Articles de revues : « Body fluids, mathematical models »

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Smith, D. J., E. A. Gaffney et J. R. Blake. « Mathematical modelling of cilia-driven transport of biological fluids ». Proceedings of the Royal Society A : Mathematical, Physical and Engineering Sciences 465, n^o 2108 (2 juin 2009) : 2417–39. http://dx.doi.org/10.1098/rspa.2009.0018.

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Cilia-driven flow occurs in the airway surface liquid, in the female and male reproductive tracts and enables symmetry-breaking in the embryonic node. Viscoelastic rheology is found in healthy states in some systems, whereas in others may characterise disease, motivating the development of mathematical models that take this effect into account. We derive the fundamental solution for linear viscoelastic flow, which is subsequently used as a basis for slender-body theory. Our numerical algorithm allows efficient computation of three-dimensional time-dependent flow, bending moments, power and particle transport. We apply the model to the large-amplitude motion of a single cilium in a linear Maxwell liquid. A relatively short relaxation time of just 0.032 times the beat period significantly reduces forces, bending moments, power and particle transport, the last variable exhibiting exponential decay with relaxation time. A test particle is propelled approximately one-fifth as quickly along the direction of cilia beating for scaled relaxation time 0.032 as in the Newtonian case, and mean volume flow is abolished, emphasizing the sensitivity of cilia function to fluid rheology. These results may have implications for flow in the airways, where the transition from Newtonian to viscoelastic rheology in the peri-ciliary fluid may reduce clearance.

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Purwati, Endah, et Sugiyanto Sugiyanto. « Pengembangan Model Matematika SIRD (Susceptibles-Infected-Recovery-Deaths) Pada Penyebaran Virus Ebola ». Jurnal Fourier 5, n^o 1 (1 avril 2016) : 23. http://dx.doi.org/10.14421/fourier.2016.51.23-34.

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Ebola is a deadly disease caused by a virus and is spread through direct contact with blood or body fluids such as urine, feces, breast milk, saliva and semen. In this case, direct contact means that the blood or body fluids of patients were directly touching the nose, eyes, mouth, or a wound someone open. In this paper examined two mathematical models SIRD (Susceptibles-Infected-Recovery-Deaths) the spread of the Ebola virus in the human population. Both the mathematical model SIRD on the spread of the Ebola virus is a model by Abdon A. and Emile F. D. G. and research development model. This study was conducted to determine the point of disease-free equilibrium and endemic equilibrium point and stability analysis of the dots, knowing the value of the basic reproduction number (R0) and a simulation model using Matlab software version 6.1.0.450. From the analysis of the two models, obtained the same point for disease-free equilibrium point with the stability of different points and different points for endemic equilibrium point with the stability of both the same point and the same value to the value of the basic reproduction number (R0). After simulating the model using Matlab software version 6.1.0.450, it can be seen changes in the behavior of the population at any time.

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Pietribiasi, Mauro, Jacek Waniewski et John K. Leypoldt. « Mathematical modelling of bicarbonate supplementation and acid-base chemistry in kidney failure patients on hemodialysis ». PLOS ONE 18, n^o 2 (24 février 2023) : e0282104. http://dx.doi.org/10.1371/journal.pone.0282104.

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Acid-base regulation by the kidneys is largely missing in end-stage renal disease patients undergoing hemodialysis (HD). Bicarbonate is added to the dialysis fluid during HD to replenish the buffers in the body and neutralize interdialytic acid accumulation. Predicting HD outcomes with mathematical models can help select the optimal patient-specific dialysate composition, but the kinetics of bicarbonate are difficult to quantify, because of the many factors involved in the regulation of the bicarbonate buffer in bodily fluids. We implemented a mathematical model of dissolved CO2 and bicarbonate transport that describes the changes in acid-base equilibrium induced by HD to assess the kinetics of bicarbonate, dissolved CO2, and other buffers not only in plasma but also in erythrocytes, interstitial fluid, and tissue cells; the model also includes respiratory control over the partial pressures of CO2 and oxygen. Clinical data were used to fit the model and identify missing parameters used in theoretical simulations. Our results demonstrate the feasibility of the model in describing the changes to acid-base homeostasis typical of HD, and highlight the importance of respiratory regulation during HD.

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KORNAEVA, E. P., A. V. KORNAEV, I. N. STEBAKOV, S. G. POPOV, D. D. STAVTSEV et V. V. DREMIN. « CONCEPT OF A MECHATRONIC INSTALLATION FOR RESEARCHING THE RHEOLOGICAL PROPERTIES OF PHYSIOLOGICAL FLUIDS ». Fundamental and Applied Problems of Engineering and Technology, n^o 1 (2021) : 83–95. http://dx.doi.org/10.33979/2073-7408-2021-345-1-83-95.

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The properties of physiological fluids, blood primarily, contain important information about the state of a body. This article deals with the development of a new portable device of inertial viscometer for the physiological fluids. Based on the analysis of mathematical and simulation models of viscous media flows in capillaries, recommendations for the choice of design parameters are formulated. Processing the data of a video capillaroscopy for the intralipid flow under conditions close to the conditions for measuring blood viscosity showed the possibility of using the laser speckle contrast imaging method to determine the velocity profile over the channel thickness. The results obtained have created sufficient grounds for the design of a mechatronic test rig and its information-measuring system.

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Sankar, D. S., et Yazariah Yatim. « Comparative Analysis of Mathematical Models for Blood Flow in Tapered Constricted Arteries ». Abstract and Applied Analysis 2012 (2012) : 1–34. http://dx.doi.org/10.1155/2012/235960.

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Pulsatile flow of blood in narrow tapered arteries with mild overlapping stenosis in the presence of periodic body acceleration is analyzed mathematically, treating it as two-fluid model with the suspension of all the erythrocytes in the core region as non-Newtonian fluid with yield stress and the plasma in the peripheral layer region as Newtonian. The non-Newtonian fluid with yield stress in the core region is assumed as (i) Herschel-Bulkley fluid and (ii) Casson fluid. The expressions for the shear stress, velocity, flow rate, wall shear stress, plug core radius, and longitudinal impedance to flow obtained by Sankar (2010) for two-fluid Herschel-Bulkley model and Sankar and Lee (2011) for two-fluid Casson model are used to compute the data for comparing these fluid models. It is observed that the plug core radius, wall shear stress, and longitudinal impedance to flow are lower for the two-fluid H-B model compared to the corresponding flow quantities of the two-fluid Casson model. It is noted that the plug core radius and longitudinal impedance to flow increases with the increase of the maximum depth of the stenosis. The mean velocity and mean flow rate of two-fluid H-B model are higher than those of the two-fluid Casson model.

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Sudi Mungkasi. « Modelling And Simulation of Topical Drug Diffusion in The Dermal Layer of Human Body ». Journal of Advanced Research in Fluid Mechanics and Thermal Sciences 86, n^o 2 (24 août 2021) : 39–49. http://dx.doi.org/10.37934/arfmts.86.2.3949.

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We consider the problem of drug diffusion in the dermal layer of human body. Two existing mathematical models of the drug diffusion problem are recalled. We obtain that the existing models lead to inconsistent equations for the steady state condition. We also obtain that solutions to the existing models are unrealistic for some cases of the unsteady state condition, because negative drug concentrations occur due to the inappropriate assumption of the model. Therefore, in this paper, we propose a modified mathematical model, so that the model is consistent, and the solution is nonnegative for both steady and unsteady state conditions of the drug diffusion problem in the dermal layer of human body. For the steady state condition, the exact solution to the proposed model is given. For unsteady state condition, we use a finite difference method for solving the models numerically, where the discretisation is centred in space and forward in time. Simulation results confirm that our proposed model and method preserve the non-negativity of the solution to the problem, so the solution is more realistic than that of the old model.

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Khapalov, Alexander. « The well-posedness of a swimming model in the 3-D incompressible fluid governed by the nonstationary Stokes equation ». International Journal of Applied Mathematics and Computer Science 23, n^o 2 (1 juin 2013) : 277–90. http://dx.doi.org/10.2478/amcs-2013-0021.

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We introduce and investigate the well-posedness of a model describing the self-propelled motion of a small abstract swimmer in the 3-D incompressible fluid governed by the nonstationary Stokes equation, typically associated with low Reynolds numbers. It is assumed that the swimmer’s body consists of finitely many subsequently connected parts, identified with the fluid they occupy, linked by rotational and elastic Hooke forces. Models like this are of interest in biological and engineering applications dealing with the study and design of propulsion systems in fluids.

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Vispute, Devarsh M., Prem K. Solanki et Yoed Rabin. « Large surface deformation due to thermo-mechanical effects during cryopreservation by vitrification – mathematical model and experimental validation ». PLOS ONE 18, n^o 3 (9 mars 2023) : e0282613. http://dx.doi.org/10.1371/journal.pone.0282613.

