1. User Defined Element Enables modeling of user defined element using an external dll. The external dll estimates the forces, stiffness and damping. 1.1. External dll interfaces The external dll must contains five functions with names userdef_files_init() userdef_element_init() userdef_element_calculate() userdef_element_finish() userdef_files_finish() Description of the input and the interface for the external userdefined element is given in User defined element.