Offshore wind turbines(OWTs) suffer wind, wave and earthquake loads. The investigation of OWTs' dynamic response under environmental loads is essential for structural safety assessment. The soil-structure interact...Offshore wind turbines(OWTs) suffer wind, wave and earthquake loads. The investigation of OWTs' dynamic response under environmental loads is essential for structural safety assessment. The soil-structure interaction(SSI)significantly affects the responses of OWT under environmental loads. However, there is few systematic research about the difference in the dynamic response of different SSI models under environmental loads. In order to solve the problem, the OWT is modeled by shell element, and several SSI models are built. The wind, wave and earthquake loads are taken into account. Moreover, the dynamic response, fatigue and buckling analysis are performed by ANSYS. The results indicate that SSI cannot be ignored in the dynamic response of the OWT under wind and wave loads. The SSI can decrease the displacement response of the OWT by 19% under wind and wave loads and reduce the fatigue damage of the pile. Multi-layer SSI can strongly influence the OWT's dynamic response under wind and wave loads or earthquake-only load. The vertical earthquake load increases the dynamic response in three directions.Besides, in order to simulate real environment, multi-layer SSI, soil damping and vertical SSI must be considered to evaluate the displacement response of the OWT under wind, wave and earthquake loads. The earthquake and gravity loads can cause more obvious response of the OWT than that of only wind and wave loads. The top and bottom of the tower are prone to occur buckling.展开更多
Gradient nanostructure was introduced to enhance the strength and ductility via deformation incompatibility accommodated by geometrical necessary dislocations for most metallic materials recently.However,few intensive...Gradient nanostructure was introduced to enhance the strength and ductility via deformation incompatibility accommodated by geometrical necessary dislocations for most metallic materials recently.However,few intensive researches were carried out to investigate the effect of gradient structure on the deformation twin evolution and resulting performance improvements.In the present paper,we produced gradient-structured AZ31 Mg alloy with fine-grain layers,parallel twin laminates and a coarse-grain core from two upmost surfaces to the center of plate.Surprisingly,this architected Mg alloy exhibited simultaneous enhancement of strength and ductility.Subsequent microstructural observations demonstrated that abundant twin-twin interactions resulting from higher strength and multi-axial stress state could make great contributions to the increase of work-hardening capability.This was further proved by the measurement of full-field strain evolution during the plastic deformation.Such a design strategy may provide a new path for producing advanced structure materials in which the deformation twinning works as one of the dominant plasticity mechanisms.展开更多
Black holes are recognized by Newton’s gravitational theory and Einstein’s general relativity, but there is still a lack of understanding the spatial structure of events, especially the nature of event horizon. In t...Black holes are recognized by Newton’s gravitational theory and Einstein’s general relativity, but there is still a lack of understanding the spatial structure of events, especially the nature of event horizon. In this paper, a theoretical analysis is used to compare the structures of tropical cyclone in the atmosphere and black hole in the astronomy so that five results are: 1) Both of them share the similar spatial structure, with tropical cyclone and black hole having the outflow cloud shield and the horizon sphere in the central part, respectively, while four spiral material bands exist in the rotating plane around them;2) In theoretically, the energy density formed by the orthogonal interaction of the four spiral material bands is as times as the total kinetic energy of the head-on interaction;3) This region of high energy density can lead to the conversion from mass to energy and the creation of new physical states of matter, which is a black hole event;4) The outer horizon of a black hole is the outermost interface of events, or the orthogonal interaction interface of particles;5) High-speed plasma jets extended at the poles of the black hole are directly associated with the shear stress of orthogonal interaction.展开更多
The existing research for unsteady flow field and the corresponding flow induced vibration analysis of centrifugal pump are mainly carried out respectively without considering the interaction between fluid and structu...The existing research for unsteady flow field and the corresponding flow induced vibration analysis of centrifugal pump are mainly carried out respectively without considering the interaction between fluid and structure. The ignorance of fluid structure interaction (FSI) means that the energy transfer between fluid and structure is neglected. To some extent, the accuracy and reliability of unsteady flow and rotor deflection analysis should be affected by this interaction mechanism. In this paper, a combined calculation between two executables for turbulent flow and vibrating structure was established using two-way coupling method to study the effect of FSI. Pressure distributions, radial forces, rotor deflection and equivalent stress are analyzed. The results show that the FSI effect to pressure distribution in flow field is complex. The pressure distribution is affected not only around impeller outlet where different variation trends of pressure values with and without FSI appear according to different relative positions between blade and cutwater, but also in the diffusion section of volute. Variation trends of peak values of radial force amplitude calculated with and without FSI are nearly same under high flow rate and designed conditions while the peak value with FSI is slightly smaller, and differently, the peak value with FSI is larger with low flow rate. In addition, the effect of FSI on the angle of radial force is quite complex, especially under 0.5Q condition. Fluctuation of radial deflection of the rotor has obvious four periods, of which the extent is relatively small under design condition and is relatively large under off-design condition. Finally, fluctuations of equivalent stress with time are obvious under different conditions, and stress value is small. The proposed research establishes the FSI calculation method for centrifugal pump analysis, and ensures the existing affect by fluid structure interaction.展开更多
Journal bearings are important parts to keep the high dynamic performance of rotor machinery. Some methods have already been proposed to analysis the flow field of journal bearings, and in most of these methods simpli...Journal bearings are important parts to keep the high dynamic performance of rotor machinery. Some methods have already been proposed to analysis the flow field of journal bearings, and in most of these methods simplified physical model and classic Reynolds equation are always applied. While the application of the general computational fluid dynamics (CFD)-fluid structure interaction (FSI) techniques is more beneficial for analysis of the fluid field in a journal bearing when more detailed solutions are needed. This paper deals with the quasi-coupling calculation of transient fluid dynamics of oil film in journal bearings and rotor dynamics with CFD-FSI techniques. The fluid dynamics of oil film is calculated by applying the so-called "dynamic mesh" technique. A new mesh movement approacb is presented while the dynamic mesh models provided by FLUENT are not suitable for the transient oil flow in journal bearings. The proposed mesh movement approach is based on the structured mesh. When the joumal moves, the movement distance of every grid in the flow field of bearing can be calculated, and then the update of the volume mesh can be handled automatically by user defined function (UDF). The journal displacement at each time step is obtained by solving the moving equations of the rotor-bearing system under the known oil film force condition. A case study is carried out to calculate the locus of the journal center and pressure distribution of the journal in order to prove the feasibility of this method. The calculating results indicate that the proposed method can predict the transient flow field of a journal bearing in a rotor-bearing system where more realistic models are involved. The presented calculation method provides a basis for studying the nonlinear dynamic behavior of a general rotor-bearing system.展开更多
