Decrease In Wave Amplitude Research Articles

Hydrodynamic Performance Improvement of a Tirhandil Yacht by Stern Form Modifications

This paper presents a comprehensive investigation to improve the hydrodynamic performance of a Tirhandil hull form by modification efforts on the stern region. The form improvement approach combines computational fluid dynamics (CFD) methods with computer-aided design (CAD) systems. The design process for the reference and modified models was carried out by using CAD systems. The hydrodynamic characteristics of the reference hull form were evaluated by employing CFD methods and it was determined that form improvements should be concentrated on the stern region. The modification process was conducted by considering constraints on the design variables in the stern region and the main dimensions of the reference model. A grid independence study was performed to evaluate various grid structures to determine the optimal mesh configuration for the numerical analyses. The SST k-Omega turbulence model was used for the numerical analyses to simulate turbulence structure around the hull form. Achieving around a 13.4% reduction in the total resistance coefficient, the modified model also exhibited decreased wave amplitudes, smoother wave transitions, and a significant reduction or cancellation of shoulder and stern waves.

A Whole-Brain Model of the Aging Brain During Slow Wave Sleep.

Age-related brain changes affect sleep and are reflected in properties of sleep slow-waves, however, the precise mechanisms behind these changes are still not completely understood. Here, we adapt a previously established whole-brain model relating structural connectivity changes to resting state dynamics, and extend it to a slow-wave sleep brain state. In particular, starting from a representative connectome at the beginning of the aging trajectory, we have gradually reduced the inter-hemispheric connections, and simulated sleep-like slow-wave activity. We show that the main empirically observed trends, namely a decrease in duration and increase in variability of the slow waves are captured by the model. Furthermore, comparing the simulated EEG activity to the source signals, we suggest that the empirically observed decrease in amplitude of the slow waves is caused by the decrease in synchrony between brain regions.

SPECTRUM AND CHARACTERISTICS OF THE ELECTROCARDIOGRAPHIC CHANGES IN CHILDREN WITH TYPE I DIABETES MELLITUS

Introduction. Type I diabetes mellitus (T1D) is one of the most widespread and socially significant diseases. Well-known as a co-occurring condition with youth-onset type 1 diabetes mellitus, cardiovascular disease manifests early after initial diagnosis as signs of cardiovascular remodeling. Growing data indicates that type 1 diabetic children and young adults experience subclinical heart dysfunction, central aortic stiffening, and accelerated peripheral vascular disease. Increased morbidity and mortality in adults have been linked to peripheral artery, heart, and cerebrovascular diseases, and early vascular alterations have been demonstrated to exist since childhood. Little is known to date concerning the development of early cardiac structural and functional problems in children with T1D. Early diagnostic is of high importance. Aim. To assess the frequency and spectrum of electrocardiography (ECG) abnormalities in children with type 1 diabetes. Materials and methods. Records of 60 patients with type I diabetes included into the analysis. ECG data, main anamnestic, clinical and laboratory data analyzed. Results. So-called "small ECG abnormalities" were found. Incomplete left/right blockade bundle branch block found in 22.5% of children, shortened PQ interval in 15%, extrasystoles, tachycardia, bradycardia in 52.5%, T wave amplitude decrease in 60%. 87.5% of the examinees have a combination of 2–3 of the above changes on the ECG. Only 12% of the examined children had an ECG without pathological changes. All children with newly diagnosed type 1 DM had at least 1 of the described ECG abnormalities. Correlation analysis done. Substantial positive correlations between Hb1Ac levels and number of ECG changes, serum cholesterol levels and number of ECG changes were found. Conclusions. The results of the study indicate that the majority of children with type I diabetes have so-called "small ECG abnormalities." According to the type of disturbances, they can be classified as rhythm and conduction disturbances and combined changes. These findings are promising in terms of management tactics for children with type I diabetes, early detection and timely therapeutic correction of ECG abnormalities.

