Wave Slope Research Articles

Asymptotic interpretation of the Miles mechanism of wind-wave instability

When wind blows over water, ripples are generated on the water surface. These ripples can be regarded as perturbations of the wind field, which is modelled as a parallel inviscid flow. For a given wavenumber $k$ , the perturbed streamfunction of the wind field and the complex phase speed are the eigenfunction and the eigenvalue of the so-called Rayleigh equation in a semi-infinite domain. Because of the small air–water density ratio, $\rho _{{a}}/\rho _{{w}}\equiv \epsilon \ll 1$ , the wind and the ripples are weakly coupled, and the eigenvalue problem can be solved perturbatively. At the leading order, the eigenvalue is equal to the phase speed $c_0$ of surface waves. At order $\epsilon$ , the eigenvalue has a finite imaginary part, which implies growth. Miles (J. Fluid Mech., vol. 3, 1957, pp. 185–204) showed that the growth rate is proportional to the square modulus of the leading-order eigenfunction evaluated at the so-called critical level $z=z_c$ , where the wind speed is equal to $c_0$ and the waves extract energy from the wind. Here, we construct uniform asymptotic approximations of the leading-order eigenfunction for long waves, which we use to calculate the growth rate as a function of $k$ . In the strong wind limit, we find that the fastest growing wave is such that the aerodynamic pressure is in phase with the wave slope. The results are confirmed numerically.

Modeling the Evolution and Runup of Breaking Solitary and Solitary-Like Waves on Straight and Composite Slopes

Understanding the runup and inundation of long waves on coasts is of great importance for coastal community as flooding hazards are closely related to safety issues. For many years, solitary and solitary-like waves are frequently considered as a surrogate of extremely long waves for estimating runup and inundation. Since scaling issues are of concern when extending to real-world conditions, large-scale experiments for solitary waves on uniform beaches are reviewed and additional experiments for solitary waves on composite slopes are performed in this study. As such, those experimental data obtained from large-scale physical modeling can be used to validate numerical models and then to extend the range of parameters in terms of wave conditions and slope geometries which cannot be straightforwardly achieved in large-scale experimental works. Considering the computational efficiency, an open-source non-hydrostatic wave-flow model SWASH is used herein. Detailed model-data comparisons in terms of free surface elevation time series and maximum runup heights are carried out for long waves running up and down on beaches with different slope gradients to ensure the accuracy of the SWASH model for such applications. Finally, a simple method for estimating maximum shoreline excursion for solitary waves on a particularly designed composite slope is provided.

Experimental Study of Wave Runup Variability on a Dissipative Beach

AbstractWave runup is an important process due to its effects on sediment transport and its role in coastal hazards. Despite decades of research on this topic, much uncertainty still exists in the estimation and prediction of runup. A recent numerical study has shown that there is appreciable variability in runup among wave groups on a dissipative beach due to sequencing of bichromatic waves and the resulting merging of bores. The current work further explores, in a highly controlled laboratory setting, runup variability due to wave sequencing. It is found that considerable runup variability exists among wave groups, and that this variability can differ greatly depending on the incident wave conditions. The observations suggest that the largest runup results from a higher number of bore merging events and involves a carrier wave that is positioned behind the infragravity wave crest, while the smallest runup results from a lower number of bore merging events and a carrier wave in front of the infragravity wave. A relationship is presented between runup variability and wave height, wave length, and the number of waves in a group. It is also found that an increase in runup variability is associated with an increase, at the first bore merging event, in the surface elevation at the crest of the carrier wave. Runup variability is also larger when the first bore merging event occurs further offshore, and when the local surface slope of the infragravity wave is higher.

Numerical investigation of nonlinear wave loads on a trestle-netting enclosure aquaculture facility

The rapid development of the marine industry offers more opportunities to combine aquaculture with other marine uses. This study reports a trestle-netting enclosure aquaculture facility that combines an offshore steel trestle with a marine aquaculture facility in which the trestle acts as a supporting substructure. In this study, the numerical models include one configuration without netting and three configurations with netting in different regular waves, which are generated based on stream function theory owing to nonlinear wave problems. The time series of the horizontal wave forces were obtained and analyzed in the four models. Numerical results showed that netting can significantly increase the positive amplitudes of horizontal wave forces, and the wave forces of trestle with the lee-side netting were almost smaller than those of the wave-side netting. Moreover, we investigated the nonlinear features of the wave forces and profiles. The horizontal asymmetry factors of the wave forces are affected by those of the wave profiles, while the vertical asymmetry factors of the wave forces are affected by those of the wave slope profiles. The effects of the netting on the force-positive amplitudes agree with the horizontal asymmetry factors of the wave forces but not with the vertical asymmetry factors.

