Energy harvesting from train vibrations

In this paper, linear mechanical oscillators are designed to harvest energy from train-induced vibrations. The harvested energy could be used, for example, to charge sensors mounted on the rail track for structural health monitoring. The dominant frequencies due to a passing train are determined for a specific train and speed from a recorded acceleration time-history. Using a simple model of an oscillator, the total energy harvested for the passage of one train is calculated. The stiffness, and hence the tuning frequency of the device, is varied in simulations to determine the optimum frequency at which to tune the device for a constant value of mass and damping in the device. Further simulations are conducted to investigate the power that could be harvested from multiple oscillators tuned at several dominant frequencies, and their performances are analysed and compared. The constraint for maximum relative displacement is considered in the design of each harvester, and this is adopted to assure that the amplitude of the oscillation is finite and does not exceed the physical size of the device. The robustness of the harvester is also analysed for different train speeds

Receptance based approach for control of floor vibrations

This is the author accepted manuscript. The final version is available from the publisher via the link in this record.Advances in design, materials and construction technologies, coupled with client and architectural requirements, are some of the drivers for light-weight and slender pedestrian structures, which are becoming increasingly susceptible to human induced vibrations. The use of active control techniques is progressively being viewed as a more feasible approach for suppressing such vibrations compared with traditional passive technologies. In this paper, the principles of the receptance based approach are exploited to design appropriate feedback gains that place the eigenvalues of selected vibration modes of an experimental footbridge structure at selected locations thereby enhancing its vibration performance. These studies are based on a single-input multiple-output (SIMO) controller structure comprising of a single control actuator and two sensors. It is seen that this has the potential to offer additional design freedoms beyond purely a direct velocity feedback (DVF) controller. A comparative study is carried out with a DVF controller implemented in a single-input single-output (SISO) scheme. This work presents the analytical determination of appropriate feedback gains from results of experimental modal analysis (EMA) on the structure and thereafter the experimental implementation of these feedback gains. Vibration mitigation performance is evaluated through both changes in measured transfer functions and reductions in response under single pedestrian excitation

Eigenvalue sensitivity minimisation for robust pole placement by the receptance method

The problem of robust pole placement in active structural vibration control by the method of receptance is considered in this paper. Expressions are derived for the eigenvalue sensitivities to parametric perturbations, which are subsequently minimised to improve performance robustness of the control of a dynamical system. The described approach has application to a vibrating system where variations are present due to manufacturing and material tolerances, damages and environment variabilities. The closed-loop eigenvalue sensitivities are expressed as a linear function of the velocity and displacement feedback gains, allowing their minimisation with carefully calculated feedback gains. The proposed algorithm involves curve fitting perturbed frequency response functions, FRFs, using the rational fraction polynomial method and implementation of a polynomial fit to the individual estimated rational fraction coefficients. This allows the eigenvalue sensitivity to be obtained entirely from structural FRFs, which is consistent with the receptance method. This avoids the need to evaluate the M,C,K matrices which are typically obtained through finite element modelling, that produces modelling uncertainty. It is also demonstrated that the sensitivity minimisation technique can work in conjunction with the pole placement and partial pole placement technique using the receptance method. To illustrate the working of the proposed algorithm, the controller is first implemented numerically and then experimentally

Nonlinear vibrations of a stroke-saturated inertial actuator

Proof-mass actuators are typically used to supply an external control force to a structure,for the purpose of vibration suppression. These devices comprise a proof-mass suspended in a magnetic field that is accelerated in order to provide a reaction force on the actuator casing and the structure itself. If the actuator stroke length is reached or exceeded, the proof-mass will hit the end stops, resulting in a nonlinear phenomenon known as stroke saturation. In this paper, a theoretical and experimental investigation into the actuator’s dynamical behaviour is undertaken. First, the blocked inertial force of the actuator in response to an input voltage was measured experimentally using a variety of excitation amplitudes and frequencies. An analysis was conducted in the time- and frequency-domains, and the first-order force-voltage FRF of the actuator was ascertained for each excitation amplitude. The information provided by the analysis was then used to estimate the parameters for a linear piecewise stiffness model of the actuator, in order to simulate the time-domain response. Finally, a comparison of the simulated and measured signals is conducted to establish the accuracy of the model

Active control of parametrically excited systems

This article discusses active control of parametrically excited systems. Parametric resonance is observed in a wide range of applications and can lead to high levels of unwanted motion. For example, in cable-stayed bridges, the vibration of the deck excites the cables axially, inducing a periodically time-varying tension. If the frequency of deck vibration is about twice the natural frequency of the cable, a parametric resonance occurs and leads to a large-amplitude swinging motion of the cable. To tackle the consequences of parametric instability, active vibration control employing a piezoelectric actuator is proposed in this article. We consider a beam subjected to an axial harmonic load that represents a parametrically excited system with a periodically varying stiffness. Using both analytical and experimental methods, we assess the stability of the beam and propose active control aimed at relocating the transition curves and hence stabilising the system via velocity feedback and pole placement. Analytical relationship between the transition curves and the poles of the system is derived. Transition curves can be assigned to a prescribed location using appropriate velocity and displacement control gains. Finally, we demonstrate the proposed approach with experiments on a beam equipped with a macro fibre composite patch

Gust load alleviation using nonlinear feedforward control

A strategy based on feedforward control for gust loads alleviation of a nonlinear aeroelastic model is considered. The model is representative of a typical wing section with a trailing-edge flap and with a polynomial nonlinearity in the structural model. The aerodynamics is given by thin aerofoil theory. First, the effects of structural nonlinearity in the dynamic response of the open-loop system are evaluated. Then, it is shown that the performance of the controller is greatly affected by the approximations made in the internal model of the controlled plant. To suppress gust-induced vibrations of an intrinsically nonlinear plant, the control performance is degraded when using a linear representation for the internal model. The control strategy performs well when including all nonlinearities in the mode

Extended frequency bandwidth through multi-degree-of-freedom nonlinear magneto-mechanical energy harvesting

Energy harvesting from different vibration sources is typically designed by means of a single degree of freedom approach and implementing both linear and nonlinear principles and techniques. In this paper, starting from the experience of the authors in different applications and using linear magneto-inductive electromechanical oscillators, a two-degree-of-freedom energy harvester is designed with the aim of supplying sensors in a wing typical section. The energy harvester can be modelled as a system of two masses with linear springs or nonlinear elastic interactions due to magneto-static forces. The equivalent mechanical dampers of the same device are four coils that can be connected to the electric interface and then to the electric load circuit. The strong improvement of this simple extension of a linear generator with two degrees of freedom relies on the dynamic improvements of the coupling to the source that can be tuned in order to increase the frequency bandwidth of the device. The simulations show that, although the limited stroke of the magnets and the undesired mechanical friction can reduce the energy harvested, the nonlinearities of the magnetic forces and fluxes can represent an effective advantage, in particular, in a multi-degree of freedom system subject to a large frequency bandwidth input or random excitations. Potential perspectives could be also implemented through semi-active or active strategies obtained through the electric interface