APPLICATION OF NONLINEAR SYSTEM FREQUENCY ANALYSIS AND DESIGN TO VIBRATION ISOLATION AND ENERGY HARVESTING

Vibration is naturally present in the environment including engineering systems and structures. The presence of vibration can be beneficial or destructive, depending on the nature of the affected system and also the level of vibration. Vibrations at dangerously high levels can be reduced by the addition of some energy dissipation elements (dampers) or/and energy storage elements (springs). Energy dissipation elements, such as dampers, dissipate some of these destructive mechanical vibrations as heat. However, mechanical spring systems absorb and store this mechanical vibration energy as potential energy. Nonlinear analysis is primarily applied in system analysis and design of engineering systems. Many methods are available to perform this purpose including averaging method, perturbation method, harmonic balance and the recently developed Output frequency response function (OFRF). The studies presented in this thesis focus on the application of nonlinear system frequency domain analysis and design to vibration isolation and energy harvesting systems. The OFRF method is the analytical and design tool adopted for all studies presented in this thesis. This method is chosen due to its advantage over other methods. This is because the OFRF reveals a significant relationship between the system output spectrum and the parameters that define the system nonlinearities. Therefore, it can facilitate a systematic analysis, design and optimisation process which other approaches are unable to realize. The first study considered in this thesis is a frequency domain analysis, design and optimisation of a vehicle suspension system which is illustrative of a vibration isolation system. In this study, the suspension system is analysed and designed based on a performance criterion. The main aim of the study is to minimise the transmitted vibration force to a tolerable level. At the specified level, some of the vibration energy is dissipated as heat by the damping system. However, this energy can be harvested into electricity, a process known as energy harvesting. This leads to subsequent studies in this thesis. The next study considers a vibration energy harvester system with nonlinear cubic damping characteristic. In this study, a concept is investigated, using the OFRF method, which increases the average power harvested by the harvesting device compared to an equivalent linear harvester. An extension of this study is further considered with the addition of a nonlinear hardening stiffness element to primarily broaden the operational bandwidth of the harvesting device. A final study is then considered where a dual-function system is investigated. The primary function of the system is vibration isolation while its secondary function is energy harvesting. The system is therefore called a dual-function vibration isolation and energy harvester system. This system is optimised for the best dual-function performance subject to existing constraints. For all the systems considered in this thesis, nonlinearities have been integrated into the existing systems to improve their performance, correspondingly, based on a selected criterion. In addition, the OFRF method has been employed in the analysis, design and optimisation of all the systems considered

Investigative Study of the Effect of Damping and Stiffness Nonlinearities on an Electromagnetic Energy Harvester at Low-Frequency Excitations

Ambient vibration energy is widely being harnessed as a source of electrical energy to drive low-power devices. The vibration energy harvester (VEH) of interest employs an electromagnetic transduction mechanism, whereby ambient mechanical vibration is converted to electrical energy. The limitations affecting the performance of VEHs, with an electromagnetic transduction structure, include its operational bandwidth as well as the enclosure-size constraint. In this study, an analysis and design of a nonlinear VEH system is conducted using the Output Frequency Response Function (OFRF) representations of the actual system model. However, the OFRF representations are determined from the Generalised Associated Linear Equation (GALE) decompositions of the system of interest. The effect of both nonlinear damping and stiffness characteristics, to, respectively, extend the average power and operational bandwidth of the VEH device, is demonstrated

An interference management system for a shared spectrum access network

Internet access, in developing and underdeveloped countries, remains a huge challenge despite advancements in technology. Shared resources, amongst telecommunication systems, offer an affordability context to this problem. A shared spectrum interference management system is implemented by designing a geolocation database, for a television white space network, for a location in Nigeria. This is achieved using the Dynamic Spectrum Alliance framework (a rarely used methodology) and robust terrain-based propagation models. The designed spectrum coexistence manager (geolocation database) was created, presented, and evaluated, based on its channel availability, predictions, and ability to protect very weak TV signals. The result showed a 15% channel utilization of Analogue and Digital Terrestrial Television channels within the study area. Finally, key components of the framework, that can be adopted for further studies, were identified

