The 3D hydrodynamic structure of cellular detonations is modeled by a global 1D mean hydrodynamic average model. Transport properties are artificially increased to account for the high-speed behavior resulting from fast turbulent diffusion. The existence of steady state Navier-Stokes detonation structure, as studied by Wood, is critically reviewed for this purpose and compared with transient calculations. Observations reveal that in the hyper-diffuse model, the shock and reaction zone overlap, resulting in a thickened reaction zone. The 1D model is used to study diffraction dynamics, with critical diffraction occurring when the tube diameter approaches the hydrodynamic reaction zone thickness. After diffraction, the complex viscous detonation structure separates, resulting in a rapid flame transitioning into a weak detonation. The dynamics of diffraction are analyzed at several \(W / \Delta _H\) .