A three-dimensional panel method is developed to investigate the seakeeping performance of two parallel ships advancing in head and oblique waves. In this method, the fluid domain is partitioned into two regions by in...A three-dimensional panel method is developed to investigate the seakeeping performance of two parallel ships advancing in head and oblique waves. In this method, the fluid domain is partitioned into two regions by introducing a virtual control surface. In the inner part, the Taylor expansion boundary element method is used, whose kernel function is the Rankine source;in the outer part, the free surface Green function with the forward speed effect considered is adopted. The velocity potentials and normal velocities on the virtual control surface are equal for the inner and outer domains. Moreover, the numerical estimation method for viscous roll damping recommended by the ITTC is included in the present method. This hybrid method is validated through the previously measured motions of two ship models, and the present numerical results are in good agreement with those of the experiments. Furthermore, the influences of longitudinal distances and wave heading angles on six-degree-of-freedom motions and the hydrodynamic interaction between the present two ship models are discussed in detail.展开更多
Stretching polymer in fluid flow is a vital process for studying and utilizing the physical properties of these molecules,such as DNA linearization in nanofluidic channels.We studied the role of hydrodynamic interacti...Stretching polymer in fluid flow is a vital process for studying and utilizing the physical properties of these molecules,such as DNA linearization in nanofluidic channels.We studied the role of hydrodynamic interactions(His)in stretching a free star polymer in Poiseuille flow through a tube using mesoscale hydrodynamic simulations.As increasing the flow strength,star polymers migrate toward the centerline of tube due to His,whereas toward the tube wall in the absence of His.By analyzing the end monomer distribution and the perturbed flow around the star polymer,we found that the polymer acts like a shield against the flow,leading to additional hydrodynamic drag forces that compress the arm chains in the front of the star center toward the tube axis and lift the arm chai ns at the back toward the tube wall.The balanced hydrodynamic forces freeze the polymer into a trumpet structure,where the arm chains maintain a steady strongly stretched state at high flow strength.In contrast,the polymer displays remarkably large conformational change when switching off His.Our simulation results explained the coupling between His and the structure of star polymers in Poiseuille flow.展开更多
The hydrodynamics of side-by-side barges are much more complex than those of a single barge in waves because of wave shielding, viscous effects and water resonance in the gap. In the present study, hydrodynamic coeffi...The hydrodynamics of side-by-side barges are much more complex than those of a single barge in waves because of wave shielding, viscous effects and water resonance in the gap. In the present study, hydrodynamic coefficients in the frequency domain were calculated for both the system of multiple bodies and the isolated body using both low-order and higher-order boundary-element methods with different element numbers. In these calculations, the damping-lid method was used to modify the free-surface boundary conditions in the gap and to make the hydrodynamic results more reasonable. Then far-field, mid-field and near-field methods were used to calculate wave-drift forces for both the multi-body system and the isolated body. The results show that the higher-order method has faster convergence speed than the low-order method for the multi-body case. Comparison of different methods of computing drift force showed that mid-field and far-field methods have better convergence than the near-field method. In addition, corresponding model tests were performed in the Deepwater Offshore Basin at Shanghai Jiao Tong University. Comparison between numerical and experimental results showed good agreement.展开更多
This paper numerically and experimentally investigates the hydrodynamic interaction between two semi-submersible type VLFS modules in the frequency domain. Model tests were conducted to investigate the relationship be...This paper numerically and experimentally investigates the hydrodynamic interaction between two semi-submersible type VLFS modules in the frequency domain. Model tests were conducted to investigate the relationship between interactions and wave headings. Numerical studies were performed by solving the radiation-diffraction problem and were validated against the experimental results. Motion Response Amplitude Operators (RAOs) were obtained from numerical and experimental studies. The dependency of the hydrodynamic interaction effect on wave headings is clarified. The influence of different wave periods on the motion responses of two-module VLFS and wave elevations in the gap is studied. The results indicate that the hydrodynamic interactions of the two modules are directly related to the wave headings and the periods of the incident wave. The shielding effect plays an important role in short wave, and the influence decreases with the increase of the incident wavelength. The numerical results based on the diffraction-radiation code can give a relatively good estimation to the responses in short wave while for long wave, it would over-predict the response.展开更多
In this paper, a 3D time domain technique is adopted to calculate the coupled hydrodynamic interaction between two bodies without flare in waves. For verifying the code, two same cylinders are selected to calculate co...In this paper, a 3D time domain technique is adopted to calculate the coupled hydrodynamic interaction between two bodies without flare in waves. For verifying the code, two same cylinders are selected to calculate coupled hydrodynamic effects by comparison with the results obtained by 3D frequency method which has been proved to be efficient for solving such problems. In order to improve efficiency of calculation, the effect of history time has been discussed, and an improved method is presented. Moreover, the effect of lateral separation distance is also discussed in detail. The technique developed here may serve as a more rigorous tool to analyze the related transient problems of two ships doing underway replenishment in waves.展开更多
