Our first article on automated meta-modeling of path-dependent materials accepted in CMAME12/7/2018 In this work, we introduce a single-player game in which we attempt to use the formation of directed graph to represent the thought process / decision process of writing a cohesive zone model. In this work, the AI uses deep reinforcement learning to form knowledge of mechanics represented by directed graph, this knowledge is then used to generate constitutive law. Unlike previous supervised learning method, the automatically discovered/generated/implemented cohesive zone model is robust, accuracy and interpretable by human. Full details can be from the article [URL]. The second one will be coming soon.
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My PhD student Kun Wang has successfully defended his PhD qualification exam. His PhD thesis proposal "From multi-scale modeling to meta-modeling of poromechanics problems" is examined by the committee consisted of Santiago and Roberta Calatrava Family Professor George Deodatis (CEEM), and Fu Foundation Professor Qiang Du, and myself. In the proposed meta-modeling approach, Kun proposes a new method in which one uses a directed multi-graph to represent mechanics knowledge and then uses AI to form a directed graph that leads to a constitutive law. Furthermore, the AI also learns to improve its skill to write constitutive laws through practicing. Unlike previous ML which often leads to blackbox predictions and demands large amount of data, the resultant model is interpretable by human, can be trained with the same amount of data as the hand-crafted counterpart and yet much faster than sub-scale simulations. We thank all the committee members for their insightful questions, comments and time. Kun Wang joined the research group in 9/2014, first as master student, then advanced to PhD in 1/2015. His thesis focuses on the multiscale modeling and meta-modeling of porous media across multiple length and temporal scales. He has published 7 papers (including 4 CMAME papers) of which he served as the first author to 6 of them. His work is supported by ARO, AFOSR, DOE, NSF and Columbia Engineering Seed Grant. His achievement and contribution to our research group are exemplified in the published papers, which are listed below. His recent work on data-driven multiscale modeling of porous media has been awarded him a travel grant to present at the Santa Fe Meshless workshop and selected as one of the finalists in the WCCM poster competitions (along with two other group members SeonHong Na and Eric Bryant). The slides of the qualification exam can be found at the bottom of this post. Congratulations for advancing to the final chapter of your PhD study, Kun! Published Work:
Our work on mixed-mode phase field fracture with consistent kinematics has just published in CMAME9/25/2018 A mixed-mode phase field fracture model in anisotropic rocks with consistent kinematics Eric Bryant & WaiChing Sun Under a pure tensile loading, cracks in brittle, isotropic, and homogeneous materials often propagate such that pure mode I kinematics are maintained at the crack tip. However, experiments performed on geo-materials, such as sedimentary rock, shale, mudstone, concrete and gypsum, often lead to the conclusion that the mode I and mode II critical fracture energies/surface energy release rates are distinctive. This distinction has great influence on the formation and propagation of wing cracks and secondary cracks from pre-existing flaws under a combination of shear and tensile or shear and compressive loadings. To capture the mixed-mode fracture propagation, a mixed-mode I/II fracture model that employs multiple critical energy release rates based on Shen and Stephansson, IJRMMS, 1993 is reformulated in a regularized phase field fracture framework. We obtain the mixed-mode driving force of the damage phase field by balancing the microforce. Meanwhile, the crack propagation direction and the corresponding kinematics modes are determined via a local fracture dissipation maximization problem. Several numerical examples that demonstrate mode II and mixed-mode crack propagation in brittle materials are presented. Possible extensions of the model capturing degradation related to shear/compressive damage, as commonly observed in sub-surface applications and triaxial compression tests, are also discussed. [URL] An updated Lagrangian LBM-DEM-FEM coupling model for dual-permeability fissured porous media with embedded discontinuities Kun Wang & WaiChing Sun Many engineering applications and geological processes involve embedded discontinuities in porous media across multiple length scales (e.g. rock joints, grain boundaries, deformation bands and faults). Understanding the multiscale path-dependent hydro-mechanical responses of these interfaces across length scales is of ultimate importance for applications such as CO2 sequestration, hydraulic fracture and earthquake rupture dynamics. While there exist mathematical frameworks such as extended finite element and assumed strain to replicate the kinematics of the interfaces, modeling the cyclic hydro-mechanical constitutive responses of the interfaces remains a difficult task. This paper presents a semi-data-driven multiscale approach that obtains both the traction-separation law and the aperture-porosity-permeability relation from micro-mechanical simulations performed on representative elementary volumes in the finite deformation range. To speed up the multiscale simulations, the incremental constitutive updates of the mechanical responses are obtained from discrete element simulations at the representative elementary volume whereas the hydraulic responses are generated from a neural network trained with data from lattice Boltzmann simulations. These responses are then linked to a macroscopic dual-permeability model. This approach allows one to bypass the need of deriving multi-physical phenomenological laws for complex loading paths. More importantly, it enables the capturing of the evolving anisotropy of the permeabilities of the macro- and micro-pores. A set of numerical experiments are used to demonstrate the robustness of the proposed model. [DRAFT] PhD student Kun Wang and postdoc research scientist Dr. Chuanqi Liu have received travel grant to present their work at the upcoming Meshfree and Particle Methods: Application and Theory, to be held in Santa Fe, NM, September 10-12, 2018. Chuanqi will present his previous work conducted at Tsinghua University, while Kun will discuss his work on metal-modeling of complex materials in the poster session. The support will cover the registration and travel for both team members. We thank the organizers for providing the support to us.
