涡激振动对船舷安装的相干声纳条带测深系统测量精度影响分析

The Effect of Vortex Induced Vibration(VIV) on the Measure Accuracy of Overside Mounted Interferometric Seabed Inspection Sonar(ISIS) Sounding System

相干声纳条带测深系统采用船舷安装时,连接系统水下单元的钢管在水流作用下可能发生共振和频率锁定而剧烈振动,其下端的以换能器为主的系统水下单元也会随之摆动,使数据质量和测量精度受到影响。笔者通过分析在实际工作中遇到的问题发现:连接系统水下单元的钢管越长,钢管越容易在低流速条件下发生共振现象;换能器剧烈摆动会造成大量噪音信号;换能器摆动幅度较大时系统的安装校准会失效。本文通过解析计算得出了在现场操作中不同悬挂长度的钢管发生频率锁定时的控制流速以及换能器最大摆动幅度,认为实际工作中换能器距固定点在1.0m以内是可靠的,并对现场操作中如何减弱和避免涡激振动对系统精度的影响提出建议。

Using the Interferometric Seabed Inspection Sonar（ISIS） sounding system,the underwater transducer of the system is usually installed on shipboard tixed by a steel tube.However,the steel tube will possibly vibrate under current action.The phenomenon is called vortex induced vibration（VIV）.If the frequency of VIV is close to the natural frequency of the steel tube,frequency lock-in and tube resonance phenomenon will happen,whice will make the transducer sway and consequently reduce data accuracy.Based on abundant field investigations,it was found that：（1） The longer steel tube used for installing transducer,the lower current speed is needed to induce the resonation of the tube;（2） The violently vibration of transducer can induce much noises.（3） Large vibration amplitude of transducer will make the system calibration invalid.In this paper the minimum flow speed that can cause the vibration of the steel tube with different suspension lengths and the corresponding maximum swaying ranges is caculated.The results show that the suitable suspension length of transducers should be less than 1.5 m.Some suggestions about how to reduce and avoid the influences on system accuracy caused by the VIV resonance are also made.