Leonardo Soria

Finite amplitude vibrations of a sharp-edged beam immersed in a viscous fluid near a solid surface

In this paper, we study finite amplitude bending vibrations of a slender thin beam immersed in a quiescent viscous liquid and oscillating near a solid surface. We focus on the regime of low Knudsen and squeeze numbers and moderately large Keulegan-Carpenter number, for which neither squeeze film models nor unsteady Stokes hydrodynamics are suitable to describe the flow physics. In this case, the distributed hydrodynamic loading experienced by the oscillating beam is represented by a complex-valued hydrodynamic function, which explicitly depends on the Keulegan-Carpenter number to account for convection-driven nonlinearities in the fluid-structure interaction. We conduct a parametric study on the two-dimensional computational fluid dynamics of a rigid lamina oscillating in the vicinity of a solid surface to establish a handleable semianalytical formula for the hydrodynamic function in terms of the key nondimensional parameters. We validate the proposed modeling approach through experiments on centimeter-si...

Hydrodynamic coupling of two sharp-edged beams vibrating in a viscous fluid

In this paper, we study flexural vibrations of two thin beams that are coupled through an otherwise quiescent viscous fluid. While most of the research has focused on isolated beams immersed in placid fluids, inertial and viscous hydrodynamic coupling is ubiquitous across a multitude of engineering and natural systems comprising arrays of flexible structures. In these cases, the distributed hydrodynamic loading experienced by each oscillating structure is not only related to its absolute motion but is also influenced by its relative motion with respect to the neighbouring structures. Here, we focus on linear vibrations of two identical beams for low Knudsen, Keulegan–Carpenter and squeeze numbers. Thus, we describe the fluid flow using unsteady Stokes hydrodynamics and we propose a boundary integral formulation to compute pertinent hydrodynamic functions to study the fluid effect. We validate the proposed theoretical approach through experiments on centimetre-size compliant cantilevers that are subjected to underwater base-excitation. We consider different geometric arrangements, beam interdistances and excitation frequencies to ascertain the model accuracy in terms of the relevant non-dimensional parameters.

Operational Modal Analysis and the Performance Assessment of Vehicle Suspension Systems

Comfort, road holding and safety of passenger cars are mainly influenced by an appropriate design of suspension systems. Improvements of the dynamic behaviour can be achieved by implementing semi-active or active suspension systems. In these cases, the correct design of a well-performing suspension control strategy is of fundamental importance to obtain satisfying results. Operational Modal Analysis allows the experimental structural identification in those that are the real operating condi- tions: Moving from output-only data, leading to modal models linearised around the more interesting working points and, in the case of controlled systems, providing the needed information for the optimal design and verification of the controller perfor- mance. All these characters are needed for the experimental assessment of vehicle suspension systems. In the paper two sus- pension architectures are considered equipping the same car type. The former is a semi-active commercial system, the latter a novel prototypic active system. For the assessment of suspension performance, two different kinds of tests have been considered, proving ground tests on different road profiles and laboratory four poster rig tests. By OMA-processing the signals acquired in the different testing conditions and by comparing the results, it is shown how this tool can be effectively utilised to verify the operation and the performance of those systems, by only carrying out a simple, cost-effective road test.

The Lubrication Regime at Pin-Pulley Interface in Chain CVTs

This paper deals with the strongly nonstationary squeeze of an oil film at the interface between the chain pin and pulley in chain belt continuously variable transmission. We concentrate on the squeeze motion as it occurs as soon as the pin enters the pulley groove. The duration time to complete the squeeze process compared with the running time the pin takes to cover the entire arc of contact is fundamental to understand whether direct asperity-asperity contact occurs between the two approaching surfaces to clarify what actually is the lubrication regime (elastohydrodynamic lubrication (EHL), mixed, or boundary) and to verify if the Hertzian pressure distribution at the interface can properly describe the actual normal stress distribution. The Hertzian pressure solution is usually taken as a starting point to design the geometry of the pin surface; therefore, it is of utmost importance for the designers to know whether their hypothesis is correct or not. Taking into account that the traveling time, the pin spends in contact with the pulley groove, is of about 0.01 s, we show that rms surface roughness less than 0.1 μm, corresponding to values adopted in such systems, guarantees a fully lubricated EHL regime at the interface. Therefore, direct asperity-asperity contact between the two approaching surfaces is avoided. We also show that the Hertzian solution does not properly represent the actual pressure distribution at the pin-pulley interface. Indeed, after few microseconds a noncentral annular pressure peak is formed, which moves toward the center of the pin with rapidly decreasing speed. The pressure peak can grow up to values of several gigapascals. Such very high pressures may cause local overloads and high fatigue stresses that must be taken into account to correctly estimate the durability of the system.

Some issues in the structural health monitoring of a railway viaduct by ground based radar interferometry

Operational Modal Analysis (OMA) is extensively used as a tool for the modal identification and the Structural Health Monitoring (SHM) of civil constructions. However, the classical experimental techniques based on the use of accelerometers involve high costs and long times for performing the measurements, and often interrupting the service of the construction is also needed. In this paper, with reference to the specific case study of the identification of modal parameters of a typical span of a railway viaduct, we analyze the capability and the possible improvements of the ground based radar interferometric experimental set-up. This analysis is aimed at developing a fast, inexpensive and practical procedure for the periodic monitoring of the viaduct.

Experimental Nonlinear Identification of an Aircraft with Bolted Connections

Aircraft structures are known to be prone to nonlinear phenomena, especially as they constantly become lighter and hence more flexible. One specific challenge that is regularly encountered is the modeling of the mounting interfaces between aircraft subcomponents. Indeed, for large amplitudes of vibration, such interfaces may loosen and, in turn, trigger complex mechanisms such as friction and clearances. In this context, the present work intends to investigate the nonlinear dynamics of the Morane–Saulnier Paris aircraft, accessible at ONERA. This aircraft possesses multiple bolted connections between two external fuel tanks and wing tips. The objective of the paper is specifically to carry out an adequate identification of the numerous nonlinearities affecting the dynamics of this full-scale structure. Nonlinearity detection and the subsequent subspace-based parameter estimation have been performed on experimental data, collected during an on-ground test campaign. Nonlinearity detection is first achieved by the comparison of frequency response functions estimated at low excitation level, with those obtained at high amplitude level, yielding insight towards accurately characterizing the behavior of the bolted connections. Then, a nonlinear subspace identification method is applied to measured data to estimate the linear and nonlinear parameters of the structure and novel strategies and tools that overcome specific arisen problems are developed.

Active Suspension Systems for Passenger Cars: Operational Modal Analysis as a Tool for the Performance Assessment

Comfort, road holding and safety of passenger cars are mainly influenced by an appropriate design of suspension systems. Improvements of the dynamic behaviour can be achieved by implementing semi-active or active suspension systems. In these cases, the correct design of a well-performing suspension control strategy is fundamental for obtaining satisfying results. In-Operation Modal Analysis allows the experimental structural identification in real operating conditions: moving from output-only data, leading to modal models linearised around the more interesting working points and, in the case of controlled systems, providing the needed information for the optimal design and verification of the controller performance. All these characters are needed for the experimental assessment of vehicle suspension systems. In the paper, two suspension architectures are considered equipping the same car type. The former is a semi-active commercial system, the latter a novel prototypic active system. For the assessment of suspension performance, two different kind of tests have been considered, proving ground tests on different road profiles and laboratory four poster rig tests. By OMA-processing the signals acquired in the different testing conditions and by comparing the results, it is shown how this tool can be effectively utilised to verify the operation and the performance of those systems, by only carrying out a simple, cost-effective road test.