Publications

This study investigates a detailed analytical and numerical investigation of a nonlinear two-degree-of-freedom (2DOF) mechanical oscillator subjected to parametric excitation, magnetic stiffness nonlinearities, and dry friction. The considered system consists of two coupled oscillators, both of which are connected to a rotating rectangular beam that induces a time-periodic stiffness variation. The Complex-Averaging (CxA) method is employed to derive approximate analytical solutions, which are thoroughly validated through time-domain simulations and bifurcation analyses. The dynamic analysis reveals a rich spectrum of nonlinear behaviors, including periodic, quasi-periodic, and chaotic responses. Detailed bifurcation diagrams, Lyapunov exponent analysis, and Poincaré maps demonstrate the influence of nonlinear stiffness degree, mass symmetry, and frictional effects on system stability and response amplitude. The obtained results give a significant understanding of the dynamic behavior of coupled nonlinear systems and establish a conceptual framework for the development of complex vibration abatement strategies, energy harvesting devices, and advanced mechanical systems.

Muhammad Junaid-U-Rehman, Grzegorz Kudra, Krystian Polczyński, Kevin Dekemele and Jan Awrejcewicz. "Analysis of a parametrically excited 2DOF oscillator with nonlinear restoring magnetic force and rotating rectangular beam." Nonlinear Dynamics (2026): 1-19.

Torsional vibrations are undesirable in rotating machinery, and demands for better performance and material savings to reduce weight exacerbate this issue by triggering resonance conditions. The Nonlinear Energy Sink (NES) offers a robust and effective vibration attenuation solution. In this research, a 2 Degree-Of-Freedom torsionally vibrating host structure is equipped with a NES having piecewise-linear stiffness approximating a cubic nonlinearity. The first-order Complexification-Averaging (CxA) method is used to analyse the Slow Flow dynamics on the response envelope, and a NES tuning methodology based on the Slow Invariant Manifold is proposed for 1:1 resonance attenuation for two resonance frequencies of the host system. The mechanical design of the NES is optimised for minimal stresses and fatigue while avoiding local resonances of the individual components. Experiments and numerical simulations validate the CxA method, and indicate the presence of Strongly Modulated Response regime and an Isolated Resonance Curve in the vicinity of resonance. Significant resonant response attenuation is achieved for both the first mode (> 80%) and the second mode (> 65%) over a wide range of forcing amplitudes, with possibility of further improvements. In this regard, design modifications that allow for effective multi-modal attenuation are presented. As such, a complete toolchain has been developed to obtain an NES design which can be applied to a wide range of torsional vibration applications.

Harikrishnan Venupogal, Mia Loccufier and Kevin Dekemele. "Design of a Piecewise-Stiffening Nonlinear Energy Sink for Torsional Vibration Attenuation." International Journal Of Non-Linear Mechanics. 2025

Yucai Zhong, Yang Fang, Kevin Dekemele, Xinxing Ma, Zhenguo Zhang (2025). Vibration suppression using a programmable piezoelectric nonlinear energy sink. International Journal of Mechanical Sciences, 110626.

This study investigates the control of an impulsively excited one-degree-of-freedom (DOF) oscillator with softening stiffness, modelled with an arctangent characteristic. The goal is to control the host system’s vibrations by transferring the vibrational energy to an active controller. To this end, a Virtual Mechanical System (VMS) control law is implemented. This law is characterised by controller dynamics, which describe the behaviour of a mechanical system coupled to the host system skew-symmetrically in the velocities and having stiffness identical to that of the host system. The hypothesis is that this similarity and unique coupling facilitate energy transfer. By using the Complexification-Averaging (CxA) technique and examining the slow flow dynamics wrt. fixed points, bifurcations and impulsive orbits, the conditions for energy transfer are uncovered, enabling tuning of the controller.

Sarah Geykens, Jasper Juchem, Kevin Dekemele and Mia Loccufier. "Bifurcations in a controlled system with softening stiffness: The Virtual Mechanical System control law for nonlinear vibration control." Nonlinear Dynamics (2025): 1-19.

