Bottom Roughness Analysis

Depending on the seabed profile, seabed type, loads (self weight and axial loads) and environmental conditions (wave and current induced forces) an on bottom roughness assessment and span analysis is possibly required to identify if any problem areas exist, where spans do not meet the allowable maximum free span criteria.

Maximum static and dynamic allowable free span lengths may be provided to GeoLine for the on-bottom roughness assessment or alternatively we can determine the maximum allowable free spans lengths. 

The maximum allowable free span lengths are used as screening criteria to determine areas of critical spans. SAGE Profile finite element software is used to compute the pipeline profile, which is compared with the seabed elevation to determine the span height and span lengths. The computed span lengths are compared with allowable free span length criteria. Environmental loads are taken into account in the analysis.

Modelling Seabed Stiffness

Modeling the seabed stiffness (bearing capacity) is of great importance for results of on-bottom roughness analysis. Non-linear soil springs are  used to model the vertical soil reactions. The soil springs are calculated according to recommended practices  BS 8010, DNV-RP-F105 “Free Spanning Pipelines”. A sensitivity analysis should be carried out to investigate the affect of varying seabed stiffness on the span lengths. 

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