Wave Propagation Distance Research Articles

Development of a 2D analytical model for the prediction of directivity pattern of transducers in the generation of guided wave modes

The guided waves (GW) are extensively used in the nondestructive testing (NDT) and structure health monitoring (SHM) of the large and complex structures. It enables to detect the defects up to few meters away from the transducers. However, the defects could occur at longer distances. In order to cover the test area of interest for the estimation of defects and to find the exact position of the transducers to be glued/ embedded, the directivity pattern of the transducers must be known. The aim of the presented work is to develop the 2D analytical model for the estimation of directivity patterns of the transducers at various frequencies and distances. The model was developed using the Huygens's principle of wave propagation distances with considering the known phase dispersive characteristics of the guided wave modes in the medium. The principle of modelling will work to plot the directivity pattern at any distance, at any excitation frequency and with any configuration and shape of the transducers. In order to demonstrate the model, the directivity patterns of P1-type macro-fiber composite (MFC) transducer in the generation of fundamental Lamb modes and shear horizontal mode at 300 mm from the center of MFC were obtained. The input signal used was 80 kHz, 3 period signal and propagation medium was Al plate of 2 mm thickness. The prediction about the position of where MFC transducer should be placed or glued on the object and selection of proper wave modes in order to estimate the defects in various materials is also discussed. The results were validated using finite element analysis (FEA) performed in ANSYS and further verified by the experimental analysis using low-frequency (LF) ultrasonic measurement system ULTRALAB, developed by Ultrasound Research Institute, Kaunas University of Technology. The proposed analytical model will not only facilitate to decide the position and number of transducers but also leads to choosing the configuration of transducer and wave modes suitable to be used for the inspection of defects.

Experimental and Numerical Investigation into the Propagation of Entropy Waves

Entropy waves are an important source of indirect combustion noise and potentially contribute to the generation of thermoacoustic instabilities in gas-turbine combustors. Entropy fluctuations generated by unsteady combustion are known to disperse and diffuse as they convect toward the combustor exit. In this work, the propagation of entropy waves is investigated by means of experiments in a newly developed entropy rig and numerical simulations based on the large-eddy simulation approach. Both experimental and numerical results demonstrate that the amplitude of entropy fluctuations decays as a function of wave parameters and propagation distance, and it scales well with a local Helmholtz number . A new theoretical model for the computation of the entropy transfer function suitable for inclusion in low-order models for combustion instabilities is proposed. Assessment against numerical and experimental results shows the capability of the model to give a proper representation of the decay of entropy waves in terms of both magnitude and phase of the entropy transfer function. Furthermore, by comparison with the large-eddy simulation results, it is shown that, at low Helmholtz numbers, the contribution of the differential convection to the decay of entropy waves is dominant; whereas for high values of the Helmholtz number, the turbulent mixing and diffusion also become important.

A Q-Band Free-Space Characterization of Carbon Nanotube Composites.

We present a free-space measurement technique for non-destructive non-contact electrical and dielectric characterization of nano-carbon composites in the Q-band frequency range of 30 GHz to 50 GHz. The experimental system and error correction model accurately reconstruct the conductivity of composite materials that are either thicker than the wave penetration depth, and therefore exhibit negligible microwave transmission (less than -40 dB), or thinner than the wave penetration depth and, therefore, exhibit significant microwave transmission. This error correction model implements a fixed wave propagation distance between antennas and corrects the complex scattering parameters of the specimen from two references, an air slab having geometrical propagation length equal to that of the specimen under test, and a metallic conductor, such as an aluminum plate. Experimental results were validated by reconstructing the relative dielectric permittivity of known dielectric materials and then used to determine the conductivity of nano-carbon composite laminates. This error correction model can simplify routine characterization of thin conducting laminates to just one measurement of scattering parameters, making the method attractive for research, development, and for quality control in the manufacturing environment.

Conditions for laser-induced plasma to effectively remove nano-particles on silicon surfaces**Project supported by the National Natural Science Foundation of China (Grant No. 11574221).

Particles can be removed from a silicon surface by means of irradiation and a laser plasma shock wave. The particles and silicon are heated by the irradiation and they will expand differently due to their different expansion coefficients, making the particles easier to be removed. Laser plasma can ionize and even vaporize particles more significantly than an incident laser and, therefore, it can remove the particles more efficiently. The laser plasma shock wave plays a dominant role in removing particles, which is attributed to its strong burst force. The pressure of the laser plasma shock wave is determined by the laser pulse energy and the gap between the focus of laser and substrate surface. In order to obtain the working conditions for particle removal, the removal mechanism, as well as the temporal and spatial characteristics of velocity, propagation distance and pressure of shock wave have been researched. On the basis of our results, the conditions for nano-particle removal are achieved.

