Wave Tank Research Articles

Performance improvement of a full-scale oscillating water column device by employing a novel double oscillating water column

The energy present in the ocean surface waves can be extracted using an oscillating water column (OWC) device. In the present work, the performance characteristics of a normal OWC, an opposite OWC and a novel double OWC employing Savonius rotors are investigated at different sea states in a numerical wave tank (NWT) using the computational fluid dynamics (CFD) code ANSYS-CFX. The Savonius rotor is known to be an inexpensive energy harvesting device. The waves in the NWT were generated using a piston type wave-maker. The results from the computational work were compared with experimental work. For the normal OWC, a maximum power output of 18.85 kW, which corresponds to an efficiency of 22.44% was recorded at 60 rpm for the mean wave condition. On the other hand, for the opposite OWC, the peak power and efficiency were 10.4 kW and 12.38% respectively for the mean sea state. For the novel double OWC, the flow in the front OWC has more energy compared to the flow in the rear OWC for both advancing flow and retreating flow, resulting in a combined peak power of 19.5 kW at the mean sea state. This represented an increase of 3.45% in the power production.

A multi-fidelity approach for the evaluation of extreme wave loads using nonlinear response-conditioned waves

In the present study, a multi-fidelity methodology based on response-conditioned waves (RCW) is demonstrated for the probabilistic assessment of wave-induced loads and responses of offshore structures. The methodology consists of two steps: (i) the RCW are determined using a surrogate response model and (ii) they are reproduced in an experimental or CFD-based numerical wave tank (NWT) to obtain the fully nonlinear response, as a high-fidelity evaluation. The main novelty of the proposed response-conditioning technique is that it uses a fully nonlinear wave solver that calculates the wave propagation inside an NWT. In this work, the extreme Vertical Bending Moment (VBM) of a zero-speed containership is investigated. It is found that the proposed approach provides nonlinear wave sequences that can be explicitly and exactly reproduced experimentally, up to very extreme sea states (Hs=17 m, Tp=15.5 s). Moreover, through comparison of the obtained results with an experimental Monte Carlo approach, it is shown that the overall framework can predict the short-term distribution of the VBM accurately and efficiently. Finally, given that model tests are costly and not widely accessible, the implementation of the high-fidelity response evaluation within a CFD-based NWT is also demonstrated and validated against the available experimental results.

Coupled Aero–Hydrodynamic Analysis in Floating Offshore Wind Turbines: A Review of Numerical and Experimental Methodologies

Floating offshore wind turbines (FOWTs) have received increasing attention as a crucial component in renewable energy systems in recent years. However, due to the intricate interactions between aerodynamics and hydrodynamics, accurately predicting the performance and response remains a challenging task. This study examines recent advancements in the coupled aero–hydrodynamic numerical simulations for horizontal-axis FOWTs, categorizing existing research by coupling methods: uncoupled, partially coupled, and fully coupled. The review summarizes models, methodologies, and key parameters investigated. Most partially coupled analyses rely on forced oscillation, while the interplay between aerodynamics and elasticity, as well as interactions among multiple FOWTs, remain under-explored. Additionally, this review describes relevant physical model tests, including wave basin tests, wind tunnel tests, and real-time hybrid tests (RTHT). Although RTHT faces issues related to system time delays, they have garnered significant attention for addressing scale effects. The paper compares the three coupling methods, emphasizing the importance of selecting the appropriate approach based on specific design stage requirements to balance accuracy and computational efficiency. Finally, it suggests future research directions, offering a meaningful reference for researchers engaged in studying the aero–hydrodynamic behavior of FOWTs.

