Статті в журналах з теми "Uniform accelerated movement of a boundary"
Щоб переглянути інші типи публікацій з цієї теми, перейдіть за посиланням: Uniform accelerated movement of a boundary.
Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями
Ознайомтеся з топ-50 статей у журналах для дослідження на тему "Uniform accelerated movement of a boundary".
Біля кожної праці в переліку літератури доступна кнопка «Додати до бібліографії». Скористайтеся нею – і ми автоматично оформимо бібліографічне посилання на обрану працю в потрібному вам стилі цитування: APA, MLA, «Гарвард», «Чикаго», «Ванкувер» тощо.
Також ви можете завантажити повний текст наукової публікації у форматі «.pdf» та прочитати онлайн анотацію до роботи, якщо відповідні параметри наявні в метаданих.
Переглядайте статті в журналах для різних дисциплін та оформлюйте правильно вашу бібліографію.
1
Van Leeuwen, Johan L. "Why the chameleon has spiral–shaped muscle fibres in its tongue." Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 352, no. 1353 (May 29, 1997): 573–89. http://dx.doi.org/10.1098/rstb.1997.0039.
Повний текст джерелаАнотація:
The intralingual accelerator muscle is the primary actuator for the remarkable ballistic tongue projection of the chameleon. At rest, this muscle envelopes the elongated entoglossal process, a cylindrically shaped bone with a tapering distal end. During tongue projection, the accelerator muscle elongates and slides forward along the entoglossal process until the entire muscle extends beyond the distal end of the process. The accelerator muscle fibres are arranged in transverse planes (small deviations are possible), and form (hitherto unexplained) spiral–shaped arcs from the peripheral to the internal boundary. To initiate tongue projection, the muscle fibres probably generate a high intramuscular pressure. The resulting negative pressure gradient (from base to tip) causes the muscle to elongate and to accelerate forward. Effective forward sliding is made possible by a lubricant and a relatively low normal stress exerted on the proximal cylindrical part of the entoglossal process. A relatively high normal stress is, however, probably required for an effective acceleration of muscle tissue over the tapered end of the process. For optimal performance, the fast extension movement should occur without significant (energy absorbing) torsional motion of the tongue. In addition, the tongue extension movement is aided by a close packing of the muscles fibres (required for a high power density) and a uniform strain and work output in every cross–section of the muscle. A quantitative model of the accelerator muscle was developed that predicts internal muscle fibre arrangements based on the functional requirements above and the physical principle of mechanical stability. The curved shapes and orientations of the muscle fibres typically found in the accelerator muscle were accurately predicted by the model. Furthermore, the model predicts that the reduction of the entoglossal radius towards the tip (and thus the internal radius of the muscle) tends to increase the normal stress on the entoglossal bone.
2
Campos, Lucas Silveira, Éder Lima de Albuquerque, and Luiz Carlos Wrobel. "An ACA accelerated isogeometric boundary element analysis of potential problems with non-uniform boundary conditions." Engineering Analysis with Boundary Elements 80 (July 2017): 108–15. http://dx.doi.org/10.1016/j.enganabound.2017.04.004.
Повний текст джерела
3
Boag, Amir, Uri Shemer, and Raphael Kastner. "Non-uniform grid accelerated local–global boundary condition (NG-LGBC) for acoustic scattering." Computer Methods in Applied Mechanics and Engineering 195, no. 29-32 (June 2006): 3608–21. http://dx.doi.org/10.1016/j.cma.2005.02.028.
Повний текст джерела
4
Котов and P. Kotov. "CONSTRUCTIVE ASPECTS OF ELECTRODYNAMIC." Modeling of systems and processes 9, no. 1 (September 23, 2016): 8–10. http://dx.doi.org/10.12737/21617.
Повний текст джерелаАнотація:
Dynamic models of the accelerated shift of the elementary particle with a charge in the electromagnetic field of measurable intensity are considered and the substantial relations, the distinctive state and solutions of problems in connection with the equations of stable elementary particle movement in a uniform magnetic field of the fixed intensity are offered.
5
Lian, Xugang, Zoujun Li, Hongyan Yuan, Haifeng Hu, Yinfei Cai, and Xiaoyu Liu. "Determination of the Stability of High-Steep Slopes by Global Navigation Satellite System (GNSS) Real-Time Monitoring in Long Wall Mining." Applied Sciences 10, no. 6 (March 12, 2020): 1952. http://dx.doi.org/10.3390/app10061952.
Повний текст джерелаАнотація:
Surface movement and deformation induced by underground coal mining causes slopes to collapse. Global Navigation Satellite System (GNSS) real-time monitoring can provide early warnings and prevent disasters. A stability analysis of high-steep slopes was conducted in a long wall mine in China, and a GNSS real-time monitoring system was established. The moving velocity and displacement at the monitoring points were an integrated response to the influencing factors of mining, topography, and rainfall. Underground mining provided a continuous external driving force for slope movement, the steep terrain provided sufficient slip conditions in the slope direction, and rainfall had an acceleration effect on slope movement. The non-uniform deformation, displacement field, and time series images of the slope body revealed that ground failure was concentrated in the area of non-uniform deformation. The non-uniform deformation was concentrated ahead of the working face, the speed of deformation behind the working face was reduced, the instability of the slope body was increased, and the movement of the top of the slope was larger than at the foot. The high-steep slope stability in the mine was influenced by the starting deformation (low stability), iso-accelerated deformation (increased stability), deformation deceleration (reduced stability), and deformation remaining unchanged (improved stability).
