With the new capabilities of GeniE and HydroD, you create one concept model only for hydrostatics, hydrodynamics and structural analysis. Key benefits are reduced cost and higher quality.

Left: One concept model used to create analyssi models for hydrostatic, hydrodynamic and structural analyses.
Right: Compartments automatically created by GeniE, and typical filling of some of the tanks.

Left: A new equilibrium position has been computed based on structure mass, content of compartment and buoyancy.
Right: Two different GZ curves are computed when using the NMD MODU rules- tanks in deck are intact or damaged.

DNV Software selected its concept modelling techniques for a number of reasons. A key selection criterion was the ability to overcome previous limitations associated with efficient integration with CAD systems and software for rule-based capacity checking. Another was the ability to use the technology to carry relevant information throughout the whole activity flow from first modelling to final reporting.

A typical example of this is the ability to create compartments in the initial modelling and re-use these in subsequent hydrostatic code checking (intact/damaged), hydrodynamic analysis (filling degree) and structural analysis (pressure load and hydrodynamic inertia forces).

GeniE, together with HydroD, now enables our users to perform hydrostatic, hydrodynamic and structural analysis based on one concept model; different analysis models may be derived from a single concept model. These new features lead to a significant increase in productivity as well as improving the quality since
fewer models are required.

By using the concept technology our users can:create a single model for use in hydrostatic, hydrodynamic and subsequent strength analysis,

• perform hydrostatic analysis including code checks against relevant codes such as NMD and IMO for mobile offshore units in intact or damaged condition for example,
• perform hydrodynamic analysis using the equilibrium position calculated in the step above, n execute the structural analysis taking account of the hydrodynamic accelerations and loads, and
• finally model and control the complete work flow process including knowledge transfer to the next project.

Left: Hydrodynamic pressure are acting on the panel model - here shown in Xtract started from HydroD
Right: Typical example of response variable - in this case pitch for selected wave directions (using postresp from HydroD)

Left: The structural analysis model (or the finite element model)
Right: Velocities of the semi-submersible because of hydrodynamic loading.

When creating a floater model, either using a hull form or offshore type, users can perform all modelling within GeniE by using modern techniques for generating cross section curves subjected to skinning or extrusion to form the hull. Alternatively, existing data from a CAD model (e.g. SAT, 2D DXF format, offset tables) or a section scantling analysis can be used to create the same cross section curves. The inner structure (transverse or longitudinal) is now easily created by regular plate or stiffener modelling – GeniE will automatically generate connectivities with the curved surfaces, so it is easy to trim the inner structure to the outer hull.

GeniE has the unique ability to automatically define all closed volumes as compartments (or tanks); the users may adjust the compartments by specifying nonwatertight bulkheads. Compart-ments may be classified as tanks to be used in a hydrostatic or hydrodynamic analysis; a flexible solution since the filling may be adjusted when performing such analyses.

Furthermore, the compartments may be loaded with fluid or solid content; this is a significant improvement over previous modelling techniques where the user needed to define a finite element mesh that matched the loading pattern. This is no longer necessary as GeniE will create the loads (including the top shape of the content) independent of the finite element mesh. Another important feature is the ability to specify corrosion addition, as required when carrying out analyses for compliance with classification society rules like, for example, the Common Structural Rules. The figures on next page illustrate a concept model from which other models can be created along with examples of different tank loading configurations.

The hydrostatic analysis may now be performed. The additional information required is typical tank filling, which are deck tanks and need to comply with NMD MODU rules, for example, and wind area and profile. HydroD then computes equilibrium position, GZ curves, still water forces and moments, and reports on hydrostatic rule check results. These reports include important parameters such as metacentric height, mass of structure and compartment content, centre of gravity, volume of buoyancy, centre of buoyancy, centre of rotation, mass and centre of gravity for each compartment, and the free surface centre per compartment. It is easy to set up several loading and draft conditions and run all the stability computations at once, with no need to guide individual analysis runs.

The hydrodynamic analysis is also performed with a minimum of input parameters,as all relevant information is carried over from the concept model. If a hydrostatic analysis has already been carried out, there is no need to repeat the equilibrium computations since the relevant information is automatically transferred. A further enhancement is that there is no need to have an exact match between the panel and the draft, trim and heel of the panel model prior to hydrodynamic analysis.

Following a hydrostatic analysis, additional input is limited environmental information such as sea heading, occurrence and type of waves. Results such as RAOs, pressure and acceleration are computed and can be statistically postprocessed to find worst conditions for use in a subsequent structural analysis. In addition, more specific information such as centrifugal moments, radius of gyration, metacentric heights and restoring coefficients can be calculated. In common with hydrostatic analysis, it is easy to set up and execute multiple analysis runs without having to control these individually during execution.

The hydrodynamic analysis calculates pressures and accelerations that are seamlessly used in the structural analysis, with no need for manual load application to the finite element model. Furthermore, the structural analysis model may have a different (and in most cases a finer) finite element mesh than the panel model. Our programs will automatically detect differences and ensure that load mapping is performed correctly. The structural analysis is performed using Sestra; the results created may be used in general post-processing, code checking and fatigue of beams and plates.

Even though offshore structures are used as references herein, this methodology is equally applicable for maritime structures.