In this paper, the use of the combined deterministic-stochastic subspace identification algorithm for the experimental modal analysis of mechanical structures is discussed. The algorithm requires artificial forces to be applied to the structure, so it can be used for experimental modal analysis (EMA). The algorithm can also be used for operational modal analysis (OMA), since the excitation level of the artificial force(s) can be low compared to the excitation level of the ambient forces. Both the modes that are artificially excited and those that are excited by the ambient forces are identified. This type of operational modal analysis is called an OMAX analysis (Operational Modal Analysis with eXogenous inputs) [1]. The main advantages of OMAX over OMA are that the modes that are excited by the artificial forces can be scaled to unity modal mass and that a higher number of modes can be identified.

Reference-based combined deterministic-stochastic subspace identification for experimental and operational modal analysis

Piezoelectric energy harvester for rolling bearings with capability of self-powered condition monitoring

Dynamically synergistic regulation mechanism for rotation energy harvesting

Optimal Hilbert transform parameter identification of bistable structures


 The main purpose of wearable energy harvesting devices is to replace the chemical battery and supply enough power for portable devices. Therefore, this paper derives the function expression of harvested energy via frequency ratio (excitation frequency/natural frequency) and external resistance, aiming to optimize running conditions directly in practical matters. It proposes that when energy harvesting devices work at direct force excitation the optimal condition is the frequency ratio equal to one. But the optimal excitation frequency is related to damping at base excitation, When the value of the damping ratio is less than 0.258, there is a local peak output power. Conversely, the larger excitation frequency is the larger output power is. The optimal external resistance is related with back EFM constant of the electromagnetic transducer at both cases. In the end, some experiment was conducted to study the relationship between output and some parameters.

Multi-Parameter Coupling Effect of Wearable Energy Harvesting Backpack From Human Motion

Nonlinear piezoelectric structures have attracted great attention in energy harvesting, vibration control, and morphing structures recently. The most important design and dynamic analysis parameters in a nonlinear piezoelectric structure is the nonlinear stiffness force. However, the nonlinear stiffness force is difficult to calculate analytically or measure statically under complicated practical engineering conditions. Therefore, this paper utilizes signal decomposition and the Hilbert transform-based method for the precise identification of stiffness force of a class of typical nonlinear piezoelectric structures. The quasi-zero stiffness, bistable stiffness, and tristable stiffness structures are designed in the magnetic coupled piezoelectric cantilever beam system. The identification process and the applicability based on free vibration and forced frequency-swept response for different nonlinear structures will be discussed. Numerical examples of quasi-zero stiffness, bistable stiffness, and tristable stiffness nonlinear piezoelectric structures show the necessity to choose the reasonable free decay and the forced frequency-swept response for accurate identification. In the experimental condition, the identified nonlinear stiffness force keeps in good agreement with the measurement by the dynamometer.

Zehao Hou

Papers

Optimal Hilbert transform parameter identification of bistable structures

Multi-Parameter Coupling Effect of Wearable Energy Harvesting Backpack From Human Motion

Identification of Stiffness Force in Nonlinear Piezoelectric Structures Based on Hilbert Transform

Biomechanical modeling and experiments of energy harvesting backpacks