Ansys Guru Needed: Troubleshooting Offshore Wind Turbine Tower Units

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Discussion Overview

The discussion revolves around troubleshooting unit inconsistencies in Ansys while designing an offshore wind turbine tower for subarctic conditions. Participants explore the implications of using different unit systems and their effects on simulation results.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • The original poster expresses confusion regarding unit systems in Ansys, specifically using kiloponds and centimeters instead of standard SI units.
  • Some participants suggest reverting to standard SI units to avoid complications and ensure consistency in results.
  • One participant proposes creating a simple model in standard SI units and converting results afterward to verify accuracy.
  • Another participant provides two sets of consistent units that could be used, emphasizing the importance of avoiding kilopond due to its inconsistency.
  • There is a mention of a significant discrepancy in results when using different densities, leading to a large number of solutions being generated in one case.
  • One participant questions the rationale behind the supervisor's preference for non-standard units, suggesting it may relate to desired output in megapascals.
  • Corrections are made regarding the spelling and capitalization of unit symbols, highlighting the importance of precision in technical discussions.

Areas of Agreement / Disagreement

Participants generally agree that using standard SI units is preferable, but there is disagreement regarding the necessity and reasoning behind the supervisor's insistence on alternative units. The discussion remains unresolved regarding the supervisor's preferences and the implications of using different unit systems.

Contextual Notes

Some participants note the potential for confusion arising from the use of kilopond and centimeters, which may lead to inconsistent results. There are also unresolved issues regarding the original poster's simulation results and the reasons for discrepancies in output.

sisquet
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Hi!

I'm doing my master thesis about designing a offshore wind turbine tower for subarctic conditions and I have a major problem with units

I'm not much familiarised with Ansys, so I use Ansa as preprocessor and launch the solve in Ansys

The problem I have is in units. I'm using Ansys SI units but tweaked
Long. cm
Mass. Kp
Time. s

and therefore all units combinig those
P Kp/cm^2
dens Kp/cm^3
Force kp/cm·s^-2

the problem is that, my supervisor keeps on saying that for density and MASS21 elements i should use t/cm^3 and t and I don't like the reasons he has given me about it. Furthermore when i run a Block lanzos nodal calculation my first mode is around 0.3E-1 which is far away from expected result of 0.3Hz.
So when i run with density 7.85E-3 i and i tell ansys so extract 4 first modes i got in comand window like, not kidding, +400 solutions and this before cancelling the calculation after 20min when with the other density doesn't take more than 1 min to find results

Im kind of stuck, cause if the nodal is not correct it makes no sense that i waste time trying to optimise an estatic and dynamic model

Please any Ansys guru could help? thanks a million
 
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My advice woud be stop wasting your time with these questions and just use basic SI units.

Or if you really want to do this, make a simple model in basic SI units, then convert it you your own unit system and check the answers are the same. (And if they aren't the same, go back to my first piece of advice).
 
I agree with AlephZero, you're better off just using standard units and converting back to whatever you want AFTER you've gotten your solution.
 
Hi guys!

thanks a million with your answers! did a quick change to SI units and works perfect! I think going to keep with SI units...the problem will be to convince my supervisor about it...cause he was not happy of having results in Pa or J, but whatever, I'm done in going crazy as to set a consistend set of units

Problem solved, mod can close the thread
 
You can convert the results to any set of units your professor wants, but I'm having trouble understanding why he would want anything other than standard SI...
 
to get results in MPa is my guess...
 
sisquet: You can use either of the following sets of consistent units.

(1) Newton (N), meter (m), second (s), pascal (Pa), kilogram (kg), joule (J).
(2) Newton (N), millimeter (mm), second (s), megapascal (MPa), tonne (t), millijoule (mJ).

Item 1 is standard SI. Item 2 is my favorite. If in doubt, use item 1. Avoid cm.

If you use item 2, then the units of density and mass are t/mm^3 and t, respectively. Therefore, e.g., your density in post 1 would then become 7850.0e-12 t/mm^3, or 7.85e-9 t/mm^3.

By the way, some of your unit symbols are misspelled in post 1. Always use correct spelling and capitalization of units. E.g., the unit symbol for kilopond is kp, not Kp. Kp means kelvin pico.

However, completely avoid using kilopond; it is inconsistent and incoherent.

Also, always leave a space between a numeric value and its following unit symbol. E.g., 0.3 Hz, not 0.3Hz.
 
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