Simulation Of Wave Interaction Research Articles

Design and Measurement of a Terahertz Double Staggered Grating Waveguide With an Arc-Shaped Beam Tunnel

A millimeter-waveband double staggered grating waveguide (DSGW) with an arc-shaped beam tunnel was previously proposed for sheet beam traveling wave tubes. In this article, the design, fabrication, and cold test of a terahertz band DSGW with an arc-shaped beam tunnel are presented. Simulations demonstrated that the novel DSGW would have a higher coupling impedance and a better beam wave interaction in comparison to the conventional DSGW with a linear-shaped beam tunnel. Beam wave interaction simulations showed that the output power and the electronic efficiency, respectively, increased from ~420 W to ~580 W and from 7.0% to 9.3% at 240 GHz. These two kinds of DSGWs were fabricated by using the nanocomputer numerical control (CNC) milling and wire cutting techniques, and their performances were cold tested by using a vector network analyzer. The measurement results were in good agreement with the simulations and demonstrated that both the traditional and novel DSGWs achieved a wide frequency bandwidth of ~40 GHz (0.22–0.26 THz) with a transmission coefficient ${S}_{{21}}$ better than −2.7/−3.0 dB and a reflection coefficient ${S}_{{11}}$ lower than −13.0/−15.7 dB, respectively.

OpenFOAM analysis of the wave radiation by a box-type floating structure

Wave radiation due to heave, surge, and pitch by a box-type floating structure based on computational fluid dynamics (CFD) simulations using OpenFOAM is analysed. The CFD simulation results include surge and heave forces and response amplitude operator for the heave, surge, and pitch at different wave lengths. The numerical simulation results of heave force due to incoming waves and resulting motion are compared against experimental data and linearized analytical solutions based on velocity potential flow theory. The hydrodynamic effect on the width and draft of the structure in analytical results for vertical wave force, horizontal wave force, and torque are studied whilst, the effect of different wave lengths on heave, surge and pitch forces and response amplitude operator from CFD results are analysed. The comparison shows that the CFD results are in good agreement with the experimental ones and are very close to the analytical ones. The paper concludes that CFD is well capable of simulating wave interaction behaviour of a box-type floating structure for wave energy converters, and the developed analytical model can serve as an efficient middle-fidelity performance evaluation tool for such structures during design development stage.

Numerical simulation of wave interaction with deformable plates

The two-dimension problems of the interaction between waves and one, two and a series of deformable plates are discussed, respectively, in this study. The fluid motion is described by the linear wave theory. The deformable plates are simplified as the one-dimensional beams with uniform stiffness and mass distribution. A boundary element method (BEM) is used to calculate the wave field. The Euler–Bernoulli beam theory is used to describe the motion of the deformable plate, which is calculated on the basis of a finite element method (FEM) in combination with the BEM model. The numerical solutions are derived for the velocity potentials together with the displacements of the deformable plates. After the energy conservation is calculated to verity the numerical models, the effects of structural flexibilities and interval between deformable plates on the reflecting waves are investigated.

A 3D parallel particle-in-cell solver for extreme wave interaction with floating bodies

Floating structures are widely used for vessels, offshore platforms, and recently considered for deep water floating offshore wind system and wave energy devices. However, modelling complex wave interactions with floating structures, particularly under extreme conditions, remains an important challenge. Following the three-dimensional (3D) parallel particle-in-cell (PIC) model developed for simulating wave interaction with fixed bodies, this paper further extends the methodology and develops a new 3D parallel PIC model for applications to floating bodies. The PIC model uses both Lagrangian particles and Eulerian grid to solve the incompressible Navier-Stokes equations, attempting to combine both the Lagrangian flexibility for handling large free-surface deformations and Eulerian efficiency in terms of CPU cost. The wave-structure interaction is resolved via inclusion of a Cartesian cut cell method based two-way strong fluid-solid coupling algorithm that is both stable and efficient. The numerical model is validated against 3D experiments of focused wave interaction with a floating moored buoy. Good agreement between the numerical and experimental results has been achieved for the motion of the buoy and the mooring force. Additionally, the PIC model achieves a CPU efficiency of the same magnitude as that of the state-of-the-art OpenFOAM® model for an extreme wave-structure interaction scenario.

