Application of a Hybrid WKB-Galerkin Method to a Nonlinear Plate Dynamic Problem with Time Dependent Damping Coefficient

The objective of the analysis is to obtain a closed form approximate analytical solution for the nonlinear differential equation of a loaded plate considering a time variant damping coefficient. The solution of the problem is obtained by using perturbation and a hybrid WKB-Galerkin method. Results are presented of comparison of the solutions based on different approaches

Energy Harvesting based on the Hybridisation of two Smart Materials

Recently, there has been an increased demand for power harvesting as a source of providing renewable energy. One of the most promising technologies due to their high power densities are piezoelectric devices, harvesting vibrational energy. There has been extensive research done in the area of energy harvesting using smart materials. However, the majority of this work is dedicated to the application of one type of smart material, such as piezoelectric or shape memory alloy. The aim of this paper is to develop a completely novel concept of a hybrid device combining piezoelectric and shape-memory alloy effects. The resulting device has a strong potential for miniaturisation and practical biomedical applications in environments characterised by thermal fluctuations. Both finite element and analytical models were developed to describe the dynamic behaviour of this innovative device. Both models predicted parametric behaviour for an input frequency of 988 Hz. Performance of the device was comparable to existing energy harvesting devices. The limitations and benefits of each modelling approach are also discussed

Improvement of Piezoelectric Energy Harvester Efficiency Through Optimal Patch Configuration

The aim of this paper is to explore how to improve the efficiency of a vibrating hybrid energy harvester through changing the patch configuration. The results of this work identify the patch configuration that maximises output while using the same amount of piezoelectric material. Using 6 patches was found to be the most efficient when looking at the energy output from a single cycle. Stress distributions generated using ANSYS show that this was because the patches were all located in areas of high stress. The 2 patch configuration resulted in the highest energy conversion at low frequencies (peak loss factor <50Hz) while the performance of the 6 patch configuration was characterised by high energy conversion over a wider range of frequencies

Hybrid energy harvesting based on cymbal and wagon wheel inspiration

The demand for self-sufficient electronic devices is increasing as well as the overall energy use, and such demands are pushing technology forward, especially in effective energy harvesting. A novel hybrid Energy Harvesting System (EHS) has been proposed and analysed in this paper. It has been demonstrated that the EHS is capable of converting enough energy to power a typical MEMS device. This has been achieved through unification of the nine Cymbal Energy Harvester (CEH) array, as an energy harvesting core, and Shape Memory Alloy (SMA) active elements, acting as a source of force stimulated by the environmental changes. A Finite Element Model (FEM) was developed for the CEH, which was verified and used for the analysis of CEH’s response to the change of the end-cap material. This was followed by the FEM for the EHS used for analysis of the location of SMA wires and force generated by each wire individually and then all together. As a further optimisation of the EHS a novel Wagon Wheel design was explored in terms of its energy harvesting capabilities. As expected, due to the increased displacement, an increase in the power output was achieved

Motorised momentum exchange space tethers : the dynamics of asymmetrical tethers and some recent new applications

This paper reports on a first attempt to model the dynamics of an asymmetrical motorised momentum exchange tether for spacecraft payload propulsion, and it also provides some interesting summary results for two novel applications for motorised momentum exchange tethers. The asymmetrical tether analysis is very important because it represents the problematic scenario when payload mass unbalance intrudes, due to unexpected payload loss or failure to retrieve. Mass symmetry is highly desirable both dynamically and logistically, but it is shown in this paper that there is still realistic potential for mission rescue should an asymmetry condition arise. Conceptual designs for tethered payload release from LEO and lunar tether delivery and retrieval are also presented as options for future development

Application of smart honeycomb structures for automotive passive safety

Nowadays, most energy absorbing devices used in industry absorb energy through permanent deformation. In some cases, consumers have to repair or even replace energy absorbers even after a mild collision. The work presented in this paper proposes a novel re-usable solution in the form of a hybrid bumper-crush can design where a recoverable structure is integrated into the bumper beam and crush can for a mild collision situation in addition to the traditional energy absorbers recommended for more severe collisions. The main investigation is focused around the performance and optimisation of Negative Stiffness honeycomb, the recoverable structure and honeycomb-filled elements. A comprehensive study was undertaken to investigate numerically the behaviour of these energy absorbing structures under crash conditions, corresponding to real scenarios and simulated using a specially developed finite element mode