Numerical Study on Tsunami Propagation into a River

ABSTRACT Aoyama, Y.; Adityawan, M.B., Widiyanto, W., Mitobe, Y., Komori, D., and Tanaka, H., 2016. Numerical Study on Tsunami Propagation into a River. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 1017 - 1021. Coconut Creek (Florida), ISSN 0749-0208. The Tohoku Earthquake and Tsunami in 2011 caused serious damage not only to coastal structures, but also to riverine infrastructure due to long distance of wave propagation into rivers located on the coast facing the Pacific Ocean. Although there have been numerous investigations on tsunami, limited number of studies have been made for tsunami propagation into a river channel. This study investigates tsunami propagation into a river numerically by comparing with laboratory experiment data. The present numerical simulation is based on shallow water equations, which are solved with the MacCormack sch...

Numerical Simulation of Focused Shock Shear Waves in Soft Solids and a Two-Dimensional Nonlinear Homogeneous Model of the Brain.

Shear waves that propagate in soft solids, such as the brain, are strongly nonlinear and can develop into shock waves in less than one wavelength. We hypothesize that these shear shock waves could be responsible for certain types of traumatic brain injuries (TBI) and that the spherical geometry of the skull bone could focus shear waves deep in the brain, generating diffuse axonal injuries. Theoretical models and numerical methods that describe nonlinear polarized shear waves in soft solids such as the brain are presented. They include the cubic nonlinearities that are characteristic of soft solids and the specific types of nonclassical attenuation and dispersion observed in soft tissues and the brain. The numerical methods are validated with analytical solutions, where possible, and with self-similar scaling laws where no known solutions exist. Initial conditions based on a human head X-ray microtomography (CT) were used to simulate focused shear shock waves in the brain. Three regimes are investigated with shock wave formation distances of 2.54 m, 0.018 m, and 0.0064 m. We demonstrate that under realistic loading scenarios, with nonlinear properties consistent with measurements in the brain, and when the shock wave propagation distance and focal distance coincide, nonlinear propagation can easily overcome attenuation to generate shear shocks deep inside the brain. Due to these effects, the accelerations in the focal are larger by a factor of 15 compared to acceleration at the skull surface. These results suggest that shock wave focusing could be responsible for diffuse axonal injuries.

Monitoring the failure mechanisms of a reinforced concrete beam strengthened by textile reinforced cement using acoustic emission and digital image correlation

One of the most commonly used techniques to strengthen steel reinforced concrete structures is the application of externally bonded patches in the form of carbon fiber reinforced polymers (CFRP) or recently, textile reinforced cements (TRC). These external patches undertake the tensile stress of bending constraining concrete cracking. Development of full-field inspection methodologies for fracture monitoring are important since the reinforcing layers are not transparent, hindering visual observation of the material condition underneath. In the present study acoustic emission (AE) and digital image correlation (DIC) are applied during four-point bending tests of large beams to follow the damage accumulation. AE helps to determine the onset of fracture as well as the different damage mechanisms through the registered shifts in AE rate, location of active sources and change in waveform parameters. The effect of wave propagation distance, which in large components and in-situ can well mask the original information as emitted by the fracture incidents is also discussed. Simultaneously, crucial information is supplied by DIC concerning the moments of stress release of the patches due to debonding, benchmarking the trends monitored by AE. From the point of view of mechanics, conclusions on the reinforcing contribution of the different repair methodologies are also drawn.

太赫兹波段表面等离子体波传播距离的调控

太赫兹波段表面等离子体波传播距离的调控

The affect distance analysis of tunnel blasting vibration on adjacent buildings

In the formation of the blasting seismic wave transmission is a complex mechanical process. Blasting seismic wave in different geological structure formation of the interface, diffraction, reflection, projection as the incident Angle is different, all kinds of waveform transformation, formation of different types, different amplitude, frequency and phase of various wave superimposition of random composite wave. Blasting seismic wave propagation distance (horizontal distance and height difference), and the performance of the explosive, explosive charge, charge structure, priming method, congestion state what international airport, the plane and direction, topography and geological conditions will affect the blasting vibration effect. In engineering by empirical formula to estimate main parameters of blasting seismic wave and the structure of the empirical formula is the result of the use of theoretical analysis, by blasting of similar rate to determine the parameters in the formula is made up of many engineering measured data from statistical analysis, or directly by the measured parameters of the blasting seismic wave is given. In this paper, through various points were set in the prison line large speed is the most value, using the mathematical statistics regression analysis method, attenuation coefficient is obtained, and then back to the formula of single ring allows maximum dose safety distance calculated.

