Keywords

1 Introduction

The operation of ship locks on the inland river and canal in China is often restricted by the shortage of water resources, so it is necessary to build water-saving ship locks in some places. There are four main types of water-saving ship locks: the ship lock with a water-saving pool, the multi-level ship lock without waiting for navigation, the double-line ship locks filling and emptying water mutually, and the ship lock with an intermediate channel (Chen et al. 2021). At present, the water-saving ship locks that have been put into operation in China mainly include the third and fourth line ship locks in Changzhou and the second and third lines in Feilaixia. A number of new water-saving ship locks are under planning and construction (Dongle et al. 2020).

The operation experience of the third and fourth line ship locks in Changzhou shows that the throughput capacity and operation efficiency of water-saving ship locks are affected by filling and emptying water mutually.

When the double-line water-saving ship locks operate in the mode of filling and emptying mutually, the filling water process of one lock chamber and emptying water process of the other one are carried out at the same time. On the premise that other operating parameters of locks are the same, because the number of ships passing through the two locks may be different in one lockage, the situation of chambers waiting for each other is inevitable, which affects the operation efficiency of the two locks. In addition, in the mode of filling and emptying mutually, the operation of the double-line water-saving ship locks are coupled with each other. Compared with the mode of filling and emptying independently, the fluctuation of ship navigating speed and interval time may have a more significant impact on the operation efficiency of the ship lock, which cannot be ignored.

The current research of water-saving ship locks focuses on the hydraulics of water conveyance system (Chen et al. 2021), the calculation of water-saving rate (Dongle et al. 2020) and benefit analysis about water-saving (Yang and Chen 2013). But there is almost no research on the impact of water-saving mode on the throughput capacity and operation efficiency of ship lock.

Combined with the condition of a planned lock on a canal in China, the throughput capacity and operation efficiency of the double-line water-saving ship locks under the mode of filling and emptying mutually are studied. Based on the simulation model of double-line locks which filling and emptying independently, a coupled operation simulation model of double-line locks is established, in which the mode of filling and emptying mutually is adopted. The whole operation processes of the locks are simulated, under two set of ship types and proportions. Indexes such as throughput capacity, chamber occupy rate and one lockage time are collected in the model, statistic data are compared and analyzed.

2 Building, Verifying and Validating Simulation Model

2.1 Model Scope and Boundary

The model includes the anchorage, connecting section, approach channel, berthing structure, lock head at the upstream and downstream and lock chamber of the double-line locks. The upper and lower boundaries of the model are the upstream and downstream anchorages of the ship lock.

2.2 Lockage Process

Lockage process in the mode of filling and emptying water independently and mutually are shown separately in Fig. 1 and Fig. 2.

Fig. 1.
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Lockage process in the mode of filling and emptying water independently

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Fig. 2.
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Lockage process in the mode of filling and emptying water mutually

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2.3 Main Algorithms and Basic Assumptions

The model specifies the ship lock for a ship, according to the state of the double-line ship locks (upgoing or downgoing). When the ship lock allows ship to wait at waiting section, the position of the ship in the lock chamber and order in the queue are determined according to the ship arrangement algorithm, and then ships of one same lockage are sent to the waiting section. After that, the whole process of ships passing through lock are simulated. The ship arrangement algorithm is shown in Fig. 3, which is based on the two-dimension packing algorithm. For details, please refer to the ship arrangement algorithm for single lock adopted by Shang et al. (2011) and Liu et al. (2020).

Fig. 3.
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Ship arrangement algorithm

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The basic assumptions of model are listed below:

  1. (1)

    The target of the model is to calculate the capacity of the ship lock. In order to ensure the full load operation of the ship lock, there should be enough ships waiting for lock in the anchorage.

  2. (2)

    Ships are generated according to the input ship type and proportion.

