Wave Zone Research Articles

Resistance experiments on ships in a leader-follower formation

The interaction between two ships in a leader-follower formation involves interference by both waves and viscosity, making the phenomenon highly complex. A series of experiments are conducted in this study to measure the total resistance of ships moving individually and in two-ship formations on calm water. The results indicate that the shape of the bow has a more significant impact on the total resistance of single ships than the shape of the stern. Specifically, the total resistance of a single ship with a transom stern is nearly identical to that of a ship with a sharp stern. However, ships with a flat bow exhibit significantly higher total resistance compared to those with a sharp bow. In a two-ship single-file formation, the hydrostatic drag of both the leading and trailing ships is significantly reduced when the gap between the two ships is small. This reduction occurs because the hollow in the water aft the transom stern induced by flow separation is filled by the bow waves of the trailing ship. When the trailing ship is positioned in the divergent wave zone within the wake of the leading ship, wave interference between the two ships becomes the dominant factor influencing the variation in the total resistance of the trailing ship. As the gap between the two ships increases further, the wave interference weakens; however, the trailing ship still experiences a substantial reduction in resistance due to weakened flow separation and bubble drag reduction within the turbulent–bubble mixed flow region.

Investigation on the Impact of the 2022 Luding M6.8 Earthquake on Regional Low-Frequency Time Code Signals in Northern China

Low-Frequency Time Code time service technology, as an important means of ground-based radio time dissemination, can be divided into ground wave zone and sky wave zone according to different receiving and transmitting distances. Ground waves travel primarily along the Earth’s surface, while sky waves propagate over long distances by reflecting off the ionosphere. This paper utilizes the raw observation data received by the Low-Frequency Time Code dissemination monitoring stations before and after the 6.8 magnitude earthquake in Luding, Sichuan, China on 5 September 2022. A Low-Frequency Time Code time service monitoring system was built in Xi’an to continuously monitor the 68.5 kHz time signal broadcast by the BPC station. The data was then processed and analyzed through visualization. Simultaneously, we analyzed the signal fluctuation for multiple days before and after the earthquake to see the changes in the Low-Frequency Time Code signal during the earthquake. By combining seismic activity, solar activity, and geomagnetic data, this study aims to explore the causes and patterns of signal parameter variations. The results show that the field strength of the Low-Frequency Time Code signal fluctuated significantly within a short period during the earthquake. The value began to decrease about 60 min before the earthquake, dropping by approximately 8.9 dBμV/m, and gradually recovered 2 h after the earthquake. The phase also mutated by 1.36 μs at the time of the earthquake, and the time deviation fluctuated greatly compared to the 2 days before and after. Earthquake occurrences influence ionospheric variations, leading to changes in the sky wave propagation of Low-Frequency Time Code signals. Analysis of the influence of earthquakes on the propagation of Low-Frequency Time Code signals can provide references for research on Low-Frequency Time Code signal propagation models and earthquake prediction.

Hydrodynamic Performance of Half Pipe Breakwaters Experimentally and Numerically

The main objective of constructing barriers is to safeguard harbours and shores from waves and sea currents. This paper aims at presenting a study on innovative and non-traditional alternatives to breakwaters, experimentally and numerically, to assess the hydrodynamic efficiency of the suggested models in order to choose the most appropriate one. Two models of semi-submersible-type breakwaters have been studied, in the form of a cross-section of a half pipe with an internal diameter and thickness of 30.00 and 1.00 cm, respectively. Model (a) is a circular half-pipe with an upward concave, whereas model (b) has a sideways concave towards the water. Several scenarios for the breakwaters suggested in this study have been simulated using FLOW 3D. The results indicate that the transmission coefficient (Tc), provided by model (b), is 3-7% lower than model (a), while the reflection coefficient (Rc) values for model (b) are 4-8% higher than model (a). The results show that model (b) has a 10% lower (Tc) at d/h = 0.80 compared to d/h = 0.60, while (Rc) is 8% higher at d/h = 0.80 than at d/h = 0.60 for the same model. The suggested breakwater reduces inclined waves' energy more quickly than perpendicular waves. Regarding the hydrodynamic performance, the proposed breakwater in model (b) is shown to be more efficient and effective than the breakwater in model (a), so it is recommended to use it due to its effectiveness in providing protection for coastal wave zones and benefiting from the energy of waves to generate electricity.

