Finite Element (FE) model updating is crucial for identifying key parameters in structural design and improving predictive accuracy. Despite extensive research on advanced FE procedures approved for ...user applications, persistent disparities remain in real-world scenarios, especially for complex materials like wood. Capturing accurate mechanical characteristics with traditional models poses challenges in sustainability projects. This study introduces a derivative-free model updating procedure using a Single-Objective Optimisation (SOO) incorporating observed and predicted natural frequencies and vibration modes. The objective function optimises tuning parameters to minimise discrepancies between predicted and observed outcomes. The focus is on Cross-laminated Timber (CLT), a composite wooden structure gaining traction as a sustainable alternative to materials like reinforced concrete and steel. However, the mechanical properties of CLT can vary due to inherent variability in wood’s mechanical characteristics. This research identifies sensitive mechanical properties — longitudinal Young’s modulus, internal shear moduli, and rolling shear modulus of CLT — using a model updating procedure based on a comprehensive set of data from Experimental Modal Analysis (EMA). The study provides algebraic derivations of the updating procedure and a step-by-step implementation algorithm to facilitate practical application in structural engineering.
•Framework for updating Finite Element models of Cross-Laminated Timber (CLT) established.•Integration of Experimental Modal Analysis data results in optimised CLT models.•A simplex approach is used to optimise objective functions for CLT structures.•Identified key parameters: longitudinal modulus, interior, and rolling shear moduli.•The mechanical properties of CLT differ from those used in structural analysis.
This work used free vibration tests based on impulse excitation technique and experimental modal analysis using an impact hammer and an accelerometer to assess the local and global effects of the ...hygrothermal ageing of GFRP specimens exposed to salt-spray environment at 35°C and 60°C over a period of 136 days. Through the change in elastic properties, fifteen natural frequencies and damping ratios, the effects of degradation are associated with reductions in elastic properties and natural frequencies and an increase in damping ratios. In turn, the increase in elastic properties and natural frequencies – associated with a reduction in damping ratios – is mainly attributed to the post-curing effect.
•Hygrothermal ageing of FRP angle members and coupons is reported.•Impulse excitation technique is adopted to monitor reduction of elastic properties.•Experimental modal analysis is used to study variations in natural frequencies and damping ratios.•Combined influence of material degradation and ageing is discussed.
The vibro-acoustic properties of baffled laminated composite doubly curved shell panels are investigated using a coupled FEM/BEM formulation in the framework of the higher-order shear deformation ...theory. Validation of the present scheme has been established and the effect of geometry, geometrical parameters and support conditions on the acoustic radiation behaviour of the curved panels has been brought out.
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•Coupled FEM/BEM scheme based on the HOSDT is proposed and developed.•Vibro-acoustic analysis of baffled composite doubly curved panel is performed.•Desired responses are computed via MATLAB code based on the present model.•Numerical and experimental validity of the present scheme is established.•Effect of parameters on the sound radiation behaviour of curved panel is studied.
In this article, the acoustic radiation responses of doubly curved laminated composite shell panels subjected to harmonic excitation are investigated numerically in the framework of the higher-order shear deformation theory. A general mathematical model for the vibrating curved panel has been developed and the cylindrical, spherical, elliptical and hyperboloid shell panel geometries resting on an infinite rigid baffle are considered for analysis. The desired response is computed using an in-house code developed in MATLAB. Firstly, the natural frequencies of the vibrating shell panel are obtained using the present model and validated with data available in the literature with experimental test results. A coupled finite element/boundary element formulation is then used to obtain the acoustic response of the structure. The mean square velocity, radiation efficiency and the sound power radiated are chosen as the acoustic response indicators. The effect of different support conditions, lamination schemes, aspect ratio and geometry of the vibrating doubly curved shell panel on the acoustic radiation behaviour is investigated and discussed in detail. It is observed that the support conditions and the lamination scheme greatly influence the acoustic radiation from the panels. On the other hand, the radiation pattern is quite similar for different geometries with a substantial distinction for flat plate.