Tension leg platform (TLP) for offshore wind turbine support is a new type structure in wind energy utilization. The strong-interaction method is used in analyzing the coupled model, and the dynamic characteristics ...Tension leg platform (TLP) for offshore wind turbine support is a new type structure in wind energy utilization. The strong-interaction method is used in analyzing the coupled model, and the dynamic characteristics of the TLP for offshore wind turbine support are recognized. As shown by the calculated results: for the lower modes, the shapes are water's vibration, and the vibration of water induces the structure's swing; the mode shapes of the structure are complex, and can largely change among different members; the mode shapes of the platform are related to the tower's. The frequencies of the structure do not change much after adjusting the length of the tension cables and the depth of the platform; the TLP has good adaptability for the water depths and the environment loads. The change of the size and parameters of TLP can improve the dynamic characteristics, which can reduce the vibration of the TLP caused by the loads. Through the vibration analysis, the natural vibration frequencies of TLP can be distinguished from the frequencies of condition loads, and thus the resonance vibration can be avoided, therefore the offshore wind turbine can work normally in the complex conditions.展开更多
Numerical simulations of evolution characteristics of slug flow across a 90°pipe bend have been carried out to study the fluid−structure interaction response induced by internal slug flow.The two-phase flow patte...Numerical simulations of evolution characteristics of slug flow across a 90°pipe bend have been carried out to study the fluid−structure interaction response induced by internal slug flow.The two-phase flow patterns and turbulence were modelled by using the volume of fluid(VOF)model and the Realizable k−εturbulence model respectively.Firstly,validation of the CFD model was carried out and the desirable results were obtained.The different flow patterns and the time-average mean void fraction was coincident with the reported experimental data.Simulations of different cases of slug flow have been carried out to show the effects of superficial gas and liquid velocity on the evolution characteristics of slug flow.Then,a one-way coupled fluid-structure interaction framework was established to investigate the slug flow interaction with a 90°pipe bend under various superficial liquid and gas velocities.It was found that the maximum total deformation and equivalent stress increased with the increasing superficial gas velocity,while decreased with the increasing superficial liquid velocity.In addition,the total deformation and equivalent stress has obvious periodic fluctuation.Furthermore,the distribution position of maximum deformation and stress was related to the evolution of slug flow.With the increasing superficial gas velocity,the maximum total deformation was mainly located at the 90°pipe bend.But as the superficial liquid velocity increases,the maximum total deformation was mainly located in the horizontal pipe section.Consequently,the slug flow with higher superficial gas velocity will induce more serious cyclical impact on the 90°pipe bend.展开更多
Based on the train-track coupling dynamics and high-speed train aerodynamics, this paper deals with an improved algorithm for fluid-structure interaction of high-speed trains. In the algorithm, the data communication ...Based on the train-track coupling dynamics and high-speed train aerodynamics, this paper deals with an improved algorithm for fluid-structure interaction of high-speed trains. In the algorithm, the data communication between fluid solver and structure solver is avoided by inserting the program of train-track coupling dynamics into fluid dynamics program, and the relaxation factor concerning the load boundary of the fluid-structure interface is introduced to improve the fluctuation and convergence of aerodynamic forces. With this method, the fluid-structure dynamics of a highspeed train are simulated under the condition that the velocity of crosswind is 13.8 m/s and the train speed is 350 km/h. When the relaxation factor equals 0.5, the fluctuation of aerodynamic forces is lower and its convergence is faster than in other cases. The side force and lateral displacement of the head train are compared between off-line simulation and co-simulation. Simulation results show that the fluid-structure interaction has a significant influence on the aerodynam- ics and attitude of the head train under crosswind conditions. In addition, the security indexes of the head train worsen after the fluid-structure interaction calculation. Therefore, the fluid-structure interaction calculation is necessary for high-speed trains.展开更多
Understanding cardiac blood flow behaviors is of importance for cardiovascular research and clinical assessment of ventricle functions.Patient-specific Echo-based left ventricle(LV)fluid-structure interaction(FSI)mode...Understanding cardiac blood flow behaviors is of importance for cardiovascular research and clinical assessment of ventricle functions.Patient-specific Echo-based left ventricle(LV)fluid-structure interaction(FSI)models were introduced to perform ventricle mechanical analysis,investigate flow behaviors,and evaluate the impact of myocardial infarction(MI)and hypertension on blood flow in the LV.Echo image data were acquired from 3 patients with consent obtained:one healthy volunteer(P1),one hypertension patient(P2),and one patient who had an inferior and posterior myocardial infarction(P3).The nonlinear Mooney-Rivlin model was used for ventricle tissue with material parameter values chosen to match echo-measure LV volume data.Using the healthy case as baseline,LV with MI had lower peak flow velocity(30%lower at beginejection)and hypertension LV had higher peak flow velocity(16%higher at begin-filling).The vortex area(defined as the area with vorticity>0)for P3 was 19%smaller than that of P1.The vortex area for P2 was 12%smaller than that of P1.At peak of filling,the maximum flow shear stress(FSS)for P2 and P3 were 390%higher and 63%lower than that of P1,respectively.Meanwhile,LV stress and strain of P2 were 41%and 15%higher than those of P1,respectively.LV stress and strain of P3 were 36%and 42%lower than those of P1,respectively.In conclusion,FSI models could provide both flow and structural stress/strain information which would serve as the base for further cardiovascular investigations related to disease initiation,progression,and treatment strategy selections.Large-scale studies are needed to validate our findings.展开更多
