scholarly journals How to adapt numerical simulation of wave propagation and ultrasonic laboratory experiments to be comparable — A case study for a complex topographic model

Geophysics ◽  
2018 ◽  
Vol 83 (4) ◽  
pp. T195-T207 ◽  
Author(s):  
Bence Solymosi ◽  
Nathalie Favretto-Cristini ◽  
Vadim Monteiller ◽  
Dimitri Komatitsch ◽  
Paul Cristini ◽  
...  
Keyword(s):  
Wave Propagation ◽  
Numerical Simulations ◽  
Laboratory Experiments ◽  
Laboratory Data ◽  
Computational Cost ◽  
Seismic Exploration ◽  
Quality Data ◽  
Small Scale ◽  
Water Tank ◽  
Zero Offset

Numerical methods are widely used in seismic exploration to simulate wave propagation; however, the algorithms are based on various assumptions. The accuracy of numerical simulations is of particular interest in the case of realistic geologic setups. The direct comparison of numerical results can have limitations, and an alternative approach can be the comparison of synthetic results with experimental data, obtained for a small-scale physical model in laboratory conditions. Laboratory experiments are repeatable and provide high-quality data for a known configuration. We have developed a possible workflow to adapt the numerical simulations and the laboratory experiments to each other, such that the two can be easily compared with high accuracy. The model is immersed in a water tank, and a conventional pulse-echo technique is used to collect the reflection data in zero-offset and offset configurations. We use a spectral-element method for the numerical modeling. The model geometry is implemented using a nonstructured mesh, and the computational cost can be optimized using larger elements and higher-order basis functions. The real source transducer characteristics are implemented based on a new approach: laboratory characterization of the impulse response, followed by an inversion step to obtain a numerically equivalent source. The comparison of the zero-offset synthetic and laboratory results reveals an excellent fit in terms of arrival time, phase, and amplitude. Minor amplitude mismatches may be attributed to the noise recorded in the laboratory data and to the possible inaccuracy of the proposed source implementation. Comparison of the simulated and laboratory offset traces also exhibits a good fit in general, but with significantly less accuracy for some arrivals than in the zero-offset case. This can be mainly attributed to the inaccuracies of the transducer positions during the laboratory measurements combined with the strong topography of the model.

scholarly journals Seismic surveying and imaging at the laboratory scale: A framework to cross-validate experiments and simulations for a salt-body environment

Geophysics ◽  
2020 ◽  
Vol 85 (3) ◽  
pp. T123-T139
Author(s):  
Bence Solymosi ◽  
Nathalie Favretto-Cristini ◽  
Vadim Monteiller ◽  
Paul Cristini ◽  
Bjørn Ursin ◽  
...  
Keyword(s):  
Experimental Data ◽  
Laboratory Experiments ◽  
Field Experiments ◽  
Imaging Techniques ◽  
Laboratory Data ◽  
Seismic Exploration ◽  
Scale Model ◽  
Water Tank ◽  
Time Migration ◽  
Reduced Scale

Laboratory experiments have been recently reintroduced into the ideas-to-applications pipeline for geophysical applications. Benefiting from recent technological advances, we believe that in the coming years, laboratory experiments can play a major role in supporting field experiments and numerical modeling, to explore some of the current challenges of seismic imaging in terms of, for instance, acquisition design or benchmarking of new imaging techniques at a low cost and in an agile way. But having confidence in the quality and accuracy of the experimental data obtained in a complex configuration, which mimics at a reduced scale a real geologic environment, is an essential prerequisite. This requires a robust framework regardless of the configuration studied. Our goal is to provide a global overview of this framework in the context of offshore seismics. To illustrate it, a reduced-scale model is used to represent a 3D complex-shaped salt body buried in sedimentary layers with curved surfaces. Zero-offset and offset reflection data are collected in a water tank, using a conventional pulse-echo technique. Then, a cross-validation approach is applied, which allows us, through comparison between experimental data and the numerical simulation, to point out some necessary future improvements of the laboratory setup to increase the accuracy of the experimental data, and the limitations of the numerical implementation that must also be tackled. Due to this approach, a hierarchical list of points can be collected, to which particular attention should be paid to make laboratory experiments an efficient tool in seismic exploration. Finally, the quality of the complex reduced-scale model and the global framework is successfully validated by applying reverse time migration to the laboratory data.

