# Modeling of a Coal Transshipment Complex Based on a Queuing Network
## 5 Discussion of the Simulation Results  
This study addresses modeling the operation of the coal transshipment complex, which includes Toki marshaling station and Daltransugol JSC. Therefore, in addition to the arrival of coal trains, we consider the arrival of passenger and freight trains. The operation of the complex is studied in the summer, as train traffic decreases in winter conditions to reduce the wear of infrastructure, particularly rails and coal-loaded wagons. To create the model, we use part of the statistical data on the movement of trains and vessels obtained from field observation, technical parameters of the loading and unloading equipment, and the performance of the conveyor system presented in publicly available sources [40; 41; 49]. The verification of the simulation results is performed as follows. First, we compare three samples--the number of arriving trains per day, the number of departing vessels per day, and the size of the transported shipment on vessels--with the corresponding samples obtained from the remaining statistical data. To achieve this, we apply the Wilcoxon signed-rank test. Ten experiments are conducted with each pair of samples, from  
Figure 8: Experiment 3. Total blocking duration (\(b_{i}\)) of one channel in Node \(i\). which it follows that, in 95% of cases, with a significance level of 0.05, there is no reason to reject the hypothesis of sample correspondence. Second, the estimates of the throughput of individual subsystems presented in Tables 5 and 6 are compared with those obtained by other researchers from field observations. Thus, when the system load is 25-26 million tons per year, the cargo yard and berths effectively cope with the load, which corresponds to the recommended loading of the cargo yard (24.5-25 million tons) and berthing cargo yard (25.2 million tons) [49; 50]. Thus, we can claim that the presented model adequately describes the system and can be used to predict its operation. Based on the simulation results, we conclude the following. All trains arrive and depart from the receiving yard at Toki station unhindered. The conveyor system is idle 36% of the time due to the lack of vessels. The complex is currently at about 66% capacity. Its throughput can be increased to 28-29 million tons of coal yearly, 25% more than expected in 2024. Such an increase requires expanding the bulk carrier fleet to ensure the departure of an average of 16 carriers per month. After the planned modernization, the complex will be able to handle up to 46-47 million tons of coal yearly, almost two times more than the current capacity. In this case, the most significant bottleneck will be the receiving yard, which receives and processes coal trains before transferring them to Terminal 1. For efficient operation, it seems advisable to increase the number of tracks in it or build a new specialized yard at Toki station to service coal trains. The model presented has some limitations. It is not suitable for modeling individual events or solving optimization problems specifically related to planning the supply of goods and the distribution of berths. However, the obtained results make it possible to conduct scenario analysis, estimate the maximum permissible volumes of incoming material flows, the risk of the system switching to an irregular operating mode, and to assess the required fleet of transshipment equipment. The models of individual subsystems of the marine transshipment complex are relatively simple since they consider only the capacity, number of service devices, and their throughput. Equipment failures and technical interruptions are omitted. However, this makes it possible to describe essential operating parameters and functions of subsystems, discarding minor ones, such as planned maintenance breaks and dust suppression systems on coal handling equipment. This study does not address the issue of the receipt of cars with frozen coal, which need to be loosened before transferring to the railway cargo yard for unloading.