The nonlinear energy sink (NES) is a practical passive device for vibration control that has gained significant attention due to its ability to mitigate resonant vibrations across a wide frequency range. Conventional NES designs typically employ a hardening restoring force, which enables broad operational frequency coverage but faces limitations in the operational amplitude range, also due to the emergence of isolated resonance curves (IRCs). This study investigates a softening NES, where the restoring force characteristic is modeled as a saturating function. Analytical results demonstrate that the softening NES retains the beneficial amplitude saturation effect and strongly modulated response (SMR) observed in hardening NESs, while significantly expanding the range over which SMR occurs. Furthermore, the IRCs in the softening NES appear on the right of the resonance peak, unlike the leftward location in hardening NESs, making it advantageous for applications where excitation frequency ramps up. Notably, IRCs in the softening NES are less detrimental as they result in smaller amplitude jumps. We also identify parameter values that suppress the formation of IRCs without compromising the performance of the NES, providing a practical advantage over conventional designs. Despite these promising findings, the practical realization of the softening NES remains an open challenge, which will be the focus of future research. Overall, the softening NES exhibits superior performance compared to the hardening NES, presenting an effective alternative for vibration suppression in various engineering applications.

Kevin Dekemele and Giuseppe Habib. "Softening versus hardening nonlinear energy sinks: forced vibration control and isolated resonance curves." Nonlinear Dynamics (2025): 1-20.

In response to limitations in vibration suppression performance of traditional linear tuned mass damper due to energy threshold constraints and narrow vibration bands, this study proposes a magnetic tri-stable NES (MTNES) formed by combining a linear spring and magnets. Compared to the conventional nonlinear energy sink (NES), the magnetic tri-stable NES (MTNES) incorporates magnetism to enhance the nonlinear stiffness. Firstly, the mechanism of the MTNES is introduced in this study, which reveals the existence of the three stable points in the system. Subsequently, the equations of motion of the coupled system with MTNES attached to the cantilever beam are derived, and the optimal parameter combination for MTNES is determined using a global optimization method. Furthermore, the influence of MTNES parameter variations on vibration suppression efficiency is studied through parameter analysis. Then, the restoring force of the MTNES is simplified into polynomial form, and the system response is analyzed using the harmonic balance method and Runge–Kutta method. Finally, experimental studies on the coupled system are conducted. The results indicate that MTNES can effectively suppress the resonance of the host structure within a wide frequency band, with the highest vibration suppression rate of up to 66% under strong modulated response. Additionally, the results of numerical calculations and theoretical analysis are in good agreement with that of the experiment.

Jundong Fu, Shui Wan, Wenke Li, Jiwei Shen, Harikrishnan Venugopal, Mia Loccufier, Kevin Dekemele (2024). Vibration control of a cantilever beam coupled with magnetic tri-stable nonlinear energy sink. Nonlinear Dynamics, 1-23.

Accelerated bridge construction is crucial in bridge engineering. In order to improve the seismic performance of prefabricated columns, this study proposes using ultra-high performance concrete (UHPC) in the plastic hinge areas of prefabricated columns with bellows grouting connections. In particular, cyclic loading tests are carried out on four 1/3-scaled columns, including two castin-place columns and two bellows grouting connection columns. The results show that columns with UHPC in the plastic hinge areas exhibit larger lateral and ultimate bearing capacity, ductility, cumulative energy dissipation, and stiffness compared to those with conventional concrete. Additionally, bellows grouting connection column with UHPC shows superior seismic performance compared to cast-in-place column with conventional concrete. The proposed finite element analysis model is in a good agreement with the test results. Through using finite element analysis, three key parameters influencing the seismic performance of bellows grouting columns are examined, and the optimal combination of these parameters is identified.

Jundong Fu, Shui Wan, Jie Xiao, Xiao Wang, Peng Zhou, Kevin Dekemele (2024). Cyclic loading test for prefabricated ultra-high performance concrete columns with bellows grouting connection. Structural Concrete, 1-22.