Influence of the radial geometric dimensions on the propagation characteristics of detonation waves in an annular channel

Influence of the radial geometric dimensions on the propagation characteristics of detonation waves in an annular channel

Tsunami debris motion and loads in a scaled port setting: Comparative analysis of three state-of-the-art numerical methods against experiments

We present an international comparative analysis of simulated 3D tsunami debris hazards, applying three state-of-the-art numerical methods: the Material Point Method (MPM, ClaymoreUW, multi-GPU), Smoothed Particle Hydrodynamics (SPH, DualSPHysics, GPU), and Eulerian grid-based computational fluid dynamics (Simcenter STAR-CCM+, multi-CPU/GPU). Three teams, two from the United States and one from Germany, apply their unique expertise to shed light on the state of advanced tsunami debris modeling in both open source and professional software. A mutually accepted and meaningful benchmark is set as 1:40 Froude scale model experiments of shipping containers mobilized into and amidst a port setting with simplified and generic structures, closely related to the seminal Tohoku 2011 tsunami case histories which majorly affected seaports. A sophisticated wave flume at Waseda University in Tokyo, Japan, hosted the experiments as reported by Goseberget al. (2016b). Across dozens of trials, an elongated vacuum-chamber wave surges and spills over a generic harbor apron, mobilizing 3–6 hollow debris -modeling sea containers-, in 1–2 vertical layers against friction. One to two rows of 5 square obstacles are placed upstream or downstream of the debris, with widths and gaps of 0.66x and 2.2x of debris length, respectively. The work reports and compares results on the long wave generation from a vacuum-controlled tsunami wave maker, longitudinal displacement of debris forward and back, lateral spreading angle of debris, interactions of stacked debris, and impact forces measured with debris accelerometers and/or obstacle load-cells. Each team writes a foreword on their digital twin model, which are all open-sourced. Then, preliminary statistical analysis contrasts simulations originating off different numerical methods, and simulations with experiments. Afterward, team’s give value propositions for their numerical tool. Finally, a transparent cross-interrogation of results highlights the strengths of each respective method.

Numerical examination of wave forces on partially submerged horizontal circular cylinders near free surface

Determining wave forces on partially submerged horizontal circular cylinders near free surface is a significant issue. This study explores hydrodynamic coefficients and wave forces on horizontal circular cylinders near free surface under large-amplitude wave actions using a viscous fluid numerical wave tank model based on the finite volume method, with a particular aim to accurately predicting the slamming force. By analyzing the characteristics of the wave forces and slamming forces on the circular cylinder, the influences of wave amplitude, wave frequency and vertical position of the cylinder on the wave forces are investigated, and the relationships between the slamming forces and fluid velocity are discussed. Additionally, a modified Morison's equation for predicting the wave forces is derived considering the slamming force and the condition of the circular cylinder completely exposed to the air phase under the action of large-amplitude wave. The results of this study reveal that the wave forces on the circular cylinder are significantly influenced by wave amplitude, frequency and vertical position of the cylinder, and the influences of the cylinder position on the predicted minimum slamming velocity are remarkable. The present study demonstrates that modified Morison's equation is plausible and accurate in predicting the wave and slamming forces for submerged or floating structures.

Nonreciprocal spin wave channeling in ferromagnetic/heavy-metal nanostrips

Nonreciprocity, unidirectionality, and channeling are essential concepts for potential magnonic applications. Nonreciprocity and unidirectionality ensure the efficient propagation of spin waves along predetermined paths with preferential directions, disrupting the symmetry of counterpropagating waves. Channeling fosters the development of intricate spin-wave networks, enabling more sophisticated functionalities. Integrating these concepts into practical applications will shape the future of spin-wave-based information processing devices. This article theoretically studies the dynamics of spin waves in a ferromagnetic strip coupled to a heavy-metal strip, where the nonreciprocity, unidirectionality, and channeling effects are analyzed. Both backward volume (BV) and Damon–Eshbach (DE) configurations are considered, where the lateral dimensions of the heavy-metal and ferromagnetic strips can differ. Calculations show notable nonreciprocal channeling of spin waves in both DE and BV modes. In the BV configuration, the dispersion is reciprocal with nontrivial localization of lateral confined modes. It is shown that the waves can be channeled into the zones in contact with the HM, where the Dzyaloshinskii–Moriya interaction is active. In the DE configuration, the waves exhibit nonreciprocal spin-wave dispersion, allowing unidirectional and channeled spin-wave propagation. The main results are compared to micromagnetic simulations, where an excellent agreement between both methods is obtained. These findings are relevant for envisioning advanced magnonic devices, enabling precise control over spin-wave propagation for innovative, low-power, high-speed information processing.

