Head Waves Research Articles

Evanescent Acoustic Waves

A theoretical study of “geometric” SP-evanescent (head) waves propagating in an isotropic homogeneous half-space or half-plane with a free boundary shows that these waves can satisfy the condition of absence of effort on the boundary plane if and only if the Lamé parameter λ is vanishingly small, which makes the existence of head waves of this type practically impossible. The analysis is based on the Helmholtz representation for the displacement field in combination with the decomposition of the stress and strain tensor into spherical and deviatoric parts. The obtained result about the non-existence of this type of evanescent waves can find application in theoretical geophysics in the study of seismic wave fields in the vicinity of earthquake epicenters, as well as in non-destructive acoustic diagnostic methods.

Modelling Sea-Surface Wave Motion and Ship Response Using Smoothed Particle Hydrodynamics and Finite Element Analysis

The response of a ship or other vessel to surface sea waves, including extreme waves, may compromise crew and vessel safety and long-term operational capability. Herein, a novel high-fidelity numerical time-dependent simulation approach is presented using Smoothed Particle Hydrodynamics (SPH) for modelling sea waves coupled with Finite Element Analysis for modelling vessel structural response under wave loading conditions. The results are compared with physical scale model wave tank test results. Good agreement was obtained for heave and pitch motions and vertical bending moments for various forward (head) speeds in regular head waves, heave and pitch motions, and vertical bending moments. High computational demands can be met by the increasing availability of computation power. Ongoing research is outlined. The implications for the design of vessels such as ships and for through-life assessment are discussed.

Hydrodynamic Analysis of Different Formation Configurations of Catamaran in Regular Head Waves

When undertaking long-distance missions at sea, vessels aim to achieve an extended operational range through drag reduction and energy efficiency, while enhanced wave resilience also provides substantial benefits. In this work, the Delft-372 catamaran is utilized to investigate the feasibility of drag reduction and roll mitigation for catamaran formation sailing in waves, analyzing the effects of three different formation configurations and varying spacings. The overset grid method was employed to simulate vessel motions, while the Volume of Fluid (VOF) method captured the free surface. First, the numerical results of the catamaran’s resistance, pitch, and heave motion amplitudes under different wave conditions were compared with experimental data to verify the accuracy of the CFD numerical method, and a grid convergence analysis was performed. Next, numerical models of the Delft-372 catamaran were constructed in parallel, tandem, and lateral formations under wave conditions. The results of the single-ship simulation were employed as a benchmark to analyze the impact of different formation configurations and varying lateral and longitudinal spacings on the resistance, pitch, and heave motions of the catamarans. The study also examined the effects of wave interference between vessels and the combined influence of external waves on individual and overall hydrodynamic performance. Results indicated that the tandem formation outperformed the parallel and lateral formations, with optimal performance observed at the longitudinal distance of 1 LPP. Generally, during navigation, the follower catamaran should ideally be positioned in the trough of the stern wave of the leader catamaran.

Numerical simulations of the ONRT ship maneuvering in calm water and head waves with the partially rotating grid method

This research delves into the maneuverability aspects of a model-scale ONRT surface combatant ship using Computational Fluid Dynamics (CFD) simulations. A key aspect of this study is the comparison of the actuator disc (AD) model and the partially rotating grid (P) method in calm water, complemented by an in-depth analysis of the P method for simulations in waves. Utilizing these methods, the study investigates the performance of the ship in propeller open water, self-propulsion, and complex maneuvers like turning circle and zig-zag. Key findings highlight the superiority of the P method in closely aligning with experimental data, particularly in capturing complex dynamics of ship maneuvers. This research underscores the critical role of propeller side force in maneuvering simulations, a factor often neglected in simpler models like the AD. Maneuvers in head waves are also examined, revealing the nuanced effects of wave orientation on the stability and maneuverability of the ship. This study highlights the effectiveness of CFD in simulating ship maneuvers and the need for ongoing refinement of these techniques to improve accuracy and reliability.

