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General Mechanical

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Gravity affects deformation

    • Jia-Wei Liao

      I'm currently working on breast compression simulation. The simulation is moving the upper board downward to compress the breasts. Here is some images for reference.

      I would like to ask a question. I have added a gravity in the -z direction to simulate real-world conditions, as shown in the picture below.

      In the setting of load steps, the first load step only has the effect of the gravity field, and the upper board is moved down to the breasts at the beginning of the second load step.

      I have get the total deformation of the first load step(only has the effect of the gravity field), as shown in the figure below

      The simulation has converged, but it is observed that the breast is experiencing very small deformation under the influence of the gravity field. The maximum deformation is 3.855mm, and the average deformation is 1.367mm. These results seem inconsistent with real-world expectations.

      The material properties are using the Mooney-Rivlin model, and the values are obtained from the reference paper.

      Would like to ask if there is any suggestion to adjust this situation?

      Thank everyone very much for patiently reading and providing assistance!

    • peteroznewman

      A single solid with one material is an over simplification of the anatomy of a breast.

      Each breast has 15 to 20 sections, called lobes arranged like the petals of a daisy.
      Each lobe has many smaller structures called lobules.
      The lobes and lobules are linked by thin tubes called ducts that lead to the nipple.
      Fat fills the spaces between lobules and ducts and skin covers the internal structure.

      If you had a detailed model of the anatomy with appropriate material properties for each type of tissue, then you might see a more realistic response to gravity.

      Where did you obtain the initial shape of the breast, which represents the shape without gravity? Any 3D scan on earth would be in the presence of gravity. Ansys can do inverse solving which takes a deformed shape as input along with the load (gravity) and computes the shape with no load. That is the shape you want to start with.

    • Jia-Wei Liao

      The geometric model of the breast is as shown in the figure below. There are skin, fat, tissue and tumor. The shape has been simplified but it is close to reality!

      And each part has its own material properties, I use hyperelastic mooney-rivilin model, the values are as shown in the picture below.

      The geometric model and material properties should be close to the real situation, there are other reasons why gravity didn't affect the deformation?


      My breast model is reconstructed from the MRI image. The gravity of the breast MRI is towards the -y axis. How can I use ansys to eliminate the influence of this gravity? Can I directly set a gravity in the direction of the +y axis? Will it work? (It doesn't matter if the geometric model does not consider the upper and lower versions when eliminating the gravity of the -y axis)

      Thanks for your help!

    • peteroznewman

      Read the ANSYS Help chapter on Inverse Solving.

    • Jia-Wei Liao

      My customer Number is academic student.

      So it seems that the above URL cannot be opened, is there a way to open it?

    • Nanda Veralla
      Ansys Employee

      Hello Liao,

      Here is the link what peter shared already:

      8.7. Nonlinear Static Analysis with Inverse Solving (

      Here's how you can access the Ansys Online Help from within the Ansys Student products:

      1. Open Ansys Workbench (or any other Ansys product) and go to Help > Ansys Workbench Help. A browser window will open.
      2. Copy the link to the Ansys Online Help from the post on the Ansys Learning Forum.
      3. Paste the link into the address bar of the browser window opened in step 1, and you'll be able to access the desired page.

      All the best,


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