This simulation visualisation, made in 2003, is both dated and basic, even for the time.  The work is in fact the first visualisation I produced for a client, and was conducted hastily on top of an already full schedule.  The client has since kindly allowed me to publish the animation.  This is the original low-bandwidth web version and, other than my copyright, contains no sensitive or proprietary information.

 

The underlying analysis was conducted in response to the client receiving fragile high value goods in a damaged container, with the damage having occurred at some point during shipping.  The goods in question was a Liquid Apogee Engine (LAE), a medium-sized rocket motor, costing hundreds of thousands of dollars.  On visual inspection the damage was confined to the container drum itself and not the contents.  However, of course, the client's customer had to be informed.  On doing so the customer was naturally unhappy with the situation, there was no record of how the container drum had sustained damage and no understanding of what the rocket motor had been subjected to.

 

The damage to the container could have been due to static crushing at one extent, or a sudden impact at the other extent, with the latter being the most severe possibility and therefore assumed as the event for analysis.  Both static and dynamic scenarios were however analysed, but the static case was analysed as part of a preliminary approximate study.

 

A higher quality non-web version of the above animation was presented to the customer in 2003, together with test and analysis findings, to help communicate the results of my investigation.  The animation shows the relative motions of the foam suspended LAE inside its 'oil drum' packaging. The cost of such a LAE is in the region of $400k and program delays to replace it would have also been in similar figures, thus potentially a very expensive incident.  

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Interpreting the witness marks in the damaged area, it was clear that the impact that caused the damage was due to a lateral strike of some kind by a square edged flat plate or bar on the rim of the drum, almost in line with the drum's cylindrical axis.  The drum was strapped to the pallet by two standard steel band strappings, under typical tension for safe transit.  The impactor (most probably a forklift fork) is not shown in the visualisation, for clarity neither are the profiled packing foam sections.

 

Simulation notes:

• The LAE transport casing is supported on all surfaces by profiled foam packing, which in turn contacts with the internal surface of the drum container.  The foam sections were of a medium density open-cell type, the density and stress-strain relationship was measured for each foam section.  Rate sensitivity was assumed as that typical for a medium density PU open-cell foam.  With prior experience modelling highly compressible open-cell foams such as the more complex and highly rate sensitive Confor® foam, where often superimposed material models have been required, there was confidence in the choice of material model.

• Prior to impact a rectangular panel can be seen entering the drum, this panel represents the documents that were shipped with the LAE and has a thickness representative contact zone surrounding it. The 'documents' are included in the shipment under heavy damping so once inside there are no residual dynamics from their insertion and the foam surrounding the documents is conservatively compressed together with a conservative minimum gap between the documents and LAE casing. The large damping terms are removed just prior to the impact event.

• Animation framerate is 24fps.

• Simulation framerate is 1000fps.

 

The simulation was configured to produce the same damage as the permanent set deformation measured on the drum.  The impact velocity for the first iteration was calculated using some assumptions in conjunction with results processed from a nonlinear static analysis.  The first iteration correlated with the observed damage to the drum and no further simulations were needed.

 

The analysis details the nature of rotational and translational accelerations for the various interconnected bodies, in particular the LAE. These accelerations were compared to acceptance test levels for the LAE, and due to the very comfortable margins the LAE was declared unaffected by the incident and accepted by the customer.  Subsequently the LAE was integrated on the customer's satellite, which was then tested and flown on schedule.