Fatigue in floodgates due to dynamic wave loading

Abstract

The ability to predict the fatigue of flood gates due to dynamic wave loading is becoming increasingly important as coasts and waterways worldwide are being reinforced to suit a changing climate. There are few comprehensive ways to do so however, which often leads to conservative estimates. This thesis presents an integral framework with which the fatigue of flood gates due to dynamic waveloading can be described in much more detail, while also being efficient and adaptable to different circumstances. First, the fatigue experienced by a single load event is evaluated based on readily available data. This was done by creating a phase-amplitude model from a wave spectrum based on the site properties and environmental conditions. These wave loads can then be transformed to pressure spectra with linear wave theory and pressure impulse theory, which will dynamically excite the fluid-structure system. The gate is then parametrically modelled in a FEM software package in order to export the in-vacuo response modes. These are combined with a fluid-structure interaction model to derive the response of the system to external pressures. The fatigue was evaluated with the standard Eurocode method to find a fatigue damage factor. Next, the load events imposed on the gate over its lifetime were probabilistically defined. This was done by fitting two independent probability distributions to historical wind- and water level data, the latter of which was also adjusted for climate change. These probability distributions are then split into segments which are integrated to obtain discrete load cases with representative values for the average wind velocity, water level, and probability of occurrence. Two filters were also applied to remove the load cases which cause a negligible amount of fatigue. Computing the fatigue damage caused by the average values of each of these load case bins then gives a set of fatigue damage factors with an associated probability of occurrence, which can be used to perform a Monte Carlo analysis. A case study for a hypothetical parametrically defined gate with an overhang located in the Afsluitdijk was performed, where the response for different gate configurations and environmental conditions was evaluated. The fatigue response was evaluated for fatigue across the gate, at the critical coordinate, and per mode. A ULS check was also done for the chosen design. Results following from the model were also compared to those of methods commonly used in practice.The method gives insight into the relative importance of different modes and load events, can compute fatigue for the entire gate or just a critical coordinate, and does so in a much more time-efficient manner than current numerical models. It gives a more comprehensive view of the fatigue over the lifetime of the gate by modelling its entire lifespan rather than a set of design load events. The modular structure of the integral framework allows for easy adaptation to other use cases in hydraulic engineering where fatigue due to hydrodynamic loading is of interest.