Spatial variations in numerical wave tanks with active wave generating–absorbing system

Wave–structure interaction can be investigated in detail by numerical experiments, such as Navier–Stokes solvers with Volume Of Fluid models to capture the free surface. The quality of the wave field in such Numerical Wave Tanks largely depends on the boundary conditions to generate or/and absorb the waves. In case of regular waves, instead of obtaining a uniform wave field throughout the wave tank, spatial variations in crest height and trough depth are found with beat lengths smaller than the wave length. In this paper, three different wave absorbing boundary conditions are investigated for their effects on the wave field uniformity: the Original Sommerfeld Boundary Condition, a Generalized Sommerfeld Boundary Condition, and a method including Relaxation Zones. An extensive analysis, involving the decomposition of the waves into incident and reflected waves at first order and higher order harmonics is required to explain the phenomenon of spatial variations. It is concluded that Relaxation Zones provide the most spatially uniform wave fields, at the cost of larger computational domains. The spatial variations in the Original and Generalized Sommerfeld Boundary Conditions are found to also be contributed from the superposition of the second order incident bound waves and the second order reflected free waves. This effect is found to be more significant for steeper waves. A graded mesh method at the absorbing side of the tanks is proposed to minimize the spatial variations.

Cross-shore hydrodynamics and morphodynamics modeling of an erosive event in the inner surf zone

The phase-averaged and depth-integrated coastal morphodynamic model, XBeach-Surfbeat, was investigated for its capability of predicting the cross-shore hydrodynamics and morphodynamics in the inner surf zone by simulating the storm-induced berm erosion, sediment transport, and subsequent sand bar formation. By utilizing a comprehensive hydrodynamic and morphodynamic dataset measured in a large wave flume and high-fidelity 3D large-eddy simulation (LES) data, a rigorous model validation was conducted to assess its capability in predicting inner-surf zone hydrodynamics and to explore how the improved hydrodynamic performance impacts the predicted morphodynamics. Using the default model parameters of the model, the undertow was overestimated with the peak magnitude being 30%–35% larger in the inner surf zone. Combining Monte Carlo simulation, the optimum hydrodynamic calibration for the simulated undertow was achieved when the roller energy dissipation parameter (β) was maintained below 0.1, and the threshold water depth (hmin) exceeded 0.25 m. The calibrated undertow improved the morphodynamic predictions by reducing the excessive berm erosion (Event I) and sand bar growth in the inner surf zone (Event II). Further improved morphodynamic predictions were achieved by calibrating sediment transport parameters, including the onshore sediment transport coefficient (γua) and the bore interval coefficient (Tbfac) associated with turbulence-bed interaction. A consistent set of optimized model coefficients for the model is shown to be effective in simulating the entire erosive event (combined Events I and II). This study reveals that further improvement of the model's capability may require incorporating new parameterizations and physics, such as wave-breaking-induced turbulence and wave nonlinearity associated with sediment transport in the inner surf and swash zones.

