How to Build a Simple Wind Turbine, Sample of Reviews

24 pages, 11689 words

The Petroleum Institute

Abu Dhabi, United Arab Emirates

Department of Mechanical Engineering

MED Project I Fall 2010

MEEG 490

Final Report: Designing and building a wind turbine

Mentor: | | Kamal E. Amin |

Instructors: | | Sai Cheong Fok |

| | Lyes Khezzar |

| | Isoroku Kubo |

Ali Ashraf Mohamed | | 92001-3226 | | |

Mohamed Ahmed Radwan | | 92001-2857 | | |

Mohamed Fareed Al- Wahedi | | 92001-2310 | | |

Saeed Ahmed Saeed Othman Al Wahedi | | 92001-2280 | | |

Ahmed Mostafa Elsayed | | 92001-2479 | | |

Malik Sarieh | | 92001-2370 | | |

Majeed Al- Badani | | 92001-1376 | | |

Mohamed Rashed Al- Naqbi | | 92001-1401 | | |

“We pledge that we have neither given nor received any unauthorized assistance on this project”

Executive Summary

The scope of the project was to design and build a prototype wind turbine that can convert the wind kinetic energy safely into electrical energy which can be used to power a100W electrical device. In this report an introduction and background research is discussed after intensive research was conducted. The outcomes of the research lead to select three conceptual designs that are based on different models and specifications. Two of the concept designs were based on the Danish concept of wind turbines and some slight modifications were added like the number of blades and the design of the base. The last concept design was a new unusual design that is based on planes jet concepts. An evaluation matrix was done in order to select the most appropriate design. Also different software’s were used in order to find out different parameters that were used in the design of the wind turbine. After the evaluation matrix was done and some additional calculations and researches conductedit was found that 3-unit Danish design concept was the most appropriate design that best satisfies the objectives and the constraint of the project. The selected design is a wind turbine where a rotor with three blades connected to an electric generator through mechanical system that is comprised sequentially of low speed shaft, gearbox and high speed shaft.

8 pages, 3763 words

The Research paper on Design of an activity based costing system for a public hospital: a case study

This paper describes a case study of ABC system design in a new public foundation hospital in Spain focusing on design elements leading to successful conflict-free implementation, including managing resistance. The design stage has been largely ignored in the ABC literature (Arnaboldi and Lapsley, 2005). It expands on previous studies of institutional forces’ impacts on hospital management and is ...

Additional detailed researching and designing were conducted to fully utilize the specifications of each components of the system. The selected design was found to be large in size compared to the required power output due to the low wind velocity selected and the calculations done were conservative in assuming low efficiency of the power coefficient. The size of the rotor affected the rotation speed which was found low and in order to provide the generator with the required angular speed a high gear ratio was selected for the gearbox. The control system was identified, prepared but yet not designed due to the narrow schedule. It was concluded that the wind turbine is not economically feasible in to use in UAE and specifically in the coast regions of UAE because the wind velocity is low and cannot generate enough power to be consumed. It also found out that a possible solution to test the design is to build a small prototype and test it in the wind tunnel found in the Petroleum Institute’s Core measurements laboratory. The future works were identified to schedule them accordingly for the next semester. The design process was done successfully even though a lot of challenges were confronted during researching, designing and even managing the team members’ responsibilities and quality of work. Ultimately, The team was able to overcome the challenges they faced and are very excited for the approval from the client to proceed in the project.

2 pages, 635 words

The Essay on Sip for Wind Turbines

A wind turbine is a device that converts kinetic energy from the wind, also called wind energy, into mechanical energy in a process known as wind power. If the mechanical energy is used to produce electricity, the device may be called a wind turbine or wind power plant. If the mechanical energy is used to drive machinery, such as for grinding grain or pumping water, the device is called a windmill ...

Acknowledgments

We wish to express our gratitude to our parents and families who have tirelessly strived for our education and development in times of hardship as well as happiness. The preparation of this important document would not have been possible without the support, hard work and endless efforts of a large number of individuals. We would like to thank our numerous teachers and colleagues for their input throughout the course. Our sincere thank to all the people who have contributed and worked on this project. We wish to express our appreciation to our entire mechanical engineering faculty that stood with us from the first day we went to the Petroleum Institute (PI) and they helped us in progression of all different mechanical engineering courses.

And last but not least we would like to express our sincere gratitude to Dr. Kamal E. Amin for his supervision and guidance that without we would not have been able to produce such a document

Contents

Executive Summary I

Acknowledgments II

List of Figures IV

List of Tables VI

1. Introduction 1

1.1 Project Concept Statement 1

1.2 Historical Background 2

2. Design Problem Analysis 12

2.1 Design Objectives 12

2.2 Design Constraints 13

3. Concept Designs 13

3.1 4-unit Design (Concept Design one) 14

3.2 Jet Design (Concept Design two) 15

3.3 3-unit Design (Concept Design Three) 17

4. Design Decisions 18

4.1 Pugh Analysis 18

4.2 Failure Mode and Effects Analysis (FMEA) 20

5. Final Design 23

5.1 Chosen Concept Design 24

5.1.1 The Blades 24

5.1.2 The Transmission system 29

5.1.3 The Generator 31

5.1.4 The Support 35

5.1.5 Safety and control System 36

6. Design Summary 37

6.1 Current Status 37

6.2 Challenges Faced 37

6.3 Intended Future Work 38

7. Conclusion 39

8. References 40

List of Figures

Figure 1 Wind Turbine Configuration 2

7 pages, 3009 words

The Review on An Archery Test Rig Made Using Computer Aided Design

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Figure 2 Maximum at theta=0.52, max=0.375 6

Figure 4 The six coils in the starter 10

Figure 3 Generator 10

Figure 5 DC vs. AC current 11

Figure 6 Danish Concept of a practical wind turbine 14

Figure 7 Jet like wind turbine with sets of small rotors inside 15

Figure 8 Trimetric view for the jet like wind turbine with a fin installed to it 16

Figure 9 A Flow Design high efficiency Wind Turbine based on Jet [5] 17

Figure 10 3-unit Concept of a wind turbine 18

Figure 11 Front and back isometric view of the final design 24

Figure 12 Rotating annular stream tube 25

Figure 13 Rotating annular stream tube 26

Figure 14 Forces on the turbine blade 26

Figure 15 lift and drag coefficients curves 28

Figure 16 Different views for the designed blade 29

Figure 17 Assembled High Speed and Low speed Shafts 30

Figure 18 High Speed Shaft 30

Figure 19 Low Speed Shaft 30

Figure 20 Simple illustration of inducing electromotive by mechanical means 31

Figure 21 Alternator types and the corresponding rectifiers and the outputs 33

Figure 22 Isometric view for the 1 KW alternator 34

Figure 23 Power output vs. angular speed input plot 35

Figure 24 Stress analysis on the support 36

Figure 25 Support three dimensional design 36

List of Tables

Table 1 Estimation cost for the material needs for the wind mill construction 15

Table 2 Estimated cost for the second concept design 17

Table 3 Estimation cost for the material needs for the wind mill construction 18

Table 4 Pugh Analysis 19

Table 5 Occurrence rating scale (FMEA) 20

Table 6 Severity rating scale (FMEA) 20

Table 7 Detection rating scale (FMEA) 21

Table 8 The calculated values for the designed alternator to produce 100 W on a single phase alternator 32

Table 9 Specifications of the proposed alternator and its price 34

1. Introduction

In this section, both the project concept statement and project background are presented.

