This work investigated the dynamic behavior of vertical pipes conveying gas-liquid two-phase flow when subjected to external excitations at both ends.Even with minimal excitation amplitude,resonance can occur when the...This work investigated the dynamic behavior of vertical pipes conveying gas-liquid two-phase flow when subjected to external excitations at both ends.Even with minimal excitation amplitude,resonance can occur when the excitation frequency aligns with the natural frequency of the pipe,significantly increasing the degree of operational risk.The governing equation of motion based on the Euler-Bernoulli beam is derived for the relative deflection with stationary simply supported ends,with the effects of the external excitations represented by source terms distributed along the pipe length.The fourth-order partial differential equation is solved via the generalized integral transform technique(GITT),with the solution successfully verified via comparison with results in the literature.A comprehensive analysis of the vibration phenomena and changes in the motion state of the pipe is conducted for three classes of external excitation conditions:same frequency and amplitude(SFSA),same frequency but different amplitudes(SFDA),and different frequencies and amplitudes(DFDA).The numerical results show that with increasing gas volume fraction,the position corresponding to the maximum vibration displacement shifts upward.Compared with conditions without external excitation,the vibration displacement of the pipe conveying two-phase flow under external excitation increases significantly.The frequency of external excitation has a significant effect on the dynamic behavior of a pipe conveying two-phase flow.展开更多
Bends contribute to a flexible layout of pipeline system,but also lead to intensive energy costs due to the complex flow characteristic.This experimental study is conducted to investigate the impact of a single coarse...Bends contribute to a flexible layout of pipeline system,but also lead to intensive energy costs due to the complex flow characteristic.This experimental study is conducted to investigate the impact of a single coarse particle on the flow field in a bend.The velocity profiles of fluid on the axial symmetry plane of the bend are measured using time-resolved particle image velocimetry.The flow structures are extracted using the proper orthogonal decomposition method.The results reveal that there is a shear-layer flow in the bend during the transportation.With the increase in particle size,the particle has a dominant influence on the flow energy distribution of the overall flow.The impact of particles on the first few energetic flows is mainly in the latter part of the transportation,both temporally and spatially.As the particle size decreases,the most energetic unsteady flow within the bend changes from the convective flow to the flow of the shear layer.展开更多
The complex dense-phase pneumatic conveying of pulverized coal process was studied using an electrical capacitance tomography(ECT) signal that represented the motion characteristics of gas-solid two-phase flow. The fl...The complex dense-phase pneumatic conveying of pulverized coal process was studied using an electrical capacitance tomography(ECT) signal that represented the motion characteristics of gas-solid two-phase flow. The fluctuation characteristics of conveying process signals are inseparable from the flow pattern. The denoised ECT signal and noise signal were obtained by db2 wavelet analysis. It was found that all noise signals were white Gaussian noise. Based on the assumption of the equal probability distribution of pulverized coal concentration, this paper proved that the time series distribution of pulverized coal concentration in the pipeline should obey the normal distribution. Furthermore, through the analysis of the distribution characteristics of the power spectral density function of denoised ECT signals of four flow patterns, they were α-dimensional fractal Brownian motion(fBm) signals, and the parameter α was estimated by the detrended fluctuation analysis. Based on the fBm characteristics of denoised ECT signals and white Gaussian noise, this paper proposed a method for calculating the pulverized coal concentration in the dense-phase pneumatic conveying. In addition to the method of concentration estimation with the significance of engineering guidance, this research can help people to further understand essential characteristics of ECT signals in the dense-phase pneumatic conveying.展开更多
The Haidong Water Conveyance Tunnel(HWCT),a notable engineering feat located within Dali City,Yunnan Province,China,represents an ultra-long water conveyance tunnel situated in a region characterized by medium in-situ...The Haidong Water Conveyance Tunnel(HWCT),a notable engineering feat located within Dali City,Yunnan Province,China,represents an ultra-long water conveyance tunnel situated in a region characterized by medium in-situ stress conditions.As part of the Central Yunnan Water Diversion Project,this tunnel was specifically engineered for soft-rock environments.The excavation of such tunnels presents significant challenges due to rock mass deformation,commonly referred to as squeezing ground behavior.These challenges are exacerbated when navigating through diverse geological and geomorphological units,particularly in areas with complex geological conditions.To address these issues,an innovative active support system utilizing prestressed anchor cables was developed for the HWCT.This study provides a comprehensive analysis and comparison of rock mass behavior between two support systems:a conventional passive system employing steel arches and the proposed active system using prestressed anchor cables.The numerical modeling was performed using FLAC3D software to simulate various scenarios,while an extensive monitoring program was implemented in several representative tunnel sections to measure key parameters including rock mass stresses,displacements,internal forces in steel arches,and axial forces in anchor cables.The results from both the numerical simulations and field observations were systematically compared.The analyses demonstrated the superior performance of the active support system using prestressed anchor cables in the HWCT,significantly enhancing overall rock mass stability and effectively mitigating large deformation issues throughout the tunnel.展开更多
