Questions regarding sensitivity output

Hello,
I have been doing an optimization with Optistruct and now I want to do a sensitivity analysis. I optimized the gap between desired and current frequencies of some modes, using this formula:
delta_f = sum[(f_now_1 - f_desired_1)^2+...+(f_now_10 - f_desired_10)^2]
I used the OUTPUT cards to create .slk files for all iterations. I used normal orthotropic material behaviour, so I have 5 design variables and delta_f as the response. What I am looking for is something like "I change variable 1 by 10% and delta_f changes for xx%". If I do this for all 5 variables I will find out which has the most impact on the solution, right? How I understand the .slk file, I can say something like "the new value of variable 1 = 1,1* old_value of variable 1" and then it will calculate the new estimated response and I can see how much it would change.
Is my train of thought correct? If yes, which Iteration would i use for my calculations, since the sensitivities are changing? My guess would be the first iteration, because it usually has the highest change?
I have a mixture of positive and negative sensitivities, so I should use the conservative response?
Do the sensitivities have a specific unit, e.g. in %? Below is the slk file for Iteration 0, how do I interpret a sensitivity of 244 for E_P?

Hi,
sensitivities are the variation of the responses with respect to your design variables change.
Their unit is equivalent to: delta Reponse/delta desvar >. if your response is stress and your variable is thickness, it will be MPa/mm, for example. How much stress will a change in thickness bring to my design.
You need to understand that sensitivities change in each part of your design space. Imagine them as the slope of a montain when you're climbing it. It will change as you approach the peak/valley.
So sensitivities are calculated close to a certain reference value/point and they're valid around this point.
In the end, close to the reference point, they will give you what you want: if I increase E_N by a unit, I will get a descrease (-16.9) in my Response. For E_P, if I increase by a unit, it would increase my Response by 244. Again, notice that this is valid for the surroudings of your reference point, which will change in each iteration.
Hi,
sensitivities are the variation of the responses with respect to your design variables change.
Their unit is equivalent to: delta Reponse/delta desvar >. if your response is stress and your variable is thickness, it will be MPa/mm, for example. How much stress will a change in thickness bring to my design.
You need to understand that sensitivities change in each part of your design space. Imagine them as the slope of a montain when you're climbing it. It will change as you approach the peak/valley.
So sensitivities are calculated close to a certain reference value/point and they're valid around this point.
In the end, close to the reference point, they will give you what you want: if I increase E_N by a unit, I will get a descrease (-16.9) in my Response. For E_P, if I increase by a unit, it would increase my Response by 244. Again, notice that this is valid for the surroudings of your reference point, which will change in each iteration.