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discrete element method

Haiyang Zhao, Xizhong An, Dazhao Gou, Bo Zhao, Runyu Yang
The discrete element method (DEM) was used to simulate the piling of rod-like (elongated sphero-cylindrical) particles, mainly focusing on the effect of particle shape on the structural and force properties of the piles. In this work, rod-like particles of different aspect ratios were discharged on a flat surface to form wedge-shaped piles. The surface properties of the piles were characterized in terms of angle of repose and stress at the bottom of the piles. The results showed that the rise of the angle of repose became slower with the increase of particle aspect ratio...
May 21, 2018: Soft Matter
B Lambert, L Weynans, M Bergmann
The lubrication forces are short-range hydrodynamic interactions essential to describe suspension of the particles. Usually, they are underestimated in direct numerical simulations of particle-laden flows. In this paper, we propose a lubrication model for a coupled volume penalization method and discrete element method solver that estimates the unresolved hydrodynamic forces and torques in an incompressible Navier-Stokes flow. Corrections are made locally on the surface of the interacting particles without any assumption on the global particle shape...
March 2018: Physical Review. E
Mert Tuzer, Abdulkadir Yazıcı, Rüştü Türkay, Michael Boyman, Burak Acar
PURPOSE: To develop a medical ultrasound (US) simulation method using T1-weighted magnetic resonance images (MRI) as the input that offers a compromise between low-cost ray-based and high-cost realistic wave-based simulations. METHODS: The proposed method uses a novel multi-ray image formation approach with a virtual phased array transducer probe. A domain model is built from input MR images. Multiple virtual acoustic rays are emerged from each element of the linear transducer array...
May 4, 2018: International Journal of Computer Assisted Radiology and Surgery
Jeannette H Spühler, Johan Jansson, Niclas Jansson, Johan Hoffman
Due to advances in medical imaging, computational fluid dynamics algorithms and high performance computing, computer simulation is developing into an important tool for understanding the relationship between cardiovascular diseases and intraventricular blood flow. The field of cardiac flow simulation is challenging and highly interdisciplinary. We apply a computational framework for automated solutions of partial differential equations using Finite Element Methods where any mathematical description directly can be translated to code...
2018: Frontiers in Physiology
Mehran Yarahmadian, Yongmin Zhong, Chengfan Gu, Jaehyun Shin
BACKGROUND: Soft tissue modeling plays an important role in the development of surgical training simulators as well as in robot-assisted minimally invasive surgeries. It has been known that while the traditional Finite Element Method (FEM) promises the accurate modeling of soft tissue deformation, it still suffers from a slow computational process. OBJECTIVE: This paper presents a Kalman filter finite element method to model soft tissue deformation in real time without sacrificing the traditional FEM accuracy...
April 17, 2018: Technology and Health Care: Official Journal of the European Society for Engineering and Medicine
Masashi Horibe, Ryoichi Sonoda, Satoru Watano
A method for scale-up of a lubricant mixing process in a V-type blender was proposed. Magnesium stearate was used for the lubricant, and the lubricant mixing experiment was conducted using three scales of V-type blenders (1.45, 21 and 130 L) under the same fill level and Froude (Fr) number. However, the properties of lubricated mixtures and tablets could not correspond with the mixing time or the total revolution number. To find the optimum scale-up factor, discrete element method (DEM) simulations of three scales of V-type blender mixing were conducted, and the total travel distance of particles under the different scales was calculated...
2018: Chemical & Pharmaceutical Bulletin
Chang Liu, Chenyang Xue, Binzhen Zhang, Guojun Zhang, Changde He
Currently, breast cancer is one of the most common cancers in women all over the world. A novel 3D breast ultrasound imaging ring system using the linear array transducer is proposed to decrease costs, reduce processing difficulties, and improve patient comfort as compared to modern day breast screening systems. The 1 × 128 Piezoelectric Micromachined Ultrasonic Transducer (PMUT) linear array is placed 90 degrees cross-vertically. The transducer surrounds the mammary gland, which allows for non-contact detection...
