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Best representation of the sliding formulation

Best representation of the sliding formulation

Best representation of the sliding formulation

(OP)
Hello,

I'm doing a foot simulation in Abaqus standard and i don't know what is the best representation of the sliding formulation (Finite sliding or small sliding) between the bone and the cartilage.

Thank you for any help you can give!

RE: Best representation of the sliding formulation

Finite Sliding is the general formulation. Small Sliding can only be used, when you have very small relative movements (smaller that app. a 5th of the element length in the contact area). Small Sliding is computationally less expensive.

RE: Best representation of the sliding formulation

(OP)
I used small sliding but the cartilage is falling apart, shold i turn off the separation in normal behavior?

Thank you.

RE: Best representation of the sliding formulation

I don't know. It depends what the reason is, why the parts are separating. Deactivating the option to separate may lead to unrealistic results.

RE: Best representation of the sliding formulation

An image can't explain what's going on in the analysis and what is defined in the model overall.

RE: Best representation of the sliding formulation

Open up the message file (.msg) in your current working directory and look for numerical singularity messages. Also, tell us what types of warning/error messages you see in the .msg/.dat files (do NOT dump them here).

*********************************************************
Are you new to this forum? If so, please read these FAQs:

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RE: Best representation of the sliding formulation

(OP)
All the messages:
***WARNING: THE SYSTEM MATRIX HAS 1 NEGATIVE EIGENVALUES.
EXPLANATIONS ARE SUGGESTED AFTER THE FIRST OCCURRENCE OF THIS MESSAGE.
***WARNING: THERE IS ZERO MOMENT EVERYWHERE IN THE MODEL BASED ON THE DEFAULT
CRITERION. PLEASE CHECK THE VALUE OF THE AVERAGE MOMENT DURING THE
CURRENT ITERATION TO VERIFY THAT THE MOMENT IS SMALL ENOUGH TO BE
TREATED AS ZERO. IF NOT, PLEASE USE THE SOLUTION CONTROLS TO RESET
THE CRITERION FOR ZERO MOMENT
***WARNING: THERE IS ZERO PR. FLUX EVERYWHERE IN THE MODEL BASED ON THE
DEFAULT CRITERION. PLEASE CHECK THE VALUE OF THE AVERAGE PR. FLUX
DURING THE CURRENT ITERATION TO VERIFY THAT THE PR. FLUX IS SMALL
ENOUGH TO BE TREATED AS ZERO. IF NOT, PLEASE USE THE SOLUTION
CONTROLS TO RESET THE CRITERION FOR ZERO PR. FLUX.
***NOTE: THE SOLUTION APPEARS TO BE DIVERGING. CONVERGENCE IS JUDGED UNLIKELY.
I only can apply 10% of the load.

RE: Best representation of the sliding formulation

Have you tried to check the job diagnostics?

Link

RE: Best representation of the sliding formulation

(OP)
Inicial warnings:
"For two-dimensional models, if a non-unity thickness is specified for two-dimensional solid elements and these elements are involved in an interaction such as contact, the same thickness should be specified for the out-of-plane thickness of the corresponding surface under *surface interaction.

Whenever a translation (rotation) dof at a node is constrained by a kinematic coupling definition the translation (rotation) dofs for that node cannot be included in any other constraint including mpcs, rigid bodies, etc.

For contact pair (assembly_s_surf-495-assembly_m_surf-669), not all the nodes that have been adjusted were printed. Specify *preprint,contact=yes for complete printout.

For contact pair (assembly_s_surf-811-assembly_m_surf-811), not all the nodes that have been adjusted were printed. Specify *preprint,contact=yes for complete printout.

For contact pair (assembly_s_surf-501-assembly_m_surf-810), not all the nodes that have been adjusted were printed. Specify *preprint,contact=yes for complete printout.

For contact pair (assembly_s_surf-507-assembly_m_surf-814), not all the nodes that have been adjusted were printed. Specify *preprint,contact=yes for complete printout.

For contact pair (assembly_s_surf-509-assembly_m_surf-817), not all the nodes that have been adjusted were printed. Specify *preprint,contact=yes for complete printout.

For contact pair (assembly_s_surf-819-assembly_m_surf-821), not all the nodes that have been adjusted were printed. Specify *preprint,contact=yes for complete printout.