The influence of wave modelling on the motions of floating bodies

In recent years OpenFOAM studies have focused on pure wave modelling and wave-structure interaction. Considering that there is a lack of transparency concerning effects of different motion modelling settings in OpenFOAM, this paper presents the influence of different numerical setups on the accurate modelling of wave-induced motions. This is achieved by applying the interFoam solver included in OpenFOAM-v2206 with the waves2Foam toolbox. The optimal numerical setup is studied with a two-dimensional box-like ship idealisation heaving in varying wave lengths while the wave steepness remains constant. Different numerical setups are considered for accurate wave modelling, the modelling of wave excitation forces for the case of a static structure, and heave motion modelling. Finally, the optimal setup that is found is applied for a 3D ship case in head waves with heave and pitch coupling. As far as practically possible, the results are validated against experimental data. It is shown that strict requirements for mesh density and time step for accurate wave modelling result in accurate excitation force and motion results. Reflections from the relaxation zones and different mesh density layers cause inaccuracies. It is concluded that simple numerical cases are suitable for studying optimal numerical setups for more complex simulation cases.

Vertical line time domain green function and its applications in numerical simulation of ship seakeeping performance

In present study, a vertical line source time domain Green function is proposed and the subsequent numerical evaluation methods are described in detail. For which, Taylor expansion and Chebyshev approximation algorithms are originally extended from point source to line source for small parameters, as well as asymptotic expansions are extended for large parameters. Meanwhile, polynomials are originally proposed to replace the asymptotic expansions to improve the computational efficiency. The accuracy and stability of the proposed method are validated through several cases and good agreement can be obtained.Furthermore, a hybrid Green function method based on the vertical line source Green function and Rankine source is developed for time domain simulation of seakeeping performances of ships. With respect to the hybrid method, the flow domain is divided into inner part and outer part by an artificial control surface. The first-order Taylor Expansion Boundary Element Method (TEBEM) based on the Rankine panel distribution is applied in the inner part, while three-dimensional panel method based on the vertical line source Green function distribution is adopted in the outer part. Under this circumstance, motions of the single-ship (Slender Wigley and Blunt Wigley) and two-ship (two side-by-side ships) in head waves are numerically investigated. The numerical results agree well with the experimental data, which proved the feasibility and the accuracy of present hybrid Green function method for motion prediction of both single-ship and two-ship.

A comprehensive unsteady RANS numerical investigation to unveil the influence of wave steepness on the motion dynamics and added resistance of a ship in waves

In this study, we investigate the influence of wave steepness on both ship motions and added resistance in regular head waves by conducting simulations at three distinct wave steepness levels using unsteady RANS method. Numerical results show that, when wavelength comparable to the ship length, the interaction of body nonlinearity and wave nonlinearity results in highly nonlinear behavior in the time history of added resistance. The study illustrates, step-by-step, the hydrodynamic pressure distribution on the hull during an encounter period, highlighting the time-varying nature of the added resistance. Examining the visualised results, it is observed that in certain instances, high pressure may be exerted on the flat bottom of the trimmed ship and contribute significantly to the added resistance. It is observed that, when wavelength is comparable to ship length, the added resistance coefficient decreases with increasing wave steepness. Specifically, at λ/LPP = 1.15, |CAW,H/λ=1/30−CAW,H/λ=1/60|CAW,H/λ=1/60 = 27.1%. In relatively short waves the diffraction phenomena dominate and the resulting added resistance exhibits limited nonlinearity. However, obtaining stable results in such cases proves challenging. Finally, the influence of wave steepness on added resistance is quantified. The results are useful for improving the transparent methods for predicting the added resistance in wave.

The importance of data preconditioning strategies for envelope full-waveform inversion methods: Demonstration on marine seismic data

Envelope full-waveform inversion (EI) of seismic data has been proposed to overcome the cycle-skipping issue and recover long-wavelength velocity components for over a decade. However, we are aware of few published successful applications of EI on real data examples (except for some correlation- or phase-based EI methods). We implement EI methods (EI with [Formula: see text], EI with p = 1, and improved EI) on 2D marine seismic data and find that the amplitude mismatching between the modeled and observed data is a critical factor that prevents the successful application of EI methods to real data. To match the amplitude better, we include a data weighting preconditioner in the objective function of the EI methods. The preconditioner term acts as a weighting factor to compensate for the amplitude mismatch between the observed and modeled data. We develop a method for calculating the preconditioner term using the amplitude of the head waves as a reference. Furthermore, we derive the adjoint source and gradient of the EI using the data preconditioning method. We illustrate the successful application of EI methods with the data preconditioning method using the 2D marine seismic data example. In comparison to the EI methods without the data preconditioning method, those using data preconditioning yield much more geophysically reasonable velocity models and Kirchhoff image sections and common-image gathers.

