PhD Student SeonHong Na has been selected by the judges as one of the five finalists for the EMI Student Competition. He will present his work on computational thermo-hydro-mechanics for frozen porous media at finite strain at 11:30am-1pm at Room: Saratt 325 on Tuesday May 24th.
In addition, the research group will have oral presentations listed below: T-3-5 Buttrick 103 758: Modeling Thermal Softening Effects in Coupled THM Problems at Finite Strain WaiChing Sun, Claudio Tamagnini, Federica Ronchi 4:15 pm – 4:30 pm 676: Computational Cryo‐Mechanics for Frozen Soil SeonHong Na, WaiChing Sun 4:30 pm – 4:45 pm W-1-7 Buttrick 103 658: Micro‐Polar Discrete‐Continuum Coupling Method for Fluid‐Infiltrating Porous Media Kun Wang, WaiChing Sun 10:15 am – 10:30 am W-2-6 Buttrick 103 668: Staggered Schemes for Multiscale Arlequin Poromechanics Problems WaiChing Sun, Zhijun Cai 3:15 pm – 3:30 pm
1 Comment
The Columbia research group has acquired a new environmental triaxial testing system. The new apparatus will provide the research team the much needed capacity to validate numerical models for a wide range of geological materials under various drainage, degree of saturation and temperature. In particular, the apparatus may function from -10 Celsius to 60 Celsius degrees and at various degree of saturation.
A SEMI-IMPLICIT MICROPLAR DISCRETE-TO-CONTINUUM METHOD FOR GRANULAR MATERIALS
Kun Wang, WaiChing Sun Department of Civil Engineering and Engineering Mechanics, Columbia University 614 SW Mudd, Mail Code: 4709, New York, NY 10027 e-mail: {kw2534,wsun}@columbia.edu Keywords: Micropolar Continua, Discrete-to-Continuum, Granular Matters, Length Scale, Strain Localization. Abstract. A micropolar discrete-continuum coupling model is proposed to link the collectively particulate mechanical simulations at high-order representative elementary volume to field-scale boundary value problems. By incorporating high-order kinematics to the homogenization procedure, contact moment and force exerted on grain contacts are homogenized into a non-symmetric Cauchy stress and higher-order couple stress. These stress measures in return become the constitutive updates for the macroscopic finite element model for micropolar continua. Unlike the non-lcoal weighted averaging models in which the intrinsic length scale must be a prior knowledge to compute the nonlocal damage or strain measures, the proposed model introduces the physical length scale directly through the higher-order kinematics. As a result, there is no need to tune or adjust the intrinsic length scale. Furthermore, since constitutive updates are provided directly from micro-structures, there is also no need to calibrate any high-order material parameters that are difficult to infer from experiments. These salient features are demonstrated by numerical examples. The classical result from Mindlin is used as a benchmark to verify the proposed model. URL: https://www.seas.harvard.edu/calendar/event/86486
Some remarks on modeling fluid-infiltrating, thermal-sensitive, and partially-frozen porous media across length scales 23MAR Applied Mechanics Colloquia Steve WaiChing Sun, Columbia University Wednesday, March 23, 2016 - 4:00pm to 5:00pm MD G115 Many engineering applications, such as geological disposal of nuclear waste, require reliable predictions on how porous media responds to extreme environments. This presentation will discuss the relevant modeling techniques designed specific for porous media subjected to such harsh environments. In particular, we will discuss (1) a finite strain finite element model that captures the freeze-thaw action of frozen soil, (2) the stability and dispersion analyses that reveals the vanishing of physical length scale of thermal-sensitive porous media at short wavelength limit, (3) the usage of multiscale techniques to link grain-scale simulations to macroscopic predictions and hence bypass the usage of any macroscopic phenomenological law. Spurious pathological predictions