Wave Propagation Phenomena Research Articles

P.1.h.036 - Do statins impair learning and memory after long-term treatment – comparative experimental study

The accurate assessment of the fatigue strength for structures made of composite materials is difficult because of the great number of possible failure forms. The Structural Health Monitoring (SHM) systems are developed and applied in engineering structures for permanent monitoring the state of the constructions. In this paper the Lamb wave propagation method and the infrared thermography were applied to observe the fatigue damage evolution in the multilayered composite plate with an elliptical hole in the middle. The active pitch-catch measurement technique was introduced based on the surface mounted piezoelectric transducers. The localization of the piezoelectric actuator and sensors responsible for excitation and detection of the elastic wave was chosen based on the progressive failure analysis applied in finite element method. The multipoint measuring system was responsible for analysis of the elastic wave propagation phenomenon during the fatigue tests. The sequential measurement of the elastic wave parameters allow one to observe the state of the structure. The different parameters describing the wave propagation phenomenon like amplitude and time of flight was considered. The infrared thermography make possible of detection of the damage initiation and permanent monitoring of the structure. The measurement of the temperature distribution is straightforward and doesn’t need complicated algorithms and software. Application of the coupled approach to the damage detection (piezoelectric transducers in SHM system with the permanent surface temperature monitoring) allow one to build cost effective system for detection of the damage initiation and for monitoring failure form evolution.

Wave propagation in channels and cracks with elastic walls

In this paper wave propagation in the uniform and nonuniform elastic channels filled with fluid or gas is investigated. The weak discontinuities theory approach is proposed to determine the criteria of gradient catastrophe phenomena to occur for the cases of uniform and nonuniform channels. The results of the paper can be applied to studying of the nonlinear wave propagation phenomena in elastic pores, cracks and channels filled with fluid or gas.

Partial lumped mass method in longitudinal deck-pier poundings of girder bridges and its test verification

Contact element methods have been widely used in the field of bridge poundings in recent years. For deck-pier poundings of girder bridges, two kinds of contact element methods are commonly used. One is the Lumped Parameter Method (LPM), which simplifies two pounding bodies to be two particles respectively, and the stress wave propagation phenomenon is disregarded. The other one is the Watanabe and Kawashima Method (WKM), whose weakness is that the pounding stiffness introduced to describe the pounding process is supposed and artificial. A new method, named as the Partial Lumped Mass Method (PLMM), was put forward for longitudinal deck-pier poundings of girder bridges and was introduced in this paper. Its applications were discussed in detail at first. Pounding force time histories with different Partial Lumped Factors were derived. The Rational Partial Lumped Factor was suggested theoretically. At last, the analysis results using the PLMM with different Partial Lumped Factors were compared, and the validity of the PLMM suggested in this paper was verified with shaking table test results.

Nonlinear multi-frequency electromagnetic wave propagation phenomena

A generalisation of the concept of monochromatic electromagnetic waves guided by layered waveguide structures filled with non-linear medium is introduced. This generalisation leads to guided waves of a novel type: a non-linear multi-frequency guided wave. The existence of such waves, in particular guide structures, is proven using the perturbation method. Numerical experiments are presented for non-linear 1- and 2-frequency guided waves in plane and cylindrical (with a circular cross-section) waveguides. Numerically, a novel non-linear effect is found for particular cases of non-linear multi-frequency guided waves. The suggested generalisation gives not only a unified approach to treat various electromagnetic wave propagation problems but also paves the way to study non-linear interactions of guided waves.

Symplectic Hamiltonian HDG methods for wave propagation phenomena

We devise the first symplectic Hamiltonian hybridizable discontinuous Galerkin (HDG) methods for the acoustic wave equation. We discretize in space by using a Hamiltonian HDG scheme, that is, an HDG method which preserves the Hamiltonian structure of the wave equation, and in time by using symplectic, diagonally implicit and explicit partitioned Runge–Kutta methods. The fundamental feature of the resulting scheme is that the conservation of a discrete energy, which is nothing but a discrete version of the original Hamiltonian, is guaranteed. We present numerical experiments which indicate that the method achieves optimal approximations of order k+1 in the L2-norm when polynomials of degree k≥0 and Runge–Kutta time-marching methods of order k+1 are used. In addition, by means of post-processing techniques and by increasing the order of the Runge–Kutta method to k+2, we obtain superconvergent approximations of order k+2 in the L2-norm for the displacement and the velocity. We also present numerical examples that corroborate that the methods conserve energy and that they compare favorably with dissipative HDG schemes, of similar accuracy properties, for long-time simulations.

