bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterisation of the damping performance of a Stockbridge damper from laboratory tests of an overhead high-voltage transmission line conductor
Authors: Mendonça Raphael , Caetano Elsa , Moutinho Carlos , Rodrigues João , Saadi Omar
Published: June 2024

This paper presents a study to evaluate the damping effectiveness of Stockbridge dampers on an overhead high-voltage transmission line conductor and their effects on estimating the corresponding fatigue lifetime. To increase the understanding of the dynamic behaviour of Stockbridge dampers, a test setup was designed and constructed to accommodate a segment of a conductor following the normative prescriptions of CIGRÉ. A classical modal identification was initially conducted to characterise the corresponding dynamic behaviour without and with an added Stockbridge damper. The Power Method was used to assess the conductor self-damping at different vibration amplitudes and excitation frequencies. Furthermore, a set of sensors was installed on the conductor, close to the anchorage, to simulate the VIBREC device and permit the analysis of the damper’s influence in estimating the conductor’s lifetime. Through the analysis of the database collected with the tests, it was possible to assess the dynamic properties of the conductor, identify the reduction of the vibration amplitudes enabled by the Stockbridge damper, and characterise the consequent increase in the conductor’s lifetime.
Elastic waves in periodically anisotropic heterogeneous media: bridge the gap between rigorous and phenomenological approaches
Authors: Andrianov I. , Danishevskyy V. , Kaplunov J. , Kirichek Y.
Published: June 2024

Despite the growing capacity of computer codes, analytical solutions are still of great interest. As a rule, they are based on certain asymptotic approximations. In our work, we use a two-scale asymptotic procedure. Anti-plane shear waves in a layered medium are studied. To clarify the basics of the methodology, we restrict ourselves with a layered membrane. For long-wave case we obtained solutions for periodic and anti-periodic modes. We analyse them in the low- and high-contrast cases. The results obtained can be generalized for complex multiscale heterogeneous media and structures. They are useful for bridging the gap between mathematically rigorous and phenomenological approaches in dynamics of heterogeneous materials. They also can be implicated as benchmarks for numerical modelling.
Control of Flexible Structures Using Model Predictive Control and Gaussian Processes
Authors: AlQahtani N. A. , Rogers T. J. , Sims N. D.
Published: June 2024

There is a recognised need to address issues of vibration control by making use of recent developments in data-driven modelling. The present study considers the difficulties imposed by the limitations of the actuator in the range of active vibration control. The paper proposes and examines a data-based Gaussian process (GP) model of a proof mass actuator in a flexible structural framework, aiming to improve control performance. This requires incorporating an inverse GP of static nonlinearity within the Wiener-Hammerstein model. The model starts with designing model predictive control (MPC) for a cantilever beam, in which the aim is to identify the optimal control force. Utilising the GP is the second step towards quantifying the uncertainty and limitation of the proof mass actuator by designing an inverse GP for the static nonlinearity. This quantification forwards to an MPC controller using a steady-state target optimisation tracking approach, in which this controller provides the optimal voltage required to eliminate vibration within the controller’s limitations. The numerical outcome shows that the proposed scheme was capable of supplying the necessary voltage, which eliminated the structure’s vibration within an actuator’s limits. The results of this work encourage additional research into the developed strategy, particularly in the context of experimental real-time implementation.
Observer based pitch control for load mitigation and power regulation of floating offshore wind turbines
Authors: Fitzgerald Breiffni , Sarkar Saptarshi
Published: June 2024

Most commercial wind turbines use proportional-integral (PI) collective blade-pitch control to regulate rotor speed in the above-rated wind speed regime. A significant drawback of this type of controller is that it assumes that the blades have identical structural properties and are subject to similar aerodynamic loads, which is seldom the case. Also, these controllers are designed to regulate the rotor speed and are not designed for structural vibration/load reduction. However, it is well known that blade pitch control can reduce structural loads on wind turbines. This opens up the possibility of designing controllers that use existing actuators and sensors like the blade pitch actuators to reduce structural loads/vibrations while maintaining the required rotor speed. Recent studies have investigated individual blade pitch control (IPC) to address these shortcomings. However, the vast majority of studies published in the literature depend on the availability of state measurement. Although sensors are commonly placed on all wind turbines, and some information is readily available, the measurement required by the typical state-feedback controllers is usually not available. Displacements and velocities of the blade, the tower and the floating platform are difficult to measure. This paper develops an observer-based individual blade pitch controller for load mitigation and power regulation of floating offshore wind turbines. We propose to use a Kalman filter to estimate the state from the accelerometer and strain gauge measurement for use in the state-feedback controller. The state-feedback controller was proposed previously by the authors that showed excellent performance. This paper extends the capability of the state-feedback controller by designing an observer (Kalman filter) to estimate the state from limited measurements. The proposed observer based controller is compared against a baseline proportional integral collective blade pitch controller and full state-feedback controllers to evaluate its performance. Numerical results show that the proposed output feedback controller offers performance improvements over the baseline controller, similar to the full state-feedback controller.
Experimental investigation on a passive self-tuning vibration neutraliser for two distinct frequencies
Authors: Nehemy G F , Rustighi E , Gonçalves P J P , Brennan M J
Published: June 2024

