How to simulate and display gas particles moving in a box

Question

import matplotlib.pyplot as plt
import numpy as np
from matplotlib.animation import FuncAnimation
fig = plt.figure(figsize=(4, 4), dpi=80)
ax = plt.gca()
scatter = ax.scatter([], [], s=0.1)
x = dz * np.random.random(N)
y = dz * np.random.random(N)
z = Lz * np.random.random(N)
vx = np.random.normal(0, Tw, N)
vy = np.random.normal(0, Tw, N)
vz = np.random.normal(0, Tw, N)
def update(frame):
    """ Update function for animation """
    global x, y, z, scatter
        # Evolve
    for i in range(Nt):
        # Drift
        x += dt * vx
        y += dt * vy
        z += dt * vz
        
        # Collide specular wall (z=Lz)
        # Trace the straight-line trajectory to the top wall, bounce it back
        hit_top = z > Lz
        dt_ac = (z[hit_top] - Lz) / vz[hit_top]  # time after collision
        vz[hit_top] = -vz[hit_top]  # reverse normal component of velocity
        z[hit_top] = Lz + dt_ac * vz[hit_top]

    # Update scatter plot
    scatter._offsets3d = (x, y, z)

    return scatter,

# Animation update function
def animate(frame):
    update(frame)
    return scatter,

# Create the animation
num_frames = Nt
animation = FuncAnimation(fig, animate, frames=num_frames, interval=200)

# Display the animation
plt.show()

I am trying to make animation of particles in a box and I have tried everything that I knew but I can't get it running. I just get this plot.
Please ignore the constants such as N, Tw, etc. I have not added them for brevity

score 0 · Answer 1 · answered May 24 '23 at 02:32

Updated as per this answer in the duplicate.

import matplotlib.pyplot as plt
import numpy as np

# dummy variables since they weren't defined in the OP
dz =1
Lz =2
Tw = 4
N = 30
Nt = 20
dt = 30

x = dz * np.random.random(N)
y = dz * np.random.random(N)
z = Lz * np.random.random(N)
vx = np.random.normal(0, Tw, N)
vy = np.random.normal(0, Tw, N)
vz = np.random.normal(0, Tw, N)

def update(frame):
    """ Update function for animation """
    global x, y, z, scatter
        # Evolve
    for i in range(Nt):
        # Drift
        x += dt * vx
        y += dt * vy
        z += dt * vz
        
        # Collide specular wall (z=Lz)
        # Trace the straight-line trajectory to the top wall, bounce it back
        hit_top = z > Lz
        dt_ac = (z[hit_top] - Lz) / vz[hit_top]  # time after collision
        vz[hit_top] = -vz[hit_top]  # reverse normal component of velocity
        z[hit_top] = Lz + dt_ac * vz[hit_top]

    ax.scatter(x, y, z, s=0.1)

# define the figure and 3d axes
fig = plt.figure(figsize=(4, 4), dpi=80)
ax = fig.add_subplot(projection='3d')
num_frames = Nt

# Create the animation
animation = FuncAnimation(fig, update, frames=num_frames, interval=200)

animation.save('scatter.gif', writer='pillow')

How to simulate and display gas particles moving in a box

1 Answers1