Armaghan Salehian

Analysis of compliance effects on power generation of a nonlinear electromagnetic energy harvesting unit; theory and experiment

Vibration energy harvesting devices have shown potential applications to power many devices such as electronic self-sustainable units. Most traditional linear energy harvesters exploit the phenomenon of resonance to produce electric power. Nonlinear energy harvesters, however, present more interesting alternatives and there is potential for them to work well over relatively wider bandwidths due to characteristics such as bifurcation. The aim of this study is to introduce an alternative design to a nonlinear electromagnetic energy harvesting device to improve the power production of the unit. The configuration presented in the following work has demonstrated higher power efficiency over a wider range of frequencies compared to the previous design. The numerical power outputs for both designs are compared and validated against their experimental values. Finally, the validated numerical model is used to find the optimal design to produce the maximum power for the unit.

Dynamic Effects of a Radar Panel Mounted on a Truss Satellite

Presented here is an approach to find an equivalent continuum model of a radar truss structure with a radar panel mounted to the side. Kinetic and potential energy expressions of repeated truss elements are expanded in terms of the displacement components at its center. Two methods are proposed to account for the kinetic energy of the panel. The first considers the panel as a discrete set of point masses and the second method assumes a solid panel of constant density. Hamiltons principle is used to find the equations of motion for six coordinates of vibration for this structure and the original truss. For the truss-panel assembly, this results in two sets of partial differential equations resembling the extended Timoshenko beam equations. Both Euler-Bernoulli and Timoshenko formulations are derived and a finite element analysis is presented for comparison. The results are shown to be in good agreement with those of a finite element. The model demonstrates a significant change in the dynamic properties as a result of the panel. In particular, the longitudinal and torsional motions become coupled with the bending coordinates.

Distributed Actuation Requirements of Piezoelectric Structures Under Servoconstraints

This article is concerned with the analysis of actuation requirements for dynamic shape control of a piezoelectric structure. A general procedure is given for determining the distributed actuation input required to satisfy a partially specified displacement field for a generic piezoelectric shell structure. It is shown that under certain conditions, a servoconstraint that defines a finite number algebraic relations on the motion of the material points of the structure can be satisfied in steady state by an equivalent number of independent actuators. Application examples are developed to demonstrate application of the theory and its potential usefulness in the analysis and design of advanced engineering structures.

Analysis and Modelling towards Hybrid Piezo‐Electromagnetic Vibrating Energy Harvesting Devices

The efficiency of mobile electrical devices increased over the last years. Self‐supply by harvesting ambient energy became a possibility of reducing operational costs by ruling out the need of battery replacement.Many energy harvesting devices employ cantilever configurations with base excitation to increase the effective displacement. The proposed design extends this design with an electromagnetic harvesting device (EMH) placed at its tip. It features an alternating stack of magnets with opposing poles and discs of highly permeable material. The composite cylinder is encircled by coils. This EMH design has successfully been employed for ocean wave harvesting and vehicle suspension systems. Its efficiency with respect to mass and energy output is compared to a previously published design using a single magnet placed at the tip moving within a coil.There exists proof that combining readily available technologies into a so‐called coupled or hybrid design can increase the efficiency in comparison to respecti...

Damping in Periodic Structures: A Continuum Modeling Approach

A homogenized modeling technique is developed in this paper to account for viscous damping properties in beam-like lattice structures of repeated patterns. Necessary assumptions regarding the local free deformations, shear deformation beam theory, and compatibility conditions are made to obtain an equivalent continuum model of a three-dimensional lattice. A dissipated energy equivalence approach is then used to relate the energy dissipation for a general case of damping matrix in a lattice element to an equivalent proportionally damped model. As a result, a continuum model with Kelvin–Voigt damping is obtained. Damped bending natural frequencies, frequency response functions, and damping ratios are found using this method and compared to the results of a finite-element analysis for several structures for the purpose of validation.

Modeling, fabrication, and experimental validation of hybrid piezo-magnetostrictive and piezomagnetic energy harvesting units

As sources of energy are becoming more scarce and expensive, energy harvesting technologies that convert ambient energy to electrical energy are receiving more global interest. Proposed in this article are two hybrid energy harvesters that each employs a combination of piezoelectric (PZT), magnetostrictive (MSM), and electromagnetic technologies. Harvesters employ spiral geometries to allow smaller natural frequencies compared to a straight beam. In particular, the hybrid technology that uses piezoelectric and magnetostrictive has shown significant improvement in the frequency bandwidth of the device. The two harvesters are fabricated, modeled, and tested for their voltage, power, and displacement outputs. The test results are shown to be in good agreement with those obtained from the model.

On Strain-Rate Dependence of Kinetic Energy in Homogenization Approach: Theory and Experiment

The presented work pertains to a homogenization-modeling technique developed for structures of repeated pattern to predict their dynamic behavior. Strain and kinetic-energy expressions for the fundamental element are found along with necessary assumptions that are made to reduce the order of the model. Subsequently, the partial differential equations for the equivalent one-dimensional model are derived. The methodis applied to a planar truss structure,andthenatural-frequencyresultsarevalidatedagainsttheexperimentalvaluesaswellasthe finiteelement results.The advantageof the presentworkover thepreviously established homogenizationmethods thatemploy the energy-equivalence technique is that the effects of strain components are included in the kinetic energy of the fundamental elements, which results in improved accuracy in the frequency estimations.

Analysis of friction controlled motion

Control of motion through base excitation is considered for the unique circumstance where friction is the primary component of the interaction force. With a focus on the Dahl friction model, it is shown that the equations of motion can be divided into two cases: ‘large’ and ‘small’ friction. When analyzed in this manner, the corresponding models take two distinct forms, which subsequently lead to different approaches for control design and analysis. The case of large friction leads to a linear system with an unknown disturbance, the bound of which is related to constants of the friction model, thus allowing the application of standard linear control methods. The case of small friction is similar to the standard Coulomb model, and can be analyzed within the framework of sliding mode control. For both circumstances, relations between the friction constants and control variables are derived which guarantee position tracking performance in the absence of disturbance.

Dynamic Modelling of Cable-Harnessed Beam Structures with Periodic Wrapping Patterns: A Homogenization Approach

Abstract Cables and cords used for electronic purposes in space structures have shown to impact the dynamics of the system significantly. In this paper, a homogenization technique is developed to obtain analytical solutions for beam structures harnessed with cables wrapped in periodic patterns. For each fundamental element, the cable wraps entirely around the host structure. The effects of cables are studied to quantify the changes in natural frequencies as well as the free vibration frequency response functions of the system. Cables are modelled as pre-tensioned bar members that can undergo tension only. The strain and kinetic energy of the fundamental element wrapped with cable are found. Hamilton’s principle is employed to find the partial differential equation of motion (homogenized model). The results are validated using a finite element analysis. Multiple wrapping patterns and cross sections are considered for comparison.

ANALYSIS OF WRINKLED MEMBRANES BOUNDED WITH MACRO-FIBER COMPOSITE (MFC) ACTUATORS

In this paper we focus on a study which involves quantifying the effects of Macro Fiber Composite (MFC) actuators on the pattern and magnitude of wrinkles in a membrane when exposed to various loadings. An ABAQUS finite element code is employed for this research. The membrane in this study has a rectangular shape which is clamped at one edge and is free to move in the horizontal direction at the other edge. MFC actuators are bounded to the membrane to make a bimorph configuration.Copyright