Modelling of a hydro-pneumatic system for heave compensation

Abstract

Testing of control systems on simulators has been found to be both cost and time e cient. To get good results from testing, a realistic response from the simulator is important. In this thesis, a mathematical model of a hydropneumatic heave compensation system for such purposes is proposed. The emphasis has been on developing a relatively simple model which is easy to run, but also accounts for important e ects like friction, non-ideal gas behaviour and temperature variation in the gas system. The mathematical model is veri ed against log data obtained from real drilling operations. Then, it is compared to simpler versions to investigate and discuss the importance of including temperature variation and non-ideal gas behaviour. It was found that the model was in good accordance with the log data. When neglecting the temperature variation, a deviation in pressure variation of 20-30% from the original model was experienced. For the given conditions, a deviation of about 4% from non-ideal gas equations was found when assuming ideal gas. This is in good accordance with the compressibility chart. To verify the deviations found in the compressibility chart, a simulation closer to the critical point was performed. It was concluded that the compressibility chart should be used as an indication of the applicability, and accuracy obtained, under the assumption of the ideal gas in this model.