Synopsis

Pysics is a simple python module capable of simulating arbitrary 2D multibody mechanical systems obeying holonomic constraints, including systems with time-dependent constraints and forcing. It was written as a final project for the sophomore-level Dynamics class at Olin College of Engineering.

Included in this repository are approximately 10 example simulations demonstrating the range of systems that pysics is capable of simulating.

Dependencies

Pysics is dependent on several scientific computing packages for python:

• Numpy, for efficient array math
• Sympy, for symbolic manipulations
• Scipy, for numeric integration
• Matplotlib, for creationg of figures

Pysics should work both in Python 2.7 and 3.x, provided the most recent versions of the above packages are installed.

Code Example

Pysics takes great pains to only request the minimum possible amount of information about the system. For example, the snippet of code below defines a double solid pendulum with aerodynamic drag.

from pysics import *

#Create the simulation object and define gravity
sim = Sim2D()
sim.Gravity([0, -9.81])

#Define the constraints
th1, th2 = sim.DOF('th1','th2')
r1 = 0.4*s.Matrix([s.sin(th1),-s.cos(th1)])
r2 = r1 + 0.3*s.Matrix([s.sin(th2),-s.cos(th2)])

#And define the bodies and forces
pend1 = sim.RigidBody('pend1', m=1, I=0.3, r=r1, ang=th1)
pend2= sim.RigidBody('pend2', m=0.7, I=0.15, r=r2, ang=th2)
sim.Drag(TCd=0.1, power=2)
                      
#Set the initial conditions
sim.place({th1: (n.pi/3,0), th2: (n.pi/4,0)})

#And simulate! Badabing badaboom
y = sim.run([0,5,0.01])

#Finally, generate figures describing the system
sim.analyze()

Installation

Prior to installation of pysics, Python must be installed with numpy, sympy, scipy, and matplotlib. Pysics may be installed system-wide by moving the pysics folder into your system's pythonpath, or simply used on a project-by-project basis by placing a copy of the folder into each project's directory.