It is my great pleasure to announce that my PhD student SeonHong Na has accepted a tenure-track position as assistant professor in the department of civil engineering at McMaster University in Canada. He will officially join McMaster in the spring of 2019. SeonHong joined our research group as PhD student in Fall 2014 after obtained his B.S. (2008) and M.S. (2010) in civil engineering from Seoul National University, Korea. Prior to joining Columbia, he worked as a civil engineer for two years (Kunhwa, Korea) and spent another two years in Coastal Development & Ocean Energy Division in Korea Institute of Ocean Science and Technology (KIOST) as a research scientist. SeonHong's research is currently funded by Army Research Office (frozen soil) and the DOE NEUP (crystalline rock) as well as the Fulbright Fellowship and has just recently graduated in July 2018. He is the 2nd PhD graduated from our group and the 3rd research group members who secured tenure-track position, following Yang Liu (Northeastern) and Jinhyun Choo (University of Hong Kong) since 2014. His published journal articles during the last 3+ years at Columbia are listed below. Congratulations again, SeonHong!
Our team member and PhD student SeonHong Na has sucessfully defended his PhD thesis which entitled "Multiscale thermo-hydro-mechanical-chemical (THMC) coupling effects for fluid-infiltrating dual-porosity crystalline rock: theory, implementation, and validation" is examined by the committee consisted of Professor Hoe Ling (CEEM), Professor Ioannis Kougioumtzoglou (CEEM), Professor Greard Ateshian (ME), Dr. Moo Lee & Dr. Hongkyu Yoon (Sandia National Laboratories). We thank all the committee members for their insightful questions, comments and time. SeonHong Na joined the research group in 9/2014. His thesis focuses on the computational mechanics of geological media in extreme environments. His work is supported by ARO, DOE, Columbia and Fulbright Fellowship. During his study at Columbia, SeonHong has won numerous awards, including two Teaching Assistance Excellence Awards, the Mindlin Scholarship, Dongju Lee Memorial Award, and the 2nd place from the ASCE EMI Modeling Inelasticity & Multiscale Behavior poster competition, among others. His achievement and contribution to our research group are exemplified in the thesis and the published papers, which are listed below. Published Work:
7/23 #2021543 - Dual-basis Dimensional Reduction for Non-dissipative Explicit Dynamic Discrete Element Simulations with High-frequency Noises 10:45 - 11:05 Minisymposium#1701 Computational Geomechanics AuthorsKun Wang ,Xinran Zhong* ,WaiChing Sun LocationRoom # Barrymore - MM-9We present, for the first time, a dimensional reduction model based on proper orthogonal decomposition (POD) for non-dissipative explicit dynamic discrete element method (DEM) simulations. Two individual POD bases are obtained by the method of snapshots for the displacement and rotation degrees of freedom of the discrete element particles, respectively. The POD basis for rotation is extracted from the vector space of angular velocity. Since the rotation vectors are pseudovectors which adopt a different algebra, explicit Lie-group time integrator is introduced for the integration of particle rotations, while the time integrator for the displacement field is in the Euclidean space. As such, the two set of snapshots are taken from the simulations with numerically dissipative schemes. Then the derived reduced dimension bases are employed in energy-momentum conserving DEM simulations. This approach brings four important benefits. First, one may filter out the high-frequency noises and obtain accurate results without introducing artificial damping that sometimes leads to inconsistent results and reduced wave propagation speed. Second, the number of snapshots used for displacement and rotation can be different, depending on the nature of the problems. Third, since this method requires no injection of artificial or numerical damping, there is no need to tune damping parameters Finally, the suppression of high-frequency responses allows larger time step for faster explicit integration. The proposed POD-DEM scheme is important for analyzing wave propagation, mixing, rate-dependent simulations for particular materials in which how the external work applied on the system converts into internal energy and dissipation are critical to the outcomes. #2019101 - Unified modeling framework for