Creating TUIs Using RFID Sensors--A Case Study Based on the Literacy Process of Children with Down Syndrome.

Teaching children with intellectual disabilities is a big challenge for most parents and educators. Special education teachers use learning strategies to develop and enhance motivation for complex learning tasks. Literacy acquisition is an essential and life-long skill for a child with intellectual disabilities. In this context, technology can support specific strategies that will help children learn to read. This paper introduces a Tangible User Interface (TUI) system based on Radio Frequency Identification (RFID) technology to support literacy for children with Down syndrome. Our proposed system focuses on the integration of RFID tags in 3D printed objects and low cost toys. The paper describes the experience of using some materials covering the tags and the different problems related to the material and distance of radio wave propagation. The results of a preliminary evaluation in a special education institution showed that the system helps to improve the interaction between teachers and children. The use of a TUI seems to give a physical sensory experience to develop literacy skills in children with Down syndrome.

판형 웨이브가이드 초음파 센서를 이용한 소듐냉각고속로 원격주사 검사기법 개발

In a sodium-cooled fast reactor, which is a Generation-IV reactor, refueling is conducted by rotating, but not opening, the reactor head to prevent a reaction between the sodium, water and air. Therefore, an inspection technique that checks for the presence of any obstacles between the reactor core and the upper internal structure, which could disturb the rotation of the reactor head, is essential prior to the refueling of a sodium-cooled fast reactor. To this end, an ultrasound-based inspection technique should be employed because the opacity of the sodium prevents conventional optical inspection techniques from being applied to the monitoring of obstacles. In this study, a ranging inspection technique using a plate-type ultrasonic waveguide sensor was developed to monitor the presence of any obstacles between the reactor core and the upper internal structure in the opaque sodium. Because the waveguide sensor installs an ultrasonic transducer in a relatively cold region and transmits the ultrasonic waves into the hot radioactive liquid sodium through a long waveguide, it offers better reliability and is less susceptible to thermal or radiation damage. A 10 m horizontal beam waveguide sensor capable of radiating an ultrasonic wave horizontally was developed, and beam profile measurements and basic experiments were carried out to investigate the characteristics of the developed sensor. The beam width and propagation distance of the ultrasonic wave radiated from the sensor were assessed based on the experimental results. Finally, a feasibility test using cylindrical targets (corresponding to the shape of possible obstacles) was also conducted to evaluate the applicability of the developed ranging inspection technique to actual applications.

High-intensity directional surface plasmonic excitation based on the multi metallic slits with nano-antenna

Micro-nano structure optical device based on surface plasmon polariton such as super lens, micro-nano resonators and waveguides, etc. owns great applications in different research fields, especially in integrated optics and nanophotonics, for it has extremely small size and can be integrated into a micro-nano optical system. Comparatively, the directional wave exciter attracts much attention since it breaks the symmetries of wave propagation and excitation and can be applied to a micro-nano optical logic modulation system in the future. In order to realize the high-efficiency directional excitation in ultra-small structure based on surface plasmon polariton, a newly designed metal insulator metal waveguide based surface plasmon directional exciter with multiple channels and nano antenna is presented in this paper. The basic structure of the surface plasmon directional exciter is a two-slit metal plate, and the directional propagation surface plasmon wave is generated according to wave interference. To obtain a single surface plasmon wave in the specific orientation, a phase difference of π/2 between the surface waves generated by slits is necessary. To achieve the different phase differences, both heights and widths of the channels are calculated according to the waveguide mode function. It is worth noting that the directional wave exciter with dual channels is able to generate unsymmetrical wave propagation, however, the excitation efficiency is rather low, which restricts its potential applications in micro-nano optical system. In the paper, in order to further raise the coupling efficiency of the excited surface plasmon wave, and increase its propagation, other additional channels are designed in the directional wave exciter structure. Compared with the traditional dual channel system, the additional channels with similar parameters, and the same interference features are introduced in the surface plasmon directional exciter to increase the light transmission and surface wave energy. In addition, a nano antenna structure based on resonance is presented on the structure surface to enhance the surface plasmon excitation as well. The design tactics of the directional surface plasmon wave exciter are analytically explained in the paper. With numerical calculation based on the finite difference time domain method, the simulation result proves that the proposed surface plasmon wave directional exciter is able to generate single orientation surface wave with extremely high coupling ratio. Moreover, with additional multiple channels and nano antenna, the energy of the directional coupled surface plasmon wave is improved obviously, which indicates that the propagation distance of the surface plasmon wave is increased. In the simulation, both the additional channels and nano antenna are able to increase the energy and propagation distance of the surface plasmon wave obviously: the energies of directional propagated surface plasmon waves of four and six channel directional wave exciters with nano antenna are 6.74 times and 9.30 times that of the traditional dual slit directional wave exciter without nano antenna, respectively. Moreover, it is worth noting that the newly designed nano antenna based multi-channel enhanced surface plasmon wave directional exciter owns compact structure and can be easily fabricated at low cost. It is believed that this work can be an important reference for designing micro and nano photonic and plasmonic elements in integrated optics.

