2D Velocity Profiles Research Articles

Data-driven seismic prestack velocity inversion via combining residual network with convolutional autoencoder

Seismic full-waveform inversion (FWI) is a powerful imaging approach in exploration geophysics, to estimate high-resolution subsurface geophysical properties via fitting synthetic data to observed seismic records. Nevertheless, there exist several intractable issues, e.g., solution non-uniqueness, cycle-skipping phenomenon, weak robustness and high computational burden. Recently, more attention has been paid to data-driven FWI techniques based on deep neural networks. However, their success greatly depends on an ocean of training instances, which is not available in oil exploration conveniently. To cope with this situation, an effective strategy is to reduce the dimensionality of input and output spaces for given training instances. By exploiting 2D velocity profile nonlinear compressibility, we train a residual convolutional autoencoder under an unsupervised mode using velocity data, where its encoder acts as a velocity dimensionality reduction operator to transform 2D velocity profiles into low-dimensional 1D pseudo-velocity curves. Then, a residual network is trained to build a nonlinear mapping from multi-shot seismic records to 1D pseudo-velocity curves. In the inference stage, the trained decoder converts those predicted 1D curves back to 2D velocity profiles. Therefore, we propose a novel two-stage data-driven seismic inversion technique combining a residual network with a residual convolutional autoencoder. The detailed experiments on four synthetic data sets (salt body, layered, faulted and salt dome models) illustrate that our proposed method with three different residual network architectures outperforms other approaches including FCNVMB, VelocityGAN and pure residual network, according to four objective evaluation metrics and subjective visualization.

Ultrasonic Measurement of Two-Dimensional Liquid Velocity Profile Using Two-Element Transducer

The flow field or multidimensional velocity distribution of the coolant in fuel rod bundles of the reactor core in pressurized water reactors (PWRs) is an important parameter that is revealed through experimental investigations. This paper presents the two-dimensional (2D) velocity profile measurement using a two-element ultrasonic transducer with both elements acting as a transceiver. The size of the transducer is minimized for compactness, leading to a narrow sound field appropriate for applications in fuel rod bundle flow. Furthermore, the transducer’s sound pressure is evaluated via simulations and experimental measurements. In order to confirm the ability of the ultrasonic velocity profiler (UVP) with a two-element transducer, the experimental measurement is conducted in turbulent horizontal pipe flow. The 2D velocity vector profile is obtained, and then the measurement in swirling flow is conducted. The 2D velocity profile in an axial and radial plane is obtained utilizing the UVP measurement. Lastly, the ability of the UVP to derive the 2D velocity profile in the narrow area of the rod bundles is demonstrated.

Rheological and Pipe Flow Properties of Chocolate Masses at Different Temperatures.

Chocolate masses are one of the basic raw materials for the production of confectionery. Knowledge of their rheological and flow behaviour at different temperatures is absolutely necessary for the selection of a suitable technological process in their production and subsequent processing. In this article, the rheological properties (the effect of the shear strain rate on the shear stress or viscosity) of five different chocolate masses were determined—extra dark chocolate (EDC), dark chocolate (DC), milk chocolate (MC), white chocolate (WC), and ruby chocolate (RC). These chocolate masses showed thixotropic and plastic behaviour in the selected range of shear rates from 1 to 500 s−1 and at the specified temperatures of 36, 38, 40, 42, and 44 °C. The degree of thixotropic behaviour was evaluated by the size of the hysteresis area, and flow curves were constructed using the Bingham, Herschel–Bulkley and Casson models with respect to the plastic behaviour of the chocolate masses. According to the values of the coefficients of determination R2 and the sum of the squared estimate of errors (SSE), the models were chosen appropriately. The most suitable models are the Herschel–Bulkley and Casson models, which also model the shear thinning property of the liquids (pseudoplastic with a yield stress value). Using the coefficients of the rheological models and modified equations for the flow velocity of technical and biological fluids in standard piping, the 2D and 3D velocity profiles of the chocolate masses were further successfully modelled. The obtained values of coefficients and models can be used in conventional technical practice in the design of technological equipment structures and in current trends in the food industry, such as 3D food printing.

