From 67553d7eb99410d84b704198c503ebf5a67a8554 Mon Sep 17 00:00:00 2001
From: Seung Hyun Kim <skim449@illinois.edu>
Date: Sat, 8 Jun 2024 14:03:53 +0900
Subject: [PATCH] add timoshenko example using elastica_blender

---
 examples/README.md     |  7 ++++
 examples/timoshenko.py | 84 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 91 insertions(+)
 create mode 100644 examples/timoshenko.py

diff --git a/examples/README.md b/examples/README.md
index b7465d9..c4de47a 100644
--- a/examples/README.md
+++ b/examples/README.md
@@ -25,3 +25,10 @@ Examples can serve as a starting template for customized usages.
     * __Purpose__: Illustration case for Rod module
     * __Features__: Rod
     * [RigidRodSpringMotion3D](./single_rigid_rod_spring_action_3D.py)
+        * __Purpose__: In 3D motion
+
+## Case with External Simulator
+
+* [TimoshenkoBeamCase](./TimoshenkoBeamCase)
+    * __Purpose__: Example of `elastica_blender` module on simple Timoshenko beam.
+    * __Features__: elastica_blender.BlenderRodCallback
diff --git a/examples/timoshenko.py b/examples/timoshenko.py
new file mode 100644
index 0000000..df486fb
--- /dev/null
+++ b/examples/timoshenko.py
@@ -0,0 +1,84 @@
+# Originally from PyElastica example case
+
+import elastica as ea
+import numpy as np
+
+import bsr
+from elastica_blender import BlenderRodCallback
+
+
+class TimoshenkoBeamSimulator(
+    ea.BaseSystemCollection,
+    ea.Constraints,
+    ea.Forcing,
+    ea.CallBacks,
+    ea.Damping,
+):
+    pass
+
+
+timoshenko_sim = TimoshenkoBeamSimulator()
+final_time = 5000.0
+
+# setting up test params
+n_elem = 100
+start = np.zeros((3,))
+direction = np.array([0.0, 0.0, 1.0])
+normal = np.array([0.0, 1.0, 0.0])
+base_length = 3.0
+base_radius = 0.25
+base_area = np.pi * base_radius**2
+density = 5000
+nu = 0.1 / 7 / density / base_area
+E = 1e6
+# For shear modulus of 1e4, nu is 99!
+poisson_ratio = 99
+shear_modulus = E / (poisson_ratio + 1.0)
+
+shearable_rod = ea.CosseratRod.straight_rod(
+    n_elem,
+    start,
+    direction,
+    normal,
+    base_length,
+    base_radius,
+    density,
+    youngs_modulus=E,
+    shear_modulus=shear_modulus,
+)
+
+timoshenko_sim.append(shearable_rod)
+# add damping
+dl = base_length / n_elem
+dt = 0.07 * dl
+timoshenko_sim.dampen(shearable_rod).using(
+    ea.AnalyticalLinearDamper,
+    damping_constant=nu,
+    time_step=dt,
+)
+
+timoshenko_sim.constrain(shearable_rod).using(
+    ea.OneEndFixedBC,
+    constrained_position_idx=(0,),
+    constrained_director_idx=(0,),
+)
+
+end_force = np.array([-15.0, 0.0, 0.0])
+timoshenko_sim.add_forcing_to(shearable_rod).using(
+    ea.EndpointForces, 0.0 * end_force, end_force, ramp_up_time=final_time / 2.0
+)
+
+# Use elastica_blender.BlenderRodCallback to render rod-video
+timoshenko_sim.collect_diagnostics(shearable_rod).using(
+    BlenderRodCallback,
+    step_skip=500,
+)
+
+timoshenko_sim.finalize()
+timestepper = ea.PositionVerlet()
+
+total_steps = int(final_time / dt)
+ea.integrate(timestepper, timoshenko_sim, final_time, total_steps)
+
+# Save as .blend file
+bsr.save("timoshenko_beam.blend")