Effects Of Hydrodynamic Interactions Research Articles

Hydrodynamic Analysis of a Novel Modular Floating Structure System Integrated with Floating Artificial Reefs and Wave Energy Converters

A novel modular floating structure (MFS) system moored by tension legs was proposed, which is composed of hexagonal floating modules, floating artificial reefs and wave energy converters (WECs). The integration of floating artificial reefs and WECs into the MFS can improve the marine environment and produce considerable electricity. The effects of both wave characteristics and the module quantity on the hydrodynamic responses of the MFS system were studied in depth, based on a time-domain numerical model. Both the modules’ hydrodynamic interaction effect and the connectors’ mechanical coupling effect were considered. The results indicate that floating artificial reefs combined with WECs can effectively reduce wave loads and convert wave energy into electricity for the MFS system. More modules involved in the MFS system could significantly reduce motion response and produced more wave energy output, which indicates that the MFS system is suitable for large-scale expansion. The effect of different power take-off (PTO) damping coefficients on the WECs’ performance was further investigated, and the optimal damping coefficient was recommended for the MFS system. Finally, the main extreme responses of the MFS system were further investigated, and its safety was checked thoroughly. One survival strategy was proposed, which could efficiently reduce extreme connector loads by more than 50%.

Hydrodynamic model for renal microvascular filtration: Effects of physiological and hemodynamic changes on glomerular size-selectivity.

The first step in renal urine formation is ultrafiltration across the glomerular barrier. The change in its nanostructure has been associated with nephrotic syndromes. Effects of physiological and hemodynamic factor alterations associated with diabetic nephropathy (DN) on glomerular permselectivity are examined through a mathematical model employing low-Reynolds-number hydrodynamics and hindered transport theory. Glomerular capillaries are represented as networks of cylindrical tubes with multilayered walls. Glomerular basement membrane (GBM) is a fibrous medium with bimodal fiber sizes. Epithelial slit fiber spacing follows a lognormal distribution based on reported electron micrographs with the highest resolution. Endothelial fenestrae are filled with fibers the size of glycosaminoglycans (GAGs). Effects of fiber-macromolecule steric and hydrodynamic interactions are included. Focusing on diabetic nephropathy, the physiological and hemodynamic factors employed in the computation are those reported for healthy humans and patients with early-but-overt diabetic nephropathy. The macromolecule concentration is obtained as a finite element solution of the convection-diffusion equation. Computed sieving coefficients averaged along the capillary length agree well with ficoll sieving coefficients from studies in humans for most solute radii. GBM thickening and the loss of the slit diaphragm hardly affect glomerular permselectivity. GAG volume fraction reduction in the endothelial fenestrae, however, significantly increases macromolecule filtration. Increased renal plasma flow rate (RPF), glomerular hypertension, and reduction of lumen osmotic pressure cause a slight sieving coefficient decrease. These effects are amplified by an increased macromolecule size. Our results indicate that glomerular hypertension and the reduction in the oncotic pressure decreases glomerular macromolecule filtration. Reduction of RPF and changes in the glomerular barrier structure associated with DN, however, increase the solute sieving. Damage to GAGs caused by hyperglycemia is likely to be the most prominent factor affecting glomerular size-selectivity.

On the hydrodynamic mutual interactions among cells for high-throughput microfluidic holographic cyto-tomography

