6U SAT STRUCTURE DESIGN WITH CATIA AND ANALYSIS …

ISTANBUL TECHNICAL UNIVERSITY FACULTY OF AERONAUTICS AND ASTRONAUTICS

6U SAT STRUCTURE DESIGN WITH CATIA AND ANALYSIS

GRADUATION PROJECT

Bora Berk AYDINER

Department of Astronautical Engineering

FEBRUARY 2021

ISTANBUL TECHNICAL UNIVERSITY FACULTY OF AERONAUTICS AND ASTRONAUTICS


GRADUATION PROJECT

Bora Berk AYDINER

(110140154)

Department of Astronautical Engineering

Thesis Advisor: Dr. H. Barbaros SOYER

FEBRUARY 2021

Bora Berk AYDINER, student of ITU Faculty of Aeronautics and Astronautics

110140154, successfully defended the graduation entitled “6U SAT STRUCTURE

DESIGN WITH CATIA AND ANALYSIS”, which he prepared after fulfilling the

requirements specified in the associated legislations, before the jury whose signatures

are below.

Thesis Adviser : Dr. H. Barbaros SOYER ..............................

Istanbul Technical University

Jury Members : Asst. Prof. Dr. Demet BALKAN ..............................


Dr. Cemil KURTCEBE ..............................


Date of Submission : 01 FEBRUARY 2021

Date of Defense : 08 FEBRUARY 2021

III

To my family,

V

FOREWORD

I would like to express Dr. H. Barbaros Soyer my thanks for his advices and for

enabling me to work on this thesis. Also, I would like to thank my family for

providing me with moral and motivational support while preparing this thesis

during the online education resulting from pandemic.

February 2021 Bora Berk AYDINER

VII

CONTENTS

Page

ABBREVIATIONS .................................................................................................. X

LIST OF TABLES .................................................................................................. XI

LIST OF FIGURES .............................................................................................. XII

LIST OF SYMBOLS ............................................................................................ XIV

SUMMARY ............................................................................................................XV

1. INTRODUCTION ................................................................................................ 1

1.1. Purpose of Thesis ............................................................................................ 1 1.2. Definition of CubeSat ...................................................................................... 1

2. COMPUTER PROGRAMS AND THEIR BASIS ............................................ 2

2.1. Computer Aided Design (CAD) ...................................................................... 2

2.2. Computer Aided Three-Dimensional Interactive Application (CATIA) ........ 2

2.3. Finite Element Method .................................................................................... 2

2.4. ANSYS ............................................................................................................ 3

3. REQUIREMENTS ............................................................................................... 3

4. MATERIAL SELECTION .................................................................................. 4

5. DESIGN AND ANALYZES ................................................................................ 5

5.1. First Design ..................................................................................................... 5

5.1.1. Design ........................................................................................................ 5

5.1.2. Analysis ................................................................................................... 10

5.2. Second Design ............................................................................................... 18 5.2.1. Design ...................................................................................................... 18

5.2.2. Analysis ................................................................................................... 20

5.3. Third Design .................................................................................................. 25 5.1.3. Design ...................................................................................................... 25

5.1.4. Analysis ................................................................................................... 26

5. COMPARISON OF RESULTS AND FINAL STRUCTURE ........................ 31

REFERENCES ................................................................................................... 33

IX

ABBREVIATIONS

CATIA : Computer Aided Three-Dimensional Interactive Application

CAD : Computer Aided Design

FEM : Finite Element Method

AL : Aluminum

X

LIST OF TABLES

Page

Table 1 : Specifications of Arranged Mesh … ........................................................ 12

Table 2 : Natural Frequencies of the First Design .................................................. 15

Table 3 : Harmonic Analysis Results of the First Design… ................................... 18

Table 4 : Natural Frequencies of the Second Design… .......................................... 22

Table 5 : Harmonic Analysis Results of the Second Design… ............................... 24

Table 6 : Natural Frequencies of the Third Design ................................................. 28

Table 7 : Harmonic Analysis Results of the Third Design… .................................. 30

Table 8 : Results of Three Designs and Their Masses … ....................................... 31

XI

LIST OF FIGURES

Page

Figure 1.1 : Variations of CubeSats........................................................................... 1

Figure 2.1 : Action of Finite Element Method........................................................... 3

Figure 4.1 : Properties of Al 6061 – T6..................................................................... 4

Figure 5.1 : Top and bottom Surface......................................................................... 5

Figure 5.2 : Side Surface............................................................................................ 6

Figure 5.3 : Connection between bottom and side surface........................................ 6

Figure 5.4 : Corner piece........................................................................................... 7