Tuned vibration neutralisers are used to suppress the vibration of a host structure subjected to external harmonic forces. Although they are analogous to tuned vibration absorbers, the primary difference is that while absorbers are usually designed with optimum damping to attenuate vibration in a frequency range around a resonance, neutralisers are designed with relatively low damping to act as a mechanical notch-filter. The narrow band frequency in which the conventional neutralisers are effective, and the mistuning compromising their performance, are known problems. Thus, self-tuning vibration neutralisers were introduced to make them more robust. In many cases, however, these systems need an external power source to adapt. This paper concerns an investigation into a self-tuning vibration neutraliser for two distinct frequencies, that does not need an external power source. It consists of a rectangular beam with tip masses, which is held at its centre in a roller bearing that is fixed to a host structure. The rectangular cross section has two different stiffnesses in the local coordinates that can rotate with respect to the global reference. Results from some experimental tests compare very well with time domain numerical simulations. It is shown that the coupling between two orthogonal degrees-of-freedom enables the neutraliser to passively tune to one of two tuned frequencies, depending on the frequency of the external harmonic force.
Improved fatigue life of floating offshore wind turbine towers with tuned mass damper inerters (TMDIs)
Authors: McAuliffe J , Baisthakur S , Broderick B , Fitzgerald B
Published: June 2024

Floating offshore wind turbines (FOWTs) are the largest rotating structures on earth. FOWTs are very flexible and dynamically sensitive, they are also installed in very harsh environments and exposed to stochastic environmental loading from wind and ocean waves. In recent years dampers have been installed in the towers of offshore wind turbines to mitigate vibrations. In this paper, structural dynamic models are used to demonstrate improvements in the fatigue life of FOWT towers when they are equipped with a new type of damper - the tuned mass damper inerter (TMDI). A multi-body dynamic approach is used to model the wind turbine and the TMDI installed in the tower. The model is subjected to stochastically generated wind and wave loads of varying magnitudes to develop wind-induced probabilistic demand models for towers of FOWTs under model and load uncertainties. Numerical simulations are carried out to determine the improvements in fatigue life of FOWT towers that can be achieved by installing TMDIs in comparison to traditional tuned mass dampers (TMDs). The results show that the TMDI outperforms the classical TMD when considering fatigue life.
Optimal tuning and assessment of non-grounded regenerative tuned mass damper inerter (RE-TMDI) configurations for concurrent motion control and energy harvesting
Authors: Rajana K , Giaralis A
Published: June 2024

This paper addresses the optimal tuning and numerical performance assessment of regenerative tuned mass damper inerters (RE-TMDIs) in three different configurations with non-grounded inerters attached to cantilevered primary structures under Gaussian white noise base excitation. The studied RE-TMDI configurations behave linearly and differ in the placement of the electromagnetic motor (EM), modelled as viscous damping element used for transforming kinetic energy to electricity, with respect to the inerter element. The primary structure is modelled as a linear damped generalized single-degree-of-freedom system, while a connectivity index is used to account for the location of the two RE-TMDI attachment points to the primary structure. A bi-objective optimization problem formulation is adopted and numerically solved for determining optimal RE-TMDI stiffness and EM damping coefficients that minimize primary structure displacement variance and maximize the available energy for harvesting by the EM. Parametric numerical results are reported for different RE-TMDI configurations, connectivity, inertance, secondary mass ratio and relative weighting between the two optimal design objectives. These results demonstrate that improved energy generation and vibration suppression is concurrently achieved with increasing inertance and/or increasing the distance of the host structure locations where the RE-TMDI is attached to. Recommendations are provided establishing the most advantageous RE-TMDI configuration.
Seismic assessment of an inerter-based hybrid control strategy for a base-isolated liquid storage tanks
Authors: Bajad Ketan Narayanrao , Islam Naqeeb Ul , Jangid Radhey Shyam
Published: June 2024

Liquid Storage tanks play a crucial role in chemical, gas, and nuclear industries, as well as public utilities such as water delivery and fire suppression. However, during earthquakes, they are susceptible to severe damage due to their base shear response and large displacement. To address this issue, a hybrid control strategy utilizing a clutched inerter (CID) has been proposed to protect base-isolated liquid storage tanks, with a bilinear lead rubber bearing (LRB) serving as the isolation device. Six actual earthquake ground motions were used to evaluate the performance of the system, and a MATLAB code utilizing the State-Space approach was developed for analysis. A parametric analysis was conducted to determine the impact of the CID’s inertance mass ratio on various responses including the total base shear response, bearing displacement, sloshing displacement, and force in the CID. The results of the time history analysis demonstrate that the hybrid control strategy effectively reduces bearing displacement response while meeting sloshing displacement demands. The optimum inertance mass ratio of the CID significantly reduces the total base shear response.
Seismic performance evaluation of adjacent structures connected with negative stiffness and inerter-based dampers
Authors: Islam Naqeeb Ul , Jangid R S
Published: June 2024