1.1 Project Concept Statement

This project is significant because it is one of the renewable energy resources. The scope of this project is to build a prototype windmill that can convert the wind energy safely into electrical energy that can be used to power a small light bulb. The objectives of the design are to be safe, durable, reliable, efficient, easy to use, affordable and simple. Therefore, the purpose of the prototype windmill is to produce at least 100 watts to power the light bulb. This report discusses the design problem analysis, design evaluation plan, the concept designs and the tasks division among the team members. Further simulation like ANSYS analysis, wind tunnel testing and CAD simulation will be carried out for this project.

1 page, 454 words

The Essay on Steam Turbines Energy Turbine Power

Steam Turbines The invention of the water turbine was so successful that eventually, the idea came about for extracting power from steam. Steam has one great advantage over water-it expands in volume with tremendous velocity. To be the most effective, a steam turbine must run at a very high speed. No wheel made can revolve at any speed approaching the velocity that a steam turbine can. By ...

The windmill consists of many components and operations which are:

Blade Aerodynamics: The aerodynamics of the windmill discus the blade profile, change in force in the blades and blade behavior at different wind speeds. Aerodynamic modeling is used to determine the optimum tower height, number of blades and blade shape.

Transmission system: The transmission system is the link between the blades of the windmill and the generator. The transmission system consist of the hub, high speed shaft, low speed shaft, bearings, gearbox, clamping unit and the coupling.

Generator: The generator converts the mechanical energy to electrical current. The current produced from the generator is alternating current. Then the alternating current converted to direct current by using rectifier to avoid the loss when transferring the electrical current. The control and safety systems include the controller, hydraulics, tip brakes, mechanical brake and the grounding system.

Control and safety systems: The controller controls all the safety systems in the windmill.

Foundation: It supports the wind mill and prevents it from falling.

Rotor: Rotor diameter forms the size of the rotor (measured in meters).

This criterion is crucial for specifying the swept area where the rotor diameter is squared, divided by 4 and then multiplied by 3.41

1.2 Historical Background

Although non-renewable energy sources are cheap and available now, they are still limited and the need to produce energy from a renewable source is growing every day. Limit is not the only reason why renewable energy is demanded, but also because current resources mainly oil come with many issues such as pollution, global warming, safety and hazard issues, etc. As a result we propose to build a windmill which is a clean renewable energy source and in order to do that we did some research on the previous available windmills and this is what was found. Wind turbine or windmill is a turbine that is powered by the wind, and the turbine is the rotary engine in which kinetic energy (K.E) of a moving fluid is converted to mechanical energy by causing the bladed rotor to rotate [1]. Mainly there are two types of wind turbine, the first one is Vertical Axis Wind Turbine (VAWT), and the second one is Horizontal Axis Wind Turbines (HAWT).

2 pages, 521 words

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Most HAWT built today are two- or three-bladed, although some have fewer or more blades [2]. For the VAWT the axis of rotation is perpendicular to the wind stream and the ground but for the horizontal the axis of rotation is parallel [2]. Below Figure 1 show the difference between the main two types of wind mill.

Figure [ 1 ] Wind Turbine Configuration

Each type of the wind turbines discussed above have some advantages and some disadvantages, these are listed below:

Some of the advantages of the VAWT are:

* The generator, gearbox etc. may be placed on the ground, and a tower is not essential for the machine.

* A yaw mechanism isn’t needed to turn the rotor against the wind

The basic disadvantages are:

* Wind speeds are very low close to ground level, so although a tower isn’t essential, the wind speeds will be very low on the lower part of the rotor.

* The overall efficiency of the vertical axis machines is not extraordinary.

* The machine may need guy wires to hold it up, but guy wires are impractical in heavily farmed areas.

The advantages of HAWT:

* It has variable blade pitch which gives the turbine an optimum angle of angle of attack, which will help in collecting the maximum amount of wind energy.

* It has a higher efficiency than VAWT

The disadvantages of HAWT:

* It cost a lot because it is difficult to install horizontal axis wind turbine.

* It requires additional yaw control in order to turn the blades.

Aerodynamic of the wind turbine:

4 pages, 1707 words

The Term Paper on Essay On The Use Of Wind Energy

What is Wind Energy? Wind Energy is defined as an alternate source of generating electricity. Wind Energy is energy obtained from moving air. The motion of wind results from the heating and cooling of the earth. Wind power is used from a wind turbine, and electricity is generated by its magnetic fields. It is normally turned into useful energy by the action of wind currents on moving surfaces, ...

The blades design is the most important aspect of designing a wind turbine. The blades main objective is to translate the velocity kinetic energy into rotating energy for the shaft which then delivers the energy for the electric motor to induce electricity. Designing the right blades for the right velocity is vital to produce the desired power output, for example blades that do not provide enough rpm for the electric motor will result in very low output while overwhelming the electric motor rpm limit will result in burning it. The wind flows around the blades which results in forces acting on the blades, which can be expressed as two main forces, lifting force and dragging force plays an important role in designing the optimized blades angle for maximum torque and angular speed. The lift force is covered by Bernoulli Law, where the Rear side is much more curved than the front side facing the wind, thus greater velocity produces a pressure drop on the rear side of the blade, and it is this pressure drop that produces the lift.

During designing the blades many considerations need to be thought carefully. The number of blades affects the torque and rpm produced, for example a windmill with four blades will provide more torque but less rpm to weight ratio. The blades weight distribution is very important, one blade turbine can perform but due to instability of weight distribution a lot of undesirable vibrations and stresses will occur which will result in the failure of the part. Blades material also is important in consideration of the size and speed of the turbine. Steel is strong and hard but too heavy and will result in buckling the tower. Aluminum is light weight but hard to cast to the designed geometry and the machined one will suffer from cracks and fatigues. Wood is easy to produce and shape, it also resists cracks and light weighted but it cannot be used for large turbines or high speed winds.

Power obtained is depend on many parameters such as the wind velocity, blades geometry, wind flow status whether it is laminar or turbulence and even temperature of the air might affect the air density. To make predictions for the power harvested from the wind it can be assumed that the wind is moving through a cylinder and the kinetic energy of the wind will equal to:

KE= 12mv2 (J) (1)

Since the air mass is difficult to calculate it can be expressed in terms of the cylinder volume and density.

m=ρV= ρAL (Kg) (2)

The area of the cylinder can be easily expressed as a function of diameter and the length of the cylinder can be expressed as function velocity and time.

A=D24π (m2) (3)

L=vt (m) (4)

m=ρV= ρAL=ρvtD24π (Kg) (5)

KE=πD28ρv3t (J) (6)

To obtain the power the kinetic energy needs to be differentiated with time. Hence a relationship will be established among the power, the wind velocity and the blades geometry.

P=ddx (KE)=πD28ρv3 (W) (7)

The relation above shows that the power harvested is mostly affected by the cube of the velocity. The diameter has significant importance after the velocity and the density of the wind is linearly proportional to the power sent to the shaft. The above equation is an ideal but in reality it cannot be easy to achieve high efficiency by just plugging numbers, for example the shape of the blades, cylindrical or flat, does affect the efficiency of the turbine. Betz limit is the maximum efficiency limit that can be achieved by assuming certain conditions like infinite blades and incompressible flow, which air is not, is axial to the blades. The Betz limit reach only up to 59.3% of power from the supposed predictions. The actual efficiency is much less and at best engineering designs it can reach only to 40%.

Controlling the lifting and dragging forces can be achieved by tilting the blades to certain degree. Optimized angle for the blades is desirable and can be achieved by assuming tilted flat blades. The wind pressure acts as a weight on an incline where the components can be expressed with trigonometric functions.