Concrete structures suffer from crack damage under heavy vibrations, caused by seismic loads. Passive vibration control devices can be used to reduce the damage. The most common device is the tuned-mass-damper (TMD), which is tuned to match the natural frequency of the primary structure. However, under prolonged vibration load, the natural frequency of the concrete structure decreases, reducing the TMD's effectiveness in mitigating vibrations and damage, as it can only target a fixed natural frequency. Therefore, this study will propose and implement the nonlinear energy sink (NES), which is a vibration control device that can adapt to changing frequency, resulting in a larger effective bandwidth than the TMD. As a concrete structure, the cast-in-place double-column piers is seismically loaded with a shaking table with and without NES to observe the vibration and damage-mitigating properties of the NES. More specifically, a magnetic bi-stable NES (MBNES) with a viscous fluid damper (VFD) is designed and built. The bi-stable restoring force allows for a larger bandwidth than conventional NESs, and the magnets and VFD allow for easy manufacturability. An optimization method is proposed to obtain optimal parameters, and the restoring force and damping of the experimentally designed MBNES are verified using the restoring force surface method. The proposed design, optimization and identification procedure are generic and can be applied to any (concrete) civil structure. Shaking table tests are used to verify the robust performance of MBNES under continuous changes in the natural frequency of concrete double-column piers. The experimental results show that the MBNES can effectively mitigate vibrations of the pier and, consequently, reduce the damage of the pier, slow down the decrease of the stiffness of the pier, reduce the curvature and shear deformation of the pier. Numerical analysis results show that MBNES can absorb the energy of the primary structure in a wide frequency bandwidth and has excellent robust performance compared to conventional devices.

Jundong Fu, Shui Wan, Peng Zhou, Jiwei Shen, Mia Loccufier, Kevin Dekemele (2024). Effect of magnetic-spring bi-stable nonlinear energy sink on vibration and damage reduction of concrete double-column piers: Experimental and numerical analysis. Engineering Structures, 303, 117517

Mitigating vibrations in engineering structures is of key interest, as they can lead to failure and/or discomfort. However, in some cases it is not feasible to actuate all the structure’s degrees of freedom, which makes vibration mitigation difficult. In this work, we investigate the addition of a single one-degree-of-freedom virtual mechanical system (VMS), as an active controller, to attract and mitigate the energy from an impulse load on the structure. To challenge the controller, an actuation point is chosen furthest away from the impact location. As it is implemented virtually, the coupling between the structure and VMS can be chosen freely. It is found that a skew-symmetric coupling generates a gyroscopic force that enables control over the structure’s mode shapes. Using this, the controller is tuned to achieve a beating phenomenon that attracts the vibration energy to the actuation location. A nonlinear damper, based on the slope of the envelope of the virtual velocity state, avoids reflection of energy to the structure and dissipates this unwanted energy. Furthermore, the virtual damper’s robustness to timing errors is investigated: damping too soon means an incomplete energy transfer to the VMS, damping too late leads to return of energy to the building. The tuning strategy of the VMS is applied to a 4 DOF and 60 DOF building benchmark. For comparison, a tuned mass damper (TMD) and a nonlinear energy sink (NES) are tuned as well. The VMS succeeds in decreasing the settling time significantly in both cases, while the performance of the passive TMD and NES is rather limited for this specific configuration.

Jasper Juchem, Sarah Geyskens, Kevin Dekemele, Mia Loccufier (2024). A Virtual Mechanical System control law for energy transfer towards a single actuation point in n DOF buildings. Engineering Structures, 302, 117493.

