Subsea Seismic Analysis

Question

Hello community, 
 
 I am enquiring about those who have performed seismic analysis on subsea pipelines or piping. 
 I am wondering how others have handled the added mass component for the seismic analysis. 
 It is unclear to me if AutoPIPE is calculating the added mass during the analysis, or if we are required to add the hydrodynamic added mass based on selected coefficients (not the coefficients included in the hydrodynamic data). 
 
 Appreciate everyone's feedback. 
 Regards, 
 Grant

Shrey Sharma · Answer

Greetings Hoise, 
 AutoPIPE adds an additional weight component to the unit pipe weight for Static Seismic Analysis when the Additional Mass Coefficient Value is greater than zero. 
 
 The additional unit weight is calculated based on the following equation:

Where: 
 W add = Additional unit weight of pipe for Static Seismic analysis for submerged piping 
 D o = Outside diameter of pipe including Insulation and Refractory thickness 
 f s = Factor for submerged pipes: 0.0 when pipe not submerged or Segment flag for buoyancy turned off, 0.5 when one end of pipe is submerged, 1.0 when both ends of pipe are submerged 
 G = Specific gravity of Water (defined in Buoyancy dialog) 
 C a = Added mass coefficient Ca (defined in Buoyancy dialog) 
The rest of the static seismic calculations are carried out as usual after adding this additional unit weight to the weight of the pipe. 
 With this information, we can conclude that the AutoPIPE use Ca for Static Seismic and Modal analysis (affecting Response Spectrum and Time History analysis). Now the user has to decide which analysis to choose for their submerged piping. 
 Thanks