NOBEL Explosive Build-Up

As documented in Chapter 4, the build-up to detonation of heterogeneous explosives is described by the Forest Fire decomposition rate. The build-up of detonation process is described in Chapter 2. A technique was developed by Michael Gittings to include both build-up to detonation and build-up of detonation in the AMR (automatic mesh refinement) Eulerian hydrodynamic code, NOBEL. The NOBEL build-up models and computer movies of applications discussed in this section are described in a PowerPoint presentation on the CD-ROM in the /NOBEL/BUNOBEL directory. 

Numerical reactive hydrodynamic codes such as SIN, TDL or 2DE include the Forest Fire decomposition rate. For unresolved burns, it is necessary for the decomposition front of a detonation wave to occur over several computer meshes or cells so that the physics of the flow, the shock jump conditions, are properly described. Historically this was accomplished by adjusting the artificial viscosity so that the burn occurred over about 3 cells. If the mesh size changed, a new viscosity coefficient was determined empirically that would result in a realistic burn. As shown in the movie on the CD-ROM at /MOVIE/VISC.MVH, if there is insufficient viscosity, one obtains a reactive front with a peak that oscillates. If there was too much viscosity, a flat pressure profile occurs at the front. The problem is not unique to Forest Fire as other burn rates such as Arrhenius have the same numerical problems when numerically unresolved in reactive hydrodynamic codes. 

When the mesh size changes, as in an automatic mesh refinement code, it is not possible for one viscosity coefficient to be correct for varying meshes. So a new technique was developed by Michael Gittings for the AMR NOBEL code to burn explosives using the Forest Fire or Arrhenius rates. 

A semi-automatic burn resolution is controlled by varying the explosive rate sizes at 

The HERateSize and HERatePower constants are calibrated for each explosive Forest Fire rate to obtain adequate burning resolution for the range of numerical HE Sizes of interest. 

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The NOBEL density, mass fractions of undecomposed explosive, build-up fractions of low and high energy explosive color contour movies are shown on the CD-ROM in the PowerPoint NOBEL.PPT in the /NOBEL/BUNOBEL directory. 

The recently developed SAIC/LANL NOBEL code described in Chapter 6 permitted us to model build-up to detonation and build-up of detonation as one continuous time-dependent process for the first time in 2002. This capability resulted in significant improvement in the modeling of explosive performance of the applications described in Chapter 6 and the time and space dependent availability of explosive energy from both shocked but not detonated explosives and from detonating explosives. 

The numerical model used to interpret cylinder wall expansion experiments must include a realistic description of build-up of detonation, Forest Fire burn and resulting detonation wave curvature. A problem in numerical simulation of long cylinders of explosive confined by thin metal walls is to obtain sufficient numerical resolution to describe the explosive burn properly and also to follow the simulation of long cylinders. The NOBEL code includes the necessary physics and will numerically model cylinder tests as described in Chapter 6. 

The inclusion of the build up of detonation into detonator modeling using the NOBEL code is described in Chapter 6. It is required for realistic modeling of the explosive performance from detonators. 

Using the build-up to and of models in NOBEL described in this chapter determined from experimental observations of PBX-9501 and PBX-9502 described previously to model the cylinder test of the explosives are shown in Figure 6.46 for PBX-9501 and in Figure 6.47 for PBX-9502. 

Figure 6.46 The experimental and NOBEL build-up model Copper wall velocities as a function of time for a 2.54 cm diameter PBX-9501 explosive cylinder confined by 0.25 cm thick Copper. The experimental velocities are shown by triangles.

The modeling of insensitive high explosive initiators using the 2DL, 2DE and 3DE codes is described in Chapter 5, section 5.8. While the build-up to detonation process was described using Forest Fire, it was not possible to also investigate the build-up of detonation until the development of the NOBEL code described in this chapter. 

Figure 6.53 NOBEL model for a PBX-9502 initiator. The build-up fraction of low energy and high energy explosive contours are shown.

The revolution in numerical modeling has been made possible by the development of the multi-material adaptive grid Eulerian codes SAGE/NOBEL/RAGE with models to describe the build-up to detonation using the Forest Fire heterogeneous shock initiation burn model and models to describe the build-up of detonation which results in factors of two variations in the explosion energy with time. The build-up to and of detonation was first modeled in 2002 by the NOBEL code. 

Alfred Nobel s invention has benefited humankind in countless ways. The Panama Canal, Mount Rushmore, and many tunnels and mines were built with the aid of dynamite. It can break up dangerous ice and logjams and it can quickly and safely reduce large buildings to rubble. Police departments use dynamite to detonate suspicious packages. Fire departments use it to put out oil well fires. The explosion of the dynamite requires a huge amount of oxygen and suffocates the fire. 

The first commercial secondary explosive was produced by Alfred Nobel in the mid-1800s. Nobel s family owned a construction company, and he realized that a secondary explosive would be helpful for building roads (by blowing up mountains that stood in the way). However, at the time, there were no strong explosives safe enough to handle. Nobel focused his efforts on finding a way to stabilize nitroglycerin ... 

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