Finite Elements and Green’s Functions

  • Friedel Hartmann


In FE-analysis we substitute for the exact solution of the equation L u = p an approximation uh which is the exact solution of the equation L uh = ph. The special nature of the FE-solution allows to extend Betti’s Theorem (p1,u2) = (p2,u1) to the FE-solutions in the following sense (p1,uh 2,p2,u1 h) which establishes that the FE-solution is the scalar product of the approximate Green’s function Gh[x] and the original right-hand side p, namely uh(x) = (Gh[x],p). We must distinguish between weak and strong influence functions. Weak influence functions are based on the principle of virtual forces (Green’s first identity) and can only be formulated for displacement terms while strong influence functions, which can be formulated for displacement and force terms, are based on Betti’s theorem (Green’s second identity). In FE-analysis this distinction gets lost because of the approximate nature of the kernel functions. Influence functions in FE-analysis take a nodal form, that is they are evaluated by summing over the nodes (scalar product of two nodal vectors g and f or u and j). The columns of the inverse stiffness matrix are the nodal values of the Green’s functions. Infinite stresses pose a problem for influence functions because they imply that the kernel functions become unmeasurable when the dislocations, which trigger the Green’s functions, move to the singularity. The essential features of discrete FE-Green’s functions also apply in the case of mixed problems and the sensitivity of the p-method with regard to point sources also follows from the nature of the Green’s functions.


Shape Function Stiffness Matrix Nodal Displacement Influence Function Nodal Force 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


  1. Tottenham H (1970) Basic principles. In: Tottenham H, Brebbia C (eds) Finite element techniques in structural mechanics. Southampton University Press, SouthamptonGoogle Scholar
  2. Jakobsen B, Rasendahl F (1994) The Sleipner platform accident. Struct Eng Int 3:190–194CrossRefGoogle Scholar
  3. Hartmann F (1985) The mathematical foundation of structural mechanics. Springer, BerlinGoogle Scholar
  4. Strang G, Fix GJ (1973) An analysis of the finite element method. Prentice Hall, Englewood CliffszbMATHGoogle Scholar
  5. Strang G (2007) Computational science and engineering. Wellesley-Cambridge Press, WellesleyzbMATHGoogle Scholar
  6. Hartmann F, Katz C (2007) Structural analysis with finite elements, 2nd edn. Springer, BerlinGoogle Scholar

Copyright information

© Springer Berlin Heidelberg 2013

Authors and Affiliations

  1. 1.Structural MechanicsUniversity of KasselBaunatalGermany

Personalised recommendations