Semi-Submersible Heave Period Calculator
Offshore floating structure dynamics: Calculate column waterplane stiffness, pontoon hydrodynamic added mass, and natural heave period (T_nz).
Platform Structural & Column Geometry
Dynamic Heave Response
Recommended Tools & Equipment
Tested hardware and components for high reliability
Frequently Asked Questions
Why do semi-submersibles exhibit such low heave motions compared to drillships?
Semi-submersibles have small waterplane cross-sections piercing the ocean surface (columns), which keeps hydrostatic restoring stiffness (K_z) low. Meanwhile, large submerged pontoons carry massive hydrodynamic added mass (A_33), pushing the natural heave period well past 20–24 seconds, far outside the dominant ocean wave spectrum (typically 6–15 seconds).
What is the hydrodynamic wave-cancellation effect in semi-submersible pontoons?
Dynamic wave excitation forces on a semi-submersible consist of two opposing components: downward vertical Froude-Krylov dynamic pressure acting on the top surfaces of the submerged pontoons, and upward buoyancy force on the surface columns. At specific wave frequencies, these two opposing wave forces cancel each other out, producing near-zero vertical motion.
How does operating draft change semi-submersible heave response?
In transit mode (shallow draft ~8 m), the pontoons sit near the water surface, creating large waterplane area and low natural period (~10-12 s), which makes the platform lively. In deep operating/drilling draft (~20-25 m), the pontoons submerge deeply away from surface wave kinematics, reducing wave excitation while maximizing added mass and period.