Wave Research Articles

Seismic response analysis of subway station under obliquely incident SV waves

This paper aims to investigate the dynamic response characteristics of subway station under earthquakes. To this end, seismic waves are transformed into equivalent nodal loads on viscoelastic artificial boundaries using theories and methods of wave motion. The calculation formulas for equivalent nodal loads of SV waves incident at any angle are established, and ANSYS' APDL program compiles to automatically generate the viscoelastic artificial boundary and input the seismic loads. A finite element model of soil-subway station interaction was established, and the seismic response characteristics of a two-story three-span subway station under different incidence angles of SV waves were investigated using the above seismic input method. The results indicate that the incidence angle of seismic waves has a significant impact on the seismic response of subway station. Inclined incidence of seismic waves causes non-uniform loading and deformation of the subway station. Specifically, a small angle leads to predominantly transverse shear deformation, while a large angle causes mainly vertical shear deformation. The inclined incidence of seismic waves significantly increases the vertical acceleration of the subway station, with the effect becoming more pronounced as the angle increases. Additionally, special attention should be given to the joints between the structural slab and the side wall, slab and center column, as well as the two ends of the center column as they are vulnerable areas during earthquakes and require careful consideration in seismic design.

Numerical study on stem-generated turbulence due to emergent rigid vegetation in water waves

Based on the RANS equations and applying the waves2Foam solver in OpenFOAM, the study numerically investigated the turbulent kinetic energy (TKE) generated due to emergent rigid vegetation in water waves. The numerical results show that the TKE generated due to emergent vegetation in water waves increases with decreasing water depth and increasing wave height and period, as well as vegetation density and stem diameter. Moreover, compared to wave height, the influence of wave period on the stem-generated TKE in waves is more significant. Furthermore, the ratio of the amplitude of wave motion trajectory to stem spacing has a significant impact on the stem-generated TKE in waves. When the amplitude of wave motion trajectory is less than half of the stem spacing, the stem-generated TKE in waves is similar to the TKE of the bare bed in waves. In the case where the amplitude of wave motion trajectory is greater than half of the stem spacing, the stem-generated TKE in waves in the front of the vegetation will be significantly enhanced. Based on the study, an improved formula is proposed for predicting the stem-generated turbulence in waves.

Multi-pillar piezoelectric stack harvests ocean wave energy with oscillating float buoy

Piezoelectric Energy Harvesting (PEH) has emerged as a promising alternative to traditional batteries for self-powered sensors. This paper proposed a multi-pillar piezoelectric stacks oscillating float wave energy harvesting device that utilizes a unique rack, pinion, and cam system to convert the heaving motion of the float into a unidirectional rotation. Subsequently, the cam actuates a linkage rod, driving multiple piezoelectric stack pillars to generate electrical energy. The innovative cam mechanism introduces frequency upconversion to improve the efficiency of power generation in conjunction with piezoelectricity. A theoretical methodology is also derived and validated with simulation and experimental model tests to characterize the output power. The results demonstrate that the system attains a peak output voltage of 32 V and a power output of 3.5 mW when utilizing 10 piezoelectric translation units connected in parallel. This achievement is facilitated by the oceanic force generated by wave motion, which exerts a force of 500 N over a wave period of 3 s. The sustainable energy solutions are developed for remote sensor applications in marine environments, offering potential advancements in the field of autonomous and self-powered sensing systems.

Wave trapping by porous breakwater near a wall under the influence of ocean current

In this paper, oblique water wave interaction with a surface piercing box-type porous structure placed in front of a vertical rigid wall is investigated in the presence of current, which flows parallel to vertical wall. The current speed is considered distinct in different subdomains. However, in a particular subdomain current speed is uniform throughout the water depth. In this analysis, Sollitt and Cross model is used for the study of wave motion inside the porous structure. Employing small amplitude linear water wave theory, the present model of our interest is developed into a boundary value problem and solved analytically using the eigenfunction expansion method. Using the developed solution, the reflection coefficient and hydrodynamic wave forces on porous structure are computed for different values of parameters: the dimension of porous structure, the friction coefficient of porous structure, the current speed of following current and opposing current. This research paper suggests that suitable arrangement of rigid walls and surface-piercing partially extended porous structures can be an effective and economical approach for guiding ocean currents and protecting marine facilities against wave attacks.