Figure 5.5 : Connection of side surfaces, corner piece, top surface and bottom

surface................................................................................................... 7

Figure 5.6 : Interior surface........................................................................................ 8

Figure 5.7 : Connection of side surfaces, corner pieces, top surface, bottom

surface and interior surface…................................................................ 8

Figure 5.8 : Middle connector…………………………………………..……………………... 9

Figure 5.9 : Connection of side surfaces, corner pieces, top surface, bottom

surface, interior surface and middle connector…………………………….. 9

Figure 5.10 : Complete structure………………………………..…...……………………… 10

Figure 5.11 : First connection element……………………………….......………................ 11

Figure 5.12 : Complete connection elements…………….……...………………………... 11

Figure 5.13 : Mesh metrics spectrum…………….………………………………................ 12

Figure 5.14 : The quality of mesh……….…….………………………………….................. 12

Figure 5.15 : Fixed supports………………………………………………………………….. 13

Figure 5.16 : Total deformation of the first design………………………...…………….. 13

Figure 5.17 : Stress distribution of the first design………………………………………. 14

Figure 5.18 : Close-up view of maximum stress zone of the first design…………… 14

Figure 5.19 : First lateral mode in first mode of the design………………………......... 16

Figure 5.20 : First longitudinal mode in seventh mode of the design……………....... 16

Figure 5.21 : 36th mode of the first design………..……...………………………………… 17

Figure 5.22 : Top and bottom surface…..…….…………………………………………….. 18

Figure 5.23 : Side surface……...……………………………………………………………... 19

Figure 5.24 : Complete structure………………….....……………………………………… 19

Figure 5.25 : Total deformation of the second design....……………...……...…………. 20

Figure 5.26 : Stress distribution of the second design.…….……………………………. 21

Figure 5.27 : Close-up view of maximum stress zone of the second design....…….. 21

Figure 5.28 : First lateral mode in first mode of the design……………………...…….. 23

Figure 5.29 : First longitudinal mode in seventh mode of the design.……..………… 23

Figure 5.30 : 36th mode of the second design……………………...……………………... 24

Figure 5.31 : Top and bottom surface………….…………………………………………… 25

Figure 5.32 : Side surface……………………...……………………………………………... 25

Figure 5.33 : Complete structure…………......……………………………………………... 26

Figure 5.34 : Total deformation of the third design……...……………………………..... 27

Figure 5.35 : Stress distribution of the third design.………………..……………………. 27

Figure 5.36 : Close-up view of maximum stress zone of the third design…...……… 28

Figure 5.37 : First lateral mode in first mode of the design……………………………. 29

Figure 5.38 : First longitudinal mode in seventh mode of the design.……………….. 29

Figure 5.39 : 36th mode of the third design………………..……………………………… 30

XII

LIST OF SYMBOLS

ξ: Damping Ratio

𝑓𝑖: Natural Frequency

XIV


SUMMARY

In this thesis, necessary analyzes of 3 different 6U CubeSats created with CATIA

were performed in the ANSYS program for material of aluminum 6061 - T6.

Analysis results were stated for all 3 satellites and the most suitable one was chosen

among 3 satellites.

XV

1

1. INTRODUCTION

1.1. Purpose of Thesis

The main purpose of this thesis is to determine the most suitable option in

among three different 6U-CubeSats by designing, analyzing and comparing.

1.2. Definition of CubeSat

CubeSats that have a standard size are a class of nanosatellites. The standard

CubeSat size uses a "one unit" or "1U" measuring 10x10x10 centimeters and is

extendable to larger size; 2, 3, 6, and even 12U. Firstly, developed in 1999 by

California Polytechnic State University and Stanford University to provide a

platform for education and space exploration. The development of CubeSats

has advanced in accordance with rising needs. CubeSats are cost effective

platforms for space mission concepts nowadays [1].

Figure 1.1: Variations of CubeSats

2

2. COMPUTER PROGRAMS AND THEIR BASIS

2.1. Computer Aided Design (CAD)

Computer-aided design (CAD) is a software tool used by engineers, architects,

and designers to create digital 2D and 3D drawings by designing various items,

shapes, and spaces [2]. Designs can be created and edited in much less time with

CAD, besides they can be saved for future uses [3].

2.2. Computer Aided Three-Dimensional Interactive Application (CATIA)

CATIA, developed by the French company Dassault Systèmes is one of the

CAD programs. It is used globally and widely. Shipbuilding, aviation and

automotive industry companies are main users. CATIA was used as the design

program for this thesis [4].