Fiber to the home: considerations associated with a successful deployment

To realize the Nigerian Government’s goal to liver 80% mobile broadband penetration by 2018, and become one of the top twenty economies in the world by the year 2020, Fiber to the Home (FTTH) technology along with other broadband access technologies is an essential driving factor for providing broadband access. Currently most telecom operators are reluctant to deploy FTTH in the access networks as this is very costly. Most operators are also averse to the risk of regulation - unbundling of the local loop - the new fiber infrastructure. Today, majority of broadband connectivity is offered via Satellite, GSM Networks and Microwave Access. FTTH provides enormous bandwidth and long-reach offering triple play services (Data, Voice, and Video). Advancement in the electronic equipment coupled with a fall in the price of Fiber Optic Cables and equipment make FTTH deployment an affordable choice for the telecom operators that result in long term returns. An analysis of the various factors affecting FTTH Deployment in Nigeria, and possible mitigations to limiting factors, is presented here.N/

Nonlinear damper design for a vibration isolation system

In this paper, vibration transmissibility of a single-degree-of-freedom (SDOF) for a mass-springdamper system is presented. This is done with a linear damper having a configuration perpendicular to a linear vertical spring. The method is analyzed using a nonlinear frequency analysis approach. The concept of the output frequency response function (OFRF) is used to derive an explicit polynomial relationship between the system output response (relative displacement of the mass) and the nonlinear damping coefficient which is the parameter of interest. With the derived OFRF polynomial, various damping parameters were designed for desired output responses. Real-time experimental results are presented for the vibration isolation system validation with dampers orientated perpendicularly (at 90 degrees) to the linear spring. The experimental case studies are provided to demonstrate the new OFRFbased nonlinear system design and its significance in isolated vibration system applications. A force transmissibility graph showing the system output using both numerical and the OFRF methods are presented.N/

Data-Driven Based Modelling of Pressure Dynamics in Multiphase Reservoir Model

Secondary recovery involves injecting water or gas into reservoirs to maintain or boost the pressure and sustain production levels at viable rates. Accurate tracking of pressure dynamics as reservoirs produce under secondary production is one of the challenging tasks in reservoir modelling. In this paper, a data-driven based technique called Dynamic Mode Learning (DML) that aims to provide an efficient alternative approach for learning and decomposing pressure dynamics in multiphase reservoir model that produces under secondary recovery is proposed. Existing algorithms suffer from complexity and thereby resulting to expensive computational demand. The proposed DML technique is developed in the form of a learning system by first, constructing a simple, fast and efficient learning system that extracts important features from original full-state data and places them in a low-dimensional representation as extracted features. The extracted features are then used to reduce the original high-dimensional data after which dynamic modes are computed on the reduced data. The performance of the proposed DML method is illustrated on pressure field data generated from direct numerical simulations. Experimental results performed on the reference data reveal that the proposed DML method exhibits better and effective performance over standard and compressed dynamic mode decomposition (DMD) mainstream algorithms

Geometric nonlinear damper design — A frequency based approach

In this study, the vibration transmissibility of a single-degree-of-freedom (SDOF) with a linear damper having a configuration perpendicular to a linear vertical spring is analyzed using a nonlinear frequency analysis method. The concept of the output frequency response function (OFRF) is employed to derive an explicit polynomial relationship between the system output response (relative displacement of the mass) and the parameter of interest which is the nonlinear damping coefficient. With the derived OFRF polynomial, various damping parameters were designed for desired output responses.N/

Analysis, design and optimization of a nonlinear energy harvester

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Analysis and design of a nonlinear vibration-based energy harvester - a frequency based approach

The benefits of nonlinear damping in increasing the amount of energy (power) harvested by a vibration-based energy harvester (VEH) has been reported where it was revealed that more energy can be harvested using nonlinear cubic damping when compared to a VEH with linear damping. As has been reported, this only occurs when the base excitation on the VEH, at resonance, is less than the maximum base excitation. A maximum harvester base excitation results in a maximum distance the harvester mass can move due to its size and geometric limitations. The present study is concerned with the analysis and design of a VEH using a nonlinear frequency analysis method. This method employs the concept of the output frequency response function (OFRF) to derive an explicit polynomial relationship between the harvested energy (power) and the parameter of the energy harvester of interest, i.e. the nonlinear cubic damping coefficient. Based on the OFRF, a nonlinear damping coefficient can be designed to achieve a range of desired levels of energy harvesting. It is also shown that using the OFRF the harvester throw (the displacement of the mass of the harvester), can be predicted using the designed damping coefficient.N/

Performance evaluation of discrete event process algorithms for a two-tier high-performance cloud computing network architecture

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