P=12ρv2 (Pa) (8)

F=PA=12ρv2A (N) (9)

Tilted area will result in components areas in addition to the components of the wind force. The related parameters for the rotation are as follows:

Ay= A sinα (m2) (10)

Fx=PxAy=(12ρv2A sinα)cosα (N) (11)

The drag coefficient is an additional, geometry depending, parameter added to the above formula to produce more accurate predictions. The formula will be expressed as follows:

Cdx=Cd cosα (12)

Fx=12 ρv2A Cdx sinα cosα=12 ρv2A Cd sinα cosα2 (N) (13)

The experimental results for a long flat surface oriented perpendicularly with respect to the flow gave Cd=1.98. However, the drag coefficient for the model or design intended can be obtained by relating the drag coefficient with the Reynolds numbers of the flow. Eq.[10] presents a model for the blades driving force with respect to the tilting angle. Assuming the angle as the only variable in Eq.[10] the following figure can shows the most optimized angle for maximizing the driving force.

Figure [ 2 ] Maximum at theta=0.52, max=0.375

The CFD Programs (Fluent – ANSYS) will be of great help to us in order to choose the best design for the blades

The Blades design can be evaluated into more complicated standards such as the pressure coefficient distribution around the blades and how the wind streamlines behave as it pass through the blades, however, the wind turbine aimed to be designed by the group will have more controlled parameters and will be done in smaller size that why there is no need to consider such complexity and unsteady effects on the setup conditions the team might design.

The Transmission System:

The transmission system consists of 5 main components. First is the Hub where all the blades in the wind turbine are bolted to it. The hub is cast in a special type of strong iron alloy, called “SG cast iron”. Because of the complicated hub shape which is difficult to make in any other way, it is convenient to use cast iron. In addition the hub must be highly resistant to metal fatigue, and this is difficult to achieve in a welded construction. Second component is the main shaft which is is usually forged from hardened and tempered steel. Shafts are stationary or rotating components which usually take the basic shape of a cylinder. They are mainly designed to transfer energy between different components in the form of torque and friction.

In the turbine there are two shafts, the first one is the low speed shaft which is connects the hub to the gear. The second is the high speed shaft which connects the gear to the motor.

For a shaft design we need to know the

1) Forces applied

2) Torsion

3) Stress

4) Material

The shaft is subjected to two loads which are torsion due to transmitted torque by the blades and bending from transverse loads by the gears. Depending on the size of this force a lot of factors can be altered to help the shaft withstand higher loads. These depend on the application is which the shaft is used. For example to lower the stress in the shaft smaller sizes should be used, but in few applications the size cannot be changed.

For the shaft material the most common are:

• Steel (low to medium-carbon steel)

• Cast iron

• Bronze or stainless steel

• Case hardened steel

The Third component is the main bearing which is bolted to the mainframe, lubricated by grease always and sealed by using labyrinth packing. There are mainly two types of bearings:

Ball bearings

The Ball bearings uses ball shaped spheres between the upper and lower layer and can support both axial and radial loads.

Cylindrical bearings

The cylindrical bearings use cylindrically shaped tubes between the upper and lower layer of the bearing and can only support radial forces.

The bearings are used to rotate a shaft and required to support its size. Changing the size of the spheres in the ball bearings causes a change in the diameter but with the cylindrical bearings the width can be changed without the change of the diameter. Since there are no axial loads applied, the cylindrical bearings fit perfectly for job. There are different types of cylindrical bearings, the choice of bearing must be chosen accordingly with the application in which the bearing is going to be used.

There is the typical cylindrical bearing and there is the two-cylindrical bearing and the four-row cylindrical bearings.

The advantage the other types have over the typical bearing, is the higher radical load capacity, but with the four –row cylindrical bearing there is no thrust capacity. Consequently using a tow-row cylindrical bearing would be a better choice.

Placing two bearings beside each other would distribute the load between bearings reducing the load on each bearing. More importantly considering the size of the cylinders used, because if they fail the whole bearing would fail causing its break down. Using bigger cylinders would help each one to withstand a higher force.

There is also the inner ring to the outer ring ratio. If the inner ring small compared with the outer ring means that it’s rotating at a higher rpm then the outer ring, causing it to wear of faster. On the other hand using a bigger diameter for the ring would reduce the forces on it. Seemingly there are three ways that the bearing can break down:

1) Fatigue : which is caused by continuous apply of load

2) Abrasion: it is when the surface is eroded due to contact with hard containments

3) Pressure induced welding: it is when two surface are joined together due to high pressure

There is more than one type of lubricant can be used, there is the synthetic, the oil based, the water based and a lot more. The importance of the lubricant remains in its function which is:

1) Transfers heat

2) Seal of gases

3) Protects against wear

4) Prevents rust and corrosion

5) Reduces friction

This shows that the lubricant plays a significant factor in increasing the bearing life and that the type used must be chosen wisely. It happens that also lubricants have their own life and they wear faster under higher conditions (speed, temperature), therefore it would be better to choose a type that would last longer.

Third component is the clamping unit which is simply where the main shaft is coupled to the gearbox. And the Fourth component is the gearbox. The gearbox is one of the significant components in the transmission system in the wind turbine. It is located between the main shaft and the generator. The gearbox connects the low-speed shaft to the high-speed shaft and increases the rotational speeds from about 30 to 60 rotations per minute (rpm) to about 1000 to 1800 rpm which is the rotational speed required by the most generators to produce electricity.

The gearbox must be tightly connected to the wind turbine foundation which also must be rigid and have a flat mounting surface. A base plate should be placed under the gearbox and be at least as thick as the gearbox base. Both the gearbox and the base plate should be rigidly bolted to the foundation.

The gear ratio determined depending on the required output power from the generator. In general wind turbine the gear ratios range from 1:25 to almost 1:100. For example in small wind turbine the gear ratio is 1:25 and the output power will be 150 kW where the main shaft has a rotational speed of 40 rpm and the generator rotational speed is about1000 rpm.

Various gears and gearboxes are used in wind turbines for connecting low-speed shaft to the high-speed shaft and increasing the rotational speeds. The common gearboxes used in wind turbines are planetary, helical and worm gearboxes. Planetary gear composed of three components: Sun gear, Ring gear, Planet gears and the planet gears’ carrier. The gearbox is driven with the help of the main shaft, connected to a carrier plate carrying three smaller gear wheels. These gear wheels run inside a toothed outer ring and drive the central gear cut around the central output shaft. The friction between the gears decreases while the efficiency increases due to the distribution of the load among many contact points around each gear. The planet wheels in these gearboxes are generally set 120 degrees apart, leading to load equilibrium and thus resulting in balanced geared components and very low wear. Planetary gearboxes are widely used for different wind turbines. They are in demand because they have compact size, less weight, greater resistance to shock, higher torque to weight ratio, low backlash and improved efficiency.

Helical gearboxes have teeth that spiral around the gear. These gearboxes are similar to spur gears but have a greater time of contact and are quieter in operation. These gearboxes are noise free and have a modified output shaft. The gearbox can be mounted on an output flange. The long-term efficiency in the helical gearboxes is more important than the initial set up cost.

A worm gearbox consists of a shaft with screw thread, also referred as a worm that meshes with a toothed wheel. It changes the direction of the axis of rotary motion. Worm gearboxes have good heat dissipation and available in different coupling options also they are lubricated for long life and noiseless. The worm gearboxes are available with different precision levels with backlash options.

