magicme
Mechanical
- Sep 24, 2003
- 128
recent postings here on shock levels has me recalling DDAM shock analysis.
I did several DDAMs over the years, all applying to large shipboard system, and they were the worst experiences of my professional life. We used large scale FE models, and the criteria was always that no "critical" item could go about yield strength. (the list of "critical" items went on for pages and pages!)
That criteria, coupled with the interaction of modes made rational design decisions almost impossible. changing a bolt size at the bottom of the 60,000# machine would cause parts that were 15 feet away to "fail". NOT changing the bolt size would cause some other part 10 feet in another direction to "fail". every design change that we made on almost every part would change the stresses in every other part throughout the system.
I concluded that the DDAM method was intended for simplistic, small spring-mass systems using simple hand stress calculations . I think the application of large, detailed FE models (that pick up every local stress detail) is not what the original DDAM methodology was set up for.
then I retired.
so .... is DDAM still around?
regards,
magicme
------------------------------------
there's no place like gnome.
I did several DDAMs over the years, all applying to large shipboard system, and they were the worst experiences of my professional life. We used large scale FE models, and the criteria was always that no "critical" item could go about yield strength. (the list of "critical" items went on for pages and pages!)
That criteria, coupled with the interaction of modes made rational design decisions almost impossible. changing a bolt size at the bottom of the 60,000# machine would cause parts that were 15 feet away to "fail". NOT changing the bolt size would cause some other part 10 feet in another direction to "fail". every design change that we made on almost every part would change the stresses in every other part throughout the system.
I concluded that the DDAM method was intended for simplistic, small spring-mass systems using simple hand stress calculations . I think the application of large, detailed FE models (that pick up every local stress detail) is not what the original DDAM methodology was set up for.
then I retired.
so .... is DDAM still around?
regards,
magicme
------------------------------------
there's no place like gnome.