A Novel Approach to Wave Energy Conversion Using CFD Technique

Abstract This article details the development and evaluation of a novel wave energy converter (WEC) aimed at efficiently capturing wave energy for electricity production. The study employs Computational Fluid Dynamics (CFD) techniques, specifically the URANS method and the k-ω SST turbulence model, to solve the Navier-Stokes equations and capture the free surface using the Volume of Fluid (VOF) model. The CFD results are validated against experimental data to ensure accuracy. Various design parameters of the proposed device were tested, revealing that the arms and bottom angle significantly affect its performance. Unlike the floating Wave Dragon (WD) device, which utilises potential energy and is set in deep water, the new fixed-seabed device is positioned in the transitional wave region near the shore, where waves retain 80% of their energy. It can be constructed from environmentally friendly cement, making it resistant to hurricanes and suitable for any wave turbine in the open sea. The MP687 turbine was used to capture the wave energy in the proposed device, testing its performance in three positions: in the open sea, in the middle of the device, and at the device’s outlet. The results show that the device significantly enhances wave energy concentration, especially when the turbine is placed at the outlet. The proposed device offers numerous advantages, including its fixed position in a high-energy wave zone, the efficient use of turbulent kinetic energy, and robust construction that can withstand storms.

Launch and recovery of a work class ROV through wave zone in small offshore service vessel

The deployment of remotely operated underwater vehicle (ROV) from a small offshore service vessel (OSV) based on single point mooring system (SPMS) method is recently adopted in offshore renewable energy sector. However, the tension spike in wire, also known as snap load, often occurs when the ROV passes through the wave zone in launching and lifting operation of deployment. In this study, a practical numerical model for predicting wire tension during launch and recovery of ROV is developed and validated by wave flume test of a 1:10 scaled model. The numerical simulations reveal that the ROV deployment at vessel stern along with an appropriate reduction of horizontal distance from the hull are reliable safety strategies for reducing wire tension. By adopting the new deployment strategy, the annual operational capacity can be expanded by approximately 6% when the safe operational limit of ROV under a significant wave height of 1.25 m. Based on the comprehensive numerical simulation, the newly developed safe operating envelope provides a further guidance for onboard ROV operation in the O&M of offshore wind farms.

Dynamic Response and Damage Assessment of Partially Confined Metallic Cylinders Under Transverse Blast Loading

An analysis of the dynamic response and damage assessment of partially confined metallic cylinders under transverse air-blast loading is presented in this paper. The examination of the blast shock wave load distribution and the consequences of standoff distances on the plastic deformation of cylinders was conducted with meticulous attention in the experimental testing. The charges of TNT were determined to have masses of 16.3 kg and 29.5 kg, while the distances at which they were placed from the target varied between 1.5 m and 4.25 m. Three unique deformation modes were found to exist in the unilaterally supported cylinder, all of which were directly connected to the distribution of the blast load. In order to obtain an improved understanding of the dynamic behaviors exhibited in cylinders, a finite element simulation model was utilized and subsequently validated using an examination of the experimental results. The assessment of shock wave damage was conducted by utilizing the residual deformation of the metallic cylinder as an equivalent characterization under lateral blast shock wave loading. The duration of the positive pressure zone of the shock wave was determined to be between one-fourth and ten times the vibration period of a unilaterally supported cylinder, indicating that the P-I (overpressure-impulse) criterion could be utilized for damage evaluation. The incorporation of the P-I criterion was subsequently employed to evaluate the detrimental consequences, taking into consideration the radial distribution of residual deformation identified in metal cylindrical shell constructions subjected to lateral blast shock wave loading. This research contributed to a better comprehension of the dynamic behavior of partially confined metallic cylinders subjected to lateral blast loading and highlights the significance of the P-I criterion for evaluating and mitigating the damage effects in such scenarios.

