Wave Reflection Research Articles

Wave–Structure Interaction Modeling of Transient Flow Around Channel Obstacles and Contractions

This study investigated the effects of downstream channel obstacles and the lateral transition distance to the dam on dam-break wave evolution as a wave–structure interaction problem. Numerical simulations were conducted using three-dimensional Navier–Stokes equations and solved using the finite volume method. The model accurately predicted interactions between dam-break waves and downstream structures. The numerical results showed that turbulence intensity increased where the cross-section significantly changed in the downstream channel. Accordingly, transcritical flow and lateral transitions were developed around the dam site. Additionally, reducing the distance of the obstacle to the dam resulted in a significant decrease in wave height and kinetic energy. The transient flow velocity direction changed around the structures, and pressure fluctuations were pronounced. Moreover, the entrainment of air bubbles and the vortex shedding were observed due to the interaction of the wave and downstream structures. The peak discharge in the downstream channel was reduced by increasing the distance of obstacles to the dam. The model successfully captured the flow disturbance, wave reflectance from the sidewalls, and formation of hydraulic jumps. The validation of the model with experimental data in the literature showed that the model performed well in predicting the wave dynamic characteristics around the downstream structures.

Relativistic theory of reflection and refraction of electromagnetic waves at a moving interface

Relativistic theory of reflection and refraction of electromagnetic waves at a moving interface

Labour diagnostics using the intrauterine pressure through sound waves emitted by a smartphone.

Labour commencement diagnosis is still challenging in obstetrics. The majority of scientific techniques that were used to determine labour are costly and require a professional healthcare personnel to be carried out. Hence, in this work, an experiment was conducted using a 3D-printed 50% scale model of the abdomen of an average 40-week pregnant woman. The aim was to test whether the internal pressure can be evaluated from the reflection of the sound waves emitted by a smartphone. Frequencies of 4 kHz and 20 kHz were triggered at multiple distances (0.17, 0.34, 0.51 m) after inflating the 3D-printed model with water. The reflection coefficients and internal pressure were determined to have a positive linear correlation, suggesting that the hypothesis is practical. However, as the distances decreased, the reflection coefficient plateaued, indicating that the material had attained its maximum reflection coefficient at that frequency. Due to its reduced error and non-audible properties as compared to 4Hz, 20 kHz was suggested to be an optimum frequency for measuring pressure, allowing it for pain-free application for an extended amount of time.

Numerical Simulation of the Transition to Detonation in a Hydrogen–Air Mixture Due to Shock Wave Focusing on a 90-Degree Wedge

This study numerically explores the initiation of detonation through shock wave reflection and focusing on a 90-degree wedge in varying mixtures of hydrogen–air. The simulations were conducted using the ddtFoam code, an integral part of the OpenFOAM open-source Computational Fluid Dynamics (CFD) package of density-based code for solving the unsteady, compressible Navier–Stokes equations. The simulation results unveil three potential outcomes in the corner post-reflection: deflagrative ignition in the corner, deflagrative ignition with intermediate transient phases leading to a delayed transition to detonation in the trailing combustion zone close to the apex of the wedge, and ignition with an immediate transition to detonation, resulting in the formation of a detonation wave in the corner tip. In the experimental investigation, the transition velocity for the stoichiometric mixture stood at approximately 719 m/s. In contrast, the numerical simulation indicated a transition velocity of 664 m/s for the same stoichiometric mixture, reflecting a 5.5% decrease in velocity. Such an underestimation level of 5–8% by the simulation results was observed for mixtures of 25–45% H2 in air.

Correlated spin-wave generation and domain-wall oscillation in a topologically textured magnetic film.

