Different Types Of Excitation Research Articles

Unified strategy for overall impedance optimization in vibration-based electromagnetic energy harvesters

Vibration-based electromagnetic energy harvesters involve an apparent coupling effect between the dynamics of mechanical structures and electric circuit. Such a coupling effect complicates the impedance optimization of energy harvesting circuit in the design of energy harvesters. The classical impedance matching, which ignores the coupling effect, becomes inapplicable. This paper proposes a unified overall impedance optimization strategy for the harvesting circuit to achieve the maximum output power and power efficiency, and such a unified strategy is applicable to a number of cases with different structural complexity, different types of excitations, and different levels of coupling effects between mechanical and electrical systems. By converting the mechanical structures of single-degree-of-freedom (SDOF) and multiple-degree-of-freedom (MDOF) energy harvesters into equivalent circuit models, the electro-mechanical coupling is simplified as the coupling effect inside an electric circuit. This conversion provides insight into the overall impedance optimization framework from the pure electric circuit perspective. Different optimal impedance values of energy harvesting circuits under different excitation types (harmonic and random) are derived within the proposed overall impedance optimization framework. The optimal impedance values for the maximum output power depend on the circuit dynamics, structural characteristics, and excitation types. Meanwhile, the optimal impedance values for the maximum power efficiency are related to the inherent damping of the structure and transducer but independent of excitation types. Numerical simulations of various cases were conducted, including resonant, non-resonant, and random excitation, in the SDOF and MDOF harvesters. Simulation results successfully validate the effectiveness and accuracy of the proposed overall impedance optimization strategy for enhancing the harvesting performance of vibration-based electromagnetic energy harvesters.

Evaluation of Energy and Power Flow in a Nonlinear Energy Sink Attached to a Linear Primary Oscillator

Abstract The objective of this study is to develop a novel methodology to assess the energy flow between a nonlinear energy sink (NES) and the primary system it is attached to in terms of energy orientation, which is directly related to the sign of the power present on the primary system. To extend the work done in previous studies, which have focused primarily on the analytical treatment, characterization, and performance evaluation of NES as passive nonlinear dampers for structures under different types of excitations, this study incorporates a methodology for determining whether energy is entering or leaving a primary oscillator when interacting with an NES, by means of considering the power flow of the primary oscillator. Several current measures for evaluating the effectiveness of the NES at extracting and dissipating energy irreversibly are considered through numerical simulations of systems with different damping cases of the NES. Each case provides a different dissipation scenario in the combined system, which is subjected to different types of base excitation signals such as impulse and seismic records. The methodology is further validated experimentally using a two degrees-of-freedom system with an NES attached to the second mass. Comparisons of the modeled responses versus the measured responses are provided for several physical damping realization scenarios in the NES.

Assessment of a force–displacement based multiple-vertical-line element to simulate the non-linear axial–shear–flexure interaction behaviour of reinforced concrete walls

A comprehensive assessment of a new version of the macroscopic force–displacement based multiple-vertical-line element (SFI-MVLEM-FD), which can be used to simulate non-linear axial–shear–flexure interaction in RC walls, is presented. The element models the shear response taking into account all the basic physical mechanisms that transfer shear forces over cracks: (a) the dowel effect of vertical bars, (b) the axial resistance of horizontal/shear bars, and (c) the interlocking of aggregate particles in cracks. In order to provide a wide range of its use, and to enable the analysis of various types of buildings, the SFI-MVLEM-FD element was included in the local version of the OpenSees program system. The element was assessed with respect to already performed quasi-static cyclic experiments of various RC shear walls. In this paper, the results of numerical analyses of two representative rectangular walls, where the influence of shear on the overall response was of particularly significance, are presented and compared with those obtained in the experiments. In order to estimate the efficiency of the new element in more general cases, it was also assessed by means of a large-scale shake-table test of a typical non-planar lightly reinforced RC coupled wall. The test examples showed that the SFI-MVLEM-FD model can capture all the important mechanisms of the response, as well as being able to efficiently describe the axial–shear–flexure interaction in various types of RC walls: (a) rectangular and non-planar, (b) cantilever and coupled, and (c) subjected to different types of excitation, uni-axial or bi-axial. It was found that the model is capable of clearly identifying the three fundamental mechanisms, which contribute to shear resistance. This is one of the few models, which are able to describe the significant deterioration of the (shear) strength of RC walls that are near to collapse for different reasons: e.g. the buckling of their longitudinal bars, rupture of the horizontal reinforcement, and other significant degradation of different types of shear mechanism. This makes it suitable for the analysis of different types of RC walls, which are subjected to different levels of seismic excitations. It is even able to simulate the near collapse response influenced by very different collapse mechanisms.