The Correlation Between P-Wave Velocity Value With Pathways Of Geothermal Manifestation In The Area Ie Jue, Aceh Besar As Hazardous Side Study

Refraction seismic survey has been carried out in the manifestation area of Ie Jue, Seulawah Agam Volcano Region, Seulimuem, Aceh Besar Regency. This research aims to identify weak zones related to channel of geothermal outflow that would bring about a potential hazard for human activity and that goal is obtained by exstracting information from P-wave velocity. The data acquisition was conducted for two seismic lines located near to the geothermal manifestation area of Ie Jue. Both of the seismic lines were set up by linking the 24 geophones to the Seismograph PASI 16S and placing them in three meters spacing of each other. The offsets either left or right were laid out at 35 meters from first and last geophones, so the total spread length of each seismic line is 139 meters. The data recorded by the tool then were processed by using ZONDST2D and finally, the 2D velocity profile was obtained. The results show that the 2D velocity profiles illuminate us to potray and interpret the features figured out. The most valuable information provided by the profile is the existance of such the weak zones of the first and second seismic lines at relatively near-surface depth. These weak zones were suspected as the fractured or low-velocity zones, where their velocity ranges approximately at 0.2 - 1.2 km/sec. These low-velocity layers are strongly predicted as the pathways or channels of the geothermal fluids that appears to the surface. The shallow weak zones are potentially to become the hazard grounds because they are regularly traversed by timber trucks from which the dynamic load will be pushing them down. As consequence, the ground surfaces could gradually become a land subsidence endangering human activity within the vicinity of the area.

Mixing of non-Newtonian fluids in a cylindrical stirred vessel equipped with a novel side-entry propeller

A side-entry propeller was designed and introduced in this study. The mixing performance of shear thinning fluids in a cylindrical stirred vessel equipped with this propeller was experimentally investigated via an ultrasonic Doppler anemometer (UDA, experimental results were consistent with theoretical findings. The power number and Reynolds number of this propeller were evaluated by using Chhabra, Metzner and Reed equations. Results showed that the power number versus the Reynolds number curves were highly comparable with Metzner and Reed equations. The velocity jet vectors flow field of 320, 380, and 440 rpm were described in detail. These findings demonstrated that the circulation loops, cavern size, and shape were highly influenced by shear thinning parameters and operating conditions. The average of the velocity profiles from five sample lines in front of the propeller was utilized to analyze the effect of rheological properties and operating conditions on the propeller. The axial, radial and tangential 2D velocity profiles located at one sample line (200 mm) in front of the propeller at the design rotation speed were evaluated.

Seismic-refraction field experiments on Galapagos Islands: A quantitative tool for hydrogeology

Due to their complex structure and the difficulty of collecting data, the hydrogeology of basaltic islands remains misunderstood, and the Galapagos islands are not an exception. Geophysics allows the possibility to describe the subsurface of these islands and to quantify the hydrodynamical properties of its ground layers, which can be useful to build robust hydrogeological models. In this paper, we present seismic refraction data acquired on Santa Cruz and San Cristobal, the two main inhabited islands of Galapagos. We investigated sites with several hydrogeological contexts, located at different altitudes and at different distances to the coast. At each site, a 2D P-wave velocity profile is built, highlighting unsaturated and saturated volcanic layers. At the coastal sites, seawater intrusion is identified and basal aquifer is characterized in terms of variations in compressional sound wave velocities, according to saturation state. At highlands sites, the limits between soils and lava flows are identified. On San Cristobal Island, the 2D velocity profile obtained on a mid-slope site (altitude 150m), indicates the presence of a near surface freshwater aquifer, which is in agreement with previous geophysical studies and the hydrogeological conceptual model developed for this island. The originality of our paper is the use of velocity data to compute field porosity based on poroelasticity theory and the Biot-Gassmann equations. Given that porosity is a key parameter in quantitative hydrogeological models, it is a step forward to a better understanding of shallow fluid flows within a complex structure, such as Galapagos volcanoes.

