Flexible Fiber Model Reference

A bond is formed with two springs with normal stiffness $k_{n} = E A / L$ and bending stiffness $k_{b} = E I / L$ , where:

$E$ is Young’s modulus.
$A$ is cross section area.
$I$ is the second moment of area.
$L$ is the length of each segment.

The Flexible Fiber model is an alternative to modeling fibers by building clumps as strings of spheres, or using long cylinders for rigid fibers. The Flexible Fiber model can use fewer elements and is more efficient computationally, since it saves the effort spent calculating the contact between the spheres forming the fiber.

To make the fibers breakable, select the Simple Failure, Constant Rate Damage, or Impact Cutting model. With the Simple Failure model, the bond breaks if the tensile or shear stresses between particles exceed specified limits. With the Constant Rate Damage model, the undamaged bond begins to fail if tensile stress exceeds the specified limit and breaks when enough breaking work (proportional to softening rate) goes into the bond. With the Impact Cutting model, the fiber breaks when user-specified breakage criteria are met. When the bond breaks, the effect of the other selected phase interaction models is gradually introduced until full separation between segments is achieved.

Reports, plots, and XYZ internal tables treat all segments of a fiber identically. Each segment is a DEM particle.


Provided By	[phase] > Models > Particle Shape
Example Node Path	Continua > Physics 1 > Models > Lagrangian Multiphase > Lagrangian Phases > [phase] > Models > Flexible Fiber
Requires	In [physics continuum] > Models: Optional Models: Discrete Element Method (DEM) for mesh-based DEM simulations or Multiphase Dem: Discrete Element Method (DEM) for meshfree DEM simulations In [phase] > Models: Particle Type: DEM Particles
Properties	Key properties are: Moment of Inertia Scaling, Axial Stiffness Scaling, and Bending Stiffness Scaling. See Flexible Fiber Properties.
Activates	Model Controls (child nodes)	Primitive Shape. See Primitive Shape Node.
	Injector Inputs	Physics Conditions > Orientation Specification Physics Values > Number of Fiber Segments, Fiber Length, Fiber Radius, and Particle Orientation. See Flexible Fiber Injector Inputs.
	Field Functions	Cylinder Height, Cylinder Radius, Particle Component Index, Particle Projected Area, Particle Projected length. See Flexible Fiber Field Functions.

Flexible Fiber Properties

Moment of Inertia Scaling

Provides a scaling factor for each axis of the moment of inertia of a segment of the fiber. (All segments are identical.) This can be used to simulate effects such as uneven distribution of mass within the particle, or the dynamical response of a non-spherical particle. The scaling factor has an allowed range on each axis of 1E-2 to 1E5. The default value is [1.0, 1.0, 1.0].

Axial Stiffness Scaling

Scales the axial stiffness of the bond between segments. The default value is 1.

Bending Stiffness Scaling

Scales the bending stiffness of the bond between segments. The default value is 1.

Axial Restitution Coefficient

The restitution coefficient for axial motions, used in bond energy dissipation. See

C_{n rest}

in Eqn. (3257), related to

N_{n}

under Linear Spring Contact Model. The default value is 1, indicating no damping of the motion.

Bending Restitution Coefficient

The restitution coefficient for bending motions, used in bond energy dissipation. See

C_{t rest}

in Eqn. (3258), related to

N_{t}

under Linear Spring Contact Model. The default value is 1, indicating no damping of the motion.

Link Mode

Allows you to control which fiber segments are allowed to link to the boundary. The following options are available:

All Segments: every segment of a fiber is allowed to link to the boundary. This is the default for simulations created under Simcenter STAR-CCM+ version 2206 or earlier.
Both Ends: the two end segments of a fiber are allowed to link to the boundary.
Single End: only one of the end segments of a fiber is allowed to link to the boundary, the end that comes into contact with the boundary first. This is the default for simulations created after Simcenter STAR-CCM+ version 2206.

Axial Stiffness Scaling and Bending Stiffness Scaling allow you to change the stiffness of the bond in the axial (extension/compression) and bending modes. These quantities are analogous to the Bond Radius Multiplier in the Bonded Particles model. Axial Stiffness Scaling and Bending Stiffness Scaling change the axial and bending stiffness respectively, by scaling the radius of fiber bond with the specified value.

Primitive Shape

Allows you to select the primAxial Restitution Coefficientitive shape used to compose the fiber.

Type	Corresponding Type Node
Cylinder	Cylinder Display as Capsule When On, the default, the primitive shapes are displayed as round-ended capsules. When Off, the primitive shape is displayed as a flat-ended right cylinder.

Flexible Fiber Injector Inputs

The Flexible Fiber model activates the following injector conditions:

Orientation Specification: Sets the initial orientation of the particle as it is injected.

The Flexible Fiber model activates the following injector values:

Number of Fiber Segments: Sets the number of segments in the fiber model. The default is 3.
Fiber Length: Sets the length of a cylindrical segment in the fiber model. The default is 0.01 m.
Fiber Radius: Sets the radius of a cylindrical segment in the fiber model. The default is 0.01 m.
Particle Orientation: Sets the initial orientation of the particle as it is injected.

Flexible Fiber Field Functions

Cylinder Height: The height of the cylinder specified under Primitive Shape.
Cylinder Radius: The radius of the cylinder specified under Primitive Shape.
Particle Component Index: This field function displays the index numbers associated with the segments of the particles. Each particle component has a unique index that distinguishes it.
Particle Projected Area: The cross-sectional area of the particle orthogonal to the direction of the fluid velocity relative to the particle centroid. Each particle in a fiber is treated separately; overlaps of cross-sections are not addressed. All other composite particles are treated as a unit and the projected area is numerically estimated.
Particle Projected length: The average length of the particle parallel to the direction of the fluid velocity relative to the particle centroid. Each particle in a fiber is treated separately. All other composite particles are treated as a unit and the projected length is numerically estimated. +