Wave Reflection Method Research Articles

Robust Traveling Wave-Based Protection Scheme for Multiterminal DC Grids

The DC transmission line protection technology is crucial for the development of multi-terminal Voltage Source Converter (VSC)-based HVDC systems. This article proposes a robust non-unit traveling wave protection (TWP), which deals with the DC fault area identification and fault type discrimination for high impedance fault conditions. The authors applied the traveling wave (TW) reflection and refraction method for the line-mode network. The distinctive features of high-frequency components contained in the line-mode and pole-mode voltage TWs at different relay units are used for the algorithm modeling. Discrete Wavelet Transform (DWT) is selected as the time-frequency analysis tool. The performed simulations are conducted for a four-terminal VSC-HVDC system, and validate the protection feasibility and robustness. More precisely, the proposed protection scheme identifies the internal and external DC faults within 2 ms, and provides correct operation during high-impedance faults (HIF) with a 25 dB level noise interference. This protection scheme makes use of a VSC-assisted resonant current (VARC) direct current circuit breaker (DCCB), that successfully interrupts the fault currents in less than 10 ms after the fault inception. The authors also comprehensively compared the proposed scheme with the existing methods. The obtained results show that the proposed protection scheme is superior in terms of sensitivity and selectivity performance.

Comparative Analysis of Application of Seismic Wave Reflection Method in Advanced Geological Prediction

Seismic wave reflection method is an advanced geophysical detection method in tunnel geological prediction. It is more sensitive and effective in detecting geological anomalies such as fault fracture zone and karst. In order to verify the prediction efficacy and accuracy of the seismic wave reflection method with different instruments and equipment (tunnel geological prediction [TGP]/tunnel seismic prediction [TSP]) and different vibration modes (hammering, explosives), a comparison test was carried out in Jinping Tunnel. The test results showed that the time-consumption of the hammering source was short, which can greatly reduce the impact on the construction site; different vibration sources methods of seismic wave reflection can predict the unfavorable geological sections accurately.

Transient wave-leak interaction analysis for improved leak detection in viscoelastic pipelines

Transient wave reflection methods (TWRMs) have exhibited favorable capability in leak detection for elastic pipelines, but applications have demonstrated their relatively low accuracy for viscoelastic pipelines. This paper investigates the transient wave behaviour, the principal tenet for leak detection by TWRMs, in a leaky viscoelastic pipeline to understand the mechanism of wave modification by leaks and viscoelasticity. Based on the correspondence principle, this research derives analytical formulations of the leak-induced wave reflection and phase difference at any measurement point in a viscoelastic pipe. According to the measured reflection coefficient, an optimization algorithm is further developed to detect the leak. The methodologies are then assessed and discussed through sinusoidal and sigmoid perturbations in numerical and laboratory tests. The extensive analyses indicate that measurement distance and leak ratio affect the magnitude of the reflected wave, yet, the wave phase shift is relatively independent of the leak ratio for practical applications.

Amplitude-initiated open hysteresis loop of <i>P</i>-wave attenuation in sandstone: experimental study

In the area of solid state physics and materials science, new knowledge has been attained in recent years about micro-nano-plasticity using high-precision measurements at low stresses and strain. Rock microplasticity is currently poorly understood, but in the future it may prove useful in resolving problems of a fundamental and applied nature. This study examines the effect of cyclically varying pulse amplitude and wave velocity on the attenuation parameters of longitudinal wave (P-wave) in sandstone. Laboratory measurements were performed on rock specimens using the reflected wave method in the frequency range of 0.5–1.4 MHz at five values of strain amplitude ~ (0.5-2.0)10 –6 . Trial simulations were performed, in order to establish the effect of amplitude-dependent wave velocity on the parameters of wave attenuation in the sandstone. Wave attenuation behavior under combined action of the amplitude-dependent factor and wave velocity deviation is complex. The change in strain amplitude shifts the attenuation peak 1/ Q p ( f ) in the attenuation-frequency coordinates. The maximum change in peak attenuation value due to the amplitude factor and wave velocity deviation reaches 3–4 %. An open wave attenuation hysteresis loop was identified as a consequence of the closed amplitude cycle A1(+) --- A1(+) --- A1(–), where A1(+) = A1(–). Open attenuation hysteresis occurs both in the cases of constant and variable wave velocities. The length of the open part of the attenuation hysteresis loop relative to the peak value of the attenuation is as follows: for constant wave speed, 62.63 %, in the mode of increasing wave speed, 91.58 %; and, in the mode of decreasing wave speed, 47.01 %. The effect of open hysteresis of wave attenuation in sandstone can be explained by the action of microplastic deformation detected in the experiments.