Three-dimensional periodic materials as seismic base isolator for nuclear infrastructure

Recent advance of periodic materials from the field of solid-state physics into that of earthquake engineering has resulted in a novel seismic isolation technique. In this study, we developed a new configuration of structural foundation using a three-dimensional (3D) periodic material for seismic isolation of critical infrastructure, particularly nuclear infrastructure. To this aim, we first performed analytical and finite element studies to compare two different types of 3D unit cells, i.e., Bragg Scattering and Locally resonant unit cells, to investigate their characteristics and applicability as a seismic isolator. We then designed a large scale test specimen based on the Bragg-scattering type unit cell using common construction materials: reinforced concrete blocks and polyurethane sheets. The designed test specimen was constructed and tested using a shake table subjected to different types of excitations in the horizontal and vertical directions as well as the torsional mode. The dynamic response of a small modular reactor (SMR) building model protected by the 3D periodic foundation demonstrates that 90% response reduction was achieved within the frequency band gaps. The response attenuation was achieved in all three tested directions. Moreover, the periodic foundation-isolated SMR building exhibited a stable response with negligible rocking on the structural system.

The influence of vibration duration on the structure of irregular RC buildings

In the twenty-first century, the seismic design of buildings seems to have become a fully recognised topic. There are guidelines and standards which should be taken into account by designers in seismic areas. Designers using modern international guidelines have ascertained that the behaviour of structures is not as expected. This may be the result of not taking into account the duration of the shock. The duration of surface vibrations could be one of the basic reasons why some buildings collapse or suffer severe damage to bearing systems as a result of long-duration earthquakes despite being properly designed in accordance with current understanding. Another primary reason for such collapse or damage is that some buildings in seismic areas have irregular structural systems that are sensitive to torsional vibrations. In this paper, a five-storey, irregular-shaped RC building model was subjected to different types of excitations: mining tremors, short-duration earthquakes, long-duration earthquakes. The first stage was a modal analysis based on in situ measurement. After model verification using in situ measurements, the building was then subjected to the three forms of excitation. Numerical studies were performed using a verified FEA model of the building in the time domain. The results of the calculations prove that the duration of the intensive phase of extortion is one of the reasons for the lack of building collapse in mining areas. In cases of mining shocks with a short duration of surface vibration, damage to buildings may occur which does not threaten the safety of their construction. Building collapses occur with earthquakes which are characterised by a much longer duration of the intensive phase of excitation compared to mining shocks. The results of in situ observations of RC structures that have survived a history of mining shocks of varied intensities confirm the results of numerical analyses.

Design criteria for optimally tuned vibro-impact nonlinear energy sink

This paper proposes the design criteria for optimally tuned Vibro-Impact (VI) Nonlinear Energy Sink (NES) to control vibration under periodic and transient excitation. Firstly, a generalized dimensionless model of a two degrees of freedom (DOF) system comprising a harmonically excited linear oscillator (LO) strongly coupled to a VI NES is investigated. Bifurcation analysis and efficiency of Targeted Energy Transfer (TET) around the Slow Invariant Manifold (SIM) are studied with the variation of clearance. As a result, the optimal clearances for periodic and transient excitation are calculated from two transition points of the SIM, respectively. Then the procedure is extended to the case of multiple VI NESs in parallel with the LO. Two principles of additivity and separate activities of VI NESs are verified theoretically. Finally, experiments involving the whole system embedded on an electrodynamic shaker are performed. The results show that the design criteria can not only predict the efficient TET at resonance frequency, but can also achieve an optimal performance in a range of frequencies. Furthermore, the criteria can be straightforward for the application of multiple VI NESs, so as to make VI NESs work robustly under different types of excitation.

Study of luminescent properties of Al-Si-N films

In this study, we analyzed the optical properties of Ai-Si-N coatings applied on silica glass. Under the effect of optical radiation and electron beam, intense luminescence of Al-Si-N films with complex emission spectra is observed. Photoluminescence excited by the radiation with energy of 4.47 eV, which falls within the opaque range of the films, is likely connected with surface luminescence centers. The film luminescence demonstrates that luminescence spectra excited in different ways do not coincide. This indicates that there are different luminescence centers in Al-Si-N films. These centers are excited with different efficiency at different types of excitation.

