Incident Wave Angle Research Articles

Numerical Study on Wave Dissipation Performance of OWC-Perforated Floating Breakwater under Irregular Waves

This paper utilizes ANSYS-AQWA hydrodynamic simulation analysis software (2022 R2) to investigate the wave dissipation performance of an Oscillating Water Column (OWC) perforated floating breakwater under irregular wave conditions. The study examines the effect of spacing, width of the OWC opening, water depth, incident wave angle, and significant wave height on the wave dissipation performance of the floating breakwater. The results indicate that the wave dissipation performance of the OWC-perforated floating breakwater surpasses that of similar structures. The transmission coefficient is significantly influenced by spacing and water depth when subjected to irregular waves. The width of the OWC opening also affects the wave dissipation to some extent, with wider openings demonstrating improved performance in the case of long-period waves. The incident wave angle of 0 degrees yields enhanced wave dissipation performance. Although the meaningful wave height has minimal impact on wave dissipation, it increases proportionally with the rise in meaningful wave height. This study offers valuable insights for the design and implementation of floating breakwaters and holds significant practical implications for the research on integrated devices combining floating breakwaters and wave power generation.

Experimental study on an isolated oscillating water column wave energy converting device in oblique waves

The oscillating water column is the most widely used wave energy conversion technology for long-term operations, which has the potential to play a critical role in massive applications of wave energy. In this study, an isolated OWC model employing a generic cubic air chamber and an impulse turbine model was tested in a wave tank using regular and irregular wave scenarios. The wave distribution characteristics surrounding the isolated OWC model in oblique waves with various incident angles and other testing conditions were reported. As the incident waves were forward, the symmetrical wave-height distributions could be observed with enhancement and reduction zones in front of the skirt wall and in the sheltered area of the model. Furthermore, the wave distributions were asymmetrical and more complicated in oblique waves. In addition, the effects of the incident wave angle, height, period, and rotation speed of the turbine model on the staged and overall energy-harvesting performances were analyzed. The OWC model obtained the peak energy-harvesting performance, which reduced as the incident angle decreased. As the incident angle decreased to 60° and zero, the overall capture width ratio reduced to approximately two-thirds and a quarter of the value for the incident angle of 90°. Based on experimental results, the annual energy production of a prototype isolated OWC plant in a typical sea state in North China was predicted. The annual energy production of the plant in the actual sea condition was approximately two-thirds of that only in the forward wave incidence.

Wave power extraction by a dual OWC chambers over an undulated bottom

The impacts of sloping bottom and slanted impenetrable wall on dual oscillating water columns (OWCs) with a slanted front wall are examined. To tackle the physical model, a coupled eigenfunction expansion — boundary element system is employed. The concept is based on employing the anticipated amplification of scattered and reflected wave fields generated by the existence of sloping walls to enhance the absorption of wave power driven by the walls’ wave reflections. The study concludes that 100% efficiency occurs for smaller incident wave angles. It is also observed that compared with short waves, the efficiency of the device is more in the long-wave region. OWCs are observed to be more effective over the undulating bottom and sloping impermeable wall with an increased spacing between the water columns and the second OWC to the impermeable wall. Additionally, the chambers’ width and the sloping bottom angle are vital parameters for higher power extraction from the OWCs. Furthermore, the optimal values of slope bottom and wall inclination may be employed to build and implement an efficient OWC device. Moreover, the proposed model can also be used as a breakwater to protect the coastline.

