Abstract Prediction and optimisation of non-cavitating marine propeller noise at low frequency are important for design of submarine propellers that are required to operate in the non-cavitating condition. The low-frequency discrete- and broadband-spectrum forces of propellers have different generation mechanisms, and thus have not previously been studied within a unified framework. In this work, the strip method is applied to simultaneously predict and optimise these two forces. First, the panel method is applied to predict the discrete-spectrum forces of different strips in the time domain. Then, the unsteady force of the whole propeller is obtained as the linear superposition of the shifted unsteady forces of all the strips, according to a skew distribution. The strip method is then used to numerically solve an integral equation for the broadband-spectrum force, derived via the spectral method. On the basis of experimental results, the predictions of low-frequency discrete- and broadband-spectrum forces are verified to have high accuracies. An analysis of the effect of propeller skew on the unsteady forces of different strips, and the effect of strip-cutting strategy on the broadband-spectrum force, is also performed. It is found that the skew of a strip is approximately equal to the angle of the circumferential phase shift of the unsteady force of that strip, and that the strip-cutting method has an insignificant effect on the predicted broadband-spectrum force. The optimisation of propeller performance under several constraints is then considered, with the particular objectives of maximising the propulsion efficiency and minimising the low-frequency discrete- and broadband-spectrum forces. The circumferential phase-shift effect of the skew allows the optimisation model to be decoupled into two steps. The discrete-spectrum force of the whole propeller can thus be computed using linear superposition rather than a hydrodynamic calculation, which significantly improves the computational efficiency. The effectiveness of the optimisation is verified by two optimization cases. For HSP, the propulsion efficiency is increased by 2.5%, the broadband-spectrum noise is reduced by approximately 0.6 dB, and the first- and second-order values of discrete-spectrum thrust are decreased by 9% and 27%, respectively. Similarly, for E1619, the first- and second-order values of the discrete-spectrum thrust are reduced by 13% and 18%, respectively.

中文翻译：

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低频离散和宽带频谱船用螺旋桨力的预测和优化

摘要 低频非空化船用螺旋桨噪声的预测和优化对于要求在非空化条件下运行的潜艇螺旋桨的设计具有重要意义。螺旋桨的低频离散和宽带谱力具有不同的产生机制，因此以前没有在统一框架内进行研究。在这项工作中，条带法被应用于同时预测和优化这两种力。首先，应用面板方法在时域中预测不同条带的离散谱力。然后，根据偏斜分布，获得整个螺旋桨的非定常力，作为所有条带偏移的非定常力的线性叠加。然后使用条带法对宽带谱力的积分方程进行数值求解，该方程通过谱法导出。根据实验结果，低频离散和宽带谱力的预测被证实具有很高的准确性。还分析了螺旋桨偏斜对不同带材非定常力的影响，以及带材切割策略对宽带谱力的影响。发现带材的偏斜近似等于带材非定常力的圆周相移角度，并且带材切割方法对预测的宽带谱力影响不显着。然后考虑在几个约束条件下螺旋桨性能的优化，具有最大化推进效率和最小化低频离散和宽带频谱力的特定目标。偏斜的圆周相移效应允许将优化模型分解为两个步骤。整个螺旋桨的离散谱力因此可以使用线性叠加而不是水动力计算来计算，这显着提高了计算效率。通过两个优化案例验证了优化的有效性。对于HSP，推进效率提高了2.5%，宽带谱噪声降低了约0.6 dB，离散谱推力的一阶和二阶值分别降低了9%和27%。同样，对于 E1619，