Evaluation of the hydrodynamic Influence of the Hull of a towing timber transport Module on the operating Conditions of the Propellers

It is theoretically justified that the empirical formula, usually used to determine the coefficient that takes into account the hydrodynamic influence of the vessel's hull on the operating conditions of the propellers, as applied to the module under consideration, designed for towing timber transport units along medium and small rivers, can give significant errors. This is explained by the ratio of displacement to propeller diameter, which is atypical for conventional vessels, the presence of a compressed flow between the pontoons of the catamaran-type floating base, and the placement of the propellers outside the transverse dimensions of the pontoons, which weakens the influence of the following flow. As a result of a numerical experiment based on the finite element method using the SOLIDWORKS Flow Simulation program, the theoretical propositions were confirmed. When processing data on characteristic longitudinal sections, it was found that in the inter-pontoon space the flow velocity does not decrease, but increases, and only at some distance from the stern does it begin to decrease, remaining at a significant distance less than the relative velocity of the module. This is explained by the fact that in the inter-pontoon space and immediately behind it, the flow compression factor is more significant than the factor of the presence of a passing flow. Based on data from a number of cross sections, approximating dependencies were obtained for determining the velocities by coordinates in the section. Using these dependencies, a specially developed algorithm was used to calculate average speeds within circular contours for each cross-section, corresponding to the location of one propeller in the diametrical plane and two propellers symmetrical relative to it. The values of the required coefficient are established based on them. When placing propellers in the inter-pontoon space, it should be taken as - 0.08...- 0.09 when installing one propeller and - 0.09...- 0.11 when installing two. To determine this when installing propellers behind the stern of the module, approximating dependencies were obtained. The range of change of the coefficient behind the stern is from -0.08 to 0.06 when the distance from the midship changes from 3.25 to 4.90 m. Recommendations are given for determining the locations of installation of propellers, taking into account, along with the speed, other factors.