The theoretical study and experimental validation of a nonlinear shunt circuit for piezoelectric vibration damping is investigated here. The circuit consists of a resistor, an inductor and a nonlinear cubic voltage source. The shunt acts as an electrical analog to the mechanical nonlinear energy sinks (NESs). These mechanical NESs are passive vibration absorbers that typically have a cubic nonlinear stiffness. They have attractive properties such as saturation of the host system’s vibration amplitude and strongly modulated response. This increases its operational frequency bandwidth and robustness against variations in the properties of host systems compared to linear vibration absorbers. However, the nonlinear nature may induce isolated responses in the host system that induce high vibration amplitudes. This paper investigates if these attractive properties also occur in the electric nonlinear energy sink shunt. An analytical expression for the frequency response is derived through the complexification-averaging method. Bifurcations in the frequency response reveal the occurrence of a quasi-periodic vibration energy exchange between the host system and the voltage over the electrodes of piezoelectric material. This is the main mechanism behind the amplitude saturation of the host system. Other bifurcations also reveal the existence of isolated responses. The nonlinear shunt is then realized with analog multipliers and a synthetic inductor and its performance in vibration damping is experimentally verified for a cantilever beam.

Kevin Dekemele, Christophe Giraud-Audine, and Olivier Thomas. "A piezoelectric nonlinear energy sink shunt for vibration damping." Mechanical Systems and Signal Processing 220 (2024): 111615.

Jiwei Shen, Shui Wan, Jundong fu, Shuli Li, Debao Lv, Kevin Dekemele (2024). A magnetic plucking frequency up-conversion piezoelectric energy harvester with nonlinear energy sink structure. Applied Energy, 376, 124326.

Nonlinear energy sinks (NESs) are broadband passive vibration absorbers that are nonlinearly connected to a host system. If an NES is attached to a multi-degree-of-freedom mechanical host system under transient loading, the vibrations in the host system will transfer to and dissipate in the NES. During this transfer, the NES sequentially resonates with the modal frequencies of the host system, dissipating one mode at a time. This phenomenon is called resonance capture cascade (RCC). So far, RCC has only been investigated for NESs with a hardening nonlinear stiffness. Because of this stiffness, the transfer of modal vibrations happens from high to low frequency. In this study, an NES with a softening stiffness is proposed. Investigating the slow invariant manifolds reveals that an inverted resonance capture cascade occurs, where the transfer of vibrations to the NES is from low to high frequency. The analysis is carried out by exploiting high-dimensional slow invariant manifolds. The proposed NES is compared to the conventional NES with hardening stiffness.

Kevin Dekemele, Giuseppe Habib (2023). Inverted resonance capture cascade: modal interactions of a nonlinear energy sink with softening stiffness. Nonlinear Dynamics, 111(11), 9839-9861.

A novel device is proposed to obtain arbitrary restoring force characteristics and nonlinear geometric damping. It consists of linear springs and dampers that are compressed along a track. The obtained nonlinear damping and stiffness law depend on the track’s shape. The device is then applied to obtain a nonlinear energy sink (NES) to damp the vibrations of a host system. Both the case of transient vibrations, induced by shock loads, and sustained vibrations, induced by harmonic loads, are studied. For arbitrary stiffness and damping, slow flow dynamics and slow invariant manifolds (SIMs) are derived by applying harmonic balancing and multiple timescales techniques. Under transient vibrations, two performance measures are derived from the SIM, the relative residual energy and the pumping time, and are found for generic nonlinear spring force and nonlinear geometric damping. For sustained vibrations, a load-dependent frequency response (FR) is derived from the SIMs. This FR predicts the occurrence of the efficient strongly modulated responses but also the occurrence of the unfavorable detached responses called isolas, where the NES fails to mitigate and even amplifies vibrations. This research investigates the performance of a conventional cubic NES and a bistable NES (BNES) with nonlinear damping obtained from the proposed device. Especially the BNES with nonlinear damping shows attractive properties, with a high degree of robustness over a wide energy range and a low vibration threshold under transient loading. Under harmonic loads, the nonlinear damping helps reduce the effect of isolas. A novel tuning methodology is proposed to avoid isolas for a range of load magnitudes. The new device opens up a whole range of possibilities regarding energy dissipation through nonlinear damping

Kevin Dekemele (2023). Tailored nonlinear stiffness and geometric damping: Applied to a bistable vibration absorber. International Journal of Non-Linear Mechanics, 157, 104548.

