Wave Propagation Time Research Articles

Derivation of delay equation climate models using the Mori-Zwanzig formalism.

Models incorporating delay have been frequently used to understand climate variability phenomena, but often the delay is introduced through an ad hoc physical reasoning, such as the propagation time of waves. In this paper, the Mori-Zwanzig formalism is introduced as a way to systematically derive delay models from systems of partial differential equations and hence provides a better justification for using these delay-type models. The Mori-Zwanzig technique gives a formal rewriting of the system using a projection onto a set of resolved variables, where the rewritten system contains a memory term. The computation of this memory term requires solving the orthogonal dynamics equation, which represents the unresolved dynamics. For nonlinear systems, it is often not possible to obtain an analytical solution to the orthogonal dynamics and an approximate solution needs to be found. Here, we demonstrate the Mori-Zwanzig technique for a two-strip model of the El Niño Southern Oscillation (ENSO) and explore methods to solve the orthogonal dynamics. The resulting nonlinear delay model contains an additional term compared to previously proposed ad hoc conceptual models. This new term leads to a larger ENSO period, which is closer to that seen in observations.

Destructive and Non-destructive Tests of Bamboo Oriented Strand Board under Various Shelling Ratios and Resin Contents

The objectives of this study were to evaluate the effects of shelling ratio and resin content on the properties of bamboo oriented strand board (BOSB) from betung (Dendrocalamus asper) and to determine the correlation between the results of dynamic and static bending tests. Strands were steam-treated at 126 °C for 1 h under 0.14 MPa pressure and followed by washing with 1% NaOH solution. Three-layer BOSB with the core layer perpendicular to the surface was formed with shelling ratios (face:core ratio) of 30:70; 40:60; 50:50; 60:40 and binded with 7% and 8% of phenol formaldehyde (PF) resin with the addition of 1% of wax. The evaluation of physical and mechanical properties of BOSB was conducted in accordance with the JIS A 5908:2003 standard and the results were compared with CSA 0437.0 standard for commercial OSB (Grade O-1). Non-destructive testing was conducted using Metriguard Model 239A Stress Wave Timer which has a wave propagation time from 1 to 9,999 μs and a resolution of 1 μs. BOSB with 8% resin content showed better physical and mechanical properties than those with 7% resin content. The increase of the face layer ratio improved the strength of BOSB in parallel direction to the grain. The results suggested that shelling ratio of 50:50 could be used as a simple way to reduce PF resin requirements from 8% to 7% and to meet the requirements of CSA 0437.0 standard. The results of non-destructive and destructive tests showed a strong correlation, suggesting that non-destructive test can be used to estimate the bending properties of BOSB.

Contribution of travelling wave propagation time to the speed of optical link protections in multi‐terminal high‐voltage DC systems

During faults in multi-terminal high-voltage DC systems, the disturbance will quickly become evident throughout the entire system. If DC breakers are included in such systems, the entire fault clearing process needs to occur within a few milliseconds. Therefore, DC line protection schemes based on telecommunication have previously been discarded by some authors as their performance is constrained by the communication delay. However, telecommunication-based detection methods offer some very favourable features, one being that selectivity can be achieved without coordination of settings. In this study, several telecommunication-based protection schemes are evaluated with regards to their minimum possible detection time when considering telecommunication delay. It is shown that they perform best during faults located at the remote end of a line, i.e. fault locations that are difficult to reliably detect using single-ended methods. Therefore, it is reasonable that the most reliable protection system will consist of both single-ended and communication-based methods because they complement each other well. Furthermore, it is shown that the travelling wave differential protection offers the shortest theoretical detection time due to the wave propagation delay being included in the formulation.