Fluid-structure interaction (FSI) is essentially a dynamic phenomenon and always exists in fluid-filled pipe system. The four-equation model, which has been proved to be effective to describe and predict the phenome...Fluid-structure interaction (FSI) is essentially a dynamic phenomenon and always exists in fluid-filled pipe system. The four-equation model, which has been proved to be effective to describe and predict the phenomenon of FSI due to friction coupling and Poisson coupling being taken into account, is utilized to describe the FSI of fluid-filled pipe system. Terse compatibility equations are educed by the method of characteristics (MOC) to describe the fluid-filled pipe system. To shorten computing time needed to get the solutions under the condition of keeping accuracy requirement, two steps are adopted, firstly the time step Δt and divided number of the straight pipe are optimized, sec-ondly the mesh spacing Δz close to boundary is subdivided in several submeshes automatically ac-cording to the speed gradient of fluid. The mathematical model and arithmetic are validated by com-parisons between simulation solutions of two straight pipe systems and experiment known from lit-erature.展开更多
The objective of this paper is to present and to validate a new hybrid coupling (HC) algorithm for modeling of fluid-structure interaction (FSI) in incompressible, viscous flows. The HC algorithm is able to avoid ...The objective of this paper is to present and to validate a new hybrid coupling (HC) algorithm for modeling of fluid-structure interaction (FSI) in incompressible, viscous flows. The HC algorithm is able to avoid numerical instability issues associated with artificial added mass effects, which are often encountered by standard loosely coupled (LC) and tightly coupled (TC) algorithms, when modeling the FSI response of flexible structures in incompressible flow. The artificial added mass effect is caused by the lag in exchange of interfacial displacements and forces between the fluid and solid solvers in partitioned algorithms. The artificial added mass effect is much more prominent for light/flexible struc- tures moving in water, because the fluid forces are in the same order of magnitude as the solid forces, and because the speed at which numerical errors propagate in an incom- pressible fluid. The new HC algorithm avoids numerical instability issues associated with artificial added mass effects by embedding Theodorsen's analytical approximation of the hydroelastic forces in the solution process to obtain better initial estimates of the displacements. Details of the new HC algorithm are presented. Numerical validation studies are shown for the forced pitching response of a steel and a plastic hydrofoil. The results show that the HC algorithm is able to converge faster, and is able to avoid numerical insta- bility issues, compared to standard LC and TC algorithms, when modeling the transient FSI response of a plastic hydrofoil. Although the HC algorithm is only demonstrated for a NACA0009 hydrofoil subject to pure pitching motion, the method can be easily extended to model general 3-D FSI response and stability of complex, flexible structures in turbulent, incompressible, multiphase flows.展开更多
The closely coupled approach combined with the finite volume method (FVM) solver and the finite element method (FEM) solver is used to investigate the fluid-structure interaction (FSI) of a three-dimensional can...The closely coupled approach combined with the finite volume method (FVM) solver and the finite element method (FEM) solver is used to investigate the fluid-structure interaction (FSI) of a three-dimensional cantilevered hydrofoil in the water tunnel. The FVM solver and the coupled approach are verified and validated by compar- ing the numerical predictions with the experimental measurements, and good agreement is obtained concerning both the lift on the foil and the tip displacement. In the noncav- itating flow, the result indicates that the growth of the initial incidence angle and the Reynolds number improves the deformation of the foil, and the lift on the foil is increased by the twist deformation. The normalized twist angle and displacement along the span of the hydrofoil for different incidence angles and Reynolds numbers are almost uniform. For the cavitation flow, it is shown that the small amplitude vibration of the foil has limited influence on the developing process of the partial cavity, and the quasi two-dimensional cavity shedding does not change the deformation mode of the hydrofoil. However, the frequency spectrum of the lift on the foil contains the frequency which is associated with the first bend frequency of the hydrofoil.展开更多
Based on the working principle and the damping characteristic of hydraulic shock absorber,a fluid structure interaction method was presented,which was used to analyze the microcosmic and high-frequency processing mech...Based on the working principle and the damping characteristic of hydraulic shock absorber,a fluid structure interaction method was presented,which was used to analyze the microcosmic and high-frequency processing mechanism of fluid structure interaction between circulation valve and liquid of hydraulic shock absorber.The fluid mesh distortion was controlled by the CEL language,and the fluid structure interaction mathematical model was established.The finite element model was established by ANSYS CFX software and was analyzed by dynamic mesh technique.The local sensitive computational area was meshed by prismatic grid,which could reduce the negative volume problem during the simulation.The circulation valve and liquid of hydraulic shock absorber were simulated and analyzed under the condition of sinusoidal inlet velocity loads.Flow characteristic and dynamics characteristic were obtained.The pressure distribution and the displacement of circulation value were obtained,and the acceleration curve of circulation valve was simulated and analyzed.The conformity of the final simulation results with the experimental datum indicates that this method is accurate and reliable to analyze the dynamics characteristic between circulation valve and liquid of hydraulic shock absorber,which can provide a theoretical foundation for optimizing hydraulic shock absorber in the future.展开更多
Channel engineering stability with underground goafs is a complex three-dimensional problem, especially when considering channel leakage, and is influenced by a number of processes, such as seepage, fluid structure in...Channel engineering stability with underground goafs is a complex three-dimensional problem, especially when considering channel leakage, and is influenced by a number of processes, such as seepage, fluid structure interaction(FSI), modeling, and selection of geological mechanical parameters. In this study, stability finite element analysis by one-way FSI was performed by establishing an integrated 3D engineering geological model. The extended Fourier amplitude sensitivity test was used to quantitatively assess the first-order and total sensitivities of the engineering model to critical geological mechanical parameters. Results illustrate that the channel engineering deformation is under a reasonable range and the elastic modulus is the highest total sensitivity parameter for the channel tilt and curvature at 0.7395 and 0.7525, respectively. Moreover, the most observable coupling effects for the curvature and horizontal strain are cohesion(0.1933)and density(0.7410), respectively.展开更多
The effects of the renal artery stenosis (RAS) on the blood flow and vessel walls are investigated. The pulsatile blood flow through an anatomically realistic model of the abdominal aorta and renal arteries reconstr...The effects of the renal artery stenosis (RAS) on the blood flow and vessel walls are investigated. The pulsatile blood flow through an anatomically realistic model of the abdominal aorta and renal arteries reconstructed from CT-scan images is simulated, which incorporates the fluid-structure interaction (FSI). In addition to the investigation of the RAS effects on the wall shear stress and the displacement of the vessel wall, it is determined that the RAS leads to decrease in the renal mass flow. This may cause the activation of the renin-angiotension system and results in severe hypertension.展开更多
