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Hydraulic dampers are widely implemented in railway vehicle suspension stages, especially in high-speed passenger trains. They are designed to be mounted in different positions to improve comfort, stability, and safety performances. Numerical simulations are often used to assist the design and optimization of these components. Unfortunately, hydraulic dampers are highly nonlinear due to the complex fluid dynamic phenomena taking place inside the chambers and through the by-pass orifices. This requires accurate damper models to be developed to estimate the influence of the nonlinearities of such components during the dynamic performances of the whole vehicle. This work aims at presenting a new parametric damper model based on a nonlinear lumped element approach. Moreover, a new model tuning procedure will be introduced. Differently from the typical sinusoidal characterization cycles, this routine is based on experimental tests of real working conditions. The set of optimal model parameters will be found through a meta-heuristic iterative approach able to minimize the differences between numerical and experimental damper forces. The performances of the optimal model will be compared with the ones of the most common Maxwell model generally implemented in railway multibody software programs.

The increased demand for vibroacoustic comfort as well as regulations on noise and vibration levels have made the NVH (Noise, Vibration, Harshness) performances of a vehicle to become one of the fundamental design criteria. Therefore, predictive models for the analysis of noise and vibration transmission mechanisms represent interesting tools to support the R&D department of the automotive companies. Focusing the attention on passenger's comfort, the vibrations induced by the tyre/road interaction propagate from the contact area to the hub and finally inside the cockpit through structure-borne transmission paths. This can be regarded as one of the major contributors to the car cabin interior noise at low frequencies (between 20 and 500 Hz). Simplified models able to interpret the waves propagating inside the tyre structure and influenced by the angular speed may support the studies in this research field. To this end, an analytical model based on the theory of the flexible ring on elastic foundation has been developed. It allows analysing the tyre dynamics in both static and rolling conditions. Model parameters have been calibrated based on an Experimental Modal Analysis of the static tyre. The free response of the tyre shows the bifurcation effect at different rolling speeds, while a cleat test simulation has been carried out to investigate the forced response of the tyre.

To improve the comfort of the domestic environment, the acoustic performances of home appliances need to be optimised. During the product development stages, manufacturers typically carry out acoustic measurements to validate design strategies and to perform troubleshooting. Moreover, several experimental techniques can be used depending on the target of the analyses. In this paper, the sound field radiated by an operating washing machine is investigated. A combined acoustic testing is carried out by means of a sound intensity probe and a microphone array. The details on the tests' execution and the data processing are presented. The experimental results are discussed, providing a synthesis of the two sets of measurements.

The increasing demand for acoustic comfort in vehicles has popularized the vibroacoustic analysis using computer-aided engineering (CAE) tools and boosted the development of various noise control measures. Concerning the often-unknown reliability of a CAE tool and the high cost of testing control strategies in a real vehicle, this paper proposes a test bench called Noise-Box, for benchmarking the CAE tools and testing new control measures. The test bench is designed towards a simple plate-cavity system that is easy to model and analyze, so that any vibroacoustic test performed on it can be accurately reproduced by numerical models. Specifically, it is a concrete box with six rigid walls and an opening that can be covered by flexible or soundproofing panels. The complete design is elaborated, including the cavity's shape and dimensions, the panel's installation and the device's overall configuration. Moreover, the acoustic field provided by the test bench is characterized for the typical features that will guide the device's future applications, covering modal property, reverberation time (or sound absorption) and field diffuseness. This work could be informative and instructive not only for the presentation of the novel test bench but also for the utilized methodologies in its design and characterization.

Nowadays, finite element tyre models are often used to perform vehicle NVH (noise, vibration, harshness) simulations. To account for the specific operating conditions, a road surface must be properly included in the model. This paper deals with a methodology to experimentally evaluate and process road irregularity measurements, so as to generate a road surface input. These surfaces are used to simulate the tyre/road interaction at the footprint, which is modelled as a contact surface in finite element tyre models. For this reason, a linear profile of the road surface is not suitable for these simulations and the whole surface must be considered. Starting from the measurements taken through a test equipment specifically designed to carry laser sensors and scan road profiles, the Power Spectral Density (PSD) of a specific track is estimated and then interpolated considering piecewise functions. Finally, a model to generate a road surface starting from the measured PSD is developed, discussed and validated.