Wave propagation time optimization for geodesic distances calculation using the Heat Method

Abstract Finding the geodesic path defined as the shortest paths between two points on three-dimensional surface P is a well known problem in differential and computational geometry. Surfaces are not differentiable in a discrete way, hence known geometry algorithms can’t be used directly - they have to be discretized first. Classic algorithms for geodesic distance calculation such as Mitchell-Mount-Papadimitriou method (MMP) are precise but slow. Therefore modern solutions are developed for fast calculations. One of them is Heat Method which approximates such paths with some accuracy. In this paper we propose the extension of Heat Method to reduce the approximation error. A new formula for calculating value of the parameter t (wave propagation time step) which outperforms the original one in terms of mean and median error is presented. Also, correlation between mesh properties and best wave propagation time step as well as influence of variable node spacing on heat map based method were thoroughly analysed.

Laboratory Evaluation of Railway Ballast Consolidation by the Non-Destructive Testing

The property of railway track to resist the irreversible deformation for a long-term operational loading considerably depends on the ballast layer. The ballast layer is the element of a railway track whose mechanical properties and state are formed in-situ with the help of the ballast cleaning, tamping and distributing machines. The varied properties of the ballast material to obtain the form during the maintenance and retain it during the operation are equally important for the ballast layer. The control over the processes of the ballast consolidation and deconsolidation by means of measurement methods could potentially provide great possibilities for improvement of its properties both during the maintenance and operation. The paper deals with an experimental study of the railway ballast consolidation and deconsolidation processes under the vibration loading of the sleeper. A non-destructive measurement method is proposed to investigate the distribution of the ballast consolidation along the sleeper. The method is based on the measurement of time of mechanical wave propagation. Modern low-cost sensors and powerful microcontroller techniques enable creating smart measurement systems for automatic multi-point data acquisition, online processing and statistical estimation of the ballast consolidation distribution.

Least-squares based rectangular-grid cross and rhombus stencils for acoustic wave propagation and reverse time migration

Recent researches on migration focus on computational efficiency and imaging accuracy. Modeling is at the heart of the reverse time migration (RTM), a powerful tool for imaging geologically complex structures, and controls its efficiency and accuracy. Finite-difference (FD) method is widely used in modeling. Though the rhombus stencil FD scheme has high accuracy, it is expensive and only applicable to square grids. In order to make the high-accuracy FD scheme more efficient and flexible, we develop a rectangle-grid cross and rhombus stencils FD scheme (RCR). To further improve accuracy, the optimal FD method based on least squares (LS) is introduced into the RCR. Correspondingly, the absorbing boundary condition (ABC) should be extended to rectangular grids for suppressing the boundary reflections of modeling, we therefore develop the rectangular-grid hybrid ABC. To obtain high-efficiency and high-accuracy RTM images, the adaptive variable-length spatial operators scheme is combined with the LS-based RCR when implementing the wavefield extrapolation, and the efficient boundary condition is adopted when performed on GPU card. By comparing the RCR with the rectangular-grid on cross stencil FD scheme (RC) in terms of their phase dispersion, stability and snapshot, we demonstrate the superiority of the LS-based RCR. We have also proven the effectiveness of the rectangular-grid hybrid ABC on absorption, and shown that under the similar accuracy, the RCR-based RTM can achieve higher efficiency than the RC-based one by adopting a larger time interval. Finally, the RCR-based RTM obtains a well-imaged profile for field data.

Study of the Acoustoelastic Effect in an Anisotropic Plastically Deformed Material

The paper discusses the dependence of shear elastic waves birefringence on applied mechanical stress and preliminary plastic deformation of a material. A technique involving precision acoustic pulse echo measurements and software processing of the received time scan of signals from a piezoelectric transducer is described, which makes it possible to determine the propagation time of elastic waves with an accuracy of at least 0.5 ns. The dependences of the intrinsic acoustic birefringence and the acoustoelastic coefficient on plastic deformation in a carbon steel sample are investigated. After 12% plastic deformation of the sample, the average value of the acoustoelastic coefficient changes by 30%; the average value of the intrinsic acoustic birefringence changes by 60%. A correlation is observed between the intrinsic acoustic birefringence and the acoustoelastic coefficient. Using the theory of elastic wave propagation in a solid, the obtained experimental data are explained by manifestation of the acoustoelastic effect and the influence of the structural state on the effective elastic properties. The effect of plastic deformation on the accuracy of determining stress is qualitatively assessed. The error in determining stress during 1% plastic deformation is about 40 MPa, i.e., 13% of the yield strength for this material in the initial state.

