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Monitoring of bridge has received a significant amount of attention over the past years, as the condition of these infrastructure elements is crucial to guarantee uninterrupted traffic of people and goods between regions. Most monitoring systems identify the dynamic properties of the structure, such as the resonance frequency. The resonance frequency is however not the best measure for the presence of damage. Moreover, in case the dynamics of the passing vehicle interact significantly with the dynamics of the bridge, the analysis becomes complex. Often, only the free vibration is used. Here, the Wavelet-based Synchro-Squeezed Transformation is proposed as a method to extract the instantaneous resonance frequency of the vehicle-bridge system. This allows to eliminate both operational and environmental influences. Analysis on a numerical model reveals that the method has potential to be a more robust in the identification of damage in bridge-like structure passed by a relatively heavy vehicle. A first validation based on field measurements on Irish Boyne viaduct support the capabilities of the method as predicted by the results of the numerical model.

This paper presents a novel approach to linearize the input-output (IO) response of nonlinear mechanical systems by using model predictive control (MPC) with integral action and solving a one-step-ahead reference tracking problem. The discrete-time MPC controller, which builds on a nonlinear data-driven state-space model, controls a continuous-time plant. State estimation is performed by means of the unscented Kalman filter (UKF). The overall effectiveness of this MPC-based approach is validated in the time and frequency domains by conducting simulations on a mechanical system with output nonlinearities of polynomial type. The obtained results show that the proposed method is superior in terms of performance and robustness when compared to the classical feedback linearization techniques based on Lie algebra.

Parts with geometrical complexity bring significant challenges in nondestructive testing (NDT). The Process Compensated Resonance Testing (PCRT) method has recently shown promising results for inspecting complex-shaped metallic parts. PCRT is a broadband vibrational testing procedure that relies on the extraction of resonant frequencies coupled to advanced learning methods. Once a suitable classifier is determined, it is then applied to unknown test samples in order to classify them as healthy/defected. The target of this work is to upgrade the PCRT with an advanced classifier to increase the classification performance. For this purpose, first the inclusion of the Q-factors to the available PCRT feature set i.e., only frequencies, is investigated and then, a novel classifier fusion based on Dempster-Shafer theory of evidence (DST) has been proposed to combine several constituent models. The constituent models are selected to be adaptively boosted NNs (ABNNs) trained by using different numbers of features. The proposed algorithm (ABNN + DST) is applied to polycrystalline Nickel alloy first-stage turbine blades with complex geometry. The results indicate that the proposed DST-based fusion algorithm increase the classification accuracy from 93.5% to 96.5%.

The complex geometry of metallic components combined with the variety of possible damage features limits the application of conventional NDT technologies. For parts with complex geometric shapes relevant product quality assurance tools are needed. Process Compensated Resonance Testing (PCRT) is an advanced and sensitive non-destructive evaluation method. It employs Mahalanobis Taguchi System (MTS) to classify the components as Good/Bad by evaluating the variations on resonance frequencies in Mahalanobis space. However, the process of feature selection and threshold determination in MTS is questionable. In the present paper, a two-stage Mahalanobis Classification System (MCS) approach is proposed coupled with binary particle swarm optimization procedure. The proposed MCS approach is applied to equiaxed Nickel alloy first-stage turbine blades with various possible defects. The obtained results demonstrate the high classification accuracy and evidence of the superior performance of the proposed approach.

In this paper, a finite element model-based damage scenario analysis tool is developed to assess the structural performance of a bridge using the deflection influence lines. This provides the option to convert from the subjective damage indication number based on expert opinion to a physics-based damage indication number. The tool is implemented for a case study bridge using open-source software to provide an economically viable solution.

In this work, a recently developed superelement formulation in the floating frame of reference is implemented for plates. By using Craig-Bampton modes, a coordinate transformation from the absolute floating frame coordinates and local elastic coordinates to the absolute interface coordinates is established. Several benchmark problems are considered to validate the formulation for plates. Results from the superelement formulation for plates are in good agreement with other formulations, meaning that the formulation can successfully be used for the efficient description of plates in flexible multibody systems, such as flexure mechanisms that can no longer be modelled as beam elements because of their unbeamlike dimensions.

In this work, a strategy for the model order reduction of large stroke flexure mechanisms is presented. In this, geometrically nonlinear finite element models of each flexible body within the mechanism are projected onto a reduction basis. This basis consists of the body’s Craig-Bampton modes and corresponding modal derivatives. Validation simulations that are performed on commonly used flexure mechanisms show good accuracy of the reduced order models. Therefore, the proposed reduction strategy can be efficiently applied to reduce computational costs of structural optimizations that are required to improve the design of flexure mechanisms.