Correlations of shock Mach number attenuation in small size diameter tubes

From previous works on the shock Mach number attenuation along small size diameter tubes, two different power-law correlations in laminar and turbulent flows in shock tube are proposed in this paper for describing this attenuation and the shock wave behavior. These correlations are based on a local scaling ratio built from driven gas conditions, hydraulic diameter tube, and shock wave propagation distance. A comparison to numerical and experimental existing data is presented and discussed.

Modeling nonlinearities of ultrasonic waves for fatigue damage characterization: Theory, simulation, and experimental validation

A dedicated modeling technique for comprehending nonlinear characteristics of ultrasonic waves traversing in a fatigued medium was developed, based on a retrofitted constitutive relation of the medium by considering the nonlinearities originated from material, fatigue damage, as well as the “breathing” motion of fatigue cracks. Piezoelectric wafers, for exciting and acquiring ultrasonic waves, were integrated in the model. The extracted nonlinearities were calibrated by virtue of an acoustic nonlinearity parameter. The modeling technique was validated experimentally, and the results showed satisfactory consistency in between, both revealing: the developed modeling approach is able to faithfully simulate fatigue crack-incurred nonlinearities manifested in ultrasonic waves; a cumulative growth of the acoustic nonlinearity parameter with increasing wave propagation distance exists; such a parameter acquired via a sensing path is nonlinearly related to the offset distance from the fatigue crack to that sensing path; and neither the incidence angle of the probing wave nor the length of the sensing path impacts on the parameter significantly. This study has yielded a quantitative characterization strategy for fatigue cracks using embeddable piezoelectric sensor networks, facilitating deployment of structural health monitoring which is capable of identifying small-scale damage at an embryo stage and surveilling its growth continuously.

Research on the Laws of the Environmental Vibration Induced by Elevated Rail Transit

Established the Car Line - Bridge coupling dynamic model, then entered the actual parameters of train, track and bridge structural, obtained the dynamic excitation at the rail bridge pier bottom when the train passes. On this basis, established the pier - soil - building coupling dynamic model by combining finite element method and infinite boundary element method, analysed the vibration characteristics of soil and buildings surrounding the elevated rail way, brought an in-depth study to the effects of elevated rail transit train running on the environment. The results show that: 1)The the environmental vibration induced by elevated rail transit is low-frequency vibration, the vertical ground boils down to low-frequency vibration of 10 - 25Hz, the transverse vibration of housing column is fundamental frequency vibration near 10Hz, the vertical floor boils down to low-frequency vibration of 10 - 25Hz. 2) The vertical ground vibration response level decreases with the increase of distance to the rail centerline when the train passes. 3) With the increase of vibration wave propagation distance, components of higher frequency decay more quickly.

High Resolution Numerical Simulation of Shock-to-Detonation Transition of Condensed-Phase Explosives

In this paper, shock-to-detonation transition for condensed phase explosives is numerically simulated by adopting high resolution numerical scheme. Fifth-order WENO scheme and third-order TVD Runge-Kutta method are employed to discretize Euler equations with chemical reaction source in space and time respectively, and parallel high resolution code is developed. Applying this code, the influence of incident pressure and pulse width on the run distance to detonation is investigated. The numerical results show that incident pressure and pulse width govern the initiation process. If appropriate values are taken for incident pressure and pulse width, the pressure will increase with the enlarging of the shock wave propagation distance, and finally the explosives reach steady detonation. The run distance to detonation is also influenced by those two factors, and it gets shorter with the increase of pulse width and incident pressure. When the incident pressure and the pulse width are small enough, the retonation phenomenon can be observed, and it becomes obvious along with the decreasing of incident pressure and pulse width.