Reconstruction of space-dependent potential and/or damping coefficients in the wave equation

In this paper, nonlinear reconstructions of the space-dependent potential and/or damping coefficients in the wave equation from Cauchy data boundary measurements of the displacement and the flux tension are investigated. This is a very interesting and challenging nonlinear inverse coefficient problem with important applications in wave propagation phenomena. The uniqueness and stability results that are revised and in some cases proved demonstrate an advancement in understanding the stability of the inverse coefficient problems. However, in practice, the inverse coefficient identification problems under investigation are still ill-posed since small random errors in the input data cause large errors in the output solution. In order to stabilize the solution we employ the nonlinear Tikhonov regularization method. Numerical reconstructions performed for the first time are presented and discussed to illustrate the accuracy and stability of the numerical solutions under finite difference mesh refinement and noise in the measured data.

Experimental assessment of the influence of welding process parameters on Lamb wave transmission across ultrasonically welded thermoplastic composite joints

One of the advantages of thermoplastic composites relative to their thermoset counterparts is the possibility of assembling components through welding. Ultrasonic welding in particular is very promising for industrialization. However, uncertainty in the fatigue and fracture behaviour of composites is still an obstacle to the full utilisation of these materials. Health monitoring is then of vital importance, and Lamb wave techniques have been widely recognised as some of the most promising approaches for that end. This paper presents the first experimental study about the influence of welding travel on the transmission of Lamb waves across ultrasonically welded thermoplastic composite joints in single-lap configuration. The main aim of this research is to start to understand how guided waves interact with the internal structure of ultrasonic welds, so that benign, manufacturing-related structural features can be distinguished from damaging ones in signal interpretation. The power transmission coefficient and the correlation coefficient proved to be suitable for analysing the wave propagation phenomena, allowing quantitative identification of small variations of weld-line thickness and intermolecular diffusion at the weld interface. The conclusions are used to develop a tentative damage detection criterion which can later on assist the design of a Lamb wave based structural health monitoring system for thermoplastic composite structures. The Lamb wave test results are backed up by phased-array inspections, which also provide some extra insight on the internal structure of ultrasonic welds.

Animations of electromagnetic transients in power transmission lines by means of the two-dimensional numerical Laplace transform

This paper presents the use of animations of the wave propagation phenomena on power transmission lines as a valuable tool for research and educational purposes. These animations are generated from data obtained by transient analysis in the frequency domain applying the two dimensional numerical Laplace transform. Since the line electrical parameters are defined in the frequency domain, the frequency dependence of such parameters is directly taken into account. These animations allow an insightful illustration of how travelling waves propagate along transmission lines during an electromagnetic transient, making them a useful tool to determine transient overvoltages that occur at internal points along power transmission lines. In the educational field, using these animations in electrical engineering courses can help students to have a better understanding of the traveling wave concept and how it differs from the circuit theory. In addition, it allows detailed comparison of the wave propagation along lines under different conditions, such as type of excitation, type of load, introduction of losses, etc.

Interactive Toolbox for the Visualization of Typical Antenna Attributes

To understand wave propagation phenomena, complex mathematical and physical theory is needed. Therefore, many undergraduate students find it very difficult to deal with this area of research. In this paper, an interactive toolbox is proposed which can help students to gain profounder knowledge and understanding of wave propagation effects. Great importance was attached to the design of a very simple user interface to help the students focus on the essential. The data interface was created to be very general and simple for an easy extension.