  3. (3)

    The acceleration and deceleration process of the ship navigation are not simulated in the model. Ships move at a fixed speed, which will change dynamically and immediately. When this ship has speed less than the speed of the front ship, or is more than 1.5 m away from the front ship, it will move at the preset speed. When this ship has higher speed than the front ship, and is within 1.5 m away from the stern of the front ship, it will move at the same speed as the front ship, to keep a safety distance.

  4. (4)

    When arrange ships in chamber, the lock chamber shall be filled as full as possible.

2.4 Statistic Data and Key Performance Indicators

These data are collected: total number of ships passing through single lock upstream or downstream, total number of lockages, total number of bulk ships, total number of container ships, total DWT of bulk ships, total container capacity of container ships, average DWT of one lockage, the occupy rate of chamber, average number of ships per lockage, average lockage time, and average number of lockages per day.

These key performance indicators are calculated: total DWT of ships passing through one-line lock upstream or downstream per year (A TEU is treated as 15 ton), one-way annual capacity of one-line ship lock, which equals to the total DWT of ships passing through one-lock upstream or downstream per year × ship loading coefficient/unbalanced coefficient of traffic volume, and one-way capacity of double-line ship locks.

2.5 Model Verification and Validation

The model is verified and validated using the upgoing data of the Three Gorges double-line five-level locks in 2013. The plane dimension of lock chamber of each level in Three Gorges is 280 m × 34 m (length × width). The length of lock head is 50 m. The locks operate in one-way and ships wait at waiting section just before the lock head. Assume that ships enter and exit chamber in turn one by one, and the entering speed is set to 0.4 m/s, the exiting speed is set to 1.0 m/s. The safety interval time between two ships is set to 2 min. Ships are arranged in chamber according to the first-come-first-serve rule, and ships are generated randomly following the same rule within a year. The unbalanced coefficient of traffic volume is 1.1, which is used to amend the total one-direction cargo ton or the total DWT of ships passing through one-line lock collected in the model.

The results of model verification and validation show that the simulation model has correct logic and can get reasonable results, which can be used for the next research.

3 Simulation Experiment

3.1 Experiment Scheme

The model does not simulate the process that the ship lock cannot operate (accident, maintenance, flood and dry season, etc.), so the simulation model runs 340 days per year and 22 h per day. The warmup period of the model is 10 days. The experiment scheme is shown in Table 1 below.

Table 1. Experiment scheme
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In Table 1, “no variation” means that the ship enters and exits the lock at the base value of speed and safety interval time. And “variation ±30%” “variation ±50%” means that ship speed and safety interval time are randomly sampled from 70%–130% of the input basic value and 50%–150%, which are decided when ships are generated. Those random values are input in the model, but can only be treated as expected, because the actual speed and safety interval time of a ship will be affected by the speed of the front ship. When this ship has speed less than the speed of the front ship, or is more than 1.5 m away from the front ship, it will move at the preset speed. When this ship has higher speed than the front ship, and is within 1.5 m away from the stern of the front ship, it moves at the same speed as the front ship.

As a result, if input the same entering and leaving speeds in “variation” experiments as in “no variation” experiments, the average speeds of those two type of experiments are not the same for sure. To study the influence of variation, the average value of entering and leaving speeds are adjusted to be the same among all experiments, thus the input value is a little higher in “variation” experiment schemes.

3.2 Input Parameters

3.2.1 Plane Layout

The lock chamber is 300 m in length and 34 m in width. Considering the safe distance between the ship in chamber and the chamber wall and between ships, the length and width of the lock chamber for arranging ships are 280 m and 32.8 m (Fig. 4).

Fig. 4.
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Ship lock layout in the model

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3.2.2 Ship Type and Proportion

According to the history statistic data, length and width of ships of each type are ranges. As input in the model, each level of tonnage and container capacity are subdivided into three grades: ship length and width taking the lower limit of its range, taking the average value and taking the upper limit, and the corresponding proportion of each grade are 33%, 34% and 33% in its tonnage level or container capacity level. Besides, the DWT value of bulk ships is equal to its tonnage, the DWT value of container ships is equal to the container capacity (in TEU) × 15t.