6
Meng, Jun-Nan, Guang Pan, and Yong-Hui Cao. "Element-Free Galerkin method for dynamic boundary flow problems." Modern Physics Letters B 34, no. 24 (July 1, 2020): 2050257. http://dx.doi.org/10.1142/s0217984920502577.
Повний текст джерелаАнотація:
This paper focuses on the study of dynamic boundary flow problems based on the Element-Free Galerkin method. First, Navier–Stokes equation is discretized with the Galerkin method. The inertial term in the equation is discretized with the method of the speed term and direct deduction, respectively. The penalty function method is used to deal with the pressure and the essential boundary condition in the equation, and the discretization of two-dimensional N–S equation based on the EFG method is established. However, irregular changes in boundary conditions are often encountered in practical fluid problems. For example, the motion of flapping-foil is not uniform relative to the flow. In this paper, numerical experiments are carried out for the flow problems with non-uniform boundary motions. The problem which a plate with non-uniform drag movement above a rectangular tank filled with water is studied with the EFG method. The feasibility of the proposed algorithm is verified by comparison with the FEM method. Then, the procession of the water in the tank is stimulated. In the end, the influence of different calculation time steps on the accuracy of the solution is discussed.
7
Ehrenstein, Uwe, Matthieu Marquillie, and Christophe Eloy. "Skin friction on a flapping plate in uniform flow." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 372, no. 2020 (July 28, 2014): 20130345. http://dx.doi.org/10.1098/rsta.2013.0345.
Повний текст джерелаАнотація:
To calculate the energy costs of swimming or flying, it is crucial to evaluate the drag force originating from skin friction. This topic seems not to have received a definite answer, given the difficulty in measuring accurately the friction drag along objects in movement. The incoming flow along a flat plate in a flapping normal motion has been considered, as limit case of a yawed cylinder in uniform flow, and applying the laminar boundary layer assumption it is demonstrated that the longitudinal drag scales as the square root of the normal velocity component. This lends credit to the assumption that a swimming-like motion may induce a drag increase because of the compression of the boundary layer, which is known as the ‘Bone–Lighthill boundary-layer thinning hypothesis’. The boundary-layer model however cannot predict the genuine three-dimensional flow dynamics and in particular the friction at the leeward side of the plate. A multi-domain, parallel, compact finite-differences Navier–Stokes solution procedure is considered, capable of solving the full problem. The time-dependent flow dynamics is analysed and the general trends predicted by the simplified model are confirmed, with however differences in the magnitude of the friction coefficient. A tentative skin friction formula is proposed for flow states along a plate moving at steady as well as periodic normal velocities.
8
Du, Jin Song, and Xin Bi. "An Adaptive Interacting Multiple Model for Vehicle Target Tracking Method." Advanced Materials Research 718-720 (July 2013): 1286–89. http://dx.doi.org/10.4028/www.scientific.net/amr.718-720.1286.
Повний текст джерелаАнотація:
In the field of traffic safety vehicle target tracking prediction as the background, this paper proposes an adaptive interacting multiple model tracking algorithm. According to the field of transportation vehicle movement state characteristics, based on the uniform (CV) and uniformly accelerated motion (CA) model, based on new information structure model of motion of the likelihood function, online adaptive adjustment model of the noise variance and the Markov matrix, realization of maneuvering target movement model and model set adaptation, not only improved IMM algorithm for tracking accuracy, and enhances the real-time performance of system, the simulation results show that, the algorithm for tracking precision compared to the traditional IMM method has bigger improvement.
9
Zhou, Wenting. "Is the Fulling–Davies–Unruh effect valid for the case of an atom coupled to quantum electromagnetic field?" Modern Physics Letters A 31, no. 34 (October 21, 2016): 1650189. http://dx.doi.org/10.1142/s0217732316501893.
Повний текст джерелаАнотація:
We study, from the viewpoint of a co-accelerated observer, the average rate of change of atomic energy for an atom in uniform acceleration and coupled to quantum electromagnetic field at a thermal state with an arbitrary temperature T. We show that only when the temperature of the thermal state in the co-accelerated frame is assumed to be the Fulling–Davies–Unruh (FDU) temperature, T = a/2[Formula: see text], can the average rate of change of atomic energy in a local inertial frame be recovered, which exemplifies the equivalence between the Minkowski vacuum and a thermal bath of Rindler particles. This conclusion is verified to be valid not only in a free spacetime, but also in a spacetime with a boundary.
10
Beldi, M., and A. Maghrebi. "Some New Results for the Study of Acoustic Radiation within a Uniform Subsonic Flow Using Boundary Integral Method." Advanced Materials Research 488-489 (March 2012): 383–95. http://dx.doi.org/10.4028/www.scientific.net/amr.488-489.383.
