Hydrodynamic Interaction Forces Research Articles

Unmanned Underwater Vehicle Autonomy and Control near Submarines Using Actively Sampled Surrogates

Many tools have been developed to simulate unmanned underwater vehicle (UUV) motion and autonomous behaviors to evaluate UUV capabilities. However, there is no simulator that performs real-time modeling of the complex hydrodynamic interaction forces that a UUV experiences when operating near a moving submarine. These hydrodynamic interactions must be determined in real time to simulate the launch and recovery of UUVs from submarines. Potential flow models may be fast enough to solve the hydrodynamic interactions in real time, but by oversimplifying the physics and neglecting viscosity, they introduce inaccuracies into the simulations. Computational fluid dynamics (CFD) is capable of accurately modeling these hydrodynamic interactions, but simulations take hours or days to solve. To overcome this obstacle, a machine learning method known as Gaussian process (GP) regression is used to create a surrogate reduced-order-model that predicts the hydrodynamic interactions in real time. The GP regression model is trained by actively sampling CFD simulations in order to accurately model complex hydrodynamic interactions. This new approach allows the GP regression model to be incorporated into a UUV motion simulator and evaluate how the UUV is affected by the hydrodynamic interactions. Operating envelopes are developed that outline regions where the UUV safely overcomes the hydrodynamic interactions and where the UUV is overpowered and collides with the submarine. By incorporating this surrogate model into the autonomy architecture, new autonomous behaviors are created that compensate for the hydrodynamic interactions by adjusting the desired UUV heading and speed which allows it to better stay on course.

Reduced order modeling of hydrodynamic interactions between a submarine and unmanned underwater vehicle using non-myopic multi-fidelity active learning

Several efforts have been dedicated to developing computational tools capable of predicting the hydrodynamic forces and moments of Unmanned Underwater Vehicles (UUVs). However, there is no method at the moment that allows for real-time computational modeling of all the complex hydrodynamic interaction forces and moments that a UUV experiences when operating in close proximity to a moving submarine. Real-time modeling of these hydrodynamic interactions is essential to simulate the motion required to launch and recover UUVs from submarines. Potential flow models are often fast enough to be used in real time, but lack the accuracy of Computational Fluid Dynamics (CFD) simulations, which often take hours or days to solve. Here, we formulate the problem in the context of machine learning, specifically active learning. The goal is to develop a surrogate model capable of predicting the UUV and submarine hydrodynamic interactions in real time using a very small number of carefully selected CFD simulations. We introduce a new active learning framework called Non-Myopic Multi-Fidelity Active Learning for Gaussian Process (GP) regression that accelerates the convergence of the surrogate model by utilizing the low cost of the low fidelity simulations to explore the domain, as well as optimally selected high fidelity simulations to improve the model accuracy. The resulting surrogate model can be integrated into UUV control and autonomy systems and motion simulators to further enable UUV launch and recovery from submarines. This new active learning method may also be used to create higher accuracy and lower cost surrogate models in other real world applications.

Numerical Analysis of Propeller-Induced Hydrodynamic Interaction between Ships

The hydrodynamic interaction effects between ships are significantly pronounced in restricted waters, and this may potentially threaten the safety of ships, especially given that ship dimensions and waterway traffic have kept increasing. Although there has been a good amount of research on ship hydrodynamic interactions, the study of the effect of the propeller on the ship’s hydrodynamic interaction is very limited. In this paper, a series of RANSE-based numerical simulations are carried out to study the characteristics of the propeller in near-field interaction between ships without speed. The hydrodynamic forces and moment acting on the ship are calculated and analyzed. Through the analysis of the characteristics of the flow field and the behavioral pattern of the hydrodynamic forces, it is found that the propeller has a significant influence on the pressure distribution on the hull as well as on the hydrodynamic interaction forces. The maximum lateral force acting on the interacting ship could reach 0.58 times the standard thrust of a KP458 propeller (the revolution is 594 rpm and the velocity coefficient is 0.25 in open water).

A numerical study on the ship-bank interaction at various water depths of a surface ship.