A mixed Eulerian-Lagrangian simulation of nonlinear wave interaction with a fluid-filled membrane breakwater

This paper introduces a time-domain potential flow method for simulating fully nonlinear wave interaction with a fluid-filled membrane mounted on the seabed. The numerical method is based on a mixed Eulerian-Lagrangian method, which tracks the free water surface and the membrane using a Lagrangian method and solves the flow fields inside and outside the membrane using an Eulerian method. To remove the numerical instability, a method that satisfies the no-flux condition on the membrane at any location and any time was developed to calculate the radial displacement of the membrane at every time step and a Fourier series expression for the radial displacement of the membrane was used to calculate the local curvature of the membrane accurately. Experimental results from an existing experimental study were used for model validation and verification. The response of the membrane and the nonlinear wave scattering were simulated. The simulation results show that the transmission coefficients of the fundamental waves, second harmonic free and locked waves approach zero when a resonant response of the membrane to waves occurs. Sample results of the simulated tension in the membrane and interior pressure are also included in the discussion.

NUMERICAL STUDY OF WAVE INTERACTION WITH A SUBMERGED POROUS BREAKWATER IN COMBINATION WITH A FLOATING BREAKWATER

Conventional emerged rubble mound breakwaters are commonly built to protect ports and marinas from direct wave action. With increased high-valued developments in the coastal region, engineers have to design innovative coastal protection structures that can provide adequate harbor tranquility with minimum visual impact. One such solution is the combination of a submerged breakwater with a floating breakwater. In this paper, the open-source CFD model REEF3D (Bihs et al. 2016) is used to simulate wave interaction with a submerged porous breakwater with a floating breakwater on the lee side. The wave interaction with the submerged porous breakwater is validated by comparison with experimental data from Hieu and Tanimoto (2006). The validated model is then used to simulate the wave interaction with a combination of the submerged breakwater and the floating breakwater. The transmission coefficient across the combination is calculated to be about 12.5%, demonstrating the possibility to provide harbor tranquility with minimum visual impact.

A new implementation method of sharp interface boundary conditions for particle methods in simulating wave interaction with submerged porous structure

A new formulation of interface boundary conditions for simulating water waves over submerged porous media using particle method is presented. The fluid flow over and through a porous media is modelled by the standard NS equations for the free flow and volume averaged NS equation based on the Forcheimmer's type resistant force for the flow in the porous media, respectively. As the porosity and resistant forces exist only within the porous media, the continuity of Darcy velocity and flow stresses need to be enforced at the interface boundary between the free flow and the flow in the porous media. These boundary conditions are implemented simultaneously at the stage of solving the Poisson pressure equation (PPE) by transforming the velocity condition to an expression of pressure gradient and then applying the pressure expression at the sharp interface incorporating the stress conditions. Implementing the new formulation within the framework of an existing particle-based code (MLPG_R), a set of numerical ‘experiments’ is performed to demonstrate the method's effectiveness as compared with analytical solutions and experimental data including solitary wave and regular propagating wave with wave breaking.

Numerical simulation of stress wave interaction in short-delay blasting with a single free surface.

It is generally believed that stress wave superposition does occur and plays an important role in cutting blasting with a single free surface, in which explosive columns of several blast holes with short spacing are simultaneously initiated. However, considering the large scatter of pyrotechnic delay detonators that are used in most underground metal mines in China, the existence of stress wave superposition and the influence of this effect on rock fragmentation are questionable. In the present study, the stress wave interaction in short-delay blasting with a single free surface was studied through the use of the LS-DYNA code. Stress waves induced by two blast holes blasting with different delays were compared with the single blast hole case, and the effects of delay time, detonating location and spacing on stress wave superposition were investigated. The numerical results showed that for blast holes with a 1 m spacing, stress wave interaction only occurs when the delay time is 0 ms and does not occur for blasting with delays of more than 1 ms. An increase in the duration of a stress wave via optimizing the detonation location does not improve the stress wave interaction. For a 1 ms delay, stress wave superposition only occurs when the spacing is more than 4 m, which is a rare case in practice. The results indicated that the occurrence of stress wave superposition for blasting with a single free surface is strictly limited to conditions that would be difficult to achieve under the existing delay accuracy of detonators. Therefore, it is unrealistic to improve fragmentation via the stress wave interaction in field blasting. Furthermore, the numerical results of the stress wave interaction also show that there would be a great potential to reduce the hazardous vibrations induced by short-delay blasting by using electronic detonators with better control of delays in an order of several milliseconds.

