Wave Propagation Distance Research Articles

Bender elements in stiff cemented clay: shear wave velocity (Vs) correction by applying wavelength considerations

For the quality control of cement mixing in clays, small-strain shear stiffness Gmax is now increasingly being used due to enhanced repeatability in shear wave velocity (Vs) measurements. These stiff cemented clays have higher resonant frequencies that require the use of higher input frequencies in bender element testing for reliable Vs measurements. However, the practical requirements for suitable signals (with minimal near-field effects and wave reflections) can often be difficult to implement. To facilitate such Vs measurements, the current study proposes a methodology that can correct Vs values corresponding to lower wave propagation distance to wavelength ratios (Ltt/λ) to more reliable values of Vs at reference Ltt/λ criterion suggested in previous studies (e.g., 2, 3.33, and 4). Two clay types are mixed with ordinary Portland cement and various mix ratios are utilized to cover a wider range of soil stiffnesses. Based on the collected database, it is found that the resulting fitting functions enable the reasonable estimation of the stabilized Vs values corresponding to the suggested Ltt/λ criterion regardless of the nature of the input sine signal.

Attenuation of gravity waves in fast ice

The attenuation coefficients of sea waves in ice in the coastal zone of the Sea of Okhotsk with periods from 4 to 30 s were estimated as a function of their wavelength based on observations. We used the model dispersion relation for these waves in ice and calculated the theoretical attenuation coefficients. We compared them with those from the data of experiments based on the relation of the spectral energies of waves in ice-free water and in ice. It is possible to use the estimated attenuation coefficients for waves of different periods to calculate the distance of wave propagation in fast ice with the critical amplitude where ice breaking is possible.

Study on the factors of acoustic emission wave velocity in concrete

Concrete is frequently used as construction material, because of its favourable properties. However, concrete material is a kind of artificial multiphase composite material, which has the inevitable flaws, such as the anisotropy. As a result, it is necessary for structure to make real time monitoring. The wave speed has a significant effect on the AE location results. The experiments between AE wave velocity and different distances condition under concrete was conducted. With the increase of distance in concrete, the wave propagation speed will have a little reduction. However, the acoustic emission location system adopts constant wave velocity, so the error will be tremendous. For this reason, this paper utilizes the thought of mutative speed and find a influence between wave velocity and propagation distance, max aggregate and water-cement ratio.

Attenuation of Gravity Waves in Fast Ice

The attenuation coefficients of sea waves in ice in the coastal zone of the Sea of Okhotsk with periods from 4 to 30 s were estimated as a function of their wavelength based on observations. We used the model dispersion relation for these waves in ice and calculated the theoretical attenuation coefficients. We compared them with those from the data of experiments based on the relation of the spectral energies of waves in ice-free water and in ice. It is possible to use the estimated attenuation coefficients for waves of different periods to calculate the distance of wave propagation in fast ice with the critical amplitude where ice breaking is possible.

Numerical Investigation of the Gas Flow Effects on Surface Wave Propagation and Discharge Properties in a Microwave Plasma Torch

Gas flow plays an important role in determining the discharge properties in microwave plasma torches sustained by the propagating surface wave. This paper aims to investigate the gas flow effects on the plasma column length, the surface wave propagation, and the heavy species temperature in a surface wave plasma torch operated at atmospheric pressure. The steadystate discharges of pure argon gas at atmospheric pressure under different gas inflow rates in the plasma torch are characterized by an improved 2-D axisymmetric fluid model. The obtained results demonstrate that increasing the gas inflow rate is able to decrease the surface wave propagation distance, accelerating the contraction of the plasma column length. The discharge instability is found to be motivated by the disappearance of the sustaining surface wave at high gas inflow rates. Besides, a temperature drop of about 64 °C is observed at the temperature-maximum point of the glass tube with an increase in the gas inflow rate from 1 to 16 L · min -1 . Therefore, for the surface wave plasma torch operated with only the axial gas flow, increasing the gas inflow rate cannot solve the glass overheating problem.

