scholarly journals Improving the propulsion speed of a heaving wing through artificial evolution of shape

2019 ◽  
Vol 475 (2221) ◽  
pp. 20180375 ◽  
Author(s):  
Sophie Ramananarivo ◽  
Thomas Mitchel ◽  
Leif Ristroph
Keyword(s):  
Optimization Problems ◽  
Three Dimensional ◽  
Artificial Evolution ◽  
Complex Flows ◽  
Cross Sectional ◽  
Evolutionary Scheme ◽  
Edge Sharpness ◽  
Measured Speed ◽  
And Performance ◽  
Sectional Shape

Aeronautical studies have shown that subtle changes in aerofoil shape substantially alter aerodynamic forces during fixed-wing flight. The link between shape and performance for flapping locomotion involves distinct mechanisms associated with the complex flows and unsteady motions of an air- or hydro-foil. Here, we use an evolutionary scheme to modify the cross-sectional shape and iteratively improve the speed of three-dimensional printed heaving foils in forward flight. In this algorithmic-experimental method, ‘genes’ are mathematical parameters that define the shape, ‘breeding’ is the combination of genes from parent wings to form a daughter, and a wing's measured speed is its ‘fitness’ that dictates its likelihood of breeding. Repeated over many generations, this process automatically discovers a fastest foil whose cross-section resembles a slender teardrop. We conduct an analysis that uses the larger population to identify what features of this shape are most critical, implicating slenderness, location of maximum thickness and fore-aft asymmetries in edge sharpness or bluntness. This analysis also reveals a tendency towards extremely thin and cusp-like trailing edges. These findings demonstrate artificial evolution in laboratory experiments as a successful strategy for tailoring shape to improve propulsive performance. Such a method could be used in related optimization problems, such as tuning kinematics or flexibility for flapping propulsion, and for flow–structure interactions more generally.

Enamel Crystal Shape: History of an Idea

1987 ◽  
Vol 1 (2) ◽  
pp. 322-329 ◽  
Author(s):  
H. Warshawsky
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Cross Sections ◽  
Three Dimensional ◽  
Unit Cell ◽  
Cross Sectional ◽  
Transmission Electron ◽  
History Of ◽  
Sectional Shape ◽  
Imaging Plane

The purpose of this paper is to review evidence which casts doubt on the interpretation universally applied to hexagonal images seen in sectioned enamel. The evidence is based on two possible models to explain the hexagonal profiles seen in mammalian enamel with transmission electron microscopy. The "hexagonal ribbon" model proposes that hexagonal profiles are true cross-sections of elongated hexagonal ribbons. The "rectangular ribbon" model proposes that hexagonal profiles are caused by three-dimensional segments that are parallelepipeds contained in the Epon section. Since shadow projections of such rectangular segments give angles that are inconsistent with the hexagonal unit cell, a model based on ribbons with rhomboidal cut ends and angles of 60 and 120° is proposed. The "rhomboidal ribbon" model projects shadows with angles that are predicted by the unit cell. It is suggested that segments of such crystallites in section project as opaque hexagons on the imaging plane in routine transmission electron microscopy. Morphological observations on crystallites in sections - together with predictions from the hexagonal, rectangular, and rhomboidal ribbon models - indicate that crystallites in rat incisor enamel are flat ribbons with rhomboidal cross-sectional shape. Hexagonal images in electron micrographs of thin-sectioned enamel can result from rhomboidal-ended, parallelepiped-shaped segments of these crystallites projected and viewed as two-dimensional shadows.

scholarly journals Characterization and Control for the Laminar Flow of Liquid Polyurethane System in a Wide Angle Diffuser with Transversely Arrayed Obstacles

2020 ◽  
Vol 10 (4) ◽  
pp. 1228
Author(s):  
Son ◽  
Lee ◽  
Chang
Keyword(s):  
Laminar Flow ◽  
Flow Velocity ◽  
Three Dimensional ◽  
Flow Uniformity ◽  
Cross Sectional ◽  
Lumped Parameter ◽  
Vorticity Vector ◽  
Rms Error ◽  
Sectional Shape ◽  
And Control