Ship maneuvering in restricted waters is a significant challenge in navigation safety due to the complex flow around the ship. In particular, when a ship travels close to a lateral bank and shallow water, the hydrodynamic interaction forces significantly influence the maneuvering motion of the ship. Maneuverability in restricted water is even more difficult for an autonomous surface ship. Therefore, it is necessary to assess the effects of maneuvering near a bank and in shallow water for an autonomous surface ship. In this study, maneuvering simulations considering the bank effect at various water depths are implemented based on hydrodynamic forces estimated using computational fluid dynamics simulation. First, virtual captive model tests at various water depths and simulations of various lateral distances to the banks are performed to estimate the hydrodynamic forces using computational fluid dynamics simulation. The simulation method is validated by comparing the simulation results of the static drift test in deep water with the measured one in the experimental method. Second, the maneuvering simulations for the turning circle test and zig-zag test at various water depths are conducted using the obtained hydrodynamic coefficients. Then, the maneuvering simulations in deep water are compared with the experiment results, and a good agreement is observed. Finally, the simulation considering the bank effects at various water depths is evaluated and discussed.

Hydrodynamic interaction forces on different ship types under various operating conditions in restricted waters

To accurately understand the behavior of ships sailing in restricted waterways, it is necessary to scientifically analyze the influence of the bank effect on the hydrodynamic force of a ship. In this study, the water depth to draft ratio, distance between the wall and ship, speed of the ship, and loading condition are classified as factors influencing the confined water effect. Numerical analyses were performed on two different very large vessels to investigate the effects of the factors on hydrodynamic interaction using CFD. The sway force was gradually decreased as the water became shallower. The sway force acted on the container ship as a repulsion force in the very shallow water. The roll and yaw moments acted as the greatest hydrodynamic forces in the very shallow water. For the tanker, the direction of the yaw moment changed to bow-in as the speed increased. The effect of hydrodynamic force on the vessel is different depending on the loading condition, navigation area, and speed of the vessel. Comprehensive considerations and countermeasures according to ship type must be prepared to ensure the safe navigation of ships.

Research on accurate modeling of hydrodynamic interaction forces on AUVs operating in tandem

The hydrodynamic interaction force between autonomous underwater vehicles (AUVs) operating in tandem can adversely affect the hydrodynamic prediction of individual AUVs and the formation control of the tandem fleet. Accurate modeling of hydrodynamic interaction forces is crucial to the model-based controller design of AUVs. In this paper, we innovatively propose a modeling method that can describe the hydrodynamic interaction relationship accurately and continuously (when the spacing between adjacent AUVs changes). First, an accurate hydrodynamic model for individual AUVs in tandem fleets is established by modifying the typical model through the consideration of memory effects. Second, a model of hydrodynamic interaction forces is derived by subtracting hydrodynamic forces acting on a single AUV operating independently from those acting on an AUV operating in tandem. To enable this model to continuously describe the hydrodynamic interaction relationship when the spacing changes, this model is further derived by taking the spacing as an independent variable based on the parameter conversion method. Finally, planar motion mechanism (PMM) tests are carried out using the computational fluid dynamics (CFD) method to verify the accuracy and continuity of the proposed modeling method. The results show that compared with the typical model, the average error of hydrodynamic forces predicted by the proposed model is reduced by 5.36%, which verifies the feasibility and effectiveness of the proposed modeling method.

Model development of tangential hydrodynamic force on particles with pendular liquid bridge of power-law fluid

In this study, new models are proposed for hydrodynamic interaction forces acting on particles through a pendular liquid bridge. The liquid considered is a power-law fluid, and the tangential forces due to both translational and rotational motions of particles are independently modelled, which can be superposed as long as the Reynolds number is sufficiently small. The force models are derived by obtaining improved expressions for the pressure profile inside a liquid bridge which can be reduced to the solutions of the pressure equations based on the lubrication theory in the limiting cases. Direct Numerical Simulation (DNS) is also performed to provide reference data to compare. The forces obtained from the proposed model and DNS are in reasonable agreement compared to the model in the literature where significant overestimation can be seen especially when the power-law index is small. Furthermore, the models proposed are written in a closed-form and can be easily implemented in Discrete Element Method (DEM) for wet particle simulation in the future. • New models of tangential hydrodynamic forces on particles are developed. • The models consider a pendular liquid bridge of power-law fluid between particles. • Good agreement between the model developed and DNS are observed. • The models are written in a closed-form and can be easily implemented in DEM.