brittle, quasi-brittle, and ductile failures of pressure-sensitive rocks 14:20 - 14:40 Minisymposium#1701 Computational Geomechanics Authors Jinhyun Choo (now assistant professor at HKU)* ,WaiChing Sun LocationRoom # Barrymore - MM-9Rocks display a wide range of failure modes depending on the confining pressure. The failure mode is localized and brittle fracture under a low confining pressure, but it increasingly becomes more diffuse and ductile as the confining pressure increases. Moreover, it has been shown that a rock under tensile loading can show a hybrid fracture mode in which tensile and shear fracture modes are mixed. Nevertheless, existing computational models usually focus on one of these failure modes. This talk will introduce a recently developed computational framework for unified modeling of these different failure modes under a wide range of confining pressure [1]. The framework couples a phase-field approach to fracture and pressure-sensitive plasticity. By doing so, it can capture the brittle failure mode using a phase-field approach, whereas it can simulate the ductile failure mode by plasticity. The coupling of phase-field and plasticity also allows for simulating quasi-brittle shear fracture and hybrid fracture as observed from experiments. The key ideas of this new coupling, such as the use of phase-field effective stress, will be discussed. Reference: [1] Choo, J. and Sun, W. C. (2018). Coupled phase-field and plasticity modeling of geological materials: From brittle fracture to ductile flow. Computer Methods in Applied Mechanics and Engineering, 330, 1–32. #2021537 - Modeling High-strain-rate Responses Brittle Porous Media with Fracture Opening and Closure 14:20 - 14:40 Minisymposium#212 Variational Fracture Modeling for Brittle and Ductile Materials Authors SeonHong Na*, WaiChing Sun LocationRoom # Brecht - MM-4In engineering applications that involves impacts, earthquake, and explosion, geomaterials are subjected to unusually high strain rate loading. This high strain rate leads to material responses significantly different than the quasi-static counterpart. The competition between elastic wave propagation and fracture propagation often leads to complex features, such as multiple fracture branches, coalescence, and closure. These mechanisms in return affect the two-way hydro-mechanical coupling between the fractured solid skeleton and the pore fluid. In this work, we use an implicit function to approximate cracks to dynamic crack growth and closure in brittle porous materials under high-strain-rate loading. To model the crack opening, closing, and slip behaviors under the dynamic conditions, we introduce a homogenization procedure to convert interface plasticity for strong discontinuity to a regularized anisotropic plasticity model with nonlocal plastic flow aligned with the gradient of the phase field. Both the two-field u-p and the three-field u-w-p and u-U-p formulations are implemented. The results are compared in numerical experiments. #2021515 - A Multi-phase-field/Polycrystal Plasticity for the Brittle-ductile Transitions of Crystalline Rock with Precipitating Fluid 14:40 - 15:00 Minisymposium#1701 Computational Geomechanics Authors SeonHong Na* ,WaiChing Sun LocationRoom # Barrymore - MM-9A safe and permanent repository for nuclear waste disposal using rock salt has drawn attention due to increasing demand of a sustainable and clean energy. The usage of rock salt for the geological repository is highly related to its desired characteristics, such as high thermal conductivity, low permeability and self-healing mechanism. These complicated physical and chemical mechanisms are closely related to the microscopic properties of rock salt. Previous efforts for investigating rock salt have focused on capturing the phenomenological behaviors. Nevertheless, the induced anisotropy and the rate-dependent behaviors of polycrystalline salt are often originated from the microstructures. In this work, we present an alternative approach in which the crystalline nature and the migration of brine as inclusions and precipitated fluid along the ground boundaries are explicitly modelled. We formulate a phase field framework for rock salt that explicitly model the interactions among crystal grain, grain boundaries and brine inclusions. A multi-phase-field method to capture brine migration due to dissolution and precipitation mechanism of halite under temperature gradient. Meanwhile, the crystal plasticity theory is adopted for modeling each grain to account for the crystallographic properties of rock salt. The texture of the multi-grains of salt is assumed to be random by assigning different sets of orientations to each grain. Numerical examples demonstrate that the proposed model is able to capture the brine migrations, interactions of the brine inclusion inside the halite grain and the fluid precipitating in grain boundaries. 