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[Display omitted] • Study evaluated potential of FEA to answer questions about device design iterations. • Comprehensive "end-to-end" orthopedic example of the ASME V&V 40-2018 standard. • Validation showed good agreement between the FEA model and experiment. • Study illustrated benefits of VVUQ for establishing credibility of FEA models. Computational modeling and simulation (CM&S) is a key tool in medical device design, development, and regulatory approval. For example, finite element analysis (FEA) is widely used to understand the mechanical integrity and durability of orthopaedic implants. The ASME V&V 40 standard and supporting FDA guidance provide a framework for establishing model credibility, enabling deeper reliance on CM&S throughout the total product lifecycle. Examples of how to apply the principles outlined in the ASME V&V 40 standard are important to facilitating greater adoption by the medical device community, but few published examples are available that demonstrate best practices. Therefore, this paper outlines an end-to-end (E2E) example of the ASME V&V 40 standard applied to an orthopaedic implant. The objective of this study was to illustrate how to establish the credibility of a computational model intended for use as part of regulatory evaluation. In particular, this study focused on whether a design change to a spinal pedicle screw construct (specifically , the addition of a cannulation to an existing non-cannulated pedicle screw) would compromise the rod-screw construct mechanical performance. This question of interest (?OI) was addressed by establishing model credibility requirements according to the ASME V&V 40 standard. Experimental testing to support model validation was performed using spinal rods and non-cannulated pedicle screw constructs made with medical grade titanium (Ti-6Al-4V ELI). FEA replicating the experimental tests was performed by three independent modelers and validated through comparisons of common mechanical properties such as stiffness and yield force. The validated model was then used to simulate F1717 compression-bending testing on the new cannulated pedicle screw design to answer the ?OI, without performing any additional experimental testing. This E2E example provides a realistic scenario for the application of the ASME V&V 40 standard to orthopedic medical device applications. [ABSTRACT FROM AUTHOR]

Planetary gear system is widely used in wind power, construction machinery and helicopters, because of its large transmission ratio, strong load-bearing capacity and small size. Because the gears are usually in high-speed operation, their key components are subject to severe wear and impact damage. When the gearbox is subjected to a failure, it is often difficult to judge the operating status of the gearbox in real time. Since the gearbox system is complex, moreover, it is still difficult for the simulation model to accurately identify the gearbox fault. To address this issue, this paper proposes a digital twin-based signal fusion model to accurately identify gearbox faults at the signal level. The proposed model can identify minor faults occurring in planetary gearboxes by fusing actual and virtual signals. Firstly, on the basis of virtual prototype and the multibody dynamics software, a digital physical model based on Hertz theory and extended finite element method is proposed for gearbox dynamic monitoring and digital simulation, in which the gearbox can be visualized. Secondly, the data-driven method is used to extract and select features from real and simulation signals, and the fault of the planetary gearbox is detected by feature matching. Finally, the real and simulation signals are fused effectively based on variational mode decomposition and phase correction of generalized cross-correlation coefficient. The fault diagnosis result of the gearbox is finally determined by using the envelope spectrum of the fused signal. The experimental results show that the virtual real fusion method effectively improves the performance of the traditional signal diagnosis methods, and the fusion of the actual and virtual signals strengthens the fault features of the fused signals effectively. [ABSTRACT FROM AUTHOR]

This study uses a hybrid finite element method to predict dynamic behavior of truncated conical shells with ring stiffeners under fluid loading. The proposed approach combines classical shell theory and the finite element method, making use of displacement functions derived from exact solutions of Sanders' shell equilibrium equations for conical shells. The analysis of the shell-fluid interface involves leveraging the velocity potential, Bernoulli's equation, and impermeability conditions to determine an explicit expression for fluid pressure. To the best of our knowledge, this paper is the first to compare the methods applied to ring-stiffened shells against other numerical and experimental findings. Our results on conical shells in various conditions, with and without ring stiffeners, are largely consistent with previous findings. This study also explores the influence of geometric parameters, stiffener quantity, cone angle, and applied boundary conditions on the natural frequency of fluid-loaded ring-stiffened conical shells. The paper concludes with a discussion of several useful implications for further research. • Vibration analysis of fluid-filled ring-stiffened conical shells. • Finite element method for hydroelastic stability of conical shell. • The solid model based on Sanders' shell theory. • Fluid pressure is expressed using velocity potential and Bernoulli's equation. • Natural frequency is determined for different boundary conditions and geometries. [ABSTRACT FROM AUTHOR]

Dispersion diagrams play a crucial role in examining, analyzing and designing wave propagation in periodic structures. Despite their ubiquity and current research interest, introductory papers and reference scripting tailored to novel researchers in the field are lacking. This paper aims to address this gap, by presenting a comprehensive educational resource for researchers starting in the field of periodic structures and more specifically on the study of dispersion relations captured by dispersion surfaces or curves in dispersion diagrams. The objective is twofold. A first objective is to give a detailed explanation of dispersion diagrams, with graphical illustrations. Secondly, a documented Matlab code is provided to compute dispersion curves of 3D structures with 2D periodicity using the so-called inverse approach. These dispersion curves are obtained with numerical simulations using the finite element method. The code is written for elastic wave propagation and orthogonal periodicity directions, but can be extended to other types of linear wave propagation, non-orthogonal periodicity directions or 1D and 3D periodicity. The aim of this code is to serve as a starting point for novice researchers in the field, to facilitate their understanding of different aspects of dispersion diagrams and serve as a stepping stone in their future research. • Educational paper targeting researchers starting in the field of periodic structures. • Introduction to derive and interpret dispersion curves. • Focus on numerical dispersion curve calculations with the FE method. • Implementation provided for calculation of 2D periodic dispersion curves in Matlab. [ABSTRACT FROM AUTHOR]

This paper explores the dynamic behavior of metamaterial-like structures by investigating the evolution of their band gap under the influence of geometrical nonlinearities in the large displacement/rotations field. The study employs a unified framework based on the Carrera Unified Formulation (CUF) and a total Lagrangian approach to develop higher-order one-dimensional beam theories that account for geometric nonlinearities. The axis discretization is achieved through a finite element approximation. The equations of motion are solved around nonlinear static equilibrium states, which are determined using a Newton–Raphson algorithm combined with a path-following method of arc-length type. The CUF approach introduces two key innovations that are highly suitable for the evolution of the band gap: (1) Thin-walled structures can be effectively represented using a single one-dimensional beam model, overcoming the common limitations of standard finite elements. This is crucial as three-dimensional solid elements would result in significant computational costs, and two-dimensional elements based on von Kármán theory pose limitations for this type of investigation. Moreover, employing one-dimensional finite elements usually requires a combination of elements, leading to additional mathematical complexities in their connections and lacking geometric precision. (2) CUF enables the use of the full Green–Lagrange strain tensor without the need for assumptions, as is the case with von Kármán nonlinearities. The paper specifically compares results obtained with linear and nonlinear stiffness matrices, highlighting the differences. Numerical investigations are conducted on thin-walled structures composed of repeatable cells, assessing mode changes under traction and compression loading. Additionally, the paper presents a more complex metamaterial-like structure. The findings emphasize that the band gap is an inherent property of the equilibrium state, underscoring the necessity of a proper nonlinear analysis for accurately evaluating frequency transitions. • Dynamics of metamaterial-like structures investigating the evolution of band gap. • Analysis of the mode and frequency change in the geometrical nonlinear field. • CUF for 1D Finite element model of thin-walled metamaterial-like structures. • Lagrange polynomials for the description of complex geometries. • Comparison between linear and nonlinear approaches. [ABSTRACT FROM AUTHOR]

• A dynamic model for coupled unit-plant structure of PSPS is constructed. • The transient process of HGS is integrated into the unit and plant structure. • The kinetic properties of coupled unit-plant structure are scrutinized. • The grounds behind the unsteady state oscillations on structures are explored. • Suppression laws of MRD on vibration in coupled unit-plant structure are elucidated. The versatile regulatory capacity of pumped storage power station (PSPS) stems from the reversible pumped turbine unit switching between multiple operating conditions. Nevertheless, the unit and plant structure experience heightened vibrations owing to the intricate interplay of hydraulic, electrical, and mechanical excitations during transition processes, and the vibration responses fluctuate as operating conditions shift, posing a significant challenge to the safety and high quality operation of power station. To tackle the practical engineering issue, this paper delves into the sudden load-up scenario in power generation situation of pumped turbine, leveraging a finite element model encompassing the coupled hydraulic-mechanical-electrical-structural system (HMES) of PSPS and a mathematical model of unit shaft system, the impacts of dynamic loads induced by various vibration source on the unit and plant structure during transient condition, are meticulously analyzed and discussed through numerical simulations. Additionally, the magnetorheological damper (MRD), is incorporated into the PSPS to explore the effectiveness of MRD in controlling transient vibration in the interconnected unit-plant structure. The results indicate that the system parameters and associated load excitations undergo rapid fluctuations during the load-up process, bringing about noticeable oscillations in vibration amplitudes of rotor and turbine. The floors and fan hood of plant are the most vulnerable areas in terms of structural strength, with associated displacement amplitudes being most noticeable. The incorporation of MRD proves to be highly effective in mitigating the unsteady vibrations in both the unit and the plant structure during load-up course, as well as optimizing the motion patterns of rotor and turbine, promoting a notable reduction in frequency amplitudes of spectrum. Moreover, the maximal transient displacement amplitude of unit is significantly diminished, with the rotor experiencing a decrease of approximately 79%, while the amplitude of turbine declines by 16%. The displacement fluctuation ranges of the plant structure are observably diminished, and the complex frequency components of vibration signal are efficiently controlled. The transient vibration characteristics of the coupled unit-plant structure and the damping behavior of MRD during the transition process are unveiled by the research findings in this paper, which can offer valuable insights for the stability assessment and the research on vibration management of HMES for PSPS under the unsteady operation conditions. [ABSTRACT FROM AUTHOR]