The seismic performance evaluation of two adjacent single-degree-of-freedom structures (SDOF) connected with a novel negative stiffness-inerter-based damper (NSID), tuned inerter damper (TID) and viscous damper (VD) is studied under base excitation. The two SDOF structures are typical of adjacent bridge structures that are vulnerable to pounding during strong seismic activity. The base excitation is modelled as a stationary white noise random process. The equations of motion are written in state space form, and optimal parameters for maximum possible response reduction are evaluated. The optimal parameters are based on minimising the total relative energy of two adjacent structures under white noise base excitations. The optimal parameters obtained for TID and NSID show that adding an inerter to a VD lowers the optimum damping ratio. Also, adding negative stiffness to TID further lowers the optimum inertance and damping ratio. The performance of optimised dampers connecting adjacent SDOF systems is then assessed under real earthquake records. Numerical results indicate that NSID and TID can achieve similar or even better response reduction than VD using a smaller damping coefficient. Among the two connected systems, more flexible ones show higher response reduction. The analytical study demonstrates that the effective damping of viscous dampers can be enhanced by adding the negative stiffness and inerter elements to the dashpot.
A full-scale numerical study on aerodynamic force conditions of high sided vehicles on the Queensferry Crossing Bridge
Authors: Zhu Licheng , McCrum Daniel , Keenahan Jennifer
Published: June 2024

Hazardous wind conditions can lead to critical safety problems for long-span bridges, either through dynamic oscillations or overturning of high sided vehicles. Engineers need to understand the local wind effects to ensure the safety and acceptable performance of bridge infrastructure. Traditionally, aerodynamic studies were carried out in wind tunnel facilities, however the opportunities of using computational fluid dynamics (CFD) modelling for wind assessments in place of wind tunnel tests are significant. To date, most of the existing studies are aimed at validation of wind tunnel tests and do not investigate full-scale effects. In this study, a validated full-scale 3D CFD model is developed in OpenFOAM using the k-ω-SST turbulence model for the world’s longest three-tower cable-stayed bridge: the Queensferry Crossing Bridge, which located at Edinburgh in the United Kingdom. The 3D CFD model contains details such as wind shields and wind conditions were created based on field monitoring data which was provided by Transport Scotland. The aerodynamic force conditions of the high sided vehicle on the bridge are subsequently determined and analysed. Results suggested that the truck would be more vulnerable to variations in the lift force coefficient and rolling moment coefficient than the double-decker bus.
Performance of photovoltaic systems supported by twin-hull floating structures in offshore and coastal regions
Authors: Magkouris Alexandros , Belibassakis Kostas
Published: June 2024

Floating photovoltaic (FPV) systems offer significant advantages over corresponding land-based ones. These include the ample surface available for arrangements in arrays, the possibility of exploiting the cooling effect of sea water on panel performance as well as the potential of integration of solar tracking techniques in a much more cost-effective way. However, application to coastal and offshore regions has proven to be a challenge, as FPV interaction with various environmental factors is not yet fully understood. In this work a twin hull floating platform is studied, featuring enhanced stability characteristics, in conjunction with lightweight structure, and quite efficient mobility. A novel Boundary Element Method developed for the hydrodynamic analysis of floating twin-hull structures is used for the calculation of responses in waves and its effect on the system power production. For the demonstration of the studied system, preliminary results - concerning the performance of a particular module in a selected coastal area of the Greek Seas - are presented and discussed. Finally, the effects of wave-induced dynamic motions on floating PV performance are presented, indicating significant variations of the performance index depending on the sea state.
Design and Modeling of Impact and Vibratory Installation of Piles in a 1g Laboratory Scale Test
Authors: Wehbe Tamara , Anoyatis George , Rattez Hadrien , François Stijn
Published: June 2024

The widespread deployment of offshore wind turbines requires the use of fast, low-cost, and reliable installation methods. While impact pile driving is predominantly used for offshore monopile foundations, vibratory pile driving provides an interesting alternative. The selection of a suitable installation technique is based on cost, marine environment, noise pollution, and soil conditions. To study installation effects, this research aims to develop 1g laboratory scale tests of both impact and vibratory pile driving in a sand filled and saturated container. Numerical models are employed to study the dynamic behavior of the 1g scale test, and are used to design (and optimize) the test setup. Particular attention is related to the reflection of waves at the boundary of the container and the frequency content of the vibratory and impact driving force, as to get the best correspondence with the full-scale pile installation in situ. The numerical model includes (1) a multi-body dynamic models to compute the impact or vibratory loads on the pile head, and (2) a finite element model of the sand box – pile system. This allows us to study the dynamic interaction between the pile and the soil, wave propagation in the sand box, and estimate the soil’s response. The comparison of both scales is then used to optimize the test setup, achieving a good correspondence to a full–scale test, both statically and dynamically.
Experimental and numerical assessment of soil-structure interaction effects in the case of mine-induced vibrations
Authors: Kuzniar Krystyna , Tatara Tadeusz , Zajac Maciej
Published: June 2024

