Angular accelerations

Nikon6260 · 2014-09-06 13:35:37

Tell me please, how I can apply angular acceleration in static analysis.
I can't find special keyword.

Last edited by Nikon6260 (2014-09-06 13:59:18)

jeanpierreaubry · 2014-09-06 14:30:40

hello

in AFFE_CHAR_MECA keyword ROTATION
you can set agular velocity and vector direction
look in U4..44.01

jean pierre aubry

Nikon6260 · 2014-09-06 14:37:47

jeanpierreaubry wrote:

hello
in AFFE_CHAR_MECA keyword ROTATION
you can set agular velocity and vector direction
look in U4..44.01
jean pierre aubry

It's angular velocity, but I need angular ACCELERATION.

jeanpierreaubry · 2014-09-06 15:07:10

Nikon6260 wrote:

It's angular velocity, but I need angular ACCELERATION.

please read the part in the documentation it is written in there

Nikon6260 · 2014-09-06 15:16:35

jeanpierreaubry
Please tell me which section to read.

jeanpierreaubry · 2014-09-06 15:26:12

i told you just above

in AFFE_CHAR_MECA, U4..44.01, keyword ROTATION
section may change according to version
and there is a table of content at the begining

Nikon6260 · 2014-09-06 15:41:17

jeanpierreaubry wrote:

i told you just above
in AFFE_CHAR_MECA, U4..44.01, keyword ROTATION
section may change according to version
and there is a table of content at the begining

U4..44.01 (AFFE_CHAR_MECA) -> keyword ROTATION
"The key word factor ROTATION is usable to apply a field of force equivalent to the centrifugal force applying to a structure in rotation. Either OMEGA rotational speed and (ar, br, cr) the rotational axis."

Keyword ROTATION it's rotation velocity - OMEGA [rad/sec]

I need angular acceleration [rad/sec^2].

keeswouters · 2014-09-07 08:50:05

Hoi Nikon

you cannot use angular acceleration in a static calculation.
Since an angular velocity already yields a (linear) acceleration in the part (and force dF = rho*dV*omega*omega), the forces caused by an angular acceleration will depend on the state and hence cannot be used in a static calculation.

Nikon6260 · 2014-09-07 15:48:01

keeswouters wrote:

Hoi Nikon
you cannot use angular acceleration in a static calculation.
Since an angular velocity already yields a (linear) acceleration in the part (and force dF = rho*dV*omega*omega), the forces caused by an angular acceleration will depend on the state and hence cannot be used in a static calculation.

keeswouters

I can use the angular acceleration in the static analysis.
For example, together with the linear acceleration (ax, ay, az) angular acceleration (ex, ey, ez) are used to balance the body under loads (for example Inertia relief from Ansys and Nastran).

paster · 2014-09-07 21:14:39

Hello

Beautiful example of endless discussion due to a mutual misunderstanding.
The initial goal is not exactly said and this capability very useful for unconstrained structures (not usual in nuclear industry) is not planned in Code-Aster (because no need). It is a fact and maybe it will be possible to plan this development (or made by yourself in an open environment)
At the initial question, the best reply has to say: it is not possible at time in Code-ASTER!

Good evening

jeanpierreaubry · 2014-09-08 06:44:31

paster wrote:

At the initial question, the best reply has to say: it is not possible at time in Code-ASTER!

not exactly "not possible"!

as if you perform a STAT_NON_LINE analysis with the right law for increasing speed
at the final step you will get the equivalent of an applied acceleration
if just like keeswouters i remember well my basic physics courses!

(this used to be stated in U4..44.01 (AFFE_CHAR_MECA) -> keyword ROTATION in earlier version, e.g. 9.2)

there are many things Nastran can do in a direct manner that Code_Aster cannot do in the same way
and probably just as many Code_Aster can do and Nastran cannot!!!

Nikon6260 · 2014-09-08 08:03:04

Initial question was simple:
"how I can apply angular acceleration in static analysis".

As a result we obtain a simple answer:
"it is not possible at time in Code-ASTER!".

Thanks

jeanpierreaubry · 2014-09-08 13:47:35

Nikon6260 wrote:

Initial question was simple:
"how I can apply angular acceleration in static analysis".
As a result we obtain a simple answer:
"it is not possible at time in Code-ASTER!".

