teether box

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BONAFIDE CERTIFICATE

Certified that this project report FAILURE ANALYSIS AND DESIGN

MODIFICATION OF TEETER DAMPER BOX OF A TWO BLADED WIND

TURBINE USING ANSY S is the bonafide work of BALAJI.

M(41501114019)ELANGO. S(41501114025) who carried out the project work under

my supervision.

Mr.T.V.GOPALHEAD OF THE DEPARTMENT SUPERVISOR

Assistant Professor

MECHANICAL ENGINEERING MECHANICAL ENGINEERING

S.R.M.Engineering College S.R.M.Engineering Co llege

Kattankulathur - 603 203 Kattankulathur - 603 203

Kancheepuram District Kancheepuram Distr ict

ABSTRACT

The Renewable Energy Research laboratory (RERL) at the University of

Massachusetts runs an Experimental wind turbine on Mount Tom. It is the origina l

prototype unit for the ESI-80 wind turbine manufactured by ESI Inc. In the 198 0s.

This turbine is a two bladed machine with a teetered rotor. Hence to damp the

teeter motion the Teeter damper box is used .In the year of 95-96 the teeter damper

box had a failure that caused it to lock up and no longer retract as the blades teet ered.

The loads predicted from this model needed to cause failure were in the range of

93,430 N (21,000 pounds) to 1, 02,330 N (23,000 pounds) which was detected us ing

strain gauges. These loads were below the previously expected maximum loads on the

teeter box by the factor of two.


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The main aim of the project is to provide a suggestion to reduce the s tress

concentration on the teeter box and also to improve the life and quality of the same by

suggesting a suitable design modif ication.

In this project, first of all the finite element model of the Teeter damper box

was constructed using Analysis package- ANSYS,V8 .Since the teeter box is

symmetrical about both axis, only 1/4 th of the original model is taken for analyz ing

purpose.

After analyzing existing model, the stress concentration was found to be more

in side members of the teeter damper box. Then the design modification has been

carried by trying out with stiffeners of different cross sections. Finally it was found

that the stress concentration reduced by 87.215 N/mm2 (4 Psi) using T section which

was more when compared with other sections

OBJECTIVE:

The main objective of the project is as follows

To identify loads those are acting in the existing model of the teeter

damper box of two bladed wind turbine.

To analyze the existing model and to find the deformation and stress

concentration in the same.

To modify the existing model by providing stiffeners to withstand the

loads and stresses to the required horizon.

To analyze the modified model and to compare the results.

To provide a conclusion for the improved design and life of the teeter

damper box.


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LIST OF FIGURES

FIGURES

Basic components of wind turbine

PAGE NO.

6

Line diagram of two bladed wind turbine 20

Existing model of teeter damper box 241/4 th meshed view of existing mode l 28

Deformed shape in X d irec tion 29

Deformed shape in Y d irec tion 30

Deformed shape in Z direction 31

Overall deformation 32

Total deform ati on 33

Stress obtained 34

Modified model of teeter damper box 38

Full meshed view of modified mode l 39

1/4 th meshed view of modified mode l 40

Deformed shape in X direc tion 41

Deformed shape in Y direc tion 42

Deformed shape in Z direction 43

Overall deformation 44

Total deform ati on 46

Stress obtained 47

ACKNOWLEDGEMENT

This project was the result of the throughput process combined, of not just

ourselves, but also a group of other people. This thesis would be incomplete withou t

expressing our heartfelt gratitude to them.

We would like to thank Prof.D.Prithviraj, HOD Mechanical eng ineeringDepartment, S.R.M. Engineering College for permitting us to undertake this project.

Mr.T.V.Gopal, Assistant Professor, Mechanical engineering Depar tmen t,

who guided us for performing this project, needs more than a word of mention as he

was the driving force behind our work. Our special thanks to him for being a constant

source of inspiration and his encouragement and extensive suggestions throughout the


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tenure of our work. He has made many important and imaginative improvements

towards successful completion of our work.