Magnetic field and thermal environment effects on sound transmission loss of double-walled cracked piezoelectric cylindrical nanoshells

Based on a non-local strain gradient theory (NSGT), this article analytically studies the sound transmission loss (STL) performance of a special type of double-walled partially cracked piezoelectric nanoshell structures of cylindrical shape undergoing initial electric potential and longitudinal magnetic field. The structure, which includes a specific number of axial and circumferential surface cracks, is struck by a plane wave in a thermal setting. Such cracks have minimal size compared to the nano-shell structure as a whole, minimizing the effects of curvature for this problem. The first-order shear deformation theory (FSDT) is utilized to explain the displacement components, and Hamilton’s concept is applied to obtain the coupled vibroacoustic equations that are used to generate the governing equations of the system for the two crack types, giving us an idea of the resulting structural stiffness in the presence of cracks using coefficients of crack compliance that are derived from the line spring model (LSM). The mechanical and acoustic properties are then checked to see their effect on the system response followed by a series of validation case studies. This evaluation also allows one to optimize a similar structure by selecting appropriate external parameters such as electric voltage, magnetic field intensity, different crack types, nonlocal and strain gradient parameters, variations of temperature, and incident angle of sound waves.

Dynamic Response Analysis of Intake Tower-Hydrodynamic Coupling Boundary Based on SV Wave Spatial Incidence

In view of the insufficient analysis of the coupled joint seismic response of the intake tower–reservoir water–foundation boundary under the oblique incidence of SV wave space, a three-dimensional dynamic equation of the oblique incidence of SV wave space is established in this paper. The external wave input method of viscoelastic artificial boundary combined with equivalent load and the acoustic medium theory are used to simulate the action of reservoir water, and the angle change in the SV wave incidence is realized by controlling the incident vector. The dynamic response of the structure is analyzed and the dynamic response characteristics of the structure at different incidence angles are discussed. The results show that the dynamic response and damage degree of the intake tower decreases first and then increases with the change in angle. When the vertical incidence is 0°, the maximum displacement drop is 82.05%, and the displacement response of the intake tower is more sensitive to the change in SV wave incidence angle. When SV wave is vertically incident at 0° and 35° (near the maximum critical angle of incident), the dynamic response, dynamic water pressure, damage diffusion velocity, damage area, and damage degree of the intake tower are relatively large, which seriously affects the safety and stability of the intake tower. Therefore, the influence of the oblique incidence should be considered comprehensively in the aseismic stability design of the water intake tower to provide a new idea for the safety evaluation of the same type of engineering.

Theoretical design and investigation of VO2-based tunable broadband terahertz metasurface absorber

Terahertz devices is promising in the development of next-generation infrared photodetectors. However, the performances of photodetectors are largely limited by their poor light absorption and small detection range. Here, we designed a vanadium dioxide (VO2) based tunable broadband terahertz (THz) metasurface absorber (VO2-BTMA) for a wider tunable broadband detection range. The results show that the VO2- BTMA is able to maintain more than 90% absorption in the range of 2.21–5.64 THz with an ultra-wide bandwidth of 3.43 THz. When the absorption peaks are at 2.607 THz and 5.064 THz, the absorption rates of VO2- BTMA devices reaches 96.8% and 96.4% respectively. Meanwhile, we found that the conductivity of VO2 can be controlled by changing the temperature, thus affecting the absorption rate of the device and achieving tunability. When the incident angle of terahertz wave increases from 0° to 50°, the absorber can still maintain 80% of the absorption rate, and the absorber has excellent stability.

Flow Characteristics of the Rip Current System near a Shore-Normal Structure with Regular Waves

Rip currents are the strong narrow seaward current produced by waves breaking on the coast. Of the many types of rip currents, the present study investigates, experimentally and numerically, the rip current system produced by the wave reflection on a finite-length shore-normal structure (corresponding to groin, jetty and headland in a real-word environment) with strong wave reflection strength. The incident wave condition of an obliquely propagating monochromatic surface gravity wave is considered for the bottom topographies of planar and barred beaches without or with a rip channel. The corresponding laboratory experiment was conducted and used to validate the numerical model. A set of higher order Boussinesq equations is used to reproduce the experimental observation and produce the results for the related prototype cases, with the latter considering more factors which may influence the formation and evolution of rip current flow patterns. The resulting rip current system contains two parts: the node rips formed due to the presence of the longshore standing wave in the wave reflection field and the deflection rip formed due to the interaction between the incoming longshore current and the reflection wave field mentioned above. A new formation mechanism of the deflection rip has been proposed, i.e., the deflection rip is formed by the meeting and then deflection of the longshore current and lateral flow. The effects of different wave reflection strengths of the structure, wave incident angles and bathymetric conditions on the pattern and flow volume of the deflection rip are also studied.

