Based on the generalized Hamilton's principle,the nonlinear governing equation of an axially functionally graded(AFG)pipe is established.The non-trivial equilibrium configuration is superposed by the modal functio...Based on the generalized Hamilton's principle,the nonlinear governing equation of an axially functionally graded(AFG)pipe is established.The non-trivial equilibrium configuration is superposed by the modal functions of a simply supported beam.Via the direct multi-scale method,the response and stability boundary to the pulsating fluid velocity are solved analytically and verified by the differential quadrature element method(DQEM).The influence of Young's modulus gradient on the parametric resonance is investigated in the subcritical and supercritical regions.In general,the pipe in the supercritical region is more sensitive to the pulsating excitation.The nonlinearity changes from hard to soft,and the non-trivial equilibrium configuration introduces more frequency components to the vibration.Besides,the increasing Young's modulus gradient improves the critical pulsating flow velocity of the parametric resonance,and further enhances the stability of the system.In addition,when the temperature increases along the axial direction,reducing the gradient parameter can enhance the response asymmetry.This work further complements the theoretical analysis of pipes conveying pulsating fluid.展开更多
As an important part of nonstructural components,the seismic response of indoor water supply pipes deserves much attention.This paper presents shaking table test research on water supply pipes installed in a full-scal...As an important part of nonstructural components,the seismic response of indoor water supply pipes deserves much attention.This paper presents shaking table test research on water supply pipes installed in a full-scale reinforced concrete(RC)frame structure.Different material pipes and different methods for penetrating the reinforced concrete floors are combined to evaluate the difference in seismic performance.Floor response spectra and pipe acceleration amplification factors based on test data are discussed and compared with code provisions.A seismic fragility study of displacement demand is conducted based on numerical simulation.The acceleration response and displacement response of different combinations are compared.The results show that the combination of different pipe materials and different passing-through methods can cause obvious differences in the seismic response of indoor riser pipes.展开更多
Urban sewer pipes are a vital infrastructure in modern cities,and their defects must be detected in time to prevent potential malfunctioning.In recent years,to relieve the manual efforts by human experts,models based ...Urban sewer pipes are a vital infrastructure in modern cities,and their defects must be detected in time to prevent potential malfunctioning.In recent years,to relieve the manual efforts by human experts,models based on deep learning have been introduced to automatically identify potential defects.However,these models are insufficient in terms of dataset complexity,model versatility and performance.Our work addresses these issues with amulti-stage defect detection architecture using a composite backbone Swin Transformer.Themodel based on this architecture is trained using a more comprehensive dataset containingmore classes of defects.By ablation studies on the modules of combined backbone Swin Transformer,multi-stage detector,test-time data augmentation and model fusion,it is revealed that they all contribute to the improvement of detection accuracy from different aspects.The model incorporating all these modules achieves the mean Average Precision(mAP)of 78.6% at an Intersection over Union(IoU)threshold of 0.5.This represents an improvement of 14.1% over the ResNet50 Faster Region-based Convolutional Neural Network(R-CNN)model and a 6.7% improvement over You Only Look Once version 6(YOLOv6)-large,the highest in the YOLO methods.In addition,for other defect detection models for sewer pipes,although direct comparison with themis infeasible due to the unavailability of their private datasets,our results are obtained from a more comprehensive dataset and have superior generalization capabilities.展开更多
Controlling inner-wall band segregation is one of the difficulties in the production of high-strength antisulfur pipes.Comparative tests were carried out on different casting processes(superheat,mold electromagnetic s...Controlling inner-wall band segregation is one of the difficulties in the production of high-strength antisulfur pipes.Comparative tests were carried out on different casting processes(superheat,mold electromagnetic stirring,end electromagnetic stirring,casting speed and soft reduction)for the smelting of high-strength antisulfur pipes.The microstructures of continuous-casting billets and hot-rolled or tempered pipes were analyzed using a metallographic microscope and scanning electron microscope.The mechanism and evolution law regarding the inner-wall band segregation of high-strength antisulfur pipes were studied,and the influence of different casting processes was explored.展开更多
BACKGROUND More recent data are required relating to disease risk for use of various smoked products and of other products containing nicotine.Earlier we published metaanalyses of recent results for chronic obstructiv...BACKGROUND More recent data are required relating to disease risk for use of various smoked products and of other products containing nicotine.Earlier we published metaanalyses of recent results for chronic obstructive pulmonary disease and lung cancer on the relative risk(RR)of current compared to never product use for cigarettes,cigars and pipes based on evidence from North America,Europe and Japan.We now report corresponding up-to-date evidence for acute myocardial infarction(AMI),ischaemic heart disease(IHD)and stroke.AIM To estimate,using recent data,AMI,IHD and stroke RRs by region for current smoking of cigarettes,cigars and pipes.METHODS Publications in English from 2015 to 2020 were considered that,based on epidemiological studies in the three regions,estimated the current smoking RR of AMI,IHD or stroke for one or more of the three products.The studies should involve at least 100 cases of stroke or cardiovascular disease(CVD),not be restricted to populations with specific medical conditions,and should be of cohort or nested case-control study design or randomized controlled trials.A literature search was conducted on MEDLINE,examining titles and abstracts initially,and then full texts.Additional