In digital holography (DH) modality for lab on chip application the cells passing through the field of view (FOV) of the microscope can be detected and analyzed even if they are flowing at different depths. In fact, in-focus imaging of each cell can be easily retrieved thanks to the ability of DH to obtain numerical focus ex-post the recording process. An advantageous and preferred configuration for DH in flow-cytometry modality provides that the cells rotate along the microfluidic channel. This gives the unique chance to probing cells by light beams alongside many different directions while they cross the holographic FOV. Thus, it is possible to retrieve the 3D refractive index map of each flowing cell, i.e. a 3D phase-contrast tomogram. Although many cells can be analyzed in the same FOV, thus giving the possibility to increase the throughput of the system, until now no investigations have been made to establish how close the cells can be to avoid mutual disturbing effects on their rotation. Nevertheless, to estimate the maximum achievable throughput, it is indispensable to comprehend the effects of hydrodynamic interactions on adjacent cells in a tomographic flow cytometer. Here we show by means of an experimental and a numerical simulation of the fluid dynamics that hydrodynamic interactions have a quantitative effect on cells rotational behavior and neither on their mechanical deformation. However, in the considered scenario we demonstrate that the effect is negligible as it does not affect the possibility of recovering the tomograms. The reported results will allow to estimate which is the optimum density of cells to analyze by the holographic flow-cyto-tomograph thus opening the route for biomedical applications.

The effect of inter-particle hydrodynamic and magnetic interactions in a magnetorheological fluid

A magnetorheological fluid, which consists of magnetic particles suspended in a viscous fluid, flows freely with well-dispersed particles in the absence of a magnetic field, but particle aggregation results in flow cessation when a field is applied. The mechanism of dynamical arrest is examined by analysing interactions between magnetic particles in a magnetic field subject to a shear flow. An isolated spherical magnetic particle undergoes a transition between a rotating state at low magnetic field and a static orientation at high magnetic field. The effect of interactions for spherical dipolar and polarisable particles with static orientation is examined for an unbounded dilute viscous suspension. There are magnetic interactions due to the magnetic field disturbance at one particle caused by the dipole moment of another, hydrodynamic interactions due to the antisymmetric force moment of a non-rotating particle in a shear flow, and a modification of the magnetic field due to the particle magnetic moment density. When there is a concentration variation, the torque balance condition results in a disturbance to the orientation of the particle magnetic moment. The net force and the drift velocity due to these disturbances is calculated, and the collective motion generated is equivalent to an anisotropic diffusion process. When the magnetic field is in the flow plane, the diffusion coefficients in the two directions perpendicular to the field direction are negative, implying that concentration fluctuations are unstable in these directions. This instability could initiate field-induced dynamical arrest in a magnetorheological fluid.

Brownian dynamics simulations of shear-induced aggregation of charged colloidal particles in the presence of hydrodynamic interactions

HypothesisIn spite of the abundant literature on Brownian simulations of the aggregation behavior of colloidal suspensions both under quiescent conditions and in the presence of shear, few works performed simulations including the effect of hydrodynamic interactions. Even fewer works have investigated the effects of shear on the aggregation of electrostatically-stabilized colloidal suspensions. SimulationsIn this work, we employed Brownian dynamics simulations implementing the Rotne-Prager-Yamakawa approximation to account for hydrodynamic interactions and investigated the aggregation kinetics of electrostatically-stabilized colloidal suspensions exposed to simple shear, for various Péclet number values, particle volume fractions and surface potential values. ResultsThe increase in Péclet number (i.e., in the shear rate), leads to an overall increase in the aggregation rate and the formation of large aggregates that, for sufficiently high volume fractions, rapidly grow, leading to either breakup and restructuring phenomena or percolation of the system. In some cases, a bimodal distribution of the cluster population was observed. Our simulations further indicate that at the highest Péclet, the aggregation dynamics is independent of the energy barrier and entirely controlled by shear. A comparison with a simple BD method reveals that neglecting long-range hydrodynamic interactions leads to a substantial underestimation of the aggregation rate.