Modelling of the landslide-induced impulse waves in the Artvin Dam reservoir by empirical approach and 3D numerical simulation

Due to the burgeoning energy demand in Turkey, there has been a significant increase in the number of dams and hydroelectric power plants constructed; >250 dams have been built in the past 10 years. Consequently, various engineering problems were encountered due to landslides near reservoirs, both during and after the construction. Generally, two-dimensional (2D) and three-dimensional (3D) empirical equations have been used to calculate the physical properties and propagation of the landslide-induced impulse waves; however, 3D numerical simulation-based methodologies are rarely used, although they can model the complex geometry of dam reservoirs better, using detailed topographic data. In this study, therefore, 3D numerical analysis is carried out for a potential generation of impulse waves, using the data of paleo-landslide at the Artvin Dam reservoir (NE Turkey), and the results are compared with the calculated results by empirical equations. A finite element method-based shear strength reduction analysis (FEM-SSR) was performed to analyse the slope stability. After the establishment of the correct propagation model, the equations were utilised with different input parameters and 3D numerical analysis-based simulations to evaluate the characteristics of the impulse waves. In the numerical model created using the FLOW-3D software, the ‘drift-flux model’ was used to simulate the probable landslides. The Reynolds-averaged Navier–Stokes equations were used in a free-surface modelling technique together with the volume of fluid (VOF) model for simulating the wave generation. The renormalised group model (RNG) for viscous flow and k-ε turbulence model for fluid–fluid coupled condition, were used as the boundary conditions. The results indicated that the values obtained from the proposed empirical equations and 3D numerical analysis were not similar. Thus, if the reservoir geometry is very complex and the wave propagation distance is more than a few kilometers (as in this study), highly detailed engineering geological studies should be performed to accurately define the boundary conditions, and three-dimensional numerical analyses should be performed to construct the impulse wave model.

Across-night dynamics in traveling sleep slow waves throughout childhood.

Sleep slow waves behave like traveling waves and are thus a marker for brain connectivity. Across a night of sleep in adults, wave propagation is scaled down, becoming more local. Yet, it is unknown whether slow wave propagation undergoes similar across-night dynamics in childhood-a period of extensive cortical rewiring. High-density electroencephalography (EEG; 128 channels) was recorded during sleep in three groups of healthy children: 2.0-4.9 years (n = 11), 5.0-8.9 years (n = 9) and 9.0-16.9 years (n = 9). Slow wave propagation speed, distance, and cortical involvement were quantified. To characterize across-night dynamics, the 20% most pronounced (highest amplitude) slow waves were subdivided into five time-based quintiles. We found indications that slow wave propagation distance decreased across a night of sleep. We observed an interesting interaction of across-night slow wave propagation dynamics with age (p < 0.05). When comparing the first and last quintiles, there was a trend level difference between age groups: 2- to 4.9-year-old children showed an 11.9% across-night decrease in slow wave propagation distance, which was not observed in the older two age groups. Regardless of age, cortical involvement decreased by 10.4%-23.7% across a night of sleep. No across-night changes were observed in slow wave speed. Findings provide evidence that signatures of brain connectivity undergo across-night dynamics specific to maturational periods. These results suggest that across-night dynamics in slow wave propagation distance reflect heightened plasticity in underlying cerebral networks specific to developmental periods.

Investigating the critical aspects of evaluating the material nonlinearity in metal plates using Lamb waves: Theoretical and numerical approach

The present study focuses on critical analysis of various aspects related to the evaluation of amplitude based material nonlinearity parameter γamp through the numerical simulations and theoretical justifications. Two different materials with distinct nonlinearities are interrogated using Lamb waves in the numerical simulations. The effects of input force amplitude, number of cycles in the tone burst, tone burst windowing functions, material model parameters, excitation frequency, and wave propagation distance on γamp are studied in detail. Also, γamp estimated for the data obtained from the numerical simulations considering S0-S0 mode pair at low frequencies and resonant S1-S2mode pair at higher frequencies are compared with the physics based material nonlinearity parameter γphy. The difference between the results is marginal. Thus, the nonlinear Lamb wave technique can be effectively used even at low frequencies to estimate the actual material nonlinearity of the (metallic) plate materials with fair accuracy using the proposed nonlinearity models.

