Dynamic Amplification Factor

[ul92]

Gents,

Can anybody let me know what Dynamic Amplification Factor depends on?

Thanks in advance.
Ulvi

 

[Ussuri]

The DAF is the ratio between your dynamic load and your static load.

 

[GregLocock]

Interesting, where I come from it is the ratio of the response to a given force at a given frequency to that statically. Typically at its peak it depends on the damping ratio of the structure and nothing else, in a single degree of freedom system.

http://en.wikipedia.org/wiki/Resonance

In more complex systems then it is also affected by the presence of other modes

Cheers

Greg Locock


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[Ussuri]

Fair point. I should have been more specific. I was referring to offshore/subsea lifting operations. The dynamic effects are simplistically covered by inclusion of a factor, applied to static loads. Or vice versa depending what you are calculating.

I'm not sure this link will work, it is to DNV RP H103 Modelling and Analysis of Marine Operations.

http://www.google.co.uk/url?sa=t&rc...ZGl2VX3u0Ld09ZZ9zrGBNiw&bvm=bv.51156542,d.d2k

Perhaps the OP can clarify in what context he is asking?

 

[ul92]

Gents,

Many thanks for feedbacks. They are very usefull.

Let me give you more details to create real senario in your mind:
-As I am designing 10t SWL Lifting beam, DNV 2.22 is being used. Test load for this structure is 2 x SWL if DAF is less than 1.33. But if this amount exceed 1.33 it effects test load. My questions are starting from know. How to define right DAF?

Please note that any information is deeply appreciated.
Many thanks for attention,
Ulvi.

 

[Ussuri]

Firstly, I do not know DNV 2-22 so cannot comment on the specifics.

Secondly, I am assuming you are talking about offshore lifts as you are referring to the DNV standards. Correct me if i'm wrong.

So speaking generally, if you wanted to assess the DAF in your situation you would need undertake a dynamic analysis. The dynamic load is caused by a number of effects but primarily the motion of the crane and vessel, the speed at which you are hoisting and the movement of the object being lifted.

Things you would need to consider in the analysis would include the environmental conditions, the type and size of the crane vessel, the vessel response to the environmental conditions, the stiffness of the crane and crane boom, the properties of the lifted object, whether it is an in air or subsea lift (for subsea lifts you also have the hydrodynamic effects on the object).

So in your case you need to assess whether your DAF is 1.33 or less. You need to work it out.

From a design perspective it is the responsibility of the designer to identify an appropriate DAF for the situation you have.

DNV Rules for the Planning and Execution of Marine Operations suggests some DAF figures for in air lifts, but it would be up to the designer to ensure they are suitable. DAF's for subsea lifts you pretty much always need to calculate because the hydrodynamic properties of the objects are lift specific.