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ABSTRACT Molecular dynamics (MD) and the material point method (MPM) are both particle methods in spatial discretization. Molecular dynamics is a discrete particle method that is widely applied to predict fundamental physical properties and dynamic materials behaviors at nanoscale. The MPM is a continuum‐based particle method that was proposed about three decades ago to simulate large‐deformation problems involving multiphase interaction and failure evolution beyond the nanoscale. However, it is still a challenging task to validate MD responses against the experimental data due to the spatial limitation in impact and/or shock tests. The objective of this investigation is therefore to compare the MPM and MD solutions for the impact responses of porous solids at nanoscale. Since the governing equations for MD and explicit MPM are similar in temporal domain with different spatial discretization schemes, the MPM solutions could be verified against the MD ones, and the MD solutions might then be indirectly validated against the MPM ones as validated beyond the nanoscale. Since both MD forcing functions and MPM constitutive modeling are well‐formulated for metallic solids, we report a comprehensive comparative study of 40×40×40nm$40\ \times \ 40\ \times \ 40\ {\mathrm{nm}}$ porous and non‐porous gold cubic targets impacted by full density non‐porous gold cubic flyers using the MPM and MD, respectively. The overall deformation patterns and particle‐velocity histories are demonstrated and analyzed, as obtained with the two particle methods. It appears that the MD and MPM solutions are consistent in capturing the physical responses, which shows the potential of using the MPM for multiscale simulations of extreme events involving porous solids, such as underground penetration and space exploration. In addition, MD solutions might be indirectly validated against the MPM ones for evaluating geological responses to extreme loadings, which provides an alternative route for multiscale verification and validation. [ABSTRACT FROM AUTHOR]

Fluid-structure interaction (FSI) problems with strong nonlinearity and multidisciplinarity pose challenges for current numerical FSI algorithms. This work proposes a monolithic strategy for solving the equations of motion for both the fluid and structural domains under the unique Lagrangian framework of the B-spline material point method (BSMPM). A node-based density smoothing BSMPM (referred to as ds-BSMPM) is proposed to eliminate pressure instability and oscillation in the simulation of weakly compressible fluids, which is straightforwardly implemented using B-spline basis functions without the need for any sophisticated particle search algorithm. The interaction between the fluid and structure is conducted using the Lagrangian multiplier method on the tensor product grid, whose actual position is determined by the Greville abscissa and is used to detect contact. The proposed method is verified and validated against existing numerical approaches and experimental results, demonstrating the effectiveness of the proposed method in eliminating the oscillations of water pressure and solid stress, and avoiding premature and erroneous contact. In particular, this work presents a promising monolithic approach for achieving high-fidelity solutions to complex FSI problems. [ABSTRACT FROM AUTHOR]

The material point method (MPM) aims to avoid mesh distortion problems occurring in the commonly used finite element method (FEM). To achieve this, the continuum is discretized as a set of material points, while the solution of the weak form of the underlying partial differential equations is conducted on an Eulerian background mesh. As this process works similar to FEM, the MPM also displays volumetric locking for near‐incompressible materials. However, this also means that mitigation techniques developed for FEM can be adapted to the MPM. The main difficulty for this process lies in the higher‐continuity basis functions, which are required in MPM to achieve reasonable results. This study first reviews the applicability of different locking mitigation techniques in MPM. Then, a framework for a locking‐free implicit MPM is presented and validated using common tests investigating the locking behavior and stress oscillations. Finally, the presented methods are applied to a viscoelastic material model representing unvulcanized rubber to show the potential of MPM for tire molding simulations. [ABSTRACT FROM AUTHOR]

Being a fully Lagrangian particle method, the material point method (MPM) discretizes a material domain by using a collection of material points. The momentum equations in MPM are solved on a predefined regular background grid, so that the grid distortion and entanglement are completely avoided in MPM. The contact algorithm of MPM is developed via the background grid and the impenetrability condition between bodies. The contact algorithm of MPM is applied to solve some impact and perforation problems. This study concerns the validation of the contact algorithm of MPM. Solutions from MPM with the contact algorithm are compared to those from the finite element method (FEM) with the penalty method. For two impact problems, the results from MPM with the contact algorithm are in good agreement with those obtained with the FEM penalty method. For the perforation problem of aluminum plate, the results obtained using MPM with the contact algorithm are better than those from the FEM penalty method. We think that for impact problems without extreme large deformations, it is better to use the FEM penalty method. For impact problems with extreme large deformations, it is better to use the contact algorithm of MPM. [ABSTRACT FROM AUTHOR]

In order to advance the understanding of the impact dynamics of granular flow in complex geological settings, this paper studied the impact dynamics of granular flow on rigid barriers with a number of Material Point Method (MPM) numerical tests. The impact behavior of granular flow on a rigid barrier was characterized by the initial dynamic impact stage, dynamic surge impact stage, compression impact stage and static stage of granular flow, where the impact force of granular flow was comprised of the dynamic and static forces of granular flow. The impact behavior of granular flow on a rigid barrier was characterized by the states of the fast or slow impact behavior of granular flow. The angle of slope and aspect ratio of granular soil greatly affected the impact behavior of granular flow on a column rigid barrier, where a power model was proposed to quantify the residual (Fnr) - over - maximum (Fnmax) normal impact force ratio of granular flow Fnr/Fnmax incorporating the effects of the angle of slope and aspect ratio of granular soil. With the increase of the column rigid barrier up to the semi - infinite column rigid barrier, the impact dynamics of granular flow gradually increased up to a maximum by progressively transforming the overflow into the dynamic surge impact of the incoming flow on the rigid barrier to capture more granular soil of granular flow against the rigid barrier. Presence of water in granular flow, i.e., a mixture of solid and liquid in granular flow, yielded a dynamic coupling contribution of the solid and liquid, being accompanied by the whole dynamic process of granular flow, on the impact behavior of granular flow on a rigid barrier, where the liquid - phase material of granular flow, i.e., the water, was predominant to contribute on the normal impact force of granular flow in comparison with the solid - phase material of granular flow. In addition, other factors, e.g., the shape of rigid barrier (i.e., the column barrier, arch barrier and circle barrier), and the gravity (i.e., in the gravitational environment of the Moon, Earth and Mars), greatly affected the impact behavior of granular flow on a rigid barrier as well. [ABSTRACT FROM AUTHOR]