Study of Performance Improvement for a <inline-formula> <tex-math notation="LaTeX">${Q}$ </tex-math> </inline-formula>-Band Sheet-Beam Traveling-Wave Tube

The study of performance improvement for a ${Q}$ -band sheet-beam traveling-wave tube (SB-TWT) based on an improved double-staggered grating waveguide slow-wave structure (SWS) is presented. To enhance the tube performance, such as reducing the driving power requirement and increasing the electronic efficiency, three approaches were combined together in the tube design, including making the operating frequency be closer to the cutoff frequency of the SWS, improving the SWS with a curved beam tunnel, and introducing the phase velocity tapering technique. Beam–wave interaction simulations predicted that great improvements have been achieved. The output power, gain, and electronic efficiency at 42.5 GHz have, respectively, increased from 7.5 to 20.2 kW, from 23.7 to 60 dB, and from 13.9% to 30.3%, in comparison with a previously designed SB-TWT.

Water surface wavelets

The current state of the art in real-time two-dimensional water wave simulation requires developers to choose between efficient Fourier-based methods, which lack interactions with moving obstacles, and finite-difference or finite element methods, which handle environmental interactions but are significantly more expensive. This paper attempts to bridge this long-standing gap between complexity and performance, by proposing a new wave simulation method that can faithfully simulate wave interactions with moving obstacles in real time while simultaneously preserving minute details and accommodating very large simulation domains. Previous methods for simulating 2D water waves directly compute the change in height of the water surface, a strategy which imposes limitations based on the CFL condition (fast moving waves require small time steps) and Nyquist's limit (small wave details require closely-spaced simulation variables). This paper proposes a novel wavelet transformation that discretizes the liquid motion in terms of amplitude-like functions that vary over space, frequency, and direction , effectively generalizing Fourier-based methods to handle local interactions. Because these new variables change much more slowly over space than the original water height function, our change of variables drastically reduces the limitations of the CFL condition and Nyquist limit, allowing us to simulate highly detailed water waves at very large visual resolutions. Our discretization is amenable to fast summation and easy to parallelize. We also present basic extensions like pre-computed wave paths and two-way solid fluid coupling. Finally, we argue that our discretization provides a convenient set of variables for artistic manipulation, which we illustrate with a novel wave-painting interface.

Optimization of elastodynamic finite integration technique on Intel Xeon Phi Knights Landing processors

This work describes the development and optimization of an implementation of an isotropic elastodynamic finite integration technique (EFIT) code for parallelized computation on Intel Knights Landing (KNL) hardware. EFIT is a numerical approach resulting in standard staggered-grid finite difference equations for the elastodynamic equations of motion to simulate bulk waves in solids. The computationally efficient simulation of elastodynamic wave propagation and interactions in aerospace materials is of high-interest in the fields of nondestructive evaluation (NDE) and structural health monitoring (SHM). Ultrasonic inspection uses an ultrasonic signal, generated at the surface of the material/structure via use of a piezoelectric transducer, to propagate sound waves into the material where it interacts with any existing defects, as well as with structural boundaries and any material inhomogeneity. Reflections from defects and boundaries are then measured by a transducer. Realistic ultrasound simulation tools can significantly aid the development and optimization of inspection techniques and can assist in the interpretation of experimental data.The optimization of an elastodynamics simulation code for the KNL Many Integrated Core processor was performed. The optimization focused on data locality and vectorization. Results show that tiling of the data to exploit the cache behavior and allow for significant utilization of the KNL hardware. The MPI implementation allows for a scalable implementation enabling large problems to be simulated. The model results were validated against theoretical dispersion curves to within 2% of the group velocity, and within 0.5% of the phase velocity of the A0 mode. Aggressive use of tiling, threading, and vectorization techniques allowed for dramatically improved time to solution.

Coupled finite particle method for simulations of wave and structure interaction

A coupled finite particle method (FPM) is proposed to model wave-structure interaction. The coupled FPM combines the advantages of FPM, smoothed particle hydrodynamics (SPH), δ-SPH model and particle shifting technology (PST). The coupled FPM is more accurate than SPH for evaluating the interior fluid particles and more flexible than FPM for evaluating the free surface. The density diffusive term of δ-SPH model can allow for a relatively large CFL condition number and maintain a high computational efficiency. With the help of PST, the particle clustering and fracturing are eliminated effectively, and the well-conditioned corrective matrix is acquired. The coupled FPM method is tested by simulations of regular waves and the interaction between waves and the rigid plate. Then, the coupled FPM method is applied to model Oscillating Wave Surge Converter (OWSC) including two-dimensional (2-D) and three dimensional (3-D) simulations. All numerical results show that the coupled FPM is robust, and is capable to simulate wave-structure interaction accurately. The linked data are be associated to this paper, and the readers are able to download the source code that can be used to test regular waves contained in the paper. The web site of the code is https://data.mendeley.com/datasets/xjk3ccgr8t/draft?a=622fb107-3cb9-4c68-af8e-7b3ac1b3fc48.