An inverseQfiltering approach based on a varying stabilization factor

The stable approach of inverse Q filtering based on wavefield continuation theory can simultaneously perform amplitude compensation and phase correction. The instability of conventional full inverse Q filtering is overcome through adding a stabilization factor to the wavefield continuation, and a good application effect is achieved. However, the method is likely to lead to noise amplification while compensating for the effective signal of the seismic data, resulting in the decrease of the signal-to-noise ratio (SNR) of seismic data. This phenomenon is due to the constant stabilization factor being added to the inverse Q filtering method. This paper presents an inverse Q filtering method based on a varying stabilization factor, which is a function of the propagation distance of a seismic wave, frequency of seismic data, and quality factor Q. This method can avoid the amplification of noise energy which can be caused by using the constant stabilization factor. The results of the synthetic and real seismic data show that compared with the compensation effect of the conventional inverse Q filtering, this method can avoid the amplification of the shallow and middle noise energy of seismic data, and effectively improves the SNR and resolution of the seismic data.

Decoherence of gravitational wave oscillations in bigravity

Following up on our recent study, we consider the regime of graviton masses and gravitational wave propagation distances at which decoherence of the wave packets plays a major role for phenomenology. This regime is of particular interest, as it can lead to very striking phenomena of echo events in the gravitational waves coming from coalescence events. The power of the experimental search in this case lies in the fact that it becomes sensitive to a large range of graviton masses, while not relying on a specific production mechanism. We are thus able to place new relevant limits on the parameter space of the graviton mixing angle.

Detecting the spatial chirp signals by fractional Fourier lens with transformation materials

Fractional Fourier transform (FrFT) is the general form of the Fourier transform and is an important tool in signal processing. As one typical application of FrFT, detecting the chirp rate (CR, or known as the rate of frequency change) of a chirp signal is important in many optical measurements. The optical FrFT that based on graded index lens fails to detect the high CR chirp because the short wave propagation distance of the impulse in the lens will weaken the paraxial approximation condition. With the help of transformation optics, the improved FrFT lens is proposed to adjust the high CR as well as the impulse location of the given input chirp signal. The designed transformation materials can implement the effect of space compression, making the input chirp signal is equivalent to have lower CR, therefore the system can satisfy the paraxial approximation better. As a result, this lens can improve the detection precision for the high CR. The numerical simulations verified the design. The proposed device may have both theoretical and practical values, and the design demonstrates the ability and flexibility of TO in spatial signal processing.

Structural broadband absorbing metamaterial based on three-dimensional printing technology

In order to verify the feasibility of three-dimensional (3D) printing technology in preparing the metamaterial absorbers with complex structure, a three-layer broadband absorbing metamaterial is designed and fabricated by 3D printing technology. The surface layer and middle layer of the metamaterial are composed of periodic arrays with different unit dimensions and the bottom layer of a slab structure. The optimized thickness of the metamaterial is 4.7 mm. A composite absorbent which consists of carbonyl iron powder and nylon is used to fabricate the absorber. In experiment, the obtained absorber is vertically irradiated by an electromagnetic (EM) wave. Two strong absorption peaks at 5.3 GHz and 14.1 GHz are achieved, with the reflection losses of -15.1 dB and -12.5 dB, respectively. The superposition of the two absorption peaks results in a reflection loss below -10 dB in a range from 4 to 18 GHz. The effective EM parameters of the surface layer and the middle layer are calculated by the S parameter inversion method. An effective model of the three-layer structure absorber is proposed and its reflectivity is calculated by using a multilayer structure reflectivity formula. The calculated reflectivity agrees well with the measured one. The absorbing and resonance mechanisms of the two absorption peaks are investigated by analyzing the dynamic distributions of power density loss, electric field and magnetic field. It can be clearly confirmed that the reflection losses at 5.3 GHz and 14.1 GHz are primarily concentrated on the bottom layer and surface layer, and the broadband absorption performance can be derived from the superposition of broadband absorptions of the three absorbing layers. Meanwhile, the strong electric coupling effect between the adjacent units in the surface layer is demonstrated by analyzing the electric-field distributions, which indicates that the strong reflection loss at 14.1 GHz is mainly caused by the electric response. The multiple scattering effects among the three layers are also considered according to the magnetic field distributions at two resonance frequencies. It is shown that there are two magnetic responses at 5.3 GHz and 14.1 GHz, respectively, and the multiple scattering contributes to increasing the EM wave propagation distance and enhancing the power loss. The designed absorbing metamaterials in this paper achieve good broadband absorption performances, particularly in the low frequency band. Combined with 3D printing rapid technology, a promising route to constructing 3D absorbing metamaterials with complex structures is proposed, which would be of great significance and broad practical prospect.

