Hydrodynamic Interactions of Three Barges in Close Proximity in A Floatover Installation

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.

Numerical and Experimental Investigation of Hydrodynamic Interactions of Two VLFS Modules Deployed in Tandem

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.

Hydrodynamic interactions between two bodies in waves in 3D time domain

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.

HYDRODYNAMIC INTERACTIONS BETWEEN TWO BODIES

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.

Role of Hydrodynamic Interactions in the Deformation of Star Polymers in Poiseuille Flow

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.

The hydrodynamic interactions of an array of truncated circular cylinders as each cylinder oscillates independently with different prescribed modes

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.

Computation of Ship Hydrodynamic Interaction Forces in Restricted Waters using Potential Theory

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.

Hydrodynamic studies on two wiggling hydrofoils in an oblique arrangement

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.

Numerical Prediction of Hydrodynamic Forces on A Ship Passing Through A Lock

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.

Modeling of fluid-induced vibrations and identification of hydrodynamic forces on flow control valves

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%.

Numerical Prediction of Hydrodynamic Forces on A Berthed Ship Induced by A Passing Ship in Different Waterway Geometries

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.

Multi-Objective Optimal Design of the Wind-Wave Hybrid Platform with the Coupling Interaction

An offshore wind-wave hybrid platform could consistently and cost-effectively supply renewable power.A multi-objective optimization process is proposed for a hybrid platform with hydrodynamic coupling interaction.The effects of various critical structural parameters,spacing values,and wave directions are studied for higher energy capture and offshore platform stability.Approximation models of various key parameters are established to optimize the hybrid system,with the objects of the power capture width ratio and the stability index of the platform.The optimization results are affected by the hydrodynamic coupling interaction,with a tendency to affect the higher frequency of hydrodynamic performance in the hybrid system.After the optimization,an appropriate spacing value effectively improves energy capture performance.The optimal array distance D_(Ff),D_(Fp),the optimal structural parameters R_(p),r_(p),d_(f),r_(f),and B_(PTO)are 11.57,12.75,5.1,3.3,1.5,6.5 m,and 80436 Nm s^(-1),respectively.The peak value of the wave energy converter capture width ratio in the hybrid system increases by almost 50%,with a 54%decrease in the stability index.

Diffusion behavior of polyelectrolytes in dilute solution: coupling effects of hydrodynamic and Coulomb interactions

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.

Safety Assessment for a Side-by-side Offloading Mooring System

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.

Numerical study on wave loads and motions of two ships advancing in waves by using three-dimensional translating-pulsating source

A frequency domain analysis method based on the three-dimensional translating-pulsating （3DTP） source Green function is developed to investigate wave loads and free motions of two ships advancing on parallel course in waves. Two experiments are carried out respectively to mea- sure the wave loads and the free motions for a pair of side-by- side arranged ship models advancing with an identical speed in head regular waves. For comparison, each model is also tested alone. Predictions obtained by the present solution are found in favorable agreement with the model tests and are more accurate than the traditional method based on the three dimensional pulsating （3DP） source Green function. Numer- ical resonances and peak shift can be found in the 3DP pre- dictions, which result from the wave energy trapped in the gap between two ships and the extremely inhomogeneous wave load distribution on each hull. However, they can be eliminated by 3DTP, in which the speed affects the free sur- face and most of the wave energy can be escaped from the gap. Both the experiment and the present prediction show that hydrodynamic interaction effects on wave loads and free motions are significant. The present solver may serve as a validated tool to predict wave loads and motions of two ves- sels under replenishment at sea, and may help to evaluate the hydrodynamic interaction effects on the ships safety in replenishment operation.