Numerical Simulation and Experimental Study of Sub-THz and THz CW Clinotron Oscillators

Results of computer modeling for the sub-THz and THz continuous-wave clinotrons are presented together with the results of their experimental investigations. Presented simulation results are obtained with both the computation methods and the statistical processing of real device operational parameters. This combination provides relevant output results. The effect of weakly inhomogeneous magnetic field on the electron beam adjustment in clinotron oscillator is clearly shown with the carried out 3-D particle tracking modeling. The effect of the surface roughness and thermal heating of the grating structure on a clinotron operation is also considered, and obtained results were considered during computer modeling. The 3-D thermal heating analysis in clinotron was performed, and its influence on ohmic losses was analyzed. Comparison of beam–wave interaction simulation and experimental results has been presented and discussed.

Fully nonlinear simulation of wave interaction with a cylindrical wave energy converter in a numerical wave tank

Convergence and accuracy of fully nonlinear time-domain simulation of wave interaction with a submerged cylindrical wave energy converter oscillating about an off-center axis which was conducted using a two-dimensional numerical wave tank are examined in this study. A high-order boundary element method is used to compute the fluid flow in the Eulerian frame. Fully nonlinear boundary conditions are applied to achieve the unique solution of the boundary value problem. Hence, kinematics of the fluid particles on the exact free surface boundary is calculated using the material node approach in the Lagrangian frame. Runge-Kutta time integration is employed to update the boundary values and the computational control volume. To implement the body condition, the time derivative of the velocity potential is computed implicitly using the acceleration potential. An artificial wave maker and two artificial sponge layers are provided to retain the open water condition. The power absorption efficiency of the submerged Bristol cylinder is compared with experimental data and numerical solutions for different incident waves to verify the present numerical model and the accuracy of the solution is also investigated. The convergence of the present fully nonlinear model in the simulation of the freely rotating cylinder about the off-centered axis as a wave energy converter is evaluated for different submergence depths, off-center distances, and a robust nonlinear incident wave.

Improved numerical wave generation for modelling ocean and coastal engineering problems

We introduce a dynamic-boundary numerical wave generation procedure developed for wave structure interaction (WSI) simulations typical of ocean and coastal engineering problems. This implementation relies on a dynamic mesh which deforms in order to replicate the motion of the wave-maker, and it is integrated in wsiFoam: a multi-region coupling strategy applied to two-phase Navier-Stokes solvers developed in our previous work [Martínez Ferrer et al. A multi-region coupling scheme for compressible and incompressible flow solvers for two-phase flow in a numerical wave tank. Computer & Fluids 125 (2016) 116–129]. The combination of the dynamic-boundary method with a multi-region mesh counteracts the increase in computational cost, which is intrinsic to simulations featuring dynamic domains. This approach results in a high performance computing wave generation strategy that can be utilised in a numerical wave tank to carry out accurate and efficient simulations of wave generation, propagation and interaction with fixed structures and floating bodies.We conduct a series of benchmarks to verify the implementation of this wave generation method and the capabilities of the solver wsiFoam to deal with wave structure interaction problems. These benchmarks include regular and focused waves, wave interaction with a floating body and the modelling of a wave energy converter, using different wave-maker geometries: piston, flap and plunger. The results gathered in this work agree well with experimental data measured in the laboratory and other numerical simulations.

Theoretical analysis and Vsim simulation of a low-voltage high-efficiency 250 GHz gyrotron

Low-voltage, high-frequency gyrotrons with hundreds of watts of power are useful in radar, magnetic resonance spectroscopy and plasma diagnostic applications. In this paper, a 10 kV, 478 W, 250 GHz gyrotron with an efficiency of nearly 40% and a pitch ratio of 1.5 was designed through linear and nonlinear numerical analyses and Vsim particle-in-cell (PIC) simulation. Vsim is a highly efficient parallel PIC code, but it has seldom been used to carry out electron beam wave interaction simulations of gyro-devices. The setting up of the parameters required for the Vsim simulations of the gyrotron is presented. The results of Vsim simulations agree well with that of nonlinear numerical calculation. The commercial software Vsim7.2 completed the 3D gyrotron simulation in 80 h using a 20 core, 2.2 GHz personal computer with 256 GBytes of memory.

