A Helium Balloon in the Air - 3-D Acoustic FDTD Simulation Demo
(Native JavaScript with three.js version / rev.20150105)

Brief Notes

This is a truly physical simulation program of the sound wave propagation in a three-dimensional field filled with fluid media and Mur's 1st order absorbing boundary. (Mur's 1st order absorbing boundary is one of the easiest way to realize an absorbing boundary although the performance is not the best.)

This program solves the equations of the "3D Acoustic FDTD (finite-difference time-domain) method". The dark part consists of air (332 m/s) and the brighter part of the oval sphere consists of a mixture of air and helium (718 m/s). The grid resolution is 15 mm/pixel and the time step is 12 μs/step (μs = micro second = 1/1000000 second). A single pulse of sinusoidal sound wave at 1 kHz with Hann window is transmitted.

Have fun!!

Technical Notes

This program has been tested with Opera 26 (Blink), Firefox 31 (Gecko), Internet Explorer 11, and Spartan on Windows. It may be run also on smartphones compatible with HTML5 and WebGL. A touch operation is expected to work with Blink, WebKit, and Gecko.
The speed of calculation depends on the power of your PC. Intel Core i3 series or higher is recommended. In addition to the speed of CPU, the speed of drawing 3-D images depends on the power of your GPU because the WebGL technology is used for the 3-D rendering.

 For Safari 5.1 to 7.1 Users:
  - Open the Safari menu and select Preferences.
  - Then, click the Advanced tab in the Preferences window.
  - Then, at the bottom of the window, check the Show Develop menu in menu bar checkbox.
  - Then, open the Develop menu in the menu bar and select Enable WebGL.
  (Yosemite (Safari 8) users are not required to do the operation above.)

For more detailed information about FDTD method (including 3-D elastic simulation), please refer our papers on simulation.
⇒ http://ultrasonics.jp/nagatani/e/

Thank you.

Acknowledgement

I deeply appreciate Dr. Ryosuke TACHIBANA (@ro_tachi) (The University of Tokyo) providing an insightful idea of creating visualized simulation projects and testing the program. I also would like to thank Mr. Takaaki IBARAKI of Gehirn Inc. for reviewing the codes and giving a lot of important comments on coding.
In addition, "three.js" library is used for the 3-D rendering. I would like to express my thanks to the contributors of the powerful library.

History

Apr. 5th, 2015

Confirmed the compatibility with Spartan (Windows 10 TP 10049). (Nothing was changed.)

Jan. 5th, 2015

Added a function to reset the scene regularly to remove possible dusts in 3-D images.

Jan. 3rd, 2015

Implemented the 3-D rendering function for stereoscopic view.

The physical parameters of helium are changed for the better visual effect (Of course, it is still truly physical).

Jan. 1st, 2015

first version.