Andrzej Rysak

Experimental analysis of the dynamical response of energy harvesting devices based on bistable laminated plates.

The use of bistable laminates is a potential approach to realize broadband piezoelectric based energy harvesting systems. In this paper the dynamic response of a piezoelectric material attached to a bistable laminate plate is examined based on the experimental generated voltage time series. The system was subjected to harmonic excitations and exhibited single-well and snap-through vibrations of both periodic and chaotic character. To identify the dynamics of the system response we examined the frequency spectrum, bifurcation diagrams, phase portraits, and the 0–1 test.

Dynamic Response of a Pendulum-Driven Energy Harvester in the Presence of Noise

This paper presents time- and frequency-domain analyses of a previously reported wave energy harvesting system in the presence of noise. The energy harvester comprises a pendulum that drives two DC generators connected electrically in series. A mechanical model of the wave energy harvester is developed and simulated in Matlab. The output voltage and output power of the energy harvester is evaluated and compared for two input signal types: a deterministic case and a stochastic case. The latter consists of a white noise random excitation source that is bounded in amplitude at a fixed standard deviation. Simulation results indicate that a stochastic input signal shows considerable influence on the output characteristics of the energy harvester. The simulation models developed in this paper can be used to complement the design of resonant frequency tuning electronics for energy harvesting systems.

Self-aggregation Phenomenon and Stable Flow Conditions in a Two-Phase Flow Through a Minichannel

Abstract By increasing a water flow rate of the two-phase (air–water) flow through a minichannel, both the partitioning of air slugs into air bubbles of different sizes and small air bubbles aggregation into larger air bubbles were identified. These phenomena were studied in detail by using the corresponding sequences of light transmission time series recorded with a laser-phototransistor sensor. To distinguish any instabilities in air slugs along with their break-ups and aggregations, the recurrence plots and recurrence quantification analysis were applied.

Vertical beam modal response in a broadband energy harvester

We examined energy harvesting using a vertical composite laminate beam with an additional moving mass subjected to kinematic harmonic excitation. The gravity effect and the moving tip mass applied to the system cause considerable changes in effective spring-mass characteristics of the bending beam. Simultaneously, we observed dynamical beam damping by an additional degree of freedom and non-linear effects including friction between the moving mass and the beam structure. The experiments were performed on the beam excited kinematically by a shaker, while beam velocity measurements were made by a scanning laser vibrometer. We applied modal analysis in the limit of a fairly low excitation level. The selected modal vibrations are illustrated by corresponding output time series.

Analysis of Non-stationary Signals by Recurrence Dissimilarity

We propose a new method for testing non-stationary and intermittent signals. Using a basic recurrence plot quantifier, i.e. a recurrence rate, we create a relative measure which is sensitive to changes in the nature of signal. Given the specificity of this measure, we call it recurrence dissimilarity (RD). First, we test it using well-known non-linear systems for which we generate signals with different intermittent characteristics. In addition, the generated signals are disturbed by noise. The effectiveness of our measure is verified by applying different variables and noise levels. The results allow us to draw a number of conclusions concerning the proposed method. Finally, we give examples of using this method for experimental data analysis. We report the results of detecting changes in flowing patterns in two-phase flows and of switching heart modes in the signals recorded in ECG Holter tests.

Dynamics of Two-Phase Flow through a Minichannel: Fourier and Multiscale Entropy Analyses

By changing a air flow rate of the two-phase (air-water) flow through a minichannel weidentified aggregation and partitioning of air bubbles and slugs of different sizes and air bubble arrangement into periodic patterns. The identification of these spatio-temporal behaviour was doneby digital camera. Simultaneously, we provide the detailed studies of these phenomena by using thecorresponding sequences of light transmission time series recorded by a laser-phototransistor sensor.To distinguish the instabilities in air slags and their breakups and aggregations we used the Fourierand multiscale entropy analysis.

Dynamics of Composite Milling: Application of Recurrence Plots to Huang Experimental Modes

We study the dynamics of a milling process of a composite material basing on the experimental time series of cutting force components measured in the feeding direction. By using the recurrence plots we observe the differences in the response of the system depending on the feeding direction with respect to composite fibers orientation. This effect has been found after decomposition on the Huang experimental modes. Showing the results of recurrences in particular experimental modes we advocate to use this quantity to analyze the stability of the cutting of composites. The difference between different cases was also noticed using Fourier transform and statistical parameters such as RMS and kurtosis, but for these methods the necessary time interval of the examined time series has to be much longer, while recurrence approach is designed for shorter time series.

Gas Bubbles and Slugs Crossover in Air–Water Two-phase Flow by Multifractals

Abstract Slugs and bubbles two-phase flow patterns dynamics in a minichannel are analysed. During the experiment, the volume flow rates of air and water were changed. We study transition of bubbles to slugs two-phase flow patterns using Fourier and multifractal approaches to optical transitivity signal. The sequences of light transmission time series are recorded by a laser-phototransistor sensor. Multifractal analysis helps to identify the two-phase structure and estimate the signal complexity. Especially, we discuss occurrence and identification of a self-aggregation phenomenon. These results are compared to corresponding Fourier spectra. The results indicate that the fractality is a an important factor influencing the distribution of the gas phase in water.

Study of the High-Amplitude Solutions in the System of Magnetic Sliding Oscillator with Many Degrees of Freedom

Magnetic interactions are strongly non-linear, especially for small distances between magnets. Their implementation to the oscillator gives it the ability to display complex non-linear and chaotic behaviours. These phenomena under certain conditions can lead to widening of the vibration bandwidth of the system which in the case of energy harvesting systems increases their efficiency, especially under varying excitation conditions. In this paper we compare the numerical and experimental study of different systems of longitudinal magnetic oscillators with one and many degrees of freedom. Tested oscillator configurations differ in magnet parameters and system rigidity. In systems modelling we look for conditions in which the high-amplitude solutions occur over a wide frequency range. Predictions of models are next verified in experimental investigations.

Dynamics and Noise Level Estimation in Two-Phase Flow through a Mini Channel

By changing air to water flow rates of a two-phase flow through a minichannel we identified aggregation and partitioning of air bubbles and slugs of various sizes. It was found that for some flowconditions air bubbles formed periodic patterns. The identification of the spatio-temporal behaviourswas performed with a laser transitivity sensor and confirmed by a digital camera. We used the Hurstexponent to distinguish instabilities in air slugs, their breakups and aggregations. In addition, we performed noise level estimation.