Investigation of the dynamic range restrictions influence of the fiber-optic towed seismic streamer on the seismogram quality

In this paper, we presented results of influence of the dynamic range in fiber-optic streamer signal processing circuit on the quality of recorded seismograms. By contrast with the existing hydroacoustic systems, which based on piezoceramic transducers, dynamic range limitations in a fiber-optic towed streamer do not lead to clipping of acoustic signals, but to complex nonlinear distortions that affect both the amplitude and phase frequency characteristics of the recorded signals. Therefore, main task of this work is to assess the distortion of seismograms obtained from acoustic signals recorded under limited dynamic range conditions of fiber-optic towed seismic streamer. To solve this problem, seismic signals obtained during field tests for various types of seismic streamers in the water area of Kola Bay are used. The recorded acoustic signals in the form of digital readings, converted into radians, taking into account the known sensitivity coefficient of hydrophones of the towed seismic streamer, are converted into digital reports of optical interference signals. Interference signals in digital form are equivalent to real optical signals recorded by the receiving path in the signal processing unit of the fiber optic streamer. The digital form of the recorded acoustic signals makes it possible to amplify them by multiplying them by a given gain factor, simulating various energy levels of an acoustic source. Further, these signals served as input data in the mathematical model of the signal processing circuit of the fiber-optic towed streamer, which takes into account the fundamental limitations of the dynamic range due to the finite sampling frequency of the interference signal, the fixed frequency of the auxiliary phase modulation, and the finite bandwidth of the low-pass filters used. Thus, it is possible to simulate the process of recording acoustic signals of a fiber-optic towed seismic streamer both without distortion and under conditions of limited dynamic range. As a result, signals from the output of the processing circuit model are used to construct seismograms of the same shelf area with different levels of acoustic amplification using the reflected wave method. The results demonstrate that the limitations of the dynamic range of signal processing circuit of fiber-optic towed seismic streamer have a significant impact on the quality of seismograms, on reducing the signals detailing, and also on decreasing the amplitudes of the recorded waves (in the presented data, the amplitude decreases by 5 times). The quality of seismograms drops significantly in areas of sharp transition between layers with different densities, which generate the most distinct and strong reflected seismic vibrations. The results obtained are of great practical importance, since they allow evaluating the effect of complex nonlinear distortions of acoustic signals under the conditions of limited dynamic range of the signal processing circuit of a fiber-optic towed seismic streamer on the received seismograms. These results are presented for the first time due to the lack of world analogues of the developed fiber-optic towed seismic streamer. In addition, taking into account the known sensitivity of the fiber-optic hydrophones of the streamer, the constructed model of the signal processing path allows choosing the optimal energy of the acoustic source for seismic exploration with the most efficient use of the dynamic range of the fiber-optic streamer.

Research on inter-turn short circuit fault location of SF6 circuit breaker energy storage motor coil based on traveling wave reflection method

—The traveling wave reflection method is proposed to locate the inter-turn short circuit fault of the circuit breaker energy storage motor coil. The capacitance and inductance matrices of the energy storage motor coil are calculated by finite element simulation, and the wave impedance model of the coil is established based on ATP-EMTP. The low-voltage square wave pulse signal is injected at the winding head to detect the characteristic curve of reflected wave when inter-turn short circuit fault occurs. The variation law of generalized fractal dimension of reflection wave characteristic curve with short circuit position is analyzed. The short-circuit position is evaluated based on BP neural network, and the evaluation accuracy is 100 %, indicating that this method is feasible.