Experimental Study on Propagation and Attenuation Regularity of Landslide Surge

On the basis of landslide surge model test by adopting generalized simulation of waterways, this paper, for the first time, established a four-dimensional mathematical model between wave height transmissibility rate and the initial wave height, water depth, azimuth angle as well as propagation distance through utilizing the method of tensor space mapping. Using the new model, we proposed an empirical wave field covering all areas of the channel including the attenuation area within the width of a landslide mass, the straight channel attenuation area outside the width of the landslide mass, the curved channel attenuation area and the after-curve attenuation area, which comprehensively reflects the progressive changes of surge wave factors. The transmissibility of wave height and propagation distance are in a bivariate negative exponential distribution, and the wave height gradually reduces and the attenuation also slows down as the propagation distance increases; wave height transmissibility rate, azimuth and propagation distance are in a trivariate negative exponential distribution, the attenuation of the wave height in the straight channel within the width of the landslide mass was the slowest, followed by that of wave in the straight channel outside the width of the landslide mass, and the attenuation of the wave height in the curved channel is the greatest. This empirical wave field was based on test data, scientifically abstracted the general regularity of the propagation and attenuation of landslide surge, which can be applied to similar analyses and forecasts on landslide surge and can scientifically and accurately determine the damage range of landslide surge.

Detection of nonlinear Lamb wave using a PVDF comb transducer

The detection of the nonlinear Lamb wave using a PVDF comb transducer is described in this research. The construction features of the PVDF comb transducer is firstly described. Then, the harmonic-frequency characteristic of PVDF comb transducer as the receiver in the nonlinear Lamb wave inspection is qualitatively investigated by the output-vector addition method. The theoretical result shows that, when the wavelength of the fundamental Lamb wave is equal to the PVDF comb transducer's finger spacing, the transducer can receive the fundamental wave. When the frequency of the higher-harmonic Lamb wave is integral multiple of the frequency of the fundamental one, the PVDF comb transducer can also receive the higher-harmonic Lamb wave. In order to verify the harmonic-frequency characteristic of the PVDF comb transducer, we conducted an experiment based on the cumulative effect of the nonlinear Lamb wave. That is, the value of the relative nonlinearity parameter will grow higher when the propagation distance increases. In order to receive the fundamental and second-harmonic Lamb waves, a PVDF comb transducer with special finger spacing was made and pasted on an aluminum plate surface. The desired Lamb-wave mode was generated by a wedge transducer. It had been observed that the value of relative nonlinearity parameter increased with the wave propagation distance. That means that the PVDF comb transducer had received both the fundamental and the second-harmonic Lamb waves. Both the theoretical and experimental results show that, because of the PVDF comb transducer's simultaneous response to the fundamental and second-harmonic signals, the nonlinear Lamb wave can be detected using a PVDF comb transducer.

A novel expression of the spherical-wave reflection coefficient at a plane interface

Abstract The spherical-wave reflection coefficient (SRC) describes the reflection strength when seismic waves emanating from a point source impinge on an interface. In this study, the SRC at a plane interface between two infinite half-spaces is investigated. We derive an analytical equation of the SRC when kR → 0 (k is the wave number and R is the wave propagation distance). It only depends on the density ratio; it is independent of the velocity ratio and incidence angle. On the other hand, we find that the SRCs at different kR lie along an elliptical curve on the complex plane (the complex plane is a geometric representation of the complex numbers established by the real axis and perpendicular imaginary axis). Based on this feature, we construct a new analytical equation for the reflected spherical wave with high accuracy, which is applicable to both small and large kR. Using the elliptical distribution of the SRCs for a series of frequencies recorded at only one spatial location, the density and velocity ratios can be extracted. This study complements the spherical-wave reflection theory and provides a new basis for acoustic parameters inversion, particularly density inversion.

