRACT FROM AUTHOR]

In the framework of direct Structural Health Monitoring approaches, this paper presents a low frequency range analysis performed on a steel truss bridge designed in 1946 and built up in Northern Italy. The bridge is instrumented with a permanent structural health monitoring system, that guarantees a continuous flux of data and information from a heterogeneous set of sensors. In this analysis, static and quasistatic bridge responses are considered. These experimental data are merged with the analogous outputs obtained from numerical simulations, performed on FE models representative of the actual bridge, with the purpose of identifying damage‐sensitive indexes. Simulations are performed considering the healthy structure and modelling different damage scenarios. The static analysis consists in the construction of a regressive model able to estimate sensor output responses starting from environmental measurements, with the primary purpose to reduce the effect of temperature over measured static response. This procedure allows to relate the damages simulated by means of a numerical model with the real data, so that the monitoring rules can effectively defined. [ABSTRACT FROM AUTHOR]

Bridges and viaducts are facing growing traffic, increasing loads as well as ageing and deterioration. Nowadays, vibration‐based Structural Health Monitoring (SHM) represents an effective solution to extract quantitative information regarding bridge structural condition. Bridge frequencies are fundamental parameters capable to reflect and summarize bridge dynamics and health condition. Typically, their identification is performed by direct approaches, which rely on the use of sensors installed on the structure under analysis. A cost‐efficient, movable, and flexible alternative is offered by drive‐by methods, consisting in the use of instrumented vehicles to extract bridge frequencies. This paper presents an experimental campaign carried out on a multiple‐span mixed railroad bridge, with the aim to identify its frequencies through onboard measurements. A set of MEMS wireless accelerometers is deployed on the vehicle, firstly allowing for vehicle pitch component mitigation. Vehicle accelerations were then used to extract bridge frequencies, by means of a Most Probable Modal Frequencies approach, relying on synchrosqueezed wavelet transform. At a cruise speed of 30 km/h promising results in terms of indirect frequency estimation were found, with no traffic disruption. [ABSTRACT FROM AUTHOR]

Structural health monitoring of civil infrastructure, such as bridges and buildings, has become a trending topic in the last few years. The key factor is the technological push given by new technologies that permit the acquisition, storage, processing and visualisation of data in real time, thus assessing a structure's health condition. However, data related to anomaly conditions are difficult to retrieve, and, by the time those conditions are met, in general, it is too late. For this reason, the problem becomes unsupervised, since no labelled data are available, and anomaly detection algorithms are usually adopted in this context. This research proposes a novel algorithm that transforms the intrinsically unsupervised problem into a supervised one for condition monitoring purposes. Considering a bridge equipped with N sensors, which measure static structural quantities (rotations of the piers) and environmental parameters, exploiting the relationships between different physical variables and determining how these relationships change over time can indicate the bridge's health status. In particular, this algorithm involves the training of N models, each of them able to estimate the quantity measured via a sensor by using the others' N − 1 measurements. Hence, the system can be represented by the ensemble of the N models. In this way, for each sensor, it is possible to compare the real measurement with the predicted one and evaluate the residual between the two; this difference can be addressed as a symptom of changes in the structure with respect to the condition regarded as nominal. This approach is applied to a real test case, i.e., Candia Bridge in Italy, and it is compared with a state-of-the-art anomaly detector (namely an autoencoder) in order to validate its robustness. [ABSTRACT FROM AUTHOR]

Low-flatcar wagons represent a good alternative to freight truck transportation. In fact, the whole truck can be easily loaded on these wagons. However, due to the railway vehicle gauge, these vehicles present a particular design with an important impact on the dynamics of the trainset and on its derailment risk. The present work aims at analysing the dynamic behaviour of the trainset and the influence of the freight train composition on the derailment risk. Numerical simulations have been performed to identify the most critical conditions. Then, an experimental campaign has been carried out to evaluate the derailment risk associated to these conditions. [ABSTRACT FROM AUTHOR]

The actual European regulations for the acceptance of railway vehicles prescribe the measurement of not only accelerations but also contact forces exchanged at wheel–rail interface, in order to assess the level of running safety, track loading and vibration behaviour. It is important to point out that the standards do not prescribe any specific method to measure forces, or define the measurement of forces. The aim of this paper is to investigate the metrological properties of a dynamometric wheelset in order to determine the associated measurement uncertainty and to verify its readiness in the range of frequencies where the force analysis must be performed. With reference to a specific instrumented wheelset, a method for increasing the accuracy of the measure when critical running conditions (i.e. large values of the derailment coefficient Y/Q) are detected is proposed. The proposed method can be applied to any instrumented wheelset, but it is particularly effective on non-conventional wheelsets, where only few measurements are available and the classical methods cause large estimation errors. [ABSTRACT FROM AUTHOR]

In this paper we report on nonreciprocal wave propagation in a 2D radial sonic crystal with space–time varying properties. We show that a modulation traveling along the radial direction reflects in omni-directional and isotropic nonreciprocal wave propagation between inner and outer shells. The nonreciprocal behavior is verified both analytically and numerically, demonstrating that space–time radial crystals can be employed as one-way emitter or receiver of acoustic or elastic signals. [ABSTRACT FROM AUTHOR]