scholarly journals On the limitations of some popular numerical models of flagellated microswimmers: importance of long-range forces and flagellum waveform

2019 ◽  
Vol 6 (1) ◽  
pp. 180745 ◽  
Author(s):  
C. Rorai ◽  
M. Zaitsev ◽  
S. Karabasov
Keyword(s):  
Stokes Flow ◽  
Numerical Models ◽  
Shape Change ◽  
Three Dimensional ◽  
Head Shape ◽  
Dimensional Finite Element ◽  
Flow Approximation ◽  
Resistive Force Theory ◽  
Three Dimensional Finite Element ◽  
Benchmark Solutions

For a sperm-cell-like flagellated swimmer in an unbounded domain, several numerical models of different fidelity are considered based on the Stokes flow approximation. The models include a regularized Stokeslet method and a three-dimensional finite-element method, which serve as the benchmark solutions for several approximate models considered. The latter include the resistive force theory versions of Lighthill, and Gray and Hancock, as well as a simplified approximation based on computing the hydrodynamic forces exerted on the head and the flagellum separately. It is shown how none of the simplified models is robust enough with regards to predicting the effect of the swimmer head shape change on the swimmer dynamics. For a range of swimmer motions considered, the resulting solutions for the swimmer force and velocities are analysed and the applicability of the Stokes model for the swimmers in question is probed.

scholarly journals Nearby boundaries create eddies near microscopic filter feeders

2009 ◽  
Vol 7 (46) ◽  
pp. 851-862 ◽  
Author(s):  
Rachel E. Pepper ◽  
Marcus Roper ◽  
Sangjin Ryu ◽  
Paul Matsudaira ◽  
Howard A. Stone
Keyword(s):  
Three Dimensional ◽  
Pond Water ◽  
Filter Feeder ◽  
Dimensional Finite Element ◽  
Flow Approximation ◽  
The Common ◽  
Filter Feeders ◽  
Three Dimensional Finite Element ◽  
Approximate Equations ◽  
Good Agreement

We show through calculations, simulations and experiments that the eddies often observed near sessile filter feeders are frequently due to the presence of nearby boundaries. We model the common filter feeder Vorticella , which is approximately 50 µm across and which feeds by removing bacteria from ocean or pond water that it draws towards itself. We use both an analytical stokeslet model and a Brinkman flow approximation that exploits the narrow-gap geometry to predict the size of the eddy caused by two parallel no-slip boundaries that represent the slides between which experimental observations are often made. We also use three-dimensional finite-element simulations to fully solve for the flow around a model Vorticella and analyse the influence of multiple nearby boundaries. Additionally, we track particles around live feeding Vorticella in order to determine the experimental flow field. Our models are in good agreement both with each other and with experiments. We also provide approximate equations to predict the experimental eddy sizes owing to boundaries both for the case of a filter feeder between two slides and for the case of a filter feeder attached to a perpendicular surface between two slides.

scholarly journals Effects of multiple vein microjoints on the mechanical behaviour of dragonfly wings: numerical modelling

2016 ◽  
Vol 3 (3) ◽  
pp. 150610 ◽  
Author(s):  
H. Rajabi ◽  
N. Ghoroubi ◽  
A. Darvizeh ◽  
E. Appel ◽  
S. N. Gorb
Keyword(s):  
Numerical Models ◽  
Complex Structure ◽  
Three Dimensional ◽  
Micro Air Vehicles ◽  
Insect Wings ◽  
Computational Data ◽  
Dimensional Finite Element ◽  
Biological Composites ◽  
Three Dimensional Finite Element ◽  
Dragonfly Wings

Dragonfly wings are known as biological composites with high morphological complexity. They mainly consist of a network of rigid veins and flexible membranes, and enable insects to perform various flight manoeuvres. Although several studies have been done on the aerodynamic performance of Odonata wings and the mechanisms involved in their deformations, little is known about the influence of vein joints on the passive deformability of the wings in flight. In this article, we present the first three-dimensional finite-element models of five different vein joint combinations observed in Odonata wings. The results from the analysis of the models subjected to uniform pressures on their dorsal and ventral surfaces indicate the influence of spike-associated vein joints on the dorsoventral asymmetry of wing deformation. Our study also supports the idea that a single vein joint may result in different angular deformations when it is surrounded by different joint types. The developed numerical models also enabled us to simulate the camber formation and stress distribution in the models. The computational data further provide deeper insights into the functional role of resilin patches and spikes in vein joint structures. This study might help to more realistically model the complex structure of insect wings in order to design more efficient bioinspired micro-air vehicles in future.