7/24 #2021780 - Deep-learning Enhanced Computational Failure Mechanics across Multiple Scales 10:45 - 11:05 Minisymposium#1701 Computational Geomechanics Authors WaiChing Sun* LocationRoom # Barrymore - MM-9We introduce a new hybridized deep-learning/material modeling framework to capture localized failures, in particular, shear bands and fracture across multiple length scales. This modeling framework introduces deep learning as a mean to connect simulations and data across different scales through recursive homogenization. Directed graph, a concept to analyze the hierarchy of information will be used to generate optimal configurations of hybrid deep-learning/material models for a given set of data across length scale such that the effects of evolving microstructures due to micro-cracks, plastic slip and wear can be propagated to the macroscopic scales. To ensure efficiency, an ensemble of theoretical and deep-learning-based material models of different sophistication will be used to predict constitutive responses within a phase field framework. Each phase field represents the weights of a model of a particular scale in the ensembled constitutive predictions. By evolving the phase fields, the ensemble predictions will always capture the domain of interests, such as the moving crack tips during crack growth or shear bands forming in the softening regime, with the most sophisticated predictions, while the far field predictions will be adaptively simplified for efficiency. These evolutions of the phase fields in the space-time continuum is controlled by the driving force. This driving force is a scalar function that depends on the results of validations. Meanwhile, unconventional information from the microstructures, such as coordination number, fabric tensors, void size distribution, grain size distribution, will be analyzed and put into the directed graph that represents the hybridized constitutive laws without hand-crafting new phenomenological models as surrogates. #2021560 - Computational Unsaturated Poromechanics Enhanced by Deep Learning 11:05 - 11:25 Minisymposium#1701 Computational Geomechanics Authors Kun Wang ,Nikolaos Vlassis* ,WaiChing Sun LocationRoom # Barrymore - MM-9Many engineering applications and geological processes involve unsaturated porous media across multiple length scales (e.g. rock joints, grain boundaries, deformation bands, and faults). Understanding the multiscale path-dependent hydro-mechanical responses of these interfaces across length scales is of ultimate importance for applications such as CO2 sequestration and hydraulic fracture. Nevertheless, unlike the saturated counterpart, the path-dependent behaviors of the unsaturated porous media may originate from both the irreversible damage and plasticity of the solid skeleton, the hysteresis of the water retention behaviors and the resultant path-dependent hydraulic responses. For convenience, numerical models often neglect the hysteresis effect of the retention curves. This simplification often leads to unrealistic predictions. In this work, we introduce a hybrid hand-crafted/machine-learning model in which we combine a class of recurrent neural network model (based on long-short-term-memory neuron) that replicates the path-dependent water retention behaviors and classical constitutive critical state plasticity model to replicate the hydro-mechanical responses of unsaturated porous media. This approach allows one to bypass the need of deriving complex phenomenological law for the portion of the constitutive model that lacks clean physical underpinnings while retaining the part of the model that can be justified with sufficient physical arguments (e.g. critical state plasticity). A set of numerical experiments are used to demonstrate the robustness of the proposed model. #2021544 - A Modified Phase Field Model for Mixed-mode Crack Propagation with Consistent Kinematic Modes 11:25 - 11:45 Minisymposium#1701 Computational Geomechanics Authors Eric Bryant* ,WaiChing Sun LocationRoom # Barrymore - MM-9 Cracks in