Orbital Motion Simulator

A velocity Verlet algorithm integrator for simulating the motion of celestial objects

Compilation:

Using the provided Makefile:

From within the project root, execute

make

Manually:

1. Compile modules:

gfortran -c src/constants.f90 src/input_parser.f90 src/potential.f90 src/data_writer.f90 src/main.f90

2. Link produced binaries:

gfortran constants.o input_parser.o potential.o data_writer.o main.o -o planetSim

3. (Optional) Clean main folder by running: rm -f *.o *.mod

Usage:

To run the simulator, copy the executable planetSim to run/ and execute it using

./planetSim

Input

The input file should be named input.dat and contain initial simulation parameters in the following format:

<Number_of_planets>
<Length_of_timestep>
<Length_of_simulation>
Time_between_data_writes
<Time_between_data_to_screen>
<mass1> <x1> <y1> <z1> <vx1> <vy1> <vz1> [Name1]
<mass2> <x2> <y2> <z2> <vx2> <vy2> <vz2> [Name2]
...

where the masses are given in solar masses, the coordinates are given in astronomical units and the velocities in AU/s. The names are optional and can be up to 50 characters in length.

The sample input, input_nasa.dat has the actual positions of the planets as of December 4th 2017, according to data from NASA.

Output

A typical simulation produces two output files:

output.dat A XYZ coordinate file containing all coordinates in astronomical units and the time in seconds. All objects are given an identifying number, beginning from 1, which usually is the star. Format:

<ID> <x>  <y>  <z>  <time>

output.movie A XYZ-file separated into frames, each containing a set of coordinates for all objects. Format:

<Number_of_objects>
Frame number; <number>  Time: <time>
<ID>  <x> <y>  <z>
...

This repo contains sample outputs (output_inner_planets.dat and output_inner_planets.movie) for the four innermost planets, simulated for roughly one orbital period of Mars.

Visualization

The produced movie file can be easily visulized as an animation using e.g. Ovito and reading the movie file columns as particle type and the three spatial coordinates, respectively. The trajectory utility of Ovito can also be used for visualizing orbits.

The *.dat files can be visualized using the attached Python script. Make sure to first install the dependencies using e.g.

pip3 install -r utils/requirements.txt

after which plotting works as

python3 utils/plot_orbits.py <output-file>