ABSTRACT. Flexural waves propagating inside a vibrating structure can be manipulated through the so-called Acoustics Black Holes (ABH) effects. Upon a proper tailoring of the structural thickness, the phase velocity of the bending wave gradually reduces alongside thickness thinning, thus entailing high energy concentration and effective energy dissipation using a small amount of damping materials. The phenomenon arouses increasing interests from the scientific community and inspires innovative design solutions for light-weight and highly damped structures. In addition, the reduced structural wave velocity allows the creation of acoustically slow waves so that subsonic sound radiation regions can be formed inside a structure vibrating above the critical frequency, the consequent of which is the impaired sound radiation efficiency and reduced sound radiation. These unique features show promise of the ABH-based technology for potential applications such as wave manipulation, vibration suppression, energy insulation, sound radiation reduction, energy harvesting etc. In this talk, some of the recent progress on ABH research made by the team led by the speaker and his close collaborators will be highlighted. Topics to be discuss would cover modelling and analysis methods, exploration of underlying mechanisms of various ABH-specific phenomena, ABH structural design and potential industrial applications.

ABSTRACT. Unveiling complex behaviour in dynamical systems often relies on in-depth analysis using robust low dimensional models, which can be effectively used for parametric computational studies. The most effective way to obtain new insights is having these low dimensional models calibrated with high fidelity experiments.

In this lecture I will introduce the recent advances in the field of nonlinear dynamics with a special focus on non-smooth dynamical systems [1], which is the newest and vastly developing area with new phenomena such as grazing induced bifurcations [2] and a broad suite of application in science and engineering. In the first part, I will define nonlinearity and nonlinear dynamics. Specifically I will focus on a class called non-smooth dynamical systems. Then I will show how such problems can be effectively modelled and analysed by low dimensional dynamical systems [3,4]. The generic complexity of non-smooth dynamics will be demonstrated by an elastic impact oscillator – an archetypal model for modelling of high frequency vibro-impact drilling [5]. The second part will be devoted to what we might call Nonlinear Dynamics for Engineering Design where I will present results from my recent projects, where nonlinear dynamic interactions have been used to enhance the performance of real systems and structures. I will put a special emphasis on one large projects from energy industry, where we have developed a revolutionary downhole drilling technology [6] tested in our unique drilling laboratories [7,8]. I will argue that this would not be possible without calibrated low dimensional models.

1. Wiercigroch, M. Modelling of dynamical systems with motion dependent discontinuities. Chaos Soliton Frac 11(15), 2429-2442, 2000. 2. Jiang, H., Chong, A.S.E., Ueda, Y. and Wiercigroch, M. Grazing-induced bifurcations in impact oscillators with elastic and rigid constraints. Int J Mech Scie 127, 204-214, 2017. 3. Ing, J., Pavlovskaia, E., Wiercigroch, M. and Banerjee, S. Bifurcation analysis of an impact oscillator with one sided elastic constraint near grazing, Physica D 239, 312-321, 2010 4. Cao, Q. Wiercigroch, M., Pavlovskaia, E.E., Thompson, J.M.T. and Grebogi, C. Piecewise linear approach to an archetypal oscillator for smooth and discontinuous dynamics. Phil T Roy Soc A 366, 635-652, 2008. 5. Pavlovskaia, E.E., Wiercigroch, M. and Grebogi, C. Modelling of an impact system with a drift. Phys Rev E 64, 056224, 2001. 6. Wiercigroch, M. Resonance Enhanced Drilling: Method and Apparatus. Patent No WO2007141550, 2007. 7. Kapitaniak, M., Vaziri, V., Paez, J., Nandakumar, K. and Wiercigroch, M. Unveiling complexities of drill-string vibration: Experiments and modelling, Int J Mech Sci 101-102, 324-337, 2015. 8. Liao, M., Wiercigroch, M., Sayah, M., Ing, J., 2021 Experimental verification of the percussive drilling model. Mech Syst Signal Process 146, 107067.