Spin waves, or magnons, are essential for next-generation energy-efficient spintronics and magnonics. Yet, visualizing spin-wave dynamics at nanoscale and microwave frequencies remains a formidable challenge due to the lack of spin-sensitive, time-resolved microscopy. Here we report a breakthrough in imaging dipole-exchange spin waves in a ferromagnetic film owing to the development of laser-free ultrafast Lorentz electron microscopy, which is equipped with a microwave-mediated electron pulser for high spatiotemporal resolution. Using topological spin textures, we captured the emission, propagation, reflection and interference of spin waves from spin anti-vortices under radio-frequency excitations. Remarkably, we show that spin-wave generation is closely tied to the oscillatory motion of specific magnetic domain walls, providing the missing link between wave emission and wall dynamics near magnetic singularities. This work opens new possibilities in magnonics, offering a nanoscopic view of spin dynamics via transmission electron microscopy and enabling controlled excitation via radio-frequency fields for exploring non-equilibrium states in magnetic and multiferroic systems.

Measurement of pressure dependent variations in local pulse wave velocity within a cardiac cycle from forward travelling pulse waves

The local pulse wave velocity (PWV) from large elastic arteries and its pressure-dependent changes within a cardiac cycle are potential biomarkers for cardiovascular risk stratification. However, pulse wave reflections can impair the accuracy of local PWV measurements. We propose a method to measure pressure-dependent variations in local PWV while minimizing the influence of pulse wave reflections. The PWV is computed from the pulse transit time between two forward-traveling pulse waveforms obtained across known path length, after measured/modelled flow-based wave separation analysis (WSA). An in-vivo study of 60 participants (24 female), was conducted to compare inter- and intra-cycle variations in PWV obtained from measured and forward pulse waves. For this, proximal and distal diameter waveforms from the carotid artery, along with carotid tonometry, were recorded using a custom bi-modal arterial probe. The carotid blood flow for WSA was captured with an ultrasound imaging system. The reference PWV was derived from the Bramwell-Hill equation. After WSA, the reliability of PWV measurement improved with coefficient of variation reducing from 25% to 10% near the peak of the pulse waves and matched the reference PWV with no statistically significant difference. The average PWV at foot of the pulse wave before and after WSA were comparable to the reference PWV with no statistically significant difference. The coherence of carotid pulse pressure obtained from the mean values of PWV within a cardiac cycle after WSA with that of the carotid pulse pressure from tonometry, substantiates the results obtained for reflection-free PWV. The reliability of measuring local PWV and its pressure dependent variations within a cardiac cycle is improved by combining transit-time approach with WSA.

P0325 Is the augmentation index a good marker of cardiovascular risk in Crohn’s disease?

Abstract Background The axiom which defines that the high prevalence of cardiovascular risk factors is by definition correlated with the risk of cardiovascular events does not seem to apply to subjects with IBD, according to several studies which have reported that the prevalence of classic cardiovascular risk factors is lower in subjects with IBD than in the general population. This leads us to look for other markers to identify this risk at an early stage. The Augmentation index (Aix) is one such marker, based on the reflection of the pulse wave in the blood, and is a recognised measure of arterial stiffness and a risk factor for cardiovascular disease Methods This was a prospective cross-sectional study of 107 patients with Crohn’s disease (CD) diagnosed on the basis of clinical, endoscopic, morphological and histological criteria. Classical cardiovascular risk factors were analysed, as well as data concerning CD: duration, location, phenotype, clinical relapse, extradigestive manifestations, ano-perineal lesions (APL) and C-reactive protein (CRP). The augmentation index (Aix) was assessed using the SphygmoCor-XCEL Sydney. The Chi2 test was used for qualitative variables and the Kruskal Wallis test for quantitative variables. The informed consent of all patients was obtained. Results 57.9% were men, mean age was 36.9 ± 11.7 years, 5.6% of patients had coronary heredity, 11.2% hypertensive, mean systolic blood pressure: 120.1 ± 12.7 mm/hg, mean diastolic blood pressure: 74.4 ± 8.1 mm/hg, pulse pressure: 45.7 ±9.3 mm/hg, AIx was positive in 31.8% of patients, 7.5% of women were postmenopausal, mean BMI was 22 ± 5.91 Kg/m2, 9.3% were obese, 11.2% were sedentary, 20.6% were active smokers, only two patients were diabetic. 57.9% had dyslipidaemia, and 13.1% had a low cardiovascular risk according to the Framingham score. 74% had an ileal location, 6.8% colonic and 19.2% ileocolic, 19.8% had an inflammatory form, 43,4% stenosing and 36,8% penetrating, 25.5% with ano-perineal lesions, 31.4% had an extradigestive manifestation, 59.4% of patients were in clinical relapse, 47.2% of whom had a CRP > 6mg/l, 38% of subjects had had at least one relapse in the year prior to recruitment, and the mean duration of the disease was 57.3 ± 57 months. Statistical analysis showed a significant association between AIx and clinical relapse (p=0.03), disease duration (p=0.008), and no significant association with phenotype, location, APL, extradigestive manifestations and CRP (p>0.05). Conclusion Our results suggest that the augmentation index could be a good tool for detecting subclinical cardiovascular damage in Crohn’s disease. Clinical relapse and the duration of the disease would be two predominant factors in the increase in this index

