Target Wave Research Articles

Self-Organized Target Wave Chimeras in Reaction-Diffusion Media

Self-Organized Target Wave Chimeras in Reaction-Diffusion Media

2D Model For Addu City Project - Wave Transformation Over Reef Flat

Van Oord DMC was awarded the Contract for the Reclamation by Dredging and Shore Protection works for land in Addu City by The Ministry of National Planning, Housing and Infrastructure of the Maldives. The Scope of Works consists of the Design and Construction of (among others) Reclamation and Shore Protection Works on various locations in the Addu City atoll. The project execution started in 2022 and has been finalized at the end of 2023. The design of the Shore Protection Works has been verified in 2022 by means of 2D physical model testing in the wave flume of DHI in Denmark. Cross-sections of shore protection works for three different reclamation areas have been tested, where this abstract will focus on 2 locations at the outside of the atoll: Maradhoo and Four Lane Link Road (4LLR). All dimensions given in this abstract are prototype values, unless otherwise specified. The length scale of the both models was selected at 1:30. The foreshore of the 2 tested cross-sections is very typical for atolls, consisting of a relatively shallow reef flat followed by a very steep slope to deep water. The modelled foreshores are presented in Figure 1. This figure also shows the locations of the wave gauges, which were placed both offshore (near the wave generator) and on top of the reef flat (in front of the structure). The tested seabed levels directly at the toe of the 4LLR and Maradhoo structures were MSL-0.70m and MSL-0.40m respectively. The target wave conditions were defined in deep water (in front of the wave generator), with design wave heights (Hm0) between 3.8m and 4.4m and 120% overload conditions. The tested peak wave periods (Tp) varied between 11.9s and 19.7s.

Validation Of An Efficient Non-Hydrostatic Wave Model As A Design Tool For Foreshores In Physical Models

In the design of physical model experiments in coastal engineering, it is common that the construction of a foreshore is necessary to obtain the desired wave conditions at a given location, usually close to a structure being tested. In addition to the commonly used spectral wave parameters to describe the target wave conditions, the wave height distribution and associated parameters (such as Hmax and H2%), wave periods and infra-gravity waves can be important to reproduce properly as well. Wave height distributions are typically important for tests where e.g. wave run-up or wave forces are of interest. Since the construction of foreshores is labour intensive (and thus expensive), it is useful to be able to check a priori whether the target wave conditions are met with a given foreshore design and whether the chosen transition slope does not significantly influence the wave conditions. One way to do this is by using numerical wave models. For a numerical model to be a useful design tool for physical model layouts, the predicted wave transformation (over the foreshore) needs to be sufficiently accurate. One option is to use detailed CFD wave models for this purpose, such as OpenFOAM, which has been shown to accurately reproduce wave transformation (Jacobsen et al., 2015; Jacobsen et al., 2018). CFD models, however, typically feature high computational demand and consequentially computational times in the order of days. This is a significant disadvantage in the context of designing a physical model experiment, for which the layout and configuration is often an iterative process, which would be hampered by overly long computational times. On the other hand, spectral wave models, like SWAN (Booij et al., 1996), are much faster but do not model all the individual waves rendering it unable to model exceedance distributions. As a middle-ground, it seems that the XBeach model (Roelvink et al., 2009) used in its 2-layer non-hydrostatic mode (De Ridder et al., 2021) might present a workable compromise between computational time and accurate representation of the wave transformation. The model has been validated by De Ridder et al. (2021) on bichromatic waves, complex barred beach geometry and a fringing reef for bulk wave parameters and spectral properties. Expanding on earlier validation work, in this work the ability of the XBeach 2-layer non-hydrostatic model (XBeach-nh) to reproduce wave height exceedance distributions over a sloping foreshore is validated using wave flume data, described in Sections 2 and 3. The preliminary results of the validation effort are shown in Section 4.

