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Tarpaulin closed compartment > Brackish water

Brackish water

Last reviewed version: 2.22

Now we introduce brackish water on the outside of the tarpaulin closed compartment. This parameter is found in Export > Non linear density field, see Figure 22. Fluid density for brackish water is assumed 1010 kg/m3.

Figure 22 Brackish water for fluid outside the tarpaulin
Figure 22 Brackish water for fluid outside the tarpaulin

A fluid density of 1025kg/m3 is kept on the inside of the tarpaulin. Having analyzed static equilibrium, we see that the floater moves approximately 8 cm downwards. This is seen in Figure 23, where one also can see the bottom of the tarpaulin displaced downwards.

Figure 23 Vertical displacement of floater
Figure 23 Vertical displacement of floater

The bottom of the tarpaulin, Figure 24, displace about 6.5 meters downwards.

Figure 24 Vertical displacement of tarpaulin closed compartment
Figure 24 Vertical displacement of tarpaulin closed compartment

At equilibrium, the inner waterline is about 15.9 cm below the mean water surface, see Figure 25.

Figure 25 Location of inner waterline at equilibrium
Figure 25 Location of inner waterline at equilibrium

This means that if you would like to have the inner waterline above the outer waterline, you will have to introduce more water to the system.

The relative pressure between the outside- and inside water is shown in Figure 26.

Figure 26 Relative pressure, positive value is inwards the enclosed volume
Figure 26 Relative pressure, positive value is inwards the enclosed volume

As seen from Figure 26there is a net pressure inward in the upper part of the tarpaulin, and net pressure outwards in the lower part.

As seen from the figures in this section, brackish water means more weight needs to be carried by the floater. Intuitively, there is a risk by having the inner waterline below the outer: rainfall or waves pouring more water into the tarpaulin closed compartment will increase the weight carried by the floater. Eventually one risks the structure to sink. One must be able to transport excess water out of the enclosed volume. Systems may have valves in the bottom area, in this case with brackish water it may be a good choice to have valves closed to the bottom in cases where the outer density is lower on the outside compared to inside the volume as there is higher pressure on the inside in this area as seen in Figure 26.