New Cubipod armoured breakwater in Hanstholm, Denmark: design and construction

The Port of Hanstholm, located on the exposed North Sea coast of Denmark was expanded during the years 2017–2020. The port expansion features a new large western breakwater in 9–13.5 m water depth with 15 t to 32.5 t Cubipods as its main protective armour. The breakwater head towards the harbour entrance is established by a large prefabricated concrete caisson (40 × 22 × 18 m). The breakwater was extensively tested in the 3D wave basin at Aalborg University, which revealed some remarkably benefits of Cubipods over other concrete armour units. Detailed design of the breakwater, the largest ever built in Denmark, was carried out by COWI A/S for the marine contractor Per Aarsleff A/S, who won the port expansion design–build contract. This paper presents the design consideration for the new western breakwater, including considerations of different breakwater concepts and details on why Cubipods in one layer was eventually chosen as the preferred armour for the breakwater. In addition, the paper describes the laboratory testing of the breakwater and its performance under severe wave conditions. The paper also touches on some of theinnovative methods which were developed by the contractor to keep a high armour layer production rate under challenging wave conditions.

Effect of electroacupuncture on the characteristic signal of electroencephalogram in the patients with chronic insomnia： a randomized controlled trial

To observe the effect of electroacupuncture (EA) on sleep quality and electroencephalogram (EEG) signal in the patients with chronic insomnia and to explore its mechanism. Sixty patients with chronic insomnia were randomized into an EA group (30 cases, 3 cases dropped out) and a health learning group (30 cases, 3 cases dropped out). In the health learning group, the sleep health education was provided. In the EA group, besides the health education as the health learning group, EA was delivered at Baihui (GV20), Yintang (GV24+), bilateral Shenmen (HT7), bilateral Sanyinjiao (SP6), with continuous wave, 2 Hz in frequency, once every other day, and 3 interventions a week. EA was given for 4 weeks successi-vely, composed of 12 treatments. The score of Pittsburgh sleep quality index (PSQI), Hamilton anxiety scale (HAMA), and patient health questionnaire-9 (PHQ-9) before and after treatment were compared between the two groups. The EEG signals were collected and the relative power and entropy of EEG before and after treatment were compared between the two groups. After treatment, the scores of PSQI, HAMA and PHQ-9, the relevant power of β wave in F8 and T3 channels, and that of α wave in T4 channel, and the entropy in T3 channel under the eyes-open (EO) resting state, as well as the relevant power and the entropy of γ wave in F8 channel under the eyes-closed (EC) resting state in the EA group were lower (P<0.05) than those before the treatment. All of the above results were lower than those of the health learning group at the same time points (P<0.05). Under the EO resting state, the relevant power of the θ and δ waves of T3 channel and θ wave of T4, O2 and Pz channels of patients in the EA group after the treatment were increased (P<0.05) than those before the treatment, and higher (P<0.05) than those of the health learning group at the same time points. Acupuncture is effective on chronic insomnia, which may be related to the regulation EEG signals.

Experimental and numerical study on the hydrodynamic responses of a novel offshore floating photovoltaic system

Over the past decade, floating photovoltaics (FPVs) have experienced rapid growth. To effectively reduce costs and actively promote the engineering application of floating photovoltaic systems, an innovative FPV design characterized by low cost, high stability, and excellent seakeeping performance is proposed in this paper. A series of floating pontoons serve as buoyant elements within the system, offering the necessary buoyancy, and solar panels are installed on a support structure which is made up of a truss frame. A series of regular and irregular wave model tests were conducted at the wave basin of Jiangsu University of Science and Technology with model scale determined as 1:20 to assess hydrodynamic characteristics of the FPV. Twenty-One regular wave tests were conducted to establish the Response Amplitude Operator (RAO) of the FPV. Furthermore, irregular wave tests were performed to predict hydrodynamic performance of the FPV under more realistic scenarios. It was found that the FPV system encounters the highest level of danger during beam sea conditions, as compared to when it faces heading sea and quartering sea conditions. Additionally, a comparative numerical model which has been validated by experimental data was applied to study hydrodynamics of the FPV and mooring tensions under extreme sea conditions, thus providing design considerations and profound insights for the future development of this FPV system.

