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Numerical study of the near-wall vortical structures in particle-laden turbulent flow by a new vortex identification method-Liutex

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Journal of Hydrodynamics 2024年第1期36卷 53-60页

作者： Farid Rousta Goodarz Ahmadi Bamdad Lessani Chaoqun Liu Department of Mechanical and Aerospace Engineering Clarkson UniversityPotsdamNYUSA Mechanical Engineering and Engineering Science The University of North Carolina at CharlotteNCUSA Department of Mathematics University of Texas at ArlingtonArlingtonTXUSA

This study investigates turbulent particle-laden channel flows using direct numerical simulations employing the Eulerian-Lagrangian method.A two-way coupling approach is adopted to explore the mutual interaction between particles and fluid flow.The considered cases include flow with particle Stokes number varying from St=2 up to St=100 while maintaining a constant Reynolds number of Reτ=180 across all cases.A novel vortex identification method,Liutex(Rortex),is employed to assess its efficacy in capturing near-wall turbulent coherent structures and their interactions with particles.The Liutex method provides valuable information on vortex strength and vectors at each location,enabling a detailed examination of the complex interaction between fluid and particulate phases.As widely acknowledged,the interplay between clockwise and counterclockwise vortices in the near-wall region gives rise to low-speed streaks along the wall.These low-speed streaks serve as preferential zones for particle concentration,depending upon the particle Stokes number.It is shown that the Liutex method can capture these vortices and identify the location of low-speed streaks.Additionally,it is observed that the particle Stokes number(size)significantly affects both the strength of these vortices and the streaky structure exhibited by particles.Furthermore,a quantitative analysis of particle behavior in the near-wall region and the formation of elongated particle lines was carried out.This involved examining the average fluid streamwise velocity fluctuations at particle locations,average particle concentration,and the normal velocity of particles for each set of particle Stokes numbers.The investigation reveals the intricate interplay between particles and near-wall structures and the significant influence of particles Stokes number.This study contributes to a deeper understanding of turbulent particle-laden channel flow dynamics.

关键词： Turbulent channel flow particle-laden flow direct numerical simulation(DNS) Eulerian-Lagrangian vortex identification turbulence coherent structures Liutex

Determination of the critical rainfall of runoff-initiated debris flows by the perspective of physical mechanics and Shields stress

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Journal of Mountain Science 2024年第4期21卷 1160-1173页

作者： MA Chao ZHU Yongtai LU Lu DU Cui LYU Liqun DONG Jie School of Soil and Water Conservation Beijing Forestry UniversityBeijing 100083China Beijing Institute of Geological Hazard Prevention Beijing 100120China School of Software Engineering Chengdu University of Information TechnologyChengdu610225China Civil and Environmental Engineering Department Clarkson UniversityNY 13699USA

The critical rainfall of runoff-initiated debris flows is utmost importance for local early hazard forecasting.This paper presents research on the critical rainfall of runoff-initiated debris flows through comparisons between slope gradients and three key factors,including topographic contributing area,dimensionless discharge,and Shields stress.The rainfall amount was estimated by utilizing in-situ rainfall records and a slope-dependent Shields stress model was created.The created model can predict critical Shields stress more accurately than the other two models.Furthermore,a new dimensionless discharge equation was proposed based on the corresponding discharge-gradient datasets.The new equation,along with factors such as contributing area above bed failure sites,channel width,and mean diameter of debris flow deposits,predicts a smaller rainfall amount than the in-situ measured records.Although the slope-dependent Shields stress model performs well and the estimated rainfall amount is lower than the in-situ records,the sediment initiation in the experiments falls within sheet flow regime due to a large Shields stress.Therefore,further sediment initiation experiments at a steeper slope range are expected in the future to ensure that the sediment transport belongs to mass failure regime characterized by a low level of Shields stress.Finally,a more accurate hazard forecast on the runoff-initiated debris flow holds promise when the corresponding critical slope-dependent dimensionless discharge of no motion,fluvial sediment transport,mass flow regime,and sheet flow regime are considered.

