I'm a graduate student studying the coupled elastic vibration prolbem of structures and soils. However, I'm not very interested in that, as I think the practical coupled structure and soil vibration problem is totally inelastic, and I don't think it is of great importance to study the elastic case.
Is there anybody studying the vibration problem here and can you tell me what's the importance of studying the elastic vibration problem? Are you interested in inelastic vibration prolbem?
On the relevance of elastic vibration theory
There is a lot of interest in earthquake mitigation using transformation elastodynamics. The field is in its infancy and we still don't know how useful these ideas will be. Large amplitude elastodynamics is the next obvious step in that direction.
The field of crustal seismology uses elastic (and poroelastic) models but still matches observations to a high degree of accuracy. Inelastic effects do not seem to be first-order effects in many situations. Perhaps you can prove that inelastic effects are first order?
You can also explore the possibility of guiding vibrations aways from structures using "cloaking" concepts. Weak shocks in saturated/partially staurated soils are not well understood aas are their effects on structures connected to those soils (but not necessarily supported). The number of open questions is limited only by our imagination.
-- Biswajit
In reply to On the relevance of elastic vibration theory by Biswajit Banerjee
Is elastic vibration theory enough?
Hello, Biswajit:
Thanks for your comment. In my opinion, it's suitable to study the "far-field" wave propagation problems (such as the transmission of earthquake waves from one place to other place) using elastic models, however, if a "near-filed" problem (such as the prediction of the motion and bearing capacity of a wind turbine built on the seabed. The soils in the vicinity of the turbine is of great importance, and they will be inelastic when the turbine starts work), in this kind of problem, I think in order to be enough accurate, inelastic effects should be considered in the vibration theory. Do you think so?
Rui
Soil - Structure Interaction
Dear Rui,
I think the problem you are considering belongs to a class of problems widely known as "Soil - Structure Interaction problems", (SSI). The subject of SSI deals with how the soil compliance affects the vibration of a superstructure founded on it and, on the other hand, how the soil response is modified due to a nearby vibrating superstructure. A vast amount of literature regarding SSI treats the problem in an elastic way. By assuming linear elastic behaviour the soil-structure system can be divided into substructures which are connected with each other in simplified ways (e.g. springs and/or dashpots).
The consideration of nonlinear effects leads to problems of increased difficulty (computationally as well as theoretically). So I recommend you to start from linear elasticity. An interesting subject would be to investigate how the dynamic response and dynamic characteristics (eigenperiod, damping ratio, etc.) change due to nonlinear effects.
Regards,
George Papazafeiropoulos
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First Lieutenant Infrastructure Engineer, Hellenic Air Force
Civil Engineer, M.Sc., Ph.D. candidate
Can we model nonlinear SSI using elastic vibration theroy?
Dear George,
Thanks very much for your recommendation. Actually, when I deal with the dynamic SSI, linear elasticity is accepted. However, what comes into my consideration now is can we model nonlinear SSI by using elastic vibration theory?
As we know, dynamic characteristics of the structure-soil system is highly influenced by the surrounded (“near filed”) soil, and the near filed soil will behave a high nonlinearity, while the far filed soil is still elastic, can we use two in series springs (one for the rigidity of the near filed, while the other for the far field) in parallel with two in series dashpots to model a (vertically loaded) rigid disc-soil system?
As you have mentioned above, how the dynamic response and dynamic characteristics (eigenperiod, damping ratio, etc.) change due to nonlinear effects are interesting. I'm wondering how that can be studied except for numerical approaches and experimental measurements?
Best Regards,
Rui He