by previous DEM-FEM models are examined and the remedies are proposed. Speaker Bio: WaiChing Sun is an assistant professor in the Department of Civil Engineering and Engineering Mechanics at Columbia University. Prior to joining the Columbia faculty, he is a senior member of technical staff at Sandia National Laboratories. Professor Sun works in the fields of theoretical and computational poromechanics with a special emphasis on geomechanical applications. His research includes multiscale modeling porous media, multiscale verification and validation with CT images, digital rock and granular physics, applications of mathematical tools, such as graph theory, Lie algebra for modern engineering problems. He received the Dresden Junior Fellowship in 2016, Army Young Investigator Program Award in 2015, and the Caterpillar Best Paper Prize in 2013. He holds BS degree from UC Davis, MS degrees from Stanford and Princeton and PhD degrees from Northwestern. Host: Chris Rycroft Contact: Rebekah Stiles Email: rstiles@seas.harvard.edu A semi-implicit discrete-continuum coupling method for porous media based on the effective stress principle at finite strain
Kun Wang, WaiChing Sun A finite strain multiscale hydro-mechanical model is established via an extended Hill-Mandel condition for two-phase porous media. By assuming that the effective stress principle holds at unit cell scale, we established a micro-to-macro transition that links the micromechanical responses at grain scale to the macroscopic effective stress responses, while modeling the fluid phase only at the macroscopic continuum level. We propose a dual-scale semi-implicit scheme, which treats macroscopic responses implicitly and microscopic responses explicitly. The dual-scale model is shown to have good convergence rate, and is stable and robust. By inferring effective stress measure and poro-plasticity parameters, such as porosity, Biot’s coefficient and Biot’s modulus from RVE, the multiscale model is able to predict effective poro-elasto-plastic responses without introducing additional phenomenological laws. The performance of the proposed framework is demonstrated via a collection of representative numerical examples. Fabric tensors of the representative elementary volumes are computed and analyzed via the anisotropic critical state theory when strain localization occurs. Micropolar effect on the cataclastic flow and brittle-ductile transition in high porosity rocks
A micro-mechanical DEM model is adopted to analyze the grain-scale mechanism that leads to the brittle-ductile transition in cohesive-frictional materials. The cohesive-frictional materials are idealized as a particulate assemblies of circular disks. While the frictional sliding of disks is sensitive to the normal compressive stress exerted on contacts, normal force can be both caused by interpenetration and long-range cohesive bonding between two particles. Our numerical simulations indicate that the proposed DEM models is able to replicate the gradual shift of porosity change from dilation to compaction, and failure pattern from localized failures to cataclastic flowupon rising confining pressure in 2D biaxial tests. More importantly, the micropolar effect is examined by tracking couple stress and micro-crack initiation to interpret the transition mechanism. Numerical results indicate that the first invariant of the couple stress remains small for specimen sheared under low confining pressure but increases rapidly when subjected to higher confining pressure. The micropolar responses inferred from DEM simulations reveal that micro-cracking may occur in a more diffuse and stable manner when the macroscopic couple stress are of higher magnitudes. I am writing to invite your contirbution to the mini-symposium on failure and instability in soft materials and geomaterials co-organized by myself, Joshua White, Pencheng Fu, Nikolaos Bouklas, Wei Wang and Christian Linder for the upcoming ICCM conference at Berkeley.
