We propose a multi-modal vibration energy harvesting approach based on arrays of coupled levitated magnets. The equations of motion which include the magnetic nonlinearity and the electromagnetic damping are solved using the harmonic balance method coupled with the asymptotic numerical method. A multi-objective optimization procedure is introduced and performed using a non-dominated sorting genetic algorithm for the cases of small magnet arrays in order to select the optimal solutions in term of performances by bringing the eigenmodes close to each other in terms of frequencies and amplitudes. Thanks to the nonlinear coupling and the modal interactions even for only three coupled magnets, the proposed method enable harvesting the vibration energy in the operating frequency range of 4.6-14.5 Hz, with a bandwidth of 190% and a normalized power of 20.2 mW cm g 3 2 --.

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Date palm, the most important tree in Saudi Arabia and the Middle East, produces a huge amount of waste yearly in the form of fibrous materials, dried fruits, and seeds. Such waste is a great source of excellent degradable biomass that can be used in numerous applications as natural fiber composites, active carbon precursors, and even nano-featured sheets. That rich resource is yearly burned on date palm farms due to the lack of effective processing strategies. This review offers a scientific evaluation for date palm waste in terms of specifications and applications, and it proposes pre-treatment processes to produce fibrous and powder raw materials to be used in some engineering and industrial applications. Additionally, some possible advanced industrial applications, such as active carbon and natural fiber composites, will be discussed and reviewed.

International audienceKeywords: Sandwich GHM viscoelastic model FEM Model reduction methods Frequency analysis Time analysis This paper deals with modeling and model reduction methods intended to sandwich structures with viscoelastic materials. The modeling step is carried out by combining the First order shear deformation theory (FSDT) with the Golla–Hughes–Mc Tavish (GHM) model. The GHM model introduces auxiliary coordinates to take into account the frequency dependence of viscoelastic materials which, combined with the finite element method (FEM), leads to large order models. This paper focuses on the use of model reduction methods. The reduced models compared to the full model are illustrated by three numerical examples in order to outline the performance, the practical interest of these methods and their validity domains