They don’t use hairspray. I’m sure it has a lot to with shear of hair. Can someone explain this, or add other pertinent physics?
I figured the air was pretty dry and the effect was due to electrostatics.
Not sure how shear stress would factor into it.
The air inside space vehicles need not be horribly dry. Low cabin humidity is typical in commercial airliners, which fly through air that is 50 or 60 degrees below zero, causing nearly all the humidity to condense out onto the interior surface of the hull. But that’s not the case for space vehicles.
Still, even with some humidity, a small electrostatic charge may be present. In the absence of gravity, that might provide the dominant force on an astronaut’s hair.
An additional influence might be the direction in which the follicle is pointing; straight hair will want to point straight out from its follicle.
One more thought: wavy or curly hair doesn’t want to lay flat to begin with, so it will be exceptionally prone to spreading out when gravity is removed.
It’s similar to hair underwater. If it is not pulled down, it will stay up. Any movement of the head downward will leave the ends of the individual hairs where they started until they get tugged along. That will work to separate the hairs over time.
I was thinking that the phenomenon could be analyzed by the “head whip” time and the resistance over the length of the hair; like the end of a snapping rope exceeding speed of sound. Here the whipping would not be planar, and that’s where I thought it was a matter of shear over the length of a single hair (and with a mane of hair I haven’t a clue how it would be modeled).
I remember when animation physics models for hair motion were coming into play. I wonder what their math was. I’ll report back.
I’m looking at pictures of astronauts in space, and just not seeing it.
Maybe I should look at someone other than Storey Musgrave.
Electrostatic would be the most dominant factor. If you could estimate the surface area wrapped around every individual hair, it’is teaming with electrons.
Remove gravity, and continued inertia will just increase the static in your hair, so that they all want to repel each other.
Hair-modelers for animation–a niche profession, with its own software packages–is undergoing a boom phase, apparently. A new Pixar movie, I think, was hyped in every science and mass-market pub this July specifically for its cutom-designed hair simulation (key to the animated star’s identity).
Some of you might be interested in the following. Friction, electrical, and structural methods run riot. I kept the full abstracts, for people who know what they mean. 
Computing Static Electricity on Human Hair
G. Sobottka A. Weber Institut für Informatik II, Universität Bonn, Germany
Abstract
We present a framework to study electrical charge phenomena on human hair. We propose a fiber based hair model which bases on the special theory of Cosserat Rods to overcome the well known difficulties one has to deal with when simple particle systems are used. We show how such models can efficiently be employed in conjunction with the fast multipole method to account for Coulomb far-field interactions. Furthermore, we extend our model such that we can account for environmental conditions.
The following are all available at Hair/Rods/Rope » Physics-Based Animation. Note that the original authors’ names are sometimes suppressed in favor of the indexer’s.
Super-Clothoids
By christopherbatty | Published April 11, 2012
Florence Bertails-Descoubes
Piecewise clothoids are 2D curves with continuous, piecewise linear curvature. Due to their smoothness properties, they have been extensively used in road design and robot path planning, as well as for the compact representation of hand-drawn curves. In this paper we present the Super-Clothoid model, a new mechanical model that for the first time allows for the computing of the dynamics of an elastic, inextensible piecewise clothoid. We first show that the kinematics of this model can be computed analytically depending on the Fresnel integrals, and precisely evaluated when required. Secondly, the discrete dynamics, naturally emerging from the Lagrange equations of motion, can be robustly and efficiently computed by performing and storing formal computations as far as possible, recoursing to numerical evaluation only when assembling the linear system to be solved at each time step. As a result, simulations turn out to be both interactive and stable, even for large displacements of the rod. Finally, we demonstrate the versatility of our model by handling various boundary conditions for the rod as well as complex external constraints such as frictional contact, and show that our model is perfectly adapted to inverse statics. Compared to lower-order models, the super-clothoid appears as a more natural and aesthetic primitive for bridging the gap between 2D geometric design and physics-based deformation.
