为什么降温法模拟钢绞线（桁架单元）后处理云图中会这样？

Solver problem. Zero pivot when processing D.O.F. 2 of 4 nodes. The nodes have been identified in node set WarnNodeSolvProbZeroPiv_2_1_1_1_1.

Solver problem. Zero pivot when processing D.O.F. 1 of 6 nodes. The nodes have been identified in node set WarnNodeSolvProbZeroPiv_1_1_1_2_1.

Solver problem. Zero pivot when processing D.O.F. 2 of 6 nodes. The nodes have been identified in node set WarnNodeSolvProbZeroPiv_2_1_1_2_1.

Solver problem. Zero pivot when processing D.O.F. 3 of 4 nodes. The nodes have been identified in node set WarnNodeSolvProbZeroPiv_3_1_1_2_1.

Solver problem. Zero pivot when processing D.O.F. 1 of 6 nodes. The nodes have been identified in node set WarnNodeSolvProbZeroPiv_1_1_1_3_1.

Solver problem. Zero pivot when processing D.O.F. 2 of 6 nodes. The nodes have been identified in node set WarnNodeSolvProbZeroPiv_2_1_1_3_1.

Solver problem. Zero pivot when processing D.O.F. 3 of 4 nodes. The nodes have been identified in node set WarnNodeSolvProbZeroPiv_3_1_1_3_1.

Solver problem. Zero pivot when processing D.O.F. 1 of 5 nodes. The nodes have been identified in node set WarnNodeSolvProbZeroPiv_1_1_1_4_1.

Solver problem. Zero pivot when processing D.O.F. 2 of 5 nodes. The nodes have been identified in node set WarnNodeSolvProbZeroPiv_2_1_1_4_1.

Solver problem. Zero pivot when processing D.O.F. 3 of 3 nodes. The nodes have been identified in node set WarnNodeSolvProbZeroPiv_3_1_1_4_1.