We propose a novel solid-fluid interaction method for coupling elastic solids with impulse flow maps. Our key idea is to unify the representation of fluid and solid components as particle flow maps with different lengths and dynamics. The solid-fluid coupling is enabled by implementing two novel mechanisms: first, we developed an impulse-to-velocity transfer mechanism to unify the exchanged physical quantities; second, we devised a particle path integral mechanism to accumulate coupling forces along each flow-map trajectory. Our framework integrates these two mechanisms into an Eulerian-Lagrangian impulse fluid simulator to accommodate traditional coupling models, exemplified by the Material Point Method (MPM) and Immersed Boundary Method (IBM), within a particle flow map framework. We demonstrate our method's efficacy by simulating solid-fluid interactions exhibiting strong vortical dynamics, including various vortex shedding and interaction examples across swimming, falling, breezing, and combustion. [ABSTRACT FROM AUTHOR]

Copyright of Journal of the Kanagawa Odontological Society / Kanagawa Shigaku is the property of Kanagawa Odontological Society and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Rainfall-induced landslides are a frequent and severe natural hazard in the southern regions of Ethiopia. These occurrences substantially threaten the welfare of workers, equipment, and the efficient completion of construction projects. This paper provides an insight into the mechanism and kinematic behavior of rainfall-induced landslides in southern Ethiopia. A comprehensive investigation was carried out on the Jinka landslide, a notable case study in June 2018. The investigation involved Material Point Method numerical simulations, which were informed by extensive geotechnical investigations and laboratory tests. Historical landslide events and rainfall data were also systematically analyzed to establish critical rainfall thresholds for predicting landslide occurrences. It was observed that excess pore water pressure near the sliding surface significantly reduces effective stress, leading to a notable decrease in shear resistance and increased soil mobility. The landslide followed a regressive pattern, initiating from the lower toe, propagating through the middle sections, and ultimately reaching the upper crest. The kinematic parameters of the sliding mass demonstrated varying velocities, with the mass sliding downslope exhibiting a greater velocity than the block positioned above it. The kinematic characteristics indicate that the landslide exhibits distinct movement patterns relative to varying microtopography. Additionally, threshold analysis revealed that the critical rainfall that triggers landslides is the maximum daily rainfall of 44 mm with 30 days antecedent rainfall of 304 mm and the minimum average daily rainfall of 4 mm with 30 days antecedent rainfall of 378 mm. The results indicated that soil saturation from rainfall diminishes strength and increases the acceleration of sliding masses, while antecedent rainfall is pivotal in landslide events. This study can provide a reference for understanding the mechanism of the landslides induced by rainfall and guidelines for future infrastructure planning and early warning systems in the region. [ABSTRACT FROM AUTHOR]

The large deformation and fluidization process of a solid–fluid mixture includes significant changes to the temporal scale of the phenomena and the shape and properties of the mixed material. This paper presents an extended B‐spline (EBS)‐based implicit material point method (EBS‐MPM) for the coupled hydromechanical analysis of saturated porous media to enhance the overall versatility of MPM in addressing such diverse phenomena. The proposed method accurately represents phenomena such as high‐speed motion in both the quasi‐static and dynamic states by employing a full formulation of coupled hydromechanical modeling. The weak imposition of boundary conditions based on Nitsche's method allows representing the boundary conditions independent of the relative position of the particles and computational grid. In addition, it enables dynamic changes in the boundary domain based on the deformation. The robustness of this boundary representation is reinforced using EBS basis functions, which prevent the degradation of the condition number of the system matrices regardless of the position of the boundary domain with respect to the computational grid. Furthermore, a stabilization method based on a variational multiscale method (VMS) approach is employed to provide the flexibility in choosing arbitrary basis functions for spatial discretization, facilitating the effective construction of EBS. Numerical examples including comparisons between a full formulation and a simplified formulation are presented to demonstrate the performance of the developed method under various boundary conditions and loading states across different time scales. [ABSTRACT FROM AUTHOR]

Multiple barriers are usually installed to effectively mitigate large-volume debris flows. Existing multiple-barrier design recommendations ignore the effects of solid–fluid interaction and may cause uncertainties in estimating the flow impact force on subsequent barriers. In this study, a fully coupled, two-layer, two-phase material point method with an incompressible fluid phase is implemented and validated using the experimental results of dry sand, water and sand–water mixture flows impacting on rigid barriers. Numerical parametric study is carried out using the validated model to investigate the effects of Froude number (Fr) and barrier spacing on second barrier impact force. A debris flow volume of 500 m3 is modelled, with the Fr ranging from 2 to 6; these are values relevant to the gentle and steep terrains in Hong Kong. Simulation results show the importance of changes in fluidisation ratio, which is the ratio of basal pore fluid pressure and total stress. The debris flow, after impacting the first barrier, overflows and lands on the slope between the two barriers. The fluidisation ratio of debris flow after landing increases by up to 30%, leading to an increase of impact velocity at the second barrier by up to 80%. Consequently, the impact force of debris flows on the second barrier is underestimated by up to 50% compared with existing design guidelines. This implies that neglecting the fluidisation ratio may lead to non-conservative design of multiple barriers. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