Reflection of plane waves in a microelongated thermoelastic porous medium with Hall current under modified Green–Lindsay model

Reflection of plane waves in a microelongated thermoelastic porous medium with Hall current under modified Green–Lindsay model

Unconventional Coastal Structures (Kemit Armor Layer)

ABSTRACTThe growth of the marine sector induces substantial demand to develop new types of coastal structures that have minimal impact on neighboring ecosystems and reduce the environmental footprint. This study aims to introduce and check the efficiency of an innovative armor layer for coastal protection towards fostering sustainable coastal management practices. The proposed truncated cube (named Kemit) design incorporates features such as two hollow opposite elbows, half rings, and incomplete pyramidal shapes to enhance wave absorption and promote marine biodiversity. The proposed armor unit has been investigated physically in the wide wave flume of the Coastal Research Institute Egypt. The armor layer performance was introduced through wave reflection, wave dissipation coefficients, and wave overtopping. Six wave conditions (wave height and wave period) were performed to the armor layer in two states of submergence. A comparative analysis with traditional cube‐armored breakwaters under the same circumstances (wave height, wave period, and water depth) reveals superior performance of the proposed “Kemit” armor layer, exhibiting lower wave reflection coefficients (0.56 to 0.68) and lower overtopping, particularly evident in medium water depths. However, in case of lower water depth, the traditional cubes show better efficiency, lower reflection coefficient (0.46 to 0.68), and higher dissipation (0.74 to 0.89). Moreover, the proposed Kemit armor layer decreased the wave overtopping and run‐up over the breakwater cross‐section due to the Kemit steps and porosity. Furthermore, the adoption of innovative technologies can help policymakers increase the resilience of coastal infrastructure and ecosystems.

Approximation for reflection and transmission at a thin isotropic poroelastic bed between two isotropic elastic half‐spaces

AbstractSeismic responses from a horizontal poroelastic layer provide chances to detect fluids and characterize reservoirs. The poroelastic layer can be considered a thin poroelastic bed if the layer's thickness is less than about one‐eighth of the P‐wave wavelength. Most previous theoretical studies on the reflection and transmission of waves in a model containing a thin poroelastic bed employ fluid or poroelastic medium as the overlying media. Existing approximate formulas of PP‐wave reflection coefficients are given for P‐wave normal‐incidence. Thus, this paper derived the wave reflection and transmission approximate formulas of a thin poroelastic bed between two elastic half‐spaces with P‐wave oblique incident. First, we illustrated the exact reflection and transmission matrix equations for P‐wave incidents based on poroelasticity theory and the boundary conditions. Assuming the poroelastic bed's thickness is far less than wavelengths of S‐ and P‐waves, approximate reflection and transmission formulas are expanded in Taylor series centred at value of the parameter defined as the product of angular frequency, thickness and slowness. Numerical results show that the thinner the poroelastic layer, the closer the approximate reflection and transmission coefficients are to the exact ones. The approximate formulas are valid for small and medium angles. Approximated PP‐wave reflection and transmission coefficients are closer to the exact values than those of the converted waves, which is caused by the fact that P‐wave has a lower slowness than S‐wave.

