On the use of AR models for SHM: A global sensitivity and uncertainty analysis framework

This paper proposes a complete sensitivity analysis of the use of Autoregressive models (AR) and Mahalanobis Squared Distance in the field of Structural Health Monitoring (SHM). Autoregressive models come from econometrics and their use for modelling the response of a physical system has been well established in the last twenty years. However, their aware application in engineering should be supported by knowledge about how they describe phenomena which are well defined by physics. Since autoregressive models are estimated by a least square minimization, statistical tools like Global Sensitivity Analysis and uncertainty propagation are powerful methods to investigate the performance of AR models applied to SHM. These methodologies allow one to understand the role of the uncertainty and uncorrelated noise by a rigorous approach based on statistical motivations. Moreover, it is possible to quantify the link between the mechanical properties of a system and the AR parameters, as well as the Mahalanobis Squared Distance. By fixing a factor prioritization among the variables of a AR model, it is possible to understand which are the parameters playing a main role in damage detection and which type of structural changes is possible to efficiently detect

Comparison of different approaches for analysing cross-wind effects on high sided vehicles passing by a bridge tower

One of the risks connected to running safety of heavy vehicles is associated to rollover due to the high cross winds which may occur in exposed sites such as embankments, bridges, etc. Specifically, the present paper compares two methodologies for investigating the interaction between a tractor semitrailer combination and the wake of a tower bridge in cross wind conditions. The first methodology employs moving vehicle CFD simulations to evaluate the aerodynamic loads acting on the vehicle. In particular, motion of the vehicle is introduced into the CFD model using a moving mesh approach. The second methodology is instead base on a multi-body vehicle model coupled with a force distribution approach to calculate the aerodynamic forces acting on the vehicle during the tower wake crossing, which relies on static vehicle CFD simulations/wind tunnel tests. In the paper, the results of the two methodologies are presented and compared, illustrating relative advantages and drawbacks

A force-distribution approach to simulate the aerodynamic loads acting on a vehicle passing by a bridge tower: comparison with CFD simulations

Rollover of high-sided vehicles represents a serious concern for running safety, especially when they run on exposed sites such as viaducts and bridges. In particular, the present paper investigates the interaction between a tractor semitrailer combination and the wake of a tower bridge in cross wind conditions. The proposed methodology is based on a multi-body ve-hicle model coupled with a force distribution approach to calculate the aerodynamic forces acting on the vehicle during the tower wake crossing, which relies on static vehicle CFD simula-tions/wind tunnel tests. To asses reliability of the developed methodology, obtained results are compared with moving vehicle CFD simulations (based on a moving mesh approach). Numerical results state that the developed model may represent a valuable tool for investigating wind-shield-ing solutions at the design stage of bridges. The developed model in fact provides results in good agreement with moving vehicle CFD data, but allows to significantly reduce computation effort and the coupling with a driver model

Nonlinear 3D Dynamic Model of an Automotive Dual Mass Flywheel

Internal combustion engines produce a fluctuating torque due to discrete pistons combustion, as well as induced inertial imbalance of the reciprocating pistons. In standard operating conditions, the resulting torsional oscillations of the crankshaft are transferred to the gearbox, leading to a number of comfort problems. Rattle noise is one of these problems and it is caused by impulsive forces caused by clearances across the driveline and especially in the gearbox. In order to prevent rattle, dual mass flywheels may be used to reduce torsional oscillations in automotive powertrains. The present paper presents a 3D nonlinear dynamic model of an automotive dual mass flywheel. The model is made of primary and secondary masses and the arc springs between them. Centrifugal effects and redirection forces acting on the springs as well as nonlinear contact forces due to stoppers and flanges bounding spring motion are accounted for. Moreover, friction occurring in seals and friction resulting from the spring radial forces are included. The developed dual mass flywheel model is included into a multi-body model of the vehicle powertrain to assess the effect of its main parameters on the driveline behaviour (e.g. modes of vibration, radial forces)

Preoperative Localization in Colonic Surgery (PLoCoS Study): a multicentric experience on behalf of the Italian Society of Colorectal Surgery (SICCR)

: The aim of this prospective multicentric study was to compare the accurate colonic lesion localization ratio between CT and colonoscopy in comparison with surgery. All consecutive patients from 1st January to 31st December 2019 with a histologically confirmed diagnosis of dysplastic adenoma or adenocarcinoma with planned elective, curative colonic resection who underwent both colonoscopy and CT scans were included. Each patient underwent conventional colonoscopy and CT to stage the tumour, and the localization results of each procedure were registered. CT and colonoscopic localization were compared with surgical localization, adopted as the reference. Our analysis included 745 patients from 23 centres. After comparing the accuracy of colonoscopy and CT (for visible lesions) in localizing colonic lesions, no significant differences were found between the two preoperative tools (510/661 vs 499/661 correctly localized lesions, p = 0.518). Furthermore, after analysing only the patients who underwent complete colonoscopy and had a visible lesion on CT, no significant difference was observed between conventional colonoscopy and CT (331/427 vs 340/427, p = 0.505). Considering the intraoperative localization results as a reference, a comparison between colonoscopy and CT showed that colonoscopy significantly failed to correctly locate the lesions localized in the descending colon (17/32 vs 26/32, p = 0.031). We did not identify an advantage in using CT to localize colonic tumours. In this setting, colonoscopy should be considered the reference to properly localize lesions; however, to better identify lesions in the descending colon, CT could be considered a valuable tool to improve the accuracy of lesion localization