Surface Wave Measurements Research Articles

Automated Surface Wave Measurements for Evaluating the Depth of Surface-Breaking Cracks in Concrete

The primary objective of this study is to investigate the feasibility of an innovative surface-mount sensor, made of a piezoelectric disc (PZT sensor), as a consistent source for surface wave velocity and transmission measurements in concrete structures. To this end, one concrete slab with lateral dimensions of 1500 by 1500 mm and a thickness of 200 mm was prepared in the laboratory. The concrete slab had a notch-type, surface-breaking crack at its center, with depths increasing from 0 to 100 mm at stepwise intervals of 10 mm. A PZT sensor was attached to the concrete surface and used to generate incident surface waves for surface wave measurements. Two accelerometers were used to measure the surface waves. Signals generated by the PZT sensors show a broad bandwidth with a center frequency around 40 kHz, and very good signal consistency in the frequency range from 0 to 100 kHz. Furthermore, repeatability of the surface wave velocity and transmission measurements is significantly improved compared to that obtained using manual impact sources. In addition, the PZT sensors are demonstrated to be effective for monitoring an actual surface-breaking crack in a concrete beam specimen subjected to various external loadings (compressive and flexural loading with stepwise increases). The findings in this study demonstrate that the surface mount sensor has great potential as a consistent source for surface wave velocity and transmission measurements for automated health monitoring of concrete structures.

The acquisition and measurement of surface waves of high-speed liquid jets.

The instability analysis of the liquid jet issuing into ambient air was conducted with an emphasis placed upon the evolution of surface waves of the jet. An experiment was designed to visualize the microscopic morphology on the surface of a liquid jet. A spectral method was proposed to measure wavelength from the obtained jet images. We also discuss key setup parameters that significantly affect the resolution of desired jet features and the accuracy of the spectral measurement. The results show that the liquid jet near the nozzle exit can be divided into a laminar section, a transition section, an instability section, and a turbulence section. Surface wave scales range from 0.06 to 0.11 times of the nozzle diameter with the atomization breakup regime. For the atomization breakup regime, the growth ratio of the surface waves of the instability section is 0.06 which is 1.5 times the value of the second wind-introduced breakup regime and 3 times the value of the first wind-introduced breakup regime.Graphical abstract

Interstation phase speed and amplitude measurements of surface waves with nonlinear waveform fitting: application to USArray

Interstation phase speed and amplitude measurements of surface waves with nonlinear waveform fitting: application to USArray

The Reliability of Low Cost Data Logger for Active Seismic (Surface-Wave) Data Measurements

Seismic data acquisition needed a relatively fast data logger and multi channels input capability. For this purpose, we construct a measuring instruments based on low cost voltage data logger DI710ULS from DATAQ. The sensors (geophones) have 4.5 [Hz] natural frequency, produce an alternating electric voltage at rate 28 [V/m/s]. The ground shaking / velocity rate of active seismic surface-wave measurement from 5 kg hammer, at 3m distances, is less than 2 [mm/s]. This will produce an alternating voltage at less than 100 [mV].The active seismic surface wave measurements need around 1 ms time sampling for every channels and this instruments can record 7200 data for 8 differential channels, which is sufficient for this purpose. The DI710ULS has a standalone capability and all digital data were recorded in SDcard, whose very light and compact for field acquisition. By only 14[bit] DAC, the data shows reliable and seems good enough by 12.2 [μV] sampling. The data collected by using this data logger were successfully processed for surface wave analysis, and giving a reasonable result.

Ocean surface wave measurements from fully polarimetric SAR imagery

A new method for the retrieval of ocean wave parameters from SAR imagery is developed, based on the shape-from-shading (SFS) technique. Previously, the SFS technique has been used in the reconstruction of 3D landform information from SAR images, in order to generate elevation maps of topography for land surfaces. Here, in order to retrieve ocean wave characteristics, we apply the SFS methodology, together with a method to orient the angular measurements of the azimuth slope and range slope, in the measurement of ocean surface waves. This method is applied to high resolution fine-quad polarization mode (HH, VV, VH and HV) C-band RADARSAT-2 SAR imagery, in order to retrieve ocean wave spectra and extract wave parameters. Collocated in situ buoy measurements are used to validate the reliability of this method. Results show that the method can reliably estimate wave height, dominant wave period, dominant wave length and dominant wave direction from C-band SAR images. The advantage of this method is that it does not depend on modulation transfer functions (MTFs), in order to measure ocean surface waves. This method can be used in monitoring ocean surface wave propagation through open water areas into ice-covered areas, especially the marginal ice zone (MIZ) in polar oceans.