Aerodynamic discrepancies of high-speed trains meeting within two types noise barriers: considering modeling scale ratio

PurposeSustainable urban rail transit requires noise barriers. However, these barriers’ durability varies due to the differing aerodynamic impacts they experience. The purpose of this paper is to investigate the aerodynamic discrepancies of trains when they meet within two types of rectangular noise barriers: fully enclosed (FERNB) and semi-enclosed with vertical plates (SERNBVB). The research also considers the sensitivity of the scale ratio in these scenarios.Design/methodology/approachA 1:16 scaled moving model test analyzed spatiotemporal patterns and discrepancies in aerodynamic pressures during train meetings. Three-dimensional computational fluid dynamics models, with scale ratios of 1:1, 1:8 and 1:16, used the improved delayed detached eddy simulation turbulence model and slip grid technique. Comparing scale ratios on aerodynamic pressure discrepancies between the two types of noise barriers and revealing the flow field mechanism were done. The goal is to establish the relationship between aerodynamic pressure at scale and in full scale.FindingsThe aerodynamic pressure on SERNBVB is influenced by the train’s head and tail waves, whereas for FERNB, it is affected by pressure wave and head-tail waves. Notably, SERNBVB's aerodynamic pressure is more sensitive to changes in scale ratio. As the scale ratio decreases, the aerodynamic pressure on the noise barrier gradually increases.Originality/valueA train-meeting moving model test is conducted within the noise barrier. Comparison of aerodynamic discrepancies during train meets between two types of rectangular noise barriers and the relationship between the scale and the full scale are established considering the modeling scale ratio.

Experimental and numerical study of wet-deck slamming characteristic for a trimaran in regular head waves

Wet deck may suffer from strong slamming effects when sailing under severe sea conditions, which could damage it locally and compromise the structural integrity of trimarans. The wet-deck slamming characteristic for trimaran sailing in head waves is studied in this work using both experimental and numerical simulation methods. We found that the negative pressure occurred at the front of the wet deck, which is caused by the wet deck exit from the wave crest. Regarding the spatial distribution in longitudinal, the slamming behaviour is more severe at the front part of the wet deck, as the relative vertical impact velocity decreased from the front to the back part of it. Simultaneously, the wet-deck slamming is more severe under the short-wave condition. Regarding the spatial distribution in lateral, we found that the water-entry of the main hull could cause the wet-deck slamming pressure near the outrigger larger than that of the main hull. Moreover, the wet deck has been divided into three regions according to their different lateral distribution characteristics of the wet-deck slamming. These results can provide a better understanding of the wet-deck slamming characteristics when trimaran sailing in waves, which can be considered in future designs for the trimaran.

Study on numerical simulation and mitigation of parametric rolling in a container ship under head waves

To investigate the parametric rolling motion of container ships navigating in head seas, this study utilizes the unsteady RANS approach combined with dynamic overlapping grid technology to simulate parametric roll in a container ship under the coupled motions of roll, pitch, and heave. Initially, the model was validated against experimental results, demonstrating good agreement and thus confirming the reliability of the computational method. Furthermore, the paper investigates the impacts of the initial roll angle, encounter frequency, and the addition of bilge keels on parametric rolling. The research findings indicate that the initial angles of rolling impact the duration needed to attain a steady roll condition, yet they have minimal effect on the amplitude post-stabilization. The likelihood of parametric rolling arises when the frequency of encounters doubles that of the ship's inherent roll frequency. Furthermore, the likelihood of parametric rolling escalates when the wavelengths approach the length of the ship. Installing bilge keels markedly reduces the parametric rolling movement in vessels, and the occurrence of parametric rolling is also delayed.

Numerical simulation of borehole compressional wave and shear wave in 3D vug formation

The staggered grid finite difference method (SGFDM) of a monopole source is used to simulate a three-dimensional vug reservoir model and study the effect of acoustic logging responses of different vug models on radial probing depth. The results show that the first arrival of the head wave peak of the compressional wave (P-wave) and the shear wave (S-wave) is unrelated to the radius of the vug, and the amplitude of the head wave peak of the P-wave and S-wave decreases as the vug volume increases. Compared with the volume change of the vug, the radial distance from the vug wall has little influence, while the vertical source distance has large influence on the P-wave and S-wave. When there are multiple vugs in the model, the amplitudes of the P-wave and S-wave head wave peaks change sinusoidally with the angle between the vugs. The ellipsoidal vug model with the same volume has a greater influence on the P-wave and S-wave than the spherical vug model. In the ellipsoidal vug model, the axial vug size has a greater impact on the first arrival of the head wave peak, while the radial vug size significantly influences the amplitude of the head wave peak. Finally, we validate the numerical simulation conclusions by comparing them with actual logging data responses in complex formations, demonstrating the practical value of the elastic wave response simulations for vugs.