Some parameters of ships in the model are not considered, such as the height above the waterline and the loading rate (Table 2).

Table 2. Ship type and proportion input in the model
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3.2.3 Time Related Parameters and Other Inputs

The time of opening and closing gate are all 4 min. And the time of filling and emptying water are all 14 min.

The basic values of ship speed entering and leaving locks are 0.8 m/s and 1.2 m/s in “variation” experiments, 1.0 m/s and 1.4 m/s in “no variation” experiments. The actual speed of the ship entering and leaving the lock is randomly determined by the basic value and variation range. The basic value of the safety interval time between two adjacent ships entering and leaving the lock is 2 min. The actual value of a ship entering and leaving the lock are the same, and are also randomly determined by the basic value and variation range.

According to the ship lock design code in China, the ship loading coefficient is taken as 0.8 when there is no relevant statistic. The unbalanced coefficient of traffic volume is taken as 1.1.

4 Simulation Experiment Results and Analysis

In this study, the speed of the ship entering and leaving the lock and the safety interval time between two adjacent ships are the two main factors that may influence the throughput capacity and operation efficiency of ship locks, under the condition of filling and emptying water mutually or independently.

After preliminary analysis, the above factors mainly have impact on total number of ships passing through one-line lock upstream or downstream, total number of lockages, one-way annual capacity of one-line ship lock, one-way capacity of double-line ship locks and average lockage time, but have no impact on average DWT of one lockage, the occupy rate of chamber, average number of ships per lockage. The one-way capacity of double-line ship locks and the average lockage time can fully reflect the influence, so the two indexes are mainly analyzed. See Table 3 and Table 4 for simulation results.

Table 3. Simulation results of the one-way capacity of double-line ship locks
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Table 4. Simulation results of the average lockage time in “no variation” experiments
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  1. (1)

    The throughput capacity of the double-line ship locks will be reduced comparing filling and emptying water mutually with independently. The range of capacity reduction is related to the composition of ships, and the variation amplitude of ship speeds entering and leaving locks. Different composition of ships may lead to different value of average ship number per lockage, and the greater the average ship number per lockage, the greater the reduction of capacity. The greater the variation of speeds and safety interval time, the greater the reduction of capacity.

  2. (2)

    According to the boundary conditions and input parameters in the simulation experiments, the throughput capacity is reduced by 5.6%–7.8%, and the average lockage time is increased by about 10.8%, when comparing the mode of filling and emptying water mutually with independently. It should be noted that the filling and emptying water time of the ship lock in this study are the same in the two filling and emptying modes. But generally, it is slightly longer in the mode of filling and emptying water independently. If then, it is hard to tell whose average lockage time is longer, and further research is needed.

  3. (3)

    In terms of the influence of the variation of the ship speed entering and leaving locks and safety interval time, if the variation is 30%, the throughput capacity will be reduced by 1.9%–2.2%, comparing the mode of filling and emptying water mutually with independently. And if the variation is 50%, the throughput capacity will be reduced by 3.6%–4.0%. Those reductions are not significant. The results of this case shows that it is acceptable to use average value of navigation speed and safety interval time when doing research on the throughput capacity and operation efficiency of ship locks.

5 Conclusions

  1. (1)

    On the premise of the same time of filling and emptying water, the throughput capacity will be reduced if the double-line ship locks operate in the mode of filling and emptying water mutually compared with independently. The range of capacity reduction is related to the composition of ships, and the variation amplitude of ship speeds entering and leaving locks and safety interval time between two adjacent ships.

  2. (2)

    Under the boundary conditions and input parameters of this study, the throughput capacity is reduced by 5.6%–7.8%, the average lockage time is increased by about 10.8%, comparing the mode of filling and emptying water mutually with independently.

  3. (3)

    The speed of ships entering and leaving locks and safety interval time with no variation or different degrees of variation, have little impact on the throughput capacity of ship lock. Therefore, it is acceptable to use average value of speed and safety interval time of ships when doing research on the throughput capacity and operation efficiency of ship locks.