内压作用下含体积型缺陷弯管极限载荷研究

油气管道一旦发生泄漏失效容易引发爆炸等灾难性事故,而管路中的弯管段是容易发生失效的部分,弯管段承载能力的高低将影响整个管道系统的安全性。为了解决油气管线中弯管的失效问题,考虑几何和材料非线性,建立内压作用下含体积型缺陷弯管的有限元模型,并与爆破试验结果对比验证模型的有效性,确定管道的失效判定准则。研究表明影响弯管极限载荷的主要因素有缺陷的几何尺寸、相对位置以及弯曲半径。基于模拟计算,讨论各因素对含缺陷弯管极限载荷的影响规律,通过对计算结果进行非线性拟合,提出内压作用下含体积型缺陷弯管的极限内压预测公式。该公式将为含缺陷弯管的剩余强度评价和完整性评价提供一定依据。     

基于RBF神经网络的火灾报警系统失效概率预测

报警系统失效主要包括漏报、误报,对系统进行失效概率预测,可以帮助判断设备质量优劣,评估系统效能。利用Matlab软件编程,通过神经网络预测失效概率。根据不同场所正在使用的火灾报警器的失效数据作为原始数据,归纳总结失效原因,建立事故树,结合专家打分法与模糊理论得到网络的输入值与输出值。通过网络训练,得到可以对系统失效概率进行预测的RBF神经网络,测算效率大幅提高。以70组不同品牌、用途的火灾报警系统作为算例,通过训练数据,最终达到输入底事件发生概率可直接输出顶事件发生概率的目的。结果表明,RBF神经网络相较于BP网络与事故树算得的失效概率具有更高的拟合度,RBF神经网络模型在进行系统失效概率预测时具有可靠性。     

A reliability evaluation method based on the weakest failure modes for side-by-side offloading mooring system of FPSO

Offshore structures are complex systems, and numerous failure modes must be taken into consideration when reliability analysis in different loads and environment conditions are conducted on them. It is difficult to obtain structural system reliability with respect to complicated systems with numerous failure modes and dependency consideration among them. This paper applies the combination of the weakest failure modes theory with structural reliability theory to conduct reliability analysis on of side-by-side offloading mooring system of FPSO. Firstly, the numerical simulation of the system in different conditions is addressed to acquire the statistical data of time-history stress of components including hawsers, fenders and yoke, based on which, the reliability indexes of all the failure modes and correlation coefficient matrix are derived. Then the weakest failure modes, i.e. the representative failure modes that have significant impact on the system, are located through Probability Network Evaluation Technique. The probability of structural system is estimated through the weakest failure modes by considering the system as series. The analysis results indicate that two environment conditions (0°&0°&0° and 0°&30°&45° in combinations of wave, wind and current) are relative dangerous, which is in good correspondence with the practical expertise. The method is verified to be an effective and convenient evaluation approach for structural reliability analysis in terms of complex systems. It is beneficial for the identification of structure indicators from the weakest failure mode group and conduct optimum of structural system configurations in the design stage.     

基于数字图像处理的含孔洞裂纹花岗岩破裂过程数值模拟

在细观尺度上,采用数字图像处理技术表征花岗岩中由石英、长石和云母等材料的形状、大小及分布对花岗岩材料造成的非均匀性,结合RFPA-DIP程序建立了能准确反映材料真实细观结构的含缺陷花岗岩数值模型,并进行了常规单轴压缩模拟试验,再现了外载荷作用下含缺陷花岗岩的真实破裂过程。试验结果表明:花岗岩的预制孔洞裂纹对其最终破坏产生了重要影响;在单轴压缩试验中,由于花岗岩中各矿物颗粒不同的力学特性影响,试件中出现应力集中现象并萌生局部裂纹,且细观结构直接决定着裂纹的扩展路径,各局部裂纹的贯通导致试件最终产生拉伸破坏。     