High-Order Spectral Irregular Wave Generation Procedure in Experimental and Computational Fluid Dynamics Numerical Wave Tanks, with Application in a Physical Wave Tank and in Open-Source Field Operation and Manipulation

The accurate generation of a target sea state in numerical or experimental wave tanks is a fundamental line of research for the ocean engineering community. It guarantees the quality and relevance of wave–structure interaction tests. This study presents a reproducible irregular wave generation and qualification procedure, accounting for the nonlinear aspects of wave propagation. It can be used for both numerical simulation and experiments. The presented numerical and experimental results are obtained from the OpenFOAM solver and the Ecole Centrale Nantes wave tank facilities, respectively. The procedure comprises two steps: First, the wavemaker motion is calibrated numerically to generate the target wave spectrum at the position of interest. This is achieved with a wavemaker-equipped nonlinear potential flow solver. The open-source HOS-NWT solver, based on the high-order spectral method, was employed in this study. Then, the corrected wavemaker motion is used directly in the experimental wave tank. OpenFOAM simulations were performed to generate waves with the relaxation method, using wave elevation and velocity field data from HOS-NWT. The procedure was finally tested for mild and extreme breaking sea states. The waves generated by the HOS-NWT solver, the experiment, and the OpenFOAM simulation were compared from both stochastic and deterministic perspectives.

A numerical study of added resistance performance and hydrodynamics of KCS hull in oblique regular waves and estimation of resistance in short-crested irregular waves through spectral method

Research on multidirectional waves is increasing as studies on added resistance advance. In this study, the added resistance of the multidirectional regular waves of the KCS hull was estimated by numerical analysis. The direction of the grid was changed according to the heading angle to consider waves in multiple directions. In addition, the method in which the entire domain moved along the movement of the hull was used without using the overset method to minimize the numerical errors. The added resistance and motion RAOs for each angle and the flow characteristics were compared to support the results. For fluid dynamics, time-averaged stern dynamics pressure, boundary layer, and nominal wake for each heading angle were compared, and differences compared to calm water were also reviewed. Based on the bow quartering sea condition analysis results, the added resistance in long-crested and short-crested irregular wave conditions was estimated using the spectral method. The JONSWAP spectrum was used as the target wave spectrum, and the cos-power type was considered the directional spreading function.

Numerical Study of Nonlinear Effects on the Performance of the Self-Protected Energy Concentrator

Wave concentrators have important application value in ocean engineering. Moreover, the performance of a concentrator on structural protection is important in the context of the complex ocean environment. A series of numerical simulations of the self-protected energy concentrator (SPEC) is performed under nonlinear wave conditions. The SPEC includes eight truncated cylinders arranged in a concentric circle. The performance of SPEC and the distribution of fluid field are studied by establishing a computational fluid dynamics (CFDs) model. It can be concluded that increasing wave steepness can weaken the self-protection performance and concentration effects due to its strong nonlinearity. The wave directions have little effect on the performance of SPEC. In addition, the change based on the target wave number can result in poor performance of SPEC.

The Intersection of Computational Design and Wearable‐Optimized Electrospun Structural Nanohybrids for Electromagnetic Absorption

AbstractBy leveraging the principles of electromagnetic theory and materials science, the characteristics of dielectric polymer composites can be optimized, eliminating repetitive trial‐and‐error in their application as electromagnetic absorbers (EMAs). Herein, a systematic framework for optimizing the thickness and composition of double‐layer EMAs is proposed, using a combination of transmission line, Debye relaxation, and Maxwell–Garnett theories. Following theoretical optimization, a double‐layered electrospun EMA is fabricated, which comprises a ≈1.17 mm thick matrix of styrene–butadiene–styrene (SBS) decorated with MXene on its fibrous structure. The second SBS layer, with a thickness of ≈0.52 mm, incorporates a hybrid of MXene and graphene nanoribbons (GNR) as conductive additives. The EMA exhibits durable electrical performance after 2000 tensile cycles, owing to the surface chemistry engineering and the novel in situ assembly technique. It is capable of shielding 99.9% of the incident wave and >80% absorptivity (A) over almost the entire Ku‐band. The EMA also exhibits desirable mechanical characteristics, such as >300% stretchability and full twist and wrinkle recoveries, making it an excellent choice for protective attire applications. Additionally, the introduced approach provides solutions for the advancement of tailorable polymer composite EMAs, with respect to specific criteria of the target wave frequency, effective absorption bandwidth, and absorption levels.