Gearboxes are constructed from a variety of materials. High quality materials are used to manufacture gearboxes for ensuring reliability, ease of maintenance and long life. Aluminum, cast iron and stainless steel are the most common materials used in wind turbine gearboxes. Aluminum is non magnetic metal is also used to manufacture different types of gearbox. Moreover the aluminum has light weight and it resists corrosion, also it is durable. Cast iron is commonly used to manufacture gearboxes in wind turbines. The metal is strong, durable, resists corrosion and good heat dissipater. Stainless steel is not commonly used due to the high cost factor where it cost almost twice as much as the cast iron. Therefore, the stainless steel is anti corrosion, anti rusting, anti stain and recyclable metal.

The Generator

The electric generator is a device that is used to convert mechanical energy into electrical energy. A wind generator is powered by a large propeller called a wind turbine. When wind blows, it creates lift on the blades of the turbine which is pulling them to the side and making the whole turbine to spin. On the other hand the turbine is connected to a shaft and in which in turn is attached to the generator. The generator is the creation of the electricity.

* Figure [ 3 ] Generator

The electricity of the generator:

The generator consists of a permanent magnet which is put inside a coil of wire. And when this magnet rotates it will cause a moving in a magnetic field and also the coil. Because of the changing in a magnetic field direction this will create a electric current in the wire. This electricity is called alternating current.

Wind turbines can be divided into two basic groups, the horizontal axis variety and the vertical axis design.

Most large modern wind turbine is horizontal axis turbines.

Horizontal turbine components include:

The Rotor is responsible for converting the energy in the wind to rotational shaft energy and drive train which consist of gear box and a generator. The other equipment is a tower which is support the rotor and drive train.

The asynchronous generator is the most common type of generator used in the Danish wind turbine. It is a type of motor that can double as a generator. This motor consists of two parts, the stator and the rotor. The stator has a set of coils, usually six coils, placed in slots on the inside of it. The rotor is placed on an axle inside the stator. Both stator and rotor are assembled of thin iron plates.

In the outer surface of the rotor there is a row of thick aluminium bars linked at each end with aluminium ring. The rotor structure looks slightly like a squired cage. To ensure that there is a magnetic field inside the stator the coil in stator should be connected together two by two to the three different phases of the electrical grid, as show in the figure1.

Figure [ 4 ] The six coils in the starter

There are two cases were discussed to understand how a generator operates as a motor. In the first case, the rotor is at held at rest and the stator turns. This will make the coils in the rotor rapid variations of a powerful magnetic field in that way a powerful current is induced in the short circuited rotor wire windings. This makes the current create a strong magnetic field around the rotor. In this magnetic field the North Pole attracted with the South Pole in the stator’s turning magnetic field and this will supply a torque for the rotor in the same direction as moving magnetic field. After that, the rotor will start turning at the same speed as the stator and this is the second case. As the stator magnetic field and the rotor are synchronized, the rotor coils will not be subjected to variation in the magnetic field, so the current will not be induced in the short circuit rotor windings therefore there will be magnetic field in the rotor coils.

The asynchronous motor can also work as a generator by an outside energy source, such as a set of wind turbine rotor blades. If the difference between the rotating magnetic field of the stator and the speed of rotor is large the torque produce by the rotor also will be large.

When a working as a generator the rotating filed however acts as brake in slowing the rotor. The stator experiences a variable magnetic field from the rotor that it’s rotating magnetic field and there by induces an electrical current in the stator.

When there is no wind, if the wind turbine is connected to the grid the asynchronous generator will operate as a motor. The wind turbine is also likewise disconnected when the wind speed is low, and at certain per-set level the system permits a gradual. The cut-in to the grid carried out by Thyristors a kind of electronic contacts.

Figure [ 5 ] DC vs. AC current

There is also the rectifier which Change the AC current into DC current. It consists of many Diodes, however the full Wave Rectifier we will use will consist of four diodes arranged as a diode bridge and will have an output Voltage of Vdc = Vav = 2Vp/π, Vrms = Vp/√2

Safety and Control

* The Controller:

* Involved in almost all decision-making processes in the safety systems.

* The Mechanical Brake:

* Prevent the rotational speed of the blades from increasing above the rated rotational speed.

* Hydraulics:

* Operates the braking systems.

* Tip Brakes:

* Stop the driving force of the blades.

2. Design Problem Analysis

Every design has its own objectives and constrains. There are a number of objectives for the design which are set by the sponsor. In this section, the project design objectives and constraints are discussed.

2.3 Design Objectives

Safe: Means that the design will not harm the user nor the environment and if fails it will not endanger anybody around.

Durable: How long will the design operate before failure and how high the forces it can maintain.

Reliable: Works as expected and dependable.

Efficient: Means that the design will produce the maximum power it can base on the environment.

Easy to use/ install: The ease of harvesting the electricity produced with an easy installation and maintenance.

Affordable: The parts should meet the minimum standards for windmill design and in the same time cheap in price.

Simple: How hard is it to manufacture the system? And, depending on the complexity of the system, how hard is it to assemble all the parts together?

This objective can be achieved using the following procedure:

1. Designing the wind mill blades and wind turbine profile that satisfy the objective of this project, this is done using the momentum theory along with the blade element theory.

2. Using Fluent and FEA analysis to find out the maximum stress acting on the blades and hence getting the best material to be used.

3. Using the required power to be produced, analysis is made to the shaft, gearbox, and bearings to find out the required dimensions and materials.

4. Designing the generator that best fit our objective.

5. Wind tunnel test environment. The wind tunnel test will permit a testing environment having a uniform upstream velocity profile with low turbulence intensity. This eliminates the fan modeling variable in CFD analysis.

6. Analyses are made using the numerical along with the computational analysis to maximize the accuracy of the results.

2.4 Design Constraints

The limits and constraints of the design are as follows.

* The prototype to be build later on should produce enough electricity in order to power a small light build. In other words, the prototype should produce a minimum of a 100W

* Also the windmill turbine generator should be designed so that it works and is applicable here in the United Arab Emirates where there is very low wind speed compared to other countries who use wind energy

* The prototype to be build should not cost more than $2000 since the use of wind energy is not very applicable here in the UAE so the design should be affordable in order to be appealing.

3. Concept Designs

In this section, three concept designs of a windmill turbine will be presented. The three concept designs fulfill the objectives required but not equally but they all apply to the constraints. The three concept designs are based on the studies from the literature review and also through some communication with the project mentor. Since the blades are the most important component in our project we decided to choose three different concept designs based on the three different blades configurations.

3.5 4-unit Design (Concept Design one)

The first design will be based on the Danish concept of wind turbine but with a rotor with 4 four blades connected to an electric generator through mechanical system that is comprised sequentially of low speed shaft, gearbox and high speed shaft. The turbine will be supported by a beam to elevate it to a suitable height and to support the weight of the system. Newly introduced features the group intends to embed them to the design are to install the wind turbine over a 360o free rotating disk so the rotor can be rotated slowly to confront the highest wind velocity and harvest the energy. The second feature is to motorize the rotor blades by installing a motor at their base so the angle of attack can be controlled which lead to control on the power output, however, an optimized blade design is very important for the whole system to be efficient and effective.

Figure [ 6 ] Danish Concept of a practical wind turbine

The Blades design can be evaluated into more complicated standards such as the pressure coefficient distribution around the blades and how the wind streamlines behave as it pass through the blades, however, the wind turbine aimed to be designed by the group will have more controlled parameters and will be done in smaller size. In addition, computational predictions will be conducted and discussed later in the detailed design report. The following table shows the estimated cost of building the design.

