The Research Of Numerical Prediction Of Towing Hydrodynamic Characteristics Of Floating Body With Drift Angle

At present,the development of shipping industry drives the increase of towing operation,which is required for the dispatch,transportation and emergency towing of various non-self-propelled structures.And the accurate prediction of towing resistance plays an important role in determining the towing scheme and choosing the tug.In the actual towing process,the towed object,under the effect of various factors,often forms a certain angle with the direction of the coming flow,which makes the flow situation more complicated than that of the longitudinal towing,and the prediction method of towing resistance is very different at different drift angles.Therefore,the prediction of towing hydrodynamic characteristics with drift angle has great research significance.Based on the Datengxia project and taking the floating overhaul gate as the research object,the numerical prediction of hydrodynamic characteristics of the floating body when towed at different drift angles is studied in this paper.The main contents are given as follows:(1)The viscous flow field with free liquid surface is simulated when the gate is towed at different drift angles,and the consistency between the numerical prediction results and the test values is improved from aspects of mesh generation and turbulence model selection.Within the scope of drift angle from 0°to 90°and speed from 0.1m/s to 1.1m/s,the corresponding calculation model is set up.Grid independence analysis is conducted to study the influence of grid factor on the numerical calculation accuracy of resistance,and the most economical meshing scheme is selected.Adopting RNG k-? turbulence model and SST k-? turbulence model respectively,towing resistance values are obtained.Comparing numerical results with test results,the influence of turbulence model on numerical calculation of towing resistance at different drift angles is analyzed,and optimal turbulence model at each drift angle is determined.(2)Sensitivity analysis of each factor in numerical simulation is carried out.Through range analysis and variance analysis,the order of influence of each factor on resistance response value is: velocity > drift angle > turbulence model > grid.Velocity and drift angle have significant effects on numerical simulation.The influence of turbulence model factors on resistance prediction is greater than that of grid factors.To improve the prediction accuracy,changing the type of turbulence model is preferred.(3)According to the numerical prediction results of the gate at various drift angles,the flow characteristics of the flow field are analyzed.Based on this,the hydrodynamic characteristics at different drift angles such as free surface waveform,velocity vector diagram,streamline figure,underwater vortex distribution and so on are analyzed.It is observed that the crest is generated at the first point of the incident flow surface contacting with the water flow,and the backflow surface is in the trough.The velocity around the gate is generally low,and the farther from the gate,the higher the speed.The formation and development of underwater vortices vary,and the disturbance range increases with the increase of drift Angle.(4)Considering the huge computational cost of two-phase flow simulation,the numerical simulation method of stack mode is adopted at low speed.Similar to that of two phase flow simulation,calculation model at different drift angle is set up,and the grid independence analysis is analyzed.Compared with model test values,the accuracy of numerical forecast considering the Standard k-? turbulence model and SST k-? turbulence model respectively,is discussed.The results show that at low speed,the calculation of resistance adopting the stack mode can save computing resources and meet the engineering precision requirements.(5)Comparing the calculation results of empirical formulas with the experimental data,except that the calculated value obtained by using the formula proposed in "Load Code for Harbour Engineering" is in good agreement with the experimental value when the drift angle is less than 45 degrees,the calculation error of other empirical formulas is very large,and the accuracy of the empirical formula is far less than that of numerical prediction.Most empirical formulas do not take into account the drift angle and particularity of shape of floating body,which is of little practical reference value for the research object in this paper.