bluuebunny/crossref_metadata_2025 huggingface dataset:
Solitary waves of M-fractional low-pass nonlinear electrical transmission line model arising in network system
Authors: Yel Gülnur
Published: June 2024

In this study, we analyze the solitary wave behavior of a truncated M-fractional low-pass nonlinear electrical transmission line (NLETLs) model. NLETL models are relevant to computer network systems, particularly for high-speed data transmissions. They influence the behavior of signals traveling through network cables. To investigate the dynamics of solitary waves in the model, we applied the modified Sardar sub-equation and extended the sinh-Gordon equation expansion methods. We illustrated the 2D, 3D, and contour shapes of selected solutions for appropriate values of the NLETLs dynamics using Mathematica-14. Kink, anti-kink, bright-dark bell, dark bell, M-shaped periodic soliton, and logarithmic wave solutions were obtained. The results indicate that the proposed techniques may provide valuable, powerful, and efficient insights into the dynamics of nonlinear evolution models. The role of the fractional order derivative in making optical solutions is investigated in detail, which opens up opportunities for the creation of more complex models that can more accurately simulate optical phenomena in the real world.
Machine learning-assisted prediction of the electronic features of a Schottky diode interlaid with PVP:BaTiO3 composite
Authors: Azizian-Kalandaragh Yashar , Barkhordari Ali , Özçelik Süleyman , Altındal Şemsettin
Published: June 2024

This study employs two Machine Learning (ML) models to predict the electronic current and then analyze the main electronic variables of Schottky diodes (SDs), including leak current (I0), potential barrier height (ΦB0), ideality factor (n), series resistance (Rs), shunt resistance (Rsh), rectifying ratio (RR), and interface states density (Nss). The I-V characteristics are examined for both without and with an interlayer. The polyvinylpyrrolidone (PVP) polymer and BaTiO3 nanostructures are combined to form the nanocomposite interface. The ML algorithms that are employed include the Gaussian Process Regression (GPR) and Kernel Ridge Regression (KRR). The thermionic emission theory is used to gather training data for ML algorithms. Ultimately, the effectiveness of these ML methods in anticipating the electric characteristics of SDs is evaluated by contrasting the predicted and experimental findings in order to identify the optimal ML model. Whereas the GPR algorithm has given values that are closer to the actual values, the ML predictions of fundamental electric variables by practically both algorithms have the best level of agreement with the actual values. Also, the obtained findings indicate that when the nanocomposite interface is used, the amount of I0 and Nss for metal-semiconductor (MS) Schottky diodes reduces and φ
B0 increases.
Bayesian inference methodology for primordial power spectrum reconstructions from Large Scale Structure
Authors: Martínez-Somonte G. , Marcos-Caballero A. , Martínez-González E. , Cañas-Herrera G.
Published: June 2024

We use Bayesian inference to develop a non-parametric method to reconstruct the primordial power spectrum Pℛ
(k) from Large Scale Structure (LSS) data. The performance of the method is assessed by testing it against simulations of the clustering of high-z (QSOs) objects. Their clustering is derived from different templates of the primordial power spectrum motivated by models of inflation: the Standard Model power law characterized by the two parameters As
and ns
; a local feature template; and a global oscillatory template. The primordial power spectrum is reconstructed using N knots in the log {k, Pℛ
(k)} plane while sampling the cosmological parameters {H
0, Ω
b
, Ω
c
}. We use two statistical tests to examine the reconstructions for signs of primordial features: a global test comparing the evidences and a novel local test quantifying the power of the hypothesis test between the power law model and the marginalized probability over N model. We also discuss results of an application to low-z (ELGs) objects with two different photometric errors keeping the cosmology fixed. The method shows good performance in all scenarios considered. In particular, the tests show no feature detection for the standard power-law primordial power spectrum; yet, the method is able to detect power spectrum deviations at a percent level for all considered features, combining either the low-z or the high-z redshift bins. In addition, we include a test proof-of-concept application to real data from the Sloan Digital Sky Survey Luminous Red Galaxy Data Release 4 (SDSS LRG 04), finding no preference for deviations from the primordial power law. The method is flexible, model independent, and suitable for its application to existing and future LSS surveys.
Design and optimisation of 3D-printed energy harvesters for railway bridges
Authors: Cámara-Molina J.C , Romero A , Galvín P , Moliner E , Martínez-Rodrigo M.D
Published: June 2024

