Structural Analysis of Contra Rotating Propeller by Using FEA

Structural Analysis of Contra Rotating Propeller by Using FEA

Satya Amarnadh Parimi1, Kiran Kumar Bunga2

1IV Sem, M.Tech (CAD/CAM), Department of Mechanical Engineering, Sasi Institute of Technology and Engineering, Tadepalligudem, Andhra Pradesh, India-534101

2Assistant Professor, Department of Mechanical Engineering, Sasi Institute of Technology and Engineering, Tadepalligudem, Andhra Pradesh, India-534101.

ABSTRACT

Contra Rotating Propellers (CRP) is a type of propulsion system which consists of two propellers on the same line of shaft, spaced at short axial distance apart and rotating in opposite directions. In this project the Structural Analysis of Contra Rotating Propeller is carried out by Finite Element Analysis (FEA). The softwares used are CATIA V5R19, HYPERMESH-10 and ANSYS-14.5. This type of propeller has a hydrodynamic advantage of recovering part of the rotational energy which would otherwise be lost in a conventional single screw system. In this structural analysis, the static and the dynamic response are observed and evaluated.

Keywords: Contra rotating propeller, Static and Harmonic analysis, Finite Element Analysis

1. INTRODUCTION

   The component of a ship which converts the engine power into the driving force of the ship is called as Propeller. Contra-rotating propellers (CRP) is a type of propulsion system which consists of two propellers on the same line of shaft, spaced at short axial distance apart and rotating in opposite directions. The pitch and loading of the propellers are designed such that the resulting rotational energy in the wake is zero. To reduce shaft vibrations the number of blades of both propellers is different, so that not all blades pass each other simultaneously. The diameter of the front propeller is often slightly larger than that of the rear propeller, to account for the contraction of the propeller wake and to avoid the rear propeller to hit the tip of vortex of the front propeller.

2. DESCRIPTION

   In this work static and dynamic analysis of the contra rotating propeller is carried out.

   In this design, we need to design the contra rotating propeller in such a way that it should withstand the thrust force acting on its blades. Material considered for this is Carbon Fiber Reinforced Plastic (CFRP).

   Material properties of CFRP Youngs modulus = 1.5x 105 MPa Poissons Ratio = 0.28

   Density = 1.5 x 10-12Kg/mm3

   Thermal expansion =12 x10-6/C

3. MODELLING AND MESHING

   The CRP is considered as 3-D solid model. The structure is modeled using CATIA V5R19 modeling software as shown in Fig. 1. The model is meshed using hypermesh 10 with tetra mesh.

   The model consists of 26,816 elements and 45,790 nodes. Fig. 2 shows the solid 92 element considered for meshing. FE model of the contra rotating propeller is shown in Fig. 3. Appropriate boundary conditions are incorporated in the analysis. The solid 92 is defined by ten nodes having three degrees of freedom (UX, UY and UZ) at each node – translations in the nodal x, y and z directions. The element has Plasticity, Creep, Swelling, Elasticity, Stress stiffening, Large deflection, Large strain, Adaptive descent, Initial stress import capabilities.

   Fig . 1: Solid model of CRP

   Fig.2 : Finite element model of CRP with boundary conditions

   Table 1 : Quality parameters of mesh

   Aspect Ratio	5
   Tet collapse	0.1
   Length	10
   Min. angle of trias	20
   Max. angle of trias	120

   Fig. 3: Solid 92 element

4. Analysis of contra rotating propeller

   Static Analysis

   Static analysis is carried out to know the strength of the propeller blade by applying thrust force.

   Harmonic Analysis

   Harmonic analysis is carried out to know the frequency response of the contra rotating propeller.