• A damage localization and quantification method without damage labels is proposed. • An efficient method to quantify bridge damage severity level is proposed. • An efficient method for generating damaged structure dynamic responses is proposed. Among the existing unsupervised bridge damage detection methods, it is difficult to quantify bridge damage severity levels, although some of the methods can achieve the localization of bridge damage. In the existing research, the damage index (DI) curve is calculated by the monitoring point dynamic response (inclination or deflection) of the bridge in the damage state, and the localization of the bridge damage can be achieved by the DI curve without the need for damage labels. Based on this bridge damage localization method, this paper proposes an efficient bridge damage severity level quantification method. Since the different DI curves calculated under the same damaged state basically coincide with each other, the DI curves will change with the bridge-damaged state. Therefore, the quantification of the bridge damage severity level is achieved by only calculating DI curves of different damage degrees at the damage location. To efficiently calculate the DI curve, this paper proposes a method for generating the monitoring point dynamic response of the specified damage bridge. By the specified damage bridge finite element model (FEM) static simulation to obtain arbitrary vertical nodal loads and monitoring point responses of the relationship function, and then combined with the healthy state of the bridge monitoring point dynamic response can be generated monitoring point dynamic response of the specified damage bridge. Since the method in this paper is based on real measured data to calculate the DI curve, it is more robust to noise and modeling errors than the FEM dynamic simulation method, and the modeling of this method only needs to update the model stiffness parameter to reduce the modeling cost. In the example of this paper, the method of this paper calculates the DI curve of one damage state only needs about 7 s about 437 times the computational efficiency of the FEM dynamic simulation method, which can achieve the fast quantification of bridge damage severity levels. Numerical simulations demonstrate that the method can localize and quantify multi-damage in bridges under unknown loads, a small number of sensors, noise, and modeling errors. However, the method in this paper still has limitations that do not apply to the localization and quantification of bridge pier damage and nonlinear models. [ABSTRACT FROM AUTHOR]

• This article introduced the stiffness characteristics of the joint surface between the mechanical connection structures of the spindle-tool holder, tool holder-spring clamp, and spring clamp-tool of the spindle system in the robot machining system into the prediction of machining stability. • This paper proposed a method for establishing a tool tip frequency response prediction model for robot milling systems, which improves the accuracy of theoretical prediction of the tool tip dynamic characteristics of robot milling systems under different postures, Compared to the method of obtaining tool tip frequency response of robot milling system through experiments to support milling stability prediction, the method proposed in this paper effectively improves the efficiency of robot milling stability prediction. • The prediction results of the proposed tool tip frequency response prediction model were imported, and a two-degree-of-freedom chatter prediction model considering the regenerative effect is established, and the robot milling chatter is predicted considering redundant degrees of freedom. The accuracy of prediction results is verified by milling experiment. The change of tool tip frequency response caused by the posture dependence of robot dynamic is one of the key problems that make it difficult to accurately predict the milling stability of robot. In this paper, a tool tip frequency response prediction method considering the interface stiffness characteristics of spindle-tool system is proposed for stability prediction of robotic milling under the condition of posture variation. Firstly, the interface stiffness models of spindle-toolholder, toolholder-spring clip and spring clip-tool are established based on Yoshimura's unit area method. Then, The dynamics model for the robot body and the interface stiffness models for spindle-tool system are imported into the finite element analysis model of the spindle system, so that the prediction of the tool tip frequency response is realized by harmonic response analysis. Compared with the experimental results, the maximum error of the natural frequency was not more than 2 %, and the maximum error of the amplitude was not more than 12 %. Finally, the 2 DOF robot milling stability prediction model is established. Then the robot milling chatter is predicted considering redundant degrees of freedom from the perspective of regenerative chatter prediction theory, and the accuracy of prediction results is verified by milling experiment. [ABSTRACT FROM AUTHOR]

Exact dynamic stiffness (DS) models for three-dimensional (3D) cavities in cylindrical coordinates under any classical acoustic boundary conditions (BCs) are proposed in this paper. The paper first derives the exact general solutions that satisfy the governing differential equations. Then, these general solutions are used to develop the DS matrices for 3D cavities in cylindrical coordinates by substituting them into the acoustic pressure and normal velocity BCs. Subsequently, the Wittrick–Williams algorithm, along with the analytical expressions of the j 0 count for various shaped cavities, is applied to compute natural frequencies. Finally, reliable and efficient techniques for dynamic response solution are employed. The DSM provides benchmark solutions for various 3D cavities. The convergence, universality, and efficiency of the proposed method in modal and response analysis are illustrated by comparing the results obtained using the DSM and FEM. The calculation time when using the DSM is only 0.1% of that when using the commercial finite element method, while maintaining the same accuracy. This research not only provides an effective technique for analyzing the cylindrical acoustic pressure field in engineering, but also establishes a foundation for the analysis of structural–acoustic coupling in tubular structures. • Dynamic stiffness derived for circular/sectorial/annular/sectorial annular 3D cavities. • Different BCs can be modeled and non-uniform acoustic excitations can be applied. • Analytical j0 count of W–W algorithm in cylindrical coordinates is derived. • High efficiency and exactness is demonstrated for broadband modal/response analyses. • Benchmark solutions are provided for various 3D cavities subjected to different BCs. [ABSTRACT FROM AUTHOR]

In this paper we investigate the nonlinear dynamic behavior of a rotor with an architecture targeting space turbopumps. Depending on the rotor speed of rotation, these pumps can be supported by ball bearings with a loose fit, i.e. having an outer-race housing clearance, and by annular seals providing radial fluid forces thanks to the Lomakin effect. Moreover, such turbopumps often operate in supercritical regime, which means that they must pass through critical speeds while undergoing the lowest vibration levels to ensure pump safety. In this context, the aim of the paper is to analyze the case of an academic rotor test bench designed to present a dynamic bending behavior similar to that of space turbopumps. The investigation focuses on the test bench equipped with two hydrodynamic bearings and two ball bearings with loose fit. The rotor response when passing through its first critical speed and triggering nonlinear bearing-housing contact phenomena is assessed experimentally and numerically. The hydrodynamic bearings are located at the two shaft ends and the ball bearings at the middle of the shaft. The rotor finite element model is detailed first and the test bench presented. Then, the nonlinear dynamic response of the rotor subject to a mass unbalance and a permanent bow is obtained. The numerical results are computed using either a full transient step-by-step time integration technique or an arc-length continuation method. The main objective is to assess how the nonlinearity stemming from the loose fit of the ball bearings alters the original rotordynamics. Moreover, a parametric analysis based on mass unbalance and on outer-race housing clearance is conducted. Major nonlinear phenomena are highlighted such as the resonance peak flattening at the critical speed, and the numerous harmonics triggered by the hydrodynamic bearing and contact forces. The results obtained and the model proposed here are of considerable relevance for the design of space turbopumps and other pumps having a similar architecture. [ABSTRACT FROM AUTHOR]

• A highly efficient structural dynamic analysis method with controllable accuracy is proposed. • It is applicable to a wide range of coupled and nonlinear dynamic systems with time-varying modal characteristics.. • It can attain high-precision solutions with a minimal number of elements. Matrix perturbation theory (MPT) is widely used in sensitivity analysis and reanalysis of structural eigenvalue problems when small changes are imposed on parameters. However, the conventional MPT based on the finite element method is only applicable to the cases with small parameter variations, and it is difficult to avoid cumulative errors caused by multi-step perturbations. A key issue for the application of MPT is how to evaluate the error of perturbation solution and correct the results during the process of multi-step perturbation solution. By invoking the dynamic stiffness method (DSM), Wittrick-Williams algorithm, and the precise integration method (PIM), in this paper, we propose an improved method with controllable accuracy, self-checking and elimination of accumulated errors, referred to as the dynamic stiffness matrix perturbation theory (DSMPT). In present method, the rationality of the results can be estimated preliminarily according to dynamic stiffness equation, which is not present in the original MPT, can greatly enhance the accuracy of the perturbation results and evaluate the errors. Case studies prove that the DSMPT combined with PIM provides a convenient way to realize accuracy self-inspection and rectification of the perturbation results, and the maximum relative error of eigenvalue and response can be controlled to be smaller than 0.2% and 0.025%, respectively. Besides, DSMPT can also be applied to the analysis of coupled and nonlinear dynamic system with time-varying modal characteristics. Finally, a thermally-induced vibration analysis of tensegrity modules during space deployment is taken as an example to further illustrate the advancements of the DSMPT in solving time-varying dynamic problems. Results show that the DSMPT effectuate an almost sixfold reduction in computational time. In this paper, an improved structural dynamic analysis method with controllable accuracy, self-checking and elimination of accumulated errors is proposed. It is applicable to a wide range of coupled and nonlinear dynamic systems with time-varying modal characteristics. [Display omitted] [ABSTRACT FROM AUTHOR]