This paper investigates energy harvesting on railway bridges. The type of harvester studied is a cantilever bimorph beam with a mass at the tip and a load resistance. These parameters are adjusted to find the optimal design that tunes the harvester to the fundamental frequency of the bridge. An analytical model based on a variational formulation to represent the electromechanical behaviour of the device is presented. The optimisation problem is solved using a genetic algorithm with constraints of geometry and structural integrity. Additive manufacturing to 3D print energy harvesters is used to maximise design flexibility and energy performance. The proposed procedure is implemented in the design and manufacture of an energy harvesting device for a railway bridge on an in-service high-speed line. The structure under study corresponds to a six-arched concrete bridge with double ballasted track. The proposed design is experimentally validated and the performance under operating conditions is evaluated in a test field.
Estimating the foundation parameters of offshore wind turbines through Bayesian model updating
Authors: Simpson H A , Tatsis K E , Abdallah I , Chatzi E N , Chatzis M N
Published: June 2024

The rapid growth of the wind industry has resulted in larger wind turbines with modal properties that lie in the lower frequency range, rendering accurate fatigue assessment increasingly important. However, high uncertainty associated with the support conditions and foundation properties can pose challenges in the condition assessment and fatigue life estimation. One approach to improve these estimates is to use structural monitoring data (e.g. from sensors mounted on the towers) to update the foundation parameters of offshore wind turbine models. However, the low identifiability of the parameters to be estimated can lead to divergent estimates across different frameworks, which, combined with uncertainty in foundation properties, can compromise remaining useful life estimates. In this work, a Bayesian model updating framework is applied to update the foundation parameters of an offshore wind turbine, and its results are compared against a deterministic framework in a numerical example. The advantages of the Bayesian framework over the deterministic framework are discussed in detail and the importance of accurately accounting for uncertainties as part of the model updating process is highlighted.
Stochastic flutter analysis of a torsional-vibration-based energy harvester affected by random aeroelastic loads and wind turbulence
Authors: Piciucco Davide , Caracoglia Luca
Published: June 2024

This paper investigates the energy production of a “meso-scale”, wind-based energy harvester that exploits the torsional aeroelastic instability of a rigid blade-airfoil, elastically supported at equidistant supports. Torsional flutter is a single mode aeroelastic instability phenomenon, in which a diverging dynamic angular rotation of a body occurs. The apparatus relies on a simple mechanism that uses flow-induced pitch motion to extract and convert airflow kinetic energy to electrical energy. The system is composed by a rigid blade-airfoil, connected to a support structure through a non-linear restoring force (torsional spring-like) mechanism that enables the rotation about a reference pivot axis. The proposed technology is designed to be efficient in the range of low and medium wind speeds (10-13 m/s), in which horizontal-axis wind turbines and other harvesters are not efficient. Deterministic pre-flutter, incipient flutter and post-critical vibrations of the apparatus have been already explored in a previous study. This work aims to further investigate the aeroelastic behavior of the “flapping foil” by examining the effect of turbulence, random experimental error and modeling simplifications of the aeroelastic forces. The analysis is conducted at incipient flutter in the frequency domain using classical unsteady force models. Monte Carlo methods are employed to solve for the probability of incipient flutter speed. Several configurations are considered to improve the efficiency of the energy harvester.
Identification of human-structure interaction from full-scale observations: The impact of modeling errors
Authors: Nimmen Katrien Van , Broeck Peter Van den
Published: June 2024

The added-damping effect of human-structure interaction (HSI) is of great importance on the vibration serviceability of footbridges. To account for the interaction effects between the human body and the footbridge, the former is often described by a mass-spring-damper (MSD) system. The parameters of this MSD system are in this contribution estimated by minimizing the discrepancy between the experimentally derived and the numerically simulated power spectral density of the structural response. The methodology assumes that the dynamic behavior of the empty structure, the average weight and the distribution of step frequencies in the crowd are known. This contribution furthermore focuses on the impact of modeling errors. It is shown that the result is mostly sensitive to errors related to the mean value of the distribution of step frequencies and the structural natural frequencies. It is also shown that the impact of modeling errors decreases as the impact of HSI increases. The results are used to refect on the suitability of two real footbridges for the parameter estimation problem. When the impact of the reasonably expected modeling errors is taken into account and the results of both case studies are combined, a natural frequency and damping ratio of approximately 3.0±0.2 Hz and 34±8% are estimated for the MSD interaction model.
Physics-informed machine learning for moving load problems
Authors: Kapoor Taniya , Wang Hongrui , Núñez Alfredo , Dollevoet Rolf
Published: June 2024

This paper presents a new approach to simulate forward and inverse problems of moving loads using physics-informed machine learning (PIML). Physics-informed neural networks (PINNs) utilize the underlying physics of moving load problems and aim to predict the deflection of beams and the magnitude of the loads. The mathematical representation of the moving load considered involves a Dirac delta function, to capture the effect of the load moving across the structure. Approximating the Dirac delta function with PINNs is challenging because of its instantaneous change of output at a single point, causing difficulty in the convergence of the loss function. We propose to approximate the Dirac delta function with a Gaussian function. The incorporated Gaussian function physical equations are used in the physics-informed neural architecture to simulate beam deflections and to predict the magnitude of the load. Numerical results show that PIML is an effective method for simulating the forward and inverse problems for the considered model of a moving load.
Interaction of a simple linear structure and a ball-type vibration absorber for harmonic and random loads
Authors: Náprstek Jiří , Fischer Cyril
Published: June 2024

