[수렴과 관련된 에러들] Numerical Singularities / Zero Pivots / Negative Eigenvalues

Convergence issues spectific to Abaqus/Standard (Noncontact Related)

• Numerical Singularities
  : These indicate that so many digits are lost during linear equation solution that the results are not reliable.
    The most common cause is an unconstrained rigid body mode in a static stress analysis
    e.g. 경계조건이 부족하여 rigid body mode 발생 (방정식 개수 < 미지수 개수)

• Zero Pivots
  : These occur during linear equation solution when there is a force term but no corrensponding stiffness.
    Common causes are unconstrained rigid body modes and overconstrained degrees of freedom
    e.g. 경계조건 과다 (방정식 개수 > 미지수 개수)

• Negative eigenvalues
  : Negative eigenvalues indicate that the stiffness matrix is not positive definite.
    For example, a buckling load may have been exceeded.
  e.g. 재질에서 좌굴이 발생할 소지가 있는지 확인 (|D|<0, 역행렬을 못 구함)