The cluster model of energy transduction in biological systems

The central problem in transduction is to explain how the energy caught from sunlight by chloroplasts becomes biological work. Or to express it in different terms: how does the energy remain trapped in the biological network and not get lost through thermalization into the environment? The pathway consists of an immensely large number of steps crossing hierarchical levels – some upwards, to larger assemblies, others downwards into energy rich molecules – before fuelling an action potential or a contracting cell. Accepting the assumption that steps are executed by protein domains, we expect that transduction mechanisms are the result of conformational changes, which in turn involve rearrangements of the bonds responsible for the protein fold. But why are these essential changes so difficult to detect? In this presentation, the metabolic pathway is viewed as equivalent to an energy conduit composed of equally sized units – the protein domains – rather than a row of catalysts. The flow of energy through them occurs by the same mechanism as through the cytoplasmic medium (water). This mechanism is based on the cluster-wave model of water structure, which successfully explains the transfer of energy through the liquid medium responsible for the build up of osmotic pressure. The analogy to the line of balls called “Newton's cradle” provides a useful comparison, since there the transfer is also invisible to us because the intermediate balls are motionless. It is further proposed that the spatial arrangements of the H-bonds of the α and β secondary structures support wave motion, with the linear and lateral forms of the groups of bonds belonging to the helices and sheets executing the longitudinal and transverse modes, respectively.

Influences of two sizes of nano-Fe3O4 on stereolithography 3D printing properties of gel photoresist for photothermal-responsive hydrogel

Nanocomposite hydrogels enable augmented properties, functions, and responsive behaviors. In the field of stereolithography 3D printing of the photothermal responsive nanocomposite hydrogel, the influence of the size of nano-Fe3O4 on 3D printing properties is significant due to the sedimentation, but the relevant research is rare. In this study, for the fabrication of photothermal responsive hybrid hydrogel, poly(N-isopropylacrylamide-acrylamide)/nano-Fe3O4 [P(NIPAM-AM)/nano-Fe3O4] gel photoresist was prepared and digital light processing (DLP)-based 3D printing as one of the popular stereolithography 3D printing technology was utilized. The influences of two sizes of Fe3O4 nanoparticles (10 and 50 nm) denoted as nano-Fe3O4(10) and nano-Fe3O4(50) on DLP 3D printing properties of the gel photoresist were investigated in detail. The results reveal that the gel photoresist with nano-Fe3O4(10) obtained long exposure time for the basic prototype, low overcuring degree (Od), and good uniformity of nanoparticles in hybrid hydrogels, while those with nano-Fe3O4(50) had the merits of printing high 3D sample due to the low release fore. Unfortunately, the gel photoresist with a high content of nano-Fe3O4 such as 3.11 wt% failed in 3D printing of a high and uniform gel cylinder. A strategy of preparing P(NIPAM-AM)/nano-Fe3O4 gel photoresist with mixed nano-Fe3O4(10) and (50) for 3D printing was proposed. Using the gel photoresist (nano-Fe3O4 content: 3.11 wt%) with two sizes of nano-Fe3O4 mixed with 50% each and the exposure time of 8 s, a gel cylinder with a height of 1 cm was successfully printed with uniform nano-Fe3O4 distribution and low Od values (≤ 1.17%). Further, a biomimetic hydrogel octopus was 3D printed by using the gel photoresist with mixed nano-Fe3O4 and thereafter a near-infrared-light-driven waving motion of octopus tentacle was achieved successfully.