Table [ 1 ] Estimation cost for the material needs for the wind mill construction

Item | Price per item | Quantity | Cost |

Cast Iron beam | 200 AED | 1 | 200 AED |

Cast Iron head | 100 AED | 1 | 100 AED |

Cast Iron blades | 120 AED | 4 | 480 AED |

steel shaft | 475 AED | 2 | 950 AED |

Gears (spur,worm…etc) | 70 AED | 5 | 350 AED |

Handmade generator | 1620 AED | 1 | 1620 AED |

Generator (optional) | 2100 AED | 1 | 2100 AED |

Peripherals (wires, diodes…etc) | 25 AED | 20 | 500 AED |

Total | | 6300 AED |

3.6 Jet Design (Concept Design two)

A new concept was derived from turbo machinery course and the internship in ADNOC facilities. The concept is to develop a wind turbine that has sets of rotors a stator to regulate the wind entrance to the rotors. The concept was searched and it is still in development because it has many difficulties to be practically used commercially. For example, the weight ratios of the design and the wind distribution as well as the size of the wind intercepting area are all need to be optimized technically and economically. However, the concept is good enough to be investigated and find whether it is possible to be adapted for the project.

Figure [ 7 ] Jet like wind turbine with sets of small rotors inside

The concept of this design is to reduce the size of the wind turbine blades and creates sets of rotors in favor of mixing air in front of the rotors to create vortexes shaped turbulence flow that can rotates the rotors. The design will be able to support the generator with a high speed enough to remove the low speed shaft and stick with a gearbox connected to high speed shaft thus reducing some of the cost. The fin can be used to rotate the turbine freely around itself to confront the highest wind velocity. The most important aspect in this design is to mix the air to produce turbulence that can act to rotate the rotors. To create turbulence from an assumed uniform wind a flow over a cantilever beam effect should be considered. When the fluid flow over an obstacle it reaches its stagnation properties at the point of collision with the obstacle then the fluid tend to flow over the obstacle and create turbulence flow at the back of the obstacle.

Figure [ 8 ] Trimetric view for the jet like wind turbine with a fin installed to it

The turbulence flow can be created by installing a tilted stator in front of the rotors so the flow behaves turbulently at the entrance. Additional turbulence can be created by letting another entrance for the flow to enter and mixes with the initial flow at a different angle creating a vortex that can rotate the rotors. The concept theoretically seems viable and the principles of thermodynamics of energy and mass conservation can be applied easily to this design but the only problem is that no practical data was found for such design which makes it interesting design for experimentation but it could be not reliable as source of efficient wind power harvester. The design systems for the conventional wind turbine still can be applied in this design such as blades design, electric generator and transmission and peripherals systems.

Figure [ 9 ] A Flow Design high efficiency Wind Turbine based on Jet [5]

The concept looks promising but one of its drawback that a high velocity is needed for cut-in speed to be achieved, also due to lack of practical data the concept design can be evaluated either as great choice or poor one. [5] assumes that the design can achieve high efficiency with small sized turbine yet a further investigation need to be done to find if that possible or the group will end building similar sizes to conventional wind turbines. Hence, an evaluation will be conducted to find the suitable design the group will carry on for further investigation. The following table shows estimation for the design cost

Table [ 2 ] Estimated cost for the second concept design

Item | Price per item | Quantity | Cost |

Wooden beam | 200 AED | 1 | 200 AED |

Wooden rotors with etched blades | 150 AED | 2 | 300 AED |

Wooden stator with etched blades | 150 AED | 1 | 150 AED |

steel shaft | 475 AED | 1 | 475 AED |

Gears (spur, worm…etc) | 70 AED | 4 | 280 AED |

Handmade generator | 1620 AED | 1 | 1620 AED |

Generator (optional) | 2100 AED | 1 | 2100 AED |

Peripherals (wires, diodes…etc) | 500 AED | 21 | 500 AED |

Plastic mixer | 150 AED | 1 | 150 AED |

Plastic cover with fins | 325 AED | 1 | 325 AED |

Total | | 6100 AED |

3.7 3-unit Design (Concept Design Three)

The third concept design is very similar to the first concept design except with a few changes. In this concept design, the team decided to use 3 blades instead of four blades because of higher speed to weight ratio. The team also chose the support to have to two beams instead of one for better stability and fixture.

Figure [ 10 ] 3-unit Concept of a wind turbine

Table [ 3 ] Estimation cost for the material needs for the wind mill construction

Item | Price per item | Quantity | Cost |

Cast Iron beam | 200 AED | 2 | 400 AED |

Cast Iron head | 100 AED | 1 | 100 AED |

Cast Iron blades | 120 AED | 3 | 360 AED |

steel shaft | 475 AED | 2 | 950 AED |

Gears (spur,worm…etc) | 70 AED | 5 | 350 AED |

Handmade generator | 1620 AED | 1 | 1620 AED |

Generator (optional) | 2100 AED | 1 | 2100 AED |

Peripherals (wires, diodes…etc) | 25 AED | 20 | 500 AED |

Total | | 6380 AED |

4. Design Decisions

In this section, a Pugh analysis is used to decide on the best design for the wind turbine generator. A Failure Mode and Effect Analysis (FMEA) is subsequently undertaken to minimize risk of failure.

4.8 Pugh Analysis

Pugh analysis is one the analysis methods used to help engineers to decide on the best design from a number of conceptual designs by comparing all the conceptual designs together based on the objectives that are required by the client and the constraints as well. The priority/weight of the objectives was decided by using a pair-wise comparison chart.

Using Pugh analysis, table 4, shows how each concept design perform relative to each other with respect to the objectives and criteria’s mentioned before in section 2.1

Table [ 4 ] Pugh Analysis

EvaluationCriterion | Weighing Factor | Comparative Performance | Reasoning |

| | Concept Designs | |

Reliable | 1 | +++ | ++ | +++ | For both the Danish and delta designs the blades and the system used have been already tested before, so it is very dependable but for the jet design there are too many factors that can easily disrupt the operation. |

Safe | 4 | + | + | +++ | All design is environmentally safe but if the first two designs broke they can easily harm people around. As for the last design there is almost a zero probability of breaking. |

Durable | 5 | ++ | + | +++ | The jet design is least durable because it has a lot of moving parts that are in touch. The Danish design will be more durable since it has less moving parts but less durable than the Delta design because it has one support that has to withstand many forces. |

Efficient | 6 | +++ | +++ | +++ | All three conceptual designs are operational since they all use the same concept of electricity generation. |

Easy to use/ install | Does it involve many steps to operate a bulb | 2 | ++ | ++ | ++ | All three designs have to go through the same steps to obtain electricity but it is not that easy. |

Economically feasible | Cost of parts | 3 | ++ | ++ | + | The first two designs took a higher factor than the third one because they have fewer parts than the third design with a cheaper cost. |

| Cost of maintenance | 3 | ++ | + | ++ | The first and third designs had the same factor because both need maintenance regularly for the motor, generator and shaft. For the Jet design it took the least because it has many parts in it which need more maintenance than the other designs. |

Design | Design for Manufacturing | 4 | +++ | ++ | +++ | The Jet design is the most difficult design to manufacture, since it has many parts and due to the complexity of the parts. However, the other two designs are equally easy, since they have the same moving parts. |

| Design for Assembly | 4 | ++ | + | ++ | The Jet design is the most difficult to assemble, due to its complex components. When comparing it to the other two designs, it is found that the other design is easier to assemble due to fewer parts and less complexity in the parts. |

Total: | 71 | 54 | 81 | Based on the results obtained, the Delta design is chosen. |