Dynamic modelling and engineering simulation of fluid mechanics in water injectors

To study the fluid dynamic response mechanism under the working condition of water injection well borehole, based on the microelement analysis of fluid mechanics and the classical theory of hydrodynamics, a fluid microelement pressure-flow rate relationship model is built to derive and solve the dynamic distribution of fluid pressure and flow rate in the space of well borehole. Combined with the production data of a typical deviated well in China, numerical simulations and analyses are carried out to analyze the dynamic distribution of wellbore pressure at different injection pressures and injection volumes, the delayed and attenuated characteristics of fluid transmission in tube, and the dynamic distribution of wellbore pressure amplitude under the fluctuation of wellhead pressure. The pressure loss along the wellbore has nothing to do with the absolute pressure, and the design of the coding and decoding scheme for wave code communication doesn't need to consider the absolute pressure during injecting. When the injection pressure is constant, the higher the injection flow rate at the wellhead, the larger the pressure loss along the wellbore. The fluid wave signal delay amplitude mainly depends on the length of the wellbore. The smaller the tubing diameter, the larger the fluid wave signal attenuation amplitude. The higher the target wave code amplitude (differential pressure identification root mean square) generated at the same well depth, the greater the wellhead pressure wave amplitude required to overcome the wellbore pressure loss.

GENERATION OF LINEAR WAVES WITH BOTTOM WAVE MAKERS IN A FLUME: AN EFFICIENT WAY TO ABSORB REFLECTED WAVES

When waves are generated in a flume by the conventional piston or flap wave maker, waves reflected from structures will arrive at the wave maker and experience re-reflection. These re-reflected waves will propagate to the structures so that the target wave energy cannot be accurately obtained. Since 1980s, methods of internally generating waves inside a computational domain and putting sponge layers at the domain end have been developed in numerical modelling. Internally generated waves will propagate both directions from the wave generation zone and waves reflected from the structures will pass through the wave generation zone without any reflection by the wave maker and be absorbed in the sponge layers. Using the idea of internal generation of waves, Jung et al. (2018) developed bottom wave makers in a flume which have paddles moving up and down from the bottom (see also Lu et al. (2017)). In this study, following Jung et al.’s (2018) techniques, we numerically develop both rectangular and triangular bottom wave makers in a flume using the analytical method and the extended mild-slope equations.

Fabrication of a multifaceted mapping mirror using two-photon polymerization for a snapshot image mapping spectrometer.

A design and fabrication technique for making high-precision and large-format multifaceted mapping mirrors is presented. The method is based on two-photon polymerization, which allows more flexibility in the mapping mirror design. The mirror fabricated in this paper consists of 36 2D tilted square pixels, instead of the continuous facet design used in diamond cutting. The paper presents a detailed discussion of the fabrication parameters and optimization process, with particular emphasis on the optimization of stitching defects by compensating for the overall tilt angle and reducing the printing field of view. The fabricated mirrors were coated with a thin layer of aluminum (93nm) using sputter coating to enhance the reflection rate over the target wave range. The mapping mirror was characterized using a white light interferometer and a scanning electron microscope, which demonstrates its optical quality surface (with a surface roughness of 12nm) and high-precision tilt angles (with an average of 2.03% deviation). Finally, the incorporation of one of the 3D printed mapping mirrors into an image mapping spectrometer prototype allowed for the acquisition of high-quality images of the USAF resolution target and bovine pulmonary artery endothelial cells stained with three fluorescent dyes, demonstrating the potential of this technology for practical applications.

Cross sections for single-electron capture from heliumlike targets by fast heavy nuclei

