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.

As the core structure of the shiplift, the ship chamber is a typical rectangular container with filling water depth less than 0.1. Even small pitching excitation could produce large liquid sloshing and significant capsizing moment, and lead to a catastrophic overturning accident. As a basis of dynamical modeling and simulation of the shiplift, a fluid dynamic model is presented to predict the capsizing moments based on the Housner theory. Assuming a time-harmonic pitching excitation, the potential solution reflecting dynamic characteristics between pitching excitation and the fluid free surface oscillation angle is expanded analytically. A series of engineering formulas for the capsizing moments, including impulsive and convective parts, are then imposed. Comprehensive numerical analysis further extends the applicability of formulations to the cases for most of ship chambers or other rectangular tanks with similar filling water depth. The validation of proposed scheme is extensively demonstrated through comparison with other theoretical method and experimental results, and the interaction between the forcing frequency, the capsizing moments and fluid natural frequency has been qualitatively descripted. The results exhibited that the present model has accurate description under the conditions of small pitching angles and only considering the capsizing moments coming from the convective pressures can ensure high accuracy in engineering design.

To analyze the pitching stability of the fully balanced hoist vertical shiplift, this paper develops a fluid velocity potential and dynamical model of the vertical shiplift based on an improved energetic exponent method, to study the influence of the primary structural parameters on the pitching stability of an actual shiplift installed in GuoPitan shiplift (GuiZhou province, China). With the linearized potential theory and the undetermined coefficient method, the numerical analytical expression of the velocity potential is obtained by discussing the pitching motion of ship chamber. Applying the Lagrange equation of the second kind to establish a dynamical model of the shiplift having multiple degrees of freedom, the energetic calculated model for ship chamber in respect to the pitching motion is proposed. To accurately analyze the variation of the pitching stability, this paper develops the slope of energetic varied curve, based on the orthogonal polynomial approximation and the subsection averaging method. Also, the influence of the parameters is studied, including the distance of lifting point, the synchronous synchronous shaft stiffness, and the hoist radius, with the optimized design of these three structural parameters: a = 40.0 m, C = 2.0 × 10 9 N/m, and R = 1.8 m. The changing range of the absolute value of energetic exponent for the distance of lifting points is the largest of the three structural parameters (5.00-12.80), indicating that the distance of lifting points has the most remarkable influence on the pitching stability. Moreover, by the Runge-Kutta algorithm, the response of the angle displacement is analyzed before and after optimization, and then the reliability of results is demonstrated. The four angle displacements at the peak values close to 300 s decrease by 11.11%, 13.33%, 15.91%, and 10.86% respectively after optimization. It reveals that the pitching stability of shiplift is enhanced evidently after optimization.

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The existing critical buckling load calculation methods of horizontal hydraulic cylinder failed to fully reflect the initial boundary conditions and some critical influence factors, resulting in an unjustified critical buckling load. A new method to analyze the buckling behavior of the horizontal hydraulic cylinder articulated at both supports is developed on basis of large deflection theory and Timoshenko beam theory. Friction at supports, self-weight and initial misalignment by clearances are taken into account. Friction moments of supports are built according to Hertz contact theory. Bending stiffness of cylinder-rod junction is figured out in terms of elastic deformation theory. Runge–Kutta and Newton–Raphson method are used in numerical calculation for the critical buckling load. Practical calculation and stability test are carried out to verify the necessity of considering large deflection and shear effect in the proposed method. Experimental work shows the critical buckling load by the proposed method can well match to that by stability test with 0.55% deviation. Moreover, the numerical calculation results demonstrate that the friction moment of the support at piston rod end is crucial for the buckling behavior. The critical buckling load rises increasingly as the friction coefficient [Formula: see text] rises. As the friction coefficients [Formula: see text] increases from 0 to 0.020, the rise rate of critical buckling load increases from 1.782% to 8.055% per 0.001. And the clearance at cylinder-rod junction is a minor factor on the critical buckling load. As the clearances increase by 10 times, the critical buckling load decreases by 3.542%.