Pure axial flow of viscoelastic fluids in rectangular microchannels under combined effects of electro-osmosis and hydrodynamics

This paper presents an analysis of the combined electro-osmotic and pressure-driven axial flows of viscoelastic fluids in a rectangular microchannel with arbitrary aspect ratios. The rheological behavior of the fluid is described by the complete form of Phan-Thien–Tanner (PTT) model with the Gordon–Schowalter convected derivative which covers the upper convected Maxwell, Johnson–Segalman and FENE-P models. Our numerical simulation is based on the computation of 2D Poisson–Boltzmann, Cauchy momentum and PTT constitutive equations. The solution of these governing nonlinear coupled set of equations is obtained by using the second-order central finite difference method in a non-uniform grid system and is verified against 1D analytical solution of the velocity profile with less than 0.06% relative error. Also, a parametric study is carried out to investigate the effect of channel aspect ratio (width to height), wall zeta potential and the Debye–Huckel parameter on 2D velocity profile, volumetric flow rate and the Poiseuille number in the mixed EO/PD flows of viscoelastic fluids with different Weissenberg numbers. Our results show that, for low channel aspect ratios, the previous 1D analytical models underestimate the velocity profile at the channel half-width centerline in the case of favorable pressure gradients and overestimate it in the case of adverse pressure gradients. The results reveal that the inapplicability of the Debye–Huckel approximation at high zeta potentials is more significant for higher Weissenberg number fluids. Also, it is found that, under the specified values of electrokinetic parameters, there is a threshold for velocity scale ratio in which the Poiseuille number is approximately independent of channel aspect ratio.

Flow field in a reservoir subject to pumped-storage operation – in situ measurement and numerical modeling

In pumped-storage reservoirs, turbulent kinetic energy input from plant operation can be considerably high. Flow velocities were measured by Acoustic Doppler Current Profilers near the intake/outlet structure to describe flow patterns induced by pumped-storage operation in an Alpine reservoir. Recorded data allowed reproducing 1D and 2D velocity profiles along the water column. The comparison between the main frequencies of the velocity signal and the discharge series from the plant reveals correlation between recorded flow patterns and pumped-storage operation. Numerical modeling enhanced the understanding of flow patterns developing near the intake/outlet structure. Both results reveal that water withdrawal by pumping only marginally affects flow patterns in front of the intake, whereas water injected during turbine mode leads to backflow areas and large-scale recirculation cells. Numerical modeling further revealed that steady flow patterns are developing only after some 2.5 h of continuous turbine operation.

Experimental study and Large Eddy Simulation of thermal mixing phenomena of a parallel jet with perforated obstacles

Thermal mixing and flow field due to two parallel jets which have different temperatures are investigated both experimentally and numerically. The perforated passive obstacles are used with different geometrical specifications. They are located in front of the jets to control flow field and mixing behavior of the jets. An experimental setup designed and manufactured and Large Eddy Simulation turbulence model with the WALE subgrid-scale stress model were used to simulate same experimental conditions. Three perforated obstacles (POs) with different porosity values were used in the study and these obstacles inserted into a rectangular cross-section confined channel. Results demonstrated that increasing the values of temperature differences enhance thermal mixing performance along the channel. The best mixing quality was captured at the same flow rates of the jets. The perforated obstacle has significant positive effect on the mixing performance and this effect increase with higher porosity values. Dominant frequency of mixing region was found as 5 Hz in all cases. The temperature profiles showed that as porosity decreases thermal oscillations are starting to reach the wall. Both 2D and 3D velocity profiles demonstrated that using of POs reduces the domination of turbulence area in the channel.

Use of the μPIV technique for an indirect determination of the microchannel cross-section passage geometry

In this work the possible use of the μPIV technique for the experimental determination of the microchannel cross-section geometry has been investigated by means of a blind test in which a series of experimental measurements obtained using glass microchannels having a declared rectangular cross-section with a depth of 100 μm and width of 300 μm and a square microchannel with a 300 μm side have been compared with the direct SEM visualisation of the real cross section of the microchannels. For the (oPIV measurements water is used as working fluid. The laminar fully developed 2D velocity profile has been reconstructed by moving the focal plane of the microscope objective from the bottom to the top of the microchannel. The results shown in this paper demonstrate that the real cross section geometry of the microchannel can be predicted by minimizing the difference between the theoretical and the experimental 2D velocity profiles. When the right passage geometry is determined, the average difference between the theoretical and the experimental velocity is within 4-6%.