brittle, isotropic, homogeneous materials often propagate such that the pure Mode I kinematic mode is maintained at the crack tip. However, numerous geo-materials, such as sedimentary rock, shale, mudstone, concrete and gypsum, the Mode I and Mode II critical fracture energies are distinct. In such cases, it is likely that secondary Mode II and mixed-mode propagation may occur. This has previously been exhibited by experiments where wing cracks and secondary cracks develop from pre-existing flaws under a combination of shear and tensile or shear and compressive loadings. To capture the mixed-mode fracture propagations, a mixed-Mode I/II fracture model that employs multiple critical critical energy release rates based on Shen and Stephansson, IJRMMS, 1993 is adopted in a phase field framework. Within each incremental time step, an explicit-implicit operator-split scheme is used such that a local energy minimization problem is solved such that the crack propagation direction and the corresponding kinematics modes are determined. This step is followed by the update of the phase field and that of the displacement. Several numerical examples that demonstrated the Mode II and mixed mode crack propagations in brittle materials are presented. Possible extensions of the model that captures the degradation related to shear/compressive damage commonly observed in sub-surface applications and triaxial compression tests are discussed. 7/27 #2021536 - Hybridizing Neural Network and Hand-crafted Critical State Plasticity Model for Forward Prediction of Geomaterials in a Directed Graph 13:40 - 14:00 Minisymposium#1708 Constitutive Modeling of Geomaterials: Development, Implementation, and Performance Assessment Authors Kun Wang* ,WaiChing Sun LocationRoom # Lyceum - Marriott Marquis-5This work presents a novel component-based approach on the development of constitutive models for materials having complex path-dependent mechanical properties. Critical state plasticity models for capturing the complex cyclic response of sands have been proposed, yet lack the prediction accuracy against experiments. To extend the capability of the existing models, we propose the introduction of machine learning on experimental data into the conventional plasticity formulations. The directed graphs of the constitutive models are constructed, with the nodes representing the physical quantities (stress, strain, porosity, fabric tensor, etc.) and the edges representing the universal principles, definitions or constitutive equations relating these quantities. The discrepancy between the different constitutive models lies in the configuration of the directed graphs. The fully mathematical plasticity model involves yield surfaces, plasticity potentials, and evolution equation of internal variables. The fully data-driven constitutive model relates the stress to strain directly via the neurons in the artificial neural networks conserving material frame indifference. The development of hybrid data-driven plasticity model consists of selective replacement of mathematical formulation by machine learning. The choices of data-driven nodes and edges in the directed graph result in different configurations, hence lead to different hybrid models. We present a group of model designs with various degree of hybridization and compare them against experimental data on cyclic responses of sands. Their accuracy and computational efficiency are compared within our proposed model evaluation framework. This work offers the community a novel graph-based systematic approach on developing and assessment of hybrid data-driven constitutive models. These research are supported by the Columbia University 2018 Interdisciplinary Research Seed funding program, Army Research Office under grant contracts W911NF-15-1-0442 and W911NF-15-1-0581, Air Force Office of Scientific Research under grant contract FA9550-17-1-0169, the nuclear energy university program from department of energy under grant contract DE-NE0008534 as well as the Mechanics of Materials and Structures program at National Science Foundation under grant contract CMMI-1462760. We gratefully acknowledge the listed supports. The views and conclusions contained in this document are those of the authors, and should not be interpreted as representing the official policies, either expressed or implied, of the sponsors, including the Army Research Laboratory or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation herein.
