High-fidelity modeling of a backhoe digging operation using an explicit multibody dynamics finite element code with integrated discrete element method

Abstract

In this thesis, a high- fidelity multibody dynamics model of a backhoe for simulating the digging operation is developed using the DIS (Dynamic Interactions Simulator)multibody dynamics software. Sand is used as a sample digging material to illustrate the model. The backhoe components (such as frame, manipulators links,track segments, wheels and sprockets) are modeled as rigid bodies. The geometry of the major moving components of the backhoe is created using the Pro/E solid modeling software. The components of the backhoe are imported to DIS and connected using joints (revolute, cylindrical and prismatic joints). Rotary and linear actuators along with PD (Proportional-Derivative) controllers are used to move and steer the backhoe and to move the backhoes manipulator in the desired trajectory. Sand is modeled using cubic shaped particles that can come into contact with each other, the backhoes bucket and ground. A cubical sand particle contact surface is modeled using eight spheres that are rigidly glued to each other to form a cubical shaped particle, The backhoe and ground surfaces are modeled as polygonal surfaces. A penalty technique is used to impose both joint and normal contact constraints (including track-wheels, track-terrain, bucket-particles and particles-particles contact). An asperity-based friction model is used to model joint and contact friction. A Cartesian Eulerian grid contact search algorithm is used to allow fast contact detection between particles. A recursive bounding box contact search algorithm is used to allow fast contact detection for polygonal contact surfaces and is used to detect contact between: track and ground; track and wheels; bucket and particles; and ground and particles. The governing equations of motion are solved along with joint/constraint equations using a time-accurate explicit solution procedure. The sand model is validated using a conical hopper sand flow experiment in which the sand flow rate during discharge and the angle of repose of the resulting sand pile are experimentally measured. The results of the conical hopper simulation are compared with previously published experimental results. Parameter studies are performed using the sand model to study the e ffects of the particle size and the orifi ces diameter of the hopper on the sand pile angle of repose and sand flow rate. The sand model is integrated with the backhoe model to simulate a typical digging operation. The model is used to predict the manipulators actuator forces needed to dig through a pile of sand. Integrating the sand model and backhoe model can help improving the performance of construction equipment by predicting, for various vehicle design alternatives: the actuator and joint forces, and the vehicle stability during digging.