Research on Fault Location of SF6 Circuit Breaker Relay Coil Based on Traveling-Wave Reflection Method

—The traveling wave-reflection method is proposed to locate the short circuit fault of the opening/closing coil of the circuit breaker, the capacitance and inductance matrix of the opening/closing coil are calculated by finite element simulation, and the wave impedance model of the coil is established based on ATP-EMTP. A low-voltage square wave pulse signal is injected into the head end of the winding to detect the characteristic curve of the reflected wave when an inter-turn short-circuit fault occurs. The generalized fractal dimension of reflection wave characteristic curve was calculated and its variation as the position of short circuit change was analysed. Compared with box dimension, the variation of information dimension and correlation dimension are more obvious, thus information dimension and correlation dimension are selected as inpus, and the evaluation model of inter-turn short circuit position is established based on probabilistic neural network.

Seismic site characterization with shear wave (SH) reflection and refraction methods

Reflection and critically refracted seismic methods use traveltime measurements of body waves propagating between a source and a series of receivers on the ground surface to calculate subsurface velocities. Body wave energy is refracted or reflected at boundaries where there is a change in seismic impedance, defined as the product of material density and seismic velocity. This article provides practical guidance on the use of horizontally propagating shear wave (SH-wave) refraction and reflection methods to determine shear wave velocity as a function of depth for near-surface seismic site characterizations. Method principles and the current state of engineering practice are reviewed, along with discussions of limitations and uncertainty assessments. Typical data collection procedures are described using basic survey equipment, along with information on more advanced applications and emerging technologies. Eight case studies provide examples of the techniques in real-world seismic site characterizations performed in a variety of geological settings.

High-Precision Forward Analysis and Field Test of Boulder Detection on Zero-Offset Elastic Wave Method in Shield Tunnel

Efficient and accurate boulder detection technology is essential for shield tunneling safely under complex floodplain geological conditions. The traditional seismic reflection method is not suitable for complex geological conditions and small targets near the surface, the elastic wave reflection method based on zero-offset observation is proposed in this article. Forward is the basis of inversion, a high-order staggered grid finite difference algorithm based on least-squares optimization (LS-SGFD) is established, which has the advantages of higher accuracy and smaller dispersion. Three typical geological models are designed, and the elastic wave reflection characteristics of the method proposed in this paper and the traditional method are systematically analyzed. From the dual perspectives of field experiment and engineering application, the effectiveness of zero-offset observation for the detection of boulders is discussed, and the basic criteria for boulder identification are given. Research shows that this method has good results in detecting boulders on the surface, and it has certain reference significance for similar projects.

Low Strain Detection and Numerical Simulation of Pile Integrity

The low strain reflected wave method is used to detect the integrity of pile foundation of a domestic bridge, and various types of defective pile models are constructed. A large number of tests are carried out to analyze the complete pile installation and different defects. At the same time, considering the influence of pile material properties, soil parameters around the pile, boundary conditions and damping coefficient on the reflected wave, the test results are compared with the numerical simulation results. The results show that: low strain detection technology is convenient and easy to operate, but due to its own limitations, it should be combined with numerical simulation and other methods to learn from each other, comprehensive analysis, in order to better judge the integrity of the pile.

Integrity Detection of Pile Foundation in High-rise Buildings Based on Reflected Wave Method

The existing methods cannot effectively obtain the response signals generated by multiple defects of the pile body, which leads to the inaccuracy of the pile foundation integrity detection results, a high-rise building pile foundation integrity detection method based on the reflected wave method is proposed. The continuous wavelet transform coefficient is used to locate the defect position of pile foundation. Referring to the positioning results, according to the material density and cross-sectional area of pile foundation, the cross-sectional force and reflected wave velocity at the defect of pile foundation are calculated. Because the stress wave will be affected by the defect of pile foundation, and the fluctuation of stress wave will affect the amplitude and phase, it can be concluded that the section impedance is related to the cross-sectional force and velocity of reflection wave. According to this characteristic, the integrity of pile foundation of high-rise building is detected by the amplitude and phase characteristics of reflected wave signal. The results show that the design method can accurately determine the defects of pile foundation, accurately classify the integrity of pile body, and the integrity test results of the method can meet the relevant engineering standards, which verifies the effectiveness of the method.