We would like to thank Mr.C.Venkataramanan, Manager Human resource

and development Department and Mr.K.R.Daniel Assistant Manager, Operations and

maintenance of SUZLON Coimbatore who extended their timely and valuable help in between their busy work schedule for completing this pro ject.

We would like to thank our project coordinator Mr.Z.Edward Kennedy,

senior lecturer Mechanical engineering Department, for extending his kind

cooperation to us. We profoundly thank all the staff members of Mechanical

engineering Department for their continuous encouragement and help towards the

successful completion of this project.

TABLE OF CONTENTS

CHAPTER TITLE PAGE NO.

1.

ABSTRACT

OBJECTIVE

i

iii LIST OF FIGURES

BASICS OF WIND POWER

1.1 Basic def initions.

i v

1

1.2 History of wind energy. 2

1.3 Advantages and disadvantages

of wind energy. 4

1.4 Picture of wind turbine. 6

1.5 Important components

and construction of wind turbine. 7

1.6 Working principle of wind turbine. 10

1.7 Classification of wind turbines. 11

2. TWO BLADED WIND TURBINE

2.1 Why two bladed wind turbine? 14


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2.2 Specifications of UMT 80

wind turbine 15

2.3 Mechanisms. 17

2.2.1 Teetering mechanism. 17

2.2.2 Yaw mechanism. 182.4 Purpose of teeter damper box. 19

3. TEETER DAMPER BOX

3.1 Line diagram of wind turbine. 20

3.2 Specifications 21

3.3 Loads. 22

3.3 Failures encountered. 23

4. ANALYSIS OF EXISTING DESIGN

4.1 Model creation. 244.2 Meshing consider ati on.

4.2.1 Assumptions. 25

4.2.2 Mode of analyzing. 26

4.2.3 Element selection. 27

4.2.5 1/4 th meshed view. 28

5. RESULTS OF THE EXISTING MODEL

5.1 F igures

5.1.1 Deformed shape in X direction. 295.1.2 Deformed shape in Y direction. 30

5.1.3 Deformed shape in Z direction. 31

5.1.4 Overall deformation. 32

5.1.5 Total deformation. 33

5.1.6 Stress obtained. 34

5.2 Summary of the result. 35

5.3 Observations. 36

6. DESIGN MODIFICATION 6.1 Modifications done on the existing model. 37

7. ANALYSIS OF MODIFIED DESIGN

7.1 Modified model. 38

7.2 Meshing.

7.2.1 Full meshed view. 39


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7.2.2 1/4 th meshed view. 40

8. RESULTS OF THE MODIFIED DESIGN

8.1 Figures.

8.1.1 Deformed shape in X dire cti on. 41

8.1.2 Deformed shape in Y dire cti on. 428.1.3 Deformed shape in Z d irec tion. 43

8.1.4 Overall deform ati on. 44

8.1.5 Total deformation. 46

8.1.6 Stress obta ined. 47

8.2 Summary of the resu lt. 48

8.3 Observ ations. 49

9. COMPARISION OF THE RESULTS 50

10. CONCLUSION 52

11. SCOPE FOR FURTHER WORK 53

REFERENCES


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CHAPTER-1

BASIC DEFINITIONS :

TURBINE:

It is a machine for producing power in which a wheel or rotor, typically f itt ed

with vanes and is made to revolve by a fast moving flow of a f luid.

WIND TURBINE :

It is a turbine driven by wind.

TEETER :

The unsteady and rocking motion.

HISTORY OF WIND ENERGY:

Since early-recorded history, people have been harnessing the energy of wind.Wind energy propelled boats along the Nile River as early as 5000B.C.By 200B.C

simple windmills in China were pumping water, while vertical-axis windmills with

woven reed sails were grinding in Persia and the Middle Eas t.

