Relative Velocity Changes Research Articles

A novel ultrasonic-velocity-based concrete carbonation monitoring method based on step-wise stretching technique

Carbonation is a common and slow process that occurs in cement-based material, resulting in durability degradation of reinforced concrete structures. In this research, the relative velocity change (d v/ v) of both ultrasonic direct waves and coda waves are extracted based on the step-wise stretching method for concrete carbonation monitoring. To this end, two-dimensional mesoscale models are established to investigate the ultrasonic propagation behaviors and assess the effectiveness of direct waves and coda waves on concrete carbonation monitoring. The numerical results indicate that direct waves could evaluate the initial carbonation, but exhibit limited sensitivity for severe carbonation. Conversely, the d v/ v values of coda waves show a linear correlation with carbonation depth in all conditions. Accelerated concrete carbonation experiments are conducted to validate the numerical findings. The experimental results and numerical findings mutually corroborate, validating the effectiveness of velocity changes of coda waves on all-stage concrete carbonation monitoring. This research contributes a novel method for monitoring concrete carbonation and enhances the understanding of ultrasonic wave propagation in concrete.

Influence of aggregate size on relative velocity change of high-frequency ultrasound in progress of concrete curing

Previous research revealed that wave interferometry can be more effective than existing ultrasonic techniques in monitoring the strength development of early-age concrete. To improve its accuracy, this study aims to examine the impact of aggregate size on the relative velocity change of high-frequency ultrasound during the concrete curing process. Concrete cubic specimens with 150 mm sides were prepared using two different maximum aggregate sizes, 4.75 mm and 20 mm. These specimens were subjected to water curing for the first 28 days, followed by air curing until 150 days. Ultrasonic tests employing a 1 MHz frequency were performed throughout the curing process, and the measured signals were analyzed by applying wave interferometry techniques. The test results suggest that the influence of aggregate size was evident in both the initial water curing and the subsequent air curing. During the initial curing, the specimen with larger aggregates exhibited a greater increase in relative velocity change. Thereafter, the velocity change decreased during the subsequent air curing in both specimens. Based on the results, the correlation between relative compressive strength and relative velocity change was proposed considering the maximum aggregate size. The findings offer insights into the use of ultrasonic methods to evaluate the characteristics of early-age concrete.

Quantitative evaluation of bolt pre-load using coda wave interferometry and nonlinear coda wave interferometry: a comparative study

AbstractThe quantitative evaluation of bolt pre-load is crucial for the maintenance and prevention of accidents in bolt-connected structures. This study introduces the coda wave interferometry (CWI) method and the nonlinear coda wave interferometry (NCWI) method for quantitative evaluation of bolt pre-load. Experimental tests across three different scales of bolt pre-load changes were conducted on a bolt to compare the performances of CWI and NCWI in the quantitative evaluation of bolt pre-load. The results demonstrate that both CWI and NCWI can effectively characterize changes in bolt pre-load. For CWI, the relative velocity change (∆v/v) exhibits a linear relationship with the bolt pre-load. Meanwhile, for NCWI, the effective nonlinear level, denoted as $${\alpha }_{\Delta v/v}$$ α Δ v / v , demonstrates a quadratic dependence on the bolt pre-load. In CWI, the calculation of ∆v/v is dependent on the correlation coefficient between the coda waves of signals before and after bolt pre-load changes. It is prone to failure when there are significant changes in bolt pre-load. Conversely, NCWI demonstrates enhanced robustness in evaluating bolt pre-load changes across a range of magnitudes.

