Simulation Of Wave Interaction Research Articles

Publisher's Note: “A modified weakly compressible smoothed particle hydrodynamics mixture model for accurate simulation of wave and porous structure interaction” [Phys. Fluids 36, 047128 (2024)

Publisher's Note: “A modified weakly compressible smoothed particle hydrodynamics mixture model for accurate simulation of wave and porous structure interaction” [Phys. Fluids <b>36</b>, 047128 (2024)

A modified weakly compressible smoothed particle hydrodynamics mixture model for accurate simulation of wave and porous structure interaction

A modified weakly compressible smoothed particle hydrodynamics mixture model for accurate simulation of wave and porous structure interaction

A generating absorbing boundary condition for simulating wave interaction with maritime structures in current or at forward speed

The lack of suitable boundary conditions in practical surface wave simulations with maritime structures in current or at forward speed may cause energy in the computational domain to accumulate due to spurious wave reflection. The common way to prevent wave reflection is to use passive wave absorbers, such as damping zones or relaxation zones, which requires larger domains at the cost of computational effort. Our goal is to derive a local generating absorbing boundary condition (GABC) for long-crested irregular waves on top of a mean flow, using the flow to model the forward speed of a structure such as a ship. Earlier work has demonstrated that a local GABC for free surface waves has a performance similar to passive wave absorbers, but at a reduced computational effort. New in the present work is that we extend, verify and validate the GABC in the presence of a nonzero mean flow. The GABC is designed to be accurate for a range of wave components in irregular sea states, with the resulting reflection coefficients for each component lower than a chosen value, say 5%. Having used potential flow theory for its derivation means that the boundary should not be placed at the exact location where wave breaking is expected, such as very close to the structure in the domain, or in the surf zone in coastal modeling. For the application with ships in this article that does not pose a limitation. The performance is demonstrated for a range of dimensionless wave number between 0 and 6. Such a boundary condition is obtained through a rational approximation of the linear dispersion relation with a mean flow, in combination with vertical derivatives of the solution variables along the boundary. Local linearization means that the GABC incorrectly considers bound, nonlinear wave components to be freely propagating wave components. Bound components, however, tend to have smaller amplitudes and do not appear to affect performance for the considered cases. Results of simulations with regular and irregular waves, on top of flows with different magnitudes and directions, are found to agree with the theory. The main source of differences is the implementation of the second derivate in the GABC near the free surface. Simulations of a Wigley hull at forward speed in irregular waves are compared to an experiment that was conducted specifically for validating the ABC. The data of the experiment are available as open data through doi: 10.4121/21320604. The comparison between simulation and experiment demonstrates that the GABC with a mean flow can be applied not only for theoretical simulations with propagating waves, but also for more practical applications with a structure in the domain.

Numerical simulations of breaking wave propagation through the vegetation on a slope based on a drag coefficient prediction model

Coastal vegetation plays a key role in wave attenuation on sloping beaches. However, accurately predicting the vegetation-related drag coefficient (CD) under breaking waves on slopes remains a challenge. In this study, the Reynolds-averaged Navier–Stokes equations were modified by incorporating a vegetation resistance term to consider the vegetation-induced momentum loss. The stabilized k-ω shear stress transport turbulence model was improved by introducing the vegetation-induced turbulence generation and dissipation terms. The numerical model was validated by two laboratory experiments. Based on experimental wave height data, the CD was determined via a calibration method. The numerical results were found to be highly sensitive to the CD. The calibrated CD achieved excellent agreement with experimental data (RMSE < 0.2). In addition, the calibrated CD showed a high correlation (R2 = 0.85) with the Iribarren number ξ. Finally, a CD prediction formula expressed by the combination of Reynolds number and ξ was proposed via regression analysis, and its performance was evaluated by two additional cases. The limitations and applicability of the CD prediction formula were also discussed. The proposed numerical model and CD prediction formula have the potential to be useful for the numerical simulation of wave interactions with vegetation on slopes.