China has a wealth of abundant coalbed methane (CBM) resources at great depths. However, the low permeability of these deep coal seams coupled with the challenges posed by high-stress pressure environments, hampers efficient gas extraction. Water jet punching and cavitation in horizontal wells is a new technology for relieving pressure and enhancing the permeability of coal seam over a wide area. Nevertheless, the mechanisms underlying rock breaking and pore formation in deep environment remain to be studied. Because the deep coal seam exists in the geological environment of high ground stress and high stress difference, it is difficult to carry out the physical simulation experiment in the laboratory. Consequently, a numerical model of water jet punching and rock breaking is established based on the viscoelastic-plastic theory and material point method. The model integrates the advantages of the Lagrange and Euler algorithms, proficiently simulating the whole process of momentum exchange, large deformation of coal, rock breaking, fluid erosion and rock carrying and reverse drainage throughout the process of jet rock breaking. Subsequently, based on this numerical model, the mechanism and influencing factors of rock breaking and pore-forming by water jet in deep coal seams are studied, and the conclusions are as follows: ① the shear failure caused by high in-situ stress load in deep coal seams is the leading mechanism of rock breaking, while jet mainly plays the role of erosion and rock carrying and reverse drainage. The tensile failure caused by stress wave generated by water jet collision with coal rock is the leading mechanism of rock breaking when there is no stress load. Due to the strong plasticity of coal rock, water wedge effect is not obvious. ② The high in-situ stress load accelerates the rock breaking process of deep coal seams. The amount of rushed-out coal under high in-situ stress load is higher than that without stress load. Meanwhile, the stress load causes the coal body to move towards the opening direction, resulting in a decrease in cavity volume, but the plastic damage zone is significantly increased compared with that without stress load. ③ The amount of rushed-out coal and the area of plastic damage zone increase with the increase of jet time, but the increase rate gradually slows down. The amount of rushed-out coal and the area of plastic damage zone show a downward trend with the increase of incident angle. The smaller the jet angle, the better the effect of water jet punching and rock breaking. The vertical incidence of jet is not the best way to break rock. ④ The amount of rushed-out coal and the area of plastic damage area increase with the increase of stress difference and the width of coal-rock opening, but the increase of stress difference has little effect on jet rock breaking in deep coal seams. The width of coal seam opening should not be too high, and the rock breaking efficiency of jet can be improved by increasing the width of the opening hole appropriately.

Abstract Spoil sites, as loose accumulations, are prone to instability after disturbances and are a serious threat to the safety of downstream communities. This research aims to rapidly and accurately assess the potential hazards of the numerous spoil sides. An integrated approach that combines spatial, aerial, and ground techniques was developed to rapidly identify and interpret the key factors influencing the stability of spoil sites. Subsequently, based on the results of numerical simulation of multiple combinations of unfavorable working conditions by the material point method, a hazard assessment methodology for spoil sites is proposed, which combines the limit equilibrium method with the improved hierarchical analysis. The proposed method is applied and validated on spoil sites along an expressway. The achieved results reveal that remote sensing combined with unmanned aerial vehicle (UAV) verification technology is capable of quickly and accurately identifying the critical elements of spoil sites. The hazard assessment of the spoil site is represented by the hazard coefficient (P), where 0

Abstract Geological hazards related to soft–hard interbedded rock are frequent in rock engineering. The material point method (MPM) is a mesh-free numerical approach specifically designed for analyzing large deformations. Notably, significant grid-crossing errors frequently arise when material points traverse the underlying grid. To investigate the failure mechanism of soft–hard interbedded rock, an enhanced MPM incorporating B-spline basis functions and Voronoi polygon discretization is developed and subsequently validated through comparisons with uniaxial compression test data and other numerical methods. The numerical results of soft–hard interbedded rock specimens associated with different soft layer dips (SLD) and confining pressures indicate that the SLD has a great effect on compressive strength and crack extension at low confining pressure. Rocks from SLD-30° to SLD-75° correspond to the “sliding failure along discontinuities” failure mode and have lower compressive strength than rocks with other SLD angles. It is also demonstrated that the propagation of cracks leads to a significant alteration in the internal stress state of the rock, and that stress concentrations at the crack tip exacerbate the development of failure surface. Furthermore, the failure mode of soft–hard interbedded rock can be categorized into four types: (1) sliding failure across multiple discontinuities, (2) tensile fracture across multiple discontinuities, (3) sliding failure along discontinuities, (4) tensile-split along discontinuities.

The work at hand introduces a regularized microplane damage formulation into the Material Point Method (MPM) using an implicit time integration scheme. A material characterization at finite deformations to describe rock‐like materials is applied, which is characterized by strain‐softening behavior. The nonlinear response of the material is captured by a damage formulation within the microplane framework. Regularization of the model is achieved by an implicit gradient enhancement. The model is implemented into an in‐house MPM code, and its capabilities are shown by a numerical example. [ABSTRACT FROM AUTHOR]

The dynamic interaction between granular flowing masses and rigid obstacles is a complex phenomenon characterised by both large displacements and high strain rates. In case the flowing mass is modelled as a continuum, its numerical simulation requires both advanced computational tools and constitutive relationships capable of predicting the mechanical behaviour of the same material under both fluid and solid regimes. In this paper, the authors employed the open‐source ANURA3D code, based on the Material Point Method (MPM), and a multi‐regime constitutive model. A series of impacts characterised by different velocities, initial void ratios, front inclinations and impacting mass lengths have been simulated. The MPM numerical results are critically compared with those obtained by using a Discrete Element Method (DEM) numerical code. The model capability of simulating material regime transitions, from fluid to solid and vice versa, is shown to be crucial for reproducing the mechanical response of the flowing mass put in evidence by DEM data. [ABSTRACT FROM AUTHOR]