Ball-type tuned mass absorbers are attractive for use in lightweight and slender designs because they combine multi-directional action with compact dimensions. However, their main disadvantage is the limited ability to adjust the damping level to a prescribed value, making them susceptible to undesirable effects arising from their non-linear nature. A 2D and 3D mathematical models of a ball-type absorber coupled to a simple linear elastic structure are presented, which show the effectiveness of such a damper for harmonic and random excitation. To prevent the occurrence of auto-parametric resonance conditions for safety reasons, the structure and damping equipment must be designed based on system parameters and the characteristics of possible excitation. The paper presents the dependence of the damped structure’s response on damper parameters for each type of resonant behaviour, the origin and nature of longitudinal and spatial response, and the influence of resonant conditions on the behaviour of the damped structure. The work is complemented by a simplified analysis of the response to random excitation, with examples of typical auto-parametric response patterns and possible applications in practical engineering.
The role of spine elasticity on legged locomotion
Authors: Zanotti A , Laurenza M , Pepe G , Carcaterra A
Published: June 2024

Robot locomotion has become increasingly common in transporting and assisting humans in complex environments. However, most existing quadrupedal robots have been developed with only a single rigid trunk and limited actuation to the legs and associated joints to reduce design and controls complexity. This paper presents a non-linear optimization process to identify the highest performance gait parameters of a quadruped robot with a flexible trunk. The optimization process is conducted using evolutionary algorithms, which are based on a heuristic search inspired by Charles Darwin’s theory of natural evolution and reflect the process of natural selection. Since identifying optimal gaits requires the complete definition of ground reaction forces coupled with the optimal trajectories of the body and its vibrational modes, it is possible to determine the influence of the main parameters linked to the vibration of the trunk on the optimal gait resulting from the optimization process. The paper’s final part presents a comparison between results obtained in the case of a flexible spine and the case of a rigid trunk to demonstrate the benefits of the elastic model in terms of efficiency.
A DDA enhanced locally resonant metamaterial: experimental testing on a Lego® Technic assembly
Authors: Kalderon M. , Mantakas A. , Chondrogiannis K.A. , Antoniadis I.A.
Published: June 2024

Locally resonant metamaterials (LRMs), with periodic elements that exhibit local resonance, have been recently investigated by numerous researchers as a means to pursue vibration attenuation and wave manipulation. These structures are able to generate bandgaps in specific frequency ranges depending on their mass, stiffness and geometrical characteristics; however, they present certain limitations when bandgaps in the low-frequency domain are sought, since they require heavy oscillating masses. This research work harnesses the potency of a novel dynamic directional amplifier, namely the DDA, that is introduced as a means to artificially increase the inertia of an oscillating mass. The DDA is realized by imposing kinematic constraints to the degrees of freedom (DoFs) of the oscillator, hence inertia is increased by coupling the horizontal and vertical motion and forcing the model to move along a circumference. Herein, the DDA is applied on the resonating mass of a scaled LRM structure, assembled using LEGO® components. Experimental and analytical calculations are subsequently undertaken to investigate the dynamic properties of this DDA-enhanced metamaterial. Results showcase the low-frequency attenuation properties of the structure and serve as a proof of concept of the mechanism.
Non-linear 3D seismic analysis of a RC bridge and retrofit alternatives with passive protective systems
Authors: Nanclares G , Ambrosini D , Curadelli O
Published: June 2024

In this paper a proposal of a partially restrained seismic isolation (PRSI) system is presented for the retrofit of existing continuous girder RC bridges. A pure-friction system is used with auto centring force provided by the stiffness of the deck and the frictional forces generated at the contact acting as an energy dissipation mechanism. The proposal has the advantage that the very small height of the system allows its application to existing bridges. In order to study the proposed system, the dynamic response until collapse of an existing bridge subjected to seismic accelerations is assessed through a detailed 3D nonlinear numerical model. An explicit integration scheme is employed that avoids numerical convergence drawbacks due to strength and stiffness degradation of concrete structures. The numerical model identifies the collapse mechanisms, such as the development of cracks in the concrete elements. Two retrofit systems are studied: a) steel jacketing reinforcement and b) PRSI proposal. The efficiency of each alternative is evaluated in terms of displacements and shear forces.
Damage detection using different types of sensors
Authors: Kullaa Jyrki
Published: June 2024