papers were sought from reference lists of selected papers,reviews and meta-analyses.For each study identified,we entered the most recent available data on current smoking of each product,as well as the characteristics of the study and the RR estimates.Combined RR estimates were derived using random-effects meta-analysis for stroke and,in the case of CVD,separately for IHD and AMI.For cigarette smoking,where far more data were available,heterogeneity was studied by a wide range of factors.For cigar and pipe smoking,a more limited heterogeneity analysis was carried out.A more limited assessment of variation in risk by daily number of cigarettes smoked was also conducted.RESULTS Current cigarette smoking:Ten studies gave a random-effects RR for AMI of 2.72[95%confidence interval(CI):2.40-3.08],derived from 13 estimates between 1.47 and 4.72.Twenty-three studies gave an IHD RR of 2.01(95%CI:1.84-2.21),using 28 estimates between 0.81 and 4.30.Thirty-one studies gave a stroke RR of 1.62(95%CI:1.48-1.77),using 37 estimates from 0.66 to 2.91.Though heterogeneous,only two of the overall 78 RRs were below 1.0,71 significantly(P<0.05)exceeding 1.0.The heterogeneity was only partly explicable by the factors studied.Estimates were generally higher for females and for later-starting studies.They were significantly higher for North America than Europe for AMI,but not the other diseases.For stroke,the only endpoint with multiple Japanese studies,RRs were lower there than for Western studies.Adjustment for multiple factors tended to increase RRs.Our RR estimates and the variations by sex and region are consistent with earlier meta-analyses.RRs generally increased with amount smoked.Current cigar and pipe smoking:No AMI data were available.One North American study reported reduced IHD risk for non-exclusive cigar or pipe smoking,but considered few cases.Two North American studies found no increased stroke risk with exclusive cigar smoking,one reporting reduced risk for exclusive pipe smoking(RR 0.24,95%CI:0.06-0.91).The cigar results agree with an earlier review showing no clear risk increase for IHD or stroke.CONCLUSION Current cigarette smoking increases risk of AMI,IHD and stroke,RRs being 2.72,2.01 and 1.62.The stroke risk is lower in Japan,no increase was seen for cigars/pipes.展开更多
A kimberlite field, represented by fertile and sterile kimberlite pipes (chimneys) is located in the region of Kenieba (West Mali, Kédougou-Kenieba inlier, West African Craton). Thirty pipes and kimberlite dykes ...A kimberlite field, represented by fertile and sterile kimberlite pipes (chimneys) is located in the region of Kenieba (West Mali, Kédougou-Kenieba inlier, West African Craton). Thirty pipes and kimberlite dykes have been identified in the birimian formations, composed mainly of metasediments and granitoids, covered by sedimentary formations (sandstones and conglomerates) of Neoproterozoic age. All these formations are injected with dykes and doleritic sills of Jurassic age. The study of kimberlite pipes is still stammering in Mali, and thus no previous study has allowed to characterize the structures controlling their implementation. The reinterpretation of aeromagnetic data validated by field work indicates that the major structures of the Kenieba region are oriented NNE-SSW, NE-SW, E-W and NW-SE. These structures (faults and kimberlite pipes) are often associated with dolerite dykes, which would imply an injection of dolerite magma into the other formations. The location of the known kimberlite pipes makes it possible to say that the direction NW-SE is the most favorable for the exploration of kimberlites in the region of Kenieba.展开更多
The coupling vibration of a hydraulic pipe system consisting of two pipes is studied.The pipes are installed in parallel and fixed at their ends,and are restrained by clips to one bracket at their middle points.The pi...The coupling vibration of a hydraulic pipe system consisting of two pipes is studied.The pipes are installed in parallel and fixed at their ends,and are restrained by clips to one bracket at their middle points.The pipe subjected to the basement excitation at the left end is named as the active pipe,while the pipe without excitation is called the passive pipe.The clips between the two pipes are the bridge for the vibration energy.The adjacent natural frequencies will enhance the vibration coupling.The governing equation of the coupled system is deduced by the generalized Hamilton principle,and is discretized to the modal space.The modal correction is used during the discretization.The investigation on the natural characters indicates that the adjacent natural frequencies can be adjusted by the stiffness of the two clips and bracket.The harmonic balance method(HBM)is used to study the responses in the adjacent natural frequency region.The results show that the vibration energy transmits from the active pipe to the passive pipe swimmingly via the clips together with a flexible bracket,while the locations of them are not node points.The adjacent natural frequencies may arouse wide resonance curves with two peaks for both pipes.The stiffness of the clip and bracket can release the vibration coupling.It is suggested that the stiffness of the clip on the passive pipe should be weak and the bracket should be strong enough.In this way,the vibration energy is reflected by the almost rigid bracket,and is hard to transfer to the passive pipe via a soft clip.The best choice is to set the clips at the pipe node points.The current work gives some suggestions for weakening the coupled vibration during the dynamic design of a coupled hydraulic pipe system.展开更多
Although most pipes are restrained by retaining clips in aircraft,the influence of the clip parameters on the vibration of the fluid-conveying pipe has not been revealed.By considering the clip width,a new dynamic mod...Although most pipes are restrained by retaining clips in aircraft,the influence of the clip parameters on the vibration of the fluid-conveying pipe has not been revealed.By considering the clip width,a new dynamic model of a fluid-conveying pipe restrained by an intermediate clip is established in this paper.To demonstrate the necessity of the proposed model,a half pipe model is established by modeling the clip as one end.By comparing the two models,it is found that the half pipe model overestimates the critical velocity and may estimate the dynamical behavior of the pipe incorrectly.In addition,with the increase in the clip stiffness,the conversion processes of the first two modes of the pipe are shown.Furthermore,by ignoring the width of the clip,the effect of the flow velocity on the accuracy of a concentrated restraint clip model is presented.When the flow velocity is close to the critical velocity,the accuracy of the concentrated restraint clip model significantly reduces,especially when the width of the clip is large.In general,the contribution of this paper is to establish a dynamic model of the fluid-conveying pipe which can describe the influence of the clip parameters,and to demonstrate the necessity of this model.展开更多