Theoretical investigation on integrating a heaving WEC in the semicircle opening of a vertical breakwater

Despite so many investigations on the WEC-breakwater integration system, the practical wave energy extraction efficiency still needs to be improved. Recently, using specially designed arc breakwaters to focus the wave energy to a certain area was found to be a feasible method. In this paper the integration strategy of setting a heaving WEC at the central of a semicircle opening of a vertical solid breakwater is investigated based on the linear potential flow theory, with a semicircle thin curtain wall set outside the opening to give protection on the heaving WEC. The boundary value problem is solved using the method of separation of variables and eigenfunction expansion matching, and the multi-term Galerkin method is adopted to handle the singularity at the thin curtain wall. After successful validation of the proposed theoretical model, a comparison study between the proposed integration systems with different permeability of the curtain wall is conducted, and the cases with a heaving WEC in front of a flat vertical wall and an isolated heaving WEC are considered as a comparison. Then a parametric study is carried out on the effects of the incident wave angle, the porosity, radius, and draft of the semicircle curtain wall, and the dimension of the heaving WEC.

Evaluation of the effects of the seismic wave incidence angle on soil-structure interactions via advanced finite beam elements

This work investigates the interactions between the soil and a superstructure subjected to various seismic waves using variable-kinematics finite beam elements. Artificial boundary conditions based on springs and dashpots with appropriate elastic and viscous coefficients were adopted to ensure the absorption of the incident waves and simulate the infinite domain condition. The one-dimensional finite element formulation is obtained with a unified formalism that enables arbitrary structural models to be adopted. Lagrange-type expansions have been used in this work to approximate the beam kinematics and facilitate the application of artificial boundary conditions. Both pressure and shear waves with different incidence angles have been considered, and the dynamic responses calculated with the current approach have been compared with analytical solutions when available. The results have demonstrated the accuracy and potentialities of the methodology and provided reasonable confidence for future applications.

Three-Layered Thin Films for Simultaneous Infrared Camouflage and Radiative Cooling.

With the rapid advancements in aerospace technology and infrared detection technology, there are increasing needs for materials with simultaneous infrared camouflage and radiative cooling capabilities. In this study, a three-layered Ge/Ag/Si thin film structure on a titanium alloy TC4 substrate (a widely used skin material for spacecraft) is designed and optimized to achieve such spectral compatibility by combining the transfer matrix method and the genetic algorithm. The structure exhibits a low average emissivity of 0.11 in the atmospheric windows of 3-5 μm and 8-14 μm for infrared camouflage and a high average emissivity of 0.69 in 5-8 μm for radiative cooling. Furthermore, the designed metasurface shows a high degree of robustness regarding the polarization and incidence angle of the incoming electromagnetic wave. The underlying mechanisms allowing for the spectral compatibility of the metasurface can be elucidated as follows: the top Ge layer selectively transmits electromagnetic waves ranging from 5-8 μm while it reflects those in the ranges of 3-5 μm and 8-14 μm. The transmitted electromagnetic waves from the Ge layer are first absorbed by the Ag layer and then localized in the Fabry-Perot resonance cavity formed by Ag layer, Si layer and TC4 substrate. Ag and TC4 make further intrinsic absorptions during the multiple reflections of the localized electromagnetic waves.