For contact pair (assembly_s_surf-822-assembly_m_surf-849), not all the nodes that have been adjusted were printed. Specify *preprint,contact=yes for complete printout.

Not all the nodes that do not find intersection with the master surface are printed. However all of these nodes have been included in a node set.

For contact pair (assembly_s_surf-846-assembly_m_surf-846), not all the nodes that have been adjusted were printed. Specify *preprint,contact=yes for complete printout.

For contact pair (assembly_s_surf-697-assembly_m_surf-823), not all the nodes that have been adjusted were printed. Specify *preprint,contact=yes for complete printout.

For contact pair (assembly_s_surf-843-assembly_m_surf-843), not all the nodes that have been adjusted were printed. Specify *preprint,contact=yes for complete printout.

For contact pair (assembly_s_surf-1010-assembly_m_surf-1011), not all the nodes that have been adjusted were printed. Specify *preprint,contact=yes for complete printout.

For contact pair (assembly_s_surf-827-assembly_m_surf-826), not all the nodes that have been adjusted were printed. Specify *preprint,contact=yes for complete printout.

The ratio of the maximum incremental adjustment to the average characteristic length is 1.41952e-02 at node 20621 instance suportepe-33-1 on the surface pair (assembly_s_surf-529,assembly_m_surf-850).

Not all the nodes that do not find intersection with the master surface are printed. However all of these nodes have been included in a node set.

For contact pair (assembly_s_surf-529-assembly_m_surf-850), not all the nodes that have been adjusted were printed. Specify *preprint,contact=yes for complete printout.

For contact pair (assembly_s_surf-829-assembly_m_surf-828), not all the nodes that have been adjusted were printed. Specify *preprint,contact=yes for complete printout.

For contact pair (assembly_s_surf-831-assembly_m_surf-830), not all the nodes that have been adjusted were printed. Specify *preprint,contact=yes for complete printout.

For contact pair (assembly_s_surf-719-assembly_m_surf-719), not all the nodes that have been adjusted were printed. Specify *preprint,contact=yes for complete printout.

For contact pair (assembly_s_surf-537-assembly_m_surf-712), not all the nodes that have been adjusted were printed. Specify *preprint,contact=yes for complete printout.

For contact pair (assembly_s_surf-541-assembly_m_surf-541), not all the nodes that have been adjusted were printed. Specify *preprint,contact=yes for complete printout.

For contact pair (assembly_s_surf-543-assembly_m_surf-543), not all the nodes that have been adjusted were printed. Specify *preprint,contact=yes for complete printout.

Not all the nodes that do not find intersection with the master surface are printed. However all of these nodes have been included in a node set.

For contact pair (assembly_s_surf-833-assembly_m_surf-833), not all the nodes that have been adjusted were printed. Specify *preprint,contact=yes for complete printout.

For contact pair (assembly_s_surf-734-assembly_m_surf-734), adjustment was specified but no node was adjusted more than the adjustment distance = 2.22000e-16.

For contact pair (assembly_s_surf-721-assembly_m_surf-721), adjustment was specified but no node was adjusted more than the adjustment distance = 2.22000e-16.

For contact pair (assembly_s_surf-835-assembly_m_surf-837), not all the nodes that have been adjusted were printed. Specify *preprint,contact=yes for complete printout.

For contact pair (assembly_s_surf-555-assembly_m_surf-838), not all the nodes that have been adjusted were printed. Specify *preprint,contact=yes for complete printout.

For contact pair (assembly_s_surf-701-assembly_m_surf-704), not all the nodes that have been adjusted were printed. Specify *preprint,contact=yes for complete printout.

The ratio of the maximum incremental adjustment to the average characteristic length is 1.21836e-02 at node 20416 instance suportepe-33-1 on the surface pair (assembly_s_surf-570,assembly_m_surf-851).

For contact pair (assembly_s_surf-570-assembly_m_surf-851), not all the nodes that have been adjusted were printed. Specify *preprint,contact=yes for complete printout.

2956 nodes are either missing intersection with their respective master surface or are outside the adjust zone. The nodes have been identified in node set WarnNodeMissMasterIntersect.

153 nodes are used more than once as a slave node in *TIE keyword. One of the *TIE constraints at each of these nodes have been removed. The nodes have been identified in node set WarnNodeOverconTieSlave.