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This study presents a simplified thermal-fluids (TF) mathematical model to analyze large surface deformations in cryoprotective agents (CPA) during cryopreservation by vitrification. The CPA deforms during vitrification due to material flow caused by the combined effects of thermal gradients within the domain, thermal contraction due to temperature, and exponential increase in the viscosity of the CPA as it is cooled towards glass transition. While it is well understood that vitrification is associated with thermo-mechanical stress, which might lead to structural damage, those large deformations can lead to stress concentration, further intensifying the probability to structural failure. The results of the TF model are experimentally validated by means of cryomacroscopy on a cuvette containing 7.05M dimethyl sulfoxide (DMSO) as a representative CPA. The TF model presented in this study is a simplified version of a previously presented thermo-mechanics (TM) model, where the TM model is set to solve the coupled heat transfer, fluid mechanics and solid mechanics problems, while the TF model omits further deformations in the solid state. It is demonstrated in this study that the TF model alone is sufficient to capture large-body deformations during vitrification. However, the TF model alone cannot be used to estimate mechanical stresses, which become significant only when the deformation rates become so small that the deformed body practically behaves as an amorphous solid. This study demonstrates the high sensitivity of deformation predictions to variation in material properties, chief among which are the variations of density and viscosity with temperature. Finally, this study includes a discussion on the possibility of turning on and off the TF and TM models in respective parts of the domain, in order to solve the multiphysics problem in a computationally cost-effective manner.

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Yakovlev, A. A., S. G. Postupaeva, V. N. Grebennikov et N. V. Fedorova. « DEVELOPMENT OF TECHNICAL SYSTEMS BASED ON HEURISTIC MODELING OF THE PHYSICAL OPERATION PRINCIPLE ». IZVESTIA VOLGOGRAD STATE TECHNICAL UNIVERSITY, n^o 8(243) (28 août 2020) : 83–86. http://dx.doi.org/10.35211/1990-5297-2020-8-243-83-86.

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A logical-mathematical model has been developed to represent the physical principles of the operation of technical systems with a fluid and gas working body. Example of modeling a gas turbine twin-shaft installation. Heuristic modification methods for developing improved models of the physical principle of action are proposed.

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Knezevic, Darko, Aleksandar Milasinovic, Zdravko Milovanovic et Sasa Lalos. « The influence of thermodynamic state of mineral hydraulic oil on flow rate through radial clearance at zero overlap inside the hydraulic components ». Thermal Science 20, suppl. 5 (2016) : 1461–71. http://dx.doi.org/10.2298/tsci16s5461k.

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In control hydraulic components (servo valves, LS regulators, etc.) there is a need for precise mathematical description of fluid flow through radial clearances between the control piston and body of component at zero overlap, small valve opening and small lengths of overlap. Such a mathematical description would allow for a better dynamic analysis and stability analysis of hydraulic systems. The existing formulas in the literature do not take into account the change of the physical properties of the fluid with a change of thermodynamic state of the fluid to determine the flow rate through radial clearances in hydraulic components at zero overlap, a small opening, and a small overlap lengths, which leads to the formation of insufficiently precise mathematical models. In this paper model description of fluid flow through radial clearances at zero overlap is developed, taking into account the changes of physical properties of hydraulic fluid as a function of pressure and temperature. In addition, the experimental verification of the mathematical model is performed.

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Guyton, A. C. « Long-term arterial pressure control : an analysis from animal experiments and computer and graphic models ». American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 259, n^o 5 (1 novembre 1990) : R865—R877. http://dx.doi.org/10.1152/ajpregu.1990.259.5.r865.

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Long-term arterial pressure control is very different from acute control, because many of the acute control systems are overridden by a single long-term mechanism that has little to do with short-term control. This is the renal fluid volume mechanism for pressure control. It is based on a simple functional property of the kidney: as the arterial pressure rises, the kidney output of water and electrolytes increases dramatically. When the output rises above the net intake of water and electrolytes, negative body fluid balance occurs, causing both the body fluid volume and the pressure to decrease. This decrease continues until the kidney fluid output exactly balances the net fluid intake. Conversely, if the pressure falls below the exact level for balance, intake becomes greater than output; then fluid builds up in the body and the pressure rises until intake and output again exactly balance each other. This fluid mechanism for pressure control has been known from the beginning of blood pressure research. However, its overpowering importance was not appreciated until a mathematical computer analysis in 1966 demonstrated the renal-fluid feedback mechanism to have infinite feedback gain for long-term pressure control. This is the principal topic of the present review.

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FRIEDMAN, AVNER. « MATHEMATICAL ANALYSIS AND CHALLENGES ARISING FROM MODELS OF TUMOR GROWTH ». Mathematical Models and Methods in Applied Sciences 17, supp01 (novembre 2007) : 1751–72. http://dx.doi.org/10.1142/s0218202507002467.

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In the last four decades, various cancer models have been developed in which the evolution of the densities of cells (abnormal, normal, or dead) and the concentrations of biochemical species are described in terms of differential equations. In this paper, we deal with tumor models in which the tumor occupies a well-defined region in space; the boundary of this region is held together by the forces of cell-to-cell adhesion. We shall refer to such tumors as "solid" tumors, although they may sometimes consist of fluid-like tissue, such as in the case of brain tumors (e.g. gliomas) and breast tumors. The most common class of solid tumors is carcinoma: a cancer originating from epithelial cells, that is, from the closely packed cells which align the internal cavities of the body. Models of solid tumors must take spatial effects into account, and are therefore described in terms of partial differential equations (PDEs). They also need to take into account the fact that the tumor region is changing in time; in fact, the tumor region, say Ω(t), and its boundary Γ(t), are unknown in advance. Thus one needs to determine both the unknown "free boundary" Γ(t) together with the solution of the PDEs in Ω(t). These types of problems are called free boundary problems. The models described in this paper are free boundary problems, and our primary interest is the spatial/geometric features of the free boundary. Some of the basic questions we shall address are: What is the shape of the free boundary? How does the free boundary behave as t → ∞? Does the tumor volume increase or shrink as t → ∞? Under what conditions does the tumor eventually become dormant? Finally, we shall explore the dependence of the free boundary on some biological parameters, and this will give rise to interesting bifurcation phenomena. The structure of the paper is as follows. In Secs. 1 and 2 we consider models in which all the cells are of one type, they are all proliferating cells. The tissue is modeled either as a porous medium (in Sec. 1) or as a fluid medium (in Sec. 2). The models are extended in Secs. 3 and 4 to include three types of cells: proliferating, quiescent, and dead. Finally, in Sec. 5 we outline a general multiphase model that includes gene mutations.

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Sharma, Sunil Kumar, Rakesh Chandmal Sharma, Yeongil Choi et Jaesun Lee. « Experimental and Mathematical Study of Flexible–Rigid Rail Vehicle Riding Comfort and Safety ». Applied Sciences 13, n^o 9 (22 avril 2023) : 5252. http://dx.doi.org/10.3390/app13095252.

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This paper analyses the dynamic behavior of a rail vehicle using experimental and simulation analysis on a multi-rigid–flex body model. The mathematical models are developed considering the car body, bogie frame, and wheel axle for rail vehicles of rigid–flexible and multi-rigid formulations, taking the car body as rigid for the rigid body analysis and the flexible car body for flex–rigid analysis. A finite element model of the car body was developed in ANSYS, and substructure and modal analyses were performed. The mathematical model is validated through an experiment conducted by the Research Design and Standards Organization. Then, the validated model is further analyzed to evaluate the running comfort, using the Sperling ride index and the running safety, by investigating the derailment coefficient and wheel load reduction rate. The impact of flexibility on the vehicle’s running stability is investigated using the rigid body dynamics model and experimental data. Compared to experimental data, the simulation results reveal that elastic vibration cannot be neglected in vehicle dynamics, since the rigid–flexible coupling model is slightly more significant than the rigid-body model for ride comfort and safety.

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Meyer, Aurelien G. « Measuring Simplified Pore-Throat Angularity Using Automated Mathematical Morphology ». SPE Journal 24, n^o 01 (31 décembre 2018) : 243–53. http://dx.doi.org/10.2118/194193-pa.