Повний текст джерелаАнотація:
In this paper, a reformulation of the Helmholtz integral equation for tridimesional acoustic radiation in a uniform subsonic flow is presented. An extension of the Sommerfeld radiation condition, for a free space in a uniform movement, makes possible the determination of the convected Green function, the elementary solution of the convected Helmholtz equation. The gradients of this convected Green function are, so, analyzed. Using these results, an integral representation for the acoustic pressure is established. This representation has the advantage of expressing itself in terms of new surface operators, which simplify the numerical study. For the case of a regular surface, the evaluation of the free term associated with the singular integrals shows that it is independent of the Mach number of the uniform flow. A physical interpretation of this result is offered. A numerical approximation method of the integral representation is developed. Furthermore, for a given mesh, an acoustic discretization criterion in a uniform flow is proposed. Finally, numerical examples are provided in order to validate the integral formula.
11
Sun, Kuan, Cong Liu, Shile Feng, and Yahua Liu. "Directional Bouncing of Impacting Droplets on Non-Uniform Rough Surfaces with High Temperature." E3S Web of Conferences 261 (2021): 02030. http://dx.doi.org/10.1051/e3sconf/202126102030.
Повний текст джерелаАнотація:
Directional transport of high-temperature droplets enjoys broad application prospects in the fields of drag reduction and heat transfer. In this paper, two adjacent regions with different surface roughness were constructed on 304 stainless steel by laser etching to control the directional movement of high-temperature droplets. It is found that the regions with different surface roughness have different Leidenfrost temperatures, and the Leidenfrost temperature is lower under smaller roughness. When the droplet hits the boundary of the adjacent regions at high temperatures, it will bounce towards the region with larger roughness spontaneously, and the directional bouncing distance tends to first increase and then decrease with the increase of temperature and Weber number. In addition, when the droplet impacts at the boundary of the adjacent regions which have different Leidenfrost temperatures, the two parts of the droplet will be in transition boiling and film boiling respectively. The resulting Young’s force is the main factor that drives the droplets to bounce directionally.
12
Mao, Deming, Xueying Xie, Raymond M. Jones, Albert Harvey, and John M. Karanikas. "A Simple Approach for Quantifying Accelerated Production Through Heating Producer Wells." SPE Journal 22, no. 01 (July 11, 2016): 316–26. http://dx.doi.org/10.2118/181757-pa.
Повний текст джерелаАнотація:
Summary This paper focuses on techniques for quantifying accelerated-production rates achieved by installing wellbore heaters in heavy-oil-producer wells. The uniform injection of heat into the wellbore of heavy-oil producers reduces local near-well fluid viscosity, lowers dynamic pressure, and results in increased production rates. Wellbore heat penetrates into the surrounding reservoir through conduction. Because of the exponential dependence of heavy-oil viscosity on temperature, small changes in temperature can substantially reduce near-wellbore oil viscosity. Conduction-heat transfer into the formation is balanced by convection back into the wellbore by the inflowing produced fluids. The higher the flow rate, the lower the heat-penetration depth is for a fixed heater-injection rate. Schild (1957) presented a steady-state model that deploys boundary condition at an infinite radial location, resulting in the prediction of an infinite-influence region for the temperature when the Péclet number is smaller than unity. Production-improvement factor (PIF) on the order of 100 is reported and will be shown to be overoptimistic when the transient nature is properly represented. In this paper, a transient model is presented dependent on the boundary conditions at a finite radial distance from the wellbore. Predictions of the PIF suggest values on the order of three at small Péclet numbers. Influence of the formation thermal conductivity and permeability can be lumped into a defined Péclet number. The developed correlation is demonstrated to cover the effect of this Péclet number, together with the viscosity ratio, on the PIF.
13
Singh, Jitendra Kumar, Gauri Shenker Seth, and Saikh Ghousia Begum. "Unsteady MHD natural convection flow of a rotating viscoelastic fluid over an infinite vertical porous plate due to oscillating free-stream." Multidiscipline Modeling in Materials and Structures 14, no. 2 (June 4, 2018): 236–60. http://dx.doi.org/10.1108/mmms-06-2017-0054.
Повний текст джерелаАнотація:
Purpose The purpose of this paper is to present an analytical study on an unsteady magnetohydrodynamic (MHD) boundary layer flow of a rotating viscoelastic fluid over an infinite vertical porous plate embedded in a uniform porous medium with oscillating free-stream taking Hall and ion-slip currents into account. The unsteady MHD flow in the rotating fluid system is generated due to the buoyancy forces arising from temperature and concentration differences in the field of gravity and oscillatory movement of the free-stream. Design/methodology/approach The resulting partial differential equations governing the fluid motion are solved analytically using the regular perturbation method by assuming a very small viscoelastic parameter. In order to note the influences of various system parameters and to discuss the important flow features, the numerical results for fluid velocity, temperature and species concentration are computed and depicted graphically vs boundary layer parameter whereas skin friction, Nusselt number and Sherwood number at the plate are computed and presented in tabular form. Findings An interesting observation is recorded that there occurs a reversal flow in the secondary flow direction due to the movement of the free stream. It is also noted that a decrease in the suction parameter gives a rise in momentum, thermal and concentration boundary layer thicknesses. Originality/value Very little research work is reported in the literature on non-Newtonian fluid dynamics where unsteady flow in the system arises due to time-dependent movement of the plate. The motive of the present analytical study is to analyse the influences of Hall and ion-slip currents on unsteady MHD natural convection flow of a rotating viscoelastic fluid (non-Newtonian fluid) over an infinite vertical porous plate embedded in a uniform porous medium with oscillating free-stream.
