A Micro-Scale Swimmer Propelled by Traveling Surface Waves

2011 ◽  
Author(s):  
Izhak Bucher ◽  
Eyal Setter
Keyword(s):  
Travelling Wave ◽  
Superior Performance ◽  
Small Scale ◽  
Micro Scale ◽  
Viscous Forces ◽  
Macro Scale ◽  
Robotic Devices ◽  
Compact Design ◽  
Micro Organisms ◽  
Efficient Power

Micro-scale slender swimmers are frequently encountered in nature and recently in micro-robotic applications. The swimming mechanism examined in this article is based on small transverse axi-symmetrical travelling wave deformations of a cylindrical long shell. In very small scale, inertia forces become negligible and viscous forces dominate most propulsion mechanisms being used by micro-organisms and robotic devices. The present paper proposes a compact design principle that provides efficient power to propel and maneuver a micro-scale device. Shown in this paper is a numerical analysis which couples the MEMS structure to the surrounding fluid. Analytical results compare the proposed mechanism to commonly found tail (flagella) driven devices, and a parametric comparison is shown suggesting it has superior performance. Numerical studies are preformed to verify the analytical model. Finally, a macro-scale demonstrator swimming in an environment with similar Reynolds numbers to the ones found in small scale is shown and its behavior in the laboratory is compared to the theory.

Analysis of High-Speed Electrical Generators for Utility Applications

2013 ◽  
Author(s):  
Miroslav P. Petrov
Keyword(s):  
Electricity Generation ◽  
High Speed ◽  
Renewable Energy Sources ◽  
Scale Up ◽  
Energy Utilization ◽  
Superior Performance ◽  
Electricity Production ◽  
Small Scale ◽  
Technical Challenges ◽  
Compact Design

High-speed alternators are believed to be well developed nowadays, following the improvement in performance and decrease of costs for electronic power converters and permanent magnet materials. Their compact design and their ability to vary the rotational speed in off-design conditions promise superior performance when compared to conventional generators. High-speed alternators are only available in limited sizes for small-scale applications, whereas improvements in efficiency and optimized part-load behavior are particularly important especially for small-scale electricity generation. Enhanced energy utilization for electricity production by small utility plants or by distributed units located at private homes or commercial buildings, based on thermodynamic cycles powered by natural gas or various renewable energy sources, is possible to be achieved through a wider application of grid-integrated high-speed technology. This study presents a critical review of previous research and demonstration work on high-speed electrical machines and a summary of the technical challenges limiting their performance and their expansion into larger sizes. Conclusions are drawn for finding appropriate solutions for practical high-speed electricity generation units and their readiness for a much wider deployment. Closer analysis is attempted on the thermal and mechanical integrity of high-speed alternators and the technical challenges that slow down their scale-up to MW-size units for utility applications. The necessary research and development work that needs to be done in the near future is outlined and discussed herein.

scholarly journals Impact of Micro-Scale Stochastic Zonal Flows on the Macro-Scale Visco-Resistive Magnetohydrodynamic Modes

Mathematics ◽  
2020 ◽  
Vol 8 (3) ◽  
pp. 443
Author(s):  
Sara Moradi ◽  
Anantanarayanan Thyagaraja
Keyword(s):  
Mach Number ◽  
Stochastic Model ◽  
Kinematic Viscosity ◽  
Small Scale ◽  
Stochastic Representation ◽  
Zonal Flows ◽  
Micro Scale ◽  
Mode Amplitude ◽  
Macro Scale ◽  
Scale Turbulence

A model is developed to simulate micro-scale turbulence driven Zonal Flows (ZFs), and their impact on the Magnetohydrodynamic (MHD) tearing and kink modes is examined. The model is based on a stochastic representation of the micro-scale ZFs with a given Alfvén Mach number, MS. Two approaches were explored: (i) passive stochastic model where the ZFs amplitudes are independent of the MHD mode amplitude, and (ii) the semi-stochastic model where the amplitudes of the ZFs have a dependence on the amplitude of the MHD mode itself. The results show that the stochastic ZFs can significantly stabilise the (2,1) and (1,1) MHD modes even at very low kinematic viscosity, where the mode is linearly unstable. Our results therefore indicate a possible mechanism for stabilisation of the MHD modes via small-scale perturbations in poloidal flow, simulating the turbulence driven ZFs.