Different types of sensors are installed in many structural health monitoring systems. Correlation between heterogeneous response quantities is often small, which makes it difficult to utilize all sensor data for damage detection. A possible solution to handle diverse response data in the time domain is to use autocovariance function (ACF) estimates instead of direct sensor data. If the excitation is stationary random, different response quantities yield functionally similar ACFs. Due to phase differences, applying only spatial correlation between different ACFs is insufficient, whereas spatiotemporal correlation is justified. Therefore, ACFs at different lags are used to estimate a spatiotemporal correlation model of the undamaged structure under different environmental or operational conditions. If the correlation model is violated, it is an indication of damage. A monitoring campaign was carried out using a finite element model of a bridge deck to validate the proposed method. Neither the excitation nor the environmental variables were measured. Noisy response was measured with displacement, velocity, acceleration, and strain sensors in different locations of the deck. Using diverse types of sensors resulted in almost similar damage detection performance than if only a single type of sensor was used.
Mode tracking for a steel railway bridge in presence of changing support conditions
Authors: Maes Kristof , Lombaert Geert
Published: June 2024

Vibration-based damage detection commonly relies on a monitoring of the modal characteristics of a structure over time. It is assumed that damage will result in a change of the structural stiffness, which will in turn lead to a change of the natural frequencies and the displacement/strain mode shapes. The monitoring of the modal characteristics generally consists of two consecutive steps. First, the modal characteristics are identified by application of operational modal analysis (OMA) on a time series of response data, typically accelerations. This process is repeated on a regular, e.g. hourly, basis. In a second step, which is referred to as the mode tracking, the modes obtained from multiple OMA are linked across time windows, resulting in a subset of modes which can be tracked in time. The mode tracking typically relies on criteria that measure the similarity of the natural frequencies and mode shapes, assuming these do not change significantly over two time windows. In this paper, we consider the case of a bowstring railway bridge in Halle, Belgium, where the modes of the bridge can be assigned to two different states. This is observed from the identified natural frequencies, which are characterized by sudden shifts between consecutive time windows, which complicate the mode tracking. Displacement measurements at the bearings show that the transition is due to a change in support conditions under thermal action. It is explained how these transitions are explicitly accounted for in the mode tracking.
Multi-dataset OMA and Finite Element Model Updating of Steel Observation Tower
Authors: Ratnika Lasma , Gaile Liga , Nicoletti Vanni , Gara Fabrizio
Published: June 2024

Operational modal analysis for identifying dynamic parameters, together with finite element model updating algorithms, is a promising and powerful tool for detailed analysis of complex civil engineering structures. It is also an integral part of vibration-based methods in structural health monitoring. In this work, the identification of the dynamic parameters was performed based on output-only vibration data recorded in a testing campaign on a 36 m high steel structure used as an observation tower for tourists in Latvia. To correctly interpret the experimental results, a finite element model of the tower has been developed within the Ansys environment. The model updating is performed by adopting an artificial intelligence algorithm called Particle Swarm Optimization. The calibration is performed with the aim of obtaining a numerical model that simulates the real dynamic behaviour of the case study with high accuracy. The calibrated model can be used as a base for the development and design of the structural health monitoring system of the tower.
Modal Parameters identification in existing bridges based on free vibration tests
Authors: Mazzeo M , De Domenico D , Quaranta G , Santoro R
Published: June 2024

The dynamic identification of modal parameters plays a fundamental role in structural health monitoring: mode shapes, frequencies and damping ratios can be exploited to assess the current state of a structure, used for damage detection or in numerical model validation. In recent years, vibration-based methods have become a popular solution for the state of health estimation of strategic civil infrastructures such as bridges: in particular, free vibration tests represent a fast and economic method only requiring the temporary installation of a limited number of sensors on the structure. This contribution presents a procedure for the identification of modal properties of existing bridges exploiting their free decay responses: each mode’s contribution is adaptively extracted from free vibration tests data using the Empirical Fourier Decomposition and a noise-robust area-based approach is exploited to identify modal damping ratios. The method is preliminarily validated on a synthetic multi-modal signal showing excellent results even in case of closely spaced modes. The performance of the proposed approach is also tested for a real existing structure: the selected case study deals with the identification of modal parameters for a steel railway bridge deck.
Output-only response mapping of bridges for dynamic response estimation of gusset plate using convolutional neural networks
Authors: Dabbaghchian Iman , Eshkevari Soheila Sadeghi , Marasco Giulia , Pakzad Shamim N.
Published: June 2024

Structural health monitoring of bridges aims to provide an assessment of the condition of the structure, using collected structural response. The efficacy of the methods usually is constrained by the number and spatial distribution of sensors. Developing methods to map the response from known to unknown locations has been a challenging yet interesting area of study in recent years. In this research, we propose and study a novel framework to estimate and reconstruct the dynamic response of bridges at the connection level from the vibration response at global locations. The bridge is considered as a dynamic system in which vehicle excitations are the input and responses at sensor locations are the outputs. The proposed method studies an output-only problem and the input is considered unknown. The response at two types of output locations of the bridge, one at a global and one at the connection detail level are used to learn the dynamic relationship between the time signals via convolutional neural networks. This model-free framework is validated through a finite element simulation to reconstruct the strain response at the gusset plate of a truss bridge from the responses at other nodes along the bridge.
Effect of optimally placed sensors on the quality of estimated modal parameters
Authors: Tcherniak D , Steffensen M T
Published: June 2024

