Learning Forum

[maurya]

 

this is image of body 

1) outer is cortical hard one 

2) inner is cancellous porous

this i not meshed, the surface which is visible is having so many faces 62000.

is there any method to remove or decrease this faces?

second problem with meshing 

1) i want solid shell in outer 1mm thick cortical bone in ansys workbench 18.1 

    i am using command 

  et,matid, solsh190

  r,matid,

  keyopt,1,0

keyopt,2,0

but it fail. 

when i mesh default error was there

sir in one of you post i read 

" I projected a shape onto the wall to apply a force or connect a ligament or a spring to represent the ligament."

i want to know how to project a shape.

and one question in mind 

ligaments works only in tension and not in compression but spring works in both

 

either it is compression or tension spring.

after solid length spring does not allow to move the body but in ligament this does not occurs. 

please suggest solution 

[peteroznewman]

Hello maurya,

I'm glad to see you did some searching on this site and found something relevant.

GEOMETRY
The solid body has the outer shape of a bone, but the inside looks like a 3D fill pattern that is used to fill an STL shell of a solid part prior to 3D printing in an additive manufacturing device. I expect that the thickness of the outer shell in that geometry is constant, which is not true for real bones. You would be better off ignoring the interior and using either shell elements or solid shell elements as you describe.

A separate license for SpaceClaim provides Reverse Engineering tools ideal for STL bodies and one of the capabilities is the ability to apply a "skin surface" over an area of small faces of a body with large faces that are easier to mesh. That would be the best way to improve the ability of the mesher to complete mesh creation.

If you don't have the STL license for SpaceClaim, inside Mechanical is the Virtual Topology feature that will automatically overlay large faces over small faces. Right click on Model in the Outline and Insert, Virtual Topology.

To project a curve onto a surface, create a Plane off to the side of the part, sketch a curve on that plane, then use the Project button.

SPRINGS
Real compression springs have a solid length and have an almost linear spring rate until compressed to their solid length. Mathematical springs in ANSYS have two attachment points and either a free length or a preload. You can compress mathematical springs as much as you like and even pass one end point past the other and they continue to be linear.

Read this post about other kinds of springs that are available with command snippets. It is possible to define a tension-only spring by using the COMBIN39 element.  With the ANSYS Help Viewer open, press Ctrl+Shift+D and paste in the Go to Page box: help/ans_elem/Hlp_E_COMBIN39.html

[maurya]

thanks for your valuable suggestion i will implement and ask if any problem is there.

 removing the cancellous bone is not suitable for me. As i am attaching one image for comparing the result of vertebrae whether cancellous is important or not.

my results shows cancellous  is important.

here is the two models one is with two layer(left) and other is only cortical(right). loading condition is 2000N in vertical loading.

 

sir i already mentioned solid shell command is not working in workbench.

if any suggestion please ...

[peteroznewman]

Mechanical has the Virtual Topology feature that will automatically overlay large faces over small faces. Right click on Model in the Outline and Insert, Virtual Topology.

If you would like me to try meshing, in Workbench, File, Archive... and create a .wbpz file that you can attach to a post as long as the file size is < 120 MB.

When you say "my results shows cancellous is important", I don't doubt that you can build two models with and without an interior mesh and get two results that show a large difference, but that doesn't mean that your model accurately represents the behavior of real bones. Do you have any experimental data to validate that your models predict physical testing of real bones?

[maurya]

thank you for your attention. my file is more than 120 Mb. please mail me on deepmech.maurya@gmail.com so that i can mail you file.

 

i want to write  all my work in detail error is coming on add post.

thank you

[maurya]

hello sir 

 i don't have any experimental data which show cancellous bone is important but i have to work on osteoporosis(increase of porosity of bone).

In that case cancellous is as important as cortical mentioned in research article.

my work is in lumbar and sacral region but to get answer of some question/doubt i am using femur as it is single bone easy to understand and most research has done on it.

meshes body before virtual topology.

[maurya]

sorry sir i am using different post as one single post is showing error.

i tried virtual topology with automatic method, it works nice but still only tetrahedral meshing is possible .

even single vertebrae meshing other than of default setting showing errors.

meshing by multizone ,hexadominant others are not working

my system specification is i5 processor and 28 GB ram. 

[peteroznewman]

I applied Virtual Topology and it was able to mesh all bodies except for this one.

I tried Merge Faces but went too far and "broke" the geometry.

I am trying again but this time will be less aggressive.

 You can't merge these faces on the flat or a new surface appears that covers the hole.