PtNPs/Short MWCNT-PEDOT: PSS-Modified Microelectrode Array to Detect Neuronal Firing Patterns in the Dorsal Raphe Nucleus and Hippocampus of Insomnia Rats.

Research on the intracerebral mechanism of insomnia induced by serotonin (5-HT) deficiency is indispensable. In order to explore the effect of 5-HT deficiency-induced insomnia on brain regions related to memory in rats, we designed and fabricated a microelectrode array that simultaneously detects the electrical activity of the dorsal raphe nucleus (DRN) and hippocampus in normal, insomnia and recovery rats in vivo. In the DRN and hippocampus of insomnia rats, our results showed that the spike amplitudes decreased by 40.16 and 57.92%, the spike repolarization slope decreased by 44.64 and 48.59%, and the spiking rate increased by 66.81 and 63.40%. On a mesoscopic scale, the increased firing rates of individual neurons led to an increased δ wave power. In the DRN and hippocampus of insomnia rats, the δ wave power increased by 57.57 and 67.75%. Furthermore, two segments’ δ wave slopes were also increased in two brain regions of the insomnia rats. Our findings suggest that 5-HT deficiency causes the hyperactivity of neurons in the hippocampus and DRN; the DRN’s firing rate and the hippocampal neuronal amplitude reflect insomnia in rats more effectively. Further studies on alleviating neurons affected by 5-HT deficiency and on achieving a highly effective treatment for insomnia by the microelectrode array are needed.

Variations in Wave Slope and Momentum Flux From Wave‐Current Interactions in the Tropical Trade Winds

AbstractObservations from six Lagrangian Surface Wave Instrument Float with Tracking drifters in January‐February 2020 in the northwestern tropical Atlantic during the Atlantic Tradewind Ocean‐atmosphere Mesoscale Interaction Campaign are used to evaluate the influence of wave‐current interactions on wave slope and momentum flux. At observed wind speeds of 4–12 ms−1, wave mean square slopes are positively correlated with wind speed. Wave‐relative surface currents varied significantly, from opposing the wave direction at 0.24 ms−1 to following the waves at 0.47 ms−1. Wave slopes are 5%–10% higher when surface currents oppose the waves compared to when currents strongly follow the waves, consistent with a conservation of wave energy flux across gradients in currents. Assuming an equilibrium frequency range in the wave spectrum, wave slope is proportional to wind friction velocity and momentum flux. The observed variation in wave slope equates to a 10%–20% variation in momentum flux over the range of observed wind speeds (4–12 ms−1), with larger variations at higher winds. At wind speeds over 8 ms−1, momentum flux varies by at least 6% more than the variation expected from current‐relative winds alone, and suggests that wave‐current interactions can generate significant spatial and temporal variability in momentum fluxes in this region of prevailing trade winds. Results and data from this study motivate the continued development of fully coupled atmosphere‐ocean‐wave models.

Second-order difference-frequency wave loads on a floating body in uniform current in the frequency domain

ABSTRACT In this study, a formulation for the second-order difference-frequency wave load in the presence of steady uniform current (or forward speed) is presented, and a practical approximate approach is proposed. A potential flow-based solution is formulated to include terms up to the second-order in wave slope and first-order in current speed. In the uniform-flow approximation, the body disturbed and ship-generated steady flows are neglected, assuming slender bodies and low uniform flow speed. The free-surface integral is not included in evaluating the difference-frequency force quadratic transfer function (QTF) considering its relatively unimportant contribution compared to other terms, which significantly reduces the cost of the computational implementation. The present numerical results compare well against published experimental and numerical result. The importance of directly calculating off-diagonal terms of the QTF in the presence of uniform flow is investigated by comparing the present model with other existing approximation methods and with cases without uniform flow.