Experimental investigation on L-Oscillating Water Column wave energy converter integrated with floating cylindrical breakwater

One promising renewable energy source for the future is wave energy, harnessed through L-Oscillating Water Column (L-OWC) Wave Energy Converters (WECs). Combining this device with lightweight floating breakwaters can have several advantages, including absorbing wave energy and attenuating waves. L-OWC and two cylindrical floating breakwaters, one in front of the structure and one at the back are coupled in the current study. Previous research indicates that the L-shaped OWC configuration is highly effective due to its increased added mass and enhanced structural stability. The 1:30 scale model, combining a floating breakwater with an Oscillating Water Column (OWC) system, was experimentally investigated in the wave flume at the NITK, Department of Water Resources and Ocean Engineering. This setup included L-shaped OWCs integrated with cylindrical breakwater configurations (2C, 3C, and 4C). OWCs integrate with lightweight floating breakwaters, offering both wave attenuation and energy extraction. The OWC achieved maximum efficiency of 30% under optimal conditions, with a wave period of approximately 1.8s and a wave height of 0.06 m for the model with three floating breakwaters. The work aligns with the United Nations' Sustainable Development Goals (SDG), specifically addressing clean and affordable energy (SDG 7), industry, innovation, and infrastructure (SDG 9), life below water (SDG 14), and life on land (SDG 15), highlighting its significant impact.

Nearshore Migration of Munitions and Canonical Objects Under Large-Scale Laboratory Forcing

A quantitative understanding of the migration of munitions and canonical objects in the nearshore is needed for the effective management of contaminated sites. Migrations of munitions with a density range of 2000 kg/m3 to 5720 kg/m3 were quantified in a large-scale wave flume. The forcing consisted of six cases of varying wave heights, periods, still water depths, and durations. The cross-shore profile, typical of natural sandy beaches, was sub-divided into swash, surf, and offshore zones. Overall, 2228 migration measurements were recorded with 16% and 84% of the migration observations classified as “motion” (net distance &gt; 0.5 m) and “no motion” (net distance ≤ 0.5 m), respectively. The probability of munitions migration increased with proximity to the shoreline. There was a nearly equal probability of onshore or offshore migration in the swash zone. Migration in the surf zone tended to be offshore-directed (65%), while migration was onshore-dominant (65%) in the offshore zone. Migration in the offshore zone was preferentially onshore due to skewed waves over flat bathymetry. Less dense munitions in the offshore zone may have migrated offshore likely still related to the skewed nature of the wave profile causing transport in both directions through the majority of the wave phase. The largest migration distances occurred in the surf zone likely due to downslope gravity. Migration in the surf and swash zones is a balance between skewed/asymmetric forcing and downslope gravity, with downslope gravity tending to be pronounced provided the forcing is sufficient to initiate motion. An exception was sometimes observed in the swash zone where onshore forcing was sufficient to transport munitions to the seaward side of the berm where they became trapped in a bathymetric depression between the dune and berm. Relating overall migration (Lagrangian) to fixed hydrodynamic measurements (Eulerian) was ineffective. Parameters such as the Shields number, wave skewness, and wave asymmetry estimated from the closest measurement location were insufficient to predict migration. Large scatter in the migration data resulting from competing hydrodynamic, morphodynamic, and munitions response processes makes robust deterministic predictions with flow statistics and dimensionless numbers difficult.

Experimental study of coupling response characteristics of offshore monopiles, seabed, and waves in various sea conditions

