A semisubmersible drilling platform has an operational draft equal to 25 m. The hull consists of a ring pontoon and four circular cylindrical columns with 15 m diameter. The height of the pontoon is 8 m. The density of sea water is 1025 kg/m². During inspection the platform is de ballasted to a draft equal to 15 m. . . How much ballast water is it necessary to remove? What is the natural heave period for this platform if the total platform mass (including added mass) is 60000 tonnes? The natural period for heave motion is: T, = 211 m ✓m is the total mass, including hydrodynamic (added) mass vk is the "stiffness" corresponding to heave motion . It is considered to use this rig in an area where the largest waves have a peak period around 18 seconds. How will you evaluate the platform for this area?

To determine the amount of ballast water to remove, find the difference in draft and calculate the volume. The heave period can be calculated using the total mass and stiffness. Evaluate the platform by comparing the heave period to the peak period of the waves.

Explanation:

To determine how much ballast water needs to be removed, we need to find the difference between the initial draft and the final draft. In this case, the difference is 25 m - 15 m = 10 m. The volume of water that needs to be removed can be calculated by taking the area of the circular pontoon and columns and multiplying it by the difference in draft. The heave period for the platform can be calculated using the formula T = 2π√(m/k), where m is the total platform mass (including added mass) and k is the stiffness corresponding to heave motion.

Given that the total platform mass is 60000 tonnes (60000000 kg) and the largest waves in the area have a peak period of 18 seconds, we can evaluate the platform by comparing the natural heave period to the peak period of the waves. If the natural heave period is close to the peak period of the waves, it means that the platform will experience significant motions in response to the waves, which may not be desirable.

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