scholarly journals Microstructure and mechanical performance of dissimilar metal joints of aluminium alloy and stainless steel by cutting-assisted welding-brazing

2021 ◽  
Author(s):  
Huibin Xu ◽  
Wei Cong ◽  
Donghua Yang ◽  
Yanlong Ma ◽  
Wanliang Zhong ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Aluminium Alloy ◽  
Cutting Tool ◽  
Mechanical Performance ◽  
Interfacial Structure ◽  
304 Stainless Steel ◽  
Small Scale ◽  
Joint Interface ◽  
Micro Scale ◽  
Macro Scale

Abstract The 5052 aluminium alloy and 304 stainless steel were successfully joined by cutting-assisted welding-brazing (CAWB) method without using flux. Dual-scale interfacial structures were achieved by manipulating the cutting tool profile. Results indicated that the macro-scale interfacial structure was produced at the joint interface when the taper step-shape cutting tool was adopted. As the cutting tool step was increased to 6-step, the micro-scale interface took on serrated morphology and a layer of continuous and wavy intermetallic compound (IMC) with an average thickness of 3.3 μm was formed at the interface. The τ 4 IMC particles and the FeAl 6 phases on a small scale were dispersed homogeneously in the welded seam. The maximum tensile strength of the joints reached 152.3 MPa upon tensile loading, 75% that of the 5052 aluminium base metal. The strong and reliable Al/steel dissimilar joints were attributed to the particle reinforced weld metal and the macro- and micro-scale dual self-locking structure at the interface.

Flow Characterization of an Electrostatic Resonant Plate Micropump-Mixer by a Scaled Model

2006 ◽  
Author(s):  
Oyvind Nilsen ◽  
Kamran Mohseni
Keyword(s):  
Reynolds Numbers ◽  
Small Scale ◽  
Actuation Frequency ◽  
Scaled Model ◽  
Micro Scale ◽  
Future Design ◽  
Flow Characterization ◽  
Macro Scale ◽  
Flow Phenomena

Flow characterization of an electrostatically activated resonant-plate micropump-mixer was investigated. Detailed visualization of the mixing process at the tip of the resonant plate, which is almost impossible due to the high actuation frequency (10–30 kHz) and small scale of the resonant plate (250 micron) under normal conditions, was realized with a macro scale flow visualization experiment within the range of common visualization equipment such as a SLR camera. Flow phenomena such as distinct circulative regions, observed at the micro scale by Linderman et. al [1,2], were observed in this study. In addition, the transition between two different flow regimes was observed, corresponding to vortex shearing and vortex shedding respectively. This transition took place in a gradual manner over a range of Reynolds numbers between 20 and 98. Below this regime the resonant plate will only generate limited deformation of the interface between the two fluids. However, for larger Reynolds numbers, equivalent to higher plate frequencies, organized vortex roll-up is observed. Vortex roll-up indicates significant fluid entrainment, and consequently mixing. The visualization of the flow, generated by the resonating fan shed new light on the detailed flow phenomena involved, and may help guide future design and optimization of micro scale fans/mixers based on this principle.

scholarly journals 2D-wavelet based micro and macro texture analysis for asphalt pavement under snow or ice condition

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Feng Li ◽  
Gulnigar Ablat ◽  
Siqi Zhou ◽  
Yixin Liu ◽  
Yufeng Bi ◽  
...  
Keyword(s):  
Wavelet Transform ◽  
Asphalt Pavement ◽  
Asphalt Mixture ◽  
Micro Scale ◽  
Braking System ◽  
Macro Scale ◽  
Texture Characteristics ◽  
The Mean ◽  
Resistance Performance

AbstractIn ice and snow weather, the surface texture characteristics of asphalt pavement change, which will significantly affect the skid resistance performance of asphalt pavement. In this study, five asphalt mixture types of AC-5, AC-13, AC-16, SMA-13, SMA-16 were prepared under three conditions of the original state, ice and snow. In this paper, a 2D-wavelet transform approach is proposed to characterize the micro and macro texture of pavement. The Normalized Energy (NE) is proposed to describe the pavement texture quantitatively. Compared with the mean texture depth (MTD), NE has the advantages of full coverage, full automation and wide analytical scale. The results show that snow increases the micro-scale texture because of its fluffiness, while the formation of the ice sheets on the surface reduces the micro-scale texture. The filling effect of snow and ice reduces the macro-scale texture of the pavement surface. In a follow-up study, the 2D-wavelet transform approach can be applied to improve the intelligent driving braking system, which can provide pavement texture information for the safe braking strategy of driverless vehicles.