14
Popov, Igor'. "MOVEMENT OF OPERATING MEMBERS OF MECHANISMS ALONG ELLIPTIC AND CIRCULAR TRAJECTORIES." Transport engineering 2022, no. 01-02 (February 21, 2022): 53–59. http://dx.doi.org/10.30987/2782-5957-2022-01-02-53-59.
Повний текст джерелаАнотація:
The work objective is to generalize the principle of combining movements into circular movements.
The problem to which the article is devoted is the analytical description of the trajectories of combined movements.
Research methods. Analytical geometry methods are used. The coordinate system x'0'y' is considered, which rotates in the coordinate system x0y without angular acceleration with ω velocity. The rotation radius is equal to ρ1. At the same time 0x || 0'x', 0y || 0'y'. Object a rotates in the coordinate system x'0'y' without angular acceleration at the velocity ± ω. The rotation radius is equal to ρ2.
The novelty of the work realises in ellipse formulas expressed in terms of radii of opposite directions.
The results of the study: it is established that during rotations in opposite directions, the trajectory of the total motion is an ellipse; all the standard characteristics of the ellipse are determined in relation to the case under consideration; the inclination of the elliptical trajectory is established; it is shown that if the trajectory of the total motion is elliptical and the semi-axes are equal to (ρ1 + ρ2) and |ρ1 – ρ2|, then object a moves along a circular in the coordinate system x'0'y' without angular acceleration with velocity - ω; just as the result of the superposition of two non-accelerated movements is also non-accelerated, i.e. uniform and rectilinear motion, with rotations in one direction, the trajectory of the total motion is a circle; with circular movements with multiple velocities, the trajectory of the total motion is snail.
Conclusions: the practical aspect of the study is determined by the fact that the formulas obtained can be directly used in CAD when performing design work.
15
Ozaki, Hiroaki, and Hua Chiu. "Trajectory Planning of Manipulator Using Optimization of Uniform B-Spline." Journal of Robotics and Mechatronics 6, no. 6 (December 20, 1994): 491–98. http://dx.doi.org/10.20965/jrm.1994.p0491.
Повний текст джерелаАнотація:
A basic optimization algorithm is presented in this paper, in order to obtain the optimum solution of a two-point boundary value variational problem without constraints. The solution is given by a parallel and iterative computation and described as a set of control points of a uniform B-spline. This algorithm can also be applied to solving problems with some constraints, if we introduce an additional component, namely the potential function, corresponding to constraints in the original objective function. The algorithm is very simple and easily applicable to various engineering problems. As an application, trajectory planning of a manipulator with redundant degrees of freedom is considered under the conditions that the end effector path, the smoothness of movement, and the constraints of the control or the state variables are specified. The validity of the algorithm is well confirmed by numerical examples.
16
HAYASHI, Shinichi, Toru TAKAHASHI, Hiroshi ISAKARI, and Toshiro MATSUMOTO. "2010 A fast multipole-accelerated boundary element method using the non-uniform B-Spline isogeometric element for 2D Helmholtz equation." Proceedings of The Computational Mechanics Conference 2013.26 (2013): _2010–1_—_2010–3_. http://dx.doi.org/10.1299/jsmecmd.2013.26._2010-1_.
Повний текст джерела
17
Zhang, Fan, Shouqi Yuan, Qiang Fu, Feng Hong, and Jianping Yuan. "Investigation of Transient Flow in a Centrifugal Charging Pump during Charging Operating Process." Advances in Mechanical Engineering 6 (January 1, 2014): 860257. http://dx.doi.org/10.1155/2014/860257.
Повний текст джерелаАнотація:
Centrifugal charging pumps are important components of nuclear power plants and must be operated under multioperating conditions for the requirements of the system. In order to investigate the internal flow mechanism of the centrifugal charging pump during the transient transition process of charging operating from Q = 34 m3/h to Q = 110 m3/h, numerical simulation and experiment are implemented in this study. The relationship between flow rate and time is obtained from the experiment and worked as the boundary condition to accurately accomplish the numerical simulation during the transient process. External and internal characteristics under the variable operating conditions are analyzed through the transient simulation. The results show that the liquid viscosity, large scale vortexes exist in the flow passages in the beginning of the variable operating conditions, which indicates flow separation and the sudden changes in direction of velocity. As the flow rate increases gradually, the flow angles of the fluid in inlet accelerate correspondingly and the flow along the blade is more uniform, which leads to a decrease and movements of the vortexes. The contents of the current work can provide references for the design optimization and fluid control of the pump used in the transient process of variable operating conditions.
18
Roveimiab, Ziba, Francis Lin, and Judy E. Anderson. "Traction and attraction: haptotaxis substrates collagen and fibronectin interact with chemotaxis by HGF to regulate myoblast migration in a microfluidic device." American Journal of Physiology-Cell Physiology 319, no. 1 (July 1, 2020): C75—C92. http://dx.doi.org/10.1152/ajpcell.00417.2019.