ABSTRACT. Dredging operation is happening at an increased rate due to the impetus gained towards inland navigation and land reclamation. The spud system is integral component of a Cutter suction dredger (CSD) which anchors the hull at the dredging location. The spud embedded on soil maintains the position of the dredger and offers resistance to the motion of the CSD. In this present study the spud was modeled as an Euler Bernoulli beam using finite element analysis. The resistance offered by the soil was evaluated experimentally. Soil stiffness is modeled using two spring elements which restraints the motion of the spud in the transverse and rotational direction. The spud system was subjected to external force due to wave loading. The wave load was determined along the length of the spud using Morison equation. Heave and pitch are the degrees of freedom of the dredge hull which were restraint by the spud. The ship rigid body dynamics was identified using the experimental study. The identified dredge hull was coupled to the spud. Numerical model of the spud system was subjected to random wave loading . A case study was carried out using Montecarlo simulation by varying the soil stiffness. The maximum response was system is evaluated at the top of the spud. A meta model for the system was developed based on the maximum response at spud and soil stiffness using Gaussian process emulator (GPE). During the validation study it was observed that the metamodel was predicting the soil stiffness accurately. This indicates that the condition monitoring of the embedment of the spud can be assessed by the metamodel developed using GPE.

ABSTRACT. This research article presents the methodology for the evaluation of metro rail tracks which can be used to produce a vibration map, also it is very fundamental for track maintenance, where we predict vehicle body vibration based on deep learning, which represents one of the newest areas in the Artificial Intelligence field. As we all know, in the entire world the evaluation of track quality had been done through established track geometry standards. However, these types of standards may not be capable of detecting some abnormality of track geometry conditions that can cause vehicle body vibration. These vibrations also shake up nearby residents; measurements are carried out to evaluate the risk for structural integrity. With the help of solid works software and structure, health diagnosis using Ansys software integration with experimental data for feature extraction used EEMD and for classification apply artificial neural network (ANN) where a model is proposed to make an accurate and point-wise prediction, due to which we can achieve optimal performance. This case study is based on the Delhi metro, for track health monitoring system was installed on several trains running on the green line in the underground which aims to improve the maintenance process. The early detection and surveillance of defects help to extend the service life of the tracks and it also reduced operating costs. A data acquisition system is used to analyze the continuously recorded measurements (vehicle body vibration), which consist of vertical bogie acceleration and surrounding noise, each sampled with a frequency of 22 kHz. In particular, achieving optimal performance, and exploring the internal mechanism of the model, structural configuration, and inner states are mostly studied. However, ANN-LSTM can predict vertical vehicle-body vibration below 10Hz and lateral vehicle-body vibration below 1 Hz. The above analysis shows that the performance of metro rail tracks by using the vehicle body vibration method acts as a performance-based model which evaluates the index of track quality.

ABSTRACT. In this article, the vibration troubleshooting steps of a 10 MW reciprocating Hydrogen compressor related to an oil refinery have been done. In this project, by carefully examining the various equipment used in the relevant unit, after studying and familiarizing with the history of the installation and operation of the compressor, how its various parts work, including the foundation, turbine, gearbox, coupling, shafts, compressor, pulsation dampener, piping and finally the foundation was examined separately. In these studies, processes including vibration level analysis, frequency analysis, phase difference analysis, modal analysis, compressor modeling in working conditions, as well as design conditions and analysis of gas input to the compressor have been implemented and finally after summarizing the factors affecting vibrations. The collections were discovered and prioritized according to their level of importance. Finally, the main factor identified is the impermissible flexibility of the foundation of the turbine driving the compressor. The foundation is modified after the present project and the problem is solved, successfully.

ABSTRACT. The rolling element bearing's relevance and technical uses are clear, and it is subjected to various types of loading. The rolling bearing may crack because of fatigue loading. The presence of crack causes a change in physical properties of a bearing and thus reducing the stiffness of the rolling element bearing with invisible natural frequencies are being reduced. The essential parameters of vibration of bearing analysis are crack depth and location. The current study used Finite Element Analysis (FEA) and Particle Swarm Optimization (PSO) technology to create methodologies for fracture detection of a solitary crack in a cracked rolling bearing. Different crack location effects are taken into account, and the results are compared to different rolling bearing crack depths. Then Particle swarm optimization algorithm has been developed using the first three relative natural frequencies taken from FE analysis. For comparative study, both Standard PSO and APSO is used for crack diagnosis of the bearing. The feasibility of proposed PSO techniques is compared through error analysis. The research paper, the objective has been related to the design a Particle swarm optimization technique for the prediction of crack location and crack depth in a uniform cracked bearing.

