## 4 Discussion and Conclusions
### Conclusions  
1. In this paper, in contrast with traditional research on the force of grab excavation, the unit integration method for analyzing the force of the grab excavation material was proposed. During the excavation process of the grab, the force on the grab produced active pressure \(F_{B}\) and passive pressure \(F_{E}\). \(F_{B}\) and \(F_{E}\), as expressed by integral equations, and the material was divided into units. Digging force \(F_{D}\) was obtained by subtracting \(F_{B}\) and \(F_{E}\). Depending upon the characteristics of the material unit, this method can analyze the functional expression between the grab bucket digging force and the digging parameters.
2. Based on the DEM theory, the process of excavating materials with a grab was simulated. In the simulation process, reasonable data parameters were set, and the the grab flat digging force obtained. The simulation data shows that the digging force first increases and then decreases. Through comparative analysis, we found that the simulation results of the force of the grab flat digging are basically consistent with the theoretical calculation by the unit integration method, which verifies the correctness of the relevant theoretical models.
3. This study sought to control the movement distance of the closing wires and the hoist wires through the equation of motion, to carry out theoretical precision calculations and experimental research into grab flat digging. A flat digging test was carried out on land in fine weather conditions. The flat digging test was carried out on both dry soil and wet soil, and both demonstrated similar precisions (6.8 mm vs. 7.2 mm) at a depth of 100 mm. By comparing theoretical data and test data, the following conclusion is drawn: the deviation of the theoretical flat digging precision from the test data falls within the allowable range, at 3.15%. It is already known that sea tests differ from land tests, but land tests provide a foundation--and can provide supporting data--for future sea tests. Such sea tests will be completed in our follow-up work, which will more realistically reflect the flat digging test.  
Conceptualization, C.X. and Z.L. ([PERSON]); methodology, C.X. and Z.Z.; software, C.X. and Z.L. ([PERSON]); validation, C.X., Z.L. ([PERSON]), Z.Z., and Z.L. ([PERSON]); formal analysis, C.X. and Z.Z.; investigation, C.X. and Z.L. ([PERSON]); resources, C.X. and Z.Z.; data curation, C.X. and Z.L. ([PERSON]); writing--original draft preparation, C.X. and Z.L. ([PERSON]); writing--review and editing, C.X., Z.L. ([PERSON]), Z.Z., and Z.L. ([PERSON]); visualization, C.X. and Z.Z.; supervision, C.X., Z.L. ([PERSON]), Z.Z., and Z.L. ([PERSON]); project administration, C.X., Z.L. ([PERSON]), Z.Z., and Z.L. ([PERSON]); funding acquisition, C.X., Z.L. ([PERSON]), Z.Z., and Z.L. ([PERSON]). All authors have read and agreed to the published version of the manuscript.  
This research was funded by University-Industry Collaborative Education Program (Project no. 202002162010). And this research also was funded by \"Startup project of scientific research on newly introduced talents of Guangzhou Railway Polytechnic\" (Project no. GTXFR2104).  
Not applicable.  
Data Availability StatementData are contained within the article.  
The authors declare no conflict of interest.