Lift booms with flexibility are often used in machinev. The lifting and lowering motion is usually achieved by a double-acting hydraulic cylinder. The flexible lift boom is a paticular case of a flexible multibody system.
Modelling hydraulic cylinder contribution in the boom system motion by using a non-linear finite element method can be done by several ways 11.21. Here we uresent three methods for modelling the lifting motion of the boom. The methods are based on a non-linear finite element method where/ dependent variables are measured by means of an inertial framce . We have chosen the geometric exact approach over the fundamental beam hypothesis. The placement field of the beam element is measured with respect to an inertial frame and no co-rotational frames are involved. This yields a more complicated stiffness matrix but a very simple mass matrix and constraint equations.
In the next case, we simulate the hydraulic cylinder movement by a length controlled bar element . During the analysis the cwent unstressed length of bar
, varies in time. In this modelling technique, the governing equations are a type of ordinq differential equations without constraint equations.
In our third case, the lift boom movement is caused by the modelling of the hydraulic cylinder as a first order differential equation. This approach will lead to a mixed order ODE-system and requires a special treatment from the time stepping scheme.