Structural Evolution and Motion Characteristics of a Hard Roof During Thickening Coal Seam Mining

This study combined theoretical analysis, physical simulation, and numerical simulation to discuss the influences of the structural evolution and motion characteristics of a hard roof during thickening coal seam mining on working face pressure. Results showed that during the mining of the thickening coal seam with a hard roof, the settlement curve of low-level strata was a stepwise wave slope, and the settlement curve of high-level strata shifted from a “V-shaped” distribution pattern to a parabola under the full mining of the coal seam. When the mining thickness was relatively small, the mining space expanded with the increase in mining thickness due to the “masonry beam” structure formed by the low-level, sub-critical overlying strata. The low-level critical strata formed a “composite cantilever beam” structure with a hard immediate roof after advancing into the caving zone. After complete recovery, the overlying strata were in a steady-movement state, and the plastic failure zone of the overlying strata of the thickening coal seam presented obvious distribution characteristics of longitudinal and transverse partitions. This study provides theoretical reference for coal seam mining under similar geological conditions.

Can cardiac shear wave elastography detect the presence of septal scar in patients with left bundle branch block?

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): FWO: Fonds Wetenschappelijk Onderzoek (fund for scientific research Flanders) Background Cardiac resynchronization therapy (CRT) is an established treatment for heart failure patients with left bundle branch block (LBBB). Regardless, CRT has proven to be less effective in patients with ischemic cardiomyopathy, in particular when the septum is affected. The detection of septal scar prior to CRT implantation could therefore help to improve response rate. However, magnetic resonance imaging (MRI), the gold standard to assess myocardial scar, cannot be used in every patient due to already implanted devices or impaired renal function. Cardiac shear wave elastography (SWE) allows for the non-invasive assessment of myocardial stiffness via the detection of shear waves, for example induced by mitral valve closure (MVC), that travel through the myocardium. Shear wave speed is directly related to tissue stiffness. Recently, SWE has shown to be capable to detect myocardial scar, however this has never been demonstrated in the presence of LBBB. Purpose To evaluate whether SWE is able to detect the presence of septal scar in patients with LBBB. Methods We included 34 heart failure patients with LBBB (age: 69 ± 13 y; 56% males) and with ischemic (n = 9) or non-ischemic (n = 25) cardiomyopathy and 9 age-matched healthy volunteers (age: 68 ± 4 y; 66% males) as controls. In order to obtain native ventricular conduction biventricular (BiV) pacing was turned off. All ischemic patients had septal scar only, proven by MRI or scintigraphy. For SWE, left ventricular parasternal long-axis views were acquired with an experimental high frame rate ultrasound scanner (frame rate: 932 ± 32 fps). Shear waves were visualized in M-modes of the septum, colour coded for tissue acceleration. The slope of the shear waves in the M-mode represents their propagation speed (Figure A). Results Patient characteristics including echocardiographic parameters are shown in Table 1. Shear wave speed after MVC was significantly higher in patients with LBBB with or without septal scar compared to healthy controls (7.9 ± 1.2 m/s vs 4.5 ± 1.1 m/s; p = 0.044; 5.6 ± 1.2 m/s vs 4.5 ± 1.1 m/s: p < 0.001; figure B). This implies that the presence of LBBB alone increases myocardial stiffness. Most importantly, however, shear wave speed was significantly higher in LBBB patients with a septal scar compared to LBBB patients without a septal scar (7.9 ± 1.2 m/s vs 5.6 ± 1.2 m/s; p < 0.001; figure B), indicating that the presence of scar increases myocardial stiffness even more than LBBB alone. Conclusions LBBB causes a mild but significant increase in shear wave propagation speed in non-ischemic patients compared to controls. The presence of septal scarring leads to an additional and more significant increase. This indicates that SWE is capable of detecting stiffer scarred myocardium even in the presence of LBBB. Therefore, SWE could potentially be used as a novel method to detect septal scarring in LBBB patients before CRT implantation. Abstract Figure. Abstract Figure.