Planning is an important part of any modal test. Optimal Sensor Placement techniques can assist in finding the optimal number of sensors, their location and orientation. The presented study demonstrates the effect of the techniques on the quality of modal test results: the uncertainty of the estimated natural frequencies and damping, as well as the quality of the full field mode shapes expanded from the experimentally obtained mode shapes.
Improving Acoustic Methods of Pipeline Leak Location with Distributed Sensing
Authors: Hooper Joshua Z. , Kalkowski Michal , Muggleton Jennifer M.
Published: June 2024

Leaks in water distribution mains are a big problem, with around 20% of supplied potable water lost to leaks during transport. Correlation-based acoustic techniques have provided an accurate and non-invasive way of detecting and locating these leaks for a few decades. These methods have almost exclusively been using two sensors, and so this paper presents work aiming to explore leak detection and location with multiple sensors distributed along a pipe. Beamforming is a well-established method for using arrays of sensors to locate sources, among other purposes. With this premise, the present work adopts an array processing algorithm (MUSIC) in the context of water leak detection, intending to develop a framework for detecting multiple leaks using a sensor array. The concept, processing and implementation details are first supported with numerical simulations using existing acoustic models of water pipes. Then, experiments are presented on a short section of water-filled pipe with leak-like disturbances. These are captured with an array of accelerometers and processed using an implementation of the algorithm, testing the impact of real-world effects studied in simulations. The study considers several aspects of practical interest: (i) the effect of noise, both correlated and uncorrelated; (ii) the effect of reflections from discontinuities, such as pipe fittings and connections; (iii) the number and the distribution of sensors; as well as (iv) the presence of multiple leaks. The results pave the way for implementing this algorithm on practical installation designs, including the rod method developed during a wider research project associated with this study.
Perturbation-invariant eigenvalue assignment for statistical damage localization
Authors: Ulriksen Martin D. , Greś Szymon , Bernal Dionisio
Published: June 2024

The present paper reviews a recently proposed eigenvalue assignment scheme for structural damage localization. The eigenvalue assignment is, under the assumption of system controllability and observability, formulated with the objective of rendering an eigenspectrum subset invariant to low-rank perturbations in the considered system. Damage localization follows with the perturbations being realized as damage patterns postulated in different subdomains using a model of the system. The damage location can thus be inferred from the damage-induced shifts in the assigned eigenvalues, which, ideally, will be zero when postulating a pattern that entails the physical damage distribution. In real applications, eigenvalue invariance is unattainable due to, among other phenomena, stochastic disturbances, so the localization is conducted by hypothesis testing with the assigned eigenvalues and their uncertainty bounds. The paper reviews the proposed damage localization method and tests its applicability in the context of a numerical example.
Assessment of the metawedge as a mitigation measure for railway induced ground vibration
Authors: Bracci Alessandro , Fărăgău Andrei , Metrikine Andrei , Dalen Karel van , Corradi Roberto , Vlijm Eliam
Published: June 2024

Railway induced ground vibrations are of increasing importance for structures and inhabitants in the vicinity of railway tracks. This study investigates the capabilities of a novel mitigation measure, a so-called metawedge, in reducing the ground-borne vibration at the receiver end. A metawedge is series of barriers (i.e., resonators) arranged periodically in the longitudinal direction and each one is offset with respect to the others in depth direction (i.e., while the first barrier is completely on the surface, the last barrier can be completely embedded). The advantage of this countermeasure is that it can convert the incoming Rayleigh (surface) waves into body ones, redirecting the energy content deep into the ground. Simulation results show that the metawedge is capable of significantly reducing the vibration levels with as few as five resonators. Furthermore, while conventional single trenches are efficient as mitigation measures only at a certain angle of the incoming waves (outside the critical cone), the metawedge is efficient inside this cone. Although the metawedge solution is promising, this paper serves solely as a proof of concept, and additional studies are necessary to design realistic resonators that can comply with the low frequencies of the railway induced ground vibrations. Nonetheless, this study shows that metamaterials-inspired solutions can play an important role in addressing present and future challenges of the railway transportation.
Ground-borne noise and vibration: classification of railway vehicles based on a track-independent vehicle indicator
Authors: Ntotsios E , Thompson D , Reumers P , Nélain B , Degrande G , Bouvet P
Published: June 2024