Investigation on collision-coalescence of droplets under the synergistic effect of charge and sound waves: orthogonal design optimization

As an efficient approach to improve visibility, defogging technology is essential for the operation of ports and airports. This paper proposes a new and hybrid defogging technology, i.e. an electric–acoustic defogging method. Specifically, the droplets are charged by corona discharge, which is beneficial to overcome the hydrodynamic interaction force to improve the droplet collision efficiency. Meanwhile, sound waves (especially acoustic turbulence) promote the relative movement of droplets to increase the collision probability. In this study, the effects of acoustic frequency (f), sound pressure level (SPL), and voltage (V) on the droplet growth ratio were studied by orthogonal design analysis. The results of difference analysis and multi-factor variance analysis show that frequency and SPL are the dominant factors that affect the collision of droplets, and the effect of voltage is relatively weak. And f= 400 Hz, SPL = 132 dB, and V = −7.2 kV are the optimal parameters in our experiment. In addition, we further studied the impact of single factor on droplet growth ratio. The results show that there exists an experimental optimal frequency of 400 Hz. The droplet growth ratio increases with SPL and voltage level. The new technology proposed in this paper can provide a new approach for defogging in open space.

Theoretical approximation of hydrodynamic and fiber-fiber interaction forces for macroscopic simulations of polymer flow process with fiber orientation tensors

Flow processes of discontinuous fiber reinforced polymers (FRPs) are the essence of several polymer-based manufacturing processes. FRPs show a transient chemo-thermomechanical matrix behavior and fiber-induced anisotropic physical properties. Therefore, they are one of the most complex materials used in volume production. The general flow behavior is influenced by fibers and their interactions with the matrix and other fibers. The consideration of individual fibers is numerically not capable for process simulation of FRP parts. Therefore, orientation tensors are used in macroscopic simulations, leading to a loss of information about the fiber network. Within this work, novel approximation schemes are presented to determine hydrodynamic and fiber-fiber contact forces with information provided by the second order fiber orientation tensor. Approximation of these forces can henceforth facilitate fiber breakage modeling in macroscopic process simulations. The results are verified by numerical simulations with individual fibers of different orientation states and lengths, showing good agreement with the verification results.

Experimental and CFD investigation of the effects of a high-speed passing ship on a moored container ship

The effects of a high-speed frigate model passing close to a moored container model alongside a closed quay are experimentally and numerically investigated with a focus on ship-generated waves, transient ship motions, and hydrodynamic forces acting on the moored ship. Scaled model experiments are conducted to investigate the hydrodynamic interactions between the passing ship-generated waves and the moored ship. A RANS-based CFD method is applied to solve the hydrodynamic problem including the effect of the free surface. The overset mesh technique is adopted to simulate the relative movements between the two vessels. The numerical method is compared with experimental results for the ship-generated waves and total resistance in open water, then validated for the passing ship problem in restricted water. Numerical simulations are carried out to study the effect of different parameters on the passing ship effects. Results show that water depth, passing speed, and separation distance are important parameters that influence the transient interaction. The shape of hydrodynamic interaction forces and moments on the moored ship at relatively high speeds is different from the well-known behaviour at slow speeds. In practice, the most effective measure to reduce the effects of passing ship is to control the speed of the passing ship.

A Fast Algorithm for the Prediction of Ship-Bank Interaction in Shallow Water

The hydrodynamic interaction induced by the complex flow around a ship maneuvering in restricted waters has a significant influence on navigation safety. In particular, when a ship moves in the vicinity of a bank, the hydrodynamic interaction forces caused by the bank effect can significantly affect the ship’s maneuverability. An efficient algorithm integrated in onboard systems or simulators for capturing the bank effect with fair accuracy would benefit navigation safety. In this study, an algorithm based on the potential-flow theory is presented for efficient calculation of ship-bank hydrodynamic interaction forces. Under the low Froude number assumption, the free surface boundary condition is approximated using the double-body model. A layer of sources is dynamically distributed on part of the seabed and bank in the vicinity of the ship to model the boundary conditions. The sinkage and trim are iteratively solved via hydrostatic balance, and the importance of including sinkage and trim is investigated. To validate the numerical method, a series of simulations with various configurations are carried out, and the results are compared with experiment and numerical results obtained with RANSE-based and Rankine source methods. The comparison and analysis show the accuracy of the method proposed in this paper satisfactory except for extreme shallow water cases.

Experimental Validation of a Direct Fiber Model for Orientation Prediction

Predicting the fiber orientation of reinforced molded components is required to improve their performance and safety. Continuum-based models for fiber orientation are computationally very efficient; however, they lack in a linked theory between fiber attrition, fiber–matrix separation and fiber alignment. This work, therefore, employs a particle level simulation which was used to simulate the fiber orientation evolution within a sliding plate rheometer. In the model, each fiber is accounted for and represented as a chain of linked rigid segments. Fibers experience hydrodynamic forces, elastic forces, and interaction forces. To validate this fundamental modeling approach, injection and compression molded reinforced polypropylene samples were subjected to a simple shear flow using a sliding plate rheometer. Microcomputed tomography was used to measure the orientation tensor up to 60 shear strain units. The fully characterized microstructure at zero shear strain was used to reproduce the initial conditions in the particle level simulation. Fibers were placed in a periodic boundary cell, and an idealized simple shear flow field was applied. The model showed a faster orientation evolution at the start of the shearing process. However, agreement with the steady-state aligned orientation for compression molded samples was found.

