Acoustic Pressure Recovery Theory

The Adams modal synthesis method and its advantages are already covered in MSR help. During Adams simulation, we assume that the fluid loading on structure is negligible. Then we export modal deformations from Adams to Nastran in MDF file format. Adams provides two options to user to recover acoustic pressure in Nastran from the modal co-ordinate data.

The modal co-ordinates from Adams are directly used to find modal loading on fluid portion.

The second equation in Eq. 13-65 of Nastran Reference Manual (NRM) can be rewritten in terms of modal load vector from Adams:

By knowing right hand side vector for every frequency step from Adams, the above equation can be solved for . From here, acoustic pressure {p} can be recovered using following equation.

The modal co-ordinates from Adams are used to recover the modal structural load. The fluid-structure coupled equations are then solved to get corrected modal co-ordinates for structure and fluid.

Assemble the right hand side of Eq. 13-65 of NRM with the modal load vector from Adams:

By making use of Nastran Eq. 13-66 to Eq. 13-70, the fluid modal co-ordinates can be written in terms of Adams structural modal co-ordinates.

The correction matrix [C] in above equation can be used to get judgment of fluid loading on structure. This is useful matrix to check the validity of assumption made during Adams simulation.

Finally, the corrected fluid modal co-ordinates can be get as,

By knowing right hand side vector for every frequency step from Adams, the above equation can be solved for . From here, acoustic pressure {p} can be recovered using following equation.