Multiscale mechanics

Multiscale mechanics is about multi-scale correlation and strong coupling between scales,which widely exists in engineer-ing applications with a broad range of spatial and temporal scales.The averaging method and the perturbation method have been employed in the past to deal with weak coupling problems.For strong coupling problems,the methods based on small parameter expansion are no longer applicable.Fluid turbulence and solid fail-ure are two typical cases in nonlinear mechanics [1-3] .The chal-lenge of turbulence arises from the cascade of momentum,energy,and other conserved quantities across a wide range of spatial and temporal scales.The solid failures in heterogeneous media,on the other,result from the trans-scale cascade of micro-damage evolu-tions.

Research in the field of nonlinear mechanics includes both mechanism study on the characteristics of multiscale processes and the development of methodologies for modeling nonlinear mechanics.This special issue publishes eight most recent studies on the mechanism and methodology of multiscale mechanics un-der the support of the Natural Science Foundation of China,Ba-sic Science Center Program for Multiscale Problems in Nonlinear Mechanics (Grant No.11988102).The mechanism on the interac-tion between bottom-heavy rods and turbulence is studied in Ref.[4] .Wall-resolved and constrained large-eddy simulation methods [5-6] are used to investigate the multiscale turbulent motions and roughness-induced effects in flows over rough walls.The modula-tion of near-wall turbulent structures by large-scale motions in the outer region of turbulent channel flows is studied in Ref.[7] .The orbit of an ellipsoidal particle under the interaction with a vorti-cal flow confined by a microcavity is investigated using the lattice-Boltzmann method in Ref.[8] .The authors of [9] propose a multi-scale algorithm to speed up the calculation of dislocation creep at elevated temperature for plastic deformation in crystalline metals.In Ref.[10] the authors propose a stable heat jet approach for accu-rate temperature control of nonlinear Fermi-Pasta-Ulam beta chain based on the machine learning method.In Ref.[11],the nonlin-ear energy dissipation is used to measure the microscopic degra-dation status and is proved to be the same in two multiscale meth-ods,i.e.,the first-order computational homogenization (FOCH) and reduced-order homogenization (ROH) method.

This special issue includes most recent works in turbulent flows and solid failure from experts from the corresponding fields.We hope this special issue can help the readers get a deep insight into the state-of-the-art of multiscale mechanics and intrigue more fas-cinating studies in this challenging field.At last,we sincerely thank all the authors and reviewers for their contributions to this special issue.

G.W.He

G.D.Jin