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Using FLOATSOFT data in Excel for additional calculations
If you require additional calculations that are not directly available in FLOATSOFT, it can be very easy to set up a simple Excel spreadsheet to interrogate simulation data.
In this example, let’s take a look at a 30ft powerboat design that has design displacement of 2200 kilograms.
With this displacement, the powerboat has a draft of 0.34 meters, with the center of buoyancy at the location marked with the blue square.
In this example, our design process requires us to figure out how high will this powerboat ride with 3° trim angle at 14 knots (7.2 m/s).
To answer this question, we will need to iterate through a range of draft values at 3° trim, measure the bottom surface area, and calculate lift force. By subtracting lift force from the buoyancy force, we get a net force – and the draft where it is zero, is the ride height of the powerboat.
To start, we will set up a study in FLOATSOFT, asking it to provide us with draft, displacement, trim angle, wetted surface area and wetted transom area. We are only interested in the bottom surface area, since the transom is at a wrong angle to provide lift, so we will later be able to obtain it by subtracting these two areas.
We will also set up Iterate Through Draft mode from 0.25 to 0.35 meters, since we can reasonably assume the draft we’re looking for will be somewhere in this range.
After a minute or so, FLOATSOFT provides us with the results. We can then export the data table to .csv and import it into Excel, or just directly copy-paste the desired range.
In Excel, we can transpose and format the data if required to make it easier to build equations.
We can add a few more static cells for design displacement, water density and velocity. Finally, we add a few more columns to calculate bottom area, lift force, buoyancy force and net force.
In this case, the equations are as follows:
Bottom area = Wetted surface area – Wetted transom area
Lift force = (Water density * Velocity^2) / 2 * Bottom area * COS(Trim angle)
Buoyancy force = Displacement * 9.82
Net force = Design Displacement * 9.82 – Lift Force – Buoyancy Force
Note that in Excel, degrees need to be converted to radians. The lift force equation is a fair approximation of the real lift force that assumes a relatively flat bottom with no lifting wings or tabs, but for critical applications you might want to run CFD simulations to confirm it and add a fudge factor for any future calculations.
With this information, it is very easy to see that the force equilibrium, where net force is 0, is between 0.295m and 0.3m draft, probably around 0.296m. Using this information, we can put in this number back into FLOATSOFT, and continue on from there for any additional calculations or measurements that we might need.
This is just one example of how to manipulate data from FLOATSOFT to obtain additional calculations that you might need. You can download the Excel file used in this tutorial here.