Earthquakes are the most intensive sources of free-field vibration. However, mine-induced rockbursts, as a result of underground exploitations in mining areas, are also a hazard to buildings. Additionally, as in the case of earthquake-induced vibrations, also in the case of mining tremors the soil-structure interaction (SSI) phenomenon is observed. In this paper, an investigation of the one of SSI effects – differences between the simultaneously recorded free-field and building foundation vibration, is performed. The research was carried out on the example of an actual, typical, masonry, low-rise office building situated in a coal basin in Poland – the Upper Silesian Coalfield (USC). Two approaches were considered in the analysis: experimental full-scale tests, and numerical assessment using Finite Element Method (FEM) modelling. A rich set of experimental data was collected from the free-field and foundation. Using the measurement data, the most important parameters that affect the SSI phenomenon were considered, e.g. magnitude of mining tremor energy, epicentre distance from mining rockburst, and peak ground acceleration of vibration. Numerical analysis of the transmission of the incident wave to the building foundation is carried out using a three-dimensional (3D) FEM model.
Comparative Study of Simplified Dynamic Soil-Structure Interaction Modelling Techniques
Authors: Bapir Baban , Abrahamczyk Lars
Published: June 2024

Modelling of soil-structure interaction (SSI) problem has always been a challenging topic for structural engineers. In the last half-century, several simplified modelling techniques have been proposed to consider SSI by idealizing the soil domain. The behaviour of these models is different in terms of complexity, accuracy, parameter definition and application cases. Thus, selecting a reasonably accurate and efficient model to simulate seismic soil-structure interaction is an essential issue for structural engineers. The current study makes an attempt to assess the performance of three simplified modelling techniques (Gazetas spring and dashpots, Cone model, and Beam on Nonlinear Winkler Foundation BNWF model) through a comparative study, which is conducted on nine reinforced concrete moment-resisting frame (MRF) structures with various structural height and widths supported by two different soil profiles. The seismic responses of the structures are investigated through a nonlinear time history analysis, and the performance of the models is compared in terms of capturing the period lengthening, lateral displacement, inter-story drift, and total base shear in the structures. The strengths, limitations and application cases of each model are also discussed. In addition, the influences of soil-structure interaction on the seismic response of MRF structures on soft soil deposits are investigated. Two main parameters (structure-to-soil stiffness ratio and structural slenderness ratio) are introduced, which have shown significant effects on controlling the role of SSI on building structures.
Enhancing Leak Location in Buried Water Pipes using Array Signal Processing Techniques: the Effect of Wave Velocity Variation
Authors: Matos P H , Muggleton J M , Brennan M J , Almeida F C L , Campos B C , Paupitz P J , Iwanaga M K , Karimi M , Rustighi E
Published: June 2024

Leakage in buried pipelines is a significant cause of water wastage in distribution systems, resulting in water losses ranging from 30% to 50% in many countries. To address this issue, techniques have been developed to detect leaks in buried pipes over the last few decades. The leak detection procedure typically involves three steps: (1) leak detection, which involves analysis of water pressure/flow measurements along the pipelines; (2) estimation of the approximate region where the leak occurred through local pressure variations; and (3) pinpointing the estimated location of the leak to perform maintenance procedures. Acoustic pinpointing techniques are among the most effective ones to deal with the latter step. These techniques exploit the delays in time of arrival of acoustic waves, caused by the leak, between different sensors placed around the suspected leak. By calculating the cross-spectral densities (CSDs) between sensors and analysing their phase difference over frequency, it is possible to infer the estimated location of the radiating source. Existing methods rely on access points to the pipeline through correlators. However, the buried pipe acts as a radiating source, and its location could also be estimated through ground vibration signals. Although array signal processing techniques applied to source localization are well-established in the acoustics field, their adaptation to the vibroacoustic field is less well developed. Among the many challenges, the identification of wave velocity is one of the most troublesome. In this paper, the effect of the wave velocity variation on the leak pinpointing is investigated and tested against numerical data. Results show that the estimation of the leak position is sensitive to the wave velocity variabilities. The pinpointing error is found to be more significant in terms of the depth of the pipe, compared to the error on the ground surface.
The effect of high-frequency torsion in vibratory pile installation: the Gentle Driving of Piles method
Authors: Tsetas Athanasios , Tsouvalas Apostolos , Metrikine Andrei
Published: June 2024

The Gentle Driving of Piles (GDP) is a new technology for vibratory (mono)pile installation that is based on simultaneous application of low-frequency/axial and high-frequency/torsional vibrations. In this paper, a numerical modelling framework, that has been developed and successfully applied to axial vibratory driving, is employed to study GDP. In that manner, the major driving mechanism of this method is comprehended on the basis of field observations and numerical analyses. As regards the numerical model, the pile is described as a thin cylindrical shell and the soil medium is treated as a linear elastic layered half-space. The pile-soil coupling is realized via a history-dependent frictional interface, that accounts for friction force degradation due to the accumulation of loading cycles at the soil material points. The redirection of the friction force vector due to the high-frequency torsion manifests as the main driving mechanism of GDP. Finally, the soil disturbance during installation is compared for the cases of GDP and axial vibratory driving, showcasing the dissimilar characteristics of the induced soil motion.
Improved double-point material point method for dynamic geotechnical problems
Authors: Chmelnizkij A
Published: June 2024

