Sine Environment

[sushi75]

Hi all,

I'm going through dynamic analysis, and I've got a simple question: why is it so important to have the structure outside the sine environment??

If the first natural frequency is outside this range, let's say above 100 Hz, it doesn't mean that it will not be met.

Hope someone can clarify that point; I'm a bit confused!

Thanks!

 

[jimkinney]

Usually you want the response of the structure to be outside of your vibration frequency of interest. Then you don't usually have to worry about the structure responding the vibration. This only works if you know exactly what you frequency of interest is.

For space applications, random vibration is usually assessed from 20-2000 Hz. That doesn't mean there is no vibration above 2 kHz, there is, but the damage potential is lower as the frequency increases, so that's where we focus.

For components mounted to structure, you want the response of the component to be above the response of the structure so they don't couple together. It's not necessarily bad if they couple (it can be), but it's less analysis if they don't.

For spacecraft attached to launch vehicles, if the response of the spacecraft modes are above about 35 Hz, you don't have to assess the coupling between them. 35 Hz is launch vehicle dependent.

Hopefully this helps.

Jim

Jim Kinney
Kennedy Space Center, FL

 

[sushi75]

Thanks a lot for this first reply, it's helpful already!

I dealing with spacecrafts, so yes it makes sense now to avoid the sine environment if it's related to the launch vehicle frequencies.

As you know, vibrations and dynamics is essential for this industry, and I'm just starting, but it's a lot of information to absorb and I still cannot understand much, at least having a physical sense of what is happening.

Frequency domain is not straightforward, even looking at the spec curves for example for shock, it's not clear to me.

Do you any source/book/on line video which I can use to get a better understanding? I've been looking for that, but could not find anything really applicable to the space industry I've joined recently.

Thanks a lot for your help!! I'm willing to understand and that will make the topic even more interesting!

Cheers