In this study, a new finite element formulation is presented for straight beams with an edge crack, including the effects of shear deformation, and rotatory inertia. The main purpose of the study is ...to present a more accurate formulation to improve the beam models used in crack detection problems. Stiffness matrix, consistent load vector, and mass matrix of a beam element is obtained using the exact solution of the governing equations. The formulation for frame structures is also presented. Crack is modelled utilizing from the concepts of linear elastic fracture mechanics. Several numerical examples existing in the literature related to the vibrations of such structures are solved to validate the proposed model. Additionally, an experimental modal analysis is performed to see the superiority of the present method for high modes of vibration, which are generally not taken into account in crack detection problems. The inverse problem is also solved using a well–known optimization technique called genetic algorithms. Effects of shear deformation, rotatory inertia, and number of natural frequencies considered, on the accuracy of the estimation of crack parameters are investigated. It is found that considering more number of frequencies yields better estimation of crack parameters, but require a better modelling of the dynamics of the beam. Therefore, the present formulation is found to be an essential tool in crack detection problems.
•The modal properties of an ultrasonic stack are studied numerically and experimentally.•The wide horn is designed with adequate frequency separation from other modes.•All detected mode shapes from ...the FE simulation are identified by the experimental tests.•The average difference between the simulation and experimental results is 1.42%.
In the present study, the modal properties of an ultrasonic stack are investigated. The ultrasonic stack comprises a wide horn. The horn of the ultrasonic stack is designed with the genetic algorithm. The objectives of the problem are: the main longitudinal mode shape frequency should be similar to the frequency of the transducer-booster, and this mode has adequate frequency separation from other modes. The finite element simulation is used to calculate the natural frequencies and mode shapes. An experimental modal analysis using the roving hammer method is utilized to detect real natural frequencies, and mode shapes and verify the simulation results. Based on the simulation results and due to the complex structure of the ultrasonic stack, three different setups are utilized for the experimental modal analysis. The results show that the experimental test identifies all detected modes from the finite element simulation. Also, the frequency difference between the simulation and experimental results is less than 1% in most cases. The average frequency difference between the simulation and experimental results is 1.42%. The simulation frequency of the main longitudinal mode is 14 Hz (0.07%) lower than the experimental result.
•Response controlled stepped sine test¨ is proposed for experimental modal analysis of nonlinear systems.•Modal parameters of nonlinear structures are identified as functions of modal ...amplitude.•Identified modal parameters are used to synthesize FRFs for untested harmonic forcing scenarios.•¨Harmonic force surface¨ approach is proposed for measuring unstable branches of frequency response curves.•The method is validated using a numerical example, a benchmark structure and a real missile structure.
Although the identification and analysis of structures with a localized nonlinearity, either weak or strong, is within reach, identification of multiple nonlinearities coexisting at different locations is still a challenge, especially if these nonlinearities are strong. In such cases, identifying each nonlinearity separately requires a tedious work or may not be possible at all in some cases. In this paper, an approach for experimental modal analysis of nonlinear systems by using Response-Controlled stepped-sine Testing (RCT) is proposed. The proposed approach is applicable to systems with several nonlinearities at various different locations, provided that modes are well separated and no internal resonances occur. Step-sine testing carried out by keeping the displacement amplitude of the driving point constant yields quasi-linear frequency response functions directly, from which the modal parameters can be identified as functions of modal amplitude of the mode of concern, by employing standard linear modal analysis tools. These identified modal parameters can then be used in calculating near-resonant frequency response curves, including the unstable branch if there is any, for various untested harmonic forcing cases. The proposed RCT approach makes it also possible to extract nonlinear normal modes experimentally without using sophisticated control algorithms, directly from the identified modal constants, and also to obtain near-resonant frequency response curves experimentally for untested constant-amplitude harmonic forcing cases by extracting isocurves of constant-amplitude forcing from the measured Harmonic Force Surface (HFS), a new concept proposed in this paper. The key feature of the HFS is its ability to extract unstable branches together with turning points of constant-force frequency response curves directly from experiment, accurately. The method is validated with numerical and experimental case studies. The numerical example consists of a 5 DOF lumped system with strong several conservative nonlinear elements. Experimental case studies consist of a cantilever beam supported at its free-end by two metal strips which create strong stiffening nonlinearity, and a real missile structure which exhibit moderate damping nonlinearity mostly due to several bolted joints on the structure.
In this study, the dynamic characteristics (i.e. natural frequencies and associated mode shapes) of a partially filled horizontal cylindrical shell are investigated experimentally and by an ...isogeometric finite element-boundary element method. The proposed numerical procedure is divided into two parts. In the first part, the dynamic characteristics of the cylindrical shell under in-vacuo conditions are obtained by the isogeometric finite element method (IGAFEM) based on a linear Kirchhoff-Love shell formulation. In the second part, the fluid-structure interaction effects are calculated in terms of generalized added mass coefficients by using the isogeometric boundary element method (IGABEM), assuming that the structure vibrates in its in-vacuo principle mode shapes. By adopting the linear hydroelasticity theory, it is assumed that the fluid flow is ideal, i.e., an incompressible flow and inviscid fluid. In order to show the versatility of the numerical method, the results are compared with those obtained by the conducted experiments. Relevant numerical challenges in the hydroelastic vibration analysis are highlighted and it is shown that the numerical predictions and experimental results are in good agreement.