Fluid-conveying pipes are widely used to transfer bulk fluids from one point to another in many engineering applications.They are subject to various excitations from the conveying fluids,the supporting structures,and ...Fluid-conveying pipes are widely used to transfer bulk fluids from one point to another in many engineering applications.They are subject to various excitations from the conveying fluids,the supporting structures,and the working environment,and thus are prone to vibrations such as flow-induced vibrations and acoustic-induced vibrations.Vibrations can generate variable dynamic stress and large deformation on fluid-conveying pipes,leading to vibration-induced fatigue and damage on the pipes,or even leading to failure of the entire piping system and catastrophic accidents.Therefore,the vibration control of fluid-conveying pipes is essential to ensure the integrity and safety of pipeline systems,and has attracted considerable attention from both researchers and engineers.The present paper aims to provide an extensive review of the state-of-the-art research on the vibration control of fluid-conveying pipes.The vibration analysis of fluid-conveying pipes is briefly discussed to show some key issues involved in the vibration analysis.Then,the research progress on the vibration control of fluid-conveying pipes is reviewed from four aspects in terms of passive control,active vibration control,semi-active vibration control,and structural optimization design for vibration reduction.Furthermore,the main results of existing research on the vibration control of fluid-conveying pipes are summarized,and future promising research directions are recommended to address the current research gaps.This paper contributes to the understanding of vibration control of fluid-conveying pipes,and will help the research work on the vibration control of fluidconveying pipes attract more attention.展开更多
A novel vibration absorber is designed to suppress vibrations in fluidconveying pipes subject to varying fluid speeds.The proposed absorber combines the fundamental principles of nonlinear energy sinks(NESs)and nonlin...A novel vibration absorber is designed to suppress vibrations in fluidconveying pipes subject to varying fluid speeds.The proposed absorber combines the fundamental principles of nonlinear energy sinks(NESs)and nonlinear energy harvesters(NEHs).The governing equation is derived,and a second-order discrete system is used to assess the performance of the developed device.The results demonstrate that the proposed absorber achieves significantly enhanced energy dissipation efficiency,reaching up to 95%,over a wider frequency range.Additionally,it successfully harvests additional electric energy.This research establishes a promising avenue for the development of new nonlinear devices aimed at suppressing fluid-conveying pipe vibrations across a broad frequency spectrum.展开更多
In this study,a coupling model of fluid-conveying pipes made of functionally graded materials(FGMs)with NiTiNOL-steel(NiTi-ST)for vibration absorption is investigated.The vibration responses of the FGM fluid-conveying...In this study,a coupling model of fluid-conveying pipes made of functionally graded materials(FGMs)with NiTiNOL-steel(NiTi-ST)for vibration absorption is investigated.The vibration responses of the FGM fluid-conveying pipe with NiTi-ST are studied by the Galerkin truncation method(GTM)and harmonic balance method(HBM).The harmonic balance solutions and the numerical results are consistent.Also,the linearized stability of the structure is determined.The effects of the structure parameters on the absorption performance are also studied.The results show that the NiTi-ST is an effective means of vibration absorption.Furthermore,in studying the effect of the NiTi-ST,a closed detached response(CDR)is first observed.It is noteworthy that the CDR may dramatically change the vibration amplitude and that the parameters of the NiTi-ST may determine the emergence or disappearance of the CDR.This vibration absorption device can be extended to offer more general vibration control in engineering applications.展开更多
It is a new attempt to extend the differential quadrature method(DQM)to stability analysis ofthe straight and curved centerline pipes conveying fluid.Emphasis is placed on the study of the influences ofseveral paramet...It is a new attempt to extend the differential quadrature method(DQM)to stability analysis ofthe straight and curved centerline pipes conveying fluid.Emphasis is placed on the study of the influences ofseveral parameters on the critical flow velocity’.Compared to other methods,this method can more easily dealwith the pipe with spring support at its boundaries and asks for much less computing effort while giving ac-ceptable precision in the numerical results.展开更多
Three-way pipes, T and Y pipes, are very important connecting components in pipeline systems, their strength are related to the safety of pipelines. In the case that crack is not detected in the three-way pipe, ANSYS ...Three-way pipes, T and Y pipes, are very important connecting components in pipeline systems, their strength are related to the safety of pipelines. In the case that crack is not detected in the three-way pipe, ANSYS finite element program version 5.6 is applied to study the stress distribution of the three-way pipe and to obtain the optimum fillet radius in the crotch region of the two pipes. The reasonable intersection angle of the two pipes is also obtained. In the case that a surface crack is detected in the three-way pipe, the maximum stress intensity factor (SIF) near the front of the surface crack is studied.展开更多