5. RESULTS & DISCUSSION

   1. Static Analysis

      Static analysis of contra rotating propeller made with carbon fiber reinforced plastic is performed. Displacements in X, Y and Z directions are shown in Fig. 4, Fig. 5 and Fig. 6 respectively. Fig. 7 shows stress in X

      direction. Stress in Y direction is shown in Fig. 8. Fig. 9 shows stress in Z direction. The Vonmises stress of the CRP is shown in Fig.10

      Fig.4: Displacement in X-direction

      Table 2: Static analysis of CRP

      Name	Results as per Analysis	Allowable stresses and deflection	Reference figure
      Displacement in X-direction, mm	0.436	6.0	4
      Displacement in Y-direction, mm	0.432325	6.0	5
      Displacement in Z-direction, mm	0.388783	6.0	6
      Stress in X- direction, MPa	52.0294	550	7
      Stress in Y- direction, MPa	132.679	550	8
      Stress in Z- direction, MPa	137.885	550	9
      Vonmises stress, MPa	122.25	550	10

      Fig. 5 : Displacement in Y direction Fig. 7 : Stress in X direction

      Fig. 6 : Displacement in Z direction

      Fig. 8 : Stress in Y direction

      Fig. 9 : Stress in Z direction Fig. 10 : Vonmises Stress

   2. Dynamic analysis

      1. Modal analysis of contra rotating propeller made up with CFRP is done to find the natural frequency and the first set result is shown in Fig. 11

         Fig. 11 : First set result is 67195Hz

      2. Harmonic Analysis is carried out to find the frequency response of the CRP within the given range 50,000 to 80,000. amplitude vs frequency graphs in X,Y,Z directions are shown in Figs. 12, 13, 14

         Fig. 12 : Disp. vs Freq. along X direction

         Fig. 13 : Disp. vs Freq. along Y direction

         Fig. 14 : Disp. vs Freq. along Z direction

6. CONCLUSIONS

   The following conclusions are drawn from the present work.

   1. The maximum deflection induced is 0.4323 mm under 87 MPa load which is within the allowable limits i.e. < 6mm.

   2. The maximum stress induced is 137.88 MPa which is less than allowable limit of 550 MPa. Hence the factor of safety is 3.98.

   3. The natural frequency of the CRP is 67195Hz which is obtained in the first set of modal analysis.

   4. The maximum displacement of the nodes is 6.2mm in the frequency range 50000 to 80000 Hz where there is a chance for resonance.

7. REFERENCES

1. Taylor, D.W, The speed and power of ships, Washington,1933

2. Chang-Sup Lee, Yong-Jik Kim, Gun-Do Kim and In-Sik Nho. Case Study on the Structural Failure of Marine Propeller Blades.

3. Ziencowich and Taylor, Finite element method for solid and mechanics

4. Robert Cook, The Basis,Finite Element Analysis.

5. Terje Sontvedt, Propeller Blade Stress, Application of Finite Element Methods Computers and Structures, Vol. 4, pp.193-204.

6. M.Jourdain, visitor and J.L.Armand. Strength of Propeler Blades-A Numerical Approach, the society of naval architects and marine engineers, May 24-25, 1978, pp 20-1-21-3.

7. G.H.M.Beek, visitor, Lips B.V., Drunen. Hub-Blade Interaction In Propeller Strength, the society of naval architects and marine engineers, May 24-25, 1978, pp 19-1-19-14.

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9. Christoph Leyens, Frank Kocian, Joachim Hausmann. Materials and design concepts for high performance compressor components.

10. P.Castellini, C.Santolini. Vibration measurements on blades of a naval propeller rotating in water with tracking laser vibrometer. Department of mechanics, university of Ancona, pp 43-54.

11. Robert Latorre, M. Mizina. Design study for outboard propeller with spoiler. Ocean Engineering 26 (1999), pp 727-737.

12. Shigeki Nishiyama, Yoshitaro Sakamoto, Shunichi Ishida and Minoru Oshima. Development of contra rotating-propeller system for Juno- a 37 000-dwt class Bulk.

13. Ansys and Hyper mesh help manuals.