Coupling operations for trains fitted with automatic couplers can result in high forces and accelerations, but they can be decreased by means of shock absorbers attached to the couplers. The longitudinal dynamics are very dependent on the type and parameters of the shock absorbers used at the vehicles interfaces.

This thesis proposes a computer program developed in MATLAB that simulates the longitudinal dynamics of two trains, with an arbitrary number of carbodies, at coupling. This program allows to control if the shock absorbers to be used are suitable for the coupling conditions required and, otherwise, calculate what parameters would be proper.

The program focuses on the modelling and behavior of the shock absorbers, especially gas-hydraulic buffers. Rubber springs and friction springs are also modelled.

The model of the trains is simpler, where every carbody consists of two masses joined with the carbody stiffness, and the interfaces between the carbodies are represented by three masses: two of the masses corresponding to the centre couplers of both adjacent carbodies, and the other one corresponding to the coupler heads. It is possible to use another train model equivalent to a single mass per carbody and where the carbody stiffness is added to the elements at the interfaces.

The force and stroke histories of the model for the gas-hydraulic buffer are compared against test data for the compression phases and good agreement is achieved. Simulations performed with Stockholm Metro C20 trains also agree satisfactorily with measured data obtained at coupling operations at various speeds.

Simulations performed with the program, since it can also simulate tensile forces, show that at relatively low coupling speeds the tensile forces that appear at recoil for the set of gas-hydraulic buffer and friction spring can sometimes be higher than at compression. This should be considered since most coupling operations occur at low speeds and this effect is usually disregarded.