In this paper, the authors present airflow field characteristics of human upper airway and soft palate movement attitude during breathing. On the basis of the data taken from the spiral computerized tomography images ...In this paper, the authors present airflow field characteristics of human upper airway and soft palate movement attitude during breathing. On the basis of the data taken from the spiral computerized tomography images of a healthy person and a patient with Obstructive Sleep Apnea-Hypopnea Syndrome (OSAHS), three-dimensional models of upper airway cavity and soft palate are reconstructed by the method of surface rendering. Numerical simulation is performed for airflow in the upper airway and displacement of soft palate by fluid-structure interaction analysis. The reconstructed threedimensional models precisely preserve the original configuration of upper airways and soft palate. The results of the pressure and velocity distributions in the airflow field are quantitatively determined, and the displacement of soft palate is presented. Pressure gradients of airway are lower for the healthy person and the airflow distribution is quite uniform in the case of free breathing. However, the OSAHS patient remarkably escalates both the pressure and velocity in the upper airway, and causes higher displacement of the soft palate. The present study is useful in revealing pathogenesis and quantitative mutual relationship between configuration and function of the upper airway as well as in diagnosingdiseases related to anatomical structure and function of the upper airway.展开更多
In the underwater-shock environment, cavitation occurs near the structural surface. The dynamic response of fluid-structure interactions is influenced seriously by the cavitation effects. It is also the difficulty in ...In the underwater-shock environment, cavitation occurs near the structural surface. The dynamic response of fluid-structure interactions is influenced seriously by the cavitation effects. It is also the difficulty in the field of underwater explosion. With the traditional boundary element method and the finite element method (FEM), it is difficult to solve the nonlinear problem with cavitation effects subjected to the underwater explosion. To solve this problem, under the consideration of the cavitation effects and fluid compressibility, with fluid viscidity being neglected, a 3D numerical model of transient nonlinear fluid-structure interaction subjected to the underwater explosion is built. The fluid spectral element method (SEM) and the FEM are adopted to solve this model. After comparison with the FEM, it is shown that the SEM is more precise than the FEM, and the SEM results are in good coincidence with benchmark results and experiment results. Based on this, combined with ABAQUS, the transient fluid-structure interaction mechanism of the 3D submerged spherical shell and ship stiffened plates subjected to the underwater explosion is discussed, and the cavitation region and its influence on the structural dynamic responses are presented. The paper aims at providing references for relevant research on transient fluid-structure interaction of ship structures subjected to the underwater explosion.展开更多
Failure pressure is a key parameter in reservoir hydrofracturing operation. Existing analytical methods for calculating the failure pressure are based on the assumption that borehole fluid is under two extreme conditi...Failure pressure is a key parameter in reservoir hydrofracturing operation. Existing analytical methods for calculating the failure pressure are based on the assumption that borehole fluid is under two extreme conditions: non-infiltration or complete infiltration. The assumption is not suitable for the actual infiltration process, and this will cause a great error in practical calculation. It shows that during the injection process, the dynamic variation in effective stress-dependent permeability has an influence on the infiltration, and the influence also brings about calculation errors. Based on the fluid-structure interaction and finite element method (FEM), considering partial infiltration during injection process, a numerical model for calculating rock failure pressure is established. According to the analysis of permeability test results and response-surface method, a new variation rule of rock permeability with the change of effective stress is presented, and the relationships among the permeability, confining pressure and pore pressure are proposed. There are some differences between the dynamic value of permeability-effective-stress coefficient observed herein and the one obtained by the classical theory. Combining with the numerical model and the dynamic permeability, a coupling method for calculating failure pressure is developed. Comparison of field data and calculated values obtained by various methods shows that accurate values can be obtained by the coupling method. The coupling method can be widely applied to the calculation of failure pressure of reservoirs and complex wells to achieve effective fracturing operation.展开更多
The dynamic characteristics of a single liquid-filled pipe have been broadly studied in the previous literature.The parallel liquid-filled pipe(PLFP)system is also widely used in engineering,and its structure is more ...The dynamic characteristics of a single liquid-filled pipe have been broadly studied in the previous literature.The parallel liquid-filled pipe(PLFP)system is also widely used in engineering,and its structure is more complex than that of a single pipe.However,there are few reports about the dynamic characteristics of the PLFPs.Therefore,this paper proposes improved frequency modeling and solution for the PLFPs,involving the logical alignment principle and coupled matrix processing.The established model incorporates both the fluid-structure interaction(FSI)and the structural coupling of the PLFPs.The validity of the established model is verified by modal experiments.The effects of some unique parameters on the dynamic characteristics of the PLFPs are discussed.This work provides a feasible method for solving the FSI of multiple pipes in parallel and potential theoretical guidance for the dynamic analysis of the PLFPs in engineering.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 51976131, 52006148, and 52106262)。
文摘Offshore wind turbines(OWTs) suffer wind, wave and earthquake loads. The investigation of OWTs' dynamic response under environmental loads is essential for structural safety assessment. The soil-structure interaction(SSI)significantly affects the responses of OWT under environmental loads. However, there is few systematic research about the difference in the dynamic response of different SSI models under environmental loads. In order to solve the problem, the OWT is modeled by shell element, and several SSI models are built. The wind, wave and earthquake loads are taken into account. Moreover, the dynamic response, fatigue and buckling analysis are performed by ANSYS. The results indicate that SSI cannot be ignored in the dynamic response of the OWT under wind and wave loads. The SSI can decrease the displacement response of the OWT by 19% under wind and wave loads and reduce the fatigue damage of the pile. Multi-layer SSI can strongly influence the OWT's dynamic response under wind and wave loads or earthquake-only load. The vertical earthquake load increases the dynamic response in three directions.Besides, in order to simulate real environment, multi-layer SSI, soil damping and vertical SSI must be considered to evaluate the displacement response of the OWT under wind, wave and earthquake loads. The earthquake and gravity loads can cause more obvious response of the OWT than that of only wind and wave loads. The top and bottom of the tower are prone to occur buckling.