•An isogeometric FE-BE method based is proposed to analyze hydroelastic vibration characteristics of shell structures.•A horizontal circular cylindrical shell partially filled with fluid is studied with the proposed numerical framework.•Hydroelastic vibration of the cylindrical shell under study is also investigated experimentally.•The validity of the proposed method is shown by comparing the calculated results with those experimentally measured..
In this paper, Active Vibration Control (AVC) of a rectangular carbon fibre composite plate with free edges is presented. The plate is subjected to out-of-plane excitation by a modal vibration ...exciter and controlled by Macro Fibre Composite (MFC) transducers. Vibration measurements are performed by using a Laser Doppler Vibrometer (LDV) system. A fractional-order Positive Position Feedback (PPF) compensator is proposed, implemented and compared to the standard integer-order PPF. MFC actuator and sensor are positioned on the plate based on maximal modal strain criterion, so as to control the second natural mode of the plate. Both integer and fractional-order PPF allowed for the effective control of the second mode of vibration. However, the newly proposed fractional-order controller is found to be more efficient in achieving the same performance with less actuation voltage. Moreover, it shows promising performance in reducing spillover effect due to uncontrolled modes.
Experimental Modal Analysis (EMA) allows to assess the dynamical properties of a mechanical component or structure by estimating the modal parameters. Whereas EMA is usually based on local ...accelerometers or laser vibrometer data, in this paper we focus on camera-based EMA as cameras offer full field and contact-less data. However, besides few very specific controlled cases, camera-based EMA is limited by the low frame rate of the camera in comparison to accelerometers and vibrometers. In this paper we propose a novel acquisition scheme that allows to estimate modal parameters above the Nyquist–Shannon limit (i.e., half of the camera frame rate) by employing a random sampling scheme in time in combination with one accelerometer. With this information we reconstruct the Impulse Response Function (IRF) modal model through a nonlinear optimization problem, where the accelerometer ensures a global solution by providing an initial guess of the eigenfrequencies. We investigate numerically the accuracy of the methodology by simulating multiple damped sine waves. Furthermore, we present an experimental validation on a clamped–clamped beam excited by an impact hammer. Thereby, the displacement information is captured by a single camera triggered by random pulses, and computed by Lucas–Kanade (LK) optical flow. The complexity and modal assurance criterion (MAC) of the modes show that all modes whose amplitudes are higher than the noise level are measured successfully with only one excitation hit, where the highest mode, at 218Hz, is measured with a random sampling scheme comparable to 50fps (to reach 218Hz, a regular sampling with 436fps would be required).
•Go beyond Nyquist–Shannon sampling limit in camera-based EMA by random sampling.•Contact-less measurement to obtain spatially dense vibration modes.•No repetition of the experiment is required to achieve wide frequency bandwidth.•Random sampling relaxes the requirement of the camera data storage and transfer.
Design of modern timber floors is often governed by the vibration serviceability requirements. One way to improve vibration serviceability is through the design of two-way floor systems. In this ...paper, the behaviour of two-way LVL–concrete composite plates and a plate strip is investigated experimentally, with an emphasis on the performance of proposed dovetail joint for connecting the adjacent LVL panels. The investigations consist of the experimental modal analysis and static load deformation tests, performed under multiple support conditions. The results show a significant two-way action, indicated by about 45% higher fundamental natural frequency when four edges are supported instead of two. The point load deflection in the centre of the plate was reduced of about 9%. Furthermore, a numerical model for two-way TCC plates was developed and results show a wide agreement with the experimental behaviour, except for discrepancies related to deflections on the plate edge. The results from the experimental and numerical investigations indicate that the dovetail joint can produce a stiff connection, such that the LVL layer could be regarded as continuous in the connected direction.
•Experimental investigations of two-way LVL–concrete composite floor plates with various support conditions.•Continuity between LVL panels provided by a novel dovetail joint.•Experiments include experimental modal analysis (EMA) and static deformations under concentrated loads.•Presented numerical model shows a wide agreement with the experimental results.•Effectivity of the dovetail joint and considerable two-action of the plates are identified.
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