Rotordynamics: unbalance loads due to displacement - FEA

In summary, the conversation is about how commercial FEA codes handle additional unbalance forces in a jeffcott rotor model. The question is whether the codes take into account the off-axis displacement of masses and how they incorporate this in the analysis. The person is also wondering if the mass matrix is updated and how it would factor in the new locations of the disk. They are seeking clarification and input from anyone knowledgeable on the topic.
  • #1
tricha122
20
1
Hi,

Im wondering if / how commercial FEA codes take into account additional unbalance forces due to the off-axis displacement of masses.

For instance, if I am modeling a jeffcott rotor with an unbalance, I would traditionally represent this unbalance with a force that increases with speed^2. However during the analysis, the jeffcott rotor moves off axis (whirls) and should have an additional unbalance force equal to the mass of the disk times the displacement of the CG times the speed^2.

I am not sure how commercial FEA codes account for this force (if they do) - would this come about due to mass matrix being updated? Even if the mass matrix were updated, how would it take into account the new locations (displacements) of the disk into the generation of the new load? Mass matrix is just multiplied by acceleration... unless the mass is fictitiously increased in a non-linear update (a la tangent stiffness matrix for geometric stiffening/softening)

Anyone that could shed some light on the situation would be greatly appreciated! Thanks!
 
Engineering news on Phys.org

1. What is rotordynamics?

Rotordynamics is the study of the dynamic behavior of rotating machinery, such as turbines, compressors, and motors. It focuses on understanding and predicting the vibration and stability of these machines under different operating conditions.

2. What are unbalance loads in rotordynamics?

Unbalance loads refer to the uneven distribution of mass in a rotating component, which can cause vibration and potentially lead to mechanical failure. This can occur due to manufacturing imperfections, wear and tear, or other external factors.

3. How do displacement and FEA relate to rotordynamics?

Displacement is the movement of a component from its original position, and it can affect the balance and stability of a rotating system. Finite Element Analysis (FEA) is a computational method used to analyze the structural behavior of rotating machinery, including displacement and its effects on unbalance loads.

4. Why is FEA important in rotordynamics?

FEA allows engineers to simulate and analyze the complex behavior of rotating machinery under varying operating conditions. This helps identify potential issues, such as unbalance loads due to displacement, and allows for the optimization of designs to improve the performance and reliability of these systems.

5. What are some applications of rotordynamics and FEA?

Rotordynamics and FEA are used in a wide range of industries, including aerospace, automotive, power generation, and manufacturing. They are essential in the design, analysis, and maintenance of various rotating machinery, such as jet engines, wind turbines, and pumps.

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