On the use of Lagrange Multiplier State-Space Substructuring in dynamic substructuring analysis

In this article, the formulation of Lagrange Multiplier State-Space Substructuring (LM-SSS) is presented and extended to directly compute coupled displacement and velocity state-space models. The LM-SSS method is applied to couple and decouple state-space models established in the modal domain. Moreover, it is used together with tailored postprocessing procedures to eliminate the redundant states originated from the coupling and decoupling operations. This specific formulation of the LM-SSS approach made it possible to develop a tailored coupling form, named Unconstrained Coupling Form (UCF). UCF just requires the computation of a nullspace and does not rely on the selection of a subspace from a nullspace. By exploiting a numerical example, LM-SSS was compared with the Lagrange Multiplier Frequency Based Substructuring (LMFBS) approach, which is currently widely recognized as a reference approach. This was done both in terms of: a)coupled FRFs derived by coupling the state-space models of two substructures and b) decoupled FRFs derived by decoupling the state-space model of a component from the coupled model. LM-SSS showed to be suitable to compute minimal order coupled models and UCF turned out to have similar performance as other coupling forms already presented to the scientific community. As for the decoupling task, the FRFs derived from the LM-SSS approach perfectly matched those obtained by LM-FBS. Moreover, it was also demonstrated that the elimination of the redundant states originated from the decoupling operation was correctly performed. The approaches discussed were exploited on an experimental substructuring application. LM-SSS resulted to be a reliable SSS technique to perform coupling and decoupling operations with state-space models estimated from measured FRFs as well as to provide accurate minimal-order models

Pixel frequency based railroad surface flaw detection using active infrared thermography for Structural Health Monitoring

Abstract With rapid increase in operation and development of high-speed trains, inspection of railroad surface flaws has become an important aspect for safe and reliable operation of rail network. Non-destructive testing using active infrared thermography has been useful in determining the structural health of different structures with additional benefit of robustness in overall inspection system. This study is based on detection of artificial surface flaws on an in-service railroad. Transverse and longitudinal flaws of various dimensions were machined on rough and smooth rail surface. The railroad surface was thermally stimulated to a temperature equivalent to practical conditions. Emitted radiations from rail surface were captured by an infrared camera to detect cracks. Results show a comparison between the surface flaws on rough and smooth rail surface. Subsequently, raw infrared images were post-processed by statistical image improvement to quantitatively analyse the results. Significant change in the frequency distribution of pixel intensity is observed as the flaw size and depth changes giving a clear quantification of crack topology. A comprehensive and inexpensive solution for damage diagnosis will be offered to railway authorities for Structural Health Monitoring (SHM) and NDT by the proposed framework

Acoustic Attenuation of COVID-19 Face Masks: Correlation to Fibrous Material Porosity, Mask Breathability and Bacterial Filtration Efficiency

none7openMartarelli, Milena; Montalto, Luigi; Chiariotti, Paolo; Simoni, Serena; Castellini, Paolo; Battista, Gianmarco; Paone, NicolaMartarelli, Milena; Montalto, Luigi; Chiariotti, Paolo; Simoni, Serena; Castellini, Paolo; Battista, Gianmarco; Paone, Nicol

Exploiting the laser scanning facility for vibration measurements

SIGLEAvailable from British Library Document Supply Centre- DSC:DXN055608 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Similar and dissimilar FSWed joints in lightweight alloys: heating distribution assessment and IR thermography monitoring for on-line quality

The heating distribution assessment on similar and dissimilar friction stir welded joints in AA6082 and AA5754 aluminium alloy sheets was investigated. The FSW experiments were carried out using constant rotational and welding speeds of 1500 rpm and 60 mm/min, respectively. Temperature was locally measured by means of K-type thermocouples inserted into thin grooves located on the bottom side of the sheets, in fixed positions, very close to the welding line. It was observed that the mechanical properties of joints are related to the heat distribution. In order to obtain a completely non intrusive temperature monitoring, that was able to follow the process dynamic, a non-contact measurement system based on infrared thermography was also developed. Such system, used for the experimental evaluation of temperature on the upper surface of the joints, is also able to detect the presence of flow defects with a non-destructive method, demonstrating its effectiveness as a diagnostic instrument for the on-line quality control of welded joints

Similar and Dissimilar FSWed Joints in Lightweight Alloys: Heating Distribution Assessment and IR Thermography Monitoring for On-Line Quality Control