Thanks

excuse my lengthy answers
i thought you were trying to find a solution to a practical problem!

keeswouters · 2014-09-08 18:28:27

hoi allemaal

oeps.
Summer is not over yet.

Last edited by keeswouters (2014-09-08 18:29:19)

Nikon6260 · 2015-01-08 16:39:32

Hello.

Code for apply angular acceleration in static analysis:

#density
dens=7800;

#angular accelerations
ACC_EX=10
ACC_EY=20
ACC_EZ=30

#definition inertia loads
F_X=FORMULE(VALE='(ACC_EY*sqrt(X*X+Z*Z)*cos(atan2(X,Z))*(dens))*(-1)+(ACC_EZ*sqrt(X*X+Y*Y)*sin(atan2(Y,X))*(dens))', NOM_PARA=('X','Y','Z',),);
F_Y=FORMULE(VALE='(ACC_EX*sqrt(Y*Y+Z*Z)*sin(atan2(Z,Y))*(dens))+(ACC_EZ*sqrt(X*X+Y*Y)*cos(atan2(Y,X))*(dens))*(-1)', NOM_PARA=('X','Y','Z',),);
F_Z=FORMULE(VALE='(ACC_EX*sqrt(Y*Y+Z*Z)*cos(atan2(Z,Y))*(dens))*(-1)+(ACC_EY*sqrt(X*X+Z*Z)*sin(atan2(X,Z))*(dens))', NOM_PARA=('X','Y','Z',),);
 
ACC_ANG=AFFE_CHAR_MECA_F(MODELE=MODEL,
		FORCE_INTERNE =(
				_F(TOUT='OUI',
				FX=F_X,
				FY=F_Y,
				FZ=F_Z,
				   ),
                                ),
                                );

Last edited by Nikon6260 (2015-01-11 10:18:42)

reiteres · 2015-01-08 21:21:20

Hi!

I quite don't understand why you make it so complicated? If you need rotational acceleration, but only have rotational speed, one always can use the simple relation
a(t) = dv(t)/dt.
Only integrate your acceleration function and you are fine.

Edit: Ok I oversaw that this only supports centrifugal forces. You are right. Thank you for sharing.

Last edited by reiteres (2015-01-08 21:51:31)

kaengo · 2018-01-20 18:03:32

Salut à tous ici !

I also need ( better: 'would need', of cause I am also able to switch to ANSYS, but I don't want...) the rotational acceleration

I must calculate the craddles, which are needed to transport monopiles on a barge.

Because
the rotational inertia of the monopiles is very big (above the cross axes only of cause ...)
and there are transversal and rotational accelerations acting from motion of the sea,

there are also some loads from rotational accelerations acting onto the craddles,
which I must not neglect.

I'm new with CA, so I can't code it, but I think, it would be relatively simple,
your work Nikon6260 is directing in the correct direction.
(I think, somebody needs only to duplicate the code of rotational velocity and change the formulas of the field ...)

I will play a bit with your script, but at this time I am not familiar enough with CA.

Greetings,
Holger

Edit: Hello Nikon6260,
I have checked you script, it is working fine.
But I will go to remove the ,doubled' trignonmetric functions.
Greetings,
Holger

Last edited by kaengo (2018-01-22 19:24:20)

#1 2014-09-06 13:35:37

Angular accelerations

#2 2014-09-06 14:30:40

Re: Angular accelerations

#3 2014-09-06 14:37:47

Re: Angular accelerations

#4 2014-09-06 15:07:10

Re: Angular accelerations

#5 2014-09-06 15:16:35

Re: Angular accelerations

#6 2014-09-06 15:26:12

Re: Angular accelerations

#7 2014-09-06 15:41:17

Re: Angular accelerations

#8 2014-09-07 08:50:05

Re: Angular accelerations

#9 2014-09-07 15:48:01

Re: Angular accelerations

#10 2014-09-07 21:14:39

Re: Angular accelerations

#11 2014-09-08 06:44:31

Re: Angular accelerations

#12 2014-09-08 08:03:04

Re: Angular accelerations

#13 2014-09-08 13:47:35

Re: Angular accelerations

#14 2014-09-08 18:28:27

Re: Angular accelerations

#15 2015-01-08 16:39:32

Re: Angular accelerations

#16 2015-01-08 21:21:20

Re: Angular accelerations

#17 2018-01-20 18:03:32

Re: Angular accelerations

Board footer