New ways of using the wind eventually spread around the world. By the 11 th

century, people in Middle East were using windmills extensively for food production;

returning merchants and crusaders carried this idea back to Europe. The Dutch ref ined

the windmill and adapted it for draining lakes and marshes in the Rhine River Del ta.When settlers took this technology to the New world in the late 19 th century, they

began using windmills to pump water for farms and ranches, and later, to generate

electricity for homes and industry.


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Wind energy is fueled by the wind, so it s a clean fuel source. Wind energy

does nt pollute the air like power plants that rely on combustion of fossil fuels, such

as coal or natural gas. Wind turbines dont produce atmospheric emissions that cause

acid rain or greenhouse gasses.

Wind energy is a domestic source of energy, produced in the United Sta tes.

The nati ons wind supply is abundan t.

Wind energy relies on the renewable power of the wind, which cant be used

up. Wind is actually a form of solar energy; winds are caused by the heating of

atmospheric by the sun, the rotation of the earth, and the ea rths surface irregu lari tie s.

Wind energy is one of the lowest-priced renewable energy technologies

available today, costing between 4 and 6 cents per kilowatt-hour, depending upon the

wind resource and the particular pro ject .

Wind turbines can be built on the farms or ranches, thus benefiting the

economy in rural areas, most of the best wind sites are found. Farmers and ranchers

can continue to work the land because the wind turbines use only a fraction of the

land. Wind power plant owners make rent payments to the farmer or rancher for the

use of the land.

DISADVANTAGES:

Wind power must compete with conventional generation sources on a cost

basis. Depending on how energetic a wind site is, the wind farm may or may not be

cost competitive. Even though the cost of wind power has decreased dramatically in

the past 10 years, the technology requires a higher initial investment than foss il-fueled

genera tors.

The major challenges to using wind as a source of power is that the wind is

intermittent and it does not always blow when electricity is needed. Wind energy

cannot be stored (unless batteries are used); and not all wins can be harnessed to mee t

the timing of electricity demands.


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Good wind sites are often located in remote locations, far from cites where the

electricity is needed.

Wind resource development may compete with other uses for the land and

those alternate uses may be more highly valued than electricity generation.

Although wind power plants have relatively little impact on the env ironmen t

compared to other conventional power plants, there is some concern over the noise

produced by the rotor blades, aesthetic (visual) impacts, and sometimes birds have

been killed by flying into the rotors. Most of these have been resolved or grea tly

reduced through technological development or by properly siting wind plants.

PICTURE OF WIND TURBINE:


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LOW-SPEED SHAFT:

The rotor turns the low-speed shaft at about 30 to 60 rotations per minute.

NACELLE:

The rotor attaches to the nacelle, which sits a top tower and includes the gear

box, low-and high-speed shafts, generator, controller, and brake. A cover protects the

components inside the nacelle. Some nacelles are large enough for a technician to

stand inside while working.

PITCH:

Blades are turned, or pitched, out of the wind to keep the rotor from turning in

winds that are too high or too low to produce e lectric ity.

ROTOR:

The blades and the hub together are called the rotor.

TOWER:

Towers are made from tubular steel or steel lattice. Because wind speed

increases with height, taller towers enable turbines to capture more energy and

generate more electricity.

WIND DIRECTION:

Upwind turbine operates facing into the wind. A Downwind turb ine

operates away from the wind dire ction.

WIND VANE:

Measures wind direction and communicate with the yaw drive to orient the

turbine properly with respect to the wind.

YAW DRIVE:


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On the other hand, there is also some wind shade in front of the tower, i.e.

wind starts bending away from the tower before it reaches the tower itself, even if the

tower is round and smooth. Therefore, each time the rotor passes the tower, the power

from the wind turbine drops slightly.

The basic drawback of upwind designs is that the rotor needs to be made

rather inflexible, and placed at some distance from the tower (as some manufacturers

have found out to their cost). In addition an upwind machine needs a yaw mechanism

to keep the rotor facing the wind.