Systolic shear wave propagation speed as a novel non-invasive marker of myocardial contractility

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Research Foundation Flanders - FWO Background Shear wave elastography is a novel echocardiographic method that tracks shear wave propagation in the cardiac wall using high frame rate ultrasound. Shear waves can be induced by e.g. aortic valve closure (AVC). The propagation speed of these waves is related to the stiffness of the myocardium. Previous work has suggested that systolic shear wave speed is related to myocardial contractility. The current gold standard reference method for the evaluation of left ventricular (LV) contractility is pressure-volume loop analysis. However, the invasive nature of this method limits its clinical applicability. Purpose To compare non-invasively assessed shear wave propagation speed after AVC to invasive pressure-volume loop-derived measurements of contractility. Methods In 12 pigs (31.9 ± 4.3 kg), dobutamine was administered intravenously. Conventional and high frame rate echocardiographic images were acquired simultaneously with invasively measured pressure-volume loops before and after the administration of dobutamine. High frame rate echocardiographic datasets were acquired with an experimental ultrasound scanner at an average frame rate of 1304 ± 115 frames per second. Shear waves after AVC were visualized on M-mode displays along the interventricular septum which were colour coded for tissue acceleration (Figure 1A). The propagation speed was calculated by semi-automatically measuring the spatiotemporal slope of the shear wave. A set of pressure-volume loops were acquired during preload reduction by balloon occlusion of the vena cava inferior. The end-systolic elastance (Ees) of the ESPVR and preload recruitable stroke work (PRSW) were used as measures of contractility. Results Heart rate (72 ± 20 bpm vs. 105 ± 25 bpm; p < 0.05) and LV ejection fraction (61 ± 4% vs. 74 ± 7%; p < 0.001) significantly increased after the administration of dobutamine, while the LV end-systolic pressure remained similar (92 ± 21 mmHg vs. 106 ± 23 mmHg; p = 0.08). Pressure-volume loop-derived measures of contractility increased during dobutamine infusion (Ees: 1.3 ± 0.5 mmHg/ml vs. 2.1 ± 1.0 mmHg/ml; p < 0.01 and PRSW: 41 ± 25 mmHg vs. 86 ± 23 mmHg; p < 0.01). Likewise, shear wave propagation speed after AVC increased after dobutamine administration compared to baseline (3.1 ± 0.6 m/s vs. 5.3 ± 1.1 m/s; p < 0.001). Shear wave speed after AVC had a strong positive correlation with Ees (r = 0.68; p < 0.001) (Figure 1B) and PRSW (r = 0.65; p = 0.001) (Figure 1C). Conclusions Systolic shear wave propagation speed is related to invasively determined measurements of LV contractility. The results of this study indicate the potential of shear wave speed after AVC as a novel non-invasive parameter for the assessment of LV contractile function. Abstract Figure.

Dyssynchrony significantly increases myocardial stiffness at mitral valve closure

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): FWO: Fonds Wetenschappelijk Onderzoek (fund for Scientific Research Flanders) Background Recently, shear wave elastography (SWE) has emerged as a promising, non-invasive technique to determine myocardial tissue stiffness. SWE is based on the detection of shear waves, for example induced by mitral valve closure (MVC), that propagate through the myocardium. The propagation speed of these shear waves is directly dependent on myocardial stiffness. However, the effect of a dyssynchronous contraction pattern – as it occurs in left bundle branch block (LBBB) – on shear wave speed is currently unknown. Purpose To investigate the effect of the dyssynchronous contraction pattern caused by LBBB on shear wave speed. Methods We included 25 non-ischemic heart failure patients with LBBB (age: 68 ± 15y; 52% males), all implanted with a CRT device. Dyssynchrony was reintroduced by turning biventricular (BiV) pacing off to allow native ventricular conduction. Echocardiographic images were taken during BiV pacing on and BiV pacing off, both with a conventional ultrasound machine and an experimental high frame rate ultrasound scanner (frame rate: 932 ± 32 fps). For SWE, left ventricular parasternal long-axis views were acquired. Shear waves were visualized in M-modes of the septum, colour coded for tissue acceleration. The slope of the shear waves in the M-mode represents their propagation speed. Speckle tracking of the four-chamber apical view was used to asses longitudinal strain of the mid-septal segment. To further investigate how dyssynchrony affects shear wave speed, the following time points were measured: onset of QRS, MVC and onset of septal contraction. Results Acutely switching BiV pacing on and off did not significantly affect left ventricular ejection fraction, nor end-diastolic or end-systolic volumes (all p > 0.05). Shear wave speed was significantly higher during BiV pacing off compared to BiV pacing on (5.6 ± 1.2 m/s vs 4.9 ± 1.3 m/s; p = 0.003; figure A). Furthermore, the onset of septal contraction was significantly earlier during BiV off (11 ± 15 ms vs 105 ± 57 ms; p < 0.0001). As a result, during BiV pacing off, the septal wall was further into the contraction phase at the time of MVC, leading to an increased myocardial stiffness, and thus increased shear wave speed (figure B). Our interpretation that increased shear wave speed could be attributed to an earlier onset of contraction of the septum was further strengthened by a strong correlation between the change in shear wave speed and the change in septal longitudinal strain at MVC when BiV pacing is turned off (r = 0.83; p < 0.001; figure C). Conclusion A dyssynchronous contraction caused by LBBB significantly increases shear wave propagation speed at MVC. This could be attributed to the early-systolic contraction of the septum during dyssynchrony. These results indicate that changes in contraction pattern caused by LBBB significantly influence myocardial stiffness at MVC. Abstract Figure.