Effect of propagation distance on acoustic emission fracture mode classification in textile reinforced cement

Textile reinforced cement (TRC) is a composite material being increasingly used for load bearing applications. Damage in TRC as in all cementitious materials is an important issue in civil engineering. Acoustic emission (AE) exhibits promising outcomes in laboratory and in in-situ monitoring applications. Evaluation of the fracture mode is crucial as generally, shearing phenomena occur later than tensile (bending) cracking and indicate more severe damage. The acoustic signatures of the damage modes influence most of AE parameters including the average frequency AF and RA-value. However, there are no universal classification boundaries between tensile and shear signals mainly due to geometric effects, material properties, as well as sensor location and response function. In order to highlight this problem and discuss the possibility of a solution, the study occupies not only with the evaluation of the damage mode based on AE parameters but in addition uses multiple sensors to investigate the effect of the wave propagation distance. This is crucial in thin cementitious laminates since damping, scattering, reflections and plate wave dispersion seriously distort the signal having a strong effect on the classification result. It is seen that the classification boundaries between tensile and shear fracture should incorporate the information of propagation distance.

Microsphere-based super-resolution scanning optical microscope.

High-refractive index dielectric microspheres positioned within the field of view of a microscope objective in a dielectric medium can focus the light into a so-called photonic nanojet. A sample placed in such nanojet can be imaged by the objective with super-resolution, i.e. with a resolution beyond the classical diffraction limit. However, when imaging nanostructures on a substrate, the propagation distance of a light wave in the dielectric medium in between the substrate and the microsphere must be small enough to reveal the sample's nanometric features. Therefore, only the central part of an image obtained through a microsphere shows super-resolution details, which are typically ∼100 nm using white light (peak at λ = 600 nm). We have performed finite element simulations of the role of this critical distance in the super-resolution effect. Super-resolution imaging of a sample placed beneath the microsphere is only possible within a very restricted central area of ∼10 μm2, where the separation distance between the substrate and the microsphere surface is very small (∼1 μm). To generate super-resolution images over larger areas of the sample, we have fixed a microsphere on a frame attached to the microscope objective, which is automatically scanned over the sample in a step-by-step fashion. This generates a set of image tiles, which are subsequently stitched into a single super-resolution image (with resolution of λ/4-λ/5) of a sample area of up to ∼104 μm2. Scanning a standard optical microscope objective with microsphere therefore enables super-resolution microscopy over the complete field-of-view of the objective.

Accelerated damage visualization using binary search with fixed pitch-catch distance laser ultrasonic scanning

Laser ultrasonic scanning, especially full-field wave propagation imaging, is attractive for damage visualization thanks to its noncontact nature, sensitivity to local damage, and high spatial resolution. However, its practicality is limited because scanning at a high spatial resolution demands a prohibitively long scanning time. Inspired by binary search, an accelerated damage visualization technique is developed to visualize damage with a reduced scanning time. The pitch-catch distance between the excitation point and the sensing point is also fixed during scanning to maintain a high signal-to-noise ratio (SNR) of measured ultrasonic responses. The approximate damage boundary is identified by examining the interactions between ultrasonic waves and damage observed at the scanning points that are sparsely selected by a binary search algorithm. Here, a time-domain laser ultrasonic response is transformed into a spatial ultrasonic domain response using a basis pursuit approach so that the interactions between ultrasonic waves and damage, such as reflections and transmissions, can be better identified in the spatial ultrasonic domain. Then, the area inside the identified damage boundary is visualized as damage. The performance of the proposed damage visualization technique is validated excusing a numerical simulation performed on an aluminum plate with a notch and experiments performed on an aluminum plate with a crack and a wind turbine blade with delamination. The proposed damage visualization technique accelerates the damage visualization process in three aspects: (1) the number of measurements that is necessary for damage visualization is dramatically reduced by a binary search algorithm; (2) the number of averaging that is necessary to achieve a high SNR is reduced by maintaining the wave propagation distance short; and (3) with the proposed technique, the same damage can be identified with a lower spatial resolution than the spatial resolution required by full-field wave propagation imaging.