A series of plate loading tests on clay has been conducted in the centrifuge. The aim of the tests is to create a data set, which is freely downloadable, to validate numerical tools that account for geometrical nonlinearities. The tests include two sources of geometrical non-linearities. The first source is the reducing clay layer thickness below the plate, which causes an increase in resistance. The second source is the backflow of the clay around the tip of the plate. The backflow has a reducing effect on the plate resistance. This paper outlines four tests: two involving a wide plate and two with a small plate. Each plate geometry is investigated under both smooth and rough side model boundaries. An material point method (MPM) schematization is used for numerical analysis. The schematization and parameter selection are initially validated by comparing the MPM results against CPTu data in each test. The numerical analysis examines the impact of a finite layer thickness by analyzing various layer thicknesses. Furthermore, the analysis shows the influence of the backflow on the plate resistance by analyzing different ratios of shaft to plate width. In this study, the pore pressures below the plate and vertical and horizontal displacement fields are considered in addition to the load displacement curves. The MPM simulations are in good agreement with the centrifuge data. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Computational Mechanics / Jisuan Lixue Xuebao is the property of Chinese Journal of Computational Mechanics Editorial Office, Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chinese Journal of Computational Mechanics / Jisuan Lixue Xuebao is the property of Chinese Journal of Computational Mechanics Editorial Office, Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Verifying and validating explosion-resistant design models are challenging tasks due to the difficulties in accurately capturing the failure evolution within a setup influenced by the combined effects of fluid–solid interactions (FSI), blast waves, fragmentation, and impact. Curtain wall system, as a key structural component, is widely used in various types of buildings for its aesthetic appeal and weather protection. Hence, optimizing the explosion-resistance of such systems is necessary to improve building safety. In this work, we develop computational procedures that can be used to enhance the design of blast-resistant structures. This paper focuses on studying a representative component (e.g., window panels) from a typical curtain wall system, as well as a small-scale modeling of shock tube testing. For that, the material point method (MPM) simulations are verified against the finite element method (FEM) simulations, and the computational results are validated against shock tube testing. The work objective is to evaluate the simulation fidelity of explosion responses in several case studies. The first case study demonstrates how the MPM captures damage and fragmentation in a typical confined explosion event involving FSI, thus, providing an improved physical description compared to the FEM. The second case study qualitatively compares the MPM's ability to simulate the shock tube response with experimental observations. Since the second study validates that the MPM solution is qualitatively consistent with the experimental data, the MPM model is then used in the third case study to establish an FEM model that could capture the same physics. This FEM model can be scaled up to model field experiments. The fourth case study involves the development of an FEM model for a representative curtain wall system component, which is validated against experimental results and then scaled down and employed to validate a corresponding MPM model. The proposed procedure provides a feasible approach to verifying and validating explosion-resistant designs for more general cases. [ABSTRACT FROM AUTHOR]

A numerical method has been presented to simulate hypervelocity impacts on metal targets. The target is a rectangular prism and is positioned at various inclined angles relative to the impact direction, while four different projectiles such as square prism, triangular prism, truncated cone, and ogival shape are chosen. This numerical model employs an open-source code, MPM3D-F90, which is based on the Material Point Method. In order to enhance flexibility of the code for defining projectiles and target bodies in the material domain, a preprocessor is developed to create a variety of geometrical shapes for a given volume. In addition to supplementing and defining various geometrical bodies, this tool also simplifies the preprocessing process to create the user's specific preferences for the problem. To demonstrate the utility of the preprocessor tool and investigate the influence of geometry on hypervelocity impacts, simulations are conducted using various projectile and target configurations. The analysis results reveal that the structure of the debris cloud formations, scattering behavior of the ejected particle from both front and rear faces, and penetration depth measures are significantly influenced by the projectile shape and impact angles. [ABSTRACT FROM AUTHOR]

Springs are fundamental components in mechanical systems, crucial for ensuring the safety and functionality of mechanisms. Timoshenko's stiffness formula accounts for both bending and torsional energy effects, providing accurate results for small deformations. However, when the deformation becomes large, the spring stiffness becomes a nonlinear problem due to the changing inclination angle and radius during deformation. In this study, we derive a formula for the cylindrical spring stiffness under nonlinear large deformation by considering two assumptions: the invariability of the polar angle at any point and spring wire length during deformation. This formula incorporates the effects of inclination and radius changes on the spring wire. We analyze the stiffness of the cylindrical spring with different initial inclinations using the finite element method (FEM). FEM results were compared with those obtained from Timoshenko's formula, Hiroyuki's formula, and the derived formula. For small deformations, the FEM results matched well with all three formulas. However, for nonlinear large deformations, the calculated results from Timoshenko's formula showed a discrepancy of up to 32.58% compared to the FEM results. The modified Hiroyuki formula also exhibited slightly poorer agreement with the FEM results than the formula proposed in this paper. On the other hand, our derived formula demonstrated excellent agreement with the FEM results for nonlinear large deformations. Therefore, our stiffness formula for cylindrical springs is recommended for mechanical engineering spring design applications involving nonlinear large deformations. [ABSTRACT FROM AUTHOR]