Acoustic scattering of a pair of rigid spheroids based on the T-matrix method

In this study, the T-matrix method combined with the addition theorems of spherical basis functions is applied to semi-analytically compute the underwater far-field acoustic scattering of a pair of rigid spheroids with arbitrary incident angles. The involvement of the addition theorems renders the multiple scattering fields of each spheroid to be translated into an identical origin. The accuracy and convergence property of the proposed method are verified and validated. The interference of specular reflection wave and Franz wave can be spotted from the oscillations of the form function. Furthermore, the propagation paths of specular reflection and Franz waves are quantitatively analyzed in the time domain with conclusions that the Franz waves reach the observation point subsequent to specular reflection waves and the time interval between these two wave series is equal to the time cost of the Franz waves traveling along the sphere surfaces. Finally, the effects of separation distances, aspect ratios (the ratio of the polar radius to equatorial radius), non-dimensional frequencies, and incidence angles of the plane wave on the far-field acoustic scattering of a pair of rigid spheroids are studied by the T-matrix method.

Axisymmetric reflectors in wave energy converter arrays: Harnessing scattering to increase energy extraction

We elucidate the effect of non-extracting reflectors on the performance of wave energy converter (WEC) arrays. We consider an infinitely periodic row of converters parallel to an infinitely periodic row of discrete axisymmetric reflectors (C-R arrays), and we study how the spatial configuration affects energy extraction. Using a multiple-scattering algorithm for linear wave-array interactions, we conduct a series of simulations of C-R arrays for a range of spatial configuration parameters, wavenumbers, and wave incident angles. We find that C-R arrays can significantly increase energy extraction compared to a WEC array by itself. We offer a simplified theoretical model, based on the far-field response of periodic rows in isolation, which shows that the large increases in energy extraction result from the constructive Bragg and Laue interferences caused by wave interactions with the reflector row. For the pertinent case of incident waves of the WEC-resonant frequency, we find that optimized C-R arrays can achieve energy extraction gains of O(500%). Remarkably, the optimal C-R array extracts more energy than two rows of converters of optimal configuration even though the C-R array consists of only half as many WECs.

A Rectifier With Less Sensitivity to the Incident Angle of Incoming Waves Based on Quadrature Coupler

A Rectifier With Less Sensitivity to the Incident Angle of Incoming Waves Based on Quadrature Coupler

Strong shock solutions in symmetric wedge flows: Unphysical or unstable?

This paper investigates the strong shock solutions in a supersonic wedge experimentally, analytically, and numerically. Experiments and computations are conducted on scaled-down models for the two types of shock reflection to be possible. The time-resolved schlieren observation of the flow evolution revealed that the shock formation is a highly dynamic transition of the starting shock from a strong Mach reflection (MR) to a weak regular reflection (RR) via a strong RR reflection over a constant shock wave angle for a wedge angle less than the detachment criterion angle for the shock transition. However, when the wedge angle is greater than the detachment criterion angle, the shock moves over the wedge with the MR structures of diminishing Mach stem height at a constant incident shock wave angle. These intermediate shock reflections are found to be unstable and oscillate at high amplitude and low frequencies to upstream pressure fluctuations. The nature of the intermediate shock reflection during the shock transition over the wedge has also been studied using an unsteady second-order two-dimensional compressible Navier–Stokes solver code with shear stress transport k-ω turbulence modeling. The computed flow parameters around the intermediate shock reflections confirmed that these are indeed strong shock reflections believed to be unphysical in steady wedge flows.

Effect of geometrical parameters and additional mass on the acoustic and vibration control of the bilayer resonant metamaterials

Due to the advantages of lightweight, small size, high stiffness, and adjustable parameters, plate metamaterials have shown great practical application value in the field of acoustic vibration control in engineering. For low-frequency vibration and noise control, an annular slotted bilayer plate metamaterial is designed, which can realize sound insulation and vibration reduction at 100–150 Hz (low-frequency range). By changing the geometric parameters of the annular slotted bilayer plate, the structural parameters of the additional mass, the material parameters, and its distribution position, the acting frequency band is reduced and the band gap of sound insulation and vibration reduction is widened. The integral metamaterial panels of circular and square PA12 were fabricated by 3D printing technology, and then, the acoustic and vibration characteristics were tested in the ZK1030 impedance tube system and Polytec full-field scanning laser vibration measurement system, respectively. The results show that the structure has the best performance by varying the resonant ring thickness of the lattice structure, controlling the wave incidence angle to 0°, and pointing force excitation in the X direction. However, when the mass of the additional mass block is certain, the distribution position of the mass block has less effect. The experimental result was reasonably consistent with the simulation analysis result. This work can provide a reference for the design of bilayer plate acoustic metamaterials with low-frequency broadband acoustic insulation and low-damping vibration based on periodic structures in engineering.