scholarly journals Numerical modeling of 3D zero-offset laboratory data by a discretized Kirchhoff integral method

Geophysics ◽  
2014 ◽  
Vol 79 (2) ◽  
pp. T77-T90 ◽  
Author(s):  
Anastasiya Tantsereva ◽  
Bjørn Ursin ◽  
Nathalie Favretto-Cristini ◽  
Paul Cristini ◽  
Arkady M. Aizenberg
Keyword(s):  
Integral Method ◽  
Structural Changes ◽  
Laboratory Data ◽  
Quality Data ◽  
Water Tank ◽  
Head Waves ◽  
In Situ Experiments ◽  
Zero Offset ◽  
Kirchhoff Integral

Accurate simulation of seismic wave propagation in complex geologic structures is of particular interest nowadays. However, difficulties arise for complex geologic structures with great and rapid structural changes, due, for instance, to the presence of shadow zones, head waves, diffractions and/or edge effects. Different methods have thus been developed and are typically tested on synthetic configurations against analytical solutions for simple canonical problems, reference methods, or via direct comparison with real data acquired in situ. Such approaches have limitations, especially if the propagation occurs in a complex environment with strong-contrast reflectors and surface irregularities because it can be difficult to determine the method that gives the best approximation of the “real” solution or to interpret the results obtained without an a priori knowledge of the geologic environment. An alternative approach for seismics consists in comparing the synthetic data with data obtained in laboratory experiments. In contrast to in situ experiments, high-quality data are collected under controlled conditions for a known configuration. In contrast with numerical experiments, laboratory data possess many of the characteristics of field data because real waves propagate through models with no numerical approximations. Our main purpose was to test the approach of using laboratory data as reference data for benchmarking 3D numerical methods and techniques using the setup that we have designed for this study. We performed laboratory-scaled measurements of zero-offset reflection of broadband pulses from a strong topographic environment immersed in a water tank. We compared these measurements with numerical data simulated by means of a discretized Kirchhoff integral method. The comparisons of synthetic and laboratory data indicated a good quantitative fit in terms of time arrivals and acceptable fit in amplitudes. Thus, the first step of the approach was successfully applied.

scholarly journals Experiments on wave propagation in grease ice: combined wave gauges and particle image velocimetry measurements

2019 ◽  
Vol 864 ◽  
pp. 876-898 ◽  
Author(s):  
Jean Rabault ◽  
Graig Sutherland ◽  
Atle Jensen ◽  
Kai H. Christensen ◽  
Aleksey Marchenko
Keyword(s):  
Wave Propagation ◽  
Particle Image Velocimetry ◽  
Particle Image ◽  
Wave Attenuation ◽  
Laboratory Data ◽  
Decomposition Analysis ◽  
Small Scale ◽  
Wave Tank ◽  
Wave Elevation ◽  
Image Velocimetry

Water wave attenuation by grease ice is a key mechanism for the polar regions, as waves in ice influence many phenomena such as ice drift, ice breaking and ice formation. However, the models presented so far in the literature are limited in a number of regards, and more insights are required from either laboratory experiments or fieldwork for these models to be validated and improved. Unfortunately, performing detailed measurements of wave propagation in grease ice, either in the field or in the laboratory, is challenging. As a consequence, laboratory data are relatively scarce, and often consist of only a couple of wave elevation measurements along the length of the wave tank. We present combined measurements of wave elevation using an array of ultrasonic probes, and water kinematics using particle image velocimetry (PIV), in a small-scale wave tank experiment. Experiments are performed over a wider frequency range than has been previously investigated. The wave elevation measurements are used to compute the wavenumber and exponential damping coefficient. In contrast to a previous study in grease ice, we find that the wavenumber is consistent with the mass loading model, i.e. it increases compared with the open water case. Wave attenuation is compared with a series of one-layer models, and we show that they satisfactorily describe the viscous damping occurring. PIV data are also consistent with exponential wave amplitude attenuation, and a proper orthogonal decomposition analysis reveals the existence of mean flows under the ice that are a consequence of the displacement and packing of the ice induced by the gradient in the wave-induced stress. Finally, we show that the dynamics of grease ice can generate eddy structures that inject eddy viscosity into the water under the grease ice, which would lead to enhanced mixing and participating in energy dissipation.