Summary: In this paper, a generalized particle domain method (GPDM) is proposed and developed within the framework of the convected particle domain interpolation method. This new method generates particles directly from non‐uniform rational B‐spline (NURBS)‐based CAD file of a continuum body. The particle domain corresponds to a NURBS element even for trimmed elements of solids with complex geometries. The shape functions and the gradient of shape functions are evaluated using NURBS basis functions to map material properties between particles and grid nodes. It approves that this proposed GPDM can track the domain of particles accurately and avoid the issue of cell‐crossing instability. Several numerical examples are presented to demonstrate the high performance of this proposed new particle domain method. It is shown that the results obtained using the proposed GPDM are consistent with the experimental data reported in the literature. Further development of the generalized particle domain method can provide a link to the material point method and isogeometric analysis. [ABSTRACT FROM AUTHOR]

The material point method (MPM) adopts the dual description of Lagrangian particles and Euler grids, so it can deal with large deformation and contact problems conveniently. The large deformation problem of thin shell structures was analyzed based on the framework of the convected particle domain interpolation material point method (CPDIMPM) . The quadrilateral mesh was used to discretize the shell structure. The basis function was calculated by the double mapping from the material point to the shell element node and then to the background grid node. The momentum equation was solved on the background grid, and the internal force of the material point was updated based on the Belytschko-Tsay (BT) shell element theory. In the numerical example, the comparison of large deformations of the shell structure with reference solutions verifies the accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

In this study, a numerical framework based on the material point method is presented for the simulation of material extrusion (MEX)-based 3-D printing processes. The melt flow during material extrusion is assumed to be viscous flow including phase changes. To apply the free surface boundary conditions, the framework utilizes the level set method to track the free surface and the ghost fluid method for the application of the boundary conditions. For validation, three representative problems are first investigated to show the versatility of the model. Then, the numerical framework is adapted for the simulation of material extrusion (MEX) based 3-D printing processes. An in-depth parametric study is presented to show how printing parameters affect the overall extruded printing material. [ABSTRACT FROM AUTHOR]

This paper presents a modified relationship between small and large strain convergence by applying a small (residual) dilation angle, which behaves accurately for rock mass with the strain-softening behavior and complex dilatancy model. The modified relationship extends its applicability to a more general two- and three-dimensional excavation problems than previous study, irrespective of the constitutive behavior and rock dilatancy. On this basis, the longitudinal displacement profile (LDP) considering finite-strain is proposed, which can be corrected simply from the small strain analysis or obtained according to the actual parameters related to large deformation. The capability of the finite-strain LDP for estimating large convergences during tunnel advancement is verified by several comparisons with the existing numerical simulation and theoretical analysis results. The developed finite-strain LDP is promising to improve the convergence − confinement method when it applied to the rock-support interaction analysis in problems involving large deformation. The applicability of the displacement-release coefficient obtained from the small strain analysis for quantifying the stress relief to squeezing ground conditions is also investigated. Highlights: A relationship between small and large strain convergence is modified to accurately calculate large convergences from small strain analysis. Two equivalent formulas for the longitudinal displacement profile in squeezing ground considering finite strain are proposed. The applicability of displacement-release coefficient by small strain analysis for quantifying the stress relief to squeezing ground is obtained. [ABSTRACT FROM AUTHOR]

This contribution discusses the influence of different barrier update strategies on the performance and robustness of an interior point algorithm for single-crystal plasticity at small strains. To this end, single-crystal plasticity is first briefly presented in the framework of a primal-dual interior point algorithm to outline the general algorithmic structure. The manner in which the barrier parameter is modified within the interior point method, steering the penalization of constraints, plays a crucial role for the robustness and efficiency of the overall algorithm. In this paper, we compare and analyze different strategies in the framework of crystal plasticity. In a thorough analysis of a numerical example covering a broad range of settings in monocrystals, we investigate robust hyperparameter ranges and identify the most efficient and robust barrier parameter update strategies. [ABSTRACT FROM AUTHOR]

Frictional heating–induced thermal pressurization is a key mechanism responsible for the exceptional long-runout distances and high-speed movement of some massive landslides. In this paper, a novel framework for modelling landslides with frictional heating–induced thermal pressurization is developed based on the material point method (MPM). In this MPM framework, the basal terrain is idealised as a rigid material, while the sliding mass is treated as a thermo-hydro-mechanical porous mixture. The sliding mass interacts with the rigid terrain via the generalized multi-material contact model accounting for frictional heating and water pressurization effect. Special scaling treatment is applied for the temperature and liquid pressure diffusion calculations within the sliding mass to better approximating the thermal pressurization effect within the thin shear band. The validity of the thermal pressurization model and the sensitivity of its parameters have been demonstrated through two benchmark examples, corresponding to thermo-poro-elastic blocks sliding on a horizontal surface with an imposed constant velocity and along an inclined plane under gravity. Finally, the capability of the proposed framework is verified by satisfyingly reproducing both the dynamic runout and the friction-induced thermal pressurization processes of the giant Daguangbao landslide. [ABSTRACT FROM AUTHOR]

