I would like add mass + inertia in a model I was able to add the mass using *MASS but i did not find nothing about inertia.

Is there any work around in order to add Inertia to the system like

Ixx,Iyy,Izz,Ixy,Ixz,Iyz

In abaqus there the *ROTARYI element in order to do it

hi, it seems possible by eccentricity and rigid body models when only one mass moment of inertia being considered. Also, It’s limited to flexure mode only, i.e no torsional.

below simple example of cantilever beam (massless) with point mass and eccentricity.

I’ve investigated something in this regard in the past few weeks but with a focus on *MASS and 1D beams. The results are in this other thread. Here I verified that no matter the eccentricity of the mass, the frequency results remain unchanged, so no rotary inertia is considered in CalculiX formulation. Maybe some valid workaround is to connect a very stiff beam (E=99999GPa for example) between the mass element and the structure you are interested in. However, I did not try this yet.

Do the frequency results change when you modify the distance of the point mass? When I tried this with 1D beams, nothing changed. I am curious about what happens if one uses solid elements, my intuition is that if it did not work for expanded solids, it would not work for intrinsic ones…

it’s required another approach in model for beam element, but it seems to be possible.

my previous example shown an eccentricity being considered since flexure mode occurs.

Not sure if I understood you properly.

In any case, I decided to investigate a little bit further. 3D beam with no weight, 10x20x150mm, steel, meshed densely with 2nd order tetrahedrons. The first model considers a 10kg mass attached to a point 30mm away from the beam centroid, the second one is 990mm. The connection is made using only the translation node a *RIGID BODY element.

I get different results for frequency in the two models.

So in some way, CalculiX is accounting for the distance of the mass in solid models. One still needs to check if this makes sense or not, probably comparing against analytical results . An interesting note is that I requested 5 modes, but only the first 3 converged.

of courset in further, for now i’m in understanding the behavior of the solver and seek the possibilities.

please read my first comment, i has been notified “only one mass moment of inertia can capture” two of them are translation inertia.

my second post also shown, frequency in translation inertia did not change but not for rotational inertia so i did not post before.

i did not know why your model given random result and inconsistent.

it;s a basic principle and fundamental when load or wieght placed at some eccentricity from center of nodes e.g beam section there will be additional moment occurs by equivalency

Static

P = P

M = P*e

Dynamic

M = W/g

MMI = W*e^2/g

the bahavior of CalculiX solver in rigid body and reference nodes should be following this assumption. Verification and validation or benchmark is another story.

*edited

add another example with no eccentricity, it has given similar and consistent results.

I’ll try to explain my problem in a different way: I would like add in a point a specific inertia to the system supposing that i would like add to a cantilever part of the beam the following information:

M=0.01

Ixx=100

Iyy=101

Izz=102

Ixy=11

Ixz=12

Iyz=13

I read that there is the possibility to add a super element however i’m not able to do it. Does anyone have a example in order to add an external mass matrix to a model?

You can use `*FREQUENCY, SOLVER=MATRIXSTORAGE`

to save mass matrix but then the problem is how to use it in a subsequent analysis. Abaqus has `*MATRIX INPUT`

for this purpose. In CalculiX, substructures seem to be the only way but I’m not sure if they would work here.