Research On Driving Resistance Of Baiting Boat Based On CFD

The baiting boat is one of the feasible schemes to spread bait all over the crab pond,and has become a research hotspot to solve the problem of crab-pond feeding.The driving resistance is an important factor affecting the rapidity of the baiting boat.The good drag reduction effect of the baiting boat can improve the endurance,which directly affects the applicability of the baiting boat.It is always a difficult problem in engineering to find the boat type with the best drag reduction performance.The calculation and prediction of boat resistance has important academic and engineering value.Based on the fact that the floating stems and leaves in the aquatic grass area of crab pond will drift to the driving channel of the baiting boat and contact with the bottom of the boat to increase the driving resistance,this thesis optimizes the bottom profile of the crab pond baiting boat,establishes the hydrodynamic calculation model of the crab pond baiting boat under various working conditions,analyzes the influence of the optimized profile on the driving resistance of the baiting boat.According to the research results,a crab pond baiting boat suitable for large water surface is designed.The actual boat speed test shows that the research results are correct,which provides a reference for the follow-up design of crab pond baiting boat.The main research contents and achievements are as follows:(1)The cause of the driving resistance of the baiting boat was studied,the driving resistance of the baiting boat is mainly composed of friction resistance,viscous pressure resistance,and wave resistance.The difference between the two-dimensional method and the three-dimensional method was compared.It was found that there were deviations in driving resistance obtained by the conversion method of the real boat and the boat model,and the real boat was used in the subsequent tank drag test.As the research object to reduce the test error.The basic principle of numerical simulation algorithm is explored,according to the simulation requirements of the driving resistance of the baiting boat,a suitable turbulence model and discrete method were selected.(2)Based on the characteristics that streamlined shape will reduce the flow of water flow,reduce the pressure difference between the bow and stern of the baiting boat and reduce the driving resistance,two parametric design schemes of sharp bottom and round bottom are proposed,and the hydrodynamic calculation models of three boat types are established.In order to avoid the influence of the domain on the internal flow field,the appropriate domain size was selected according to the boat size.The grid is divided into blocks to improve the accuracy and reduce the time.The residual error and resistance curve are convergent,which proves the feasibility of the solution scheme.(3)The resistance of crab pond baiting boat with different line size,boat speed of0.5 ～ 2m / s and draft of 0.1 ～ 0.22 m is simulated.The results show that the wave making situation of the baiting boat changes obviously with the increase of boat speed,the wave height increases gradually,the wave crest moves back gradually,and the pressure difference between the front and back of the boat increases gradually.;the size of the bottom profile has a greater impact on the driving resistance,when the boat speed is 1.5m/s,the maximum drag reduction rate can reach 12.25% with the change of design parameters;Compared with the sharp bottom boat,the round bottom boat has a better drag reduction effect,with a drag reduction rate of up to 16.27%;The economic boat speed of the three boat types is not more than 1.5m/s,and the economic draft is not more than 0.18m;the designed sharp bottom boat and round bottom boat can reduce the sliding friction resistance between the bottom of the boat and the water grass,and it is more suitable for crabs pond bait.(4)In order to verify the accuracy of the simulation calculation results,a flat bottom baiting boat drag test was carried out in the indoor tank of Shanghai Ocean University.The speed-regulating motor pulled the flat bottom boat to move forward at a constant speed in the pool to control the speed of the boat.The tension sensor and the bow of the boat were connected with triangles to ensure that the boat was always traveling in a forward direction.The test measurement resistance and the calculated resistance within the boat speed of 0.5～1.5m/s were compared and the errors were found,the highest rate is only 9.65%,so the calculation results can be considered credible.(5)According to the research results,a large round bottom boat with a load capacity of 100 kg is designed.By modifying the main dimensions of the boat to reduce its diamond coefficient and square coefficient,the theoretical drag reduction effect of the large round bottom boat is better than that of a flat bottom boat.Polyethylene is selected for the boat material to reduce the boat’s own weight and increase the load capacity,and the blow molding process is selected for the mold opening process.The simulation results show that the maximum difference of the no-load driving resistance between the large round bottom boat and the small flat bottom boat is only 6.43 N when the boat speed is within 0.5 ～ 2m / s,and the large round bottom boat has more obvious wave reduction effect at high speed.The results of interval velocity measurement show that the speed difference between large round bottom boat and small flat bottom boat is less than 5.4%,which shows the good drag reduction performance of round bottom boat.The simulation calculation based on CFD software can accurately observe the changes of the flow field and boat pressure distribution in the stern of the baiting boat for three types of bottom profiles,which is convenient for comparison and selection of the best optimization plan.The calculated drag reduction effect of the designed large round bottom boat is consistent with the actual boat test results,indicating that the CFD simulation calculation results are accurate and have good application value for the research on the resistance of crab pond baiting boat.The round bottom boat can indeed reduce the resistance of crab pond baiting boat and the resistance of water weeds.It breaks the current design of baiting boats that only have flat bottom and sharp bottom,which provides a good reference value for the follow-up design of baiting boat.