高等级公路采动变形破坏数值模拟研究

以南屯矿区及其上方的邹济公路为背景,采用FLAC~(3D)软件,对采动影响下的高等级公路破坏机理和破坏过程进行了研究。研究表明:高等级公路采动变形经历先"上凸"后"下凹"过程,且破坏程度随着公路级别的降低而增加。应尽量使公路位于采空区正上方,且延伸方向和工作面推进的方向一致;若公路位于采空区一侧时,路面向采空区一侧整体滑移和倾斜;若公路延伸方向与工作面推进方向垂直,应注意采空区公路两端的上凸变形;应避免公路与采空区斜交。在相同地质采矿条件下,随着深厚比的增加,路面破坏程度减小,且在一定范围内,路面最大下沉值与深厚比存在非线性关系。研究成果为邹济公路下开采方案和公路维修治理提供必要的理论和技术支持。     

弹用O型硅橡胶密封圈失效机理及模型

目的利用日常收集到的使用数据来判断密封圈寿命,为预测弹药寿命提供依据。方法分析O型圈故障模式,引入了故障率经验公式。规范化O型密封圈的故障率公式,导出综合考虑了密封圈尺寸、接触应力与密封圈硬度、流体黏度、温度的密封圈故障率模型,并用算例验证这一模型的有效性。结果 O形硅胶密封圈的主要故障模式是泄漏,导出了综合考虑各因素后的密封圈故障率模型,并用该模型准确算出了某弹药的寿命。结论文中导出的故障率模型对于在弹药保障工作中评估某些种类弹药储存期限有借鉴意义。     

某型末制导炮弹控制舱贮存加速寿命试验应力研究

目的研究某型末制导炮弹控制舱贮存加速寿命试验应力类型。方法在明确某型末制导炮弹控制舱结构特征的基础上,逐一对各部组件进行失效模式及失效机理分析,归纳出影响控制舱失效的主要应力类型。结果影响末制导炮弹控制舱贮存可靠度的主要环境应力是温度和湿度。结论选取温度做单应力加速寿命试验。     

钢框架梁柱节点抗震性能拟静力试验研究

梁柱节点在钢框架结构中处于竖向荷载和水平荷载交汇关键部位,直接决定结构的受力性能和抗震能力。依托北京市档案馆新馆工程,根据工程需要和设计规范要求,对3个采用传统连接形式的钢框架梁柱节点,采取循坏加载的拟静力试验方法进行抗震性能研究,探讨了连接构造形式、冷作硬化效应和加载方案等对节点承载力、延性和破坏模式的影响。试验结果表明,传统连接形式节点具有承载力高、变形小、设计和施工简便的优点,但易发生脆性破坏;冷作硬化可以提高试件的承载力和变形能力,但不改变最终失效模式;加载方案对失效模式没有影响。     

Reviewing University Community Gardens for Sustainability: taking stock,comparisons with urban community gardens and mapping research opportunities

Community gardens (CGs) in university settings are faced with challenges associated with a transient and inexperienced population of student gardeners, but they also have the potential to have a lasting impact on the food behaviours of many young people. This paper undertakes a systematic critical review of literature about University Community Gardens for Sustainability (UCGS) in order to suggest directions of future research in the emerging field research about CGs within and outside of universities. The literature shows that UCGS have similar benefits to those identified in urban CG literature; but with greater emphasis on both the educational and environmental sustainability benefits, suggesting an under-used potential of CGs in these areas. We argue that a better understanding of the particular challenges and benefits of UCGS could improve outcomes of CGs in all settings. Therefore we recommend that future should explore: (1) participant transience in CGs, thereby helping sustainability projects with large volunteer bases learn to cope with challenges this poses in order to maximise the garden’s impacts; (2) whether/how participating in CGs can contribute to changes in attitudes/behaviours with regards to sustainability and be used as a tool for Education for Sustainability in and outside of university settings and (3) failed cases of CGs to genuinely understand factors that contribute to success. By addressing these areas we can improve our understanding of how community gardening can contribute to our communities, universities and environment, and can begin to make these potential contributions a reality.