Single charge-exchange in collisions of heavy bare nuclei with the ground state of two-electron atomic targets is described perturbatively as a four-body problem. The employed four-body boundary-corrected continuum intermediate state (BCIS-4B) method considers the correlated and uncorrelated target wave functions ${\ensuremath{\varphi}}_{i}.$ A thorough examination is performed for the formation of any final hydrogen-like $nlm$ state of the captured electron. For arbitrary projectile and target nuclear charges, the nine-dimensional integral in the transition amplitude is reduced to a two-dimensional numerical quadrature. The general analysis is applied to one-electron capture by protons from helium targets beginning with the lower edge (10 keV) of intermediate energies and extending to the higher (12.5 MeV) domain. These include the main peaks (Massey, Thomas) due to single and double scattering, respectively. The results encompass over 70 state-selective and state-summed cross sections $(n\ensuremath{\le}6,\phantom{\rule{0.16em}{0ex}}0\ensuremath{\le}l\ensuremath{\le}n\ensuremath{-}1,\phantom{\rule{0.16em}{0ex}}\ensuremath{-}l\ensuremath{\le}m\ensuremath{\le}l).$ In comparison to measurements, the electronic correlations in ${\ensuremath{\varphi}}_{i}$ greatly improve the overall performance of the BCIS-4B method around the Massey peak, below about 100 keV. Moreover, while largely outperforming the three-body boundary-corrected continuum intermediate state method, the cross sections in the BCIS-4B with the correlated ${\ensuremath{\varphi}}_{i}$ compare excellently overall with the available experimental data at 10 to 12 500 keV. Hence, the BCIS-4B method, with its built-in two main capture mechanisms (one-step Massey and two-step Thomas) is capable of spanning impact energies covering three or more orders of magnitude at which the state-summed cross sections vary over 11 orders of magnitude.

Mode-Selective Elastic Metasurfaces

The existence of multimodes is a unique characteristic of various elastic wave systems, including elastic metasurfaces. Nevertheless, most of the previous research on elastic metasurfaces has focused on a single mode only, so the related physics is largely unknown and noise is generated by the undesired incident wave mode. Here, we present a mode-selective elastic metasurface that can tailor the target wave mode while filtering out the undesired wave mode. To this end, analytical investigation is carried out for an elastic metasurface with multimode incidence such that the metasurface can operate for both longitudinal and shear wave modes. After that, the mode-selective elastic metasurface is designed and validated numerically and experimentally. With our research, it is now possible to explicitly design an elastic metasurface for the multimode incidence case. Furthermore, since the noise caused by the undesired wave mode is barely generated with the proposed mode-selective metasurface, various elastic wave devices and physical findings are expected from the current research.

A simple approach for wave absorbing control of plunger wavemakers using machine learning: Numerical study

Due to the complex geometry, the research for theoretical methods on wave absorption with plunger-type wavemakers is not easy. Therefore, this paper proposes a simple approach for wave absorbing control of plunger wavemakers using machine learning. The main contribution of this approach is to control plunger wavemakers to absorb waves in the time domain, and no theoretical derivation is required. The neural networks are trained to map the time-independent relationship between the wavemaker velocity and recorded wave variables (i.e. wave period, water depth, free-surface elevation along the wavemaker, velocities of the free-surface elevation along the wavemaker and position of the wavemaker). A penalty term is proposed to avoid the overfitting of neural networks. A numerical wave flume is applied to generate training data and simulate wave absorption. Taking a wedge plunger wavemaker as an example, the regular wave absorption with full reflection is tested. The simulated wave profiles and wave orbital velocities are validated with analytical solutions, showing that the proposed approach is effective at eliminating the reflected wave. A cylinder plunger wavemaker is also performed to absorb the solitary and irregular waves. The irregular wave can be absorbed stably in a long-term simulation. The solitary wave with a small height can also be absorbed well, illustrating the potential of the proposed approach in different plunger shapes and wave conditions. • This paper proposes a simple approach for wave absorbing control of plunger wavemakers using machine learning, and no complex theoretical derivation is required. • Penalty term based on wave mechanisms is introduced to prevent neural networks from overfitting. • Once the target wave profiles in front of the wavemaker are given, it can realize generating waves and absorbing reflected waves at the same time. • The proposed approach is suitable for different plunger shapes and wave conditions.