4.9 Failure Mode and Effects Analysis (FMEA)

In this section, the application of Failure Mode and Effect Analysis (FMEA) is illustrated to enhance the design reliability. Values for Occurrence, Severity and Detection ratings are presented in tables 5, 6 and 8 respectively. Using these respective tables, FMEA’s Risk Priority Number (RPN) results are presented in the following tables

Table [ 5 ] Occurrence rating scale (FMEA)

Rating | Description of occurrence |

1 | Slight chance of occurring |

2 | Occasional chance of occurring |

3 | Moderate chance of occurring |

4 | High chance of occurring |

Table [ 6 ] Severity rating scale (FMEA)

Rating | Severity description |

1 | Project can continue |

2 | Project can continue but will, have minor discrepancies in results |

3 | Project can continue but will, have significant discrepancies in results |

4 | Project cannot continue |

Table [ 7 ] Detection rating scale (FMEA)

Rating | Description of detection |

1 | Easy to detect |

2 | Medium chance of detection |

3 | Slight chance of detection |

4 | No chance of detection |

| | | | | | | | | | |

| Bending | | 2 | Reduce efficiency | 1 | Strain gage | 1 | 2 | | |

| Erosion | | 3 | Reduce the strength of material | 2 | Visible expectation | 1 | 6 | | |

| Vibration | | 1 | – Project may not continue- Reduce efficiency- Reduce the strength of material | 3 | Using sensors | 2 | 6 | | |

| | | | | | | | | | |

| Fatigue | | 1 | – Reduce efficiency- Lead to failure | 4 | Using sensors | 3 | 12 | | |

| Failure from axial forces | | 1 | Failure | 4 | Cannot be detected | 4 | 16 | | |

| | | | | | | | | | |

| Fatigue | | 1 | Project may not continue | 3 | Using sensors | 2 | 6 | | |

| | | | | | | | | | |

| Erosion | | 1 | Reduce the strength of material | 1 | Visible expectation | 2 | 2 | | |

| Vibration | | 2 | – Project may not continue- Reduce efficiency- Reduce the strength of material – Braking | 2 | Using sensors | 2 | 8 | | |

| | | | | | | | | | |

| Fatigue | | 1 | Reduce efficiency | 4 | Using sensors | 2 | 8 | | |

5. Final Design

In this section, the chosen design from the three previously mentioned designs will be shown and each system in the design will be discussed in more details as much as possible.

5.10 Chosen Concept Design

Figure [ 11 ] Front and back isometric view of the final design

As it was decided based on the Pugh analysis, the chosen concept design was the final design, i.e. the 3 unit design, since it got the highest score of 81. The design complies with all the required objectives and does not contradict with any of the constraints. As a result Solid Works simulation has been created in order to help us perform ANSYS and Fluent simulation later on the design. This is how the design basically looks like.

This design has basically five main systems, the Blades, the transmission system, the generator, the support and the safety and control system. Each system will be discussed in detail in the following section

5.11.1 The Blades

Blade design:

There are many complicated methods used for either analysis of existing wind turbine blades or the design of new one. This section demonstrate the calculation method used to design blades of the wind turbine In this design the blade element momentum (BEM) theory will be used because it has the advantages of being simple and easy to understand. Blade element momentum theory connects two methods of examining how wind turbine operates the momentum theory and the blade element theory. The first method is to use a momentum balance on a rotating annular stream tube passing through a turbine. The second is examine the forces generated by the aerofoil lift and drag coefficients at different sections along the blade. These two methods generate several equations that can be solved iteratively.

Momentum theory

The momentum theory considers axial and tangential forces. The axial forces can be obtained using Bernoulli’s equation on the stream tube around the wind turbine shown in figure1.

Figure [ 12 ] Rotating annular stream tube

Four positions are in the above figure, 1: some way upstream of the turbine, 2: just before the blades, 3: just after the blades, 4: some way downstream of the blades. Therefore the change in the pressure between 2 and 3 will result the following equation:

P2-P3=12ρV12V42

Where the force is the pressure times the area.

dFx=P2-P3dA

The axial induction factor is defined as:

a=V1-V2V1

The combination of these equations will result in the axial force on the blades:

dFx=12ρV12[4a1-a]2πrdr

Figure [ 13 ] Rotating annular stream tube

Consider the conservation of angular momentum in the annular stream tube shown in figure 1. The blade wake rotates with an angular velocity ω and the blades rotates with an angular velocity Ω.

For the rotating annular element the tangential force is:

dT=ρV2ωr22πdr

The angular induction factor defined as:

a’=ω2Ω

Then the tangential force is given by the following equation:

dT=4a'(1-a)ρVΩr3πdr

Therefore the momentum theory has yielded equations for the axial and tangential force on an annular element.

Blade element theory

Figure [ 14 ] Forces on the turbine blade

Blade element theory relies on two important assumptions. First there are no aero dynamic interactions between different blade elements. Second the forces on the blade elements are only determined by the lift and the drag coefficients. Blade element theory involves dividing up the blade into sufficient number of elements usually from 10 to 20 and calculating the flow at each one. The forces on the blade element are shown in figure1.

For each blade element the forces are:

dFx=B12ρW2CLsinβ+CDcosβcdr

dFθ=B12ρW2CLcosβ-CDsinβcdr

The torque on each blade element:

dT= B12ρW2CLcosβ-CDsinβcrdr

The first step for the blades design is determining the required rotor diameter. The rotor diameter can be determined form the output power equation:

P=12ρACPV3

Where ρ is the air density, A is the swept area of the rotor, CP is the expect coefficient of performance with maximum theoretical value of 0.59 and V is the air velocity. Taking into consideration the mechanical transmission losses including gearbox and the electrical generation losses the equation will be:

P=12ρACPηgηdV3

Where, ηgis electrical generation efficiency, and ηdis the drive train efficiency.

The relationship between the wind speed and the rotational speed of the rotor is characterized by a non-dimensional factor, known as the Tip Speed Ratio (λ).

λ=UV

Where U is the tip speed for the blade. This dimensionless factor arises from the detailed treatment of the aerodynamic theory of wind power extraction. The choice of the tip speed ratio for a particular wind turbine design depends on several factors such as the rotor airfoil profile used, as well as the number of used blades. In general a high tip speed ratio is a desirable feature since it results in a high shaft rotational speed that is needed for the efficient operation of the electrical generator. A high tip speed ratio however results in several possible disadvantages such as vibration, noise generation and erosion of the leading edge.

The rotor diameter was obtained using the maximum wind speed which is 5.67 m/s. Using the minimum required power for wind turbine P =100 W, the rotor diameter was found from the output power equation and D = 2.32 m, where ηg=0.85 and ηd=0.9.

The tip speed ratio for three blades turbine ranged from 4-6, therefore the chosen value λ=4 to avoid the vibration and noise generation. Then the rotational speed of the blades was calculated by the following equation:

N=U*60πD

N=186.6 RPM

Blade profile

Proper selection of the blade airfoil is required to obtain higher performance for the wind turbine. NACA 0012 airfoil is chosen due several reasons. The thickness of the airfoil is equal to12% of the chord length which is not very thick. The thicker boundary layer causes a large increase in pressure drag, so that the overall drag increases sharply near and past the stall point. The airfoil has symmetric geometry which can generate lift at zero angle of attack. Also, symmetric airfoil can be used to increase the range of angles of attack to avoid spin-stall. This profile has suitable Reynolds number range for the design. Also is has good stall characteristic and the roughness has little effect.