On the basis of model tests, potential flow theory, and viscous Computational Fluid Dynamics （CFD） method, the hydrodynamic interactions between two underwater bodies were investigated to determine the influencing f...On the basis of model tests, potential flow theory, and viscous Computational Fluid Dynamics （CFD） method, the hydrodynamic interactions between two underwater bodies were investigated to determine the influencing factors, changing rule, interaction mechanism, and appropriate methods describing them. Some special phenomena were discovered in two series of near-wall interaction experiments. The mathematical model and predicting methods were presented for interacting forces near wall, and the calculation results agreed well with the experimental ones. From the comparisons among numerical results with respect to nonviscosity, numerical results with respect to viscosity, and measured results, data on the influence of viscosity on hydrodynamic interactions were obtained. For hydrodynamic interaction related to multi-body unsteady motions with six degrees of freedom that is difficult to simulate in tests, numerical predictions of unsteady interacting forces were given.展开更多
An analytical method based on the eigenfunction expansion and the Graf＇s addition theorem for Bessel functions is developed to study the hydrodynamic interactions of an array of truncated circular cylinders with each...An analytical method based on the eigenfunction expansion and the Graf＇s addition theorem for Bessel functions is developed to study the hydrodynamic interactions of an array of truncated circular cylinders with each cylinder oscillating independently in different prescribed modes. The hydrodynamic radiation and diffraction of linear waves by such an array of cylinders are investigated and the analytical solutions of the velocity potentials are obtained. After comparisons for degenerated cases and program verifications, several cases for an array of truncated cylinders with each cylinder oscillating independently in surge, sway, heave, roll, and pitch modes with different prescribed amplitudes, are studied and the hydrodynamic forces and moments acting on the cylinders are obtained.展开更多
This paper presents a hydrodynamic analysis of a hybrid system consisting of a floating platform coupled with an array of oscillating bodies that move along the weather sidewall of the platform.Using the Lagrange mult...This paper presents a hydrodynamic analysis of a hybrid system consisting of a floating platform coupled with an array of oscillating bodies that move along the weather sidewall of the platform.Using the Lagrange multiplier method,the motion equation governing this type of motion characteristic is formulated,and the formula of the extracted wave power is derived.The numerical results demonstrate a significant increase in the hydrodynamic efficiency of oscillating bodies within specific frequency ranges in the presence of the floating platform.The incorporation of proper power take-off damping of the oscillating bodies results in a reduction in the heave motion of the platform,but it may lead to an increase in pitch motion.The analysis of the response behaviour of the system shows that both the heave motion and pitch motion of the platform contribute to the power extraction and relative motion between the buoys and the platform.Parametric investigations are conducted to explore the hydrodynamic interactions between the floating platform and the buoy array.Additionally,the concept of“hydrodynamic synergy”is proposed to describe the synergetic effect of different components of a multi-purpose platform,which is of considerable engineering interest.展开更多
The equilibrium dynamics and nonlinear rheology of unentangled polymer blends remain inadequately understood,especially regarding the influence of short-chain matrix length N_(S) on the structure and rheological behav...The equilibrium dynamics and nonlinear rheology of unentangled polymer blends remain inadequately understood,especially regarding the influence of short-chain matrix length N_(S) on the structure and rheological behavior of dispersed long chains.Using molecular dynamics simulations based on the Kremer-Grest model,we systematically explore the N_(S)-dependence of static conformations,equilibrium dynamics,and nonlinear shear responses in unentangled long-chain/short-chain polymer blends.Our results demonstrate a decoupling between the static and dynamic sensitivity to N_(S):while the static chain size,R_g,follows Flory theory with slight swelling at small N_(S) due to incomplete excluded volume screening,the diffusion coefficient,D,and the relaxation time,τ_(0),exhibit a strong,non-monotonic N_(S)-dependence,transitioning from monomeric friction dominance at small N_(S) to collective segmental rearrangement at large N_(S).Additionally,we observe partial decoupling between the viscous and normal stress responses:while the zero-shear viscosity,η,is strongly N_(S)-dependent,the first and second normal stress coefficients,Ψ_(1) and Ψ_(2),collapse onto universal curves when scaled by the dimensionless shear rate,γτ_(0),suggesting a common mechanism of orientation and stretching.Under shear,long chains compress in the vorticity direction λ_(z)~Wi^(-0.2),which reduces collision frequency and contributes to shear thinning,while the scaling of weaker orientation resistance m_(G)~Wi^(0.35)reflects hydrodynamic screening by the short-chain matrix.These findings highlight the limitations of single-chain models and emphasize the necessity of considering N_(S)-dependent matrix dynamics and flow-induced structural changes in understanding the rheology of unentangled polymer blends.展开更多
A computer code based on the double-body potential flow model and the classic source panel method has been developed to study various problems of hydrodynamic interaction between ships and other objects with solid bou...A computer code based on the double-body potential flow model and the classic source panel method has been developed to study various problems of hydrodynamic interaction between ships and other objects with solid boundaries including the seabed. A peculiarity of the proposed implementation is the application of the so-called ＂moving-patch＂ method for simulating steady boundaries of large extensions. The method is based on an assumption that at any moment just the part of the boundary （＂moving patch＂） which lies close to the interacting ship is significant for the near-field interaction. For a specific case of the fiat bottom, comparative computations were performed to determine optimal dimensions of the patch and of the constituting panels based on the trade-off between acceptable accuracy and reasonable efficiency. The method was applied to estimate the sway force on a ship hull moving obliquely across a dredged channel. The method was validated for a case of ship-to-ship interaction when tank data were available. This study also contains a description of a newly developed spline approximation algorithm necessary for creating consistent discretizations of ship hulls with various degrees of refinement.展开更多