Simple Numerical Models for Pipeline Walking Accounting for Mitigation and Complex Soil Response

2011 ◽  
Author(s):  
Daniel Carneiro ◽  
David Murphy
Keyword(s):  
Numerical Models ◽  
Three Dimensional ◽  
Interaction Model ◽  
Soil Response ◽  
Dimensional Finite Element ◽  
Loading And Unloading ◽  
Three Dimensional Finite Element ◽  
Internal Pressures ◽  
Subsea Pipelines ◽  
Pipeline Design

Non-buried subsea pipelines subjected to high internal pressures and high operational temperatures (HP/HT) may experience significant axial expansion. Asymmetries in the loading and unloading in startups and shutdowns (e.g. due to seabed slope, temperature transients or riser tension) may cause the axial displacements to accumulate over operational cycles, in a ratcheting process often called “pipeline walking”. Despite the complexity of the pipe-soil interaction governing this behavior, several analytical and simple numerical models have been used for estimating the total accumulated pipeline axial displacement. These simple models are powerful tools in preliminary phases of a pipeline design, although their use is limited due to the simplifications. This paper presents results of a simple numerical model able to account for additional features in the preliminary walking assessment, such as loads on mitigation systems. The models were originally prepared to assess walking mitigation for some rigid flowlines in a recently installed subsea system, and remarkable agreement with complex three-dimensional finite element models was observed. The effect of different types of mitigation systems on the global behavior of the pipelines is presented and discussed. The influence of the pipe-soil interaction model employed is also investigated.

scholarly journals Parametric Analysis of Rib Pillar Stability in a Longitudinal Sublevel Open Stoping Operation in an Underground Copper Mine in Southern Africa

2021 ◽  
Vol 5 (1) ◽  
pp. 11
Author(s):  
Kostas Kaklis ◽  
Zach Agioutantis ◽  
Munyindei Masialeti ◽  
Jerome Yendaw ◽  
Thierry Bineli Betsi
Keyword(s):  
Parametric Analysis ◽  
Numerical Models ◽  
Three Dimensional ◽  
Stability Factor ◽  
Finite Element Models ◽  
Pillar Stability ◽  
The Third ◽  
Mining Project ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element

The pillar stability factor (PSF) is calculated in three different mining stages for a sublevel open stoping mining project located in northern Botswana. Several three-dimensional finite element models were developed by varying the stope span. Pillar strength was estimated using the Lunder and Pakalnis equation and pillar stress was obtained from the numerical models. As mining progresses, both the first and second mining stages meet the rib pillar stability factor requirement for safe extraction. Geometrical improvements are suggested in the mining layout for the third mining stage to achieve the required PSF, which is based on international practices.

Effects of pile shape in improving the performance of monopiles embedded in onshore clays

2015 ◽  
Vol 52 (8) ◽  
pp. 1144-1158 ◽  
Author(s):  
B. Pedram
Keyword(s):  
Numerical Models ◽  
Three Dimensional ◽  
Elastoplastic Material ◽  
Lateral Capacity ◽  
Pile Diameter ◽  
Overconsolidated Clays ◽  
Dimensional Finite Element ◽  
Clay Layers ◽  
Three Dimensional Finite Element ◽  
Pile Length

This paper presents the results from a series of three-dimensional finite element analyses, which examine the benefits of adopting square pile–tower structures instead of circular monopiles. The advantages of square monopiles are brought out in this paper through a parametric study with a Tresca soil model, where the shear strength and modulus of elasticity varied with depth and the pile–tower structures were modelled as an elastoplastic material. The effects of pile diameter, pile thickness, eccentricity, and pile length for free-head pile–towers embedded in lightly overconsolidated and heavily overconsolidated clays were investigated. From the results of the numerical models, it is clear that the ultimate lateral capacity and stiffness of square pile–tower structures are substantially higher than of circular structures embedded in clay layers. Moreover, the amount of rotation and displacement of square structures are not significantly affected compared to circular monopiles.