Повний текст джерелаАнотація:
Cell migration is central to development, wound healing, tissue regeneration, and immunity. Despite extensive knowledge of muscle regeneration, myoblast migration during regeneration is not well understood. C2C12 mouse myoblast migration and morphology were investigated using a triple-docking polydimethylsiloxane-based microfluidic device in which cells moved under gravity-driven laminar flow on uniform (=) collagen (CN=), fibronectin (FN=), or opposing gradients (CN-FN or FN-CN). In haptotaxis experiments, migration was faster on FN= than on CN=. At 10 h, cells were more elongated on FN-CN and migration was faster than on the CN-FN substrate. Net migration distance on FN-CN at 10 h was greater than on CN-FN, as cells rapidly entered the channel as a larger population (bulk-cell movement, wave 1). Hepatocyte growth factor (HGF) stimulated rapid chemotaxis on FN= but not CN=, increasing migration speed at 10 h early in the channel at low HGF in a steep HGF gradient. HGF accelerated migration on FN= and bulk-cell movement on both uniform substrates. An HGF gradient also slowed cells in wave 2 moving on FN-CN, not CN-FN. Both opposing-gradient substrates affected the shape, speed, and net distance of migrating cells. Gradient and uniform configurations of HGF and substrate differentially influenced migration behavior. Therefore, haptotaxis substrate configuration potently modifies myoblast chemotaxis by HGF. Innovative microfluidic experiments advance our understanding of intricate complexities of myoblast migration. Findings can be leveraged to engineer muscle-tissue volumes for transplantation after serious injury. New analytical approaches may generate broader insights into cell migration.
19
Rajakumar, J., P. Saikrishnan, and A. Chamkha. "Non-uniform mass transfer in MHD mixed convection flow of water over a sphere with variable viscosity and Prandtl number." International Journal of Numerical Methods for Heat & Fluid Flow 26, no. 7 (September 5, 2016): 2235–51. http://dx.doi.org/10.1108/hff-05-2015-0189.
Повний текст джерелаАнотація:
Purpose The purpose of this paper is to consider axisymmetric mixed convection flow of water over a sphere with variable viscosity and Prandtl number and an applied magnetic field. Design/methodology/approach The non-similar solutions have been obtained from the origin of the streamwise co-ordinate to the point of zero skin friction using quasilinearization technique with an implicit finite-difference scheme. Findings The effect of M is not notable on the temperature and heat transfer coefficient when λ is large. The skin friction coefficient and velocity profile are enhance with the increase of MHD parameter M when λ is small. Viscous dissipation has no significant on the skin friction coefficient under MHD effect. For M=1, the movement of the slot or slot suction or slot injection do not cause any effect on flow separation. The slot suction and the movement of the slot in downstream direction delay the point of zero skin friction for M=0. Originality/value The present results are original and new for water boundary-layer flow over sphere in mixed convection flow with MHD effect and non-uniform mass transfer. So this study would be useful in analysing the skin friction and heat transfer coefficient on sphere of mixed convection flow of water boundary layer with MHD effect.
20
MARQUES, F., J. SANCHEZ, and P. D. WEIDMAN. "Generalized Couette–Poiseuille flow with boundary mass transfer." Journal of Fluid Mechanics 374 (November 10, 1998): 221–49. http://dx.doi.org/10.1017/s0022112098002560.
Повний текст джерелаАнотація:
A generalized similarity formulation extending the work of Terrill (1967) for Couette–Poiseuille flow in the annulus between concentric cylinders of infinite extent is given. Boundary conditions compatible with the formulation allow a study of the effects of inner and outer cylinder transpiration, rotation, translation, stretching and twisting, in addition to that of an externally imposed constant axial pressure gradient. The problem is governed by η, the ratio of inner to outer radii, a Poiseuille number, and nine Reynolds numbers. Single-cylinder and planar problems can be recovered in the limits η→0 and η→1, respectively. Two coupled primary nonlinear equations govern the meridional motion generated by uniform mass flux through the porous walls and the azimuthal motion generated by torsional movement of the cylinders; subsidiary equations linearly slaved to the primary flow govern the effects of cylinder translation, cylinder rotation, and an external pressure gradient. Steady solutions of the primary equations for uniform source/sink flow of strength F through the inner cylinder are reported for 0[les ]η[les ]1. Asymptotic results corroborating the numerical solutions are found in different limiting cases. For F<0 fluid emitted through the inner cylinder fills the gap and flows uniaxially down the annulus; an asymptotic analysis leads to a scaling that removes the effect of η in the pressure parameter β, namely β=π2R*2, where R*=F(1−η)/(1+η). The case of sink flow for F>0 is more complex in that unique solutions are found at low Reynolds numbers, a region of triple solutions exists at moderate Reynolds numbers, and a two-cell solution prevails at large Reynolds numbers. The subsidiary linear equations are solved at η=0.5 to exhibit the effects of cylinder translation, rotation, and an axial pressure gradient on the source/sink flows.
21
Bächer, Christian, Markus Bender, and Stephan Gekle. "Flow-accelerated platelet biogenesis is due to an elasto-hydrodynamic instability." Proceedings of the National Academy of Sciences 117, no. 32 (July 27, 2020): 18969–76. http://dx.doi.org/10.1073/pnas.2002985117.