Initiation process of non-premixed continuous rotating detonation wave through Schlieren visualization

High-speed schlieren visualization on the initiation process of non-premixed air and hydrogen continuous rotating detonation (CRD) is carried out in a well-designed rounded-rectangle hollow combustor in this study. The CRD initiation processes of pre-detonator ignition and spark plug ignition are comprehensively revealed by synchronous high-speed schlieren images and high-frequency dynamic pressure results. The results show that the CRD undergoes three processes after ignition, including initiation process, adjustment process and stable propagation process. The CRD initiation process of pre-detonator ignition involves the upstream-propagation phase of leading shock wave and reaction zone and the coupling phase of circumferentially-propagating shock wave and reaction zone, while that of spark plug ignition includes the upstream-propagation phase of reaction zone, and the coupling phase of circumferentially-propagating pressure wave and reaction zone. The formation of deflagration combustion flowfield and re-establishment of combustible mixture layer after ignition are important prerequisites for CRD initiation. The strong interaction between circumferentially-propagating shock wave and post-shock wave reaction conduces to the rapid initiation of CRD by pre-detonator ignition, while the pressure wave gradually interacts with reaction leading to the detonation initiation by spark plug ignition. The CRD initiation time and adjustment time of pre-detonator ignition are shorter than those of spark plug ignition. This study provides detailed insight into the physics of CRD initiation process of pre-detonator and spark plug ignition, which can deepen the understanding of the initiation mechanism and provide practical guidance for the optimal design of CRDE ignitor.

On the possibility of changing the trajectory of a projectile or rocket based on aerodynamic impact in the shock wave zone

A physical hypothesis is proposed that it is possible to change the design trajectory of the projectile on the basis of mechanical action on the entire volume of shockwave zones with a unilateral, asymmetric presence of the second projectile. Deviating from the original trajectory results in a positive result when it comes to a defensive task. A new semi-empirical model has been developed and compiled, which allows you to calculate the trajectory of the projectile taking into account the air resistance to movement. In the new model, it is recommended that only four easily detectable values​ ​ be used in upcoming experiments: the initial departure speed , the maximum altitude , the maximum flight range and the full time. The calculation scheme uses iterative calculations. On the basis of which the values ​ ​ of numerical coefficients in the semi-empirical model are specified. The physical idea that external powerful laser radiation can heat the side surface of the projectile and the entire zone of wave jumps of the seal is justified. On one side of the semi-plant, that is, it is one-way heating. The asymmetrical thermal state on both sides of the missile may cause the missile or projectile to deviate from the previously assigned heading. This circumstance is also in favor of the proposed idea.

Research on the Optimal Spacing of Multiple Roof Smoke Blocking Structures in a Long Corridor

In a long and narrow corridor, the installation of roof smoke blocking structures is a measure to slow down the spread of fire smoke. When employing multiple smoke blocking structures, the spacing between these structures is a critical parameter that needs to be considered for optimal effectiveness. This paper analyzes the smoke blocking performance of double structures at different spacing and measures the smoke flow velocity both upstream and downstream of the double structures. According to the analysis of the smoke velocity vector obtained from numerical simulation, the smoke can be divided into three zones based on the flow state of the smoke after passing through the front smoke screen structure, namely the vortex zone, surge wave zone, and steady flow zone. When the rear smoke screen is located in the surge zone, the smoke blocking effect is optimal. Analysis of the morphology of the smoke layer indicates that the length of the vortex region is directly proportional to the upstream smoke flow velocity. The numerical and experimental results both indicate that an excessively large or small spacing between the structures fails to achieve optimal smoke control effectiveness. When the spacing is within an optimal range, the smoke velocity is the lowest. Finally, using a real architectural corridor as a case background, this paper presents a design example of roof smoke blocking structures. In order to arrange as many smoke blocking structures as possible, an appropriate spacing between the structures should be slightly larger than the vortex region. The smoke control effectiveness of multiple roof structures was validated through numerical simulation. As a result, the time required for smoke to pass through the corridor increases by 110 s.