This study examines the nonlinear behaviors of a clamped-clamped porous pipe made of a functionally graded material(FGM)that conveys fluids and is equipped with a retaining clip,focusing on primary resonance and subcr...This study examines the nonlinear behaviors of a clamped-clamped porous pipe made of a functionally graded material(FGM)that conveys fluids and is equipped with a retaining clip,focusing on primary resonance and subcritical dynamics.The nonlinear governing equations for the FGM pipe are derived by the extended Hamilton's principle,and subsequently discretized through the application of the Galerkin method.The direct method of multi-scales is then used to solve the derived equations.A thorough analysis of various parameters,including the clip stiffness,the power-law index,the porosity,and the clip location,is conducted to gain a comprehensive understanding of the system's nonlinear dynamics.Through the analysis of the first natural frequency,the study highlights the influence of the flow velocity and the clip stiffness,while the comparisons with metallic pipes emphasize the role of FGM composition.The examination of the forced response curves reveals saddle-node bifurcations and their dependence on parameters such as the detuning parameter and the power-law index,offering valuable insights into the system's nonlinear resonant behavior.Furthermore,the frequency-response curves illustrate the hardening nonlinearities influenced by factors such as the porosity and the clip stiffness,revealing nuanced effects on the system response and resonance characteristics.This comprehensive analysis enhances the understanding of nonlinear behaviors in FGM porous pipes with a retaining clip,providing key insights for practical engineering applications in system design and optimization.展开更多
Multi-constrained pipes conveying fluid,such as aircraft hydraulic control pipes,are susceptible to resonance fatigue in harsh vibration environments,which may lead to system failure and even catastrophic accidents.In...Multi-constrained pipes conveying fluid,such as aircraft hydraulic control pipes,are susceptible to resonance fatigue in harsh vibration environments,which may lead to system failure and even catastrophic accidents.In this study,a machine learning(ML)-assisted weak vibration design method under harsh environmental excitations is proposed.The dynamic model of a typical pipe is developed using the absolute nodal coordinate formulation(ANCF)to determine its vibrational characteristics.With the harsh vibration environments as the preserved frequency band(PFB),the safety design is defined by comparing the natural frequency with the PFB.By analyzing the safety design of pipes with different constraint parameters,the dataset of the absolute safety length and the absolute resonance length of the pipe is obtained.This dataset is then utilized to develop genetic programming(GP)algorithm-based ML models capable of producing explicit mathematical expressions of the pipe's absolute safety length and absolute resonance length with the location,stiffness,and total number of retaining clips as design variables.The proposed ML models effectively bridge the dataset with the prediction results.Thus,the ML model is utilized to stagger the natural frequency,and the PFB is utilized to achieve the weak vibration design.The findings of the present study provide valuable insights into the practical application of weak vibration design.展开更多
Aimed at the long and narrow geometric features and poor generalization ability of the damage detection in conveyor belts with steel rope cores using the X-ray image,a detection method of damage X-ray image is propose...Aimed at the long and narrow geometric features and poor generalization ability of the damage detection in conveyor belts with steel rope cores using the X-ray image,a detection method of damage X-ray image is proposed based on the improved fully convolutional one-stage object detection(FCOS)algorithm.The regression performance of bounding boxes was optimized by introducing the complete intersection over union loss function into the improved algorithm.The feature fusion network structure is modified by adding adaptive fusion paths to the feature fusion network structure,which makes full use of the features of accurate localization and semantics of multi-scale feature fusion networks.Finally,the network structure was trained and validated by using the X-ray image dataset of damages in conveyor belts with steel rope cores provided by a flaw detection equipment manufacturer.In addition,the data enhancement methods such as rotating,mirroring,and scaling,were employed to enrich the image dataset so that the model is adequately trained.Experimental results showed that the improved FCOS algorithm promoted the precision rate and the recall rate by 20.9%and 14.8%respectively,compared with the original algorithm.Meanwhile,compared with Fast R-CNN,Faster R-CNN,SSD,and YOLOv3,the improved FCOS algorithm has obvious advantages;detection precision rate and recall rate of the modified network reached 95.8%and 97.0%respectively.Furthermore,it demonstrated a higher detection accuracy without affecting the speed.The results of this work have some reference significance for the automatic identification and detection of steel core conveyor belt damage.展开更多
Experiments of dense-phase pneumatic conveying of pulverized coal using nitrogen are carded out in an experimental test facility with the conveying pressure up to 4. 0 MPa and the gas-solid ratio up to 450 kg/m^3. The...Experiments of dense-phase pneumatic conveying of pulverized coal using nitrogen are carded out in an experimental test facility with the conveying pressure up to 4. 0 MPa and the gas-solid ratio up to 450 kg/m^3. The influences of different conveying differential pressures, coal moisture contents, gas volume flow rates and superficial velocities on the solid-gas ratios are investigated. Shannon entropy analysis of pressure fluctuation time series is developed to reveal the flow characteristics. Through investigation of the distribution of the Shannon entropy under different conditions, the flow stability and the evolutional tendency of the Shannon entropy in different regimes and regime transition processes are discovered, and the relationship between the Shannon entropy and the flow regimes is also established. The results indicate that the solid-gas ratio and the Shannon entropy rise with the increase in conveying differential pressure. The solid-gas ratio and the Shannon entropy reveal preferable regularity with gas volume flow rates. The Shannon entropy is different for different flow regimes, and can be used to identify the flow regimes. Both mass flow rate and the Shannon entropy decrease with the increase in moisture contents. The Shannon entropy analysis is a feasible approach for researching the characteristics of flow regimes, flow stability and flow regime transitions in dense-phase pneumatic conveying under high pressure.展开更多
