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Invisible Winds at Egypt’s Great Sphinx Revealed 

air field shape and pressure values
The Line Integral Convolution plane visualized both the air field shape and the the pressure values using colors. Courtesy of Bibliotheca Alexandrina, International School of Information Science/IBM Center for Advanced Studies, Cairo

Secondary phenomenon visualized via stream ribbons
Secondary phenomenon visualized via stream ribbons. Courtesy of Bibliotheca Alexandrina, International School of Information Science/IBM Center for Advanced Studies, Cairo

The Great Sphinx is a monumental statue that is considered the first truly colossal sculpture in Egypt and a national symbol of both ancient and modern Egypt. It would have disappeared long ago had it not been buried under sand for so long. Unfortunately, the now-exposed statue is eroding due to the effects of wind, humidity and the smog from Cairo. Wind is one of the most critical denudation factors causing the erosion, especially when it carries dust.

In order to investigate the formation of the low-speed wind over the Sphinx model, researchers have simulated the wind’s formation by solving 3-D incompressible Navier-Stokes equations on a computational mesh with several millions of points. A collaboration between IBM and Bibliotheca Alexandrina, the work is based upon research conducted in IBM’s Center for Advanced Studies in Cairo.

Virtual Immersive Science and Technology Applications (VISTA) is a project established by the International School of Information Science (ISIS) at Bibliotheca Alexandrina in order to provide an interactive virtual reality environment. The environment allows researchers to transform numerical and 2-D data sets into 3-D simulations and to step into them. The VISTA team has implemented visualization of the researchers’ wind simulation results on a CAVE system using Avizo Wind software’s advanced visualization and analysis tools to provide new insights and better understanding of the data.

“The VISTA team has chosen Avizo Wind because of its ability to display and manipulate meaningful graphics representations of natural phenomena. Using Avizo Wind, VISTA is able to use advanced visualization techniques to understand complex simulation data.”

VISTA CAVE system displaying 3-D stereoscopic images
VISTA Computer Aided Virtual Environment system displaying 3-D stereoscopic images in an immersive environment. Courtesy of Bibliotheca Alexandrina, International School of Information Science/IBM Center for Advanced Studies, Cairo
Vorticity magnitude on the Sphinx surface is mapped to colors
Vorticity magnitude on the Sphinx surface is mapped to colors. Courtesy of Bibliotheca Alexandrina, International School of Information Science/IBM Center for Advanced Studies, Cairo

Thanks to the calculation and visualization of complex algorithms, the researchers are able to see the invisible and to better understand the degradation of the Great Sphinx. Key algorithms used in this project include

Stream Ribbons: The CAVE system helps scientists to study phenomena, such as the secondary phenomena at the corners and cavities of the left of the statue. It is not possible to study such phenomena using traditional methods.

Line Integral Convolution (LIC) Algorithm: This algorithm is useful to visualize the shape of the air flow as well as the pressure values. This helps to emphasize the non-existence of dynamic load due to low speed northwest wind acting on the head.

Illuminated Stream Lines (ISL) Algorithm: ISL Algorithm provides a 3-D animated representation of the whole air flow field. The CAVE system allows the user to get immersed inside the ISL field, which gives better insights and, hence, understanding of it than the 2-D screens.

Vorticity: The vorticity magnitude (a measure of the friction stress) on the surface of the statue is visualized as color contours on the Sphinx surface. The Sphinx’s weak areas, which are the left shoulder and the top of the hunches, are exposed to maximum wind friction. The back of the head and the top of the trunk are also considered vulnerable areas.

For further information: http://vista.bibalex.org

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