######## WORK NOTES COPIED FROM INCIDENT 533085 ########


QUESTION:

Do you have an example demonstrating modeling procedure used to simulate the response of a structure to incident acoustic radiation?



ANSWER:

Please see zip file attached to this solution. This is an unsupported plate subjected to harmonically varying acoustic pressure source. A spherical volume of acoustic medium is subdivided so that you end up with a plane of nodes with uniform spacing (area apportioned to each node is a constant). F,,FLOW is used to define fluid 'flow' at each node in this immersed surface to make it serve as an acoustic radiation source. I believe this allows acoustic energy reflected off the plate to pass back through the acoustic source. I'm suspect that a 'hard' acoustic source defined with D,,PRES would not allow reflected radiation to pass through and so not accurately represent incoming radiation from a distant source.

Please note that FLOW on the F command is NOT what you think. From our knowledge base:

#230323 - Acoustics: use & physical significance of "FLOW" in FLUID29/30

From the acoustics tutorial DN-TO44:50 June 11, 1992:

Ff = -A*rho0*d2u/dt2 (eq 23, page 2-13)

In words, the "flow" at a boundary node equals the surface area associated with the node times the nominal density of the acoustic medium times the second derivative of mechanical displacement (acceleration). Flow is applied with the F command, label FLOW.

Physically, this is NOT flow (like FLOTRAN flow, that is, flow through a stationary Eulerian mesh or "control volumes"). Instead, it represents the motion of the fluid associated with acoustic waves propagating through it. I think.

The plate is modeled w/SOLID45. Infinite acoustic boundary elements (FLUID130) are superimposed on the sperical boundary of the fluid domain to absorb outgoing acoustic radiation.


######## WORK NOTES COPIED FROM INCIDENT 533085 ########


QUESTION:

Do you have an example demonstrating modeling procedure used to simulate the response of a structure to incident acoustic radiation?



ANSWER:

Please see zip file attached to this solution. This is an unsupported plate subjected to harmonically varying acoustic pressure source. A spherical volume of acoustic medium is subdivided so that you end up with a plane of nodes with uniform spacing (area apportioned to each node is a constant). F,,FLOW is used to define fluid `flow` at each node in this immersed surface to make it serve as an acoustic radiation source. I believe this allows acoustic energy reflected off the plate to pass back through the acoustic source. I'm suspect that a `hard` acoustic source defined with D,,PRES would not allow reflected radiation to pass through and so not accurately represent incoming radiation from a distant source.

Please note that FLOW on the F command is NOT what you think. From our knowledge base:

#230323 - Acoustics: use & physical significance of "FLOW" in FLUID29/30

From the acoustics tutorial DN-TO44:50 June 11, 1992:

Ff = -A*rho0*d2u/dt2 (eq 23, page 2-13)

In words, the "flow" at a boundary node equals the surface area associated with the node times the nominal density of the acoustic medium times the second derivative of mechanical displacement (acceleration). Flow is applied with the F command, label FLOW.

Physically, this is NOT flow (like FLOTRAN flow, that is, flow through a stationary Eulerian mesh or "control volumes"). Instead, it represents the motion of the fluid associated with acoustic waves propagating through it. I think.

The plate is modeled w/SOLID45. Infinite acoustic boundary elements (FLUID130) are superimposed on the sperical boundary of the fluid domain to absorb outgoing acoustic radiation.





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