FD生成的PMM数据在初步设计阶段进行评估英文文献和中文翻译(7)
In order to meet the criteria a number of iterations were performed increasing the number of data-points in the MTP. Different approaches were tested for example adding points mainly focusing on static points and correspondingly adding points mainly focusing on dynamic points. The final minimum test program comprised the total matrix of dynamic test points from the STP while the static part only contained 58 data points of the total 82 in the STP. In fact the final MTP did not meet all the tolerances, but it was accepted as close enough and robust enough to fulfill the purpose. The criteria values, i.e. differences between final MTP and STP maneuvering parameter, are listed in Table 11. The final minimum test matrix is presented in Table 12. Table 10: Acceptable tolerances between results of MTP and STP simulated manoeuvres, where zz is zigzag, OS is overshoot angle, ITA is initial turning ability and tc is turning circle. 10/10 zz 1st OS [deg] +/- 0.5 10/10 zz 2nd OS [deg] 0.8 ITA [Lpp] 0.02 20/20 zz 1st OS [deg] 0.8 20/20 zz 2nd OS [deg] 0.8 35 tc advance [Lpp] 0.05 35 tc tactical diameter [Lpp] 0.05 35 tc steady drift [deg] 1.0 Table 11: Difference between results of MTP and STP simulated manoeuvres. Port Starboard 10/10 zz 1st OS [deg] -0.7 -0.9 10/10 zz 2nd OS [deg] -1 -1.1 ITA [Lpp] 0.02 0.05 20/20 zz 1st OS [deg] -0.5 -0.9 20/20 zz 2nd OS [deg] -0.6 -0.3 35 tc advance [Lpp] -0.01 0.02 35 tc tactical diameter [Lpp] -0.11 0.02 35 tc steady drift [deg] 0.6 0 As the next step in line towards a full model test matrix of pure numerical model tests the static part of the found MTP was generated using CFD. The purpose was to substitute the static derivative found from the model tests with static derivatives evaluated from numerical model tests. The numerical data was evaluated just as if they have been recorded in the towing tank, i.e. the calculated hydrodynamic forces are faired by the same combination of independent variables as presented in equation 28 to 30. The dynamic coefficients are not reevaluated based on the new static coefficients; to make it simple the static coefficients from the MTP is just replace by the new “CFD” static coefficients. The predicted static hydrodynamic derivatives are presented in Table 13. Simulations were made using both sets of hydrodynamic derivatives presented in Table 11. The main values for 35/-35 degree turning circles and 10/10 and 20/20 starboard and port zigzag manoeuvres are presented in Table 14 and Table 15. The simulation results are plotted in Figure 20 to Figure 23.Abstract The present paper covers the work made in order to be able to perform standard deep water IMO manoeuvring simulations based on a combination of computed and measured hydrodynamic input data. Based on a full set of measured PMM data a reduced test matrix was identified and the standard 10-10 and 20-20 zigzag and the 35 turning circle manoeuvres was simulated. Based on the reduced test matrix all the static PMM conditions were computed with the RANS code STAR-CCM+ in order to obtain the hydrodynamic forces and moments. The computed static PMM data was subsequently used to replace the corresponding measured static PMM data in the simulations. Comparison between the computed and measured forces and moments showed a quite good agreement. Formal verification and validation, taking numerical and experimental uncertainties into account, was made for a selected condition. The result showed that the X-force is validated, while the Y-force and the yaw moment are not. For the simulated manoeuvres, the results also look promising, since reasonable good agreement was found when comparing the simulated turning circle and zigzag manoeuvres, obtained with measured and computed input data.
Introduction Today manoeuvring simulators are used to find the trajectory of the ship in arbitrary manoeuvres. During the ship design phase, focus is mainly on the requirements to the IMO standard manoeuvres (10/10 and 20/20 zigzag and 35 turning circle), which the new ship must comply with. The simulator models are based on integral quantities and the idea is to solve the equations of motion together with large measured sets of hydrodynamic force/moment data. The major advantage of the simulators compared to CFD is their ability to simulate general manoeuvres in real time. But, since they rely on usage of experimental PMM data, which is costly and time consuming to produce, they are usually used late in the design phase, after the final hull form is known and the scale model can be built. Consequently, the manoeuvring characteristics of the ship are evaluated late in the design process. Using CFD instead of the experiment for the data generation would not require the scale model and the simulation could therefore be done earlier in the design process. It is well known that CFD requires much CPU time when it comes to producing hydrodynamic force/moment data by sweeping through large test matrices. But, taking into account how much extra useful information the CFD results provide about the flow field, this is acceptable. Maneuvers have traditionally been simulated by empirical methods, for instance as done in Agdrup (2008) or by simulators based on mathematical models using experimental rotating arm or PMM data, for instance as done in Otzen (2008). The application of CFD in connection with maneuvering has shown promising results in the past. However, much of the work performed so far has primarily focused on inpidual PMM conditions like static drift and static rudder configurations, e.g. Simonsen and Stern (2003), Simonsen and Stern (2005) and Simonsen et. al (2006) or pure yaw, e.g. Simonsen and Stern (2008). The SIMMAN2008 manoeuvring workshop, showed the same tendency, except for very few cases where CFD was used to predict the final manoeuvres directly. Only one participant, Hochbaum et. al (2008), tried the approach used in this present paper, i.e. CFD based PMM. The approach was somewhat simplified, since effects of free surface and dynamic sinkage and trim were not taken into account, but even so quite good results were obtained for the final manoeuvres.