A novel particle-size conveying model was established to examine the effects of the dimension relationships of the groove depth and particle size on the solids conveying mechanism of the helically grooved feed section...A novel particle-size conveying model was established to examine the effects of the dimension relationships of the groove depth and particle size on the solids conveying mechanism of the helically grooved feed section. In the model, one or two shear interfaces were proposed based on the dimension relationships of the groove depth and particle size, and the solid-plug embedded in the groove and screw channel were divided into two or three layers by the shear interfaces to consider the solids conveying mechanism of each layer by the boundary condition equation for positive conveying. By the particle-size model, the effects of different dimension relationships on the transformation of solids conveying mechanisms between the friction-drag conveying and the positive conveying were discussed and compared with the on-line measuring experimental data. The results showed that the shear interfaces among the solids existed indeed and the dimension relationships determined the conveying mechanism and the throughput of helically grooved extruders, which was well confirmed by the excellent consistence between the predicted and measured data.展开更多
The sampling auger used in lunar sampling and return mission is to transmit power and convey soil, and its performance is the key factor of the whole mission. However, there is currently a lack of the optimization res...The sampling auger used in lunar sampling and return mission is to transmit power and convey soil, and its performance is the key factor of the whole mission. However, there is currently a lack of the optimization research on soil conveying volume and power consumption models in auger structure design. To provide the drilled object, the simulation lunar soil, whose physical and mechanical property is the same as the real soil, is made by reducing soil void ratio. The models are formulated to analyze the influence of auger structure parameters on power consumption and soil conveying volume. To obtain the optimized structure parameters of auger, the multi-objective optimization functions of the maximum soil conveying volume and minimum power consumption are developed. To verify the correctness of the models, the performances of different augers drilling simulation soil are tested. The test results demonstrate that the power consumption of optimized auger is the lowest both in theory and test, and the experimental results of soil conveying volume are in agreement with theoretical analysis. Consequently, a new method for designing a lunar sampling auger is proposed which includes the models of soil conveying volume and transportation power consumption, the optimization of structure parameters and the comparison tests. This method provides a reference for sampling auger designing of the Chinese Lunar Sample Mission.展开更多
The lateral vibration differential equation for a marine riser conveying fluid is derived by use of the small deflection theory, and the effect of internal flow velocity and top tension on the natural frequency of the...The lateral vibration differential equation for a marine riser conveying fluid is derived by use of the small deflection theory, and the effect of internal flow velocity and top tension on the natural frequency of the riser is studied by use of FEM. At the same time, the preliminary relationship between the natural Frequency and riser span under different internal flow velocities is obtained, the effect of riser supports on the vibration frequency is computed. It is found that the natural frequency of the marine riser increases with the increase of top tension, however decreases with the increase of internal flow velocity. In addition, the Frequency decreases drastically with the increase of riser span.展开更多
This paper deals with the three-dimensional dynamics and postbuckling behavior of flexible supported pipes conveying fluid, considering flow velocities lower and higher than the critical value at which the buckling in...This paper deals with the three-dimensional dynamics and postbuckling behavior of flexible supported pipes conveying fluid, considering flow velocities lower and higher than the critical value at which the buckling instability occurs. In the case of low flow velocity, the pipe is stable with a straight equilibrium position and the dynamics of the system can be examined using linear theory. When the flow velocity is beyond the critical value, any motions of the pipe could be around the postbuckling configuration(non-zero equilibrium position) rather than the straight equilibrium position, so nonlinear theory is required. The nonlinear equations of perturbed motions around the postbuckling configuration are derived and solved with the aid of Galerkin discretization. It is found, for a given flow velocity,that the first-mode frequency for in-plane motions is quite different from that for out-of-plane motions. However, the second-or third-mode frequencies for in-plane motions are approximately equal to their counterparts for out-of-plane motions, keeping almost constant values with increasing flow velocity. Moreover, the orientation angle of the postbuckling configuration plane for a buckled pipe can be significantly affected by initial conditions, displaying new features which have not been observed in the same pipe system factitiously supposed to deform in a single plane.展开更多
This paper investigates the dynamics of cantilevered CNTs conveying fluid in lon- gitudinal magnetic field and presents the possibility of controlling/tuning the stability of the CNT system with the aid of magnetic fi...This paper investigates the dynamics of cantilevered CNTs conveying fluid in lon- gitudinal magnetic field and presents the possibility of controlling/tuning the stability of the CNT system with the aid of magnetic field. The slender CNT is treated as an Euler-Bernoulli beam. Based on nonlocal elasticity theory, the equation of motion with consideration of magnetic field effect is developed. This partial differential equation is then discretized using the differen- tial quadrature method （DQM）. Numerical results show that the nonlocal small-scale parameter makes the fluid-conveying CNT more flexible and can shift the unstable mode in which flutter instability occurs first at sufficiently high flow velocity from one to another. More importantly, the addition of a longitudinal magnetic field leads to much richer dynamical behaviors of the CNT system. Indeed, the presence of longitudinal magnetic field can significantly affect the evolution of natural frequency of the dynamical system when the flow velocity is successively increased. With increasing magnetic field parameter, it is shown that the CNT system behaves stiffer and hence the critical flow velocity becomes higher. It is of particular interest that when the mag- netic field parameter is equal to or larger than the flow velocity, the cantilevered CNT conveying fluid becomes unconditionally stable, indicating that the dynamic stability of the system can be controlled due to the presence of a longitudinal magnetic field.展开更多
It is a new attempt to extend the differential quadrature method(DQM) to stability analysis of the straight and curved centerlinepipes conveying fluid. Emphasis is placed on the study of theinfluences of several param...It is a new attempt to extend the differential quadrature method(DQM) to stability analysis of the straight and curved centerlinepipes conveying fluid. Emphasis is placed on the study of theinfluences of several parameters on the critical flow velocity.Compared to other methods, this method can more easily deal with thepipe with spring support at its boundaries and asks for much lesscomputing effort while giving ac- ceptable precision in the numericalresults.展开更多