基金This work was financially supported by National Natural Science Foundation of China(Grant Nos.11772268 and 12025205).The authors would like to appreciate the researchers in Nanjing university of science and technology for their support in preparation of gradient structured materials.
文摘Gradient nanostructure was introduced to enhance the strength and ductility via deformation incompatibility accommodated by geometrical necessary dislocations for most metallic materials recently.However,few intensive researches were carried out to investigate the effect of gradient structure on the deformation twin evolution and resulting performance improvements.In the present paper,we produced gradient-structured AZ31 Mg alloy with fine-grain layers,parallel twin laminates and a coarse-grain core from two upmost surfaces to the center of plate.Surprisingly,this architected Mg alloy exhibited simultaneous enhancement of strength and ductility.Subsequent microstructural observations demonstrated that abundant twin-twin interactions resulting from higher strength and multi-axial stress state could make great contributions to the increase of work-hardening capability.This was further proved by the measurement of full-field strain evolution during the plastic deformation.Such a design strategy may provide a new path for producing advanced structure materials in which the deformation twinning works as one of the dominant plasticity mechanisms.
文摘Black holes are recognized by Newton’s gravitational theory and Einstein’s general relativity, but there is still a lack of understanding the spatial structure of events, especially the nature of event horizon. In this paper, a theoretical analysis is used to compare the structures of tropical cyclone in the atmosphere and black hole in the astronomy so that five results are: 1) Both of them share the similar spatial structure, with tropical cyclone and black hole having the outflow cloud shield and the horizon sphere in the central part, respectively, while four spiral material bands exist in the rotating plane around them;2) In theoretically, the energy density formed by the orthogonal interaction of the four spiral material bands is as times as the total kinetic energy of the head-on interaction;3) This region of high energy density can lead to the conversion from mass to energy and the creation of new physical states of matter, which is a black hole event;4) The outer horizon of a black hole is the outermost interface of events, or the orthogonal interaction interface of particles;5) High-speed plasma jets extended at the poles of the black hole are directly associated with the shear stress of orthogonal interaction.
基金supported by National Outstanding Young Scientists Founds of China (Grant No. 50825902)Jiangsu Provincial Innovative Scholars "Climbing" Project of China (Grant No. BK 2009006)+1 种基金National Natural Science Foundation of China (Grant No. 50979034)Jiangsu Provincial Project for Innovative Postgraduates of China (Grant No. CX10B_262Z)
文摘The existing research for unsteady flow field and the corresponding flow induced vibration analysis of centrifugal pump are mainly carried out respectively without considering the interaction between fluid and structure. The ignorance of fluid structure interaction (FSI) means that the energy transfer between fluid and structure is neglected. To some extent, the accuracy and reliability of unsteady flow and rotor deflection analysis should be affected by this interaction mechanism. In this paper, a combined calculation between two executables for turbulent flow and vibrating structure was established using two-way coupling method to study the effect of FSI. Pressure distributions, radial forces, rotor deflection and equivalent stress are analyzed. The results show that the FSI effect to pressure distribution in flow field is complex. The pressure distribution is affected not only around impeller outlet where different variation trends of pressure values with and without FSI appear according to different relative positions between blade and cutwater, but also in the diffusion section of volute. Variation trends of peak values of radial force amplitude calculated with and without FSI are nearly same under high flow rate and designed conditions while the peak value with FSI is slightly smaller, and differently, the peak value with FSI is larger with low flow rate. In addition, the effect of FSI on the angle of radial force is quite complex, especially under 0.5Q condition. Fluctuation of radial deflection of the rotor has obvious four periods, of which the extent is relatively small under design condition and is relatively large under off-design condition. Finally, fluctuations of equivalent stress with time are obvious under different conditions, and stress value is small. The proposed research establishes the FSI calculation method for centrifugal pump analysis, and ensures the existing affect by fluid structure interaction.