The purpose of this study is to propose an innovative solution for evaluating the performance of a full-scale Active Mass Damper (AMD). The AMD adopted is a custom hydraulic actuator, developed for active control of existing buildings against earthquakes. For vibration control, a sky-hook algorithm was implemented. Its characteristics ensure good robustness, which is fundamental in structural engineering since buildings are subjected to significant variation in dynamic properties in presence of damage or ambient conditions. A Hardware-In-the-Loop (HIL) test bench was specifically designed to simulate the actual working condition of the anti-seismic system. The HIL setup consists of a shaking table moved by a hydraulic actuator in accordance with the roof’s displacement, evaluated using a structural numerical model of the building to which the AMD is fixed. The presence of two distinct active systems (HIL and AMD) could generate control issues; therefore, a Triple Variable Control logic was introduced to reduce the interaction delay. The effectiveness of the proposed AMD is validated comparing the roof’s displacement in an uncontrolled structure with that in a controlled one. Also, the robustness of the control algorithm was verified using a non-linear structural model and applying seismic excitation at different intensities.

The noise generated by the rolling tyre contributes significantly to the car's interior noise. This is caused by the tyre-road contact, and at low frequencies (0–500 Hz) is mostly transmitted inside the cockpit through the structure-borne transmission path. In support of the studies in this research field, an interpretative model of the tyre-wheel system accounting for the effects induced by the angular speed represents a useful tool. To this aim, we implemented an analytical model based on a flexible ring on an elastic foundation to analyze the dynamics of the tyre-wheel system, in both static and rotating configurations. We fine-tuned the parameters of the tyre based on data coming from experimental modal analysis of the static tyre. Particular attention has been paid to the system's free and forced responses, commonly analyzed with the so-called cleat test. The results are discussed interpreting the behavior in different reference systems.

The secondary suspensions of high-speed trains are designed to guarantee high comfort levels to passengers by reducing the perceived vibrations. Recent studies have shown that, besides the vertical...

This work proposes an active control logic that uses a linear quadratic regulator (LQR) controller and a Kalman-Bucy (KB) state observer to improve the acoustic performance of single-layer panels. When the panel is subjected to an acoustic excitation, the proposed strategy can automatically adapt to the acoustic disturbance by tuning some of the decisive weighting factors in the LQR and the KB filter according to the spectrum of the signals from sensors. This control acts on the panel with PZT patches as actuators and accelerometers as sensors, forming a smart structure. The vibroacoustic model of the smart panel is formulated using modal functions, from which the transmitted power and the transmission loss of the panel are derived. Accordingly, the control strategy is designed using the state-space representation under modal coordinates, during which the spillover effect is considered and the placement of actuators and sensors is optimized by a modified modal H2 norm approach. It is noticeable that several advanced techniques in the active control of noise and vibration are implemented in this development of the smart panel. Following this, numerical and experimental studies oriented to the effectiveness of the proposed control logic are performed. While the numerical simulations are carried out under the assumption that the two sides of the panel are a reverberant and a free field, respectively, the experiments are conducted using the test equipment called Noise-Box, whose inner space is considered able to simulate a field incidence. Two scenarios are provided: one for the monotone at 500 Hz or 1,000 Hz; the other for the white noise within 750 Hz – 1,000 Hz. The results validate that the active control improves the acoustic performance of the panel for sound insulation, whether the acoustic disturbance is a monotone of any frequency or a band-limited noise with a given frequency range.

Monitoring and diagnosis of civil structures has become a popular topic in the last years, especially through the use of non-invasive tests and techniques. Moreover, the spread of operational modal analysis, that exploit ambient excitations of structures to estimate their modal parameters, allowed to reduce the costs associated to the dynamic identification. In this paper, a technique for the diagnosis of common civil structures, such as residential buildings or warehouses, is presented in order to identify local stiffness decreases that can potentially be associated to structural failures. The technique has been tested on a real warehouse built in 1960 and the results have been analyzed demonstrating the effectiveness of the methodology.