An approximate method for describing the plastic hardening-softening behaviour of circular pipes subjected to pure bending is presented.Theo-retical estimation based on the uniform ovalization model and local collapse...An approximate method for describing the plastic hardening-softening behaviour of circular pipes subjected to pure bending is presented.Theo-retical estimation based on the uniform ovalization model and local collapse modelproposed in the paper is incorporated to give several simple formulations with rea-sonable accuracy for determining the relationship between bending moment(M)andcurvature(k)in the purely bended pipes.Attention is focused on the critical cur-vature associated with maximum resistant moment and the maximum change in theoriginal diameter before the end of uniform ovalization stage as well as the localcollapse behaviour.Some comparisons between analytical results and experimentalresults are made in order to examine the theory.展开更多
The ceramic lined pipes had been produced by gravitational separation SHS method and influential factors on combustion synthesis was investigated.The experimental results showed that the ceramic lined pipes had been p...The ceramic lined pipes had been produced by gravitational separation SHS method and influential factors on combustion synthesis was investigated.The experimental results showed that the ceramic lined pipes had been produced easily under condition that selecting pipes well distributed on the wall thickness ,proper preheating temperature and appropriate additive.展开更多
In several previous studies,it was reported that a supported pipe with small geometric imperfections would lose stability when the internal flow velocity became sufficiently high.Recently,however,it has become clear t...In several previous studies,it was reported that a supported pipe with small geometric imperfections would lose stability when the internal flow velocity became sufficiently high.Recently,however,it has become clear that this conclusion may be at best incomplete.A reevaluation of the problem is undertaken here by essentially considering the flow-induced static deformation of a pipe.With the aid of the absolute nodal coordinate formulation(ANCF)and the extended Lagrange equations for dynamical systems containing non-material volumes,the nonlinear governing equations of a pipe with three different geometric imperfections are introduced and formulated.Based on extensive numerical calculations,the static equilibrium configuration,the stability,and the nonlinear dynamics of the considered pipe system are determined and analyzed.The results show that for a supported pipe with the geometric imperfection of a half sinusoidal wave,the dynamical system could not lose stability even if the flow velocity reaches an extremely high value of 40.However,for a supported pipe with the geometric imperfection of one or one and a half sinusoidal waves,the first-mode buckling instability would take place at high flow velocity.Moreover,based on a further parametric analysis,the effects of the amplitude of the geometric imperfection and the aspect ratio of the pipe on the static deformation,the critical flow velocity for buckling instability,and the nonlinear responses of the supported pipes with geometric imperfections are analyzed.展开更多
Axial and hoop stiffness can describe the elastic responses of reinforced thermoplastic pipes(RTPs)subjected to axisymmetric loads,such as tension,compression,pressure,and crushing loads.However,an accurate analytical...Axial and hoop stiffness can describe the elastic responses of reinforced thermoplastic pipes(RTPs)subjected to axisymmetric loads,such as tension,compression,pressure,and crushing loads.However,an accurate analytical prediction cannot be provided because of the anisotropy of RTP laminates.In the present study,a stiffness surface method,in which the analytical expressions of the axial and hoop stiffness are derived as two concise formulas,is proposed.The axial stiffness formula is obtained by solving the equilibrium equations of RTPs under a uniaxial stress state based on the homogenization assumption,whereas the hoop stiffness formula is derived from the combination of the elastic stability theory,the classical lamination theory,and NASA SP-8007 formula.To verify the proposed method,three types of RTPs are modeled to conduct the quasi-static analyses of the tension and crushing cases.The consistency between numerical and analytical results verifies the effectiveness of the proposed method on the prediction of the axial and hoop stiffness of RTPs,which also proves the existence of stiffness surfaces.As the axial stiffness is proportional to the radii,the axial stiffness surface consists of a series of straight lines,which can be used to predict both thin-walled and thick-walled RTPs.Meanwhile,the hoop stiffness is more applicable for thin-walled RTPs because the proposed method ignores the proportional relationship between the homogenized hoop elastic moduli and the reciprocal radii in helical structures.展开更多
This paper presents an analytical solution to the unsteady flow of the second-order non-Newtonian fluids by the use of intergral transformation method.Based on the numerical results,the effect of non-Newtonian coeffic...This paper presents an analytical solution to the unsteady flow of the second-order non-Newtonian fluids by the use of intergral transformation method.Based on the numerical results,the effect of non-Newtonian coefficient Hc and other parameters on the flow are analysed.It is shown that the annular flow has a shorter characteristic time than the general pipe flow while the correspondent velocity,average velocity have a(?)aller value for a given Hc.Else,when radii ratio keeps unchanged,the shear stress of inner wall of annular flow will change with the inner radius compared with the general pipe flow and is always smaller than that of the outer wall.展开更多
This paper presents a study on the tensile properties of reinforced thermoplastic pipes(RTPs). A mechanical model of RTPs with an arbitrary number of reinforced layers under tensile action is constructed by combining ...This paper presents a study on the tensile properties of reinforced thermoplastic pipes(RTPs). A mechanical model of RTPs with an arbitrary number of reinforced layers under tensile action is constructed by combining the constitutive relationship of elastoplastic materials with the continuous displacement condition. On this basis, the effects of various parameters such as the winding angle, the number of structurally reinforced layers, and the inner polyethylene(PE) liner thickness on the tensile properties of the RTPs were analyzed, and a tensile test was carried out for validation. The results showed that the winding angle of the structurally reinforced layers was the main factor affecting an RTP's tensile performance— decreases in the winding angle significantly improved its tensile ability,especially the longitudinal strength. With ±45° as the demarcation point, the winding angle smaller than ±45° will result in higher strength in longitudinal direction, and the lifting effect on RTP's mechanical properties of the increasing number of reinforcement layers was better than that of the increasing thickness of the lining layer;when the winding angle was larger than ±45°, the opposite results were obtained. The fibre load was more sensitive to the winding angle than the PE load.展开更多