Sandy shoreline recovery ability after breakwater removal

The removal of coastal structures has emerged as an increasingly considered alternative nature-based solution to sandy coastal erosion due to unsuited structure construction. However, its effectiveness remains uncertain because the ability of natural beach recovery is unclear due to little understanding of shoreline response to the structure removal. In this study, we use a recently developed numerical model to explore the sandy shoreline recovery ability after the removal of an attached breakwater. Both recovery duration and recovery ratio are analyzed concerning various breakwater configurations and environmental settings in a simplified and generalized framework. We find that the sandy shoreline has the ability to naturally recover after breakwater removal but with different recovery durations (years to centuries) and recovery ratios (full to partial). A higher shoreline recovery ability (i.e., shorter duration and larger ratio) is related to shorter effective breakwater length, downdrift inclined breakwater direction, lower angle of wave incidence, and greater longshore sediment transport rate. We reveal that the behavior of sand spit evolution, including the extension and split of the sand spit, is the dominant mechanism for distinct shoreline recovery processes. Two simple formulas are finally proposed to preliminarily estimate shoreline recovery ability for practical purposes. The results of the present study provide new insights into coastal morphological resilience to engineering interventions.

An analytical solution for the dynamic response of a seawater‐sloping seabed‐bedrock system under an oblique incident P wave

AbstractMany offshore marine structures are built on seabeds with slight or considerable slopes, while most analytical studies have focused on the dynamic responses of horizontal seabeds. Based on the theory of porous media, an analytical solution for the response of a sloping seabed to earthquakes is developed in this paper. Stress and displacement responses can be shown at any location of the seabed. Using numerical examples, we analyze the influence of the slope angle, frequency and angle of incident waves, and thicknesses of the seawater and sediment layers on the dynamic response of the seabed. The results show that the solid displacement amplification factor of the surface of the horizontal seabed is always constant, while that of the sloping seabed changes periodically along the seabed surface. Even at a small site, the difference between a horizontal seabed and a sloping seabed is still significant. The slope angle has different effects on the seabed at different depths, and the inclination plays an amplification role at some depths and a reduction role at other depths. With an increase in slope angle, the difference between a horizontal seabed and a sloping seabed becomes more significant. Especially at natural frequencies, the amplification factor becomes more significant with increasing slope angle. Therefore, even though the same seawater depth is used in the model, a horizontal seabed model cannot be used to analyze the dynamic response of a sloping seabed or significant errors will occur.

Structural Design of the Substructure of a 10 MW Floating Offshore Wind Turbine System Using Dominant Load Parameters

