北京谱仪BESⅢ漂移室中预应力细丝张拉的全过程有限元模拟分析

FEA FOR ENTIRE PROCEDURE OF THREAD STRETCHING IN MAIN DRIFT CHAMBER OF BEIJING SPECTROMETERⅢ

为研究北京正负电子对撞机中谱仪主漂移室细丝张拉过程中的力学规律,对张拉精度进行有效控制,利用有限元法建立张拉全过程和全结构的等效计算模型。建模过程中,采用"单元激活"技术处理变拓扑的结构特征,避免结构模型变化带来的网格重构,保证计算效率和精度。通过应力松弛试验确定细丝的粘弹性本构关系,进而运用单向耦合算法对动态张拉进程中的耦合力学问题线性化,理论分析和试验结果表明,这种处理方法是合理可靠的。计算给出不同阶段细丝张力的变化结果,提出通过预紧张拉方法对张力变化进行有效控制,并确定了预应力杆的分布方案,保证漂移单元精度。有限元模拟分析结果已经运用于北京正负电子对撞机重大改造工程,将对谱仪主漂移室的建造起指导作用。

The calculational model of main drift chamber in spectrometer of Beijing electron-positron collider （BEPC Ⅱ ） and the entire thread stretching procedure is built based on FEM for the research of mechanics rule and the control of accuracy the and structure. The ＂element activation＂ technic is used to avoid element rebuliding because of structure change and ensure the efficiency and accuracy of calculation. The calculation is linearized with the sequential couple method after the viscoelasticity of the wires investigated by stress relaxation experiment. The method is proved effective by both theory and experiment. The result of the change of the wires＇ initial stress is gained and the stretching method with pretightening force for the control of the change of the wire stress is used to ensure the accuracy of the drift element. The result used in the BEPCII modification works will exert an important role for the building of main drift chamber.