Operating Force Characteristics of Sector Gates Based on Prototype Testing

Navigation locks, as an essential infrastructure for navigation, are widely utilized to facilitate the smooth passage of vessels through waterways with varying water levels, including canals, natural rivers, and tidal rivers [1,2]. Vertically hinged sector gates are commonly used as lock gates in seaports and estuarine areas due to their ability to open and close under water flow and hydrostatic loads, as well as their capacity to withstand reverse head conditions [3,4], which address tidal-induced water level fluctuations. The use of sector gates in design and engineering dates back to 1924 when Swedish engineers successfully implemented them at the upper and lower gates of the Södertälje Canal Lock near Stockholm [1,4,5,6]. According to recent statistics from a survey of over 300 lock gate types in mainland China, sector gates have become the second most widely used gate type after miter gates. This is particularly true in the tidal reaches of the Yangtze River, where they are used to accommodate seasonal and tidal variations in water levels [7]. Additionally, the skin plates and trusses of sector gates create zones for dissipating collision forces, which can absorb the impact loads of vessels. The bent skin plates only experience localized loads, unlike miter gates which experience global compression. This preserves the overall stability of the lock gate system [1,8]. Engineers have adopted sector gates due to their low-damage characteristic following vessel impact [9]. The United States and Canada have embraced the design concept of sector gates when integrating lock gates with urban landscapes. This is exemplified by projects such as the Chicago Harbor Lock [10] and No. 7 Welland Canal Lock [11].

The utilization of hydraulic cylinders for gate operation presents notable advantages and has emerged as the predominant method for driving newly constructed large-scale sector gates, such as the Yuxi Lock [7] and the IHNC Surge Barrier Project [1]. Their precise control capabilities facilitate the effortless operation of gates across varying dimensions, while their efficiency and adaptability ensure swift responsiveness to gate operational commands [12]. In contrast to traditional gear-driven mechanisms, hydraulic cylinder driven systems obviate the need for gear transmission components, thereby mitigating maintenance costs and reducing the risk of system failures [13,14]. Furthermore, hydraulic cylinder operation exhibits enhanced smoothness, precision, and stability, thereby augmenting operational efficiency and adaptability. Notably, it necessitates lesser operating force for gate motion [14]. Research conducted by Buzzel suggests that hydraulic cylinder systems effectively dampen small oscillations of the gates compared to traditional mechanical driver systems, ensuring seamless and accurate gate movements [15]. Additionally, investigations by Haehnel underscore the influence of factors such as the layout of horizontal and vertical beams in the gate structure, the configuration of the gate lips on both sides of the gate leaf, the design of seals, and the geometric dimensions of the gate recesses accommodating sector gates on gate operation [8,16]. The selection of hydraulic cylinders is closely related to the above factors [16].

Excessive reverse head can cause sector gates to stall at small opening or damage the hydraulic cylinder system during extreme operating conditions. Incidents and accidents have occurred in the initial operations of locks such as Bayou Boeuf Lock, Freshwater Lock, and Calcasieu Lock in the United States [17]. Therefore, analyzing the operating force characteristics and influencing factors of sector gates is particularly important. The common approach to this issue is constructing physical models for experimental research. The U.S. Army Engineer Waterways Experiment Station has conducted extensive experiments on this matter [11,18,19,20]. Oswalt [17] established a 1:20 scale model to reduce the gate operating force under forward head conditions. This was achieved by removing the skin-plate lip closure, extending the panels, or combining both methods. Additionally, the operating force under reverse head conditions was reduced by shortening the lengths of accessories such as seal supports. Harrold [6] made changes to the design of center and side seals as well as the shape of the gate recess. These changes aimed to reduce operating forces by smoothing the flow of water along the gate sides during the opening and closing processes, avoiding the direct impact of the water flow on the gate axis. The studies mentioned above were conducted in locks with gate filling and emptying in very low lift. However, the lock upgrade project for the Inner Harbor Navigation Canal in New Orleans utilized sector gates at higher head differentials for deep-draft vessels, resulting in satisfactory hydraulic conditions within the lock chamber and desirable filling and emptying times [18].

In early studies, the operating force was measured by load cells and the signal was transmitted to direct-writing recorders [6,17]. The accuracy of data collection has been optimized with the continuous updating and improvement of electronic control devices such as pressure sensors. Wu et al. [21] carried out physical model experiments to analyze the operating force of sector gates under different water level combinations in tidal river with automated equipment. The critical conditions for lock operation were determined based on the maximum design value of the operating force and hydraulic conditions of the waterway. Zhu [22] added additional criteria, including flow patterns, maximum lateral flow velocity, and maximum longitudinal flow velocity, to refine the critical conditions for tidal differences, building upon Wu’s research. Wang [23] investigated pulsating pressure on plate during small opening. Guo [24] supplemented the study by focusing on flow conditions inside the lock chamber for sector gates with asymmetric openings under special circumstances. Prototype testing, compared to physical model experiments, provide more direct and accurate data as they are not affected by scale effects. Hydraulic forces and friction were found to be much greater than expected during prototype testing at different gate openings and head differentials [19]. Prototype testing effectively complements friction values that cannot be measured in physical model experiments. Currently, prototype testing is widely applied in newly constructed sector gates, such as at Dalu Lock and Yuxi Lock. The test data provide crucial support for the design of lock gate hydraulic systems in the future [7,25].

This paper is organized as follows. Section 2 introduces the principles, methods, and contents of prototype testing for hydraulic cylinder systems of sector gates. Section 3 presents the testing results, analyses the effects of influencing factors such as forward and reverse head conditions, head differentials, and flow velocities on the operating forces of sector gates, and reveals the characteristics of operating force variations during the opening and closing processes. Section 4 discusses the significance of the results and outlines avenues for future research. Finally, Section 5 presents the conclusions.

The most common method for evaluating the operating force of sector gates is through tension load cells in physical models. This approach, validated through prototype testing by the United States Army Corps of Engineers, has revealed that simulating hydrodynamic loads in physical models is generally accurate [17,20]. However, frictional forces often exceed expected values, sometimes doubling the original design estimates [20]. To date, there is no precise method for estimating gate operating forces. The highlight of this paper is the analysis of operating force characteristics under different influencing conditions and operational states through prototype testing. The core of this analysis lies in examining variations in operating force under different heads and flow velocities.

The characteristics of opening force under flowing conditions can serve as initial design guidelines for newly constructed sector gates. By extrapolating from the operating force of similar-sized locks in still water, estimates can be made for the operating force required to open gates under various water level combinations and differing head differentials. In practical lock operations, gates are often opened preemptively during the final stages of filling or emptying with the head differentials [21]. This allows water to flow through the gate gap, aligning the water level in the chamber with that of the navigation channel and thereby enhancing navigation efficiency [25]. This operational approach places specific demands on the driving capacity of hydraulic cylinders. The research into the characteristics of gate opening under flowing conditions offers scientific support in this regard.

Furthermore, in some river sections with minimal water level differences due to tidal influences, locks may allow vessels to pass freely with gates fully open. However, since it is necessary to close the gates before the tide rises to restore normal lock operations, the closing force becomes a crucial safety factor for this operational method. For example, the critical flow velocity of Nantong Lock in this operational method is 2.0 m/s [21,22]. The lock near the mouth of the Yangtze River faces a significant operational challenge during flood seasons when rapid tide rises occur. Thus, the relationship between flow velocity and the closing force under flowing conditions also has significant implications for the practical operation of locks.