Ion energy and angular distributions in low-pressure capacitive oxygen RF discharges driven by tailored voltage waveforms

We investigate the energy and angular distributions of ions reaching the electrodes in low-pressure, capacitively coupled oxygen radio-frequency discharges. These distributions, as well as the possibility of the independent control of the ion flux and the ion energy are analysed for different types of excitation: single- and classical dual-frequency, as well as valley- and sawtooth-type waveforms. The studies are based on kinetic, particle-based simulations that reveal the physics of these discharges in great detail. The conditions cover weakly collisional to highly collisional domains of ion transport via the electrode sheaths. Analytical models are also applied to understand the features of the energy and angular distribution functions.

Approximate Solution of the Fokker–Planck Equation for a Multidegree of Freedom Frictionally Damped Bladed Disk Under Random Excitation

Bladed disks are subjected to different types of excitations, which cannot, in any, case be described in a deterministic manner. Fuzzy factors, such as slightly varying airflow or density fluctuation, can lead to an uncertain excitation in terms of amplitude and frequency, which has to be described by random variables. The computation of frictionally damped blades under random excitation becomes highly complex due to the presence of nonlinearities. Only a few publications are dedicated to this particular problem. Most of these deal with systems of only one or two degrees-of-freedom (DOFs) and use computational expensive methods, like finite element method or finite differences method (FDM), to solve the determining differential equation. The stochastic stationary response of a mechanical system is characterized by the joint probability density function (JPDF), which is driven by the Fokker–Planck equation (FPE). Exact stationary solutions of the FPE only exist for a few classes of mechanical systems. This paper presents the application of a semi-analytical Galerkin-type method to a frictionally damped bladed disk under influence of Gaussian white noise (GWN) excitation in order to calculate its stationary response. One of the main difficulties is the selection of a proper initial approximate solution, which is applicable as a weighting function. Comparing the presented results with those from the FDM, Monte–Carlo simulation (MCS) as well as analytical solutions proves the applicability of the methodology.

A two-step method for damage identification in beam structures based on influence line difference and acceleration data

This article presents a two-step approach for structural damage identification in beam structure. Damages are located using the influence line difference before and after damage, the calculation of damage severity is accomplished by acceleration data and bird mating optimizer algorithm. Local damages are simulated as the reduction of both the elemental Young’s modulus and mass of the beam. The technique for damage localization based on displacement influence line difference and its derivatives for beam structure has been outlined. An objective function that comprises dynamic acceleration is utilized in bird mating optimizer. All data are originated from only a few measurement points. Two numerical examples, namely, a simply supported beam and a four-span continuous beam, are investigated in this article. Identification results from different objective functions are compared with results from objective function conventional modal assurance criterion, which shows the superiority of the proposed function. In addition, results of dynamic responses under different types of excitation are presented. The effect of measurement noise level on damage identification results is studied. Studies in the article indicate that the proposed method is efficient and robust for identifying damages in beam structures.

Parameter design of a multi-delayed isolator with asymmetrical nonlinearity

In this study, based on the analysis of multiple nonlinear vibration properties, the criterions of parameter design for different types of excitations and structural nonlinearities are proposed for vibration isolation. For a nonlinear vibration isolation system with Quasi-Zero-Stiffness property, the assembly process and stiffness property with different masses of isolation object are taken into account. In order to improve the isolation effectiveness in a wide frequency band, the relation between vibration performances and parameters is established. The effect of adjustable parameters on the vibration features and the effect mechanisms of multiple time delays are discussed in details based on the method of multiple scales. Because the study takes full consideration of the effect of structural nonlinearity and transition mechanism of vibration performances, the proposed criterions for parameter design could solve the conflict between the improvement of isolation effectiveness and complexity or bifurcation brought by nonlinearity. The results in this paper show that without changing the High-Static-Low-Frequency advantage brought by the nonlinear isolation structure, the isolation effectiveness could be improved in a wide frequency band.