Interaction Between Waves and An Array of Floating Porous Circular Cylinders

The present study theoretically as well as experimentally investigates the interaction between waves and an array of porous circular cylinders with or without an inner porous plate based on the linear wave theory. To design more effective floating breakwaters, the transmission rate of waves propagating through the array is evaluated. Each cylinder in the array is partly made of porous materials. Specifically, it possesses a porous sidewall and an impermeable bottom. In addition, an inner porous plate is horizontally fixed inside the cylinders. It dissipates the wave more effectively and eliminates the sloshing phenomenon. The approach suggested by Kagemoto and Yue （1986） is adopted to solve the multiple-scatter problem, while a hierarchical interaction theory is adopted to deal with hydrodynamic interactions among a great number of bodies, which efficiently saves computation time. Meanwhile, a series of model tests with an array of porous cylinders is performed in a wave basin to validate the theoretical work and the calculated results. The draft of the cylinders, the location of the inner porous plate, and the spacing between adjacent cylinders are also adjusted to investigate their effects on wave dissipation.

Brownian dynamics simulation of two confined colloidal particles

The dynamics of two confined colloidal particles is studied by means of Brownian dynamics simulation. The autocorrelation function and cross-correlation function of the two colloidal spheres are computed by utilizing the formulae of hydrodynamic diffusion matrix expanded to different orders, as well as the accurate tensor through numerical algorithm. Furthermore, the numerical results are compared with the experimental results and the theoretical approximation. It is found that the relatively simple theoretical approximation gives good predictions when two spheres are far away from each other, but fails when the two spheres are very close.

Material Selection for Hawsers for a Side-by-side Offloading System

In order to provide a theoretical guide for choosing the material for the hawsers for the FPSO side-by-side offloading system, which is moored by the yoke system, the 3D potential flow theory and full coupled time-domain analysis are presented to study the dynamic response of the offloading system. The MingZhu FPSO offloading system in the field BZ25-1 is simulated here; and four different characteristic fiber ropes are used as the material for the hawsers. To acquire an accurate hawser line tension, the polynomial fitting method is used to calculate the nonlinear stiffness of the hawsers. By comparing the hawser lines＇ tension and the relative motion between the FPSO and the shuttle tanker, a suitable material for the hawser lines is chosen and discussed in this paper. The results indicate that the nonlinear stiffness characteristic of the fiber rope has a small effect on the relative motion of the vessels, but the hawser lines＇ tension is greatly influenced by the different characteristics of the fiber ropes. The hawser lines＇ tension with nonlinear stiffness is in accordance with the one with the upper and lower bound linear stiffness, which proves this method of fitting the fiber ropes＇ nonlinear stiffness is reasonable and reliable.

Nondriven Polymer Translocation Through a Nanopore: Scaling for Translocation Time with Chain Length

We investigated the dynamics of the passage for a polymer chain through a nanopore in the absence of any external driving force with Weeks-Chandler-Andersen potential in two-dimensional simulations, in particular, focused our attention on the scaling law of the mean translocation time. We found that the effect of hydrodynamic interactions is the major factor in determining the scaling exponents with increasing pore size. The scaling close to N1＋2v was observed when the hydrodynamic interactions were screened in the cases of small pore sizes, while the scaling close to N3v was obtained when the hydrodynamic interactions were present in the cases of large pore sizes.

Stability of Couette flow past a gel film

We study instability of a Newtonian Couette flow past a gel-like film in the limit of vanishing Reynolds number. Three models are explored including one hyperelastic（neo-Hookean） solid, and two viscoelastic（Kelvin–Voigt and Zener） solids. Instead of using the conventional Lagrangian description in the solid phase for solving the displacement field, we construct equivalent ‘‘differential＇＇ models in an Eulerian reference frame, and solve for the velocity, pressure, and stress in both fluid and solid phases simultaneously. We find the interfacial instability is driven by the first-normal stress difference in the basestate solution in both hyperelastic and viscoelastic models. For the neo-Hookean solid, when subjected to a shear flow, the interface exhibits a short-wave（finite-wavelength） instability when the film is thin（thick）. In the Kelvin–Voigt and Zener solids where viscous effects are incorporated, instability growth is enhanced at small wavenumber but suppressed at large wavenumber, leading to a dominant finitewavelength instability. In addition, adding surface tension effectively stabilizes the interface to sustain fluid shear.