hi
I am trying to model box on the back of the truck that is only fixed by bolts from it bottom.
I want to model the effect of the inertia force when the truck accelerates and decelerates.
so i am not sure which model to use for this case and how to impose the inertia force as a function of time.
should it be dynamic or harmonic study or non linear static study

I think that the easiest way to model the inertia effects is by using a volume load:

You should input a volume load with a magnitude equal to acceleration times density of the part. This can also be done with a table input to specify an acceleration curve.

thanks for your reply
Iam aiming at modeling the effect of the acceleration and deceleration, so ideally I was willing to input a velocity (function in time) for the frame fixed on the truck back to model the frame inertia. how this can be done in the dynamic analysis?
Also, I want to add more mass to the frame I am modeling and this mass needs to be considered in the inertia force.
another issue is the fatigue on the bolts that are used to mount the frame on the truck back which is subjected to this load for many cycles, it there any way yo model get an estimation for cycles before it fails
thanks

The indication above should allow you to specify the acceleration curve. Otherwise, you can specify all the displacement history with a Fixed Value boundary condition.

To add some mass that is not in the CAD model, you can use a Point Mass:

About the fatigue, I am sorry to say that we do not have computation of cycles. You need to manually compute the life from your simulation results.

regarding the fixed value boundary condition if I need to simulate the frame that is mounted on the truck using bolts, so I will set the fixed value boundary condition to the whole domain, and at the same time set a fixed support boundary condition to the bolts used for mounting

The fixed value to specify the movement would bye applied to the supported faces, as the movement is driven by the truck. It wonâ€™t be specified on the whole domain.

I have tried a simple case to model the effect of inertia while fixing the bottom of the model but the displacement plots showed that the whole object has the same displacement as a rigid body. I have also tried fixing the bottom of the object for one trial and another trial without imposing this boundary condition. surprisingly, both cases have the same results which are not logical at all.

I want to apply a displacement boundary condition to the frame, which is fixed to the truck back via 4 bolts. the main idea is to test the effect of inertia on the frame e and the bolts. so what I am trying to do
1- apply fixed boundary conditions to the bolts to test the effect of acceleration and deceleration on the bolts.
2- apply a displacement boundary condition to the frame to model the truck acceleration and acceleration

the point that I do not fully understand is how to imposed a fixed boundary condition on the bolts and at the same time, a displacement will be applied to the frame as a fixed value boundary