2.3. Finite Element Method (FEM)

A complex computational domain is divided into small patches and finding

local solutions that satisfy the differential equation within the boundary of this

patch. A global solution is obtained by stitching the individual solutions on these

patches back together. This can be named basic definition of FEM. It provides

lots of advantages in terms of engineering solutions by analyzing much more

easily, accurately and quickly [5].

3

Figure 2.1: Action of Finite Element Method [6]

2.4. ANSYS

ANSYS is a computer-aided engineering program based on the finite element

method that allows analysis and simulations in engineering studies. ANSYS

program enables effective studies in different disciplines such as mechanics,

structural analysis, computational fluid dynamics and heat transfer. ANSYS was

used as an analysis program for this thesis [7].

3. REQUIREMENTS

Consideration of structural robustnesses under a determined load and

fundamental frequencies in terms of designed satellites are requirements in this

thesis. In order to can be determined the load that be applied is a very important

factor choosing of launch vehicle. Specifications of launch vehicle play a role

in carrying out analyses of designed CubeSats. Falcon 9 launch vehicle was

selected for this thesis. In Falcon 9 user guide, it is stated that Falcon 9 launch

vehicle has 6g maximum acceleration in the longitudinal direction, 2g in the

lateral direction, and fundamental mode must be greater than 25 Hz in the

longitudinal axis and 10 Hz in the lateral axis. In addition, safety factor is 1.4

4

for Falcon 9 according to the guide [8]. Thus, maximum accelerations were

assessed as 8.4g in the longitudinal direction and 2.8g in the lateral direction.

4. MATERIAL SELECTION

Aluminum 6061-T6 which is largely used aerospace industry and especially

construction of CubeSats was chosen for this thesis because of the fact that it

meets the required criteria of high strength, light weight, easy machinability,

and cost [9]. Therefore, Aluminum 6061-T6 was preferred for all three designs.

Aluminum 6061 - T6 is not included in the material library of ANSYS

program. So, the necessary properties of this material have been obtained from

external sources [10].

Figure 4.1: Properties of Al 6061 - T6

5

5. DESIGNS AND ANALYZES

All of 3 designs were created in the CATIA V5 program.

5.1. First Design

5.1.1. Design

The first design was created with sharp cornered form. All steps of the first

design are shown in following figures.

Figure 5.1: Top and bottom surface

6

Figure 5.2: Side surface

Figure 5.3: Connection between bottom and side surface

7

Figure 5.5: Connection of side surfaces, corner piece, top

surface, and bottom surface

Figure 5.4: Corner piece

8

Figure 5.6: Interior surface

Figure 5.7: Connection of side surfaces, corner pieces,

top surface, bottom surface, and interior surface

9

Figure 5.8: Middle connector

Figure 5.9: Connection of side surfaces, corner pieces, top

surface, bottom surface, interior surface, and middle

connector

10

5.1.2. Analysis

The analyzes were carried out in ANSYS WORKBENCH 2020 R2

ACADEMIC provided by Istanbul Technical University.

There are some points that need to be expressed before doing analysis. Firstly,

the connection elements were made in ANSYS instead of CATIA. Thus, both

increasing on the number of nodes and reducing the quality of the mesh was

prevented because of the fact that the beam connection elements is excepted

from meshing in ANSYS.

Figure 5.10: Complete structure

11

Another point is meshing. The quality of default mesh that has 19,879 mm

element size was "bad" level according to the mesh spectrum. Hence, the

meshing process was arranged to bring the mesh quality to the least "acceptable"

level for truer results of analysis. Specifications of arranged mesh are shown in

Table 1.

Figure 5.11: First connection element

Figure 5.12: Complete connection elements

12

Figure 5.13: Mesh Metrics Spectrum [11]

Table 1

Default Mesh Arranged Mesh

Element Size 19,879 mm 4 mm

Resolution 2 5

Transition Fast Slow

After meshing, fixing and acceleration was applied for static structural

analysis. Top and bottom parts were fixed because of horizontal load placement.

As mentioned in the requirements section, acceleration was applied as 8.4g in

the longitudinal direction and 2.8g in the lateral direction.

Figure 5.14: The quality of mesh was increased up to 0,22 and positioned

at a "good" level for mesh metrics spectrum after reformation of mesh.

13

Figure 5.15: Fixed supports

Figure 5.16: Total deformation for the first design

14

After static analysis, modal analysis was carried out. Natural frequencies are

assessed in the range of 0 to 2000 Hz in accordance with the user’s guide of

Falcon 9 Launch Vehicle. The natural frequencies of first 36 modes in this range

were found for first design. The lowest frequency should not be less than 25 Hz

Figure 5.17: Stress distribution for the first design

Figure 5.18: Close-up view of maximum stress

zone of the first design

15

and 10 Hz for longitudinal axis and lateral axis in order to prevent resonance.