ПРИМЕНЕНИЕ МЕТОДОВ СЕЙСМОТОМОГРАФИИ ДЛЯ РЕШЕНИЯ РАЗЛИЧНЫХ ЗАДАЧ В ГОРНО-ГЕОЛОГИЧЕСКОМ НАПРАВЛЕНИИ

The Karaganda coal basin is characterized by a complex structure. The presence of geological inconsistencies such as tectonic disturbances, washouts, variable reservoir hypsometry, etc. makes it difficult to conduct underground mining operations. Currently, in the world practice, mine seismic exploration is widely used for the purpose of studying the geological structure and solving various mining problems. Safe and productive operation of treatment faces in underground coal mining requires a timely and reliable forecast of the mining and geological conditions of the structure and condition of the coal-bearing mass from the mine workings. The most accurate and reliable picture of the tectonic structure of the Carboniferous massif can be obtained using methods of mine seismic exploration to study the geological structure and conditions of the coal bed and host rocks. The main goal of implementing modern methods of mine seismic exploration was to conduct mathematical modeling to assess the possibility of identifying tectonic disturbances with an offset amplitude of the order of magnitude and higher than the reservoir capacity using various methods of underground seismic exploration - the seismic transmission method (STM) and the reflected wave method (RWM). For this purpose, physical models of sections of the Carboniferous massif were developed, including a geometric description of geological structures, the distribution of rock densities, velocities, wave propagation and their influence on compression, and the shift of the mountain range. One of the models corresponded to a section of the formation without geological disturbances, and the second one - to a section with tectonic disturbances with displacement amplitudes from 5 to 15 m. The results obtained can be used in the development of modern effective methods for predicting the state of the mountain range in complex mining and geological conditions of both the Karaganda coal basin and other coal basins with a complex geological structure. Initially, seismic surveys were performed using the method of reflected waves using the common depth point method. However, the problem of obtaining an objective image of the geological environment is still relevant, due to the peculiarities of elastic wave excitation in mine conditions (features of the generated wave field, patterns of its propagation, the direction of the source). The method of mine seismic survey based on channel and boundary waves registration was developed and applied. This method allows obtaining a detailed geological and geophysical model of the field site. Due to the processing of both types of waves, the resolution of the method is increased to obtain information about both the coal bed and the host rocks, and, in particular, the state of the roof of the formation. The method of measurements in mine conditions is presented, the results of testing the method of performing field work in mine conditions are shown, and seismic characteristics with high contrast and clear traceability of reflecting boundaries are obtained.

An Image Processing Method for Extraction of the Stress Wave Reflection Period

The stress wave reflection method is widely used in the detection of structure size and integrity due to its advantages of low environmental impact and convenience. The detection accuracy depends on the accurate extraction of the stress wave reflection period. The traditional peak–peak method (PPM) measures the time interval between the first two peaks of the reflected waves to extract the reflection period. However, human interpretation is not avoidable for identifying the weak peak due to signal energy leaks into the surrounding environment. This paper proposes an algorithm for automatic extraction of the stress wave reflection period based on image processing to avoid human interference. The image is the short-time Fourier transform (STFT) spectrogram of the reflected wave signal after applying wavelet denoising and quadratic self-correlation operations. The edge detection method of image processing is used to extract the periodically occurring trough in the image. Graying and filtering are performed to eliminate interference. The frequency of the trough distribution is calculated by using the fast Fourier transform (FFT), and then the reflection period of the stress wave is obtained. The effectiveness and accuracy of the proposed method are validated by measuring the different lengths of two buried metal piles in soil. Comparing with the existing method of extracting the stress wave reflection period, this new algorithm comprehensively utilizes the time–frequency domain information of the stress wave reflection signal.

