Abaqus/Standard提供了無數個控制收斂與積分精度的參數設置。通常使用默認的參數值可以處理大多數問題，只有一部分的非線性問題需要用戶調整參數，當然用戶必須是具有豐富經驗的CAE分析師，調整時要格外小心！

在Analysis Manual Documentation 中的7.2章節詳細介紹了這些參數的作用及設置方法。

 

7.2.1 Convergence and time integration criteria: overview

Numerous control parameters are associated with the convergence and integration accuracy algorithms in Abaqus/Standard. These parameters are assigned default values that are chosen to optimize the accuracy and efficiency of the solution for a wide spectrum of nonlinear problems. You can change the solution control parameters, as described in the following sections:

A brief synopsis of the more important solution control parameters, together with a description of the circumstances in which they can be used effectively, is provided in “Commonly used control parameters,” Section 7.2.2. This section is likely to be the most useful for the general user and should be read first.

Abaqus/Standard incorporates an empirical algorithm designed to solve the equilibrium equations of nonlinear systems accurately and economically. The criteria used to establish convergence of nonlinear increments and the automatic adjustment of increment size based on the convergence rate are described in “Convergence criteria for nonlinear problems,” Section 7.2.3.

Abaqus/Standard allows you to choose “time integration accuracy parameters” in problems that have a physical time scale. The algorithms that use these parameters for automatically controlling time increment sizes are described in “Time integration accuracy in transient problems,” Section 7.2.4.

 

常用的控制參數

Defining tolerances for field equations

residual control

solution correction control

average flux

initial time average flux

Controlling the time incrementation scheme

the equilibrium iteration for a residual check

the equilibrium iteration for a logarithmic rate of convergence 收斂率對數check

Avoiding premature cutbacks in difficult analyses

Automatically setting the time incrementation parameters

Activating the “line search” algorithm

Defining tolerances for constraint equations

Controlling the solution accuracy in direct cyclic analysis

Imposing the periodicity condition

Defining tolerances for stabilized state and plastic ratchetting detections

 

控制參數調整有兩個目的：一是調整非線性方程求解精確度；二是調整時間增量。

Step-Other-General Solution Controls-Edit

會出現罕見的warning對話框，然后才能繼續下去。說明對于一般的問題和普通用戶，abaqus并不建議調整這些參數。

Abaqus/Standard默認采用牛頓法進行迭代，以利用它的二次收斂速度。接觸，或塑性應變變向等行為是嚴重非連續行為，其收斂相對較難。單元類型對收斂有影響。按容易收斂的排序：簡約單元(增強)>簡約單元(默認)>普通單元。有時候接觸問題很難收斂，此時可以在step步中將（Convert severe discontinuity iterations）打開。如果依然碰到PENETRATION ERROR的問題，可以進一步在step模塊other-general solution control-time incrementation中將discontinuous analysis選中（I0=8,IR=10），還可以將每一增量步中所允許的最大縮減次數（IA）增大，以保證不收斂時能有足夠小的收斂步長。還可以將Tcont(contact and slip compatibility tolerance)值改大些，但需要檢查結果的合理性

另外出現“DISP CORRECTION TOO LARGE COMPARED TO DISP INCREMENT”這類出錯信息時，可以采用準牛頓法代替默認的完全牛頓法求解。注意，采用準牛頓法時，之前的分析步的求解方式不能是“接觸迭代”（Contact iteration），否則無法求解。

轉自公眾號——ABAQUS大世界

旨在分享，若侵即刪.