Climate warming accelerates permafrost thawing, causing warming‐driven disasters like ground collapse and retrogressive thaw slump (RTS). These phenomena, involving intricate multiphysics interactions, phase transitions, nonlinear mechanical responses, and fluid‐like deformations, and pose increasing risks to geo‐infrastructures in cold regions. This study develops a thermo‐hydro‐mechanical (THM) coupled single‐point three‐phase material point method (MPM) to simulate the time‐dependent phase transition and large deformation behavior arising from the thawing or freezing of ice/water in porous media. The mathematical framework is established based on the multiphase mixture theory in which the ice phase is treated as a solid constituent playing the role of skeleton together with soil grains. The additional strength due to ice cementation is characterized via an ice saturation‐dependent Mohr–Coulomb model. The coupled formulations are solved using a fractional‐step‐based semi‐implicit integration algorithm, which can offer both satisfactory numerical stability and computational efficiency when dealing with nearly incompressible fluids and extremely low permeability conditions in frozen porous media. Two hydro‐thermal coupling cases, that is, frozen inclusion thaw and Talik closure/opening, are first benchmarked to show the method can correctly simulate both conduction‐ and convection‐dominated thermal regimes in frozen porous systems. The fully THM responses are further validated by simulating a 1D thaw consolidation and a 2D rock freezing example. Good agreements with experimental results are achieved, and the impact of hydro‐thermal variations on the mechanical responses, including thaw settlement and frost heave, are successfully captured. Finally, the predictive capability of the multiphysics MPM framework in simulating thawing‐triggered large deformation and failure is demonstrated by modeling an RTS and the settlement of a strip footing on thawing ground. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Computer-Aided Design & Computer Graphics / Jisuanji Fuzhu Sheji Yu Tuxingxue Xuebao is the property of Gai Kan Bian Wei Hui and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Background: Implementing Hazard Analysis and Critical Control Point (HACCP) management across the supply chain is promoted globally to ensure the safety of marine food products due to their rapid quality deterioration. However, many seafood retail stores deviate from adopting these practices. Therefore, in this study, we aimed to create a flowchart based on HACCP and validate it in retail stores. Methods: Chub mackerel (Scomber japonicus), scallops (Patinopecten yessoensis), and whiteleg shrimp (Litopenaeus vannamei) specimens were purchased from a supermarket from August to December 2020. The handling information of these products from receipt to sales was obtained to prepare an HACCP plan for retail stores. Groups adhering to and deviating from flowchart conditions were categorized as Critical Control Point (CCP)- compliant and CCP-deviant, respectively. Four samples of each product for each condition were analyzed. Bacterial viability was evaluated using the flat agar culture method. Escherichia coli and Vibrio parahaemolyticus were detected using the Brilliant Green-Lactose-Bile and material point methods, respectively. Product freshness was assessed by determining K-values using High-Performance Liquid Chromatography. Results were compared using Student's t-test. Results: At elevated storage temperatures, bacterial growth rates were higher in chub mackerel and whiteleg shrimp than those in scallops. E. coli was not detected in any sample, whereas V. parahaemolyticus was detected in scallops and whiteleg shrimp but not in chub mackerel. CCP-deviant refrigerated scallops had increased V. parahaemolyticus counts; however, it did not differ between the frozen scallop and whiteleg shrimp. K-values increased more rapidly in CCP-deviant chub mackerel, whiteleg shrimp, and refrigerated scallops, but not in frozen scallops. Inadequate temperature control during display and sale markedly deteriorated the quality of marine products. Conclusion: Setting CCPs for marine food product display and sale while controlling temperature can preserve product quality. The flowchart created in this study can be broadly used for marine retail stores. [ABSTRACT FROM AUTHOR]

Background: Complications are common after major visceral surgery. Besides the patients, also surgeons may experience negative feelings by the patients suffering. Some studies have evaluated the mental burden caused by complications, mainly focusing on residents in different surgical specialties. No evidence exists on the mental burden of board-qualified visceral surgeons in Germany. Materials and Methods: A point prevalence study was conducted using an online questionnaire. For the inclusion of participants, all departments of visceral surgery at German university hospitals were addressed. The objective of the online questionnaire was to elaborate the perception of complications and the coping mechanisms used by the surgeons with the aim to characterize the mental burden and possible improvement strategies. Results: A total of 113 questionnaires were answered, 98 being complete. 73.2% of the participants were male, 46.9% were consultants and had a working experience of 11–20 years. Most common specialties were colorectal and general surgery and 91.7% claimed to have caused complications Clavien-Dindo grade IV or V. Subsequently, predominant feelings were anger, grief, self-doubt and guilt. The fear of being blamed by colleagues or to lose reputation were high. Especially female and younger surgeons showed those fears. Coping mechanisms used to overcome those negative feelings were interaction with friends and family (60.6%) or proactive training (59.6%). Only 17.2% of the institutions offered professional support. In institutions where no support was offered, 71.6% of the surgeons asked for support. Conclusion: Surgical complications cause major psychological burden in surgeons in German university hospitals. Main coping mechanisms are communication with friends and families and professional education. Vulnerable subgroups, such as younger surgeons, may be at risk of suffering more from perceived mental distress. Nonetheless, the majority did not receive but asked for professional counselling. Thus, structured institutional support may ameliorate care for both surgeon and patient. [ABSTRACT FROM AUTHOR]

A computational framework is proposed for modelling particle bonding in cold spray. The model is based on the commonly-held view that bonding is a consequence of jetting, namely, the large plastic strains occurring at extreme rates upon particle impact. The model incorporates a bonding criterion at contacting boundaries by introducing a novel strain-like history variable referred to as the bonding parameter conjugate to a rate-dependent evolution law. In doing so, an analogy is made with classic damage mechanics where bonding is viewed as a similar but opposite process to fracture. Two new material constants are introduced, namely, the bonding toughness and the bonding toughness rate. Furthermore, a numerical implementation of the model in the Material Point Method (MPM) is presented which, thanks to a proposed regularization technique, is free of non-physical dependence on discretization parameters. The mesh-free nature of the MPM allows avoiding the numerical issues in conventional Lagrangian and Eulerian methods such as mesh distortion and artificial dissipation. The model is calibrated numerically for aluminum-aluminum material pair using an in-house computer program. Several numerical results are presented to demonstrate that the model can accurately capture material jetting and directly relate it to bonding within the simulation. [ABSTRACT FROM AUTHOR]