Modeling particle-particle binary coagulation rate constants for spherical aerosol particles at high volume fractions using Langevin Dynamics simulations

Effect of volume-fraction and particle-particle hydrodynamic interactions on the coagulation rate of particles are investigated. Particle coagulation is modeled using Langevin Dynamics (LD) based trajectory simulations of N mono-sized spherical particles in a periodic domain. The extended Kirkwood-Risemann approach (J. Fluid Mechanics 855, 535 (2018)) is invoked to compute particle-particle hydrodynamic interactions whose effect is parameterized as a function of the momentum Knudsen number (Kn). The results are summarized as a model for coagulation rate constant (βij) that depends on the diffusive Knudsen number (KnD) used in prior work to parameterize coagulation in the dilute regime (Aerosol Sci. Tech. 45, 1499 (2011)), Kn and particle volume-fraction ηv. In the absence of hydrodynamic interactions, it is observed that the coagulation rate constant in the continuum limit for mass transfer (KnD→0) is significantly enhanced by a factor of ∼80 at ηv∼0.3 due to particle crowding. While considering hydrodynamic interactions for ηv≥0.05, we use a screening distance around each particle that scales inversely with ηv beyond which the contribution of farther neighbors is neglected owing to the rapid decay of hydrodynamic interactions with distance. We also present new LD calculations of βij and elucidate the dependence of the same on Kn1 and the particle radii ratio θr for the coagulation of two particles in the dilute limit ηv→0. It is observed that the reduction of βij becomes significant as Kn1→0: at the lowest momentum Knudsen number considered (Kn1=0.1): βij is reduced by a factor of ∼10 for equally sized particles (θr=0.5). At high KnD,Kn1, the particle size disparity is not significant, and it is seen that βij matches hard sphere predictions, indicating the insignificant contributions by hydrodynamic interactions. A series of animations of 2-particle simulations are presented as part of the Supplemental Information to illustrate the role of hydrodynamic interactions in particle coagulation. Computational results are summarized as regressions for convenient incorporation into particle/droplet growth sectional models.

Two-dimensional hydrodynamic schooling of two flapping swimmers initially in tandem formation

The effect of hydrodynamic interactions on the collective locomotion of fish schools is still poorly understood. In this paper, the flow-mediated organization of two tandem flapping foils, which are free in both the longitudinal and lateral directions, is numerically studied. It is found that the tandem formation is unstable for two foils when they can self-propel in both the longitudinal and lateral directions. Three types of resultant regular formations are observed, i.e. semi-tandem formation, staggered formation and transitional formation. Which type of regular formation occurs depends on the flapping parameters and the initial longitudinal distance between the two foils. Moreover, there is a threshold value of the cycle-averaged longitudinal distance (which is approximately 0.55) below which both velocity enhancement and efficiency augmentation can be achieved by two foils in regular formations. The results obtained here may shed some light on understanding the emergence of regular formations of fish schools.

Hydrodynamic interaction of floating bridge pontoons and its effect on the bridge dynamic responses

As pontoons of floating bridges respond to the dynamic actions of the wind and wave loading, additional forces are imposed on the pontoons due to the hydrodynamic interaction of these floating bodies. The wave forces on a selected pontoon and consequently its motion are affected by the presence and motion of adjacent pontoons through the motion of the fluid between the bodies. Here, we investigate the effect of such interactions on the global bridge dynamic responses. The hydrodynamic interaction effects are modeled using multibody potential theory with added artificial damping. The stochastic dynamic analyses of the bridge in the frequency-domain under combined wind and wave excitation revealed significant differences in the girder section forces when the interaction effects were included. The results imply that the hydrodynamic interaction effects should be considered in the design of such structures. The methodology presented here provides practical means for the analytical assessment of such effects.

Passive hydrodynamic interactions in minimal fish schools

It is a long-held perception that schooling swimming of fish can provide individuals in a group with additional hydrodynamic benefits. However how fish maintain a stable schooling formation, and the underlying interaction bases, are still unknown. This study aims to investigate effects of pure passive hydrodynamic interactions on schooling swimming and deal with whether fish can solely rely on the interactions to maintain a stable formation. The study is a pure numerical investigation based on a two-dimensional 3-DoF self-propelled model. Three two-fish formations, namely, tandem, side-by-side, and staggered formation, are investigated to explore the effects of the interactions. The study presents that the passive interactions do bring performance benefits to individuals, but swimmers cannot maintain the benefits for a long time when only relying on the pure passive interactions. The work also discusses different effects induced by the hydrodynamic interactions in some detail, including effects of deflection, wake, phase, attraction and repulsion. Essentially the hydrodynamic effects can be explained by considering time-varying pressure field. Due to the effects, a small disturbance or unbalanced moment may cause a large difference in the swimming directions of individuals in a group. The findings could offer some insights into understanding the schooling swimming mechanism.

