scholarly journals Buckling of elastic fibers in a shear flow

2021 ◽  
Author(s):  
Agnieszka M. Slowicka ◽  
Nan Xue ◽  
Pawel Sznajder ◽  
Janine K Nunes ◽  
Howard A Stone ◽  
...  
Keyword(s):  
Shear Flow ◽  
Flow Direction ◽  
Three Dimensional ◽  
Shear Plane ◽  
Elastic Fibers ◽  
Small Range ◽  
Qualitative Comparison ◽  
Flow Vorticity ◽  
Flexible Fibers ◽  
Long Time

Abstract Three-dimensional dynamics of flexible fibers in shear flow are studied numerically, with a qualitative comparison to experiments. Initially, the fibers are straight, with different orientations with respect to the flow. By changing the rotation speed of a shear rheometer, we change the ratio A of bending to shear forces. We observe fibers in the flow-vorticity plane, which gives insight into the motion out of the shear plane. The numerical simulations of moderately flexible fibers show that they rotate along effective Jeffery orbits, and therefore the fiber orientation rapidly becomes very close to the flow-vorticity plane, on average close to the flow direction, and the fiber remains in an almost straight configuration for a long time. This ``ordering'' of fibers is temporary since they alternately bend and straighten out while tumbling. We observe numerically and experimentally that if the fibers are initially in the compressional region of the shear flow, they can undergo a compressional buckling, with a pronounced deformation of shape along their whole length during a short time, which is in contrast to the typical local bending that originates over a long time from the fiber ends. We identify differences between local and compressional bending and discuss their competition, which depends on the initial orientation of the fiber and the bending stiffness ratio A. There are two main finding. First, the compressional buckling is limited to a certain small range of the initial orientations, excluding those from the flow-vorticity plane. Second, since fibers straighten out in the flow-vorticity plane while tumbling, the compressional buckling is transient - it does not appear for times longer than 1/4 of the Jeffery period. For larger times, bending of fibers is always driven by their ends.

Off-plane motion of a prolate capsule in shear flow

2013 ◽  
Vol 721 ◽  
pp. 180-198 ◽  
Author(s):  
C. Dupont ◽  
A.-V. Salsac ◽  
D. Barthès-Biesel
Keyword(s):  
Shear Flow ◽  
Capillary Number ◽  
Three Dimensional ◽  
Shear Plane ◽  
Plane Motion ◽  
Boundary Integral ◽  
Boundary Integral Method ◽  
Simple Shear Flow ◽  
Flow Vorticity ◽  
Wall Deformation

AbstractThe objective of this study is to investigate the motion of an ellipsoidal capsule in a simple shear flow when its revolution axis is initially placed off the shear plane. We consider prolate capsules with an aspect ratio of two or three enclosed by a membrane, which is either strain-hardening or strain-softening. We seek the equilibrium motion of the capsule as we increase the capillary number$\mathit{Ca}$, which measures the ratio between the viscous and elastic forces. The three-dimensional fluid–structure interaction problem is solved numerically by coupling a boundary integral method (for the internal and external flows) with a finite element method (for the wall deformation). For any initial inclination with the flow vorticity axis, a given capsule converges towards a unique equilibrium configuration which depends on$\mathit{Ca}$. At low capillary number, the stable equilibrium motion is the rolling regime: the capsule aligns its long axis with the vorticity axis, while the membrane tank-treads. As$\mathit{Ca}$increases, the capsule takes a complex wobbling motion at equilibrium, precessing around the vorticity axis. As$\mathit{Ca}$is further increased, the capsule long axis oscillates about the shear plane, while the membrane rotates around a capsule cross-section that also oscillates over time (oscillating–swinging regime). The amplitude of the oscillations about the shear plane decreases as$\mathit{Ca}$increases and the capsule finally takes a swinging motion in the shear plane. It is found that the transitions from rolling to wobbling and from wobbling to oscillating–swinging depend on the mean energy stored in the membrane.

The long-time behaviour of incompressible swept-wing boundary layers subject to impulsive forcing

1998 ◽  
Vol 355 ◽  
pp. 359-381 ◽  
Author(s):  
M. J. TAYLOR ◽  
N. PEAKE
Keyword(s):  
Boundary Layer ◽  
Flow Direction ◽  
Three Dimensional ◽  
Cross Flow ◽  
Leading Edge ◽  
Rotating Disk ◽  
Linear Stability Theory ◽  
Swept Wing ◽  
Long Time ◽  
Layer Flow