Relative Seismic Velocity Variations at Axial Seamount Observed With Ambient Seismic Noise Capture Transition Point in Volcanic Inflation

AbstractTemporal changes in seismic velocity estimated from ambient seismic noise can be utilized to infer subsurface properties at volcanic systems. In this study, we process 7 years of continuous seismic noise at Axial Seamount and use cross‐correlation functions to calculate the relative seismic velocity changes (dv/v) beneath the caldera. We find a long‐term trend of decreasing velocity during rapid inflation, followed by slight increase in velocities as background seismicity increases and inflation rate decreases. Furthermore, we observe small short‐term increases in dv/v which coincide with short‐term deflation events. Our observations of changes in dv/v and their correlation with other geophysical data provide insights into how the top ∼1 km of the crust at Axial Seamount changes in response to subsurface magma movement and capture the transition from a period of rapid reinflation to a period where the caldera wall faults become critically stressed and must rupture to accommodate further inflation.

A novel strategy of concrete monitoring: The application of the integrated sensing element (ISE)

This study strategically provides an innovative pattern for concrete monitoring at the service and deterioration stages by the integrated sensing element (ISE). The advantage of the ISE is that it can independently respond to loading variation and cooperate with other sensors. The results show that the ISE can independently identify the cracking state, monitor stress conditions, and distinguish the creep behavior of concrete with different compressive strength levels. By applying this novel monitoring pattern, the relationships between stress and relative velocity change (∆v/v) can be accurately traced; meanwhile, concrete with different creep degrees can be identified. Additionally, by tracing the de-correlation coefficients (Kd), this study also reveals that the binding behavior between sensors and concrete has a significant impact on signal variation. Specifically, the maximum Kd value derived from the signal of ISE at the loading process (46.5% of the maximum uniaxial compressive strength) is lower than 0.1, while that value derived from the signal of the conventional contact transducers can exceed 0.5. At a short-time fixed loading experiment, the Kd values derived from the signal of ISE show no significant increasing trend.

Effectiveness of wave interferometry in monitoring strength and stiffness development of early-age concrete

With the aim of developing a nondestructive technique for monitoring the progression of the strength and stiffness of early-age concrete, this research investigated the effectiveness of wave interferometry in such applications. Lab-scale concrete specimens with a water/cement ratio of 0.45 were cast and subjected to water or air curing. The microstructural evolution of early-age concrete along the curing process was characterized by employing ultrasonic and mechanical parameters. The wave interferometry results showed that the relative velocity change had a gradual increase of 8.9% and 5.2% from 1 to 28 days of curing in water- and air-cured samples, respectively. Accordingly, the relative velocity change exhibited a strong correlation with the compressive strength as well as the modulus of elasticity. In addition, wave interferometry sensitively differentiated the effects of the two curing methods.

An enhanced ultrasonic method for monitoring and predicting stress loss in multi-layer structures via vibro-acoustic modulation

A sensitivity and reliability enhanced ultrasonic method for monitoring and predicting stress loss in pre-stressed multi-layer structures is developed in this study. The enhancement is based on the idea of leveraging the potential breathing effect of porous cushion materials in the structures to increase the sensitivity of the signal feature to stress loss, and is achieved via vibro-acoustic modulation by mixing a low-frequency pumping wave and an ultrasonic probing wave. A mathematical model correlating the stress state with the relative change in velocity of the coda portion of the received wave is derived. A pre-stressed five-layer mockup structure made of three materials with vastly different properties is manufactured and used for experimental investigation. Different stress states are simulated by bolting the structure with prescribed torques. Data are acquired for model calibration and verification. Independent data are further acquired to validate the prediction performance of the proposed method using the calibrated model. A thorough comparison between the proposed method and the conventional method is made. Results show that the proposed method offers improved accuracy, reliability, and sensitivity to stress change.