Title:
Open-source support toward validating and falsifying discrete mechanics models using synthetic granular materials Part I: Experimental tests with particles manufactured by a 3D printer Author: Ritesh Gupta, Simon Salager, Kun Wang and WaiChing Sun Abstract: This article presents a new test prototype that leverages the 3D printing technique to create artificial particle assembles to provide auxiliary evidences that supports the validation procedure. The prototype test first extracts particle shape features from micro-CT images of a real sand grain and replicates the geometrical features of sand grain using a 3D printer. The quantitative measurements of the particle shape descriptors reveal that the synthetic particles inherit some attributes such as aspect ratio and sparseness of the real materials while exhibiting marked differences for sphericity and convexity. While it is not sufficient to consider the printed particle assembles a replica of the real sand, the repeatable manufacture process provides convention tools to generate additional data that supports the validation procedure for particulate simulations. Oedometric compression tests are conducted on a specimen composed of the printed particles of identical size and shape to create benchmark cases for calibrating and validating discrete element models. Results from digital image correlation on the synthetic sand assemblies reveal that the fracture and fragmentation of the synthetic particles are minor, which in return makes particle position tracking possible. As our prototype test and research data are designed to be open-source, the dataset and the prototype work will open doors for modelers to design further controlled experiments using synthetic granular materials such that the individual influence of each morphological feature of granular assemblies (e.g. shape and size distribution, void ratio, fabric orientation) can be individually tested without being simultaneously affected by other variables. [PDF] Our research group has received a three-year grant from Army Research Office to study the formation of ice lens and the thawing plasticity of frozen soils. In collaboration with the cold regions research and engineering laboratory of US Army Corps of Engineers, our goal is to formulate a new model that predicts the evolution of ice lens. We also introduce a new validation metric to analyze the model performance in matching calibrated results and making forward predictions. In particular, we have identified modeling components that lead to seemingly excellent calibrations but does not provide real benefits for forward prediction ability (LEFT figure) and proposed remedies to enforce the consistency and robustness in the models (RIGHT figure). With this new start point, we introduce inverse problems and models to capture the growth of the ice lens and the corresponding implications on geosystems. Our first journal article co-authored with an undergraduate researcher published in Acta Geotechnica6/10/2018 The research group published the first journal article co-authored with our former undergraduate researcher Steven Lowinger yesterday. The paper describes a simple DEM/flow-network model to predict the hydromechanical responses of Lac du Bonnet granite. The first author is the former visiting scholar of our group Dr. Guang Liu. [URL]
Seven EMI-MIT Presentations by Sun Research Group (Room 4-231 Thursday afternoon to Friday morning)5/27/2018 Our research group will present our latest findings in 7 oral presentations at ASCE Engineering Mechanics Institute Conference at MIT on Thursday (May 31st) and Friday (June 1st) . The schedule of the presentations is listed below in chronological order. Most of the presentations will be given at Room 4-231 (see the map below). Please note that the lectures might not begun on time.
Part of the research findings have been published in the following journal articles:
PhD candidate SeonHong Na received the Mindlin Scholarship and Teaching Assistant Excellence Award5/6/2018 PhD candidate SeonHong Na has received two special honors from Columbia University, (1) the Mindlin Scholarship and (2) the Teaching Assistant Excellence Award.
Congratulations for these wonderful achievements! Our new paper on prediction of permeability and formation factor of sandstone with hybrid lattice Boltzmann/finite element simulation on microtomographic images has published in IJRMMS. In this work, we compare the hybrid lattice Boltzmann/finite element calculation with experimental data on Fontainebleau sandstone specimens of a variety of porosity. We found that the LB simulations actually yield quite accuracy predictions, both on formation factor and permeability tensors. Special thanks for my co-author Professor Teng-fong Wong from Chinese University of Hong Kong who taught me a lot during the research. [URL]
The Engineering Mechanics Institute (EMI) of ASCE has announced that Professor Steve Sun is the winner for the 2018 EMI Leonardo da Vinci Award. The purpose of the award is to recognize outstanding young investigators early in their careers for promising ground-breaking developments in the field of Engineering Mechanics and Mechanical Sciences as relevant to Civil Engineering, understood in the broadest sense. The award is given every year to a young investigator, generally under 35 years of age or have worked no more than 7 years since receiving their doctoral degree, and whose contributions have the promise to define new directions in theory and application of Engineering Mechanics, in the vein of Leonardo da Vinci (1452-1519), a man of unquenchable curiosity and feverishly inventive imagination. The EMI of ASCE selected Professor Sun "for his fundamental contributions to computational multiscale poromechanics. The 2018 EMI Leonardo da Vinci Award will be presented to Professor Sun on Thursday, May 31st, 2018 at the Awards Banquet of the EMI 2018 Conference to be held at MIT, Cambridge, USA. This is the second EMI da Vinci award given to Columbia faculty members, following the 2014 award to Professor Haim Waisman. Columbia University is the first and only institution received the EMI da Vinci award more than once. Source 1: http://www.asce.org/templates/award-detail.aspx?id=452&all_recipients=1 Source 2: civil.columbia.edu/professor-waiching-steve-sun-wins-2018-emi-leonardo-da-vinci-award Sun will join the editorial board of Computer Modeling in Engineering and Science as an associate editor, a journal of which Professor Shaofan Li serves as editor-in-chief effectively on April 1st, 2018. Found by Professor Satya N. Atluri, CMES publishes original research papers of reasonable permanent value, in the areas of computational mechanics, computational physics, computational chemistry, and computational biology, pertinent to solids, fluids, gases, biomaterials, and other continua. Various length scales (quantum, nano, micro, meso, and macro), and various time scales( picoseconds to hours) are of interest. Papers which deal with multi-physics problems, as well as those which deal with the interfaces of mechanics, chemistry, and biology, are particularly encouraged. New computational approaches, and more efficient algorithms, which eventually make near-real-time computations possible, are welcome. Original papers dealing with new methods such as meshless methods, and mesh-reduction methods are sought.
