Gate Driving Mechanisms and Dynamics

Abstract

Vertical sliding valves that are part of a filling and emptying system of a lock are often subjected to an underflow of water during emptying and filling. The flow induces time varying forces on the structure which leads to dynamic behaviour of the valve. Whether the structure is in the range of resonance and what the amplitude of the vibrations will be depends on the mass, damping, stiffness and forcing quantities of the system. This thesis focussed on gaining insight in the behaviour of such a cylinder and its various components in terms of stiffness and damping of the total system including the vertical sliding valve. The research questions focussed on whether it is possible to influence the dynamic characteristics of a system (natural frequency and dynamic amplification) by adjusting the geometry of the hydraulic cylinder. Furthermore it is investigated which components are influencing the dynamic characteristics of the system and which damping and stiffness components are found to be subordinate to the dominant sources. Results were based on a Python script that included all relevant sources of damping and stiffness of a hydraulic cylinder, as well as the fluid structure interaction components such as added mass, damping and stiffness. The added damping components included the self-excitation suction damping. The sensitivity of different components to the natural frequency and dynamic amplification was explored. This was done for different cases, where in each case one variable varied while the others were kept constant. The results from the sensitivity analysis were used to find an optimal parameter that would lead to an optimal design in terms of natural frequency increase or decrease, reduction of the dynamic amplification and a minimal influence on the mass of the system. Besides these two studies, a third study was adopted to find the relative influence of different damping and stiffness components of the hydraulic cylinder for varying boundary conditions such as water level difference and gate opening. The study showed four components of a hydraulic cylinder that influenced the dynamic characteristics the most when varying their dimensions in a realistic range. These where the diameter of the hydraulic cylinder, the cylinder length, the thickness of the rod and the length of the tube that transport fluid into the cylinder. From these, the tube length and the cylinder diameters turned out to be the most effective design variables for tuning the stiffness, damping and correspondingly the natural frequency and the dynamic amplification of the system. Furthermore it was found that under all conditions (varying water level, gate opening height, pressure and stiffness), the stiffness was mostly determined by the axial stiffness of the rod and piston as well as the stiffness due to compaction of the cylinder fluid. For damping it was found that the cylinder only had limited influence and that most damping resulted from friction between the valve and the guiding rails.