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Summary Fluid flow in sedimentary rocks is controlled mainly by the morphology of pore-connecting throats. Pore throats (PTs) typically exhibit diverse converging/diverging morphologies such as biconic, parabolic, or hyperbolic geometries. These different geometries are defined by variable opening angle, or angularity, between the throat walls from the narrowest point of the throat toward the pore body. Importantly, each of these geometries imposes different constraints on fluid flow. However, current pore-level flow models usually favor simple cylindrical or biconic throat morphologies, in part because of the difficulty to extract the throat angularity from pore-space imagery. An image-analysis technique called mathematical morphology has been used to characterize porosity in laterally continuous pore networks (e.g., in sandstones) from thin-section microphotographs. This method allows the extraction of petrophysical parameters such as pore and throat diameters through successive image alterations—namely, erosion/dilation cycles using an expanding structuring element (SE). This study proposes a novel application of this technique and quantifies PT angularity. Angularity can be measured from the throat toward the pore body so that the true geometry—biconic, parabolic, or hyperbolic—can be recognized. The technique is tested on simple geometries to demonstrate the correctness of the mathematic equations involved. Because all equations assume perfect, nonpixelated geometries while images are composed of square pixels, the accuracy of measurements depends strongly on image resolution. Pixelation causes significant fluctuations of ±2 to 10° around the correct angularity values that decrease in amplitude as image resolution increases. Finally, potential implications of this parameter on fluid-flow modeling are discussed.

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Thomas, S. Randall, Pierre Baconnier, Julie Fontecave, Jean-Pierre Françoise, François Guillaud, Patrick Hannaert, Alfredo Hernández et al. « SAPHIR : a physiome core model of body fluid homeostasis and blood pressure regulation ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 366, n^o 1878 (19 juin 2008) : 3175–97. http://dx.doi.org/10.1098/rsta.2008.0079.

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We present the current state of the development of the SAPHIR project (a Systems Approach for PHysiological Integration of Renal, cardiac and respiratory function). The aim is to provide an open-source multi-resolution modelling environment that will permit, at a practical level, a plug-and-play construction of integrated systems models using lumped-parameter components at the organ/tissue level while also allowing focus on cellular- or molecular-level detailed sub-models embedded in the larger core model. Thus, an in silico exploration of gene-to-organ-to-organism scenarios will be possible, while keeping computation time manageable. As a first prototype implementation in this environment, we describe a core model of human physiology targeting the short- and long-term regulation of blood pressure, body fluids and homeostasis of the major solutes. In tandem with the development of the core models, the project involves database implementation and ontology development.

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Obertyukh, Roman, Andrіі Slabkyі, Leonid Polishchuk, Oleksandr Povstianoi, Saule Kumargazhanova et Maxatbek Satymbekov. « DYNAMIC AND MATHEMATICAL MODELS OF THE HYDROIMPULSIVE VIBRO-CUTTING DEVICE WITH A PRESSURE PULSE GENERATOR BULT INTO THE RING SPRING ». Informatyka, Automatyka, Pomiary w Gospodarce i Ochronie Środowiska 12, n^o 3 (30 septembre 2022) : 54–58. http://dx.doi.org/10.35784/iapgos.3049.

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Structural calculation scheme of the hydropulse device for vibration cutting with built-in ring with pressure pulse generator (PPG) is considered. On the basis of the structural scheme and cyclogram of the working cycle of the device, its dynamic and mathematical models were developed, in which the hydraulic link is represented by a visco-elastic model of the working fluid (energy carrier) composed of the inertial elastic and dissipative elements (Kelvin-Foyga's body).

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Andreassen, S., et S. E. Rees. « Mathematical Models of Oxygen and Carbon Dioxide Storage and Transport : Interstitial Fluid and Tissue Stores and Whole-Body Transport ». Critical Reviews in Biomedical Engineering 33, n^o 3 (2005) : 265–98. http://dx.doi.org/10.1615/critrevbiomedeng.v33.i3.20.

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Tanveer, Shakera, et V. P. Rathod. « Gravity flow of pulsatile blood through a porous medium under periodic body acceleration and magnetic field in an inclined tube ». International Journal of Biomathematics 09, n^o 02 (14 janvier 2016) : 1650025. http://dx.doi.org/10.1142/s179352451650025x.

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Mathematical model for the pulsatile blood flow through a porous medium under the influence of periodic body acceleration for gravity flow along an inclined tube by considering blood as a couple stress, incompressible and electrically conducting fluid in the presence of magnetic field has been investigated. Analytical expressions for axial velocity, flow rate, fluid acceleration and shear stress are obtained by applying the Laplace and finite Hankel’s transforms. The velocity profiles for various values of Hartmann number, couple stress parameters and the angle of inclination are shown graphically. Also the effects of body acceleration, Womerseley parameters and permeability parameters have been discussed. The results obtained in the present mathematical model for different values of the parameters involved in the problem show that the flow of blood is influenced by the effect of magnetic field, the porous medium and the inclination angle. The present model is compared with the other existing models. Through this theoretical investigation, the applications of magnetic field have also been indicated in the field of biological, biomedical and engineering sciences.

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Yudenkov, A. V., et A. M. Volodchenkov. « Stability of mathematical models of the main problems of the anisotropic theory of elasticity ». Vestnik Udmurtskogo Universiteta. Matematika. Mekhanika. Komp'yuternye Nauki 30, n^o 1 (mars 2020) : 112–24. http://dx.doi.org/10.35634/vm200108.

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The boundary problems of the complex-variable function theory are effectively used while investigating equilibrium of homogeneous elastic mediums. The most complicated systems of the boundary value problems correspond to the case when an elastic body exhibits anisotropic properties. Anisotropy of the medium results in the drift of boundary conditions of the function that in general disrupts analyticity of the functions of interest. The paper studies systems of the boundary value problems with drift for analytic vectors corresponding to the primal elastic problems (first, second and mixed problems). Systems of analytic vectors with drift are reduced to equivalent systems of Hilbert boundary value problems for analytic functions with weak singularity integrators. The obtained general solution of the primal boundary value problems for the anisotropic theory of elasticity allows us to check the above problems for stability with respect to perturbations of boundary value conditions and contour shape. The research is relevant as there is necessity to apply approximate numerical methods to the boundary value problems with drift. The main research result comes to be a proof of stability of the systems of the vector boundary value problems with drift for analytic functions on the Hölder space corresponding to the primal problems of the elastic theory for anisotropic bodies in the case of change in the boundary value conditions and contour shape.

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Griffith, Boyce E., et Neelesh A. Patankar. « Immersed Methods for Fluid–Structure Interaction ». Annual Review of Fluid Mechanics 52, n^o 1 (5 janvier 2020) : 421–48. http://dx.doi.org/10.1146/annurev-fluid-010719-060228.

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Fluid–structure interaction is ubiquitous in nature and occurs at all biological scales. Immersed methods provide mathematical and computational frameworks for modeling fluid–structure systems. These methods, which typically use an Eulerian description of the fluid and a Lagrangian description of the structure, can treat thin immersed boundaries and volumetric bodies, and they can model structures that are flexible or rigid or that move with prescribed deformational kinematics. Immersed formulations do not require body-fitted discretizations and thereby avoid the frequent grid regeneration that can otherwise be required for models involving large deformations and displacements. This article reviews immersed methods for both elastic structures and structures with prescribed kinematics. It considers formulations using integral operators to connect the Eulerian and Lagrangian frames and methods that directly apply jump conditions along fluid–structure interfaces. Benchmark problems demonstrate the effectiveness of these methods, and selected applications at Reynolds numbers up to approximately 20,000 highlight their impact in biological and biomedical modeling and simulation.

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Epstein, Yoram, et Lawrence E. Armstrong. « Fluid-Electrolyte Balance during Labor and Exercise : Concepts and Misconceptions ». International Journal of Sport Nutrition 9, n^o 1 (mars 1999) : 1–12. http://dx.doi.org/10.1123/ijsn.9.1.1.

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Body water and electrolyte balance are essential to optimal physiological function and health. During exercise, work, or high temperatures, a significant level of dehydration can develop, and the ratio of extracellular to intracellular fluid can change, despite an ample supply of water. Physical and cognitive performance are impaired at 1-2% dehydration, and the body can collapse when water loss approaches 7%. Because fluid needs and intakes vary, formulating one general guideline for fluid replacement is difficult. Knowing the amount of water lost in sweat may enable predicting fluid needs via mathematical models for industrial, athletic, and military scenarios. Sodium imbalance might result from excessive Na+ loss or from gross o verity dration. In most work or exercise lasting < 3-4 hr, the major concern is that fluid be available to prevent heat-related illnesses, which can be prevented if fluid and electrolyte losses are balanced with intake, using the recommendations presented.

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Velmisov, Petr A., et Andrey V. Ankilov. « Mathematical modeling in problems about dynamics and stability of elastic elements of wing profiles ». Cybernetics and Physics, Volume 10, 2021, Number 3 (30 novembre 2021) : 201–12. http://dx.doi.org/10.35470/2226-4116-2021-10-3-201-212.

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The mathematical models describing the dynamics of elastic elements of wing structures and representing the initial-boundary value problems for systems of partial differential equations are proposed. The dynamics and stability of elastic elements of wings, flown around by a gas or liquid stream in a model of an incompressible medium, are investigated. To study the dynamics of elastic elements and a gas-liquid medium, both linear and nonlinear models of the mechanics of a solid deformable body and linear models of the mechanics of liquid and gas are used. On the basis of the constructed functionals for partial differential equations, the sufficient stability conditions are obtained in analytical form. The conditions impose restrictions on the parameters of mechanical systems. The obtained stability conditions are necessary for solving the problems of controlling the parameters of the aeroelastic system. On the basis of the Galerkin method, a numerical study of the dynamics of elastic elements was carried out, the reliability of which is confirmed by the obtained analytical results.

