Discontinuous Media Research Articles

Random Walk Modeling of Conductive Heat Transport in Discontinuous Media

AbstractWe consider heat transport within a discontinuous domain by relying on the modeling approach proposed by Baioni et al. Such approach has been specifically designed to address diffusive processes in media with discontinuous physical properties and generalized boundary conditions at the discontinuities. Three algorithms are here applied to estimate the conductive heat transport in a bimaterial medium. The algorithms undergo testing using two test cases that share the same computational domain but differ in terms of their initial conditions. According to the numerical results all the algorithms ensure the conservation of thermal energy and preserve thermal equilibrium under steady state conditions. The Generalized Uffink Method (GUM) and Generalized HYMLA demonstrate sensitivity to the choice of the time step, whereas the Generalized Skew Brownian Motion appears to be unaffected by the value of $$\Delta t$$ Δ t . The GUM algorithm presents an optimal trade-off between accuracy and computational time.

Modeling obliquely incident seismic wave propagation in rocks via the FDM-DEM coupling scheme: Algorithms and applications

The incidence angle of seismic waves plays a pivotal role in the stability analysis of structures in near-field zones. Despite its importance, the application of obliquely incident seismic waves within models of discontinuous media has been limited. This study introduces a novel approach that integrates the oblique incidence of seismic waves into a coupled model employing both the Finite Difference Method (FDM) and the Discrete Element Method (DEM). We validate the accuracy of seismic wave propagation under oblique incidence in two FDM-DEM coupling models—overlapping coupling and interface coupling—through comparisons with theoretical solutions. For vertically incident seismic P-waves, both models yield similar results. However, under oblique incidence, the overlapping coupling model demonstrates superior accuracy, with a maximum error of approximately 4.217 %, compared to about 10 % in the interface coupling model. Our findings also show that while the relative sizes of particle diameter and overlap length minimally affect accuracy, the arrangement of particles markedly influences the results. Furthermore, we apply this method to a slope model to investigate the failure process, revealing that the nature of the sliding body shifts from tensile sliding to tensile ejection as the incidence angle increases.

Mechanical Behavior of Sediment-Type High-Impurity Salt Cavern Gas Storage during Long-Term Operation

With the development of salt cavern gas storage technology, the construction of large-scale salt cavern gas storage using sediment voids is expected to solve the problems of low effective volume formation rate and poor construction economy of high-impurity salt mines. At present, there are few studies on the long-term operational mechanical behavior of salt cavern gas storage under the influence of sediment accumulation. The present paper studies the influence of sediment height, particle gradation, and operating pressure on the stability of salt caverns by constructing a coupling model of sediment particle discontinuous medium and surrounding rock continuous medium. The continuous–discontinuous coupling algorithm is suitable for analyzing the influence of sediment height and particle gradation on the creep shrinkage of salt caverns. The increase in sediment height slows down the creep shrinkage of the cavern bottom, which strengthens the restraining effect on the surrounding rock of the cavern. As a result, the position of the maximum displacement of the surrounding rock moves to the upper part of the cavern. The sediment particle gradation has little effect on the cavern volume shrinkage rate. The greater the coarse particle content, the smaller the cavern volume shrinkage rate. The greater the operating pressure, the more conducive to maintaining the stability of the cavern. This situation slows down the upward movement of the sediment accumulation and increases the gas storage space in the upper part of the cavern. The obtained results can provide a reference for evaluating the long-term operational stability of sediment-type high-impurity salt cavern gas storage.

