# How do I applied the acceleration load to point mass in Calculix

I have a model where I apply an acceleration to a point mass and I’m trying to observe the reaction force values in solid models. I used the following code for the model. However, I’m not sure if the mass element is properly receiving the acceleration load. When I change the mass within the *Mass element, the results vary, but I still think the reaction force is coming out too low. Is there an additional card I should be using in my code? Should I incorporate the gravity constant? Here’s the part of the code I wrote.

*Node
17852, 100, 100, 100
17853, 100, 100, 100

*ELEMENT, TYPE=MASS, ELSET=mass
999999, 17852
*MASS, ELSET=mass
0.01

*Rigid body, Nset=fix1, Ref node=17852, Rot node=17853
mass,GRAV,9800,-1.5,0.,-4.

What is it and what would you expect it to be ? How do you read it ?

1 Like

Hi Calc_em,

I read it from Rf node output. For an example case, reaction forces differs 10N with respect to analytical solution. I expect 50N but i got 40N. The error is about 25 percent which is very high?
Additionally, is it the true definition of applying acceleration on two direction?
mass,GRAV,9800,-1.5,0.,-4.

Should i define it like in two rows for applying acceleration on both x and z direction?
mass,GRAV,9800,-1.5,0.,0.
mass,GRAV,9800,0.,0.,-4.
I try to apply 4g acceleration on z axis and at the same time apply -1.g acceleration on x axis.

Could you share the full inp.?

I guess that you mean -1.5g for x. In such a case, PrePoMax generates:

``````*Dload
Internal_Selection-1_Gravity-1, Grav, 41908.3383707825, -3.51123442E-001, 0, 9.36329178E-001
``````

Internally, PrePoMax calculates the resultant acceleration and adds its magnitude and direction to the input file.

Are we sure about the accuracy of Prepomax in calculating the correct vector? How does Prepomax perform this calculation? Would it be incorrect if I define acceleration in the x-direction as 1.5g and in the z-direction as 4g like this?
mass,GRAV,13700, 1,0.,0.
mass,GRAV,39200,0.,0.,1.

Actually rest of the code is *Node and same things . Nothing more than this

Check signs.

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Don’t worry about that. Abaqus generates the same:

``````*Dload
, GRAV, 41908.3, -0.351123, 0., 0.936329
``````
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[quote=“osmcnkrtn, post:6, topic:1933”]
Thanks Calc_em and Disla. I think we can close this task. Thank you for your help.