Continuous isolated noise sources induce repeating waves in the coda of ambient noise correlations


 Continuous excitation of isolated noise sources leads to repeating wave arrivals in cross correlations of ambient seismic noise, including throughout their coda. These waves propagate from the isolated sources. We observe this effect on correlation wavefields computed from two years of field data recorded at the Gräfenberg array in Germany and two master stations in Europe. Beamforming the correlation functions in the secondary microseism frequency band reveals repeating waves incoming from distinct directions to the West, which correspond to well-known dominant microseism source locations in the Northeastern Atlantic Ocean. These emerge in addition to the expected acausal and causal correlation wavefield contributions by boundary sources, which are converging onto and diverging from the master station, respectively. Numerical simulations reproduce this observation. We first model a source repeatedly exciting a wavelet, which helps illustrate the fundamental mechanism behind repeated wave generation. Second, we model continuously acting secondary microseism sources and find good agreement with our observations. Our observations and modelling have potentially significant implications for the understanding of correlation wavefields and monitoring of relative velocity changes in particular. Velocity monitoring commonly assumes that only multiply scattered waves, originating from the master station, are present in the coda of the correlation wavefield. We show that repeating waves propagating from isolated noise sources may dominate instead, including the very late coda. Our results imply that in the presence of continously acting noise sources, which we show is the case for ordinary recordings of ocean microseisms, velocity monitoring assuming scattered waves may be adversely affected with regard to measurement technique, spatial resolution, as well as temporal resolution. We further demonstrate that the very late coda of correlation functions contains useful signal, contrary to the common sentiment that it is dominated by instrument noise.

Comparison of computational fluid dynamics with transcranial Doppler ultrasound in response to physiological stimuli.

Cerebrovascular haemodynamics are sensitive to multiple physiological stimuli that require synergistic response to maintain adequate perfusion. Understanding haemodynamic changes within cerebral arteries is important to inform how the brain regulates perfusion; however, methods for direct measurement of cerebral haemodynamics in these environments are challenging. The aim of this study was to assess velocity waveform metrics obtained using transcranial Doppler (TCD) with flow-conserving subject-specific three-dimensional (3D) simulations using computational fluid dynamics (CFD). Twelve healthy participants underwent head and neck imaging with 3T magnetic resonance angiography. Velocity waveforms in the middle cerebral artery were measured with TCD ultrasound, while diameter and velocity were measured using duplex ultrasound in the internal carotid and vertebral arteries to calculate incoming cerebral flow at rest, during hypercapnia and exercise. CFD simulations were developed for each condition, with velocity waveform metrics extracted in the same insonation region as TCD. Exposure to stimuli induced significant changes in cardiorespiratory measures across all participants. Measured absolute TCD velocities were significantly higher than those calculated from CFD (P range < 0.001-0.004), and these data were not correlated across conditions (r range 0.030-0.377, P range 0.227-0.925). However, relative changes in systolic and time-averaged velocity from resting levels exhibited significant positive correlations when the distinct techniques were compared (r range 0.577-0.770, P range 0.003-0.049). Our data indicate that while absolute measures of cerebral velocity differ between TCD and 3D CFD simulation, physiological changes from resting levels in systolic and time-averaged velocity are significantly correlated between techniques.

Relativistic dynamical friction in stellar systems

Aims.We extend the classical formulation of the dynamical friction effect on a test star by Chandrasekhar to the case of relativistic velocities and velocity distributions, also accounting for post-Newtonian corrections to the gravitational force.Methods.The original kinetic framework was revised and used to construct a special-relativistic dynamical friction formula where the relative velocity changes in subsequent encounters are added up with Lorentz transformation, and the velocity distribution of the field stars accounts for relativistic velocities. Furthermore, a simple expression is obtained for systems where the post-Newtonian correction on the gravitational forces become relevant even at non-relativistic particle velocities. Finally, using a linearized Lagrangian we derived another expression for the dynamical friction expression in a more compact form than previously used.Results.Comparing our formulation with the classical one, we observe that a given test particle undergoes a slightly stronger drag when moving through a distribution of field stars with relativistic velocity distribution. Vice versa, a purely classical treatment of a system where post-Newtonian (PN) corrections should be included, overestimates the effect of dynamical friction at low test particle velocity, regardless of the form of velocity distribution. Finally, a first-order PN dynamical friction covariant formulation is weaker its classical counterpart at small velocities, but much higher for large velocities over a broad range of mass ratios.

Neurovascular coupling in severe aortic valve stenosis.

