Simulation of Magneto Static of Linear Generator Driven by Vortex Induced Vibration (Full Paper)

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Simulation of Magneto static of Linear Generator Driven by Vortex Induced Vibration

Indra Ranu KUSUMA*11

Department of Marine Engineering, Faculty of Marine Technology, ITS-Surabaya. *E-mail: kusuma@its.ac.id Abstract

Vortex Induced Vibration (VIV) phenomenon that oscillate objects in the current has become one alternative energy in marine. Vortex resulting vibrations are usually avoided in various design structures, but on the linear generator system, the phenomenon of vibration can be used as energy to move the rotor of linear generator. The reciprocating motion of objects move the rotor of generator to across magnetic field that resulted by stator. Continuously movement of rotor, it results electric current. This paper concerns about investigation on magneto static of Linear Generator driven by VIV. The methodology of this research is done by drawing 3D (Three dimensions) model then converts it into the 3D finite element field simulator for electromagnetic and electromechanical software. Material properties, Loads and restraints, a multipleturn winding of a conductor and force distributions are defined in the 3D finite element field simulator. Next, apply mesh control on the model and mesh model created. Finally, the result of magneto static analysis is Magnetic Flux density, magnetic field intensity, applied current density, eddy current density, and force distribution of the model of linear generator. . Keywords: Linear generator; Vortex induced Vibration (VIV); Alternative Energy, Marine Current, Magneto static.

1. Introduction Nowadays, the utilisation of fossil fuels in human life starts facing problem. The price of fossil fuels continues to rise due to the limitation of fossil fuel reserves and dependency on fossil fuel is still high. Next, the amounts of fossil fuels are limited and gradually decreased every year. It is because fossil fuel is non renewable energy and it takes hundreds of millions of years old to produce. Moreover, fossil fuels not only have problem in their availability but it also gives contribution to emission. Emissions of fossil fuels can be resulted from exhaust gas of vehicle. Therefore, the renewable energy or alternative energy is the most important for human being. Environmentally friendly energy resource is the next frontier. One of prospect renewable energy resource is a marine. Marine energy is the world's largest energy savings. It is clean energy, renewable, and abundant. It comes in five forms, such as currents, waves, tides, thermal gradient, and salinity gradient. In this research, it focuses on the marine currents induced vortex vibration. Vortex power plant or called VIVACE (Vortex Induced Vibration for Aquatic Clean Energy) is one of the technologies in hydropower. Vortex in general result in vibration and an effect that is usually avoided in various design marine structures. But in this system, the vibrations are resulted generated which can be harnessed energy to generate electrical energy. Recently, a new method has been proposed researcher extracted the marine energy from currents. This conversion tool produces kinetic energy from slow-moving water currents, where the principle of works is to take advantage of the natural instability phenomenon of Vortex Induced Vibration (VIV). The VIV occurs when current flows through stationary object. During this time, vortices will come out on the object caused the process of shedding. Then vortex shedding oscillates the object. The oscillation or vibration of object is avoided within most marine structure because it causes fatigue and damage on the structure. Although the phenomenon VIV should be eliminated, it can be used as energy to move rotor of linear generator produced electric energy.

Seminar Nasional Teori dan Aplikasi Teknologi Kelautan, 15 Desember 2011

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The novel of VIV has been proposed as shown in figure 1. It illustrates the structure of a flexible platform for vortex induced vibration power plant. It consists of oscillating part, linear generator, propulsor and base rig. The movement of oscillating part due to vortex produces electrical Energy. Then, it transmits to base rig. Function of base rig is for processing and transmitting the electric power for offshore to on shore. Rig base is as same as body of Ship SWATH. It can sail from one place to another place. The propulsor is placed at the stern of base rig. The advantage of the propelled base rig is for adjusting marine current in order to find appropriate place in order to oscillate object.