SPH numerical model of wave interaction with elastic thin structures and its application to elastic horizontal plate breakwater

This paper develops a Smoothed Particle Hydrodynamics (SPH) model to simulate wave interaction with elastic thin structures. This is achieved by coupling the δ-SPH and the Total Lagrangian SPH (TL-SPH) models for solving the fluid and structure phases, respectively. To this aim, a multiresolution algorithm within the ghost particles framework is introduced in order to treat the thin elastic components of the structure. The main idea of the proposed technology is to evaluate the hydrodynamic forces acting on the structure and the elastic dynamic at the finest solid particle resolution. Then, the information is transferred to the coarse solid particles, which act as a non-penetrating boundary condition for the fluid phase. The present enforcement is introduced with the aim of overcoming the disadvantages in terms of CPU time for heavy SPH simulations, in which the choice of the initial spatial resolution is driven by the presence of elastic thin structures immersed in the fluid environment. The present elastic thin-wall boundary treatment is verified through several numerical cases, in which it is proved that the proposed technology can block non-physical interaction of fluid particles located at opposite sides of the elastic thin-wall boundary, ensures the stability of the fluid pressure field, and reasonably predicts the motion of elastic structures when these are subjected to hydrodynamic loads. Successively, the proposed numerical model is applied to simulate wave interaction with an elastic horizontal plate breakwater. The hydrodynamic performances of the breakwater, with focus on the reflection and transmission coefficients, are analyzed. The results of elastic and rigid horizontal plate breakwaters are compared in order to better understand the effects of the structure deformation on the hydrodynamics. Finally, an analysis of the structural deformation of the breakwater is also reported.

Coupling SPH with a mesh-based Eulerian approach for simulation of incompressible free-surface flows

This paper presents a coupling algorithm for the simulation of incompressible free-surface flows over the near and far fields by solving the Navier-Stokes equations. The coupling combines the Smoothed Particle Hydrodynamics (SPH) with the Finite Difference (FD) method implemented on structured Eulerian grids. Based on the domain decomposition, the SPH is applied to the near-field core region for modeling with high-fidelity the severe free-surface deformation and even fragmentation of flow, while the FD method is used to resolve the remaining far-field region with relatively high efficiency. The primary purpose of the hybrid approach is to mitigate the computational load of SPH applications through combination with a mesh-based Eulerian method while maintaining high accuracy for both the near-field and far-field simulations. Two-way coupling between the FD and SPH models is achieved by the overlapping region between the computational subdomains, in which the Eulerian solutions and the Lagrangian solutions are coupled with each other through interpolation in the overlapping region for the fluid transfer and free-surface movement between the near-field and far-field regions. The proposed algorithm is validated by several test cases, showing favorable accuracy, convergence, and applicability in the simulation of wave interactions with complex bathymetry and structures.

Two-dimensional numerical simulations of solitary wave interaction with a vertical elastic plate

In this study, we numerically investigated the interaction between a solitary wave and a bottom-mounted, submerged elastic plate. The fluid structure interaction (FSI) solver (solids4Foam), the stabilized k-ω SST turbulence closure model, and the geometric volume of fluid approach (isoAdvector) were combined to simulate the dynamic process, including the plate movement and the flow field. The model package was first validated by using experimental data, and the effects of plate height, plate thickness, and the Young's modulus of plate material on the hydrodynamics were further investigated. Moreover, the Euler-Bernoulli beam theory was used to calculate the plate displacement. Lengthening the plate height, reducing the plate thicknesses, or reducing Young's modulus can all increase the plate displacement. Among them, lengthening the plate height has the greatest impact. Finally, the effects of the wave nonlinearity and plate material property on wave reflection, transmission, and dissipation were also analyzed. The results show that while the height of the plate has the most significant effect on the reflection coefficient, the plate thickness and the plate material have little influence on the reflection coefficient. The more flexible the plate is, the smaller the transmitted coefficient, and the larger the dissipation coefficient are.

Performance Improvement of Helix Traveling- Wave Tubes Based on Multiobjective Optimization Technique

An optimization design tool for helix traveling-wave tubes (TWTs) is developed by combining the nondominated sorting genetic algorithm II (NSGA-II) and the beam–wave interaction simulator (BWIS), which can realize multiobjective optimization of various TWT figures of merit (FoMs). FoMs include the output power, gain, efficiency, and nonlinear distortion characteristics. This optimization design tool can automatically construct a Pareto-optimal solution set according to FoMs. Then, the final simulation design can be obtained by analyzing the output power variation over the operating band of the individuals in the optimized solution set. In order to ensure the comprehensiveness and accuracy of FoMs, a workflow is established in the optimization tool, which can simulate the physical process by transferring the data between different computing tasks automatically during the design of beam–wave interaction. Based on this design tool, the performance of an L-band helix TWT has been improved significantly. For the demonstrated interaction, the output power, phase distortion, interaction, and recovery efficiency are taken as objectives. After analyzing the output power variation over the operating band, the final parameter set is determined from the Pareto-optimal solution set.