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YASHINA, M. V., et M. T. ALEROEV. « ON PROBLEM OF PROPERTIES OPTIMIZING FOR VISCOELASTIC MATERIALS USING THE BEGLEY-TORVIK EQUATION ». T-Comm 17, n^o 8 (2023) : 63–68. http://dx.doi.org/10.36724/2072-8735-2023-17-8-63-68.

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Recently, fractional calculus has been the focus of attention of many researchers in the field of science and technology, since a more detailed study of physical processes leads to the need to complicate the mathematical models that describe them, and, consequently, to the study of the behavior of solutions of differential equations containing, along with " ordinary", or "classical", derivative, also fractional. Processes of this kind can include: studies of continuous media with memory, fluid filtration in media with fractal geometry, physical aspects of stochastic transfer and diffusion, mathematical models of a viscoelastic body, models of damped oscillations with fractional damping (for example, vibrations of rocks during earth-quakes or vibrations nanoscale sensors), models of non-local physical processes and phenomena of a fractal nature; climate models, etc. The paper studies boundary value problems for the equation of motion of an oscillator with viscoelastic damping (the Begley-Torvik equation) in the case when the damping order is greater than zero but less than two. Such problems model many physical processes, in particular, the vibration of a string in a viscous medium, the change in the deformation-strength characteristics of polymer concrete under loading, etc. This paper is devoted to optimizing the parametric control of the Begley-Torvik model. A fundamentally new, efficient algorithm is proposed that allows estimating the parameters of a model of real material.

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Yang, Lin Jia, et Yi Han Tao. « CFD-Based Calculation of Regular Transverse Wave Force in the Maneuvering Mathematical Modeling Group (MMG) Model ». Applied Mechanics and Materials 380-384 (août 2013) : 1716–20. http://dx.doi.org/10.4028/www.scientific.net/amm.380-384.1716.

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The accuracy of mathematical model has a great effect on the prediction of ships maneuverability. Wave disturbing force is an important element of the Maneuvering Mathematical Modeling Group (MMG). Building regression formula of wave disturbing force acting on the ship hull can not only increase ship mathematical models accuracy but also help to predict ships maneuverability. The wave force can be calculated by the Computational Fluid Dynamics (CFD) method, which is more accurate and economical. The 3D model of M/V YUKUN was established and the cut-cell mesh was made. A numerical wave tank was developed in this work, based on the FLUENT software. The calculation results were obtained with different height, length, and period of waves. After analyzing the calculated data obtained by the CFD simulation, a regression formula was built about the above parameters. Finally, after comparing the regression formula and tradition wave force model based on the slender body theory, it can be concluded that the regular transverse wave force regression formula of the YUKUN is valid and better to make simulation for the prediction on ships maneuverability.

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souza, Nikhil D. « Physics Based Animation Using Computer Graphics ». INTERANTIONAL JOURNAL OF SCIENTIFIC RESEARCH IN ENGINEERING AND MANAGEMENT 08, n^o 04 (11 avril 2024) : 1–5. http://dx.doi.org/10.55041/ijsrem30046.

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Physics-based animation is a multidisciplinary area that uses ideas from physics, computer science, and mathematics to create realistic and dynamic movements in virtual settings. The basic ideas and methods of physics-based animation are introduced in this research paper, with an emphasis on how mathematical models and physical laws are used to produce realistic motion in computer-generated images. To construct realistic virtual environments, key disciplines covered include fluid simulation, fabric simulation, rigid body dynamics, and soft body dynamics. The report highlights recent developments in real-time physics simulations and addresses other topics such as processing economy, accuracy, and scalability. Applications for physics-based animation can be found in many different fields, such as virtual reality, simulation training, movies, and video games. The pursuit of more precise and effective physics-based animation is essential as technology develops to produce captivating and realistic virtual worlds. Keywords— Physics-based animation(PBA), virtual environment, Physics simulation, Dynamics, Animation software, Real-time physics, Collision detection, Fluid dynamics, Particle systems, Cloth simulation, Smooth particle hydrodynamics, finite element method, Navier-Stokes, Rigid body dynamics, Soft body dynamics, Deformation, Motion capture, Character animation, Kinematics, Rendering, Game development, Virtual reality, Augmented reality, Computer graphics, Simulation accuracy

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Velmisov, Petr A., Yuliya A. Tamarova et Yuliya V. Pokladova. « Investigation of the dynamic stability of bending-torsional deformations of the pipeline ». Zhurnal Srednevolzhskogo Matematicheskogo Obshchestva 23, n^o 1 (31 mars 2021) : 72–81. http://dx.doi.org/10.15507/2079-6900.23.202101.72-81.

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Nonlinear mathematical models are proposed that describe the dynamics of a pipeline with a fluid flowing in it: a) the model of bending-torsional vibrations with two degrees of freedom; b) the model describing flexural-torsional vibrations taking into account the nonlinearity of the bending moment and centrifugal force; c) the model that takes into account joint longitudinal, bending (transverse) and torsional vibrations. All proposed models are described by nonlinear partial differential equations for unknown strain functions. To describe the dynamics of a pipeline, the nonlinear theory of a rigid deformable body is used, which takes into account the transverse, tangential and longitudinal deformations of the pipeline. The dynamic stability of bending-torsional and longitudinal-flexural-torsional vibrations of the pipeline is investigated. The definitions of the stability of a deformable body adopted in this work correspond to the Lyapunov concept of stability of dynamical systems. The problem of studying dynamic stability, namely, stability according to initial data, is formulated as follows: at what values of the parameters characterizing the gas-body system, small deviations of the body from the equilibrium position at the initial moment of time will correspond to small deviations and at any moment of time. For the proposed models, positive definite functionals of the Lyapunov type are constructed, on the basis of which the dynamic stability of the pipeline is investigated. Sufficient stability conditions are obtained that impose restrictions on the parameters of a mechanical system.

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Afanaseva, Anna, et Alexander Starchenko. « Numerical Study of the Influence of Changes in Electrical Conductivity on the Solution of the Direct Problem of Electrical Impedance Tomography ». Mathematical Physics and Computer Simulation, n^o 3 (octobre 2023) : 76–90. http://dx.doi.org/10.15688/mpcm.jvolsu.2023.3.6.

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Electrical Impedance Tomography (EIT) uses electrical stimulation and measurement at the body surface to image the electrical properties of internal tissues. It has the advantage of non-invasiveness and high temporal resolution but suffers from poor spatial resolution and sensitivity to electrode movement and contact quality. EIT can be useful to applications where there are conductive contrasts between tissues, fluids or gases, such as imaging of cancerous or ischemic tissue or functional monitoring of breathing, blood flow, gastric motility and neural activity. The work uses a complete electrode model (CEM), which is a practical model in EIT, which most realistically models electrodes. This model can simulate EIT measurements with much greater accuracy than continuum models. The mathematical formulation of the problem is written as follows: In the article [15] shows that in order for the problem to have a unique solution, the following condition must be met: Numerical studies are consistent with the conclusions from the article [14]. Useful information in the EIT is contained mainly on a small part of the boundary, i.e., on the electrodes close to the perturbations of the electrical conductivity. Boundary measurements, which are the input to the inverse conductivity problem, are more sensitive to anomalies near the boundary and to larger anomalies. This study is useful in order to know the critical values of the parameters (size, location) of a low-amplitude perturbation of conductivity, at which the measurements are insensitive and, therefore, inhomogeneities cannot be detected.

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Ndiaye, Jean François, Fahima Nekka et Morgan Craig. « Understanding the Mechanisms and Treatment of Heart Failure : Quantitative Systems Pharmacology Models with a Focus on SGLT2 Inhibitors and Sex-Specific Differences ». Pharmaceutics 15, n^o 3 (20 mars 2023) : 1002. http://dx.doi.org/10.3390/pharmaceutics15031002.

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Heart failure (HF), which is a major clinical and public health challenge, commonly develops when the myocardial muscle is unable to pump an adequate amount of blood at typical cardiac pressures to fulfill the body’s metabolic needs, and compensatory mechanisms are compromised or fail to adjust. Treatments consist of targeting the maladaptive response of the neurohormonal system, thereby decreasing symptoms by relieving congestion. Sodium–glucose co-transporter 2 (SGLT2) inhibitors, which are a recent antihyperglycemic drug, have been found to significantly improve HF complications and mortality. They act through many pleiotropic effects, and show better improvements compared to others existing pharmacological therapies. Mathematical modeling is a tool used to describe the pathophysiological processes of the disease, quantify clinically relevant outcomes in response to therapies, and provide a predictive framework to improve therapeutic scheduling and strategies. In this review, we describe the pathophysiology of HF, its treatment, and how an integrated mathematical model of the cardiorenal system was built to capture body fluid and solute homeostasis. We also provide insights into sex-specific differences between males and females, thereby encouraging the development of more effective sex-based therapies in the case of heart failure.