The Material Point method is a suitable numerical method to simulate large deformations often occurring in geotechnical engineering. The Double-Point MPM (2P-MPM) extends the simulations for water-saturated materials. In the present work, a coupled dynamic formulation is used to account for coupled wave propagation in porous media in addition to large deformations. The computational cost of 2P-MPM is expensive because information between material points and grid nodes must be approximated at each time step. In conventional 2P-MPM formulations, linear shape functions are used for this approximation, leading to well-known grid crossing and loss of contact problems. We use the moving least square approximation for the 2P-MPM to handle these problems better. In addition, a parallelization approach is shown to improve the computation time, especially for large boundary value problems. The developed methods can be combined with non-saturated materials, such as fluids and dry soil, to simulate complex geotechnical issues. The performed computations of wave propagation and large deformations using the proposed methods show improved convergence behavior and increased efficiency.
Recommendations on finite element modelling of non-seismic excitation in soil-structure interaction problems
Authors: Schepers W , Brinkgreve RBJ , Appel S
Published: June 2024

Nowadays geotechnical engineering firms have powerful software tools to extent their consulting business also into dynamic soil-structure interaction, which before has been restricted to a rather small community of specialized experts in this field, and they certainly do. This is particularly true with respect to non-seismic sources, that is all kinds of human induced vibrations. Hence, there is a demand from clients as well as from contractors to have guidance on the requirements as well as the limits of numerical modelling of soil-structure interaction. From the literature as well as from relevant standards, recommendations for the numerical modelling of soil-structure interaction problems involving seismic actions are well known, e. g. ASCE/SEI 4-16. There are, however, some particularities when dealing with human-induced vibrations, which are absent in seismic analyses. For human-induced excitations very little specific guidance has been published in the past. A machine foundation on a homogeneous half space excited by harmonic loads with excitation frequency between 4 Hz and 64 Hz has been analysed by means of several commercially available software packages. Parametric studies have been performed to verify if recommendations for seismic soil-structure analyses are valid for non-seismic analyses as well. This paper provides details on the benchmark example and the most important conclusions from the undertaken parametric studies.
Experimental and numerical analysis of piercing with shaped charge of armor steel
Authors: Pyka Dariusz , Bocian Mirosław , Kurzawa Adam , Jamroziak Krzysztof
Published: June 2024

The tests of resistance to dynamic impact with shaped charge (ŁK) were carried out on a homogeneous armor plate made of Armox 370T Class 1 steel, commonly used in the production of ballistic shields. The chemical composition of the steel was determined in spectrometric tests using a spark discharge spectrometer S1 MiniLab 150 by GNR INDIA and confirmed by a GDS-750-QDP glow discharge spectrometer by LECO. Composition tests confirmed the compliance of the chemical composition of the board with the EN 10029 standard for the Armox 370T grade. Numerical calculations of the considered penetration with a shaped charge were carried out in the ABAQUS program. For this purpose, geometric models were made in the Inventor program and then the geometric models were exported in the .step format to the computing environment. The Johnson-Cook (J-C) mathematical model was used for elastic-plastic materials, including plastic behavior of material. The calculations were based on numerical models separately established for individual elements of the load and cover, assuming material constants appropriate for the materials used for the transition from hybrid methods using the SPH and FEM methods.
Settlement at transition zones in railway tracks – is modelling the soil as a 2-D continuum important?
Authors: Fărăgău Andrei B. , Metrikine Andrei V. , van Dalen Karel N.
Published: June 2024

While most recent models of railway tracks include the nonlocal nature of the foundation reaction force, few studies have investigated the influence of its nonlocal nature on the response. Accounting for the nonlocal nature of the foundation force is computationally expensive and increases the complexity of the model, thus, knowing when and when not to account for it is important. This paper aims to shed light on the influence of the nonlocal, both in time and space, reaction force provided by the foundation on the transient response at railway transition zones. To this end, a 2-D system in which the soil layer is modelled as a visco-elastic continuum is compared to an equivalent 1-D system with a local foundation reaction force (i.e., Winkler foundation). Results show that, in general, the response of the 2-D system with shallow and/or stiff soil layers can be well captured by the equivalent 1-D model. However, for medium-to-deep and/or soft soil layers, the nonlocality of the foundation reaction force is influential and the transient response at transition zones cannot be satisfactorily captured by 1-D models. Finally, the ballast settlement is also poorly captured for medium-to-deep and/or soft soil layers, with the main cause being the inability of the 1-D model to separate between ballast and soil stresses, and not the locality of the reaction force.
Seismic soil-structure interaction analysis considering a layered half space subjected to geothermal induced seismicity
Authors: Taddei Francesca , Yuan Shihao , Freisinger Julian , Müller Gerhard
Published: June 2024

