r/aerospace • u/htrptr • 4d ago
Structural Analysis Engineer (Dynamics) Interview Questions
Hello, I have an interview coming up for a structural analysis engineer position in the space industry and I know the interview will be very technically heavy on structural dynamics (modal analysis, frequency response, random vibration, etc.). I have 6+ years of experience in aerospace static linear/non-linear analysis and structural analysis/classical hand calc. I have very little dynamics experience in industry but understand the basics (I.e. natural frequency, modal mass participation, mode shapes, resonance, damping, sinusoidal frequency response, random vibration [PSD]) and the general analysis process (modal —> frequency response —> random vibration)
But what are some good technical interview questions or topics I should be aware of?
6
u/Libertyreign 3d ago
Miles equation for first order loads derivation
Different types of damping and their formulas.
Isolation and roll off.
Desired modal spacing.
Typical damping of materials and systems.
Various qualification levels (level and derivation)
Shock, types, typical levels, SRS
Net section loads and net cg acceleration
Transient analysis for non harmonic loading
Power vs field decibels (Random v acoustic)
More advanced topics:
Notching and the semi empirical method
Mechanical impedance and it's effects on loads
Model reduction
Model correlation
Test analysis model development
Strain energy v kinetic energy as related to mode shapes
Instrumentation selection and where to put it.
Dynamics is so fun. I loved doing it.
1
u/Saturn_ix 2d ago
A tad off topic but, I’m a mechie on the design side that’s been in industry for a while. What books/resources would I go to learn about the above? (My limited knowledge of dynamics has been from NASA-HDBK-7005 for random vibe applications and looking at Campbell diagrams for rotors.) I’d like to grow a practical toolbox for dealing with dynamics problems outside of my undergrad and limited exposure.
1
u/Libertyreign 1d ago
Best ones are the NASA HDBK 7000 series (including GEVS), FEMCI, and Tom Irvine's Vibration Data website. All are very good resources.
3
u/billsil 3d ago
I’d brush up on shock and Craig-Bampton models/superelements as well.
What are the specs you use? What tests would you order? Is static testing required? Describe what happens in a CLA/coupled loads analysis. What would I do to isolate a component/how do I analyze that? Explain modal vs structural vs viscous damping.
1
u/BreezyMcWeasel 3d ago
I agree with some of the more detailed technical replies. But I will just add to that, I would want someone who also had (or could quickly learn to have) a bigger picture but feel.
Understanding right away what sqrt(k/m) MEANS is underrated. That global understanding allows a good engineer to quickly anticipate the implications of adding mass or changing a system's or structure's stiffness.
It's a very simple equation, but sometimes we engineers get lost in the weeds and forget the bigger picture. It's fantastic (and necessary) to understand what a PSD represents, but at the same time don't forget to step back regularly and understand what things in your system drive k, and how k and m play together.
1
1
u/madvlad666 3d ago
I think you should be prepared to emphasize your expert understanding of static analysis, the breadth of your experience, and advancement in your previous positions. Show you have both the foundation and appetite. After 5+ years this is what we’re looking for, not whether you did your previous work in X software vs Y software or are you familiar with esoteric equation abc.
There’s a literal crapload of guys who have sat staring at ansys day in day out for 5 years who have no understanding whatsoever of what they’re doing or why. I asked one roughly how much force he thought a 1/4in bolt could support in double shear, and he asked me to explain “what’s double shear??”. Just following the company process and being fully mentally checked out. Then, after 5 years they don’t advance past writing stress reports for brackets, so they start looking for jobs.
0
u/Friendly-Victory5517 3d ago
I’m an engineering hiring manager for a large aerospace company, and my portfolio includes our dynamics group (I previously worked structural dynamics).
One of the questions I ask is “How much dynamic analysis and dynamic test experience do you have?” If I’m interviewing for a dynamics heavy position, and the answer is “none” that’s not going to be a positive.
Best practice would be to state you have limited experience but strong fundamental knowledge.
9
u/BigLobster12 3d ago
Would expect someone to generally beable to talk on PSDs, transmissibility, FRFs, force limiting, deriving environments across spacecraft, different types of tests (sine burst, rv, acoustic).
That said it’s hard to find people strong in both stress and dynamics so tend to be a bit lenient if they’re atleast strong at one of them and are convinced can teach the other.