RE: jet engine penetration depth -- CORRECTION !

Marvin Resnikoff wrote on Monday November 05, 2001 7:18 PM :

<SNIP>
Our calculations for concrete penetration do not assume the structure moves. As must be clear to you, one cannot infer from the Sandia test that a 767 engine moving 500 mph will penetrate 6 cm of concrete. If the building or storage cask were stationary, the penetration depth of the 767 jet engine is closer to 4 feet, and several U.S. reactors have a thinner concrete containment. Our method of calculating the penetration depth is identical to the method used by NRC staff and DOE contractors.
Marvin Resnikoff
<END QUOTE>

Marvin, this is pure nonsense !

Whether the impact block in the 1988 Sandia F-4 Phantom crash test moved or not makes very little difference.
I will tell you exactly how little difference.

The Sandia test was performed much the same way one would do the classic Ballistic Pendulum experiment for measuring the impact speed of a bullet : a block of wood is suspended by strings, so that there is no external force, such as friction, acting along the line of impact -- the same was achieved (nearly) by putting the reinforced concrete block atop an air-bearing platform. Quoting from the report,

The target consisted of a block of reinforced concrete 7 m square and 3.66 m thick mounted atop an air-bearing platform with a combined weight of 469 tonnes (almost 25 times the weight of the F-4)
.....
Ten air bearings were installed in "pockets" in the lower surface of the air-bearing platform. After inflating the air bearings, a force of only 816 Kg (less than 0.2% of the weight of the target) was required to initiate movement of the target.

When the bullet in the Ballistic Pendulum experiment hits the block of wood, it stops within it and thus transfers all its kinetic energy to the combined block-with-bullet mass. The movement of the block-with-bullet mass can then be used to calculate the initial speed of the bullet, or -- and this is the important part -- if you know the speed of the bullet, it can be used to measure the amount of energy expended in different ways in the collision.

It turns out that in the case of such an inelastic collision, its easy to demonstrate that the fraction of energy going into destruction of the colliding objects is simply the total energy (i.e. initial kinetic energy), minus the ratio of the mass of the bullet (or the F-4 Phantom) versus that of the target-with-bullet. For example, a 5-gram bullet hitting a 2000 gram block of wood will result in ( 1 - 5/2005 = ) 99.75 % of the total impact energy converted to destructive energy (mechanical crushing, heat, shrapnel spray, etc.).

Similarly for the Sandia impact test, where the ratio of airplane mass to concrete block mass was 1-to-25, the amount of impact energy converted into destructive energy is ( 1 - 1/26 = ) 96.2 % of the total.

This may be compared to the case where the concrete block had been fixed perfectly to the ground, which is exactly analogous to having a block with infinite mass. In this case the amount of impact energy converted into destructive energy is ( 1 - 1/10000000.... = ) 100 % of the total.

Note that there is a difference of only ( 100% - 96.2% = ) 4 % between the case where the block is fixed to the ground (infinite mass equivalent), and where it is floating frictionlessly. That of course is because of the large mass difference in both cases.

Note also that Mr. Resnikoff and other critics are telling us is that a 4% difference in impact energy conversion to destructive energy, makes the difference between the 2½" penetration of the concrete wall in the actual experiment, and the 4 feet ( 48") penetration calculated by them.

A 4% difference in energy results in 19-times deeper penetration according to them.

Just as amazing is that this is grade eleven high school physics.... the bullet example I cited above comes from my 1966 edition of the Physics text book by Halliday & Resnick, page 220.

Radsafe colleagues, please make sure everyone gets the message ! ...no more screwing around with antinuke-motivated misinterpretations of the historic Sandia crash test !