Towing a plow along the seafloor is often the preferred method for burying cables, recovering seafloor minerals or measuring seafloor soil properties. This paper presents a nonlinear time-domain numerical model for simulating the global response of the seafloor plow as it traverses a seafloor with rapid changes in elevation. This model is useful for planning the course of the tow ship, determine changes in the length of the tow cable, and analyzing the efficiency of the plow operation. Even for highly erratic plowing maneuvers, the model exhibits a surprisingly high level of nonlinear solution robustness.
A complete seafloor plow system consists of three distinct substructures: ship, cable and plow, as shown in Fig. 1. The plow has a blade that penetrates the seafloor and a sled that rides on the seafloor surface. The ship tows the plow in any azimuthal direction using a cable that is somewhat longer than the water depth. By adjusting the length of cable, the ship pulls the plow along a desired seafloor route, following changes in seafloor elevation. Many physical parameters determine the efficiency of the overall cable plow operation. These time-varying parameters include the tow path, dynamic ship motion, hydrodynamic drag, plow design, seafloor bathymetry, soil type, and rate at which cable is paid-out or reeled-in. Optimal plowing performance means minimum plow weight, maximum plow depth, minimal spikes in cable tension, and maximum adhesion to the desired seafloor route. Recognizing the obvious difference in physical behavior of the three local substructures, an ideal numerical simulation model for the complete seafloor plow system should include three coupled submodels, one each for the ship, cable, and plow. Given cable resistance forces at the tow point, the ship submodel computes dynamic motions. Given dynamic soil resistance, the plow submodel computes plow forces and movement along the seafloor.
