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1、PAT328, Section 3, March 2001MAR120, Lecture 4, March 2001S12 - 1MAR101 Course Notes, Sec. 12, November 2005SECTION 12RESOLVING CONVERGENCE PROBLEMSPAT328, Section 3, March 2001MAR120, Lecture 4, March 2001S12 - 2MAR101 Course Notes, Sec. 12, November 2005OverviewqNonlinear Analysis GuidelinesqInfor
2、mation Available to HelpqAnalysis Troubleshooting: GeneralqAnalysis Troubleshooting: Criteria BehaviourqAnalysis Troubleshooting: EXIT NumbersPAT328, Section 3, March 2001MAR120, Lecture 4, March 2001S12 - 3MAR101 Course Notes, Sec. 12, November 2005Nonlinear Analysis GuidelinesqConvergence of a non
3、linear problem is mostly not simply to do with the convergence tolerance values or the criteria specifiedit is an overall issue of model integrity and representation of realityqIt is strongly recommended that small tests be performed to gain experience of unknown (to you) element and solution types:
4、1.To understand its limitations 2.To ensure that it does provide the required behaviour for the actual simulation to be carried out 3.To prevent expensive “surprises” at the end of a projectqSingle element tests are preferable (where possible) since it is so much quicker and easier to verify the inp
5、ut and to evaluate the response with only a few degrees of freedomqThere are a number of sources of examples and benchmarks available that may help in this regard1.The MARC User Guide manual. This contains an increasing amount of worked examples written with the express intention of demonstrating th
6、e use of the facilities clearly 2.The MARC Demonstration Problem manual (volume E). It is in Marc data file format only. The data files associated with this manual can be located in the Marc installation directory 3.The NAFEMS suite of examples. Further information is available on their website (www
7、.nafems.org)PAT328, Section 3, March 2001MAR120, Lecture 4, March 2001S12 - 4MAR101 Course Notes, Sec. 12, November 2005Nonlinear Analysis GuidelinesqPerform and scrutinise the results from a static linear analysis to check the integrity and behaviour of the basic model. If the nonlinear model alrea
8、dy exists1.For contact analyses, this would mean changing all contact conditions to GLUED2.For material nonlinearity simply increase the failure criteria so that it cannot be reached3.For geometrically nonlinear analyses turn off Large Displacement as well as any large strain material optionsqAdd ea
9、ch of the nonlinearities one by one to determine their effect on the solution and its convergence behaviour. For instance, start with contact, adding next any geometric nonlinearity and then finally any material nonlinearity, etc.1.For contact analyses, contact conditions can be set to GLUED2.The ne
10、xt step would be TOUCHING, but with a separation force of 1e20qIf buckling is expected, a linear eigenvalue buckling analysis should be performed to obtain the linear buckling load. This will act as both a benchmark value to compare against as well as a useful aid in determining the load magnitude t
11、o be applied in the subsequent geometrically nonlinear analysisqAlways use engineering common sense and verify the plausibility of the results before making design decisions based upon themPAT328, Section 3, March 2001MAR120, Lecture 4, March 2001S12 - 5MAR101 Course Notes, Sec. 12, November 2005Inf
12、ormation Available to HelpPAT328, Section 3, March 2001MAR120, Lecture 4, March 2001S12 - 6MAR101 Course Notes, Sec. 12, November 2005qThe problem begins with error messages like: “Failure to converge to tolerance” (EXIT 3002) “Error encountered in stress recovery” (EXIT 1009/1005) “The time step ha
13、s become too small due to too many step cut-backs” (EXIT 3009) “Unable to reduce the time step below the minimum value allowed” (EXIT 3015) “Node on the boundary of a deformable body tried to slide out of surface definition in a contact analysis” (EXIT 2400)qThe main place to look is the end of the
14、OUTPUT file (.out)qA successful analysis looks like: * This is a successful completion to an MSC.Marc analysis, indicating that no additional incremental data was found and that the analysis is complete *MSC.Marc Exit number 3004qAn unsuccessful analysis looks like: * Analysis has failed to converge
15、 to required convergence tolerances. One of several error conditions has been detected and the run aborted. The output will specify additional messages *MSC.Marc Exit number 3002Analysis MessagesEXIT NumberAssociated message for EXIT numberPAT328, Section 3, March 2001MAR120, Lecture 4, March 2001S12 - 7MAR101 Course Notes, Sec. 12, November 2005A typical nonlinear output file section:start of assembly cycle number is 0 wall time = 12.00solver workspace needed for out-of-cor