Experimental Determination of the 2D Velocity Laminar Profile in Glass Microchannels using μPIV

In this work an experimental campaign for the determination of the 2D velocity profile in laminar regime of water flowing through glass microchannels is described. Two channels are considered: a microchannel with a side of 300μm (test #1) having an aspect ratio (height/width) equal to 1 and a microchannel having a width of 300μm and a height of 100μm (test #2). Firstly, the real cross section of the glass microchannels has been determined by means of a Scanned Electron Microscope (SEM). The SEM images of the cross sections highlight how the real cross section of these channels differs from the cross section declared by the manufacturer. In particular, both the tested glass microchannels have evidenced a trapezoidal cross section and not a rectangular one as specified in the manufacturer data sheet. For both the channels, the experimental velocity data acquired by using the μPIV system have been compared with the theoretical values obtained by solving the Navier-Stokes equation for a incompressible fluid under steady state conditions. The results have evidenced that μPIV is able to determine the velocity profile within the glass microchannel with an average relative difference with respect the theoretical values of the order of 1-4% depending on the aspect ratio of the channel in the central part of the channels. On the contrary, moving towards the walls, the relative difference between the theoretical and experimental velocity grows up by reaching the maximum values close to the walls. The results presented in this paper are used in order to discuss how the accuracy of the velocity measurements obtained byμPIV can be optimized.

Comparison of patient‐specific inlet boundary conditions in the numerical modelling of blood flow in abdominal aortic aneurysm disease

Three inlet boundary condition datasets were derived from phase-contrast MRI: (i) centre line velocity data converted to two-dimensional (2D) velocity profile using Womersley equations (Womersley), (ii) 2D velocity profile with one axial component of velocity (1CV), (iii) 2D velocity profile with three components of velocity (3CV). Computational fluid dynamics was performed using a rigid wall approach with geometry data extracted from the computed tomography dataset. Helical flow was present in the 1CV and 3CV simulations, with more complex patterns for the 3CV case. The Womersley method produced simplified flow patterns with an absence of helical flow. Mean values of quantitative indices (helical flow index, mean wall shear stress, oscillatory index) were compared with the 3CV inlet data. These were lower for both the Womersley inlet data (28%, 71%, 56%) and the 1CV inlet data (9%, 24%, 69%). It was concluded that inlet methods based on centre line velocity, such as might be obtained from Doppler ultrasound, lead to significantly simplified abdominal aortic aneurysm haemodynamics and thus are not recommended. Single velocity component (axial) data from MRI might suffice when general flow characteristics and spatial wall shear stress are required. Ideally 2D MRI velocity profiles with 3-velocity component data are preferred to fully account for helical flow.

Discharge Imbalance Mitigation in Francis Turbine Draft-Tube Bays

Rehabilitation of ageing power plant is a growing market with specific needs: we have to deal with non up-to-date elements in terms of hydraulic behavior. Refurbishment projects are often focused on the guide vane and runner modification. But for low-head refurbishment projects, the draft-tube is a non negligible part of the overall performance. In some cases, pathological draft-tubes have been encountered with a significant efficiency drop near the best efficiency point. Modification of the draft-tube in order to attenuate, and even eliminate, this effect can thus have a real impact on improving the performance of the power plant, and therefore become economically justified (that heavily depends on the addition or removal of material from the draft-tube walls). Laser Doppler Velocimetry (LDV) measurements near draft-tube outlet have been achieved for both original and modified draft-tube. It offers 2D velocity profiles and permits to calculate discharge repartition in each bay. Pressure recovery factor measured separately for each bay is used to quantify losses.