Hydrodynamic resolved simulation of a char particle combustion by immersed boundary-lattice Boltzmann method

A Lattice-Boltzmann model coupled with boundary method is proposed for the hydrodynamic resolved simulation of a single char particle combustion. A pure lattice Boltzmann scheme with multi distribution functions is presented for this low Mach reactive flows. Real varying thermodynamic and transport properties are considered, and the fluid density can bear significant change depending on the varying temperature and species concentrations. The recently proposed boundary-thickening based direct forcing-immersed boundary method is extended to implement the boundary conditions of velocity, temperature, and species concentrations at the char particle surface. Two heterogeneous reactions at particle surface and one homogeneous reaction in fluid are adopted to describe the combustion. The Stefan flow near the particle surface caused by the heterogeneous reactions is also considered. A satisfactory agreement can be found between the present simulation results and the previous experimental and numerical results. Three flame modes of a char particle combustion and the transition mechanisms between them are investigated. Furthermore, the effect of hydrodynamic interaction and the oxygen concentration in O2/CO2 atmosphere on particle combustion behavior are explored in detail. The present work establishes the foundation for the efficient simulations of particle combustion with size change and motion.

General rigid bead-rod theory with hydrodynamic interaction for polymer viscoelasticity

General rigid bead-rod theory is actively used for connecting the complex viscosity of polymeric liquids to the structure of macromolecules. Using general rigid bead-rod theory, the rheological properties of polymeric liquids have been investigated theoretically and applied practically. In this paper, we include the hydrodynamic interaction of the nearest neighboring beads into general rigid bead-rod theory. By applying our new method, structure by structure, to backbone branched macromolecular configurations, we investigate the interplay of hydrodynamic interaction with the number of branches, branch length, and branch positions. We learn that the effect of hydrodynamic interaction is greater in branched macromolecules than in unbranched. In the future, this method will play an important role in the study of the rheological properties of polymeric liquids, wherever hydrodynamic interaction matters.

Hydrodynamics induce superdiffusive jumps of passive tracers along critical paths of random networks and colloidal gels.

We present a numerical study on the effect of hydrodynamic interactions (HI) on the diffusion of inert point tracer particles in several fixed random structures. As expected, the diffusion is hampered by the extra hydrodynamic friction introduced by the obstacle network. However, a non-trivial effect due to HI appears in the analysis of the van-Hove displacement probability close to the percolation threshold, where tracers diffuse through critical fractal paths. We show that the tracer dynamics can be split up into short and long jumps, the latter being ruled by either exponential or Gaussian van Hove distribution tails. While at short time HI slow down the tracer diffusion, at long times, hydrodynamic interactions with the obstacles increase the probability of longer jumps, which circumvent the traps of the labyrinth more easily. Notably, the relation between the anomalous diffusion exponent and the fractal dimension of the critical (intricate) paths is greater than one, which implies that the long-time (long-jump) diffusion is mildly superdiffuse. A possible reason for such a hastening of the diffusion along the network corridors is the hydrodynamically induced mobility anisotropy, which favours displacements parallel to the walls, an effect which has already been experimentally observed in collagen gels.

