Abstract:The point-peak method has been used for many years to analyze the linear displacement amplitude-frequency response curve of dynamic foundation. In this method, however, the subsoil damping ratio is low and is thus low in the code for dynamic foundation design.In this study, a multi-peak method is presented for measurement and analysis to increase the damping ratio.This method is used in the design of a hydraulic vibrator foundation with better economic results and has been also been used in well operation.This paper describes the differences in the two methods, including stiffness.The point-peak method has limitations.With increasing frequency, the damping ratio unusually decreases.The ratio value is zero at peak frequency but is 0.707 at the origin.Moreover, stiffness is larger at peak frequency but smaller at the origin.Therefore, the damping ratio is smaller in the peak area, and thus in our code for design of dynamic machine foundation, resulting in an excessively large and wasteful foundation.In addition, one parameter group is obtained by analyzing the single response curve with the point-peak method, and different groups from other curves of one foundation unusually appear because there is only one group for one foundation.On the contrary, in the multi-peak method, the parameters obtained by analyzing two curves, namely two by two, are generally very close and may be averaged.This method is more economical, and stiffness is decreased along an increase in frequency, and the static stiffness is larger than dynamic stiffness.This result agrees with the half space theory of foundation.The code for design of a dynamic machine foundation is mainly applied to the foundation design of a reciprocating compressor with a single working frequency.Resonance can be avoided if the natural frequency is larger or smaller than the working frequency.In such cases, the effect of damping is less, and the damping ratio may be small. In hydraulic vibrators with a wider working frequency zone, however, resonance cannot be avoided.In such cases, the damping ratio must be larger to control the resonance.