Conventional nonlinear energy sinks (NES) are considered to be a more robust alternative to linear vibration absorbers such as the tuned-mass-damper (TMD). While the conventional NES has a larger efficient frequency bandwidth than the TMD, it is only really efficient for a small energy range. This implies a deterioration of the NES's mitigation properties if the primary system's amplitude varies. To overcome this issue, other researchers resort to increasing the complexity of the NES by adding degrees-of-freedom. Here, another line of thought is presented, by proposing an unconventional stiffness characteristic. To increase the energy bandwidth the NES in this paper features a non-smooth, periodically extended stiffness characteristic. This NES is attached to an uncertain primary system and its performance is compared with that of the conventional NES and of the TMD by deriving the slow invariant manifolds (SIMs) in transient 1:1 resonance. The SIMs are curves that relate the vibration amplitudes of the primary system and the NES, and serve as an easy and computationally efficient tool to analyze performance. The research in this paper will prove that the newly proposed NES can be both robust regarding energy and frequency uncertainty, by considering the novel periodically extended stiffness characteristic.

Kevin Dekemele, Giuseppe Habib, Mia Loccufier (2022). The periodically extended stiffness nonlinear energy sink. Mechanical Systems and Signal Processing, 169, 108706.

Resonant piezoelectric shunts are a well-established way to reduce vibrations of mechanical systems suffering from resonant condition. The vibration energy is transferred to the electrical domain through the bonded piezoelectric material where it is dissipated in the shunt. Typically, electrical and mechanical resonance frequencies are several orders apart. As such, finding a suitable high inductance component for the resonant shunt is not feasible. Therefore, these high inductance values are mimicked through synthetic impedances, consisting of operational amplifiers and passive components. A downside of these synthetic impedances is that standard operational amplifiers can only handle up to 30 V peak to peak and the state-of-the-art amplifiers up to 100 Vpp. However, as mechanical structures tend to become lighter and more flexible, the order induced voltages over the piezoelectric material electrode voltages increase above these limitations. In this research, a high-voltage synthetic inductor is proposed and built by combining the bridge amplifier configuration and the output voltage boost configuration around a single operational amplifier gyrator circuit, effectively quadrupling the range of the synthetic inductor to 400 Vpp. The impedance of the circuit over a frequency range is numerically and experimentally investigated. The synthetic inductor is then connected to a piezoelectric material bonded to a cantilever beam. Numerical and experimental investigation confirms the high-voltage operation of the implemented circuit and its suitability as a vibration damping circuit.

Kevin Dekemele, Patrick Van Torre, Mia Loccufier (2021). High-voltage synthetic inductor for vibration damping in resonant piezoelectric shunt. Journal of Vibration and Control, 27(17-18), 2047-2057.

Contribution: An education innovation in control engineering using practical setups and its evaluation based on a three-year student feedback study and examination grades. Background: Based on extensive research, education’s transition toward active learning and more practical experience has been shown to increase learning outcomes. Contrary to virtual and remote labs, a practical session with an individual setup for each student provides the most practical experience. Intended Outcomes: To show a positive effect on learning performance by integrating practical sessions in basic control engineering. Application Design: Presenting low cost setups that can be mass produced and adapt to the course’s growing complexity. These setups are evaluated during a three-year feedback study. Findings: The developed setups increased understanding of theoretical concepts. The new methodology significantly improved students’ average grades. The students’ interest in control theory is triggered. This case study could guide other institutions toward successfully implementing highly individual practical sessions for large groups.

Amélie Chevalier, Kevin Dekemele, Jasper Juchem, Mia Loccufier (2021). Student feedback on educational innovation in control engineering: active learning in practice. IEEE Transactions on Education, 64(4), 432-437.