scholarly journals Predicting Fault Slip via Transfer Learning

2021 ◽  
Author(s):  
Kun Wang ◽  
Christopher Johnson ◽  
Kane Bennett ◽  
Paul Johnson
Keyword(s):  
Machine Learning ◽  
Numerical Simulations ◽  
Transfer Learning ◽  
Laboratory Experiments ◽  
Laboratory Data ◽  
Fault Slip ◽  
Geophysical Data ◽  
Training Data ◽  
Data Sets ◽  
Earthquake Cycle

Abstract Data-driven machine-learning for predicting instantaneous and future fault-slip in laboratory experiments has recently progressed markedly due to large training data sets. In Earth however, earthquake interevent times range from 10's-100's of years and geophysical data typically exist for only a portion of an earthquake cycle. Sparse data presents a serious challenge to training machine learning models. Here we describe a transfer learning approach using numerical simulations to train a convolutional encoder-decoder that predicts fault-slip behavior in laboratory experiments. The model learns a mapping between acoustic emission histories and fault-slip from numerical simulations, and generalizes to produce accurate results using laboratory data. Notably slip-predictions markedly improve using the simulation-data trained-model and training the latent space using a portion of a single laboratory earthquake-cycle. The transfer learning results elucidate the potential of using models trained on numerical simulations and fine-tuned with small geophysical data sets for potential applications to faults in Earth.

A multiscale method for wave propagation in 3D heterogeneous poroelastic media

Geophysics ◽  
2019 ◽  
Vol 84 (4) ◽  
pp. T237-T257
Author(s):  
Wensheng Zhang ◽  
Hui Zheng
Keyword(s):  
Wave Propagation ◽  
Computational Cost ◽  
Mesh Size ◽  
Multiscale Method ◽  
Small Scale ◽  
Physical Parameters ◽  
Local Problem ◽  
Wave Simulation ◽  
Poroelastic Media ◽  
Coarse Grids

A new multiscale method for wave simulation in 3D heterogeneous poroelastic media is developed. Wave propagation in inhomogeneous media involves many different scales of media. The physical parameters in the real media usually vary greatly within a very small scale. For the direct numerical methods for wave simulation, a refined grid is required in mesh generation to maintain the match between the mesh size and the material variations in the spatial scale. This greatly increases the computational cost and computer memory requirements. The multiscale method can overcome this difficulty due to the scale difference. The basic idea of our multiscale method is to construct computational schemes on two sets of meshes, i.e., coarse grids and fine grids. The finite-volume method is applied on the coarse grids, whereas the multiscale basis functions are computed with the finite-element method by solving a local problem on the fine grids. Moreover, the local problem only needs to be solved once before time stepping. This allows us to use a coarse grid while still capturing the information of the physical property variations in the small scale. Therefore, it has better accuracy than the single-scale method when they use the same coarse grids. The theoretical method and the dispersion analysis are investigated. Numerical computations with the perfectly matched layer boundary conditions are completed for 3D inhomogeneous poroelastic models with randomly distributed small scatterers. The results indicate that our multiscale method can effectively simulate wave propagation in 3D heterogeneous poroelastic media with a significant reduction in computation cost.

Numerical Simulation of Seismic Wave Propagation in Different Media

2014 ◽  
Vol 596 ◽  
pp. 616-619
Author(s):  
Zhi Ren Feng
Keyword(s):  
Numerical Simulation ◽  
Wave Propagation ◽  
Seismic Wave ◽  
Model Simulation ◽  
Homogeneous Medium ◽  
Seismic Wave Propagation ◽  
Seismic Exploration ◽  
Scale Model ◽  
Small Scale ◽  
Simulation Accuracy

Theory of elastic waves layered homogeneous medium or even medium for the study can not meet the actual demand for seismic exploration, especially for fine rock to construct reservoirs for the study, had to consider small-scale heterogeneity of seismic wave propagation effects. In this thesis, multi-scale model of a complex medium, in ensuring the premise to further improve simulation accuracy simulation efficiency issue, the introduction of a variable grid numerical simulation techniques, and were analyzed for different types of grid difference, establish a different media model simulation results verify the validity of simulation and analyzes its efficiency and accuracy problems.