The list of frequencies is shown in following table.

Table 2

Natural Frequencies (Hz) of the first design

1. 97,668

2. 106,04

3. 117,18

4. 118,39

5. 157,53

6. 157,85

7. 195,15

8. 213,14

9. 238,75

10. 301,63

11. 306,39

12. 313,28

13. 323,56

14. 326,3

15. 429,02

16. 437,93

17. 471,33

18. 471,49

19. 472,76

20. 475,74

21. 499,79

22. 504,08

23. 538,91

24. 540,22

25. 564,44

26. 580,62

27. 584,55

28. 590,48

29. 592,4

30. 599,32

31. 601,84

32. 603,53

33. 603,95

34. 619,78

35. 626,63

36. 631,32

16

Figure 5.20: First longitudinal mode in seventh mode of the design

Figure 5.19: First lateral mode in first mode of the design

17

This design meets the requirements due to the fact that the lowest frequencies

in both longitudinal axis and lateral axis are greater than required minimum

frequencies.

Final analysis is harmonic analysis. Five natural frequency modes were

chosen for the harmonic analysis. Damping ratios were calculated for this

analysis according to formula shown below:

where: ξ is the damping ratio and 𝑓𝑖 is the satellite natural frequency in (Hz)

[12]. Damping ratios and results of harmonic analyses are shown in Table 3.

Figure 5.21: 36th mode of the first design

18

Table 3

5.2. Second Design

5.2.1. Design

Second design was created to have a rounded form as compared with the

first design. The assembly style and connection parts like corner piece are the

same as in the first design.

Damping Ratio

Maximum

Deformation

(mm)

Maximum

Stress

(MPa)

117,18 0,0630 0,2871 64,154

Natural 213,14 0,0484 0,2057 72,521

Frequency 429,02 0,0317 0,0285 17,076

(Hz) 538,91 0,0270 0,0380 12,901 626,63 0,0241 0,0238 11,063


19



20

5.2.2. Analysis

The applied method in the meshing system, connection elements, acceleration

values, fixed supports, and types of analyzes are the same as those carried out

for the first design.

Figure 5.25: Total deformation for the second design

21

After static analysis, the natural frequencies of first 36 modes were assessed

in the range of 0 to 2000 Hz for the modal analysis of second design. The list of

frequencies is shown in following table.

Figure 5.27: Close-up view of maximum

stress zone of the second design

Figure 5.26: Stress distribution for the second design

22

Table 4

Natural Frequencies (Hz) of the second design

1. 97,781

2. 105,57

3. 117,09

4. 118,42

5. 155,41

6. 156,08

7. 194,89

8. 213,49

9. 235,19

10. 301,38

11. 302,37

12. 305,07

13. 323,15

14. 326,36

15. 446,43

16. 459,75

17. 468,29

18. 475,81

19. 476,

20. 477,2

21. 520,85

22. 526,56

23. 538,88

24. 549,97

25. 564,63

26. 587,1

27. 592,51

28. 594,44

29. 595,7

30. 607,63

31. 608,4

32. 615,9

33. 620,59

34. 624,54

35. 632,66

36. 634,74

23



24

This design also meets the requirements of frequency like the first design

because lowest frequencies are higher than 25 Hz and 10 Hz which are required

minimum frequencies for the longitudinal axis and the lateral axis.

Thirdly, harmonic analysis was performed for the second design using

damping ratio formula mentioned in analysis of the first design. After that,

obtained five results of harmonic analysis are expressed in following table.

Table 5

Damping Ratio

Maximum

Deformation

(mm)

Maximum

Stress

(MPa)

155,41 0,0562 0,1777 56,582

Natural 326,36 0,0379 0,0401 15,213

Frequency 475,81 0,0295 0,0313 15,232

(Hz) 595,7 0,0251 0,0347 21,009 632,66 0,0240 0,0307 11,656

Figure 5.30: 36th mode of the second design

25

5.3. Third Design

5.3.1. Design

The third design was created to have a compact form as compared with the

other designs. The assembly style and connection parts are the same as in the

other ones.



26

5.2.2. Analysis

As in the other designs, the applied method in the meshing system, connection

elements, acceleration values, fixed supports, and types of analysis are the same

in also third structure.


27

Figure 5.34: Total deformation for the third design

Figure 5.35: Stress distribution for the third design

28

The second analysis is modal analysis like the previous ones. Natural

frequencies of first 36 modes in the range of 0 to 2000 Hz are shown in Table

6.

