Related Experiment Video
Updated: Oct 21, 2025
06:42
Magnetically Induced Rotating Rayleigh-Taylor Instability
Published on: March 3, 2017
9.8K
Origin of the Sharkskin Instability: Nonlinear Dynamics.
Stylianos Varchanis1,2, Dionisis Pettas1, Yannis Dimakopoulos1
1Laboratory of Fluid Mechanics & Rheology, Department of Chemical Engineering, University of Patras, Patras 26500, Greece.
Physical Review Letters
|September 3, 2021
Summary
Surface distortions, or sharkskin instability, in polymer extrusion arise from polymer chain stretching and recoil. A physical model explains this transition to elastic turbulence through a series of bifurcations.
Area of Science:
- Polymer Science and Rheology
- Fluid Dynamics
Background:
- Sharkskin instability is a prevalent surface defect in polymer melt extrusion.
- Understanding its origin is crucial for controlling extrudate quality.
Purpose of the Study:
- To develop a physical model explaining the onset of sharkskin instability.
- To link surface defects to polymer chain dynamics and flow bifurcations.
Main Methods:
- Development of a simple physical model for polymer melt extrusion.
- Analysis of polymer chain stretching and recoil at the die exit.
- Mathematical modeling of the transition to elastic turbulence via bifurcations.
Main Results:
- The model links sharkskin inception to intense polymer chain stretch and recoil.
- A Hopf bifurcation marks the transition from smooth to wavy extrudates.
- Period doubling bifurcations lead to elastic turbulence under creeping flow.
Conclusions:
- The proposed physical model successfully predicts sharkskin instability.
- The findings provide a theoretical framework for understanding and potentially mitigating surface defects in polymer extrusion.
Related Concept Videos
02:17Microtubule Instability
5.4K
Microtubules are hollow cylindrical filaments having a diameter of approximately 25 nm and a length that varies from 200 nm to 25 μm. GTP-bound tubulin subunits form αβ-heterodimers for microtubule assembly. These core building blocks interact longitudinally, polymerizing into protofilaments. The protofilaments then interact with one another through lateral bonding forces to form stable cylindrical microtubules. These cylindrical filaments are dynamic as they undergo repeated...
5.4K
01:28Navier–Stokes Equations
987
For incompressible Newtonian fluids, where density remains constant, stresses show a linear relationship with the deformation rate, defined by normal and shear stresses. Normal stresses depend on the pressure exerted on the fluid and the rate of deformation in specific directions, which determines how fluid flows under varying pressures. Shear stresses, on the other hand, act tangentially across fluid layers. They explain how adjacent fluid layers slide relative to one another, connecting...
987
01:23Stability of Equilibrium Configuration
577
Understanding the stability of equilibrium configurations is a fundamental part of mechanical engineering. In any system, there are three distinct types of equilibrium: stable, neutral, and unstable.
A stable equilibrium occurs when a system tends to return to its original position when given a small displacement, and the potential energy is at its minimum. An example of a stable equilibrium is when a cantilever beam is fixed at one end and a weight is attached to the other end. If the weight...
A stable equilibrium occurs when a system tends to return to its original position when given a small displacement, and the potential energy is at its minimum. An example of a stable equilibrium is when a cantilever beam is fixed at one end and a weight is attached to the other end. If the weight...
577
01:04Oscillations about an Equilibrium Position
5.9K
Stability is an important concept in oscillation. If an equilibrium point is stable, a slight disturbance of an object that is initially at the stable equilibrium point will cause the object to oscillate around that point. For an unstable equilibrium point, if the object is disturbed slightly, it will not return to the equilibrium point. There are three conditions for equilibrium points—stable, unstable, and half-stable. A half-stable equilibrium point is also unstable, but is named so...
5.9K
01:14Stability of structures
283
In mechanical engineering, the stability of systems under various forces is critical for designing durable and efficient structures. One fundamental way to explore these concepts is by analyzing systems like two rods connected at a pivot point, O, with a torsional spring of spring constant k at the pivot point. This system is similar in appearance to a scissor jack used to change tires on a car. In this case, the arms of the linkage (equivalent to the rods in this system) are entirely vertical,...
283
01:24Pole and System Stability
516
The transfer function is a fundamental concept representing the ratio of two polynomials. The numerator and denominator encapsulate the system's dynamics. The zeros and poles of this transfer function are critical in determining the system's behavior and stability.
Simple poles are unique roots of the denominator polynomial. Each simple pole corresponds to a distinct solution to the system's characteristic equation, typically resulting in exponential decay terms in the system's...
Simple poles are unique roots of the denominator polynomial. Each simple pole corresponds to a distinct solution to the system's characteristic equation, typically resulting in exponential decay terms in the system's...
516