Adding mass

Rahul_P1

Hi guys,

I have problem with mass estimation. My model weighs approximately 2x less than it should. I have the data: cab mass+ 'equip'= 760 kg and my model weighs around 300 kg. The problem is that CAD model I received did not have any 'equipment' parts thus I do not know clearly how the rest of the mass is distributed. I am using GRAV card image hence it is important mass matches to the real model (more mass= more inertia load).

My question is how to increase the mass if you do not know how it is distributed?

I have few ideas but I do not know how good these ideas are:

1) I am using only one material. Could I just increase the density of material until I get the final value of mass? Changing density should not affect stiffness or any other behaviour of material?

2) I concentrate the rest of the mass (400 kg out of 700 kg) to the centre of gravity?

Any other suggestions?

Thank you very much.

Rahul_P1

What is the type of analysis you are performing? if it is the dynamic response of your structure that you are interested in you can use the non structural mass, NSM is the Mass that is present in the system and will affect the dynamic response but it is not a part of the structural mass (e.g. the payload). see User's Guide > What is Altair RADIOSS? > Bulk Data Format Input > Finite Element Analysis > Elements, Super Elements and Materials:Non-structural Mass

Changing the density may not affect a simple static analysis, but with the grav card you may have to consider how this mass is actually distributed, i.e. in reality.

Option 2 looks good

From the Student guide -
If the assembly of several components is involved then only the critical parts are meshed
appropriately. Other parts are either coarse meshed or represented approximately by
1-D beams, springs, concentrated mass,

you can also create rigid elements connecting your mass. so that it is only applied to the areas connected by the rigid elements, to simulate more realistically.