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UBC Theses and Dissertations

Vertical forces on the coupling of a pusher tug-barge Mumford, David K.


This thesis presents a method of calculating the vertical force on the coupling between a pusher mg-barge unit where the tug is able to pitch relative to the barge. Alternate methods assume that the hydrodynamic forces on each hull have no effect on the other hull. The method presented here assumes that there is a hydrodynamic interaction between the two hulls. A numerically-fast three-dimensional solution method (unified slender body theory) is used to develop this interaction between the two hulls in coupled modes of motion at zero speed. Only the heave and pitch modes are considered. Experimental work was done on a coupled tug-barge model. The model was instrumented to determine the barge heave and trim, the relative pivot angle between the tug and barge and the vertical and horizontal pin forces. The experiments were run in head and stern sea conditions with two separate pivot locations. Only the horizontal forces are found to be non-linear. The peak vertical force occurs at wavelengths of 1.21Barge in head seas and /Barge in stern seas. The amplitude of the hull motions increases with the wavelength except for the pivot angle which steadies at about 1.51Barge. The pin force is more sensitive to the pivot location than the barge motions. The pivot angle is also sensitive to the pivot location. Two numerical models of the tug-barge unit are compared to the experimental results. One model (Case 1) evaluates the two hulls separately while the second (Case 2) evaluates the hydrodynamic cross-coupling terms. Results show that both models underestimate the hull motions. The Case 1 model over-predicts the pin forces while the Case 2 model under-predicts them. The hydrodynamic cross-coupling terms are found to be significant. The Case 2 model is considered successful but needs to be refined numerically to improve on the solution.

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