MS27: Computational Geomechanics
WaiChing Sun, Columbia University Jose Andrade, Caltech Ronaldo Borja, Stanford University Jinhyun Choo, University of Hong Kong Majid Manzari, George Washington University Richard Regueiro, University of Colorado Boulder AbstractGeomaterials, such as soil, rock, and concrete, are multiphase porous materials whose macroscopic mechanical behaviors are governed by grain size distribution and mineralogy, fluid-saturation, pore space, temperature, loading paths and rate, drainage conditions, chemical reactions, and other factors. As a result, predicting the mechanical responses of geomaterials often require knowledge of how several processes, which often take place in different spatial and temporal domains, interact with each other across length scales. This mini-symposium is intended to provide a forum for researchers to present contributions to recent advances in computational geomechanics problems. Topics of interest include, but are not limited to (1) development and validation of constitutive models that addressed multi-physical coupling effects, (2) discrete and continuum formulations for geomechanics problems, (3) iterative sequential couplings of fluid and solid solvers, (4) uncertainty quantification and spatial variability of soil properties, (5) multiscale mechanics, (6) modeling of weak and strong discontinuities, (7) regularization techniques to circumvent pathological mesh dependence and (8) techniques to model crack growth and fragmentation processes in geomaterials. Submission link: https://www.openconf.org/emi2018/openconf.php Our manuscript on crystallization-induced damage in porous media has been accepted by CMAME1/24/2018 Cracking and damage from crystallization in pores: Coupled chemo-hydro-mechanics and phase- eld modeling Jinhyun Choo WaiChing Sun Abstract Cracking and damage from crystallization of minerals in pores center on a wide range of problems, from weathering and deterioration of structures to storage of CO2 via in situ carbonation. Here we develop a theoretical and computational framework for modeling these crystallization-induced de- formation and fracture in infiltrated porous materials. Conservation laws are formulated for coupled chemo-hydro-mechanical processes in a multiphase material composed of the solid matrix, liquid solution, gas, and crystals. We then derive an expression for the effective stress tensor that is energy-conjugate to the strain rate of a porous material containing crystals growing in pores. is form of effective stress incorporates the excess pore pressure exerted by crystal growth—the crystallization pressure—which has been recognized as the direct cause of deformation and fracture during crystallization in pores. Continuum thermodynamics is further exploited to formalize a constitutive framework for porous media subject to crystal growth. e chemo-hydro-mechanical model is then coupled with a phase- eld approach to fracture which enables simulation of complex fractures without explicitly tracking their geometry. For robust and e cient solution of the initial-boundary value problem at hand, we utilize a combination of nite element and nite volume methods and devise a block-partitioned preconditioning strategy. rough numerical examples we demonstrate the capability of the proposed framework for simulating complex interactions among unsaturated ow, crystallization kinetics, and cracking in the solid matrix. [PDF] Our manuscript on using recurrent neural network to perform offline homogenization for multi-phase multi-permeability porous media has been accepted by CMAME today. This technique break down the computational barrier commonly exhibited in DEM-FEM and FEM2 models and therefore allow simulations connected across multiple scales. Spectral decomposition is used to correct the frame-dependent issues exhibited in RNN constitutive laws; issues on over- and under-fitting are regularized; k-fold validation techniques are used; and a model selection procedure on a directed graph is introduced. [PDF]
Thank you Professors Jidong Zhao and Jinhyun Choo for hosting me at HKU and HKUST. It's a great visit.