A three-dimensional high-order panel method based on non-uniform rational B-spline(NURBS) is developed for predicting the hydrodynamic interaction forces on a moored ship induced by a passing ship in shallow water. An...A three-dimensional high-order panel method based on non-uniform rational B-spline(NURBS) is developed for predicting the hydrodynamic interaction forces on a moored ship induced by a passing ship in shallow water. An NURBS surface is used to precisely represent the hull geometry. Velocity potential on the hull surface is described by B-spline after the source density distribution on the boundary surface is determined. A collocation approach is applied to the boundary integral equation discretization. Under the assumption of low passing speed, the effect of free surface elevation is neglected in the numerical calculation, and infinite image method is used to deal with the finite water depth effect. The time stepping method is used to solve the velocity potential at each time step. Detailed convergence study with respect to time step, panel size and Green function is undertaken. The present results of hydrodynamic forces are compared with those obtained by slender-body theory to show the validity of the proposed numerical method. Calculations are conducted for different water depths and lateral distances between ships, and the detail results are presented to demonstrate the effects of these factors.展开更多
The propulsive performance of an oblique school of fish is numerically studied using an immersed boundary technique. The effect of the spacing and wiggling phase on the hydrodynamics of the system is investigated. The...The propulsive performance of an oblique school of fish is numerically studied using an immersed boundary technique. The effect of the spacing and wiggling phase on the hydrodynamics of the system is investigated. The hydrodynamics of the system is deeply affected by the spacing between each fish in the school. When the horizontal separation is smaller than the length of the fish body, the downstream fish exhibits a larger thrust coefficient and greater propulsive efficiency than the isolated fish. However, the corresponding values for the upstream fish are smaller. The opposite behavior occurs when the horizontal separation increases beyond the length of fish body. The propulsive performance of the entire oblique school of fish can be substantially enhanced when the separations are optimized.展开更多
While passing through a lock, a ship usually undergoes a steady forward motion at low speed. Owing to the size restriction of lock chamber, the shallow water and bank effects on the hydrodynamic forces acting on the s...While passing through a lock, a ship usually undergoes a steady forward motion at low speed. Owing to the size restriction of lock chamber, the shallow water and bank effects on the hydrodynamic forces acting on the ship may be remarkable, which may have an adverse effect on navigation safety. However, the complicated hydrodynamics is not yet fully understood. This paper focuses on the hydrodynamic forces acting on a ship passing through a lock. The unsteady viscous flow and hydrodynamic forces are calculated by applying an unsteady RANS code with a RNG k-e turbulence model. User-defined function （UDF） is compiled to define the ship motion. Meanwhile, the grid regeneration is dealt with by using the dynamic mesh method and sliding interface technique. Numerical study is carried out for a bulk carrier ship passing through the Pierre Vandamme Lock in Zeebrugge at the model scale. The proposed method is validated by comparing the numerical results with the data of captive model tests. By analyzing the numerical results obtained at different speeds, water depths and eccentricities, the influences of speed, water depth and eccentricity on the hydrodynamic forces are illustrated. The numerical method proposed in this paper can qualitatively predict the ship-lock hydrodynamic interaction. It can provide certain guidance on the manoeuvring and control of ships passing through a lock.展开更多
Dynamics and vibration of control valves under flow-induced vibration are analyzed. Hydrodynamic load characteristics and structural response under flow-induced vibration are mainly influenced by inertia, damping, ela...Dynamics and vibration of control valves under flow-induced vibration are analyzed. Hydrodynamic load characteristics and structural response under flow-induced vibration are mainly influenced by inertia, damping, elastic, geometric characteristics and hydraulic parameters. The purpose of this work is to investigate the dynamic behavior of control valves in the response to self-excited fluid flow. An analytical and numerical method is developed to simulate the dynamic and vibrational behavior of sliding dam valves, in response to flow excitation. In order to demonstrate the effectiveness of proposed model, the simulation results are validated with experimental ones. Finally, to achieve the optimal valve geometry, numerical results for various shapes of valves are compared. Rounded valve with the least amount of flow turbulence obtains lower fluctuations and vibration amplitude compared with the flat and steep valves. Simulation results demonstrate that with the optimal design requirements of valves, vibration amplitude can be reduced by an average to 30%.展开更多
An investigation has been conducted to quantify the effect of waterway geometry on the form and magnitude of forces and moment experienced by a berthed ship due to a passing ship.By using the dynamic mesh technique an...An investigation has been conducted to quantify the effect of waterway geometry on the form and magnitude of forces and moment experienced by a berthed ship due to a passing ship.By using the dynamic mesh technique and solving the unsteady RANS equations in conjunction with a RNG k？ε turbulence model,numerical simulation of the three-dimensional unsteady viscous flow around a passing ship and a berthed ship in different waterway geometries is conducted,and the hydrodynamic forces and moment acting on the berthed ship are calculated.The proposed method is verified by comparing the numerical results with existing empirical curves and a selection of results from model scale experiments.The calculated interaction forces and moment are presented for six different waterway geometries.The magnitude of the peak values and the form of the forces and moment on the berthed ship for different cases are investigated to assess the effect of the waterway geometry.The results of present study can provide certain guidance on safe maneuvering of a ship passing by a berthed ship.展开更多