Due to the complexity of fluid–structure interactions (FSI), the majority of studies in the literature dealing with the sloshing problem are restricted to rigid tanks. This paper is devoted to a numerical investigation of the liquid sloshing behavior in a flexible tank subjected to external loading. A numerical methodology is proposed, taking into account the FSI problem by coupling two open-source codes: OpenFOAM for the fluid and FEniCS for the solid, using the preCICE library, a free library for fluid–structure interaction. The Arbitrary Lagrangian–Eulerian formulation is used for the two-phase flow system to solve the Navier–Stokes equations in the fluid domain using the finite volume method. Simultaneously, the linear-elastic equation of the structure is solved using the finite element method. An implicit coupling scheme is considered at the fluid–structure interface. The numerical methodology is validated by the results given in literature for harmonic excitation at different frequencies. Subsequently, an analysis of complex external loading, such as Gabor wavelets and earthquake ground motion, is conducted to highlight the significant impact of the wall flexibility on sloshing, as well as the influence of hydrodynamic forces on the structure's deformation. The proposed coupling methodology is robust and effective, it can be applied to all types of liquids and materials. A dataset of one of the studied cases is given as a supplement to the paper (Kha et al., 2024). [ABSTRACT FROM AUTHOR]

This paper presents a new framework for stochastic updating of a finite element model for a composite plate, considering the influence of temperature on Lamb wave propagation. The framework involves deterministic updating to optimize mechanical properties and stochastic updating to derive probability density functions for key parameters. It utilizes sensitivity analysis and Bayesian inference with Markov-Chain Monte Carlo simulations and the Metropolis–Hastings sampling algorithm. This paper proposes a machine learning surrogate model based on artificial neural networks to improve computational efficiency. This surrogate modeling approach allows parallelized Monte Carlo simulations, reducing updating time significantly without compromising the accuracy of the resulting probability density functions for model parameters. These advancements show a promising way to enhance composite plate modeling and Lamb wave propagation studies, providing a more efficient and accurate approach to verify and validate finite element models with potential applications in engineering simulations. [ABSTRACT FROM AUTHOR]

The parasitic motion of microgripper jaws affect clamping accuracy. The parallelogram mechanism (PM) is often used as the last-stage of the multi-stage amplification mechanisms (AMs) because of its parallel clamping characteristics. However, the PM traditionally used in multi-stage AMs is asymmetrically stressed, which will affect its parallel clamping accuracy. Based on this, a PM with symmetrical forces is designed. The paper addresses the issue of parasitic motion in microgripper jaws and its impact on clamping accuracy, which is a relevant concern in micro-scale manipulation systems. The design of a symmetrically stressed PM for use in a two-stage asymmetric microgripper is a novel contribution to the field. Based on the minimum potential energy principle and the Castigliano's second theorem, the mechanical modeling of the mechanism's parasitic displacement, magnification and parallel clamping accuracy is carried out. Comparing the mechanical model, finite element analysis (FEA) and experimental measurement results, the values given by the three different methods are close. The method given in this paper to improve the clamping accuracy of the mechanism is also applicable to similar compliant mechanisms. [ABSTRACT FROM AUTHOR]

In this paper, we have implemented the three-dimensional Boundary Element Method (BEM) to solve the hydrodynamic forces in arrays of two, three, and five thin beams oscillating with small amplitudes in a fluid. We solve the unsteady Stokes equation by considering the oscillatory Stokeslet. The non-dimensional hydrodynamic function is validated through numerical solutions obtained using the Finite Element Method (FEM) at various frequency parameters and gap ratios. We analyse the influence of the relative phase and amplitude ratio of a uniform beam and a non-uniform two-beam array in terms of added mass and damping coefficients. Additionally, we compare the solution with experimental results available in the literature as a function of gap ratio. The analysis presented in this paper can be useful for optimizing arrays used in Atomic Force Microscope (AFM), biosensors, and energy harvesters. [Display omitted] • BEM and FEM modelling of non-uniform beams arrays. • Tuning of hydrodynamic forces due in-phase and out-of-phase motions of two beams array. • Hydrodynamic coupling can be controlled by utilizing different combination of non-uniform beams. • Hydrodynamic forces are more on the middle beams of an array at small gap. [ABSTRACT FROM AUTHOR]

Acoustic Black Holes (ABH) embedded within structures can efficiently damp vibrations above the cut-on frequency but fails below it, particularly when the flexural wavelength exceeds the size of the ABH. Therefore, addressing low-frequency vibration mitigation becomes imperative. Periodic ABH structures and shunt damping have been employed individually and proved effective, yet their combined application has not been explored previously. This paper introduces a novel approach for broadband vibration mitigation. It combines a periodic ABH beam, damping layer, and a resonant element comprising a piezoelectric patch and an inductance–resistance shunting circuit (referred as lossy PZT-ABH metabeam). This design addresses the shortcomings in the attenuation performance within the pass bands of conventional periodic structures and allows for easy adjustment of the attenuated bands without the need for physical structural modification. To characterize this system, a semi-analytical model of the electromechanical problem is developed using the Rayleigh–Ritz method, and the complex dispersion curve is obtained to evaluate the mitigation performance. The obtained results are validated against Finite Element Method (FEM) simulations, demonstrating that the lossy PZT-ABH metabeam achieves broadband vibration mitigation covering the entire frequency spectrum with remarkable flexibility. To facilitate designs, a detailed analysis is conducted on the length and attached position of the piezoelectric patch, thickness of the damping layer and the value of inductance and resistance. Furthermore, a thorough investigation into the mechanism of electromechanical resonance (ER) is carried out to deepen our understanding of the ER attenuated band. • Achievement of broadband vibration mitigation covering the entire frequency range. • Semi-analytical model of Gaussian expansion method for the multi-physical problem. • Merging periodic ABH beam, damping layer and piezoelectric resonant element. • Flexibility for changing local attenuated band at arbitrary frequencies. [ABSTRACT FROM AUTHOR]

• A comprehensive stiffness model of intermediate bearing is presented. • A reduced model of dual rotor-bearing-casing coupling system is developed. • The effects of typical parameters on the vibration of the system are discussed. • The mechanism of the comprehensive stiffness and system vibration is revealed. This paper focuses on the vibrational properties of a dual rotor-casing coupled system with nonlinear clearance in the intermediate bearing, considering both the oil film stiffness and Hertzian contact stiffness between rolling elements and raceways. A comprehensive stiffness model for the intermediate bearing has been developed based on elastohydrodynamic lubrication (EHL) and Hertz contact theory. Subsequently, a dynamical model of the dual rotor-bearing-casing system is established using the finite element method, thereby verifying the feasibility of simulating the casing with beam elements. The dimensionality of the system equation is reduced using the fixed-interface component mode synthesis (CMS) method, and the resulting reduced-dimensionality equation is solved using the improved Newmark- β method. The effects of casing support, rotational speed, and radial clearance on the vibration characteristics of the system are investigated. Then, the comprehensive stiffness and coupled vibration characteristics of the system are analyzed to elucidate its intrinsic mechanism. Finally, the contact characteristics within the intermediate bearing under dynamic load are also studied. The results indicate that the support stiffness of the casing has a more significant impact on the second resonance caused by both the inner and outer rotors. The system is prone to experiencing varying compliance (VC) resonance at low rotational speeds. The excessive bearing clearance leads to complex vibrational characteristics of the system, making it challenging to predict its motion. The impact of minor changes in stiffness on system vibration is small when the comprehensive stiffness is large. At this time, the limited effect of oil film stiffness allows it to be disregarded in terms of comprehensive stiffness. Furthermore, the speed significantly influences the contact characteristics within the intermediate bearing under the unbalanced force of the rotor and gravity. [ABSTRACT FROM AUTHOR]

