Motions

Learn how to create and customize animations using the veux.Motion class. This page covers how to create, configure, and display animations of structural simulations performed with OpenSeesRT.

class Motion

Examples

import numpy as np
import veux
from math import sin, cos

# ---------------------------------------------------------
# 1) Build a simple finite element "beam" for visualization
# ---------------------------------------------------------
def create_simple_beam(ndm=3):
    """
    Creates a trivial 3D beam model with a fixed support at node 1
    and a free end at node 2, just for demonstration.
    Returns the model object.
    """
    import opensees.openseespy as ops

    length = 1.0
    # Create a model with 2 nodes, each having 6 DOF (3D)
    model = ops.Model(ndm=ndm, ndf=6)
    model.node(1, (0.0, 0.0, 0.0))
    model.node(2, (length, 0.0, 0.0))

    # Fix node 1
    model.fix(1, 1,1,1, 1,1,1)

    # Just a dummy section & element so we can visualize a 'beam'
    E, I = 1.0, 2.0
    sec_tag = 1
    model.section("FrameElastic", sec_tag, "-E", E, "-G", 1.0, "-A", 2.0,
                  "-J", 2.0, "-Iy", I, "-Iz", I, "-Ay", 2.0, "-Az", 2.0)
    transf_tag = 1
    model.geomTransf("Linear", transf_tag, 0, 0, 1)
    model.element("ElasticBeamColumn", 1, (1, 2),
                  section=sec_tag,
                  transform=transf_tag)

    return model

# ---------------------------------------------------------
# 2) Create an Artist for drawing the beam
# ---------------------------------------------------------
model = create_simple_beam()
artist = veux.create_artist(model,
                            vertical=2,  # y-axis is 'vertical' in this setup
                            model_config=dict(
                                extrude_outline="square",
                                extrude_scale=0.5
                            ))
artist.draw_axes()
artist.draw_outlines()

# ---------------------------------------------------------
# 3) Define exact (closed-form) solutions for rotation & position
#    under a constant moment M about the z-axis
# ---------------------------------------------------------
E, I = 1.0, 2.0
L    = 1.0

def exact_position_rotation(M):
    """
    Returns two callable objects:
    - position(node) -> (x, y, z)
    - rotation(node) -> (qx, qy, qz, qw) with scalar last
    representing the beam's deformation under a constant moment M.
    """
    def position(node):
        # nodeCoord(1) -> (0.0, 0.0, 0.0)
        # nodeCoord(2) -> (L,   0.0, 0.0)
        xi = model.nodeCoord(node)[0]
        theta = xi * M / (E * I)

        # For M = 0, avoid dividing by zero
        if abs(M) < 1e-12:
            return (xi, 0.0, 0.0)

        x_def = xi + (E * I / M) * sin(theta)
        y_def = (E * I / M) * (cos(theta) - 1.0)
        return (x_def, y_def, 0.0)

    def rotation(node):
        xi = model.nodeCoord(node)[0]
        theta = xi * M / (E * I)
        # Rotation about z-axis by angle theta:
        # quaternion with scalar last -> (0, 0, sin(theta/2), cos(theta/2))
        return (0.0, 0.0, sin(theta / 2.0), cos(theta / 2.0))

    return position, rotation

# ---------------------------------------------------------
# 4) Animate using veux.Motion
#    We vary M from 0 to 2 (dimensionless) to show large rotations
# ---------------------------------------------------------
from veux.motion import Motion

motion = Motion(artist)
moments = np.linspace(0, 2.0, 50)
for M in moments:
    pos_func, rot_func = exact_position_rotation(M)
    # Draw the beam outlines at this "load" configuration
    motion.draw_outlines(position=pos_func, rotation=rot_func)
    motion.advance()

# Insert the motion into the canvas and serve interactively
motion.add_to(artist.canvas)
veux.serve(artist)