This project deals with models of hydraulic drive systems which appear in construction machinery, agricultural machinery, machine tools, steel mills, offshore platforms, or traction drives. Such systems consist of hydraulic and mechanical parts that are mutually coupled. For a prediction of pressure pulsations and mechanical vibrations, accurate coupled hydraulic-mechanical models are required. This project shall demonstrate how experiments can help to improve dynamic models of coupled hydraulic-mechanical systems.

Although it has been attempted to calculate the mechanical vibrations of pipelines that are filled with a pulsating fluid, the results sometimes failed to agree with measurements. On the other hand, the respective models contain parameters that are not known exactly. It is obvious to ask how parameters can be found to obtain an optimal match between theory and experiment; this is the purpose of model updating.

Experimental data for model updating shall be provided by experiments in which the coupled hydraulic-mechanical system is excited by a hydraulic or a mechanical device, such as a valve or an impact hammer. Pressure pulsations and mechanical vibrations shall be measured, the transfer behavior shall be calculated in the frequency domain, and resonance frequencies shall be identified; coupled hydraulic-mechanical vibration mode shapes shall be extracted by modal analysis. Resonance frequencies and mode shapes shall also be calculated from theoretical models and compared with experimental results. Using the sensitivities of theoretical models with respect to parameter changes, optimal parameter values shall be found by minimizing the error between theoretical and experimental resonance frequencies, mode shapes, or other dynamic characteristics.

If necessary, model structures shall be extended to obtain more appropriate system descriptions.

Although model updating has been developed for mechanical systems and is frequently applied in structural dynamics, the concept is new for hydraulic and coupled hydraulic-mechanical systems. Two case studies shall demonstrate the process of model updating. The first case study treats the torsional vibrations of a pump drivetrain in combination with the pressure pulsations of an attached hydraulic system. The second case study investigates fluid-structure interaction in hydraulic pipeline systems; by an extension of the model structure and subsequent model updating, successful predictions are expected where models failed in the past.