RJEEC, Volume 2, no. 2, 2020

Dams and hydraulic structures are used for the supply and control of water, which have great importance on human life. The sluice gate is one of the hydraulic control structures. Sluice gates release excessive water from the reservoir to the downstream side in a controlled manner with a certain discharge for controlling the level of the reservoir. A hydraulic jump is created to dissipate the energy of flow coming from under the gates. A hydraulic jump occurs when flow regime is changed from subcritical to supercritical. However, the position of the hydraulic jump in channel should be known exactly in order to prevent damage to surrounding structures. In this study, an open channel system with a sluice gate is used to produce a hydraulic jump. Experiments are conducted for two different gate opening (a1=1.5 cm and a2=2 cm) and 16 discharge values. For each case position of the hydraulic jump is determined. In addition, flow depths at 5 different points were measured including before and after hydraulic jump. The results obtained from the experimental study were compared with the numerical model in terms of the position of hydraulic jump and flow depths. According to the results obtained, the numerical model and the physical model showed between 80% -91% consistency.

Sulfate salts which available in seawater with high concentrations cause the formation of ettringite in hydrated structures which formed as a result of the hydration of cement. On the other hand, ettringite causes excessive volume expansions and eventually leads to cracking of the concrete due to the internal stresses in concrete since it is a large volume mineral structure. In this study, ultrafine cement and silica fume as mineral additive were used together for binder design. Besides, microfiber has been added to the binder systems produced in different proportions. The produced specimens were kept separately in water, in solutions containing 2% Na2SO4 and 2% MgSO4 by weight for 90 days. The compressive strength test was performed at 28th and 90th days on cured specimens. In addition to the compressive strength test, the solution samples were taken from the curing solutions every 10 days and the change of sulfate concentrations was followed in the solutions. According to the results, in Na2SO4 solution higher compressive strength values were observed up to 66 MPa while strength loss was observed in the specimens cured in the MgSO4 solution. In parallel to this result, the remaining concentrations of SO42- ions in the MgSO4 solution were lower than those in the Na2SO4 solution. It was inferred that in Na2SO4 solution, the fibers could compensate for the internal stresses. This situation shows that especially the microfiber additive can compensate for the expansion that will occur as a result of ettringite formation, and thus it can help the mechanical stability of the concrete.

Broad crested weirs and steps are used to regulate the flow in the channel, increase the water level at the upstream side, and measure the discharge. The construction of the broad crested weirs is more practical and also they are more stable compared with the other types of weirs. To serve in accordance with the purpose of their construction, broad crested weirs should be designed and built by considering certain criteria. Before the hydraulic structures are built, model experimental setups are constructed in the laboratory and problems to be encountered are tried to be determined. However, there may be differences between the structure to be built in real life (prototype) and model due to scale effect. These possible differences must be determined and necessary measures must be taken. In this study, the model and prototype of the broad crested weir are constructed in two different open channel systems by using Froude similarity. The geometric similarity between model and prototype is determined as Lr = 4. 44 experimental data were collected from model and prototype. The results obtained from the model and prototype are compared according to hydraulic similarity rules. In addition to the physical experimental setups, numerical models were created using the ANSYS Fluent for the model and prototype separately. By comparing the numerical model and physical experimental setups, optimum mesh size is tried to be determined. According to the results obtained from experimental setups, differences were observed in the position of critical flow depths and downstream water levels due to scale effects.