Near-wall dynamics of a neutrally buoyant spherical particle in an axisymmetric stagnation point flow

The motion of a neutrally buoyant spherical particle along the axis of an axisymmetric stagnation point flow at a rigid and smooth flat wall (Hiemenz–Homann flow) is investigated in the presence of low-to-moderate inertia effects. The particle dynamics is elucidated using numerical simulation. At distances large compared to the characteristic thickness of the boundary layer \delta=(\nu/B)^{1/2}, with \nu the kinematic viscosity and B the strain rate of the carrying flow, the particle decelerates as it approaches the wall, due to the ambient pressure increase toward the stagnation point. In this part of the path, its velocity is nearly identical to that of the local undisturbed fluid at the position of its centre. Relative motion between the particle and fluid increases as the wall–particle gap reduces, due to wall-induced hydrodynamic interaction forces. Two distinct evolutions of the net force on the particle are observed, depending on the relative particle size, a/\delta=Re^{1/2}, where a is the particle radius and Re=2Ba^2/\nu is the Reynolds number. For a/\delta=2, the force decays monotonically to zero, while it undergoes a sharp rise before returning to zero for larger particles. In the latter case, the particle retains a sufficient velocity even for very small gap widths such that, under usual roughness levels, a rebounding collision would occur. The stress profiles at the particle surface are investigated to separate the various contributions to the hydrodynamic force. Theoretical predictions for near-wall viscous and inertial forces available in the creeping-flow and low-but-finite Reynolds-number limits, respectively, are used to pinpoint the origin of the dominant inertia effect that controls the particle dynamics when the particle gets very close to the wall.

A Numerical Method for Calculation of Ship–Ship Hydrodynamics Interaction in Shallow Water Accounting for Sinkage and Trim

AbstractSinkage and trim, which often occur to ships moving in shallow water, do not only have an effect on the ship–ship hydrodynamic interaction forces but also increase the risk of grounding. Potential flow-based online calculation of ship–ship hydrodynamic interaction forces without accounting for dynamic sinkage and trim is able to capture the hydrodynamic interaction effects with fair accuracy; however, there are still discrepancies in many cases, especially in the case of shallow water. An algorithm based on the potential theory has been devised for real-time simulation of the hydrodynamic interaction between two ships in shallow water accounting for sinkage and trim. The shallow water condition is modeled using the mirror image method. The sinkage and trim are solved iteratively based on the principle of hydrodynamic balance, where a mesh trimming procedure is carried out when the waterline is changed. Simulations are performed with and without accounting for the sinkage and trim, and comparison with experimental results shows a fair agreement.

Parametric modelling of interacting hydrodynamic forces in 3 DOF for underwater vehicles operating in close proximity

In this paper we present a parametric model of the hydrodynamic interaction forces for two underwater vehicles operating in close proximity. We first review the models for interacting forces in the horizontal plane of surface vessels and empirical approximations that can be potentially applied to underwater vehicles. Then, based on both potential theory and experimentally derived models available in the literature, we propose a partially-fixed model structure of the hydrodynamic interaction forces. This partially-fixed model structure is used for the identification of a full parametric model for the hydrodynamic interaction forces. The data set considered to validate the model represents a fully-submerged hull shape (an enlarged Explorer AUV hull shape) that moves holding its course at a forward speed and another hull shape (a SUBOFF hull of reduced size) that overtakes Explorer in a parallel course. We exploit the novel model structure together with the experimentally validated data to obtain a parametric model of the interaction forces on the overtaking vessel at different transverse separation distances. We estimate the parameters using one dataset and then validate the model for other sets. The results obtained are considered accurate for the intended purpose of the model, which is the future design of a motion control system for the SUBOFF manoeuvring in close proximity to the Explorer.

