scholarly journals Analytical study for swimmers in a channel

2019 ◽  
Vol 881 ◽  
pp. 365-383 ◽  
Author(s):  
A. Farutin ◽  
H. Wu ◽  
W.-F. Hu ◽  
S. Rafaï ◽  
P. Peyla ◽  
...  
Keyword(s):  
Swimming Speed ◽  
Mammalian Cells ◽  
Analytical Study ◽  
Order Effect ◽  
Numerical Results ◽  
Normal Velocity ◽  
Numerical Studies ◽  
Geometric Confinement ◽  
Amoeboid Motion ◽  
Shape Changes

There is an overabundance of microswimmers in nature, including bacteria, algae, mammalian cells and so on. They use flagellum, cilia or global shape changes (amoeboid motion) to move forward. In the presence of confining channels, these swimmers exhibit often non-trivial behaviours, such as accumulation at the wall, navigation and so on, and their swimming speed may be strongly influenced by the geometric confinement. Several numerical studies have reported that the presence of walls either enhances or reduces the swimming speed depending on the nature of the swimmer, and also on the confinement. The purpose of this paper is to provide an analytical explanation of several previously obtained numerical results. We treat the case of amoeboid swimmers and the case of squirmers having either a tangential (the classical situation) or normal velocity prescribed at the swimmer surface (pumper). For amoeboid motion we consider a quasi-circular swimmer which allows us to tackle the problem analytically and to extract the equations of the motion of the swimmer, with several explicit analytical or semi-analytical solutions. It is found that the deformation of the amoeboid swimmer as well as a high enough order effect due to confinement are necessary in order to account for previous numerical results. The analytical theory accounts for several features obtained numerically also for non-deformable swimmers.

scholarly journals A robotic crawler exploiting directional frictional interactions: experiments, numerics and derivation of a reduced model

2014 ◽  
Vol 470 (2171) ◽  
pp. 20140333 ◽  
Author(s):  
Giovanni Noselli ◽  
Antonio DeSimone
Keyword(s):  
Numerical Simulations ◽  
Solid Substrate ◽  
Numerical Results ◽  
Reduced Model ◽  
Shape Changes

We present experimental and numerical results for a model crawler which is able to extract net positional changes from reciprocal shape changes, i.e. ‘breathing-like’ deformations, thanks to directional, frictional interactions with a textured solid substrate, mediated by flexible inclined feet. We also present a simple reduced model that captures the essential features of the kinematics and energetics of the gait, and compare its predictions with the results from experiments and from numerical simulations.

scholarly journals Liquid interfaces in viscous straining flows: numerical studies of the selective withdrawal transition

2008 ◽  
Vol 613 ◽  
pp. 171-203 ◽  
Author(s):  
MARKO KLEINE BERKENBUSCH ◽  
ITAI COHEN ◽  
WENDY W. ZHANG
Keyword(s):  
Steady State ◽  
Dynamic Range ◽  
Model Problem ◽  
Numerical Results ◽  
Experimental Measurements ◽  
Liquid Interfaces ◽  
Selective Withdrawal ◽  
Interface Evolution ◽  
Numerical Studies ◽  
Good Agreement

This paper presents a numerical analysis of the transition from selective withdrawal to viscous entrainment. In our model problem, an interface between two immiscible layers of equal viscosity is deformed by an axisymmetric withdrawal flow, which is driven by a point sink located some distance above the interface in the upper layer. We find that steady-state hump solutions, corresponding to selective withdrawal of liquid from the upper layer, cease to exist above a threshold withdrawal flux, and that this transition corresponds to a saddle-node bifurcation for the hump solutions. Numerical results on the shape evolution of the steady-state interface are compared against previous experimental measurements. We find good agreement where the data overlap. However, the larger dynamic range of the numerical results allows us to show that the large increase in the curvature of the hump tip near transition is not consistent with an approach towards a power-law cusp shape, an interpretation previously suggested from inspection of the experimental measurements alone. Instead, the large increase in the curvature at the hump tip reflects a robust trend in the steady-state interface evolution. For large deflections, the hump height is proportional to the logarithm of the curvature at the hump tip; thus small changes in hump height correspond to large changes in the value of the hump curvature.

Numerical Studies of the Influence of Heterogeneity on Rock Failure and Induced Earthquake Precursors

2005 ◽  
Vol 297-300 ◽  
pp. 2648-2653
Author(s):  
Ming Ruo Jiao ◽  
Chun An Tang ◽  
W.F. Sun ◽  
Shu Hong Wang
Keyword(s):  
Numerical Simulations ◽  
Rock Failure ◽  
Earthquake Precursors ◽  
Numerical Results ◽  
Mechanical Heterogeneity ◽  
Induced Earthquake ◽  
Numerical Studies ◽  
Good Agreement

A series of numerical simulations were performed to investigate the effects of geometric and mechanical heterogeneity of pre-existing faults of rocks on their failure and induced earthquake precursors. The numerical results revealed that rock failures with the different heterogeneity produce the different earthquake precursors, which are in a good agreement with those of observations in nature.