Evaluation of site effect within the tectonic basin in the northern side of Ankara

This study mainly concentrates on the determination of site effects for the Plio-Quaternary and especially alluvial soils of the Çubuk district and its close vicinity in Ankara, Turkey. In the study area, particularly in the vicinity of the asymmetric graben that has formed due to the tectonic activities along the NE–SW trending normal faults, a microtremor survey was implemented to identify the local site response under a possible seismic event. The results were compared and correlated by using passive and active surface wave measurements, engineering geological and geotechnical deep borehole logs along with information on local geology and geological tectonic setting. Regarding the microtremor results, larger fundamental periods were acquired than expected over the area and the effect of the tectonic deformation on the stiffness of the soils was also observed at either the H/V curves or the shear wave velocity profiles. The results have demonstrated that geotechnical information down to a depth of 30m may not be compared with the H/V parameters. The H/V amplitudes were not always accompanied with the higher periods in the Quaternary sediments. This could be due to the basin and basin edge effects observed particularly at the center and boundary of the basin, respectively. Additionally, the microtremor survey showed that the spectral ratio amplitudes derived by the H/V ratio are debatable and are not a direct indicator of local soil behavior under a seismic excitation.

Surface Wave Measurements from Subsurface Floats

AbstractPressure gradient measurements on a subsurface Lagrangian float are used to measure the spectrum of surface waves for 100 days of measurements at Ocean Weather Station Papa. Along Lagrangian trajectories of surface waves, the pressure is constant and the vertical pressure gradient fluctuations equal the Eulerian fluctuations at the mean float depth to second order in wave height. Measurement of the pressure difference between the top and the bottom of the float can thus be used to measure the waves. Corrections for the wave decay with depth, for the vertical motion of the float, for the finite sampling interval, and for the sampling noise (among others) are necessary to obtain accurate results. With these corrections, scalar spectra accurately match those from a nearby Waverider buoy for significant wave heights greater than about 3 m. For smaller wave heights, noise in the pressure measurements biases the float spectral measurements. Significant wave height is measured with an rms error of 0.37 m over the measured range of 1–9 m. This demonstrates that Lagrangian floats accurately follow the Lagrangian trajectories of surface waves. More detailed and quieter measurements of float motion could likely measure directional wave spectra from below the surface. Similar methods could be used to infer surface wave properties from other subsurface vehicles.

Firmness evaluation of watermelon flesh by using surface elastic waves

We measured the velocity of surface elastic waves on watermelon flesh for firmness evaluation. The Rayleigh waves at frequencies ranging from 800 to 2400Hz propagate on the flesh and are detected by a piezo-bimorph sensor in contact with the flesh. We determined the shear elasticity from the velocity for two types of Japanese watermelons, Matsuribayashi777 and Wasenissho, to be 1.18 and 0.74MPa, respectively. These correlated well with a sensory firmness evaluation. The values of Young modulus obtained by the surface-wave measurements were nine times larger than those by the compression tests performed, which can be explained by the differences in measurement displacement and frequency. We also investigated the effect of storage on the surface-wave velocity for Matsuribayashi777. The velocity decreased by about 10% after ten days of storage. The present results suggest that this technique can be applied to estimating the elastic properties of various fruits.

Numerical Simulation of Laser Ultrasonic Surface Wave Measurement of Residual Stress

The propagation of surface wave which induced by the laser ultrasonic shock processing was simulated in half-space elastic materials by ABAQUS software. First,the effect of laser shock processing was equivalent to a modulated Gaussian pulse. To eliminate the undesirable reflections from boundary edges,the infinite elements were placed along the appropriate edges of the model.The received waves agree with the Rayleigh surface waves. Secondly, the effective elastic modulus method was introduced to simulate the initial residual stress in the surface region.Detection of surface velocity based on ultrasonic time-difference method was introduced. The numerical value and theory well fit experimental datas, which provid a way of using laser ultrasonic to measure of the residual stress.

