船舶机械振动源激励力的间接估计工程方法

船舶机械设备输出到船体上的激励力对船舶结构振动预报有着重要意义,文章讨论了两种间接估算激励力的方法,目的是希望在工程现场应用这些工程方法取代激励力的直接测量.对刚性安装的机器推荐采用最小二乘方法,该方法是基于支撑结构的加速度导纳特性进行估算.对弹性安装的机器而言,推荐采用基于隔振器阻抗特性的激励力间接估算方法.力的估算是逆问题,文中采用奇异值分解技术来处理会遇到的病态问题,从而尽量降低估算误差.文中还对估算的准确度、估算质量评价等进行了讨论.条件数的倒数在最小二乘法响应点的选取时可作为优选的先验判据,归一化残差可作为估算质量的后验判据.实验证明了间接估算方法是确定船舶机械激励力的恰当选择,实验结果的最小二乘法相对误差为3分贝.测试中的信噪比被认为在力估算过程中有重要影响,低信噪比很可能是实际测试时的首要误差来源.该文也可用于指导船舶振动源特性描述的研究.

Indirect Engineering Estimation of Force Excited by Machinery Vibration Sources of Ship

For the prediction of ship structural vibration it is of much importance to estimate exciting forces acting on ship hull from machinery in ships. Two indirect force estimation approaches are discussed in this paper.It is aimed to employ these engineering methods instead of direct force measurement in situ. For rigidly-mounted machine, least squares approach based on accelerances of the supporting structure is recommended. For resiliently-mounted machine,indirect force estimation based on impedances of the isolator is discussed.An inverse problem exists in the process of estimating forces,and singular value decomposition is employed to deal with ill-posed problem for minimizing the estimation error.There are detailed discussions in this paper about estimating accuracy and quality assessment.The inverse of condition number is recommended as a good prior criterion for choosing response positions in least squares approach.Normalized residue is recommended as another criterion to assess the quality of estimation afterwards.Experiments demonstrated that indirect approaches could be good choices for determining output forces of machinery in ships. The relative error of the results from least squares approach is 3dB. SNR (Signal to noise ratio) of the measurement plays an important role in force estimation process.Low SNR would probably be the chief cause of the error in practice. This paper can also be used to guide the characterization of vibrational source in ships.