Construction of fluid-solid coupling model of flexible multibody system for pipeline robots driven by differential pressure

The movement of the differential pressure pipeline robots in the pipeline driven by the fluid belongs to the complex fluid structure coupling dynamics problem. It is of great engineering significance to analyze the dynamic responses of the robots and evaluate the ability of the robot to patrol the pipeline by numerical simulation. Based on the coupled Eulerian Lagrangian (CEL) method, a fluid structure coupling dynamic model of the flexible multibody system for pipeline robots driven by differential pressure was constructed in this paper. The govening equations of the pipeline robots and its surrounding compressible Newton’s fluid were derived and represented with CEL frame. In order to efficiently describe the experienced large deformation process of the sealing cups, two-parameter Mooney-Rivilin model was used and its coefficients was obtained based on the uniaxial tensile tests of polyurethane. Based on the method of immersion boundary, the volume fraction in each fluid element contained wass used to track the fluid boundary by piecewise linear interface calculation. A novel penalty coupling method was used to simulate the interaction of the fluid with the robot by implementing a virtual spring bwteen the nodes at structural surface element and the anchor points at the fluid interface. The adaptability of the robot to the pipeline environment was evaluated by the average driving pressure difference, the average friction and the Mises stress peak value of the sealing cup. The parametric model of the pipeline robots with three and five cabins were developed to investigate the influence of pipeline geometrical parameters on the robots adaptability to internal pipeline environment. The numerical analysis results indicated that compared with the pipeline robot with three cabins, the average velocity and amplitude of velocity of the pipeline robot with five cabins were decreased by 5.3% and 18.6%,. and the running stability was better than that of the pipeline robot with three cabins, the average driving different pressure, friction force and peak values of mises stress of the sealing cups for the the pipeline robot with five cabins increased by 56.9%, 95.7% and 42.0% compared with the pipeline robot with three cabins, which showed that with the increase of the numbers of the cabins, the deformation of the sealing cup increased further, and the fluid needed to provide a larger driving pressure difference to overcome the friction, but the running stability of the robot was improved. For the pipeline robots with three and five cabins, the average friction force, the average driving pressure difference and the Mises stress peak value of sealing cups were all the maximum when the height of weld beading was 20 mm, the bending angle of bending section was 90° and the radius of curvature was 300 mm, thats of the pipeline robot with three cabins were 0.63 MPa, 5.64 kN and 24.16 MPa, respectivly, and 0.98 MPa, 10.61 kN and 28.30 MPa for the pipeline robot with five cabins Therefore, compared with the pipeline robot with three cabins, the pipeline robot with five cabins need to consume more fluid pressure energy to overcome the constraint resistance of the pipeline under dangerous conditions, the sealing cup is easier to wear, which weakens the sealing performance and has higher risk of brittle fracture. The research results can provide reference for the evaluation and design optimization of pipeline robot. © 2020, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.