Experimental Modal Analysis Of Elastic Vibration Isolation Foundation Of Offshore Platform Compressor System

Identifying the modal parameter(frequency and damping)of elastic vibration isolation foundation of offshore platform compressor system is a vital vibration monitor measure.Modal analysis was made to test the vibration properties of the elastic vibration isolation foundation of offshore platform compressor system.Covariance driven stochastic subspace identification algorithm and orthogonal polynomial fitting algorithm were applied to conduct the modal parameter identification,and parameters(frequency,damping)are finally calculated.Specific researches are conducted as followings:1.According to the properties of the elastic vibration isolation foundation of offshore platform compressor system a modal testing experiment plan was made:Natural excitation experiment method was chosen on the horizontal direction experiment,artificial(hammer)excitation experiment method was chosen on the vertical direction experiment.Excitation and response vibration data was collected on each direction.2.Covariance driven stochastic subspace identification was applied on horizontal modal parameter identification.Top nine parameters were identified from X-direction vibration data.Results show that:the first and ninth modal frequency are 1.167Hz,frequency region 13.24-20.685Hz required by DIN4024-1 is avoided.Other eight model frequencies are beyond 14.895-18.205Hz required by DIN4024-1.On the Y direction,top fifth parameters are identified from Y-direction vibration data.Results show that:the first frequency:1.7462Hz,is far below the resonance region,other four model frequencies are beyond 14.895-18.205Hz required by DIN4024-1.Vibration isolation foundation has good vibration characteristics on horizontal direction.3.Orthogonal polynomial fitting algorithm was applied to vertical direction modal parameter identification.On vertical direction,top eight modal parameters were identified from vertical vibration data.Results show that:the first,fourth and fifth modal frequencies are 4.9988Hz,which are not within the resonance region 13.24-20.685Hz.other four model frequencies are beyond 14.895-18.205Hz required by DIN4024-1.Vibration isolation foundation has good vibration characteristics on vertical direction.