This study explores how parametric uncertainties in the production affect failure tensile loads of reinforced thermoplastic pipes(RTPs)under combined loading conditions.The stress distributions in RTPs are examined wi...This study explores how parametric uncertainties in the production affect failure tensile loads of reinforced thermoplastic pipes(RTPs)under combined loading conditions.The stress distributions in RTPs are examined with three-dimensional(3D)elasticity theory,and the analytical micromechanics of composites are evaluated.To evaluate the failure mechanisms for RTPs,3D Hashin–Yeh failure criteria are combined with the damage evolution model to establish a progressive failure model.The theoretical model has been validated through numerical simulations and axial tensile tests data.To analyze how randomness of relevant parameters affects the first-ply failure(FPF)tensile load and final failure(FF)tensile load in RTPs,many samples are produced with the Monte–Carlo approach.The stochastic analysis results are statistically evaluated through the Weibull probability density distribution function.For the randomness of production parameters,the failure tensile load of RTPs fluctuates near the mean value.As the ply number at the reinforced layer increases,the dispersion of failure tensile load increases,with a high probability that the FPF tensile load of RTPs is lower than the mean value.展开更多
基金Project supported by the National Natural Science Foundation of China (Nos.12002195 and 12372015)the National Science Fund for Distinguished Young Scholars of China (No.12025204)the Program of Shanghai Municipal Education Commission of China (No.2019-01-07-00-09-E00018)。
文摘Based on the generalized Hamilton's principle,the nonlinear governing equation of an axially functionally graded(AFG)pipe is established.The non-trivial equilibrium configuration is superposed by the modal functions of a simply supported beam.Via the direct multi-scale method,the response and stability boundary to the pulsating fluid velocity are solved analytically and verified by the differential quadrature element method(DQEM).The influence of Young's modulus gradient on the parametric resonance is investigated in the subcritical and supercritical regions.In general,the pipe in the supercritical region is more sensitive to the pulsating excitation.The nonlinearity changes from hard to soft,and the non-trivial equilibrium configuration introduces more frequency components to the vibration.Besides,the increasing Young's modulus gradient improves the critical pulsating flow velocity of the parametric resonance,and further enhances the stability of the system.In addition,when the temperature increases along the axial direction,reducing the gradient parameter can enhance the response asymmetry.This work further complements the theoretical analysis of pipes conveying pulsating fluid.
基金Scientific Research Fund of Institute of Engineering Mechanics,China Earthquake Administration under Grant Nos.2021EEEVL0204 and 2018A02。
文摘As an important part of nonstructural components,the seismic response of indoor water supply pipes deserves much attention.This paper presents shaking table test research on water supply pipes installed in a full-scale reinforced concrete(RC)frame structure.Different material pipes and different methods for penetrating the reinforced concrete floors are combined to evaluate the difference in seismic performance.Floor response spectra and pipe acceleration amplification factors based on test data are discussed and compared with code provisions.A seismic fragility study of displacement demand is conducted based on numerical simulation.The acceleration response and displacement response of different combinations are compared.The results show that the combination of different pipe materials and different passing-through methods can cause obvious differences in the seismic response of indoor riser pipes.
基金supported by the Science and Technology Development Fund of Macao(Grant No.0079/2019/AMJ)the National Key R&D Program of China(No.2019YFE0111400).
文摘Urban sewer pipes are a vital infrastructure in modern cities,and their defects must be detected in time to prevent potential malfunctioning.In recent years,to relieve the manual efforts by human experts,models based on deep learning have been introduced to automatically identify potential defects.However,these models are insufficient in terms of dataset complexity,model versatility and performance.Our work addresses these issues with amulti-stage defect detection architecture using a composite backbone Swin Transformer.Themodel based on this architecture is trained using a more comprehensive dataset containingmore classes of defects.By ablation studies on the modules of combined backbone Swin Transformer,multi-stage detector,test-time data augmentation and model fusion,it is revealed that they all contribute to the improvement of detection accuracy from different aspects.The model incorporating all these modules achieves the mean Average Precision(mAP)of 78.6% at an Intersection over Union(IoU)threshold of 0.5.This represents an improvement of 14.1% over the ResNet50 Faster Region-based Convolutional Neural Network(R-CNN)model and a 6.7% improvement over You Only Look Once version 6(YOLOv6)-large,the highest in the YOLO methods.In addition,for other defect detection models for sewer pipes,although direct comparison with themis infeasible due to the unavailability of their private datasets,our results are obtained from a more comprehensive dataset and have superior generalization capabilities.
文摘Controlling inner-wall band segregation is one of the difficulties in the production of high-strength antisulfur pipes.Comparative tests were carried out on different casting processes(superheat,mold electromagnetic stirring,end electromagnetic stirring,casting speed and soft reduction)for the smelting of high-strength antisulfur pipes.The microstructures of continuous-casting billets and hot-rolled or tempered pipes were analyzed using a metallographic microscope and scanning electron microscope.The mechanism and evolution law regarding the inner-wall band segregation of high-strength antisulfur pipes were studied,and the influence of different casting processes was explored.
