Field Pressure Map Results Interpretation

Hi Dilan,

field.nff

• This file represents an output field map on the actual finite element mesh used in the Actran computation.
• It provides a color map visualization of a result quantity (e.g., pressure, displacement) across the computational domain for specific frequencies.
• Use this when you want to visualize results directly on the mesh that participated in the simulation, such as structural or cavity meshes.

field_psd.nff

• This file represents an output field map on a post-processing mesh, which is different from the computational mesh.
• The post-processing mesh (sometimes called a dummy mesh) does not participate in the computation. It is used solely for plotting contour maps, often in regions like the acoustic far field.
• Use this when you need to visualize results (e.g., acoustic pressure distribution) in areas outside the main computational domain, such as in the far field or on a special observation surface.

I hope this helps!

-JP

Hi Dilan, just to add to Praveen's answer, normally when running an analysis with Random Excitations (Diffuse sound field, for example) Actran outputs two files for any output requested (maps + FRF curves in plt file format). This is the field.nff and field_psd.nff you are getting.

The diffuse sound field (DSF) is generated via a sampling approach. This means you have defined a number of samples (typically 30 because of Central Limit Theorem) and the excitation is in reality 30 individual deterministic loadings that considered in isolation are not particularly meaningful, but considered together in a statistical sense satisfy the mathematical definition of what a Diffuse Sound Field is. Each individual sample is a different loadcase passed to the solver, and the response to all the individual loadcases are output in field.nff. 

field_psd.nff on the other hand applies a Power Spectral Density operator on the results in field.nff. In practice, this operation is essentially a sum of squares average for each loading, as per our ActranVI user guide. For indicators that are already quadratic (think acoustic radiated power, or mean square pressure, for instance), this is just an average of all loadcases.

For typical industrial and engineering applications, only field_psd.nff needs to be considered. If you are performing some academic research into unusual statistical analysis + random excitations in numerical methods, then the field.nff can be analyzed with your own post processing operations. In my daily work, I just consider it an intermediary result.