ABSTRACT. This paper aims to use a deep convolution neural network (CNN) to classify pipework vibrations based on the vibration levels. Vibration levels are a good indicator of the risk of vibration-induced fatigue failures (VIF). Vibrations in pipework are very common in oil and gas and petrochemical plants which are a result of flow-induced forces from turbulent flows in the pipe, flow momentum change, or fluid pulsations. Stain measurements are usually used to accurately identify the risk of VIF; however, that is not always easy due to the surface operations required prior to the installation of the strain gauge, such as removal of insulations for hot pipes, waiting for cool down, paint removal, the shutdown of the pipework to avoid installation on a shaky pipe. Another alternative would be relying on vibration measurements using accelerometers and signal analyzers since the dynamic stresses are correlated to the vibration velocity. The dominant frequency of vibration and the root mean square of the velocity are currently used for the vibration acceptance criteria to categorize the vibration levels into three categories: OK, CONCERN, and PROBLEM. The motivation here is to use the collected experimental data for both vibration and stress measurements for multiple pipework plants to train a deep CNN on the images of a continuous wavelet transform from the time-frequency features to be used to predict the classification of new data based on the vibration levels. The results show that the developed CNN can successfully classify the vibration data 93% of the time.

ABSTRACT. The propagation of acoustic gravity waves in a compressible fluid of finite depth is discussed. The fluid considered here is bounded above by free surface and below by an infinite magnetoelastic layer of constant magnetic field. Frequency relationship satisfied by acoustic wave modes has been calculated. Different physical parameters (phase velocity, free surface elevation, etc.) are obtained analytically. Numerical investigation of the results are given for different progressive wave modes. A comparison of the results of the present problem with the case of rigid bottom is given.

ABSTRACT. Vibration energy harvesting has developed tremendous growth and advancement with the rise in green energy initiatives. The use of piezoelectric materials has great performance efficiency in converting mechanical strain to electrical energy in cantilevered arrangements with a proof mass. Energy harvesting from rotating systems are able to convert ambient lost energy into something useful that can be used in remote sensing applications. The inherent nonlinearity of rotational energy harvesting addresses the limitations of conventional linear systems with a narrowband frequency response. This project investigates the nonlinear modelling of a continuous system in a rotating body with the use of macro-fiber composites. An analytical model combined with finite element analysis can be used to investigate the various mode shapes and the conversion efficiency. Such applications can be used to power small sensors and transmitters in the automotive industry, household items and bicycles.

ABSTRACT. The gyroscopic stabilizer is a device that protects a transported cargo from the undesirable effects of vehicle tilting. The characteristic parameters of such a system are the angular momentum of its gyroscopes and the magnitude of the feedback of the correction and compensation systems, or the so-called radial corrections, which are integral parts of the gyroscopic stabilizer. Radial corrections represent non-conservative forces of positional coordinates and positive feedback. Thus, they could cause instability in the system. Therefore, and in view of the purpose of the gyroscopic stabilizer, parameters of radial corrections must be chosen carefully. In this paper, we will present an approach to the tuning radial corrections of the two-axis gyroscopic stabilizer intended to improve the vibration-isolation of the lying human body during roadway transport in an ambulance car. Our approach starts with roadway design standards, vehicle homologation standards and uses experimentally-obtained real trafgic data.

ABSTRACT. We investigate the nonlinear vibrations of a metamaterial structure that consists of a host Euler–Bernoulli beam attached to a periodic array of spring–mass–damper subsystems deployed for vibration absorption. The main objective is to demonstrate that the capability of the metastructure to suppress vibration can be significantly enhanced when the absorbers are tuned to the optimal frequency. The results show that the simultaneous suppression of several modes is possible by tuning and properly placing each absorber along the host structure. Furthermore, the impact of the resonators on the nonlinear behavior of the main structure when subjected to external forcing over an extended frequency range is investigated. The numerical study reveals that proper tuning of the local resonators allows significant vibration suppression of the metamaterial beam when being excited in the neighborhood of the natural frequencies. The optimization results show that significant mitigation can be achieved by tuning properly the absorbers in the vicinity of the host structure’s natu-ral frequencies.

ABSTRACT. The primary purpose of this study is to experimentally investigate the damping performance of an innovative hybrid electromagnet damper. The developed damper consists of a twin-tube viscous damper (VD) integrated with an Eddy Current Damper (ECD). The ECD uses the electromagnetic resistive force generated from the interaction between a conductor and an induced magnetic field to eliminate and isolate unwanted vibrations. The experimental investigation was conducted using a testing apparatus that generated a sinusoidal motion at a fixed frequency of 0.43 Hz, while the excitation current that feeds the ECD magnetic circuit was increased from 0 to 2 A with a 1A increment. At the maximum current of 2A, the hybrid damper was found to generate 18% more of the damping effect.