Slave node 3 instance suportepe-31-1 found no intersection with the master surface. The initial clearance provided for that node is ignored

Slave node 80 instance suportepe-31-1 found no intersection with the master surface. The initial clearance provided for that node is ignored

Slave node 81 instance suportepe-31-1 found no intersection with the master surface. The initial clearance provided for that node is ignored

Slave node 82 instance suportepe-31-1 found no intersection with the master surface. The initial clearance provided for that node is ignored

Not all the nodes that are part of slave surface assembly_s_surf-846 that did not find intersecion with the master surface assembly_m_surf-846 were printed. The initial clearance provided for these nodes are ignored. Specify *preprint,contact=yes for complete printout.

Slave node 20727 instance suportepe-33-1 found no intersection with the master surface. The initial clearance provided for that node is ignored

Slave node 20737 instance suportepe-33-1 found no intersection with the master surface. The initial clearance provided for that node is ignored

Not all the nodes that are part of slave surface assembly_s_surf-529 that did not find intersecion with the master surface assembly_m_surf-850 were printed. The initial clearance provided for these nodes are ignored. Specify *preprint,contact=yes for complete printout.

Slave node 75 instance suportepe-31-1 found no intersection with the master surface. The initial clearance provided for that node is ignored

Slave node 124 instance suportepe-31-1 found no intersection with the master surface. The initial clearance provided for that node is ignored

Slave node 130 instance suportepe-31-1 found no intersection with the master surface. The initial clearance

Not all the nodes that are part of slave surface assembly_s_surf-833 that did not find intersecion with the master surface assembly_m_surf-833 were printed. The initial clearance provided for these nodes are ignored. Specify *preprint,contact=yes for complete printout.

Slave node 20350 instance suportepe-33-1 found no intersection with the master surface. The initial clearance provided for that node is ignored

C3d10hs and hybrid tetrahedral elements will enforce volumetric continuity across material boundaries. In order to allow discontinuities in the volumetric field use *tie.

MPCS (EXTERNAL or INTERNAL, including those generated from rigid body definitions), KINEMATIC COUPLINGS, AND/OR EQUATIONS WILL ACTIVATE ADDITIONAL DEGREES OF FREEDOM

684 elements are distorted. Either the isoparametric angles are out of the suggested limits or the triangular or tetrahedral quality measure is bad. The elements have been identified in element set WarnElemDistorted."

RE: Best representation of the sliding formulation

(OP)
During simulation:
I have the mentioned warnings and Max penetration.
"MAX. PENETRATION ERROR 846.571E-09 AT NODE SUPORTEPE-35-1.6369 OF CONTACT
PAIR (ASSEMBLY_S_SURF-746,ASSEMBLY_M_SURF-725)
MAX. CONTACT FORCE ERROR 8.91911E-03 AT NODE SUPORTEPE-35-1.6369 OF CONTACT
PAIR (ASSEMBLY_S_SURF-746,ASSEMBLY_M_SURF-725)
PENETRATION ERROR TOO LARGE COMPARED TO DISPLACEMENT INCREMENT.

AVERAGE FORCE 1.712E-05 TIME AVG. FORCE 8.79
(FROM MOMENT FIELD)
LARGEST RESIDUAL FORCE 0.726 AT NODE 1 DOF 1
INSTANCE: LIGA-9-1
LARGEST INCREMENT OF DISP. 5.273E-06 AT NODE 6842 DOF 3
INSTANCE: SUPORTEPE-35-1
LARGEST CORRECTION TO DISP. 5.273E-06 AT NODE 6842 DOF 3
INSTANCE: SUPORTEPE-35-1
THE FORCE IS ZERO EVERYWHERE BUT THE FORCE RESIDUAL OR
THE DISP. CORRECTION IS NON-ZERO

AVERAGE MOMENT 2.410E-07 TIME AVG. MOMENT 2.410E-07
LARGEST RESIDUAL MOMENT 1.757E-05 AT NODE 1 DOF 5
INSTANCE: LIGA-6-1
LARGEST INCREMENT OF ROTATION 2.738E-04 AT NODE 1 DOF 4
INSTANCE: LIGA-8-1
LARGEST CORRECTION TO ROTATION 2.738E-04 AT NODE 1 DOF 4
INSTANCE: LIGA-8-1
MOMENT EQUILIBRIUM NOT ACHIEVED WITHIN TOLERANCE.

