victor007
Marine/Ocean
- Feb 13, 2012
- 17
Hi,
One of the design requirements for my offshore structure is an impact from a mass with a given velocity. (Mass and Velocity are given.)
I am looking for a realistic way to translate that "impact load" into an "equivalent static load", and geting rid of doing any impact dynamic analysis.
Here is my methodology: m (mass) and V(velocity) are given, so I know the input energy is 0.5MV^2.(eq.1)
On the other hand I know if a force of F applys on my structure, it makes it deflect about "X". So the energy absorbed by the structure at that point is 0.5F.X.(eq.2) . Since it is a linear analysis, I konw F=K.X (eq.3)which K is the stifffness of that degree of freedome on the structure. By replacing (eq.3) into (eq.2) we will have: Absorbed energy=0.5K.X^2 (eq.4)
If we ignore the absorbed energy by the structure due to its damping and inertia, and also the energy lost at the impact, we could say: Input energy=Absorbed energy -> 0.5mv^2=0.5k.x^2
so x=v(m/k)^2. (K is known because we have our static model in place)
F=k.x -> F=m^2.(v/k)
Sorry for this long introduction. But I needed to generate a base for my question.
Do you think this result for F is a realistic value?
I appreciate your feedbacks.
One of the design requirements for my offshore structure is an impact from a mass with a given velocity. (Mass and Velocity are given.)
I am looking for a realistic way to translate that "impact load" into an "equivalent static load", and geting rid of doing any impact dynamic analysis.
Here is my methodology: m (mass) and V(velocity) are given, so I know the input energy is 0.5MV^2.(eq.1)
On the other hand I know if a force of F applys on my structure, it makes it deflect about "X". So the energy absorbed by the structure at that point is 0.5F.X.(eq.2) . Since it is a linear analysis, I konw F=K.X (eq.3)which K is the stifffness of that degree of freedome on the structure. By replacing (eq.3) into (eq.2) we will have: Absorbed energy=0.5K.X^2 (eq.4)
If we ignore the absorbed energy by the structure due to its damping and inertia, and also the energy lost at the impact, we could say: Input energy=Absorbed energy -> 0.5mv^2=0.5k.x^2
so x=v(m/k)^2. (K is known because we have our static model in place)
F=k.x -> F=m^2.(v/k)
Sorry for this long introduction. But I needed to generate a base for my question.
Do you think this result for F is a realistic value?
I appreciate your feedbacks.
