Strake system for submerged or partially submerged structures
A submerged or partially submerged structure includes one or more non-cylindrical support columns interconnected at the lower ends thereof by horizontally disposed pontoons. The support columns include one or more strakes mounted thereon. The columns and strakes contribute to the stability of the structure during free floating operations and installation by reducing vortex induced motion.
1. A strake system for reducing vortex induced motion of a submerged or partially submerged structure, comprising:
a) at least one support column extending upwardly to an elevation above a water surface;
b) said support column including at least two sidewalls joined along a respective longitudinal edge forming a longitudinal corner at the point of juncture;
c) at least one strake secured on said support column, said strake intersecting said longitudinal corner of said support column at an angle Φ relative to said longitudinal corner; and
d) wherein said strake comprises a substantially planar body having a first edge defining a first longitudinal side of said body, a second edge defining an upper end of said body, a third edge defining a lower end of said body, a fourth edge defining a second longitudinal side of said body, and wherein said fourth edge includes a first segment extending downwardly from said second edge at an angle less than 90° relative to said second edge and a second segment extending upwardly from said third edge at an angle less than 90° relative to said third edge.
2. The system of claim 1 wherein said second and third edges are oriented substantially perpendicular to said first edge.
3. The system of claim 2 wherein said second edge and said third edge define a curved or tapered profile.
4. The system of claim 1 wherein said strake intersects said longitudinal corner of said support column at an angle between 0° to 90°.
5. The system of claim 1 wherein said strake extends across less than 50% the width of said sidewalls of said support column.
6. The system of claim 1 wherein said angle Φ is in the range of 30° to 45°.
7. The system of claim 1 wherein said strake includes an upper strake fin fixed to one of said sidewalls of said support column and a separate lower strake fin fixed to an adjacent other of said sidewalls of said support column, wherein said upper strake fin and said lower strake fin are fixed to each respective said sidewalls at an angle Φ relative to said longitudinal corner of said support column and are laterally offset from said longitudinal corner of said support column.
8. The system of claim 1 including one or more apertures extending through said strake body.
9. The system of claim 1 wherein at least two of said strake edges project outside the perimeter of said support column for all angles of rotation about a vertical axis.
10. An offshore structure, comprising:
a) a hull including at least one support column extending upwardly to an elevation above a water surface;
b) said support column including at least two sidewalls joined along a respective longitudinal edge forming a longitudinal corner at the point of juncture;
c) at least one strake secured to said support column, said strake intersecting said longitudinal corner of said support column at an angle Φ relative to said longitudinal corner; and
d) wherein said strake comprises a substantially planar body having a first edge defining a first longitudinal side of said body, a second edge defining an upper end of said body, a third edge defining a lower end of said body, a fourth edge defining a second longitudinal side of said body, and wherein said fourth edge includes a first segment extending downwardly from said second edge at an angle less than 90° relative to said second edge and a second segment extending upwardly from said third edge at an angle less than 90° relative to said third edge.
11. The offshore structure of claim 10 wherein said second and third edges are oriented substantially perpendicular to said first edge.
12. The offshore structure of claim 10 wherein said strake intersects said longitudinal corner of said support column at an angle between 0° to 90°.
13. The offshore structure of claim 10 wherein said strake extends across less than 50% the width of said sidewalls of said support column.
14. The offshore structure of claim 10 wherein said angle Φ is in the range of 30° to 45°.
15. The system of claim 10 wherein said strake includes an upper strake fin fixed to one of said sidewalls of said support column and a separate lower strake fin fixed to an adjacent other of said sidewalls of said support column, wherein said upper strake fin and said lower strake fin are fixed to each respective said sidewalls at an angle Φ relative to said longitudinal corner of said support column and are laterally offset from said longitudinal corner of said support column.
16. A strake for reducing vortex induced motion of a submerged or partially submerged structure, comprising:
a) a substantially planar body;
b) a first edge defining a first longitudinal side of said body;
c) a second edge defining an upper end of said body;
d) a third edge defining a lower end of said body;
e) a fourth edge defining a second longitudinal side of said body; and
f) wherein said fourth edge includes a first segment extending downwardly from said second edge at an angle less than 90° relative to said second edge and a second segment extending upwardly from said third edge at an angle less than 90° relative to said third edge.