Discussion Forum

Posted: 1 decade ago 3 ago 2010, 01:12 GMT-4

Hi If you say you have no air, only water inside your rubber baloon, with a relative pressure >0 so everything is under some stress, then I would say you have only normal surface pressure interactions inside. This means that your liquid, with a given denisty (hence mass that will act on the eigenmode), could be simulated by a "solid" material with no shear forces (poisson =0). This is rather crude and should certainly be checked and validated against a more detailed fluid-solid interaction model. But I would have started simple (only in the solid mode) and only afterwards going to next step By the way, I would suggest to start by not using the library material data, these are often very complex and you easily forget some important parameters such as Temperature, Temref or pressure, with errors in the simulations -- Good luck Ivar

Posted: 1 decade ago 3 ago 2010, 07:47 GMT-4

Ivar, Thank you very much for your reply! Simplicity is always the best. I will see if I can get a more detailed model. Best regards, Pablo

Posted: 1 decade ago 3 ago 2010, 08:25 GMT-4

Hi Carefull though, if water has a defined density, as such it does not have a bulk E Young modulus, you would have to estimate an equivalent value from lets say sound speed in water => v^2=E/rho (and use Poisson=0). check a good book on fluidics -- Good luck Ivar

Posted: 1 decade ago 1 mag 2012, 08:55 GMT-4

[QUOTE] I hope everybody in the forum is doing well. I am trying to simulate a "water balloon" being hit by a "soft hammer". The hammer hits the balloon and then leaves the balloon interaction lasts for about .5 s. I will like to study the way the eigenfrequencies of this structure. The balloon is made from rubber and it can be imagine to be attached to a wall. I have no problem in simulating the empty balloon. I do my analysis in an axisymmetric domain. The hammer hitting the balloon is modeled as a body load and the body load is a function of time namely a gaussian pulse. How should I model the liquid inside? That is what type of interaction exists with the wall and the water ? I do realize that perhaps my question is more dealing with the physics then COMSOL. If any can help with the COMSOL part and more importantly a good reference to read on these type of interactions I would really appreciate it. I have included here my model and will like to finish and share it with the community afterwards. This is the last step in my project that needs to be simulated. Thank you in advance for your time! Best regards, Pablo [/QUOTE] Hi Pablo and Iva, Could you please let me know how the balloon modeling was done? What was the boundary condition of the balloon which allows inflation and not solid wall? Thanks Ehsan