宽高频耦合激振下可控震源平板疲劳损伤机理及可靠性优化研究

A vibroseis baseplate (also called vibrator baseplate), which is a key device for the excitation of a vibroseis seismic signal in green and high efficiency oil-gas prospecting technology, is subjected to long-term earthquake excitation with a wide bandwidth and a high frequency, such that it may cause cracking or fatigue failure in the vibrator baseplate, the damage mechanism is still unclear. Such an earthquake excitation may in turn reduce the service life of the baseplate and seriously affect the geophysical prospecting signal quality. In this work the dynamic response law of the baseplate is firstly studied by establishing the wide and high frequency vibration mechanics model of coupling vibrator-ground, creatively considering the soil parameters such as the dynamic stiffness and dynamic damping. The macroscopic and microscopic morphology analysis of the baseplate fracture have been carried out to reveal the damage mechanism. According to the fatigue damage mode and characteristics of the baseplate, the quantitative description of the mechanics behavior law is carried out, by considering the coupling effect of the baseplate stress response and welding residual stress. Then, the fatigue life prediction model is established by using the fatigue cumulative damage and fracture mechanics theory, as well as the fatigue life test results. Besides, the fatigue reliability and parameters sensitivity analysis have been researched due to the randomness of the fatigue parameters. Finally, the most critical random parameters are optimized based on the reliability analysis, and an optimal design scheme of the anti-fatigue is put forward. The research results could greatly improve the life and reliability of the vibrator and baseplate. It is of great significance for oil and gas exploration equipment to prolong life, increase efficiency, safe and reliable operation.

震源平板（也称振动器平板）是绿色、高效油气勘探装备—可控震源地震信号激发的关键装置，但复杂随机近地表条件下宽、高频激振所致的平板裂纹，突发断裂，其内在损伤机理尚不明确，不仅大大折损平板工作寿命，而且严重降低物探信号质量。本项目通过考虑大地动刚度、动阻尼等参数，构建振动器-大地宽高频耦合振动力学模型，研究平板结构动力学响应规律，结合平板开裂断口宏微观形貌试验，揭示平板在宽高频激振下的损伤机理；考虑受载平板应力-焊接残余应力场的耦合作用，定量描述平板力学行为规律；综合运用疲劳累积损伤、断裂力学理论和三点弯曲疲劳试验结果建立平板寿命预测模型，研究不确定条件下平板疲劳可靠性和参数敏感性，掌握影响其疲劳性能的关键因素集和敏感规律，据此有针对性地开展参数优化设计，提出平板抗疲劳优化设计准则和方案。研究成果将有效提高振动器、及平板的抗疲劳可靠性和寿命，对油气勘探装备延寿增效、安全可靠运行具有重要意义。

高精度可控震源一种高效、环保、安全和低成本的地球物理勘探装备，振动器平板是可控震源地震信号激发的关键装置，但复杂随机近地表条件下宽、高频激振所致的平板裂纹，突发断裂，其内在损伤机理尚不明确，不仅大大折损平板工作寿命，而且严重降低物探信号质量。本项目开展宽高频耦合激振下可控震源平板疲劳损伤机理及可靠性优化研究，完成了以下研究内容：（1）振动器-大地宽高频耦合振动下的平板损伤机理研究；（2）考虑焊接残余应力的振动器平板力学性能影响规律研究；（3）宽、高频耦合作用下可控震源振动器平板疲劳可靠性研究；（4）基于平板疲劳可靠性的参数敏感性分析及抗疲劳优化研究。形成了以下主要成果：（1）在Sallas模型的基础上运用系统动力学理论，建立了振动器-大地宽高频耦合振动力学模型，掌握了平板激振力的计算方法和平板受载规律，揭示了振动器平板疲劳损伤机理。（2）提出了一种基于正交试验参数优化的振动器平板动力学仿真分析研究方法，振动器平板存在周期性的“上凸”和“下凹”变形，该区域是平板的疲劳关键部位，拟合了考虑焊接残余应力的平板疲劳热点应力响应与输入参数之间的函数表达式，具有较高精度。采用S-N曲线法和断裂力学法预测了平板疲劳寿命。（3）运用决策理论中的模糊综合评价方法，提出了一种既考虑宏观结构载荷因素，又兼顾微观材料组织因素两种优势的振动器平板疲劳可靠性模糊综合分析法，并计算得出平板疲劳关键部位的可靠度为0.9759，提高了平板疲劳可靠性计算精度。（4）采用Monte-Carlo可靠性灵敏度分析法，开展了平板关键部位疲劳可靠性对随机疲劳参数的敏感性研究，构建了基于可靠度的振动器平板结构优化设计模型，对平板关键参数进行了优化，优化后平板综合疲劳可靠度提高至0.9935，提高了1.8%。研究成果有效提高了振动器、及平板的抗疲劳可靠性和寿命，对油气勘探装备延寿增效、安全可靠运行具有重要意义。