A geometrically nonlinear shear deformable beam model for piezoelectric energy harvesters

An electromechanical model for beam-like piezoelectric energy harvesters based on Reissner’s beam theory is developed in this paper. The proposed model captures first-order shear deformation and large displacement/rotation, which distinguishes this model from other models reported in the literature. All governing equations are presented in detail, making the associated framework extensible to investigate various piezoelectric energy harvesters. The weak formulation is then derived to obtain the approximate solution to the governing equations by the finite element method. This solution scheme is completely coupled, and thus allows for two-way interaction between mechanical and electrical fields. To validate this model, extensive numerical examples are implemented in the linear and nonlinear regime. In the linear limit, this model produces results in excellent agreement with reference data. In the nonlinear regime, the large amplitude response of the piezoelectric beam induced by strong base excitation or fluid flow is considered, and the comparison of results with literature data is encouraging. The ability of this nonlinear model to predict limit cycle oscillations in axial flow is demonstrated.

Nonlinear Shear Effects of the Secondary Current in the 2D Flow Analysis in Meandering Channels with Sharp Curvature

In order to analyze the shear effect of secondary currents on the flow structures in a meandering channel, this research developed a two-dimensional shallow water model, which included the dispersion stress term accounting for the shear effect in the vertical velocity profile. A new equation for the vertical velocity profile that included nonlinear shear effects was derived from the equation of motion in the meandering channel with sharp curvature. Using the experiment data obtained from large-scale meandering channels, the ratio of the depth over the radius-of-curvature was incorporated into the shear intensity of the secondary flow in the proposed equation. Comparisons with the experimental results by Rozovskii (1957) showed that the computed values of the primary velocity distribution by the proposed model showed better fit with the observed data than the simulations with linear models and models without secondary flow consideration. The simulated results in the large-scale meandering channels demonstrated that simulations with the nonlinear secondary flow effect added into modeling gave higher accuracy, reducing the relative error by 19% in reproducing the skewed distributions of the primary flow in meandering channels, particularly in the regions where the effects from spiral motion were strong, due to sharp meanders.

An elastic phenomenological material law of technical textile with a nonlinear shear behaviour

In technical textile engineering, macro-level phenomenological modelling effectively describes the material’s highly nonlinear behaviour. However, existing material laws concentrate on the normal stiffness in the orthotropic yarns and simplify the shear effect because of the two orders of magnitude difference between shear and normal stiffness. This article introduces an improved phenomenological model that includes nonlinear shear behaviour, and it determines the material parameters with a previously applied data fitting method for exponential functions. The nonlinear shear behaviour is valid for the elastic state, that is, at the service level of the loads. Time-dependent, cyclic loading or plastic behaviour is not considered.

Influence of Preload on Failure Modes of Hybrid Metal-Composite Protruding Bolted Joints

This paper presents the effects of torque preload on the damage initiation and growth in the CFRP (Carbon Fiber Reinforced Polymer) composite laminated adherent of the single-lap, single-bolt, hybrid metal-composite joints. A detailed 3D finite element model incorporating geometric, material and friction-based contact full nonlinearities is developed to numerically investigate the preload effects on the progressive damage analysis (PDA) of the orthotropic material model. The PDA material model integrates the nonlinear shear response, Hashin-tape failure criteria and strain-based continuum elastic properties degradation laws being developed using the UMAT user subroutine in Nastran commercial software. In order to validate the preload effects on the failure modes of the joints with hexagonal head bolts, experiments were conducted using the SHM (Structural Health Monitoring) technique. The results showed that the adherent torque level is an important parameter in the design process of an adequate bolted joint and its effects on damage initiation and failure modes were quite accurately predicted by the PDA material model, which proved to be computational efficient and can predict failure propagation and damage mechanism in hybrid metal-composite bolted joints.

Solar Orbiter observations of magnetic Kelvin-Helmholtz waves in the solar wind

<p>The Kelvin-Helmholtz instability (KHI) is a nonlinear shear-driven instability that develops at the interfaces between shear flows in plasmas. KHI is ubiquitous in plasmas and has been observed in situ at planetary interfaces and at the boundaries of coronal mass ejections in remote-sensing observations. KHI is also expected to develop at flow shear interfaces in the solar wind, but while it was hypothesized to play an important role in the mixing of plasmas and exciting solar wind fluctuations, its direct observation in the solar wind was still lacking. We report first in-situ observations of ongoing KHI in the solar wind using Solar Orbiter during its cruise phase. The KHI is found in a shear layer in the slow solar wind near the Heliospheric Current Sheet. We find that the observed conditions satisfy the KHI onset criterion from linear theory and the steepening of the shear boundary layer is consistent with the development of KH vortices. We further investigate the solar wind source of this event to understand the conditions that support KH growth. In addition, we set up a local MHD simulation using the empirical values to reproduce the observed KHI. This observed KHI in the solar wind provides robust evidence that shear instability develops in the solar wind, with obvious implications in the driving of solar wind fluctuations and turbulence. The reasons for the lack of previous such measurements are also discussed.</p>