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Rabadjieva, Diana, Rumiana Gergulova, Kostadinka Sezanova, Daniela Kovacheva et Rositsa Titorenkova. « Mg, Zn Substituted Calcium Phosphates—Thermodynamic Modeling, Biomimetic Synthesis in the Presence of Low-Weight Amino Acids and High Temperature Properties ». Materials 16, n^o 20 (11 octobre 2023) : 6638. http://dx.doi.org/10.3390/ma16206638.

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The preparation of specially doped calcium phosphates (CaPs) is receiving a great deal of attention from researchers due to CaPs’ enhanced capabilities for application in medicine. Complexation and precipitation in a complicated electrolyte system including simulated body fluids that are enriched with Mg2+ and Zn2+ ions and modified with glycine, alanine and valine were first evaluated using a thermodynamic equilibrium model. The influence of the type and concentration of amino acid on the incorporation degree of Mg and Zn into the solid phases was predicted. Experimental studies, designed on the basis of thermodynamic calculations, confirmed the predictions. Amorphous calcium phosphates double-doped with Mg and Zn were biomimetically precipitated and transformed into Mg, Zn-β—tricalcium phosphates (TCP) upon calcination. The Rietveld refinement confirmed that Mg2+ and Zn2+ substituted Ca2+ only at the octahedral sites of β-TCP, and in some cases, fully displacing the Ca2+ from them. The resulting Mg, Zn-β–TCP can serve as a reservoir for Mg and Zn ions when included in the formulation of a biomaterial for bone remodeling. The research conducted reveals the effect of combining mathematical models with experimental studies to pre-evaluate the influence of various additives in the design of materials with predetermined properties.

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Cao, Yihua, Shuai Nie et Zhenlong Wu. « Numerical simulation of parachute inflation : A methodological review ». Proceedings of the Institution of Mechanical Engineers, Part G : Journal of Aerospace Engineering 233, n^o 2 (12 mai 2017) : 736–66. http://dx.doi.org/10.1177/0954410017705900.

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The parachute inflation process involves fluid–structure interaction problems posing several mathematical and engineering challenges, e.g. accurate aerodynamics calculations for bluff-body geometries involving with moving boundary, appropriate structural models in predicting the behavior of canopy, and realization of the coupling between the fluid and structure. These challenges attract the attention of scholars worldwide, and considerable achievements have been obtained in applying numerical methods and simulations to design multifarious parachutes. In this paper, the authors highlight the advances in the following fields: the methods suitable for time-dependent flow around bluff-body geometries, the accurate structural models in consideration of the under-constrained and no-compression nature of the canopy, and the advantages and disadvantages of different coupling algorithms in terms of numerical stability and computational economics. Moreover, in order to simulate the parachute inflation more realistically, we focus on accurate representation of three physical phenomena, as follows: an appropriate model of the flow through porous media, an accurate treatment of the wrinkling phenomenon of the canopy, and a consistent representation of the impact-contact problem associated with the inflation process. Finally, based on a review of existing literature, we offer recommendations for future research on the application of numerical methods for simulating the inflation process.

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BIGDELI, MOHAMMAD REZA, SOHRAB HAJIZADEH, BEHZAD BANIEGHBAL et MOHAMMAD REZA MASJDI. « A COMPREHENSIVE SIMULATOR OF THE HUMAN PULMONARY SYSTEM : VALIDATION WITH DETERMINATION OF TOTALCO2AND DIAGNOSIS OF ACID-BASE ABNORMALITIES ». Journal of Biological Systems 17, n^o 01 (mars 2009) : 153–71. http://dx.doi.org/10.1142/s0218339009002818.

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In previous models, heart-lung-blood interactions and their physicochemical properties have not been considered in comprehensive simulators and an integrated mathematical model has not been presented. The aim of the present study is to combine different phenomena involved in the cardiopulmonary function, which are often considered separately. In this study, the variables that constitute a comprehensive model; which includes physicochemical reactions of O2and CO2in the blood and fluid compartments, V/Q, pH , body temperature and diffusion limitation in the adult human and its ability to provide realistic response under different physiological and pathophysiological conditions; have been evaluated. The new biological system model consists of two subsystems: physicochemical properties of blood and physiological subsystem models. Based on the mentioned parameters, comprehensive simulator model has been suggested as following: [Formula: see text] According to the literature, all patients [COPD (20) and asthma (20)] showed acid-base imbalances. The mathematical model has been validated by diagnosis of acid-base abnormalities via calculating the total CO2and T40HCO3in physiological and pathophysiological conditions, and then the results compared to literature experimental data. Our comprehensive model provides results consistent with dynamic and steady state responses measured in subjects undergoing physiological and pathophysiological conditions. This might enable us to deepen our understanding of the cardiopulmonary system as a whole.

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Dey, Indrakshi, et Nicola Marchetti. « Channel Emulator Framework for Underwater Acoustic Communications ». Applied Sciences 13, n^o 9 (8 mai 2023) : 5818. http://dx.doi.org/10.3390/app13095818.

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In this paper, we develop a tractable mathematical model and an emulation framework for communicating information through water using acoustic signals. Water is considered one of the most complex media to model due to its vastness and variety of characteristics, which depend on the scenario, the type of water body (lakes, rivers, tanks, sea, etc.), and the geographical location of the water body being considered. Our proposed mathematical model involves the concept of damped harmonic oscillators to represent the medium (water); Milne’s oscillator technique is used to map the interaction between the acoustic signal and water. Wave equations formulated for acoustic pressure and acoustic wave velocity are employed to characterise the travelling acoustic signal. The signal strength, phase shift, and time delay generated from the mathematical model are then inputted into a Simulink-based emulator framework to generate channel samples and channel impulse responses. The emulator utilises the wide sense stationary uncorrelated scattering (WSSUS) assumption and a finite sum-of-sinusoids (SOS) approach with a uniformly distributed phase to generate the channel samples. By utilising this emulator platform, it becomes feasible to generate profiles for amplitude variation, the Doppler shift, and spread experienced by any travelling signal in various underwater communication scenarios. Such a platform can be employed to simulate different communication scenarios, underwater network topologies, and data for training various learning models. Additionally, it can predict the performance of different modulation, multiplexing, error correction, and multi-access techniques for underwater acoustic communication (UWAC) systems.

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Kurysheva, Natalia I., Oxana Y. Rodionova, Alexey L. Pomerantsev, Galina A. Sharova et Olga Golubnitschaja. « Machine learning–couched treatment algorithms tailored to individualized profile of patients with primary anterior chamber angle closure predisposed to the glaucomatous optic neuropathy ». EPMA Journal 14, n^o 3 (17 août 2023) : 527–38. http://dx.doi.org/10.1007/s13167-023-00337-1.

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Abstract Background Primary angle closure glaucoma (PACG) is still one of the leading causes of irreversible blindness, with a trend towards an increase in the number of patients to 32.04 million by 2040, an increase of 58.4% compared with 2013. Health risk assessment based on multi-level diagnostics and machine learning–couched treatment algorithms tailored to individualized profile of patients with primary anterior chamber angle closure are considered essential tools to reverse the trend and protect vulnerable subpopulations against health-to-disease progression. Aim To develop a methodology for personalized choice of an effective method of primary angle closure (PAC) treatment based on comparing the prognosis of intraocular pressure (IOP) changes due to laser peripheral iridotomy (LPI) or lens extraction (LE). Methods The multi-parametric data analysis was used to develop models predicting individual outcomes of the primary angle closure (PAC) treatment with LPI and LE. For doing this, we suggested a positive dynamics in the intraocular pressure (IOP) after treatment, as the objective measure of a successful treatment. Thirty-seven anatomical parameters have been considered by applying artificial intelligence to the prospective study on 30 (LE) + 30 (LPI) patients with PAC. Results and data interpretation in the framework of 3P medicine Based on the anatomical and topographic features of the patients with PAC, mathematical models have been developed that provide a personalized choice of LE or LPI in the treatment. Multi-level diagnostics is the key tool in the overall advanced approach. To this end, for the future application of AI in the area, it is strongly recommended to consider the following: Clinically relevant phenotyping applicable to advanced population screening Systemic effects causing suboptimal health conditions considered in order to cost-effectively protect affected individuals against health-to-disease transition Clinically relevant health risk assessment utilizing health/disease-specific molecular patterns detectable in body fluids with high predictive power such as a comprehensive tear fluid analysis.

