Modeling and Simulation of the Accumulator During Active Heave Compensation Operations

Abstract

The paper presents the modeling and simulation of the thermodynamics of the accumulator system of the heave compensation system. Heave compensators in offshore and subsea applications are used to reduce the relative vertical motion of the load caused by the vessel movement. The accumulator system is an integral part of the power system, which typically can be the hydraulic system of the crane cylinders or the winch motor. The accumulators are mainly used to reduce the power consumption during heave compensation through regenerating power. Hence, the working properties of the accumulator gas become important, and these properties are very dependent upon the temperature and pressure. Modeling of the dynamics of the accumulator and the hydraulic system is complex due to the nonlinear characteristics of fluid dynamics and thermal processes. The derivation of the constitution formula for the accumulator dynamics is described, and the modeling is presented using the Bond Graph method. The implementation of the modeling and simulation is done in a software tool called 20-sim. The temperature and pressure variations of the accumulator during heave compensation were discussed considering the impacts of the heat transfer process and the pipe flow between the accumulator and the gas bank. Compared to the experimental testing data, the simulation results appear realistic and convincing. The simulation model provides useful information for system design and analysis.