Understanding a Static vs Dynamic problem
Understanding a Static vs Dynamic problem
(OP)
Can anyone provide background the choices between a static and dynamic problem, are there any good books/literature on this. Thanks.
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Understanding a Static vs Dynamic problem
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Understanding a Static vs Dynamic problemUnderstanding a Static vs Dynamic problem(OP)
Can anyone provide background the choices between a static and dynamic problem, are there any good books/literature on this. Thanks.
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RE: Understanding a Static vs Dynamic problem
There are numerous texts on how to analyze either, but the decision to analyze in a certain way is left to the engineer in responsible charge, and keeping with the standard of care of his practice area.
RE: Understanding a Static vs Dynamic problem
For electronic packaging, Dave Steinberg's Vibration Analysis for Electronic Equipment may be a good start.
Tobalcane
"If you avoid failure, you also avoid success."
RE: Understanding a Static vs Dynamic problem
Thanks again.
RE: Understanding a Static vs Dynamic problem
Tobalcane
"If you avoid failure, you also avoid success."
RE: Understanding a Static vs Dynamic problem
Tobalcane
"If you avoid failure, you also avoid success."
RE: Understanding a Static vs Dynamic problem
0s 0.12s 0.32s 0.5s 0.62s 1s
300.0N 3000.0N 1500.0N 3000.0N 300.0N 300.0N
I don't see this as so much a vibration problem, but more of a shock impact.
RE: Understanding a Static vs Dynamic problem
RE: Understanding a Static vs Dynamic problem
Strain rate can also be an influential factor. With polymers and bio materials visco-elastic responses should probably be looked at for either a static or a dynamic analysis.
RE: Understanding a Static vs Dynamic problem
300.0N 3000.0N 1500.0N 3000.0N 300.0N 300.0N
From this type of force-time history you get a response from an elastic system which in simple terms depends on the natural frequencies of the structure.
In general, if the lowest structural natural frequency is significantly lower than the dominant spectral terms in the shock, then the problem can be treated as static, using the highest value of force in the shock as the input.Or, another way,if the width of the shock pulse is much less than the lowest natural period of the structure.
Otherwise you must treat it as a classical shock-vibration problem.
In that case , you get the spectral content of the shock and vectorially sum the response,to your dynamic system, a usually tedious process.Or use the numerical methods in the time domain ( e.g.Duhamel) to find the response.
Good references abound.I like the series, Shock and Vibration Handbook, Harris and Crede, McGraw Hill.
RE: Understanding a Static vs Dynamic problem
0s 0.12s 0.32s 0.5s 0.62s 1s
300.0N 3000.0N 1500.0N 3000.0N 300.0N 300.0N
From this type of force-time history you get a response from an elastic system which in simple terms depends on the natural frequencies of the structure.
In general, if the lowest structural natural frequency is significantly higher than the dominant spectral terms in the shock, then the problem can be treated as static, using the highest value of force in the shock as the input.Or, another way,if the width of the shock pulse is much greater than the lowest natural period of the structure.
Otherwise you must treat it as a classical shock-vibration problem.
In that case , you get the spectral content of the shock and vectorially sum the response,to your dynamic system, a usually tedious process.Or use the numerical methods in the time domain ( e.g.Duhamel) to find the response.
Good references abound.I like the series, Shock and
Vibration Handbook, Harris and Crede, McGraw Hill.
For your input it looks like the "shock" pulse is the order of about 1/2 second which means that for structures with natural frequencies >> 2pi/.5sec= about 12Hz , the static solution is valid.
RE: Understanding a Static vs Dynamic problem
......>>1/.5sec=2Hz
Which probably means all structures you are looking at can be treated with static answer.
RE: Understanding a Static vs Dynamic problem
RE: Understanding a Static vs Dynamic problem
My point is that we should never rule out dynamics just because we can or because dynamics is much more complicated.
btw, shock impact is generally treated as dynamic. But, zekeman's post is certainly is a very good reference for determining the coupling pt. between dynamic and static.
Although, for your application I think you should do a dynamic shock isolation analysis.
This way the shock that the body sees can be minimized while at the same time providing not too much compliance.
this would make for a good design instead of a "solid metal bar".
Fe
RE: Understanding a Static vs Dynamic problem
Fe
RE: Understanding a Static vs Dynamic problem
Chicopee, the problem does involve movement and rotation.
Thanks again
RE: Understanding a Static vs Dynamic problem
I suggest you start with a spring mass system, then expand to your system if you are not familiar with the methodology.
Fe
RE: Understanding a Static vs Dynamic problem
Also I understand that I need to base the analysis on a linear model for a modal analysis and also my component in my FE model are in contact. Will this cause any problem with the modal analysis?
Thanks in adavance
RE: Understanding a Static vs Dynamic problem
A good reference for shock isolation is this thesis:
http://eprints.soton.ac.uk/64538/
I'm not sure what this means though "also my component in my FE model are in contact. Will this cause any problem with the modal analysis?"
Fe
RE: Understanding a Static vs Dynamic problem
The natural frequencies and modes shapes of a structure can be used to characterise its dynamic response to loads in the linear regime....
It then goes on to state:
A problem should have the following characteristics for it to be suitable for linear transient dynamic analysis:
The system should be linear: linear material behavior, no contact conditions, and no nonlinear geometric effects.
The response should be dominated by relatively few frequencies. As the frequency content of the response increases, such as is the case in shock and impact problems, the modal superposition technique becomes less effective.
The dominant loading frequencies should be in the range of the extracted frequencies to ensure that the loads can be described accurately.
The initial accelerations generated by any suddenly applied loads should be described accurately by the eigenmodes.
The system should not be heavily damped.
RE: Understanding a Static vs Dynamic problem
From what I can see now you have a mechanism which has contact. I understand that an FE contact model is possible but it is not the same as a standard linear FE model.
I am not familiar with FE contact modeling. I know a few book that theoretically develop come contact mechanics models. However, the only thing numerical I can suggest for this is to try another dynamic and static modeling software like MapleSim.
Other than this, I could not say for certain.
Fe
RE: Understanding a Static vs Dynamic problem