Resistance to Accidental Ship Collisions. Outline. General principles Impact scenarios Impact energy distribution External impact mechanics Collision forces Energy dissipation in local denting Energy dissipation in tubular members Strength of connections Global integrity.
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The installation shape governs the deformation field of the ship. This deformation field is used to calculate total and local concentrations of contact force due to crushing of ship.The installation is then designed to resist total and local forces.
Note analogy with ULS design.
The vessel shape governs the deformation field of the installation. This deformation field is used to calculate force evolution and energy dissipation of the deforming installation.
The installation is not designed to resist forces, but is designed to dissipate the required energy without collapse and to comply with residual strength criteria.
The strain energy dissipated by the ship and installation equals the total area under the load-deformation curves, under condition of equal load. An iterative procedure is generally required
Note: Bow impact against large diameter columns only
Breadth mld 18.80m
Depth mld 7.60m
Draught scantling 6.20m
Max strain 12%
distributed over this
Area with high force
Deformed stern cornerSHIP COLLISIONContact force distribution for strength design of large diameter columns
Strong bow- tube and bow deforms
Medium strength bow - tube undamaged
Brace must satisfy the following requirement
Joints and adjacent structure must be strong enough to support the reactions from the brace.
Approximate expression including effect of axial force
Include local denting
If collapse load in bending, R0/Rc < 6 neglect local denting
Bending & membrane
F - R
SHIP COLLISIONElastic-plastic resistance curve for bracings collision at midspanFactor c includes the effect of elastic flexibility at ends
Kinetic energy absorbed by brace prior to rupture: 6 ~ 7 MJ
Stress-strain distribution - bilinear material
Axial variation of maximum strain for a cantilever beam with circular cross-section
Assumption: Bilinear stress-strain relationship
Local buckling does not need to be considered if the follwowing conditions is metAssumption: Membrane tension larger than compression in rotation(NORSOK N-004)
The degree of plastic deformation at fracture exhibits a significant scatter and depend upon the following factors:
Welds normally contain defects. The design should hence ensure that plastic straining takes place outside welds (overmatching weld material)
Steel grade ecr H
S 235 20 % 0.0022
S 355 15 % 0.0034
S 460 10 % 0.0034