Prolonged Kelvin–Helmholtz Waves at Dawn and Dusk Flank Magnetopause: Simultaneous Observations by MMS and THEMIS

Abstract The Kelvin–Helmholtz (K-H) waves predominantly excited at the Earth’s low-latitude magnetopause were suggested to be dawn–dusk asymmetric. We report a prolonged simultaneous observations of the K-H waves on the dawn and dusk magnetopause by Magnetospheric Multiscale (MMS) and THEMIS-A (THA) spacecraft, respectively. The quasi-periodic K-H waves on both flanks have unambiguous low-density and high-speed patterns. The wave periods vary gradually on both flanks, with similar average periods (303 ± 107 s for MMS and 266 ± 102 s for THA). The lag time between the variations of the wave periods is close to the wave propagation time from THA to MMS, which suggests that the K-H waves generate and propagate quasi-symmetrically on both flanks. Larger local magnetic shear angles are observed on the trailing edges by MMS than by THA, which is probably due to the strong magnetic field distortion during the tailward propagation. The increased magnetic shear may excite magnetic reconnection, thus contributing to the formation of the low-latitude boundary layer.

Relationship Between the Characteristics of the Crystallographic Texture of Low-Carbon Steels with Accumulation of Damages at the Early Stages of Fatigue Failure

We studied texture change of low-carbon steel during high-cycle fatigue by ultrasonic echo-pulse method. We received the orientation distribution function coefficients using precise ultrasonic measurements of the elastic wave propagation times. Then pole figures were constructed. It is found that the texture sharpness nonmonotonic depends on the number of loading cycles. It is shown that the texture sharpness can be used as an indicator of the structural state of the alloy.

Determination of stresses and strains in the shaping structure under spatial load

The computational model of the machine – environment system, taking into account the mutual influence of the working body and compaction mixture was developed. It is based on the condition of determining the contact forces of interaction between the subsystems and estimation of the ratio of the time of action and time of wave propagation. This approach is new, since it takes into account the real relationship between the dynamic parameters of the machine and the environment and degree of interaction. The study and determination of stresses and strains in time confirmed the hypothesis of their significant influence on the process. A fundamentally new result was revealed, which consists in the fact that the transition process should take into account the determination of parameters and locations of vibrators. The laws of stress and strain variations during spatial oscillations of the shaping surface were established. Modes of natural oscillations of the system are implemented with higher oscillation amplitudes and correspondingly lower frequency. And this opens up a real opportunity to reduce the energy intensity of the vibration machine. Numerical values of stresses and the nature of their distribution in the shaping surface, depending on the angle of the instantaneous action of the external force of vibrators, the presence of bending and torsional oscillations were obtained.So under the condition of two excitation forces, the points of application of which are displaced relative to each other by ½ of the length of the structure, placing the force application points symmetrically at a distance of ¼ of the size of the structure on both sides allowed obtaining cophased and anti-phase directions of stresses and acting external force.In calculations of vibration machines using shaping surfaces, it was proposed to take into account output numerical values of the amplitude-frequency mode of the oscillation exciter. Practical recommendations for the rational design of sections of shaping structures were developed and technological parameters were determined. To construct such shaping structures, the installation sites for vibrators were determined. The results obtained can be successfully used in related processes, for example, in the mining industry, as active surfaces for ore transportation, for the transfer of suspensions and solutions in the chemical industry

Data-Driven Estimation of Frequency Response From Ambient Synchrophasor Measurements