INTERNATIONAL DEVELOPMENT AND VALIDATION OF A DISTRIBUTED SIMULATION FOR NAVAL SHIP REPLENISHMENT AT SEA

Navies from Canada, France, Germany, Italy, and the United Kingdom collaborated to develop and validate a distributed simulation of ship replenishment at sea. The simulation models the seaway, ship motions including hydrodynamic interaction effects between ships, and the transfer of a solid payload between ships using replenishment gear. The simulation was developed using the High Level Architecture (HLA), which facilitates sharing of data and synchronization of simulation time among software components on networked computers. Simulation results were validated using experimental data. The project demonstrated successful application of distributed simulation to complex naval platform systems. Lessons learned are shared for several areas, including seaway modelling, ship hydrodynamic interaction, and planning of model tests and sea trials for simulation validation.

Effects of Gap Resonance on the Hydrodynamics and Dynamics of a Multi-Module Floating System with Narrow Gaps

Multi-module floating system has attracted much attention in recent years as ocean space utilization becomes more demanding. This type of structural system has potential applications in the design and construction of floating piers, floating airports and Mobile Offshore Bases (MOBs) generally consists of multiple modules with narrow gaps in which hydrodynamic interactions play a non-neglected role. This study considers a numerical model consisting of several rectangular modules to study the hydrodynamics and dynamics of the multi-module floating system subjected to the waves. Based on ANSYS-AQWA, both frequency-domain and time-domain simulations are performed to analyze the complex multi-body hydrodynamic interactions by introducing artificial damping on the gap surfaces. Parametric studies are carried out to investigate the effects of the gap width, shielding effects of the multi-body system, artificial damping ratio on the gap surface, and the dependency of the hydrodynamic interaction effect on wave headings is clarified. Based on the results, it is found that the numerical analysis based on the potential flow theory with artificial damping introduced can produce accurate results for the normal wave period range. In addition, the effects of artificial damping on the dynamics and connector loads are investigated by using a simplified RMFC model. For the case of adding an artificial damping ratio of 0.2, the relative heave and pitch motions are found to be reduced by 33% and 50%, respectively. In addition, the maximum cable and fender forces are found to be reduced by 50%, compared with the case without viscosity correction.

Study of temperature influence on the rheological behavior of magnetic fluids

The influence of temperature on the inertial structures in magnetic fluid was previously assumed to be based on a single mechanism. In this work, specialized rheological experiments were performed and their results have shown that different structural evolution paths can take place under the function of hydrodynamic and thermal interaction. The widely adopted Mason number was proved to be unsuitable to describe the magnetoviscous effect of magnetic fluids under different temperatures. To give a proper description on the combined effect of magnetic dipolar interaction, hydrodynamic interaction and thermal interaction in magnetic colloidal system, a novel structural number S was proposed and found to be applicable to superimposed the data under various temperatures onto a master curves.

Investigation on the damping of rectangular water tank with bottom-mounted vertical baffles: Hydrodynamic interaction and frequency reduction effect

Internal obstructions are commonly employed in Tuned Liquid Damper (TLD) tanks to produce sufficient inherent damping for improving its vibration control performance. However, the hydrodynamic interaction between obstacles has a significant effect on damping ratio of liquid sloshing when the obstacles are becoming close to each other. At the same time, the natural sloshing frequency of the water tank decreases because of the added mass produced by these obstacles. By adopting potential flow and linear wave theory, a linearized analysis model is proposed in this paper to estimate the damping ratio of rectangular water tank with bottom-mounted vertical baffles. The formula of its damping ratio is then further modified to take into account the effect of hydrodynamic interaction between vertical baffles on the fluid velocity and the added mass coefficient. In this study, reduction in the natural frequency of liquid sloshing due to vertical baffles is also investigated in detail. Shaking table tests were conducted on scaled models of the rectangular tank with bottom-mounted vertical baffles to validate the accuracy of the proposed analytical model in this study. Parametric studies are performed to study the effect of the distance between vertical baffles, different water depth ratios, various sinusoidal excitation amplitudes, and the different number of bottom-mounted vertical baffles on the damping ratio. The analyzed results showed that good agreement between the proposed analytical solutions and the experimental results was found. The study also showed that the proposed methodology can effectively estimate the damping ratio by considering the hydrodynamic interaction and natural frequency reduction effect due to the installed bottom mounted vertical baffles.