A multiparameter simulation-driven analysis of ship response when turning concerning a required number of irregular wave realizations

The growing implementation of Decision Support Systems on modern ships, digital-twin technology, and the introduction of autonomous vessels cause the marine industry to seek accurate modeling of vessel response. Despite the contemporary 6DOF models can be used to predict ship motions in irregular waves, the impact of their stochastic realization is usually neglected and remains under-investigated. Especially in the case of turning, differences arising from the stochastic representation of the waves may result in excessive ship motions or even stability failure during maneuver execution. Therefore, in this study, statistical distributions of maximum amplitudes of roll, pitch, and lateral acceleration calculated in two representative locations on board a passenger vessel were analyzed concerning stochastic wave realization and existing extremes. The research utilized 6DOF simulation data and numerous realizations of the irregular wave with random phases of its components. Furthermore, the required number of wave realizations allowing for capturing the actual ranges of ship response at an assumed confidence level has been determined and analyzed. Ultimately, the results were compared in the safety-critical cases concerning various wave and operational conditions. The outcome of this study may be found useful by all parties involved in developing maritime autonomous systems and modeling ship motions.

Vibration control of a monopile offshore wind turbines under recorded seismic waves

The dynamics and vibration control of offshore wind turbines (OWTs) under wind, wave, and earthquake loads is an important but understudied topic, especially for fully coupled seismic analysis considering pile foundation flexibility of OWTs. In this work, we study the effect of multiple passive tuned mass dampers (MTMD) on a monopile OWT by using the fully coupled seismic analysis method. A combined shutdown procedures and MTMD vibration control strategy is proposed for the OWT. First, a state-of-the-art aeroelastic tool, FAST, is extended with a seismic load calculation module, and the numerically modeled monopile OWT addresses the effect of pile-soil interaction (PSI) by establishing ElasPile module in the updated FAST. Then, the focus is placed on the normal operation and emergency shutdown status of OWTs under the combined earthquakes, wind and wave conditions, and structural and motion responses are analyzed under various combination conditions through time-domain simulations, the dynamic characteristics of the OWT during realistic seismic events are shown. Sequentially, based on the proposed MTMD, the vibration migitation effects are evident for the operation OWT and the OWT with shutdown strategies during the combined loading conditions. The reduction in the extreme responses can be as high as 10.53% and 55.02% for the bending moment at the mudline in different OWT conditions, respectively. Therefore, the combined shutdown procedures and MTMD vibration control strategy of OWT is an effective vibration reduction method. Additionally, it is found that PSI has a significant impact on the dynamic characteristics and vibration control effects of OWT structures under wind, wave, and earthquake loads, and the coupled spring boundary condition on the basis of developed ElasPile module is recommended for seismic control analysis of OWT using the combined shutdown procedures and MTMD vibration control strategy.

An APSO-based TPA-BLSTM model for predicting ship motion in irregular waves using wave-series input

ABSTRACT Combining the bidirectional long short-term memory neural network and temporal pattern attention mechanism, a machine learning model based on multi-feature inputs is developed to predict ship motion in irregular waves. An adaptive particle swarm optimisation algorithm is proposed to adapt the parameters of neural network to different feature inputs. The study indicates that the improved particle swarm optimisation algorithm avoids the problem of poor adaptability of empirical parameters to different advance time. The combination of bidirectional long short-term memory neural network and temporary pattern attention mechanism further enhances the data mining ability. Compared with the prediction mode solely based on the ship motion input, the inclusion of wave elevation input can effectively improve the accuracy and advance time for ship’s motion prediction. Importantly, the prediction accuracy will improve with an increased number of inputs of wave probes, which are arranged along the wave propagation direction.

