## Materials

#### Modal Analysis on a unit Jello Cube.

• kn02061
Subscriber
Hello everyone
I am trying to use ANSYS to predict the natural frequencies of a Jello (gelatin deserts) cube. I believe this is done using Modal Analysis.

However, going through the engineering data sources I’m not sure if there are material types that match the properties of gelatin.

I would like help in this. Is it possible to perform Modal Analysis on ‘soft’ materials such as that? Also, does gelatin or related materials exist in the ANSYS material library.

Thanks
• peteroznewman
Subscriber

You can go into Engineering Material and create a new material called Jello. You need a minimum of two properties to do a Modal analysis.

Add Density from the Physical Properties category. The density of Jello is slightly higher than water. Doesn't Jello sink in water?

Add Isotropic Elasticity from the Linear Elastic category. There are two values: Young's Modulus and Poisson's Ratio. Jello is almost incompressible, so use a value of 0.49 for Poisson's Ratio.

You will have to do some experiments to estimate the Young's Modulus of Jello. You could hit the plate the cube of Jello is sitting on while recording a video on your phone. Estimate the period of wobble of the cube. Make a model of that cube and sweep through a range of Young's Modulus values to plot the first modal frequency vs the Young's Modulus to pick the value that matches the Jello wobble frequency captured on video.

ANSYS Workbench has a Parametric Sweep capability that automates the above study so it is very easy to do.  You just click the P box in the Engineering Materials module next to Young's Modulus and that becomes an input. Then click the box next to the Modal Frequency in the Deformation Result in the Modal analysis. That becomes an output in the Parameter table.

• kn02061
Subscriber

Thank you! That helped a lot.

I have a question about the sweep parameter. I have the young's modulus as the input parameter and the Frequency as output. How do I set the young's modulus to sweep?

Best

• peteroznewman
Subscriber

In Workbench, under the Modal block is a Parameter block. Double click on that and the Design Parameter table is available. It has one row where the current value of Young's Modulus is in one column and the Frequency of the Modal results is in another column.  There there is a blank row. In the Young's modulus column, type in values, or paste from Excel,as many rows as you want. Then click the button Update All Design Points and it will fill in the column of results.

• kn02061
Subscriber

Thank you!