• A hybrid multi-scale/arbitrary Lagrangian-Eulerian finite element method is proposed. • The novel method is used for predicting nonlinear structural-acoustic responses. • The novel method offers valuable insights into structural-acoustic interaction mechanisms. This paper introduces a novel hybrid multi-scale/arbitrary Lagrangian-Eulerian finite element method (HMS/ALE-FEM) for addressing the nonlinear vibro-acoustic problem of a large-deformed beam in an infinite fluid. In the HMS/ALE-FEM, the vibrational response of the beam is tackled through modal superposition and a temporal multi-scale approach, while the acoustic wave emitted from the beam is addressed using the arbitrary Lagrangian-Eulerian finite element method (ALE-FEM). An alternating frequency/time domain technique is employed to handle the displacement and velocity of the moving mesh and the acoustic pressure on the beam surface. To validate the HMS/ALE-FEM, it is compared against the finite element method for beam response and the ALE-FEM for acoustic response, serving as a reference method. Taking the nonlinear vibro-acoustic problem of a buckled beam with 2:1 internal resonance as an example, the results of the HMS/ALE-FEM are compared with those of the reference method. The results show that the HMS/ALE-FEM is in good agreement with the reference method under different harmonic excitation amplitudes and frequencies. Due to the 2:1 internal resonance, double modes can be generated, and the second mode amplitudes of both beam displacement and acoustic pressure remain constant as the excitation amplitude varies. Notably, the HMS/ALE-FEM provides direct access to mode amplitude and phase information for beam displacement and acoustic pressure on the beam surface, offering valuable insights into fluid-structure interaction mechanisms in both single- and double-mode scenarios. [ABSTRACT FROM AUTHOR]

[Display omitted] Boundary conditions are crucial for the construction of physical models of concrete-filled steel tube (CFST) arches, but the current model updating methods seldom consider boundary conditions and usually necessitate repeated modifications and recalculations of finite element models, which are not efficient enough. Moreover, the current physics-informed neural network (PINN) provides a new approach for solving physical equations through physical constraint merging into the neural network, but it is still limited by complex structures, multiple scales, and unknown physical model engineering problems. Therefore, this paper proposed a boundary recognition method for physically-enhanced machine learning. First, the basic variables of the physical equation and the variables to be optimized were taken as inputs to enhance the neural network's ability to predict the target response. Then, similar to the handling of physical loss constraints in the PINN, the physical loss between the physical model (FE) and the neural network predictions was used to update the parameters. Then, a physical feedback-enhanced neural network (PFENN) meta -model was established, and modified mutation particle swarm optimization (MMPSO) was adopted to optimize the identification of boundary parameters. The identification process involves validation via mutual verification using a finite element model, meta -model, and experimental model. The prediction accuracy is higher than that of classical Kriging, response surface (RS), support vector machine regression (SVR), and neural network (NN) meta -models; additionally, the proposed model has good optimization stability, and reliable optimization results, and its computational efficiency is increased by 4.57 times compared with that of the traditional non-metamodel method. Moreover, the proposed method enhances the accuracy and interpretability of surrogate models by enhancing physical parameters and reducing physical losses, which is suitable for boundary recognition and physical model construction of different structures. [ABSTRACT FROM AUTHOR]

In this paper, a numerical approach able to evaluate the sound power emitted by a non-cavitating flexible marine propeller blade is proposed. With asymptotic expansions and order of magnitude analysis, two main phenomena are identified: the so-called propulsion and vibroacoustic phenomenon. The propulsion phenomenon is nonlinear and models the lift generation along the blade. It creates a pre-stress and a pre-strain on a deformed configuration on which the blade vibrates and emits sound waves. The vibroacoustic phenomenon is linearized and has no retroaction on the first static phenomenon. This simplified model allows to solve the fully coupled fluid–structure system in order to compute the radiated noise of a pre-stressed blade. • Lift generation and small vibrations are partially decoupled for marine propeller. • Propulsion phenomenon is solved using a simple iterative solver. • Vibro-acoustic phenomenon is solved using monolithic FEM-FEM formulation. • Blade deformation significantly changes lift generation. • The pre-strain and pre-stress on a blade have an impact on its vibrations. [ABSTRACT FROM AUTHOR]

This paper introduces a novel approach that focuses on application of cooperative game theory model for automated finite element model updating. The approach involves transforming the conventional single-objective optimization finite element model updating problem into a game theory problem. Among the different alternatives, a cooperative game model is considered to solve the transformed updating problem. This new approach overcomes the limitations of the conventional single-objective optimization formulation, which include challenges related to selecting appropriate weighting factor of residuals and analysing their influence on optimization results. To demonstrate the effectiveness of the proposed approach, an ultralight fibre reinforced polymer footbridge is considered. The numerical model of the footbridge is updated using the experimentally determined inherent properties (natural frequencies and mode shapes) using the proposed approach. A comparison with the conventional sensitivity-based weighted single objective method reveals that the inclusion of the weighting factor in the optimization process under the cooperative game model method allows for more efficient solution of the single-objective updating optimization problem, while maintaining accuracy and quality in the updated model. [ABSTRACT FROM AUTHOR]

This paper presents a coupled algorithm for gas foil bearing simulation with considering three-dimensional structure. In the discretization process of the top foil, the plate and shell elements are compared to evaluate their advantages in terms of computational time and deviation. Based on the displacement constraints, the bump foil is simplified as a series of separated bumps and their interaction forces are calculated by the penalty function method. To solve the nonlinearity of the foil deflection caused by the frictional contact, the incremental iteration method is introduced in the simulation. The calculation accuracy of the proposed algorithm is verified by the experimental results and its efficiency is superior to the existing methods. [ABSTRACT FROM AUTHOR]

In this paper, we develop a class of high-order conservative methods for simulating non-equilibrium radiation diffusion problems. Numerically, this system poses significant challenges due to strong nonlinearity within the stiff source terms and the degeneracy of nonlinear diffusion terms. Explicit methods require impractically small time steps, while implicit methods, which offer stability, come with the challenge to guarantee the convergence of nonlinear iterative solvers. To overcome these challenges, we propose a predictor-corrector approach and design proper implicit-explicit time discretizations. In the predictor step, the system is reformulated into a nonconservative form and linear diffusion terms are introduced as a penalization to mitigate strong nonlinearities. We then employ a Picard iteration to secure convergence in handling the nonlinear aspects. The corrector step guarantees the conservation of total energy, which is vital for accurately simulating the speeds of propagating sharp fronts in this system. For spatial approximations, we utilize local discontinuous Galerkin finite element methods, coupled with positive-preserving and TVB limiters. We validate the orders of accuracy, conservation properties, and suitability of using large time steps for our proposed methods, through numerical experiments conducted on one- and two-dimensional spatial problems. In both homogeneous and heterogeneous non-equilibrium radiation diffusion problems, we attain a time stability condition comparable to that of a fully implicit time discretization. Such an approach is also applicable to many other reaction-diffusion systems. • High order conservative LDG-IMEX methods for non-equilibrium radiation diffusion problems are developed. • Degeneracy, strong nonlinearity and stiff source are all taken into account. • A predictor-corrector procedure based on an IMEX scheme is proposed. • Only mildly nonlinear system needs to be solved and is robust for convergence. • The scheme is of high order, conservative, positivity-preserving and allow large time steps. [ABSTRACT FROM AUTHOR]

Health monitoring technologies, empowered by sensor-driven information and model updating, play an important role in assessing the status of civil structures and detecting anomalies. However, significant domain discrepancies exist in the distribution of physical parameters between numerical structural models and their real-world counterparts. As a result, many health monitoring theories struggle to be effective in practice, even if they perform perfectly in the simulated data. To bridge the domain discrepancies, this paper proposes an unsupervised domain adaptation approach based on an adapted cycle-consistent generative adversarial network (CycleGAN) that incorporates physical constraints and a self-attention mechanism. The approach focuses on the mutual transformation of the multi-channel time series obtained from numerical models and actual structures. Specifically, the physical constraints are derived from the governing equation of linear dynamic systems, while the self-attention mechanism is achieved by adding transformer structures to both the generator and discriminator. Through free-vibration experiments on a steel beam and a large-scale steel bridge model, the physical constraints and transformer structures have proven beneficial for improving the learning capability and training stability of the GAN model. Furthermore, the proposed approach is not only verified as effective in transforming acceleration responses between the test structures and their corresponding finite element models in both time and frequency domains but has also been shown to reproduce mode shapes accurately. [ABSTRACT FROM AUTHOR]

Bolted joints are the major connection form to hold the aero-engine rotor system as a discontinuous entirety. What is noteworthy is that the bolt assembly process (BAP) directly relates the uniformity of preload and the symmetry of joint stiffness when the rotor comes to assembly, thereby introducing a heightened level of complexity and unpredictability to the dynamic response of the rotor system. In this paper, the effect of BAP on the stiffness softening of bolted flange joints is analyzed based on a finite element contact model. Then, a bolted joint rotor system finite element model is established to discuss the magnitude-frequency characteristic under three assembly sequences of bolts. The rotor vibration response is further compared between the three sequences considering the stiffness loss. Finally, the theoretical studies are verified by a rotor test rig. Results demonstrate that the stiffness softens to varying degrees with the increase of external load, and the softening mechanism is intricately associated with the contact state of the joint interfaces. Intriguingly, joint stiffness and its softening law are also affected by the BAP, leading to substantial discrepancies in rotor critical speed and vibration response among different assembly sequences. It is further observed that the tangential stiffness softening complicates the dynamic properties of the rotor system and enhances the nonlinear features. [ABSTRACT FROM AUTHOR]