This paper presents a novel First Order Plus Fractional Diffusive Delay (FOPFDD) model, capable of modeling delay dominant systems with high accuracy. The novelty of the FOPFDD is the Fractional Diffusive Delay (FDD) term, an exponential delay of non-integer order α, i.e. e−(Ls)α in Laplace domain. The special cases of α = 0.5 and α = 1 have already been investigated thoroughly. In this work α is generalized to any real number in the interval ]0, 1[. For α = 0.5, this term appears in the solution of distributed diffusion systems, which will serve as a source of inspiration for this work. Both frequency and time domain are investigated. However, regarding the latter, no closed-form expression of the inverse Laplace transform of the FDD can be found for all α, so numerical tools are used to obtain an impulse response of the FDD. To establish the algorithm, several properties of the FDD term have been proven: firstly, existence of the term, secondly, invariance of the time integral of the impulse response, and thirdly, dependency of the impulse response’s energy on α. To conclude, the FOPFDD model is fitted to several delay-dominant, diffusive-like resistors-capacitors (RC) circuits to show the increased modeling accuracy compared to other state-of-the-art models found in literature. The FOPFDD model outperforms the other approximation models in accurately tracking frequency response functions as well as in mimicking the peculiar delay/diffusive-like time responses, coming from the interconnection of a large number of discrete subsystems. The fractional character of the FOPFDD makes it an ideal candidate for an approximate model to these large and complex systems with only a few parameters.

Jasper Juchem, Amélie Chevalier, Kevin Dekemele, Mia Loccufier (2021). First order plus fractional diffusive delay modeling: interconnected discrete systems. Fractional Calculus and Applied Analysis, 24(5), 1535-1558.

To passively reduce the vibration energy in mechanical systems under shock load, nonlinear energy sinks (NES) can be locally attached, serving as vibration absorbers. The NES is an alternative to the standard tuned-mass-damper (TMD). While the TMD has a linear connecting spring, the NES has a nonlinear one. As a consequence, the NES has an energy dependent natural frequency. Because of this property, the NES is able to mitigate multi-modal transient vibrations sequentially from high to low frequency through a resonance capture cascade (RCC). This is a major advantage over the TMD, which is tuned only to reduce vibrations in a narrow frequency band, typically a single mode. Recently, three performance measures for the NES were derived, 1) The energy dissipation, the amount of total vibration energy dissipated by the NES. 2) The pumping time that estimates the time required for the NES to absorb a single frequency and 3) the cascading time, estimating the time the NES engages in RCC, absorbing all the modal frequencies. The novelty of these measures is that they only require the knowledge of the system's parameters. In this research, a complete implementation of a NES is presented, from design and practical realization, to verifying the performance measures experimentally. The performance measures thus allow to predict experimental performance of the NES without simulations or experiments, opposite to what literature does. The NES is constructed with a novel design methodology. This methodology allows for tailor made purely nonlinear stiffness. The NES is placed on a frame representing a scale model single-story building, to validate the single-mode performance. To obtain resonance cascading, a second story is added to obtain a two-mode dominant vibrating structure. The cascading time is predicted and confirmed by the experiments. The experiments agree well with both simulations and predictions regarding performance. This work validates the ease of use of the performance measures and their ability to predict experimental performance of a NES mitigating multi-modal vibrations

Kevin Dekemele, Patrick Van Torre, Mia Loccufier (2020). Design, construction and experimental performance of a nonlinear energy sink in mitigating multi-modal vibrations. Journal of Sound and Vibration, 473, 115243.

In this paper, an evolutionary-based sparse regression algorithm is proposed and applied onto experimental data collected from a Duffing oscillator setup and numerical simulation data. Our purpose is to identify the Coulomb friction terms as part of the ordinary differential equation of the system. Correct identification of this nonlinear system using sparse identification is hugely dependent on selecting the correct form of nonlinearity included in the function library. Consequently, in this work, the evolutionary-based sparse identification is replacing the need for user knowledge when constructing the library in sparse identification. Constructing the library based on the data-driven evolutionary approach is an effective way to extend the space of nonlinear functions, allowing for the sparse regression to be applied on an extensive space of functions. The results show that the method provides an effective algorithm for the purpose of unveiling the physical nature of the Duffing oscillator. In addition, the robustness of the identification algorithm is investigated for various levels of noise in simulation. The proposed method has possible applications to other nonlinear dynamic systems in mechatronics, robotics, and electronics.