In the near future, geothermal energy is bound to play a critical role in the transition to sustainable energy sources. Micro-earthquakes may be induced by the underground operations performed at the geothermal power plants. In most cases, these vibrations are considered a general nuisance similar to the vibrations resulting from railway track operations. However, given the heightened public concern regarding induced seismicity, it is crucial to identify and analyze the effects of these micro-seismic events on the built environment. In this contribution, we present a numerical technique for the simulation of buildings subjected to geothermal induced seismicity. We apply a substructure method, where the soil is represented as a continuum using the integral transform method (ITM) and the building as a discrete structure using the finite element method (FEM). For the semi-analytical elastodynamical solution, as in the ITM case, the seismic excitation can be converted to an equivalent load acting at the interaction nodes between soil and structure. To obtain these equivalent loads, one has to compute in advance the free field displacements at these interaction nodes. We apply the presented approach to a plate underlain by a layered half space that is subjected to a geothermal-induced earthquake with characteristics typical for the Greater Munich Area in Germany.
Further Dynamic-integrity-based Reliability Analysis
Authors: Provasi Rodrigo , Mazzilli Carlos E. N. , Franzini Guilherme R.
Published: June 2024

Non-linear dynamical systems of different areas of engineering and technology are subject to parameters that should most of the times be realistically modelled as random variables, although they are usually considered to be deterministic. This paper addresses in a simple, almost naïve fashion, the reliability analysis of those systems, starting from a deterministic analysis, but then bringing into it the statistical properties of input variables. Although the concept of dynamical integrity has greatly contributed to establishing safe thresholds in dynamical systems, requiring that the basins of attraction should be robust, a reliability measure is still missing in that respect. In fact, supposing that the erosion curve of a dynamic integrity measure I (for instance, the integrity factor) has been obtained in terms of a system parameter A (for instance, a load amplitude, a load frequency, or still an imperfection parameter) using a deterministic approach, one can estimate the output statistical properties for I, in terms of those of the input parameter A, now considered as a random variable in its own right. Hence, once reference values for the integrity measure I
ref and the system parameter A
ref have been established, and assuming that increase of A beyond A
ref may prove to be dangerous, the probability that I ≥ I
ref, provided that A ≤ A
ref, would give a sound reliability assessment. A very simple approach towards this aim is proposed and applied herewith to an archetypal model of a rigid column asymmetrically constrained by a linear spring, subject to a conservative axial compression and a small dynamical transversal load, playing the role of a random dynamical imperfection. It should be said that this work is a continuation of another one, with the same archetypal model, yet taking into account only the effect of a statical imperfection. A versatile in-house code is used to obtain the basins of attraction and the erosion curves that give support to the proposed methodology. The reliability assessment is carried out in two different scenarios, namely varying either the dynamical imperfection amplitude or its frequency. The influence of nearness to either buckling, or to external resonance or even parametric resonance can be studied according to the proposed methodology. It is simple and easy to be applied. Therefore, one hopes that it can be absorbed in engineering design practice without its traditional resistance to incorporate new trends.
Nonlinear dynamic analysis of a cylindrical panel with a discontinuous unilateral elastic base
Authors: Morais Jordana L , Silva Frederico M A , Gonçalves Paulo B
Published: June 2024

This work evaluates the nonlinear dynamic behavior and dynamic instability of an imperfect cylindrical panel with a discontinuous unilateral elastic base. The cylindrical panel is described by Donnell’s nonlinear shallow shell theory, being discretized by the Galerkin method, using a previous reduced order model obtained by a perturbation method. It is shown that an efficient modal solution with two degree-of-freedom is sufficient to describe the non-linear softening behavior of the cylindrical panel with a discontinuous elastic base. The Heaviside and the Signum function are used to describe the elastic base domain and the unilateral contact force respectively. The obtained results, using the fourth order Runge-Kutta method, demonstrate the influence of the discontinuous unilateral elastic base and initial geometrical imperfection on the bifurcation diagrams, phase portraits and resonance curves of the cylindrical panel. They demonstrate the important changes in the stable and unstable regions of the nonlinear equilibrium paths and dynamics instability regions due to the unilateral contact constraint and the localized foundation.
Nonlinear dynamics of a 3D-printed pre-compressed beam structure: an experimental investigation
Authors: Anastasio D , Daga A P , Fasana A , Garibaldi L , Marchesiello S , Cheng P
Published: June 2024