Electroviscous effects on the squeezing flow of thin electrolyte solution films

We present a detailed analysis of the electroviscous effect in the squeeze out of thin electrolyte films confined between two charged surfaces. The two charged surfaces consist of a curved surface and a flat surface, which closely simulate the tip–substrate configuration in the force measurement of electrolyte solutions with dynamic atomic force microscopy. In the lubrication limit, we find the analytical solution of the electroviscous-effect-modified squeezing flow field in the thin electrolyte film confined between the tip and substrate by solving the Nernst–Planck–Poisson/Navier–Stokes equation under the justified condition of pseudo-steadiness. We also derive the solution of the tip–substrate interaction, which comprises of a conservative electric double layer (EDL) force and an electroviscous-effect-enhanced dissipative hydrodynamic force. The current work focuses on the dissipative hydrodynamic force since the conservative EDL force has been well described by the well-known Derjaguin–Landau–Verwey–Overbeek theory. We introduce a power-law index ( $n$ ) for the tip surface, which enables an unprecedented quantitative characterization of the tip profile effect on the electroviscous effect. We observe a seemingly counter-intuitive effect that, for a given tip–substrate separation, the electroviscous effect is the strongest at one particular value of the zeta ( $\unicode[STIX]{x1D701}$ ) potential and diminishes as the $\unicode[STIX]{x1D701}$ potential departs from this value. We reveal the counterion conductivity of the EDL to be the governing factor for the electroviscous effect under a given $\unicode[STIX]{x1D701}$ potential. In addition to enhancing the dissipative hydrodynamic interaction force, the electroviscous effect modifies the velocity profiles in the thin electrolyte solution films such that they are much sharper.

Mechanism of Moving Particle Aggregates in a Viscous Fluid Subjected to a Varying Uniform External Field

A mechanism is proposed for moving aggregates of spherical particles in a viscous fluid, and their dynamics under an applied uniform external field is numerically simulated. A particle aggregate is treated as a set of particles with a charge or dipole moment influenced by both hydrodynamic interaction forces and internal forces retaining the particles in the aggregate. In the absence of an external field, the particles are in the position of minimum interaction energy and the total charge or dipole moment of the system is zero. After applying an external field, the aggregate deforms and, after switching off the field, the aggregate undergoes a restoring process caused by internal forces tending to return it to equilibrium. The relative motion of the aggregate particles gives rise to a viscous flow around the aggregate, which creates a hydrodynamic force shifting the aggregate barycenter in a certain direction with respect to the applied field. The motion of six model aggregates consisting of charged or dipolar particles is numerically simulated. The proposed mechanism of moving the aggregates can be used to control mass transfer in colloidal suspensions.

Effect of normal contact forces on the stress in shear rate invariant particle suspensions

We theoretically predict, that, in sphere suspensions, hydrodynamic interaction forces produce a negligible first normal stress difference, while contact forces produce a positive first normal stress difference.

Numerical study on hydrodynamic interaction between two tankers in shallow water based on high-order panel method

Abstract A three-dimensional high-order panel method based on Non-Uniform Rational B-Spline (NURBS) for predicting the ship–ship hydrodynamic interaction during meeting and overtaking in shallow water is developed. The NURBS surface is used to precisely represent the hull geometry. The velocity potential on the body 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, and the velocity potential is being solved at each time step. Under the low-speed assumption, the effect of free surface elevation is neglected in the numerical calculation, and the infinite image method is used to deal with the finite water depth effect. Two tankers in model tests are investigated, and the predicted hydrodynamic interaction forces and moments are compared with experimental measurements to clarify the validity of the proposed numerical method. Calculations are then conducted for different water depths, lateral ship–ship distances and ship speeds, and the detailed results are discussed to demonstrate the effects of these factors.

Numerical prediction of hydrodynamic forces on a moored ship due to a passing ship

The passing ship effect on berthed vessel is a well-known problem and is studied over many years. These interaction effects induce dynamic loads in the mooring system that can exceed the design values and lead to severe accidents. A study has been conducted to analyze the effect of various parameters such as passing ship speed, separation distance, depth to draft ratio and waterway geometry on the hydrodynamic interaction effects between berthed and a passing ship. Numerical simulation for three-dimensional unsteady viscous flow have been conducted using the overset mesh methodology and solving the Reynolds-averaged Navier–Stokes equations with k-ω shear-stress transport turbulence model for various cases, and interaction effect on berthed ship have been calculated. The method recommended in this study is validated by comparing the computational fluid dynamics (numerical) results with existing model scale experiments and mathematical curves from empirical formulas. The hydrodynamic interaction forces are computed for five types of waterway geometries. The magnitude and time histories of the forces and moment on the moored ship for various cases are analyzed to evaluate the effect of various parameters such as waterway geometries and separation distance. The results and conclusions made by this study can give definite guidance on safe maneuvering of a ship passing by a moored ship.