The Mechanics of Motorised Momentum Exchange Tethers when applied to Active Debris Removal from LEO

The concept of momentum exchange when applied to space tethers for propulsion is well established, and a considerable body of literature now exists on the on-orbit modelling, the dynamics, and also the control of a large range of tether system applications. The authors consider here a new application for the Motorised Momentum Exchange Tether by highlighting three key stages of development leading to a conceptualisation that can subsequently be developed into a technology for Active Debris Removal. The paper starts with a study of the on-orbit mechanics of a full sized motorised tether in which it is shown that a laden and therefore highly massasymmetrical tether can still be forced to spin, and certainly to librate, thereby confirming its possible usefulness for active debris removal (ADR). The second part of the paper concentrates on the modelling of the centripetal deployment of a symmetrical MMET in order to get it initialized for debris removal operations, and the third and final part of the paper provides an entry into scale modelling for low cost mission design and testing. It is shown that the motorised momentum exchange tether offers a potential solution to the removal of large pieces of orbital debris, and that dynamic methodologies can be implemented to in order to optimise the emergent design

The Mechanics of Motorised Momentum Exchange Tethers when applied to Active Debris Removal from LEO

The concept of momentum exchange when applied to space tethers for propulsion is well established, and a considerable body of literature now exists on the on-orbit modelling, the dynamics, and also the control of a large range of tether system applications. The authors consider here a new application for the Motorised Momentum Exchange Tether by highlighting three key stages of development leading to a conceptualisation that can subsequently be developed into a technology for Active Debris Removal. The paper starts with a study of the on-orbit mechanics of a full sized motorised tether in which it is shown that a laden and therefore highly massasymmetrical tether can still be forced to spin, and certainly to librate, thereby confirming its possible usefulness for active debris removal (ADR). The second part of the paper concentrates on the modelling of the centripetal deployment of a symmetrical MMET in order to get it initialized for debris removal operations, and the third and final part of the paper provides an entry into scale modelling for low cost mission design and testing. It is shown that the motorised momentum exchange tether offers a potential solution to the removal of large pieces of orbital debris, and that dynamic methodologies can be implemented to in order to optimise the emergent design

Experimental investigation of the thermoelastic performance of an aerospace aluminium honeycomb composite panel

Aluminium composite sandwich panels are widely used to enhance the design of structures subjected to dynamic mechanical loading in thermally harsh environments. Spacecraft structures fall into this category because typical environmental conditions include combined and variable mechanical and thermal loading. Usually mechanical loadings arise as a consequence of localised structural dynamics and the thermal loadings are attributable principally to the effects of solar irradiation and eclipse during the vehicle’s orbit. Together these have the potential to influence satellite de-point in particular. Therefore, building a combined physics model which is representative of the thermal and mechanical loadings has emerged as an interesting and useful aim, which can be thought of as defining an important thermoelastic deformation problem in this application. The performance of such a structure loaded in this way could obviously be considered in the context of separate thermodynamic and mechanical interpretations. However, multiphysics modelling is currently in hand based on the premise that the pseudo-static thermal loadings and the mechanical loadings encountered in various operating environments are not necessarily decoupled processes, and this will be the subject of a separate publication. The analytical modelling fully represents both static and dynamic mechanical and thermal loading conditions. It has become clear that predictive accuracy may be compromised by separation of the phenomena, at least without the introduction of a judicious correction factor. Therefore, in this paper an attempt has been made to identify experimentally the presence, and then to understand the attendant effects, of the coupling between the thermal and mechanical effects in an aluminium composite sandwich panel under test. The authors have performed a series of experiments on an aluminium honeycomb composite panel under three-point mechanical bending and controlled environmental temperature. The panel was subjected to a controllable, centrally located, very slowly increasing mechanical load in conjunction with thermal loading in the form of precisely controlled lowered and elevated environmental temperature. The tests were performed on a computer controlled Instron 8801 100 kN test machine for which the rate of change of applied mechanical load was automatically linked through feedback control to the rate of change of displacement. This ensured that the exact load-deflection profile can be obtained, even for materials with highly nonlinear characteristics. Both forms of loading have been shown to influence the displacement of the panel in significant ways, thereby confirming the importance of a combined physics approach