With the wide deployment of synchrophasor technology, measurement-based dynamic modeling and studies have been becoming increasingly useful for real-time grid operations. This paper considers the problem of estimating the power system frequency response from ambient synchrophasor measurements. Specifically, we develop the analytical conditions for establishing the equivalence between the cross correlation of ambient generator speed data and the system frequency response between any two locations. Our conditions, relying on uniformly damped and equally excited oscillation modes, extend earlier work on electromechanical wave propagation modeling to nonhomogeneous power networks. Numerical results suggest that the validity of the cross correlation approach would hold for more realistic conditions such as nonuniform damping and high-order generator model. Its practical value is further corroborated by real-data results, which closely match with the actual propagation time of electromechanical waves recorded during the 2008 Florida blackout in the Eastern Interconnection system.

Development and Preliminary Application of Resonant Column-Bending Elements Combined Testing Apparatus

Due to the influence of near-field effect and soil filterability, there are still many disputes for determining the shear wave propagation time, which hinders further development and application of the bending element test. Based on the Stokoe type resonance column instrument (RC), a pair of bending elements (BES) was implanted into the system, which achieved the combined test of RC and BES on a same soil specimen. In order to test the device reliability, combined tests of dry Fujian standard sand with different initial densities under different confining pressure were carried out to measure the dynamic shear modulus. Results show that the improved equipment can give play to both the advantages of RC and BES. For the same specimen, the BES calibration is achieved by RC system, which effectively overcomes the problem of time determination in BES test. When BES excitation frequency satisfies the condition (2<Rd<7), the near-field effect can be weakened effectively. When the initial arrival wave method is used to determine the shear wave propagation time in BES test, the take-off point of the previous peak of the received main wave crest should be taken as the arrival time of the shear wave.

Improvement of Accuracy of Control of Physical‑Mechanical Characteristics of Materials By Ultrasonic Pulse Method Due to Reduction of Measurement Error of Propagation Time of Elastic Waves

Ensuring the reliability of buildings, structures, analysis of their structural elements during reconstruction or major repair includes the task of determining the physical and mechanical characteristics of materials — strength, homogeneity, evaluation of structural heterogeneity, the presence of microcracks, etc. In solving this problem, an ultrasonic pulse method of non-destructive quality control is used. The basis of the method is the dependence of the parameters of ultrasonic oscillations, on these characteristics when they pass through the material. As the main parameter of the information ultrasonic signal, the time of its passage from the radiating to the receiving ultrasonic transducers is used. The amplitude of the information ultrasonic signal to a large extent depends on the structure of the investigated material, its acoustic resistance. At significant violations of the structure of the material there is a significant decrease in the amplitude of the information signal, which causes an increase in the error of measuring the time of its passage, and hence the definition of characteristics, quality of the investigated material.&#x0D; The article describes the developed method of increasing the accuracy of measuring the time of passage of the ultrasonic signal from the radiating to the receiving ultrasonic transducers. The essence of the technique is to use the mathematical modeling of the shape of the ultrasound signal, in particular the form of its so-called «first introduction».

Acoustic study of the texture characteristics of 15YuTA construction steel in fatigue failure conditions

Ultrasonic echo-pulse method is used to study the texture changes and Poisson’s coefficients of 15YuTA construction steel upon fatigue failure in the range of high-cycle fatigue. To describe the texture change, pole figures were constructed using the values of the orientation distribution functions (W400 and W420) obtained from the results of precise measurements of the propagation time of elastic bulk waves in sheet materials. The intensity ratio in the center of the pole figure and the point remote from the center of the pole figure by 45° along the rolling direction was used as a parameter characterizing the texture sharpness. It is shown that change in the texture sharpness is attributed to the development of microplastic strain and accumulation of the microdamages. A nonmonotonic dependence of the change in the texture sharpness on the number of loading cycles is observed. At the initial stage of loading, there is some increase in the sharpness of the texture, which can be attributed to the development of micro-strains on the most favorably oriented sliding planes. At the second stage, a decrease in the texture sharpness is associated with the scattering of the texture as the density of microdefects increases during the destruction of the alloy. The parameter characterizing the texture sharpness can be used as a pre-destruction indicator when monitoring the material of the structure by the ultrasonic method.