Super-Clothoids
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A Hybrid Iterative Solver for Robustly Capturing Coulomb Friction in Hair Dynamics
By christopherbatty | Published December 5, 2011
Gilles Daviet, Florence Bertails-Descoubes, Laurence Boissieux
Dry friction between hair fibers plays a major role in the collective hair dynamic behavior as it accounts for typical nonsmooth features such as stick-slip instabilities. However, due the challenges posed by the modeling of nonsmooth friction, previous mechanical models for hair either neglect friction or use an approximate smooth friction model, thus losing important visual features. In this paper we present a new generic robust solver for capturing Coulomb friction in large assemblies of tightly packed fibers such as hair. Our method is based on an iterative algorithm where each single contact problem is efficiently and robustly solved by introducing a hybrid strategy that combines a new zero-finding formulation of (exact) Coulomb friction together with an analytical solver as a fail-safe. Our global solver turns out to be very robust and highly scalable as it can handle up to a few thousand densely packed fibers subject to tens of thousands frictional contacts at a reasonable computational cost. It can be conveniently combined to any fiber model with various rest shapes, from smooth to curly. Our results, visually validated against real hair motions, depict typical hair collective effects and greatly enhance the realism of standard hair simulators.
A Hybrid Iterative Solver for Robustly Capturing Coulomb Friction in Hair Dynamics
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Large-Scale Dynamic Simulation of Highly Constrained Strands
By christopherbatty | Published August 1, 2011
Shinjiro Sueda,Garrett L. Jones,David I. W. Levin,Dinesh K. Pai
A significant challenge in applications of computer animation is the simulation of ropes, cables, and other highly constrained strand-like physical curves. Such scenarios occur frequently, for instance, when a strand wraps around rigid bodies or passes through narrow sheaths. Purely Lagrangian methods designed for less constrained applications such as hair simulation suffer from difficulties in these important cases. To overcome this, we introduce a new framework that combines Lagrangian and Eulerian approaches. The two key contributions are the reduced node, whose degrees of freedom precisely match the constraint, and the Eulerian node, which allows constraint handling that is independent of the initial discretization of the strand. The resulting system generates robust, efficient, and accurate simulations of massively constrained systems of rigid bodies and strands.
Large-Scale Dynamic Simulation of Highly Constrained Strands
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Solid Simulation with Oriented Particles
By christopherbatty | Published May 18, 2011
We propose a new fast and robust method to simulate various types of solid including rigid, plastic and soft bodies as well as one, two and three dimensional structures such as ropes, cloth and volumetric objects. The underlying idea is to use oriented particles that store rotation and spin, along with the usual linear attributes, i.e. position and velocity. This additional information adds substantially to traditional particle methods. First, particles can be represented by anisotropic shapes such as ellipsoids, which approximate surfaces more accurately than spheres. Second, shape matching becomes robust for sparse structures such as chains of particles or even single particles because the undefined degrees of freedom are captured in the rotational states of the particles. Third, the full transformation stored in the particles, including translation and rotation, can be used for robust skinning of graphical meshes and for transforming plastic deformations back into the rest state.
Solid Simulation with Oriented Particles
Posted in Deformables, Hair/Rods/Rope, Rods, Shells | Leave a comment
A Nonsmooth Newton Solver for Capturing Exact Coulomb Friction in Fiber Assemblies
By christopherbatty | Published February 2, 2011
We focus on the challenging problem of simulating thin elastic rods in contact, in the presence of friction. Most previous approaches in computer graphics rely on a linear complementarity formulation for handling contact in a stable way, and approximate Coulombs’s friction law for making the problem tractable. In contrast, following the seminal work by Alart and Curnier in contact mechanics, we simultaneously model contact and exact Coulomb friction as azero finding problem of a nonsmooth function. A semi-implicit time-stepping scheme is then employed to discretizethe dynamics of rods constrained by frictional contact: this leads to a set of linear equations subject to an equality constraint involving a non-differentiable function. To solve this one-step problem we introduce a simple and practical nonsmooth Newton algorithm, which proves to be reasonably efficient and robust for systems that are not over-constrained. We show that our method is able to finely capture the subtle effects that occur when thin elastic rods with various geometries enter into contact, such as stick-slip instabilities in free configurations, entangling curls, resting contacts in braid-like structures, or the formation of tight knots under large constraints. Our method can be viewed as a first step towards the accurate modeling of dynamic fibrous materials.
A Nonsmooth Newton Solver for Capturing Exact Coulomb Friction in Fiber Assemblies
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Hybrid Multiresolution Wire
By christopherbatty | Published January 2, 2011
We describe a method for the visual interactive simulation of wires contacting with rigid multibodies. The physical model used is a hybrid combining lumped elements and massless quasistatic representations. The latter is based on a kinematic constraint preserving the total length of the wire along a segmented path which can involve multiple bodies simultaneously and dry frictional contact nodes used for roping, lassoing and fastening. These nodes provide stick and slide friction along edges of the contacting geometries. The lumped element resolution is adapted dynamically based on local stability criteria, becoming coarser as the tension increases, and up to the purely kinematic representation. Kinematic segments and contact nodes are added and deleted and propagated based on contact geometries and dry friction configurations. The method gives dramatic increase on both performance and robustness because it quickly decimates superfluous nodes without loosing stability, yet adapts to complex configurations with many contacts and high curvature, keeping a fixed, large integration time step. Numerical results demonstrating the performance and stability of the adaptive multiresolution scheme are presented along with an array of representative simulation examples illustrating the versatility of the frictional contact model.
