A CNN-based surrogate model of isogeometric analysis in nonlocal flexoelectric problems

We proposed a convolutional neural network (CNN)-based surrogate model to predict the nonlocal response for flexoelectric structures with complex topologies. The input, i.e. the binary images, for the CNN is obtained by converting geometries into pixels, while the output comes from simulations of an isogeometric (IGA) flexoelectric model, which in turn exploits the higher-order continuity of the underlying non-uniform rational B-splines (NURBS) basis functions to fast computing of flexoelectric parameters, e.g., electric gradient, mechanical displacement, strain, and strain gradient. To generate the dataset of porous flexoelectric cantilevers, we developed a NURBS trimming technique based on the IGA model. As for CNN construction, the key factors were optimized based on the IGA dataset, including activation functions, dropout layers, and optimizers. Then the cross-validation was conducted to test the CNN’s generalization ability. Last but not least, the potential of the CNN performance has been explored under different model output sizes and the corresponding possible optimal model layout is proposed. The results can be instructive for studies on deep learning of other nonlocal mech-physical simulations

Two-dimensional imaging of dense tissue-simulating turbid media by use of sonoluminescence

An optical imaging technique that is believed to be novel was developed for noninvasive cross-sectional imaging of tissuelike turbid media. By use of a sonoluminescence signal generated internally in the media with a 1-MHz continuous-wave ultrasound, two-dimensional images were produced for objects embedded in turbid media by a raster scan of the media. Multiple objects of different shapes were resolved with this imaging technique. The images showed a high contrast and good spatial resolution. The spatial resolution was limited by the focal size of the ultrasonic focus

Sonoluminescent tomography

A novel optical imaging technique called sonoluminescent tomography (SLT) was developed for cross-sectional imaging of strongly scattering media noninvasively. Sonoluminescence, which was generated internally in the medium by continuous-wave ultrasound, was used to produce a two-dimensional image of an object embedded in a scattering medium by raster scanning the medium. The image had a high contrast and good spatial resolution. The spatial resolution was limited by the focal spot size of the ultrasound and can be improved by tightening the focus. This inexpensive imaging technique has potential applications in medicine and other fields related to scattering media

Sonoluminescent tomography of strongly scattering media

A novel optical imaging technique called sonoluminescent tomography was developed for cross-sectional imaging of strongly scattering media noninvasively. Sonoluminescence, which was generated internally in the medium by cw ultrasound, was used to produce a two-dimensional image of an object embedded in a scattering medium by means of raster scanning the medium. The image had a high contrast and good spatial resolution. The spatial resolution was limited by the focal-spot size of the ultrasound, and one could improve the resolution by tightening the focus. This inexpensive imaging technique has potential applications in medicine and other fields related to scattering media

Sonoluminescence tomography of turbid media

A novel optical imaging technique was developed for noninvasive cross-sectional imaging of tissue-like turbid media. By use of a sonoluminescence signal generated internally in the media by continuous-wave ultrasound, two-dimensional images were produced for objects embedded in turbid media by raster scanning the media. Multiple objects of different shapes were resolved using this imaging technique. The images showed a high contrast and good spatial resolution. The spatial resolution was limited by the focal size of the ultrasonic focus

Modeling the breaking-off of icebergs from tidewater glaciers

Ice calving is the breakaway process of icebergs which plays an important role in the dy- namics and the mass balance of ice sheets. Our project is to use Akantu (An open source object-oriented Finite Element library by LSMS) to reproduce the fracturing stages of the Bowdoin glacier in Greenland. Studies were first made on the mechanisms of ice calving and the provided data, to extract the key factors for our simulation. The HPC (high performance computing) simulation model was built by Python scripts, including preprocessing mesh file, applying arbitrary loading profiles, defining boundary conditions and initial conditions, pass- ing message through the simulation process, etc. The simulation scheme has been modified to better analysis the impact of water pressure and velocity field. Simulation acceleration was also implemented by amplifying the velocity field, so that the damage initiation and propagation could be explored faster. Some preliminary results about the relationship of system energy and damage propagation was analyzed. In the end, we proposed some study direction for the future researchers on the similar subject

Sound and light in turbid media

Two imaging techniques combining ultrasound and light are reviewed. The motivation is to combine the advantages of optical information and acoustic imaging resolution. The first technique is sonoluminescence tomography, where a sonoluminescence signal generated internally in the media by continuous-wave ultrasound is used. Two-dimensional images can be produced for objects embedded in turbid media by raster scanning the media. The second technique is ultrasound- modulated optical tomography, where a frequency-swept ultrasonic wave was used to modulate the laser light passing through a scattering medium. Multiple 1D images obtained at various positions perpendicular to the ultrasonic axis were composed to obtain a 2D tomographic image of the medium

Combining sound and light in scattering media

Two imaging techniques combining ultrasound and light are reviewed. The motivation is to combine the advantages of optical information and acoustic imaging resolution. The first technique is sonoluminescence tomography, where a sonoluminescence signal generated internally in the media by continuous-wave ultrasound is used. 2D images can be produced for objects embedded in turbid media by raster scanning the media. The second technique is ultrasound-modulated optical tomography, where a frequency-swept ultrasonic wave was used to modulate the laser light passing through a scattering medium. Multiple 1D images obtained at various positions perpendicular to the ultrasonic axis were composed to obtain a 2D tomographic image of the medium

Repeated Loading Model for Elastic-Plastic Contact of Geomaterial

A new nonlinear hysteretic model with considering the loading, unloading, and reloading processes is developed based on Drucker—Prager yield criterion and finite-element analysis. This model can be used for multiple repeated elastic—plastic normal direction contact problems between two identical spherical geomaterials. After examining the influence of material properties, strain hardening, and loading histories, we found that the hysteretic phenomena (represented by residual displacement and plastic work) become weak after the first cycle, and the subsequent cycles step into elastic shakedown state eventually. A critical number of cycles can be used to estimate the state of ratchetting, plastic shakedown, as well as elastic shakedown. It also found that the subsequent curves will be stiffer than the previous ones, especially when the yield strength is high and ratchetting effect is not strong. This new model can be used for a wide range of geomaterials under different loading levels, and it can also be extended to describe the constitutive behavior of spheres under earthquake as well as aftershocks

A Simple Model for Elastic-Plastic Contact of Granular Geomaterials

We propose a simple elastic-plastic contact model by considering the interaction of two spheres in the normal direction, for use in discrete element method (DEM) simulations of geomaterials. This model has been developed by using the finite element method (FEM) and nonlinear fitting methods, in the form of power-law relation of the dimensionless normal force and displacement. Only four parameters are needed for each loading-unloading contact process between two spheres, which are relevant to material properties evaluated by FEM simulations. Within the given range of material properties, those four parameters can be quickly accessed by interpolating the data appended or by regression functions supplied. Instead of the Von Mises (V-M) yield criterion, the Drucker-Prager (D-P) criterion is used to describe the yield behavior of contacting spheres in this model. The D-P criterion takes the effects of confining pressure, the intermediate principal stress, and strain rate into consideration; thus, this model can be used for DEM simulation of geomaterials as well as other granular materials with pressure sensitivity