# Updates on Modeling a Hydrostatic Pressure with SOLIDWORKS Simulation 2015

Enhancements in **SOLIDWORKS Simulation 2015** provide more options for modeling distributed pressures and forces, allowing Cylindrical and Spherical Coordinate systems in addition to Cartesian, in three dimensions. So the interface for setting up a hydrostatic load has changed somewhat since **my original blog post in 2012**. Also, let me show you how to find out the total weight of water in your container, as requested by some readers.

The setup begins the same way, by first creating a Split Line in SOLIDWORKS to define the waterline and wetted surfaces, and then creating a custom Coordinate System to make the equation-writing more intuitive. Here’s a half-section of a rectangular bucket showing that done:

To continue, to model the water pressure, we again add a Pressure “External Load” and choose the checkbox option for “Nonuniform Distribution”. New in 2015 we also then choose which type of coordinate system we prefer. In our case we want the default Cartesian system, for a function F (x,y,z).

- Set the direction as Normal To Selected Face, since that’s how water pressure acts.
- Select all the wetted surfaces.
- For the Pressure Value, just plug in “1” unit. This value multiplies by the equation we will write. I find this approach easier than playing with the coefficients.
- Toggle Reverse Direction as needed based on the preview so that the water is on the inside or outside of your part (positive or negative).
- Select your custom Coordinate System feature.
- Choose the Cartesian Coordinate System type, and click the button to “Edit Equation”.

Recall that the formula for hydrostatic load is “negative rho, g, h”: P(*h*) = *–**ρgh*

In my previous post, I explained why the formula we want is F(x,y,z) = 0.036*”y”. Instead of building the formula one coefficient at a time, now in 2015 we simply type out the formula itself, as illustrated in the image above. Take care to put quotation marks around the name of the variable “y”, and of course we use the usual asterisk * to represent multiplication.

To finish the setup, click the green OK checkmarks. When you’re done, SOLIDWORKS Simulation even updates the preview arrows to indicate approximate pressure variation. It should look like this:

Finally, we add some Restraints and Run it and we get this:

Please Note: This example shown requires Large Displacement solution for correct results. But that’s still a topic for another blog post!

Bonus: To find out how many pounds of water are in the container, right click on the Results folder and choose “List Result Force…”. The weight of the water in your container is the sum of the reaction forces in the Y direction for the “entire model” (unless you have additional forces applied in Y, or have included Gravity forces acting on your container). In this example, the result shows 16.7 pounds. Since I modeled only half a bucket, the total capacity is twice that, 33.4 pounds, or just over 4 gallons.