The multiple-order response of a rotor equipped with a centrifugal pendulum vibration absorber (CPVA) is investigated in this study. CPVAs have been used in the abatement of torsional vibrations since the 1930s and have been extensively researched but seldom with a focus on the full multiple-harmonic response. Although the firing order in reciprocating engines dominates in amplitude, the higher-order harmonics have impact on driveline-related noise issues. This investigation is conducted in order to understand if an higher-order amplification can stem from the design of the CPVA or if this phenomenon is due an interaction between other powertrain components. Therefore, an isolated rotor-CPVA system is studied. The investigated rotor is subjected to an oscillating torque consisting of single- and multiple-order harmonics. The equations of motion are derived by Kane s method and the multiple-harmonic response of the system is analyzed. The linear steady-state response is compared with numerical time integration of the equations of motion.

Modal testing practitioners are well accustomed to FRFs which, nowadays, can be measured and analysed by a large variety of methods and tools. However, most of the tools for linear modal analysis are practically unusable when the frequency response is amplitude dependent. Hence, the methods based on the properties of the Nyquist circle become unavailable because of the loss of its circularity and completeness. Nevertheless, FRFs of well-isolated modes can still be processed by calculating the modal parameters for every pair of receptance points taken at equal amplitude either side the maximum response peak. The major limitation of this method is the absence of one branch of the response function due to unstable dynamics. The objective of this work is to show that incomplete FRF functions can be still processed to obtain the modal parameters. The method is benchmarked against a single degree of freedom both for linear and nonlinear response conditions.

This paper presents a numerical study in which the thick-wall assumption in a fluid-structure interaction analysis of liquid-filled pipes subjected to axial vibration is adopted. The influence of wall thickness on the dynamic characteristics of the system in the frequency domain is investigated and the validity of the thin-wall assumption is assessed for different scenarios. The analytical expressions are derived from the equations of motion in cylindrical coordinates and the mathematical model is compared with a 3D numerical model, developed via the finite element method. It is shown that a great range of industrial applications of pipe systems can be analyzed using a thin-wall assumption. However, for small pipe diameters such as those used in high precision machines, the wall thickness of a pipe becomes larger compared to its radius. For these scenarios, thin-walled pipe equations no longer hold since they are not able to predict stresses variation within the cross section of the pipe. Furthermore, this difference amplifies for soft wall materials.

The Norwegian Public Roads Administration is reviewing the possibility of using floating bridges as fjord crossings. The dynamic behaviour of very long floating bridges with novel designs are prone to uncertainties. Studying the dynamic behaviour of existing bridges is valuable for understanding the in-situ performance. We present a case study of the Bergsøysund Bridge, a 840 m long floating pontoon bridge located in Norway. An extensive monitoring system is installed on the bridge, including a network of accelerometers. A finite element model of the bridge is established. Using the measured acceleration output and recently developed Kalman filter based methods (a joint input-state (JIS) estimation algorithm and a dual Kalman filter (DKF)), we estimate accelerations at unmeasured locations. It is shown that the estimated response from the DKF agrees well with direct reference measurements. For the JIS, numerical instabilities in the estimates occur due to ill-conditioning of the matrices used in the system inversion.

A method is presented that incorporates hydrodynamic radiation forces in the floating frame of reference method used in flexible multibody dynamics. These hydrodynamic forces are approximated such that the fully hydro-elastically coupled problem can be solved at once using standard techniques. To this end, the elastic deformation of the body that is (partially) submerged is described using Craig-Bampton modes. The generalized hydrodynamic forces caused by motion in these modes are computed using a source panel method. In a frequency domain parameter identification procedure, the solution of the remaining radiation problem is approximated by a transfer function that represents a convenient physical system. This is done such that the corresponding differential equations in the time domain describe a mechanical system. The method is illustrated for a two-dimensional partially submerged cylinder.