Fractional Transport of Photons in Deterministic Aperiodic Structures

The propagation of optical pulses through primary types of deterministic aperiodic structures is numerically studied in time domain using the rigorous transfer matrix method in combination with analytical fractional transport models. We demonstrate tunable anomalous photon transport, including the elusive logarithmic Sinai sub-diffusion in photonic systems for the first time. Our results are in excellent agreement with the scaling theory of transport in aperiodic media with fractal spectra, and additionally demonstrate logarithmic sub-diffusion in the presence of multifractality. Moreover, we establish a fruitful connection between tunable photon diffusion and fractional dynamics, which provides analytical insights into the asymptotic transport regime of optical media with deterministic aperiodic order. The demonstration of tunable sub-diffusion and logarithmic photon transport in deterministic aperiodic structures can open novel and fascinating scenarios for the engineering of wave propagation and light-matter interaction phenomena beyond the conventional diffusive regime.

Numerical simulation of seismic wave propagation in viscoelastic-anisotropic media using frequency-independent Q wave equation

Seismic anisotropy is the fundamental phenomenon of wave propagation in the earth’s interior. Numerical modeling of wave behavior is critical for exploration and global seismology studies. The full elastic (anisotropy) wave equation is often used to model the complexity of velocity anisotropy, but it ignores attenuation anisotropy. I have presented a time-domain displacement-stress formulation of the anisotropic-viscoelastic wave equation, which holds for arbitrarily anisotropic velocity and attenuation [Formula: see text]. The frequency-independent [Formula: see text] model is considered in the seismic frequency band; thus, anisotropic attenuation is mathematically expressed by way of fractional time derivatives, which are solved using the truncated Grünwald-Letnikov approximation. I evaluate the accuracy of numerical solutions in a homogeneous transversely isotropic (TI) medium by comparing with theoretical [Formula: see text] and [Formula: see text] values calculated from the Christoffel equation. Numerical modeling results show that the anisotropic attenuation is angle dependent and significantly different from the isotropic attenuation. In synthetic examples, I have proved its generality and feasibility by modeling wave propagation in a 2D TI inhomogeneous medium and a 3D orthorhombic inhomogeneous medium.

Use of global sensitivity analysis to assess the soil poroelastic parameter influence

In this study, we show how a global sensitivity analysis method can be used to obtain relevant information for the interpretation of the mechanical wave propagation phenomena involved in a poroelastic soil that takes into account the presence of water. The present investigation addresses the issue of the identification and the ranking of the most influential parameters. The sensitivity indices provide a variance-based measure of the uncertainty effects of the input parameters on the mechanical outputs of the model. It allows quantification of, on the one hand, the influence of each parameter and on the other hand, the possible interactions between all the parameters. Numerical simulations are performed in a laboratory-scale configuration: a fluid medium overlying a poroelastic material is submitted to a transient excitation, and the coupling of the acoustic and Biot models is solved using a semi-analytical approach. The analysis of the temporal and spatial evolution of partial variances highlights the most important parameters and the complementary information contained in the signals in function of both the time and the receiver location. In particular, we show that the description of the poroelastic waves is governed by only a restricted number of parameters for the configuration under study.

Evaluation of energy contributions using inter-particle forces in granular materials under impact loading

A drop-tower based experimental setup was developed for the impact testing of 2D assembly of cylinders with impactor velocity of around 6 m/s. This drop tower setup was used to load 2D granular assemblies of polyurethane and polycarbonate cylinders of 1\(^{\prime \prime }\)–1.25\(^{\prime \prime }\) length with three different diameters of 1/4\(^{\prime \prime }\), 3/8\(^{\prime \prime }\) and 1/2\(^{\prime \prime }\). A high speed camera was used for recording the images at speeds between 10,000 and 55,000 fps to monitor the deformation of the cylinders. Kinematic and strain fields in individual grains during each experiment were measured using digital image correlation. These experimentally measured strain and kinematic fields were used as inputs for the granular element method (GEM) based force inference technique and the inter-particle forces in normal and tangential direction were determined at every contact in each experiment. The inter-particle forces at each contact can facilitate the calculation of frictional work done at each contact. The GEM based inter-particle forces for a simple 2 particle granular assembly were found to be in good agreement with predictions from ABAQUS explicit based FEM simulation. The influence of different model parameters was also characterized such as grain stiffness, frictional co-efficient was investigated qualitatively. The impact response of the various ordered granular assemblies was also investigated using the GEM approach and the effect of local defects such as voids or layering of granular materials on the wave propagation phenomena is also studied. The presence of the point or line defects have significant effects on the wave propagation in the granular assemblies due to wave scattering and attenuation.