Experimental study of internal solitary wave evolution beneath an ice keel model

Internal solitary waves (ISWs) propagating in polar seas are affected by the sea ice at upper boundary of seas and thus exhibit complex evolution characteristics. Herein, spatiotemporal changes in the wave element, flow field, and energy of ISWs beneath an ice keel model were investigated to examine the evolution of ISWs. For this purpose, laboratory experiments were conducted using dye-tracing labeling, conductivity probes, Schlieren technology, and particle image velocimetry. The results show that ice keel causes an increase in the thickness of the pycnocline and even the occurrence of breaking and internal surging of ISW. Additionally, the waveform becomes narrower or wider at different positions, and wave amplitude and speed decrease, with a maximum reduction 30%–40%. Furthermore, the ice keel strengthens the shear of the ISW-induced flow field, generating vortices and mixing. The energy of ISWs undergoes internal conversion majorly at the front slope of the ice keel, while energy dissipation occurs largely at the back slope, with dissipation rates as high as 60%.

Beam‐Driven Electron Cyclotron Harmonic and Electron Acoustic Waves as Seen in Particle‐In‐Cell Simulations

AbstractRecent study has demonstrated that electron cyclotron harmonic (ECH) waves can be excited by a low energy electron beam. Such waves propagate at moderately oblique wave normal angles (∼70°). The potential effects of beam‐driven ECH waves on electron dynamics in Earth's plasma sheet is not known. Using two‐dimensional Darwin particle‐in‐cell simulations with initial electron distributions that represent typical plasma conditions in the plasma sheet, we explore the excitation and saturation of such beam‐driven ECH waves. Both ECH and electron acoustic waves are excited in the simulation and propagate at oblique wave normal angles. Compared with the electron acoustic waves, ECH waves grow much faster and have more intense saturation amplitudes. Cold, stationary electrons are first accelerated by ECH waves through cyclotron resonance and then accelerated in the parallel direction by both the ECH and electron acoustic waves through Landau resonance. Beam electrons, on the other hand, are decelerated in the parallel direction and scattered to larger pitch angles. The relaxation of the electron beam and the continuous heating of the cold electrons contribute to ECH wave saturation and suppress the excitation of electron acoustic waves. When the ratio of plasma to electron cyclotron frequency ωpe/ωce increases, the ECH wave amplitude increases while the electron acoustic wave amplitude decreases. Our work reveals the importance of ECH and electron acoustic waves in reshaping sub‐thermal electron distributions and improves our understanding on the potential effects of wave‐particle interactions in trapping ionospheric electron outflows and forming anisotropic (field‐aligned) electron distributions in the plasma sheet.

Why Does the October Effect Not Occur at Night?

AbstractThe October effect is known as a rapid and strong decrease in the signal amplitude of radio waves with very low frequency (VLF), reflected at the lowest edge of the ionosphere. This strong decrease can be observed only during the daytime. Although the October effect is long known, it is hardly investigated and its mechanism is still unknown. To get closer to a mechanism, we answer why the October effect does not occur during nighttime. Therefore, average characteristics of the October effect are obtained from different VLF transmitter‐receiver combinations. The occurrence of the October effect is then compared with characteristics of the neutral atmosphere temperature at VLF reflection heights as it seems to act as a proxy for the unknown mechanism. The temperature shows an asymmetric seasonal behavior at daytime VLF reflection heights poleward of 50°N but not during the nighttime, resulting in the October effect.