文摘BACKGROUND More recent data are required relating to disease risk for use of various smoked products and of other products containing nicotine.Earlier we published metaanalyses of recent results for chronic obstructive pulmonary disease and lung cancer on the relative risk(RR)of current compared to never product use for cigarettes,cigars and pipes based on evidence from North America,Europe and Japan.We now report corresponding up-to-date evidence for acute myocardial infarction(AMI),ischaemic heart disease(IHD)and stroke.AIM To estimate,using recent data,AMI,IHD and stroke RRs by region for current smoking of cigarettes,cigars and pipes.METHODS Publications in English from 2015 to 2020 were considered that,based on epidemiological studies in the three regions,estimated the current smoking RR of AMI,IHD or stroke for one or more of the three products.The studies should involve at least 100 cases of stroke or cardiovascular disease(CVD),not be restricted to populations with specific medical conditions,and should be of cohort or nested case-control study design or randomized controlled trials.A literature search was conducted on MEDLINE,examining titles and abstracts initially,and then full texts.Additional papers were sought from reference lists of selected papers,reviews and meta-analyses.For each study identified,we entered the most recent available data on current smoking of each product,as well as the characteristics of the study and the RR estimates.Combined RR estimates were derived using random-effects meta-analysis for stroke and,in the case of CVD,separately for IHD and AMI.For cigarette smoking,where far more data were available,heterogeneity was studied by a wide range of factors.For cigar and pipe smoking,a more limited heterogeneity analysis was carried out.A more limited assessment of variation in risk by daily number of cigarettes smoked was also conducted.RESULTS Current cigarette smoking:Ten studies gave a random-effects RR for AMI of 2.72[95%confidence interval(CI):2.40-3.08],derived from 13 estimates between 1.47 and 4.72.Twenty-three studies gave an IHD RR of 2.01(95%CI:1.84-2.21),using 28 estimates between 0.81 and 4.30.Thirty-one studies gave a stroke RR of 1.62(95%CI:1.48-1.77),using 37 estimates from 0.66 to 2.91.Though heterogeneous,only two of the overall 78 RRs were below 1.0,71 significantly(P<0.05)exceeding 1.0.The heterogeneity was only partly explicable by the factors studied.Estimates were generally higher for females and for later-starting studies.They were significantly higher for North America than Europe for AMI,but not the other diseases.For stroke,the only endpoint with multiple Japanese studies,RRs were lower there than for Western studies.Adjustment for multiple factors tended to increase RRs.Our RR estimates and the variations by sex and region are consistent with earlier meta-analyses.RRs generally increased with amount smoked.Current cigar and pipe smoking:No AMI data were available.One North American study reported reduced IHD risk for non-exclusive cigar or pipe smoking,but considered few cases.Two North American studies found no increased stroke risk with exclusive cigar smoking,one reporting reduced risk for exclusive pipe smoking(RR 0.24,95%CI:0.06-0.91).The cigar results agree with an earlier review showing no clear risk increase for IHD or stroke.CONCLUSION Current cigarette smoking increases risk of AMI,IHD and stroke,RRs being 2.72,2.01 and 1.62.The stroke risk is lower in Japan,no increase was seen for cigars/pipes.
文摘A kimberlite field, represented by fertile and sterile kimberlite pipes (chimneys) is located in the region of Kenieba (West Mali, Kédougou-Kenieba inlier, West African Craton). Thirty pipes and kimberlite dykes have been identified in the birimian formations, composed mainly of metasediments and granitoids, covered by sedimentary formations (sandstones and conglomerates) of Neoproterozoic age. All these formations are injected with dykes and doleritic sills of Jurassic age. The study of kimberlite pipes is still stammering in Mali, and thus no previous study has allowed to characterize the structures controlling their implementation. The reinterpretation of aeromagnetic data validated by field work indicates that the major structures of the Kenieba region are oriented NNE-SSW, NE-SW, E-W and NW-SE. These structures (faults and kimberlite pipes) are often associated with dolerite dykes, which would imply an injection of dolerite magma into the other formations. The location of the known kimberlite pipes makes it possible to say that the direction NW-SE is the most favorable for the exploration of kimberlites in the region of Kenieba.
基金Project supported by the National Natural Science Foundation of China(No.12002195)the Pujiang Project of Shanghai Science and Technology Commission of China(No.20PJ1404000)。
文摘The coupling vibration of a hydraulic pipe system consisting of two pipes is studied.The pipes are installed in parallel and fixed at their ends,and are restrained by clips to one bracket at their middle points.The pipe subjected to the basement excitation at the left end is named as the active pipe,while the pipe without excitation is called the passive pipe.The clips between the two pipes are the bridge for the vibration energy.The adjacent natural frequencies will enhance the vibration coupling.The governing equation of the coupled system is deduced by the generalized Hamilton principle,and is discretized to the modal space.The modal correction is used during the discretization.The investigation on the natural characters indicates that the adjacent natural frequencies can be adjusted by the stiffness of the two clips and bracket.The harmonic balance method(HBM)is used to study the responses in the adjacent natural frequency region.The results show that the vibration energy transmits from the active pipe to the passive pipe swimmingly via the clips together with a flexible bracket,while the locations of them are not node points.The adjacent natural frequencies may arouse wide resonance curves with two peaks for both pipes.The stiffness of the clip and bracket can release the vibration coupling.It is suggested that the stiffness of the clip on the passive pipe should be weak and the bracket should be strong enough.In this way,the vibration energy is reflected by the almost rigid bracket,and is hard to transfer to the passive pipe via a soft clip.The best choice is to set the clips at the pipe node points.The current work gives some suggestions for weakening the coupled vibration during the dynamic design of a coupled hydraulic pipe system.
基金supported by the National Science Funds for Distinguished Young Scholars of China(No.12025204)the Shanghai Municipal Education Commission of China(No.2019-01-07-00-09-E00018)。
文摘Although most pipes are restrained by retaining clips in aircraft,the influence of the clip parameters on the vibration of the fluid-conveying pipe has not been revealed.By considering the clip width,a new dynamic model of a fluid-conveying pipe restrained by an intermediate clip is established in this paper.To demonstrate the necessity of the proposed model,a half pipe model is established by modeling the clip as one end.By comparing the two models,it is found that the half pipe model overestimates the critical velocity and may estimate the dynamical behavior of the pipe incorrectly.In addition,with the increase in the clip stiffness,the conversion processes of the first two modes of the pipe are shown.Furthermore,by ignoring the width of the clip,the effect of the flow velocity on the accuracy of a concentrated restraint clip model is presented.When the flow velocity is close to the critical velocity,the accuracy of the concentrated restraint clip model significantly reduces,especially when the width of the clip is large.In general,the contribution of this paper is to establish a dynamic model of the fluid-conveying pipe which can describe the influence of the clip parameters,and to demonstrate the necessity of this model.
