[MBDyn-users] aerodynamic drag question

MBDyn users list mbdyn-users at mbdyn.org
Fri Feb 11 10:18:04 CET 2022


Thank you for your promptly reply.

Your answer was very useful!
________________________________
From: MBDyn-users <mbdyn-users-bounces at mbdyn.org> on behalf of MBDyn users list <mbdyn-users at mbdyn.org>
Sent: 11 February 2022 09:12
To: mbdyn-users at mbdyn.org <mbdyn-users at mbdyn.org>
Subject: Re: [MBDyn-users] aerodynamic drag question

Quick and dirty: the damping force is actually

    D = -0.5*C_D*A*v*|v|

where "v" is a vector, as much as D is, and the force is opposite to the absolute velocity of the point.  So you can use a regular force, and compute its magnitude and direction as

       force: 0, absolute,
                0,
                position, reference, node, null,
                component,
                        string, "-model::xvelocity(NODE)*model::velocity(NODE)*0.5*A*C_D",
                        string, "-model::yvelocity(NODE)*model::velocity(NODE)*0.5*A*C_D",
                        string, "-model::zvelocity(NODE)*model::velocity(NODE)*0.5*A*C_D";

where function "velocity" returns the norm of the absolute velocity of node "NODE", and "xvelocity", "yvelocity", and "zvelocity" return the related components.

See the attached example.

Sincerely, p.


Il 11/02/22 09:53, MBDyn users list ha scritto:
Dear Members of MBDYN,

I am thankful for all the help and guidance you have given me so far.

I have a question on aerodynamic damping concerning the example of the cantilever beam available on the website.
The cantilever beam I have developed is under gravitational load instead of a point node force and, due to its interaction with air, air damping is occurring. The forces in the systems are:
Fg: gravitational load, defined by the acceleration of gravity
FD: damping forces,0.5*Drag coefficient*Area*density*(velocity)^2
I should introduce the damping force that is not referred to the global reference frame but the nodes reference frame, and it should change according to the nodes' behaviour.
How can I develop such kind of force?

Thank you for your kind attention.

Best Regards,
Antonio






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--
Pierangelo Masarati
Professore Ordinario di Costruzioni e Strutture Aerospaziali
Dipartimento di Scienze e Tecnologie Aerospaziali
Politecnico di Milano
https://www.dona.polimi.it/
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