The heating distribution assessment on similar and dissimilar friction stir welded joints in AA6082 and AA5754 aluminium alloy sheets was investigated. The FSW experiments were carried out using constant rotational and welding speeds of 1500 rpm and 60 mm/min, respectively. Temperature was locally measured by means of K-type thermocouples inserted into thin grooves located on the bottom side of the sheets, in fixed positions, very close to the welding line. It was observed that the mechanical properties of joints are related to the heat distribution. In order to obtain a completely non intrusive temperature monitoring, that was able to follow the process dynamic, a non-contact measurement system based on infrared thermography was also developed. Such system, used for the experimental evaluation of temperature on the upper surface of the joints, is also able to detect the presence of flow defects with a non-destructive method, demonstrating its effectiveness as a diagnostic instrument for the on-line quality control of welded joints

Acoustic beamforming: analysis of uncertainty and metrological performances

In this paper, the metrological performances of the acoustic beamforming technique have been investigated, and in particular, its accuracy in estimating the acoustic power of sources and in localizing their spatial position has been analysed. The uncertainty of the system has been determined combining the statistical effects of input parameters uncertainty under the basic hypothesis that the sound source can be represented as a distribution of independent monopoles. This analysis was performed using a Type B approach based on an analytical model according to the ISO Guide of the expression of uncertainty in measurement and subsequently using a numerical model based on Monte Carlo simulation. Systematic errors due to deviations of input parameters (e.g. speed of sound or source–array distance), affecting output level and spatial accuracy have been analysed. Once these inaccuracies were quantified, suggestions to minimize them were given. Finally a criterion to optimize focussing of the beamforming technique based on acoustic image contrast maximization has been developed

Performance analysis of continuous tracking laser Doppler vibrometry applied to rotating structures in coast-down

In this paper a performance analysis of the so-called tracking continuous scanning laser Doppler vibrometry (TCSLDV) exploited in coast-down has been performed. This non-contact measurement system is able to scan continuously over a rotating surface during coast-down and to determine vibration operational deflection shapes (ODSs) and natural frequencies in short time, i.e. the temporal extent of the coast-down. The method is based on a laser Doppler vibrometer (LDV) whose laser beam is driven to scan continuously over the whole rotor surface synchronously with its rotation, so that the LDV output is modulated by the structure’s ODSs. This technique has a full-field nature that enables it to measure simultaneously the time and spatial dependence of the vibration in a unique measurement. However, the TCSLDV presents some criticalities in practical applications, especially when applied to rotary transient and fast processes. In fact, if the vibration is transient and decays very fast, then the laser beam could not have had the time to scan the complete structure surface and the modulation of the ODS could be partial. An analytical model reproducing a representative experiment has been developed in order to evaluate the sensitivity of results to testing conditions. The laser beam trajectory in both the fixed and rotating reference systems has been synthesized showing its dependence on experimental parameters as the rotation speed variation during coast-down. It has been demonstrated the decrease in speed induces the deformation of the laser trajectory influencing the LDV output time history, spectrum and consequently the recovered ODS

Performance analysis of continuous tracking laser Doppler vibrometry applied to rotating structures in coast-down

In this paper a performance analysis of the so-called tracking continuous scanning laser Doppler vibrometry (TCSLDV) exploited in coast-down has been performed. This non-contact measurement system is able to scan continuously over a rotating surface during coast-down and to determine vibration operational deflection shapes (ODSs) and natural frequencies in short time, i.e. the temporal extent of the coast-down. The method is based on a laser Doppler vibrometer (LDV) whose laser beam is driven to scan continuously over the whole rotor surface synchronously with its rotation, so that the LDV output is modulated by the structure’s ODSs. This technique has a full-field nature that enables it to measure simultaneously the time and spatial dependence of the vibration in a unique measurement. However, the TCSLDV presents some criticalities in practical applications, especially when applied to rotary transient and fast processes. In fact, if the vibration is transient and decays very fast, then the laser beam could not have had the time to scan the complete structure surface and the modulation of the ODS could be partial. An analytical model reproducing a representative experiment has been developed in order to evaluate the sensitivity of results to testing conditions. The laser beam trajectory in both the fixed and rotating reference systems has been synthesized showing its dependence on experimental parameters as the rotation speed variation during coast-down. It has been demonstrated the decrease in speed induces the deformation of the laser trajectory influencing the LDV output time history, spectrum and consequently the recovered ODS