Aortic stenosis (AS) is characterized by obstruction of blood outflow from the left ventricle, which can impair target organ perfusion such as the brain. We hypothesized that hemodynamic changes in AS may lead to dysfunction of cerebral blood flow regulatory mechanisms. The aim of our study was to evaluate neurovascular coupling in patients with AS by Transcranial Doppler ultrasonography. Neurovascular coupling was assessed using visually evoked cerebral blood flow velocity responses (VEFR) calculated as relative blood flow velocity changes in the posterior cerebral artery upon visual stimulation. We analyzed peak systolic, mean and end diastolic VEFR in 54 patients with severe AS and 43 controls in 10 consecutive cycles of visual stimulation. Repeated-measures ANOVA test was used to compare cerebral hemodynamic data by group. Patients with AS had significantly higher peak systolic (12.9%±5.6% and 10.5%±4.5%; p=.009) and mean VEFR (14.4%±5.8% and 12.2%±4.9%; p=.021) compared to controls, whereas only a tendency for higher end diastolic VEFR was observed (16.7%±6.9% and 14.4%±6.2%; p=.061). We have shown for the first time that patients with severe AS exhibit higher VEFR than controls indicating dysregulation of neurovascular coupling, which can be one of the factors contributing to development of cognitive decline.

Artificial Intelligence Aided Design of Hull Form of Unmanned Underwater Vehicles for Minimization of Energy Consumption

Abstract Designing an excellent hull to reduce the sailing path energy consumption of UUVs is crucial for improving the energy endurance of UUVs. However, path energy consumption-based UUV hull design requires a tremendous amount of calculation due to the frequent changes in relative velocity and attack angle between a UUV and ocean current. In order to address this issue, this work developed a data-driven design methodology for energy consumption-based UUV hull design using artificial intelligence-aided design (AIAD). The design methodology in this work combined a deep learning (DL) algorithm that predicts UUVs’ resistance with different hull shapes under different velocities and attack angles with the particle swarm optimization (PSO) algorithm for UUV hull design. We tested the proposed methodology in a path energy consumption-based experiment, where the optimized UUV hull showed an 8.8% reduction in path energy consumption compared with the initial UUV hull, and design costs were greatly reduced compared with the traditional computational fluid dynamics (CFD)-based methodology. Our work demonstrates that AIAD has the potential to solve UUV design problems previously thought to be too complex by offering a data-driven engineering shape (body surface) design method.

An ultrasonic coda wave method for stress loss prediction in pre-stressed strongly heterogeneous multi-layer structures

A coda wave method is proposed to predict the stress loss of pre-stressed strongly heterogeneous multi-layer structures using ultrasonic testing. The method is centered on the basis that ultrasound can be multiply scattered and form the decaying coda waves in the strongly heterogeneous multi-layer structure. As the stress loss of the pre-stressed structure can alter the inter-layer contacting state and the mechanical strain of the propagation media, the signal features subject to the stress loss can be amplified in the process of multiply scattering and encoded in the coda wave. A theoretical model is developed to evaluate the stress of the muti-layer structure using the relative change in velocity of the ultrasonic coda wave. Experimental testing is performed on a five-layer pre-stressed mockup structure made of three different materials with vastly different mechanical and physical properties. Model parameters are obtained using testing data. An independent set of testing data is used to validate the developed model. The accuracy of the model is compared with an existing reference model. Results show that the proposed method can predict the stress accurately and outperform the reference model.