Multicenter retrospective evaluation of magnetic resonance imaging in pediatric and congenital heart disease patients with cardiac implantable electronic devices

Guidelines addressing magnetic resonance imaging (MRI) in patients with cardiac implantable electronic devices (CIEDs) provide algorithms for imaging pediatric and congenital heart disease (CHD) patients. Guideline acceptance varies by institution. Guidelines also do not support routine MRI scans in patients with epicardial or abandoned leads, common in pediatric and CHD patients. The purpose of this study was to determine the incidence of MRI-related complications in pediatric and CHD patients with CIEDs, including epicardial and/or abandoned leads. A multicenter retrospective review included patients with CIEDs who underwent any MRI between 2007 and 2022 at congenital cardiac centers. The primary outcome was any patient adverse event or clinically significant CIED change after MRI, defined as pacing lead capture threshold increase >0.5 V with output change, P- or R- wave amplitude decrease >50% with sensitivity change, or impedance change >50%. Across 14 institutions, 314 patients (median age 18.8 [1.3; 31.4] years) underwent 389 MRIs. There were 288 pacemakers (74%) and 87 implantable cardioverter-defibrillators (22%); 52% contained epicardial leads, and 14 (4%) were abandoned leads only. Symptoms or CIED changes occurred in 4.9% of MRI scans (6.1% of patients). On 9 occasions (2%), warmth or pain occurred. Pacing capture threshold or lead impedance changes occurred in 1.4% and 2.0% of CIEDs post-MRI and at follow-up. Our data provide evidence that MRIs can be performed in pediatric and CHD patients with CIEDs, including non-MRI-conditional CIEDs and epicardial and/or abandoned leads, with rare minor symptoms or CIED changes but no other complications.

Oxidative Model of Retinal Neurodegeneration Induced by Sodium Iodate: Morphofunctional Assessment of the Visual Pathway.

Sodium iodate (NaIO3) has been shown to cause severe oxidative stress damage to retinal pigment epithelium cells. This results in the indirect death of photoreceptors, leading to a loss of visual capabilities. The aim of this work is the morphological and functional characterization of the retina and the visual pathway of an animal model of retinal neurodegeneration induced by oxidative stress. Following a single intraperitoneal dose of NaIO3 (65 mg/kg) to C57BL/6J mice with a mutation in the Opn4 gene (Opn4-/-), behavioral and electroretinographic tests were performed up to 42 days after administration, as well as retinal immunohistochemistry at day 57. A near total loss of the pupillary reflex was observed at 3 days, as well as an early deterioration of visual acuity. Behavioral tests showed a late loss of light sensitivity. Full-field electroretinogram recordings displayed a progressive and marked decrease in wave amplitude, disappearing completely at 14 days. A reduction in the amplitude of the visual evoked potentials was observed, but not their total disappearance. Immunohistochemistry showed structural alterations in the outer retinal layers. Our results show that NaIO3 causes severe structural and functional damage to the retina. Therefore, the current model can be presented as a powerful tool for the study of new therapies for the prevention or treatment of retinal pathologies mediated by oxidative stress.

A numerical simulation study of the hydrodynamic effects caused by morphological changes in the Guadalquivir River Estuary

This study presents an analysis of the impacts of the changes in bottom depth along the Guadalquivir Estuary on tidal dynamics. A realistic non-linear 1D numerical model, incorporating changes in both breadth and bottom depth, was employed to investigate the involved effects. The findings reveal a significant amplification of the M2 tidal wave towards the upper region of the Estuary, resulting from the gradual deepening caused by multiple dredging operations. The Estuary exhibits a pronounced tendency towards resonance, which is further enhanced by its deepening, resulting in reduced bottom friction and a smaller decrease in tidal wave amplitude as it propagates through the Estuary. The alterations in depth, particularly in breadth, along the Estuary play a crucial role in determining the magnitude of the resonant response of the M2 tidal wave.