Wavefield characterization of perforation shot signals in a shale gas reservoir

Signals of perforation or string shots, which are usually used for calibrating velocity models and estimating the orientation of 3 component down-hole receivers during microseismic monitoring, are occasionally hard to identify due to poor signal-to-noise ratios (SNR) or confusion with the events induced during fracturing in adjacent wells. A significant feature for distinguishing perforation signals from hydraulic fracturing events is the tube wave, which is generated in the treatment well and received in the monitoring well. We analyze seismic wavefields from perforations during a hydraulic fracturing operation on a pad well (a group of horizontal wells with the wellheads at a same small surface area) in a shale gas reservoir to understand the wave propagation phenomena including attenuation and the identification of tube waves (guided wave in borehole) and their conversions. Since they are dominated by high frequencies and lack energy at low frequencies, the P- and S-wave arrivals of perforation shots decrease much more rapidly with propagation distance than that of induced events. We identify six modes within the wavefields of the perforation or string shots recorded in a nearby well that are related to the tube waves.The six modes include P- & S-waves converted from tube waves in the shot (treatment) well at plugs or the well bottom, an up-going tube wave in the monitoring well generated by the tube wave in the nearby treatment well, a down-going tube wave from the treatment wellhead and the multiple, a scatting body wave activated by tube waves in the treatment well. These wave modes all originate from the waves radiated at the perforation point in the treatment well as tube waves and are then radiated into the formation and received by geophones in the nearby borehole as P, S, or tube waves. If energy from the perforation shot is strong enough, the tube wave will turn back from the surface and be reflected at the well bottom or plugs, which would excite the further waves. Based on the features of the wavefield, we identify the perforation events and facilitate better use of calibration from the perforation seismic recording for microseismic data processing. We also evaluate attenuation of the signals with propagation distance and propose a procedure for developing a plan for monitoring of perforation and string shot signals.

Superluminal wave propagation in a non‐Foster negative capacitor loaded transmission line

Superluminal wave propagation phenomenon achieved from a periodic structure in which a transmission line (TL) is loaded with non-Foster negative capacitors is presented. The loading decreases the effective capacitance and the effective permittivity of the dielectric substrate of the TL. An experimental investigation of the superluminal phase and group velocity in the non-Foster loaded TL is reported. The phase and group velocities are extracted from measured S-parameters. To do so, three non-Foster negative capacitors operating over [50–350 MHz] frequency band are integrated in a TL. Superluminal broadband effects are obtained from 50 to 220 MHz. The negative capacitors loaded TL paves the way to innovative broadband leaky wave antennas, active metamaterial surfaces and cloaking devices.

Whole heart detailed and quantitative anatomy, myofibre structure and vasculature from X-ray phase-contrast synchrotron radiation-based micro computed tomography.

While individual cardiac myocytes only have a limited ability to shorten, the heart efficiently pumps a large volume-fraction thanks to a cell organization in a complex 3D fibre structure. Subclinical subtle cardiac structural remodelling is often present before symptoms arise. Understanding and early detection of these subtle changes is crucial for diagnosis and prevention. Additionally, personalized computational modelling requires knowledge on the multi-scale structure of the whole heart and vessels. We developed a rapid acquisition together with visualization and quantification methods of the integrated microstructure of whole in-vitro rodents hearts using synchrotron based X-ray phase-contrast tomography. These images are formed not only by X-ray absorption by the tissue but also by wave propagation phenomena, enhancing structural information, thus allowing to raise tissue contrast to an unprecedented level. We used a (ex-vivo) normal rat heart and fetal rabbit hearts suffering intrauterine growth restriction as a model of subclinical cardiac remodelling to illustrate the strengths and potential of the technique. For comparison, histology and diffusion tensor magnetic resonance imaging was performed. We have developed a novel, high resolution, image acquisition, and quantification approach to study a whole in-vitro heart at myofibre resolution, providing integrated 3D structural information at microscopic level without any need of tissue slicing and processing. This superior imaging approach opens up new possibilities for a systems approach towards analysing cardiac structure and function, providing rapid acquisition of quantitative microstructure of the heart in a near native state.

