Noise from impacting surfaces!

[IngMilano]

Hi,
I have to predict and calculate the noise emitted by a hydraulic hammer. The center of the problem is to calculate the noise emitted from the axial and central impact between two steel cylindrical (more or less) objects: the impacting mass and the tool. The noise is composed by a "ringing" semi-continuous component caused by the vibration of the two bodies after the impact and an "acceleration" component caused by the very fast deceleration of the impacting mass (and therefore its surfaces) during impact, wich causes a pressure perturbation wich radiates as a single pulse. Now, I know that Sysnoise is able to predict the first type of noise (ringing) due to the vibration of surfaces, but I would like to know if Sysnoise is also able to calculate the second type of noise, that is the single pulse noise emitted by rapidly decelerating surfaces. Obviously any comment or suggestion on how to solve the WHOLE problem is appreciate, since I am in the initial phase of its study.

Greetings

Luigi Milano

 

[hydtools]

Luigi,
I know nothing about Sysnoise, but I have to ask why do you want to try to predict the impact noise. I suppose it would be academically interesting.
In my experience designing, manufacturing, and testing hydraulic breakers I have found the process noise to be equal to or higher than the breaker noise. Will you account for the transmission of the initial impact pulse through the fluid, the breaker body, and the outer housing of a mounted breaker? Are you only interested in small, handheld breakers which have no housing?
Will you then coorelate the results with physical tests?
I know the response does not answer your question. I am just curious about why try to predict the sound.

Ted

Ted

 

[IngMilano]

It's a work for a local company wich produces hydraulic breakers. The breaker object of this study is not intended for hand use, but to be mounted on the articulated arm of a big machine. The purpose is to try to understand the mechanism of production of noise in order to take design provisions to limit it. Now I supposed to concentrate my efforts on the noise wich come from the inside operation of the hammer (impact between the steel bodies) rather than on the noise from the breaking of the material for various reasons: firstly because we could gain something in term of noise reduction operating on the inside mechanism (for example reducing the amount of energy left for vibration of bodies, reducing the radiation efficiency of surfaces, acoustically insulating the sources of noise, improving the efficiency and the characteristics of impact, etc.), while the noise from the breaking of material itself I think is impossible to be reduced; in second instance because the inside mechanism noise should be more predictable and less operation conditions dependent than the noise from the breaking of material.

I have to add that I'm interested to create a conceptual and numerical model (softwares CATIA, NASTRAN, SYSNOISE) of the mechanism of formation and emission of the sound rather than to the exact calculation of number of decibel emitted.

Greetings

Luigi Milano

 

[IngMilano]

Regarding acceleration noise, could it be studied in sysnoise leading an acpustic FEM transient (time domain) analysis? To do this I should put as boundary conditions the velocities of the surfaces of the impacting bodies during and after the impact. Now the questions are 3:

Is Nastran able to conduct an impact simulation?

In what type of file (output2, punch) does Nastran store datas from impact simulation (such as velocities of points of the mesh for example)?

Is Sysnoise able to read the output file of such simulation as boundary conditions?

Thanks for attention and eventual answers.

Luigi Milano

 

[IngMilano]

I have the suspicion this is a very difficult problem ... )) !