We conduct optical-tweezers experiments to investigate the average potential energies of passive plates harmonically trapped in bacterial suspensions.Our results show that the mean potential energies along both the ma...We conduct optical-tweezers experiments to investigate the average potential energies of passive plates harmonically trapped in bacterial suspensions.Our results show that the mean potential energies along both the major and minor axes increase with bacterial concentration but decrease with trap stiffness.Notably,the average potential energy along the major axis consistently exceeds that along the minor axis.This discrepancy from equilibrium systems is primarily attributed to the distinct bacterial flow fields and direct bacterium–plate collisions near the major and minor axes,as evidenced by the higher orientational order around the plate along the major compared to the minor axis,despite identical bacterial densities in these regions.Our findings highlight the critical role of hydrodynamic interactions in determining the potential energy of passive objects immersed in an active bath.展开更多
This study numerically investigates the locomotion of active matter over a circular cylinder in a confined microchannel.We consider the effects of cylinder size,swimming Reynolds number on the motion characteristic of...This study numerically investigates the locomotion of active matter over a circular cylinder in a confined microchannel.We consider the effects of cylinder size,swimming Reynolds number on the motion characteristic of three kinds of swimmers.The swimmer’s motion over a cylinder in a microchannel can be classified into seven modes.The cylinder diameter and swimming Reynolds number have no impact on the motion mode of neutral swimmers.When approaching the cylinder,pullers mainly perform periodic motion near the left side of cylinder,the pushers primarily perform periodic motion near the right side of cylinder.The mechanism of the periodic motion is mainly induced by the hydrodynamic interaction between the cylinder,channel walls,and the pressure near the swimmer.As cylinder diameter increases,pushers are more likely to exhibit periodic motion on the surface of cylinder than the pullers.Puller is unable to stabilize on the surface of cylinder at low Reynolds number,it migrates to the right side of cylinder at high Reynolds number,showing a pattern opposite to that observed for pushers.The results provide a possible new path for controlling active matter in microfluidic devices.展开更多
A mesoscopic simulation is applied to investigate the effects of hydrodynamic interactions and axial chains on the dynamics of threaded rings.The hydrodynamic interactions significantly speed up the diffusion and rela...A mesoscopic simulation is applied to investigate the effects of hydrodynamic interactions and axial chains on the dynamics of threaded rings.The hydrodynamic interactions significantly speed up the diffusion and relaxation of both free and threaded rings.The decoupled diffusion and relaxation dynamics indicate the broken of the Einstein-Stokes relationship.The diffusion of a ring threaded on a flexible chain exhibits a synergism effect compared to that on an axial rod,which originates from the self-diffusion of the ring and the reptation-like motion of the axial chain.Meanwhile,hydrodynamic interactions significantly improve the synergism effect,leading to an enhanced sliding motion of the threaded ring.The faster sliding of threaded rings suggests that the entropic barrier is negligible,which agrees well with the basic assumption of barrier-less confining tube at equilibrium in tube theory.Our results provide a new perspective on analysis of the effects of topology constraints on polymer dynamics.展开更多
The diffusion behavior of polyelectrolytes in dilute salt-free solution is studied through a hybrid mesoscale simulation technique that combines the molecular dynamics method and the multiparticle collision dynamics a...The diffusion behavior of polyelectrolytes in dilute salt-free solution is studied through a hybrid mesoscale simulation technique that combines the molecular dynamics method and the multiparticle collision dynamics approach.To elucidate the effects of hydrodynamic interactions(HI),we compare results for hydrodynamic and random solvents.When HI are taken into account,we find that the chain diffusivity decreases initially and then increases gradually with the increasing strength of the Coulomb interaction.By contrast,when HI are switched off,the electrostatic-dependent diffusivity shows three distinct regions,and a plateau of approximately constant diffusivity manifests between two decreasing regions.The findings reveal that the dynamics of polyelectrolytes in dilute solution depend on the coupling effects of hydrodynamic and Coulomb interactions,and that these dynamics can be understood by considering the conformational changes of chains,the counterion condensation,and the dynamics of counterions.展开更多
In order to improve the safety properties of an offloading system with side-by-side （SBS） mooring in which the FPSO is moored by a yoke system in the field of BZ25-1, it is necessary to analyze those properties. Acc...In order to improve the safety properties of an offloading system with side-by-side （SBS） mooring in which the FPSO is moored by a yoke system in the field of BZ25-1, it is necessary to analyze those properties. According to the experience of similar projects, tow strategies of different offioading arrangements were discussed by using the 3-D radiation/diffraction theory and quasi-static time domain method to assess their respective safety properties. Through the safety assessment analysis of different arrangement comparisons, various ways to improve the safety properties of off＇loading systems with side-by-side mooring were verified by analyzing the tension in the mooring lines and the fender deflection. Through comparison it can be concluded that by enlarging the key factors properly, including the size of the fenders and the hawsers as well as the number of hawsers, a better safety performance can be achieved.展开更多
基金financially supported by the National Natural Science Foundation of China (Grant Nos. 52071148 and 51509256)the Aeronautical Science Foundation of China (Grant No. 202000023079001)the Fundamental Research Funds for the Central Universities (Grant No.YCJJ20242103)。
文摘A three-dimensional panel method is developed to investigate the seakeeping performance of two parallel ships advancing in head and oblique waves. In this method, the fluid domain is partitioned into two regions by introducing a virtual control surface. In the inner part, the Taylor expansion boundary element method is used, whose kernel function is the Rankine source;in the outer part, the free surface Green function with the forward speed effect considered is adopted. The velocity potentials and normal velocities on the virtual control surface are equal for the inner and outer domains. Moreover, the numerical estimation method for viscous roll damping recommended by the ITTC is included in the present method. This hybrid method is validated through the previously measured motions of two ship models, and the present numerical results are in good agreement with those of the experiments. Furthermore, the influences of longitudinal distances and wave heading angles on six-degree-of-freedom motions and the hydrodynamic interaction between the present two ship models are discussed in detail.