PE-452787-2 A MULTICENTER RETROSPECTIVE EVALUATION OF MAGNETIC RESONANCE IMAGING IN PEDIATRIC AND CONGENITAL HEART DISEASE PATIENTS WITH CARDIAC IMPLANTABLE ELECTRONIC DEVICES

Guidelines addressing magnetic resonance imaging (MRI) in patients with cardiac implantable electronic devices (CIEDs) provide algorithms for imaging pediatric and congenital heart disease (CHD) patients. Guideline acceptance varies by institution; some continue to exclude patients with CIEDs from MRI. Citing insufficient data, guidelines do not support routine MRI scans in patients with epicardial or abandoned leads, common in pediatric and CHD patients. We sought to determine the incidence of MRI-related complications in pediatric and CHD patients with CIEDs, including epicardial and/or abandoned leads. A multicenter retrospective review included all patients with a CIED who underwent any MRI between 7/2007 and 7/2022 at participating congenital cardiac centers. The primary outcome was any patient adverse event, CIED malfunction, or clinically significant CIED change after MRI, defined as pacing lead threshold increase >0.5 V with change in output, P- or R- wave amplitude decrease >50% with change in sensitivity, or impedance change >50%. Adverse events among MRI-conditional and non-conditional CIEDs were compared. Across 14 institutions, 314 patients underwent 389 MRIs; median age was 18.8 [IQR 11.3 – 31.4, range 0.1-77.4] years. There were 288 (74%) pacemakers, 87 (22%) ICDs, and 14 (4%) abandoned leads only. Most were MRI non-conditional (287, 74%); 201 (51%) had epicardial leads, and 66 (17%) had abandoned leads. No MRI-related deaths, sustained symptoms, or CIED malfunction occurred. On 8 (2.1%) occasions, symptoms of warmth, tingling, or pain occurred; 5 (63%) involved abandoned lead(s), and 2 (25%) resulted in MRI termination. Other indications for MRI termination were poor image quality (13, 3.3%), claustrophobia (1, 0.2%), and incorrect device programming (1, 0.2%). A pacing capture threshold change occurred in 0.3% (1/359) and 1.8% (6/335) of patients post-MRI and at follow-up (median 36 [IQR 1-73] days after MRI). An impedance change occurred in 1.4% (5/359) and 1.2% (4/335) of patients post-MRI and follow-up. Impedance changes primarily occurred in MRI non-conditional CIEDs. Other adverse events were similar among MRI-conditional and non-conditional CIEDs. MRIs can be performed in pediatric and CHD patients with CIEDs, including non-conditional CIED systems, with rare, minor CIED changes but no other complications. Our data provide evidence that patients with epicardial and/or abandoned leads can safely undergo MRI imaging.

Solitary-like Wave Dynamics in Thin Liquid Films over a Vibrated Inclined Plane

Solitary-like surface waves that originate from the spatio-temporal evolution of falling liquid films have been the subject of theoretical and experimental research due to their unique properties that are not readily observed in other physical systems. Here we investigate, experimentally and theoretically, the dynamics of solitary-like surface waves in a liquid layer on an inclined plane that is subjected to a harmonic low-frequency vibration in a range from 30 to 50 Hz. We employ a standard boundary layer model, which describes large-amplitude deformations of the film surface, assuming that it has a self-similar parabolic longitudinal flow velocity profile, to confirm the experimental results and to explain the interplay between the short-wavelength Faraday instability and long-wavelength gravitational instability. In particular, we demonstrate that the vibration results in a decrease in the average and peak amplitude of the long solitary-like surface waves. However, the speed of these waves remains largely unaffected by the vibration, implying that they may propagate over large distances almost without changing their amplitude, thus rendering them suitable for a number of practical applications, where the immunity of pulses that carry information to external vibrations is required.