Within the SILVARSTAR project, a track-independent vehicle indicator (TVI) is proposed that can be used to identify railway vehicles which generate low ground-borne vibration and noise levels. The proposed TVI is based on applying a frequency weighting to the force density, which may be obtained at a site from the measured ground vibration velocity levels due to train passages and the measured line source transfer mobility. Two different formulations of TVI are proposed; one related to ground-borne vibration and the other to ground-borne noise. Each TVI is a single number quantity, defined as a sum over all frequency bands of the frequency-weighted force density levels. The proposed performance classification of different vehicles can be achieved by comparing the relative differences of their TVIs. A series of test cases is used to demonstrate the calculation of the TVIs and the TVI-based classification of different vehicles at the same site. Although the values of the TVIs for each vehicle may vary due to the different modelling approaches and detail, or due to the limited knowledge of the input parameters used for the target site, the TVI-based classification of different vehicles is found to be insensitive to this model and parameter uncertainty.
Simplified models to inform the base-isolation design of buildings
Authors: Edirisinghe T L , Talbot J P
Published: June 2024

Base isolation is an established method of limiting the transmission of traffic-induced vibration into buildings. Despite this, the available design guidance is limited, and significant questions remain concerning how the vibration isolation performance may be optimised for a particular building. Recent research has sought to develop simplified models that enable the prediction of building vibration levels without resorting to complex numerical methods. This paper focuses on the phenomenon of soil-structure interaction (SSI) and considers the case of a multi-storey building founded on piles adjacent an underground railway. Some simplified models are compared against a comprehensive numerical model, with the aim of establishing the extent to which the various components of SSI influence the vibration transmission into the building and which should therefore be accounted for when predicting isolation performance.
Metrological quality of the excitation force in forced vibration test of concrete dams
Authors: Martins L L , Gomes J P , Ribeiro A S
Published: June 2024

This paper describes the study of the metrological quality of the excitation force in the context of force vibration test of concrete dams. For this purpose, a measurement uncertainty evaluation was performed, based on available probabilistic information about the input quantities – rotation frequency, mass, radial position, dimension, diameter and density of the generator’s rod – which support the determination of the excitation force in an eccentric masses vibration generator, used by LNEC in concrete dam’s field observation. The uncertainty propagation from the input quantities to the output quantity was performed by a Monte Carlo method, considering the mathematical model used for the determination of the excitation force. Two experimental cases were studied: (A) the use of five weights in the generator in the frequency range of 1 Hz up to 6 Hz; and (B) the use of a single weight in the generator in the frequency interval comprised between 5 Hz and 15 Hz. In the first case, the excitation force estimates and expanded measurement uncertainties (considering a 95 % confidence interval) varied between 3.55 kN ± 0.14 kN and 127.68 kN ± 0.91 kN, being rotation frequency the major contribution for the obtained dispersion of force values. In the second case, the excitation force estimates and expanded measurement uncertainties varied between 16.71 kN ± 0.25 kN and 150.4 kN ± 1.8 kN, being the generator’s rod diameter the main contribution for the output measurement uncertainty. The obtained knowledge is essential to assure confidence and rigorous knowledge about the applied excitation force, namely, in extreme situations near dynamical structural safety limits of the observed concrete dam and of the testing equipment.
Inverse design under uncertainty with surrogate models
Authors: Walton D B , Featherston C A , Kennedy D , Kundu A
Published: June 2024

In the drive towards net zero the aerospace industry is motivated to develop more efficient aerostructures that can accommodate the next generation of propulsion systems that fall outside of the well understood types that are currently in use. The lack of established standards for such designs means that engineers are faced with an increased level of uncertainty in their design choices before any prototypes are built. Machine learning models are becoming a popular tool for expediting the development of novel designs due to their ability to explore and predict the optimal parameters of large design spaces. It is also possible to quantify and introduce uncertainty into particular models so that practitioners can be made aware of the potential variation in their realised designs. In this paper Gaussian Process surrogate models of the performance metrics of the early-stage design of an aircraft wing are created to optimize a subset of design parameters based on some prescribed limits of the intended real system response. This defines the inverse design problem that is solved using Markov Chain Monte Carlo sampling. The approach taken requires novel formulation of a Bayesian machine learning framework. In particular, the work investigates the formation of likelihood functions that are flexible given inputs of different scales, can perform marginalisation of stochastic parameters, account for uncertainty in the surrogate model, and optimise the parameters given more than one constraint. A case study is presented in this paper that highlights both a successful implementation of the framework along with a limitation. It is found that the optimization is sensitive to changes in the variances of the likelihoods such that it can be used as a weight to direct the optimization towards a quantity of interest, therefore adjustment of this parameter is used to balance the optimization.
A model-based damage identification framework for R/C bridges using vibrational measurements.
Authors: Mixios K.E. , Stefanidou S.P. , Markogiannaki O. , Papanikolaou V.K.
Published: June 2024