关键词： Infinite slope stability Shields stress Contributing area-slope gradient Rainfall back estimation

Shoaling Internal Solitary Waves and the Formation of Boluses

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Open Journal of Fluid Dynamics 2024年第2期14卷 65-82页

作者： Hooman Enayati Brian T. Helenbrook Department of Mechanical Engineering Lafayette College Easton PA USA Department of Mechanical & Aerospace Engineering Clarkson University Potsdam NY USA

An internal solitary wave of elevation in a two-layer density stratified system of an incompressible, viscous and homogeneous fluid was studied. The run-up of a wave of elevation encountering different slopes was investigated numerically based on solving the continuity, Navier-Stokes and convective-diffusion equations within the Boussinesq approximation. The commercial software COMSOL Multiphysics was used to conduct the numerical simulations. For gradual shoals, a bolus formed that transported dense fluid up the shoal. The bolus disappeared when it reached its maximum height on the slope due to the draining of the dense fluid. Various shoal angles were simulated to detect the critical angle above which a bolus does not form. An angle of 30 or less resulted in the formation of a bolus. In addition, the simulations demonstrated that the size of the bolus induced by shallower slopes was larger and that the vertical height traveled by the bolus was insensitive to the slope of the shoal.

关键词： Internal Solitary Waves COMSOL Multiphysics Wave Breaking

A GDPR Compliant Approach to Assign Risk Levels to Privacy Policies

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Computers, Materials & Continua 2023年第3期74卷 4631-4647页

作者： Abdullah R.Alshamsan Shafique A.Chaudhry Department of Computer Science Clarkson UniversityClarkson AvePotsdam13699NYUSA David D.Reh School of Business Clarkson UniversityClarkson AvePotsdam13699NYUSA

Data privacy laws require service providers to inform their customers on how user data is gathered,used,protected,and shared.The General Data ProtectionRegulation(GDPR)is a legal framework that provides guidelines for collecting and processing personal information from individuals.Service providers use privacy policies to outline the ways an organization captures,retains,analyzes,and shares customers’data with other parties.These policies are complex and written using legal jargon;therefore,users rarely read them before accepting them.There exist a number of approaches to automating the task of summarizing privacy policies and assigning risk levels.Most of the existing approaches are not GDPR compliant and use manual annotation/labeling of the privacy text to assign risk level,which is time-consuming and costly.We present a framework that helps users see not only data practice policy compliance with GDPR but also the risk levels to privacy associated with accepting that policy.The main contribution of our approach is eliminating the overhead cost of manual annotation by using the most frequent words in each category to create word-bags,which are used with Regular Expressions and Pointwise Mutual Information scores to assign risk levels that comply with the GDPR guidelines for data protection.We have also developed a web-based application to graphically display risk level reports for any given online privacy policy.Results show that our approach is not only consistent with GDPR but performs better than existing approaches by successfully assigning risk levels with 95.1%accuracy after assigning data practice categories with an accuracy rate of 79%.

关键词： GDPR machine learning natural language processing privacy assessment privacy policy text classification

Stem cells in intervertebral disc regeneration-more talk than action?

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BIOCELL 2022年第4期46卷 893-898页

作者： PETRA KRAUS ANKITA SAMANTA SINA LUFKIN THOMAS LUFKIN Department of Biology Clarkson UniversityPotsdamNY 13699USA The clarkson School Clarkson UniversityPotsdamNY 13699USA

Pain and lifestyle changes are common consequences of intervertebral disc degeneration(IVDD)and affect a large part of the aging population.The stemness of cells is exploited in the field of regenerative medicine as key to treat degenerative diseases.Transplanted cells however often face delivery and survival challenges,especially in tissues with a naturally harsh microniche environment such as the intervertebral disc.Recent interest in the secretome of stem cells,especially cargo protected from microniche-related decay as frequently present in degenerating tissues,provides new means of rejuvenating ailing cells and tissues.Exosomes,a type of extracellular vesicles with purposeful cargo gained particular interest in conveying stem cell related attributes of rejuvenation,which will be discussed here in the context of IVDD.

关键词： Stem cells MSC Intervertebral disc(IVD) Exosome Extracellular matrix(ECM)

Porosity of bimodal and trimodal sediment mixtures

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International Journal of Sediment Research 2022年第2期37卷 258-271页

作者： Chamil Perera Weiming Wu Ian Knack Department of Civil and Environmental Engineering Clarkson University

This study focuses on the prediction of the porosity of nonuniform sediment mixtures,considering the effects of particle packing.A random particle packing model has been developed for the porosity of bimodal mixtures by extending the existing random particle filling theory.Coefficients in the developed model are calibrated by fitting the model to measured data for a variety of bimodal mixtures,including spherical glass particles,rounded quarry grains,and natural sediments.The model coefficients are found to be functions of the diameter ratio of coarse and fine particles,separately for spherical glass particles and natural sediments due to differences in particle shapes.The bimodal mixture model is then extended to trimodal particle mixtures in three approaches:two based on serial packing and one based on random packing.These models are tested against experimental data of six trimodal mixtures with spherical glass beads.The results show that the random packing model and the fine-medium-coarse particle serial packing model predict well the observed trimodal mixture porosities.