April 25, 2018: Sensors
Behrooz Ferdowsi, Carlos P Ortiz, Douglas J Jerolmack
Soil creeps imperceptibly downhill, but also fails catastrophically to create landslides. Despite the importance of these processes as hazards and in sculpting landscapes, there is no agreed-upon model that captures the full range of behavior. Here we examine the granular origins of hillslope soil transport by discrete element method simulations and reanalysis of measurements in natural landscapes. We find creep for slopes below a critical gradient, where average particle velocity (sediment flux) increases exponentially with friction coefficient (gradient)...
April 23, 2018: Proceedings of the National Academy of Sciences of the United States of America
Florian Frank, Chen Liu, Alessio Scanziani, Faruk O Alpak, Beatrice Riviere
We consider an energy-based boundary condition to impose an equilibrium wetting angle for the Cahn-Hilliard-Navier-Stokes phase-field model on voxel-set-type computational domains. These domains typically stem from μCT (micro computed tomography) imaging of porous rock and approximate a (on μm scale) smooth domain with a certain resolution. Planar surfaces that are perpendicular to the main axes are naturally approximated by a layer of voxels. However, planar surfaces in any other directions and curved surfaces yield a jagged/topologically rough surface approximation by voxels...
March 17, 2018: Journal of Colloid and Interface Science
Egon A Ozer
BACKGROUND: The non-conserved accessory genome of bacteria can be associated with important adaptive characteristics that can contribute to niche specificity or pathogenicity of strains. High degrees of structural and compositional diversity in genomic islands and other elements of the accessory genome can complicate characterization of accessory genome contents among populations of strains. Methods for easily and effectively defining the distributions of discrete elements of the accessory genome among bacterial strains in a population are needed to explore the relationships between the flexible genome and bacterial adaptive traits...
April 20, 2018: BMC Bioinformatics
Astrid S Pechstein, Joachim Schöberl
The tangential-displacement normal-normal-stress (TDNNS) method is a finite element method for mixed elasticity. As the name suggests, the tangential component of the displacement vector as well as the normal-normal component of the stress are the degrees of freedom of the finite elements. The TDNNS method was shown to converge of optimal order, and to be robust with respect to shear and volume locking. However, the method is slightly nonconforming, and an analysis with respect to the natural norms of the arising spaces was still missing...
2018: Numerische Mathematik
Mariam N Ali-Mucheru, Maria T Seville, Vickie Miller, Priya Sampathkumar, David A Etzioni
OBJECTIVE: To characterize agreement in the ascertainment of surgical site infections (SSIs) between the National Surgical Quality Improvement Program (NSQIP), National Healthcare Safety Network (NHSN), and administrative data. BACKGROUND: The NSQIP, NHSN, and administrative data are the primary systems used to monitor and report SSIs for the purpose of quality control and benchmarking of hospitals and surgeons. These systems have different methods for identifying SSIs...
April 18, 2018: Annals of Surgery
Corin F Otesteanu, Valery Vishnevsky, Orcun Goksel
PURPOSE: Success of ablation treatment depends on the accurate placement of the target ablation focus and the complete destruction of the pathological tissue. Thus, monitoring the formation, location, and size of the ablated lesion is essential. As ablated tissue gets stiffer, an option for ablation monitoring is ultrasound elastography, for imaging the tissue mechanical properties. Reconstruction of elasticity distribution can be achieved by solving an inverse problem from observed displacements, based on a deformable tissue model, commonly discretized by the finite element method (FEM)...
April 17, 2018: International Journal of Computer Assisted Radiology and Surgery
Zhekai Deng, Paul B Umbanhowar, Julio M Ottino, Richard M Lueptow
Segregation and mixing of size multidisperse granular materials remain challenging problems in many industrial applications. In this paper, we apply a continuum-based model that captures the effects of segregation, diffusion and advection for size tridisperse granular flow in quasi-two-dimensional chute flow. The model uses the kinematics of the flow and other physical parameters such as the diffusion coefficient and the percolation length scale, quantities that can be determined directly from experiment, simulation or theory and that are not arbitrarily adjustable...