Ensuring the structural integrity of bridges is crucial for maintaining road safety and minimizing traffic disruptions, as well as avoiding substantial direct and indirect economic losses. This study proposes a methodology for damage identification in R/C bridge systems by utilizing measured vibrational data from both the initial and damaged responses. In this context, a finite element model is developed, and its parameters are calibrated using Particle Swarm Optimization algorithms and Dynamic Mode Decomposition, which help match the numerical data to the measured data. The proposed methodology is demonstrated through a case study of a monolithic R/C bridge, with simulated experiments (e.g., damage scenarios) conducted to validate its effectiveness.
Shock and vibration response of museum objects during transportation
Authors: Hutchin Thomas W J , Waters Timothy P , Kotonski Verena
Published: June 2024

Museum objects are frequently transported by road and air when toured internationally or when moved between storage facilities which exposes them to a range of vibration and shock inputs. Many of these vulnerable objects have incipient damage such as cracks, loose joints, partial delamination or failing repairs which can be exacerbated in transit. It is the conservator’s responsibility to select which objects are safe to travel, largely based on experience and professional judgement. A joint research programme between the University of Southampton and the British Museum aims to develop a scientific framework to aid and inform such judgements. A central research question, and the focus of this paper, is which methods of transport are potentially most damaging?

Vibration measurements were acquired during transit by car, train, ferry and commercial airliner. A moving average kurtosis is used to identify near-Gaussian and non-Gaussian segments in a time signal. Acceleration shock response spectra (SRS) are presented for a number of impulsive events, and corresponding vibration response spectra (VRS) shown for more normally distributed random inputs. Laboratory based vibration testing was carried out on a museum artefact packed in bespoke foam packaging inside a standard wooden transport crate. The modal response, combined with SRS and VRS, enabled the response of the object and the suitability of the packaging in reducing the response to different real-life stimuli to be assessed. Actual measurements on the artefact in transit also enabled the accuracy of SRS and VRS in predicting peak and RMS acceleration levels to be quantified.
Adaptation of the HQ device for suppressing wave propagation in elastic beams
Authors: Avetisov S. , Pelat A. , Gautier F. , Sorokin S.
Published: June 2024

In this work, we study the application of the Herschel–Quincke (HQ) principle to the case of bending waves in a beam structure. This type of device is well known in acoustic tubes where an HQ filter consists of the bifurcation of a primary tube into two tubes of different lengths placed in parallel. The resulting phase shift creates a destructive interference and so a zero transmission at selected frequencies. To adapt this principle to bending vibrations, a homogeneous solid beam is divided into two different strands with different thicknesses and of same length, so that the phase difference created between these two strands of different wave celerities also leads to the same interferential effects. A Timoshenko wave model is derived to analyse the scattering properties of such HQ filter for bending and longitudinal waves. The results are well confirmed by the reference finite element simulations.
Simple soil-structure interaction model for wind-induced vibrations in high-rise buildings
Authors: Carranza A , Bronkhorst A J , Gomez S S , van Dalen K N
Published: June 2024

The reliable design of high-rise buildings subject to wind-induced vibrations is important for ensuring comfort and safety. However, the Eurocode recommendations and common design practices used to estimate natural frequency and damping parameters in the design stage have been found to be inaccurate, leading to unreliable predictions of building accelerations. Previous studies have shown that soil-structure interaction (SSI) can have a significant influence on these parameters, especially for high-rise buildings on soft soils. This study presents a formulation of a simple model to include soil-structure interaction effects in the natural frequency and damping parameters. It also demonstrates the compatibility of this model with the current Eurocode procedures. The study compares the results of the simple SSI model with those of a continuous model of the New Orleans tower under design wind loading. In previous work, this continuous model was validated against in-situ measurements on the New Orleans tower. The results demonstrate that the simple SSI model significantly improves the accuracy of the predicted building accelerations under wind loading for the New Orleans tower, compared to accelerations determined in the original design and accelerations computed with the Eurocode guidelines.
FRF-based modal testing of the highest timber building in the world in operation using wireless accelerometers
Authors: Pavic Aleksandar , Kei Ao Wai , Tulebekova Saule , Malo Kjell Arne , Rønnquist Anders
Published: June 2024

