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Hydrodynamic analysis of non-linear waves in random sea states – Wamod

Linear and non-linear modelling of random sea states using the higher order spectral method (HOSM), for use in hydrodynamic analyses of wave loads and responses of marine structures.

Wamod - wave modeller

Sesam’s Wamod software can be used to create linear and non-linear realizations of a given sea-state based on the Higher Order Spectral Method, abbreviated as either HOSM or HOS. The name Wamod is short for ‘wave modeller’.

Ocean waves are an essential input for calculation of wave loads and responses of marine structures in ocean engineering. For irregular waves, engineers in the shipping and offshore industries have typically been limited to the analysis of linear, or at most second order, irregular waves. Such models are not able to capture the extreme wave events. This can be done with Wamod, which makes it possible for the hydrodynamic solver to do more reliable computations of extreme loads and responses.

Non-linear wave analysis

To achieve a more realistic description of waves and their associated effects on loads and responses, a non-linear description may be applied. In contrast to linear or second order theories, where analytical solutions are available, higher order non-linear waves must be described through numerical simulations of the basic hydrodynamic equations.

Sesam’s Wamod and Wasim tools will enable you to perform efficient seakeeping computation of both linear and nonlinear random seas. Engineers can use Wamod-generated wave kinematics as input to Wasim, in the spectral wave data (SWD) format. If the Wasim analysis must be supplemented by other types of analysis (e.g. CFD), consistency between the tools is ensured by using the same SWD-file by all tools.

What is the higher order spectral method?

The higher order spectral method is a numerical method for solving fully non-linear equations for waves on the surface of an ideal fluid. The main advantage of HOSM compared to many other methods is the numerical efficiency, enabling the description of long-crested as well as short-crested sea states in reasonable computational times. In addition, the HOSM formulation enables an efficient calculation of the water particle kinematics below the surface. These are essential inputs to tools such as Sesam’s Wasim for the calculation of wave loads and responses.

Key benefits of Wamod

  • Linear and non-linear representations of sea-states
  • Short- or long-crested sea
  • Wind sea and swell can be combined
  • Wave kinematics written to a well-documented and open file format (SWD)
  • The wave data can be shared between different applications, ensuring consistency in the analysis
  • The same wave kinematics can be used for analysis of different structures
  • The location in space and time of the largest wave crests can be identified before starting the hydrodynamic analysis, which makes this analysis much more efficient


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