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(12)
Only the two lower speeds are covered in this case. The reason is that the test program reflects the conditions the ship will experience during maneuvering and typically the combined drift and rudder angle condition occurs later in the maneuver, where the ship is experiencing a speed loss. For all the forces and moments the overall agreement between the measured and computed PMM results is fairly good. Though, it generally seems that it is most difficult to capture the measured data at the lowest speed. One of the main reasons for this is believed to be the propeller model. The rudder load is strongly dependent of the flow over the propeller since it is located in the propeller slip stream. On the other hand the propeller flow is strongly dependent of the wake field behind the ship as this generates the propeller inflow field. The simplified propeller does not really reflect the difference in propeller load distribution over the disk occurring from the change in the wake field that occurs during drift conditions and reduced speed due to the prescribed body-force approach. If the load distribution over the propeller disk is not correct, the distribution of the propeller slipstream velocity that hits the rudder will not be correct, which again means that the rudder performance will be influenced. This again will influence X´, Y´and N´ and probably lead to larger deviations between EFD and CFD, particularly for lower speeds and large drift angles, which also change the wake flow significantly. angles. Based on the above comparison the idea of generating PMM data on the basis of CFD looks promising. However, the question is if the small differences between EFD and CFD will influence the final maneuvers after applying the data as input to the maneuvering simulator. This is investigated in the following sections where simulations with both EFD and CFD data will be compared. Mathematical model applied for the manoeuvring simulations A mathematical model was generated to determine a specific set of X, Y and N derivative with the most optimal fit to the measured forces of the KCS. The analysis was performed in a classic way where initially the linear Y and N coefficients, Y’v and N’v were determined from the pure drift test at nominal speed with drift angle in the linear range between +/-4 degrees. These two coefficients were then fixed and included in the following general static analysis where the total matrix of static test data is applied to solve the total matrix of static coefficients, i.e. the remaining static derivatives are determined in a single combined analysis. The two added mass coefficients, v Y ' and v N ' was determined based on a special pure sway analysis which comprised the time series from all the dynamic pure sway tests. The general dynamic analysis was performed similar to the static analysis with a combined analysis for all of the dynamic test types. In the dynamic analysis all the static coefficients were fixed to the values adopted from the static analysis. The final coefficient formulation applied for the simulation of manoeuvres were output from the dynamic analysis (including the static analysis) supplemented with the two added mass coefficients from the pure sway analysis and an empirical value for the added mass coefficient ܺԢ௨, which was calculated as 6 percent of the non-dimensional mass of the vessel. I.e. based on the model tests the final coefficient formulation becomes: (30) In case of a 4DOF model a corresponding set of derivatives for the roll (K) moment would have been generated. However, this has been omitted due to the focus on 3DOF. Since the vessel is a single screw ship it possesses inherent asymmetry regarding port starboard manoeuvring ability. This asymmetry is reflected in a number of X, Y and N coefficients. The asymmetry is partly due to the propeller side force and partly due to unavoidable asymmetry in the physical model used for the model tests. To account for the scewness of the model, the Y and N forces acting on the model in a bare hull resistance test at drift angle zero is subtracted from Gothenburg, Sweden, 26-31 August 2012 those measured in the PMM series with the propeller working. 源:自;优尔'-论.文,网·www.youerw.com/