Figure [ 15 ] lift and drag coefficients curves

The lift and drag coefficients curves are shown in the diagram below:

Eventually, by using the obtained data the aerodynamics conditions for the design will be determined using iterative process.

This is how the blades look like when designed using Solid Works simulation program

Figure [ 16 ] Different views for the designed blade

5.11.2 The Transmission system

The upper part of the wind mill is composed of a hollow cylinder with a diameter of 25cm therefore the maximum diameter of the shaft and the gear is 25 cm

To calculate the stress on the shaft we are going to use the maximum stress equation:

Maximum stress: σmax = Torsional stress + Axial stress + Bending moment

Theoretically there should not be any axial stress or bending moment on the shaft therefore assuming there is only torsional stress, we will calculate the maximum stress using:

Torsional stress : T= (16* τ ) / π( D3)

Taking the shaft diameter to be 10 cm and using the torsion obtained from the power calculation.

T=(16*7.1)/ / π(10e-3) 3=36.2 Mpa

The material chosen for the shaft is cast iron. To ensure that the shaft would handle the amount of the force applied on it, the factor of safety (also known as safety factor) will be calculated, but first the type of material should be

Safety Factor: FoS = Tensile yield/ Maximum stress (( Cast iron Sy= 172 Mpa))

FoS=172 Mpa/36.2 Mpa

FoS= 4.76

The tensile yield was used because the material should not bend. The spur gear will be used in the design mostly because of its geometrical shape which fits our design.

The gears ratio will be used to set up the rational speed, but first the number of the second gear should be selected using:

W1N1=W2N2

N1 ((number of teeth)) = Diametral pitch * Pitch Diameter

N1=18*2

Figure [ 17 ] Assembled High Speed and Low speed Shafts

N1=36, W1N1=W2N2, N2=(187/1200)*36= 6

Knowing the number of teeth we can calculate the pitch diameter

Pitch diameter = 6/2 = 3

The diameter of the second shaft is 2cm

Using the same equation for the torsional stress and safety factor :

Torsional stress : T= (16* τ ) / π( D3)

The safety factor on the second diameter is 2

Figure [ 18 ] High Speed Shaft

Figure [ 19 ] Low Speed Shaft

5.11.3 The Generator

* Generating electrical power system

To design a generator or to select one, a careful analysis must be done by applying Faradays law of induction. The electromotive force can be induced by a magnetic field and it does vary proportionally with the variation of magnetic flux through time. If a single moving wire is to be used for inducing current the magnetic flux will be as follows with respect to the areaenclosed by the wire dA, magnetic field strength B and time rate t.

Φ= ttBr,t.dA(Wb) [1]

Φ=BA (B⊥A) [2]

As explained the electromotive force induced is equal to the derivative of the magnetic flux with respect to time.

ε=dΦdt (V) [3]

To increase the induced electromotive force loops of the same wire, N, can be added so equation [2] can be modified.

ε=NdΦdt (V) [4]

In a generator the mechanical rotation of a shaft can be used to move a loop inside a magnetic flux. The following figure illustrates a simple sketch of the concept.

Figure [ 20 ] Simple illustration of inducing electromotive by mechanical means

To maximize the magnetic flux in a generator the loop can be considered a flat area that is attached to two disks, stator and rotor, and perpendicular to the magnetic field thus gives:

A=rθl (m2) [5]

Φ=BA=Brθl (Wb) [2, 5]

ε=dΦdt=NBrldθdt=Brlω (V) [6]

P=Iε=εR ε=ε2R=(Brlω)2/R(W) [7]

The power obtained from the generator can be obtained by the previous equation which it depend on two main variables, angular velocity and the magnetic flux. To eliminate the magnetic flux variation it is possible to add multiple loops, windings, to the same setup which is technically called multi-phase alternator. The angular velocity value is similar to the high speed shaft which is a step up from the obtained wind rotor angular velocity which varies with the wind velocity. The generator efficiency is still needs to be added which according to [1] the efficiency ranges from 93-97 % but the calculation done were more conservative and efficiency of 90% wasselected. A sample calculation of N=20, B=0.2 tesla, r=0.03m, l=1m, and a 100W bulb with R=484Ω gave designated value of ω=40π rad/s. The following table shows the complete numerical results of the calculation done with respect to the theoretical analysis explained above.

Table [ 8 ] The calculated values for the designed alternator to produce 100 W on a single phase alternator

Variables |

Induced voltage | Ɛind= 12V |

Cut-in velocity | Vcut= 2.21 m/s |

Rated velocity | Vr= 5.67 m/s |

Angular speed | Nω= 1200 RPM |

The cut-in velocity is the minimum wind velocity needed from the rotor to rotate the shaft in order for the alternator to be able to overcome the inner resistance of the circuit to induce current in the circuit. The rated wind velocity is the designated value for the anticipated wind that will move the rotor in order to produce the required power. The angular speed needed for the alternator to be able to produce 100 W was found to be 1200 rpm. The most important point in the above calculation is that many assumptions were considered in the calculation like consistency of the velocity and the resistance of the circuit, however, such variables are bound to change with different other extraneous variables like the temperature and the discontinuity of the wind. In order to reduce such effects the rectifier circuit needs to be analyzed and selected accordingly.

In the generator the rotation of the high speed shaft can be used to induce an alternating current. The induced current usually is not in usable state because it varies with the turbine rotation speed thus a rectifier is used to transform the AC to DC. The rectifying circuit that was selected comprised of a diodes bridge circuit with a capacitor connected to it in series and in parallel to the load. The diodes bridge main function is to force the current to move in one direction only and to synchronize the amplitude of the AC to besequential and look like a mathematical model of y=|sin(x)|. The capacitor receives the semi direct current then it filters the current into direct current that is more useable and can be easily stored in a battery. The rectifying circuit is designed and selected depend on the alternator used. A single phase alternator will need one simple diodes bridge while the three-phase alternator will require connecting additional inductors so the output of the alternator can be fully utilized. The following figure shows and summarizes each alternator type and its corresponding rectifying circuit.

Figure [ 21 ] Alternator types and the corresponding rectifiers and the outputs

To find a suitable alternator for the project different possibility were planned and considered then were abandoned because of the difficulties of finding a reliable alternator in the local market or the difficulty to manufacture a generator due to many implications like alignments and casings and many parts that need skilled people to manufacture. Outsourcing was the only way of obtaining a good alternator that can be used. After considerable research two possible vendors were found to be able to fulfill the requirement. However, the first one which is a Japanese company was found that they sell stock wind turbines and they do not offer parts retailing which led to selecting the second vendor.

A UK based company called Future Energy sellsa 1 KW a direct drive, three-phase alternator with a Neodymium permanent magnet and a three-phase rectifying kit [2]. The company is expert in the wind turbines field and has garnered good reputation in UK. The wind turbines they sell are designed for medium to high wind velocity regions in the UK. They claim that their designs are built according to local standards but their alternators can be used in any region as long it operates under the specified range of the model.

Figure [ 22 ] Isometric view for the 1 KW alternator

The above alternator is able to induce voltage Ɛ=12V at a suitable speed for our design. The following table shows the specifications of the alternator.

Table [ 9 ] Specifications of the proposed alternator and its price

Variables |

Induced voltage | Ɛind= 12V |

Cut-in velocity | Vcut= 3.2 m/s |

Rated velocity | Vr= 12.5 m/s |

Angular speed | Nω= 390 RPM |

Dimensions | D=0.17m;T=0.071m |

Weight | M=7kg |

Price | 1380 AED |

The above specifications show that the alternator is suitable for the project budget, the required wind velocity range and the dimensions to be installed to the wind turbine. The rated wind velocity for this alternator is intended to produce 1KW which is not similar to the designated value obtained during the analysis, however, the vendor claims that 100W can be produced if the angular speed received by the alternator equal to N=270RPM and the corresponding wind speed equal to V=5.32m/s. The following figure shows the alternator power output with the angular speed received.