More information can be found in the URL listed below. http://www.sci-en-tech.com/ICCM/index.php/iccm2016/2016/schedConf/trackP... The conference will take place from August 1st to 4th. Organizers: WaiChing Sun, Columbia University Joshua White, Lawrence Livermore National Laboratory Pengcheng Fu, Lawrence Livermore National Laboratory Nikolaos Bouklas, University of Texas at Austin Wei Wang, Lawrence Livermore National Laboratory Christian Linder, Stanford University Scope: Soft materials and geomaterials both respond to environmental stimuli, such as mechanical and multi-physical loads, in the form of large deformations. Most of the geomaterials such as sand, clay, or shale are natural products of geological processes, such as weathering, sedmentation and erosion. On the other hand, soft materials can be engineered, like polymers, gels, colloids, and foams, or appear in natural form as biological tissues. The fundamental understanding of failure mechanisms and instabilities in these materials has become a topic of active research. In geomaterials, strain localization may occur at vanishing wave propagation speed or when the acoustic tensor becomes singular. Onset of instability can be used as a technique to actively trigger rapid and significant changes in the geometry and properties of soft materials. The main objective for the mini-symposium is to bring together researchers working on the mechanics of soft materials and those working on geomaterials to exchange recent advances and to inspire new ideas, unifying these often-distinct areas of research. Researchers are invited to present their recent work on topics included but not restricted to: -Mathematical frameworks to predict and model material instabilities and failure -Regularization techniques such as rate-dependent models, gradient or nonlocal methods, and high-order continua to avoid ill-posedness. -Diffusive damage and sharp discontinuity techniques to model failure. -Multiscale models for materials at post-bifurcation regimes. -Homogenization and concurrent multiscale methods to couple spatial and temporal scales. -Evolution of fabric and microstructures. Kun Wang, WaiChing Sun, a semi-implicit discrete-continuum coupling method for two-phase wetted granular solid based on the effective stress principle at finite strain
Place: Plasticity of Granular and Geomaterials IV (Room: Mauna Kea) Sheraton Kona Time: Wednesday January 6th 5pm - 5:30pm. URL: http://www.internationalplasticity.com/indexSK.htm New paper on wave propagation in thermo-sensitive fully saturated porous media accepted in IJNAMG.1/4/2016 Wave propagation and strain localization in a fully saturated softening porous medium under the non-isothermal conditions [PDF]
SeonHong Na, WaiChing Sun Abstract The thermo-hydro-mechanical (THM) coupling effects on the dynamic wave propagation and strain localization in a fully saturated softening porous medium are analyzed. The characteristic polynomial corresponding to the governing equations of the THM system is derived, and the stability analysis is conducted to determine the necessary conditions for stability for both non-isothermal and adiabatic cases. The result from the dispersion analysis based on the Abel-Ruffini theorem reveals that the roots of the characteristic polynomial for the thermo-hydro-mechanics problem can not be expressed algebraically. Meanwhile, the dispersion analysis on the adiabatic case leads to a new analytical expression of the internal length scale. Our limit analysis on the phase velocity for the non-isothermal case indicates that the internal length scale for the non-isothermal THM system may vanish at the short wavelength limit. This result leads to the conclusion that the rate-dependence introduced by multiphysical coupling may not regularize the THM governing equations when softening occurs. Numerical experiments are used to verify the results from the stability and dispersion analyses. Our research team has received a start-up award from the XSEDE program (Extreme Science and Engineering Discovery Environment). The research team has been granted access to 50K service units from the SDSC Dell Cluster with Intel Haswell Processors (Comet), (1SUs = 1 hour of computing on 1 CPU) .
Recently graduated group member Yang Liu (pictured left) will start her Postdoctoral Associate Appointment in the Department of Aeronautics and Astronautics at MIT in November 2015. She will work with Professor Raul Radovitzky on high-performance computing, computational modeling and simulation of material fracturing. Yang defended her PhD thesis entitled “Multiscale Modeling of Granular Materials” in August 2015 under the supervision of Professors WaiChing Sun and Jacob Fish in the Department of Civil Engineering and Engineering Mechanics at Columbia University. Congratulations Yang! Group member Kun Wang received travel grant to attend the upcoming SES Meeting at Texas A&M. Kun will present his work on micro-polar discrete-continuum coupling model for saturated porous media.