In the past decades,it has been reported that divergence is the expected form of instability for fluid-conveying pipes with both ends supported.In this paper,the form of instability of supported pipes conveying fluid ...In the past decades,it has been reported that divergence is the expected form of instability for fluid-conveying pipes with both ends supported.In this paper,the form of instability of supported pipes conveying fluid subjected to distributed follower forces is investigated.Based on the Pflu¨ger column model,the equation of motion for supported pipes subjected concurrently to internal fluid flow and distributed follower forces is established.The analytical model,after Galerkin discretization to two degrees of freedom,is evaluated by analyzing the corresponding eigenvalue problem.The complex frequencies versus fluid velocity are obtained for various system parameters.The results show that either buckling or flutter instabilities could occur in supported fluid-conveying pipes under the action of distributed follower forces,depending on the parameter values of distributed follower forces.展开更多
Based on the differential constitutive relationship of linearviscoelastic material, a solid-liquid coupling vibration equation forviscoelastic pipe conveying fluid is derived by the D'Alembert'sprinciple. The ...Based on the differential constitutive relationship of linearviscoelastic material, a solid-liquid coupling vibration equation forviscoelastic pipe conveying fluid is derived by the D'Alembert'sprinciple. The critical flow velocities and natural frequencies ofthe cantilever pipe conveying fluid with the Kelvin model (flutterinstability) are calculated with the modified finite differencemethod in the form of the recurrence for- mula. The curves betweenthe complex frequencies of the first, second and third mode and flowvelocity of the pipe are plotted. On the basis of the numericalcalculation results, the dynamic behaviors and stability of the pipeare discussed. It should be pointed out that the delay time ofviscoelastic material with the Kelvin model has a remarkable effecton the dynamic characteristics and stability behaviors of thecantilevered pipe conveying fluid, which is a gyroscopicnon-conservative system.展开更多
The dynamic stability in transverse vibration of a viscoelastic pipe for conveying puisative fluid is investigated for the simply-supported case. The material property of the beammodel pipe is described by the Kelvin-...The dynamic stability in transverse vibration of a viscoelastic pipe for conveying puisative fluid is investigated for the simply-supported case. The material property of the beammodel pipe is described by the Kelvin-type viscoelastic constitutive relation. The axial fluid speed is characterized as simple harmonic variation about a constant mean speed. The method of multiple scales is applied directly to the governing partial differential equation without discretization when the viscoelastic damping and the periodical excitation are considered small. The stability conditions are presented in the case of subharmonic and combination resonance. Numerical results show the effect of viscosity and mass ratio on instability regions.展开更多
Based on the Fliigge shell theory, equations of motion of ring-stiffened thin-walled cylindrical shells conveying fluid are developed with the aid of the Hamilton＇s principle. Analysis is carried out on the vibration...Based on the Fliigge shell theory, equations of motion of ring-stiffened thin-walled cylindrical shells conveying fluid are developed with the aid of the Hamilton＇s principle. Analysis is carried out on the vibration and stability of the ring-stiffened shells conveying fluid, and the effects of fluid velocity, the Young modulus, the size, and the number of the ring stiffeners on the natural frequency and the instability characteristics are examined. It is found that stiffeners can reduce the number of circumferential waves for the fundamental mode, and increase the shell＇s natural frequency, and thus the critical fluid velocity. For the number of longitudinal half waves being equal to one, the natural frequency and the corresponding critical fluid velocity are the largest for the internal-ring stiffened shell and are the smallest for the symmetrical-ring stiffened shell. The natural frequencies and the corresponding critical fluid velocity predicted by the established model increase with the increase in the Young modulus, the size, or the number of the stiffeners.展开更多
The Green function method （GFM） is utilized to analyze the in-plane forced vibration of curved pipe conveying fluid, where the randomicity and distribution of the external excitation and the added mass and damping r...The Green function method （GFM） is utilized to analyze the in-plane forced vibration of curved pipe conveying fluid, where the randomicity and distribution of the external excitation and the added mass and damping ratio are considered. The Laplace transform is used, and the Green functions with various boundary conditions are obtained subsequently. Numerical calculations are performed to validate the present solutions, and the effects of some key parameters on both tangential and radial displacements are further investigated. The forced vibration problems with linear and nonlinear motion constraints are also discussed briefly. The method can be radiated to study other forms of forced vibration problems related with pipes or more extensive issues.展开更多
In this paper, the nonlinear dynamical behavior of two coupled pipes conveying pulsating fluid is studied. The connection between the two pipes is considered as a distributed linear spring. Based on this consideration...In this paper, the nonlinear dynamical behavior of two coupled pipes conveying pulsating fluid is studied. The connection between the two pipes is considered as a distributed linear spring. Based on this consideration, the equations of motion of the coupled two-pipe system are obtained. The two coupled nonlinear partial differential equations, discretized using the fourth- order Galerkin method, are solved by a fourth-order Runge-Kutta integration algorithm. Results show that the connection stiffness has a significant effect on the dynamical behavior of the coupled system. It is found that for some parameter values the motion types of the two pipes might be synchronous.展开更多
基金financially supported by the Key Research and Development Program of Shandong Province(Grant Nos.2022CXGC020405,2023CXGC010415 and 2025TSGCCZZB0238)the National Natural Science Foundation of China(Grant No.52171288)the financial support from CNPq,FAPERJ,ANP,Embrapii,and China National Petroleum Corporation(CNPC).