Assembled structures in complex machinery usually have many joints, used to reduce assembly time and manufacturing complexity, to facilitate maintenance, ensure sealing and provide overall structural stiffness. Joints in these structures can change the stiffness and introduce friction damping and hence they impact the dynamic behaviour of the overall assembly. Currently, the joint impact on the structure is mainly considered only as defined at the design stage; however, attempts are underway to use the frictional interfaces to improve and control the overall dynamic performance during operation. This paper explores the possibility of actively manipulating the interface geometry of a frictional joint to influence its stiffness and energy dissipation capabilities. A proof of concept experimental campaign, of a novel concept that changes the hysteretic behaviour and frequency responses in dry friction contacts by means of a series of piezoelectric actuators will be presented and discussed. The experimental results are compared against simulation results obtained using a finite element model. The investigation shows that the concept is feasible and that it effectively changes the contact conditions, by changing the hysteresis loops and influencing the frequency responses from hammer test. [ABSTRACT FROM AUTHOR]

• A Hierarchical Bayesian formulation is proposed for updating structural models. • An Expectation-Maximization strategy is offered to mitigate computational costs. • Difficulties of treating close modes are resolved using a geometric approach. • Applications to an offshore platform are provided to verify the proposed method. Updating Finite Element (FE) models based on modal data has become a standard tool for condition monitoring and damage detection in structures. The basis of this approach is to minimize the discrepancy between the experimental and analytical modal frequencies and shapes through a particular loss function derived through deterministic or probabilistic methods. However, the weighting of modal features can affect the identified structural model parameters, which requires proper treatment. This paper revisits this problem by proposing a novel hierarchical Bayesian formulation, wherein the covariance matrix of modal residuals is identified from the data, leading to automated weighting of the modal residuals. As the calculation of the posterior distribution encounters computational overheads, an efficient Expectation-Maximization algorithm is proposed to approximate the optimal values of the parameters. Bayesian information criterion is employed to select the most plausible layout for the prediction errors covariance matrix. A new strategy is also established for handling dynamical modes with close modal frequencies. Finally, the proposed approaches are examined using simulated and real data from FINO3 offshore platform. As a result, reasonable estimations with desirable uncertainty bounds are acquired. Although the weighting of modal features varies on a case-to-case basis, it is observed that the proposed method might lead to non-trivial and interesting weighting factors according to the data-driven uncertainty of modal residuals. [ABSTRACT FROM AUTHOR]

This paper investigates an efficient exponential integrator generalized multiscale finite element method for solving a class of time-evolving partial differential equations in bounded domains. The proposed method first performs the spatial discretization of the model problem using constraint energy minimizing generalized multiscale finite element method (CEM-GMsFEM). This approach consists of two stages. First, the auxiliary space is constructed by solving local spectral problems, where the basis functions corresponding to small eigenvalues are captured. The multiscale basis functions are obtained in the second stage using the auxiliary space by solving local energy minimization problems over the oversampling domains. The basis functions have exponential decay outside the corresponding local oversampling regions. We shall consider the first and second-order explicit exponential Runge-Kutta approach for temporal discretization and to build a fully discrete numerical solution. The exponential integration strategy for the time variable allows us to take full advantage of the CEM-GMsFEM as it enables larger time steps due to its stability properties. We derive the error estimates in the energy norm under the regularity assumption. Finally, we will provide some numerical experiments to sustain the efficiency of the proposed method. • Multiscale reduction methods are efficient and accurate to solve problems with high-contrast media. • The presence of high-contrast coefficients reduces the stability region of time discretization. • Implicit methods must solve nonlinear equations, which can be a bottleneck computation. • Exponential integrators are alternative techniques and use robust time-stepping. [ABSTRACT FROM AUTHOR]

In this paper we give the necessary and sufficient conditions for the Discrete Maximum Principle (DMP) to hold. We prove the convergence of the nonlinear finite element method applied to the logistic equation by using that the Jacobian matrix evaluated in the supersolution, provided by the a priori bound, is a non-singular M-matrix, which is proved in a fast way using both, the positiveness of its principal eigenvalue and the DMP. Meanwhile a positive subsolution provides the coercivity constant. The numerical simulations show that the nonlinear finite element approximate solutions do not oscillate if the DMP is fulfilled. The characterization of the DMP and the mesh sizes guaranteeing the existence of positive sub- and supersolutions of the nonlinear finite element approximate problem, in the case of variable coefficients and all types of boundary conditions are some of the novelties of this paper. The excellent performance of the method is tested in two examples with boundary layers caused by very small diffusion. [ABSTRACT FROM AUTHOR]

Virtual sensing employs an estimator that combines a numerical model and a limited set of measurements to estimate the full field pressure of a vibro-acoustic system in the time domain. A key aspect of virtual sensing is to create a reduced-order model of the vibro-acoustic system, such that the numerical model can be effectively employed in the virtual sensing scheme. This paper aims to create a reduced-order vibro-acoustic finite element model with frequency-dependent admittance boundary conditions for virtual sensing applications using a Kalman filter. The frequency-dependent components in admittance boundary conditions always result in a frequency-dependent damping matrix which hinders the modeling in the time domain. This paper first treats the vibro-acoustic system as a negative feedback interconnection of two subsystems: a state-space model of admittance transfer functions and a vibro-acoustic system with rigid boundary conditions. Stacking the states of these two subsystems gives the final descriptor system. Then, due to the passivity of the admittance transfer function and the definiteness of the system matrices, the second-order form of the descriptor model is modified to give a full-order model which is proven to be stability-preserving under one-sided projection methods. A coupled vibro-acoustic system is experimentally presented which demonstrates that the proposed methodology can provide a stable reduced order model and allows the full field estimation of the pressure in the presence of frequency-dependent boundary conditions. • A time-domain vibro-acoustic model with admittance boundary conditions is derived. • The stability of the time-domain model is assessed. • A stability-preserving model order reduction scheme is presented. • A virtual sensor is created by the reduced order model and measurements. • The virtual sensor allows for full field estimation of the pressure. [ABSTRACT FROM AUTHOR]

[Display omitted] • The vibro-acoustic model of the cavity-ECCDS panel-cavity is demonstrated from an analytical perspective for the first time. • This model can calculate the sound transmission loss of ECCDS panels and its accuracy has been verified experimentally. • The effect of various parameters on the sound transmission loss of ECCDS panels is analysed in detail. The embedded co-cured composite damping structures (ECCDS) are widely used in engineering fields, it is necessary to build a predictive model of the dynamics of the ECCDS panel. In this paper, a method is promoted for the first time that can predict the acoustic-vibration coupling characteristics of the coupled cavity-ECCDS panel-cavity system. This paper innovatively combines the spectral-geometry method (SGM), penalty-function method (PFM), and the energy-generalised variational principle to develop coupling model of the ECCDS panel with two closed cavities. The displacement of the ECCDS panel and the sound pressure in the cavities are expressed as improved Fourier series. The modal parameters of the cavities and the ECCDS panel are obtained by solving the standard matrix eigenvalue problem, and the accuracy of this method is verified by comparing it with the finite element method (FEM) and experiment. On this basis, the sound transmission loss (STL) can be obtained by the sound pressure method. The factors affecting the sound insulation performance of the ECCDS panel are investigated by parametric analysis. The results show that the addition of a damping layer can improve the sound insulation performance of composite panels. This paper provides a reference for the application of ECCDS panels in engineering. [ABSTRACT FROM AUTHOR]

Damage localization based on ambient vibration data in combination with finite element models can be challenging, in particular due to the large number of parameters in the model and noisy measurement data. Changes in different structural parameters can cause similar changes in data-driven features, and vice versa, it can be challenging to identify which parameter caused the deviation in the data. The problem is ill-conditioned and slight variations in the features, due to inherent statistical uncertainty, can lead to significant errors in the result interpretation. A possible solution is sensitivity-based statistical tests in combination with a parameter clustering approach that considers the uncertainties of data-driven features. In this context, this paper introduces the concept of damage localizability , and provides a framework to evaluate it based on the minimum detectable parameter changes, possible false alarms in unchanged parameters, as well as the achievable damage localization resolution. Since clustering approaches depend on user-defined hyperparameters, such as the number of clusters, the second objective of this paper is to optimize the performance of the damage localization, by adjusting the hyperparameters for clustering. A particular strength of the approach is that the analysis can be conducted based on data and a numerical model from the undamaged structure alone, making it a suitable approach to assess and to optimize the diagnosis performance before damage occurs. For proof of concept, a laboratory case study on a simply-supported steel beam is presented, where the localizability of mass changes is analyzed and optimized. • An approach is developed to assess and optimize the performance of damage localization tests. • Clustering of sensitivity vectors avoids ill-conditioning. • Localizability is defined by the three criteria: resolution, detectability, and false alarms. • All criteria can be quantified based on data from undamaged structures, and a numerical model. • Experimental data confirm the predictive capabilities of the performance assessment. [ABSTRACT FROM AUTHOR]

