# Research on Predicting the Mechanical Characteristics of Deep-Sea Mining Transportation Pipelines
## 3 Deep Sea Mining Pipeline Mechanical Simulation  
### Establishment of Deep Sea Mining System Simulation Model  
In this paper, static and dynamic theoretical analyses were conducted on a deep-sea mining transportation pipeline, resulting in the motion control equations of the pipeline. The motion equation is a nonlinear partial differential equation that requires discrete numerical solutions through numerical methods. The numerical method employed in this paper is the concentrated mass method [40], where the conveying pipeline is discretized into a numerical model composed of multiple pipeline units. Mechanical and motion characteristic parameters are calculated using OrcaFlex 11.0 commercial software for simulation analysis platforms as shown in Figure 3a,b. To study the changes in the mechanical parameters of deep-sea mining pipelines, it is necessary to consider the system as a whole, including the mechanical characteristics of both the hard lift pipe and the flexible hose under the combined effects of wind, waves, and currents. This provides simulated sensor data for constructing a model to predict pipeline mechanical properties. Thus, within OrcaFlex 11.0, dynamic models for mining vessels, subsea lifting hard pipes, lifting pumps, intermediate storage units, flexible hoses, and mining vehicles are established. The system structure is simplified as shown in Figure 4, wherein the simulation analysis utilizes a single-arch deep-sea mining system model. The blue grid represents the sea surface, and the brown grid represents the sea bed. Models for the mining hard pipe and the flexible hose are constructed based on real dimensions and material parameters. Given that the scale of the lifting pump and intermediate storage is less than one percent of the hard lift pipe, they are simplified to pipeline structures with identical mechanical properties, represented by the blue and red modules beneath the water surface in the model. For set boundary conditions, the flexible hose is fixedly connected at both ends between the intermediate storage and the mining vehicle, with the top of the hard lift pipe sharing the six degrees of freedom of the mining vessel. Models for the mining vessel and vehicle are created using the Vessel module, while the pipeline system is simulated using the Line module. The flexible hose operates at water depths of 1600 m-1700 m, with the buoyancy bodies forming the arch of the flexible hose simulated by the Clump module. Figure 4: Schematic diagram of deep-sea mining system simulation model. Figure 3: Orcaflex simulation analysis platform: (**a**) simulation scenario near the sea surface; (**b**) simulation scenario near the seabed. The relevant parameters of the hard lift pipe and the flexible hose are shown in Tables 1 and 2, buoyancy body parameters are presented in Table 3, and the values of hydrodynamic coefficients are indicated in Table 4. This article employs the JONSWAP wave spectrum as the random wave energy spectrum for simulation analysis. In the simulation analysis, marine environmental parameters are set based on the actual sea conditions of the target area. Specifically, wind speeds are between 1 and 3 m/s, and waves are modeled using the JONSWAP random wave spectrum. The direction of the ocean currents is shown in Figure 5, with eight primary current direction angles considered. The maximum deep-sea current is 0.1 m/s, while the surface currents are 0.2 m/s. Significant wave heights range from 0.5 to 3 m, with wave periods between 8 and 10 s. The direction of the waves is set to match the direction of the ocean currents. The density of seawater is 1035 kg/m\({}^{3}\), and the depth of the rigid seabed is 1700 m. The velocities of the ocean currents for four return periods are presented in Table 5.