Congratulations Kun! A nonlocal multiscale discrete-continuum model for predicting mechanical behavior of granular materials
Yang Liu, WaiChing Sun,Zifeng Yuan, Jacob Fish Department of Civil Engineering and Engineering Mechanics, Columbia University, New York, NY 10027, USA SUMMARY A three-dimensional nonlocal multiscale discrete-continuum model has been developed for modeling mechanical behavior of granular materials. In the proposed multiscale scheme, we establish an information-passing coupling between the discrete element method (DEM), which explicitly replicates granular motion of individual particles, and a finite element continuum model, which captures nonlocal overall responses of the granular assemblies. The resulting multiscale discrete-continuum coupling method retains the simplicity and efficiency of a continuum-based finite element model, while circumventing mesh pathology in the post-bifurcation regime by means of staggered nonlocal operator. We demonstrate that the multiscale coupling scheme is able to capture the plastic dilatancy and pressure-sensitive frictional responses commonly observed inside dilatant shear bands, without employing a phenomenological plasticity model at a macroscopic level. In addition, internal variables, such as plastic dilatancy and plastic flow direction, are now inferred directly from granular physics, without introducing unnecessary empirical relations and phenomenology. The simple shear and the biaxial compression tests are used to analyze the onset and evolution of shear bands in granular materials and sensitivity to mesh density. The robustness and accuracy of the proposed multiscale model are verified in comparisons with single-scale benchmark DEM simulations. KEY WORDS: multiscale discrete-continuum model; staggered nonlocal operator; strain localization; granular materials; homogenization; shear band; anisotropy Abstract
This work presents a new staggered multilevel material identification procedure for phenomenological critical state plasticity models. The emphasis is placed on cases in which available experimental data and constraints are insufficient for calibration. The key idea is to create a secondary virtual experimental database from high-fidelity models, such as discrete element simulations, then merge both the actual experimental data and secondary database as an extended digital database to determine material parameters for the phenomenological macroscopic critical state plasticity model. The calibration procedure therefore consists of two steps. First, the material parameters of the DEM simulations are identified via the standard optimization procedure. Then, the calibrated DEM simulations are used to expand the experimental database with new simulated loading histories. This expansion of database provides additional constraints necessary for calibration of the phenomenological critical state plasticity models. The robustness of the proposed material identification framework is demonstrated in the context of the Dafalias-Manzari plasticity model. URL: http://appliedmechanics.asmedigitalcollection.asme.org/article.aspx?articleid=2443823 Professor Sun received recognitions for his work as a part of the research team that develops Albany v2.0, a computational mechanics code developed by research staffs at Sandia National Laboratories and collaborators from Universities. The research project is lead by Dr. Andrew Salinger from Sandia National Laboratories. Dr. Sun’s involvement in this project includes the theoretical development and implementations of a number of finite strain models for poromechanics and thermo-hydro-mechanics problems, and the implementation of a hydrogen embrittlement model derived by his collaborators. Prof. Sun’s work on Albany has resulted in 6 journal articles [1-6], 5 of which he served as the first author. More information can be found in the publication listed below. 