## 2 Analysis of Recent Research and Publications
In order to simplify the wagon body design, reduce its weight, and improve the mechanical properties, authors in the publication [16] suggested replacing sandwich panels with a profiled sheet. The stiffness of the wagon body was evaluated through modal analysis. It was established that the proposed panels reduced the weight of the wagon body by 600-700 kg compared to the typical design. The methodology of multi-scale design of lattice core sandwich structures was presented in the paper [17]. North American standards were used in designing the wagon. However, the proposed wagon designs did not allow the simultaneous transportation of various cargo types. The strength of the bearing structures of wagons, including the hopper wagon, which have exhausted their normative resource of operation was calculated in the work [18]. It was established that the service life of the researched wagon-bearing structures could be extended. Modernizing the wagon-bearing structures for the transportation of the assigned cargo nomenclature was proposed. However, when performing calculations, the authors did not take into account thermal loads that may act on the wagon-bearing structures in operation. The grounds for the creation of wagon-bearing structures capable of being operated both on main lines and in railway-water shipment were discussed in the work [19]. The research was carried out for a flat wagon. However, the authors did not pay attention to the technical adaptation of the hopper-wagon-supporting structure for railway ferry transportation, namely, the provision of structural units designed for secure fastening on the deck. Calculation of the strength of the wagon body was carried out in the publication [20]. The main reasons for the appearance of defects in the car components were analyzed. Measures were proposed to improve the wagon-bearing structure. Analysis of the BCNHL (bogie covered wagon, high capacity, and light weight) freight wagon design was carried out in the paper [21]. The BCNHL wagon was designed for the transport of packaged goods (cement, fertilizer, grain, etc.). However, the proposed design improvements did not contribute to the possibility of the simultaneous transportation of various cargo types in these wagons. The results of determining the wagon loading were presented in the paper [22]. When carrying this out, the authors limited themselves to normative values. The results of the strength simulation of the wagon-supporting structure were given. However, this wagon was not adapted to the transportation of high-temperature cargo. A strength analysis of the improved wagon was carried out in the paper [23]. Conclusions were given regarding the obtained stress of the wagon under shock loads. Analysis of the possibility of modernizing a freight wagon by using composite panels was carried out in the work [24]. The reasonability of the proposed introduction into the wagon-bearing structure was substantiated. However, the modernization of the wagon to increase the efficiency of cargo transportation was not considered in this work. The publication [25] provides the grounds for the use of sandwich panels in the modernization of a freight wagon. The advantages of the modernization and the prospects for its further development on wagons were marked. The load of the main wagon types during operational modes was determined in the work [26]. The rationale for the further operation of freight wagons that have exhausted their regulatory resource was given. However, these wagon designs were highly specialized and did not allow for the simultaneous transportation of various cargo types in them. The rationale for introducing articulated-type wagons into operation was considered in the publication [27]. The results of determining the dynamic load and strength of the wagons were presented. However, the process of maintenance of the proposed wagons caused difficulties in operation due to their structural features.