Повний текст джерелаАнотація:
Blood platelets are formed by fragmentation of long membrane extensions from bone marrow megakaryocytes in the blood flow. Using lattice-Boltzmann/immersed boundary simulations we propose a biological Rayleigh–Plateau instability as the biophysical mechanism behind this fragmentation process. This instability is akin to the surface tension-induced breakup of a liquid jet but is driven by active cortical processes including actomyosin contractility and microtubule sliding. Our fully three-dimensional simulations highlight the crucial role of actomyosin contractility, which is required to trigger the instability, and illustrate how the wavelength of the instability determines the size of the final platelets. The elasto-hydrodynamic origin of the fragmentation explains the strong acceleration of platelet biogenesis in the presence of an external flow, which we observe in agreement with experiments. Our simulations then allow us to disentangle the influence of specific flow conditions: While a homogeneous flow with uniform velocity leads to the strongest acceleration, a shear flow with a linear velocity gradient can cause fusion events of two developing platelet-sized swellings during fragmentation. A fusion event may lead to the release of larger structures which are observable as preplatelets in experiments. Together, our findings strongly indicate a mainly physical origin of fragmentation and regulation of platelet size in flow-accelerated platelet biogenesis.
22
Chai, Fu Jun, Jin You Xu, and Ying Xu. "Kinematics Simulation of Steel Tube Rotating Mechanism Based on ADAMS." Applied Mechanics and Materials 130-134 (October 2011): 2647–50. http://dx.doi.org/10.4028/www.scientific.net/amm.130-134.2647.
Повний текст джерелаАнотація:
Taking a new steel tube rotating mechanism as the research object, the model is simplified and the virtual prototyping model of the mechanism is established. The mechanism kinematics simulation is carried out with ADAMS simulation software. The motion law and state in two conditions are comparatively analyzed. Analysis results show that, in steel tube clamping stage the motion of the clip rod is of variable deceleration; And in rotating stage, mechanism is of accelerated rotation with variable acceleration when the cylinder input, while mechanism is of uniform rotation when the crank input； And then the cylinder is with positive and reverse swings throughout the movement process. The analysis results provide the basis for institution parameter selection and structure optimization design.
23
Nikulin, I., and A. Perminov. "The Mathematical Model of Metal Melt State under Induction Melting." Applied Mechanics and Materials 770 (June 2015): 242–47. http://dx.doi.org/10.4028/www.scientific.net/amm.770.242.
Повний текст джерелаАнотація:
In this paper mathematical model is developed for the study of metal melt flows general regularities in non-uniform alternating magnetic field, in which cylindrical area filed with paramagnetic conducting melt is considered, the symmetry axis is directed vertically. The model include the equations describing spatial magnetic field distribution, the equations for induced currents, the equation of heat energy transfer that includes movement of media and volume heat sources, the equation of melt convection in Boussinesq’s approximation including of Lorentz force action to the melt. The boundary conditions for the melt velocities, magnetic fields and heat fluxes are described detail. The governing equations and boundary conditions are given in dimensionless form. The results of numerical experiments with different magnetic Reynolds number are given.
24
Guo, Junxi, Wenbo Li, Dongqiong Wu, Bowen Pang, Jifeng Fan, and Tianyuan Wang. "Multiple Motion Modes Analysis of Assembly Based on Monopole Motor Principle." Journal of Physics: Conference Series 2242, no. 1 (April 1, 2022): 012003. http://dx.doi.org/10.1088/1742-6596/2242/1/012003.
Повний текст джерелаАнотація:
Abstract Dc monopole motor with low voltage and high current is widely used in the market. It has the advantages of high efficiency, no commutator, no iron loss and so on. In this paper, an assembly (a cylindrical battery with button-type magnets attached at both ends) is placed on aluminum foil. The phenomenon that the assembly will move based on the principle of a single motor is explained. By adjusting the specifications of the button magnets and other parameters, a variety of its movement modes are theoretically analyzed and experimentally verified. The conclusion is that when the magnets at both ends are placed at the same level relative to each other and the diameter is the same, the composite body moves in a straight line with first acceleration and then uniform speed. When the diameter is different, the circular motion is accelerated first and then uniform. Changing the magnetic property size, battery length and other parameters will affect the change of motion parameters. This provides a new idea for further innovation of monopole motor in the future.
25
Vitiaz, P. A., V. I. Moiseenko, A. G. Sidorenko, and M. V. Sotnikov. "Influence of the structure of the steel of electroslag remelting on the properties of cemented and nitrided surfaces of machine parts." Proceedings of the National Academy of Sciences of Belarus, Physical-Technical Series 64, no. 1 (March 28, 2019): 51–59. http://dx.doi.org/10.29235/1561-8358-2019-64-1-51-59.
Повний текст джерелаАнотація:
The analysis of the influence of electroslag remelting steel structure on the properties of cemented and nitrided surfaces of machine parts is carried out. It is noted that when using electroslag remelting, the greatest efficiency is achieved in the production of large-sized gearwheels, hardened by cementation and ion nitriding. It is shown that cast steel, crystallized in a water cooled crystallizer, has a strength not lower than forged or rolled with significantly lower anisotropy properties and accelerated carbon diffusion when cementation. The discovered patterns are caused by the structural and chemical homogeneity of boundary grain volumes, which formation is affected by copper impurities. Uniform density of copper in the said volumes not only reduces their propensity to localize plastic deformation, but contributes to a higher ability for uniform carburization of these steels in the process of cementation. This causes a change in the main characteristics of the cemented layers and is the basis for increasing the bearing capacity of the gearwheels. The obtained results also testify to the fact that controlling grain-boundary effects in steel material at the stage of crystallization of blanks can be a significant factor in increasing the characteristics of the hardened layer in the manufacture of nitrided gearwheels from cast blanks of the electroslag redistribution. A set of studies was carried out and results were obtained which indicate that the control of grain boundary effects in modern steel material at the stage of its crystallization may be a significant factor in improving the characteristics of the hardened layer in the manufacture of cemented and nitrated gear wheels from cast billets electroslag remelting.