Rapid flow-like landslides frequently occur in mountainous regions. To mitigate the disasters caused by these landslides, it is crucial to develop robust numerical models that can accurately predict their run-out processes. Models based on the material point method (MPM) offer significant advantages in simulating large deformation issues in geomaterials, including landslides. However, applying these models to accurately simulate real-world rapid flow-like landslides remains a challenge, primarily due to the complexities involved in handling the three-dimensional (3D) sliding bed boundary. This paper introduces a novel 3D MPM model specifically designed for simulating rapid flow-like landslides that propagate across curved beds. The constraints of the sliding bed on the landslide are imposed by the boundary nodes close to the bed. These boundary nodes carry information about the normal vector of the sliding bed, derived directly from the digital terrain model (DTM). Furthermore, the model integrates a hybrid formulation that combines the Full Lagrangian Implicit Particle (FLIP) method with the Particle In Cell (PIC) method, facilitating a stable solution for the velocity and position of material points. The effectiveness of the proposed model is confirmed through a numerical analysis of a rigid block sliding down an inclined plane and an experiment of sand flow on a curved bed. The simulation results from these two benchmark scenarios align closely with both analytical and experimental data, attesting to the validity of the model. The model is then applied to analyze a rapid flow-like landslide that occurred in Gansu Province, China, characterized by a curved sliding bed. The outcomes illustrate the model's capability to efficiently capture the landslide's climbing and turning motions induced by the meandering topography. Moreover, it successfully reproduces the main deposition characteristics observed in the field, demonstrating the model's strong suitability for simulating the propagation of rapid flow-like landslides on naturally curved beds. [ABSTRACT FROM AUTHOR]

Sinkholes are a major geohazard caused by underground mining, significantly deteriorate the ecological environment. To understand deeply the formation mechanism of widespread sinkholes in mining areas, the unsaturated Material Point Method (MPM) was employed to study the mechanical and hydraulic characteristics during the sinkhole formation process in a southwestern mining area. This study explored the impacts of different mining modes and rainfall intensities on sinkhole characteristics and validated the results with 3D laser scanning data. Results show that prolonged and concentrated rainfall and subsurface mining activities are the main factors contributed to the formation of sinkholes. The initial rainfall infiltration behavior significantly elevates groundwater levels, leading to saturation of the surface moraine soil layer. Subsequent mining activities result in double funnel-shaped fracture zones. The differences in the expansion rates of various fracture zones lead to widespread subsidence on the surface first, followed by the evolution into sinkholes in the central area. The multi-channel mining mode is identified as the main factor causing the enlarging of sinkholes, while variations in rainfall intensity affect the distribution and morphologies of these sinkholes. [ABSTRACT FROM AUTHOR]

In order to understand the dynamics of granular flow on an erodible base soil, in this paper, a series of material point method - based granular column collapse tests were conducted to investigate numerically the mobility and dynamic erosion process of granular flow subjected to the complex settings, i.e., the aspect ratio, granular mass, friction and dilatancy resistance, gravity and presence of water. A set of power scaling laws were proposed to describe the final deposit characteristics of granular flow by the relations of the normalized run - out distance and the normalized final height of granular flow against the aspect ratio, being greatly affected by the complex geological settings, e.g., granular mass, the friction and dilatancy resistance of granular soil, and presence of water in granular flow. An index of the coefficient of friction of granular soil was defined as a ratio of the target coefficient of friction over the initial coefficient of friction to quantify the scaling extent of friction change (i.e., friction strengthening or weakening). There is a characteristic aspect ratio of granular column corresponding to the maximum mobility of granular flow with the minimum index of the apparent coefficient of friction. The index of the repose coefficient of friction of granular flow decreased gradually with the increase in aspect ratio because higher potential energy of granular column at a larger aspect ratio causes a larger kinetic energy of granular soil to weaken the friction of granular soil as a kind of velocity - related friction weakening. An increase in granular mass reduces gradually the indexes of the apparent and repose coefficients of friction of granular soil to enhance the mobility of granular flow. The mobility of granular flow increases gradually with the decrease in friction angle or increase in dilatancy angle of granular soil. However, the increase of gravity accelerates granular flow but showing the same final deposit profile without any dependence on gravity. The mobility of granular flow increases gradually by lowering the indexes of the apparent and repose coefficients of friction of granular flow while changing the surroundings, in turn, the dry soil, submerged soil and saturated soil, implying a gradually increased excessive mobility of granular flow with the friction weakening of granular soil. Presence of water in granular flow may be a potential catalyzer to yield a long run - out granular flow, as revealed in comparison of water - absent and water - present granular flows. In addition, the dynamic erosion and entrainment of based soil induced by granular flow subjected to the complex geological settings, i.e., the aspect ratio, granular mass, gravity, friction and dilatancy resistance, and presence of water, were comprehensively investigated as well. [ABSTRACT FROM AUTHOR]

Recent rapid urbanization has led to an increase in tunnel construction, escalating the prevalence of ground collapses. Ground collapses, characterized by large deformation and strain-softening, pose a significant challenge for classical numerical theories and simulation methods. Consequently, a numerical framework combining the material point method (MPM) and strain-softening Drucker–Prager plasticity is introduced in this study to more accurately describe the evolution process and failure mechanism of the subgrade during tunnel excavation. The proposed numerical framework was validated against an analytic solution employing a typical 'dry bottom' dam model with solid non-linearity and large deformation; some of the results are also compared with those of the SPH method and centrifugal modeling tests to verify the validity of the MPM method in this paper. The validated model was used in this study to conduct a comprehensive analysis of surface instability and ground collapse under varying soil conditions. This included factors such as strata thickness, cohesion, internal friction angle, and a quantitative description of the development of longitudinal subsidence of the surface. The aim was to clarify deformation responses, failure patterns, and excavation mechanisms, providing insights for underground tunneling practices. [ABSTRACT FROM AUTHOR]