Development of a piezo stack – Laser doppler vibrometer sensing approach for characterizing shear wave dispersion and local viscoelastic property distributions

Laser Doppler vibrometry and wavefield analysis have recently shown great potential for nondestructive evaluation, structural health monitoring, and studying wave physics. However, there are limited studies on these approaches for viscoelastic soft materials, especially, very few studies on the laser Doppler vibrometer (LDV)-based acquisition of time–space wavefields of dispersive shear waves in viscoelastic materials and the analysis of these wavefields for characterizing shear wave dispersion and evaluating local viscoelastic property distributions. Therefore, this research focuses on developing a piezo stack-LDV system and shear wave time–space wavefield analysis methods for enabling the functions of characterizing the shear wave dispersion and the distributions of local viscoelastic material properties. Our system leverages a piezo stack to generate shear waves in viscoelastic materials and an LDV to acquire time–space wavefields. We introduced space-frequency-wavenumber analysis and least square regression-based dispersion comparison to analyze shear wave time–space wavefields and offer functions including extracting shear wave dispersion relations from wavefields and characterizing the spatial distributions of local wavenumbers and viscoelastic properties (e.g., shear elasticity and viscosity). Proof-of-concept experiments were performed using a synthetic gelatin phantom. The results show that our system can successfully generate shear waves and acquire time–space wavefields. They also prove that our wavefield analysis methods can reveal the shear wave dispersion relation and show the spatial distributions of local wavenumbers and viscoelastic properties. We expect this research to benefit engineering and biomedical research communities and inspire researchers interested in developing shear wave-based technologies for characterizing viscoelastic materials.

Calculation of ship motions in steep waves with restoring and Froude-Krylov forces on an adaptive panel mesh with Gauss and analytic integration methods

Calculation of ship motions in steep waves with restoring and Froude-Krylov forces on an adaptive panel mesh with Gauss and analytic integration methods

SWENet: A Physics-Informed Deep Neural Network (PINN) for Shear Wave Elastography.

Shear wave elastography (SWE) enables the measurement of elastic properties of soft materials in a non-invasive manner and finds broad applications in various disciplines. The state-of-the-art SWE methods rely on the measurement of local shear wave speeds to infer material parameters and suffer from wave diffraction when applied to soft materials with strong heterogeneity. In the present study, we overcome this challenge by proposing a physics-informed neural network (PINN)-based SWE (SWENet) method. The spatial variation of elastic properties of inhomogeneous materials has been introduced in the governing equations, which are encoded in SWENet as loss functions. Snapshots of wave motions have been used to train neural networks, and during this course, the elastic properties within a region of interest illuminated by shear waves are inferred simultaneously. We performed finite element simulations, tissue-mimicking phantom experiments, and ex vivo experiments to validate the method. Our results show that the shear moduli of soft composites consisting of matrix and inclusions of several millimeters in cross-section dimensions with either regular or irregular geometries can be identified with excellent accuracy. The advantages of the SWENet over conventional SWE methods consist of using more features of the wave motions and enabling seamless integration of multi-source data in the inverse analysis. Given the advantages of SWENet, it may find broad applications where full wave fields get involved to infer heterogeneous mechanical properties, such as identifying small solid tumors with ultrasound SWE, and differentiating gray and white matters of the brain with magnetic resonance elastography.

Vortex shedding from a square cylinder interacting with an undular bore wave train

In this work, we studied the wave-induced vortex generation and shedding from a semi-submerged vertical square cylinder interacting with an upcoming undular bore wave train under a shallow water configuration. This unsteady and rapid process was investigated by means of numerical and experimental approaches. A numerical simulation, solving the full turbulent viscous Navier–Stokes equations, was carried out in order to study and characterize both the undular bore wave properties and the vortex dynamics triggered during this unsteady interaction. Starting with fluid at rest, the undular bore was generated by the impulsive translational motion of a piston wavemaker at laboratory scale in both a numerical and an experimental wave tank. When the undular bore impinges on the cylinder, filamentary vortex structures were formed at the four cylinder's edges synchronized with the propagating wave motion, leading to the vortex shedding phenomena at a frequency that matched the wave instantaneous frequency. These vortices extended along the entire cylinder span under the water column, from the free surface to the seabed. At the trailing edge of the cylinder, a pairing process of two shed vortices was observed, similar to a Lamb–Oseen vortex pair. These vortices were present during the whole undular bore wave train dynamic forcing. An overall agreement was found with the experimental version of the bore–cylinder interaction, carried out in a physical wave tank. Laser sheet bore profiling and particle image velocimetry measurements of the velocity field confirmed undular bore properties, the onset of vortex formation, subsequent shedding, and pairing in the experiments performed in similar conditions with the numerical approach.