Saeideh Khatiry Goharoodi, Kevin Dekemele, Mia Loccufier, Luc Dupre, Guillaume Crevecoeur (2020). Evolutionary‐Based Sparse Regression for the Experimental Identification of Duffing Oscillator. Mathematical Problems in Engineering, 2020(1), 7286575.

A nonlinear energy sink (NES) passively reduces transient vibration energy of a typically impact loaded mechanical system. It is locally connected to the vibrating system through a nonlinear connecting stiffness. For a NES to perform efficiently, through targeted energy transfer (TET), the vibration levels need to exceed a well-defined threshold, below which the NES performs poorly. This threshold can be lowered by considering a NES with a bi-stable connecting stiffness. A bi-stable NES (BNES) has two stable equilibria. Besides vibrating in TET regime, a BNES can also vibrate chaotically or close to one of its equilibria, called intra-well vibrations. However, during both chaotic and intra-well vibrations, the mitigating performance of the BNES is poor. Here, a novel tuning method is developed, which finds the boundary between chaotic and TET regime, such that the BNES avoids the chaos and operates with the more performant TET. This boundary is found by numerically calculating the Lyapunov exponent, a measure for chaos. To quantify performance, two algebraic expressions, requiring no simulations, are derived in the paper expressing the speed of vibration mitigation and expressing the residual vibration energy left after TET. The result is a generic tuning methodology that not only ensures the BNES operates in the efficient TET regime, but also guarantees optimal speed of vibration mitigation. The developed performances measures in function of the NES’s parameters are to the point and easy to use. The tuned BNES shows a superior robustness w.r.t detuning compared to the linear vibration absorbers.

Kevin Dekemele, Patrick Van Torre, Mia Loccufier (2019). Performance and tuning of a chaotic bi-stable NES to mitigate transient vibrations. Nonlinear Dynamics, 98, 1831-1851.

In vibrating mechanical systems, the targeted energy transfer mechanism (TET) of nonlinear energy sinks (NES) is employed as an alternative to linear tuned mass dampers (TMD) as passive vibrations absorbers for transient vibrations. The major advantages a NES has over a linear TMD are (1) an increased robustness to detuning and (2) the ability to dissipate multiple frequencies with only a single NES through so-called resonance capture cascading (RCC). The performance, especially the speed, of TET and RCC has rarely been a topic of research. In this research, algebraic performance measures for the speed of both TET and RCC are derived, called the pumping time and the cascading time, respectively. It shows that cascading time can be seen as a sum of single-mode pumping times, by introducing a novel modal decomposition. The strength of both measures is that they do not require numerical simulations, allowing easy optimization of the NES. The influence of different nonlinearities on the TET and RCC performance is investigated. Actual numerical simulations presented in the study validate the merit of both the pumping time and cascading time.

Kevin Dekemele, Robin De Keyser, Mia Loccufier (2018). Performance measures for targeted energy transfer and resonance capture cascading in nonlinear energy sinks. Nonlinear Dynamics, 93, 259-284.

In this paper, a technique is presented for the detection and localization of an open crack in beam-like structures using experimentally measured natural frequencies and the Particle Swarm Optimization (PSO) method. The technique considers the variation in local flexibility near the crack. The natural frequencies of a cracked beam are determined experimentally and numerically using the Finite Element Method (FEM). The optimization algorithm is programmed in MATLAB. The algorithm is used to estimate the location and severity of a crack by minimizing the differences between measured and calculated frequencies. The method is verified using experimentally measured data on a cantilever steel beam. The Fourier transform is adopted to improve the frequency resolution. The results demonstrate the good accuracy of the proposed technique

Samir Khatir, Kevin Dekemele, Mia Loccufier, Tawfiq Khatir, Magd Abdel Wahab (2018). Crack identification method in beam-like structures using changes in experimentally measured frequencies and Particle Swarm Optimization. Comptes Rendus. Mécanique, 346(2), 110-120.