Engineering applications have conventionally aimed to avoid phenomena related to mechanical instabilities or buckling, as they can bring undesired nonlinear effects or even failure. In recent years however the research in this field has experienced an inversion of direction making use of such phenomena to improve the performance of solids and structures. In this context, the adoption of pre-compressed slender beam elements is one of the most common solutions. A typical application is the development of quasi-zero stiffness (QZS) vibration isolators, that bring a high static stiffness and an extremely low dynamic stiffness. As a general rule, the QZS characteristics can be obtained by coupling a negative stiffness effect with a positive one. When considering beam elements, the application of a compressive axial force can lead to a mechanical instability and to a negative stiffness region in the force-displacement characteristics. This paper studies the dynamical behaviour of such elements by comparing experimental measurements with a mathematical model. To this end, a 3D-printed V-shaped structure is considered, comprising two pre-compressed beam elements and a controllable pre-load. The regulation of the pre-load allows the V-structure to undergo tensile or compressive forces, thus altering its characteristics. In particular, the restoring force of the system can show regions of negative or quasi-zero stiffness when compressive forces are applied. The system is excited with an electromagnetic shaker considering different pre-loads, and the nonlinear dynamic behaviour is estimated from the measured responses. A comparison between experimental measurements and model predictions is eventually carried out to strengthen the understanding of the observed dynamical phenomena.
Advancing Steel Component Repair by Investigating the Surface Properties of Mild Steel Plates Coated with Alumina Using Metal Inert Gas Welding
Authors: Mwema F M , Shagwira H , Jen T C , Wambua J M , Bodunrin M O , Akinlabi E T
Published: June 2024

Arc-welding coatings are extensively employed within the informal sectors of many African countries to repair various machine components, such as gear teeth, machine shafts, bushings, and many others. In the pursuit of advancing steel component repair techniques, this study investigates the surface properties of mild steel plates coated with alumina using the Metal Inert Gas (MIG) welding process. Mild steel wire of diameter 1.6 mm, alumina particles of size 1 µm, and mild steel plates were used. The prepared samples were analysed for microstructural, hardness, wear, and corrosion properties. For the first time, and through a traditional welding process, it is demonstrated that the hardness, wear, and corrosion resistance of steel parts can be improved by the inclusion of alumina particles on their surfaces. As such, this work will have an impact on the informal engineering sector (Jua Kali sector as known in Kenya) involved in the surface repair of steel components.
Experimental study on dynamic characteristics of wall pressure in supersonic combustor of kerosene fuel
Authors: Jiao Guiqian , Song Wenyan , Zeng Xianglong
Published: June 2024

In order to study the rationality and feasibility of kerosene-fueled supersonic combustor wall pressure as the controlled parameter of scramjet, a series of supersonic combustor ground direct-connected tests were carried out on the ground direct-connected test bench of Northwestern Polytechnical University. The test simulated the actual process of ignition and combustion in a double-cavities supersonic combustor under the conditions of inlet total pressure of 800 kPa and 900 kPa, total temperature of 810 K, and Mach number 2.0. The characteristics of pressure distribution and sensitivity on the wall of the combustor were measured and analyzed. The results show that the combustor wall pressure fluctuates obviously in steady state, and the fluctuation is positively correlated with the oil-gas ratio. The relative variation of wall pressure difference value and equivalent oil-gas ratio can reflect the sensitivity of wall pressure change under different oil-gas ratios. The wall sensitivity at X=370 mm is the largest, which is most suitable as the controlled parameter of the engine kerosene flow.
An Energy Stable Alternative WENO Scheme with a New Smoothness Indicator for Hyperbolic Conservation Laws
Authors: Lou Shuai , Ren Yi-peng , Yang Xue-jun , Wang Zhao-wei , Zhong Kang , Yan Chao
Published: June 2024

An energy stable alternative weighted Essentially Non-Oscillatory (WENO) scheme with a new smoothness indicator (EAWN) is proposed in this paper. The developed EAWN scheme is stable for linear problems by adding a correction operator and can recover the designed order of accuracy at critical points with no dependency on user-defined parameter for smoothness indicators. Application of EAWN in one-dimensional and two-dimensional hyperbolic conservation laws also indicates the superiority of the new method over its non-modified version in terms of shock-capturing and vorticity-resolving.
Structural and electrical conductivity studies of Polyaniline - WO3 hybrid nanocomposites for gas sensing applications
Authors: Jaiswal Rohan , Chandra Joshi Manish , Ramadurai Ranjith , Sunkara Manorama , Kannan Vijayanandhini
Published: June 2024