Numerical Studies of the Periodically Forced Bonhoeffer van der Pol System

1997 ◽  
Vol 07 (12) ◽  
pp. 2653-2689 ◽  
Author(s):  
Belinda Barnes ◽  
Roger Grimshaw
Keyword(s):  
Parameter Space ◽  
Chaotic Behavior ◽  
Physiological Model ◽  
Numerical Results ◽  
System Behavior ◽  
Dimensional Representation ◽  
Van Der Pol ◽  
Numerical Studies ◽  
Fixed Parameter ◽  
General Parameter

The Bonhoeffer van der Pol system, with an applied constant forcing, was invoked by Fitzhugh [1961] as a two-dimensional representation of the four-dimensional Hodgkin–Huxley system [1952], a well-known physiological model representing the electrical behavior across a nerve membrane. The system has been analyzed within a particular parameter regime relevant to the physiology (see [Fitzhugh, 1961]) and for the full parameter space with emphasis on the prediction of periodic solutions (see [Barnes & Grimshaw, 1995]). In this paper the system is considered with a time dependent sinusoidal forcing term in which form it represents a nonlinear, nonautonomous system of differential equations with five parameters. The study is motivated by physiological experiments with neurons subjected to periodic stimuli (see, e.g. [Hayashi et al., 1982]). A few aspects pertaining to the system behavior have been explored by others for particular fixed parameter combinations (and with different purposes from those here), for example [Wang, 1989; Rajasekar & Lakshmanan, 1988, 1993; Yasin et al., 1993; Braaksma & Grasman, 1993; Rabinovitch et al., 1994]). In this paper we present the numerical results of simulations for a more general parameter space and propose theoretical interpretations for a broad range of the behavior states incurred. Further, we present numerical results describing how the system dynamics change as each of the five parameters is varied, and thus predict regions where periodic, quasiperiodic or chaotic behavior can be expected.

HOPF BIFURCATIONS AND THEIR DEGENERACIES IN CHUA'S EQUATION

2011 ◽  
Vol 21 (09) ◽  
pp. 2749-2763 ◽  
Author(s):  
ANTONIO ALGABA ◽  
MANUEL MERINO ◽  
FERNANDO FERNÁNDEZ-SÁNCHEZ ◽  
ALEJANDRO J. RODRÍGUEZ-LUIS
Keyword(s):  
Analytical Study ◽  
Numerical Results ◽  
Hopf Bifurcations ◽  
Codimension Two ◽  
Strong Agreement

We perform an analytical study of the Hopf bifurcations and their degeneracies in Chua's equation. In the case of the equilibrium at the origin only codimension-two Hopf bifurcations appear. However, for the nontrivial equilibria we prove the existence of codimension-three Hopf bifurcations. Numerical results are in strong agreement with the analytical ones.

Thermal Radiation in Laminar Boundary Layers on Continuous Moving Surfaces

1974 ◽  
Vol 96 (1) ◽  
pp. 32-36 ◽  
Author(s):  
C. A. Rhodes ◽  
C. C. Chen
Keyword(s):  
Heat Transfer ◽  
Thermal Radiation ◽  
Boundary Layers ◽  
Analytical Study ◽  
Radiation Flux ◽  
Radiation Heat Transfer ◽  
Normal Velocity ◽  
Radiation Heat ◽  
Flat Plates ◽  
Laminar Boundary Layers

Thermal radiation heat transfer is studied in boundary layers on continuous moving surfaces. An analytical study is performed for two-dimensional laminar flow of an absorbing and emitting fluid. Solutions were obtained for limiting conditions of optically thin and thick boundary layers. Comparisons indicate that the radiation flux in these boundary layers is less than that for flow over semi-infinite flat plates for optically thin flows. The radiation contribution becomes more nearly equal as optical thickness increases. The normal velocity induced in the free stream by the wall motion significantly affects the radiation heat transfer.

Numerical Analysis and Experimental Validation of Added Resistance on Ship in Waves

2019 ◽  
Vol 63 (4) ◽  
pp. 268-282
Author(s):  
Yonghwan Kim ◽  
Dong-Min Park ◽  
Jae-Hoon Lee ◽  
Jaehoon Lee ◽  
Byung-Soo Kim ◽  
...  
Keyword(s):  
Momentum Conservation ◽  
Numerical Results ◽  
Added Resistance ◽  
Irregular Wave ◽  
Numerical Studies ◽  
Motion Responses ◽  
Calm Water ◽  
National University ◽  
The Difference ◽  
Seoul National University

In this study, the added resistance of a liquefied natural gas carrier (LNGC) in the presence of waves is studied experimentally and numerically.The ship model is an LNGC designed by Samsung Heavy Industries (SHI). Experiments on ship motion responses and added resistance under head sea conditions were conducted at the Seoul National University and SHI. The influences of the experimental methods (captive and self-propulsion methods), incident wave amplitude, and regular and irregular wave conditions on the added resistance are evaluated using the same model ship set at different scales. In the numerical studies, the motion responses and added resistance are obtained using three methods—the strip method by adopting momentum conservation; Rankine panel method using pressure integration; and computational fluid dynamics method, using the difference in the resistances in waves and calm water. The experimental and numerical results under various conditions are compared, and the characteristics of the experimental and numerical results are discussed.