Modeling Diffusion in One Dimensional Discontinuous Media under Generalized Permeable Interface Conditions: Theory and Algorithms

Modeling Diffusion in One Dimensional Discontinuous Media under Generalized Permeable Interface Conditions: Theory and Algorithms

A hybrid finite-discrete element method for modelling cracking processes in sandy mudstone containing a single edge-flaw under cyclic dynamic loading

Rock mass deformation and failure are macroscopic manifestations of crack initiation, propagation, and coalescence. However, simulating the transition of rocks from continuous to discontinuous media under cyclic dynamic loading remains challenging. This study proposes a hybrid finite-discrete element method (HFDEM) to model crack propagation, incorporating a frequency-dependent cohesive-zone model. The mechanical properties of standard sandy mudstone under quasi-static and cyclic dynamic loading were simulated using HFDEM, and the method's reliability was verified through experimental comparison. The comparative analysis demonstrates that HFDEM successfully captures crack interaction mechanisms and accurately simulates the overall failure behavior of specimens. Additionally, the effects of pre-existing flaw inclination angle and dynamic loading frequency on rock failure mechanisms were investigated. The numerical results reveal that rock samples exhibit significantly higher compressive strength under dynamic loading compared to quasi-static loading, with compressive strength increasing with higher cyclic dynamic load frequencies. Furthermore, by analyzing the strength characteristics, crack propagation, and failure modes of the samples, insights into the failure mechanisms of rocks under different frequency loads were obtained. This study provides valuable insights into crack development and failure of rocks under seismic loads, offering guidance for engineering practices.

Application of discrete element method (DEM) in pharmaceutical process of solid traditional Chinese medicine preparations

In recent years, the application of numerical simulation in the research and development(R&D) as well as the pharmaceutical processes of new drugs has expanded considerably. The discrete element method(DEM), an important approach among numerical simulation methods, offers an effective tool for the simulation of discontinuous media. Referring to the research progress of DEM and the formulation of solid traditional Chinese medicine(TCM) preparations in recent years, this paper summarizes and analyzes the application of DEM in the pharmaceutical processes of solid TCM preparations, and discusses the challenges of its application in these processes, in order to provide new methods and ideas for promoting the high-quality production of TCM preparations.

Stress wave in the mesoscopic discontinuous medium by fractional approach

A fractional approach based on the generalized Taylor's formula is proposed to describe the dynamic responses in the meso-discontinuous medium (e.g., oyster shell). The governing equations with the Caputo-defined fractional derivatives in space are derived. In order to describe the dynamic effect of geometric structures in the meso- discontinuous medium, the finite element method (FEM) is employed together with the fractional governing equations to establish the relation of the equivalent fractional order (α¯) with the fractal dimension (D), and the linear relation is obtained as: α¯=0.99D−0.97. The results also show that the equivalent effects of porous structure on wave propagation could be determined by fractal dimension and fractional order. The CO2 pulse laser together with VISAR measurement is then employed to investigate the dynamic responses in the oyster shell specimens. The evaluated equivalent fractional order decreases with increasing of the density, and the equivalent fractional orders (α¯) of pure nacre and pure chalk are estimated to be respectively 0.61 and 0.69, while the estimated α¯ of pure nacre and pure chalk by FEM are 0.63 and 0.79. The difference of estimated α¯(0.79) with actual α¯(0.69) of chalk is due to the irregular interface, which would cause greater wave attenuation. Due to the stronger and much more meso-discontinuous interfaces (i.e., the brick-mud structures) in the nacre, wave amplitude decays more seriously in the nacre (denser with higher density) than those in the chalk (looser with lower density), and measured velocities decrease with increasing of the density. This work provided a new approach to investigate the dynamic mechanical properties of meso-discontinuous mediums.

Thermal diffusion in discontinuous media: A hybrid peridynamics-based machine learning model

This paper introduces a novel hybrid formulation of a peridynamics-based machine learning model for thermal diffusion analysis in one-dimensional and two-dimensional problems with evolving discontinuities. The hybrid model employs a multivariate linear regression approach to establish the relationship between the temperature values of material points, their neighboring points, and the applied external heat flux. The thermal modal analysis method uses the finite element method to generate training and testing data. An efficient numerical procedure is also developed to couple the peridynamics model and the peridynamics-based machine learning model. The model is analyzed under multiple configurations of micro-thermal conductivity functions for one-dimensional thermal bar problems, under both steady-state and transient loading conditions, to identify the configuration that exhibits superior convergence behavior towards the local solution. Furthermore, benchmark problems demonstrate the high accuracy of the formulated hybrid model, including the analysis of thermal plates with discontinuities, such as a plate with a hole, a plate with a pre-existing insulated crack, and plate with a bi-material interface with stationary and evolving discontinuances. The hybrid model effectively captures intricate discontinuities and boundaries while being computationally efficient, indicating its potential for thermal diffusion analysis in one- and two-dimensional problems with stationary and evolving discontinuities.