Study on cable fault location based on fast identification of starting point of reflection wave

Traveling wave reflection method is widely used in cable length measurement and fault location. How to effectively remove noise interference and accurately identify the starting point of pulse reflection is the key problem to be solved by this method. In this paper, two new methods, the improved weighted coefficient method based on the wavelet theory and the curve fitting method, are proposed for different identification accuracy and velocity by analyzing the measured reflected wave signal. The improved weighted coefficient method was used to process the traditional denoising threshold with the same value of ± thr, and then the calculated weighted threshold was used to reduce the noise of the measured signal, so as to highlight and identify the starting point of reflection pulse. The curve fitting method is adopted to compare the reflected wave anomaly with the threshold value of the corresponding length cable. If the threshold value is exceeded, the fault reflection can be judged as fault reflection. Then the quadratic function fitting is carried out here, and the starting point of the reflected pulse is directly determined by using the intersection point of the quadratic curve and the reference voltage. The experimental and simulation results show that the improved weighted coefficient method solves the problems of unsmoothness of denoising and discontinuity of derivative of denoising function, improves the accuracy of identifying the starting point of reflection wave, provides a new algorithm for improving the measurement accuracy. The curve fitting method has high speed, low demand for hardware, and the error can be controlled within 10ns, which is more suitable for low-cost equipment based on Microcontrollers.

Continuous strength measurements of cement pastes and concretes by the ultrasonic wave reflection method

Concrete compressive strength is a critical design criterion for concrete elements and should, as a consequence, be carefully controlled to ensure structural integrity and intended functionality. As the cementitious binder of concrete hydrates, its strength and elastic modulus increase with time as concrete transitions from a fluid with suspended particles to a rigid but porous solid. Porosity of the material decreases as hydration products fill available space to create a densified structure. Ultrasonic instruments are able to continuously measure the material properties of cementitious materials. This is a significant advantage over destructive, quasi-static compression test of cylinders or cubes at discrete time intervals. Here, we estimate the elastic modulus and compressive strength of a cement paste or concrete from the amplitude of a reflected ultrasonic wave. A series of cement pastes and concretes are tested in quasi-static compression to establish a correlation between compressive strengths estimated from ultrasonic methods and classical compression test. The differences between the compressive strengths obtained by quasi-static compression tests and ultrasonic wave reflection differ by ±20% over a range of compressive strengths spanning more than 3 decades.

Deep structure of the Anapa flexural-rupture zone, Western Caucasus

In the period from 2007 to 2017 complex geological and geophysical studies were carried out in the three largest flexural-rupture fault zones in the North-West Caucasus (Anapa, Akhtyrka and Moldavan). The micro-seismic sounding (MSM) was used as the main geophysical method. Studies with the help of MSM allowed us to identify the features of the deep structure of the earth’s crust in the study area and to associate them with specific tectonic structures on the surface.The binding was carried out by harmonizing the results of the MSM and the parameters of the section of the sedimentary cover and crustal boundaries according to the drilling data and the work previously performed by the reflected wave method (MOVZ). It was found that the Anapa flexure and longitudinal tectonic zones have clear deep roots, and also separate the pericline of the North-Western Caucasus from the Taman Peninsula and from the lowered blocks of the Northern slope of the folded system.Faults in the study area are divided into: (1) deep faults of the Caucasian stretch, penetrating into the lower crust and even to the upper mantle, and (2) near-surface faults, do not extend to the depths beyond the thickness of the sedimentary cover. The seismogenic role of these tectonic disturbances in the studied seismically active region has been determined.