Geotectonic architecture beneath Northern Vietnam revealed by local earthquake tomography combining seismic data from multiple networks

Extrusion tectonics driven by the collision of Indian-Eurasian continents and the relative motion among microcontinents (e.g. South China, Simao-Indochina blocks) has led to multi-phase and complex geological activity and structures in Northern Vietnam. While extensively studied, its detailed crustal architecture in association with multiple large-scale shear zones and plate boundaries remains unclear and is key to resolving long-lasting tectonic debates. This study constructs the first 3-D regional S-wave velocity (Vs) model with consistent P-wave velocity (Vp) and Vp/Vs ratio models by jointly using the crustal and head waves (e.g. Pg/Sg and Pn/Sn phases) from an augmented earthquake catalog combining the Vietnam National Earthquake Catalog (VNCAT) and the data from multiple adjacent seismic networks. The quality of phase picking and earthquake location incorporating seismic data from various sources are carefully examined and collected for the tomographic inversion. We use a stepwise joint inversion scheme to subsequently constrain the earthquake location, 1-D and 3-D velocity models. The output models suggest that the Song Ma suture represents a better candidate for the Indochina-South China boundary rather than the Red River Shear Zone. The latter seems to act as a crustal structure while the former and the Dien Bien Phu Fault are likely lithospheric ones. Several other geologic features such as the Tu Le volcanic basin, the Song Hong basin, and the Day Nui Con Voi metamorphic complex are also clearly depicted and discussed in the model. This new set of the Vp, Vs, and Vp/Vs models could further contribute to better assessment to seismic hazards in the northern Vietnam.

Real-Time Method and Implementation of Head-Wave Extraction for Ultrasonic Imaging While Drilling

Extracting head waves and subsequently uploading their results from the downhole to the surface system in real time could improve the real-time guidance of ultrasonic imaging logging while drilling (UILWD) for drilling operations. To realize the downhole real-time extraction of head waves in this logging, three aspects were explored in this study. First, an improved energy ratio head-wave arrival extraction algorithm based on the weighting coefficients and characteristic functions, along with an amplitude detection method relying on peak-to-peak values, was proposed. Second, an echo reception pre-processing analog circuit and a digital signal processing circuit based on FPGA were designed. A pipeline algorithm was developed in FPGA to extract the arrival time and amplitude of the head wave. Finally, software simulations, laboratory tests, and field experiments related to this method were conducted. Our results showed that the real-time head-wave extraction method demonstrated a strong anti-noise ability in real time. The maximum relative error of the arrival time was less than 5%. The relative error of the amplitude was acceptable, and 90% of this value was within 5%. Through the measurement, the time of processing a single-channel waveform by a downhole algorithm was less than 15 ms, thus meeting the requirements for the real-time processing of downholes.

Impacts of regular head waves on thrust deduction at model self-propulsion point

The results obtained from the self-propulsion simulations using Computational Fluid Dynamics (CFD) in the current study, for a ship free to heave, pitch and surge with the means of a weak spring system, are combined with the formerly executed CFD results of the bare hull and propeller open water simulations to investigate the impacts of regular head waves on the propeller-hull interactions in comparison to calm water, at the self-propulsion point of the model. Despite a rather significant dependency of the nominal wake on the wave conditions, the Taylor wake fraction remains almost unchanged in different studied waves which is around 12% lower than the calm water value. The thrust deduction factor in waves is reduced (12.8%–26.1%) in comparison to the calm water value. The change of thrust deduction factor is found to be associated with the boundary layer contraction/expansion and vortical structure dynamics, originating from the wave orbital velocities as well as the significant shaft vertical motions and accelerations that resulted in a modified propeller action, and consequently diminished suction effect on the aft ship. The altered thrust deduction factor and wake fraction in waves in comparison to calm water underlines the significance of waves on the propulsive factors and propeller design.