An effective approach for VARANS-VOF modelling interactions of wave and perforated breakwater using gradient boosting decision tree algorithm

In this paper, we propose a systematic and time-efficient approach to calibrate 2D VARANS-VOF models for simulation of wave interaction with porous plate in numerical wave tank. To reach this goal, we develop a data-driven approach in combination with numerical and experimental data to figure out the optimal empirical coefficient associated with linear and non-linear drag force coefficients (α, β). Advanced gradient boosting decision trees algorithms (GBDT) are adopted to capture the accuracy of the prediction model. Although only limited samples, for instance 72 samples are generated and chosen to train and test the prediction model, the GBDT model is able to identify the trend in non-linear influence of model parameters. The advantage of GBDT algorithm can obviously be seen through the regression analysis with very high regression coefficient (R2 > 0.99). The developed model is subsequently employed for a large range of considered parameters as input features of the models to predict the possible hydrodynamics characteristics. The smallest mean squared error between predicted and experimental results, which is 0.00204, is found and used to determine the best performing combination of these model parameters. The numerical model together with selected values of empirical coefficients is then validated using available experimental data in literature. The free surface elevations in front of and behind the structure from the numerical model are nearly identical with the experimental data.

Metamaterial-Inspired Interaction Structure for MW-Level Klystron at 714 MHz

A metamaterial (MTM)-inspired interaction structure for MW-level klystron at 714 MHz is proposed. The electromagnetic characteristics of MTM-inspired resonant cavities with single-bridge complementary electric split ring resonators (CeSRRs) are studied, and the cold-tested results confirm the feasibility of miniaturizing the resonant cavity. Furthermore, the beam–wave interaction simulation for the interaction structure constructed by MTM-inspired resonant cavities with single-bridge CeSRRs is carried out, demonstrating 2.28 MW of output power at 714 MHz for a 100 kV, 40 A electron beam. The radius and length of the MTM-inspired interaction structure are 1/2 and 2/3 of the conventional counterparts, respectively. The promising performance makes it attractive for future applications such as linacs.

Boussinesq Simulation of Coastal Wave Interaction with Bottom-Mounted Porous Structures

A Boussinesq-type wave model is developed in this paper to simulate the interaction of coastal waves with bottom-mounted porous structures. The governing equations are rewritten in the conservative form to facilitate the use of hybrid finite volume (FV) and finite difference (FD) method. Higher-order slope terms are also inserted into the equations to account for rapidly varying bathymetry. The convective flux is approximated using the FV method, while the remaining terms are discretized using the FD method in a uniform rectangle grid system. The time integration is implemented using the third order Runge–Kutta method with an adaptive time step. A single GPU parallel computation is also implemented to save computation costs. The numerical model is validated against a series of experimental datasets, including data acquired in a new laboratory experiment. The predictions are in overall agreement with the measurements, proving that the model is capable of handling wave interaction with porous structures in the coastal region for a wide range of scenarios.

A CIP-based numerical simulation of wave interaction with a fluid-filled membrane submerged breakwater

This study proposes an CIP (Constraint Interpolation Profile) viscous flow model that couples the Finite Element Method for structural deformation, to investigate the wave interaction with a fluid-filled membrane submerged breakwater. A modified ghost-cell immersed boundary method is adopted to achieve an accurate simulation of the fluid-structure interaction. After validation by published experimental data, the model is used to study the interaction between regular waves and a fluid-filled membrane submerged breakwater. The excess internal pressure, vorticity field, elastic modulus and structural responses are analyzed. The results show that, in lower excess internal pressure, the wave reflection, vortex shedding and energy dissipation are more significant. Besides, through the analysis of displacement and velocity distribution, three different vibration modes of the membrane structure are identified at different wave frequencies.