A novel method for simulating nuclear explosion with chemical explosion to form an approximate plane wave: Field test and numerical simulation

A nuclear explosion in the rock mass medium can produce strong shock waves, seismic shocks, and other destructive effects, which can cause extreme damage to the underground protection infrastructures. With the increase in nuclear explosion power, underground protection engineering enabled by explosion-proof impact theory and technology ushered in a new challenge. This paper proposes to simulate nuclear explosion tests with on-site chemical explosion tests in the form of multi-hole explosions. First, the mechanism of using multi-hole simultaneous blasting to simulate a nuclear explosion to generate approximate plane waves was analyzed. The plane pressure curve at the vault of the underground protective tunnel under the action of the multi-hole simultaneous blasting was then obtained using the impact test in the rock mass at the site. According to the peak pressure at the vault plane, it was divided into three regions: the stress superposition region, the superposition region after surface reflection, and the approximate plane stress wave zone. A numerical simulation approach was developed using PFC and FLAC to study the peak particle velocity in the surrounding rock of the underground protective cave under the action of multi-hole blasting. The time-history curves of pressure and peak pressure partition obtained by the on-site multi-hole simultaneous blasting test and numerical simulation were compared and analyzed, to verify the correctness and rationality of the formation of an approximate plane wave in the simulated nuclear explosion. This comparison and analysis also provided a theoretical foundation and some research ideas for the ensuing study on the impact of a nuclear explosion.

A novel method for supersonic plasma measurement using a double-jacketed enthalpy probe

A novel method to characterize a supersonic plasma jet using a double-jacketed enthalpy probe is presented and applied to Ar supersonic plasma jets generated by a plasma torch operated at an input power level of 5.7 kW and a chamber pressure of 2.3 kPa. The basis of this method is to measure total stagnation pressure, total enthalpy, and static pressure at the backside of a shock wave formed in front of the probe with a single insertion of the probe. Once these three variables are known, normal shock relations before and after the shock wave can disclose information on static pressures, Mach numbers, temperatures, and velocities of the supersonic plasma jet under a calorically perfect gas assumption. For example, measurement experiments carried out with the proposed probe revealed that static pressure of Ar supersonic plasma jet oscillated around the chamber pressure of 2.3 kPa in a range of 1–5 kPa along the jet axis, clearly showing an aerodynamic non-equilibrium. Corresponding to the behaviors of static pressures, Mach numbers also oscillated in the range of 1.1–3.5 along the jet axis. In addition, oscillation patterns of static pressures and Mach numbers agreed well with those of compression and expansion wave zones observed in the photograph of an over-expanded Ar supersonic plasma jet. Although relatively large errors were accompanied due to a low input power level, plasma temperatures and velocities were measured to be decreasing and increasing, respectively, in the expansion wave zone while opposite behaviors were observed in the compression wave zone.

PLANE PROBLEMS ABOUT THE ACTION OF OSCILLATING LOAD ON THE BOUNDARY OF AN ELASTIC ISOTROPIC LAYER IN THE PRESENCE OF SURFACE STRESSES

In this paper, symmetric and antisymmetric plane problems about the action of oscillating load on the boundary of an elastic isotropic nanothin layer are considered. The nanoscale layer thickness is considered by introducing surface stresses in accordance with the Gurtin-Murdoch theory. According to this theory, it is assumed that, in addition to external loads, surface stresses act on the layer boundaries, which are described by Hooke's “surface” law. As a result, the properties of the elastic material of the layer with nanoscale thickness become different from the properties of the material of a regular-sized body, which is typical for nanomechanics problems. A standard technique was used for the solution of formulated problems, including the application of limiting absorption principle, the Fourier transform over infinitely extended coordinate and the theory of residues for finding the inverse Fourier transform. It is shown how it is possible to obtain solutions in the form of series in natural waves, in which the wave numbers are defined as the roots of the corresponding dispersion equations. For a specific example, dispersion relations were studied and graphs of the first dispersion curves were plotted. The behavior of barrier frequencies, changes in wave numbers and zones of existence of backward waves at different nanoscale layer thicknesses are analyzed. The results of the analysis showed that for an ultrathin layer, surface effects have a significant impact on the dispersion relations, and the trends in the dispersion curves can differ significantly for different modes and layer thicknesses.