• A structure-preserving method is proposed to investigate the vibration of the axially moving cracked cantilevered beam. • We find that when the beam moves with a high speed, the appearance of crack will intensify the vibration of beam sharply. • We find that the vibration amplitude of the cracked beam is suddenly larger in five narrow circular frequency bands. Considering the existence of the opening crack, the axially motion as well as the transverse harmonic excitation, the dynamic response of the beam is studied by a structure-preserving method in this paper. With the equivalent bending stiffness introduced to describe the effect of the crack on the flexibility of the beam, the vibration model of the axially moving cracked cantilevered beam subjected to a transverse harmonic load at its free end is presented. A structure-preserving method in the generalized multi-symplectic framework is developed subsequently. Finally, the effects of the crack's parameters, the axially moving speed and the circular frequency of the transverse harmonic load on the steady vibration amplitude of the cracked beam are investigated by the structure-preserving method in detail. From numerical results, it can be found that when the beam moves with the high speed, the appearance of the crack on the beam will intensify the vibration of the beam sharply. In addition, the vibration amplitude of the cracked beam is suddenly larger in five narrow circular frequency bands. Comparing with the results of the wavelet spectral finite element method, the center circular frequencies of the narrow five circular frequency bands obtained by the generalized multi-symplectic method are highly agreed with the first five natural frequencies of the cracked beam, which illustrates the precision of the numerical results reported in this paper directly. [ABSTRACT FROM AUTHOR]

We present a new exactly divergence-free and well-balanced hybrid finite volume/finite element scheme for the numerical solution of the incompressible viscous and resistive magnetohydrodynamics (MHD) equations on staggered unstructured mixed-element meshes in two and three space dimensions. The equations are split into several subsystems, each of which is then discretized with a particular scheme that allows to preserve some fundamental structural features of the underlying governing PDE system also at the discrete level. The pressure is defined on the vertices of the primary mesh, while the velocity field and the normal components of the magnetic field are defined on an edge-based/face-based dual mesh in two and three space dimensions, respectively. This allows to account for the divergence-free conditions of the velocity field and of the magnetic field in a rather natural manner. The non-linear convective and the viscous terms in the momentum equation are solved at the aid of an explicit finite volume scheme, while the magnetic field is evolved in an exactly divergence-free manner via an explicit finite volume method based on a discrete form of the Stokes law in the edges/faces of each primary element. The latter method is stabilized by the proper choice of the numerical resistivity in the computation of the electric field in the vertices/edges of the 2D/3D elements. To achieve higher order of accuracy, a piecewise linear polynomial is reconstructed for the magnetic field, which is guaranteed to be exactly divergence-free via a constrained L 2 projection. Finally, the pressure subsystem is solved implicitly at the aid of a classical continuous finite element method in the vertices of the primary mesh and making use of the staggered arrangement of the velocity, which is typical for incompressible Navier-Stokes solvers. In order to maintain non-trivial stationary equilibrium solutions of the governing PDE system exactly, which are assumed to be known a priori , each step of the new algorithm takes the known equilibrium solution explicitly into account so that the method becomes exactly well-balanced. We show numerous test cases in two and three space dimensions in order to validate our new method carefully against known exact and numerical reference solutions. In particular, this paper includes a very thorough study of the lid-driven MHD cavity problem in the presence of different magnetic fields and the obtained numerical solutions are provided as free supplementary electronic material to allow other research groups to reproduce our results and to compare with our data. We finally present long-time simulations of Soloviev equilibrium solutions in several simplified 3D tokamak configurations, showing that the new well-balanced scheme introduced in this paper is able to maintain stationary equilibria exactly over very long integration times even on very coarse unstructured meshes that, in general, do not need to be aligned with the magnetic field. • Semi-implicit FV/FE method for incompressible viscous and resistive MHD equations. • Well-balanced and exactly divergence-free on general unstructured mixed-element grids. • Constrained L2 projection for an exactly divergence-free reconstruction. • Thorough study of the lid-driven MHD cavity problem (reference solution is provided). • Stable long-time simulation of Grad-Shafranov equilibria in 3D tokamak geometries. [ABSTRACT FROM AUTHOR]

This paper presents a boundary element method for calculating the sound pressure level on and above a ground-board placed on an infinite ground plane with constant impedance. This method uses the Green's function for the Helmholtz equation in a half-space bounded by an infinite impedance plane and therefore avoids the complications which occur when modeling the ground as a finite impedance plane (which results in diffraction from the edges of the ground plane). Two formulations are presented: the first one models a finite thickness ground-board, whilst the second one models a zero-thickness ground-board with the upper surface coplanar with the ground plane. The method is validated against an equivalent finite element method simulation and example calculations are presented for typical ground-board designs used for outdoor noise measurements on different ground impedance planes and incidence angles. It is shown that the sound pressure level on the upper surface of a ground-board placed on a non-rigid ground can vary significantly and that this variation is dependant on the ground impedance, angle of incidence and frequency. These findings are consistent with previous investigations and highlight the fact that noise measurements made using ground-board mounted microphones on a non-rigid ground are dependant on the impedance of the surrounding ground surface. The method presented in this paper could be used to develop corrections to straightforwardly account for this effect. [ABSTRACT FROM AUTHOR]

In this paper, the principal time-domain system identification methods are studied and used to carry out the experimental modal analysis of a single-link flexible manipulator with curved geometry in a comparative fashion. The identification process carried out in this study is aimed at deriving first-order state-space dynamical models and second-order configuration-space dynamical models of the single-link flexible manipulator by using an array of fundamental system identification procedures, which includes the ARX (AutoRegressive eXogenous method), SSEST (State-Space ESTimation method), N4SID (Numerical Algorithm for Subspace State-Space System Identification), ERA/OKID (Eigensystem Realization Algorithm combined with the Observer/Kalman Filter Identification method), and TFEST (Transfer Function ESTimation method) methods. The main goal of this paper is, therefore, to perform a comparative study between the most fundamental system identification procedures applied to the numerical and experimental analysis of the structural vibrations of a flexible manipulator having a curved geometric shape. First, this paper poses the theoretical foundations for the development of the numerical study and the experimental testing to be performed for the case study. Subsequently, the flexible manipulator analyzed in this work is modeled with various levels of complexity, which range from a simple lumped parameter model to a linear finite element model developed by integrating the interconnections between the SOLIDWORKS and ANSYS software. By doing so, the computational procedures applied to the time-domain experimental measurements of the dynamic behavior of the flexible manipulator allow for reconstructing first-order and second-order mechanical models of the structural system of interest in the MATLAB simulation environment. The numerical results and the experimental tests reported in this investigation demonstrate the effectiveness of all the time-domain system identification approaches considered in the paper. [ABSTRACT FROM AUTHOR]

• Imaging of delamination in CFRP laminates based on integration of multiple LDR modes. • LDR frequencies calculated by frequency-domain finite element approach. • Quantitative assesment of delamination with various shapes and sizes. Accurately visualizing the geometry and dimensions of internal delamination in fiber-reinforced polymer (CFRP) composites is a challenging endeavor. In this paper, we develop a method to identify and characterize delamination in composites by the integration of multiple local defect resonance (LDR) modes. The proposed method was validated by using T300/M914 CFRP plates containing three distinct defect geometries, employing both numerical simulations and experimental measurements. The approach commences with the application of a frequency-domain finite element method for LDR frequency determination, emphasizing improved computational efficiency. This technique is further corroborated through the use of the defect-to-background ratio (DBR) method, which identifies LDR frequencies in both numerical simulations and experimental testing. The integration of multiple LDR modes (IMLDR) at various frequencies enables precise imaging of delamination defects of diverse geometries and sizes. Experimental results closely align with the numerical findings, confirming that the integrated imaging results accurately correspond to artificial defects. This method furnishes precise descriptions of damage location, geometry, and dimensions. The obtained results indicate that the proposed IMLDR-based technique significantly enhances the accuracy and reliability of delamination imaging in composites. Consequently, it offers an effective approach for quantitatively assessing delamination damage in composites. [ABSTRACT FROM AUTHOR]

