Trade-off analysis and design of a Hydraulic Energy Scavenger

In the last years there has been a growing interest in intelligent, autonomous devices for household applications. In the near future this technology will be part of our society; sensing and actuating will be integrated in the environment of our houses by means of energy scavengers and wireless microsystems. These systems will be capable of monitoring the environment, communicating with people and among each other, actuating and supplying themselves independently. This concept is now possible thanks to the low power consumption of electronic devices and accurate design of energy scavengers to harvest energy from the surrounding environment. In principle, an autonomous device comprises three main subsystems: an energy scavenger, an energy storage unit and an operational stage. The energy scavenger is capable of harvesting very small amounts of energy from the surroundings and converting it into electrical energy. This energy can be stored in a small storage unit like a small battery or capacitor, thus being available as a power supply. The operational stage can perform a variety of tasks depending on the application. Inside its application range, this kind of system presents several advantages with respect to regular devices using external energy supplies. They can be simpler to apply as no external connections are needed; they are environmentally friendly and might be economically advantageous in the long term. Furthermore, their autonomous nature permits the application in locations where the local energy grid is not present and allows them to be ‘hidden' in the environment, being independent from interaction with humans. In the present paper an energy-harvesting system used to supply a hydraulic control valve of a heating system for a typical residential application is studied. The system converts the kinetic energy from the water flow inside the pipes of the heating system to power the energy scavenger. The harvesting unit is composed of a hydraulic turbine that converts the kinetic energy of the water flow into rotational motion to drive a small electric generator. The design phases comprise a trade-off analysis to define the most suitable hydraulic turbine and electric generator for the energy scavenger, and an optimization of the components to satisfy the systems specification

A systematic approach for modeling and identification of eddy current dampers in rotordynamic applications

Eddy current dampers (ECDs) exploit Lorentz forces due to the induced eddy currents in a conductor subject to a time–varying magnetic field. ECDs can be used to introduce damping in rotordynamic applications without mechanical contact to the rotor, thus introducing negligible impact on the dynamic response of the whole system. They are suitable for applications where contactless support of a rotor is required, thus being a perfect match for passive magnetic bearings such as permanent magnet bearings and superconducting bearings. However, modeling and identification of the amount of damping induced by ECDs is a difficult task due to complicated geometry and working conditions. A novel and systematic approach for modeling and identification of the damping characteristics of ECDs in rotordynamic applications is proposed in the present paper. The proposed approach employs an analytical dynamic model of the ECD and curve fitting with results of finite element (FE) models to obtain the parameters characterizing the ECD’s mechanical impedance. The damping coefficient can be obtained with great accuracy from a single FE simulation in quasi-static conditions. Finally, the accuracy of the identification approach is verified by comparing the results with experimental tests. The validity of this approach is in the cases where ECDs employ an axisymmetric conductor, thus covering most cases in rotordynamic applications

Análise modal de um modelo simplificado de um conjunto moto-gerador

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A 2D magnetic and 3D mechanical coupled finite element model for the study of the dynamic vibrations in the stator of induction motors

This paper presents a coupled Finite Element Model in order to study the vibrations in induction motors under steady-state. The model utilizes a weak coupling strategy between both magnetic and elastodynamic fields on the structure. Firstly, the problem solves the magnetic vector potential in an axial cut and secondly the former solution is coupled to a three dimensional model of the stator. The coupling is performed using projection based algorithms between the computed magnetic solution and the three-dimensional mesh. The three-dimensional model of the stator includes both end-windings and end-shields in order to give a realistic picture of the motor. The present model is validated using two steps. Firstly, a modal analysis hammer test is used to validate the material characteristic of this complex structure and secondly an array of accelerometer sensors is used in order to study the rotating waves using multi-dimensional spectral techniques. The analysis of the radial vibrations presented in this paper firstly concludes that slot harmonic components are visible when the motor is loaded. Secondly, the multidimensional spectrum presents the most relevant mechanical waves on the stator such as the ones produced by the space harmonics or the saturation of the iron core. The direct retrieval of the wave-number in a multi-dimensional spectrum is able to show the internal current distribution in a non-intrusive way. Experimental results for healthy induction motors are showing mechanical imbalances in a multi-dimensional spectrum in a more straightforward form

Test and theory of electrodynamic bearings coupled to active magnetic dampers

Electrodynamic bearings exploit repulsive forces due to eddy currents to produce positive stiffness by passive means. Such a feature would make this type of bearing a viable alternative to active and permanent magnet bearings. Although electrodynamic bearings do not violate Earnshaw’s theorem, the open issue remains the stabilization system that is needed to make the rotating body stable, due to the low rotational speeds. Stabilizing solutions proposed in the literature are partially effective and not totally convincing. This limits real industrial applications. The present paper proposes a combination of electrodynamic and active magnetic bearings. At low speed the active part behaves as a conventional active magnetic bearing, while at high speed it provides damping. The readiness of the proposed solution is demonstrated by experimental results obtained using a dedicate test rig

Rotational Power Loss on a Rotor Radially Supported by Electrodynamic Passive Magnetic Bearings

Homopolar radial electrodynamic bearings (EDBs) are one type of passive magnetic bearing that exploits eddy currents developing in a rotating conductor to produce levitation forces. When the rotor spins at high speed and an external force causes the axis of rotation to move radially with respect to the symmetry axis of the static magnetic field, the relative motion between the two members causes currents to be induced in the rotor which in turn generate a reaction force. Since the currents are induced inside the rotor, the rotational loss is converted into heat in the rotating member. Because EDBs are especially suitable for applications that run continuously and that usually work in vacuum, e.g., flywheels and turbomolecular pumps, an evaluation of the bearing's losses in working conditions is of extreme importance. The present paper investigates the amount of rotational loss that is produced by an EDB in working conditions. The analysis is performed using an electromechanical model of the EDB coupled to a Jeffcott rotor model. The analysis allows deducing a set of design equations that can be used to predict the bearing's losses during the design phase. The model is validated by comparison with finite element model

Electromechanical Test Rig for Characterisation of Viscoelastic Material

Viscoelastic materials are widely used for passive damping of undesired vibrations. The characteristics of this kind of materials cannot be obtained theoretically; however, experimental modeling should be performed. In this paper, a test rig is developed in order to characterize the viscoelastic material experimentally. Moreover, a particular kind of material is used to test the validity of the new device. Unlike the devices in the previous works, the torque here is not measured directly using a torque transducer which is quite expensive. However, in this test rig a current sensor is used for measuring the current, thereafter the torque is calculated indirectly. Furthermore, the operating frequency of this device is relatively higher than the other devices used for the same purpose. The results showed the validity of the device at characterizing the viscoelastic material