Analysis of Blast Wave Parameters Depending on Air Mesh Size

Results of numerical simulations of explosion events greatly depend on the mesh size. Since these simulations demand large amounts of processing time, it is necessary to identify an optimal mesh size that will speed up the calculation and give adequate results. To obtain optimal mesh sizes for further large‐scale numerical simulations of blast wave interactions with overpasses, mesh size convergence tests were conducted for incident and reflected blast waves for close range bursts (up to 5 m). Ansys Autodyn hydrocode software was used for blast modelling in axisymmetric environment for incident pressures and in a 3D environment for reflected pressures. In the axisymmetric environment only the blast wave propagation through the air was considered, and in 3D environment blast wave interaction and reflection of a rigid surface were considered. Analysis showed that numerical results greatly depend on the mesh size and Richardson extrapolation was used for extrapolating optimal mesh size for considered blast scenarios.

Numerical simulation of wave interactions during sudden stratospheric warming

Parameterizations of normal atmospheric modes (NAMs) and orographic gravity waves (OGWs) are implemented into the mechanistic general circulation model of the middle and upper atmosphere (MUA). Numerical experiments of sudden stratospheric warming (SSW) events are performed for climatological conditions typical for January and February using meteorological reanalysis data from the UK MET Office in the MUA model averaged over the years 1992–2011 with the easterly phase of quasi-biennial oscillation (QBO). The simulation shows that an increase in the OGW amplitudes occurs at altitudes higher than 30 km in the Northern Hemisphere after SSW. The OGW amplitudes have maximums at altitudes of about 50 km over the North American and European mountain systems before and during SSW, as well as over the Himalayas after SSW. At high latitudes of the Northern Hemisphere, significant (up to 50–70%) variations in the amplitudes of stationary planetary waves (SPWs) are observed during and after the SSW. Westward travelling NAMs have local amplitude maximums not only in the Northern Hemisphere, but also in the Southern Hemisphere, where there are waveguides for the propagation of these modes. Calculated variations of SPW and NAM amplitudes correspond to changes in the mean temperature and wind fields, as well as the Eliassen-Palm flux and atmospheric refractive index for the planetary waves, during SSW. Including OGW thermal and dynamical effects leads to an increase in amplitude (by 30–70%) of almost all SPWs before and during SSW and to a decrease (up to 20–100%) after the SSW at middle and high latitudes of the Northern Hemisphere.

Numerical simulation of nonlinear long waves in the presence of discontinuous coastal vegetation

We presented numerical simulations of long waves, interacting with arrays of emergent cylinders inside regularly spaced patches, representing tsunamis interacting with discontinuous patchy coastal vegetation. We employed the fully nonlinear and weakly dispersive Serre-Green-Naghdi equations (SGN) until the breaking process starts, while we changed the governing equations to nonlinear shallow water equations (NSW) at the vicinity of the breaking-wave peak and during the run-up stage. We modeled the cylinders as physical boundaries rather than approximating them as macro-roughness friction. Our results show that the cylinders provide protection for the areas behind them. However they might also cause amplification in local water depth in those areas. The presented results are extensively validated against the existing numerical and experimental data. Our results demonstrate the capability and reliability of our model in simulating wave interaction with emergent cylinders.

Numerical analysis of shock wave and supersonic turbulent boundary interaction between adiabatic and cold walls

ABSTRACTDirect numerical simulations of shock wave and supersonic turbulent boundary layer interaction in a 24° compression ramp with adiabatic and cold-wall temperatures are conducted. The wall temperature effects on turbulence structures and shock motions are investigated. The results are validated against previous experimental and numerical data. The effects of wall cooling on boundary layer characteristics are analysed. Statistical data show that wall cooling has a significant effect on the logarithmic region of mean velocity profile downstream the interaction region. Moreover, the influence of wall temperature on Reynolds stress anisotropy is mainly limited in the near-wall region and has little change on the outer layer. As the wall temperature decreases, the streamwise coherency of streaks increases. Based on the analysis of instantaneous Lamb vector divergence, the momentum transport between small-scale vortices on cold-wall condition is significantly enhanced. In addition, spectral analysis of wall pressure signals indicates that the location of peak of low-frequency energy shifts toward higher frequencies in cold case. Furthermore, the dynamic mode decomposition results reveal two characteristic modes, namely a low-frequency mode exhibiting the breathing motion of separation bubble and a high-frequency mode associated with the propagation of instability waves above separation bubble. The shape of dynamic modes is not sensitive to wall temperature.