Application of the Surface Wave Survey Method on Multi-Scale Engineering Problems: Laboratory and Field Testing Case Studies

Abstract The geometric dispersion of surface waves offers the feature to infer the properties of a medium. The surface wave survey method is under continuous evolution and its applications include the noninvasive characterization of a medium at a small scale and the earthquake geotechnical survey at a large scale. Despite the significant difference in scales, these applications generally utilize the propagation of the surface waves along the boundary of a layered medium. This paper discusses standard steps involved in surface wave surveys. Two application case studies are conducted and presented in detail. In the small scale laboratory application case, a nondestructive testing (NDT) methodology is proposed for the coating investigation using laser interferometric measurements of surface waves. In the large scale field application, an accelerometer-based passive surface wave survey is designed for earthquake geotechnical engineering site characterization. Finally, recommendations for practical application of surface waves in multi-scale engineering problems are presented.

Surface Current and Wave Measurement during Cyclone Phailin by High Frequency Radars along the Indian Coast

Cyclone Phailin originated in the east central Bay of Bengal (BoB) and crossed into the Indian mainland after traversing through the BoB. High frequency radar (HFR) operated by the National Institute of Ocean Technology could track the surface currents and high wave activity within its measuring limits. The radar data provide valuable information on the surface dynamics during the cyclone period. The HFR observations compare well with those of wave rider buoy. This opens up opportunities for observing the wave conditions during the cyclonic period over longer distances from the shore. This method is relatively more robust as HFR is less likely to be disrupted due to the passage of cyclones, unlike moored systems.

Simultaneous in-situ Stiffness and Anomalies Measurement on Pavement Subgrade Using Tomography Surface Waves Technique

Non-destructive testing (NDT) has been developed as a effective tool in road evaluation system in order to in-situ assess the stiffness parameter of pavement layer, partcularly in conducting a quick assessment on soil subgrade layer. The NDT method based on the seismic surface wave measurement has been recently developed and applied for material evaluation of road-pavement, i.e. the shear wave velocity, Poisson's ratio and dynamic elastic modulus. In this paper, an improved technique of tomography surface waves measurement for simultaneously evaluation of stiffness and anomalies of pavement soil-subgrade is presented. The method performs the time-frequency spectrum analysis on recorded seismic wave data, which is non-destructively sampling the subgrade layers properties. An interactive wavelet analysis is used in the spectrum analysis to produce the real phase velocity and its corresponding shear wave velocity. Using principal of stress-strain material in elastic behavior, the elastic modulus parameter of soil-subgrade layers is then generated. This method is improved for producing the 2-D elastic modulus profile and at the same time, it shows the structure anomalies in the investigated subgrade layers. The higher elastic modulus values can be found in the subgrade layer with more homogeneous soil densities that may be produced from a good degree of compaction. While the lower elastic modulus can be identified in the subgrade layers which are having many structural anomalies. From this study, it can be shown that the tomography seismic surface wave technique is able to simultaneously determine the stiffness and structure anomalies within existing road pavement. Thus, this method can be potentially advanced and developed as an innovative material evaluation device for pavement structures.

The effect of bedding errors on the accuracy of plate load tests

During conventional plate load tests the stiffness of the ground is determined by measuring the settlement of a plate placed on the ground surface. If the contact between the plate and the ground is rough, bedding errors may occur during the test when plastic deformation occurs at the contacts between the plate and the ground. This paper addresses the effect of bedding errors on the accuracy of plate load tests. Three different surface preparation methods were investigated. In addition, a modified plate load test was designed to eliminate the effect of bedding errors that occur during these tests. Telescopic probes were used to measure the relative displacement at two points below the centre of the plate. The stiffness values, determined from the vertical displacement of the plate, were compared with the internal stiffness values determined by means of the telescopic probes. All stiffness values were compared with Continuous Surface Wave (CSW) measurements performed on the same material. The test apparatus, methods and results are discussed in this paper.

