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VESSEL IMPACT ANALYSIS FOR RISER PROTECTION FRAME AND 15
PROTECTION NET SUPPORTS ON SEMI-SUBMERSIBLE OFFSHORE STRUCTURES

01, RPF-02, PN-01 and PN-02 structures, respectively.

Figures 37 ~ 40 show the plastic strain on the CPF column due to collisions at different
points of the RPF and PN supports. Figures 41 ~ 46 show the displacements of the RPF and
PN supports after collisions. Appendix B shows the capacities of the CPF column for
collisions at different points of the RPF and PN supports. Figures 47 - 54 show the stress
distribution plot of the CPF column due to collision at different points of the RPF and PN
supports. Figures 55 ~ 62 show the strain distribution plot of the CPF column due to
collision at different points of the RPF and PN supports.

Table 6. Results of the collision analysis of RPF-01 Structure

Load Case Disp (mm) % Plastic strain on % Plastic strain on Capacity (No
RPF-01_LC01 175 (14MJ)
Outer-shell – 20MJ Outer-shell – 14MJ plastic strain)
- 4.5% 0 MJ
7 MJ
RPF-01_LC02 150 (14MJ) - 0.5% 13 MJ
20 MJ
RPF-01_LC03 250 (20MJ) 0.25% No strain 20 MJ
20 MJ
RPF-01_LC04 750 (20MJ) No strain No strain 20 MJ

RPF-01_LC05 400 (20MJ) No strain No strain

RPF-01_LC06 <50 (20MJ) No strain No strain

RPF-01_LC07 250 (20MJ) No strain No strain

The plastic strain for RPF-01_LC01 for 14MJ is 4.5%, since the point of collision is very
close to CPF column. Appendix B shows the detailed graph from which the amount of
colliding energy for 5% plastic strain can be obtained. It is to be noted that the load
cases RPF-01_LC01~LC02 are the load cases where the collision points are very close to the
CPF column and hence the collision capacities are very low i.e. less than 14MJ and
hence the collision results for higher kinetic energy i.e. 20MJ is irrelevant and hence not
calculated.

Table 7. Results of the collision analysis of RPF-02 Structure

Load Case Disp. (mm) % Plastic strain on % Plastic strain on Capacity (No
RPF-02_LC01 200 (20MJ) plastic strain)
Outer-shell – 20MJ Outer-shell – 14MJ
3.90% 0.90% 0 MJ
6 MJ
RPF-02_LC02 185 (20MJ) 1.40% 0.65% 20 MJ
20 MJ
RPF-02_LC03 500 (20MJ) No strain No strain 20 MJ

RPF-02_LC04 590 (20MJ) No strain No strain

RPF-02_LC05 520 (20MJ) No strain No strain

The plastic strain for PN-01_LC01 for 14MJ is high (about 6.8%) since the point of collision
is very close to CPF column. From the results it can be understood that the capacity of
collision at this point is less than 14MJ and to achieve 0.0% plastic strain the energy should

Sayı 3, 2015 GiDB|DERGi