Table 6

Natural Frequencies (Hz) of the third design

1. 97,651

2. 105,3

3. 116,96

4. 118,44

5. 150,88

6. 151,2

7. 196,01

8. 213,02

9. 233,48

10. 300,03

11. 304,15

12. 310,7

13. 322,87

14. 326,41

15. 348,98

16. 361,69

17. 394,41

18. 408,61

19. 433,26

20. 453,18

21. 466,35

22. 473,7

23. 511,94

24. 523,61

25. 537,82

26. 538,09

27. 541,77

28. 542,46

29. 563,61

30. 571,02

31. 573,23

32. 577,58

33. 587,66

34. 588,7

35. 599,45

36. 600,2

Figure 5.36: Close-up view of maximum

stress zone of the third design

29



30

The third design also meets the requirements of frequency like the other

designs.

Finally, harmonic analysis of the third design was performed. The results are

shown in Table 7.

Table 7

Damping Ratio

Maximum

Deformation

(mm)

Maximum

Stress

(MPa)

105,3 0,0655 0,0922 38,853

Natural 213,02 0,0484 0,1994 79,985

Frequency 348,98 0,0364 0,0359 18,060

(Hz) 433,26 0,0315 0,0318 22,956 588,7 0,0253 0,0196 14,979

Figure 5.39: 36th mode of the third design

31

6. COMPARISON OF RESULTS AND FINAL STRUCTURE

For comparison, maximum values of the results of three designs and their

masses are presented in Table 8.

Table 8

In the view of the results in Table 8, it is obvious that the maximum stress of

the third design for harmonic analysis is higher than the first design's when other

little differences are ignored among first design and third design. As for the

second and first designs, the second design has both low stress and low

deformation for harmonic analysis and static analysis compared to the third

design. Also, the second design has the lowest mass of the three designs.

Consequently, the second design becomes a best choice than the other designs.

Static Structural

Analysis

Harmonic Analysis

Mass

(kg)

Maximum

Deformation

(mm)

Maximum

Stress

(MPa)

Maximum

Deformation

(mm)

Maximum

Stress

(MPa)

First

Design

1,0475

0,10274

27,215

0,2057

72,521

Second

Design

1,0259

0,10338

22,068

0,1777

56,582

Third

Design

1,2485

0,10505

27,922

0,1994

79,985

33

REFERENCES

[1] E. Mabrouk, "What are SmallSats and CubeSats?," 07 08 2017. [Online]. Available:

https://www.nasa.gov/content/what-are-smallsats-and-cubesats.

[2] K. Pace, "CAD Definition & Meaning," [Online]. Available:

https://www.webopedia.com/definitions/cad/.

[3] "CAD - Computer Aided Design," [Online]. Available: https://www.smartdraw.com/cad/.

[4] "What is CATIA," [Online]. Available: https://www.educba.com/what-is-catia/.

[5] B. E. Rapp, "Finite Element Method," 2017. [Online]. Available:

https://www.sciencedirect.com/topics/engineering/finite-element-method.

[6] C. S. A. Erman Tekkaya, "Finite Element Method," [Online]. Available:

https://link.springer.com/referenceworkentry/10.1007%2F978-3-642-20617-7_16699.

[7] F. Hensler, "ADVANTAGE," 2014. [Online]. Available: https://www.ansys.com/-

/media/ansys/corporate/resourcelibrary/article/ansys-advantage-academic-aa-v8-i1.pdf.

[8] "Falcon 9 Launch Vehicle," 2009. [Online]. Available:

https://www.spaceflightnow.com/falcon9/001/f9guide.pdf.

[9] [Online]. Available: http://www.ae.utexas.edu/courses/ase463q/design_pages/spring03/cubesat/

web/Paper%20Sections/6.0%20Structural%20Subsystem.pdf.

[10] "Aluminum 6061-T6; 6061-T651," [Online]. Available:

http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MA6061T6.

[11] "Mesh Quality & Advanced Topics," 2015. [Online]. Available:

http://200.19.248.10:8002/professores/mauro/Curso%20Ansys/Meshing_CD_16/

lectures_trainee/Mesh-Intro_16.0_L07_Mesh_Quality_and_Advanced_Topics.pdf.

[12] N. A. A. H. Gasser F. Abdelal, "Mechanical fatigue and spectrum analysis of

small-satellite structure," 09 2008. [Online]. Available:

https://www.researchgate.net/publication/226543313_Mechanical_fatigue_

and_spectrum_analysis_of_small-satellite_structure.

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