This paper describes practical application of a novel and oven-controlled crystal oscillator (OCXO) high-precision synchronised wireless data acquisition system for a modal testing of the tallest all-timber building in the world – the 18-storey, 88.8m tall Mjøstårnet (the Mjøsa Tower) in Brumunddal, Norway. The modal testing was challenging as it was conducted in an occupied building in normal operation and was based on measuring both dynamic excitation and response yielding a set of frequency response functions (FRFs) across four different floors of the building. To the best knowledge of the authors, this was the first time that an FRF-based modal test was attempted on such a large building structure in operation. Moreover, although the structure was in operation, the testing was completed in only 48h, including commissioning and de-commissioning of all of the instrumentation, yielding a full set of point- and transfer accelerance FRFs. The paper presents the equipment used, key logistical challenges and quality assurance steps made to assure measurement of good quality FRF data in such short period of time demonstrating feasibility of the whole exercise. A total of seven modes of vibration, including higher order modes of vibration were estimated by curve-fitting the measured FRF data. This includes the 3rd bending and 2nd torsion modes difficult to measure via the standard ambient vibration testing of tall buildings. These modes could be used to investigate a number of uncertain modelling features in tall timber buildings, such as the stiffness of timber joints.
A framework for fatigue damage estimate in single-axis solar trackers
Authors: Frontini Giorgio , Argentini Tommaso , Muggiasca Sara , Belloli Marco
Published: June 2024

Solar trackers are constructions consisting of a series of photovoltaic modules mounted on a motorized supporting structure; such systems are usually characterized by limited torsional stiffness and low number of torsional constraints, factors that lead to lower structural frequencies. At these frequencies, trackers are typically susceptible to turbulent wind, and when excited by it, the expected responses can lead to significant deformations and, with its cyclical load variation, also to fatigue damage. On this premise, the presented article proposes a methodology for estimating fatigue damage caused by dynamic wind effects in single-axis solar trackers. As observed in full-scale scenarios, it is assumed that the fatigue damage accumulates in correspondence of the elements connecting the photovoltaic modules to the underlying structure. To this end, a transfer function that relates the pressure acting on the panel to the stress state in a specific point is evaluated with a finite element (FE) model and then experimentally validated with a cyclical load test. Acting forces time histories, derived by wind tunnel measurements, are used with the transfer function to infer the evolution of the stresses acting in the regions of interest. Finally, the rainflow cycle count method is used in conjunction with the Wöhler curve of the investigated structural detail to analyze the stress history and derive a fatigue damage estimate. It is expected that the proposed approach can aid designers in the damage estimation and verification procedures.
BCM-LES for moving cIBM on aeroelastic stability of a tall building with various modes
Authors: Tamura T , Kawaguchi M , Nishiguchi K , Shimada T , Bale R
Published: June 2024

This study analysed the mechanism of unsteady negative pressure around a square cylinder during forced oscillation in the rocking or the first order beam-bending mode, using an advanced large eddy simulation solver on the hierarchical Cartesian grid system using the constraint immersed boundary method for arbitrary moving boundary shape. The study also investigated an onset of negative damping force in relation to the reduced velocity and the oscillation amplitude. The results showed that in the beam-bending mode, the phase of pressure generally advanced more for the reduced velocity defined by the cylinder width, wind velocity and oscillation frequency compared to that of the rocking mode, and the transition to negative damping force occurring at a lower reduced velocity. The findings also indicate that the generation of negative pressure was influenced by timing and location of the vortex formation in the wake of 3D square cylinder.
Bivariate Processes Evolutionary Power Spectral Density Estimation Using Energy Spectrum Equations
Authors: Spanos Pol D. , Matteo Alberto Di , Zhang Hanshu , Yue Qingxia
Published: June 2024

In this paper a novel procedure is developed for evolutionary cross power spectra (ECPS) estimation of bivariate nonstationary stochastic processes. Specifically, the ECPS is determined by estimating the statistical moments of energy-like response quantities of lightly damped linear filters excited by nonstationary stochastic processes. In this context, a smoothing procedure is incorporated by using the Savitzky-Golay (S-G) moving average filter to obtain reliable ECPS based even from a limited number of available records. Further, a refinement of the approach is proposed relying on polynomial based functions of the system output. Several numerical examples, including nonstationary processes with known spectra, and historic accelerograms are used to assess the reliability and accuracy of the proposed procedure.
Noise radiated by ground surface vibrations due to passing trains.
Authors: Jean P , Villot M , Guigou-Carter C
Published: June 2024

Noise radiated by passing trains is usually modelled without considering the radiation of the soil free surface. Models such as TWINS will only consider the acoustic radiation of the different trains and tracks components as a sum of individual acoustic sources defined by their power and directivity expressed in the frequency domain and used as elementary sources in acoustic propagation models. The vibroacoustic model Mefissto, developed at CSTB, can be used to compute the propagation of vibrations from a train to a building as well as the ground borne noise inside lodgings. To compute the noise radiated by the ground free surface one will use the vibration field of a rectangular portion of the surface computed in 3D and evaluate its radiation in the air by means of the Rayleigh integral representation. The Rayleigh integral can be extended by using more complex Green functions, computed by the source image method allowing to consider the presence of one or two buildings. On site acoustic and vibration measurements have been made near a railway line. The calibrated soil model has been used to estimate the noise radiated by the ground which compared to the measured sound pressure levels has showed that the soil radiation is important below 160 Hz.