文摘This work investigated the dynamic behavior of vertical pipes conveying gas-liquid two-phase flow when subjected to external excitations at both ends.Even with minimal excitation amplitude,resonance can occur when the excitation frequency aligns with the natural frequency of the pipe,significantly increasing the degree of operational risk.The governing equation of motion based on the Euler-Bernoulli beam is derived for the relative deflection with stationary simply supported ends,with the effects of the external excitations represented by source terms distributed along the pipe length.The fourth-order partial differential equation is solved via the generalized integral transform technique(GITT),with the solution successfully verified via comparison with results in the literature.A comprehensive analysis of the vibration phenomena and changes in the motion state of the pipe is conducted for three classes of external excitation conditions:same frequency and amplitude(SFSA),same frequency but different amplitudes(SFDA),and different frequencies and amplitudes(DFDA).The numerical results show that with increasing gas volume fraction,the position corresponding to the maximum vibration displacement shifts upward.Compared with conditions without external excitation,the vibration displacement of the pipe conveying two-phase flow under external excitation increases significantly.The frequency of external excitation has a significant effect on the dynamic behavior of a pipe conveying two-phase flow.
基金supported by the Hainan Provincial Joint Project of Sanya Yazhou Bay Science and Technology City(Grant No.2021CXLH0003)the Innovational Fund for Scientific and Technological Personnel of Hainan Province(Grant No.KJRC2023D37).
文摘Bends contribute to a flexible layout of pipeline system,but also lead to intensive energy costs due to the complex flow characteristic.This experimental study is conducted to investigate the impact of a single coarse particle on the flow field in a bend.The velocity profiles of fluid on the axial symmetry plane of the bend are measured using time-resolved particle image velocimetry.The flow structures are extracted using the proper orthogonal decomposition method.The results reveal that there is a shear-layer flow in the bend during the transportation.With the increase in particle size,the particle has a dominant influence on the flow energy distribution of the overall flow.The impact of particles on the first few energetic flows is mainly in the latter part of the transportation,both temporally and spatially.As the particle size decreases,the most energetic unsteady flow within the bend changes from the convective flow to the flow of the shear layer.
基金funding from Shanghai Sailing Program (22YF1417600)Guangxi Science and Technology Major Program (AA23062019)
文摘The complex dense-phase pneumatic conveying of pulverized coal process was studied using an electrical capacitance tomography(ECT) signal that represented the motion characteristics of gas-solid two-phase flow. The fluctuation characteristics of conveying process signals are inseparable from the flow pattern. The denoised ECT signal and noise signal were obtained by db2 wavelet analysis. It was found that all noise signals were white Gaussian noise. Based on the assumption of the equal probability distribution of pulverized coal concentration, this paper proved that the time series distribution of pulverized coal concentration in the pipeline should obey the normal distribution. Furthermore, through the analysis of the distribution characteristics of the power spectral density function of denoised ECT signals of four flow patterns, they were α-dimensional fractal Brownian motion(fBm) signals, and the parameter α was estimated by the detrended fluctuation analysis. Based on the fBm characteristics of denoised ECT signals and white Gaussian noise, this paper proposed a method for calculating the pulverized coal concentration in the dense-phase pneumatic conveying. In addition to the method of concentration estimation with the significance of engineering guidance, this research can help people to further understand essential characteristics of ECT signals in the dense-phase pneumatic conveying.
基金support provided by the Technology Development Service Project Funds of China,Railway 5th Bureau Group Fifth Engineering Co.,Ltd and Yunnan Institute of Water&Hydropower Engineering Investigation,Design and Research(Grant No.20230525)the Major Science and Technology Special Plan of Yunnan Province Science and Technology Department(Grant No.202002AF080003)the Fundamental Research Funds for the Central Universities(Grant No.2022YJSSB04).
文摘The Haidong Water Conveyance Tunnel(HWCT),a notable engineering feat located within Dali City,Yunnan Province,China,represents an ultra-long water conveyance tunnel situated in a region characterized by medium in-situ stress conditions.As part of the Central Yunnan Water Diversion Project,this tunnel was specifically engineered for soft-rock environments.The excavation of such tunnels presents significant challenges due to rock mass deformation,commonly referred to as squeezing ground behavior.These challenges are exacerbated when navigating through diverse geological and geomorphological units,particularly in areas with complex geological conditions.To address these issues,an innovative active support system utilizing prestressed anchor cables was developed for the HWCT.This study provides a comprehensive analysis and comparison of rock mass behavior between two support systems:a conventional passive system employing steel arches and the proposed active system using prestressed anchor cables.The numerical modeling was performed using FLAC3D software to simulate various scenarios,while an extensive monitoring program was implemented in several representative tunnel sections to measure key parameters including rock mass stresses,displacements,internal forces in steel arches,and axial forces in anchor cables.The results from both the numerical simulations and field observations were systematically compared.The analyses demonstrated the superior performance of the active support system using prestressed anchor cables in the HWCT,significantly enhancing overall rock mass stability and effectively mitigating large deformation issues throughout the tunnel.