Lightweight and dual-peak H-pattern metamaterial absorber based on discontinuous dielectric media in the L-band range

In view of the problem of heavy weight of the low-frequency band metamaterial absorber, the weight of the metamaterial absorber is mainly concentrated in the medium dielectric substrate. Different from the previous metamaterial absorbers based on continuous dielectric substrate, a new lightweight metamaterial absorber based on discontinuous dielectric medium is proposed and verified in the L-band (1–2[Formula: see text]GHz). Compared with metamaterial absorber based on the continuous dielectric substrate, the weight of the metamaterial absorber designed based on discontinuous media is reduced by 42.58%. The dual-peak reflection losses of −17.29[Formula: see text]dB and −15.99[Formula: see text]dB are obtained at 1.23[Formula: see text]GHz and 1.72[Formula: see text]GHz, respectively. Our work provides a new method for constructing light dual-peak metamaterial absorbers in the L-band.

Influence of homogeneous discontinuous medium on the propagation law of explosion shock wave pressure

Influence of homogeneous discontinuous medium on the propagation law of explosion shock wave pressure

Water Erosion and Extension of Ground Fissures in Weihe Basin Based on DEM-CFD Coupled Modeling

The Weihe Basin is one of the regions with the highest concentrations of ground fissure development and the most serious disasters in China. Hidden ground fissures are formed in the shallow soil layer due to preexisting fissures generated by tectonism, hidden ground fissures suddenly exposed to the surface after heavy rainfall. Because the details of the water erosion process cannot be replicated by geological survey methods, the erosion and extension mechanism has not fully developed and the discontinuous medium numerical simulation method is well suited for simulating large deformations and facilitates a microscopic perspective in elucidating the underlying causal mechanisms. This paper deploys the discrete element method (DEM)–computational fluid dynamics (CFD) fluid–solid coupled method modeling the growth process of hidden fissures containing different soil types (sand and clay) under heavy rainfall, revealing a mechanism for the development of hidden fissures into surface fissures. The findings include: (1) the emergence process of hidden fissures into surface fissures under heavy rainfall can be summarized into four stages: subsurface erosion into hidden holes, traction into arches, collapse into sinkholes, and horizontal extension; (2) the emergence process of clay is slower than that of sand due to the constraint of cohesion; (3) the shape of the bottom seepage point affects the fissure emergence process, which is an important factor in the macroscopic performance of the exposed surface fissures. The intuitive and reproducible DEM-CFD coupled modeling used in this paper possesses important reference value for the study and prevention of water erosion ground fissures.

Effect of aggregate sphericity on the mechanical properties of ERCC based on highly detailed simulation

Electrically conductive roller-compacted concrete (ERCC) is a novel functional construction material with self-heating ability, which can be applied to solve problems of low efficiency of crushed snow removal and deicing on expressway and airport runway, and difficult temperature control of dam structures. Natural aggregates with high sphericity and crushed aggregates with low sphericity are the sources of ERCC construction. However, the impact of aggregate sphericity on ERCC is currently unclear. This study performed the macro and micro experiments of the core samples from a large-scale ERCC specimen with rolling construction technology. Based on the experimental results, the mechanical properties of ERCC with different aggregate sphericities are analyzed with the highly detailed simulation method by coupling continuous medium method and discontinuous medium method. The results show that increased sphericity of the aggregate can lead to a decrease in the number of aggregates generated, and the simplified spherical model adopted in the traditional mesoscale simulation method will underestimate the strength of concrete. Furthermore, When the sphericity of aggregate is 0.645, the compressive strength and splitting tensile strength of ERCC are increased by 25.34% and 35.04% compared with that of spherical aggregate respectively. In engineering, the crushed aggregate is suggested for rolling construction of ERCC. The results are in accordance with the statistical laws of the field statistical data in engineering practice.