基金supported by the National Natural Science Foundation of China(Nos.21574134,21774127,21790342,and 21504093)the Key Research Program of Frontier Sciences,CAS(No.QYZDY-SSW-SLH027).
文摘Stretching polymer in fluid flow is a vital process for studying and utilizing the physical properties of these molecules,such as DNA linearization in nanofluidic channels.We studied the role of hydrodynamic interactions(His)in stretching a free star polymer in Poiseuille flow through a tube using mesoscale hydrodynamic simulations.As increasing the flow strength,star polymers migrate toward the centerline of tube due to His,whereas toward the tube wall in the absence of His.By analyzing the end monomer distribution and the perturbed flow around the star polymer,we found that the polymer acts like a shield against the flow,leading to additional hydrodynamic drag forces that compress the arm chains in the front of the star center toward the tube axis and lift the arm chai ns at the back toward the tube wall.The balanced hydrodynamic forces freeze the polymer into a trumpet structure,where the arm chains maintain a steady strongly stretched state at high flow strength.In contrast,the polymer displays remarkably large conformational change when switching off His.Our simulation results explained the coupling between His and the structure of star polymers in Poiseuille flow.
基金financially supported by Lloyd’s Register Foundation(LRF),a UK-registered charity and sole shareholder of Lloyd’s Register Group Ltdthe Youth Innovation Fund of State Key Laboratory of Ocean Engineering(Grant No.GKZD010059-21)
文摘The hydrodynamics of side-by-side barges are much more complex than those of a single barge in waves because of wave shielding, viscous effects and water resonance in the gap. In the present study, hydrodynamic coefficients in the frequency domain were calculated for both the system of multiple bodies and the isolated body using both low-order and higher-order boundary-element methods with different element numbers. In these calculations, the damping-lid method was used to modify the free-surface boundary conditions in the gap and to make the hydrodynamic results more reasonable. Then far-field, mid-field and near-field methods were used to calculate wave-drift forces for both the multi-body system and the isolated body. The results show that the higher-order method has faster convergence speed than the low-order method for the multi-body case. Comparison of different methods of computing drift force showed that mid-field and far-field methods have better convergence than the near-field method. In addition, corresponding model tests were performed in the Deepwater Offshore Basin at Shanghai Jiao Tong University. Comparison between numerical and experimental results showed good agreement.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51709170 and 51979167)the Ministry of Industry and Information Technology of China(Mooring position technology:floating support platform engineering(Ⅱ))+1 种基金the Shanghai Sailing Program(Grant No.17YF1409700)the China Scholarship Council(Grant No.201806230206)
文摘This paper numerically and experimentally investigates the hydrodynamic interaction between two semi-submersible type VLFS modules in the frequency domain. Model tests were conducted to investigate the relationship between interactions and wave headings. Numerical studies were performed by solving the radiation-diffraction problem and were validated against the experimental results. Motion Response Amplitude Operators (RAOs) were obtained from numerical and experimental studies. The dependency of the hydrodynamic interaction effect on wave headings is clarified. The influence of different wave periods on the motion responses of two-module VLFS and wave elevations in the gap is studied. The results indicate that the hydrodynamic interactions of the two modules are directly related to the wave headings and the periods of the incident wave. The shielding effect plays an important role in short wave, and the influence decreases with the increase of the incident wavelength. The numerical results based on the diffraction-radiation code can give a relatively good estimation to the responses in short wave while for long wave, it would over-predict the response.
文摘In this paper, a 3D time domain technique is adopted to calculate the coupled hydrodynamic interaction between two bodies without flare in waves. For verifying the code, two same cylinders are selected to calculate coupled hydrodynamic effects by comparison with the results obtained by 3D frequency method which has been proved to be efficient for solving such problems. In order to improve efficiency of calculation, the effect of history time has been discussed, and an improved method is presented. Moreover, the effect of lateral separation distance is also discussed in detail. The technique developed here may serve as a more rigorous tool to analyze the related transient problems of two ships doing underway replenishment in waves.
文摘On the basis of model tests, potential flow theory, and viscous Computational Fluid Dynamics （CFD） method, the hydrodynamic interactions between two underwater bodies were investigated to determine the influencing factors, changing rule, interaction mechanism, and appropriate methods describing them. Some special phenomena were discovered in two series of near-wall interaction experiments. The mathematical model and predicting methods were presented for interacting forces near wall, and the calculation results agreed well with the experimental ones. From the comparisons among numerical results with respect to nonviscosity, numerical results with respect to viscosity, and measured results, data on the influence of viscosity on hydrodynamic interactions were obtained. For hydrodynamic interaction related to multi-body unsteady motions with six degrees of freedom that is difficult to simulate in tests, numerical predictions of unsteady interacting forces were given.