Spatial-Pattern-Induced Evolution of a Self-Replicating Loop Network

2006 ◽  
Vol 12 (4) ◽  
pp. 461-485 ◽  
Author(s):  
Keisuke Suzuki ◽  
Takashi Ikegami
Keyword(s):  
Pattern Formation ◽  
Spatial Pattern ◽  
Spatial Patterns ◽  
Spiral Structure ◽  
Scale Interactions ◽  
Micro Scale ◽  
Macro Scale ◽  
Loop Network ◽  
Spatial Pattern Formation

We study a system of self-replicating loops in which interaction rules between individuals allow competition that leads to the formation of a hypercycle-like network. The main feature of the model is the multiple layers of interaction between loops, which lead to both global spatial patterns and local replication. The network of loops manifests itself as a spiral structure from which new kinds of self-replicating loops emerge at the boundaries between different species. In these regions, larger and more complex self-replicating loops live for longer periods of time, managing to self-replicate in spite of their slower replication. Of particular interest is how micro-scale interactions between replicators lead to macro-scale spatial pattern formation, and how these macro-scale patterns in turn perturb the micro-scale replication dynamics.

Wind Tunnel Tests of a Model Small-scale Horizontal-axis Wind Turbine Developed from Blade Element Momentum Theory

2021 ◽  
pp. 1-16
Author(s):  
Ojing Siram ◽  
Niranjan Sahoo ◽  
Ujjwal K. Saha
Keyword(s):  
Wind Tunnel ◽  
Horizontal Axis ◽  
Superior Performance ◽  
Speed Ratio ◽  
Small Scale ◽  
Blade Design ◽  
Horizontal Axis Wind Turbine ◽  
Blade Element Momentum Theory ◽  
Momentum Theory ◽  
Blade Element

Abstract The small-scale horizontal-axis wind turbines (SHAWTs) have emerged as the promising alternative energy resource for the off-grid electrical power generation. These turbines primarily operate at low Reynolds number, low wind speed, and low tip speed ratio conditions. Under such circumstances, the airfoil selection and blade design of a SHAWT becomes a challenging task. The present work puts forward the necessary steps starting from the aerofoil selection to the blade design and analysis by means of blade element momentum theory (BEMT) for the development of four model rotors composed of E216, SG6043, NACA63415, and NACA0012 airfoils. This analysis shows the superior performance of the model rotor with E216 airfoil in comparison to other three models. However, the subsequent wind tunnel study with the E216 model, a marginal drop in its performance due to mechanical losses has been observed.

scholarly journals Experimental study of the effects of wire EDM on the characteristics of ferritic steel, at a micro-scale on the contour cut surface

2018 ◽  
Vol 115 (4) ◽  
pp. 413
Author(s):  
Nida Naveed
Keyword(s):  
Residual Stress ◽  
Stress Measurement ◽  
Surface Characteristics ◽  
Surface Damage ◽  
Cutting Process ◽  
Contour Method ◽  
X Ray Diffraction ◽  
Micro Scale ◽  
Macro Scale ◽  
Cut Surface

This study, on a micro-scale, of the WEDM cut surfaces of specimens to which the contour method of residual stress measurement is being applied provides detailed information about the effects of the cutting process on the surface quality. This is defined by a combination of several parameters: variation in surface contour profile, sub-surface damage and surface texture. Measurements were taken at the start, the middle and at the end of the cut. This study shows that during WEDM cutting, a thin layer, extending to a depth of a few micrometres below the surface of the cut, is transformed. This layer is known as the recast layer. Using controlled-depth etching and X-ray diffraction, it is shown that this induces an additional tensile residual stress, parallel to the plane of the cut surface. The WEDM cut surface and sub-surface characteristics are also shown to vary along the length of the cut. Moreover, these micro-scale changes were compared with macro-scale residual stress results and provides an indication of the point at which the changes occurred by cutting process can be significantly relative to the macro-scale residual stress in a specimen.