文摘This study examines the nonlinear behaviors of a clamped-clamped porous pipe made of a functionally graded material(FGM)that conveys fluids and is equipped with a retaining clip,focusing on primary resonance and subcritical dynamics.The nonlinear governing equations for the FGM pipe are derived by the extended Hamilton's principle,and subsequently discretized through the application of the Galerkin method.The direct method of multi-scales is then used to solve the derived equations.A thorough analysis of various parameters,including the clip stiffness,the power-law index,the porosity,and the clip location,is conducted to gain a comprehensive understanding of the system's nonlinear dynamics.Through the analysis of the first natural frequency,the study highlights the influence of the flow velocity and the clip stiffness,while the comparisons with metallic pipes emphasize the role of FGM composition.The examination of the forced response curves reveals saddle-node bifurcations and their dependence on parameters such as the detuning parameter and the power-law index,offering valuable insights into the system's nonlinear resonant behavior.Furthermore,the frequency-response curves illustrate the hardening nonlinearities influenced by factors such as the porosity and the clip stiffness,revealing nuanced effects on the system response and resonance characteristics.This comprehensive analysis enhances the understanding of nonlinear behaviors in FGM porous pipes with a retaining clip,providing key insights for practical engineering applications in system design and optimization.
基金Project supported by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China(No.12421002)the National Science Funds for Distinguished Young Scholars of China(No.12025204)+1 种基金the National Natural Science Foundation of China(No.12372015)China Scholarship Council(No.202206890065)。
文摘Multi-constrained pipes conveying fluid,such as aircraft hydraulic control pipes,are susceptible to resonance fatigue in harsh vibration environments,which may lead to system failure and even catastrophic accidents.In this study,a machine learning(ML)-assisted weak vibration design method under harsh environmental excitations is proposed.The dynamic model of a typical pipe is developed using the absolute nodal coordinate formulation(ANCF)to determine its vibrational characteristics.With the harsh vibration environments as the preserved frequency band(PFB),the safety design is defined by comparing the natural frequency with the PFB.By analyzing the safety design of pipes with different constraint parameters,the dataset of the absolute safety length and the absolute resonance length of the pipe is obtained.This dataset is then utilized to develop genetic programming(GP)algorithm-based ML models capable of producing explicit mathematical expressions of the pipe's absolute safety length and absolute resonance length with the location,stiffness,and total number of retaining clips as design variables.The proposed ML models effectively bridge the dataset with the prediction results.Thus,the ML model is utilized to stagger the natural frequency,and the PFB is utilized to achieve the weak vibration design.The findings of the present study provide valuable insights into the practical application of weak vibration design.
文摘Aimed at the long and narrow geometric features and poor generalization ability of the damage detection in conveyor belts with steel rope cores using the X-ray image,a detection method of damage X-ray image is proposed based on the improved fully convolutional one-stage object detection(FCOS)algorithm.The regression performance of bounding boxes was optimized by introducing the complete intersection over union loss function into the improved algorithm.The feature fusion network structure is modified by adding adaptive fusion paths to the feature fusion network structure,which makes full use of the features of accurate localization and semantics of multi-scale feature fusion networks.Finally,the network structure was trained and validated by using the X-ray image dataset of damages in conveyor belts with steel rope cores provided by a flaw detection equipment manufacturer.In addition,the data enhancement methods such as rotating,mirroring,and scaling,were employed to enrich the image dataset so that the model is adequately trained.Experimental results showed that the improved FCOS algorithm promoted the precision rate and the recall rate by 20.9%and 14.8%respectively,compared with the original algorithm.Meanwhile,compared with Fast R-CNN,Faster R-CNN,SSD,and YOLOv3,the improved FCOS algorithm has obvious advantages;detection precision rate and recall rate of the modified network reached 95.8%and 97.0%respectively.Furthermore,it demonstrated a higher detection accuracy without affecting the speed.The results of this work have some reference significance for the automatic identification and detection of steel core conveyor belt damage.
基金The National Basic Research Program of China(973 Program) (No2004CB217702-01)the Foundation of ExcellentPhDThesis of Southeast University
文摘Experiments of dense-phase pneumatic conveying of pulverized coal using nitrogen are carded out in an experimental test facility with the conveying pressure up to 4. 0 MPa and the gas-solid ratio up to 450 kg/m^3. The influences of different conveying differential pressures, coal moisture contents, gas volume flow rates and superficial velocities on the solid-gas ratios are investigated. Shannon entropy analysis of pressure fluctuation time series is developed to reveal the flow characteristics. Through investigation of the distribution of the Shannon entropy under different conditions, the flow stability and the evolutional tendency of the Shannon entropy in different regimes and regime transition processes are discovered, and the relationship between the Shannon entropy and the flow regimes is also established. The results indicate that the solid-gas ratio and the Shannon entropy rise with the increase in conveying differential pressure. The solid-gas ratio and the Shannon entropy reveal preferable regularity with gas volume flow rates. The Shannon entropy is different for different flow regimes, and can be used to identify the flow regimes. Both mass flow rate and the Shannon entropy decrease with the increase in moisture contents. The Shannon entropy analysis is a feasible approach for researching the characteristics of flow regimes, flow stability and flow regime transitions in dense-phase pneumatic conveying under high pressure.