Hydrodynamic performance of vertical cylindrical wave energy absorbers in front of a vertical wall

This paper studies the hydrodynamic performance of vertical cylindrical absorbers in front of a vertical wall. All the absorbers are independent of each other and restricted to only the heave motion. Based on a linear potential flow theory, an analytical solution is developed for the problems of wave diffraction and radiation by absorbers. In the solving procedure, the hydrodynamic problem is first transformed into an equivalent problem in an open water domain using the image principle. The number of absorbers in the equivalent problem is twice that in the real problem, and the plane layout is symmetric about the original vertical wall. The velocity potential of the fluid domain is obtained using the method of variable separation, and the unknown expansion coefficients in the velocity potential are determined by the matched boundary conditions. The heave excitation force, added mass, radiation damping, motion response, and energy capture width of the absorbers are calculated. Case studies are presented to show the effects of the wall reflection and hydrodynamic interaction on the energy extraction performance of the wave energy converter (WEC) system. Subsequently, the WEC performance under the action of irregular waves is analyzed by considering an incident wave spectrum, and the mean annual absorbed power of the device is estimated by considering the wave data statistics at the actual sites. The results indicate that when the wave motion resonates with the absorber motion, the energy extraction performance of the absorbers is significantly improved. The performance of the absorbers can be effectively improved when the structures are close to the antinodes of a standing wave field. By designing a reasonable plane layout, the hydrodynamic interaction can play a constructive role in the performance of the WEC system.

Three-Dimensional Shear Wave Elastography Using Acoustic Radiation Force and a 2-D Row-Column Addressing (RCA) Array.

Acoustic radiation force (ARF)-based shear wave elastography (SWE) is a clinically available ultrasound imaging mode that noninvasively and quantitatively measures tissue stiffness. Current implementations of ARF-SWE are largely limited to 2-D imaging, which does not provide a robust estimation of heterogeneous tissue mechanical properties. Existing 3-D ARF-SWE solutions that are clinically available are based on wobbler probes, which cannot provide true 3-D shear wave motion detection. Although 3-D ARF-SWE based on 2-D matrix arrays have been previously demonstrated, they do not provide a practical solution because of the need for a high channel-count ultrasound system (e.g., 1024-channel) to provide adequate volume rates and the delicate circuitries (e.g., multiplexers) that are vulnerable to the long-duration "push" pulses. To address these issues, here we propose a new 3-D ARF-SWE method based on the 2-D row-column addressing (RCA) array which has a much lower element count (e.g., 256), provides an ultrafast imaging volume rate (e.g., 2000 Hz), and can withstand the push pulses. In this study, we combined the comb-push shear elastography (CUSE) technique with 2-D RCA for enhanced SWE imaging field-of-view (FOV). In vitro phantom studies demonstrated that the proposed method had robust 3-D SWE performance in both homogenous and inclusion phantoms. An in vivo study on a breast cancer patient showed that the proposed method could reconstruct 3-D elasticity maps of the breast lesion, which was validated using a commercial ultrasound scanner. These results demonstrate strong potential for the proposed method to provide a viable and practical solution for clinical 3-D ARF-SWE.