The data here reported refer to the numerical examples shown in the research article “Wave based method for flexural vibration of thin plate with general elastically restrained edges” (Liu et al., 2020 [1]). Within the examples, only the datasets regarding the plates with elastic or elastic-damping supports are provided. The datasets contain the raw data directly obtained from the forced vibration simulations. The simulations are carried out using two methods: the finite element method realized in ANSYS Mechanical APDL and the proposed wave based method (Liu et al., 2020 [1]), implemented in a MATLAB code. The data obtained from ANSYS serves as reference for the response of the plate under different boundary conditions. For each frequency, the transverse displacements of the plate at two pre-selected points are listed in the spreadsheet (e.g. MS Excel). When damping is present, they are separated into real part and imaginary part. This part of data can be used as reference when other novel methods are developed. The datasets obtained from MATLAB include the contribution factors as well as the wave functions. Based on them, one can obtain the displacement as a complex number at any point of the plate after a simple postprocessing. Postprocessing codes to obtain the frequency response function for a user-given point and the displacement field at a user-given frequency are also provided. This part of data presents much more information than the previous part as well as the corresponding results in the related research article. It makes it possible to see the responses at other points or other frequencies that are not considered in the research article, without repeating the time-consuming simulations. Moreover, if someone wants to further improve the wave based method, this part of data will be helpful, either for analysing the limitations of the proposed method or for more direct comparisons. Any research related to the flexural vibration of plate can also consider the data provided in this article.

Friction between moving bodies in mutual contact is a field studied in depth. A strategy to improve the tribological performance of mechanical components consists of modifying the surface microstru...

Wave based method is a numerical technique to predict steady-state vibration and solve vibroacoustic problems. It is a deterministic approach that is acknowledged to be more efficient than the element based methods in the mid-frequency range. The wave based method for plates with prescribed boundary conditions has been proposed and verified for the ideal constraint cases such as clamped, free and simply supported. To deal with different kind of or more realistic boundary conditions, this paper proposes a modified wave based method. The method is aimed at analyzing the flexural vibration of thin plates with general elastically restrained edges, and it can also consider the damping effect associated with the edge restraint. A number of numerical validation examples are shown, where the plate edges are uniform, non-uniform or partially supported. Within the examples, the responses of the plate under different edge conditions are compared, including elastic supports with different translational and rotational stiffness and damping parameters, rigid supports like clamped and simply supported, and free edges. For all the considered cases, the proposed method is proved to be effective, though the convergence performance is influenced by the boundary conditions. More wave functions may be required for simply supported, non-uniform or partially supported cases.

Wave based method is an efficient numerical technique that can be used to solve the structural dynamic problems, especially the vibration of plates. The approach expands the dynamic field variables to a weighted sum of wave functions, and the contribution factors are determined by minimizing the errors on the boundary conditions. While the governing equation is satisfied a priori, the boundary conditions are satisfied in the integral sense, using preferably a weighted residual formulation. However, the weighted residual formulation is not always suitable for all kinds of boundary conditions. In plate bending problems, the plate edges can be modelled as clamped, simply supported, free, symmetric or (visco) elastically restrained against translation or/and rotation, depending on how they are restrained in reality. But the currently available weighted residual formulations are suitable either only for the non-elastic restraints (clamped, simply supported, free and symmetric) or only for the general (visco) elastic restraints with both translational and rotational elasticities. In this paper, a general formulation is proposed for all the aforementioned types of edge restraints. It is equivalent to the conventional one when the plate edges are non-elastically restrained, but performs better with the introduction of corner residuals for the plate with general elastically restrained edges. Apart from the ideal non-elastic and the general full-elastic restraints, this modified formulation also works well for the partial-elastic ones with only either translational or rotational elasticity. Numerical cases are studied on a rectangular plate for all the restraint types, where the proposed formulation is validated. The restraint types can be identical or different among the plate edges, and how to apply the formulation to the non-uniformed situation is also demonstrated. Throughout the considered cases, this paper shows the accuracy and efficiency of the wave based method by comparing with the finite element method in computing the forced vibration of the thin plate. With the modified weighted residual formulation, the method further shows its great convenience in changing the restraint types or stiffness (and damping) parameters of plate edges.

