8. Hull modelling
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Note: Many data points (points or curves in surface construction) will not only increase the accuracy of geometry. We also increase the probability to have a less accurate result, due to the numerical processing.
Local models
Details for all types of structure – single models or integrated with global model
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Assemble the concept xml model files
- Exploit symmetry (xml export/import)
Share the same starting curves(!)
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Bi-directional Rhino3D interface
Plug-in installed with Rhino3D Exports a Jscript command file that GeniE reads GeniE file export: Guiding Curves to Rhino Exports a .grc file
More analysis demands better hull/surface modelling - Offshore floaters - Ships - Local models
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Mid-ship CH
Aft most CH
Foremost CH
Forward CH region
Forward CH region Target hold 2
After CH region Target hold 4
After CH region
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- Extract (new) points from curve - Cubic curves keep the degree low and are flexible - Smooth and continuous curves (where needed) - Straight lines of two points
Reduce the cardinality of the data!
Keep the degree of the splines and the number of segments as low as possible. Approximate a polygon of many points with a curve having just a few segments. This can be done by: - Fairing methods, e.g. Cubic Spline from Poly-line (red) - Interpolation methods, e.g. Shape-preserving spline (blue)
Several modelling strategies
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Top-down modelling
Type of curves determines modelling approach
Reuse CAD data
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Two alternatives in GeniE
Import 3D DXF
- All CAD and design packages can export DXF - Import DXF files into GeniE
Area covered by FEA
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Example: A bulk carrier will require 5 models
Mid ship CH. Target hold 3 Foremost CH Target hold 1 / Aft most CH. Target hold 5
SesamTM 40 years of success
New possibilities in Sesam GeniE for hull modelling – how can you benefit
Ole Jan Nekstad, Product Director Sesam 30 August 2013
Complex models
Surface models are often rich in details
- Structure - Properties - Stiffeners
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- The finite element strength assessment of the hull girder, primary supporting structural members and bulkheads - Cargo hold strength analysis: Mandatory from collision bulkhead to the forward machinery transverse bulkhead
Submodels – one or more cargo holds
Sets containing whole cargo hold, bulkhead, frame etc Exploit symmetry
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Assembly of submodels
Separate submodels to support work in parallell
- One or more cargo holds
Rebuild the curves either in CAD system or GeniE
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Rectangular NURBS Surfaces
,
,
,
,
, : degree + number of parametric sub-intervals + internal multiplicities in the knot vector (in , direction respectively)
Offshore floaters
FPSO, Semi, TLP, Spar, Barge, Jack-up++
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Cargo Hold Analysis - Scope
Merchant ships, tank, bulk, container ++ Upcoming Harmonized CSR
Assemble concept xml models
Steps
Export half model Import half model with mirror transformation Delete beams and plates in centre plane Import half model
Two different types of DXF curves
SPLINE (control points) NURBS POLYLINE (interpolation points) Linear segments
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Offset tables Waterlines, buttocks Constant parametric value Feature and knuckle lines
Need to test and practice
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Check the quality of imported data
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Quality of imported curves
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