Figure [ 23 ] Power output vs. angular speed input plot

The alternator offered by the vendor is anticipated that it will meet expectations since the local standards in UK are usually high standards and they enforce the quality of the product. One important point is that if such an alternator is selected to be purchased it will be helpful in determining the gear ratio of the gearbox since the output of the rotor at the rated speed will be N=187 RPM so doubling the gear ratio to reach 300 RPM will be more feasible and cost effective than trying to reach to 1200 RPM according to the numerical analysis done previously. Ultimately, the selection of the alternator will depend mainly in the conclusions of this report which will be discussed later.

Control System

The control system which is part of the generator will be one of the pending analyses to do since it has impact on the power control of the wind turbine and the safety of the components. For example a controlling system will be able to identify an increase in the power output and will activate the braking system to reduce the rotation of the rotor and thus decrease the speed limit of the turbine to the specified range. Another example is that if the battery was fully stored then the control will make a detour from the battery and send the current to a heating element to avoid any damages to the battery.

5.11.4 The Support

The support of the design is fairly simple. It consists of a base which has a hollowed cylindrical part where the hub and the blades attach. At the bottom of that base, 2 support legs are attached which fix the windmill to the ground. In order to test the strength of the support, the design was drawn on the Solid Works. The pressure applied from the wind and on the support was calculated and found to be 15.433 Pascal using this equation

Pressure = 0.5 x C x D x V^2

C= Drag Coefficient, D=Density of air, V=velocity of air in m/s

Figure [ 24 ] Stress analysis on the support

Figure [ 25 ] Support three dimensional design

This pressure was applied on the simulation of the solid works and the support was found to be strong enough to handle the pressure as is clearly seen below.

5.11.5 Safety and control System

The Safety and control system is what ensures that the windmill does not break down and does not require maintenance often. It consists of:

* The Controller:

* It’s a Computer automated system which is involved in almost all decision-making processes in the safety systems.

* The Mechanical Brake:

* Prevents the rotational speed of the blades from increasing above the rated rotational speed. Similar to a car braking system but automated by the controller

* Hydraulics:

* Operates the braking systems.

* Tip Brakes:

* Stop the driving force of the blades.

Further and detailed analysis of this system has been put off for next semester.

6. Design Summary

In this section, the status of the project is presented along with the challenges faced.

6.11 Current Status

As of the submission of the final report, the designs required for construction have been decided on. All the systems still require further detailed analysis to ensure they will function correctly and establish the manufacturing and assembly procedures. This will be undertaken as part of next semester.

6.12 Challenges Faced

The designing process is a tedious process where a lot of observation is needed to be able to move in the correct path. The wind turbine project was no exception to the previous statement where a lot of issues where confronted and dealt with. The most notable challenges were confronted while researching, designing and managing time and the team will be discussed.

The researching was a vital part of the project since most of the fundamentals of the project are obtained through researching the topic either in online sources or books of expertise in the wind turbine field. The researching took a lot of times and intensive effort to complete it first because most of the online sources found were claiming different techniques and analysis that are useful, however, through rigorous observation it was found out that most of the analysis given were scientifically not true and more like frauds. The few remains of the online sources were verified by relating them to the engineering that were found in the library. The following issue that appeared that there are no solid fundamentals in designing a wind turbine but more like agreements or rules of thumb in designing a rotor or any components. Hence, the researching in such topic was intensive and time consuming but was managed carefully and successfully by the team.

Since no solid fundamentals were obtained the following process of designing was a mix between analysis techniques like Pugh analysis, FMEA and more deterministic approaches like iterations and trials and errors. The wind turbine consists of multiple systems that integrate each other. To obtain good designation values the rotor system and the generator were taken as two different starting points for the calculations to make the results sound and compatible. The trial and error approach was used in the rotor because the results obtained for the rotor diameter was unexpectedly large. A lot of calculations were done to reduce the size of the wind turbine but with no success and finally it was figured that the low wind velocity assumed is the main cause of the such issue which was unavoidable because it was selected as a project constraint. The transmission system had its share of the same approach when designing the shafts, bearings and even the gearbox which was the most important components because it is the center of the operation. The designing of the rotor blades took a more iterative approach by dividing each blade into ten or twenty sections and then try to design them separately depending on the torque and the other factors of the blade profile selected such as the lift and drag coefficients. Ultimately, the group was able to comprehend such difficulties and process most of the data to able to obtain a solid design.

An important issue that was looming above the team is the unusual large number of the team members. Trying to process an engineering design project in already narrow schedule was very difficult let alone dividing the work among the team members and ensuring that every team member finish the part assigned to him. Also, distributing the work load evenly was not possible because some parts of the project needed more time and efforts than other parts. The team was able to pass such test by applying some project management’s techniques such as work break-down structure, linear responsibility chart, Gantt chart and Project network chart. The previous techniques were helpful for the team to optimize the project performance and enhance the distribution of the work load with minimum time slack.

The challenges faced were an important part of the project because it boosts the team experience in finding suitable methods to use and to prepare the team for the later stages of the project where a lot of challenges will be confronted in building and verifying the design.

6.13 Intended Future Work

We’re going to undergo a cost analysis for a fully-functional turbine. A fluent simulation is also going to be made, from which a small-size scale prototype will be built. Then the design will be further altered and modified based on wind tunnel requirements. The final phase of this project will be testing and validating this prototype so we can proceed with manufacturing.

7. Conclusion

The team studied the system of the wind turbine and its components, three conceptual designs were created. A Pugh along with the FMEA analysis were employed to choose between the three conceptual designs; the third one was ranked the highest, which can be summarized into a 3-unit design concept consisting of mainly three rotating blades. Functional calculations were performed. Detailed analysis and calculations of each system of the design has been performed. Analyses were made using different types of software’s that aided in the designing process of the wind turbine. The current status and challenges faced throughout the semester were mentioned and the future intended work for next semester has been decided.

8. References

[1] Mills A.F, “Convection Fundamentals and Correlations”, Heat Transfer, Second Edition, Prentice Hall, 1999, ch.4, P.316.

[2] Hansen M.O.L. Sorensen J.N. Voustinas S. Sorensen N. and Madsen H.Aa., “State of the art in wind turbine aerodynamics”, 42:285-330, 2006.

[3] CarcangiuCarlo,”CFD-RANS StudyofHorizontal Axis Wind Turbines”, University ofdegliStudi di Cagliari, January 2008, Ch2, P.33-40.

[4] Electronic Teachers website,”Phase rotation”,http://www.electronicsteacher.com/alternating-current/polyphase-ac-circuits/phase-rotation.php.

[5] FloDesign high efficiency Wind Turbine,

[1] Fundamentals of Turbomachinery; Peng.William; Wind Turbine; CH.11; P.308.

[2]Future Energy for Wind Turbines Company; UK; 1KW permanent magnet alternator;

http://www.futurenergy.co.uk/turbine.html

http://www.engineeringtoolbox.com/torsion-shafts-d_947.html

http://www.roymech.co.uk/Useful_Tables/Drive/Shaft_design.html

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19840018973_1984018973.pdf

[4]

How Does a Generator Work? | eHow.com http://www.ehow.com/how-does_4564043_generator-work_.html#ixzz144iCQ3FW [3]

Acknowledgments

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