On the method of ultrasonic control of mechanical stresses

A method of ultrasonic control of the mechanical stresses which takes into account the heterogeneity of the material structure and does not require unloading of the structure or using reference samples is considered. The procedure is based on echo-method of measuring time of the bulk elastic wave propagation and determination of the relative values ν31 and ν32 related to the material structure and mechanical stresses. It is shown that stresses violate the linearity of the relationship observed between the parameters in the absence of the mechanical stresses in the rolled material. This effect formed a basis for developing a method of the deviator stress determination. The purpose of the study is to demonstrate the main advantages of the developed method against the known ultrasonic techniques used for evaluation of the mechanical stresses, give theoretical grounds to the effect which allows taking into account the heterogeneity of the material structure, and also to exemplify the procedure. An analytical expression is derived using bulk elastic wave velocity in an orthotropic material composed of cubic crystallites and an assumption on the existence of simple proportional relationship between the coefficients of the orientation distribution function in rolled metal. Presented results of the mathematical modeling confirm the experimentally observed linear dependence between the parameters ν31 and ν32 in the absence of mechanical stresses. The results of evaluating residual stresses in a welded steel plate are presented as an example of the applicability of the developed procedure. Data of ultrasonic technique and data of strain gage measurements are compared. The features of the described method of stress determination are marked and the applicability limits are specified.

Adaptive perimeter control for multi-region accumulation-based models with state delays

Enhancing macroscopic fundamental diagram (MFD) dynamic models and improving perimeter control algorithms are the current main research challenges in the MFD research area. Over the last decade, different accumulation-based dynamic models, describing the traffic flow dynamics of one or multi-region systems, have been developed in different forms relying on vehicle conservation equations.In this research, two enhanced accumulation-based models are developed by incorporating into model structure the time-delay (time-lag) effects as an important factor. The first model incorporates state delay in the MFD output to improve the dynamics, to better represent wave propagation and travel time evolution within the region, especially when the change in demand is fast. While in the second model delayed interconnections are introduced in the dynamic equations to model data processing and communication delays between interconnected regions. The two linearized models are formulated in interconnected forms. Then, the reference model adaptive control approach has been implemented to allow us designing distributed adaptive perimeter control laws. The developed adaptive control scheme postulates one controller structure, however, the controllers’ gains vary with time to adapt themselves against the model parameter uncertainties and state delays. The numerical results demonstrate the flexibility of the distributed adaptive perimeter controllers in handling different cases and various traffic situations with state delays.

Formation, breaching and flood consequences of a landslide dam near Bujumbura, Burundi

Abstract. This paper investigates the possible formation of a landslide dam on the Kanyosha River near Bujumbura, the capital of Burundi, as well as the interplay between the breaching of this landslide dam and the flooding along the river. We present an end-to-end analysis, ranging from the origin of the landslide up to the computation of flood waves induced by the dam breaching. The study includes three main steps. First, the mass movement site was investigated with various geophysical methods that allowed us to build a general 3-D model and detailed 2-D sections of the landslide. Second, this model was used for dynamic landslide process modelling with the Universal Distinct Element Code. The results showed that a 15 m high landslide dam may form on the river. Finally, a 2-D hydraulic model was set up to find out the consequences of the breaching of the landslide dam on flooding along the river, especially in an urban area located downstream. Based on 2-D maps of maximum water depth, flow velocity and wave propagation time, the results highlight that neglecting the influence of such landslide dams leads to substantial underestimation of flood intensity in the downstream area.

