This paper presents the results of numerical simulations of a non-linear, tristable system for harvesting energy from vibrating mechanical devices. Detailed model tests were carried out in relation to the system consisting of a beam and three permanent magnets. Based on the derived mathematical model and assuming a range of control parameter variability, a three-dimensional image of the distribution of the largest Lyapunov exponent was plotted. On its basis, the regions of chaotic and predictable movement of the considered system exist have been established. With reference to selected plane of the largest Lyapunov exponent cross-sections, possible co-existing solutions were identified. To identify multiple solutions, a diagram of solutions (DS) diagram was used to illustrate the number of existing solutions and their periodicity. The proposed calculation tool is based on the so-called fixed points of Poincaré cross-section. In relation to selected values of the control parameter ω, coexisting periodic solutions were identified for which phase trajectories and basins of attraction were presented. Based on the model tests carried out, it was found that in order to efficiently harvest energy, appropriate transducer adjustment is required. Calibration of the transducer is necessary to obtain the greatest amplitude of vibration of the beam, which corresponds to the phase trajectory limited by external energy potential barriers. As expected, the average voltage induced on the electrodes of the piezoelectric transducer and the average electrical power recorded on the resistive element are directly proportional to the amplitude and average kinetic energy of the beam.
In this paper, we apply empirical mode decomposition by Huang and Hilbert to transform signals recorded during a milling process.Vibroacoustic sensors recorded vibrations of a tool-workpiece system while milling with the end mill of a special shape of "Hi-Feed".The results of Huang-Hilbert analysis provide the information about amplitudes and frequencies of empirical modal components.Application of Huang-Hilbert transform to cutting conditions monitoring allows the separation of various vibration components caused by phenomena associated with the drive system and the machine components.Therefore, the analysis highlights vibrations caused by known sources of vibration, such as spindle speed, the number of teeth of the cutting tool or the frequency of vibration tools.Furthermore, signal components generated in the cutting zone were identified.The resulting information helps to assess the working conditions of cutting tools, selection of cutting parameters and tool wear monitoring.
This work introduces the aspects of the proper choice of the exploitation data connected with heat supplied to a building in order to estimate the influence of wind speed, insolation or level of cloudiness on energy consumption. The analyzed building had a traditional, central heating installation with vertical risers in each flat and convective radiators and supplied with the heating medium (80/60 °C). The exploitation data from one heating season were analyzed and the influence of the wind speed within the range below 3 m/s, 3÷6 m/s and above 6 m/s on the value of the heat power delivered to the building was presented. Different times of the day and night were taken into account and the attention to the accuracy of obtained results was paid.
Roving composites are used in the production process of critical supporting structures. The mechanical properties of the composites depend on the even distribution of the fibers. Monitoring of geometrical measures of composites microstructure can be used for prediction of material strength and durability. In the paper results from the research performed on the production samples of girders of helicopter blades are presented. Some geometrical properties, like: the average fiber diameter D, matrix film thickness average GAB and its standard deviation were used for specimens classification by the value of the flexural elastic modulus. The topological measure GAB is intendent to evaluate of the fibers distribution. Applicability of the measure has been checked based on strength tests results. The uniformity of the fiber distribution expressed by the averaged GAB measurement allows for estimation of the composite strength. Additionally the quantitative character of the measure GAB take in defects occuring in the internal structure of composites.
Abstract The objective of this study is to investigate the possibility of enhancing mechanical properties of poly(lactic acid) (PLA) samples processed by a rapid manufacturing (RM) technique by increasing PLA crystallinity degree via thermal annealing. The samples are manufactured by fused deposition modeling (FDM) at different temperatures and subsequently evaluated by three‐point bending flexural and tensile tests. The polymer processed at 215 °C is thermally annealed over its glass transition temperature in order to increase the degree of crystallinity to the maximum attainable level as measured by the differential scanning calorimetry and confirmed by X‐ray diffraction. The increase in the degree of crystallinity of FDM‐PLA enhances flexural stress of the samples by 11–17%. The study also demonstrates applicability of radiation sterilization for FDM‐PLA parts. Therefore, thermal annealing might be introduced into a standard RM technology of PLA, particularly for sterilizable customized implants, to efficiently improve their mechanical properties.
A concept of non-linear electromagnetic system with the rotational magnetic pendulum for energy harvesting from mechanical vibrations was presented. The system was stimulated by vertical excitation coming from a shaker. The main assumption of the system was the montage of additional regulated stationary magnets inside coils creating double potential well, and the system was made with a 3D printing technique in order to avoid a magnetic coupling with the housing. In validation process of the system, modelling of electromagnetic effects in different configurations of magnets positions was performed with the application of a finite element method (FEM) obtaining the value of magnetic force acting on the pendulum. A laboratory measurement circuit was built and an experiment was carried out. The voltage and power outputs were measured for different excitations in range of system operational frequencies found experimentally. The experimental results of the physical system with electrical circuit and numerical estimations of the magnetic field of a stationary magnet’s configuration were used to derive a mathematical model. The equation of motion for the rotational pendulum was used to prove the broadband frequency effect.
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