Down wind turb i nes

Downwind machines have the rotor placed on the lee side of the tower. They

have the theoretical advantage that they may be build without yaw mechanism, if the

rotor and nacelle follow the wind passively. For large wind turbines this is somewhat

doubtful advantage, however, since you do need cables to lead the current away from

the generator.

A more flexible advantage is that the rotor may be made more flexible. This is

an advantage both in regard to weight, and the structural dynamics of the machine, i.e.

the blades will bend at high wind speeds, thus taking part of the load off the tower.

The basic advantage of the downwind machine is thus, that it may be built somewhat

lighter than an upwind machine.

The basic drawback is the fluctuation in the wind power due to the rotor

passing through the wind shade of the tower. This may give more fatigue loads on the

turbine than with an upwind des ign.

ACCORDING TO THE SIZE OF WIND TURBINE:

Small sized wind turb i ne

This type of wind turbines will have the tower height less than 80 feet.

Large sized wind turbine

This type of wind turbines will have the tower height of 80 feet and above.


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CHAPTER-2

WHY TWO BLADED WIND TURBINE?

There are many advantages and disadvantages by using two bladed w ind

turbine. They are as fol lows.

ADVANTAGES:

Two bladed wind turbine designs have many advantages when compared to

the general purpose three bladed turbine design. They are,

Weight reduction of the third b lade

Cost reduction of one blade

Reduced time in fabrication

Easy erecting

DISADVANTAGES:

However they tend to have some difficulties in penetrating the market, partly

because of the following reasons.

Requires high rotational speed to yield the same energy output

Stability and Balancing problem due to even number of blades


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SPECIFICATION OF UMT-80 (TWO BLADED) WIND TURBINE:

ROTOR:

80ft. Diameter

Two Bladed

Fixed Pitch

Downwind

Wood/Epoxy Laminate

60 RPM

Free Yaw

HUB:

3 degrees free teet er

Abex gas spring/hydraulic dampers for 3 more degrees

Adjustable Delta-3 hinge

TRANSMISSION:

Flender Planetary Gearbox

30:1 Ratio


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GENERATOR:

250 kW Marathon Electric Induction Generator

480-vo lt

3 Phase

Vectrol Soft Star t

BRAKE:

Industrial Clutch Mechanical Disk Brake

Spring Appl ied

Pneumatic Re leased

TOWER:

80 feet tall

Open Truss

Free S tanding

Tilt Down/Tilt Up


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So to facilitate the turbine to work even under small variations in the direc tion

of wind, the Yaw mechanism is used. This mechanism used to follow the w ind

direction as the direction changes.

For this Yaw mechanism a Yaw motor is used. It allows the rotor to be

operated at high Yaw angles that is turned edgewise to the wind, and with var iable

yaw rates. An electric clutch allows free yaw operation.

PURPOSE OF TEETER DAMPER BOX:

The teetering mechanism normally, teeters the hub continuously to some

angle. Due to this teetering effect, vibration is created and it affects the whole drive

train very badly. This may cause severe damage to the wind turbine.

Along with this teetering mechanism, the Yaw mechanism will also transmits

shock and loads to the drive train. So, this effect may also leads to the failure of w ind

turbine. Due to this noise is created inside the turbine.

In order to reduce these vibrations and shock loads, a damping element is used

between the hub and the drive train, which is called as Teeter Damper Box .

The main aim of using this Teeter Damper Box is to give smooth running and

to damp the v i br ati on.

CHAPTER-3

LINE DIAGRAM OF WIND TURBINE:

1. HUB 6. GENERATOR

2. BLADE 7. SUPPLY LINES

3. TEETER DAMPER BOX 8. CASING

4. GEAR BOX 9. TOWER

5. COUPLING


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SPECIFICATIONS OF THE TEETER DAMPER BOX:

Specifications of teeter box of two bladed wind turbine are given below.

Dimens i ons:

The end that dampers the bolt are 1 inch th ick.

The rest is inch thick.

Length is 24 inch.

Height is 11.06 inch.

Width is 14 inch.

