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Review Article

Appl. Mech. Rev. 2018;70(4):040801-040801-17. doi:10.1115/1.4040838.

Stably stratified wall-bounded turbulence is commonly encountered in many industrial and environmental processes. The interaction between turbulence and stratification induces remarkable modifications on the entire flow field, which in turn influence the overall transfer rates of mass, momentum, and heat. Although a vast proportion of the parameter range of wall-bounded stably stratified turbulence is still unexplored (in particular when stratification is strong), numerical simulations and experiments have recently developed a fairly robust picture of the flow structure, also providing essential ground for addressing more complex problems of paramount technological, environmental and geophysical importance. In this paper, we review models used to describe the influence of stratification on turbulence, as well as numerical and experimental methods and flow configurations for studying the resulting dynamics. Conclusions with a view on current open issues will be also provided.

Commentary by Dr. Valentin Fuster
Appl. Mech. Rev. 2018;70(4):040802-040802-20. doi:10.1115/1.4041660.

Pneumatic artificial muscles (PAMs) are linear pneumatic actuators consisting of a flexible bladder with a set of in-extensible fibers woven as a sheath on the outside. Upon application of pressure, the actuators contract or expand based on the angle of winding of the braid. Due to the similarity in properties of the actuators with biological muscles and the advantages thereof, these are increasingly being used in many robotic systems and mechanisms. This necessitates the development of mathematical models describing their mechanics for optimal design as well as for application in control systems. This paper presents a survey on different mathematical models described in the literature for representing the statics of PAM. Since it is observed that the validity of existing static models, based on energy balance methods, is not consistent with changes in parameters when applied to their miniaturized versions of pneumatic artificial muscles (MPAM), a new model has been proposed. The model takes into account material properties of the bladder as well as the end-effects which are prominent for MPAMs. Experiments conducted on fabricated MPAMs, of different diameters and lengths, show that the proposed model predicts the pressure-deformation characteristics of MPAMs with maximum error of less than 7%.

Commentary by Dr. Valentin Fuster

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