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Unit System

Creator
Creator

Sorry guys but I need help.Im doing frequency analysis and my accelerations are way to high(aroung 98 m/s^2) for construction where translation is just 5 mm at top .I used milimeters , kilograms and milinewtons but i read somewhere that my results will not be correct if i use milimeters instead of meters.So where is the problem, because i think that units are consistent and how to fix it(without changing measures)?Thank you .

4 REPLIES

Re: Unit System

Solution Partner Phenom Solution Partner Phenom
Solution Partner Phenom

Hello!,

If you plan to work in milimeters & force in Newtons (this is the way I do in general) the mass comes in Tons, then density units should be defined in Tons/mm3 (simply multiply the density value in Kg/m3 by factor of 1e-12), pressure & stress is in MPa.

 

Best regards,

Blas.

Blas Molero Hidalgo, Ingeniero Industrial, Director
IBERISA • 48004 BILBAO (SPAIN)
WEB: http://www.iberisa.com
Blog Femap-NX Nastran: http://iberisa.wordpress.com/

Re: Unit System

Creator
Creator

Thank you Blas but that is not my problem.My problem is that accelration is way to high for my construction but my units are consistent.So i dont know how this is possible but i read somewhere that results of frequency (hz) are wrong if i use milimeters intead of meters.Best regards!

Re: Unit System

Solution Partner Phenom Solution Partner Phenom
Solution Partner Phenom

Not at all, you can work perfectly in mm, this is simply related with mass: to be consistent in dynamic asnalysis the mass is in Tons (not in kg), and then the density should be defined in Tons/mm3, OK?.

Best regards,

Blas.

Blas Molero Hidalgo, Ingeniero Industrial, Director
IBERISA • 48004 BILBAO (SPAIN)
WEB: http://www.iberisa.com
Blog Femap-NX Nastran: http://iberisa.wordpress.com/

Re: Unit System

Creator
Creator

many thanks Blas!

just to ask you , is this acceralation(98m/s2) to much for this construction?