Propagation velocity and time laws of backpressure wave in the wellbore during managed pressure drilling

When gas invasion, especially overflow, occurs at the bottom hole in the process of managed pressure drilling (MPD), it is common to apply backpressure on the wellbore by adjusting the backpressure pump and throttle valve, so as to rebuild bottom hole pressure balance. If it is still thought that the wellhead backpressure is loaded to the bottom hole instantaneously, there will be larger errors between the calculated wellbore parameters and the actual wellbore flow parameters, which will result in well control failure and even well blowout. In this paper, a pressure wave propagation equation suitable for the gas–liquid two-phase flow in the annulus was established based on the global averaged gas–liquid two-phase flow model to investigate the propagation velocity and time of backpressure wave in the wellbore. Then, gas–liquid interaction was introduced to carry out coupling solution on the equation set. It is shown that pressure wave velocity increases with the increase of drilling mud density, but decreases with the increase of void fraction and virtual mass force coefficient. It changes drastically at first, and then slows down. What's more, when the void fraction is greater than 0.1 or the virtual mass force coefficient exceeds 0.2, the momentum between gas phase and liquid phase is fully exchanged, and the pressure wave velocity decreases slowly, approaching a stable value. In Well Penglai 9 in the Sichuan Basin, for example, the average time of single pressure wave propagation is about 50 s, and the total propagation time of 4 rounds is about 200 s, which accounts for more than 67% of the total time of system control response. It is indicated that the propagation velocity and time of the pressure wave in the annulus calculated by this method can greatly improve the accuracy of managed pressure response time of MPD drilling system and the control precision of adaptive throttle valve.

Experimental studies of forming design at dynamic load

The object of research is the movement process of forming structures of a vibration unit with spatial oscillations. The main disadvantage of such vibration systems is the lack of data on the mutual influence of machines and media. Experimental vibration unit is developed and manufactured. The unit is equipped with two asymmetrically mounted vibration exciters that are attached directly to the forming surfaces. A new technique for measuring the motion of forming structures with the location of sensors in the areas of dynamic load is proposed. The basis of their location is the premise of determining the contact forces of the interaction of the subsystems with each other. As well as an assessment of the ratio of time of action and time of wave propagation. This approach is new, because it takes into account the real relationship of the dynamic parameters of the machine and the environment between them and the degree of interference. In the course of research, records of continuous fixation of the distribution of active oscillations of forming surfaces are used. A fundamentally new result is obtained, which consists in the fact that the transition process is envisaged to take into account when determining the parameters and locations of vibrators. Due to this, the forms of natural oscillations of the system with large amplitudes of oscillation and correspondingly lower frequency are realized. Compared with similar known designs of vibration units, this can significantly reduce the energy intensity of the causes of the vibration machine. The use of pneumatic generators in real factory conditions reduces the noise level and accelerates the speed of the process of compacting concrete. Practical recommendations for the rational constructive design of sections of forming structures are developed. Technological parameters of oscillations with new values of the output numerical values of the amplitude-frequency mode of the exciter of oscillations are determined. To construct such forming structures, the sites for vibration units are determined. The obtained results can be used in related processes, for example, in the mining industry, as active surfaces for transporting ore, for moving suspensions and solutions in the chemical industry.

Contactless Technique for Measuring Blood-Pressure Variability from One Region in Video Plethysmography

Sudden changes in blood pressure are frequently caused by daily events such as exercise, stressful work, and moving between different temperature environments. Sometimes, an abrupt change in blood pressure can endanger human lives. To mitigate such a risk, several studies have previously proposed contactless methods for monitoring changes in blood pressure; however, the number of studies on this issue is insufficient. In previous methods, changes in blood pressure were estimated using the propagation time of the pulse waves obtained from two different skin areas on the basis of an analysis of images from video recordings, which is called a video plethysmogram. However, the relative positional relationship of the two skin areas had to be maintained during the measurement, making the approach restrictive. To solve this problem, in the present study, we propose a new method using the video plethysmogram obtained from only one skin area. In particular, the degree of distortion in the video plethysmogram is calculated as a new index to estimate the blood pressure. On the basis of the results of our experiments with 20 healthy human subjects, we ascertain that the proposed index obtained from the palm area is correlated with the blood-pressure variability as well as the previous approach.