Hypersonic shock wave and turbulent boundary layer interaction in a sharp cone/flare model

A direct numerical simulation of hypersonic Shock wave and Turbulent Boundary Layer Interaction(STBLI) at Mach 6.0 on a sharp 7° half-angle circular cone/flare configuration at zero angle of attack is performed. The flare angle is 34° and the momentum thickness Reynolds number based on the incoming turbulent boundary layer on the sharp circular cone is Reθ = 2506. It is found that the mean flow is separated and the separation bubble occurring near the corner exhibits unsteadiness. The Reynolds analogy factor changes dramatically across the interaction, and varies between 1.06 and 1.27 in the downstream region, while the QP85 scaling factor has a nearly constant value of 0.5 across the interaction. The evolution of the reattached boundary layer is characterized in terms of the mean profiles, the Reynolds stress components, the anisotropy tensor and the turbulence kinetic energy. It is argued that the recovery is incomplete and the near-wall asymptotic behavior does not occur for the hypersonic interaction. In addition, mean skin friction decomposition in an axisymmetric turbulent boundary layer is carried out for the first time. Downstream of the interaction, the contributions of transverse curvature and body divergence are negligible, whereas the positive contribution associated with the turbulence kinetic energy production and the negative spatial-growth contribution are dominant. Based on scale decomposition, the positive contribution is further divided into terms with different spanwise length scales. The negative contribution is analyzed by comparing the convective term, the streamwise-heterogeneity term and the pressure gradient term.

Numerical study on the surface signature of internal solitary waves

The propagation of internal solitary waves (ISWs) underwater and their interactions with surface waves can affect the sea surface state and generate distinct surface signatures of bright–dark striped patterns in remote sensing imagery. These patterns have been one of the most important methods for wide coverage detection and observation of ISWs. This study establishes a fully nonlinear numerical model for ISW–surface wave interaction simulation based on the multi-domain boundary element method. By numerical simulation, the formation mechanism, characteristics, and influencing factors of ISW surface signatures are revealed. The physical essence of the ISW surface signature is the spatially inhomogeneous wavelength and roughness changes in the surface waves due to the convergence and divergence effects of the ISW. Based on the surface wave wavelength changes, the surface area affected by an ISW is divided into three regions from front to back—the converging, diverging, and restoring regions—corresponding to the regions where the surface waves are compressed, stretched, and recover, respectively. By comparing different cases, it is found that the ISW amplitude, surface wave amplitude, and surface wave wavelength are the main factors influencing the ISW surface signature. ISWs with larger amplitudes have stronger convergence and divergence effects on surface waves, making the overall scale of the ISW surface signature larger. Larger surface wave amplitudes provide stronger resistance to the ISW divergence effect and lead to smaller diverging regions, and larger surface wave wavelengths make the converging region larger and the diverging and restoring regions smaller.

Design and high-power test of 800-kW UHF klystron for CEPC

To reduce the energy demand and operation cost for circular electron positron collider (CEPC), the high efficiency klystrons are being developed at Institute of High Energy Physics, Chinese Academy of Sciences. A 800-kW continuous wave (CW) klystron operating at frequency of 650-MHz has been designed. The results of beam–wave interaction simulation with several different codes are presented. The efficiency is optimized to be 65% with a second harmonic cavity in three-dimensional (3D) particle-in-cell code CST. The effect of cavity frequency error and mismatch load on efficiency of klystron have been investigated. The design and cold test of reentrant cavities are described, which meet the requirements of RF section design. So far, the manufacturing and high-power test of the first klystron prototype have been completed. When the gun operated at DC voltage of 80 kV and current of 15.4 A, the klystron peak power reached 804 kW with output efficiency of about 65.3% at 40% duty cycle. The 1-dB bandwidth is ±0.8 MHZ. Due to the crack of ceramic window, the CW power achieved about 700 kW. The high-power test results are in good agreement with 3D simulation.

Numerical Simulation of Wave Interaction With a Pair of Fixed Large Tandem Cylinders Subjected to Regular, Non-Breaking Waves

Abstract This paper presents the application of a two-phase computational fluid dynamics (CFD) model to carry out a detailed investigation of the nonlinear wave field surrounding a pair of columns placed in the tandem arrangement in the direction of wave propagation and corresponding harmonics. The numerical analysis is conducted using the unsteady Reynolds-averaged-Navier-Stokes/volume of fluid (VOF) model based on the openfoam framework combined with the olaFlow toolbox for wave generation and absorption. For the simulations, the truncated cylinders are assumed vertical and surface piercing with a circular cross section subjected to regular, non-breaking fifth-order Stokes waves propagating with moderate steepness in deep water. Primarily, the numerical model is validated with experimental data for a single cylinder. Future, the given simulations are conducted for different center-to-center distances between the tandem large cylinders. The results show the evolution of a strong wave diffraction pattern, and consequently, high wave amplification harmonics around cylinders are apparent.

