Gravity

By default, Discovery adds a gravity condition to your analysis to simulate self weight, added mass, and/or buoyancy effects, for structural and fluid physics respectively. If neither of these are selected, then the gravity specification will have no effect on your simulation. You can review the Gravity settings in the Physics tree or double-click it to access the full settings.

When enabled, self weight is simulated in the specified direction of gravity. Including self weight depends on the density of the material. If the self weight is negligible in comparison with other forces, you can turn self weight off by clearing the selection of Include self weight. Turning on self weight also means that the gravitational acceleration is used in combination with any added mass inputs.

When enabled, buoyancy is simulated in a fluid flow analysis. For fluids, buoyant flow is the most important effect of gravity. Because the force of gravity is proportional to fluid density, buoyant flow can arise whenever the fluid density varies due to the temperature or material specification. The addition of buoyancy simulates natural or free convection, where the fluid density varies in temperature.

For many applications involving buoyancy, it is sufficient to assume a constant fluid density when the change in density over the expected range of conditions is relatively small. This is often true for many liquids. When the fluid density is not a function of pressure or temperature, the Boussinesq model is applied.

The Boussinesq model uses a constant density fluid model, but applies a local gravitational body force throughout the fluid that is a linear function of fluid thermal expansivity, and the local temperature difference with reference to the Fluid Initial Temperature.

In general, it is good practice to specify the initial temperature as an approximate average value of the expected domain temperature for steady-state problems.

If the effects of buoyancy are not important in your simulation (for example, where the velocity of the fluid is such that buoyancy has little impact), you can turn it off by clearing the selection of Include buoyancy.