Hybrid Multiresolution Wire
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Stable Inverse Dynamic Curves
By christopherbatty | Published September 17, 2010
2d animation is a traditional but fascinating domain that has recently regained popularity both in animated movies and video games. This paper introduces a method for automatically converting a smooth sketched curve into a 2d dynamic curve at stable equilibrium under gravity. The curve can then be physically animated to produce secondary motions in 2d animations or simple video games. Our approach proceeds in two steps. We first present a new technique to fit a smooth piecewise circular arcs curve to a sketched curve. Then we show how to compute the physical parameters of a dynamic rod model (super-circle) so that its stable rest shape under gravity exactly matches the fitted circular arcs curve. We demonstrate the interactivity and controllability of our approach on various examples where a user can intuitively setup efficient and precise 2d animations by specifying the input geometry.
Stable Inverse Dynamic Curves
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Discrete Viscous Threads
By christopherbatty | Published May 26, 2010
We present a continuum-based discrete model for thin threads of viscous fluid by drawing upon the Rayleigh analogy to elastic rods, demonstrating canonical coiling, folding, and breakup in dynamic simulations. Our derivation emphasizes space-time symmetry, which sheds light on the role of time-parallel transport in eliminating — without approximation — all but an O(n) band of entries of the physical system’s energy Hessian. The result is a fast, unified, implicit treatment of viscous threads and elastic rods that closely reproduces a variety of fascinating physical phenomena, including hysteretic transitions between coiling regimes, competition between surface tension and gravity, and the first numerical fluid-mechanical sewing machine. The novel implicit treatment also yields an order of magnitude speedup in our elastic rod dynamics.
Discrete Viscous Threads
Unified Simulation of Elastic Rods, Shells, and Solids
By christopherbatty | Published May 5, 2010
We develop an accurate, unified treatment of elastica. Following the method of resultant-based formulation to its logical extreme, we derive a higher-order integration rule, or elaston, measuring stretching, shearing, bending, and twisting along any axis. The theory and accompanying implementation do not distinguish between forms of different dimension (solids, shells, rods), nor between manifold regions and non-manifold junctions. Consequently, a single code accurately models a diverse range of elastoplastic behaviors, including buckling, writhing, cutting and merging. Emphasis on convergence to the continuum sets us apart from early unification efforts.
Unified Simulation of Elastic Rods, Shells, and Solids
Linear Time Super-Helices
By christopherbatty | Published January 15, 2009
Thin elastic rods such as cables, phone coils, tree branches, or hair, are common objects in the real world but computing their dynamics accurately remains challenging. The recent Super-Helix model, based on the discrete equations of Kirchhoff for a piecewise helical rod, is one of the most promising models for simulating non-stretchable rods that can bend and twist. However, this model suffers from a quadratic complexity in the number of discrete elements, which, in the context of interactive applications, makes it limited to a few number of degrees of freedom – or equivalently to a low number of variations in curvature along the mean curve. This paper proposes a new, recursive scheme for the dynamics of a Super-Helix, inspired by the popular algorithm of Featherstone for serial multibody chains. Similarly to Featherstone’s algorithm, we exploit the recursive kinematics of a Super-Helix to propagate elements inertias from the free end to the clamped end of the rod, while the dynamics is solved within a second pass traversing the rod in the reverse way. Besides the gain in linear complexity, which allows us to simulate a rod of complex shape much faster than the original approach, our algorithm makes it straightforward to simulate tree-like structures of Super-Helices, which turns out to be particularly useful for animating trees and plants realistically, under large displacements.
Linear Time Super-Helices
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Actually, these abstracts make perfect sense as abstracts. I would be interested in any comments any of you might have on the formal paper, especially as to any (trivial?) issues with microgravity.
The “viscous strands” paper would be good for those underwater analogues. How close is the analogue to OP? (I did understand the thrust of that post, nonetheless.) And I always wanted an underwater sewing machine.
Plus they have neat images and video.