Multi-scale Numerical Simulation of Powder Metallurgy Densification Process

In order to reduce defects such as pores, gold phases and cracks in powder metallurgy, scholars have studied the densification process of powder metallurgy. Based on the study of the powder metallurgy deformation mechanism, this paper classifies and summarizes the numerical simulation theory and the methods. At present, the numerical simulation of the densification process of powder metallurgy is carried out mainly in macroscopic, mesoscopic and microscopic directions. Macro scale is an application of finite element method based on continuum theory. The meso-scale is an application of the discrete element method based on the discontinuous media theory. Cellular automata simulation is the main numerical simulation method in the microscale. Different modeling theories and methods have their own adaptability and limitations. By combining the numerical simulation theory and the method of various scales, the process of densification of the material can be realized more accurately and accurately.

A novel BEM-DEM coupling in the time domain for simulating dynamic problems in continuous and discontinuous media

This work presents a novel scheme to couple the Boundary Element Method (BEM) and the Discrete Element Method (DEM) in the time domain. The DEM captures discontinuous material behaviour, such as fractured and granular media. However, applying the method to real-life applications embedded into infinite domains is challenging. The authors propose a solution to this challenge by coupling the DEM with the BEM. The capability of the BEM to model infinite domains accurately and efficiently, without the need for numerical artifices, makes it the perfect complement to the DEM. This study proposes a direct monolithic interface-based coupling method that resolves any incompatibilities between the two methods in two dimensions. The benchmark results show that the proposed methodology consistently produces results that align with analytical solutions. The final example in the paper showcases the full potential of this innovative methodology, where the DEM models a fracturing process, and the BEM evaluates its far-field effect.

Porous Structural Microfluidic Device for Biomedical Diagnosis: A Review.

Microfluidics has recently received more and more attention in applications such as biomedical, chemical and medicine. With the development of microelectronics technology as well as material science in recent years, microfluidic devices have made great progress. Porous structures as a discontinuous medium in which the special flow phenomena of fluids lead to their potential and special applications in microfluidics offer a unique way to develop completely new microfluidic chips. In this article, we firstly introduce the fabrication methods for porous structures of different materials. Then, the physical effects of microfluid flow in porous media and their related physical models are discussed. Finally, the state-of-the-art porous microfluidic chips and their applications in biomedicine are summarized, and we present the current problems and future directions in this field.

Spatial domain localization method for multi-damage in plate-like structure based on coefficient matrix of reflected guided waves

Structural health monitoring (SHM) is a multidisciplinary damage detection technique that incorporates various mechanisms, of which guided waves (GWs) -based damage detection is one of the critical fields of research. To realize the complete process of SHM, research on GWs has concentrated on diagnosis and localization. GWs-based damage detection technology is widely used in plate structure, combining different sensor placement algorithms and equipment such as scanning laser doppler vibrometry (SLDV) to achieve accurate damage location. Simultaneously, developing the finite element method (FEM) allows for precise simulation in discontinuous media and complex sharp structures. Therefore, this paper combines the theoretical calculation approach of elastic wave propagation with the orthogonal matching pursuit (OMP) algorithm, using the excitation signal and signal reflected by damage as the input matrix and target matrix, respectively. Thus, the reflection-waves coefficient matrix (RCM) containing damage information could be obtained after calculation by the OMP algorithm. Besides, a prediction approach of reference reflected signal based on four-layers recurrent neural networks (RNNs) is proposed with experiments data to reduce the difficulty of expanding a dictionary matrix in a plate with multiple defects, which allows for predicting the damage reflection signal under different distances with 88.14% accuracy. And finally, considering the aluminum plate with hole damage as an example, the experiment results show that the proposed approaches are effective for the localization of single damage and muti-damage. Meanwhile, the prospects and limitations of the algorithm for precise localization are also addressed in the last.

JPEG 2000 Extensions for Scalable Coding of Discontinuous Media.