基金supported by National Hi-tech Research and Development Program of China (863 Program, Grant No. 2009AA04Z413)Zhejiang Provincial Natural Science Foundation of China (Grant No. Y1110109)
文摘Journal bearings are important parts to keep the high dynamic performance of rotor machinery. Some methods have already been proposed to analysis the flow field of journal bearings, and in most of these methods simplified physical model and classic Reynolds equation are always applied. While the application of the general computational fluid dynamics (CFD)-fluid structure interaction (FSI) techniques is more beneficial for analysis of the fluid field in a journal bearing when more detailed solutions are needed. This paper deals with the quasi-coupling calculation of transient fluid dynamics of oil film in journal bearings and rotor dynamics with CFD-FSI techniques. The fluid dynamics of oil film is calculated by applying the so-called "dynamic mesh" technique. A new mesh movement approacb is presented while the dynamic mesh models provided by FLUENT are not suitable for the transient oil flow in journal bearings. The proposed mesh movement approach is based on the structured mesh. When the joumal moves, the movement distance of every grid in the flow field of bearing can be calculated, and then the update of the volume mesh can be handled automatically by user defined function (UDF). The journal displacement at each time step is obtained by solving the moving equations of the rotor-bearing system under the known oil film force condition. A case study is carried out to calculate the locus of the journal center and pressure distribution of the journal in order to prove the feasibility of this method. The calculating results indicate that the proposed method can predict the transient flow field of a journal bearing in a rotor-bearing system where more realistic models are involved. The presented calculation method provides a basis for studying the nonlinear dynamic behavior of a general rotor-bearing system.
文摘Tension leg platform (TLP) for offshore wind turbine support is a new type structure in wind energy utilization. The strong-interaction method is used in analyzing the coupled model, and the dynamic characteristics of the TLP for offshore wind turbine support are recognized. As shown by the calculated results: for the lower modes, the shapes are water's vibration, and the vibration of water induces the structure's swing; the mode shapes of the structure are complex, and can largely change among different members; the mode shapes of the platform are related to the tower's. The frequencies of the structure do not change much after adjusting the length of the tension cables and the depth of the platform; the TLP has good adaptability for the water depths and the environment loads. The change of the size and parameters of TLP can improve the dynamic characteristics, which can reduce the vibration of the TLP caused by the loads. Through the vibration analysis, the natural vibration frequencies of TLP can be distinguished from the frequencies of condition loads, and thus the resonance vibration can be avoided, therefore the offshore wind turbine can work normally in the complex conditions.
基金sponsored by the National Natural Science Foundation of China(Grant No.51779143)the Oceanic Interdisciplinary Program of Shanghai Jiao Tong University(Grant No.SL2020ZD101)the Cultivation of Scientific Research Ability of Young Talents of Shanghai Jiao Tong University(Grant No.19X100040072).
文摘Numerical simulations of evolution characteristics of slug flow across a 90°pipe bend have been carried out to study the fluid−structure interaction response induced by internal slug flow.The two-phase flow patterns and turbulence were modelled by using the volume of fluid(VOF)model and the Realizable k−εturbulence model respectively.Firstly,validation of the CFD model was carried out and the desirable results were obtained.The different flow patterns and the time-average mean void fraction was coincident with the reported experimental data.Simulations of different cases of slug flow have been carried out to show the effects of superficial gas and liquid velocity on the evolution characteristics of slug flow.Then,a one-way coupled fluid-structure interaction framework was established to investigate the slug flow interaction with a 90°pipe bend under various superficial liquid and gas velocities.It was found that the maximum total deformation and equivalent stress increased with the increasing superficial gas velocity,while decreased with the increasing superficial liquid velocity.In addition,the total deformation and equivalent stress has obvious periodic fluctuation.Furthermore,the distribution position of maximum deformation and stress was related to the evolution of slug flow.With the increasing superficial gas velocity,the maximum total deformation was mainly located at the 90°pipe bend.But as the superficial liquid velocity increases,the maximum total deformation was mainly located in the horizontal pipe section.Consequently,the slug flow with higher superficial gas velocity will induce more serious cyclical impact on the 90°pipe bend.
基金supported by the National Natural Science Foundations of China(Nos.50821063 and 50823004)973 Program(No.2007CB714701)the Fundamental Research Funds for the Central Universities(No.2010XS34)
文摘Based on the train-track coupling dynamics and high-speed train aerodynamics, this paper deals with an improved algorithm for fluid-structure interaction of high-speed trains. In the algorithm, the data communication between fluid solver and structure solver is avoided by inserting the program of train-track coupling dynamics into fluid dynamics program, and the relaxation factor concerning the load boundary of the fluid-structure interface is introduced to improve the fluctuation and convergence of aerodynamic forces. With this method, the fluid-structure dynamics of a highspeed train are simulated under the condition that the velocity of crosswind is 13.8 m/s and the train speed is 350 km/h. When the relaxation factor equals 0.5, the fluctuation of aerodynamic forces is lower and its convergence is faster than in other cases. The side force and lateral displacement of the head train are compared between off-line simulation and co-simulation. Simulation results show that the fluid-structure interaction has a significant influence on the aerodynam- ics and attitude of the head train under crosswind conditions. In addition, the security indexes of the head train worsen after the fluid-structure interaction calculation. Therefore, the fluid-structure interaction calculation is necessary for high-speed trains.
文摘Understanding cardiac blood flow behaviors is of importance for cardiovascular research and clinical assessment of ventricle functions.Patient-specific Echo-based left ventricle(LV)fluid-structure interaction(FSI)models were introduced to perform ventricle mechanical analysis,investigate flow behaviors,and evaluate the impact of myocardial infarction(MI)and hypertension on blood flow in the LV.Echo image data were acquired from 3 patients with consent obtained:one healthy volunteer(P1),one hypertension patient(P2),and one patient who had an inferior and posterior myocardial infarction(P3).The nonlinear Mooney-Rivlin model was used for ventricle tissue with material parameter values chosen to match echo-measure LV volume data.Using the healthy case as baseline,LV with MI had lower peak flow velocity(30%lower at beginejection)and hypertension LV had higher peak flow velocity(16%higher at begin-filling).The vortex area(defined as the area with vorticity>0)for P3 was 19%smaller than that of P1.The vortex area for P2 was 12%smaller than that of P1.At peak of filling,the maximum flow shear stress(FSS)for P2 and P3 were 390%higher and 63%lower than that of P1,respectively.Meanwhile,LV stress and strain of P2 were 41%and 15%higher than those of P1,respectively.LV stress and strain of P3 were 36%and 42%lower than those of P1,respectively.In conclusion,FSI models could provide both flow and structural stress/strain information which would serve as the base for further cardiovascular investigations related to disease initiation,progression,and treatment strategy selections.Large-scale studies are needed to validate our findings.
