| The ship shafting is influenced by several dynamic factors during navigating, such as vibration force of main engine, propeller hydrodynamic force and oil film pressure. The power of main engine and the shaft diameters are both increasing with the trend of larger-sized vessels, and the effects of those dynamic factors are becoming increasingly significant which lead to different bearing loads depending on whether the ship shafting is running or not. Previous shaft load measurements are carried out under static states and the dynamic load of shaft cannot be measured in accordance with actual situations of the ship.A dynamic shafting load measuring system is developed on the basis of the original strain gauge method in this article. Firstly, with the study on dynamic load calculation algorithm and the collection of whole strain wave, the signals are analyzed by digital filter technology and frequency domain analysis before designing a digital filter to eliminate relevant errors. Through the waveform analysis of the rotating shaft, the maximum strain and the bending moment of shaft cross section and can be deduced, and the bearing load distribution can be calculated with the balance equations of force and moment.Secondly, in order to acquire the required variables in algorithm including dynamic stress wave of shafting and rotation angle of strain gauge, a hardware measuring system of dynamic load is designed in this paper. Dynamic strain signals from strain gauge are collected by a wireless strain transmitter-receiver while the rotation angle of strain gauge is recorded by a magnetic angle sensor. Measurement processes are designed relevantly based on different measurement equipment. Measurement software program is developed by hybrid programming with VB.NET and MATLAB according to the designed algorithm and hardware manipulating process. Finally, the feasibility of the measurement method is verified by the collection and calculation of subsistent vessel data. |
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