Vertical Flow-Induced Vibrations of Valves in Navigation Locks

Abstract

Navigation locks are used to transport vessels between waterways with different water levels. In the nearby future many navigation locks will be renovated or replaced. During the design of a new lock still some unknown factors are encountered. One of these factors is the vibration of the valve. The valve is part of the filling and emptying system that is responsible for the levelling of the water in the lock chamber. The most used valve type is a vertical-lift valve. During the filling and emptying of the lock, water flows with high velocity underneath the valve. The flow of water can cause vibrations. These vibrations are called flow-induced vibrations and could lead to failure of the valve system. Possible failures are for example that the operating machinery will not be able to open the valve or that the valve will hit other elements due to the vibrations. As a consequence the lock gate complex cannot meet its requirements anymore. Several types of flow-induced vibrations can be distinguished. This distinction is based on the cause of the vibration. This research only focussed on vibrations due to turbulence and instability of the flow. The above-mentioned types can be experienced in two directions. The two directions are in-flow (horizontal in the direction of the flow) and cross-flow (perpendicular to the direction of the flow). A valve is more likely to vibrate in a vertical direction than a horizontal direction, because the majority of the valves is positioned in a niche of a gate or culvert. Currently not much information regarding the flow-induced vibrations due to turbulence or instability of the water flow is available and the information that is available is often out dated. The shape could have an effect on the flow-induced vibrations. This seal has to ensure the water tightness of the valve. No research has been done on the effects of the seal shapes, which are used nowadays, on the dynamic behaviour. Therefore, the information of the effect of seal shapes as used in practice is missing. In the current situation a guideline involving the natural frequency of the valve system is used. This guideline states that the natural frequency of the valve has to be larger than three times the excitation frequency. Therefore, the main research question of this research is: What is the effect of the shape of the lower edge seal on the vertical flow-induced vibrations of a valve in a filling and emptying culvert? The vibration phenomena have been investigated by means of a physical model. A simplified scale model of the valve is constructed and tested in a current flume under varying conditions. The varying parameters during these tests are the flow velocity underneath the valve, the stiffness of the vertical suspension, the gate opening underneath the valve and the shape of the lower edge seal. Four different seal shapes have been tested. The tests have been executed under steady state conditions. In addition to the steady state tests, free-decay tests (to determine the natural frequency and damping) and tests to determine the contraction have been executed. The physical tests showed that the shape did have an effect on the presence of the flow-induced vibrations and on the amplitude of the vibrations. However some other parameters influenced the vibrations. For example the relative gate opening and the Reynolds number. The study has proven the presence of the flow-induced vibrations. However, the executed physical model test should be optimized to get a more accurate view on the different phenomena. Also should the effect of certain parameters (Reynolds number, water levels) be further investigated.