基金Project supported by the National Natural Science foundation of China(Grant Nos. 11072246, 10702073)the National High Technology Research and Development Program of China(863 Program, Grant No. 2006AA09Z350)
文摘An analytical method based on the eigenfunction expansion and the Graf＇s addition theorem for Bessel functions is developed to study the hydrodynamic interactions of an array of truncated circular cylinders with each cylinder oscillating independently in different prescribed modes. The hydrodynamic radiation and diffraction of linear waves by such an array of cylinders are investigated and the analytical solutions of the velocity potentials are obtained. After comparisons for degenerated cases and program verifications, several cases for an array of truncated cylinders with each cylinder oscillating independently in surge, sway, heave, roll, and pitch modes with different prescribed amplitudes, are studied and the hydrodynamic forces and moments acting on the cylinders are obtained.
基金supported by the National Key Research and Development Project of China(Grant No.2023YFC3106904)National Natural Science Foundation of China(Grant No.52001086)+1 种基金the Fundamental Research Funds for the Central Universities,China(Grant No.3072023JC0101)Additionally,this work contributes to the Strategic Research Plan of the Centre for Marine Technology and Ocean Engineering(CENTEC),which is financed by the Portuguese Foundation for Science and Technology(Fundação para a Ciência e Tecnologia-FCT)under contract UIDB/UIDP/00134/2020.
文摘This paper presents a hydrodynamic analysis of a hybrid system consisting of a floating platform coupled with an array of oscillating bodies that move along the weather sidewall of the platform.Using the Lagrange multiplier method,the motion equation governing this type of motion characteristic is formulated,and the formula of the extracted wave power is derived.The numerical results demonstrate a significant increase in the hydrodynamic efficiency of oscillating bodies within specific frequency ranges in the presence of the floating platform.The incorporation of proper power take-off damping of the oscillating bodies results in a reduction in the heave motion of the platform,but it may lead to an increase in pitch motion.The analysis of the response behaviour of the system shows that both the heave motion and pitch motion of the platform contribute to the power extraction and relative motion between the buoys and the platform.Parametric investigations are conducted to explore the hydrodynamic interactions between the floating platform and the buoy array.Additionally,the concept of“hydrodynamic synergy”is proposed to describe the synergetic effect of different components of a multi-purpose platform,which is of considerable engineering interest.
基金financially supported by the National Natural Science Foundation of China(Nos.22341304,22303100 and 12205270)the National Key R&D Program of China(Nos.2023YFA1008800 and 2020YFA0713601)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDC0180303)。
文摘The equilibrium dynamics and nonlinear rheology of unentangled polymer blends remain inadequately understood,especially regarding the influence of short-chain matrix length N_(S) on the structure and rheological behavior of dispersed long chains.Using molecular dynamics simulations based on the Kremer-Grest model,we systematically explore the N_(S)-dependence of static conformations,equilibrium dynamics,and nonlinear shear responses in unentangled long-chain/short-chain polymer blends.Our results demonstrate a decoupling between the static and dynamic sensitivity to N_(S):while the static chain size,R_g,follows Flory theory with slight swelling at small N_(S) due to incomplete excluded volume screening,the diffusion coefficient,D,and the relaxation time,τ_(0),exhibit a strong,non-monotonic N_(S)-dependence,transitioning from monomeric friction dominance at small N_(S) to collective segmental rearrangement at large N_(S).Additionally,we observe partial decoupling between the viscous and normal stress responses:while the zero-shear viscosity,η,is strongly N_(S)-dependent,the first and second normal stress coefficients,Ψ_(1) and Ψ_(2),collapse onto universal curves when scaled by the dimensionless shear rate,γτ_(0),suggesting a common mechanism of orientation and stretching.Under shear,long chains compress in the vorticity direction λ_(z)~Wi^(-0.2),which reduces collision frequency and contributes to shear thinning,while the scaling of weaker orientation resistance m_(G)~Wi^(0.35)reflects hydrodynamic screening by the short-chain matrix.These findings highlight the limitations of single-chain models and emphasize the necessity of considering N_(S)-dependent matrix dynamics and flow-induced structural changes in understanding the rheology of unentangled polymer blends.
基金Supported by the Portuguese Foundation for Science and Technology under Grant No.PTDC/ECM/100686/2008
文摘A computer code based on the double-body potential flow model and the classic source panel method has been developed to study various problems of hydrodynamic interaction between ships and other objects with solid boundaries including the seabed. A peculiarity of the proposed implementation is the application of the so-called ＂moving-patch＂ method for simulating steady boundaries of large extensions. The method is based on an assumption that at any moment just the part of the boundary （＂moving patch＂） which lies close to the interacting ship is significant for the near-field interaction. For a specific case of the fiat bottom, comparative computations were performed to determine optimal dimensions of the patch and of the constituting panels based on the trade-off between acceptable accuracy and reasonable efficiency. The method was applied to estimate the sway force on a ship hull moving obliquely across a dredged channel. The method was validated for a case of ship-to-ship interaction when tank data were available. This study also contains a description of a newly developed spline approximation algorithm necessary for creating consistent discretizations of ship hulls with various degrees of refinement.
