Help with Setting Up Random Vibration Analysis in Creo Simulate 10.0 (CubeSat Modal/Random Case)

[EP_13234518]

Hi everyone,

I’m working on a Random Vibration Analysis in Creo Simulate for a 6U-XL CubeSat structure, which is mounted inside a deployer and tested on a shaker table.

So far, I’ve successfully completed the Modal Analysis:

- I constrained the side rails (interfaces with deployer).

- Assigned material to the structure.

- Used point masses for each unit to replicate the payloads, and added weighted links to distribute the masses.

- Element mesh was created using AutoGEM (solid)

Now, I’m moving to the Random Vibration (PSD) Analysis and have a few questions I hope someone can help with:
- I’m applying an enforced motion (base excitation) on the constrained rail surfaces, simulating the shaker input. Is this the right approach for replicating a vibration test inside a deployer?
- I used weighted links to connect the point masses to the payload mounting holes. The holes are not constrained (only the rails are). Is that correct, or should the payload attachment holes be constrained too?
- For the PSD table, should I use linear or logarithmic frequency spacing? The vibration profile is based on a launcher-provided spec. Where should I insert the values to get the results? (I pressed on f(x) under PSD and created my table with the launcher values. Is this the correct way?)
- Any other best practices I should consider to obtain valid results?

Unfortunately, I can’t share the actual files, but I’m happy to describe my setup further or provide screenshots of the model and settings if needed. I would really appreciate some step-by-step guidance on how to properly fill in the required inputs when creating the Random Vibration study in Creo.

Thank you in advance for your time and support!

[Catalina]

Hi @EP_13234518 

Thank you for your question. 

Your post appears well documented but has not yet received any response. I am replying to raise awareness. Hopefully, another community member will be able to help.

Also, feel free to add any additional information you think might be relevant. For example:

• Is applying enforced motion (base excitation) on the constrained rail surfaces the correct approach for replicating a vibration test inside a deployer?
• Should the payload attachment holes be constrained, or is it correct to only constrain the rails?
• Where should you insert the values to get the results? Is pressing on f(x) under PSD and creating the table with the launcher values the correct way?

Best regards,

[Lewis_Maina_M]

Hello, I hope it’s not too late to contribute to this discussion. I found your post while looking into PSD-related topics in Creo Simulate. I’ve worked on Random Vibration (PSD) analyses before, and I’ll try to address your questions based on my experience.
Base Excitation on the Rails — Is This Correct?

Yes if your test configuration matches that assumption.

In a shaker test:

• The deployer is bolted to the shaker.

• The CubeSat is constrained by the deployer rails.

• The base motion is transmitted through the rail interfaces.

So in your model:

• Constraining the rail contact faces

• Applying enforced acceleration (base excitation PSD) at those same rails

is the correct way to simulate a shaker-driven vibration environment.

Should Payload Mounting Holes Be Constrained?
I think its a NO: if you already modeled payload mass correctly.

You said:( This is correct)

• You used point masses

• Connected them using weighted links

• Only rails are constrained

why NO:

• In reality, payloads are attached internally, not fixed to the deployer.

• The only external constraint should be the rail interface.

• If you constrain payload holes, you artificially stiffen the structure.

So:

Rails constrained
Payload masses connected via weighted links
Do NOT additionally constrain payload holes

PSD Table — Linear or Logarithmic?

For launch vehicle random vibration specs:

Almost always use logarithmic frequency spacing ( I am not 100% sure , I did some research)

From Research:

"Launcher PSD profiles are typically defined in log-log format:

• Breakpoints at specific frequencies

• Slopes defined in dB/octave

• Constant PSD plateaus"

In Creo:

• Using f(x) and entering the table manually with the launcher-provided frequency points is correct.

• Enter exactly the breakpoints provided in the specification.

• Do not over-interpolate unnecessarily.

Tip: Use Review to generate Graph of your inputs

So yes to your question

Using f(x) to input the PSD table is correct.
 Enter launcher spec values exactly as given.
 Logarithmic interpretation is appropriate.

Best Practices

What damping are you using?

Random response is highly sensitive to damping near resonance.

If damping is too low → unrealistic stresses.
If too high → unconservative.

Modal Mass Participation?---Note Random analysis depends entirely on modal completeness.

I hope this helps clarify your setup and gives you more confidence in your Random (PSD) analysis approach. If anything is unclear or you’d like to discuss specific results, feel free to share more details.

I also share some Creo basic Simulate tutorials and dynamic related content on my YouTube channel ,you’re welcome to check them out here:

https://www.youtube.com/watch?v=oOr8aHcm92w