Nonlinear Numerical Simulations of Magneto-Acoustic Wave Propagation in Small-Scale Flux Tubes

Solar Physics ◽  
2008 ◽  
Vol 251 (1-2) ◽  
pp. 589-611 ◽  
Author(s):  
E. Khomenko ◽  
M. Collados ◽  
T. Felipe
Keyword(s):  
Wave Propagation ◽  
Acoustic Wave ◽  
Numerical Simulations ◽  
Small Scale ◽  
Acoustic Wave Propagation ◽  
Flux Tubes

scholarly journals NUMERICAL SIMULATIONS AND ASSESSMENTS OF PERFORATED BREAKWATERS

2018 ◽  
pp. 19
Author(s):  
Philip L.-F. Liu ◽  
Pablo Higuera
Keyword(s):  
Numerical Simulations ◽  
Laboratory Experiments ◽  
Numerical Solutions ◽  
Scale Effects ◽  
Laboratory Data ◽  
Physical Processes ◽  
Hydrodynamic Processes ◽  
Wave Trains ◽  
Perforated Breakwater ◽  
Rectangular Columns

In this paper we study the physical processes of regular wave trains impacting on a perforated breakwater. The breakwater consists of an array of vertical rectangular columns and a backwall. We have performed numerical simulations in which reflection coefficients have been calculated based on the Mansard and Funke (1980) theory and compared with laboratory data and analytical solutions (Kakuno et al. 1992, Kakuno & Liu, 1993). The numerical solutions will be further analyzed to describe the hydrodynamic processes, identify the limitations of the analytical theory and the scale effects in the laboratory experiments.

Vortices in oscillating spin-up

2007 ◽  
Vol 573 ◽  
pp. 339-369 ◽  
Author(s):  
M. G. WELLS ◽  
H. J. H. CLERCX ◽  
G. J. F. VAN HEIJST
Keyword(s):  
Numerical Simulations ◽  
Power Law ◽  
Large Scale ◽  
Laboratory Experiments ◽  
Passive Scalar ◽  
Decay Rates ◽  
Small Scale ◽  
Two Dimensional ◽  
Ekman Pumping ◽  
Viscous Boundary Layer

Laboratory experiments and numerical simulations of oscillating spin-up in a square tank have been conducted to investigate the production of small-scale vorticity near the no-slip sidewalls of the container and the formation and subsequent decay of wall-generated quasi-two-dimensional vortices. The flow is made quasi-two-dimensional by a steady background rotation, and a small sinusoidal perturbation to the background rotation leads to the periodic formation of eddies in the corners of the tank by the roll-up of vorticity generated along the sidewalls. When the oscillation period is greater than the time scale required to advect a full-grown corner vortex to approximately halfway along the sidewall, dipole structures are observed to form. These dipoles migrate away from the walls, and the interior of the tank is continually filled with new vortices. The average size of these vortices appears to be largely controlled by the initial formation mechanism. Their vorticity decays from interactions with other stronger vortices that strip off filaments of vorticity, and by Ekman pumping at the bottom of the tank. Subsequent interactions between the weaker ‘old’ vortices and the ‘young’ vortices result in the straining, and finally the destruction, of older vortices. This inhibits the formation of large-scale vortices with diameters comparable to the size of the container.The laboratory experiments revealed a k−5/3 power law of the energy spectrum for small-to-intermediate wavenumbers. Measurements of the intensity spectrum of a passive scalar were consistent with the Batchelor prediction of a k−1 power law at large wavenumbers. Two-dimensional numerical simulations, under similar conditions to those in the experiments (with weak Ekman decay), were also performed and the simultaneous presence of a k−5/3 and k−3−ζ (with 0 < ζ « 1) power spectrum is observed, with the transition occurring at the wavenumber at which vorticity is injected from the viscous boundary layer into the interior. For higher Ekman decay rates, steeper spectra are obtained for the large wavenumber range, with ζ = O(1) and proportional to the Ekman decay rate. Movies are available with the online version of the paper.

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