Ultrasonic guided wave attenuation in submerged steel pipes

Pipe structures play a pivotal role in various industrial sectors, necessitating the assurance of their structural stability to ensure safe and reliable operations. Non-destructive Testing (NDT) methods are commonly employed to assess the integrity of these systems. Among the array of NDT techniques, Ultrasonic Guided Wave (UGW) inspection has emerged as a reliable method for assessing large mechanical structures, particularly addressing challenges associated with accessibility. This study focuses on investigating the impact of water immersion on UGW attenuation in steel pipes. To investigate the behaviour of guided waves in water-immersed scenarios, a comprehensive experimental setup was designed and implemented. The study involved testing four distinct cases: (a) an empty bare pipe as a reference case, (b) a bare pipe filled with stagnant water, (c) an empty pipe fully submerged in plain water, and (d) a pipe with combined loads (i.e., filled with stagnant water and submerged). The amplitude variation and Time of Flight (ToF) were analysed to assess wave propagation characteristics. The experimental results revealed notable differences in amplitude and ToF among all the four tested cases. Introduction of stagnant water inside the bare pipe resulted in decreased wave amplitudes, indicating increased wave attenuation compared to the empty pipe scenario. This research provides valuable insights for applications involving steel pipes submerged in water, offering guidance for accurate and reliable inspection and monitoring of pipe integrity. Future investigations may focus on understanding the underlying mechanisms behind wave attenuation in water-immersed scenarios and developing techniques to mitigate or compensate for these effects, thereby advancing inspection and monitoring capabilities in real-world applications.

Instability of non-REM sleep in older women evaluated by sleep-stage transition and envelope analyses.

Traditionally, age-related deterioration of sleep architecture in older individuals has been evaluated by visual scoring of polysomnographic (PSG) recordings with regard to total sleep time and latencies. In the present study, we additionally compared the non-REM sleep (NREM) stage and delta, theta, alpha, and sigma wave stability between young and older subjects to extract features that may explain age-related changes in sleep. Polysomnographic recordings were performed in 11 healthy older (72.6 ± 2.4 years) and 9 healthy young (23.3 ± 1.1 years) females. In addition to total sleep time, the sleep stage, delta power amplitude, and delta, theta, alpha, and sigma wave stability were evaluated by sleep stage transition analysis and a novel computational method based on a coefficient of variation of the envelope (CVE) analysis, respectively. In older subjects, total sleep time and slow-wave sleep (SWS) time were shorter whereas wake after sleep onset was longer. The number of SWS episodes was similar between age groups, however, sleep stage transition analysis revealed that SWS was less stable in older individuals. NREM sleep stages in descending order of delta power were: SWS, N2, and N1, and delta power during NREM sleep in older subjects was lower than in young subjects. The CVE of the delta-band is an index of delta wave stability and showed significant differences between age groups. When separately analyzed for each NREM stage, different CVE clusters in NREM were clearly observed between young and older subjects. A lower delta CVE and amplitude were also observed in older subjects compared with young subjects in N2 and SWS. Additionally, lower CVE values in the theta, alpha and sigma bands were also characteristic of older participants. The present study shows a decrease of SWS stability in older subjects together with a decrease in delta wave amplitude. Interestingly, the decrease in SWS stability coincided with an increase in short-term delta, theta, sigma, and alpha power stability revealed by lower CVE. Loss of electroencephalograms (EEG) variability might be a useful marker of brain age.

Effect of Auditory Stimulation by Upbeat Music on Radial Pulse

Introduction: Music of varying tempo or beats have physiological as well as adverse effects on the body. This study throws light on the influence of upbeat music on properties of radial pulse, in healthy young adults. Methods: One hundred and seventy-five students between the age of nineteen and twenty-four years were included in this study. The experiment was conducted in a room, devoid of any external disturbances. Subjects were made to listen the chosen upbeat music for 4 minutes using a headphone. The radial pulse was measured before and immediately after the experiment. Data analysis was done by using SPSS software version 16.0.Results: In this study we observed that normal mean pulse rate was 76 per minute in males and 72 per minute in female young adults. Following the auditory stimulation with upbeat music, rise in pulse rate was observed in more than 70% of subjects. Whilst, 24% showed a decrease pulse rate and 5% showed no change in pulse rate. Increased pulse rate was associated with decrease in amplitude of pulse wave but no change in rhythm and character of the pulse when compared to resting state. Conclusion: This study indicates that the music can increase the pulse rate in the majority of the subjects but also decreases the pulse rate in few individuals. This study provides the preliminary evidence to promote the music therapy in many preventive programs for patients with depression, patients with depressed cardiac functioning and useful in improving daily performances.