In the manufacturing process of hard-board poly-urethane foams, the uniformity is a very important issue for the raw compound of the liquid poly-urethane system flow for the quality control of such products. One of the universal methods to generate more uniform flow is that some obstacles are located inside the diffuser at the end of injector. For the regime of non-Newtonian laminar flow, better flow uniformity can be achieved with the enhancement of mixing in the wake after the resistive obstacles. In this research, the parametric study is made for the gap interval between adjacent obstacle components as well as the cross-sectional shape with a computational fluid dynamics (CFD) technique. The flow fields around circular and elliptic cylinders are visualized for flow velocity and vorticity with the comparison of root-mean-square (RMS) error for the deviation of velocity at the outlet as a lumped parameter to estimate flow uniformity and mixing. When the blockage ratio is fixed 0.3 for the pipe of Reynolds number 58.5 based on its diameter, eliminating the effect of wall boundary ratio with the classical Blasius velocity profile, the RMS error is reduced 77% to 92% from the baseline case in the case of 60%-diameter gaps for the figure of circles and 2:1 longitudinal ellipse, respectively. The flow is visualized around obstacle components with vorticity as well as flow velocity where the three-dimensional components of vorticity vector are also elucidated in physics for the evolution of complex multi-dimensional flow wake.

E-Procurement Utilisation in the Maintenance Repair and Overhaul (MRO) Supply Chain by SMEs in India

2016 ◽  
Vol 18 (2) ◽  
pp. 51-61
Author(s):  
Munmun Basak ◽  
Indranil Guha
Keyword(s):  
Success Factors ◽  
Small And Medium Enterprises ◽  
Critical Role ◽  
Three Dimensional ◽  
Strategic Decision ◽  
Cross Sectional Survey ◽  
Cross Sectional ◽  
Systematic Analysis ◽  
And Performance ◽  
Medium Enterprises

Due to the significant contribution in output, exports and employment, the Small and Medium enterprises (SEMs) play a critical role in the Indian economic structure. In this study a three dimensional; namely information, transactional and strategic decision making perspectives of the e-procurement functionalities are investigated. A cross-sectional survey is used as the methodology for the data collection. After a systematic analysis it was found that in the MRO industry the MSEMs used the e-procurement system mainly for purchasing, communication and transactional purposes. However, strategic utilisation of the e-procurement for the optimisation of SCM process in the MRO industry in India is still in its nascent stage. The results are limited to its sample size due to the size of the MRO and its MSEMs industry. Thereafter, success factors and performance of the e-procurement in these MSEMs is also studied to analyse the utilisation of e-procurement in detail.

A Study on the Cross-Sectional Shape of Kerf Cut with Micro Abrasive Air Jet

2012 ◽  
Vol 500 ◽  
pp. 236-241 ◽  
Author(s):  
Quan Lai Li ◽  
Chuan Zhen Huang ◽  
Jun Wang ◽  
Hong Tao Zhu
Keyword(s):  
Incidence Angle ◽  
Three Dimensional ◽  
Traverse Speed ◽  
Cross Sectional ◽  
Air Jet ◽  
Analysis Technique ◽  
Hard And Brittle Materials ◽  
The Cross ◽  
Sectional Profile ◽  
Sectional Shape

Micro abrasive air jet (MAAJ) cutting is a promising technology for the fabrication of three-dimensional microstructures in hard and brittle materials. In this paper, a study on the cross-sectional shape of the kerf cut with MAAJ is presented. It shows that the machining depth and slope of the sidewall increase with an increase in air pressure, abrasive flow rate and jet incidence angle, while decrease with an increase in nozzle traverse speed. Using a dimensional analysis technique, predictive model for cross-sectional profile is developed. The research results may be meaningful to the highly precision three-dimensional micro-structural cutting.

Non-Contact Area Measurement Techniques for Cross Sectional Properties of Soft Tissues

2003 ◽  
Author(s):  
Dipan Bose ◽  
Jason R. Kerrigan ◽  
Johan Ivarsson ◽  
N. Jane Madeley ◽  
Steve A. Millington ◽  
...  
Keyword(s):  
Cross Section ◽  
Soft Tissues ◽  
Cruciate Ligament ◽  
Measurement Techniques ◽  
Three Dimensional ◽  
Area Measurement ◽  
Cross Sectional ◽  
Knee Ligaments ◽  
Human Knee ◽  
Sectional Shape

In this study, a non-contact optical three-dimensional digitization technique is described to account for area measurement problems related to soft tissue. The technique is used to generate digitized models of human knee ligaments (collateral and cruciate ligament bundles). Cross-sectional area of knee ligaments is determined by applying Green’s theorem on data obtained from the digitized models. The surface concavity features of different ligaments shown in this study signify the extent of approximation done by projection based methods. The study also reports the variation in cross-sectional shape of a ligament along its long axis, indicating the importance of deciding the appropriate cross section for stress calculation measurements.