26
Zhang, Chi, and Wenting Zhou. "Radiative Processes of Two Accelerated Entangled Atoms Near Boundaries." Symmetry 11, no. 12 (December 13, 2019): 1515. http://dx.doi.org/10.3390/sym11121515.
Повний текст джерелаАнотація:
By considering the interaction between a two-atom system and the vacuum massless scalar field in the viewpoint of an instantaneously inertial observer, we study the rates of transition of a uniformly accelerated two-atom system in the symmetric/antisymmetric entangled state near a reflecting boundary and in a cavity, respectively. We find that both the downward transition | ψ ± ⟩ → | g A g B ⟩ and the upward transition | ψ ± ⟩ → | e A e B ⟩ occur for the accelerated two-atom system, as in sharp contrast with the case of a static two-atom system, in which the upward transition can never happen. Similar to the rates of transition of atoms immersed in a thermal bath with the FDU temperature, both the downward transition rate and the upward transition rate are characterized by the Plank factor ( e 2 π ω 0 / a − 1 ) − 1 . This character of the transition rates is very different from the other radiative properties of the accelerated two-atom system, such as the resonance interatomic energy, for which the revisions of the effects of uniform acceleration are never characterized by such a factor. We show with analytical and numerical results that both the downward transition and the upward transition processes can be effectively manipulated by the atomic non-inertial motion and by the presence of boundaries. By comparing the upward transition rate with the downward transition rate, we discover that, when ω 0 ≫ a , with ω 0 and a being the energy space and the proper acceleration of the two-atom system, the disentanglement caused by the upward transition is negligible, while, if ω 0 ≪ a , the disentanglement caused by the upward transition becomes as important as that caused by the downward transition.
27
Huang, Ya Ming, Qiang Fu, and Chun Xu Pan. ""In Situ-Tracking” Observation of Stainless Steel Microstructural Development during Elevated Service Using EBSD and SEM." Materials Science Forum 561-565 (October 2007): 2087–90. http://dx.doi.org/10.4028/www.scientific.net/msf.561-565.2087.
Повний текст джерелаАнотація:
Electron backscatter diffraction (EBSD) has been developed as a novel technique for characterizing crystallographic textures in recent years. The present paper proposes an “in-situ-tracking” approach using SEM and EBSD to examining the microstructural development and grain boundary variation of stainless steel during elevated 1200 °C service. The results revealed that in addition to the coarsened grains the fraction of low angle grain boundaries (LABG) became increased and flattened obviously during service. Comparing to the regular high temperature service (below 900 °C), the present “recovery and recrystallization” process was accelerated due to dislocation fastened movement and intensive interaction. However, the grain growth mechanism still meet the well-accepted dislocation model of subgrain combination.
28
Zhang, Dai Dong, Hu Zhang, Xue Hua Yu, Xiao Ru Zhang, and Da Qing Fang. "Effects of Gd on Microstructure and Mechanical Properties of AZ61 Magnesium Alloy." Advanced Materials Research 284-286 (July 2011): 500–504. http://dx.doi.org/10.4028/www.scientific.net/amr.284-286.500.
Повний текст джерелаАнотація:
The effects of different amounts of rare earth Gd added into AZ61 on the microstructure and mechanical properties of magnesium alloys were studied in this paper. And it adopts T6 heat treatment. When 2% Gd has been added, the microstructure of the alloy becomes uniform. The grains are refining. Gd is prior to reacting with Al for forming Al2Gd phase with high melting point. It is in the form of dot-like and globosity along the grain boundary. And β-Mg17A112 phase is reduced and its shape is thinner. The Al2Gd phase hinders dislocation movement. It markedly improves the mechanical properties of the alloy at room temperature and high temperature.
29
Alexeevich Prakht, Vladimir, Vladimir Alexandrovich Dmitrievskii, Fedor Nikitich Sarapulov, Anton Aleksandrovich Dmitrievskii, and Nail Ramazanovich Safin. "Computer-based modeling of moving cylindrical ferromagnetic billets induction heating." COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering 33, no. 1/2 (December 20, 2013): 273–85. http://dx.doi.org/10.1108/compel-09-2012-0182.
Повний текст джерелаАнотація:
Purpose – Nowadays, various software is available for simulating physical processes in induction heating. The software is often limited in its ability to simulate the billet movement, sometimes assuming uniform distribution of voltages on the inductor winding, uniformity of the physical properties of the billet, etc. The mathematical model of moving cylindrical ferromagnetic billets described in this paper takes into account the billet's movement, the billet phase heterogeneity and the nonuniformity of the supply voltage distribution in the inductor turns. The paper aims to discuss these issues. Design/methodology/approach – The research methodology is based on FEM analysis of the coupled problem, including the electromagnetic and thermal boundary problem with additional algebraic equations, using Comsol 3.5a software. Findings – The electromagnetic and temperature field in the billet and the voltage distribution on the winding turns have been calculated. The phase distribution in the billet has been predicted. Significant interaction of the nonuniformity of the supply voltage distribution, the billet's movement, the billet phase heterogeneity and side effect on the ends of the inductor have been shown. Practical implications – The results received can be used for designing the induction heating unit for moving cylindrical billets made from ferromagnetic material and improving their characteristics. Originality/value – Investigation of moving cylindrical ferromagnetic billets induction heating can be done by numerical solving the coupled problem including the electromagnetic and thermal boundary problem with additional algebraic equations for the supply voltage distribution.