The Effects of Liver Cirrhosis on Electrical Autorhythmicity of Isolated Duodenum in Rats

Background: Cirrhosis reduced small bowel motility and transit time, with unknown mechanisms. Moreover, intestinal motility depends on the electrical activity and the autorhythmicity of interstitial cells of Cajal (ICC). If cirrhosis directly affects the intrinsic mechanism of intestinal motility, the isolated bowel of cirrhotic cases will also exhibit an electrical abnormality compared with normal cases. Objectives: This study aimed to identify the effects of liver cirrhosis on the electrical autorhythmicity of isolated duodenum in rats. Materials and Methods: Six weeks after bile duct ligation (BDL) surgery, animals were anesthetized, and blood samples were obtained from the heart for the evaluation of plasma cirrhosis indices, including weight, plasma albumin, serum glutamic oxaloacetic transaminase (SGOT), serum glutamic pyruvic transaminase (SGPT), bilirubin, and direct bilirubin. Then, the duodenum of rats was isolated and compared with the control group for the rate of electrical slow waves and the maximum amplitude of slow waves. Results: Significant differences were observed between the control and BDL group in terms of weight, plasma albumin, SGOT, SGPT, bilirubin, and direct bilirubin. Moreover, there was a significant decrease in the maximum amplitude of slow waves in the BDL group compared with the control. Conclusion: It seems that different factors directly harm the ICC network such as inflammation caused by microbiome amplification as a result of cirrhosis, which in turn reduces small bowel motility.

Analytical and Numerical Studies of Transient Heat Transfer in Soil for Geothermal Systems

The study of geothermal systems requires a good knowledge of heat transfers in the depth of the soil. The aim of this work is to study the distribution of temperature in the ground under the climatic conditions of Togo. The analytical and numerical solutions of unidirectional heat transfer equation assuming the soil as a semi-infinite medium are found. The analytical solution is validated by comparing the results of the present work to those found in literature. A good qualitative agreement between these results was noted. The results show that the attenuation depth decreases when the attenuation accuracy of the thermal wave increases. The analysis of the effect of moisture content indicates that the increasing in soil conductivity with moisture result in the decreasing of the attenuation depth. Soil temperature increases when increasing soil thermal diffusivity. It is found also that, soil temperatures decrease with depth and stabilize around an average value of 30°C for depths greater than about 5.8 m for all type of soil studied in the month of March which is the hottest month of the year in Togo. A gradual decrease in temperature can be seen from March to August (hot period) followed by stabilization at around 28°C with a depth of 5.8 m. The phenomenon is reversed for the months of September to February (cold period). The soil warms up slowly during the day and cools down slowly at night because of the thermal inertia of the soil. A decrease in amplitude of the thermal wave near ground surface, is observed when the Leaf Area Index (LAI) increases. However, ils influence on the stabilization depth is not very significant. Stabilization of soil temperatures in March month is observed at a depth of about 40 cm for all LAI with a value of 37°C.

Mathematical Modeling of Gastric Slow Waves During Electrical Field Stimulation.

While neural modulation has been trialed as a therapy for functional gastric motility disorders, a computational model that guides stimulation protocol does not exist. In this work, a mathematical model of gastric slow wave activity, which incorporates the effects of neurotransmitter release during electrical field stimulation (EFS), was developed. Slow wave frequency responses due to the release of acetylcholine and slow wave amplitude responses due to the release of nitric oxide were modeled. The model was calibrated using experimental data from literature. A sensitivity analysis was conducted, which showed that the model yielded stable, periodic solutions for EFS frequencies in the range 0-20 Hz. A 25% increase in the input parameter (EFS frequency) from 5 Hz to 6.25 Hz resulted in a 5.2% increase in slow wave frequency and a 3.2 % decrease in slow wave amplitude. Simulated EFS showed that, for stimulation at 15 Hz, with blocking of the nitrergic neurotransmitter pathway the slow wave increased from the no stimulation scenario in frequency by only 2.4x compared to 2.7x when the nitrergic pathway was not blocked. A 21 % reduction in slow wave amplitude occurred when the cholinergic pathway was blocked, compared to a 46% reduction when no neurotransmitter pathways were blocked. Clinical relevance - This mathematical model is a step towards successful computational modeling of the effects ther-apeutic neural stimulation on the stomach. The model is also a tool for understanding of the physiology of neural stimulation.