The long-time limit of the response of incompressible three-dimensional boundary layer flows on infinite swept wedges and infinite swept wings to impulsive forcing is examined using causal linear stability theory. Following the discovery by Lingwood (1995) of the presence of absolute instabilities caused by pinch points occurring in the radial direction in the boundary layer flow of a rotating disk, we search for pinch points in the cross flow direction for both the model Falkner–Skan–Cooke profile of a swept wedge and for a genuine swept-wing configuration. It is shown in both cases that, within a particular range of the parameter space, the boundary layer does indeed support pinch points in the wavenumber plane corresponding to the crossflow direction. These crossflow-induced pinch points do not constitute an absolute instability, as there is no simultaneous pinch occurring in the streamwise wavenumber plane, but nevertheless we show here how they can be used to find the maximum local growth rate contained in a wavepacket travelling in any given direction. Lingwood (1997) also found pinch points in the chordwise wavenumber plane in the boundary layer of the leading-edge region of a swept wing (i.e. at very high flow angles). The results presented in this paper, however, demonstrate the presence of pinch points for a much larger range of flow angles and pressure gradients than was found by Lingwood, and indeed describe the flow over a much greater, and practically significant, portion of the wing.

Simiple Shear Flow of a Non-Aligning Nematic

1991 ◽  
Vol 248 ◽  
Author(s):  
W. H. Han ◽  
A. D. Rey
Keyword(s):  
Liquid Crystal ◽  
Numerical Analysis ◽  
Shear Flow ◽  
Three Dimensional ◽  
Shear Plane ◽  
Stationary Solutions ◽  
Secondary Flows ◽  
Simple Shear Flow ◽  
Continuous Transition ◽  
Discontinuous Transition

AbstractThis paper presents a nonlinear numerical analysis of the orientational instabilites, textures, and flow patterns of a characteristic rod-like nematic liquid crystal in steady simple shear flow. The parameter vector V=(λ,E) is given by the reactive parameter (λ) and the Ericksen number (E). There are two stationary solutions: in-plane(IP) and out-of-shear-plane(OP), according to whether the average orientation lies in or out of the plane of shear. For a given λ the in-plane stationary solutions may undergo a continuous transition (second order) to two dissipatively equivalent OP solutions when E=Eo or a discontinuous transition (first order) to a highly distorted IP solution when E=Ei. The continuous transition at E=Eo is a supercritical (pitchfork) bifurcation and the discontinuous transition at E=Ei is a limit point instability. Nonlinear numerical analysis shows that for the studied liquid crystal Eo < Ei. The orientation phase diagram for stable stationary solutions therefore consist of a region of OP solutions separated from a region of IP solutions by the curve Vo = (λ,Eo), describing a set of continuous supercritical bifurcations. These stable OP solutions are characterzied by the absence of sharp splay and bend deformations and by the presence of complex secondary flows arising from the three dimensional orientation. Presented results also include the dependence of the three dimensional texture, primary and secondary velocity fields on E.

Predictive Cutting Force Model and Cutting Force Chart for Milling with Cutter Axis Inclination

2013 ◽  
Vol 7 (1) ◽  
pp. 30-38 ◽  
Author(s):  
Takashi Matsumura ◽  
◽  
Motohiro Shimada ◽  
Kazunari Teramoto ◽  
Eiji Usui ◽  
...  
Keyword(s):  
Cutting Force ◽  
Cutting Forces ◽  
Flow Direction ◽  
Three Dimensional ◽  
Shear Plane ◽  
Cutting Parameters ◽  
Force Model ◽  
Chip Flow ◽  
Inclination Angles ◽  
Cutting Model

A force model for milling with cutter axis inclination is presented. The model predicts the cutting force and chip flow direction. Three-dimensional chip flow is interpreted as a piling up of the orthogonal cuttings in the planes containing the cutting velocities and the chip flow velocities in the inclined coordinate system with a ball end mill. The chip flow direction is determined to minimize the cutting energy consumed into the shear energy on the shear plane and the friction energy on the rake face. Then, the cutting force is predicted in the chip flow determined model. The presented cutting model is verified by comparing the predicted cutting forces to the measured forces in the actual cutting tests. As an advantage of the presented force model, the change in the chip flow direction during one rotation of the cutter is also predicted in the simulation for the cutter axis inclination and the cutting parameters. In the simulation, the effect of cutter axis inclination on the cutting process is discussed in terms of the tool wear and surface finish. The cutting force charts, in which the maximum values of the positive and the negative cutting forces are simulated for the inclination angles, are presented to review the cutter axis inclination. The applicable cutter axis inclination can be determined by taking into account the thresholds of the cutting force components.

scholarly journals Simulation of Flexible Fibre Particle Interaction with a Single Cylinder

Processes ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 191
Author(s):  
Naser Hamedi ◽  
Lars-Göran Westerberg
Keyword(s):  
Reynolds Number ◽  
Shear Flow ◽  
Fibre Orientation ◽  
Flow Direction ◽  
Particle Interaction ◽  
Orientation Angle ◽  
Factors Affecting ◽  
Single Cylinder ◽  
Flow Past ◽  
Fibre Suspension

In the present study, the flow of a fibre suspension in a channel containing a cylinder was numerically studied for a very low Reynolds number. Further, the model was validated against previous studies by observing the flexible fibres in the shear flow. The model was employed to simulate the rigid, semi-flexible, and fully flexible fibre particle in the flow past a single cylinder. Two different fibre lengths with various flexibilities were applied in the simulations, while the initial orientation angle to the flow direction was changed between 45° ≤ θ ≤ 75°. It was shown that the influence of the fibre orientation was more significant for the larger orientation angle. The results highlighted the influence of several factors affecting the fibre particle in the flow past the cylinder.

