Microfluidic propulsion by the metachronal beating of magnetic artificial cilia: a numerical analysis

In this work we study the effect of metachronal waves on the flow created by magnetically-driven plate-like artificial cilia in microchannels using numerical simulations. The simulations are performed using a coupled magneto-mechanical solid-fluid computational model that captures the physical interactions between the fluid flow, ciliary deformation and applied magnetic field. When a rotating magnetic field is applied to super-paramagnetic artificial cilia, they mimic the asymmetric motion of natural cilia, consisting of an effective and recovery stroke. When a phase-difference is prescribed between neighbouring cilia, metachronal waves develop. Due to the discrete nature of the cilia, the metachronal waves change direction when the phase difference becomes sufficiently large, resulting in antiplectic as well as symplectic metachrony. We show that the fluid flow created by the artificial cilia is significantly enhanced in the presence of metachronal waves and that the fluid flow becomes unidirectional. Antiplectic metachrony is observed to lead to a considerable enhancement in flow compared to symplectic metachrony, when the cilia spacing is small. Obstruction of flow in the direction of the effective stroke for the case of symplectic metachrony was found to be the key mechanism that governs this effect

Environmental Hydraulics Research

This book aims to provide research and engineering applications related to water and hydraulic problems. It is comprised of scientific papers in all topics of hydraulics, in particular, on sustainable water management, environmental hydraulics, ecohydraulics, water–energy nexus, and systems protection and efficiency. Safety and innovation issues, interdisciplinary problems, and linkage of theory to experimental and field applications can also be found within. Solutions of water problems in the form of prediction models, flow simulations, engineering systems, monitoring, management strategies covering scientific investigations and/or experimental or field studies of flow behaviour, hydrodynamics, and climate changes effects and adaptation, new design solutions, innovative approaches in the field of environment, hydraulics, techniques, methods, and analyses to address the new challenges in environmental hydraulics are alo presented and explored. This topic is studied both from a technical and environmental point of view, with the objective of protecting and enhancing the quality of the environment. In a cross-disciplinary field of study, this book comprises open channel/river flows and pressurised systems, combining, among others, new technological, social, and environmental hydraulic challenges, working in water-related fields with available information, new concepts and tools, new design solutions, eco-friendly technologies, and the advanced materials necessary to address the increasing challenges of ensuring a sustainable water environment by promoting the adaptation, flexibility, integration, and sustainability of recognised environmental solutions

Fire performance of residential shipping containers designed with a shaft wall system

seven story building made of shipping containers is planned to be built in Barcelona, Spain. This study mainly aimed to evaluate the fire performance of one of these residential shipping containers whose walls and ceiling will have a shaft wall system installed. The default assembly consisted of three fire resistant gypsum boards for vertical panels and a mineral wool layer within the framing system. This work aimed to assess if system variants (e.g. less gypsum boards, no mineral wool layer) could still be adequate considering fire resistance purposes. To determine if steel temperatures would attain a predetermined temperature of 300-350ºC (a temperature value above which mechanical properties of steel start to change significantly) the temperature evolution within the shaft wall system and the corrugated steel profile of the container was analysed under different fire conditions. Diamonds simulator (v. 2020; Buildsoft) was used to perform the heat transfer analysis from the inside surface of the container (where the fire source was present) and within the shaft wall and the corrugated profile. To do so gas temperatures near the walls and the ceiling were required, so these temperatures were obtained from two sources: (1) The standard fire curve ISO834; (2) CFD simulations performed using the Fire Dynamics Simulator (FDS). Post-flashover fire scenarios were modelled in FDS taking into account the type of fuel present in residential buildings according to international standards. The results obtained indicate that temperatures lower than 350ºC were attained on the ribbed steel sheet under all the tested heat exposure conditions. When changing the assembly by removing the mineral wool layer, fire resistance was found to still be adequate. Therefore, under the tested conditions, the structural response of the containers would comply with fire protection standards, even in the case where insulation was reduced.Postprint (published version

Experimental and Numerical Modeling of Fluid Flow

This Special Issue provides an overview of the applied experimental and numerical flow, models, which are used to investigate fluid flow in complex situations. The investigated problems are related to fundamental processes or new applications. As demonstrated, the field of the application of experimental and numerical flow models is constantly expanding

