STRUCTURAL ANALYSIS OF INTEGRATION OF A

NON-CYLINDRICAL CNG TANK

BY PRATHAMESH P. DESHPANDE

ADVISORDR. GREGORY M. ODEGARD

TOPICS

• Introduction• Objective• Design modifications• Finite Element Analysis (FEA)• Results• Conclusion• Future work

INTRODUCTION

• Use of CNG as an alternate automobile fuel• Development of non-cylindrical CNG fuel tank• Integration of the tank in the underbody• Availability of entire cargo space

[Untitled illustration of CNG powered pickup truck]. Retrieved June 22, 2015 from http://www.gmfleet.com/vehicle-overviews/fuel-efficiency/bi-fuel.html

OBJECTIVE

• Integrating heavier tanks on the frame possible

• Modifying the CAD of the vehicle underbody

• Performing FEA to validate integration of 7 rectangular tanks on the frame

Odegard, G. M. (2015). Seven quarter scale tanks positioned under truck. Retrieved June 22, 2015 from Updates on Conformable Tank Development PowerPoint presentation

CAD MODIFICATIONS

• List of modifications• Initial design • Final design

LIST OF MODIFICATIONS

• Removal of default gas tank• Redesign and relocation of

exhaust• Removal of spare tire• Inclusion of secondary small gas

tank

INITIAL DESIGN

FINAL DESIGN

FINITE ELEMENT ANALYSIS

• Original Chassis ConfigurationoStructureoMesh validationoMesh parametersoMesh patternoMaterialoLoad estimationoForces and constraintsoResults

STRUCTUREC-channel Side railsCross-membersMounting brackets

MESH VALIDATION

0 0.2 0.4 0.6 0.8 1 1.20

1

2

3

4

5

6

7

8

9

10

[X VALUE], [Y VALUE]

[X VALUE], [Y VALUE]

von Mises stress (ksi) vs Element size (inches)

Element Size (inches)

von

Mise

s str

ess (

ksi)

MESH PARAMETERS

• Mesh type - 2D mixed mesh• Element size – 0.1 inch• Aspect ratio (< 5) – 4.93• Skewness (< 45 deg) – 40• Jacobian (> 0.6) – 0.6• Connectors – 1D seam

MESH PATTERN

MATERIAL

Sr. No. Property English Metric

1 Yield Strength 55 ksi 380 MPa

2 Tensile Strength 95 ksi 650 MPa

3 Elastic Modulus 29900 ksi 206 GPa

4 Poisson’s Ratio 0.29 0.29

5 Density 0.28 lbs./in3 7.75 g/cc

GM 980X- High strength steel

Rashid, M. (1977). GM 980X - Potential Applications and Review. SAE Technical Paper 770211, 1977, doi: 10.4271/770211.

LOAD ESTIMATION

• Total load on the frame = 7120 lbs.• Load on front section = 4200.8 lbs. (233.38 lbs. on each location)• Load on rear section = 2919.2 lbs. (364.9 lbs. on each location)

Front section (passenger car)Rear section (cargo)

FORCES AND CONSTRAINTS

F = 233.38 lbs.R = 364.9 lbs.

RESULTSMaximum displacement = 0.027 inches

Maximum von Mises stress = 47.55 ksi

FINITE ELEMENT ANALYSIS

• Modified Chassis ConfigurationoStructureoMaterialoUpdated loadsoResults

STRUCTUREC-channel Side railsCross-membersMounting bracketsSide tank bracketsBack tank bracket

MATERIAL

Sr. No. Property English Metric

1 Yield Strength 36.3 ksi 250 MPa

2 Tensile Strength 58 ksi – 79.8 ksi 400 MPa – 550 MPa

3 Elastic Modulus 29000 ksi 200 GPa

4 Poisson’s Ratio 0.26 0.26

5 Density 0.284 lbs./in3 7.85 g/cc

GM 980X for frame and A36 mild steel for brackets

Matweb, LLC. (2015). ASTM A36 Steel, plate. Retrieved June 22, 2015, from http://www.matweb.com/search/datasheet.aspx?matguid=d1844977c5c8440cb9a3a967f8909c3a

UPDATED LOADS

• Load due to tank integration = 700 lbs. • Removal of weight from original load case = 215 lbs.

RESULTSMaximum displacement = 0.11 inches

Maximum von Mises stress = 51.6 ksi

RESULTS SUMMARY

Sr.

No.

Frame

Configuration

Component Material Maximum

Displacement

(inch)

Maximum von

Mises stress (ksi)

Yield

strength (ksi)

Factor of

safety

1 Original Frame GM 980X 0.027 47.55 55 1.16

2 Modified

Frame GM 980 X 0.031 45.94 55 1.2

Side brackets A36 mild steel 0.069 10.063 36.3 3.61

Back bracket A36 mild steel 0.11 51.604 36.3 0.70

CONCLUSION

• Integration of the tanks is possible• Correct approach of mounting the

front 4 tanks• Failure of back bracket cannot be

established• Essential to include trailer hitch

assembly in future simulations

FUTURE WORK

• Finalize design of brackets• Perform impact analysis on brackets and tanks• Conceptualize brackets for phase II tanks

THANK YOU