AVERAGE PR. FLUX 1.791E-10 TIME AVG. PR. FLUX 1.000E-02
LARGEST RESIDUAL PR. FLUX 3.339E-10 AT NODE 31149
INSTANCE: SUPORTEPE-35-1
LARGEST INCREMENT OF VOL. LM. -1.890E-03 AT NODE 516
INSTANCE: SUPORTEPE-35-1
LARGEST CORRECTION TO VOL. LM. -1.890E-03 AT NODE 516
INSTANCE: SUPORTEPE-35-1
THERE IS ZERO PR. FLUX EVERYWHERE
"
It's this memory data normal?

PROCESS FLOATING PT MINIMUM MEMORY MEMORY TO
OPERATIONS REQUIRED MINIMIZE I/O
PER ITERATION (MB) (MB)

1 3.01E+012 1115 11123

RE: Best representation of the sliding formulation

(OP)
I'm also using small sliding it's that realistic?

RE: Best representation of the sliding formulation

You sent this following message: "684 elements are distorted."

If you have bad elements then it can be problematic. Turn the bad elements good again.

If the mesh is good when you mesh but you still get the message, then maybe the ADJUST is moving nodes so much that the elements become bad when the analysis starts.

I use "small sliding" when sliding is "small". If sliding is large, try "finite sliding". Try both. Evaluate both.

Check the location of every node that has a warning. It can give you an idea of what the problem is.

RE: Best representation of the sliding formulation

Having worked in this domain, I have a feeling that bad elements may not be the root cause.

Also, with regard to finite vs. small sliding, the choice depends on the specific application. Within the context of the application (running, jumping, hopping, etc.), do you expect the bones in the foot to slide past each other by more than a fraction of the characteristic length of an element or not? The characteristic length for this situation would be the elements representing the bones across an interface.

*********************************************************
Are you new to this forum? If so, please read these FAQs:

http://www.eng-tips.com/faqs.cfm?fid=376
http://www.eng-tips.com/faqs.cfm?fid=1083

RE: Best representation of the sliding formulation

(OP)
I can not further reduce mesh elements so I have to stay with the "684 elements are distorted"
I wiil try to give more details about my problem.
I have small sliding interaction proprety between the bones and cartilage with tangencial behaviour frictioless and normal behaviour "hard contact"(No separation) with adjust to remove overclosure. (The bones are the surface master)
Beetween the soft tissues and the rigid body i have a finite slading interaction defined by tangencial behavior "penalty", with a coeficient of friction of 0.6.(The rigid body is the surface master)
The bones are tied to the soft tissues and adjusted to inicial position. (The bones are the surface master)
I have two steps (static general, Direct, Unsymmetric matrix, Full Newton), the first i have a small displacment in the rigid body for making contact with the foot, and the second one it the application of force in the rigid body for see foot plantar pressure.
The top of tibia fibula and soft tissues are encastrate.
I have constraint the bones with the plantar fascia and ligaments wiht coupling (continuum distributing). (The nodes of ligaments and plantar fascia are the master)
The only messages during the simulation are "***WARNING: THE SYSTEM MATRIX HAS # NEGATIVE EIGENVALUES." "***NOTE: THE SOLUTION APPEARS TO BE DIVERGING. CONVERGENCE IS JUDGED UNLIKELY" and i have the initial warnnings previously mentioned.

Thank you so much for the support.

RE: Best representation of the sliding formulation

(OP)
Adjust to remove overclosure and adjusted to inicial position makes the simulation go faster or slower?

RE: Best representation of the sliding formulation

(OP)
What this messages mean? can i ignore them?
"There is zero PR. FLUX everywhere in the model based on the default criterion. please check the value of the average PR. FLUX during the current iteration to verify that the PR. FLUX is small enough to be treated as zero. if not, please use the solution controls to reset the criterion for zero PR. FLUX.

There is zero MOMENT everywhere in the model based on the default criterion. please check the value of the average MOMENT during the current iteration to verify that the MOMENT is small enough to be treated as zero. if not, please use the solution controls to reset the criterion for zero MOMENT."

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