Gear systems play a crucial role in various machines to transmit power and motion. One common issue in the gear systems is the frequent gear collision, which results in increased wear and tear, and ultimately, damage to the gears. Consequently, the gear faults tend to develop in a compound manner rather than in isolation, i.e., a faulty gear often encompasses multiple defects, such as pitting, cracking, and so forth. Nevertheless, the existing literature has primarily centered on the gear model with a single fault, leaving a research gap in the modeling of compound faults. Further, to elucidate the root causes behind the degradation of gear systems, it is necessary to figure out the relationship between the intrinsic characteristics of gear systems and the progressive development of compound faults of gears. To address these issues, this paper proposes a compound fault gear modeling method with a generic framework to handle arbitrary spatial configuration of compound faults. The compound fault gear model is then verified by finite element model (FEM). Further, the relationship between the progressive development of gear compound faults and the evolution of time-varying meshing stiffness (TVMS) of gears is investigated, presenting a detailed comparison of the sensitivity of TVMS to different spatial configuration of gear faults. The results offer a promising avenue for modeling machinery degradation with compound faults, paving the way for a more comprehensive understanding of the intricate dynamics involved in the degeneration of gear systems. [ABSTRACT FROM AUTHOR]

The frequency response of vibrating plates with openings can be tailored through the shape and location of these openings in the mixed interfaces of vibro-acoustic systems. This paper introduces a novel method for designing the characteristics of openings in mixed interfaces to achieve the desired vibrational and acoustic responses. The core of this methodology is an analytical model that utilizes the Rayleigh–Ritz method, augmented by a radiation resistance matrix for precise estimation of sound power in a free field. This approach provides the essential flexibility to alter the shapes and locations of the openings. A Finite Element Method (FEM) is specifically employed to enhance the visualization of the interactions within the multiphysics domains of the vibro-acoustic systems. This FEM model, developed for the enclosure and coupled with the vibrating plate according to Kirchhoff's thin plate theory, is complemented by the Boundary Element Method (BEM) for the sound pressure calculations. The methodology is further substantiated by experimental validation, which confirms the theoretical predictions and enhances the credibility of the proposed models. [Display omitted] • Novel method for shaping frequency response of a vibrating plate with openings. • Analytical model to optimize vibro-acoustic system opening location and arrangement. • Estimating minimal sound power in the free field for required openings area. • Numerical and experimental visualization of vibro-acoustic interactions. [ABSTRACT FROM AUTHOR]

• Revisit the strain-based formulation for a structural system. • Formulation of Bayesian model updating utilizing strain-based modal data. • Solution methodology based on dynamic condensation is developed. • MH-within Gibbs sampler is proposed for sampling the posterior PDF. • Validation using numerical examples and an experimental study. This paper proposes a novel methodology for Bayesian model updating and damage detection of a structural system using strain-based modal data. The strain-based modal data are assumed to consist of the posterior statistics of natural frequencies and strain mode shapes corresponding to measured strains from a classically damped system. The dynamic strain-based equation of the motion is formulated utilizing the energy functional of the structural system and the strain displacement relation. The state variables in the considered strain-based formulation consist of the strains and the elemental rigid body displacements. The methodology is developed by incorporating strain-based formulation into the Bayesian framework for Finite Element (FE) model updating. Besides, additional uncertain parameters in the form of system strain-based modal parameters are introduced in the eigenvalue equation to avoid mode-matching. The model reduction technique is utilized to eliminate the rigid body displacements and the strains that are not measured. Metropolis-Hastings (MH) within Gibbs sampling is proposed to simulate samples from the posterior Probability Density Function (PDF) of the model parameters of the FE model. The effectiveness of the proposed methodology is demonstrated using simulated examples. An experimental study is also conducted to validate the proposed methodology. [ABSTRACT FROM AUTHOR]

• The dynamic geometric stiffness effect is first considered in VFIFE scheme. • A new VFIFE scheme is developed for parametric resonance of beam structures. • A filtering-based Lyapunov exponent is first used to determine stability boundary. • A parametric resonance test is conducted to verify VFIFE scheme. The parametric resonance of a beam structure may lead to a disastrous consequence. To assess the safety of a structure, structural engineers need a straightforward and practical method to calculate the large-amplitude nonlinear parametric resonance responses of the beam structure. This paper proposes a newly developed vector form intrinsic finite element (VFIFE) calculation scheme to analyse the nonlinear parametric resonance of planar beam structures. By taking into account the geometric stiffness effect of the internal axial force for the frame element, a new relationship between internal nodal forces and deformation components is first established based on the VFIFE principle and the parametric resonance mechanism of frame structures. A numerical example of a portal frame is presented to demonstrate the efficacy of this new calculation scheme. A parametric resonance test of the cantilever beam is conducted to verify the applicability of the VFIFE method. The numerical results show that the proposed scheme can well simulate the nonlinear phenomena of parametric resonances. The numerical predictions are consistent with the experimental observations. A filtering-based finite-time Lyapunov exponent approach is presented to determine the stability boundary of the structure. The numerical stability boundary of parametric resonance agrees well with the experimental boundary. Possible causes of deviations between the numerical and experimental results are discussed. The proposed VFIFE scheme is a simple and effective means of analysing the stability and nonlinear responses of the parametric resonance of planar beam structures. [ABSTRACT FROM AUTHOR]

The continuous interior penalty finite element method (CIP-FEM) has shown promise in reducing pollution errors when numerically simulating the Helmholtz equation with high wave numbers. However, its reliance on structured meshes largely limits its applicability. To address this limitation, this paper presents a novel approach to CIP-FEM on general unstructured meshes. The interior penalty parameters of the CIP-FEM are determined in an offline phase through minimizing the residual obtained by substituting the plane waves into the CIP finite element equation. To enhance accuracy, a quasi-Newton algorithm is employed to correct the penalty parameters and minimize errors of the CIP finite element approximations to the plane waves. The calculated interior penalty parameters can be saved, enabling the online solutions of CIP-FEM to be obtained by reusing these parameters for arbitrary sources during practical computations. Numerical experiments are presented to demonstrate the significant reduction of pollution errors for both linear and higher-order CIP-FEMs on unstructured meshes. Furthermore, the proposed algorithm successfully simulates high-frequency acoustic fields in a three-dimensional vehicle cabin with greatly reduced errors within certain fixed computational time, demonstrating its practical effectiveness in real-world scenarios. • The optimized CIP-FEM can be applied to unstructured meshes, addressing a notable limitation of standard CIP-FEM. • The penalty parameters are determined in an offline phase through the residual/error-minimization approaches. • The proposed algorithm successfully simulates high-frequency acoustic fields in vehicle cabin in real-world scenarios. [ABSTRACT FROM AUTHOR]

• Accurate prediction of the cantilever-structured PPC's bandgap central frequency. • Rapid calculation of the bandgap edge frequency through proximity factor. • Targeted modulation of the PPC's bandgap using negative capacitance circuit. Piezoelectric phononic crystals (PPCs) have the advantages of simplicity and efficiency in controlling elastic wave bandgaps, which can be utilized to solve NVH problems with varying frequency features, such as the low-frequency vibrations caused by the time-varying power source (i.e., motor) in the subframe and underbody of new energy vehicles. However, most of the previous studies on PPCs bandgap control are qualitative, lacking the knowledge of bandgap targeted modulation. This paper analyzes the locally resonant (LR) bandgap characteristics of PPCs with shunting circuits, and aims to achieve precise control of bandgap position by circuit parameters. A theoretical research model of cantilever-structured PPCs is established firstly, and its accuracy is verified through finite element analysis and experiments. Subsequently, the formation mechanism of the LR bandgap is analyzed, and a bandgap characteristic frequency estimation method is proposed, along with an analysis of the influence of electrical parameters using this method. Finally, from the perspective of bandgap practicality, the variable capacitance method is proposed, which can quickly calculate the capacitance value through an estimation formula under the arbitrary designation of target bandgap in the low-frequency range of 200 Hz∼500 Hz. The results show that the actual bandgap position is very close to the target bandgap position, and the bandgap always keeps enough bandwidth and attenuation amount. This method has broad prospects in the field of vibration attenuation where frequency characteristics are variable. [ABSTRACT FROM AUTHOR]