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Погудин, Андрей Владимирович. « МАТЕМАТИЧЕСКОЕ МОДЕЛИРОВАНИЕ ЭЛЕКТРОНАГРЕВНОЙ ДВИГАТЕЛЬНОЙ УСТАНОВКИ В ФОРМИРОВАНИИ МИКРОСПУТНИКОВОЙ ГРУППИРОВКИ ». Aerospace technic and technology, n^o 3 (27 juin 2018) : 45–51. http://dx.doi.org/10.32620/aktt.2018.3.06.

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The subject of the study in the article is the mathematical model of the propulsion system. It is built on the basis of the formed transfer functions of the elements. The goal is to rationalize the process of heating the onboard propulsion system on the basis of mathematical model under given constraints. Tasks: formalization of processes in an electric heating engine with a working body ammonia; formalization of the model of the onboard propulsion system; formation of the structural scheme; consideration of physical processes occurring in the nodes of the propulsion system; description of gas and hydraulic processes; the description of thermodynamic and electrokinetic processes; The construction of a mathematical model based on transfer functions. The methods used are: models of transfer functions of a tank, a filter, a steam generator, a receiver and a jet, an engine with their ranges of work. The following results are obtained. A block diagram of the onboard propulsion system was added, supplemented with a control unit and a power supply system. A formalized mathematical model of an onboard propulsion system with working body ammonia is created. From it formed a model consisting of the key elements that make up the onboard propulsion system, which is used when rationalizing the heating of the working fluid. The scientific novelty of the results is as follows. The mathematical model of the electro-heating propulsion system onboard small space vehicles has been further developed through its application to calculate the traction characteristics of the dispenser, which makes it possible to use an ammonia electric heating rocket engine in the formation of a constellation of satellites. The limitations of the operating parameters of the model are introduced. It was proposed to conduct the further workability of the model in Matlab Simulink. Thus, a rational value of the current and voltage parameters will be obtained, at which the time of the system's output to the operating mode will be minimal, and the thrust is maximum for the given operating temperature and pressure ranges

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Holechek, Susan, Lizbeth Nieves, Megan McAfee, Vanessa Guzman, Danielle Lussier, Courtney Bruce et Joseph Blattman. « Using the lymphocytic choriomeningitis virus mouse model of infection to link specific immune responses with epidemiological outcomes (P6318) ». Journal of Immunology 190, n^o 1_Supplement (1 mai 2013) : 182.11. http://dx.doi.org/10.4049/jimmunol.190.supp.182.11.

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Abstract The adaptive immune system can act to prevent infection, reduce disease, and/or prevent shedding of viral pathogens. However, little is known about which specific adaptive immune responses affect each of these epidemiologic outcomes. Lymphocytic choriomeningitis virus (LCMV) is a natural pathogen of both mice and humans. We have shown that transmission from congenitally infected carrier mice occurs at high frequency while transmission from adult persistently infected mice is relatively inefficient. The major difference between these two groups is the presence (in adult infected) or absence (in congenitally infected) of an anti-viral adaptive immune response. We have investigated how CD4 T cell and B cell/antibody responses affect virus shedding from adult LCMV persistently infected mice. CD4-/- or immunocompetent C57BL/6 mice were infected with the clone-13 strain of LCMV and shedding of virus from body fluids sampled. Although we detected high titers of virus in the saliva and blood of all infected animals, we observed higher levels of transmission to susceptible mice from CD4-/- hosts compared to wild-type mice. Because we observed no detectable LCMV-specific antibody responses in the CD4-/- infected mice, these results suggest that CD4 T cells and antibodies may play a role in limiting virus transmission. We have used these data to parameterize mathematical models linking immunological responses with epidemiological outcomes of infection to generate new avenues of inquiry.

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Afanasiy, Li, Burkhan Utepov et Satniyaz Allaniyazov. « The spraying process simulation of the low-volume sprayer working body ». E3S Web of Conferences 264 (2021) : 04004. http://dx.doi.org/10.1051/e3sconf/202126404004.

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The article presents the developed mathematical models that describe the process of spraying the working body of a low-volume sprayer. Theoretical studies show that with an increase in the supply of working fluid to the atomizing disc, the rotational speed of the pneumatic disc atomizer decreases, and in order to ensure the effect of the air flow on the droplet formation process, the radius of the disc should be larger than the radius of the base of the cone-shaped fairing, but less than its maximum critical value and for obtaining a monodisperse spray with the main droplet diameter d = 80 … 120 μm, at an axial air flow velocity of the fan installation U = 40 … 60 m/s, the parameters of the disk the sprayer and the propeller are linked together when the following values: disk radius r = 65 … 85 mm, the number of radial channels on the disk nр = 2 … 6 pcs, the width of the radial channel bр = 3 … 4 mm, and to obtain a high-quality air-droplet flow, the initial velocity of the main drops discharged from the periphery of the spraying disc must be less than the speed of the air flow and, at the same time, the rotational speed of the pneumatic disc sprayer is recommended to be used in the range of ω = 60… 200 s-1.

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Goswami, Nandu, Jerry J. Batzel, Jack A. Loeppky et Helmut Hinghofer-Szalkay. « Teaching fluid shifts during orthostasis using a classic paper by Foux et al. » Advances in Physiology Education 35, n^o 4 (décembre 2011) : 330–35. http://dx.doi.org/10.1152/advan.00071.2011.

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Hypovolemic and orthostatic challenge can be simulated in humans by the application of lower body negative pressure (LBNP), because this perturbation leads to peripheral blood pooling and, consequently, central hypovolemia. The classic paper by Foux and colleagues clearly shows the effects of orthostasis simulated by LBNP on fluid shifts and homeostatic mechanisms. The carefully carried out experiments reported in this paper show the interplay between different physiological control systems to ensure blood pressure regulation, failure of which could lead to critical decreases in cerebral blood flow and syncope. Here, a teaching seminar for graduate students is described that is designed in the context of this paper and aimed at allowing students to learn how Foux and colleagues have advanced this field by addressing important aspects of blood regulation. This seminar is also designed to put their research into perspective by including important components of LBNP testing and protocols developed in subsequent research in the field. Learning about comprehensive protocols and carefully controlled studies can reduce confounding variables and allow for an optimal analysis and elucidation of the physiological responses that are being investigated. Finally, in collaboration with researchers in mathematical modeling, in the future, we will incorporate the concepts of applicable mathematical models into our curriculum.

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Masselot, A., et B. Chopard. « A Multiparticle Lattice-Gas Model for Hydrodynamics ». International Journal of Modern Physics C 09, n^o 08 (décembre 1998) : 1221–30. http://dx.doi.org/10.1142/s0129183198001102.

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Cellular automata (CA) and lattice-Boltzmann (LB) models are two possible approaches to simulate fluid-like systems. CA models keep track of the many-body correlations and provide a description of the fluctuations. However, they lead to a noisy dynamics and impose strong restrictions on the possible viscosity values. On the other hand, LB models are numerically more efficient and offer much more flexibility to adjust the fluid parameters, but they neglect fluctuations. Here we discuss a multiparticle lattice model which reconciles both approaches. Our method is tested on Poiseuille flows and on the problem of ballistic annihilation in two dimensions for which the fluctuations are known to play an important role.

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Dziurzyński, Wacław, Andrzej Krach et Teresa Pałka. « COMPUTER SIMULATION OF THE PROPAGATION OF HEAT IN ABANDONED WORKINGS INSULATED WITH SLURRIES AND MINERAL SUBSTANCES ». Archives of Mining Sciences 59, n^o 1 (1 mars 2014) : 3–23. http://dx.doi.org/10.2478/amsc-2014-0001.

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Abstract In the paper the results of investigations aimed at further identification of the phenomena occurring in abandoned workings and connected with the flow of air-gas (methane, carbon dioxide, nitrogen, oxygen and carbon oxidation products) mixture with taking into consideration the impact of supplied mineral substances on the processes of self-heating of the coal left in goaves were presented. The known and successfully used method for the prevention of fires in abandoned workings is the technology of filling goaf with an ash-air mixture, which also raises the issue of the effective use of that mixture. The computer, i.e. digital simulation methods being developed and intended for the purpose of the process discussed here are a good complement of the use of that technology. A developed mathematical model describing the process of additional sealing of gob with wet slurry supplied with three pipelines is based on the balance of volume of the supplied mixture and contained in the body created in goaves. The form of that body was assessed on the basis of the observation results available in literature and the results of model investigations. The calculation examples carried out for the the longwall area and its goaf ventilated with the “U” system allow to state that the introduced modification of the mathematical model describing the flow of the mixture of air, gases, and wet slurry with consideration of the coal burning process in the fire source area was verified positively. The digital prognostic simulations have confirmed a vital impact of the wet slurry supplied into the goaf on the processes of coal burning and also the change of rate and volume flow rate of the air mixture in goaf. As a complement to the above it should be noted that such elements as the place of the slurry supply in comparison with the longwall inclination or fire source area location is of great importance for the effectiveness of the fire prevention used. The development of computer/ digital simulation methods requires further investigations of the model adopted in this study. Those investigations should be aimed at making credible the theoretical model of the mixture flow through porous medium and the supplied mineral material. Such investigations will allow to verify the body form based on the mixture parameters such as humidity, viscosity, and fluidity and depending on the properties of the porous medium. Further development of the modelling of the phenomena discussed in this paper should be based on the methods of use of the description of the flow of fluids and slurry on the basis of 3D models.

