Abstract: A method for modelling a drillstring in a wellbore, the method comprising providing a model of the drillstring, the model representing the drillstring by a sequence of alternating springs and elements, where each element describes the mass and/or the moment of inertia of a corresponding part of the drillstring and each spring represents at least one of: axial, torsional and/or bending stiffnesses of one of the corresponding parts of the drillstring, wherein the model describes one or more forces on each element by one or more systems of ordinary equations of first or second order, where each equation comprise a linear part that comprises constant coefficients and a non-linear part that includes one or more of: one or more non-linear terms, one or more non-smooth terms, one or more time dependent terms and/or one or more coupled terms; and the method comprises recalculating the model for a plurality of time steps, wherein recalculating the model for the respective time step comprises calculating one, two or th