This paper deals with tyre noise indoor tests in a semi-anechoic chamber and with the identification of a monopole substitution model suitable for simulating the deterministic part of the sound field generated by a rolling tyre. The first part of the paper illustrates the test procedure and the data processing methodology adopted for separating the deterministic contribution to tyre noise, i.e. that mainly related to tread pattern, from the random one. In the second part, the monopole substitution model is presented, together with the results of model identification and sound field simulation. The results reported in the paper for two commercial tyres (with the same size and similar structural characteristics, but with different tread pattern design) show how the predominance of the deterministic/random noise contributions varies with frequency and confirm the random noise spectrum to be substantially independent of the specific tread pattern. With reference to the monopole substitution model, its capability of reproducing the acoustic field radiated by a rolling tyre is assessed through the analysis of both sound spectra and space distribution.

Several examples of control strategies for the seismic protection of civil structures, ranging from passive to active and semi-active have been presented in the scientific literature, and often applied in the market. However, none of them proved to be absent of high employment costs or burdensome installations. For this reason, the low-cost Active Mass Damper (AMD) shown in this work and capable of automated self-tuning, control and continuous monitoring of the structures represents an attractive solution. The device has been designed and tested on the numerical model of a scaled steel made three story building. In particular its working principle and the ISAAC algorithm for automatic identification are presented and its robustness against modelling and estimation errors is analyzed. The methodology allows to avoid the study of specific solutions for each case, thus making possible the adoption of such systems also for already existing and common structures.

The transport and civil industry research has been aiming at improving vibro-acoustic performance of panel-like structures such as trim panels, glazing windows or separating walls. Focusing on the airborne path, the application of an active control for optimizing the plate acoustic isolation performance is here investigated. A transmission model of an acoustically excited plate is derived in the time domain predicting the plate velocity and its acoustic radiation. The dynamic system is modelled together with the control loop in MATLAB where a suitable control algorithm for enhancing the panel transmission loss performance is developed.

Active vibration control of flexible systems is still an open issue. Among the different techniques developed during the last decades resonant controllers are becoming more and more attractive. They concentrate the feedback action in a particular frequency range, optimizing the control effort and minimizing the spillover effect on nonmodeled dynamics. In particular, negative derivative feedback (NDF), feeding back the velocity through a modal compensator, reduces spillover at frequencies both lower and higher than the desired range of interest. Starting from this approach, the possibility to create a smart structure able to adapt the control parameters to the vibration characteristics represents a very promising solution. A NDF adaptive control logic has been designed and analyzed, both numerically and experimentally, on a carbon fiber plate test rig.

In this work a completely automated output-only Modal Analysis procedure is presented and all its benefits are listed. Based on the merging of different Operational Modal Analysis methods and a statistical approach, the identification process has been improved becoming more robust and giving as results only the real natural frequencies, damping ratios and mode shapes of the system. The effect of the temperature can be taken into account as well, leading to the creation of a better tool for automated Structural Health Monitoring. The algorithm has been developed and tested on a numerical model of a scaled three-story steel building present in the laboratories of Politecnico di Milano.

