Simulation-based analysis of micro-robots swimming at the center and near the wall of circular mini-channels

Swimming micro robots have great potential in biomedical applications such as targeted drug delivery, medical diagnosis, and destroying blood clots in arteries. Inspired by swimming micro organisms, micro robots can move in biofluids with helical tails attached to their bodies. In order to design and navigate micro robots, hydrodynamic characteristics of the flow field must be understood well. This work presents computational fluid dynamics (CFD) modeling and analysis of the flow due to the motion of micro robots that consist of magnetic heads and helical tails inside fluid-filled channels akin to bodily conduits; special emphasis is on the effects of the radial position of the robot. Time-averaged velocities, forces, torques, and efficiency of the micro robots placed in the channels are analyzed as functions of rotation frequency, helical pitch (wavelength) and helical radius (amplitude) of the tail. Results indicate that robots move faster and more efficiently near the wall than at the center of the channel. Forces acting on micro robots are asymmetrical due to the chirality of the robot’s tail and its motion. Moreover, robots placed near the wall have a different flow pattern around the head when compared to in-center and unbounded swimmers. According to simulation results, time-averaged for-ward velocity of the robot agrees well with the experimental values measured previously for a robot with almost the same dimensions

Hydrodynamic interaction of two unsteady model microorganisms.

The study of pair-wise interactions between swimming microorganisms is fundamental to the understanding of the rheological and transport properties of semi-dilute suspensions. In this paper, the hydrodynamic interaction of two ciliated microorganisms is investigated numerically using a boundary-element method, and the microorganisms are modeled as spherical squirmers that swim by time-dependent surface deformations. The results show that the inclusion of the unsteady terms in the ciliary propulsion model has a large impact on the trajectories of the interacting cells, and causes a significant change in scattering angles with potential important consequences on the diffusion properties of semi-dilute suspensions. Furthermore, the analysis of the shear stress acting on the surface of the microorganisms revealed that the duration and the intensity of the near-field interaction are significantly modified by the presence of unsteadiness. This observation may account for the hydrodynamic nature of randomness in some biological reactions, and supersedes the distinction between intrinsic randomness and hydrodynamic interactions, adding a further element to the understanding and modeling of interacting microorganisms

Optimization of bypass outlet guide vane for low interaction noise

An optimization approach has been developed and applied to a fan stage representative of a modern turbofan enginetoachieve novel, realistic, low-interaction-tone noise bypass outlet guide vanes with acceptable mechanical and aerodynamic properties. The incorporation of axial sweep in the design of the bypass stators is used as a passive method to achieve sizeable reductions in the discrete frequency tones generated by the impingement of the fan wakes. The acoustic benefits, mechanical properties, and aerodynamic performance of an unconventional sweep profile of the stator leading edge have been investigated numerically in an optimization framework using a combination of computational fluid dynamics and finite-element methods to solve each part of the problem. The results obtained in two separate optimizations to reduce interaction noise at the noise-critical sideline operating condition are presented and analyzed. Copyright © 2013 by Rolls-Royce plc

Acoustic optimization of ultra-low count bypass outlet guide vanes

An optimization process has been used to design an ultra-low count fan outlet guide vane with an unconventional leading edge profile to reduce the interaction noise. Computational fluid dynamics has been used to predict the aerodynamic and acoustic performance of the stator vane. The final stator design has been built and tested in a representative fan stage rig to determine its tone noise characteristics. The stator vane is found to give significant tone noise reduction at the fundamental blade passing frequency at cut-back in line with design expectations. Detailed comparisons of predicted circumferential and radial modes levels against measured mode detection data are also presented. A good agreement was found between numerical predictions and experimental data

Peri-urban agro-ecosystems in the Mediterranean: diversity, dynamics, and drivers

To address sustainability challenges of agroecosystems located in Mediterranean urban regions, this paper focuses on the multidisciplinary subject of urban agricultural systems. To better understand the diversity and dynamics of peri-urban agro-ecosystems and the main drivers of their sustainability, we compare six case studies located in Southern Europe (Montpellier, France; Pisa, Italy; Lisbon, Portugal; Athens, Greece) and the Maghreb (Constantine, Algeria; Meknes, Morocco). The research is based on fieldwork in each urban region (qualitative analysis) and literature analysis aimed to position each case study in its national and Mediterranean contexts. The comparison between local contexts indicates large discrepancies in the integration of environmental focus among the respective urban planning objectives. Generally, urbanization tends to accentuate agricultural diversity. The different forms of peri-urban agriculture evolve despite their persistent decline, and they also show a capacity to resist and even new growth in response to urban demand.Durabilité des Agricultures Urbaines en Méditerrané