평탄지형 제내지에서의 제방붕괴속도에 따른 범람홍수파 선단 거동에 관한 연구

본 연구에서는 평탄지형의 제내지에서 제방붕괴속도에 따른 범람홍수파 선단의 전파 특성을 규명하기 위하여 제내지와 하도로 이루어진 실험수조에서 실험을 수행하여 전파 거리를 산정하였다. 실험에 의해 측정된 전파거리를 시간에 대한 상관식으로 나타내기 위하여 댐붕괴에 의한 수로에서의 홍수파의 1차원 흐름 해석해인 Ritter의 해에 3차원 거동특성을 반영할 수 있는 상수 k와 m을 도입한 일반식에 실험결과를 적용하여 실험식을 도출하였다. 기존 연구에서 하도내의 초기수위가 범람홍수파의 전파속도에 지배적인 영향을 준다는 사실은 알려져 있으나, 본 실험연구를 통해 제방붕괴속도도 범람홍수파의 전파속도에 영향을 주며, k와 m이 상수가 아닌 제방붕괴속도와 선형관계를 갖는 변수임을 밝혔다. 실험결과를 이용하여 범람홍수파 선단의 전파거리를 산정할 수 실험식을 제시했으며, 범람홍수파의 전파속도 산정시 하도내의 초기수위뿐만 아니라 제방붕괴속도도 고려해야 함을 본 연구를 통해 확인할 수 있었다. 본 연구에서는 대규모 제내지 범람실험을 수행하여 범람양상을 관찰하고 수리학적 관점에서 해석하였으며, 실험결과를 토대로 제방붕괴속도에 대한 홍수파 전파속도의 상관관계도 제시하였다. 본 연구결과는 홍수위험지도 작성이나 긴급대피계획 수립시 기본적인 판단 자료로 사용할 수 있으며, 2차원 범람 수치모형 검증시 유용한 자료로 이용될 수 있을 것으로 기대된다. An experimental study was carried out to investigate the characteristics of the propagation distance of a flood wave considering the levee failure speed in a flat inundation area. The Ritter solution for one dimensional flow was considered to formulate the experimental results and a representative form with coefficients of k and m, which consider the three dimensional flow characteristics, was applied. The experiments showed that the propagation velocity of the wave front in the inundation area was influenced by the levee breach speed as well as the initial water level, which is a significant variable representing the flood wave behavior. In addition, coefficients k and m are not constants, but variables that vary with levee breach speed. An empirical formula was also suggested using the experimental results in the form of the relationships between k and m. In this study, a large-scale experiment for flood inundation was carried out to examine the behavior of flooding in the inundated area and the relationships between the levee breach speed and wave-front propagation velocity were suggested based on the experimental results. These research results are expected to be used as the baseline data to draw a flow inundation map, establish an emergency action plan, and verify the two-dimensional numerical model.

Advances in the far-field sub-diffraction limit focusing and super-resolution imaging by planar metalenses

Due to the fundamental laws of wave optics, the spatial resolution of traditional optical microscopy is limited by the Rayleigh criterion. Enormous efforts have been made in the past decades to break through the diffraction limit barrier and in depth understand the dynamic processes and static properties. A growing array of super-resolution techniques by distinct approaches have been invented, which can be assigned to two categories: near-field and far-field super-resolution techniques. The near-field techniques, including near-field scanning optical microscopy, superlens, hyperlens, etc., could break through the diffraction limit and realize super-resolution imaging by collecting and modulating the evanescent wave. However, near-field technique suffers a limitation of very short working distances because of the confined propagation distance of evanescent wave, and certainly produces a mechanical damage to the specimen. The super-resolution fluorescence microscopy methods, such as STED, STORM, PALM, etc., could successfully surpass the diffractive limit in far field by selectively activating or deactivating fluorophores rooted in the nonlinear response to excitation light. But those techniques heavily rely on the properties of the fluorophores, and the labelling process makes them only suitable for narrow class samples. Developing a novel approach which could break through the diffraction limit in far field without any near-field operation or labelling processes is of significance for not only scientific research but also industrial production. Recently, the planar metalenses emerge as a promising approach, owing to the theoretical innovation, flexible design, and merits of high efficiency, integratable and so forth. In this review, the most recent progress of planar metalenses is briefly summarized in the aspects of sub-diffractive limit focusing and super-resolution imaging. In addition, the challenge to transforming this academic concept into practical applications, and the future development in the field of planar metalenses are also discussed briefly.