Study on nonlinear heave and pitch motions of conventional and tumblehome hulls in head seas

The broadside of the tumblehome hull is inclined inward, while that of the conventional hulls is inclined outward. As a result of the geometric shape, the tumblehome hull has distinct motion characteristics compared to the conventional hulls. In this study, the nonlinear heave and pitch motion responses of a tumblehome hull are investigated experimentally and numerically. A series of model experiments at various wave slopes is performed to validate the nonlinear motion responses in head sea conditions. As a numerical approach, a time-domain B-spline 3-D Rankine panel method (RPM) and computational fluid dynamics (CFD) are adopted. During the nonlinear motion computation, a weakly-nonlinear method is applied to the RPM to consider the geometric properties of the tumblehome hull above the waterline. The S175 containership is selected as the comparative model. It is a conventional-shaped hull, and the relevant experimental results are available. For the conventional hull, the magnitudes of the motion transfer functions of the heave and pitch motions decrease as the wave slope increased. For the tumblehome hull, an opposite trend is observed in both the experimental and numerical results. The magnitudes of the motion transfer functions increase as the wave slope increased. The increase and decrease in the nonlinear motion responses are discussed.

Physics-Based Forward Modeling of Ocean Surface Swell Effects on SMAP L1-C NRCS Observations.

This paper examines the impact of ocean surface swell waves on near-coastal L-band high-resolution synthetic aperture radar (SAR) data collected using the National Aeronautics and Space Administration’s (NASA) Soil Moisture Active/Passive (SMAP) radar at 40° incidence angle. The two-scale model and a more efficient off-nadir approximation of the second-order small-slope-approximation are used for co- and cross-polarized backscatter normalized radar cross-section (NRCS) predictions of the ocean surface, respectively. Backscatter NRCS predictions are modeled using a combined wind and swell model where wind-driven surface roughness is characterized using the Durden–Vesecky directional spectrum, while swell effects are represented through their contribution to the long wave slope variance (mean-square slopes, or MSS). The swell-only MSS is numerically computed based on a model defined using the JONSWAP spectrum with parameters calculated using the National Data Buoy Center and Wave Watch III data. The backscatter NRCS model is further refined to include fetch-limited and low-wind corrections. The results show an improved agreement between modeled and observed HH-polarized backscatter NRCS when swell effects are included and indicate a relatively larger swell impact on L-band compared to higher radar frequencies. Preliminary investigations into the potential swell retrieval capabilities in the form of excess MSS are encouraging, however further refinements are required to make broadly applicable conclusions.

Mode coupling and intensity fluctuation of sound propagation over continental slope in presence of internal waves