Homogeneous Wave Load Effects on the Connections of Main Parts of Side-Anchored Straight Floating Bridge

In this paper, a numerical study is presented to investigate wave force on the connections of main parts of a side-anchored straight floating bridge concept for the Bjørnafjorden fjord crossing. The floating bridge is supported by 18 pontoons, and three groups of mooring lines are employed to restrain the bridge against horizontal loads and increase its transverse stiffness. The created wave forces at the connections of pontoon-column and column-girder of the floating bridge considering the effects of short-crested and long-crested waves, varying wave direction, hydrodynamic interaction between pontoons, and mooring system are analyzed. It is found that short-crested and long-crested waves depending on their direction decrease or increase the wave forces on the joints. Considering that the effect of hydrodynamic interaction between pontoons can increase or reduce the wave forces and moments created in the joints, which means the neglect of the hydrodynamic interaction effects between the pontoons to simplify the modeling of this type of floating bridge, may be unacceptable. Moreover, the results showed that the bridge mooring system does not merely reduce the wave forces and moments at joints along the bridge.

An optimal thrust allocation algorithm with bivariate thrust efficiency function considering hydrodynamic interactions

Thrust allocation is of great importance for the application of Dynamic Positioning System (DPS). For dynamically positioned vessels, the thrust allocation is formulated as a nonlinear optimization problem, where the demanded forces and moments are distributed among the available thrusters. Both hydrodynamic interaction effects and physical limitations of thrusters affect the thrust generation. Therefore, the thrust allocation algorithm can be improved if these effects are considered. We propose a bivariate thrust efficiency function, dealing with both the forward thruster angle and the rear thruster angle, to describe the thrust loss. The thrust efficiency function is obtained from the model tests and approximated by the Radial Basis Function (RBF) neural network. The consequent thrust allocation problem is solved by the Sequential Quadratic Programming (SQP) algorithm with slack variables. The numerical simulations demonstrate a maximum power reduction of 16.03% compared with the forbidden zone algorithm. The proposed algorithm can also enhance system stability, highlighting the advantages of taking bivariate thrust efficiency function into account.

Hydrodynamic Analysis of a Modular Floating Structure with Tension-Leg Platforms and Wave Energy Converters

This work presents a modular floating structure, which consists of five inner tension-leg platforms and two outermost wave energy converters (denoted as MTLPW). The hydrodynamic interaction effect and the mechanical coupling effect between the five inner tension-leg platforms (TLP) and the two outermost wave energy converters (WEC) are taken into consideration. The effects of the connection modes and power take-off (PTO) parameters of the WECs on the hydrodynamic performance of the MTLPW system are investigated under both operational and extreme sea conditions. The results indicate that the hydrodynamic responses of the MTLPW system are sensitive to the connection type of the outermost WECs. The extreme responses of the bending moment of connectors depend on the number of continuously fixed modules. By properly utilizing hinge-type connectors to optimize the connection mode for the MTLPW system, the effect of more inner TLP modules on the hydrodynamic responses of the MTLPW system can be limited to be acceptable. Therefore, the MTLPW system can be potentially expanded to a large degree.

Diffusion of nano-rods

Diffusion behaviors in nano-rods suspension in the fluid are investigated by Stochastic Eulerian Lagrangian Methods, where the degrees of freedom for coarse-grained microstructure are coupled with continuum stochastic field to capture both the relaxation of hydrodynamic modes and thermal fluctuations. The diffusion characteristics of a single rod and multi-rods are examined with hydrodynamic interaction in three dimensions. For a single rod, the mean square displacement is verified by comparing with prior experimental results. The effects of hydrodynamic interactions on the translational and rotational diffusivity with different aspect ratios are represented by velocity auto-correlation function and the orientational auto-correlation functions. For multi-rods cases, we obtained their diffusion in the ballistic and the short-time regime. The comparison between the SELM and the Langevin method confirms the hydrodynamic effect.