Fully coupled integrated load analyses (ILAs) to evaluate not only the load response but also the structural integrity are required to design a floating offshore wind turbine, since there has been no firmly established approach for obtaining the structural responses of a FOWT substructure in the time domain. This study aimed to explore if a direct strength analysis (DSA) technique that has been widely used for ships and offshore structures can adequately evaluate the FOWT substructure. In this study, acceleration and nacelle thrust were used for the dominant load parameters for DSA. The turbine thrust corresponding to the 50-year return period was taken from the literature. The acceleration response amplitude operator (RAO) was obtained through frequency response hydrodynamic analysis. The short-term sea states defined by the wave scatter diagram (WSD) of the expected installation area was represented by the JONSWAP wave spectrum. To account for the multi-directionality of the short-crested waves, the 0th order moments of the wave spectrum were corrected. The probabilities of each short-term sea state and each wave incidence angle were applied to derive the long-term acceleration for each return period. DSA cases were generated by combining the long-term acceleration and nacelle thrust to maximize the forces in the surge, sway, and heave directions. Linear spring elements were placed under the three outer columns of the substructure to provide soft constraints for hive, roll, and pitch motions. Nonlinear spring elements with initial tension were placed on the three fairlead chain stoppers (FCSs) to simulate the station-keeping ability of the mooring lines; they provided initial tension in the slacked position and an increased tension in the taut position. The structural strength evaluation of the coarse mesh finite element model with an element size same as the stiffener spacing showed that high stresses exceeding the permissible stresses occurred in the unstable members of the substructure. The high stress areas were re-evaluated using a fine mesh finite element model with an element size of 50 mm × 50 mm. The scope of structural reinforcement was identified from the fine mesh analyses. It was found that the DSA can be properly utilized for the substructure strength assessment of a FOWT.

Seismic Resilience Assessment of Curved Reinforced Concrete Bridge Piers through Seismic Fragility Curves Considering Short- and Long-Period Earthquakes

Curved bridges are commonly used for logistics and emergencies in urban areas such as highway interchange bridges. These types of bridges have complicated dynamic behaviors and also are vulnerable to earthquakes, so their functionality is a critical parameter for decision makers. For this purpose, this study aims to evaluate the bridge seismic resilience under the effects of changes in deck radius (50, 100, 150 m, and infinity), pier height irregularity (Regular and Irregular), and incident seismic wave angle (0°, 45°, and 90°) under short- and long-period records. In the first step, fragility curves are calculated based on the incremental dynamic analysis and probabilistic seismic demand models. Finally, seismic resilience curves/surfaces are constructed and their interpolated values of the log-normal distribution function presented for assessing system resilience. It is found that when long-period records are applied in one given direction, the angle of incidence has the most significant effect on seismic resilience, and bridges are most vulnerable when the angle of incidence tends to 0°. The effect of deck radius on seismic resilience became more remarkable as the angle of incidence increased. Additionally, results indicate that the bridge vulnerability in long-period records is more significant than that under short-period records.

Reliability Analysis on Stability of Armor Units for Foundation Mound of Composite Breakwaters

Probabilistic and deterministic analyses are implemented for the armor units of rubble foundation mound of composite breakwaters which is needed to protect the upright section against the scour of foundation mounds. By a little modification and incorporation of the previous empirical formulas that has commonly been applied to design the armor units of foundation mound, a new type formula of stability number has been suggested which is capable of taking into account slopes of foundation mounds, damage ratios of armor units, and incident wave numbers. The new proposed formula becomes mathematically identical with the previous empirical formula under the same conditions used in the developing process. Deterministic design have first been carried out to evaluate the minimum weights of armor units for several conditions associated with a typical section of composite breakwater. When the slopes of foundation mound become steepening and the incident wave numbers are increasing, the bigger armor units more than those from the previous empirical formula should be required. The opposite trends however are shown if the damage ratios is much more allowed. Meanwhile, the reliability analysis, which is one of probabilistic models, has been performed in order to quantitatively verify how the armor unit resulted from the deterministic design is stable. It has been confirmed that 1.2% of annual encounter probability of failure has been evaluated under the condition of 1% damage ratio of armor units for the design wave of 50 years return period. By additionally calculating the influence factors of the related random variables on the failure probability due to those uncertainties, it has been found that Hudson’s stability coefficient, significant wave height, and water depth above foundation mound have sequentially been given the impacts on failure regardless of the incident wave angles. Finally, sensitivity analysis has been interpreted with respect to the variations of random variables which are implicitly involved in the formula of stability number for armor units of foundation mound. Then, the probability of failure have been rapidly decreased as the water depth above foundation mound are deepening. However, it has been shown that the probability of failure have been increased according as the berm width of foundation mound are widening and wave periods become shortening.