Stevin Outlet Sluices: wave impact under a beam
datasetposted on 29.07.2013, 00:00 by G.M. (Thijs) Hofste
The research questions were: 1. How is the wave load on the northern gates depending on the presence of the military beam? 2. How large is a wave impact load on the bottom of the military beam in the Stevin outlet sluices? 3. How well can the numerical model ComFLOW and physical modelling be used to determine the wave impact on the bottom of the military beam in the Stevin outlet sluices? 2D scaled experiments were performed making use of a model with the (simplified) geometry of the Stevin outlet sluices and regular waves. It was found that the largest wave impacts occurred for water levels equal to the bottom plane of the beam or slightly under it. This happened for the shortest waves in the test domain. The largest pressure measured on the beam was approximately 50 kPa or 35H, with H representing the incident wave height in front of the model. It was also found that the spread in the peak pressures for one single experiment was large. The results of the measured impulse per peak showed far less spread. The effect of wave impacts under the beam was also found on the vertical wall under the beam. The actual pressures however were less and they were decreasing with increasing depth. Besides physical wave impact testing, a few experiments were performed with the beam removed from the model. This resulted in wave simply running up the vertical wall of the model. They did not cause a wave impact. The measurements of both type of experiments, with and without a beam, were compared. This revealed that the total wave impulse on the gate was not affected by the presence of the beam. However the distribution of the pressure within a single wave period was significantly different. In case of a beam, a large impact peak was observed, whereas the other wave only showed a small hump caused by the deflected flow against the vertical wall. When the calculated and measured wave impact results were compared it became clear that ComFLOW underestimated the peak pressures by a factor 2 to 20 for the pressures on the impact plane. The same was done for the peak impulse. This showed that the impulse of the peak on the impact plane were underestimated by a factor 2 at most. These results confirmed that the used grid was too coarse for the program to model the physics correctly. The main conclusions to the research questions were: 1. The presence of the military beam causes a different distribution of the force on the gate within a wave period. The total amount of impulse is more or less the same as for the situation without a beam. With the military beam, a wave impact results in a peak force on the gate. Without the beam, there will be no peak force. 2. The largest measured wave impact pressure is 35H. 3. Both ComFLOW and physical modelling can be used to predict wave impacts for the geometry of Stevin outlet sluices. Much care should be taken when modelling and much attention should go to the input parameters of the program.