Polyadic Cantor potential of minimum lacunarity: Special case of super periodic generalized unified Cantor potential

Abstract To bridge the fractal and non-fractal potentials we introduce the concept of generalized unified Cantor potential (GUCP) with the key parameter $N$ which represents the potential count at the stage $S=1$. This system is characterized by total span $L$, stages $S$, scaling parameter $\rho$ and two real numbers $\mu$ and $\nu$. Notably, the polyadic Cantor potential (PCP) system with minimal lacunarity is a specific instance within the GUCP paradigm. Employing the super periodic potential (SPP) formalism, we formulated a closed-form expression for transmission probability $T_{S}(k, N)$ using the $q$-Pochhammer symbol and investigated the features of non-relativistic quantum tunneling through this potential configuration. We show that GUCP system exhibits sharp transmission resonances, differing from traditional quantum systems. Our analysis reveals saturation in the transmission profile with evolving stages $S$ and establishes a significant scaling relationship between reflection probability and wave vector $k$
through analytical derivations.

Sex-specific ultrasound imaging biomarkers of neurodegeneration in a mouse model.

Early detection of neurodegeneration is essential for optimizing interventions. The highly reproducible progression of neurodegeneration in the decrepit (dcr) mouse allows investigation of early biomarkers and mechanisms of brain injury. Using high-frequency ultrasound, the common carotid arteries of female and male dcr and control mice were imaged longitudinally at time points bracketing the disease progression (50, 75, and 125 days of age) (n = 6 mice/group/sex). Over the disease time course, the female dcr mice demonstrated increased carotid artery blood flow and pulse wave velocity while the male dcr mice had a decrease in heart rate and no change in carotid artery ultrasound parameters. Early imaging biomarkers were sex-specific, with decreased carotid artery blood flow in female dcr mice and increased carotid artery diameter and decreased pulse wave velocity in males. Carotid artery and wave reflection ultrasound is a promising screening tool for early detection of neurodegeneration.

Wave transformation in transmission lines with rapid connection and disconnection of reactive elements

Rapid switching of transmission line parameters has emerged as a way to manipulate signals and as a testbed for various electromagnetic processes in time-varying media, including metamaterials. In general, the switching results in wave reflection and transmission similar to that for a spatial interface but at new frequencies. Here, various realizations of parameter switching are studied: connection and disconnection of reactive elements (capacitors and inductors) in series and in parallel. The temporal boundary conditions for the current and voltage distributions are derived rigorously based on the telegrapher’s equations that explicitly model additional elements, instead of taking the equivalent values. It is shown that the temporal boundary conditions depend not only on the parameter values before and after switching but on its specific realization. Connecting or disconnecting reactive elements always involves energy losses. When new elements are added, two types of losses are identified. The first type is related to the creation of static magnetic and electric fields in the elements after switching. The second type is related to a very rapid energy dissipation during switching even for a vanishingly small resistivity in the line. When elements are removed, their energy is also removed from the waves. The effects of finite switching times are discussed. This study defines some serious constraints in using switchable transmission lines for the realization of photonic time crystals and efficient wave manipulation without externally added energy. The results are also applicable to wave propagation phenomena in other media with time-varying parameters.

Observations of umbral flashes in the resonant sunspot chromosphere

Context. In sunspot umbrae, the core of some chromospheric lines exhibits periodic brightness enhancements known as umbral flashes. The consensus is that they are produced by the upward propagation of shock waves. This view has recently been challenged by the detection of downflowing umbral flashes and the confirmation of a resonant cavity above sunspots. Aims. We aim to determine the propagating or standing nature of the waves in the low umbral chromosphere and confirm or refute the existence of downflowing umbral flashes. Methods. Spectroscopic temporal series of Ca II 8542 Å, Ca II H, and Hα in a sunspot were acquired with the Swedish Solar Telescope. The Hα velocity was inferred using bisectors. Simultaneous inversions of the Ca II 8542 Å line and the Ca II H core were performed using the code NICOLE. The nature of the oscillations were determined and insights into the resonant oscillatory pattern were gained by analyzing the phase shift between the velocity signals and examining the temporal evolution. Results. Propagating waves in the low chromosphere are more common in regions with frequent umbral flashes, where the transition region is shifted upward, making resonant cavity signatures less noticeable. In contrast, areas with fewer umbral flashes show velocity fluctuations that align with standing oscillations. Evidence suggests dynamic changes in the location of velocity-resonant nodes due to variations in the transition region height. Downflowing profiles appear at the onset of some umbral flashes, but upflowing motion dominates during most of the flash. These downflowing flashes are more common in standing umbral flashes. Conclusions. We confirm the existence of a chromospheric resonant cavity above sunspot umbrae. It is produced by wave reflections at the transition region. The oscillatory pattern depends on the transition region height, which exhibits spatial and temporal variations due to the impact of the waves.