Mate ri al:


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Mild s teel.

LOADS ACTING ON THE TEETER DAMPER BOX:

Normally there are two types of loads that are acting on the Teeter Damper

Box. They are as fo llows

Static Load

Dynamic Load

STATIC LOAD:

Static load is the load, due to the self weight of Rotor (weight of blades and

weight of hub) on the cantilever beam at the free end.

DYNAMIC LOAD:

Dynamic loads are the load, due to the Vibration effect caused by the

Teetering and Yaw mechanism.

FAILURES ENCOUNTERED:

In the teeter box of two bladed wind turbine due to heavy shocks that are

transmitted by teetering and yaw mechanism, the side member of the teeter damper

box has been failed. The forces were great enough that the teeter damper box failed.

This caused the box to lock up and no longer retract as the blade teeters.

The exact forces exerted by the teeter blades on the teeter dampers and thus on

the teeter damper box are unknown. From dynamic model created by the ESI 80 these

forces are estimated to be in the range of 2, 00,204 N to 4, 44,898 N (45,000 to

100,100 pounds) force.\


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CHAPTER-4

MODEL CREATION:

The full model of teeter damper box is created using Ansys software for the

given specification. The created model is given below.


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ASSUMPTIONS MADE IN ANALYSIS:

The system could be modeled by of the teeter damper box due to the

symmetry of the box. On the edges cut by symmetry, the model was constrained in

the degree of freedom perpendicular to the cut surface

The forces on the box could be modeled by a static equivalent force app lied

perpendicularly to the end of the box.

The bottom of the model of the teeter damper box was constrained in all

degrees of freedom.

The load acting on the teeter damper box is being shared equally by the seven

bolts which hold the damping ma terial.

The wind turbine shaft, the bearing which mounts the shaft, the damp ing

material around the bearing all are assumed to be rigid. So that no deformations or

failures occurs to them.

The material of the teeter damper box is throughout homogenous and

isotropic.

MODE OF ANALYZING:

ACTUAL LOAD ACTING AREA:

In two bladed wind turbines the shaft is held by the bearing. The bearing is

held by the damping material. The damping material is rigidly bolted to the teeter

damper box. So all the loads acting over the teeter damper box acts directly to the bolt

holes of the damping ma ter ial.

INTENSITY OF LOAD:

The teeter damper box should be designed to with stand a minimum load of

45000 pounds and a maximum load of 100000 pounds. So the minimum intensity load

of 45000 pounds was taken into account for analyzing purpose at first s tage.


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DIRECTION OF THE LOAD:

The load or force acting on the teeter damper box compresses it at the face and

hence the tensile force is acting at the X axis towards the rotor.

AREA OF APPLICATION OF LOADS IN ANALYSIS:

Since it was found out that the load is directly acting on the bolt holes to

which the damping material is bolted, in our analysis the load or force is applied to

the nodes which are attached to the areas of the bolt holes.

ELEMENT SELECTION:

Even though many type of elements are available for analyzing purpose, the

element chosen for analyzing in this problem was 3-D, 10 noded tetrahedra l

structural So li d.

REASON FOR CHOOSING THE ELEMENT:

Normally in ANSYS package any type of geometrical structure can be

analyzed by choosing particular element type. The property of the particular elemen t

chosen will match for the geometrical profile of the structure which is being analyzed.

Since the load acting in our problem is on the bolt holes which have the geometrica l

profile of circle, the above said element is chosen.


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This element will give very good accuracy while analyzing the sections with

circular profile. The other brig elements will not give much accuracy while analyz ing

circular profiles.


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SUMMARY OF THE RESULTS:

Thus the maximum deformation, overall deformation, and stress obtained in

the existing model of the teeter damper box is given below.

Maximum deformation in X-direction : 0.0007188 mm (0.0000283 inch.)

Maximum deformation in Y-direction : 0.02962 mm (0.001166 inch.)

Maximum deformation in Z-direction : 0.059868 mm (0.002357 inch.)