基金Funded by the National Natural Science Foundation of China(No.50873014)
文摘A novel particle-size conveying model was established to examine the effects of the dimension relationships of the groove depth and particle size on the solids conveying mechanism of the helically grooved feed section. In the model, one or two shear interfaces were proposed based on the dimension relationships of the groove depth and particle size, and the solid-plug embedded in the groove and screw channel were divided into two or three layers by the shear interfaces to consider the solids conveying mechanism of each layer by the boundary condition equation for positive conveying. By the particle-size model, the effects of different dimension relationships on the transformation of solids conveying mechanisms between the friction-drag conveying and the positive conveying were discussed and compared with the on-line measuring experimental data. The results showed that the shear interfaces among the solids existed indeed and the dimension relationships determined the conveying mechanism and the throughput of helically grooved extruders, which was well confirmed by the excellent consistence between the predicted and measured data.
基金Supported by National Defense Science and Technology Major Project(Grant Nos.TY3Q20110001,TY3Q20110005)College Discipline Innovation Wisdom Plan of China(111 Project,Grant No.B07018)National Natural Science Foundation of China(Grant No.51105092)
文摘The sampling auger used in lunar sampling and return mission is to transmit power and convey soil, and its performance is the key factor of the whole mission. However, there is currently a lack of the optimization research on soil conveying volume and power consumption models in auger structure design. To provide the drilled object, the simulation lunar soil, whose physical and mechanical property is the same as the real soil, is made by reducing soil void ratio. The models are formulated to analyze the influence of auger structure parameters on power consumption and soil conveying volume. To obtain the optimized structure parameters of auger, the multi-objective optimization functions of the maximum soil conveying volume and minimum power consumption are developed. To verify the correctness of the models, the performances of different augers drilling simulation soil are tested. The test results demonstrate that the power consumption of optimized auger is the lowest both in theory and test, and the experimental results of soil conveying volume are in agreement with theoretical analysis. Consequently, a new method for designing a lunar sampling auger is proposed which includes the models of soil conveying volume and transportation power consumption, the optimization of structure parameters and the comparison tests. This method provides a reference for sampling auger designing of the Chinese Lunar Sample Mission.
基金National 95 Science an Technology Project(96-922-03-03)
文摘The lateral vibration differential equation for a marine riser conveying fluid is derived by use of the small deflection theory, and the effect of internal flow velocity and top tension on the natural frequency of the riser is studied by use of FEM. At the same time, the preliminary relationship between the natural Frequency and riser span under different internal flow velocities is obtained, the effect of riser supports on the vibration frequency is computed. It is found that the natural frequency of the marine riser increases with the increase of top tension, however decreases with the increase of internal flow velocity. In addition, the Frequency decreases drastically with the increase of riser span.
基金supported by the National Natural Science Foundation of China (Grants 11602090, 11622216, and 11672115)
文摘This paper deals with the three-dimensional dynamics and postbuckling behavior of flexible supported pipes conveying fluid, considering flow velocities lower and higher than the critical value at which the buckling instability occurs. In the case of low flow velocity, the pipe is stable with a straight equilibrium position and the dynamics of the system can be examined using linear theory. When the flow velocity is beyond the critical value, any motions of the pipe could be around the postbuckling configuration(non-zero equilibrium position) rather than the straight equilibrium position, so nonlinear theory is required. The nonlinear equations of perturbed motions around the postbuckling configuration are derived and solved with the aid of Galerkin discretization. It is found, for a given flow velocity,that the first-mode frequency for in-plane motions is quite different from that for out-of-plane motions. However, the second-or third-mode frequencies for in-plane motions are approximately equal to their counterparts for out-of-plane motions, keeping almost constant values with increasing flow velocity. Moreover, the orientation angle of the postbuckling configuration plane for a buckled pipe can be significantly affected by initial conditions, displaying new features which have not been observed in the same pipe system factitiously supposed to deform in a single plane.
基金partially supported by the National Natural Science Foundation of China(Nos.11622216 and 11572133)
文摘This paper investigates the dynamics of cantilevered CNTs conveying fluid in lon- gitudinal magnetic field and presents the possibility of controlling/tuning the stability of the CNT system with the aid of magnetic field. The slender CNT is treated as an Euler-Bernoulli beam. Based on nonlocal elasticity theory, the equation of motion with consideration of magnetic field effect is developed. This partial differential equation is then discretized using the differen- tial quadrature method （DQM）. Numerical results show that the nonlocal small-scale parameter makes the fluid-conveying CNT more flexible and can shift the unstable mode in which flutter instability occurs first at sufficiently high flow velocity from one to another. More importantly, the addition of a longitudinal magnetic field leads to much richer dynamical behaviors of the CNT system. Indeed, the presence of longitudinal magnetic field can significantly affect the evolution of natural frequency of the dynamical system when the flow velocity is successively increased. With increasing magnetic field parameter, it is shown that the CNT system behaves stiffer and hence the critical flow velocity becomes higher. It is of particular interest that when the mag- netic field parameter is equal to or larger than the flow velocity, the cantilevered CNT conveying fluid becomes unconditionally stable, indicating that the dynamic stability of the system can be controlled due to the presence of a longitudinal magnetic field.