EXTREME TRANSLATIONAL IMPACT OF TRIPLE-SHOCK CONFIGURATIONS OF BLAST WAVES IN A CONFINED VOLUME OF AN ORBITAL STATION

The translational effects of gas streams, which form after the triple-shock configurations at Mach reflection of blast waves with normal main shock (so-called stationary Mach configurations), were analyzed. Unlike in the case of an elevated explosions of fuel as rocket starts in initially stagnant air, which is considered here as a private case, it was supposed that this shock-wave structure moves in a preceding flow with arbitrary velocity (and corresponding flow Mach number). Analyzing relations of the dynamic pressures across the slipstream, which emanates from the triple point of the Mach reflection, it was shown that the flows after the triple-shock configuration usually differ much in their translational action on surrounding objects. It was found and discussed that some configurations drag the objects initially situated above and below the triple-point trajectory in opposite directions. Moreover, the “trigger” structure was found that remains previous flow drag action on the object above the triple-point trajectory, but switches it to exactly opposite one, if the object is situated below the triple point.

Adjoint‐State Reflection Traveltime Tomography for Velocity and Interface Inversion With Its Application in Central California Near Parkfield

AbstractTraveltime tomography considering reflection arrivals is a promising approach for investigating interface topography and near‐interface velocity heterogeneity. In this study, we formulate this inverse problem as an eikonal equation‐constrained optimization problem, in which the traveltime field of the reflection wave is accurately described by a two‐stage eikonal equation. The novelty lies in deriving the Fréchet derivative with respect to interface topography. By employing the coordinate transformation technique to convert an irregular physical domain with an undulating interface to a regular computational domain, we successfully encode the interface topography into the anisotropic parameters in the eikonal equation. This approach enables us to derive explicit forms of the Fréchet derivatives related to interface topography and velocity based on the adjoint‐state method, which is not only computationally efficient but also avoids potential inaccuracy in ray tracing. Several numerical experiments are conducted to verify our new method. Finally, we apply this method to central California near Parkfield by inverting traveltimes of both first‐P and Moho‐reflected waves (named PmP). The low‐velocity anomalies imaged in the lower crust are consistent with the along‐strike variations of low‐frequency earthquakes (LFEs) beneath the San Andreas Fault (SAF), suggesting the presence of fluids that may influence the occurrence of LFEs in this region.

Physics-guided neural network for structural health monitoring with lamb waves through boundary reflection elimination

Lamb-wave-based structural health monitoring (SHM) technology for damage location in plate-like structures relies on the postprocessing of captured signals after interacting with damage. Traditional methods typically leverage the time of flight (ToF) of scattered waves from damage. However, these methods are prone to reflected waves from structural boundaries which mix with scattered waves from damage. This is a vital problem faced by most ToF-based detection methods, which seriously narrows the inspection area. To tackle this problem, a machine learning framework, consisting of a multiscale spatiotemporal (MSST) fusion network, is proposed to facilitate the accurate extraction of the ToF of scattered waves through eliminating the influence of boundary reflections. Experiments are conducted with the time-domain Lamb wave signals recorded by a tactically designed piezoelectric sensor array on a 2-mm-thick Al-6061 plate. A pair of circle magnets is attached onto the plate as the wave reflectors. Through step-by-step moving of the magnets in the predefined grids, the corresponding Lamb wave signals are measured to construct a database. An MSST is subsequently designed to minimize the error between estimated and theoretical ToFs, with wavelet coefficients of the signals and transducer position as inputs. The model is trained with the Adam algorithm where 80% of samples in the database are used for training and the rest for evaluation. The final validations are conducted with the scatters off the predefined grids. Results demonstrate that the designed neural network architecture can effectively eliminate boundary reflections and enable precise ToF extraction of the scattered waves from damage. This allows the enlargement of the detection area and presents a promising and useful tool for enhancing the detection performance of existing SHM methods in complex structures.