关键词： Porosity Particle filling Particle packing Bimodal mixture Trimodal mixture

Fabrication of self-assembling nanofibers with optimal cell uptake and therapeutic delivery efficacy

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Bioactive Materials 2017年第4期2卷 260-268页

作者： Dawei Xu Damien SKSamways He Dong Department of Chemistry&Biomolecular Science Clarkson UniversityPotsdamUSA Department of Biology Clarkson UniversityPotsdamUSA

Effective strategies to fabricate finite organic nanoparticles and understanding their structure-dependent cell interaction is highly important for the development of long circulating nanocarriers in cancer therapy.In this contribution,we will capitalize on our recent development of finite supramolecular nanofibers based on the self-assembly of modularly designed cationic multidomain peptides(MDPs)and use them as a model system to investigate structure-dependent cell penetrating activity.MDPs selfassembled into nanofibers with high density of cationic charges at the fiber-solvent interface to interact with the cell membrane.However,despite the multivalent charge presentation,not all fibers led to high levels of membrane activity and cellular uptake.The flexibility of the cationic charge domains on self-assembled nanofibers plays a key role in effective membrane perturbation.Nanofibers were found to sacrifice their dimension,thermodynamic and kinetic stability for a more flexible charge domain in order to achieve effective membrane interaction.The increased membrane activity led to improved cell uptake of membrane-impermeable chemotherapeutics through membrane pore formation.In vitro cytotoxicity study showed co-administering of water-soluble doxorubicin with membrane-active peptide nanofibers dramatically reduced the IC50 by eight folds compared to drug alone.Through these detailed structure and activity studies,the acquired knowledge will provide important guidelines for the design of a variety of supramolecular cell penetrating nanomaterials not limited to peptide assembly which can be used to probe various complex biological processes.

关键词： Supramolecular assembly Cell penetrating peptide Drug delivery Cell uptake Membrane activity

Refining safety considerations for intradialytic blood flow restriction exercise. Commentary on “Concerns on the application of blood-flow restriction resistance exercise and thrombosis risk in hemodialysis patients”

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Journal of Sport and Health Science 2024年第4期13卷 455-456页

作者： Matthew J.clarkson Institute for Health and Sport Victoria UniversityMelbourneVIC 8001Australia

I read with great interest the article“Concerns on the application of blood flow restriction resistance exercise and thrombosis risk in hemodialysis patients”by Correa et al.1 The study presents complementary data from a previous randomized controlled trial,2 exploring the application of intradialytic blood flow restriction exercise for hemodialysis patients.

关键词： patients hemodialysis

Modeling ocean wave propagation under sea ice covers

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Acta Mechanica Sinica 2015年第1期31卷 1-15页

作者： Xin Zhao Hayley H. Shen Sukun Cheng Department of Civil and Environmental Engineering clarkson university

Operational ocean wave models need to work globally, yet current ocean wave models can only treat ice covered regions crudely. The purpose of this paper is to provide a brief overview of ice effects on wave propagation and different research methodology used in studying these effects. Based on its proximity to land or sea, sea ice can be classified as： landfast ice zone, shear zone, and the marginal ice zone. All ice covers attenuate wave energy. Only long swells can penetrate deep into an ice cover. Being closest to open water, wave propagation in the marginal ice zone is the most complex to model. The physical appearance of sea ice in the marginal ice zone varies. Grease ice, pancake ice, brash ice, floe aggregates, and continuous ice sheet may be found in this zone at different times and locations. These types of ice are formed under different thermalmechanical forcing. There are three classic models that describe wave propagation through an idealized ice cover： mass loading, thin elastic plate, and viscous layer models. From physi cal arguments we may conjecture that mass loading model is suitable for disjoint aggregates of ice floes much smaller than the wavelength, thin elastic plate model is suitable for a con tinuous ice sheet, and the viscous layer model is suitable for grease ice. For different sea ice types we may need different wave ice interaction models. A recently proposed viscoelas tic model is able to synthesize all three classic models into one. Under suitable limiting conditions it converges to the three previous models. The complete theoretical framework for evaluating wave propagation through various ice covers need to be implemented in the operational ocean wave models. In this review, we introduce the sea ice types, previous wave ice interaction models, wave attenuation mechanisms,the methods to calculate wave reflection and transmission between different ice covers, and the effect of ice floe breaking on shaping the sea ice morphology. Laboratory experiments, field measurements and numeric

关键词： Ocean waves Sea ice Cryospheric change