Flexible pipes function effectively in practical applications only when they are securely connected to specific components using specially designed end fittings.These end fittings must be precisely manufactured to ens...Flexible pipes function effectively in practical applications only when they are securely connected to specific components using specially designed end fittings.These end fittings must be precisely manufactured to ensure a tight connection,preventing any potential leakage.Otherwise,even perfectly manufactured flexible pipes will fail to perform their intended function.Although extensive research exists on the mechanical analysis of flexible pipes,studies on pipes connected to end fittings are scarce.The primary challenge in investigating this combined structure lies in the complex interaction between flexible pipes and end fittings after assembly,in addition to the already intricate structural behavior of flexible pipes.This paper presents both experimental and numerical analyses.Experimentally,we conducted comprehensive torsion tests on steel strip reinforced flexible pipes connected to commonly used end fittings,observing various torsional failure modes.On the numerical side,we developed a method to model the interaction between flexible pipes and end fittings.The proposed approach enables the prediction of torsional failure modes in practical applications and lays the groundwork for further failure analysis under different loading conditions and for various end fitting designs.展开更多
Nonbonded flexible pipes consist of polymer materials that experience stress relaxation at high temperatures,which ultimately affects the sealing performance of end sealing systems.To assess stress relaxation curves u...Nonbonded flexible pipes consist of polymer materials that experience stress relaxation at high temperatures,which ultimately affects the sealing performance of end sealing systems.To assess stress relaxation curves under varying temperatures and pre-strains,this paper conducts both tensile and stress relaxation tests on PVDF materials.To describe the stress relaxation characteristics of these materials,the Prony series is utilized.In order to identify the parameters of the series,the paper employs the Levenberg-Marquardt method of nonlinear regression.A finite element model is established to verify the accuracy of the parameter identification method.Subsequently,the paper establishes a two-dimensional axisymmetric finite element model of the sealing system in the end fitting,while taking into account fluid pressure inside the pipeline using a pressure penetration method.The impact of stress relaxation on the sealing performance is then discussed.Finally,the paper alters the coefficients of the Prony series to explore their significance on the sealing performance of the sealing system.展开更多
Cemented and mechanically clamped types of end fittings(fitting-C and fitting-M)are commonly used in transformer bushings.During the Luding Ms 6.8 earthquake that occurred in China on September 5,2022,all transformer ...Cemented and mechanically clamped types of end fittings(fitting-C and fitting-M)are commonly used in transformer bushings.During the Luding Ms 6.8 earthquake that occurred in China on September 5,2022,all transformer bushings with the two types of end fittings in a 500 kV substation were damaged.Post-earthquake field investigations were conducted,and the failures of the two types of bushings were compared.Two elementary simulation models of the transformer-bushing systems were developed to simulate the engineering failures,and further compute their seismic responses for comparison.The results indicate that the hitch lugs of the connection flange are structurally harmful to seismic resistance.Fitting-M can decrease the bending stiffness of the bushing due to the flexible sealing rubber gasket.Since it provides a more flexible connection that dissipates energy,the peak accelerations and relative displacements at the top of the bushing are significantly lower than those of the bushing with fitting-C.Compared with fitting-C,fitting-M transfers the high-stress areas from the connection flange to the root of the porcelain,so the latter becomes the most vulnerable component.Fitting-M increases the failure risk of the low-strength porcelain,indicating the unsuitability of applying it in high-intensity fortification regions.展开更多
文摘Flexible pipes function effectively in practical applications only when they are securely connected to specific components using specially designed end fittings.These end fittings must be precisely manufactured to ensure a tight connection,preventing any potential leakage.Otherwise,even perfectly manufactured flexible pipes will fail to perform their intended function.Although extensive research exists on the mechanical analysis of flexible pipes,studies on pipes connected to end fittings are scarce.The primary challenge in investigating this combined structure lies in the complex interaction between flexible pipes and end fittings after assembly,in addition to the already intricate structural behavior of flexible pipes.This paper presents both experimental and numerical analyses.Experimentally,we conducted comprehensive torsion tests on steel strip reinforced flexible pipes connected to commonly used end fittings,observing various torsional failure modes.On the numerical side,we developed a method to model the interaction between flexible pipes and end fittings.The proposed approach enables the prediction of torsional failure modes in practical applications and lays the groundwork for further failure analysis under different loading conditions and for various end fitting designs.
基金the National Natural Science Foundation of China[Grant No.52088102,52001208,52111530135]Joint Funds of the National Natural Science Foundation of China[Grant No.U19B2013]+2 种基金Young Elite Scientists Sponsorship Program by CAST[Grant No.2020QNRC001]Chenguang Program of Shanghai Education Development Foundation and Shanghai Municipal Education Commission[Grant No.21CGA15,19CG10]Natural Science Foundation of Shanghai[Grant No.21ZR1434500,22ZR1434100].
文摘Nonbonded flexible pipes consist of polymer materials that experience stress relaxation at high temperatures,which ultimately affects the sealing performance of end sealing systems.To assess stress relaxation curves under varying temperatures and pre-strains,this paper conducts both tensile and stress relaxation tests on PVDF materials.To describe the stress relaxation characteristics of these materials,the Prony series is utilized.In order to identify the parameters of the series,the paper employs the Levenberg-Marquardt method of nonlinear regression.A finite element model is established to verify the accuracy of the parameter identification method.Subsequently,the paper establishes a two-dimensional axisymmetric finite element model of the sealing system in the end fitting,while taking into account fluid pressure inside the pipeline using a pressure penetration method.The impact of stress relaxation on the sealing performance is then discussed.Finally,the paper alters the coefficients of the Prony series to explore their significance on the sealing performance of the sealing system.
基金National Natural Science Foundation of China under Grant No.51878508。
文摘Cemented and mechanically clamped types of end fittings(fitting-C and fitting-M)are commonly used in transformer bushings.During the Luding Ms 6.8 earthquake that occurred in China on September 5,2022,all transformer bushings with the two types of end fittings in a 500 kV substation were damaged.Post-earthquake field investigations were conducted,and the failures of the two types of bushings were compared.Two elementary simulation models of the transformer-bushing systems were developed to simulate the engineering failures,and further compute their seismic responses for comparison.The results indicate that the hitch lugs of the connection flange are structurally harmful to seismic resistance.Fitting-M can decrease the bending stiffness of the bushing due to the flexible sealing rubber gasket.Since it provides a more flexible connection that dissipates energy,the peak accelerations and relative displacements at the top of the bushing are significantly lower than those of the bushing with fitting-C.Compared with fitting-C,fitting-M transfers the high-stress areas from the connection flange to the root of the porcelain,so the latter becomes the most vulnerable component.Fitting-M increases the failure risk of the low-strength porcelain,indicating the unsuitability of applying it in high-intensity fortification regions.