The topographic variation underwater of the continental slope is one of the main causes for triggering off the formation of internal waves, and the continental slope internal waves are ubiquitous in the ocean. The horizontal variation of waveguide environment, caused by the internal wave and the continental slope, can lead to acoustic normal mode coupling, and then generate sound field fluctuation. Most of the existing research work focused on studying the effect of single perturbation factor of either the internal waves or the continental slope on acoustic mode coupling and intensity fluctuation, while it is hard to find some research work that takes into account both the internal waves and the topographic variations as influencing factors. In this work, numerical simulations for the sound waves to propagate through the internal waves in the downhill direction are performed by using the acoustic coupled normal-mode model in four waveguide environments: thermocline, internal wave, continental slope and continental slope internal wave. And the mode coupling and intensity fluctuation characteristics and their physical mechanisms are studied by comparing and analyzing the simulation results of the four different waveguide environment constructed. Some conclusions are obtained as follows. The intra-mode conduction coefficients are symmetric with respect to the center of the internal wave, while the inter-mode coupling coefficients are antisymmetric around it. As the sound waves propagate toward or away from the center of the internal wave, the acoustic mode coupling becomes enhanced or weakened, and the coupling coefficients curves for large mode oscillate. The influence of internal wave perturbation makes the energy transfer from the smaller modes to the larger modes, which increases the attenuation of sound field intensity. The number of the waveguide modes increases and the mode intensity attenuation decreases, when the sound waves propagate downhill. The total intensity of all modes for the continental slope internal wave environment is greater than for the internal wave environment and less than for the continental environment, and the energy transfer between mode groups is stronger than for individual effect of internal wave or continental slope, which leads more energy to transfer from the smaller to larger mode groups and the energy of the sound field above the thermocline to increase.

Real-Time Wave Mitigation for Water-Air OWC Systems via Beam Tracking

In a water-air optical wireless communication (OWC) channel, dynamic ocean waves may significantly deflect the light beam from its original direction, thus deteriorating the communication performance. In this letter, a beam tracking system to mitigate wave-induced communication degradation is experimentally demonstrated. By employing the beam tracking on the PAM6 system, a maximum of 486% improvement (from 140 Mb/s to 820 Mb/s) in throughput is realized at a 1.2-m air distance for an average wave slope changing rate of 0.34 rad/s. For PAM4 signals, the packet loss rate reduces significantly from 75% to 11%, and a maximum throughput of 1.25 Gb/s is achieved.

Up-to-Downwave Asymmetry of the CFOSAT SWIM Fluctuation Spectrum for Wave Direction Ambiguity Removal

The surface wave investigation and monitoring (SWIM) aboard the China-France Oceanography Satellite (CFOSAT), a pioneer conically scanning wave spectrometer, was successfully launched on October 29, 2018. Its innovative configuration composed of one nadir and five rotating near-nadir beams is designed to simultaneously observe the directional wave spectrum at a global scale. In this study, we systematically implement the spectral analysis of the radar backscattering with the periodogram technique to obtain the fluctuation spectrum for each azimuth direction. The 2-D fluctuation spectrum of the three spectral beams ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\theta = 6^\circ $ </tex-math></inline-formula> , 8°, and 10°) combines all the azimuth directions within one entire rotation of 360°. The case study demonstrates that the wave features (peak wavelength and direction) are roughly consistent between the estimated fluctuation spectrum and the collocated WaveWatch III wave slope spectrum. A marked up-to-downwave asymmetry of the fluctuation spectrum with larger spectral level in the upwave direction for all the three spectral beams is observed. A ratio is defined between the fluctuation spectrum within the [0°, 180°] sector relative to the [180°, 360°] sector. Statistics display that this ratio is greater than 1 when it denotes the up-to-downwave ratio and smaller than 1 for the down-to-upwave ratio. This observed spectrum asymmetry is linked to the asymmetric modulation from upwind to downwind. In addition, we employ such finding to help remove the 180° wave direction ambiguity from a practical point of view. Preliminary results of the direction ambiguity removal display a bias of 41.3°, 40.6°, and 36.7° for the beams. The 10° beam shows slightly better performance compared to the other two beams in terms of bias and standard deviation. This shall lay a strong basis for the operational implementation of such algorithm to resolve the direction ambiguity.

Dynamic Response of Rock-like Materials Based on SHPB Pulse Waveform Characteristics.