Real time prediction of cutting tool condition and machined surface finish have been attractive research objectives over the last decades. However, providing practical and reliable solutions is still a demanding task for milling machine tools. One of the most challenging literature goals is to obtain a robust estimation of the cutting forces through indirect sensor measurements since many process and tool related quantities are indirectly linked to cutting forces. Another challenging issue in machining process monitoring and control is prediction of surface finish and quality. As the vibration plays a major role in the surface generation, this can be done by accurate prediction of the vibrational displacements at the tool tip during machining operation. In this paper, a novel model based estimation of cutting force and tool tip acceleration is designed and tested based on data fusion of different sensors measurements. In this context, two sensors (piezoelectric accelerometer and eddy-current displacement both mounted inside the spindle structure) have been utilized to acquire the experimental signals over a wide range of frequencies. In order to predict the above mentioned quantities, an optimal state estimator based on Kalman Filter (KF) is used. The models have been obtained by system identification method based on experimental measurements performed on a machine tool. The model based estimator is fed by real data. The results show that the estimation of the impulse force and tool tip acceleration can be achieved accurately in low and high frequency ranges by assigning different weights to the measurement sensors.

The spread of smart structures has recorded a significant increase during the last decades. Nowadays these solutions are applied in various fields such as aerospace, automotive and civil constructions. This kind of structures was born in the past in order to cope with the high vibrations that every lightweight structure has to face. In order to reduce weight designers usually decide to use very thin and lightweight structures. In the automotive field, for example, a reduced fuel consumption is obtained employing lightweight materials. However, in general a worsening of the vibroacoustic comfort is obtained with undesired vibrations that can be really annoying for passengers and dangerous for the structure itself. This work presents an innovative smart plate that is able to actively vary its dynamic properties, by means of an IMSC control logic, in order to improve the acoustic performances. An investigation about the system response in the high frequency range allowed to assess the behavior in terms of absorption, reflection coefficient and transmission loss.

This article presents the experimental validation of a new control technique for reducing vibration in flexible structures: Dependent modal space control. While the classic independent modal space control allows only the frequency and the damping of the controlled modes to be changed, dependent modal space control can also impose the controlled mode shapes. Depending on the kind and number of sensors and actuators available for control, the mode shape can be imposed in both a direct and an indirect way. Owing to the need for modal sensors and actuators for direct mode shape imposition, the second methodology is often preferred in many engineering applications. In the indirect method, the optimal closed loop mode shapes set is computed with an optimization algorithm in order to minimize an Input-Output Performance Index. The worsening spillover effects due to errors in the estimates of the system state variables are considered when computing the gain matrix and play an important role in the entire control logic. Experimental validation on a cantilevered beam shows the effectiveness of the dependent modal space control and a good match between the numerical and the experimental results.

Autologous stem cell transplantation (ASCT) is a potentially curative treatment of lymphoma, but peripheral blood stem cell (PBSC) mobilization fails in some patients. PBSC mobilizing agents have recently been proved to improve the PBSC yield after a prior mobilization failure. Predictive parameters of mobilization failure allowing for a preemptive, more cost-effective use of such agents during the first mobilization attempt are still poorly defined, particularly during mobilization with chemotherapy + granulocyte colony-stimulating factor (G-CSF). We performed a retrospective analysis of a series of lymphoma patients who were candidates for ASCT, to identify factors influencing PBSC mobilization outcome. Premobilization parameters-age, histology, disease status, mobilizing protocol, and previous treatments-as well as white blood cell (WBC) and PBSC kinetics, markers potentially able to predict failure during the ongoing mobilization attempt, were analyzed in 415 consecutive mobilization procedures in 388 patients. We used chemotherapy + G-CSF in 411 (99%) of mobilization attempts and PBSC collection failed (

Vibration reduction in mechanical systems is an open issue. Indeed the stresses associated to the dynamic amplifications can affect systems’ performances and life cycle time. Nowadays the possibility to integrate sensors, actuators and control logics, in order to create a smart structure able to reduce vibration levels in all the operating conditions, represents a very attractive solution. This paper presents a comparison between two control strategies for vibration suppression in flexible structures: the Direct Velocity Feedback (DVF) and the Active Tuned Mass Damper (ATMD). As test case, the model of a smart cable for electric power distribution has been investigated.

During the last years, continuum robots have been used in many applications. They are smart structures with continuous curving, similar to a worm or an elephant trunk, characterized by a very high number of sub-actuated degrees of freedom (dof). They need a robust control system, aiming at both positioning the robot and suppressing induced vibrations. The idea is to adopt such a robot on a construction machine for the concrete distribution, substituting the reinforced rubber hose with the robotic smart solution. Particular attention has been paid to a control strategy able to reduce vibrations induced by the pumping procedure.