文摘Fluid-structure interaction (FSI) is essentially a dynamic phenomenon and always exists in fluid-filled pipe system. The four-equation model, which has been proved to be effective to describe and predict the phenomenon of FSI due to friction coupling and Poisson coupling being taken into account, is utilized to describe the FSI of fluid-filled pipe system. Terse compatibility equations are educed by the method of characteristics (MOC) to describe the fluid-filled pipe system. To shorten computing time needed to get the solutions under the condition of keeping accuracy requirement, two steps are adopted, firstly the time step Δt and divided number of the straight pipe are optimized, sec-ondly the mesh spacing Δz close to boundary is subdivided in several submeshes automatically ac-cording to the speed gradient of fluid. The mathematical model and arithmetic are validated by com-parisons between simulation solutions of two straight pipe systems and experiment known from lit-erature.
基金the financial support provided by the Office of Naval Research(ONR) through grant number N00014-09-1-1204 (managed by Dr. Ki-Han Kim)supported in part by the National Research Foundation of Korea (NRF)grant funded by the Korea government (MEST) through the GCRC-SOP Grant No. 2012-0004783
文摘The objective of this paper is to present and to validate a new hybrid coupling (HC) algorithm for modeling of fluid-structure interaction (FSI) in incompressible, viscous flows. The HC algorithm is able to avoid numerical instability issues associated with artificial added mass effects, which are often encountered by standard loosely coupled (LC) and tightly coupled (TC) algorithms, when modeling the FSI response of flexible structures in incompressible flow. The artificial added mass effect is caused by the lag in exchange of interfacial displacements and forces between the fluid and solid solvers in partitioned algorithms. The artificial added mass effect is much more prominent for light/flexible struc- tures moving in water, because the fluid forces are in the same order of magnitude as the solid forces, and because the speed at which numerical errors propagate in an incom- pressible fluid. The new HC algorithm avoids numerical instability issues associated with artificial added mass effects by embedding Theodorsen's analytical approximation of the hydroelastic forces in the solution process to obtain better initial estimates of the displacements. Details of the new HC algorithm are presented. Numerical validation studies are shown for the forced pitching response of a steel and a plastic hydrofoil. The results show that the HC algorithm is able to converge faster, and is able to avoid numerical insta- bility issues, compared to standard LC and TC algorithms, when modeling the transient FSI response of a plastic hydrofoil. Although the HC algorithm is only demonstrated for a NACA0009 hydrofoil subject to pure pitching motion, the method can be easily extended to model general 3-D FSI response and stability of complex, flexible structures in turbulent, incompressible, multiphase flows.
基金Project supported by the National Natural Science Foundation of China(No.10832007)the Shanghai Leading Academic Discipline Project(No.B206)
文摘The closely coupled approach combined with the finite volume method (FVM) solver and the finite element method (FEM) solver is used to investigate the fluid-structure interaction (FSI) of a three-dimensional cantilevered hydrofoil in the water tunnel. The FVM solver and the coupled approach are verified and validated by compar- ing the numerical predictions with the experimental measurements, and good agreement is obtained concerning both the lift on the foil and the tip displacement. In the noncav- itating flow, the result indicates that the growth of the initial incidence angle and the Reynolds number improves the deformation of the foil, and the lift on the foil is increased by the twist deformation. The normalized twist angle and displacement along the span of the hydrofoil for different incidence angles and Reynolds numbers are almost uniform. For the cavitation flow, it is shown that the small amplitude vibration of the foil has limited influence on the developing process of the partial cavity, and the quasi two-dimensional cavity shedding does not change the deformation mode of the hydrofoil. However, the frequency spectrum of the lift on the foil contains the frequency which is associated with the first bend frequency of the hydrofoil.
基金Project(51275542) supported by the National Natural Science Foundation of Chinaproject(CDJXS12110010) supported by the Fundamental Research Funds for the Central Universities of China
文摘Based on the working principle and the damping characteristic of hydraulic shock absorber,a fluid structure interaction method was presented,which was used to analyze the microcosmic and high-frequency processing mechanism of fluid structure interaction between circulation valve and liquid of hydraulic shock absorber.The fluid mesh distortion was controlled by the CEL language,and the fluid structure interaction mathematical model was established.The finite element model was established by ANSYS CFX software and was analyzed by dynamic mesh technique.The local sensitive computational area was meshed by prismatic grid,which could reduce the negative volume problem during the simulation.The circulation valve and liquid of hydraulic shock absorber were simulated and analyzed under the condition of sinusoidal inlet velocity loads.Flow characteristic and dynamics characteristic were obtained.The pressure distribution and the displacement of circulation value were obtained,and the acceleration curve of circulation valve was simulated and analyzed.The conformity of the final simulation results with the experimental datum indicates that this method is accurate and reliable to analyze the dynamics characteristic between circulation valve and liquid of hydraulic shock absorber,which can provide a theoretical foundation for optimizing hydraulic shock absorber in the future.