Accuracy of MRI wall shear stress estimation

Methods Three methods for WSS estimation were studied. These methods are based on 1) linear extrapolation (LE) of MRI velocity data, 2) MRI velocity data in combination with estimation of location of vessel wall, and 3) Fourier velocity encoding (FVE). Numerical velocity fields representing axisymmetric 2D velocity profiles were generated for WSS values ranging from 1-20 N/m. Based on the numerical velocity fields, phase-contrast MRI data voxels were simulated as follows: A jinc-function was used to model the 2D point spread function (PSF), and this PSF was used to obtain each voxel’s intravoxel velocity distribution. The phasecontrast MRI signal of each voxel was simulated by taking the Fourier transform of this distribution. To account for the fact that voxels cannot be positioned exactly at the wall in an MR-experiment, all simulations were carried out for ten different voxel positions uniformly distributed over one voxel length. In the LE method the spatial velocity derivative was estimated as the velocity difference between the two adjacent nearwall voxels divided by the distance between them. In the wall-based method, WSS was estimated by dividing the linear interpolated velocity at one voxel distance from the wall by the distance to the wall. Errors in segmentations of wall position were accounted for by modeling them as normally distributed with a standard deviation of 1/4 voxel size. In the FVE-based method, the WSS was obtained by first estimating the intravoxel velocity profile via a simulated FVE measurement and then computing the spatial velocity derivative near the wall. Note that the FVE-method uses larger voxels.

Non-destructive ultrasonic velocimetry for central region velocity fields in turbulent Rayleigh–Bénard convection of mercury

A non-destructive method of measuring flow field of opaque fluids is presented for turbulent convection of liquid metal mercury. Two important properties of the turbulent state, namely 2D velocity profiles and energy spectrum, are successfully measured for Rayleigh–Bénard convection of mercury by using ultrasonic Doppler velocimetry. A few key techniques for the method are also explained.

Haemodynamics and blood flow measured using ultrasound imaging

Visualization of, and measurements related to, haemodynamic phenomena in arteries may be made using ultrasound systems. Most ultrasound technology relies on simple measurements of blood velocity taken from a single site, such as the peak systolic velocity for assessment of the degree of lumen reduction caused by an arterial stenosis. Real-time two-dimensional (2D) flow field visualization is possible using several methods, such as colour flow, blood flow imaging, and echo particle image velocimetry; these have applications in the examination of the flow field in diseased arteries and in heart chambers. Three-dimensional (3D) and four-dimensional ultrasound systems have been described. These have been used to provide 2D velocity profile data for the estimation of volumetric flow. However, they are limited for haemodynamic evaluation in that they provide only one component of the velocity. The provision of all seven components (three space, three velocity, and one time) is possible using image-guided modelling, in which 3D ultrasound is combined with computational fluid dynamics. This method also allows estimation of turbulence data and of relevant quantities such as the wall shear stress.

First-arrival traveltimes inversion based on a minimal number of parameters in shallow cross-well GPR tomography

Ground-penetrating radar (GPR) is a powerful tool to characterize the subsurface electromagnetic properties, and therefore related quantities such as the water-content. In this paper, we present a new algorithm for cross-well tomographic inversion of GPR first-arrival traveltimes. It is based on a blocky description of the propagating medium, and only a limited number of parameters are inverted. This methodology has been developed for media with significant contrast of electrical permittivity, for instance near-surface sedimentary media, where the occurrence of head waves is frequent. In a first step, the distribution of the electromagnetic wave velocity is determined between two wells. In a second step, we address the question of the layers continuity for several successive tomographic panels. This methodology allows us to obtain a 2D velocity profile of the medium between successive pairs of wells. The inversion scheme takes into account both the direct and refracted waves generated at interfaces with strong velocity contrast. It was tested on synthetic data for a single pair of wells, and on real data, first for one tomographic panel, then for a set of three successive tomographic panels. For comparison, inversion was also conducted with a classical LSQR algorithm, which delivers a smooth velocity model, and does not take into account head waves. As expected, the velocities obtained with our method are more contrasted, and free from the head waves generated artefacts.

A two-dimensional acoustic sediment flux profiler

Instantaneous sediment flux measurement is important for the study of the detailed effects of turbulent currents and their relation to the transport of sedimentary materials. This paper presents a novel acoustic sediment flux profiler which is able to measure the instantaneous sediment flux profile directly. Three 1 MHz ultrasonic transducers are employed to measure the instantaneous concentration profile and the corresponding 2D velocity profile simultaneously. The principle of operation of the system and its realization are discussed. Experimental results obtained in an open-channel sediment-laden flow are reported.