This paper presents a control strategy for the suppression of vibration due to unknown disturbance forces in large, nonlinear flexible structures. The control action proposed, based on the modal approach, consists of two contributions. The first is the well-known Independent Modal-Space Control, which increases system damping and improves its behavior close to the resonance frequencies. The second is a disturbance estimator, which calculates the modal components of the external forces acting on the system and compensates for them using actuator forces. The system modal coordinates, required by both logics, are estimated through a modal state observer. The proposed control logic is tested on a flexible boom. The paper reports the numerical and experimental results both for the linear and nonlinear (large motion) boom configuration.

Concrete pump booms are subjected to vibrations that increase mechanical stress and shorten their lifespan. This paper aims to study the problem by considering the two subsystems, the boom and the concrete pump, that have the greatest effect on the phenomenon. The authors supply numerical and experimental tools that can analyze the problem in depth in all its complexity. First, the systems were investigated independently, to identify their individual aspects. Then a numerical model was created to reproduce the behavior of the whole system and the interaction between boom and pump. The result was a new powerful tool for investigating passive and active solutions for suppressing vibration.

In this paper an active modal TMD control logic for the vibration suppression is presented. Starting from the traditional TMD theory, a closed loop formulation is proposed to calculate the active control force. The possibility to describe every mechanical systems or civil structures with a set of modal coordinates allows to act independently on each modal degree of freedom. The technique is compared with different solutions already present in literature, such as the IMSC and the PPF. Numerical simulations, based on a FEM linear model, are carried out to investigate the pro and con of each logic.

In this research, a complete system of a force control unit implemented on a home-built electro-mechanical fatigue test machine is proposed. The entire system includes an electro-mechanical shaker, a load cell, a controller, dedicated software, and an external metallic structure to constrain the specimen. Admittedly, the bending fatigue test on flat specimen has to be measured by applying a cyclic force with a constant frequency. The simplicity of the machine and its cheap overall price are the most important advantages of the proposed system. Moreover, the machine has been designed based on the specimens suggested in ASTM standard Bending Fatigue Testing for coating samples. For demonstration of machine functionality in this paper, the measured results of some fatigue tests have been presented in order to show the efficiency of the system. In this regard, Aluminium flat specimens were deposited by Bronze through cold spray coating and they have been used as samples for test. The results show that the machine is capable of following the perquisite requirements mentioned in the ASTM standard.

In this work a numerical-experimental procedure for the aerodynamic optimisation of the new train AnsaldoBreda EMUV250 in terms of behaviour to cross wind, will be presented. The first step of the research consists in evaluating the aerodynamic forces acting on the original geometry of the train by means of wind tunnel tests on scale model and of CFD numerical simulations. Thanks to the information provided by the CFD analysis (pressure distribution, velocity field, etc.), two different new versions of the train, specifically designed to achieve a better cross wind behaviour through a modification of both the train roof and the nose, have been tested in the Politecnico di Milano Wind Tunnel. A final comparison between the three versions of the train considered in this work is presented in terms of force/moment aerodynamic coefficients.

Ski manufacturers are interested in improving ski performance in terms of rapid sliding, excellent trajectory control, and reduced maintenance. A possible approach to achieve this goal is based on substitution of the base material, moving from the standard ultra-high-molecular-weight polyethylene to metallic solutions. Despite their elevated mechanical properties, however, metallic materials exhibit a poor sliding behavior, at least in their original manufacture condition. Although the interaction between the ski base and snow is still an open field, the authors investigated the relationship between ice friction and material hydrophobicity. The wettability behavior of surfaces can be managed by surface patterning techniques, among which laser surface texturing (LST) is a promising method, permitting surface feature modification from the micrometer- to millimeter-scale, and attractive for industrial applications. Herein, the tribological properties of two metallic materials are investigated and a process t...