Investigation of acoustic characterization of ultrasonic air coupling testing of NEPE propellant under strain control

To explore the acoustic characterization of composite solid propellant materials, the wave equation of the viscoelastic body was derived based on the linear viscoelastic constitutive model, and the theoretical relationship between ultrasonic sound velocity and attenuation coefficient, which are closely related to mechanical properties, such as elastic modulus, viscosity coefficient, and complex modulus, was obtained. Ultrasonic air-coupled testing experiments of the NEPE (Nitrate Ester Plasticized Polyether) propellant under different tensile strain states were carried out to obtain the variation law of ultrasonic transmission wave peak amplitude, sound velocity, and attenuation coefficient with strain variables in combination with the variation in propellant porosity under tensile strain. Furthermore, the acoustic parameters with strain and porosity were fitted by the regression equation, and the effect of mesoscopic damage on macroscopic mechanical properties was analyzed. The results show that with the increase in NEPE propellant tensile strain, the porosity increases exponentially. With the increase in porosity, the sound velocity decreases by first polynomials, the wave amplitude decreases by second polynomials, and the attenuation coefficient increases by third polynomials.

Study on resistance characteristics of submarine near water surface

The submarine is usually affected by free surface and the navigation resistance increases when sailing near the surface. In order to study the specific resistance characteristics of submarine sailing near the surface, the SUBOFF with appendages was taken as the research object, and the calculation model was built based on Star CCM+ fluid simulation software, and the resistance coefficients under different submarine depths and speeds were calculated. Through comparative analysis, the influence of the depth and speed of the submarine on the resistance components was obtained, and the cause of the formation was analyzed. The results show that the influence of the depth of submarine on friction resistance coefficient is small in general. With the increase of the depth of the submarine, the pressure resistance coefficient decreases, and the wave amplitude decreases. The shear wave of Kelvin wave system is more obvious and the effect of scattering is weakened, which is of great significance for the study of submarine concealment. With the increase of speed, friction resistance coefficient decreases, the overall change trend of pressure resistance coefficient is first increased and then decreases. The interference effect between free surface and hull increases first and then decreases at each depth. The wave shape changes and resistance results mutually confirm. The free surface mainly generates waves by interacting with the hull, which affects the resistance characteristics of the submarine. The interference effect is greatly affected by the depth and speed of the submarine.

Overcoming excessive numerical dissipation in SPH modeling of water waves

Excessive nonphysical energy dissipation is a problem in Smoothed Particle Hydrodynamics (SPH) when modeling free surface waves, resulting in a significant decrease in wave amplitude within a few wavelengths for progressive waves. This dissipation poses a limitation to the physical scale of SPH applications involving water wave propagation. Some prior solutions to this wave decay problem rely on elaborate schemes, which require a complex, or non-straightforward, implementation. Other approaches demand large smoothing lengths that lead to longer simulation times and potential degradation of the results. In this work we present an approach based on a kernel gradient correction. Our scheme is fully 3D and solves the main known drawbacks of kernel gradient corrections, such as instabilities and lack of momentum conservation. The latter is ensured by adopting an averaged correction matrix, so as to conserve reciprocity during particle interactions. We test our model with a standing wave in a basin and a progressive wave train in a wave tank, and in both cases no nonphysical decay occurs. A comparison to an approach based on large smoothing factors shows advantages both in quality of the results and simulation time.