Vortices and Performance of Internal and External Volutes

2015 ◽  
Author(s):  
Hua Chen ◽  
Ding Tong ◽  
Xiaochun Wang
Keyword(s):  
Numerical Simulation ◽  
Shear Stress ◽  
Cross Section ◽  
Centrifugal Compressor ◽  
Cross Flow ◽  
Cross Sectional ◽  
Compressor Performance ◽  
And Performance ◽  
Sectional Shape ◽  
Different Levels

In this paper, the cross flow in several internal and external volutes of a small centrifugal compressor is examined to highlight its effects on compressor performance. Different levels of the loss associated with shear stress related to the vortices in the volute cross section are shown to be the reason behind the diverse performance of internal volutes and external volutes. A numerical simulation is carried out to substantiate this and to further study this effect of cross sectional shape of volutes.

Numerical Simulation of Flow Field Around a Circular-Bladed Butterfly Wind Turbine

2015 ◽  
Author(s):  
Yutaka Hara ◽  
Takahiro Sumi ◽  
Yuhei Matsubara ◽  
Yoshiyuki Yasumoto
Keyword(s):  
Flow Field ◽  
Wind Turbine ◽  
Three Dimensional ◽  
Vertical Axis ◽  
Dynamic Stall ◽  
Speed Ratio ◽  
Half Cycle ◽  
Cross Sectional ◽  
Tip Vortices ◽  
Sectional Shape

Three-dimensional computational fluid dynamics (3D-CFD) was performed to simulate the flow field around an aluminum circular-blade butterfly wind turbine, which is a vertical-axis-type turbine with four circular blades and a diameter of 2.06 m. Under the assumption of a loss factor of 0.8 due to a generator and an AC–DC converter, the CFD results agreed with the experimental results. Although tip vortices were observed at the top and bottom portions of the blades, the vorticity intensity was weaker than that of the straight-blade rotor case. In addition, the cross-sectional shape of the tip vortices seemed to be elliptical for circular blades rather than circular as for straight blades. As the tip speed ratio was less than 2, vortices arising from dynamic stall at maximum-radius portions of blades were observed at the downwind half-cycle as well as the upwind half-cycle. A feature of the vortices shed from a circular blade at the downwind half-cycle was the looped shape.

Coupled fluid and energy flow in fabrication of microstructured optical fibres

2019 ◽  
Vol 874 ◽  
pp. 548-572 ◽  
Author(s):  
Yvonne M. Stokes ◽  
Jonathan J. Wylie ◽  
M. J. Chen
Keyword(s):  
Surface Tension ◽  
Numerical Method ◽  
Three Dimensional ◽  
External Boundary ◽  
Cross Sectional ◽  
Heating And Cooling ◽  
Standard Problem ◽  
Axial Stretching ◽  
Sectional Shape ◽  
Microstructured Optical Fibres

We consider the role of heating and cooling in the steady drawing of a long and thin viscous thread with an arbitrary number of internal holes of arbitrary shape. The internal holes and the external boundary evolve as a result of the axial drawing and surface-tension effects. The heating and cooling affects the evolution of the thread because both the viscosity and surface tension of the thread are assumed to be functions of the temperature. We use asymptotic techniques to show that, under a suitable transformation, this complicated three-dimensional free boundary problem can be formulated in such a way that the transverse aspect of the flow can be reduced to the solution of a standard Stokes flow problem in the absence of axial stretching. The solution of this standard problem can then be substituted into a system of three ordinary differential equations that completely determine the flow. We use this approach to develop a very simple numerical method that can determine the way that thermal effects impact on the drawing of threads by devices that either specify the fibre tension or the draw ratio. We also develop a numerical method to solve the inverse problem of determining the initial cross-sectional geometry, draw tension and, importantly, heater temperature to obtain a desired cross-sectional shape and change in cross-sectional area at the device exit. This precisely allows one to determine the pattern of air holes in the preform that will achieve the desired hole pattern in the stretched fibre.

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