In this paper we propose novel extensions to JPEG 2000 for the coding of discontinuous media which includes piecewise smooth imagery such as depth maps and optical flows. These extensions use breakpoints to model discontinuity boundary geometry and apply a breakpoint dependent Discrete Wavelet Transform (BP-DWT) to the input imagery. The highly scalable and accessible coding features provided by the JPEG 2000 compression framework are preserved by our proposed extensions, with the breakpoint and transform components encoded as independent bit streams that can be progressively decoded. Comparative rate-distortion results are provided along with corresponding visual examples which highlight the advantages of using breakpoint representations with accompanying BD-DWT and embedded bit-plane coding. Recently our proposed extensions have been adopted and are in the process of being published as a new Part 17 to the JPEG 2000 family of coding standards.

Study on Microscopic Characteristics of Spatial Distribution of Fractures in Deteriorated Sandstone

In the underground environment with large buried depth and high ground stress, man-made disturbance is very easy to cause the rapid expansion of primary fractures in the rock, and then developed into the macrodynamic performance of rock. Based on the propagation law of elastic waves in discontinuous media, the application of acoustic emission detection technology can quickly determine whether there are primary fractures in the rock and predict its approximate location. In this work, CT scanning experiments of intact sandstone specimens and fractured sandstone specimens were performed. The gray value distribution of intact sandstone specimens and fractured sandstone specimens was studied. The sandstone specimens were divided into 4 zones (I~IV) from top to bottom. The height of each zone is from 0 mm to 25 mm, and the upper end face of each zone is the starting face. Acoustic emission experiments of intact sandstone and fractured sandstone are carried out based on the equilateral triangle sensor array. The dispersion of AE wave velocity and amplitude in intact sandstone specimens and fractured sandstone specimens is studied. The results show that the crack evolution law of sandstone specimens before and after preloading is closely related to the density distribution. The regular trend is from low density to high density. And the decay law of AE eigenvalue before and after preloading of sandstone specimen is consistent with the change trend of gray value. This shows that it is feasible to explore the spatial location of primary fractures and the degree of development of primary fractures in the rock through the equilateral triangle sensor array. In the actual project, it can provide some guidance and suggestions for related projects.

Bearing capacity of strip footings on jointed rock mass

Rock masses are non-homogenous, discontinuous media composed of rock material and naturally occurring discontinuities such as joints, fractures and bedding planes. Due to the presence of the geological discontinuities such as joints, faults and bedding planes, the compressive strength and modulus of elasticity of jointed rock mass are significantly reduced and the measurement of the strength behaviour of these jointed rock masses below the foundation becomes a challenging task. Previous researches have dealt with the bearing capacity of strip footings on the jointed rock mass for concentric, eccentric, inclined loading, separately. But, very limited work has been carried out for determining the bearing capacity of footings on jointed rock mass under eccentric-inclined loading together. In this study, the behaviour of rock masses under the pressure of strip footing has been investigated. To make the problem, more realistic, eccentric-inclined load was applied on the strip footing resting on horizontal jointed rock mass. A parametric study has also been carried out to develop some non-dimensional correlation between different parameters including GSI, e/B ratio, inclination, bearing capacity, etc. Three-dimensional analysis has been carried out by the finite element method using PLAXIS 3D software. Modified Hoek–Brown criteria was used to simulate the behaviour of rock mass and elastic behaviour of foundation was taken into the consideration for analysis. From the results, it can be concluded that the bearing capacity values drop as the eccentricity of the load increases. This indicates that as the eccentricity of the load increases, the bearing capacity of jointed rock mass diminishes. The bearing capacity value decreases with increasing loading inclination with respect to vertical. In the current study, non-dimensional correlations have been developed using data from non-linear elasto-plastic FEA to forecast footing’ bearing capacity, settlement and tilt of shallow foundation. These connections rely on the inclination of the load as well as the eccentricity to breadth ratio. The results obtained from the non-dimensional correlations holds goods on comparing the results obtained from the FEM analysis.