Deep Structure of the Anapa Flexural–Rupture Zone, Western Caucasus

In the period from 2007 to 2017 complex geological and geophysical studies were carried out in the three largest flexural-rupture fault zones in the North-West Caucasus (Anapa, Akhtyrka and Moldavan). The micro-seismic sounding (MSM) was used as the main geophysical method. Studies with the help of MSM allowed us to identify the features of the deep structure of the earth’s crust in the study area and to associate them with specific tectonic structures on the surface.The binding was carried out by harmonizing the results of the MSM and the parameters of the section of the sedimentary cover and crustal boundaries according to the drilling data and the work previously performed by the reflected wave method (MOVZ). It was found that the Anapa flexure and longitudinal tectonic zones have clear deep roots, and also separate the pericline of the North-Western Caucasus from the Taman Peninsula and from the lowered blocks of the Northern slope of the folded system.Faults in the study area are divided into: (1) deep faults of the Caucasian stretch, penetrating into the lower crust and even to the upper mantle, and (2) near-surface faults, do not extend to the depths beyond the thickness of the sedimentary cover. The seismogenic role of these tectonic disturbances in the studied seismically active region has been determined.

Non-destructive testing on anchorage quality of hollow grouted rock bolt for application in tunneling, lessons learned from their uses in coal mines

Hollow grouted rock bolts are widely used to reinforce the surrounding rock mass in underground engineering, such as deep roadway of coal mines, deep tunneling. The anchorage capacity of hollow grouted rock bolts greatly influences the support quality. However, the anchorage capacity of hollow grouted rock bolt is usually destructively measured. In this paper, the grout ratio, defined as ratio of the grouted volume to the over-coring volume of anchorage, is introduced to measure the anchorage capacity. The quantitative relationship between the grout ratio and anchorage capacity of hollow grouted rock bolt by pull-out tests is established. Then, the non-destructive inspection on grout ratio of anchorage for hollow grouted rock bolts by stress wave reflection method is theoretically and experimentally investigated. By combining the two steps, a new non-destructive inspection method on anchorage quality of hollow grouted rock bolts is proposed. The results indicate that: (i) The anchorage capacity increases with the grout ratio increases up to 75% beyond which the benefits are lessened. (ii) The stress wave propagating along the bolt rod reflects and transmits at each interface impedance mismatch. The reflected signals can be used to identify the start and end of anchorage, and void part in anchorage. (iii) The results of wavelet transform analysis indicate the low-pass filters employed to reflected signals can be used to identify the start of anchorage, while the high-pass filters can identify the void part and the end of anchorage. (iv) A new supporting capacity monitoring method combined with pull-out tests and non-destructive method on hollow grouted rock bolts has been proposed, which can be used to inspect the on-site hollow grouted rock bolts in roadway on a large scale.

Особенности применения способа шахтной сейсморазведки на поперечных волнах с разделением отражений

The purpose of the study has been to investigate the character of distortion of the reflected signals from different semispaces using the reflection separation procedure. The knowledge of the distortion character and influencing parameters makes it possible to select an effective method of field works and processing. The article presents the underground seismic survey results obtained using the reflected wave method, i.e. common depth point procedure. In the frames of the method, with the participation of the author, an underground seismics method using shear waves with reflection separation has been developed and tested at the Verkhnekamskoye potash salt deposit. With the reflection separation, the signal distortion depends mainly on the distance between the source points lines. Following the direct task of seismic survey, the signals have been modeled for different distances between the reception lines. The study has shown clear regularities in the effect of the distance between the source point lines on the characteristics of the separated reflected signals. The quality of the signal suppression virtually independent on the distance between the source points lines. For an enhanced signal, it is the opposite: depending on the distance between the source point lines, both the signal amplitude and phase get distorted. The signal length also changes: when enhancing the signal coming from below, the elongation happens in the direction of the record beginning, and for a signal coming from above, in the direction of the record end, the quality of signal suppression being almost in no dependence to anything. Vice versa, an enhanced signal is subject to any kind of distortion when the distance between the source point lines changes. Based on the research results, it is possible to choose a distance that provides optimum reflection separation corresponding to a research task.

Reliability study on the application of reflected wave method in integrity test of pre-stressed pipe pile

Reliability study on the application of reflected wave method in integrity test of pre-stressed pipe pile