An Investigation of the Bisymmetric Hydrostatic Collapse of Flexible Pipes Based on Equivalent Layer Approaches

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
José Renato M. de Sousa ◽  
Marcelo K. Protasio ◽  
Luís Volnei S. Sagrilo ◽  
Djalene Maria Rocha
Keyword(s):  
Numerical Models ◽  
Three Dimensional ◽  
Experimental Tests ◽  
Collapse Mechanism ◽  
Fe Model ◽  
Flexible Pipe ◽  
Flexible Pipes ◽  
Dimensional Finite Element ◽  
Equivalent Ring ◽  
Three Dimensional Finite Element

Abstract The hydrostatic collapse strength of a flexible pipe is largely dependent on the ability of its carcass and/or pressure armor to resist radial loading and, therefore, its prediction involves an adequate modeling of these layers. Hence, initially, this work proposes a set of equations to estimate equivalent mechanical properties for these layers, which allows their modeling as equivalent orthotropic cylinders. Particularly, equations to predict the equivalent ring bend stiffness are obtained by simulating several two-point static ring tests with a three-dimensional finite element (FE) model based on beam elements and using these results to form datasets that are analyzed with a symbolic regression (SR) tool. The results of these analyses are the closed-form equations that best fit the provided datasets. After that, these equations are used in conjunction with a three-dimensional shell FE model (FEM) and a previously presented analytical model to study the bisymmetric hydrostatic collapse mechanism of flexible pipes. The predictions of these models agreed well with the collapse pressures obtained with numerical models and in experimental tests thus indicating the potential use of this approach in the design of flexible pipes.

Finite Element Analysis of Nonuniformity of Tires with Imperfections5

2007 ◽  
Vol 35 (3) ◽  
pp. 226-238 ◽  
Author(s):  
K. M. Jeong ◽  
K. W. Kim ◽  
H. G. Beom ◽  
J. U. Park
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Three Dimensional ◽  
Element Model ◽  
Radial Force ◽  
Element Analysis ◽  
The Finite Element Analysis ◽  
Dimensional Finite Element ◽  
Force Variation ◽  
Three Dimensional Finite Element

Abstract The effects of variations in stiffness and geometry on the nonuniformity of tires are investigated by using the finite element analysis. In order to evaluate tire uniformity, a three-dimensional finite element model of the tire with imperfections is developed. This paper considers how imperfections, such as variations in stiffness or geometry and run-out, contribute to detrimental effects on tire nonuniformity. It is found that the radial force variation of a tire with imperfections depends strongly on the geometrical variations of the tire.

Tire Modeling by Finite Elements

1992 ◽  
Vol 20 (1) ◽  
pp. 33-56 ◽  
Author(s):  
L. O. Faria ◽  
J. T. Oden ◽  
B. Yavari ◽  
W. W. Tworzydlo ◽  
J. M. Bass ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Rolling Contact ◽  
Test Problems ◽  
State Behavior ◽  
Normal Contact ◽  
New Developments ◽  
Applied Torque ◽  
Dimensional Finite Element ◽  
Tire Modeling ◽  
Three Dimensional Finite Element

Abstract Recent advances in the development of a general three-dimensional finite element methodology for modeling large deformation steady state behavior of tire structures is presented. The new developments outlined here include the extension of the material modeling capabilities to include viscoelastic materials and a generalization of the formulation of the rolling contact problem to include special nonlinear constraints. These constraints include normal contact load, applied torque, and constant pressure-volume. Several new test problems and examples of tire analysis are presented.

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