scholarly journals Configurational entropy measurements in extremely supercooled liquids that break the glass ceiling

2017 ◽  
Vol 114 (43) ◽  
pp. 11356-11361 ◽  
Author(s):  
Ludovic Berthier ◽  
Patrick Charbonneau ◽  
Daniele Coslovich ◽  
Andrea Ninarello ◽  
Misaki Ozawa ◽  
...  
Keyword(s):  
Glass Transition ◽  
Glass Ceiling ◽  
In Silico ◽  
Configurational Entropy ◽  
Supercooled Liquids ◽  
Numerical Results ◽  
Computational Tools ◽  
Experimental Glass ◽  
Glass State ◽  
Numerical Studies

Liquids relax extremely slowly on approaching the glass state. One explanation is that an entropy crisis, because of the rarefaction of available states, makes it increasingly arduous to reach equilibrium in that regime. Validating this scenario is challenging, because experiments offer limited resolution, while numerical studies lag more than eight orders of magnitude behind experimentally relevant timescales. In this work, we not only close the colossal gap between experiments and simulations but manage to create in silico configurations that have no experimental analog yet. Deploying a range of computational tools, we obtain four estimates of their configurational entropy. These measurements consistently confirm that the steep entropy decrease observed in experiments is also found in simulations, even beyond the experimental glass transition. Our numerical results thus extend the observational window into the physics of glasses and reinforce the relevance of an entropy crisis for understanding their formation.

Numerical studies of cusp formation at fluid interfaces in Stokes flow

1998 ◽  
Vol 357 ◽  
pp. 29-57 ◽  
Author(s):  
C. POZRIKIDIS
Keyword(s):  
Surface Tension ◽  
Stokes Flow ◽  
Boundary Integral ◽  
Numerical Results ◽  
Boundary Integral Method ◽  
Fluid Interfaces ◽  
Two Dimensional ◽  
Numerical Studies ◽  
Insoluble Surfactant ◽  
Cusp Formation

Numerical studies are performed addressing the development of regions of high curvature and the spontaneous occurrence of cusped interfacial shapes in two-dimensional and axisymmetric Stokes flow. In the numerical simulations, the velocity field is computed using a boundary-integral method, and the evolution of the concentration of an insoluble surfactant over an evolving interface is computed using an implicit finite-volume method. Three configurations are considered in detail, and the results are used to elucidate three different aspects of cusp formation. In the first series, the deformation of a two-dimensional bubble immersed in a family of straining flows devised by Antanovskii, and of an axisymmetric bubble immersed in an analogous family of flows devised by Sherwood, are examined. The numerical results indicate that highly elongated and cusped two-dimensional shapes, and pointed or cusped axisymmetric shapes, are unstable and should not be expected to occur in practice. In the second series of studies, the role of an insoluble surfactant on the transient deformation of bubbles subject to the Antanovskii or Sherwood flow is investigated. Under certain conditions, the reduced surface tension at the tips raises the local curvature to high values and causes the ejection of a sheet or column of gas by means of tip streaming. In the third series of studies, the coalescence of a polygonal formation of five viscous columns of a fluid placed in an arrangement that differs only slightly from one proposed recently by Richardson is examined. The numerical results confirm Richardson's predictions that transient cusps may occur at a finite time in the presence of surface tension. The underlying physical mechanism is discussed on the basis of reversibility of surface-driven Stokes flow and with reference to the regularity of the motion driven by negative surface tension. Replacing the inviscid ambient gas with a slightly viscous fluid whose viscosity is as low as one hundredth the viscosity of the cylinders suppresses the cusp formation.

Investigation on trim control of semi-planing amphibious cargo truck using experimental and numerical approaches

2021 ◽  
pp. 095440622110214
Author(s):  
Chengliang Sun ◽  
Xiaojun Xu ◽  
Tengan Zou
Keyword(s):  
Experimental Tests ◽  
Numerical Results ◽  
Maximum Speed ◽  
Key Indicator ◽  
Numerical Studies ◽  
Resistance Reduction ◽  
Speed Up ◽  
Good Agreement ◽  
Numerical Approaches

Speed on water is a key indicator of amphibious vehicles. However, due to the inherent non-streamlined configuration, when reaching a certain velocity, the resistance acting on the vehicle hull is so large and the maximum speed on water is hard to be further enhanced. Moreover, the trim gets so larger that leads the stern submerged into water when speed up. In order to solve this problem of a semi-planing amphibious cargo truck, this paper proposed a method by installing interceptors, hydrofoils, and combination of them on the stern. Experimental tests and numerical studies were performed respectively, and the numerical results were in good agreement with experiment. In what continues, the effect of interceptors, hydrofoils, and combination of them on trim and resistance was investigated. The results showed that the interceptor had a better effect than hydrofoil when height is not so big, but the effect got more and more powerful with interceptor height increasing, finally lead to an excessive trim control. Combination of interceptor with hydrofoil in suitable size were beneficial to trim control and resistance reduction.

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