A positive surge is an unsteady open channel flow motion characterized by an increase of flow depth. In previous experimental studies, a positive surge was typically induced by either a sudden increase of discharge in a channel or by the rapid closure of a downstream sluice gate, thus leading to a steep initial profile. However, in many instances, the evolution of a positive surge is of a progressive manner (e.g., in the downstream navigation canal during the emptying operation of lock chambers). In the present work, the inception and development of a positive surge induced by a progressive increase of discharge was investigated in a rectangular channel with a smooth bed. Both undular and breaking surges were studied. The results demonstrate that the maximum wave height at the first wave crest of an undular surge is in very close agreement with the McCowan theory. Additionally, the wave amplitude essentially shows a linearly increasing trend with an increasing surge Froude number up to Fr₀ = 1.26 to 1.28, whereas it tends to suggest a power law reduction for larger surge Froude numbers. Moreover, the dispersion of undular surges is consistent with the linear wave theory only for surge Froude numbers close to unity. Overall, the present study demonstrates the unique features of positive surges induced by a progressive increase of discharge.

Hydro-floating ship lifts are a milestone in the field of high dam navigation. In order to ensure the running safety of a hydro-floating ship lift, the effective integration of a numerical simulation method and cloud model theory was carried out to deal with the hydrodynamic risks presented by water surface deviations from the shafts in the filling–emptying system such as a lock. In this study, the average values of water surface deviation from the shafts were 0.2, 0.22 and 0.24 m, through numerical simulation on a similar hydro-floating ship lift at the lifting heights of 80, 100 and 120 m, respectively. An increase in the lifting height causes the water surface deviation from the shafts to increase, and the hydrodynamic risk is greatly increased in the equal inertial pipeline filling–emptying system. In addition, the water surface deviations from the shafts of the equal inertial pipeline and longitudinal culvert filling–emptying system like a lock were compared. The longitudinal culvert was better at optimizing running safety in the filling–emptying system and dealing with the uncertainty of water surface deviation from the shafts. The results show that the numerical simulation method and cloud model theory can effectively control the risk of water surface deviation from the shafts and can be used to aid in decision-making for risk prevention in relation to hydro-floating ship lifts.

In this study, the effects of the different conveyance modes of the intermediate channel in decentralized cascade locks on navigation flow conditions were investigated. A new hybrid numerical simulation method was established to evaluate navigable flow conditions in intermediate channels at different water conveyance modes. This hybrid numerical simulation method was reliably compared by physical modeling tests. We used the 33.73 m class high-head intermediate channel filled with water as a study case. The study used the maximum water surface slope and maximum flow velocity as evaluation indexes for navigable flow conditions. The results showed that the navigable flow conditions of the centralized water conveyance mode were worse compared to the decentralized water conveyance mode in the intermediate channel. Especially in the upstream region of the intermediate channel with a centralized outflow, the navigable flow conditions were exceptionally harsh. We recommend the decentralized outflow mode in the high-head intermediate channel. This study provides an effective numerical simulation method for optimizing the water conveyance mode of the high-head intermediate channel of decentralized cascade locks and saving project investment.

In long-distance, high-elevation gravitational water supply systems, it is essential to incorporate energy dissipation to lower pipeline pressures. The energy dissipation box is a novel device for pressure reduction, extensively utilized in gravitational flow transition systems. Despite its appealing contribution, systematic selection methods still need to be used regarding its optimum location. Hence, this paper considers the sum-of-the-maximum hydrostatic pressure head (SMHPH) and derives an extreme location equation for the energy dissipation box (EDB) in the design stage, and then, it comprehensively accounts for the overcurrent capacity and proposes a theoretical comparison and selection method for the optimal location (OL) between the critical and extreme locations. A theoretical analysis with an engineering case study is conducted to compare the theoretical OL, and numerical simulations are carried out to compare the pressure protection effect of the same box cross-sectional area and initial water volume of the theoretical OL and other possible locations with different initial water depths. The results show that the location of the EDB in the design stage should comprehensively consider the overcurrent capacity and the SMHPH. On the basis of both conditions, the oscillation amplitudes of the pressure gradient beyond the box are significantly decreased as the OL approaches closer to the downstream pipe. If the initial water depth in the box is large, the EDB provides greater protection to the pressure head (PH) by decreasing the cross-sectional area and then maximizing the utilization of water depth in the box and decreasing the volume of the EDB.

Due to the small cross-section coefficient of a shiplift chamber, the hydraulics problem becomes a complex water flow problem in ship operation. To prevent the ship from touching the bottom and ensure the safety of ship navigation and the docking of the chamber, a generalized physical model was used to study the ship squat of a 1000 t ship leaving the chamber. Throughout the experiment, the law of variation law in the ship squat under different chamber widths, water depths, chamber lengths, ship speeds and ship starting acceleration was obtained. In this study, the flow pattern of the ship leaving the chamber was divided into two parts: backflow and bottom flow. According to sensitivity analysis, when the shipping speed was less than 0.9 m/s, the influence of the width of the chamber on the squat was greater than that of the depth of the chamber; when the speed is greater than 0.9 m/s, the influence of the depth of the chamber on the squat was slightly greater than that of the width of the chamber. Based on our theoretical analysis, the basic expression of a ship squat was established.

The docking between ship lift chamber and upstream/downstream is an important link in the whole process of ship lift operation. The wave and flow movement generated by the hub operating downstream can easily lead to the failure of ship lift docking or ship grounding. To deal with the problem of large amplitude and high frequency of water level fluctuations downstream of Baise ship lift, an auxiliary lock is set up at the lower lock head of the ship lift. The extreme lift height of Baise auxiliary lock is 5.64 m with a two-way hydraulic head, and the size of the chamber is large, therefore it is faced with the problems of water filling/emptying efficiency and ship navigation safety. In this paper, a kind of water F/E system combining water filling under the gate and grid energy dissipation type is designed, and a scale of 1:30 Baise auxiliary lock chamber physical model and three-dimensional mathematical model are established. The berthing conditions of ships in the auxiliary lock under different water level variations and lock gate operation modes are analyzed. Besides the hydraulic characteristics of the lock filling/emptying system are measured. The operation mode of lock gate under different water level variations is recommended.