基金the National Natural Science Foundation of China(Nos.51179019 and 51309152)
文摘A three-dimensional high-order panel method based on non-uniform rational B-spline(NURBS) is developed for predicting the hydrodynamic interaction forces on a moored ship induced by a passing ship in shallow water. An NURBS surface is used to precisely represent the hull geometry. Velocity potential on the hull surface is described by B-spline after the source density distribution on the boundary surface is determined. A collocation approach is applied to the boundary integral equation discretization. Under the assumption of low passing speed, the effect of free surface elevation is neglected in the numerical calculation, and infinite image method is used to deal with the finite water depth effect. The time stepping method is used to solve the velocity potential at each time step. Detailed convergence study with respect to time step, panel size and Green function is undertaken. The present results of hydrodynamic forces are compared with those obtained by slender-body theory to show the validity of the proposed numerical method. Calculations are conducted for different water depths and lateral distances between ships, and the detail results are presented to demonstrate the effects of these factors.
基金supported by the National Natural Science Foundation of China (Grant 11462015)
文摘The propulsive performance of an oblique school of fish is numerically studied using an immersed boundary technique. The effect of the spacing and wiggling phase on the hydrodynamics of the system is investigated. The hydrodynamics of the system is deeply affected by the spacing between each fish in the school. When the horizontal separation is smaller than the length of the fish body, the downstream fish exhibits a larger thrust coefficient and greater propulsive efficiency than the isolated fish. However, the corresponding values for the upstream fish are smaller. The opposite behavior occurs when the horizontal separation increases beyond the length of fish body. The propulsive performance of the entire oblique school of fish can be substantially enhanced when the separations are optimized.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51061130548 and 51179019)
文摘While passing through a lock, a ship usually undergoes a steady forward motion at low speed. Owing to the size restriction of lock chamber, the shallow water and bank effects on the hydrodynamic forces acting on the ship may be remarkable, which may have an adverse effect on navigation safety. However, the complicated hydrodynamics is not yet fully understood. This paper focuses on the hydrodynamic forces acting on a ship passing through a lock. The unsteady viscous flow and hydrodynamic forces are calculated by applying an unsteady RANS code with a RNG k-e turbulence model. User-defined function （UDF） is compiled to define the ship motion. Meanwhile, the grid regeneration is dealt with by using the dynamic mesh method and sliding interface technique. Numerical study is carried out for a bulk carrier ship passing through the Pierre Vandamme Lock in Zeebrugge at the model scale. The proposed method is validated by comparing the numerical results with the data of captive model tests. By analyzing the numerical results obtained at different speeds, water depths and eccentricities, the influences of speed, water depth and eccentricity on the hydrodynamic forces are illustrated. The numerical method proposed in this paper can qualitatively predict the ship-lock hydrodynamic interaction. It can provide certain guidance on the manoeuvring and control of ships passing through a lock.
文摘Dynamics and vibration of control valves under flow-induced vibration are analyzed. Hydrodynamic load characteristics and structural response under flow-induced vibration are mainly influenced by inertia, damping, elastic, geometric characteristics and hydraulic parameters. The purpose of this work is to investigate the dynamic behavior of control valves in the response to self-excited fluid flow. An analytical and numerical method is developed to simulate the dynamic and vibrational behavior of sliding dam valves, in response to flow excitation. In order to demonstrate the effectiveness of proposed model, the simulation results are validated with experimental ones. Finally, to achieve the optimal valve geometry, numerical results for various shapes of valves are compared. Rounded valve with the least amount of flow turbulence obtains lower fluctuations and vibration amplitude compared with the flat and steep valves. Simulation results demonstrate that with the optimal design requirements of valves, vibration amplitude can be reduced by an average to 30%.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51061130548 and 51179019)
文摘An investigation has been conducted to quantify the effect of waterway geometry on the form and magnitude of forces and moment experienced by a berthed ship due to a passing ship.By using the dynamic mesh technique and solving the unsteady RANS equations in conjunction with a RNG k？ε turbulence model,numerical simulation of the three-dimensional unsteady viscous flow around a passing ship and a berthed ship in different waterway geometries is conducted,and the hydrodynamic forces and moment acting on the berthed ship are calculated.The proposed method is verified by comparing the numerical results with existing empirical curves and a selection of results from model scale experiments.The calculated interaction forces and moment are presented for six different waterway geometries.The magnitude of the peak values and the form of the forces and moment on the berthed ship for different cases are investigated to assess the effect of the waterway geometry.The results of present study can provide certain guidance on safe maneuvering of a ship passing by a berthed ship.
基金supports of the National Natural Science Foundation of China(Grant Nos.12304245,12374205,12475031,and 12364029)the Science Foundation of China University of Petroleum,Beijing(Grant Nos.2462023YJRC031 and 2462024BJRC010)+4 种基金the National Key Laboratory of Petroleum Resources and Engineering(Grant No.PRE/DX-2407)the Natural Science Foundation of Shandong Province(Grant No.ZR2024YQ017)the Young Elite Scientist Sponsorship Program by BAST(Grant No.BYESS2023300)the Beijing Institute of Technology Research Fund Program for Young ScholarsThis work was also supported by Beijing National Laboratory for Condensed Matter Physics(Grant Nos.2023BNLCMPKF014 and 2024BNLCMPKF009).