Size-Dependent Effects in the Modified Green–Lindsay Thermoelasticity Model: Analysis of Ultrashort Pulse Interactions in the Presence of Electromagnetic Fields

Abstract This study provides a more detailed model for wave transmission and reflection in a complex thermodynamic framework. The governing equations are developed from multiphase electromagnetic size-dependent thermoelasticity models. The main focus here is on the development of the Modified-Green Lindsay nonlocal generalized thermoelasticity model that improves previous nonlocal approaches by incorporating additional strain and temperature rate terms. This study also examines how materials react to very short pulses and the effect of external electric and magnetic fields. The highly developed nonlinear equations in this study are solved using advanced programming techniques, including an iterative approach that combines finite element methods with a Newmark time-marching scheme. The results of this work established the nonlocal heat conduction theory of generalized thermoelasticity along with nonlocal continuum theory as a new improvement and progress in the field of thermoelasticity. This model shows that without considering thermal nonlocality interactions, predictions may miss essential aspects of wave behavior. The results show that the materials experience changes in mechanical properties, particularly an increase in hardness, when exposed to stronger magnetic fields. In addition, the results show that as the duration of laser pulses decreases, the speed of wave propagation increases. Shortening the pulse duration increases the wave propagation speed, which can create steep thermal gradients. In the case of pure metals heated by ultra-short pulse lasers, the fast electron heat conduction prevents the formation of significant thermal waves, while these pulses induce more intense and localized thermal stresses. Analysis of wave propagation also shows that the return time can exceed the forward time as the waves react to applied electric and magnetic fields.

Biodegradable RF Metamaterial Perfect Absorber for Wireless Soil pH Monitoring

AbstractA wireless soil pH sensor is proposed using a sheet‐type perfect absorber metamaterial. The sensor utilizes a high‐impedance surface metamaterial, which functions as a perfect absorber at the resonant frequency. This sensor has a uniform water‐soluble Mg film at the bottom coated with hydroxyapatite that degrades depending on the pH, and a periodic square split ring resonator metamaterial structure made on top of a lossy dielectric plate. The sensor detects the dissolution of the metamaterial due to soil pH conditions through the electromagnetic wave reflection response at GHz frequency. Because of the perfect absorbing characteristics, the influence of soil on the metamaterial's electromagnetic response is blocked, allowing for robust measurement regardless of soil type. By coating the Mg with hydroxyapatite, the difference between acidic (pH = 3.0) and neutral soils can be detected by the time difference by a factor of three in the reflectance change from 40% to 75% reflectance change, indicating a transition from absorptive to reflective of the metamaterial's response, at the resonant frequency of 4.12 GHz.

Investigation of Electromagnetic Wave Propagation in Nanocones

The aim of this thorough study is to investigate the behaviour of electromagnetic wave propagation in three distinct nanostructures, each with unique shapes and material compositions. The first nanostructure under scrutiny is a butterfly-shaped nanocone formed by placing two nanostructures side by side. It consists of two nanocons. The second nanostructure is a deltoid-shaped nanocone created in a similar manner, composed of two different nanocones. The third nanostructure is a parallelogram-shaped nanocone constructed by stacking nanocones on each other and made of two different nanocones. These nanostructures differ in shape and material property parameters, each comprising two different materials with specific permeability and permittivity values. To conduct a detailed analysis, the study utilises the nonlocal theory to examine the electromagnetic wave propagation behaviour in these nanostructures. The focus of the analysis is on the travel and reflection of electromagnetic waves at three specific points along the same axis in each structure, allowing for a comprehensive comparison of their behaviours. This in-depth investigation holds significant importance as it seeks to understand the penetration and subsequent propagation of incident electromagnetic waves within nanostructures of varying shapes and material compositions, shedding light on their potential applications in advanced technology and optic science.