Computational thermomechanics of crystalline rock. Part I: a combined multi-phase-field/crystal plasticity approach for single crystal simulations SeonHong Na, WaiChing Sun Abstract: Rock salt is one of the major materials used for nuclear waste geological disposal. The desired characteristics of rock salt, i.e., high thermal conductivity, low permeability, and self-healing are highly related to its crystalline microstructure. Conventionally, this microstructural effect is often incorporated phenomenologically in macroscopic damage models. Nevertheless, the thermomechanical behavior of a crystalline material is dictated by the nature of crystal lattice and micromechanics (i.e., the slip-system). This paper presents a model proposed to examine these fundamental mechanisms at the grain scale level. We employ a crystal plasticity framework in which single-crystal halite is modeled as a face-centered cubic (FCC) structure with the secondary atoms in its octahedral holes, where a pair of Na+ and Cl− ions forms the bond basis. Utilizing the crystal plasticity framework, we capture the existence of an elastic region in the stress space and the sequence of slip system activation of single-crystal halite under different temperature ranges. To capture the anisotropic nature of the intragranular fracture, we couple a crystal plasticity model with a multi-phase-field simulation that does not require high-order terms for the phase field. Numerical examples demonstrate that the proposed model is able to capture the anisotropy of inelastic and damage behavior under various loading rates and temperature conditions. [PDF] Abstract ID and Title: 290275: Computational thermo-hydro-mechanics for freezing and thawing multiphase geological media in the finite deformation range Final Abstract Number: MR33C-0478* Presentation Type: Poster Session Date and Time: Wednesday, 13 December 2017; 13:40 - 18:00 Session Number and Title: MR33C: Multiphysics Models of Coupled Processes in Rock Mass Posters Hybrid Data-driven multiscale modeling of brittle and ductile responses of fluid-infiltrating geomaterials
WaiChing Sun* Department of Civil Engineering and Engineering Mechanics, the Fu Foundation School of Engineering and Applied Science Columbia University in the City of New York 500 West 125 Street Mudd 614, New York, New York, USA e-mail: wsun@columbia.edu, web page: http://www.poromechanics.weebly.com ABSTRACT High-rate responses of wetted granular materials are important for projectile penetration in soils, explosion, subsurface exploration, ground improvement and ballistic vulnerability of military structures. While phenomenological models have achieved great success at predicting quasi-static responses of low confining pressure, high-rate responses of wetted granular materials are not well understood, capturing the influence of pore-fluid across different degree of saturation regimes for crushable geomaterials remains a major challenge. In principle, hierarchical multiscale methods such as DEM-FEM and FEM2 are proven to be effective to link simulations, but the coupled fluid-solid interaction is often confined in small scale problems that are not directly related to field applications. The purpose of this research is to create an alternative offline method that takes advantage of deep learning, a machine learning technique, as a mean to enable multiple coupling simulations that predict the interplays among the nanometer grain-scale behavior, the mesoscale path-dependent behaviors of the heterogeneous multi-porosity porous media and the kilometer-scale field responses of geological systems. Formulated in a finite strain dual-porosity poromechanics framework, the underlying graph-based data-driven multiscale algorithm may adaptively hybridizes conventional mathematical theories and data-driven knowledge in a directed graph based on the amount of data available for verifications. This hybrid modeling technique is then applied to various applications related to geological systems including calibrating and verifying micropolar models with micro-CT images, predicting coalescence and branching of fluid-driven fractures and modeling split-Hopkinson bar. Further information about the 2017 Young Investigator Research Program Meeting can be found at: https://community.apan.org/wg/afosr/w/researchareas/19426/2017-young-investigator-research-program-yip-meeting/ Attended the ICE Award Ceremony at the Institution of Civil Engineers headquarter. I am so honored to receive the Zienkiewicz Medal. Also great to meet Prof. David Potts from Imperial College London again. What a day! #CUSEAS #Zienkiewicz #geomechanics #ICE #geotechnics
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