Energy storage and generation from thermopower waves

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references.The nonlinear coupling between an exothermic chemical reaction and a nanowire or nanotube with large axial heat conduction guides a self-propagating thermal wave along the nano-conduit. The thermal conduit accelerates the wave by rapidly transporting energy to un-reacted fuel. The reaction wave induces what we term a thermopower wave, resulting in an electrical current in the same direction. At up to 7 W/g, peak power density is larger than that of many present micro-scale power sources (e.g. fuel cells, batteries) and even about seven times greater than commercial Li-ion batteries. Thermopower waves also tend to produce unipolar voltage pulses, although conventional thermoelectric theory predicts bipolar voltage. These waves also generate thermopower in excess of previous measurements in carbon nanotubes (CNTs) and therefore could increase figures of merit in a variety of thermoelectric materials. In this thesis, I have developed the theoretical framework to describe the thermal and chemical profiles of propagating reaction waves, and their electrical properties. My analysis yielded a new analytical solution for one-dimensional reaction and thermal diffusion systems with nth order kinetics that obviates many approximate or numerical approaches from the past 80 years. A generalized logistic. function describes the temperature and concentration profiles within the solid fuel and provides a solution for the wave velocity for a wide range of conditions. This approach offers new insight into such problems spanning several fields in science and engineering, including propulsion and self-propagating high temperature synthesis (SHS) of materials, as well as the dynamics of thermopower waves. Temperature and voltage measurements of thermopower waves on CNTs show that they can generate power as much as four times greater than predictions based on reference measurements of the Seebeck coefficient for static temperature gradients. We hypothesize that the excess thermopower stems from a chemical potential gradient across the CNTs. The fuel (e.g. picramide) adsorbs and dopes the CNTs ahead of the wave and desorbs and reacts behind the wave front. Furthermore, the excess thermopower depends on the mass of fuel added (relative to CNT mass), and the chemical potential difference matches the magnitude of the excess thermopower. Thus, a major conclusion of this thesis is that coupling to a chemical reaction can boost the performance of thermoelectric materials through differential doping. Thermopower waves can have well defined velocity oscillations for certain kinetic and thermal parameter values. Cyclotrimethylene-trinitramine (fuel) on multiwalled CNTs (conduit) system generates voltage oscillations of 400 to 5000 Hz. These frequencies agree with velocity oscillations predicted by my thermochemical model of the reaction wave, extended to include thermal transport within the conduits. Thermopower waves could thus find applications as new types of alternating current (AC) batteries and self-powered signal generators, which could easily be miniaturized. Microelectromechanical systems and sensors would benefit from thermopower wave generators to enable functions such as communications and acceleration that currently require large power packs. Additionally, the "self-discharge" rate of thermopower wave generators is extremely low in contrast to electrochemical storage, since their energy is stored in chemical bonds. Thermopower waves thus enable new energy storage devices and could exceed limitations of conventional thermoelectric devices.by Joel T. Abrahamson.Ph.D

Computational and Numerical Simulations

Computational and Numerical Simulations is an edited book including 20 chapters. Book handles the recent research devoted to numerical simulations of physical and engineering systems. It presents both new theories and their applications, showing bridge between theoretical investigations and possibility to apply them by engineers of different branches of science. Numerical simulations play a key role in both theoretical and application oriented research

Full Proceedings, 2018

Full conference proceedings for the 2018 International Building Physics Association Conference hosted at Syracuse University

Experimental Mechanical and Fluid Mechanical Investigations of the Brass Instrument Lip-reed and the Human Vocal Folds

The mechanical properties of the lips are of crucial importance to the function of a brass instrument. The natural resonance modes must be able to usefully interact with the instrument air column in order to sustain oscillations. Mechanical frequency responses of human and arti cial lips used to play a brass instrument were measured using a high-speed digital video technique in an attempt to classify the true nature of the lipreed. The results revealed the presence of at least two lip modes that exhibited the characteristic outward-inward striking behaviour seen in many in vitro replica lip-reed measurements. The Q-values of the human lip resonances were considerably lower than those seen for the replica lips. Transverse mechanical response measurements were also performed on an in vitro lip-reed to investigate the coupling between the outward and inward striking modes. The two dimensional motion of the lips during full oscillations was investigated. It is shown that a computational four degree-of-freedom model would be required to fully simulate the observed mechanical motion. The uid behaviour downstream from an in vitro vocal fold model was investigated using particle image velocimetry (PIV). A `free jet' con guration with no downstream acoustical coupling was rst investigated. The measurements revealed an unsteady glottal jet ow, consisting of a high velocity jet core, a transitional region of high jet deceleration and a turbulent mixing region. The jet was consistently skewed at angles to the glottal centreline, and appeared to oscillate back and forth across the centreline during the glottal cycle. The behaviour of the jet core was investigated in detail. A temporal asymmetry was observed in the mean velocity across the jet core such that the highest jet velocities were encountered during the closing phase of the vocal folds. The overall jet behaviour also showed a strong turbulent asymmetry between the opening and closing phases. High levels of vorticity and turbulent motion encountered during the closing phase were associated with the deceleration of the jet. Three vocal fold con gurations that included static replicas of the ventricular bands were nally investigated with the aim of characterising the aerodynamic interaction between the ventricular bands and the vocal folds. A marked e ect on the glottal jet was observed for all con gurations. The most physically realistic con guration appeared to stabilise the glottal jet, leading to a reattachment of the jet to the ventricular bands and a subsequent secondary ow separation from the downstream end. The implications of the aerodynamic interaction is discussed, with particular note to its possible relevance to the lip-reed and mouthpiece interaction in brass playing