ELASTIC STRENGTH OF PROPELLERS-AN ANALYSIS BY MATRIX METHODS

The determination of displacements and stresses in a propeller blade under the influence of a hydrodynamic pressure load is investigated. Also a simplified approach to the free, undamped vibration of the blade is suggested. The finite element method of analysis is used to analyze the blade as a shell or as a combination of a three dimensional solid and a shell. For the vibration problem, the complete blade was idealized by shell elements only. Constant stress tetrahedra and rectangular prism elements were used for the analysis of the three dimensional solids. A combination of both kinds of elements was found to cause no algorithmic difficulties or inaccuracies in the results and to provide the flexibility to approximate irregular boundaries by the tetrahedron. The stiffness of the shell element was obtained by the superposition of the stiffness of the plane stress element and the fully compatible plate bending element. The results using only the shell element were good both for the static and the dynamic problems. It was felt that with comparable meshes the shell element was more powerful than either of the three dimensional elements. The process of joining two different pieces of the structure is described. The method is based on the continuity of displacements and slopes across the interface of the two pieces. Use of this joining method for an actual propeller blade is possible, but probably expensive. A comparison of the different methods of solution is made by applying them to the problem of a wide, stepped cantilever plate for which experimental results were available. The shell analysis yields very good results even though the elements close to the fixed end are too thick for a good approximation. The combination of three dimensional elements, shell elements and the joining method gave the best results. In general, positioning the joint may be difficult. Displacement and stress patterns are obtained for the load and geometry of the propeller blade investigated by Conolly. The shell approach does not force one into making the assumption that displacements normal to the propeller blade surface are a function of the radius only. The results obtained agree very well with Conollys experimental information.

  • Corporate Authors:

    University of Michigan, Ann Arbor

    Department of Naval Architects and Marine Engineers
    Ann Arbor, MI  USA  48109
  • Authors:
    • Genalis, Paris
  • Publication Date: 1970-11

Media Info

  • Features: Appendices; Figures; References; Tables;
  • Pagination: 193 p.
  • Serial:
    • Issue Number: 101

Subject/Index Terms

Filing Info

  • Accession Number: 00015541
  • Record Type: Publication
  • Source Agency: University of Michigan, Ann Arbor
  • Files: TRIS
  • Created Date: May 19 1973 12:00AM