1. Mota, W.C. Sun, J.T.Ostein, J.W. Foulk III, K.N. Long, Lie-Group interpolation and variational recovery for internal variables, Computational Mechanics, 52:1281-1299, doi:10.1007/s00466-013-0876-1, 2013. [PDF] [Bibtex] 2. W.C. Sun, J.T. Ostien, A.G. Salinger, A stabilized assumed deformation gradient finite element formulation for strongly coupled poromechanical simulations at finite strain, International Journal for Numerical and Analytical Methods in Geomechanics, 37(16):2755-2788, doi:10.1002/nag.2161, 2013. [PDF] [Bibtex] 3. W.C. Sun, M.R. Kuhn and J.W.Rudnicki, A multiscale DEM-LBM analysis on permeability evolutions inside a dilatant shear band, Acta Geotechnica, 8(5):465-480, doi:10.1007/s11440-013-0210-2, 2013. (The authors received the Caterpillar Best paper prize in the year of 2013) [PDF] [Bibtex] 4. W.C. Sun, Q. Chen, J.T. Ostien, Modeling hydro-mechanical responses of strip and circular footings on saturated collapsible geomaterials, Acta Geotechnica, 9(5):903-934, doi:10.1007/s11440-013-0276-x, 2014. [PDF] [Bibtex] 5. W.C. Sun, A. Mota, A multiscale overlapped coupling formulation for large deformation strain localization, Computational Mechanics, 54(3):803-820, doi: 10.1007/s00466-014-1034-0, 2014. [PDF] [Bibtex] [Erratum] 6. W.C. Sun, A stabilized finite element formulation for monolithic thermo-hydro-mechanical simulations at finite strain, International Journal for Numerical Methods in Engineering, 103(11):798-839, doi:10.1002/nme.4910, 2015. [PDF] [Bibtex] URL: http://www.vanderbilt.edu/emipmc2016/EMI.mini-symposia.php
EMI-MS-16: Computational Geomechanics Steve WaiChing Sun, Qiushi Chen, Xiaoyu Song, Joshua White, Richard Regueiro, Jose Andrade, Majid Manzari, Ronaldo Borja Geomaterials, such as soil, rock and concrete, are multiphase porous materials whose macroscopic mechanical behavior is 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 response of geomaterials often requires knowledge on 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 on recent advances in Computational Geomechanics. Topics within the scope of interests include, but are not limited to, the following: (1) development and validation of constitutive models that address multi-physical coupling effects, (2) discrete and continuum formulations for geomechanics problems, (3) iterative sequential couplings of fluid and solid solvers, (4) uncertainty quantification for geomechanics problems, (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. Vortragsankündigung: Im Rahmen der Forschergruppe FOR 2089 ist Prof. WaiChing Sun
als Gast am Institut für Statik und Dynamik der Tragwerke und wird über seine Arbeiten be- richten Datum: 27.08.2015 Raum: Bey 67 Zeit: 14:00 Uhr Multiscale coupling method for fluid-infiltrating porous media at the finite deformation range Department of Civil Engineering and Engineering Mechanics, Fu Foundation School of Engineering and Applied Science, Columbia University, New York Email: wsun@columbia.edu The mechanical behavior of a fluid-infiltrating porous solid is significantly influenced by the presence and diffusion of the pore fluid in the void. This hydro-mechanical coupling effect can be observed in a wide range of materials, including rocks, soils, concretes, bones and soft tissues. Due to the high computational demand, explicitly simulating the pore-scale solid-fluid interactions remains impractical for engineering problems commonly encountered in the field and basin scales. The objective of this talk is to present classes of multiscale technologies that couple hydro-mechanical simulations across different spatial and temporal scales. The first class of model is a concurrent coupling model in which deformation-diffusion problems are re-casted as a two-fold saddle point problem that optimizes the constrained partitioned incremental work of a multi-field energy functional. By enforcing compatibility across length scales, pore-scale simulations in confined domain can be coupled with large-scale field problems while maintaining numerical stability and accuracy. The combined usage of temporal operator split and Arlequin model to resolve highly refined details of space-time porous continuum will be discussed. The second class of multiscale model is a nonlocal hierarchical multiscale framework that couples grain-scale network-DEM simulations with a macroscopic hydro-mechanical mixed finite element model. This hierarchical nonlocal DEM-mixed-FEM coupling retains the simplicity and efficiency of the continuum-based finite element model, while possessing the original length scale of the granular system. Techniques for two-scale material identification with inverse problems will be discussed. The pros and cons of these different multiscale-coupling strategies will be demonstrated in numerical examples. The proposal #1462760 "A Phase Field Arlequin Model for Resolving Nonlocal Hydromechanical Effects of Porous Media Across Time and Spatial Scales" submitted to Mechanics of Material program of NSF has been awarded at the level of $300,000. The funding will support research and educational activities for a new type of computational poromechanics model that enables modeling of multi-physical events at different spatial and temporal scales.