March 2018: Proceedings. Mathematical, Physical, and Engineering Sciences
Nicolas Rivas, Stefan Frijters, Ignacio Pagonabarraga, Jens Harting
A model is presented for the solution of electrokinetic phenomena of colloidal suspensions in fluid mixtures. We solve the discrete Boltzmann equation with a Bhatnagar-Gross-Krook collision operator using the lattice Boltzmann method to simulate binary fluid flows. Solvent-solvent and solvent-solute interactions are implemented using a pseudopotential model. The Nernst-Planck equation, describing the kinetics of dissolved ion species, is solved using a finite difference discretization based on the link-flux method...
April 14, 2018: Journal of Chemical Physics
Johnson Truong, Matthew Hansen, Brian Szychowski, Tian Xie, Marie-Christine Daniel, Jong-In Hahm
We demonstrate a straightforward and effective method to synthesize vertically oriented, Cu-doped ZnO nanorods (NRs) using a novel multipurpose platform of copper silicide nanoblocks (Cu₃Si NBs) preformed laterally in well-defined directions on Si. The use of the surface-organized Cu₃Si NBs for ZnO NR growth successfully results in densely assembled Cu-doped ZnO NRs on each NB platform, whose overall structures resemble thick bristles on a brush head. We show that Cu₃Si NBs can uniquely serve as a catalyst for ZnO NRs, a local dopant source of Cu, and a prepatterned guide to aid the local assembly of the NRs on the growth substrate...
April 7, 2018: Nanomaterials
Y Guo, C Wassgren, W Ketterhagen, B Hancock, J Curtis
A discrete element method (DEM) model is developed to simulate the dynamics of wet, flexible fibers. The angles of repose of dry and wet fibers are simulated, and the simulation results are in good agreement with experimental results, validating the wet, flexible fiber model. To study wet fiber flow behavior, the model is used to simulate shear flows of wet fibers in a periodic domain under Lees-Edwards boundary conditions. Significant agglomeration is observed in dilute shear flows of wet fibers. The size of the largest agglomerate in the flow is found to depend on a Bond number, which is proportional to liquid surface tension and inversely proportional to the square of the shear strain rate...
April 3, 2018: Soft Matter
Rafal Kasztelanic, Adam Filipkowski, Alicja Anuszkiewicz, Paulina Stafiej, Grzegorz Stepniewski, Dariusz Pysz, Konrad Krzyzak, Ryszard Stepien, Mariusz Klimczak, Ryszard Buczynski
We present both a theoretical and an experimental study of a novel compact lensed fiber system utilizing a nanostructured GRIN lens. The lens can be integrated with an optical fiber, which ensures a unique and efficient focusing in any high index medium, such as a liquid. We use the effective medium approach to design lenses with arbitrary refractive index. To fabricate lenses, we utilize a discrete array of nano-sized rods made of two types of glasses, and apply a standard stack-and-draw fiber drawing technology...
March 22, 2018: Scientific Reports
Jackson R Hall, Mark H Schoenfisch
An electrochemical method capable of direct, real-time detection of hydrogen sulfide was developed using triple pulse amperometry (TPA) to mitigate sulfur poisoning and its related passivation of the working electrode surface. Through repeated cycles of discrete potential pulses, the electrooxidation of surface-adsorbed elemental sulfur to water-soluble sulfate ions was exploited to regenerate the glassy carbon electrode surface and maintain consistent sensor performance. Amperometric measurements and X-ray photoelectron spectroscopy surface analysis demonstrated that the TPA sensors provided enhanced analytical performance via decreased sulfur accumulation relative to low-potential (≤+0...
March 22, 2018: Analytical Chemistry
Saba Eshraghi, Ibrahim Esat, Amir A Mohagheghi
BACKGROUND: Hallux Valgus (HV) is the most common fore-foot deformity, which causes foot pain and limited motion that are encountered in podiatric and orthopedic practices. The purpose of this study is to develop a reliable pattern recognition method to identify the presence of HV based on plantar force measurements. METHOD: Forces at five discrete metatarsal regions are measured at discrete time intervals under the right foot. Under this method, it is hypothesized that force measurement at a given time interval is related to the forces at a previous time interval by using Markovian transition matrix (T matrix)...
March 11, 2018: Gait & Posture
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