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Yu Yudina, N., R. V. Yudin et A. I. Maksimenkov. « Simulation of loading dynamics and hydrodynamics of drives of forest machine working bodies ». IOP Conference Series : Earth and Environmental Science 875, n^o 1 (1 octobre 2021) : 012060. http://dx.doi.org/10.1088/1755-1315/875/1/012060.

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Abstract The need to take into account the dynamic processes that occur when performing technological operations using the working bodies of forest machines with a hydraulic drive is due to the fact that its absence leads to a distortion of the obtained results, since the kinematic schemes do not take into account the influence of hydraulic fluid in the elements of the hydraulic system. In this regard, it became necessary to develop models that take into account the dynamics of working body loading and the hydrodynamics of its drives. It is recommended to consider the influence of the process dynamics by introducing dynamic factors. The resulting mathematical model allows you to determine the actual values of the hydraulic cylinder, taking into account the errors associated with fluid leakage. As a result of the study, it was possible to connect the pressure change in the hydraulic cylinder, the movement of the pistons in the hydraulic cylinder and the rotor of the hydraulic motor, as well as the appearance of inertial forces. The connecting component is the balance of fluid and hydraulic system volumes.

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Abrate, Serge. « Resin flow in fiber preforms ». Applied Mechanics Reviews 55, n^o 6 (16 octobre 2002) : 579–99. http://dx.doi.org/10.1115/1.1506323.

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In a number of manufacturing processes for composite structures, resin flows through fiber reinforcement that is prearranged in a mold or a die. This article presents a review of mathematical models used to study the flow of resin through fiber reinforcement. The general approach is to consider the resin as a fluid propagating through a porous medium: the mold (or die) cavity partially filled with fiber reinforcement and other filler material. The resistance of the reinforcement to fluid flow is characterized by the permeability tensor and many analytical, numerical, and experimental techniques have been developed to predict or to measure the components of that tensor. The behavior of the resin depends on its viscosity, which depends on temperature and the degree of cure. Often mold filling is completed before any appreciable temperature change or curing occurs, so the analysis of this phase of the process is uncoupled from the thermal and curing problems. In other cases all three problems are coupled and should be solved simultaneously. Several complicating factors must be considered: 1) the deformation of the reinforcement during the preforming stage, during mold closure, or during resin injection, can affect permeabilities and flow patterns; 2) gaps between the reinforcement and the surface of the mold can cause edge flows that bypass the expected flow pattern; and 3) the inhomogeneous nature of the reinforcement with higher flow resistance inside fiber bundles than in surrounding gaps leads to complex flow patterns near the flow front and to the formation of microvoids. This article reviews the mathematical models that are required in order to simulate composite manufacturing processes in which resin flows through fiber reinforcement. The numerical implementation of these models using the finite element method or other numerical techniques is beyond the scope of this review. The bulk of the current body of knowledge in this area was developed since 1990. There are 165 references in this review article.

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Postlethwaite, Claire M., Tiffany M. Psemeneki, Jangir Selimkhanov, Mary Silber et Malcolm A. MacIver. « Optimal movement in the prey strikes of weakly electric fish : a case study of the interplay of body plan and movement capability ». Journal of The Royal Society Interface 6, n^o 34 (8 octobre 2008) : 417–33. http://dx.doi.org/10.1098/rsif.2008.0286.

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Animal behaviour arises through a complex mixture of biomechanical, neuronal, sensory and control constraints. By focusing on a simple, stereotyped movement, the prey capture strike of a weakly electric fish, we show that the trajectory of a strike is one which minimizes effort. Specifically, we model the fish as a rigid ellipsoid moving through a fluid with no viscosity, governed by Kirchhoff's equations. This formulation allows us to exploit methods of discrete mechanics and optimal control to compute idealized fish trajectories that minimize a cost function. We compare these with the measured prey capture strikes of weakly electric fish from a previous study. The fish has certain movement limitations that are not incorporated in the mathematical model, such as not being able to move sideways. Nonetheless, we show quantitatively that the computed least-cost trajectories are remarkably similar to the measured trajectories. Since, in this simplified model, the basic geometry of the idealized fish determines the favourable modes of movement, this suggests a high degree of influence between body shape and movement capability. Simplified minimal models and optimization methods can give significant insight into how body morphology and movement capability are closely attuned in fish locomotion.

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Mechighel, F., S. Ben Aoua et S. Dost. « Lattice Boltzmann Equations-Based Model of the Convection Melt Flow Driven by the Combined Effects of Buoyancy, Surface Tension and Magnetic Body Forces with Heat Generation ». Defect and Diffusion Forum 390 (janvier 2019) : 133–50. http://dx.doi.org/10.4028/www.scientific.net/ddf.390.133.

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The main topic of this paper is the development of a mathematical model, based on the Lattice Boltzmann equations (LBE), which is proposed for the simulation of the complex convective flow, held in an electrically conducting melt, driven by the combined action of buoyancy, surface-tension, and electromagnetic forces. The lattice Boltzmann method (LBM) is relatively novel and contrasts with the usual well-known methods to physical modeling in the domain of computational fluid dynamics (CFD). Indeed, the LBM describes the fluid (i.e. lattice fluid) at a microscopic level (molecular) and proposes models for the collision between molecules. The full continuum-level physics (i.e. the macroscopic hydrodynamic fields) is implicitly contained in the LB model. Indeed those macroscopic quantities are defined as moments of the so-called particle distribution functions. In the present work, a two-dimensions (2D) LBE-based model is developed to the simulation of convection melt flow driven by the combination of natural buoyancy, surface tension, and electromagnetic forces. The model is applied to numerical modeling of the problems of buoyancy, surface-tension, and electromagnetic driven convection melt flow in an enclosure. The melt system used has a low Prandtl number, which is appropriate to crystal growth melts.

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Yang, Shi-Bin, Li-Bao Wang et Dan Xu. « Computational analysis on actuator failures of flexible aircraft ». International Journal of Computational Materials Science and Engineering 07, n^o 01n02 (juin 2018) : 1850014. http://dx.doi.org/10.1142/s2047684118500148.

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A coupled model of aeroservoelasticity and hydraulic actuator used for failure simulation is presented. The mathematical model composites rigid-body modes, elastic modes, control surface modes, unsteady aerodynamic forces and failure models (jam, loss of control (LOC), oscillatory failure, and hydraulic fluid leakage). A clear framework of coupling method of airplane aeroelastic equation and control surface dynamic equation is provided to study the impacts of surface failures on rigid-elastic motion of airplane. The coupled model is shown to be effective in evaluation of gust response in both discrete gust and continuous turbulence conditions compared with results obtained from the 3-order simplified actuator. Examples of gust load alleviation (GLA) system with LOC of ailerons are given. Results show that total loss of function of GLA system is caused by the LOC. With continuous turbulence excitation, the failure loads is several times larger than that without GLA system.

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Zhang, Qi, Ruo Fei Liu, Hao Liu et Ru Wu Wang. « Numerical Simulation and Performance Study of Adjustable Steam Ejector Using CFD ». Advanced Materials Research 562-564 (août 2012) : 1150–54. http://dx.doi.org/10.4028/www.scientific.net/amr.562-564.1150.

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A djustable ejector flow control can be achieved to export in a stable area, thus reducing the jet inlet parameters on the export parameters as well as the impact of the entire system, widening of the jet's effective operating range. In this paper, the establishment of an effective mathematical models and computational methods to commercial CFD software FLUENT 6.3 as a platform for the adjustable jet to simulate the internal flow process and performance research, exploration and analysis of the main needle is moved (ie the nozzle throat orifice area change) operating parameters (including the working fluid inlet pressure, inlet pressure and the lead body jet mixing fluid outlet pressure) on the adjustable jet performance of the law, for the adjustable jet to provide important parameters to optimize the design. Studies show that: ① the needle device with adjustable spray jet in a non-rated conditions, can increase the coefficient of the jet injector; ② other parameters remain the same circumstances, the adjustable jet to varying degrees, increased work pressure , suction pressure, discharge pressure and outlet flow range.