Internal Solitary Waves within the Cold Tongue of the Equatorial Pacific Generated by Buoyant Gravity Currents

Abstract The equatorial cold tongue in the Pacific Ocean has been intensely studied during the last decades as it plays an important role in air–sea interactions and climate issues. Recently, Warner et al. revealed gravity currents apparently originating in tropical instability waves. Both phenomena have strong dissipation rates and were considered to play a significant role in cascading energy from the mesoscale to smaller horizontal scales, as well as to vertical scales less than 1 m. Here, we present Sentinel-3 satellite observations of internal solitary waves (ISWs) in the Pacific cold tongue near the equator, in a zonal band stretching from 210° to 265°E, away from any steep bottom topography. Within this band these waves propagate in multiple directions. Some of the waves’ characteristics, such as the distance between wave crests, crest lengths, and time scales, are estimated from satellite observations. In total we identify 116 ISW trains during one full year (2020), with typical distances between crests of 1500 m and crest lengths of hundreds of kilometers. These ISW trains appear to be generated by buoyant gravity currents having sharp fronts detectable in thermal infrared satellite images. A 2D numerical model confirms that resonantly generated nonlinear internal waves with amplitudes of O(10) m may be continuously initiated at the fronts of advancing gravity currents. Significance Statement Satellite imagery reveals the repeated occurrence of internal solitary waves in the near-equatorial region of the east Pacific, despite the absence of topography. These waves appear to be resonantly generated over the sheared Equatorial Undercurrent by gravity currents that propagate as frontal zones of 1000-km scale tropical instability waves, providing a physical link with viscous mixing scales.

Asymptotics and scattering for wave Klein-Gordon systems

We study the coupled wave-Klein-Gordon systems, introduced by LeFloch-Ma and then Ionescu-Pausader, to model the nonlinear effects from the Einstein-Klein-Gordon equation in harmonic coordinates. We first go over a slightly simplified version of global existence based on LeFloch-Ma, and then derive the asymptotic behavior of the system. The asymptotics of the Klein-Gordon field consist of a modified phase times a homogeneous function, and the asymptotics of the wave equation consist of a radiation field in the wave zone and an interior homogeneous solution coupled to the Klein-Gordon asymptotics. We then consider the inverse problem, the scattering from infinity. We show that given the type of asymptotic behavior at infinity, there exist solutions of the system that present the exact same behavior.

ADVANCES IN UNSTRUCTURED WAVEWATCH III AND APPLICATIONS TO NEARSHORE WAVES

The spectral wave generation and propagation model WAVEWATCH III (WW3) (WW3DG 2019) is undergoing rapid community development to extend capability and nearshore modeling applicability. An option for unstructured grids and implicit solution provides WW3 with the flexibility and efficiency to resolve complex shorelines and high-gradient wave zones to drive nearshore circulation, wave setup, and wave-driven sediment transport with multi-scale spatial coverage over approximately three orders of magnitude. A hybrid approach to parallelization uses spectral partitioning for advection in geographical space and domain decomposition for spectral advection and the source term integration. The advection part of wave action equation is integrated fully implicitly, and a new convergent action limiter derived from Komen et al. (1994) and Hersbach and Janssen (1999) is applied. The model is compatible with community-based coupling infrastructure to facilitate two-way coupling with circulation models for simulating hurricane storm surge and waves. Abdolali et al. (2020) evaluated WW3 enhancements on a large-scale numerical domain employing the new parallelization algorithm and implicit solver for unstructured grids and compared to the existing parallelization algorithm, domain decomposition, and robust explicit numerical solver of WW3 on both structured and unstructured grids. These new capabilities in the wave model push the limitations of the model, including minimum resolution (10s of meters), maximum number of model grid points (~2 million), and computational scalability, as well as better accuracy in contrast to the explicit scheme. This paper describes model enhancements and validation.

Numerical Study on the Separation Performance of Hydrocyclones with Different Secondary Cylindrical Section Diameters

The particle motion behavior in hydrocyclones has received increasing attention, but the particle circulation flow has received relatively limited attention. In this paper, the particle circulation flow is regulated by changing the secondary-cylindrical section diameter to optimize the separation effect. The effects of secondary-cylindrical section diameters on flow field characteristics and separation performance are explored using the two-fluid model (TFM). The findings demonstrate that particle circulation flows are ubiquitous in the secondary-cylindrical hydrocyclone and are induced by the axial velocity wave zone. The increase in the secondary-cylindrical section diameter intensifies the coarse particle circulation and aggrandizes the coarse particle’s aggregation degree and aggregation region, leading to an increment in cut size. The circulation flow component can be regulated by adjusting the secondary-cylindrical section, thus improving the classification effect. An appropriate diameter of the secondary-cylindrical section facilitates improved particle circulation, strengthening the separation sharpness.