The editorial discusses the challenges posed by natural hazards and anthropogenic disasters, focusing on landslides as a persistent threat worldwide. It highlights advances in monitoring tools, prediction models, innovative modeling techniques, laboratory testing, and defense structure design to mitigate landslide risks. The research emphasizes interdisciplinary efforts and the integration of machine learning and artificial intelligence in predicting and preventing geological disasters, providing a valuable resource for further studies in this critical field. [Extracted from the article]

The collapse of the tunnel face is a prevalent geological disaster in tunnelling. This study employs a three-dimensional (3D) material point method (MPM) to simulate the dynamic collapse process and post-failure mechanisms of the tunnel face. The specific focus is on the scenario where the auxiliary air pressure balanced shield with a partially filled chamber is shut down. To assess the suitability of the 3D MPM, numerical solutions are compared with the results from small-scale experimental tests. Subsequently, a series of large-scale numerical simulations is conducted to explore the dynamic collapse characteristics of the tunnel face induced by the shutdown of the EPB shield under various support air pressures and cutter head conditions. The temporal evolution of the accumulated soil masses in the soil chamber and ground responses under different support air pressures, cutter head types and opening ratios are discussed. In particular, the associated surface subsidence due to the tunnel face collapse is determined and compared with empirical solutions. Numerical results confirm the applicability of the 3D MPM for simulating the large-scale tunnel face collapse scenarios, spanning from small to large deformation analysis.

Ground hydraulic fracturing plays a crucial role in controlling the far-field hard roof, making it imperative to identify the most suitable target stratum for effective control. Physical experiments are conducted based on engineering properties to simulate the gradual collapse of the roof during longwall top coal caving (LTCC). A numerical model is established using the material point method (MPM) and the strain-softening damage constitutive model according to the structure of the physical model. Numerical simulations are conducted to analyze the LTCC process under different hard roofs for ground hydraulic fracturing. The results show that ground hydraulic fracturing releases the energy and stress of the target stratum, resulting in a substantial lag in the fracturing of the overburden before collapse occurs in the hydraulic fracturing stratum. Ground hydraulic fracturing of a low hard roof reduces the lag effect of hydraulic fractures, dissipates the energy consumed by the fracture of the hard roof, and reduces the abutment stress. Therefore, it is advisable to prioritize the selection of the lower hard roof as the target stratum.

The grid-based multi-velocity field technique has become increasingly popular for simulating the Material Point Method (MPM) in contact problems. However, this traditional technique has some shortcomings, such as (1) early contact and contact penetration can occur when the contact conditions are unsuitable, and (2) the method is not available for contact problems involving rigid-nonrigid materials, which can cause numerical instability. This study presents a new hybrid contact approach for the MPM to address these limitations to simulate the soil and structure interactions. The approach combines the advantages of point-point and point-segment contacts to implement contact detection, satisfying the impenetrability condition and smoothing the corner contact problem. The proposed approach is first validated through a disk test on an inclined slope. Then, several typical cases, such as granular collapse, bearing capacity, and deformation of a flexible retaining wall, are simulated to demonstrate the robustness of the proposed approach compared with FEM or analytical solutions. Finally, the proposed method is used to simulate the impact of sand flow on a deformable structure. The results show that the proposed contact approach can well describe the phenomenon of soil-structure interaction problems.

This study presents a semi‐implicit MPM to adequately characterize the mechanical behavior of unsaturated soil based on Biot's mixture theory. To represent the dependency of the degree of saturation on the suction, we employ the VG model along with a soil‐water characteristic curve, which determines a functional form of permeability called the Mualem model. Hencky's hyperelastic model and the Drucker‐Prager model assuming nonassociativity are adopted for elastic and plastic deformations, respectively. The novelty of this study is the incorporation of the fractional‐step method into the MPM framework so that the pore water pressure is obtained by implicitly solving the pressure Poisson's equation, which reduces numerical instability and improves computational efficiency. Also, because the drag force between solid and liquid phases is evaluated using the intermediate velocity of pore water relative to the intermediate velocity of solid skeleton, the time increment can be chosen without considering the magnitude of water permeability. In addition, to suppress "odd‐even" oscillation, we employ a sub‐grid method in which two grids with different spatial resolutions are used for the velocities and pore water pressure. Furthermore, considering the advantages and disadvantages of two different interpolation schemes for pore water pressure, we suggest switching the schemes depending on the model conditions. Several numerical examples are presented to demonstrate the performance of the proposed method. Specifically, unidirectional consolidation and leak flow analyses are performed for verification purposes, followed by validation analysis of a model experiment of infiltration‐induced landslides. [ABSTRACT FROM AUTHOR]

Rock avalanches typically entail the flow-like motion of angular rock blocks and fragments of diverse size. Numerical simulations are instrumental in understanding their dynamic process, supporting hazard and risk assessments. Simplified failure criteria, such as the Mohr-Coulomb or Drucker-Prager, are commonly adopted in landslide models relying on the material point method (MPM). However, these criteria cannot capture the transitions between solid-like, liquid-like, and gas-like behaviors exhibited by granular materials. Here, we relied on the moving least-squares MPM, which offers high computing efficiency and stability, and adopted a nonlocal μ(I) rheology model implemented by Haeri and Skonieczny (Comput Methods Appl Mech Eng, 2022). This approach can account for the rate-dependent, pressure-dependent, and size-dependent characteristics of friction in granular materials. By simulating a small-scale flume experiment as well as a large-scale event (the Nayong rock avalanche in Guizhou, China), we verified that the nonlocal μ(I) rheology model can capture the motion and deposition processes in rock avalanches effectively. This feature can be advantageous in physically based hazard assessments of such events. [ABSTRACT FROM AUTHOR]