Domainpower
Mechanical
- Sep 13, 2012
- 20
Dear all ,
I have done modal analysis of a turbine using Finite element analysis and as output i have obtained a set of natural frequencies.
Now regarding excitation frequency , i have this turbine rotating at a fixed rpm while the water jet will be acting on it at different positions as shown in the attached picture.
If the rpm of machine is 400 and has 6 water jet excitation's , for the outer blades the excitation frequency will be = (400/60)*(6) = 40Hz.
Hence the fundamental excitation frequency for outer blade becomes = 40 Hz
and its higher harmonics will be = 80,120,160Hz.........
Now the question is to evaluate dynamic amplification of stress due to resonance , do i need to include all the natural frequencies where i am close to the excitation frequencies
OR
Depending upon the type of the excitation that is 6 water jet in this case that some natural frequencies even close to the excitaion frequencies will not be able to excite the system or May be a mode shape with a particular nodal diameter can have a greater importance.
Please guide.
I have done modal analysis of a turbine using Finite element analysis and as output i have obtained a set of natural frequencies.
Now regarding excitation frequency , i have this turbine rotating at a fixed rpm while the water jet will be acting on it at different positions as shown in the attached picture.
If the rpm of machine is 400 and has 6 water jet excitation's , for the outer blades the excitation frequency will be = (400/60)*(6) = 40Hz.
Hence the fundamental excitation frequency for outer blade becomes = 40 Hz
and its higher harmonics will be = 80,120,160Hz.........
Now the question is to evaluate dynamic amplification of stress due to resonance , do i need to include all the natural frequencies where i am close to the excitation frequencies
OR
Depending upon the type of the excitation that is 6 water jet in this case that some natural frequencies even close to the excitaion frequencies will not be able to excite the system or May be a mode shape with a particular nodal diameter can have a greater importance.
Please guide.