Numerical Investigation of Reducing Wave Propagation Hazard Utilizing an Appropriate Vegetation Area

In this study, a numerical model was employed to determine the optimal location for vegetation as an environmentally friendly method of attenuating tsunami waves. The governing equations are shallow water equations solved using shock-capturing schemes with second-order accuracy model. This simulation was validated using experimental data and another numerical model for simulating the propagation of tsunami waves on a vegetated horizontal bed and vegetated sloping beach. The parameters of wave damping rate, maximum velocity, and height for the plant area at various locations and vegetation zone lengths were investigated using numerical models. By increasing the length of the plant zone, the height and velocity of the tsunami wave were reduced, and the wave damping was increased. The examination of various locations and lengths of the plant area demonstrated that the plant area’s distance from the shoreline is a significant factor in coastal protection. The results exhibit that the location of the forest area has a great impact on the control of destructive factors along the beach. As a result, this study provides some information for designing a tsunami-resistant forest area.

Theoretical study of the void collapse and shear band formation mechanism for β‐HMX

AbstractBased on molecular dynamics simulation, we obtain a shear band formation mechanism for β‐HMX. The shock wave reflected at void face induces rarefaction wave, and the velocity difference between rarefaction wave zone and shock wave zone induces slipping. A set of physical models are developed to describe the wave reflection, shear band expansion and energy dissipation. The orientation angle, face indices, expansion velocity and formation energy of shear bands are calculated. A complete physical picture for shear band formation is obtained.

Research on the broadband source localization of a vector hydrophone vertical line array in the deep sea

This paper develops an approach that estimates the range and depth of a broadband source by adopting the vector hydrophone vertical array (VHVA) in the deep ocean. The sound field in the direct wave zone is mainly composed of direct (D) and once-sea-surface-reflected (S1B0) waves. The arrival angles and time delays of the two waves are consistent. The combined beamforming technology is applied to the VHVA to accurately obtain the elevation angles and further enhance the received signal-to-noise ratio (SNR). The source ranges are then estimated according to the simple geometric relationship. The source depth estimation model is established based on the Lloyd-mirror principle, which relates the interference properties of D and S1B0 to the oscillation period of the combined signals of VHVA. The feasibility and availability of this method are validated by both simulations and sea trials in the South China Sea. The experimental results indicate the range estimation error of the moving vessel is less than 10% and the surface or submerged targets can be effectively determined. Our proposed algorithm has the strong benefits of simple principle, low computational complexity and small error. These properties indicate this algorithm can be used in target detection in the deep sea.

The role of self-fluidization in combustion synthesis of porous and granular Ni-Al intermetallics

A wide range of capillary processes participates in the structural transformation of the reacting metal powders during the combustion synthesis of intermetallics. Using additives that decompose in the combustion wave allows controlling the formation and interaction of melts that open new opportunities for direct manufacturing of materials with desired shape and structure, which are ready for applications without additional processing steps. This paper studies the combustion mechanism of Ni+Al powder mixtures (average size of particles 10 µm) doped with CaCO3. The methods of high-speed imaging, pyrometric temperature measurements, and reaction quenching were used. It was found that CaCO3 decomposes in the preheat zone of the combustion wave resulting in the fluidization of the powder mixture. In the reaction zone of the combustion wave, an ensemble of moving microdroplets with a diameter of 0.1–0.2 mm forms. Some microdroplets drift in a preheat zone of the combustion wave, which stimulates the fluidization process. The microdroplets ultimately form larger droplets with a diameter of up to 2 mm that crystallize and form spherical struts of the gas-permeable scaffold of the combustion products. Synthesis of intermetallic compounds couples with the formation of calcium aluminates, which affects the processes of reaction coalescence and the structure of combustion products. For the CaCO3 concentration below 5–8%, the combustion products represent strong porous scaffolds consisting of tightly fused spherical-like intermetallic struts forming a net of mm-sized interconnected pore channels. Brittle scaffolds comprised of detached intermetallic granules with a diameter of 25–200 µm separated by oxide layers form if CaCO3 concentration exceeds 14%. The washing-out of the oxide phases with 5% hydrochloric acid allows for obtaining the powder of the remaining granules. The effect of self-fluidization on the structure of the synthesized alloys has been discussed in detail.