Conventional analytical and numerical methods for the mechanical properties of helical threads are relied on many assumptions and approximations and thus hardly yield satisfied results. A parameterized 3D finite eleme...Conventional analytical and numerical methods for the mechanical properties of helical threads are relied on many assumptions and approximations and thus hardly yield satisfied results. A parameterized 3D finite element model of bolted joints with real helical thread geometry is established and meshed with refined hexahedral elements. The Von Mises plasticity criterion, kinematic hardening rule of materials and interfacial contacts are employed to make it possible for the suggested model be able to approach real assembly conditions. Then, the mechanical properties of bolted joints with different thread pitches, thread numbers and modular ratios are investigated, including the contact pressure distribution at joint interfaces, the axial load distribution and stress concentration in screw threads during the loading and unloading process. Simulation results indicate that the load distribution in screw threads produced by the suggested model agrees well the results from CHEN’s photoelastic tests. In addition, an interesting phenomenon is found that tightening the bolt with a large preload first and then adjusting the clamping force by unloading can make the load distribution more uniform and reduce the maximum residual equivalent stress in thread roots by up to 40%. This research provides a simple and practical approach to constructing the 3D finite element model and predicting the mechanical properties of helical thread connection.展开更多
针对新疆某油田超深井在更换密封件提起采油四通时,发现井口悬挂器卡瓦夹持处套管断裂的问题,结合现场X1井使用的ø232.5 mm W型卡瓦悬挂器结构,建立了悬挂器坐挂-卡瓦夹持套管的三维有限元模型。根据第四强度理论推导出卡瓦效应的...针对新疆某油田超深井在更换密封件提起采油四通时,发现井口悬挂器卡瓦夹持处套管断裂的问题,结合现场X1井使用的ø232.5 mm W型卡瓦悬挂器结构,建立了悬挂器坐挂-卡瓦夹持套管的三维有限元模型。根据第四强度理论推导出卡瓦效应的套管极限载荷计算公式,并通过有限元计算得到了理论公式的修正系数为0.913,同时得到在套管坐挂时,X1井卡瓦效应的套管极限载荷为6400 kN。有限元计算结果表明:卡瓦部分套管上的应力呈现非均匀分布,尤其是套管外壁非均匀程度较严重,且外壁牙痕上的应力集中是套管损伤、裂纹起裂和断裂的主要原因;如果存在较高的环空压力,在卡瓦部分或过渡区套管均有可能发生断裂失效破坏。建议选择无齿痕的卡瓦夹持套管,或者采用全金属密封的心轴式悬挂器,避免卡瓦悬挂器造成套管损伤破坏。研究方法和成果可为深井超深井卡瓦悬挂器套管的安全评价提供理论指导。展开更多
Given the challenges of re-creating complex bed load(BL)transport processes in rivers,models are preferred over gathering and examining field data.The highlight of the present research is to develop an approach to det...Given the challenges of re-creating complex bed load(BL)transport processes in rivers,models are preferred over gathering and examining field data.The highlight of the present research is to develop an approach to determine the ungauged bed load concentration(BLC_(u))utilizing the measured suspended sediment concentration(SSC)and hydraulic variables of the last four decades for the Mahanadi River Basin.This technique employs shear stress and SSC equations for turbulent open channel flow.Besides,the predicted BLC_(u)is correlated with SSC using a power relation to estimate BLC_(u)on the river and tributaries.Eventually,different BL functions(BLF)efficiency is assessed across stations.The model predicted BLC_(u)is comparable with the published data for sandy rivers and falls within±20%.Outliers in hydraulic and sedimentological statistics significantly influence estimating the BL fraction apart from higher relative ratios and catchment geology.The constants of power functions are physically linked to sediment transport configuration,mechanism,and inflow to the stream.The stream power-based BLF best predicts the BL transport,followed by shear stress and unit discharge approaches.The disparity in the estimation of BLC_(u)results from station-specific physical factors,sampling data dispersion,and associated uncertainties.展开更多
基金supported by National Natural Science Foundation of China (Grant No. 50935006)Major Project of High-end CNC Machine Tool and Basic Manufacturing Equipment of China (Grant No.2011ZX04016-031)National Hi-tech Research and Development Program of China (863 Program, Grant No. 2012AA040701)
文摘Conventional analytical and numerical methods for the mechanical properties of helical threads are relied on many assumptions and approximations and thus hardly yield satisfied results. A parameterized 3D finite element model of bolted joints with real helical thread geometry is established and meshed with refined hexahedral elements. The Von Mises plasticity criterion, kinematic hardening rule of materials and interfacial contacts are employed to make it possible for the suggested model be able to approach real assembly conditions. Then, the mechanical properties of bolted joints with different thread pitches, thread numbers and modular ratios are investigated, including the contact pressure distribution at joint interfaces, the axial load distribution and stress concentration in screw threads during the loading and unloading process. Simulation results indicate that the load distribution in screw threads produced by the suggested model agrees well the results from CHEN’s photoelastic tests. In addition, an interesting phenomenon is found that tightening the bolt with a large preload first and then adjusting the clamping force by unloading can make the load distribution more uniform and reduce the maximum residual equivalent stress in thread roots by up to 40%. This research provides a simple and practical approach to constructing the 3D finite element model and predicting the mechanical properties of helical thread connection.
文摘针对新疆某油田超深井在更换密封件提起采油四通时,发现井口悬挂器卡瓦夹持处套管断裂的问题,结合现场X1井使用的ø232.5 mm W型卡瓦悬挂器结构,建立了悬挂器坐挂-卡瓦夹持套管的三维有限元模型。根据第四强度理论推导出卡瓦效应的套管极限载荷计算公式,并通过有限元计算得到了理论公式的修正系数为0.913,同时得到在套管坐挂时,X1井卡瓦效应的套管极限载荷为6400 kN。有限元计算结果表明:卡瓦部分套管上的应力呈现非均匀分布,尤其是套管外壁非均匀程度较严重,且外壁牙痕上的应力集中是套管损伤、裂纹起裂和断裂的主要原因;如果存在较高的环空压力,在卡瓦部分或过渡区套管均有可能发生断裂失效破坏。建议选择无齿痕的卡瓦夹持套管,或者采用全金属密封的心轴式悬挂器,避免卡瓦悬挂器造成套管损伤破坏。研究方法和成果可为深井超深井卡瓦悬挂器套管的安全评价提供理论指导。
基金Ministry of Water Resources,Government of India,No.28/1/2016-R&D/228–245。
文摘Given the challenges of re-creating complex bed load(BL)transport processes in rivers,models are preferred over gathering and examining field data.The highlight of the present research is to develop an approach to determine the ungauged bed load concentration(BLC_(u))utilizing the measured suspended sediment concentration(SSC)and hydraulic variables of the last four decades for the Mahanadi River Basin.This technique employs shear stress and SSC equations for turbulent open channel flow.Besides,the predicted BLC_(u)is correlated with SSC using a power relation to estimate BLC_(u)on the river and tributaries.Eventually,different BL functions(BLF)efficiency is assessed across stations.The model predicted BLC_(u)is comparable with the published data for sandy rivers and falls within±20%.Outliers in hydraulic and sedimentological statistics significantly influence estimating the BL fraction apart from higher relative ratios and catchment geology.The constants of power functions are physically linked to sediment transport configuration,mechanism,and inflow to the stream.The stream power-based BLF best predicts the BL transport,followed by shear stress and unit discharge approaches.The disparity in the estimation of BLC_(u)results from station-specific physical factors,sampling data dispersion,and associated uncertainties.