Recently, a multiple-input/multiple-output Kalman filter technique was presented to control time-varying broadband noise and vibrations. By describing the feed-forward broadband active noise control problem in terms of a state estimation problem it was possible to achieve a faster rate of convergence than instantaneousgradient least-mean-squares algorithms and possibly also a better tracking performance. A multiple input/ multiple output Kalman algorithm was derived to perform this state estimation. To make the algorithm more suitable for real-time applications, the Kalman filter was written in a fast array form and the secondary path state matrices were implemented in output normal form. The resulting filter implementation was verified in simulations and in real-time experiments. It was found that for a constant primary path the filter had a fast rate of convergence and was able to track time-varying spectra. For a forgetting factor equal to unity the system was robust but the filter was unable to track rapid changes in the primary path. A forgetting factor lower than unity gave a significantly improved tracking performance but led to a numerical instability for the fast array form of the algorithm. To improve the numerical behavior, while enabling fast tracking and convergence, several variants are described in this paper. Results will be shown for a sliding window Recursive Least Squares filter in fast array form, which will later be extended to a full Kalman filter implementation by taking into account the uncertainty of the secondary path between the control sources and the error sensors. Multiple variants will be discussed in this paper. The first variant is the standard sliding window technique, which applies both updates and downdates to the filter coefficients. The second variant is an algorithm which only applies an update step to the filter coefficients and interprets the downdate step as an addition of a covariance matrix to the Riccati equation. The third variant uses an implicit forgetting factor. These implementations use a factorized form of the hyperbolic orthogonal transformation matrix. The different techniques will be applied to measured data of noise in houses near the runway of an airport. Results are given of the performance regarding tracking, convergence and numerical stability of the algorithms.

In this paper, methods are presented to design an acoustic source array for both directional sound generation and non-directional sound generation. The methods are based on measured transfer functions to be able to take into account different source sensitivities, to use extended sources that cannot be regarded as point sources, and complex geometries modifying the radiation characteristics. The aim of this paper is to develop a sound source that can be integrated in passenger vehicles with the objective to warn vulnerable road users while minimising noise pollution. Nowadays, sensor systems exist which are able to reveal the position of the vulnerable road users, which can be used to optimise the performance of the warning signal generator. Based on this information, the signal generator is designed to generate the specified warning signal at the location of the vulnerable road user while minimising the noise pollution at other locations. Such a directional sound beam was realised with an array of controlled acoustic sources. Changes of the relative positions of the vehicle and the vulnerable road user require continuous adjustments of the sound beam. In an alternative operation mode the sound field should not be directional but uniform in a wide horizontal sector. It will be shown how to combine the different requirements of directional sound radiation and uniform sound radiation with a single array configuration. Practical sound sources mounted in cars should be as compact as possible. Therefore the efficiency of the array is an important property. It will be shown that different beam forming approaches can lead to significant differences in the efficiency of the array. The influence of beamforming parameters on the efficiency will be discussed as well as the physical interpretation of the resulting beamformer solutions. The acoustic results shown in this paper to illustrate these effects are obtained using numerical simulations based on FEM and BEM transfer function models of acoustic sources mounted in the front of a car, combined with models of the reflecting ground and other reflecting objects.

A numerical model to predict the sound absorption of porous asphalt has been developed. The approach is a combination between a microstructural approach and a finite element approach. The model used to describe the viscothermal properties of the air inside the pores of the asphalt is the low reduced frequency model (LRF). The geometry of the porous asphalt is implemented directly in the FEM model, where a fast simulation will give both the viscothermal losses of the sound energy within the pores as well as the scattering due to the stones.

This paper presents a full finite element (FE) model of wheel-track interaction to study the wheel-rail impact noise excited by an insulated joint (IJ). The integration is performed in the time domain with an explicit central difference scheme. The vibratory behaviour of the track and wheel model are respectively validated with hammer test and Axle Box Acceleration (ABA) measurement. By making use of the calculated velocities and pressures on the vibrating surfaces, the boundary element method (BEM) based on Helmholtz equation is adopted to transform the vibrations of the wheel-track into acoustic signals. The decay rate of impact noise at different frequency bands during propagation are analysed. The predictions of total impact noise radiation and the noise contributions of different track components are in good agreement with results reported in the literature, while the effective frequency range is successfully extended from 5 kHz to 10 kHz.

The acoustic absorption coefficient is a number that indicates which fraction of the incident acoustic power impinging on a surface is being absorbed. The incident acoustic power is obtained by spatial integration of the incident intensity, which is (classically) defined as the time-averaged intensity associated with the incident sound field. The measurement of the effective, in situ, sound absorption coefficient is problematic as the determination thus requires a decomposition of the sound field in an incident and reflected field which, generally, is virtually impossible to do. This paper introduces an alternative coefficient with which the effective acoustic absorption can be expressed. This coefficient is based on an alternative definition of the incident intensity; the time average of the positive values of the instantaneous intensity. The alternative coefficient is much easier to use in a sense that it follows directly from an in situ, instantaneous intensity measurement. The coefficient does not rely on any assumptions other than the assumption that the linearized wave equation is satisfied (and thus the acoustic energy corollary). As a result, one does not need to decompose the sound field in incident and reflected waves. Hence, one does not need to have prior information about the incident sound field. Accordingly, one does not need to have prior information about the source. The coefficient can be determined in any sound field, either transient or stationary, free field and diffuse/(semi-) reverberant sound fields. The alternative coefficient is illustrated by means of several numerical examples.