The Effect of Shallow Quaternary Deposits on the Shape of the H/V Spectral Ratio

In the last two decades, the horizontal-to-vertical (H/V) spectral ratio of seismic noise technique has been widely used for site-effect estimation and geophysical exploration through the soil fundamental frequency. Usually, only one peak is observed in the H/V spectral ratio, but in some cases, a second peak can also be obtained. Nevertheless, to date, the peaks at higher frequencies are rarely studied in detail. Geological and geophysical data are especially needed to better explain the presence of this second peak, which normally is neglected. An extensive survey of H/V measurements was conducted in the Llobregat river delta, located to the south of Barcelona. At most sites, two clear peaks were identified: one at low frequencies ( 1 Hz). To understand this behaviour, a seismic noise array and active surface wave measurements have been conducted to obtain a shear-wave velocity profile (V s) up to the bedrock. Two impedance contrasts have been detected: the first one at a shallow depth and the second one between the soft sedimentary cover and the bedrock. During the modelling process, the theoretical H/V computed from the obtained V s models fits well with the experimental H/V peaks. The results from this study show that the structure of shallow quaternary layers can clearly change the shape of the H/V ratio, producing two clear peaks in some situations. In this case, the contact between the low-velocity clay layer and the gravels with a high seismic wave velocity produces a shallow impedance contrast related to the second peak observed in the H/V ratio. Comprehension of these secondary peaks could avoid a misreading of the soil fundamental frequency that could produce errors in a site-effect evaluation or in the calculation of the bedrock depth. Finally, we show that passive seismic techniques provide the quaternary overburden and bedrock geometry in urban areas and allow for the limitations of other geophysical techniques in these environments to be overcome.

An explicit relation for the apparent phase velocity of Rayleigh waves in a vertically heterogeneous elastic half-space

S U M M A R Y This paper presents the mathematical derivation of an explicit relation for the apparent (or effective) phase velocity of Rayleigh waves in a vertically heterogeneous, isotropic elastic half-space for harmonic excitation. As a kinematical feature, the apparent phase velocity captures the superposition, in a spatial Fourier series, of the individual modes of propagation of Rayleigh waves and describes the speed of propagation of a composite waveform generated by a vertically oscillating point load. The relation, which is a function of the distance from the source, frequency and depth, depends explicitly on the modal phase and group velocities of Rayleigh waves, and their corresponding wavenumbers and eigenfunctions, which can be computed directly from the solution of the Rayleigh-wave eigenproblem. A practical scenario for the application of the notion of apparent Rayleigh-wave phase velocity is the modelling of the dispersion curve in the well-known surface wave measurement methods ‘spectral analysis of surface waves’ (SASW) and ‘multichannel analysis of surface waves’ (MASW). Apart from a theoretical motivation, the availability in surface wave testing of an explicit formula for the calculation of the apparent Rayleigh-wave phase velocity may lead to the development of a new class of inversion algorithms capable of taking into account the influence of all the modes of surface wave propagation. To demonstrate the exactness of the explicit relation, the predicted values of apparent phase velocity are compared to those computed synthetically from a numerical simulation of SASW and MASW testing for three case studies, which show both single as well as multiple mode dominance effects.

Comparison of Poroviscoelastic Models for Sound and Vibration in the Lungs

Noninvasive measurement of mechanical wave motion (sound and vibration) in the lungs may be of diagnostic value, as it can provide information about the mechanical properties of the lungs, which in turn are affected by disease and injury. In this study, two previously derived theoretical models of the vibroacoustic behavior of the lung parenchyma are compared: (1) a Biot theory of poroviscoelasticity and (2) an effective medium theory for compression wave behavior (also known as a "bubble swarm" model). A fractional derivative formulation of shear viscoelasticity is integrated into both models. A measurable "fast" compression wave speed predicted by the Biot theory formulation has a significant frequency dependence that is not predicted by the effective medium theory. Biot theory also predicts a slow compression wave. The experimentally measured fast compression wave speed and attenuation in a pig lung ex vivo model agreed well with the Biot theory. To obtain the parameters for the Biot theory prediction, the following experiments were undertaken: quasistatic mechanical indentation measurements were performed to estimate the lung static shear modulus; surface wave measurements were performed to estimate lung tissue shear viscoelasticity; and flow permeability was measured on dried lung specimens. This study suggests that the Biot theory may provide a more robust and accurate model than the effective medium theory for wave propagation in the lungs over a wider frequency range.