A numerical and experimental study of temperature effects on deformation behavior of carbon steels at high strain rates

Both in research and in the light of industrial applications, there is a growing interest in methods to characterize the mechanical behavior of materials at high strain rates. This is particularly true for steels (the most important structural materials), where often the strain rate-dependent material behavior also needs to be characterized in a wide temperature range. In this study, we use the Finite Element Method (FEM), first, to model the compressive deformation behavior of carbon steels under quasi-static loading conditions. The results are then compared to experimental data (for a simple C75 steel) at room temperature, and up to testing temperatures of 1000 °C. Second, an explicit FEM model that captures wave propagation phenomena during dynamic loading is developed to closely reflect the complex loading conditions in a Split-Hopkinson Pressure Bar (SHPB) – an experimental setup that allows loading of compression samples with strain rates up to 104 s-1 The dynamic simulations provide a useful basis for an accurate analysis of dynamically measured experimental data, which considers reflected elastic waves. By combining numerical and experimental investigations, we derive material parameters that capture the strain rate- and temperature-dependent behavior of the C75 steel from room temperature to 1000 °C, and from quasi-static to dynamic loading.

Inhomogeneous waves in porous piezo-thermoelastic solids

A mathematical model for taking into consideration the interaction of mechanical, thermal and electrical dynamics in an anisotropic porous piezo-thermoelastic (APPT) medium is presented. Basic equations for APPT are derived. The three-dimensional problem of wave propagation is studied which explains the existence and propagation of six waves in the considered medium. The phase velocities and attenuation factors for each of the six attenuated waves are determined in terms of complex slowness vectors. The particular results are obtained for triclinic, monoclinic and orthotropic types of crystal symmetries. The effects of piezoelectricity, thermoelasticity, frequency, and porosity on the wave propagation phenomenon are analyzed.

Stress wave propagation analysis on vortex-induced vibration of marine risers

To analyze the stress wave propagation associated with the vortex-induced vibration (VIV) of a marine riser, this paper employed a multi-signal complex exponential method. This method is an extension of the classical Prony’s method which decomposes a complicated signal into a number of complex exponential components. Because the proposed method processes multiple signals simultaneously, it can estimate the “global” dominating frequencies (poles) shared by those signals. The complex amplitude (residues) corresponding to the estimated frequencies for those signals is also obtained in the process. As the signals were collected at different locations along the axial direction of a marine riser, the phenomena of the stress wave propagation could be analyzed through the obtained residues of those signals. The Norwegian Deepwater Program (NDP) high mode test data were utilized in the numerical studies, including data sets in both the in-line (IL) and cross-flow (CF) directions. It was found that the most dominant component in the IL direction has its stress wave propagation along the riser being dominated by a standing wave, while that in the CF direction dominated by a traveling wave.

Laboratory model of the cardiovascular system for experimental demonstration of pulse wave propagation

The velocity by which a disturbance moves through the medium is the wave velocity. Pulse wave velocity is among the key parameters in hemodynamics. Investigation of wave propagation through the fluid-filled elastic tube has a great importance for the proper biophysical understanding of the nature of blood flow through the cardiovascular system. Here, we present a laboratory model of the cardiovascular system. We have designed an experimental setup which can help medical and nursing students to properly learn and understand basic fluid hemodynamic principles, pulse wave and the phenomenon of wave propagation in blood vessels. Demonstration of wave propagation allowed a real time observation of the formation of compression and expansion waves by students, thus enabling them to better understand the difference between the two waves, and also to measure the pulse wave velocity for different fluid viscosities. The laboratory model of the cardiovascular system could be useful as an active learning methodology and a complementary tool for understanding basic principles of hemodynamics.