In additional to this single-PI proposal, the research group has also received support NSF from NSF proposal #1520732 and #1516300 in which Prof. Sun served as co-PI. Two multiscale discrete-continuum models for predicting fluid-saturated geomaterials from grain- to field-scales
Prof. Steve Waiching Sun Department of Civil Engineering and Engineering Mechanics Columbia University, New York Monday, August 10, 2015 2:00 PM – 3:00 PM Building 823 Room 2279 The mechanical behavior of a fluid-infiltrating porous solid is significantly influenced by the presence and diffusion of the pore fluid in the void. This hydro-mechanical coupling effect can be observed in a wide range of materials, including rocks, soils, concretes, bones and soft tissues. Due to the high computational demand, explicitly simulating the pore scale solid-fluid interactions remains impractical for engineering problems commonly encountered in the field and basin scales. The objective of this talk is to present two classes of multiscale technologies that couple across different spatial and temporal scales. The first class of model is a concurrent coupling model in which deformation-diffusion problems are casted as the two-fold saddle point that optimizes the constrained partitioned incremental work of a multi-field energy functional. By enforcing compatibility across length scales, pore-scale simulations in confined domain can be coupled with large-scale field problems while maintaining numerical stability and accuracy. The combined usage of temporal operator split and Arlequin model to resolve highly refined details of space-time porous continuum will be discussed. The second class of multiscale model is a nonlocal hierarchical multiscale framework that couples grain-scale discrete element simulations with a hydromechanical mixed finite element model. This hierarchical nonlocal DEM-mixed-FEM coupling retains the simplicity and efficiency of the continuum-based finite element model, while possessing the original length scale of the granular system. Techniques for two-scale material identification with Dakota will be discussed. The pros and cons of these two different coupling strategies will be demonstrated in numerical examples. PhD Candidate Yang Liu has just won the 2015 Student Poster Competition among all students presented at over 100 mini-symposia in the US National Congress of Computational Mechanics at San Diego. Congratulations Yang! [Press release from department]
From their inception in 1991, the biennial congresses of the U.S. Association for Computational Mechanics have become major scientific events, drawing computational engineers and scientists worldwide from government, academia, and industry. The congress provides a forum for researchers and practitioners all over the world to discuss the latest advancements and future directions in fields pertaining to computational engineering and sciences. The congress will feature plenary speakers, over 100 mini-symposia with keynote lectures and contributed talks, a student poster competition, and exhibits from various sponsors. Title: A Discrete Continuum-Coupling Approach for Predicting Anisotropic Damages in Water-Saturated Brittle Rocks
Minisymposium: Multiscale Modeling of Granular Materials Authors: WaiChing Sun* , Kun Wang Time/Location: July 30, 2015 @ 11:40 a.m.-noon in Cove Abstract: We develop a dual-scale model to predict the brittle behavior of water-saturated rocks under various drainage condition across length scale. In this formulation, we exploit the effect stress principle to partition stress stemming from grain contact and grain-to-grain bonding and those from fluid-solid interfaces at grain-scale. While the evolution of microstructures of solid skeleton is simulated explicitly at grain scale via discrete mechanics approach, the interaction of pore fluid and solid grain is captured at continuum scale via a mixed finite element u-p formulation. As a result, there is no need to incorporate phenomenological law to govern damage or phase field evolutions at the macroscopic continuum level. Various strategies to overcome mesh bias will be compared. Numerical examples will be used to demonstrate the accuracy and robustness of the multiscale multiphysics model. A new research conducted by group member Kun Wang has results in a journal article accepted by Journal of Engineering Mechanics. This research focuses on the hydro-mechanical responses of wetted granular matters at the pendular regime. By analyzing the tensorial Bishop's coefficient using Young-Laplace equation and DEM, we study the relation between the macroscopic apparent cohesion and the formation and rupture of liquid bridges. We also examine the path dependence and anisotropy of the Bishop's coefficient from the force chain evolution simulated in DEM. Further information can be found in the preprint [PDF].
Abstract The objective of this research is to use grain-scale numerical simulations to analyze the evolution of stress anisotropy exhibited in wetted granular matters. Multiphysical particulate simulations of unsaturated granular materials were conducted to analyze how the interactions of contact force chains and liquid bridges influence the macroscopic responses under various suction pressure and loading history. To study how formation and rupture of liquid bridges affect the mechanical responses of wetted granular materials, a series of suction-controlled triaxial tests were simulated with two grain assemblies, one composed of large particles of similar sizes, another one composed of a mixture of large particles with significant amount of fines. Our results indicate that capillary stress are anisotropic in both sets of specimens, and that the stress anisotropy is more significant in granular assemblies filled with fine particles. A generalized tensorial Bishop's coefficient is introduced to analyze the connections between microstructrual attributes and macroscopic responses. Numerical simulations presented in this paper indicate that the principal values and directions of this Bishop's coefficient tensor are path dependent. Press release from Fu Foundation School of Engineering, Columbia University:
http://engineering.columbia.edu/professor-steve-sun-receives-army%E2%80%99s-young-investigator-award# |
Group NewsNews about Computational Poromechanics lab at Columbia University. Categories
All
Archives
July 2023
|