As the global pursuit of renewable energy intensifies and the demand for offshore wind turbines rises, a comprehensive understanding of the coupling response characteristics of offshore monopiles, seabed, and waves in various sea conditions has become increasingly crucial. This paper reports on a wave flume experiment and seeks to contribute valuable insights by examining the coupling response of offshore monopiles, seabed, and waves exerting a relentless influence. The experimental results indicate that the impact of waves on monopiles is significant: there is greater pressure on the wave facing surface of the offshore piles than the other faces, and the pressure increases with increased wave height as well as the height of the monopile. The wave impact also gives rise to pile motion, squeezing the soil near the monopile and causing gradual pore water pressure around the monopile, and when the wave impact is strong enough, the monopile loses stability. Finally, the experimental results indicate significant differences in the coupling response characteristics of an offshore monopile, the seabed, and waves in various sea conditions. When the wave height was small, the pore water pressure attenuated quickly in the direction of the depth of the seabed; however, as the height and period of waves increased, when the test wave height was more than 18.6 cm and the period was more than 1.63 s, the dynamic pore water pressure around the monopile first decreased and then increased along the depth direction, which, generated by the wave impact, led to vibration and squeezing of the soil near the monopile leg. This indicates that the closer the pile bottom, the more intense the squeezing. By investigating this development across different sea conditions, this study provides a nuanced understanding that can inform the design of offshore monopiles in the face of various marine environmental challenges.

Reconstructing Signals in Millimeter Wave Channels Using Bayesian-Based Fading Models

Fading in communication channels presents eminently stochastic characteristics and is a significant challenge, especially at millimeter wave (mmW) frequencies, where the need for lines of sight and the high attenuation of obstacles complicate transmission. This article presents a model based on Bayesian fundamentals intended to improve the description and simulation of stochastic fading effects in these channels. It also includes the use of signal processing techniques to simulate and reconstruct the received signal, simulating the communication channel with an FIR filter. The results obtained by simulating the model show its ability to efficiently capture rapid and profound variations in the signal, typical of those that occur in urban and suburban environments and transmissions in the mmW spectrum. It also provides greater uniformity in signal reconstruction compared to the traditional models that are in use. Using Bayesian fundamentals, which allow dynamic adaptation to change in channel behavior, can improve the efficiency and reliability of networks, especially modern smart networks. Compared to traditional models, the proposed model offers improved signal reconstruction and fading mitigation accuracy, with prospects for future integration in smart communication systems. The better capacity in signal reconstruction presents itself as a differentiator of the model, suggesting greater precision in data transmission.

Ship-shaped vessel hydroelastic numerically supported analysis in a narrow ultra-reduced model tank with full scale extrapolation

Although the rigid body hypothesis is broadly used when studying floating bodies dynamics, it is known that a ship-shaped vessel will have hydroelastic responses. Considering a conventional closed main deck hull in which the ship's length is considerably greater than its breadth, it is expected that the vertical bending moments can represent an important load that must be considered to guarantee structural integrity. Numerical models can be developed to assess the hydroelastic response, but the validation process is necessary. Model tests can be performed to validate the numerical model and require specific considerations to properly represent hydroelastic phenomena, such as having equivalent bending stiffness when compared to the full-scale body. Many experimental facilities that can be used to perform such experiments consist of narrow wave channels, in which the wall effect will influence the model's dynamics. This work implements a Tank Green Function (TGF) to a numerical model developed in Capytaine to represent the wall effect on the body's response. The numerical results were then compared to experimental data from tests in a narrow wave channel and good adherence was found. The validated numerical model can then be used to simulate open-water conditions, so the results can be extrapolated to full scale without the need to perform model tests in an ocean tank in which the wall effect would not be relevant.

