Simulation-Based Analysis Of Hydraulic System Behaviour With Incomplete Component Data

Sammanfattning

Hydraulic simulation models often rely on component parameters that are uncertain,unavailable, or difficult to measure. This is especially challenging when modelling older orpoorly documented hydraulic systems, where parameters such as friction, leakage, bulkmodulus, and valve characteristics may not be known. This thesis investigates whether ahydraulic simulation model with incomplete component data can still provide useful insightinto measured pressure behaviour.A hydraulic test bench was modelled in the free simulation environment for fluid andmechatronic systems: Hopsan, and compared with measured rod-side and cap-side cylinderpressure data. The work included one-at-a-time sensitivity analysis, simulation-based greybox parameter estimation, and a model-complexity comparison. The sensitivity analysis wasused to identify influential parameters, while the parameter estimation was used to improveagreement between simulated and measured pressure responses.The measured data did not show a clear oscillatory transient response. Instead, the responsewas mainly characterized by a pressure step after valve actuation. Therefore, the model wasevaluated primarily based on pressure level, switching timing, and overall pressure trend. Theparameter estimation successfully reduced the objective function and showed improvedagreement between simulation and measurement. The model-complexity comparison showedthat removing hose-wall compliance, cylinder friction, or valve detail increased the error,indicating that these modelling features contributed to the final fit.The results show that hydraulic simulation models can provide useful qualitative insight evenwhen component data are incomplete. However, fitted parameters should be interpreted ascalibrated model values rather than uniquely identified physical parameters, since addedmodel complexity increases parameter uncertainty and the risk of compensation effects.