[MBDyn-users] nlsf viscous constitutive law

MBDyn users list mbdyn-users at mbdyn.org
Fri May 15 13:31:42 CEST 2020


Il 15/05/20 13:26, MBDyn users list ha scritto:
> I confirm your observation.  The "elastic" variant seems to work, 
> though.  I'm checking.

There seems to be a bug in the code of the NLSF constitutive law.  
Please open an issue, if you wish.

Sincerely, p.


>
> 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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>> MBDyn-users at mbdyn.org
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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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