When are Lumped-element models used in the design process?

[Simas]

Hi everybody,

Academic papers in mechanical engineering use often lumped-element (or lumped-parameter) models such as a typical quarter car model. However, books about the (mechanical) engineering design methodologies (such as by authors Dieter, Shigley, or Pahl-Beitz) seem to not mention this specific type of models.
Given that lumped-element models are usually strong simplifications, my guess would be that these type of models are mainly used in the Concept design phase and for system-level design, but I am not sure and I am wondering if they are also used for other purposes (maybe in more complex forms?).

Hence, to make long story short my questions are:
[1] When are these models used in the (mechanical) design process?
[2] Are this type of models only used in the industry to analyse a system (e.g. full suspension) or also to design system elements (e.g. damper or spring)?

I'm struggling for a long time to understand this, thus any help would be highly appreciated!
Thank you in advance,

Simon

 

[jrmichler]

We use the simplest model that provides the necessary information. An example is the analysis of a gearless wide web high speed flexographic printer:

The frame side sway natural frequency was analyzed using lumped masses for the rolls.
The roll natural frequencies were analyzed using full roll models with detail simplifications.
The roll vibration damping system was analyzed using a lumped mass model.
Critical roll adjustment brackets were analyzed with no simplifications.

The resulting printer met all design specifications without vibration problems over the entire speed range.

 

[Simas]

jrmichler,
Thank you very much for your swift reply!

 

[hutchphd]

Just in passing, let me put on my (dusty) physicist hat and point out that characterizing a spring using a single parameter k is already a grotesquely crude lumped-parameter model. It is the heart of all engineering practice and the hardest part of really good engineering.

 

[Dr.D]

I have used lumped parameter models for the torsional vibration response calculation of many engine-generator sets. This includes both the eigenvalue problem and the forced response.

 

[Simas]

Thank you Dr. D and hutchphd!