基金Project supported by the China National Funds for Distinguished Young Scholars(No.12025204)the Shanghai Municipal Education Commission(No.2019-01-07-00-09-E00018)。
文摘Fluid-conveying pipes are widely used to transfer bulk fluids from one point to another in many engineering applications.They are subject to various excitations from the conveying fluids,the supporting structures,and the working environment,and thus are prone to vibrations such as flow-induced vibrations and acoustic-induced vibrations.Vibrations can generate variable dynamic stress and large deformation on fluid-conveying pipes,leading to vibration-induced fatigue and damage on the pipes,or even leading to failure of the entire piping system and catastrophic accidents.Therefore,the vibration control of fluid-conveying pipes is essential to ensure the integrity and safety of pipeline systems,and has attracted considerable attention from both researchers and engineers.The present paper aims to provide an extensive review of the state-of-the-art research on the vibration control of fluid-conveying pipes.The vibration analysis of fluid-conveying pipes is briefly discussed to show some key issues involved in the vibration analysis.Then,the research progress on the vibration control of fluid-conveying pipes is reviewed from four aspects in terms of passive control,active vibration control,semi-active vibration control,and structural optimization design for vibration reduction.Furthermore,the main results of existing research on the vibration control of fluid-conveying pipes are summarized,and future promising research directions are recommended to address the current research gaps.This paper contributes to the understanding of vibration control of fluid-conveying pipes,and will help the research work on the vibration control of fluidconveying pipes attract more attention.
基金Project supported by the National Key Research and Development Program of China(No.2022YFC3002502)。
文摘A novel vibration absorber is designed to suppress vibrations in fluidconveying pipes subject to varying fluid speeds.The proposed absorber combines the fundamental principles of nonlinear energy sinks(NESs)and nonlinear energy harvesters(NEHs).The governing equation is derived,and a second-order discrete system is used to assess the performance of the developed device.The results demonstrate that the proposed absorber achieves significantly enhanced energy dissipation efficiency,reaching up to 95%,over a wider frequency range.Additionally,it successfully harvests additional electric energy.This research establishes a promising avenue for the development of new nonlinear devices aimed at suppressing fluid-conveying pipe vibrations across a broad frequency spectrum.
基金Project supported by the National Natural Science Foundation of China(Nos.12272240 and12022213)。
文摘In this study,a coupling model of fluid-conveying pipes made of functionally graded materials(FGMs)with NiTiNOL-steel(NiTi-ST)for vibration absorption is investigated.The vibration responses of the FGM fluid-conveying pipe with NiTi-ST are studied by the Galerkin truncation method(GTM)and harmonic balance method(HBM).The harmonic balance solutions and the numerical results are consistent.Also,the linearized stability of the structure is determined.The effects of the structure parameters on the absorption performance are also studied.The results show that the NiTi-ST is an effective means of vibration absorption.Furthermore,in studying the effect of the NiTi-ST,a closed detached response(CDR)is first observed.It is noteworthy that the CDR may dramatically change the vibration amplitude and that the parameters of the NiTi-ST may determine the emergence or disappearance of the CDR.This vibration absorption device can be extended to offer more general vibration control in engineering applications.
基金National Key Project of China (No.PD9521907)the National Science Foundation of China (No.19872025).
文摘It is a new attempt to extend the differential quadrature method(DQM)to stability analysis ofthe straight and curved centerline pipes conveying fluid.Emphasis is placed on the study of the influences ofseveral parameters on the critical flow velocity’.Compared to other methods,this method can more easily dealwith the pipe with spring support at its boundaries and asks for much less computing effort while giving ac-ceptable precision in the numerical results.
文摘Three-way pipes, T and Y pipes, are very important connecting components in pipeline systems, their strength are related to the safety of pipelines. In the case that crack is not detected in the three-way pipe, ANSYS finite element program version 5.6 is applied to study the stress distribution of the three-way pipe and to obtain the optimum fillet radius in the crotch region of the two pipes. The reasonable intersection angle of the two pipes is also obtained. In the case that a surface crack is detected in the three-way pipe, the maximum stress intensity factor (SIF) near the front of the surface crack is studied.
文摘An approximate method for describing the plastic hardening-softening behaviour of circular pipes subjected to pure bending is presented.Theo-retical estimation based on the uniform ovalization model and local collapse modelproposed in the paper is incorporated to give several simple formulations with rea-sonable accuracy for determining the relationship between bending moment(M)andcurvature(k)in the purely bended pipes.Attention is focused on the critical cur-vature associated with maximum resistant moment and the maximum change in theoriginal diameter before the end of uniform ovalization stage as well as the localcollapse behaviour.Some comparisons between analytical results and experimentalresults are made in order to examine the theory.
文摘The ceramic lined pipes had been produced by gravitational separation SHS method and influential factors on combustion synthesis was investigated.The experimental results showed that the ceramic lined pipes had been produced easily under condition that selecting pipes well distributed on the wall thickness ,proper preheating temperature and appropriate additive.
