Hydromax allows you to specify two different ways of simulating any fluids contained in tanks or compartments. Selecting Fluids in the Analysis menu opens the Fluids Analysis dialog.
Note
Most documented stability criteria assume that the corrected VCG method has been used. Although the computational potential is available, authorities have not adopted this more accurate calculation of the shift in centre of gravity due to fluid movement.
Tank capacities and free surface moments are calculated for the upright hull (zero trim and zero heel). The effective rise in VCG due to the tanks' free surface is calculated by summing the free surface moment of all the tanks filled to less than 98% capacity and dividing by the total vessel displacement (the free surface moment to be applied is specified in the loadcase).
This method should be used when compiling a stability booklet for a design, as it corresponds with the traditional approach used by naval architects and classification societies worldwide. It is reasonably accurate at low angles of heel and trim.
In this case, the loading window will include a column for free surface moment and cells for corrected fluid VCG. These values are automatically calculated from the maximum free surface moments of the tanks, calculated in the upright condition. There are several FSM types available. For more information, see Working with Loadcases on page 33.
This method is a faithful simulation of the static movement of the centre of gravity of the fluid in each tank. Every tank is rotated to the heel and trim angle being analysed. Hydromax iterates to find the fluid level for the rotated tank at the specified capacity. The new centre of gravity is calculated for each tank and used in the analysis. The new LCG, VCG and TCG are calculated for the whole design and used in the calculation of GZ, KG, and GM.
This approach is used when the stability of a vessel is being investigated and the closest possible simulation of the hull's behaviour is required. It is particularly useful at high angles of heel or trim, or with tanks whose heeled water plane area may be significantly different from the upright case (i.e. tall narrow tanks, or wide shallow tanks). The penalty of using this approach is that the calculation time is longer, however the results are significantly more accurate.
When fluid simulation method is selected, free surface moments and corrected fluid VCG are not applicable and are not displayed in the loadcase.
When selected, fluid simulation is used for analyses that use a loadcase, i.e. Large Angle Stability, Equilibrium Condition and Longitudinal Strength (the Longitudinal Strength analysis always uses fluid simulation). When fluid simulation is used in one of these analyses, the actual fluid level in the tank, filled to the volume specified in the loadcase, will be displayed in the View window. Otherwise the complete tank will be shown.