Comparative study of nonlinear wave-induced global loads on a container ship in regular head waves predicted with numerical methods based on weakly nonlinear potential theory and Reynolds-averaged Navier-Stokes equations

ABSTRACT Wave-induced loads on the ship hull are of significant interest for many reasons. These loads, however, are highly nonlinear in realistic wave conditions and consequently difficult to predict. In this paper, we analysed and compared wave-induced loads acting on a container vessel in regular head waves computed with a newly developed weakly nonlinear potential theory-based code and a flow solver based on the Reynolds-averaged Navier-Stokes Equations. We investigated both long and short waves with moderate steepness. Initially, the vessel was completely fixed and the ship motions were suppressed, then the vessel was free to heave and pitch motion. We compared time-histories of the computed wave-induced longitudinal and vertical global forces as well as the pitch moment and we deeply analysed nonlinear effects by applying a Fourier transformation and comparing the corresponding harmonic amplitude up to the fourth order. Our results demonstrated satisfactory agreement between the two numerical methods, especially when the ship was free to heave and pitch. Additionally, the results provided detailed information about the capabilities and limitations of the weakly nonlinear potential theory-based approach.

A Time-Domain Numerical Simulation for Free Motion Responses of Two Ships Advancing in Head Waves

A Time-Domain Numerical Simulation for Free Motion Responses of Two Ships Advancing in Head Waves

Thermal effect on the transient behavior of a piezomagnetic half-space subjected to dynamic anti-plane load

Considering the importance of understanding the propagation of transient waves in the piezomagnetic solids, the thermal effect on the transient behavior of a piezomagnetic half-space subjected to dynamic anti-plane load is investigated analytically in this paper. Using one-sided, two-sided Laplace transformation and Cagniard–de Hoop (CH) technique, an efficient and accurate analytical derivation for the solution of the anti-plane displacement, shear stress, magnetic potential, and induction in Laplace domain is presented. The study shows that the thermal stresses developed in x-axis and y-axis directions have significant influence on the transient response of the half-space. The magnetic induction B x increases obviously when the thermal stress is applied in x-axis direction, while it decreases when the thermal stress is applied in y-axis direction. Approaching time of magnetic induction B x and B y will become longer with higher thermal stress in x-axis direction. With the growth of the thermal stress in x-direction, contribution from the electromagnetic–elastic head (EH) wave increases, while the contribution from the shear elastic (SE) wave and the static value of shear stress decrease.

Planing Hull Hydrodynamic Performance Prediction Using LincoSim Virtual Towing Tank

This work shows the performance of LincoSim, a web-based virtual towing tank enabling automated and standardized calm water computational fluid dynamics (CFD) data sampling, extending previous published applications to the case of a high-speed hull. The calculations are performed for a 1:10 scale model of a 43 ft powerboat hull form in the Froude number range from 0.3 to 2.0. The counterpart physical model is the experimental fluid dynamics (EFD) campaign performed at the University of Naples Federico II, where the resistance, sinkage and trim data have been measured. The EFD/CFD data comparison is performed and shown with a discussion of the spotted differences. The average percentage differences between the EFD and CFD data for the whole speed range are 1.84, 6.87 and 6.94 for the resistance, dynamic trim, and sinkage, respectively. These results confirm the maturity of the standardized and automated CFD modeling for calm water hydrodynamic analysis included in LincoSim, even at very high Froude numbers. The wetted length of the keel and chine and the wetted surface are calculated from numerical data using the advanced post-processing. Finally, as a work in progress, we test a first comparison for the same hull of the EFD and CFD data, considering two seakeeping conditions for head waves at a given wavelength for two velocity conditions. Also, this kind of analysis confirms the tight correlation between the measured and computed outcomes. This synergic interplay of EFD and CFD can link the advantages of both methods to support hull design but also requires experiment planning and final data analysis to obtain physical parameters not easily measurable in laboratory, such as the wetted surface, wetted lengths, proper viscous contribution, and pressure distribution both in calm water and in waves.

Underwater radiated noise from small craft in shallow water: Effects of speed and running attitude

Underwater radiated noise from marine vessels is a growing problem, with a large body of evidence now showing the detrimental impact this is having on marine life. Whilst most of the discussion currently focusses on the impact of large vessels, recent evidence shows that small vessels can dominate the soundscape in shallow coastal waters. In this study, acoustic trials are carried out on two small vessels: a pilot boat and a rigid inflatable boat (RIB) across a wide speed range. The average source levels range from 156–173 dB for the pilot boat and 164–166 dB for the RIB (re1μPam). The engine noise is dominant for the RIB across the speed range, and it is further shown that the heading relative to the prevailing waves is a bigger determining factor for noise levels than speed. In upper sea state 3, the overall sound level is up to 6 dB higher when in head waves compared to following waves. Acoustic measurements are combined with onboard vibration measurements to provide further insights into the relationship between noise and vibration. Analysis of this data shows the vessel running attitude plays a key role in determining how much noise is transmitted into the water.