An Assessment of the Performance of the Original and Modified Versions of the Forest Fire Explosive Initiation Model

Abstract

The findings of this report are not to be construed as an official Department of the Army position, unless so designated by other authorized documents.The use of trade names or manufacturers' names in this report does not constitute indorsement of any commercial product. REPORT DOCUMENTATION PAGE OBNo. 070"188U,P rge~gb~u o hiciet.'.nfotanatatin i t igmated to average I howr per ruesbcnse. andudang IIItam for refwwflg gfl ctnjaofl. ,wect'ng existing dota souttet. gahun e atietahg the data W1d 4 "dculib~ dO40"am reiuang he= coletnf inforratmatci. Approved for public relase d=istMuto is unlimited. ABSTRACT (Maximum 200 words)The, Forest Fare explosive initiation model is useful because it can be calibrated from readily available sensitivity data However, assumptions used in the Forest Fare derivation limit its accuracy and applicability. Present computations Show that, while Forest Fire adequately predicts run to detonation for sustained-shock loading, it is grossly in erro when applied to pulsed-shock loading. On the otlher hand it exhibits some qualitatively correct results for finite-ratecopssn or ramp-wave loading. Several relatively simple modifications which extend the applicability of Forest Fire have bee developed. These include unproved mixtur modelig, use of a higher order reactive Hugoniot to describe ignition, and incorporation of surface ame burning into the reaction rate model. These modifications signifficantly affect the predicted respons to pulsed-shock loading. Combining surface burning with a quadratic reactive Hugoniot provides a significantly improved represenaton of response to pulsed-shock stimulus.

An Assessment of the Performance of the History Variable Reactive Bum Explosive Initiation Model in the CTH Code

“…Plots of pressure versus distance along the axis of symmetry at various times, shown in Figure 2, indicate that this delayed reaction produces a strong compression or shock wave that overtakes the initial shock (still propagating near its original strength). This behavior is different from that observed using Forest Fire, in which reaction begins immediately behind the initial shock wave and causes it to grow as a square wave during most of the transition process (Starkenberg 1993). The behavior predicted using HVRB is more consistent with experimental observations (Wackerle et al 1978;Nutt and Erickson 1984).…”

A Computational Study of Denotation Failure in Composition B and Cast TNT Charges

“…Shock and detonation waves are treated using the method of artificial viscosity with i iear artificial viscosity rather than the quadratic form commonly employed for shock stabilization. (Johnson, Tang, and Forest 1985; Wackerle and Anderson 1984), we have recently shown that this is not generally true (Starkenberg 1993).…”

Review of the Forest fire model for high explosives

“…Naturally, this idea would require further study to test whether it works, or could be modified to work, on problems of interest. Finally, we note that Starkenberg [38] implemented the Forest fire model in a 1-D code with a true discontinuous reactive shock by tracking the lead front. Tracking is considerably more difficult in 2-D.…”

“…Due to the absence of dissipation from shock heating, isentropic compression would generate fewer and weaker hot spots than shock compression to the same pressure. Consequently, the Forest fire rate would over-predict the reaction rate for isentropic compression, or more generally when a ramp pressure rather than a shock is applied to an HE; see [38].…”

“…First, a tracked reactive shock, as Starkenberg [38] implemented in a 1-D code, would have a zero reaction zone width and hence the conservation laws would imply the absence of a curvature effect. Possibly, the curvature effect could be obtained utilizing a partly resolved reaction zone [48] in which the tracked reactive shock models a fast reaction for the bulk of the burn fraction and then the final slow reaction for the remainder of the burn fraction is resolved.…”