Over all deformation : 0.8204 mm (0.032301 inch.)

Maximum stress : 88.243 N/mm 2 (12794 psi.)

OBSERVATIONS:

Even though the load is applied towards the X axis, the deformation observed

in X direction is very low, when compared to Y and Z directions. The deform ati on

observed in Y direction is also lower than the Z direction as stated earlier. So

ultimately the deformation in Z direction is more.

Since the bolt holes are directly taking the loads as tensile force, the stress

concentration is ultimately predominant at the top center of the side faces as shown in

the figure. This stress concentration elongates the teeter damper box and hence it

looses its rigidity and starts y ielding.

So the rigidity of the side faces of the teeter damper box is not sufficient to

withstand the tensile force exerted by rotor of the turbine.

This is the observation made after the analysis of the existing model of the

teeter damper box.


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CHAPTER-6

MODIFICATIONS DONE ON THE EXISTING MODEL:

As a result of analysis done on the existing model, the side members of the

teeter damper box is found to be failed and the stress concentration also more in the

side member as shown in the f igure.

In order to reduce the stress concentration in the side member of teeter damper

box stiffeners are to be added. The stiffener may of same material or different. But for

this problem it is considered as same ma terial

Normally for stiffeners we can use rectangular section, T section or I section.

But if the rectangular section is used there wont be much improvement in the results.And if the I section is used the weight of the teeter damper box may increase.

So, in this case the T section stiffeners are added to the side members of the

teeter damper box. This is the modification done on the existing model of the teeter

damper box. Now the modified model has to be created and the new deformation and

stress concentration are to be found by ana lysis.

CHAPTER-7

MODIFIED MODEL:

The new modified model was created by using analysis software. The

modified model created was shown in the f igure.


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RESULTS OF THE MODIFIED MODEL:

After modeling the modified teeter box the analysis is carried out in order to

find the deformation in X, Y & Z direction, total deformation, overall deformation,

and stress obtained. The results of the modified model are shown in the fo llowing

figures.


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EXIXTING MODIFIED

Maximum deformation in X-direction : 0.0007188 mm 0.0007188 mm

Maximum deformation in Y-direction : 0.02962 mm 0.02956 mm

Maximum deformation in Z-dire cti on : 0.059868 mm 0.0598 mm

Over all deformation : 0.8204 mm 0.08117 mm

Maximum s tress 88.243 N/mm 2 87.215 N/mm 2

Thus we can clearly identify from the above comparison that, after providing

stiffeners to the side members the deformation in Z axis, overall deformation and

stress obtained are reduced when comparing with the existing model.

GRAPH BETWEEN LENGTH OF SIDEMEMBERS AND DEFORMATION:

EXISTING MODEL:


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comparatively low with other cross sections. Thus the stiffener with T cross se cti on

improved the life of the teeter damper box by reducing the maximum stress

concentration and maximum deformation. Moreover T cross section enabled weight

reduction along with fabrication ease. So the stiffener with T cross section might be

suggested for the requirement.

CHAPTER-11

SCOPE FOR FURTHER WORK:

In our project work we had made some assumptions to simplify our problem.

In future considering some real situations the assumptions made may not be fo llowed

due to some practical difficulties. By considering such situations the following scopes

may be fo llowed.

At times the forces acting on the teeter damper box may not be uniform. A t

such situations a statically equivalent force cannot be applied for an alysis.

The material of the teeter damper box may not be homogeneous and isotropic.

At such situations assuming of material properties may differ in analysis.

At practical situations the shaft of the wind turbine, the bearing that holds the

shaft, the damping material that holds the bearing all are not rigid and undergo

deformations by taking the loads. But since our project area focuses only on teeter

damper box we assumed that all other elements other than teeter damper box are rig id.

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http://www.nrel.gov /docs/fy02os ti/2665.pdf
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http://www.synchroli te.com/1127.html

http://www.synchroli te.com/1239.html
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