[MBDyn-users] nlsf viscous constitutive law

MBDyn users list mbdyn-users at mbdyn.org
Fri May 15 13:26:18 CEST 2020


I confirm your observation.  The "elastic" variant seems to work, 
though.  I'm checking.

Sincerely, p.


Il 15/05/20 12:05, MBDyn users list ha scritto:
>
> Further to my email below about using the nlsf viscous constitutive 
> law I simplified the example further by just using a const scalar 
> function. Nothing I do seems to have any effect on the motion of the 
> two masses (which are connected by a deformable displacement 
> joint).This is using MBDyn buit from the git 'devel' branch.
>
> All this file is supposed to do is make two spherical bodies of radius 
> 0.1m and mass 1kg, clamp one, and connect the two by the deformable 
> displacement joint, which uses the nlsf viscous constitutive law. I 
> would expect to see a force from this joint when the second mass 
> begins to move, but the force from the joint remains zero. Can anyone 
> confirm they get the same result?
>
>
> begin: data;
>     problem: initial value;
> end: data;
>
> # initial value problem
> begin: initial value;
>     initial time: 0.0;
>     final time: 20.0;
>     time step: 0.100000000000000006;
>     tolerance: 0.000000001;
>     max iterations: 20;
> end: initial value;
>
>
> begin: control data;
>     structural nodes: 2;
>     rigid bodies: 2;
>     joints: 2;
>     gravity;
>     default orientation: orientation matrix;
>     output results: netcdf, no text;
> end: control data;
>
> begin: nodes;
>
>     # 6 DOF structural node
>     structural : 1, dynamic, # label, type
>         position, 0.0, 0.0, 0.0, # absolute position
>         orientation,
>         matr,
>         1.0, 0.0, 0.0,
>         0.0, 1.0, 0.0,
>         0.0, 0.0, 1.0, # absolute orientation
>         velocity, 0.0, 0.0, 0.0, # absolute velocity
>         angular velocity, 0.0, 0.0, 0.0 # absolute angular velocity
>     ; # end structural node
>
>     # 6 DOF structural node
>     structural : 2, dynamic, # label, type
>         position, 0.0, 0.0, 0.0, # absolute position
>         orientation,
>         matr,
>         1.0, 0.0, 0.0,
>         0.0, 1.0, 0.0,
>         0.0, 0.0, 1.0, # absolute orientation
>         velocity, 0.0, 0.0, 0.0, # absolute velocity
>         angular velocity, 0.0, 0.0, 0.0 # absolute angular velocity
>     ; # end structural node
>
> end: nodes;
>
> scalar function : "nlsf damping", const, 4.905000000000000249 ;
>
>
> begin: elements;
>
>     # body
>     body : 3, 1, # label, node label
>         1.0, # mass
>         0.0, 0.0, 0.0, # relative centre of mass
>         matr,
>         0.004000000000000001, 0.0, 0.0,
>         0.0, 0.004000000000000001, 0.0,
>         0.0, 0.0, 0.004000000000000001 # inertia matrix
>     ; # end one-mass body
>
>     # body
>     body : 4, 2, # label, node label
>         1.0, # mass
>         0.0, 0.0, 0.0, # relative centre of mass
>         matr,
>         0.004000000000000001, 0.0, 0.0,
>         0.0, 0.004000000000000001, 0.0,
>         0.0, 0.0, 0.004000000000000001 # inertia matrix
>     ; # end one-mass body
>
>     # clamp
>     joint : 5, clamp,
>         1, # node label
>             position, node, # absolute position
>             orientation, node # absolute orientation
>     ; # end clamp
>
>     # deformable displacement joint with name PTO_Damper
>     joint : 6, deformable displacement joint,
>         1, # node label
>             position, reference, node, null,
>         2, # node label
>             position, reference, other node, null,
>         nlsf viscous, null, null, null, "nlsf damping"
>     ; # end deformable displacement joint
>
>     gravity : uniform, single, 0.0, 0.0, -1.0, const, 
> 9.810000000000000497;
>
> end: elements;
>
>
>
> On 05/05/2020 22:51, Richard Crozier wrote:
>> Dear List,
>>
>> I wanted to implement a damper with a force limit, i.e. linear 
>> damping until a maximum allowed force was reached. To do this I tried 
>> using the nlsf viscous constitutive law with a deformable 
>> displacement joint. I used a mulitlinear scalar function to attempt 
>> to get the correct force profile. I have attached a minimal example 
>> of this. However, when I examine the output, the deformable joint 
>> force is zero. Can anyone suggest what I might be doing wrong?
>>
>> Best regards,
>>
>> Richard
>
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-- 
Pierangelo Masarati
Professore Ordinario di Costruzioni e Strutture Aerospaziali
Dipartimento di Scienze e Tecnologie Aerospaziali
Politecnico di Milano



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