I am using ANSYS APDL, I need one clarification regarding the use of force and displacement convergent values, it has default values of 0.001&0.01. But what I seen in my problem is even when I put 0.05 for force & 0.005 for displacement my problem dis nor converges, but if I drop the force convergence and only considered displacement convergence with tolerance value 0.25, then only I get somehow a near by values or else it stops meanwhile stating any one element has large displacement etc.
So anyone plz explain whether we need to use both the convergence factor upto ultimate load or we can use only with displacement conv. Values only. Plz suggest what will be the optimum range.
Mr. Pandi,
ANSYS is a finite element based software and analysis can be performed by load controlled or displacement controlled analysis. If you use load controlled analysis the displacement is the unknown and in every load step during the calculation program need to verify convergence criteria if satisfies then switch over to next load step or not satisfying it shows an error. So for load controlled analysis, the displacement factor is a convergence criteria. If you perform displacement controlled analysis then force criteria is the convergence factor. Depending upon the type of analysis you have use either force or displacement criteria for satisfying convergence. Convergence criteria is usually go with lower value like 0.005 mm as you too have used in the analysis for a value of 0.005 mm. If suppose convergence criteria is not satisfied then it is better to verify the material properties rather than modifying the convergence criteria.
If you use lower value of 0.005 mm as convergence criteria indicates solution accuracy is better. or if you use higher value like 0.25 in this case solution accuracy is less. Thought convergence criteria is satisfied but solution accuracy is poor. So, it is better to use lower value for satisfying convergence criteria. For further understanding in this regard, i recommend you to read ANSYS manual.. ok all the best..
thank you so much for your kind response, and also i have one more doubt sir.
1. i use link 180 element for prestress tendon, in ANSYS 12 version we can directly apply the prestrain which cause the beam to prestress, but now i use ANSYS 19V, their is no direct approach but can be given by inistate command.could you plz expain when this instate command need to be input, at the time element selection or at the time of loading is given.
2. how to model contact between concrete and prestress steel for bonded and unbonded post tensioned prestress concrete beams.
thank you sir,
Hi Pandi. I believe that all the three: displacement, force and moment convenience are necessary. Ignoring the force or moment convergence is not advisable. If the convenience issues are faced, the underlying cause should be corrected by using the appropriate measure ( like increasing the number of substeps per load step).
Dear Pandi,
In ANSYS software surface to surface contact or volume to volume contact interface elements are available. Surface to surface contact is used for 2-d analysis and volume to volume contact for 3-d analysis. so, use these elements to simulate the contact between concrete and prestressed steel. i have not used new version of ANSYS so i can't give correct answer to the first question. But, for the earlier question it is better to go with larger number of load step for applying the load and also to go with lesser value of convergence criteria. In ANSYS software convergence criteria is inbuilt so you need not to define the criteria. But. manually also you can set this criteria..ok all the best in your research..
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