收敛性设置 收敛性

Abaqus/Standard提供了无数个控制收敛与积分精度的参数设置。通常使用默认的参数值可以处理大多数问题，只有一部分的非线性问题需要用户调整参数，当然用户必须是具有丰富经验的CAE分析师，调整时要格外小心。( ⊙ o ⊙ )！

在Analysis Manual Documentation 中的7.2章节详细介绍了这些参数的作用及设置方法。

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7.2.1 Convergence and timeintegration criteria: overview

Numerous control parametersare associated with the convergence and integration accuracyalgorithms in Abaqus/Standard. These parameters are assigneddefault values that are chosen to optimize the accuracy andefficiency of the solution for a wide spectrum of nonlinearproblems. You can change the solution control parameters, asdescribed in the following sections:

A brief synopsis of the moreimportant solution control parameters, together with a descriptionof the circumstances in which they can be used effectively, isprovided in “Commonly used control parameters,” Section 7.2.2. Thissection is likely to be the most useful for the general user andsh ould be read first.

Abaqus/Standard incorporatesan empirical algorithm designed to solve the equilibrium equationsof nonlinear systems accurately and economically. The criteria usedto establish convergence of nonlinear increments and the automaticadjustment of increment size based on the convergence rate aredescribed in “Convergence criteria for nonlinear problems,” Section7.2.3.

Abaqus/Standard allows you tochoose “time integration accuracy parameters” in problems that havea physical time scale. The algorithms that use these parameters forautomatically controlling time increment sizes are described in“Time integration accuracy in transient problems,” Section7.2.4.

常用的控制参数

Defining tolerancesfor field equations

residualcontrol

solution correctioncontrol

averageflux

initial time averageflux

Controlling the timeincrementation scheme

the equilibrium iteration fora residual check

the equilibrium iteration fora logarithmic rate of convergence 收敛率对数check

Avoiding premature cutbacksin difficult analyses

Automatically setting thetime incrementation parameters

Activating the “linesearch” algorithm

Defining tolerancesfor constraint equations

Controlling thesolution accuracy in direct cyclic analysis

Imposing the periodicitycondition

Defining tolerances forstabilized state and plastic ratchettingdetections

控制参数调整有两个目的：一是调整非线性方程求解精确度；二是调整时间增量。

Step-Other-General SolutionControls-Edit

会出现罕见的warning对话框，然后才能继续下去。说明对于一般的问题和普通用户，abaqus并不建议调整这些参数。

Abaqus/Standard默认采用牛顿法进行迭代，以利用它的二次收敛速度。接触，或塑性应变变向等行为是严重非连续行为，其收敛相对较难。单元类型对收敛有影响。按容易收敛的排序：简约单元(增强)>简约单元(默认)>普通单元。有时候接触问题很难收敛，此时可以在step步中将（Convert severe discontinuityiterations）打开。如果依然碰到PENETRATIONERROR的问题，可以进一步在step模块other-general solutioncontrol-time incrementation中将discontinuousanalysis选中（I0=8,IR=10），还可以将每一增量步中所允许的最大缩减次数（IA）增大，以保证不收敛时能有足够小的收敛步长。还可以将Tcont(contact and slipcompatibility tolerance)值改大些，但需要检查结果的合理性

另外出现“DISP CORRECTION TOO LARGE COMPARED TO DISPINCREMENT”这类出错信息时，可以采用准牛顿法代替默认的完全牛顿法求解。注意，采用准牛顿法时，之前的分析步的求解方式不能是“接触迭代”（Contactiteration），否则无法求解。

By JUJU