Long-term ultrasonic monitoring of concrete affected by alkali-silica reaction

This article presents continuous monitoring results of alkali-silica reaction (ASR) development in concrete specimens for over 400 days using ultrasonic testing and expansion measurements. Eight concrete specimens with nonreactive aggregate (Control), reactive coarse aggregate, and reactive fine aggregates were cast with two reinforced confinement conditions. The specimens were conditioned in an environmental chamber with high temperature and humidity (38°C and 90% relative humidity) to accelerate the ASR development. A multichannel ultrasonic monitoring system was developed to collect ultrasonic signals automatically, and the expansions in three directions were measured periodically. Results showed that the relative velocity change could detect the ASR initiation in all reactive specimens and show a correlation with expansion in the early stage. However, these correlations are inconsistent for different ASR specimens, and the velocity change becomes less sensitive to ASR damage in the late stage (after 300 days). Irrecoverable velocity drop was observed during every chamber shutdown period, especially in specimens with higher levels of ASR damage. This phenomenon suggests that the nonlinear ultrasonic response caused by the ambient temperature variation may indicate the ASR damage.

Peak loads during dynamic ice-structure interaction caused by rapid ice strengthening at near-zero relative velocity

A series of ice penetration tests with a rigid structure, with controlled oscillation, and with a single-degree-of-freedom structure were performed to investigate the peak load-velocity dependence for ethanol-doped model ice during a test campaign at the Aalto Ice and Wave Tank. For the rigid structure and controlled-oscillation tests, the ice drift speed ranged between 1 and 150 mm s−1. In the controlled-oscillation tests, amplitudes of oscillation between 0.40 and 15.90 mm and frequencies of oscillation between 0.143 and 4 Hz were prescribed such that the relative velocity between ice and structure never became negative. A constant ice drift deceleration experiment with a single-degree-of-freedom structure was performed to investigate the development of frequency lock-in and intermittent crushing in the model ice and compare the results with the rigid structure and controlled-oscillation tests. It was found that the peak load-velocity dependence identified in the rigid structure tests was not always uniquely defined as identified in the controlled-oscillation tests because the loading history affected the peak load at ice failure. A rapid strengthening of the ice developed at low relative velocity and carried over to high relative velocity until the ice failure dissipated the strengthening effect. The strengthening effect, observed in the rigid structure and controlled-oscillation tests, was also observed during frequency lock-in and intermittent crushing in the single-degree-of-freedom structure test. The observations in the present study indicate that the so-called velocity and compliance effects in ice-structure interaction originate from the same strengthening effect. It then follows that peak loads on compliant structures cannot exceed peak loads on rigid structures in the same ice conditions, with the only difference being that the peak loads on compliant structures occur at apparently higher far-field ice drift speeds due to the change in relative velocity.

Monitoring Seasonal Fluctuation and Long‐Term Trends for the Greenland Ice Sheet Using Seismic Noise Auto‐Correlations

AbstractOne important feature of the Greenland Ice Sheet (GrIS) change is its strong seasonal fluctuation. Taking advantage of deployed seismographic stations in Greenland, we apply cross‐component auto‐correlation of seismic ambient noise to measure in‐situ near surface relative velocity change (dv/v) in different regions of Greenland. Our results demonstrate that dv/v measurements for most stations have less than 3 months lag times in comparison to the surface mass change. These various lag times may provide us constraints for the thickness of the subglacial till layer over different regions in Greenland. Moreover, in southwest Greenland, we observe a change in the long‐term trend of dv/v for three stations, which might be consistent with the mass change rate (dM/dt) due to the “2012–2013 warm‐cold transition.” These observations suggest that seismic noise auto‐correlation technique may be used to monitor both seasonal and long‐term changes of the GrIS.

Interaction of Air Pressure and Groundwater as Main Cause of Sub‐Daily Relative Seismic Velocity Changes

AbstractOur study investigates variations of seismic velocity that occur over short time scales of hours. We use coda wave interferometry to inspect 5 months of continuous data from a seismological array in southern Germany. This results in relative seismic velocities (dv/v) that show temporal variations on the order of 10−4. Spectra of the velocity time series contain strong daily and sub‐daily behavior indicating that the daily and sub‐daily changes in the seismic velocity are primarily caused by atmospheric tides. We also note the influence of temperature changes on daily variations, but as a second‐order effect. The explanatory model focuses on depth variations of the groundwater table, linking atmospheric pressure (loading and de‐loading the Earth's surface) to variations in seismic velocity. Our results highlight an important environmental influence on seismic velocity that needs to be considered before seismic velocity variations can be used for inspecting fluid and stress variations in situ.

