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Background

Sesam is a collection of software applications and services for design and strength assessment (finite-element analysis) of offshore wind, offshore oil & gas, and maritime structures. Sesam is actively developed by DNV, has a fifty-year old history and is in widespread use in offshore and maritime industries around the world.

As an example Sesam may be used in the design of fixed and floating offshore wind turbines (OWT) foundation structures. Structural engineers use the software to perform extensive structural analysis for all relevant loading conditions as dictated by industry standards and regulations. Calculation of the structure's fatigue life or utilization factors (from code checks) are of interest.

Sesam supports the entire workflow from 3D modelling and generation of hydrodynamic wave load conditions to finite-element analysis and fatigue- and code-check postprocessing. Analyses can be run on a desktop or in the cloud through Sesam Cloud Compute Services.

A key topic in the RaPiD project is reduced-order models (ROM). With this technology we see several opportunities for Sesam software.

 

Opportunity 1: ROM for reduced analysis time and cost

Typically a Sesam analysis must be performed many times for the same structure, for different environmental and loading conditions. Thus even for relatively small structures the total analysis time can be significant. Analysis in the cloud provides reduced analysis time, but comes at an increased cost for end users.

A reduced-order model could be used as a surrogate for the finite-element model to reduce the analysis time (or equivalently cloud computaiton cost), or alternatively allow for more exhaustive analyses across a wider range of loading or environmental conditions.

 

Opportunity 2: ROM for real-time response and predictions (digital twin)

Today Sesam may be used to assess the fatigue life of an OWT structure in its design phase based on expected or rule-based loading conditions determined from historical observations of seastates at the relevant structure location. Clearly in such analyses there is large uncertainty, which has to be accounted for with significant conservatism.

With a reduced-order model coupled to seastate observations it is possible to track the accumulated fatigue damage of the structure in real time. This may in turn be used to predict remaining fatigue life and to optimize inspection and maintenance. With this closer and more accurate tracking of fatigue damage there is opportunity to remove conservatism in the structure design, thereby reducing on construction (stell) cost.

This concept may be taken a step further if data from on-board data sensors are available. Data sensors may include wave radars, accellerometers or strain gauges. The sensor data may be used as input to a ROM, providing for more accurate fatigue life calculation, or provide alerts when the structure (or ROM simulation) experiences critical utilization (such as from a freak wave).