Conducting polymer – metal oxide based hybrid nanocomposites are a fascinating class of materials for miniaturized and flexible gas sensor devices. They exhibit enhanced physiochemical properties such as sensitivity, selectivity towards various volatile and hazardous chemical and bioanalytes. Our study focuses on conducting polyaniline (PANI) and WO3 nanocomposites, where different weight percentages (wt.%) of WO3 nanoparticles are embedded within the conducting PANI matrix using an in-situ oxidation polymerization synthesis technique. The surface morphology analysis indicated that the WO3 nanoparticles with an average grain size of ~200 nm are homogeneously distributed within the PANI nanofibers. The Fourier Transform Infra-Red (FTIR) spectrum analysis showed that the absorption peaks at 1111,1291, 1385, 1474, and 1560 cm−1 are typical of the conducting PANI emeraldine phase. We attribute the additional broad peak ranging between 840 to 720 cm−1 in the spectrum to WO3 phase, wherein, the intensity of the peak increases with WO3 content in case of hybrid composites. Current-voltage (I-V) characteristics for all our samples showed linear behaviour up to 1.2 volts. Temperature-dependent DC electrical conductivity (σ) studies measured from room temperature to 120°C for pure PANI, and PANI-WO3 composites showed an enhanced electrical conductivity of values up to 0.12 S/cm for PANI as compared to WO3 with σ ~ 1.4 x 10−3 S/cm. Pure PANI exhibits semiconducting behavior with an increase in electrical conductivity with temperature due to the charge carrier delocalization within the dispersed PANI backbone. The addition of higher concentrations of WO3 in composites leads to a metallic-like behavior, characterized by a decrease in electrical conductivity with temperature. These observations are attributed to the field-assisted band bending effects at the interfaces of PANI and WO3. Our composites show desired electrical characteristics suitable for gas sensing applications.
Impact of sol-gel and co-precipitation synthesis methods on structural properties of lithium ferrite
Authors: Sai Santoshi T , Bharadwaj S , Choudary G S V R K , Chaitanya Varma M
Published: June 2024

In the present study, lithium ferrite is synthesized by both sol-gel and chemical coprecipitation methods and then annealed at 700°C for 2 hrs. The variation in the phase transition and weight loss (%) is clearly evident from the thermo-gravimetric analysis for the lithium ferrite prepared using two different synthesis routes indicating the formation of structural changes. The lattice parameter (a), average crystallite size (D) are calculated using the cubic phase formula and Debye-Sherrer’s equation respectively and the values are in good agreement with literature. Higher value of saturation magnetization is observed in the case of lithium ferrite synthesized by sol-gel method when compared with co-precipitation method highlights the importance of phase formation.
Spectroscopic Studies of CuO-incorporated PEO Nanocomposite Films for Flexible Optoelectronic Devices
Authors: Sudhakar K. , Venugopal R. , Narsimlu N. , Srinivas CH.
Published: June 2024

Polymer nanocomposites is a promising area of research due to polymers’ unique properties and potential applications in various fields such as automotive, aerospace, defense, and biomedicine. In present work, we report preparation and characterization of copper oxide nanoparticles (CuO NPs)-incorporated polyethylene oxide (PEO) nanocomposites. CuO nanoparticles (5, 10 and 15 wt. %) were incorporated into PEO matrix, and preparation method of solution casting had been employed. These films were characterized by XRD, FTIR, SEM and UV–Vis spectroscopy. SEM Morphological studies revealed the original structure of the CuO nanoparticles in PEO matrix. The crystallinity of composite films decreases with increasing CuO weight percentage. The SEM images confirmed uniform distribution of CuO nanoparticles in composite films. UV–Vis spectroscopy of composite films revealed that absorption is more in UV region with increasing CuO wt.%. This property can be used in preparation of UV filters for glass windows to protect them from UV radiation. With addition of CuO NPs to PEO matrix, optical direct and indirect band gaps decreased from 5.32eV to 5.28eV and from 5.28 to 5.03eV, respectively. These results reveal that PEO-CuO nanocomposite films are useful for UV-shielding devices, tunable bandgap devices, photo sensors, and next-generation flexible optoelectronic devices.
The Influence of Vortex Formation on the Electrical Characteristics of Argon Plasma in a Rotating Gliding Arc Discharge
Authors: Mohan Pathak Ram , Rao Lakshminarayana
Published: June 2024

Rotating Gliding Arc (RGA) discharge exhibits the characteristics of non-thermal plasma states when operated at atmospheric pressure with argon (Ar), and this study elucidates its properties. Experimental findings from an alternating current RGA plasma generator reveal a strong dependence of current density, which increases with higher discharge current and gas flow rates (Q). This research investigates the impact of swirling on the electrical properties of argon (Ar) plasma within RGA. The study focuses on two distinct flow conditions: TRANSFLOW at 5 SLPM and HIGH-TURBFLOW at 50 SLPM. The examination incorporates two different swirl hole diameters, namely 1.6 mm and 1 mm, to analyze their influence on the electrical characteristics of the system. Based on these flow regimes different types of discharge i.e., glow and spark are get formed and their characteristics are studied well. High-speed imaging and electrical measurements were employed to acquire insights into the depth of the physics associated with the Ar plasma. Compared to 1.6 mm, V

t
is higher for 1 mm for both the Q, i.e., for TRANS-FLOW at 5 SLPM and for HIGH TURB-FLOW at 50 SLPM. Finding shows that V

t
increases from 1.2 ms−1 to 22 ms−1 for 1.6 mm and it increases from 2.5 ms−1 to 40 ms−1 for 1 mm. V

t
nearly increased twice time when swirl hole diameter decreased from 1.6 mm to 1 mm. The average electric field (E) increases from 8 Vmm−1 to 15 Vmm−1 for 1.6 mm and from 11.8 Vmm−1 to 24 Vmm−1 for 1 mm. The linear fit R² ranges from 0.78 to 0.90.