Pitch stability analysis of high-lift wire rope hoist vertical shiplift under shallow water sloshing–structure interaction

Pitch stability under shallow water sloshing–structure interaction has always been the most concerned issue in the design of the high-lift wire rope hoist vertical shiplift, which brings great challenges to the operational safety. A semi-analytical method including the developed modal system and the new coupled dynamics model is presented for pitch stability analysis. Based on the linear modal theory, the modal system is developed to describe the shallow water sloshing in the shiplift chamber, and the hydrodynamic moment associated with infinite set of modal functions is reasonably simplified by only retaining the lowest mode. Then a new 9-DOF coupled dynamics model of the complete main hoist system, shiplift chamber motion, and shallow water sloshing is established as dynamic equations by using the Lagrange equation of the second kind. Subsequently, the coefficient matrix of the dynamic equations and the Lyapunov motion stability theory are used in combination to numerically obtain the critical distance of suspension points. Taking four typical high-lift wire rope hoist shiplifts as an example, the results indicate that the proposed scheme improves the computational accuracy by 7.0–20.8% with respect to previous methods. Furthermore, for the being designed 200 m level wire rope hoist vertical shiplift, the preliminary design parameters can ensure the pitch stability safety factor not less than 1.3, increasing the wire rope stiffness or the synchronous shaft stiffness can effectively enhance the pitch stability.