Synchronisation phenomenon in three blades rotor driven by regular or chaotic oscillations

The goal of the paper is to analysed the influence of the different types of excitation on the synchronisation phenomenon in case of the rotating system composed of a rigid hub and three flexible composite beams. In the model is assumed that two blades, due to structural differences, are de-tuned. Numerical calculation are divided on two parts, firstly the rotating system is exited by a torque given by regular harmonic function, than in the second part the torque is produced by chaotic Duffing oscillator. The synchronisation phenomenon between the beams is analysed both either for regular or chaotic motions. Partial differential equations of motion are solved numerically and resonance curves, time series and Poincaré maps are presented for selected excitation torques.

Vibration Analysis of a 51-Story Tower from the Recorded Data of the Earthquake, Typhoon and Ambient Vibration

This study uses the in-structure recordings to investigate the vibration characteristics of a 51-story steel high-rise building in response to a major earthquake, typhoon and ambient vibrations. This presents an opportunity for us to compare the building behaviors, especially their modal properties under different types of excitation. First, we use a two-stage regression procedure to obtain the relations of the building response, including peak floor acceleration and velocity as a function of the wind speed and floor height of the building. Secondly, the structural dynamic characteristics of the high rise building, including the transfer functions and natural frequencies, excited by the Chi-Chi earthquake, Typhoon Aere, and ambient vibrations are also determined and compared. As a result, from the formulas for building response, the predicted peak floor acceleration is higher in the lateral (EW) component than in the longitudinal (NS) component. This is probably due to the greater stiffness of the building in the longitudinal direction than in the lateral direction. In addition, after having identified the 1st, 2nd, and 3rd natural frequencies using the recorded data from the earthquake, typhoon and ambient vibrations, the ranking of the fundamental natural frequencies from low to high is the Chi-Chi earthquake, Typhoon Aere and the ambient vibrations. This means that greater excitation forces of the earthquake have resulted in lower natural frequencies than that produced by the typhoon and ambient vibrations.

Characterizing human activity induced impulse and slip-pulse excitations through structural vibration

Many human activities induce excitations on ambient structures with various objects, causing the structures to vibrate. Accurate vibration excitation source detection and characterization enable human activity information inference, hence allowing human activity monitoring for various smart building applications. By utilizing structural vibrations, we can achieve sparse and non-intrusive sensing, unlike pressure- and vision-based methods. Many approaches have been presented on vibration-based source characterization, and they often either focus on one excitation type or have limited performance due to the dispersion and attenuation effects of the structures. In this paper, we present our method to characterize two main types of excitations induced by human activities (impulse and slip-pulse) on multiple structures. By understanding the physical properties of waves and their propagation, the system can achieve accurate excitation tracking on different structures without large-scale labeled training data. Specifically, our algorithm takes properties of surface waves generated by impulse and of body waves generated by slip-pulse into account to handle the dispersion and attenuation effects when different types of excitations happen on various structures. We then evaluate the algorithm through multiple scenarios. Our method achieves up to a six times improvement in impulse localization accuracy and a three times improvement in slip-pulse trajectory length estimation compared to existing methods that do not take wave properties into account.

Analysis and Design of Tapered Uniaxial-Anisotropic Dielectric Rod Antennas

A semi-analytical and efficient computational method is presented for the analysis of uniaxial-anisotropic tapered dielectric rod antennas (DRAs). This technique benefits of the local mode theory to predict the transverse distribution of polarization currents in the tapered dielectric rod. The method results in a formula for the radiation pattern that needs only simple integrations over the cross section of the antenna. Radiation patterns for DRAs of different length and radii are calculated. This technique is validated by the comparison with the data obtained from ANSYS Electronics Desktop full-wave simulator. Furthermore, it is demonstrated that the antenna gain and bandwidth increase over the isotropic DRAs. Also sinusoidal profiles have more gain compared to linear profiles. Moreover, the radiation patterns are calculated for different types of excitation to demonstrate that the method is applicable for any feed system.

Assessment of methodologies to estimate displacements from measured acceleration records

This study presents a comparative analysis of several methods to estimate displacements from measured accelerations records, with the objective of assessing their performance to compute displacements caused by different types of excitation (harmonic, vehicular, pedestrian, or seismic). The acceleration records were selected to be unaffected by tilts and rotation around a vertical axis. The study relevance is founded on the lack of agreement among researchers in relation to the validity/precision of displacements obtained from accelerations. Results show that there are two main groups of methods: one applies to signals with zero end displacements, and the other applies to more general movements. Except for cases with both much noise and small displacements, it is possible to compute displacements with high cross correlation coefficients and small errors, with respect to measured displacements. Results also indicate that the selection of the method to estimate displacements depends on: displacement amplitudes, type of waveform, type of information requiered (either the peak displacement or the whole displacement signal), and magnitude of the displacements at the record end.