Simulation of Gaussian electromagnetic wave interaction and its effect on the dynamics of metallic nanosphere (repulsion or even elasticity)

Simulation of Gaussian electromagnetic wave interaction and its effect on the dynamics of metallic nanosphere (repulsion or even elasticity)

Particle-in-Cell Algorithm-Based Computation of Time-Dependent-Multimode Behavior of 42-GHz Gyrotron

The analysis of the multimode behavior of the interaction cavity for 42-GHz gyrotron is presented here. The in-house developed codes single-mode cold cavity solver (SMCCS) and GYCAD and commercial particle-in-cell (PIC) simulator MAGIC are used in the design and analysis of 42-GHz gyrotron cavity. SMCCS is used for the calculation of cold cavity parameters such as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> factor, resonant frequency, and the axial electric field profile, which are further used in the beam–wave interaction computation. The PIC code is used here for the parametric optimization and time-dependent-multimode beam–wave interaction simulations of the interaction cavity. The mode purity in terms of the electromagnetic power in individual modes is also calculated using the data generated in the beam–wave interaction simulations. The single-mode analysis of the cavity is also performed using the analytical code GYCAD based on the generalized nonlinear theory. The results obtained by the PIC simulator and GYCAD are discussed and compared here. The analysis of the electron beam misalignment, which may occur due to the radial shifting or tilting of the different components during the fabrication of the device, is also performed and the effects on the efficiency, mode competition, and mode stability are discussed in detail.

On the energy conversion characteristics of a top-mounted pitching absorber by using smoothed particle hydrodynamics

The top-mounted pitching point absorber is one of the most promising wave energy converters in that it can be easily attached to an existing offshore structure. However, it is difficult to predict accurately its energy conversion performance because of the strongly nonlinear hydrodynamic behaviour. Herein, smoothed particle hydrodynamics (SPH) is used to solve this wave-structure interaction problem. The SPH method is first validated against free surface deformation measurements obtained from a wedge water entry experiment. SPH simulations of regular wave interaction with fixed and freely pitching devices agree well with measured data, providing confidence in the prediction of power conversion performance. Absorbed power and capture width ratio exhibit uni-modal behaviour with wave period. The wave period of peak power within this distribution increases with PTO damping. According to the observed scaling behaviour with device scale, an optimally damped larger scale device is effective at absorbing energy from incident waves of longer wavelength. In finite deep water, the larger device achieves higher efficiency compared with the smaller ones, and its peak efficiency at 2πh/λ=1.1 provides reference for siting.

Simulations of surface acoustic wave interactions on a sessile droplet using a three-dimensional multiphase lattice Boltzmann model.

This study reports the development of a three-dimensional numerical model for acoustic interactions with a microscale sessile droplet under surface acoustic wave (SAW) excitation using the lattice Boltzmann method (LBM). We first validate the model before SAW interactions are added. The results demonstrate good agreement with the analytical results for thermodynamic consistency, Laplace law, static contact angle on a flat surface, and droplet oscillation. We then investigate SAW interactions on the droplet, with resonant frequencies ranging 61.7-250.1 MHz. According to our findings, an increase in wave amplitude elicits an increase in streaming velocity inside the droplet, causing internal mixing, and further increase in wave amplitude leads to pumping and jetting. The boundaries of wave amplitude at various resonant frequencies are predicted for mixing, pumping, and jetting modes. The modeling predictions on the roles of forces (SAW, interfacial tension, inertia, and viscosity) on the dynamics of mixing, pumping, and jetting of a droplet are in good agreement with observations and experimental data. The model is further applied to investigate the effects of SAW substrate surface wettability, viscosity ratio, and interfacial tension on SAW actuation onto the droplet. This work demonstrates the capability of the LBM in the investigation of acoustic wave interactions between SAW and a liquid medium.