Based upon two overlapped, body-unfitted meshes, a type of unified-field monolithic fictitious domain-finite element method (UFMFD-FEM) is developed in this paper for moving interface problems of dynamic fluid-structure interactions (FSI), which is accompanied with high-contrast physical coefficients across the interface and with contacting collisions between the structure and fluidic channel wall in the immersed FSI case. In particular, the proposed novel numerical method consists of a monolithic, stabilized mixed finite element method within the frame of fictitious domain/immersed boundary method (FD/IBM) for generic fluid-structure-contact interaction (FSCI) problems in the Eulerian–updated Lagrangian description, while involving the no-slip type of interface conditions on the fluid-structure interface, and the repulsive contact force/stress on the structural surface when the immersed structure contacts the fluidic channel wall. The developed UFMFD-FEM for FSI/FSCI problems can deal with the structural motion with large rotational and translational displacements and/or large deformation in an accurate and efficient fashion, which is first validated by two benchmark FSI problems and one FSCI model problem, then by experimental results of a realistic FSCI scenario – the microfluidic deterministic lateral displacement (DLD) problem that is applied to isolate circulating tumor cells (CTCs) from blood cells in the blood fluid through a cascaded filter DLD microchip in practice, where a particulate fluid with the pillar obstacles effect in the fluidic channel, i.e., the effects of fluid-structure interaction and structure collision, play significant roles to sort particles (cells) of different sizes with tilted pillar arrays. The developed unified-field, monolithic fictitious domain-based mixed finite element method can be seamlessly extended to more sophisticated, high dimensional FSCI problems with contacting collisions between the moving elastic structure and fluidic channel wall. • A fluid-structure-contact interaction (FSCI) model involving the interaction and collision effects is developed. • A mixed FEM in the monolithic fictitious domain frame is developed with respect to a unified variable pair of velocity and pressure. • Advanced algorithms are designed to handle structural collision, nonlinear system and interpolation between fictitious fluid and structure. • Numerical approaches are validated by benchmark problems, self- and physically designed DLD problems. • Numerical simulations carried out by the developed UFMFD-FEM can help to optimize the design of DLD microchips. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two innovative strategies have been proposed to protect energy harvesters with frequency up-conversion mechanism from mechanical overload. • Finite element method has been used to model and analyse the proposed protection strategies. • Experiments have been conducted to verify the strategies and modelling. • The capability of protecting the harvesting device from unexpected overload is demonstrated. • The protection mechanisms and damping effects of the proposed strategies are discussed. Vibration energy harvesters utilising the frequency up-conversion mechanism have been effective in harvesting low-frequency ambient vibrations. However, the mechanical impact required for this process could also damage the devices when excessive load is applied. To address this issue, this paper presents novel protection strategies for energy harvesters with a frequency up-conversion mechanism, including a ring-type stopper within the resonant system and specially designed impact protection components (IPC) within the impact system. By applying these methods, the influence of excessive input excitation has been mitigated, and thus, the reliability and durability of the device have been improved. Finite element modelling has been employed to model the proposed protection methods, and then experiments have been conducted to verify and refine the modelling. Stress analysis is finally conducted based on the refined model to validate the effectiveness of the protection strategies. The results demonstrate that the proposed strategies are capable of protecting the harvesting system from excessive input excitations, which means the device functions effectively in the operating state and decelerates the growth rate of maximum stress and acceleration in the limiting state. This research contributes valuable insights into the development of effective protection strategies for energy harvesters with frequency up-conversion mechanisms, thereby improving their durability and performances in real-world applications. [ABSTRACT FROM AUTHOR]

This paper presents a model order reduction method to accelerate broadband topology optimization of structural-acoustic interaction systems by coupling Finite Element Methods and Boundary Element Methods. The finite element method is used for simulating thin-shell vibration and the boundary element method for exterior acoustic fields. Moreover, the finite element and boundary element methods are implemented in the context of isogeometric analysis, whereby the geometric accuracy and high order continuity of Kirchhoff-Love shells can be guaranteed and meantime no meshing is necessary. The topology optimization method takes continuous material interpolation functions in the density and bulk modulus, and adopts adjoint variable methods for sensitivity analysis. The reduced order model is constructed based on second-order Arnoldi algorithm combined with Taylor's expansions which eliminate the frequency dependence of the system matrices. Numerical results show that the proposed algorithm can significantly improve the efficiency of broadband topology optimization analysis. • Broadband topology optimization of 3D structural-acoustic interaction with reduced order isogeometric FEM/BEM. • Model order reduction is conducted for topology optimization of structural-acoustic interaction by coupling FEM/BEM. • The isogeometric analysis is applied to the topology optimization framework with reduced order FEM/BEM. [ABSTRACT FROM AUTHOR]

• An efficient hybrid semi-analytical and finite element method for fluid-transporting cracked pipe is proposed. • Bending-bending and bending-axial coupling responses are reported to detect crack faults. • Effects of crack and fluid parameters on the dynamic characteristics of the cracked pipe are analyzed. The fatigue cracks may develop in the pipe systems due to long-term cyclic loading, which may cause catastrophic accidents. The finite element method (FEM) is usually adopted to simulate the stress singularity and breathing effect, resulting in expensive computational costs. Therefore, in this paper, an efficient hybrid semi-analytical and finite element (SA-FE) method is proposed to study the nonlinear dynamic characteristics of the fluid-transporting cracked pipe (FTCP) considering the breathing effect. Furthermore, the crack sensitivity parameters are obtained through bending-bending and bending-axial vibration analysis. For the SA-FE method, the semi-analytical method (SAM) and FEM are separately used to construct the dynamic models of the non-cracked and cracked regions, and the connection at the interface is performed by constraint equations. Subsequently, the validity of the modeling method is substantiated through both FEM and experimental tests. Finally, the effects of crack and fluid parameters on the dynamic characteristics of the FTCP are analyzed. The results indicate that changes in crack positions may trigger different-order mode switching, and continuous switching may occur between higher-order modes. In addition, the bending-bending and bending-axial coupling responses can effectively detect crack failures of the FTCP with varying levels of damage. The proposed model can offer valuable insights for fault diagnosis and health monitoring of FTCP. [ABSTRACT FROM AUTHOR]

In this paper, the first large-scale application of multiscale-spectral generalized finite element methods (MS-GFEM) to composite aero-structures is presented. The crucial novelty lies in the introduction of A-harmonicity in the local approximation spaces, which in contrast to Babuška and Lipton (2011) [30] is enforced more efficiently via a constraint in the local eigenproblems. This significant modification leads to excellent approximation properties, which turn out to be essential to capture accurately material strains and stresses with a low dimensional approximation space, hence maximizing model order reduction. The implementation of the framework in the Distributed and Unified Numerics Environment (DUNE) software package, as well as a detailed description of all components of the method are presented and exemplified on a composite laminated beam under compressive loading. The excellent parallel scalability of the method, as well as its superior performance compared to the related, previously introduced GenEO method are demonstrated on two realistic application cases, including a C-shaped wing spar with complex geometry. Further, by allowing low-cost approximate solves for closely related models or geometries this efficient, novel technology provides the basis for future applications in optimization or uncertainty quantification on challenging problems in composite aero-structures. [ABSTRACT FROM AUTHOR]

In a previous paper, [1] , a new formulation for isothermal gas flow in a single pipeline including gravity and friction effects has been introduced and solved by finite element methods. A performance analysis has been done by using some tests both manufactured and experimental. The goal of the present work is to extend the ideas to model gas flow in a transportation network. As a first step, in this paper the network only includes pipes connected at nodes which can be emission or consumption points, or simply structural connections between pipes. In addition to the mass and momentum conservation equations inside the pipes that are partial differential equations, we need to write the mass conservation equations at the nodes. The latter appear to be a set of constraints (one per node) whose respective Lagrange multipliers are the (continuous) pressures at the nodes. Thus, the whole model is a Partial Differential-Algebraic Equation (PDAE). For numerical solution, an implicit time discretization is proposed first and then a weak formulation of the resulting semi-discrete problem is introduced. After doing a finite element discretization we are led to solve a nonlinear system of numerical equations per time step what is done by Newton's method. In order to reduce the computing time, the algorithm can be parallelized in such a way that, at each time step, every pipe can be solved separately in one processor (or core). Moreover, we show that the proposed scheme exactly conserves the mass at the nodes and in the whole network, and a new simple and compact way of computing the network line-pack over the time is given. Finally, the introduced methodology is validated by applying the computer program to a triangular network, which is a standard test in references on the subject, and to a real network for which we have got measurements that enable us to create the boundary conditions for the model and also to compare the numerical results with experimental data. • Numerical solution of Euler-like models with friction and variable topography. • An equivalent formulation with one nonlinear PDE of second order in time and space. • An implicit time discretization combined with a finite element method is used. • Accuracy has been tested with experimental data and numerical results from papers. [ABSTRACT FROM AUTHOR]

In this paper, a modelling approach is developed for predicting the vibroacoustic response of infinite, plane, 1- or 2-dimensionally periodic structures, including the forced response, sound transmission and radiation. This method combines a wave and finite element method with a space-harmonic assumption. A periodic cell of the structure is modelled using a conventional finite element method to find the mass and stiffness matrices. Wave propagation in the fluids is modelled analytically. The response at the interface between structure and fluid is represented in terms of a series of space harmonics. The effects of the fluids on the structure are modelled as a series of equivalent nodal forces. By post-processing the mass and stiffness matrices along with the applied forces using periodicity theory and equilibrium conditions, a spectral dynamic stiffness matrix is derived to calculate the response to a convected harmonic pressure. Excitation of the structure by oblique plane waves and a diffuse sound field are considered, together with the consequent sound transmission. The response to general excitation and the consequent radiation are also determined. For complex structures, model reduction using component mode synthesis is suggested. Various numerical examples are presented to illustrate this method. For simple structures, analytical solutions are available for comparison with the predictions made using the proposed method. For complicated structures, vibroacoustic analysis using analytical methods is difficult. However, the method developed in this paper provides a straightforward and efficient approach for estimating the vibroacoustic response of general plane periodic structures. [ABSTRACT FROM AUTHOR]