A topology optimization formulation for transient design of multi‐entry laminated piezocomposite energy harvesting devices coupled with electrical circuit

SummaryLaminated piezocomposite energy harvesters (LAPEHs) are multilayer arrangements of piezoelectric and nonpiezoelectric materials. Multiple materials and physics, and dynamic analysis need to be considered in their design. Usually these devices are designed for harmonic excitation; however, they are subjected to other types of excitations. Thus, a novel topology optimization formulation is developed for designing LAPEHs that considers a combination of harmonic and transient optimization problems with the aim of designing the so‐called “multi‐entry" devices in which the power generated is the same for different types of excitation. LAPEHs are modeled by the finite element method, and the material model used for the piezoelectric layer is based on penalization and polarization model who controls material distribution and corresponding polarization. To optimize the RLC circuit, a novel linear interpolation model of coupled electrical impedance is also introduced to consider different magnitudes of the coupled impedance. The topology optimization problem seeks to maximize the active power generated by the LAPEH at its RLC circuit, to minimize its response time measured as the slope of the power versus time curve, and to maximize its stiffness. Numerical examples are shown to illustrate the potential of the method.

Transition sets analysis based parametrical design of nonlinear metal rubber isolator

This research proposes the parametrical design of Metal Rubber (MR) isolation platform based on the investigation of nonlinear vibration properties under different types of excitation. Based on the mechanical model established by experiments, the restoring force of the isolation platform is proposed as a nonlinear function in consideration of the stiffness nonlinearity and Coulomb friction of metal wires. Then, the perturbation method is utilized to solve the steady states whose local stability is studied by singularity theory. The main results obtained by singularity theory show that there are five different types of vibration property, and the critical conditions for the transformation of different vibration properties are defined by transition sets. For impact excitation, the optimum structural parameters are obtained based on the vibration dissipation time via nonlinear backbone analysis; for periodic excitation, the optimum structural parameters are determined according to multiple standards including the bandwidth for effective isolation, bandwidth for multi-steady states, resonance peak and displacement transmissibility in high frequency band etc. The vibration performances for optimum structural parameters are verified by dynamical experiments. In conclusion, this paper carries out a novel sight of choosing optimum parameters, and therefore provides the guidance for the utilization of MR isolation platform for different types of excitation in engineering practices.

Dynamical Stability Limit for the Charge Density Wave in K_{0.3}MoO_{3}.

We study the response of the one-dimensional charge density wave in K_{0.3}MoO_{3} to different types of excitation with femtosecond optical pulses. We compare direct excitation of the lattice at midinfrared frequencies with injection of quasiparticles across the low energy charge density wave gap and with charge transfer excitation in the near infrared. For all three cases, we observe a fluence threshold above which the amplitude-mode oscillation frequency is softened and the mode becomes increasingly damped. We show that all the data can be collapsed onto a universal curve in which the melting of the charge density wave occurs abruptly at a critical lattice excursion. These data highlight the existence of a universal stability limit for a charge density wave, reminiscent of the Lindemann criterion for the melting of a crystal lattice.

Normalized Study of Three-Parameter System in the Time Domain and Frequency Domain

Three-parameter isolation system can be used to isolate microvibration for control moment gyroscopes. Normalized analytical model for three-parameter system in the time domain and frequency domain is proposed by using analytical method. Dynamic behavior of three-parameter system in the time domain and frequency domain is studied. Response in the time domain under different types of excitations is analyzed. In this paper, a regulatory factor is defined in order to analyze dynamic behavior in the frequency domain. For harmonic excitation, a comparison study is made on isolation performance between the case when the system has optimal damping and the case when regulatory factor is 1. Besides, phase margin of three-parameter system is obtained. Results show that dynamic behavior in the time domain and frequency domain changes with regulatory factor. Phase margin has the largest value when the value of regulatory factor is 1. System under impulse excitation and step excitation has the shortest settling time for the response in the time domain when the value of regulatory factor is 1. When stiffness ratio is small, isolation performances of two cases are nearly the same; when system has a large stiffness ratio, isolation performance of the first case is better.