Water wave cloaking using a floating composite plate

The trajectory of surface gravity waves in the potential flow regime is affected by the gravitational acceleration, water density and sea bed depth. Although the gravitational acceleration and water density are approximately constant, the effect of water depth on surface gravity waves exponentially decreases as the water depth increases. In shallow water, cloaking an object from surface waves by varying the sea bed topography is possible, however, as the water depth increases, cloaking becomes a challenge because there is no physical parameter to be engineered and subsequently affects the wave propagation. In order to create an omnidirectional cylindrical cloaking device for finite-depth/deep-water waves, we propose an elastic composite plate that floats on the surface around a to-be-cloaked cylinder. The composite plate is made of axisymmetric, homogeneous and isotropic annular thin rings which provide adjustable degrees of freedom to engineer and affect the wave propagation. We first develop a pseudo-spectral method to efficiently determine the wave solution for a floating composite plate. Next, we optimise the physical parameters of the plate (i.e. flexural rigidity and mass of every ring) using an evolutionary algorithm to minimise the energy of scattered waves from the object and therefore cloak the inner cylinder from incident waves. We show that the optimised cloak reduces the energy of scattered waves as high as 99 % for the target wave number. We quantify the effectiveness of our cloak with different parameters of the plate and show that varying the flexural rigidity is essential to control wave propagation and the cloaking structure needs to be at least made of four rings with a radius of at least three times of the cloaked region. We quantify the wave drift force exerted on the structures and show that the optimised plate reduces the exerted force by 99.9 %. The proposed cloak, due to its structural simplicity and effectiveness in reducing the wave drift force, may have potential applications in cloaking offshore structures from water waves.

Radar Cross-section of a target and attenuation of electromagnetic waves in sandstorms

The sand particles suspended in the atmosphere can cause the attenuation of electromagnetic waves (EWs) and affect the electromagnetic scattering properties of a target during sandstorms. In this study, a theoretical analysis is offered for the prediction of the EWs attenuation and the radar cross section (RCS) of a target in sandstorms. In the model, an equivalent medium approximation is performed by considering the non-uniform charge distribution on the sand particles, and the effect of the charged sand particles on the scattering characteristics of a target is also taken into account. Numerical results show that the RCS of a target is severely affected in sandstorms. Besides, the charged sand particles have a much greater effect on the target's RCS than the case of the uncharged sand particles. It can be found that the average variation value of the target's RCS decreases nearly exponentially with the increase of visibility, and increases nearly linearly with the distance between the target and incident wave source. Finally, an empirical formula is presented to calculate the RCS of an arbitrarily shaped metal target in a homogeneous lossy medium. These investigations will be of significant benefit to radar detection technology in sandstorms.

Experimental and numerical investigation on an optimization method of heaving buoy wave energy converter arrays based on a given target wave spectrum

In this paper, an active optimization method of a wave energy converter (WEC) array that focuses on the characteristics of the random sea condition is proposed. Physical model tests were conducted in both regular and irregular wave conditions. Three representative regular wave cases were determined from the target wave spectrum using the method. A rigid cylindrical heaving buoy model with different constant power take-off (PTO) damping forces and drafts was applied to find the optimal isolated WEC parameter under each regular wave condition. Three equal buoys with respective optimized parameters were arranged rectilinearly into a WEC array for irregular wave tests. The power output of arrays with different settings are compared, indicating the advantages of the different optimized array and the significance of unit order. To amplify the optimization effect, a supplementary numerical investigation of a 5-body WEC array was carried out using the boundary element method (BEM). The results demonstrate the method and show the influence of the number of different units.

Anti-phase synchronization of waves in a multiplex network of van der Pol oscillators

We study numerically the spatiotemporal dynamics and anti-phase synchronization of complex structures in a two-layer multiplex network of bidirectionally and repulsively coupled two-dimensional lattices. Each layer consists of locally and attractively coupled identical van der Pol oscillators. Depending on randomly distributed initial conditions the isolated layers can exhibit either a spiral or a target wave regime. The latter is found for first time for the locally coupled van der Pol lattice considered in this work. We vary the inter-layer coupling strength for either fixed or changing intra-layer coupling strengths in the interacting layers. The numerical results are summarized in the two-dimensional diagrams plotted in the “intra-layer coupling strength – inter-layer coupling strength” parameter plane. Anti-phase synchronization is identified by evaluating the local and global cross-correlation coefficients which are equal to −1. We also explore the impact of random de-multiplexing on the robustness of the observed spatiotemporal structures and anti-phase synchronized regimes in the two-layer network.