The Metabolist Imagination: Visions of the City in Postwar Japanese Architecture and Science Fiction by William O. Gardner

Reviewed by: The Metabolist Imagination: Visions of the City in Postwar Japanese Architecture and Science Fiction by William O. Gardner Franz Prichard The Metabolist Imagination: Visions of the City in Postwar Japanese Architecture and Science Fiction by William O. Gardner. Minneapolis: University of Minnesota Press, 2020. Pp. viii + 223. $108.00 cloth, $27.00 paper. This comparative study explores how selected Japanese architects and writers imagined, represented, or visualized the city. Describing in vivid detail their shared investments in what Gardner usefully terms the narrative "elements" of the city, this book offers a captivating mapping of two deeply entangled domains where Japan's urban imaginaries took on new contours during the decades of the 1960s and 1970s. Deftly attending to the speculative dimensions of both literary and architectural discourses of the city, Gardner's book opens new interdisciplinary entryways to Japan's vocabularies of urban environments and planetary urbanization, analyzing the role of speculative futures therein. This volume complements a growing body of scholarship that explores the architectural and visual-cultural histories of the Japanese Metabolist movement, known for its visionary attention to urban design processes that proponents likened to organic processes. This scholarship examines the impact of the Metabolist movement on Japan's architectural and design history.1 It also includes studies of individual Metabolist architects, such as Isozaki Arata 磯崎新 (b. 1931), [End Page 165] Tange Kenzō 丹下健三 (1913–2005), Kikutake Kiyonori 菊竹清訓 (1928–2011), and Kurokawa Kishō 黒川紀章 (1934–2007), as well as studies of the Metabolist movement's central role in the 1970 Osaka World's Fair, Expo '70.2 Moreover, the book makes a significant contribution to interdisciplinary scholarship on the history and contemporary afterlives of the urban transformations of Japan's discursive and built environments more broadly during the 1960s and 1970s.3 Gardner's primary focus is not the Metabolists' iconic architectural designs and large-scale regional redevelopment plans. (The book does include a number of well-chosen color illustrations and photographs of Metabolist works, for which the press should be applauded.) Rather, he focuses on an evocative survey of central Metabolist keywords, such as "process," "megastructure," "capsule," and "ruins." Gardner's aim is not merely an intellectual history of Metabolist thought. The book dynamically sifts through Metabolist vocabularies to explore the intersecting narrative dimensions of what Gardner calls "imaginative simulation" (p. 1) undertaken by both architects and science-fiction writers to reimagine Japan's built environments and social conditions. The representative central figures of this study are architect Isozaki Arata (whose early writings bleed into speculative fiction territory) and celebrated science-fiction author Komatsu Sakyō 小松左京 (1931–2011) (who participated directly in the planning of Expo '70). Bringing such figures into critical dialogue, the book traces the direct and indirect exchanges among their narrative imaginaries of the city, as well as the formative role these exchanges played in developing the discourses of information society, cybernetics, systems theory, futurology, and planetary catastrophe in Japan. Gardner's lucid inventory of the complex entanglements during this pivotal historical period thus makes significant contributions to an interdisciplinary understanding of Japanese architectural and literary visions of the future city (mirai toshi 未来都市). While the chapters proceed in a linear fashion temporally from the [End Page 166] early 1960s to roughly the early 2000s, the resultant survey of narrative and imaginative figurations of the city is decidedly nonlinear. Capturing the connective threads of discursive exchanges among discontinuous media and moments, Gardner's meticulous focus on the narrative effects and changing imaginaries of the future city weaves together a nuanced collection of recurrent motifs and circular eddies across the chapters of the book. Chapter 1 situates the emergence of Metabolist architects' diverse process-oriented visions within a shared interest in the city's continuous metamorphosis, likened to the metabolic processes of living organisms. Gardner contends that "by stressing the processes of becoming, transforming, and even disintegrating, the Metabolists introduced a narrative element into their architectural theory" (p. 43). He offers a highly compelling reading of the literary forms that Metabolist thinkers Kawazoe Noboru and Isozaki Arata, as well as non-Metabolist Itō Toyō 伊東豊雄 (b. 1941), deployed to articulate their speculative architectural visions. Chapter 2 deepens this understanding of the role of narrative form through the...