基金supported by the National Basic Research Program of China (‘‘973’’ Program, No. 2013CB035906)the National Natural Science Foundation of China (No. 51439005)the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (No. 51621092)
文摘Channel engineering stability with underground goafs is a complex three-dimensional problem, especially when considering channel leakage, and is influenced by a number of processes, such as seepage, fluid structure interaction(FSI), modeling, and selection of geological mechanical parameters. In this study, stability finite element analysis by one-way FSI was performed by establishing an integrated 3D engineering geological model. The extended Fourier amplitude sensitivity test was used to quantitatively assess the first-order and total sensitivities of the engineering model to critical geological mechanical parameters. Results illustrate that the channel engineering deformation is under a reasonable range and the elastic modulus is the highest total sensitivity parameter for the channel tilt and curvature at 0.7395 and 0.7525, respectively. Moreover, the most observable coupling effects for the curvature and horizontal strain are cohesion(0.1933)and density(0.7410), respectively.
文摘The effects of the renal artery stenosis (RAS) on the blood flow and vessel walls are investigated. The pulsatile blood flow through an anatomically realistic model of the abdominal aorta and renal arteries reconstructed from CT-scan images is simulated, which incorporates the fluid-structure interaction (FSI). In addition to the investigation of the RAS effects on the wall shear stress and the displacement of the vessel wall, it is determined that the RAS leads to decrease in the renal mass flow. This may cause the activation of the renin-angiotension system and results in severe hypertension.
基金The project supported by the National Natural Science Foundation of China(10672036,10472025 and 10421002)the Natural Science Foundation of Liaoning Province(20032109)
文摘In this paper, the authors present airflow field characteristics of human upper airway and soft palate movement attitude during breathing. On the basis of the data taken from the spiral computerized tomography images of a healthy person and a patient with Obstructive Sleep Apnea-Hypopnea Syndrome (OSAHS), three-dimensional models of upper airway cavity and soft palate are reconstructed by the method of surface rendering. Numerical simulation is performed for airflow in the upper airway and displacement of soft palate by fluid-structure interaction analysis. The reconstructed threedimensional models precisely preserve the original configuration of upper airways and soft palate. The results of the pressure and velocity distributions in the airflow field are quantitatively determined, and the displacement of soft palate is presented. Pressure gradients of airway are lower for the healthy person and the airflow distribution is quite uniform in the case of free breathing. However, the OSAHS patient remarkably escalates both the pressure and velocity in the upper airway, and causes higher displacement of the soft palate. The present study is useful in revealing pathogenesis and quantitative mutual relationship between configuration and function of the upper airway as well as in diagnosingdiseases related to anatomical structure and function of the upper airway.
基金Project supported by the Program for New Century Excellent Talents in University (No. NCET-10-0054)the Fok Ying-Tong Education Foundation,China (No. 121073)+1 种基金the National Natural Science Foundation of China (No. 10976008)the State Key Program of National Natural Science of China (No. 50939002)
文摘In the underwater-shock environment, cavitation occurs near the structural surface. The dynamic response of fluid-structure interactions is influenced seriously by the cavitation effects. It is also the difficulty in the field of underwater explosion. With the traditional boundary element method and the finite element method (FEM), it is difficult to solve the nonlinear problem with cavitation effects subjected to the underwater explosion. To solve this problem, under the consideration of the cavitation effects and fluid compressibility, with fluid viscidity being neglected, a 3D numerical model of transient nonlinear fluid-structure interaction subjected to the underwater explosion is built. The fluid spectral element method (SEM) and the FEM are adopted to solve this model. After comparison with the FEM, it is shown that the SEM is more precise than the FEM, and the SEM results are in good coincidence with benchmark results and experiment results. Based on this, combined with ABAQUS, the transient fluid-structure interaction mechanism of the 3D submerged spherical shell and ship stiffened plates subjected to the underwater explosion is discussed, and the cavitation region and its influence on the structural dynamic responses are presented. The paper aims at providing references for relevant research on transient fluid-structure interaction of ship structures subjected to the underwater explosion.
基金Supported by the National Natural Science Foundation of China (50774064)
文摘Failure pressure is a key parameter in reservoir hydrofracturing operation. Existing analytical methods for calculating the failure pressure are based on the assumption that borehole fluid is under two extreme conditions: non-infiltration or complete infiltration. The assumption is not suitable for the actual infiltration process, and this will cause a great error in practical calculation. It shows that during the injection process, the dynamic variation in effective stress-dependent permeability has an influence on the infiltration, and the influence also brings about calculation errors. Based on the fluid-structure interaction and finite element method (FEM), considering partial infiltration during injection process, a numerical model for calculating rock failure pressure is established. According to the analysis of permeability test results and response-surface method, a new variation rule of rock permeability with the change of effective stress is presented, and the relationships among the permeability, confining pressure and pore pressure are proposed. There are some differences between the dynamic value of permeability-effective-stress coefficient observed herein and the one obtained by the classical theory. Combining with the numerical model and the dynamic permeability, a coupling method for calculating failure pressure is developed. Comparison of field data and calculated values obtained by various methods shows that accurate values can be obtained by the coupling method. The coupling method can be widely applied to the calculation of failure pressure of reservoirs and complex wells to achieve effective fracturing operation.
基金Project supported by the National Natural Science Foundation of China(No.11972112)the Fundamental Research Funds for the Central Universities of China(Nos.N2103024 and N2103002)the Major Projects of Aero-Engines and Gasturbines(No.J2019-I-0008-0008)。
文摘The dynamic characteristics of a single liquid-filled pipe have been broadly studied in the previous literature.The parallel liquid-filled pipe(PLFP)system is also widely used in engineering,and its structure is more complex than that of a single pipe.However,there are few reports about the dynamic characteristics of the PLFPs.Therefore,this paper proposes improved frequency modeling and solution for the PLFPs,involving the logical alignment principle and coupled matrix processing.The established model incorporates both the fluid-structure interaction(FSI)and the structural coupling of the PLFPs.The validity of the established model is verified by modal experiments.The effects of some unique parameters on the dynamic characteristics of the PLFPs are discussed.This work provides a feasible method for solving the FSI of multiple pipes in parallel and potential theoretical guidance for the dynamic analysis of the PLFPs in engineering.