A computer-implemented method for simulating an industrial environment of a production site to simulate motion of objects in the industrial environment of the production site with collision responses, the method comprising: - creating , by a computer (104; 902), a three-dimensional model system representing the industrial environment of the production site, the model system comprising a plurality of bodies representing physical components of the industrial environment of the production site, wherein each body comprises one or more collision surfaces to define constraints representing the surface of the respective body and one or more visual surfaces to be presented to a user to visualize the respective body, - identifying , by the computer, one or more groups of bodies from the plurality of bodies, such that bodies belonging to a group are constrained in relation to each other by fixed joints, - processing, by the computer, each group of bodies, the processing comprising: if a group of bodies comprises a background object as a constituent body, then removing all constituent bodies of the group while preserving the respective collision surfaces and visual surfaces, and if a group of bodies does not comprise the background object as a constituent body, then modelling the group of bodies as a single merged body, the merged body having defined mass properties, position and orientation determined based on mass properties and structure of constituent bodies of the group, and - executing , by the computer, a simulation code solving rigid body dynamics for the model system based on said processing of each group of bodies. - creating , by a computer (104; 902), a three-dimensional model system representing the industrial environment of the production site, the model system comprising a plurality of bodies representing physical components of the industrial environment of the production site, wherein each body comprises one or more collision surfaces to define constraints representing the surface of the respective body and one or more visual surfaces to be presented to a user to visualize the respective body, - identifying , by the computer, one or more groups of bodies from the plurality of bodies, such that bodies belonging to a group are constrained in relation to each other by fixed joints, - processing, by the computer, each group of bodies, the processing comprising: if a group of bodies comprises a background object as a constituent body, then removing all constituent bodies of the group while preserving the respective collision surfaces and visual surfaces, and if a group of bodies does not comprise the background object as a constituent body, then modelling the group of bodies as a single merged body, the merged body having defined mass properties, position and orientation determined based on mass properties and structure of constituent bodies of the group, and if a group of bodies comprises a background object as a constituent body, then removing all constituent bodies of the group while preserving the respective collision surfaces and visual surfaces, and if a group of bodies does not comprise the background object as a constituent body, then modelling the group of bodies as a single merged body, the merged body having defined mass properties, position and orientation determined based on mass properties and structure of constituent bodies of the group, and - executing , by the computer, a simulation code solving rigid body dynamics for the model system based on said processing of each group of bodies. <EOS>