*hi, all,*

> I have a question about the modal shape and the forced

> response of a structure.

>

> Let say once you have done modal analysis of a linear structure,

> for certain mode N, you will know the relative displacement between

> two points in this structure. Let denotes these two points as p1, and > p2.

>

> Then for the same structure, I excited it with a harmonic force and

> the excitation freq. is the Nth modal freq. The damping is defined

> by 0.1% modal damping. So, I will know the forced displacements > of p1 and p2.

> I have a question about the modal shape and the forced

> response of a structure.

>

> Let say once you have done modal analysis of a linear structure,

> for certain mode N, you will know the relative displacement between

> two points in this structure. Let denotes these two points as p1, and > p2.

>

> Then for the same structure, I excited it with a harmonic force and

> the excitation freq. is the Nth modal freq. The damping is defined

> by 0.1% modal damping. So, I will know the forced displacements > of p1 and p2.

Is the forcing frequency approximately the same as the mode you

looked at.

*I expect that the ratio of the forced displacements should be equal or*

> very very close to the ratio I calculated based on the modal analysis > only.

> So, for the whole struture, the pattern of the forced response of this

> structure excited at Nth mode should be very similar to the pattern we

> see from the modal shape .

>

> Unfortunately, using a commerical FEM package ANSYS, I did not see

> what I expect. Is there anyting wrong with my understanding???

>

> Pls. help.

> Thanks a lot,

> William,

> very very close to the ratio I calculated based on the modal analysis > only.

> So, for the whole struture, the pattern of the forced response of this

> structure excited at Nth mode should be very similar to the pattern we

> see from the modal shape .

>

> Unfortunately, using a commerical FEM package ANSYS, I did not see

> what I expect. Is there anyting wrong with my understanding???

>

> Pls. help.

> Thanks a lot,

> William,