scholarly journals On the Two-Scale Modelling of Elastohydrodynamic Lubrication in Tilted-Pad Bearings

Lubricants ◽  
2018 ◽  
Vol 6 (3) ◽  
pp. 78 ◽  
Author(s):  
Gregory de Boer ◽  
Andreas Almqvist
Keyword(s):  
Surface Topography ◽  
Load Capacity ◽  
Three Dimensional ◽  
Elastohydrodynamic Lubrication ◽  
Multiscale Methods ◽  
Operating Conditions ◽  
Real Surface ◽  
Micro Scale ◽  
Macro Scale ◽  
Heterogeneous Multiscale

A two-scale method for modelling the Elastohydrodynamic Lubrication (EHL) of tilted-pad bearings is derived and a range of solutions are presented. The method is developed from previous publications and is based on the Heterogeneous Multiscale Methods (HMM). It facilitates, by means of homogenization, incorporating the effects of surface topography in the analysis of tilted-pad bearings. New to this article is the investigation of three-dimensional bearings, including the effects of both ideal and real surface topographies, micro-cavitation, and the metamodeling procedure used in coupling the problem scales. Solutions for smooth bearing surfaces, and under pure hydrodynamic operating conditions, obtained with the present two-scale EHL model, demonstrate equivalence to those obtained from well-established homogenization methods. Solutions obtained for elastohydrodynamic operating conditions, show a dependency of the solution to the pad thickness and load capacity of the bearing. More precisely, the response for the real surface topography was found to be stiffer in comparison to the ideal. Micro-scale results demonstrate periodicity of the flow and surface topography and this is consistent with the requirements of the HMM. The means of selecting micro-scale simulations based on intermediate macro-scale solutions, in the metamodeling approach, was developed for larger dimensionality and subsequent calibration. An analysis of the present metamodeling approach indicates improved performance in comparison to previous studies.

Arriving at the Optimum Overlap Ratio for an Elliptical-Bladed Savonius Rotor

2017 ◽  
Author(s):  
Nur Alom ◽  
Ujjwal K. Saha
Keyword(s):  
Numerical Study ◽  
Superior Performance ◽  
Navier Stokes ◽  
Speed Ratio ◽  
Small Scale ◽  
Efficient Manner ◽  
Ansys Fluent ◽  
Savonius Rotor ◽  
Velocity Magnitude ◽  
Overlap Ratio

The Savonius rotor appears to be particularly promising for the small-scale applications because of its design simplicity, good starting ability, and insensitivity to wind directions. There has been a growing interest in recent times to harness wind energy in an efficient manner by developing newer blade profiles of Savonius rotor. The overlap ratio (OR), one of the important geometric parameters, plays a crucial role in the turbine performance. In a recent study, an elliptical blade profile with a sectional cut angle (θ) of 47.5° has demonstrated its superior performance when set at an OR = 0.20. However, this value of OR is ideal for a semicircular profile, and therefore, requires further investigation to arrive at the optimum overlap ratio for the elliptical profile. In view of this, the present study attempts to make a systemic numerical study to arrive at the optimum OR of the elliptical profile having sectional cut angle, θ = 47.5°. The 2D unsteady simulation is carried out around the elliptical profile considering various overlap ratios in the range of 0.0 to 0.30. The continuity, unsteady Reynolds Averaged Navier-Stokes (URANS) equations and two equation eddy viscosity SST (Shear Stress transport) k-ω model are solved by using the commercial finite volume method (FVM) based solver ANSYS Fluent. The torque and power coefficients are calculated as a function of tip speed ratio (TSR) and at rotating conditions. The total pressure, velocity magnitude and turbulence intensity contours are obtained and analyzed to arrive at the intended objective. The numerical simulation demonstrates an improved performance of the elliptical profile at an OR = 0.15.

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