The lift height of most inland navigation locks in the Flemish region of Belgium is limited to 2-3 m. For these locks openings integrated in the lock gate sealed by vertical lift valves or butterfly valves are commonly used as lock levelling system. To improve the spreading and energy dissipation of the filling jets and hence reduce the hydrodynamic forces on the moored ships, breaking logs (also referred to as energy dissipation bars) might be mounted at the downstream side of the gate openings. Beem et al. (2000) provide some Dutch design guidelines. Since the shaping of a gate opening across the thickness of a steel gate and the integration of the valves are somewhat country-specific, it was decided to set up a generic physical model at Flanders Hydraulics Research (Antwerp, Belgium) aiming at determining the effect of breaking logs on the flow inside the lock chamber and optimization of the breaking log configurations adopted in Flanders (Verelst et al., 2016). In this contribution, an account will be given of the specific research carried out in this model during the design of the levelling system of the new lock of Sint-Baafs-Vijve (river Lys, Belgium). During the physical model research, 4 different configurations were tested. For reference purposes, the first configuration did not have any breaking logs. Next, three configurations with respectively 7, 5 and 3 breaking logs were tested. At first the discharge coefficients of the configurations were determined, for valve openings ranging between 20 % and 100 % of the total valve lift height. It turned out that the influence of the breaking logs on the discharge coefficient was negligible for valve openings below 50 % and limited for higher valve openings. Secondly, the effect of breaking logs on the energy dissipation was studied. When adding breaking logs, the spreading of the filling jet increased and the maximum velocity reduced to approximately 60 % of the velocity measured in the core of the jet compared to the configuration without breaking logs. The research revealed that the exact positioning of the breaking logs with respect to the gate opening at the upstream skin plate is more important for the spreading of the filling jets than the amount of blockage of the gate opening at the downstream skin plate. The lowest velocities were achieved with the configuration with 3 breaking logs, which is the configuration with the least blockage of the gate opening at the downstream skin plate.
References
Beem, R.C.A.; Boogaard, A.; Glerum, A.; de Graaf, M.A.; Henneberque, S.D.; Hiddinga, P.H.; Kranenburg, D.; van der Meer, M.T.J.; Nagtegaal, G.; Van der Paverd, M.; Smink, L.M.C.; Vrijburcht, A.; Weijers, J. (2000). Design of locks. Ministery of Transport, Public Works and Water Management. Civil Engineering Division: Utrecht
Verelst, K.; Vercruysse, J.B.; Ramos, P.X.; De Mulder, T. (2016). Experimental investigation of the influence of breaking logs on the flow patterns induced by lock filling with gate openings, in: Proceedings of the 4th IAHR Europe Congress, Liege, Belgium, 27-29 July 2016: Sustainable Hydraulics in the Era of Global Change. CRC Press/Balkema. ISBN 978-1-138-02977-4. pp. 618–628.