Development of the Wave Motion Induced by Near-Bottom Periodic Disturbances in a Two-Layer Shear Current

Development of the Wave Motion Induced by Near-Bottom Periodic Disturbances in a Two-Layer Shear Current

Numerical investigations on roll decay of a lifeboat in calm water and waves

Lifeboat serves an important water rescue equipment. Capable of self-righting and being stable in free roll decay is crucial for a safe and efficient rescue for a lifeboat. To better understand the roll decay of lifeboat in complex environments, this work performs systematic numerical investigations on roll motion of a lifeboat in both calm water and periodic wave conditions. Investigations of lifeboat in calm water show that it is capable of self-righting with the initial heel angle equal or less than 120°. Although the initial heel angle not affects the final stable status, it has remarkable influence on the self-righting process. Lifeboat with a large initial heel angle subjects to more violent roll motion in the early stage, and thus has weaker stability. Analysis also shows that the nonlinear component of the roll damping coefficient becomes the major part of the total damping coefficient with an increasing initial heel angle. On the other hand, in waves conditions, lifeboat undergoes periodic roll motion in beam waves, and the periodic rolling motion is primarily associated with wave frequency. When the wave frequency approaches the natural frequency of the lifeboat, the rolling motion increases drastically. The present work helps to better understand the self-righting process of a lifeboat in complex environments and also to provide guidance in design and safe operation of a lifeboat.

An Experimental Study of Three-Dimensional Separation Surface Sloshing in the Wet Storage Tank of a Floating Offshore Platform

In this work, in order to elucidate the three-dimensional (3D) resonant sloshing dynamics of the oil–water interface in an offshore cylindrical wet storage tank, a series of model experiments are conducted in a completely filled cylindrical tank containing two immiscible liquids. To begin with, a series of free damping tests are performed to experimentally determine the viscous damping rate of the system and to examine the corresponding theoretical solutions. Subsequently, the separation surface wave responses at a series of excitation frequencies including the natural frequencies of first five modes are examined. Finally, the rotary sloshing dynamics at the natural frequencies of the first and second natural modes are systematically explored. Interestingly, it is found that the separation surface rotary sloshing in a two-layer liquid system is much more intricate than one-layer liquid rotary sloshing due to the generation of multitudinous short waves in the long wave. As far as we know, this is the first investigation of 3D separation surface rotary wave motion in a two-layer liquid system without a free surface.

Phase-lag effect on the instantaneously-liquefied seabed depth under progressive waves: Explicit approximations

Instantaneous liquefaction can be induced by the upward seepage force while waves propagating over a porous seabed. In this study, the instantaneous liquefaction within a non-cohesive seabed under progressive waves is analytically investigated and verified with the existing offshore observations. To characterize the instantaneous liquefaction potential, the vertical gradient of excess pore-pressure is employed, and the explicit solutions for the liquefied soil depth are then derived to reflect the phase-lag effect. Wave scale effect is further examined by comparative analysis of the liquefaction potential between laboratory and field conditions. It is indicated that, due to the phase-lag effect, the maximum liquefaction potential and the maximum liquefied soil depth no longer appear exactly under the wave trough; nevertheless, such phase difference relative to the wave trough wouldn't exceed π/4. Neglecting the phase-lag effects would considerably underestimate the liquefaction potential as well as the liquefaction depth. Moreover, both the liquefaction potential and the corresponding liquefied soil depth are predominantly related to the non-dimensional parameter Ic for characterizing the combined influence of wave and seabed properties.

Nonlinear long waves in shallow water for normalized Boussinesq equations

In this work, we investigate a partial differential equation (PDE) derived from a Boussinesq system of two equations that describe the wave motion in shallow water when the wavelength is small compared to wave amplitude. The Lie point symmetries of the PDE are utilized to reduce it to an ordinary differential equation (ODE) the travelling wave solutions of which are obtained. These solutions are of trigonometric, hyperbolic and exponential types. Graphical representation of some solutions exhibiting solitary and cnoidal wave phenomena are presented.