# Difference between pressure in structural and acoustic analysis

Member Posts: 42
edited October 2020

What is the difference between pressure in structural and acoustic analysis?

• Posts: 778Forum Coordinator

Hi,

We can specify a Pressure load in a structural analysis, which is an excitation (force/area). On the other hand, in an acoustic analysis, "pressure" is a DOF constraint (boundary condition, not excitation), where the total pressure (e.g., incident + reflected) is being specified. The two are not interchangeable, as they have different usage in structural vs. acoustic analyses - in the former, pressure is a load/excitation whereas, in the latter, pressure is a DOF that we solve.

Regards,

Ashish Khemka

• Posts: 12,000Member
edited October 2020

When solid elements mesh a volume, the nodes are assigned different unknowns for the two types of analysis.

Structural models have displacement of the node in X, Y and Z as the unknowns. Pressure can be applied to the node to make it move to a new static or dynamic equilibrium position, or to have an amplitude and frequency of oscillation in a harmonic response analysis.

Acoustic models have pressure at the node as the unknown. Pressure can be applied to the nodes in the form of an acoustic excitation, but the nodal XYZ coordinate doesn't move, the pressure wave can move through the mesh.

• Posts: 12,000Member
edited November 2020

@skadam Let me clarify what I meant by "Pressure can be applied to the nodes in the form of an acoustic excitation". The Acoustics training material provides this equation to convert a surface velocity excitation into incident pressure:

If I want to apply an incident pressure, I divide the pressure by rho*c to get the normal surface velocity to be used in the Surface Velocity Excitation.

@akhemka Pressure shows up in two places in the Harmonic Acoustics analysis. As a load called Static Pressure and as a Boundary Condition called Pressure. Please give an example of how these would be used in a harmonic acoustics model.