敷设气囊的充水圆柱壳的声辐射特性

为降低充水圆柱壳受内部点声源激励时的水下辐射噪声,在其外壳上敷设气囊,形成气囊圆柱壳。为指导气囊圆柱壳的设计,将充水裸圆柱壳和充水气囊圆柱壳分别简化为单、双层无限长隔板。比较隔板、气体与水的波阻抗,分析气体声速与层厚对双层无限长隔板在平面声波入射时的低频声辐射的影响机理。分析表明,声速小的气体和适当的气层厚度可以降低双层障板的辐射噪声。采用声无限元法计算气囊圆柱壳的水下声辐射,结论与对隔板的机理分析吻合。优化设计出的充水CO2气囊圆柱壳的水下辐射声功率与远场辐射声压明显低于充水裸圆柱壳。

Anti-jamming method using complex ANF for GNSS receivers

In order to improve the anti jamming performance of global navigation satellite system receivers, a method based on the complex ANF(adaptive notch filter) was proposed to suppress narrow band interference on digital base band. The ANF was constructed by a series of the first order IIR notch filters, and the frequency parameters of all filters were updated with adaptive algorithm to detect jamming and to suppress it in real time. Simulation results show that the present method is able to suppress the jamming effectively and quickly, and the capability of signal acquisition is enhanced under condition of jamming. Moreover, a better performance than a conditional real ANF is achieved in simulation.