Effects of Velvet Antler Polypeptide-Collagen/Chitosan Materials on Proliferation of Osteoblast

2013 ◽  
Vol 380-384 ◽  
pp. 4295-4298
Author(s):  
Wen He Zhu ◽  
Jun Jie Xu ◽  
Wei Zhang ◽  
Yan Li ◽  
Xiao Jing Lu ◽  
...  
Keyword(s):  
Drug Treatment ◽  
Bone Defect ◽  
Three Dimensional ◽  
Chitosan Scaffold ◽  
Release Drug ◽  
Dimensional Network ◽  
Velvet Antler ◽  
Result Show ◽  
Long Time ◽  
Velvet Antler Polypeptide

A highly osteogenic hybrid bioabsorbable scaffold was developed for bone reconstruction. Though the use of a bioabsorbable collagen and chitosan scaffold for loading velvet antler polypeptide to repair bone defect and drug treatment. Velvet antler polypeptide and collagen were extracted for developing the compounded material. The SEM results show that the collagen and chitosan scaffold maintain the natural three dimensional network structures. The cell proliferation experiment result show that the can promote the osteoblast proliferation for a long time . These results indicated that this compound scaffold can sustainable to release drug and is a good material in bone defect and drug treatment.

Research on cargo-loading optimization based on genetic and fuzzy integration

2021 ◽  
Vol 40 (4) ◽  
pp. 8493-8500
Author(s):  
Yanwei Du ◽  
Feng Chen ◽  
Xiaoyi Fan ◽  
Lei Zhang ◽  
Henggang Liang
Keyword(s):  
Genetic Algorithm ◽  
Mathematical Model ◽  
Three Dimensional ◽  
Distribution Center ◽  
Long Time ◽  
Low Efficiency ◽  
Decision Making Model ◽  
The Mathematical Model ◽  
Loading Scheme

With the increase of the number of loaded goods, the number of optional loading schemes will increase exponentially. It is a long time and low efficiency to determine the loading scheme with experience. Genetic algorithm is a search heuristic algorithm used to solve optimization in the field of computer science artificial intelligence. Genetic algorithm can effectively select the optimal loading scheme but unable to utilize weight and volume capacity of cargo and truck. In this paper, we propose hybrid Genetic and fuzzy logic based cargo-loading decision making model that focus on achieving maximum profit with maximum utilization of weight and volume capacity of cargo and truck. In this paper, first of all, the components of the problem of goods stowage in the distribution center are analyzed systematically, which lays the foundation for the reasonable classification of the problem of goods stowage and the establishment of the mathematical model of the problem of goods stowage. Secondly, the paper abstracts and defines the problem of goods loading in distribution center, establishes the mathematical model for the optimization of single car three-dimensional goods loading, and designs the genetic algorithm for solving the model. Finally, Matlab is used to solve the optimization model of cargo loading, and the good performance of the algorithm is verified by an example. From the performance evaluation analysis, proposed the hybrid system achieve better outcomes than the standard SA model, GA method, and TS strategy.

scholarly journals Study of the Effect of Centrifugal Force on Rotor Blade Icing Process

2017 ◽  
Vol 2017 ◽  
pp. 1-9 ◽  
Author(s):  
Zhengzhi Wang ◽  
Chunling Zhu
Keyword(s):  
Numerical Simulation ◽  
Centrifugal Force ◽  
Rotor Blade ◽  
Flow Direction ◽  
Three Dimensional ◽  
Simulation Method ◽  
Two Phase ◽  
Numerical Simulation Method ◽  
Calculation Results ◽  
Flow Field Characteristics

In view of the rotor icing problems, the influence of centrifugal force on rotor blade icing is investigated. A numerical simulation method of three-dimensional rotor blade icing is presented. Body-fitted grids around the rotor blade are generated using overlapping grid technology and rotor flow field characteristics are obtained by solving N-S equations. According to Eulerian two-phase flow, the droplet trajectories are calculated and droplet impingement characteristics are obtained. The mass and energy conservation equations of ice accretion model are established and a new calculation method of runback water mass based on shear stress and centrifugal force is proposed to simulate water flow and ice shape. The calculation results are compared with available experimental results in order to verify the correctness of the numerical simulation method. The influence of centrifugal force on rotor icing is calculated. The results show that the flow direction and distribution of liquid water on rotor surfaces change under the action of centrifugal force, which lead to the increasing of icing at the stagnation point and the decreasing of icing on both frozen limitations.

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