Periodic Bathymetry

Periodic bathymetry tiles, interior has been hollowed out to allow insertion of metal bars (as ballast) and instrumentation. This is intended for use in fluid dynamic demonstrations and experiments, for example at the bottom of http://paoc.mit.edu/labguide/apparatus.html. Small openings in top surface allow for air to escape the hollowed interior and sensors to be inserted in the flow. Both *.stl and the OpenSCAD (http://www.openscad.org/) source files are included, please modify the generatin