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 of the straight and curved centerlinepipes conveying fluid. Emphasis is placed on the study of theinfluences of several parameters on the critical flow velocity.Compared to other methods, this method can more easily deal with thepipe with spring support at its boundaries and asks for much lesscomputing effort while giving ac- ceptable precision in the numericalresults.
基金supported by the National Natural Science Foundation of China (Nos. 10802031 and 11172107)the Program for New Century Excellent Talents in Universitythe Fundamental Research Funds for the CentralUniversities,HUST (grant number 2010MS021)
文摘In the past decades,it has been reported that divergence is the expected form of instability for fluid-conveying pipes with both ends supported.In this paper,the form of instability of supported pipes conveying fluid subjected to distributed follower forces is investigated.Based on the Pflu¨ger column model,the equation of motion for supported pipes subjected concurrently to internal fluid flow and distributed follower forces is established.The analytical model,after Galerkin discretization to two degrees of freedom,is evaluated by analyzing the corresponding eigenvalue problem.The complex frequencies versus fluid velocity are obtained for various system parameters.The results show that either buckling or flutter instabilities could occur in supported fluid-conveying pipes under the action of distributed follower forces,depending on the parameter values of distributed follower forces.
文摘Based on the differential constitutive relationship of linearviscoelastic material, a solid-liquid coupling vibration equation forviscoelastic pipe conveying fluid is derived by the D'Alembert'sprinciple. The critical flow velocities and natural frequencies ofthe cantilever pipe conveying fluid with the Kelvin model (flutterinstability) are calculated with the modified finite differencemethod in the form of the recurrence for- mula. The curves betweenthe complex frequencies of the first, second and third mode and flowvelocity of the pipe are plotted. On the basis of the numericalcalculation results, the dynamic behaviors and stability of the pipeare discussed. It should be pointed out that the delay time ofviscoelastic material with the Kelvin model has a remarkable effecton the dynamic characteristics and stability behaviors of thecantilevered pipe conveying fluid, which is a gyroscopicnon-conservative system.
基金Project supported by the National Natural Science Foundation of China (No.10372063).
文摘The dynamic stability in transverse vibration of a viscoelastic pipe for conveying puisative fluid is investigated for the simply-supported case. The material property of the beammodel pipe is described by the Kelvin-type viscoelastic constitutive relation. The axial fluid speed is characterized as simple harmonic variation about a constant mean speed. The method of multiple scales is applied directly to the governing partial differential equation without discretization when the viscoelastic damping and the periodical excitation are considered small. The stability conditions are presented in the case of subharmonic and combination resonance. Numerical results show the effect of viscosity and mass ratio on instability regions.
基金supported by the National Natural Science Foundation of China (No. 50908094)the Ph. D. Programs Foundation of Ministry of Education of China (No. 20100142120071)the Natural Science Foundation of Hubei Province (No. 2010CDB02204)
文摘Based on the Fliigge shell theory, equations of motion of ring-stiffened thin-walled cylindrical shells conveying fluid are developed with the aid of the Hamilton＇s principle. Analysis is carried out on the vibration and stability of the ring-stiffened shells conveying fluid, and the effects of fluid velocity, the Young modulus, the size, and the number of the ring stiffeners on the natural frequency and the instability characteristics are examined. It is found that stiffeners can reduce the number of circumferential waves for the fundamental mode, and increase the shell＇s natural frequency, and thus the critical fluid velocity. For the number of longitudinal half waves being equal to one, the natural frequency and the corresponding critical fluid velocity are the largest for the internal-ring stiffened shell and are the smallest for the symmetrical-ring stiffened shell. The natural frequencies and the corresponding critical fluid velocity predicted by the established model increase with the increase in the Young modulus, the size, or the number of the stiffeners.
基金Project supported by the National Science and Technology Major Project(NMP)of China(No.2013ZX04011-011)
文摘The Green function method （GFM） is utilized to analyze the in-plane forced vibration of curved pipe conveying fluid, where the randomicity and distribution of the external excitation and the added mass and damping ratio are considered. The Laplace transform is used, and the Green functions with various boundary conditions are obtained subsequently. Numerical calculations are performed to validate the present solutions, and the effects of some key parameters on both tangential and radial displacements are further investigated. The forced vibration problems with linear and nonlinear motion constraints are also discussed briefly. The method can be radiated to study other forms of forced vibration problems related with pipes or more extensive issues.
基金Project supported by the National Natural Science Foundation of China(Nos.11172107 and 11172109)the Program for New Century Excellent Talents in University(No.NCET-11-0183)
文摘In this paper, the nonlinear dynamical behavior of two coupled pipes conveying pulsating fluid is studied. The connection between the two pipes is considered as a distributed linear spring. Based on this consideration, the equations of motion of the coupled two-pipe system are obtained. The two coupled nonlinear partial differential equations, discretized using the fourth- order Galerkin method, are solved by a fourth-order Runge-Kutta integration algorithm. Results show that the connection stiffness has a significant effect on the dynamical behavior of the coupled system. It is found that for some parameter values the motion types of the two pipes might be synchronous.