Field investigation and model tests on differential settlement of houses due to liquefaction in the Niigata-ken Chuetsu-Oki earthquake of 2007

A massive earthquake struck the Niigata Chuetsu-Oki region of Japan on July 16th, 2007, claiming 11 lives and damaging about 6000 houses. The earthquake had a magnitude of 6.8, with data from an accelerograph managed by a nationwide strong-motion observation network known as Kyoshin Net (K-net) showing a maximum value of 668gal (NS). In the Matsunami district of Kashiwazaki city (located on land filled and developed as a residential area from around 1970 onward) about 3km northeast of Kashiwazaki Railway Station, many houses were damaged due to liquefaction. A field investigation, including a boring survey, surface wave exploration and measurement of differential settlement of houses knocked aslant by soil liquefaction, was conducted to determine the relationship between the extent of damage to houses and the area׳s geological structure. It was found that most houses severely damaged due to liquefaction were located around the boundary between sand dunes and the local river delta. Additionally, the relationships linking sloping geological structure, the thickness of the liquefaction layer and total/differential settlement of houses were clarified from the results of shaking table model tests conducted in this study. Test results showed that it is important to consider multidimensional influences caused by sloping geological structure in the estimation method of liquefaction potential in order to predict and assess degree of damage to houses due to liquefaction.

Experiments of ocean surface waves and underwater target detection imaging using a slit Streak Tube Imaging Lidar

This letter describes a flash Lidar imaging technique that uses a streak tube camera as a receiver to detect short scale surface wave fields for oceanographic, underwater target and coastal measurements. The range and intensity imaging of short scale sea-waves and underwater targets can be supplied by this system through light reflected from the surface of the sea and targets. Through a surface scattering model, more accurate range and intensity information can be extracted. The technique can be applied to surface wave measurements and underwater target detection with high resolution. The feasibility of this technique is demonstrated by applying the technique to data acquired by shipborne Streak Tube Imaging Lidar (STIL) in the Yellow Sea and also the East and South China Seas.

Surface Wave-Based Health Monitoring Method for a Sheet Pile Quay Wall

Port structures such as pile supported piers and quay walls generally face severe conditions, and deterioration of port structures is often observed. For an example, at a sheet pile quay wall, sheet pile is a structural component which is easily deteriorated by corrosion. As a result of deterioration of sheet pile, the backfilled soil would be washed out due to the tidal action. Suffusion, the phenomena of the washed out of fine particles and loosening of soil layer, is a problem to be considered in the maintenance of a quay wall. Therefore, a health monitoring method for the backfill of a sheet pile quay wall is necessary. In this study, the applicability of a surface-wave method for health monitoring of a sheet pile quay wall was examined. First, the variation of shear wave velocity in the ground due to suffusion and variation in water content is measured from bender element tests. Then, 2D finite element method (FEM) dynamic analysis was conducted to simulate a surface-wave measurement on a sheet pile quay wall. From the result of the analysis, the estimated shear wave velocity profile based on surface-wave method agrees fairly well with the assumed soil profile. Finally, surface-waves were measured at a sheet pile quay wall, and the measured results were compared with the result of Swedish weight sounding test at the site. Furthermore, the difference between the shear wave velocity profiles at ebb tide and that at high tide was successfully measured by the surface-wave method. Thus, the applicability of the surface-wave method for a sheet pile quay wall is demonstrated in this study.

Air-coupled detection of nonlinear Rayleigh surface waves to assess material nonlinearity

This research presents a new technique for nonlinear Rayleigh surface wave measurements that uses a non-contact, air-coupled ultrasonic transducer; this receiver is less dependent on surface conditions than laser-based detection, and is much more accurate and efficient than detection with a contact wedge transducer. A viable experimental setup is presented that enables the robust, non-contact measurement of nonlinear Rayleigh surface waves over a range of propagation distances. The relative nonlinearity parameter is obtained as the slope of the normalized second harmonic amplitudes plotted versus propagation distance. This experimental setup is then used to assess the relative nonlinearity parameters of two aluminum alloy specimens (Al 2024-T351 and Al 7075-T651). These results demonstrate the effectiveness of the proposed technique – the average standard deviation of the normalized second harmonic amplitudes, measured at locations along the propagation path, is below 2%. Experimental validation is provided by a comparison of the ratio of the measured nonlinearity parameters of these specimens with ratios from the absolute nonlinearity parameters for the same materials measured by capacitive detection of nonlinear longitudinal waves.