An approach to harvesting electrical energy from a mechanically excited piezoelectric element has been described. The topic of this paper studies the most important properties of piezoelectric polymer polyvinylidene fluoride (PVDF) in energy harvesting. We have chosen to develop a recovery application within the clothes. By the use of a piezoelectric energy harvester capable to convert the mechanical energy produced by the knee during walking to an electrical energy. This will be achieved by replacing the traditional textile of the kneepad with the one that is made of the technical textile based on acrylic knitted and PVDF as a patch stuck on the textile. Furthermore, PVDF has many unique features, such as excellent mechanical behavior, large strain without structure fatigue, which enables it to act strongly as the load bearing member, and corrosion resistance. The technical textile, functioning as multifunctional wearable human interfaces, is considered today as a useful tool in several energy fields. In this paper, a smart structure based on piezoelectric polymer (PVDF) has been presented, which a power analytical model, based on the frequency, the geometrical parameters and other factors were investigated. Furthermore, the set of numerical results illustrating the harvested power for a given size of the device has been performed and discussed and how this harvested power may be used as a source for a wearable device. Finally, the theory presented in this study can be used for the realization of other optimal designs, for a wearable sensor with low consumption and so on.
The aim of this report is to present a model of a rigid-rotor system based on computational fluid dynamics (CFD), which is applied on a vertical axis wind turbine (VAWT) research. Its originality results from the use of the average value of the variable rotational speed method taken in a periodic steady-state (PSS) of the VAWT rotor instead of the classical fixed rotational speed method. This approach was chosen in order to determine the mechanical and aerodynamic parameters of the wind turbine. The modeling method uses an implicit Euler iterative solution strategy, which resolves the coupling between fixed and moving rotor domains. The main methods that were adopted are based on the three-dimensional modeling of the interaction of the fluid flow with a rigid-rotor. The strategy consists of using the Reynolds averaged Navier Stokes (RANS) equations with the standard k-" and SST k-! models to solve the fluid flow problem. To perform the rigid-rotor motion in a fluid, the one degree of freedom (1-DOF) method was applied. In the present study, the steady-state and dynamic CFD simulations of the Savonius rotor are adopted to contribute to the validation elements of the VAWT models that are used. The dynamic study allows the investigation of the rotor behavior and the relation between velocity, pressure, and vorticity fields in and around the rotor blades. The flow fields generated by the rotation of the Savonius rotor were investigated in the half revolution period of the rotor angle  from 0 ı to 180 ı . In this range of  , the focus is on generating and dissipating vortices. Copyright © 2013 John Wiley & Sons, Ltd. NOMENCLATURE
In the last few years, a lot of research focused on increasing of smart textiles products such as woven and knitted structures, which are able to show significant change in their mechanical properties (such as shape and stiffness), in a practical way in response to the stimuli. In this paper, we investigate the potential of a flexible piezoelectric film stuck onto three woven textile matrices: cotton, polyester/cotton, and Kermel, for harvesting mechanical energy from the textile and converting it into electrical energy. At first, a brief introduction of energy harvesting using the piezoelectric material and smart textile is presented. Furthermore, a basic model showing the operation of polyvinylidene fluoride with 33 mode is established. The second part is focused on standard approach model of energy harvesting based on resistive load and freestanding piezo-polymer for the examination of the performance of 33-mode polyvinylidene fluoride energy harvester and the prediction of harvested energy quantity. A power analytical model generated by a smart structure type polyvinylidene fluoride that can be stuck onto fabrics and flexible substrates is investigated. On the other hand, the effects of various substrates and the sticking of these substrates on the piezoelectric material are reported. Additionally, the output power density of this theoretical model of woven textile matrices could reach a value that was seven times higher than freestanding piezo-polymer. Three types of the substrates have been compared as function of excitation frequency and the compressive applied force.
Three-dimensionally (3D) knitted technology textiles are expanding into industrial and technical applications of textile composites given their geometric, structural, and functional performance. However, there are many challenges in developing computational tools that allow for physics-based predictions while keeping the related computing cost low. The strong interactions between geometrical and physical elements permit determining the behavior of this type of engineering material. In the aim of understanding the specific mechanical behaviors of knitted textiles, a yarn-level simulation model framework was created to predict the nonlinear orthotropic mechanical behavior of monofilament jersey-knitted textiles. The relative contributions of many computational parameters on the global mechanical behavior of knitted fabrics are investigated, specifically, inter-yarn interactions and the boundary conditions effect. The models are saved in a format that can be read directly by Finite Element Analysis FEA software. Yarns are numerically discretized as nonlinear 3D beam components, while input parameters, such as mechanical characteristics of yarns and geometric dimensions of loops in fabrics are established experimentally. Good agreement was relieved by comparing experimental data to simulation results in a wale-wise direction tensile load.
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