Pattern formation induced by gradient field coupling in bi-layer neuronal networks

The pattern formation in heterogeneous excitable media is a common phenomenon for spatiotemporal systems. In this paper, a bi-layer neuronal network is studied in which the two layers are connected using electromagnetic field coupling with two types of coupling gradients (i.e., step-like and cone-like). It is observed that when the central intensity of a gradient fieid is small, cone-like has less destructive effect on the target wave of the first layer compared to step-like. To further study the influence of environmental factors on pattern formation, the central intensity and external stimulation in the gradient field are continuously increased. The results show that the larger central intensity of the gradient field destroys the the target wave of the first layer and may form a spiral wave, and a larger external stimulation is more effective for inducing spiral waves in the second layer. Finally, synchronization factors are used to predict the pattern and formation mechanism of the spiral wave, and it is found that spiral waves are more likely to occur at the second layer with smaller values and the opposite at the first layer.

A Study on the Influence of Sand Median Grain Size on the Short-Term Recovery Process of Shorelines

Recently, the impacts of short-term erosion caused by storm waves on coastal damages are increasingly recognized as social issues, compared to those of long-term erosion from climate change or coastal development. The erosion caused by the storm wave has an episodic characteristic that the shoreline recovers gradually after retreating for a short-term. Furthermore, if shoreline changes caused by longshore sediment transport are not taken into consideration, the shoreline position is determined by following two physical parameters based on the bulk response model. The beach response factor determines converging ultimate erosion on the assumption that incident waves constantly affects a beach, which can be estimated according to the concept of Dean’s profile. On the contrary, the beach recovery factor affects the velocity of the shoreline retreat and recovery. Therefore, the parameter plays an important role to predict the peak erosion due to the storms. However, there are still insufficient researches to utilize it as an engineering design for erosion reduction. In this study, the two methodologies (i.e., approximation formula and statistical analysis) that estimates peak erosion width caused by the storms are compared to extract the beach recovery factor. During the process, it is confirmed that peak wave height has little impact on the beach recovery factor. Instead, it is mainly determined by the median grain size. Also, the beach recovery factor is estimated as a function of median grain size based on the shoreline and sand survey data conducted over ten years. Among the 41 surveyed sites along the east coast, 11 sites of straight-type shorelines that directly react to the incident waves were applied to consider only the short-term recovery process. To prove validity, the estimated applied into the real sea and then the results were compared to the shoreline data extracted from CCTV images. Using these results, the peak erosion width for a target wave event can be predicted with only median grain size. These study results are expected to be used as a concrete and practical means to manage the coast, in preparation for the current and future shoreline erosion threats.

Emergence of hidden dynamics in different neuronal network architecture with injected electromagnetic induction

The diverse firing responses in a single neuron model as well as in a neuronal network play a major role in understanding the collective neuronal dynamics. In this paper, we consider an excitable slow-fast memristive model and study its various intrinsic dynamics by allowing a periodic external stimulus. The single model exhibits various types of spiking, bursting, mixed-mode oscillations (MMOs), and mixed-mode bursting oscillations (MMBOs) depending on the amplitude and frequency of the periodic injected current. Corresponding bifurcation analysis reveals the existence of supercritical and subcritical Hopf bifurcations in the system depending on the major predominant parameters that establish the scenarios of the neuronal responses. We have verified analytically the existence and stability of Hopf bifurcations. The memristive system can produce cascade of period doubling bifurcations for particular parameter regimes. Next, we investigate the emergence of multi-arm antispiral waves in the diffusively coupled system with proper analytical justification. We have also computed the group and phase velocities to discern the spiral and antispiral waves near the Hopf instability. A transition from target wave to multi-arm antispiral wave is observed in the diffusive system. Moreover, we use a random network architecture different from the diffusive network to study the dynamics of the coupled network for certain firing activities. It is observed that the network of heterogeneous desynchronized neurons with higher electrical couplings, can generate MMOs, MMBOs, and bursting for different external stimuli. However, the uncoupled systems cannot reveal such typical dynamics for particular parameters. Further, we introduce a reduced-order model to summarize the complete dynamics of the larger random network and report the findings.