文摘We conduct optical-tweezers experiments to investigate the average potential energies of passive plates harmonically trapped in bacterial suspensions.Our results show that the mean potential energies along both the major and minor axes increase with bacterial concentration but decrease with trap stiffness.Notably,the average potential energy along the major axis consistently exceeds that along the minor axis.This discrepancy from equilibrium systems is primarily attributed to the distinct bacterial flow fields and direct bacterium–plate collisions near the major and minor axes,as evidenced by the higher orientational order around the plate along the major compared to the minor axis,despite identical bacterial densities in these regions.Our findings highlight the critical role of hydrodynamic interactions in determining the potential energy of passive objects immersed in an active bath.
基金supported by the Major Program of the National Natural Science Foundation of China(Grant No.12132015)the National Natural Science Foundation of China(Grant Nos.12202392 and 12372251)the Joint Funds of the National Natural Science Foundation of China(Grant No.U2006221).
文摘This study numerically investigates the locomotion of active matter over a circular cylinder in a confined microchannel.We consider the effects of cylinder size,swimming Reynolds number on the motion characteristic of three kinds of swimmers.The swimmer’s motion over a cylinder in a microchannel can be classified into seven modes.The cylinder diameter and swimming Reynolds number have no impact on the motion mode of neutral swimmers.When approaching the cylinder,pullers mainly perform periodic motion near the left side of cylinder,the pushers primarily perform periodic motion near the right side of cylinder.The mechanism of the periodic motion is mainly induced by the hydrodynamic interaction between the cylinder,channel walls,and the pressure near the swimmer.As cylinder diameter increases,pushers are more likely to exhibit periodic motion on the surface of cylinder than the pullers.Puller is unable to stabilize on the surface of cylinder at low Reynolds number,it migrates to the right side of cylinder at high Reynolds number,showing a pattern opposite to that observed for pushers.The results provide a possible new path for controlling active matter in microfluidic devices.
基金supported by the Science Challenge Project(No.TZ2018004)the National Natural Science Foundation of China(Nos.21790340 and 21674113)+2 种基金Jilin Scientific and Technological Development Program(No.20180519001JH)the Programs of Chinese Academy of Sciences(Nos.QYZDY SSW-SLH027 and YJKYYQ20190084)Y.L.acknowledges the Youth Innovation Promotion Association of Chinese Academy of Sciences(No.2016204)for financial support.
文摘A mesoscopic simulation is applied to investigate the effects of hydrodynamic interactions and axial chains on the dynamics of threaded rings.The hydrodynamic interactions significantly speed up the diffusion and relaxation of both free and threaded rings.The decoupled diffusion and relaxation dynamics indicate the broken of the Einstein-Stokes relationship.The diffusion of a ring threaded on a flexible chain exhibits a synergism effect compared to that on an axial rod,which originates from the self-diffusion of the ring and the reptation-like motion of the axial chain.Meanwhile,hydrodynamic interactions significantly improve the synergism effect,leading to an enhanced sliding motion of the threaded ring.The faster sliding of threaded rings suggests that the entropic barrier is negligible,which agrees well with the basic assumption of barrier-less confining tube at equilibrium in tube theory.Our results provide a new perspective on analysis of the effects of topology constraints on polymer dynamics.
基金supported by the National Basic Research Program of China(2012CB821500 and 2010CB631102)the National Natural Science Foundation of China(21274153)+1 种基金the support of the National Natural Science Foundation of China(21120102037)Computing Center of Jilin Province for essential support
文摘The diffusion behavior of polyelectrolytes in dilute salt-free solution is studied through a hybrid mesoscale simulation technique that combines the molecular dynamics method and the multiparticle collision dynamics approach.To elucidate the effects of hydrodynamic interactions(HI),we compare results for hydrodynamic and random solvents.When HI are taken into account,we find that the chain diffusivity decreases initially and then increases gradually with the increasing strength of the Coulomb interaction.By contrast,when HI are switched off,the electrostatic-dependent diffusivity shows three distinct regions,and a plateau of approximately constant diffusivity manifests between two decreasing regions.The findings reveal that the dynamics of polyelectrolytes in dilute solution depend on the coupling effects of hydrodynamic and Coulomb interactions,and that these dynamics can be understood by considering the conformational changes of chains,the counterion condensation,and the dynamics of counterions.
基金Supported by the China National 111 project under Grant No.B07019Important National Science & Technology Specific Projects under Grant No.2008ZX05-056-03
文摘In order to improve the safety properties of an offloading system with side-by-side （SBS） mooring in which the FPSO is moored by a yoke system in the field of BZ25-1, it is necessary to analyze those properties. According to the experience of similar projects, tow strategies of different offioading arrangements were discussed by using the 3-D radiation/diffraction theory and quasi-static time domain method to assess their respective safety properties. Through the safety assessment analysis of different arrangement comparisons, various ways to improve the safety properties of off＇loading systems with side-by-side mooring were verified by analyzing the tension in the mooring lines and the fender deflection. Through comparison it can be concluded that by enlarging the key factors properly, including the size of the fenders and the hawsers as well as the number of hawsers, a better safety performance can be achieved.