Rock-like brittle materials under dynamic load will show more complex dynamic mechanical properties than those under static load. The relationship between pulse waveform characteristics and strain rate effect and inertia effect is rarely discussed in the split-Hopkinson pressure bar (SHPB) numerical simulation research. In response to this problem, this paper discusses the effects of different pulse types and pulse waveforms on the incident waveform and dynamic response characteristics of specimens based on particle flow code (PFC). The research identifies a critical interval of rock dynamic strength, where the dynamic strength of the specimen is independent of the strain rate but increases with the amplitude of the incident stress wave. When the critical interval is exceeded, the dynamic strength is determined by the strain rate and strain rate gradient. The strain rate of the specimen is only related to the slope of the incident stress wave and is independent of its amplitude. It is also determined that the inertia effect cannot be eliminated in the SHPB. The slope of the velocity pulse waveform determines the strain rate of the specimen, the slope of the force pulse waveform determines the strain rate gradient of the specimen, and the upper bottom time determines the strain rate of the specimen. It provides a reference for SHPB numerical simulation. A dynamic strength prediction model of rock-like materials is then proposed, which considers the effects of strain rate and strain rate gradient.

Evaluation of Cochlear Synaptopathy in Tinnitus Patients with Normal Hearing UsingAuditory Brainstem Response and Electrocochleography Tests

Background and Aim: Tinnitus is defined a phantom sound percept. Few studies have examined the occurrence of synaptopathy in tinnitus patients utilizing a battery of tests that indicate synaptopathy. This study aimed to investigate the role of synaptopathy in tinnitus production and compare the various characteristics of the auditory brainstem response (ABR) test and electrocochleography (ECochG) in normal-hearing people with and without tinnitus. Methods: This cross-sectional study was conducted on 34 normal-hearing individuals, 20 without tinnitus as controls (11 females and 9 males) and 14 with tinnitus (8 females and 6 men). The test components (amplitude, growth and slope of wave I, V/I ratio, action potential (AP) amplitude, and summating potential (SP)/AP) ratio were recorded during the ABR and ECochG tests for each subject. Results: The control group had higher mean values of amplitude, growth and slope of wave I, and AP amplitude compared to the tinnitus group, and this difference was statistically significant (p&lt;0.05). The mean V/I ratio and SP/AP ratio were lower in the control group than in the tinnitus group, and this difference was statistically significant (p&lt;0.05). Conclusion: The significant difference in the parameters of ABR and ECochG tests between normal-hearing people with and without tinnitus indicates that these parameters can be used to evaluate the presence of synaptopathy in tinnitus patients. These findings suggest the need for proper interpretation of the results of ABR and ECochG tests in tinnitus patients with a focus on the parameters indicating synaptopathy.

ALTERNATIVE ASSESSMENT OF WEATHER CRITERION FOR SHIPS WITH LARGE BREADTH AND DRAUGHT RATIOS BY A MODEL EXPERIMENT: A CASE STUDY ON AN INDONESIAN RO-RO FERRY

The weather criterion is one of stability criteria to verify ability of a ships to withstand the combined effects of severe wind and rolling criteria in dead ship condition. An overestimated roll angle is obtained when the weather criterion is applied to ships with breadth and draught ratios larger than 3.50 and ratios between vertical centre of gravity and draught larger than 1.50. This paper discusses the assessment of weather criterion for an Indonesian ro-ro ferry by model experiments. The drift test is performed in four wave steepnesses with wave frequencies near the roll natural frequency. The maximum roll amplitude is used to calculate the effective wave slope coefficient correponding to the wave steepness, with Bertin’s coefficient obtained by the roll decay test. The damping factors correspond to the breadth and draught ratio as well as the bilge keel contribution are determined using the formula of weather criterion with the roll angle obtained by the Japanese formula with a correction factor of 0.70 due to the irregularity of waves. The obtained effective wave slope coefficient and the damping factors due to breadth and draught ratio and the bilge keel are smaller than those used in the weather criterion.

THE DIRECT EVALUATION METHOD OF DEAD SHIP STABILITY FOR INTACT SHIP

The International Maritime Organization is currently establishing second generation intact stability criteria, the dead ship stability is considered one important criterion, so the development of its direct stability assessment regulation has become a topic undergoing close review. In this paper a peak-over-threshold (POT) method is proposed to evaluate the dead ship stability, which focuses on the statistical extrapolation that exceed the threshold, also the traditional Monte Carlo simulation is carried out to approve the method. On the basis of verification calculation of the sample ship CEHIPAR2792, the capsizing probability of a certain warship is also conducted. Moreover, the influence of initial stability height GM and effective wave slope coefficient Y on the capsizing probability is analysed. The results and the possible reason for the difference are examined. This study is expected to provide technical support for the second-generation stability criteria and establish the capsizing probability of damaged dead ship stability.