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Bissenas, Ashley, Chance Fleeting, Drashti Patel, Raja Al-Bahou, Aashay Patel, Andrew Nguyen, Maxwell Woolridge, Conner Angelle et Brandon Lucke-Wold. « CSF Dynamics : Implications for Hydrocephalus and Glymphatic Clearance ». Current Research in Medical Sciences 1, n^o 1 (décembre 2022) : 24–42. http://dx.doi.org/10.56397/crms.2022.12.04.

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Beyond its neuroprotective role, CSF functions to rid the brain of toxic waste products through glymphatic clearance. Disturbances in the circulation of CSF and glymphatic exchange are common among those experiencing HCP syndrome, which often results from SAH. Normally, the secretion of CSF follows a two-step process, including filtration of plasma followed by the introduction of ions, bicarbonate, and water. Arachnoid granulations are the main site of CSF absorption, although there are other influencing factors that affect this process. The pathway through which CSF is through to flow is from its site of secretion, at the choroid plexus, to its site of absorption. However, the CSF flow dynamics are influenced by the cardiovascular system and interactions between CSF and CNS anatomy. One, two, and three-dimensional models are currently methods researchers use to predict and describe CSF flow, both under normal and pathological conditions. They are, however, not without their limitations. “Rest-of-body” models, which consider whole-body compartments, may be more effective for understanding the disruption to CSF flow due to hemorrhages and hydrocephalus. Specifically, SAH is thought to prevent CSF flow into the basal cistern and paravascular spaces. It is also more subject to backflow, caused by the presence of coagulation cascade products. In regard to the fluid dynamics of CSF, scar tissue, red blood cells, and protein content resulting from SAH may contribute to increased viscosity, decreased vessel diameter, and increased vessel resistance. Outside of its direct influence on CSF flow, SAH may result in one or both forms of hydrocephalus, including noncommunicating (obstructive) and communicating (nonobstructive) HCP. Imaging modalities such as PC-MRI, Time-SLIP, and CFD model, a mathematical model relying on PC-MRI data, are commonly used to better understand CSF flow. While PC-MRI utilizes phase shift data to ultimately determine CSF speed and flow, Time-SLIP compares signals generated by CSF to background signals to characterizes complex fluid dynamics. Currently, there are gaps in sufficient CSF flow models and imaging modalities. A prospective area of study includes generation of models that consider “rest-of-body” compartments and elements like arterial pulse waves, respiratory waves, posture, and jugular venous posture. Going forward, imaging modalities should work to focus more on patients in nature in order to appropriately assess how CSF flow is disrupted in SAH and HCP.

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Zhang, Qianwen, Chuqi Su, Yi Zhou, Chengcai Zhang, Jiuyang Ding et Yiping Wang. « Numerical Investigation on Handling Stability of a Heavy Tractor Semi-Trailer under Crosswind ». Applied Sciences 10, n^o 11 (26 mai 2020) : 3672. http://dx.doi.org/10.3390/app10113672.

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Due to the large lateral area of the trailer and variable road conditions, the handling stability of a heavy tractor semi-trailer under crosswind is very important for road safety. In this present work, numerical simulation is performed to study the crosswind effects on handling stability of a tractor semi-trailer. The aerodynamic characteristics of the tractor semi-trailer under different crosswind were computed by computational fluid dynamics (CFD). Then, mathematical models to reveal the relationship between the aerodynamic forces and crosswind were constructed to serve as inputs of the multi-body dynamics to analyze the handling stability under crosswind. The performance of crosswind stability is evaluated by the response of lateral acceleration, yaw rate and the lateral displacement. The lateral acceleration and yaw rate were decreased by a maximum of 14.6% and 16.5% compared to the truck without the deflector, which showed that the crosswind aerodynamics and stability were obviously improved.

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Elaiw, A. M., et N. H. AlShamrani. « Modeling and stability analysis of HIV/HTLV-I co-infection ». International Journal of Biomathematics 14, n^o 05 (11 mars 2021) : 2150030. http://dx.doi.org/10.1142/s1793524521500303.

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Human immunodeficiency virus (HIV) and human T-lymphotropic virus type I (HTLV-I) are two retroviruses that infect the susceptible CD[Formula: see text]T cells. It is known that HIV and HTLV-I have in common a way of transmission through direct contact with certain body fluids related to infected individuals. Therefore, it is not surprising that a mono-infected person with one of these viruses can be co-infected with the other virus. In the literature, a great number of mathematical models has been presented to describe the within-host dynamics of HIV or HTLV-I mono-infection. However, the within-host dynamics of HIV/HTLV-I co-infection has not been modeled. In this paper, we develop a new within-host HIV/HTLV-I co-infection model. The model includes the impact of Cytotoxic T lymphocytes (CTLs) immune response, which is important to control the progression of viral co-infection. The model describes the interaction between susceptible CD[Formula: see text]T cells, silent HIV-infected cells, active HIV-infected cells, silent HTLV-infected cells, Tax-expressing HTLV-infected cells, free HIV particles, HIV-specific CTLs and HTLV-specific CTLs. We first show the nonnegativity and boundedness of the model’s solutions and then we calculate all possible equilibria. We derive the threshold parameters which govern the existence and stability of all equilibria of the model. We prove the global asymptotic stability of all equilibria by utilizing Lyapunov function and LaSalle’s invariance principle. We have presented numerical simulations to illustrate the effectiveness of our main results. In addition, we discuss the effect of HTLV-I infection on the HIV-infected patients and vice versa.

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Ren, Zhihui, Suling Wang, Kangxing Dong, Weiqiang Yu et Lu Lu. « Exploring the Mechanism of Pulse Hydraulic Fracturing in Tight Reservoirs ». Processes 11, n^o 12 (10 décembre 2023) : 3398. http://dx.doi.org/10.3390/pr11123398.

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Pulse hydraulic fracturing is capable of creating intricate seam networks for improved reservoir recovery, but its dynamic damage mechanism remains unclear, limiting its scientific guidance for fracturing construction. This study combined the statistical damage and viscoelastic models according to the D-P criterion and fluid flow continuity equation to establish a mathematical model of the fluid–solid coupling under pulsed hydraulic pressure. The finite element approach was used to investigate the dynamic response and damage accumulation law of tight reservoirs under various pulse parameters. The model’s correctness was verified with indoor triaxial pulse hydraulic fracturing studies, and the Changqing oilfield’s pulse hydraulic fracturing parameters were optimized. The results showed that the rock body around the borehole sustained dynamic damage when exposed to pulsed fluid pressure. The impact force increases with frequency; however, when the frequency is too high, the dynamic pore pressure cannot be stabilized. Consequently, the damage to the rock mass starts to increase and then progressively decreases with higher pulse frequencies. The ideal frequency was found to be 1 Hz. The rock body steadily accumulates damage as the number of pulses rises, increasing the damage value gradually. At the same frequency, the damage is higher for larger pulse amplitudes and ground stress differences, as well as a smaller modulus of elasticity. Pulse cycling reduces the rupture pressure by up to 26% compared to conventional hydraulic fracturing. Moreover, the Sine wave is 4–20% better than the triangle wave. The pulse damage mechanism and parameter optimization in this paper provide theoretical support for improving the effect of hydraulic fracture modification.

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Wang, Yuhan, Zhengdong Lei, Zhenhua Xu, Jie Liu, Xiaokun Zhang, Erhui Luo, Yuqi Liu et Pengcheng Liu. « A Novel Mathematical Model for Fracturing Effect Evaluation Based on Early Flowback Data in Shale Oil Reservoirs ». Geofluids 2021 (16 décembre 2021) : 1–14. http://dx.doi.org/10.1155/2021/1780937.

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For shale oil reservoirs, the horizontal well multistage fracturing technique is mostly used to reform the reservoir in order to achieve economic and effective development. The size of the reservoir reconstruction volume and the quantitative characterization of the fracture system are of great significance to accurately predict the productivity of shale oil wells. There are few flowback models for shale oil reservoirs. To solve this problem, first, a physical model of the simultaneous production of oil, gas, and water in the early flowback stage of shale oil development is established using the material balance equation for a fracture system. Second, the physical model of the underground fracture system is simplified, which is approximately regarded as a thin cylindrical body with a circular section. The flow of the fluid in the fracture system is approximately regarded as radial flow. In this model, the expansion of the fluid and the closure of the fracture are defined as integrated storage coefficients to characterize the storage capacity of the fracture system. Then, the curves illustrating the relationships between the oil-water ratio and the cumulative oil production and between the gas-water ratio and the cumulative gas production are drawn, and the curves are used to divide the flowback stage into an early stage and a late stage because the flowback process of shale oil wells exhibits obvious stage characteristics. Finally, the reservoir reconstruction volume and the related hydraulic fracture parameters are estimated based on the material balance method, and the rationality of the model is verified via numerical simulation. The interpretation results of this novel model are more accurate, making it an effective way to evaluate the hydraulic fracture parameters and transformation effect, and it has guiding significance for the evaluation of the hydraulic fracturing effect in the field.

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