Towards quantifying the effect of pump wave amplitude on cracks in the Nonlinear Coda Wave Interferometry method

In Non-Destructive Testing and Evaluation (NDT&E), an ultrasonic method called Nonlinear Coda Wave Interferometry (NCWI) has recently been developed to detect cracks in heterogeneous materials such as concrete. The underlying principle of NCWI is that a pump wave is used to activate the crack breathing which interact with the source probe signal. The resulting signal is then measured at receiver probes. In this work, a static finite element model (FEM) is used to simulate the pump wave/crack interaction in order to quantifies the average effect of the pump waves on a crack. By considering both crack opening and closure phases during the dynamic pump wave excitation, this static model aims to determine the pump stress amplitude for a given relative crack length variation due to the dynamic pump wave excitation at different amplitudes. Numerical results show, after reaching certain stress amplitude, a linear relationship between the relative crack length variation and the equivalent static load when considering a partially closed crack at its tips. Then, numerical NCWI outputs, e.g., the relative velocity change θ and the decorrelation coefficient Kd, have been calculated using a spectral element model (SEM). These results agree with previously published experimental NCWI results derived for a slightly damaged 2D glass plate.

Optimal Multichannel Stretch Factors for Estimating Changes in Seismic Velocity: Application to the 2012 Mw 7.8 Haida Gwaii Earthquake

ABSTRACT We propose new methods for assessing temporal changes in seismic velocity using the S-wave coda for repeating earthquakes and cross-correlation functions of ambient noise. For a pair of seismic waveforms representing a common source–receiver path, the relative change in path-averaged velocity over the corresponding time interval is directly proportional to the factor by which one waveform needs to be stretched or compressed with respect to the other to achieve maximum coherence. For an arbitrary number of waveforms, initial pair-wise stretch factors determined through standard approaches can be improved through solution of an overdetermined system and further refined through an iterative approach exploiting the singular value decomposition to minimize rank of the stretched waveform section. We apply this combined approach to both repeating earthquakes and ambient noise correlations for Haida Gwaii in western Canada, the site of a Mw 7.8 thrust earthquake in 2012. Optimal stretch factors for repeating earthquake families indicate that path-averaged S velocities dropped by up to 0.16% after the earthquake. Ambient noise correlations indicate that velocities dropped by between 0.26% and 0.39%, which we interpret to be more pronounced in the uppermost levels of the crust. We explore these results in terms of changes in crustal porosity and hydrogeologic conditions by considering the observation that hot spring activity on Haida Gwaii ceased following the 2012 mainshock and recovered over the next several years.

Ex-situ and in-situ investigations of the microstructural evolution of AA6082 aluminum alloy during heat treatment

The present study investigated the microstructural evolution of AA6082 aluminum alloy using ex-situ and in-situ methods. Microstructural characterization was performed for the individual steps of the heat treatment parameters. To identify the morphology and kinetics of changes in precipitation and grain, the microstructure of the alloy was examined using scanning electron microscopy/electron backscatter diffraction in combination with energy dispersive X-ray spectrometry. Analysis of the microstructural changes revealed coarser β-Mg2Si nucleation and growth activity, but it showed no changes related to grain growth or α-Al(FeMn)Si precipitation activity. Additionally, the formation of rod-shape β' precipitates was evaluated. Higher temperature promoted the growth and increase in length of β' rods and the appearance of β' rods outside of contact with the intermetallic precipitation. The influences of different isothermal holding temperatures on the relative change in signal velocity generated by a laser ultrasonics for metallurgy (LUMet) system were evaluated. The strong correlation between the findings of microstructural analysis and the results derived from ultrasonic measurement confirmed the efficacy of the novel in-situ model test for predicting microstructural changes.