Hybrid Testing System Development for Single Point Mooring Lines FOWT’s

Abstract To advance the development of various concepts for floating offshore wind turbines, it is imperative to have access to experimental data. These data are used in the validation of the tools for the simulation of floating turbines and also for the tuning of the models. CENER has developed a hybrid testing methodology that enhances the performance of wave basin tests for scaled models of Floating Offshore Wind Turbines (FOWTs). This approach allows us to apply forces and moments from the wind turbine to the floating platform without needing to replicate wind within the testing facility or create a complex model of the wind turbine rotor. However, when it comes to testing single point moored (SPM) platforms, a unique challenge arises. These platforms have an additional degree of freedom as they can freely rotate around the vertical axis of their mooring attachment (yaw degree of freedom). These type of platforms can present important misalignments with respect to the wind depending on the combination of wind, wave and current directions. Consequently, accurately capturing the impact of misalignment on platform dynamics, especially in yaw, is essential to assess the platform’s ability to self-align with the wind direction, a key factor known as weathervaning capacity. The X1Wind platform is an innovative floating wind system, based on a single point mooring solution with a downwind wind turbine configuration that allows it to be passively self-orientated. The concept has been extensively tested on prototypes at real sea conditions as well as on scaled models at wave basins. For the last wave basin testing campaign, X1Wind has entrusted CENER with the development of the hybrid testing methodology adapted to the requirements of SPM platforms. The testing campaign has covered different wave and wind conditions, including misalignment scenarios and has shown a good dynamic behavior of the platform on yaw. This study outlines the advancements made in the CENER Software-in-the-Loop (SiL) hybrid testing system for wave basin tests of SPM platforms. In order to correctly introduce the direction of the aerodynamic forces on the wind turbine under misaligned conditions, improvements on the software and hardware (loads actuator) of the SiL system were developed and tested. An actuator system consisting of 6 propellers was used. The numerical model that calculates the rotor aerodynamic loading were expanded to take into consideration the direction of the aerodynamic loads with respect to the platform. Additionally, the drag of the wind over the tower and other platform elements must be considered, as they can play a relevant role in the generation of the weathervaning moment. The study concludes that the use of the upgraded SiL hybrid testing system is an effective and afordable solution for the testing of scaled SPM platforms at wave basin facilities. It also summarizes the different considerations that the system has to overcome for the particularity of this type of testing application.

The suppression of ocean waves by biogenic slicks.

Ocean waves are significantly damped by biogenic surfactants, which accumulate at the sea surface in every ocean basin. The growth, development, and breaking of short wind-driven surface waves are key mediators of the air-sea exchange of momentum, heat and trace gases. The mechanisms through which surfactants suppress waves have been studied in great detail through careful laboratory experimentation in quasi-one-dimensional wave tanks. However, the spatial scales over which this damping occurs in structurally complex surfactant slicks on the real ocean have not been resolved. Here, we present the results of field observations of the spatial response of decimetre- to millimetre-scale waves to biogenic surfactant slicks. We found that wave damping in organic material-rich coastal waters resulted in a net (spatio-temporally averaged) reduction of approximately 50% in wave slope variance relative to the open ocean for low to moderate wind speeds. This reduction of wave slope variance is understood to result in a corresponding reduction in momentum input to the wave field. This significant effect had thus far evaded quantification due in large part to the enormous range of scales required for its description-spanning the sea surface microlayer to the ocean submesoscale.

Effects of a 3D basin on the near-fault ground motion by an FK-FE hybrid method

In the pursuit of accurately representing the full-process ground motion of a 3D near-fault complex site, an FK-FE hybrid method based on the idea of domain reduction is proposed. By integrating the Frequency-Wavenumber (FK) and Finite Element (FE) Methods, the hybrid method provides a new solution to seismic modeling which adaptively addresses multi-scale crustal models (from crustal to geotechnical scale) and intricate 3D site models, with consistent efficiency and precision. Then, the hybrid method is verified by comparing with results of the FK method and further validated by comparing with strong-earthquake records of the 2021 Yangbi M6.4 earthquake. Further, the proposed hybrid method is used to investigate the influence of the basin (wave velocity ratio of internal and external medium, basin's thickness) on near-fault effects due to the finite-fault source, and reveal the comprehensive mechanism of near-fault effects and basin effects. The results show that: the basin-focusing effect enhances the concentration of near-fault ground motions, and further expands the concentration range of strong-earthquake. The increases of the wave velocity ratio and basin's thickness augment the basin-focusing effect, and then the amplification effect of the basin on the fling-step effect becomes more pronounced. These results can provide a reference basis for seismic ground motion estimation and engineering seismic design in near-field complex sites.