Base Rig Propulsor Oscilating Part VIV Linear Generator

Figure.1. Flexible Platform for Vortex Induced Vibration

2. Terminology of Linear GeneratorBasic theory of the emergence of electrical energy from the linear generator is the principle of Electromagnetic Induction. Electromagnetic Induction in which it can simply be interpreted as a the process of change in mechanical energy (kinetic energy) into electrical energy. Electromagnetic induction occurs in a coil if there is a change in the number of lines of magnetic force that covered at all times. Electromagnetic induction was first studied and discovered by Michael Faraday in 1831. Electromagnetic induction or electric impact is the generation of electrical energy from the magnetic field, so that the energy change is closely related to the concept of magnetic flux. Electromagnetic Induction and to understand, then we begin by studying the Magnetic Flux and Faraday's Law. 2.1. Magnetic Flux Magnetic flux is defined as the product between the components of magnetic induction with a wide field. As the equation below: =B cos A (1) Where: = Magnetic flux (weber) B = Magnetic induction (tesla) A = Area of Field (m2) = The angle between the normal line to the magnetic field

Seminar Nasional Teori dan Aplikasi Teknologi Kelautan, 15 Desember 2011

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2.2. Faradays Law It said that if there is a change on the amount of magnetic flux when entering the coil, then the ends of the coil has become induced emf. Then, the amount of induced emf will depend on the rate of flux differences and the number of windings. The equation of induced emf is as follows:

= -N tDimana : = GGL Induksi (Volt) N = Jumlah Lilitan /t = Laju perubahan fluks magnetic. Tanda (-) = Sesuai Hukum Lenz

(2)

2.3. Lenzs Law Lenz's law is "the direction of induced currents is such that the resulting magnetic field opposite to the direction of magnetic field that causes induced currents." Based on Figure 2, it shows that the movement of the magnet inside the coil causes the galvanometer needle to deviate. If the magnetic north pole is moved close to the coil, the galvanometer needle deviated to the right. If the magnet is stationary in the coil, if the magnetic north pole is moved away from the coil, the galvanometer needle deviated to the left. Deviations galvanometer needle showed that at both ends of the coil there is an electric current. An event such as the emergence of electric current is called electromagnetic induction. The potential difference arising at the end of the coil is called electromotive force (emf) induction.

Figure.2. Working principle of induced emf The occurrence of induced emf can be explained as follows: If the magnetic north pole brought near to the coil. The number of magnetic field entering the coil increases. Changes in the number of magnetic field that causes the deviation needle galvanometer. The same thing will happen if the magnet is moved out of the coil. However, the deviation of the galvanometer needle as opposed to the original deviation. Thus, it can be concluded that the induced emf causes changing in the magnetic of field enclosed by the coil. According to Faraday, a large induced emf at both ends of the coil is proportional to the rate of change of magnetic flux enclosed coil. That is, the faster the change of magnetic flux, the greater the induced emf arising. 2.4. Component of Linear generator Linear generator consists of two main parts, namely Rotor & Strator. The stator is part of the generator that unable to move (static). Its Components is a stator core and stator. Stator laminations made from iron aims to reduce eddy current losses. Stator coil is formed of a coil of wire, where the number of coils is determined according to need. The rotor is one of the main components of a generator that can move in a linear motion. Permanent magnet generator and non permanent magnet such as copper coils is used as rotor. In design applications that have made, the basis of Linear Generator design as well as its formulation is to use the principle of induction of permanent magnets with the composition as shown figure 3.a. Two (2) pieces of magnets with different arrangements poles north (N) - South (S) and south (S) - north (N) will cut two pieces of the stator coils on different locations but with in the same core and one coil will be

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awakened induced emf due to changes in the magnetic field in the same time. For the design of the stator by using copper wire (Copper Wire), it is wrapped around the iron core will be designed like a figure 3.b

S N

Figure 3.a Permanent Magnet Linear Generator 2.5.

Figure 3.b Non Permanent Magnet LG

Magnetostatic Equation of Linear Generator Magnetostatic or so called DC Magnetic Field analysis belongs to the low-frequency electromagnetic domain or regime; i.e. displacement currents are neglected. In addition, the fields depend on position only and do not depend on time. Furthermore, the size of the object is much smaller than the wavelength. The Magnetostatic Analysis, linear and non-linear, calculates the magnetic fields produced by one the following: Permanent magnet and steady DC electric current. Maxwells equations

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