Nonlinear Properties of Lamb Waves under Modulation of Fatigue Damage: <i>Finite Element Simulation with Experimental Validation</i>

Engineering structures under cyclic loads experience continuous accumulation of fatigue damage, deteriorating at an alarming rate. Most existing structural health monitoring (SHM) techniques use linear signal features, which may be unwieldy to the detection of fatigue damage in an initial stage. A dedicated finite element (FE) modeling technique for simulating nonlinear properties of ultrasonic Lamb waves under the modulation of fatigue cracks in metallic materials was established. Piezoelectric wafers were included in the model for exciting Lamb waves and capturing nonlinear characteristics. A nonlinearity parameter was constructed to calibrate the extracted wave nonlinear properties. Feasibility of the FE technique was experimentally validated, and the results showed satisfactory consistency in between, both revealing that (i) the developed FE modeling technique is able to faithfully simulate fatigue crack-induced nonlinear properties in Lamb waves, providing repeatable characterization for fatigue cracks; (ii) the defined nonlinear parameter decreases when the direct wave path offsets from the fatigue crack, nonlinearly subject to the offset distance from the crack to a sensing path; and (iii) a cumulative growth of the nonlinearity parameter against the wave propagation distance exists. All the observations enable quantitative characterization of micro-fatigue cracks using embeddable piezoelectric wafers, facilitating development of SHM technique with a capacity of quantitatively detecting damage small in dimension.

Order analysis for measurement of Lamb wave propagation distance

The order analysis technique is utilized to directly measure the propagation distance of a Lamb wave without knowing its travel time and group velocity. The proposed algorithm relates the propagating wave-packets to the referenced wave-packet, instead of to an absolute propagating distance. The dispersion signal in the frequency domain is firstly resampled and interpolated according to the unwrapped phase derived from the referenced wave-packet. Subsequently, it is transformed into the angle domain stationary signal. The ‘order’ is defined as the propagating distance of dispersion wave-packet normalized by that of referenced wave-packet. Then the order spectrum is obtained by the Fourier transform of the equivalent angle signal. Finally, the wave-packet propagation distance is estimated precisely according to the mono-function relationship between the orders and the propagation distances. Synthetic and experimental results show that the proposed method enables the precise propagation distance estimation and mode identification regardless of the phenomenon of dispersion and multi-mode overlapping.

A Model to Describe the Dynamic Influence Length of the Vehicles on the Main Road at the Upstream Sections of Off-Street Parking Access

We research into the upstream sections of off-street parking access in the city. When the parking car turns right from the main road of the rightest lanes into the access, the vehicles which are the upstream of the access on the main road may be affected and the influence length can be presented as two parts: one is the deceleration distance of the parking car and the other is the propagation distance of traffic wave caused by the following vehicles. By the way of theoretical analysis and field investigation, we present a model that represents the dynamic influence length under the condition of different entering time and moderate saturation. Parameters were specialized to represent the characters of parking car and the vehicles following it, including park entering time and speed variation rate. Some conclusions were drawn by contrasting the simulation of VISSIM 5.3 and the model. First, when entering time was between 4 s to 8 s, saturation and the influence length were in inverse proportion; while the entering time was more than 8 s, saturation and the influence length were in direct proportion. Second, when the saturation was between 0.46 and −0.5 and entering time was between 4 s and 15 s, parking car had no effect on the vehicles. Third, when the saturation was more than 0.6 and entering time was more than 9 s, the effect of parking car on the vehicle's influential length increased significantly.

Measurements and kinetic modeling of energy coupling in volume and surface nanosecond pulse discharges

Nanosecond pulse discharge plasma imaging, coupled pulse energy measurements, and kinetic modeling are used to analyze the mechanism of energy coupling in high repetition rate, spatially uniform, nanosecond pulse discharges in air in plane-to-plane geometry. Under these conditions, coupled pulse energy scales nearly linearly with pressure (number density), with energy coupled per molecule being nearly constant, in good agreement with the kinetic model predictions. In spite of high-peak reduced electric field reached before breakdown, E/N ∼ 500–700 Td, the reduced electric field in the plasma after breakdown is much lower, E/N ∼ 50–100 Td, predicting that a significant fraction of energy coupled to the air plasma, up to 30–40%, is loaded into nitrogen vibrational mode.A self-similar, local ionization kinetic model predicting energy coupling to the plasma in a surface ionization wave discharge produced by a nanosecond voltage pulse has been developed. The model predicts key discharge parameters such as ionization wave speed and propagation distance, electric field, electron density, plasma layer thickness, and pulse energy coupled to the plasma, demonstrating good qualitative agreement with experimental data and two-dimensional kinetic modeling calculations. The model allows an analytic solution and lends itself to incorporation into existing compressible flow codes, at very little computational cost, for in-depth analysis of the nanosecond discharge plasma flow control mechanism. The use of the model would place the main emphasis on coupling of localized thermal perturbations produced by the discharge with the flow via compression waves and would provide quantitative insight into the flow control mechanism on a long time scale.