基金supported by the National Natural Science Foundation of China(Nos.11972167,12072119)the Alexander von Humboldt Foundation。
文摘In several previous studies,it was reported that a supported pipe with small geometric imperfections would lose stability when the internal flow velocity became sufficiently high.Recently,however,it has become clear that this conclusion may be at best incomplete.A reevaluation of the problem is undertaken here by essentially considering the flow-induced static deformation of a pipe.With the aid of the absolute nodal coordinate formulation(ANCF)and the extended Lagrange equations for dynamical systems containing non-material volumes,the nonlinear governing equations of a pipe with three different geometric imperfections are introduced and formulated.Based on extensive numerical calculations,the static equilibrium configuration,the stability,and the nonlinear dynamics of the considered pipe system are determined and analyzed.The results show that for a supported pipe with the geometric imperfection of a half sinusoidal wave,the dynamical system could not lose stability even if the flow velocity reaches an extremely high value of 40.However,for a supported pipe with the geometric imperfection of one or one and a half sinusoidal waves,the first-mode buckling instability would take place at high flow velocity.Moreover,based on a further parametric analysis,the effects of the amplitude of the geometric imperfection and the aspect ratio of the pipe on the static deformation,the critical flow velocity for buckling instability,and the nonlinear responses of the supported pipes with geometric imperfections are analyzed.
基金This work is supported by the National Science Fund for Distinguished Young Scholars,China(No.51625902)the Offshore Flexible Pipe Project from the Ministry of Industry and Information Technology,Chinathe Taishan Scholars Program of Shandong Province,China(No.TS201511016).
文摘Axial and hoop stiffness can describe the elastic responses of reinforced thermoplastic pipes(RTPs)subjected to axisymmetric loads,such as tension,compression,pressure,and crushing loads.However,an accurate analytical prediction cannot be provided because of the anisotropy of RTP laminates.In the present study,a stiffness surface method,in which the analytical expressions of the axial and hoop stiffness are derived as two concise formulas,is proposed.The axial stiffness formula is obtained by solving the equilibrium equations of RTPs under a uniaxial stress state based on the homogenization assumption,whereas the hoop stiffness formula is derived from the combination of the elastic stability theory,the classical lamination theory,and NASA SP-8007 formula.To verify the proposed method,three types of RTPs are modeled to conduct the quasi-static analyses of the tension and crushing cases.The consistency between numerical and analytical results verifies the effectiveness of the proposed method on the prediction of the axial and hoop stiffness of RTPs,which also proves the existence of stiffness surfaces.As the axial stiffness is proportional to the radii,the axial stiffness surface consists of a series of straight lines,which can be used to predict both thin-walled and thick-walled RTPs.Meanwhile,the hoop stiffness is more applicable for thin-walled RTPs because the proposed method ignores the proportional relationship between the homogenized hoop elastic moduli and the reciprocal radii in helical structures.
文摘This paper presents an analytical solution to the unsteady flow of the second-order non-Newtonian fluids by the use of intergral transformation method.Based on the numerical results,the effect of non-Newtonian coefficient Hc and other parameters on the flow are analysed.It is shown that the annular flow has a shorter characteristic time than the general pipe flow while the correspondent velocity,average velocity have a(?)aller value for a given Hc.Else,when radii ratio keeps unchanged,the shear stress of inner wall of annular flow will change with the inner radius compared with the general pipe flow and is always smaller than that of the outer wall.
基金financially supported by the National Key Research and Development Program of China (Grant No. 2016YFC0303800)the National Natural Science Foundation of China (Grant No. 51579245)。
文摘This paper presents a study on the tensile properties of reinforced thermoplastic pipes(RTPs). A mechanical model of RTPs with an arbitrary number of reinforced layers under tensile action is constructed by combining the constitutive relationship of elastoplastic materials with the continuous displacement condition. On this basis, the effects of various parameters such as the winding angle, the number of structurally reinforced layers, and the inner polyethylene(PE) liner thickness on the tensile properties of the RTPs were analyzed, and a tensile test was carried out for validation. The results showed that the winding angle of the structurally reinforced layers was the main factor affecting an RTP's tensile performance— decreases in the winding angle significantly improved its tensile ability,especially the longitudinal strength. With ±45° as the demarcation point, the winding angle smaller than ±45° will result in higher strength in longitudinal direction, and the lifting effect on RTP's mechanical properties of the increasing number of reinforcement layers was better than that of the increasing thickness of the lining layer;when the winding angle was larger than ±45°, the opposite results were obtained. The fibre load was more sensitive to the winding angle than the PE load.
基金financially supported by the National Natural Science Foundation of China(Grant No.U2006226]the National Key Research and Development Program of China(Grant No.2016YFC0303800)。
文摘This study explores how parametric uncertainties in the production affect failure tensile loads of reinforced thermoplastic pipes(RTPs)under combined loading conditions.The stress distributions in RTPs are examined with three-dimensional(3D)elasticity theory,and the analytical micromechanics of composites are evaluated.To evaluate the failure mechanisms for RTPs,3D Hashin–Yeh failure criteria are combined with the damage evolution model to establish a progressive failure model.The theoretical model has been validated through numerical simulations and axial tensile tests data.To analyze how randomness of relevant parameters affects the first-ply failure(FPF)tensile load and final failure(FF)tensile load in RTPs,many samples are produced with the Monte–Carlo approach.The stochastic analysis results are statistically evaluated through the Weibull probability density distribution function.For the randomness of production parameters,the failure tensile load of RTPs fluctuates near the mean value.As the ply number at the reinforced layer increases,the dispersion of failure tensile load increases,with a high probability that the FPF tensile load of RTPs is lower than the mean value.
