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comsol 4.0 drag force operator
Posted 21 nov. 2010, 00:34 UTC−5 4 Replies
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Hi, i've used drag force operator reacf() in laminar models.
but I've been trying to calculate drag force of 3d model in turbulent model. However, this reacf() operator gives only zero value.
I've searched the forum but I've only found T_x_chns / T_y_chns operators but comsol doesn't know what that means. I couldn't find it in the reference material.
Does the 'total stress' operator relate to the drag force?
So, how to derive drag force in turbulent 3d model? thanks,
but I've been trying to calculate drag force of 3d model in turbulent model. However, this reacf() operator gives only zero value.
I've searched the forum but I've only found T_x_chns / T_y_chns operators but comsol doesn't know what that means. I couldn't find it in the reference material.
Does the 'total stress' operator relate to the drag force?
So, how to derive drag force in turbulent 3d model? thanks,
4 Replies Last Post 16 févr. 2015, 17:50 UTC−5
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Posted:
1 decade ago
Hi
check if the weak form Lagrange Multipliers are "on" for your boundaries, then, if I remember right, the traditional forces via reacf() are no longer defined, and you should integrate the "xx_lm" instead
--
Good luck
Ivar
check if the weak form Lagrange Multipliers are "on" for your boundaries, then, if I remember right, the traditional forces via reacf() are no longer defined, and you should integrate the "xx_lm" instead
--
Good luck
Ivar
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Posted:
1 decade ago
how can I use xx_lm in the expression? what are the proper parameters i need to define? For reacf(u), i would define the flow in the x direction for drag force.
thanks
thanks
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Posted:
1 decade ago
Hi
the Lagrange Multiplier for a standard ST structural 3D case are u_lm, v_lm ad w_lm and exist if the "weak" constraint is checked on for fixed boundaries, or when COMSOL adds them, which is model/physics dependent. In structural the Lagrange Multiplers have the units of [Pa] so these must be integrated over an Area to get out the forces in [N]. But the lm have different units in different Physics.
Check the doc about the lm carefully, and check your model, it all depends on what you are doing and which Physics you are using.
Furthermore, 4.0 is an early version, there are many things not really working, particularly in the fluidics and FSI, you should rather get hands on a version 4.1, it's being shipped these days
--
Good luck
Ivar
the Lagrange Multiplier for a standard ST structural 3D case are u_lm, v_lm ad w_lm and exist if the "weak" constraint is checked on for fixed boundaries, or when COMSOL adds them, which is model/physics dependent. In structural the Lagrange Multiplers have the units of [Pa] so these must be integrated over an Area to get out the forces in [N]. But the lm have different units in different Physics.
Check the doc about the lm carefully, and check your model, it all depends on what you are doing and which Physics you are using.
Furthermore, 4.0 is an early version, there are many things not really working, particularly in the fluidics and FSI, you should rather get hands on a version 4.1, it's being shipped these days
--
Good luck
Ivar
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Posted:
10 years ago
Hi Ivar,
According what you said, may I regard the "Lagrange multiplier velocity" in a laminar flow physics as the reaction force on the boundary?
Yes, you are right, I checked the unit of u_lm , it is Pa. Here, we take "-u_lm" for example, can it be used to represent the pressure per m^2 on the boundary of corresponding point in the x direction?
According what you said, may I regard the "Lagrange multiplier velocity" in a laminar flow physics as the reaction force on the boundary?
Yes, you are right, I checked the unit of u_lm , it is Pa. Here, we take "-u_lm" for example, can it be used to represent the pressure per m^2 on the boundary of corresponding point in the x direction?