30
Moen, J., J. A. Holtet, A. Pedersen, B. Lybekk, K. Svenes, K. Oksavik, W. F. Denig, E. Lucek, F. Søraas, and M. André. "Cluster boundary layer measurements and optical observations at magnetically conjugate sites." Annales Geophysicae 19, no. 10/12 (September 30, 2001): 1655–68. http://dx.doi.org/10.5194/angeo-19-1655-2001.
Повний текст джерелаАнотація:
Abstract. The Cluster spacecraft experienced several boundary layer encounters when flying outbound from the magnetosphere to the magnetosheath in the dusk sector on 14 January 2001. The dayside boundary layer was populated by magnetosheath electrons, but not with quite as high densities as in the magnetosheath itself. The Cluster ground track was calculated using the Tsyganenko-96 model which appears to be a strong tool for combining high-altitude satellite and ground observations, given that the solar wind conditions are known. This paper focuses on identifying auroral responses corresponding to boundary layer dynamics observed by Cluster. The first boundary layer encounter studied was a brief visit into a closed LLBL, most likely due to a boundary wave that travelled tailward over the spacecraft. A corresponding equatorward and eastward movement was seen in the post-noon aurora between Greenland and Svalbard. The second boundary encounter was in a high-latitude cusp, and occurred as a consequence of a transient reconfiguration of the cusp. The cusp expanded duskward over the spacecraft into the late post-noon sector. NOAA-12 probed the 16:30 MLT sector of this auroral activity, and measured a 1.4 keV electron beam located poleward of the 30 keV electron-trapping boundary. A sequence of three moving auroral forms emanating from this active region are likely candidates for flux transfer events. The auroral signatures are discussed in relation to earlier observations, and appear to be an example of accelerated electrons/discrete post-noon aurora on open magnetic field lines.Key words. Ionosphere (particle precipitation) Magnetospheric physics (auroral phenomena; magnetopause, cusp and boundary layers)
31
Sitdikov, Oleg, Elena Avtokratova, Taku Sakai, Kaneaki Tsuzaki, Rustam Kaibyshev, and Yoshimi Watanabe. "Effect of Processing Temperature on Microstructure Development during ECAP of Al-Mg-Sc Alloy." Materials Science Forum 584-586 (June 2008): 481–86. http://dx.doi.org/10.4028/www.scientific.net/msf.584-586.481.
Повний текст джерелаАнотація:
Microstructural evolution taking place during equal channel angular pressing (ECAP) was studied in a commercial coarse-grained Al-6%Mg-0.4%Mn-0.3%Sc alloy in a temperature interval 200- 450oC (~0.5-0.8 Tm). Samples were pressed using route A to a total strain of 12 and quenched in water after each ECAP pass. Uniform fine-grained microstructures with the average grain sizes of 0.7 and 2.5 0m, are almost fully evolved at high ECAP strains at 250oC and 450oC, respectively, while ECAP at 300oC (~0.6 Tm) leads to the formation of bimodal grain structure with fine grains of around 1 µm and relatively coarse grains of around 8 µm. The latter are developed due to the occurrence of static recrystallization during “keeping” time in the ECAP channel and/or reheating between ECAP passes. The microstructural development under warm-to-hot ECAP conditions is discussed in terms of the large potential for grain boundary migration resulted from an overlapping of accelerated grain boundary mobility at high pressing temperatures and enhanced driving force for recrystallization, which is caused by a strong inhibition of dynamic recovery in a heavily-alloyed Al alloy.
32
Prabhakar Reddy, Bijjula. "THERMO—DIFFUSION AND HALL EFFECT ON RADIATING AND REACTING MHD CONVECTIVE HEAT ABSORBING FLUID PAST AN EXPONENTIALLY ACCELERATED VERTICAL POROUS PLATE WITH RAMPED TEMPERATURE." Journal of the Serbian Society for Computational Mechanics 14, no. 1 (June 30, 2020): 12–28. http://dx.doi.org/10.24874/jsscm.2020.14.01.02.
Повний текст джерелаАнотація:
Numerical investigation is undertaken to study the effects of thermo-diffusion and Hall current on unsteady magneto-hydrodynamic convective flow of a viscous, incompressible, electrically conducting, radiating and heat absorbing fluid past an exponentially accelerated infinite vertical porous plate with ramped temperature in the presence of chemical reaction. A uniform magnetic field is applied transversely in the direction of the flow. The governing system of partial differential equations along with initial and boundary conditions is transformed to dimensionless form and then solved by employing finite element method. The impact of various flow parameters on the primary and secondary fluid velocities, fluid temperature and fluid concentration as well as shear stress, rate of heat and mass transfer at the plate are displayed through the graphs and tables. It can be observed that the temperature profiles are slower in case of ramped temperature plate than that of isothermal plate.
33
Abd Aziz, N. H., Iswadi Jauhari, H. A. Mohd Yusof, and Nor Wahida Ahamad. "Influence of Strain Rate and Strain on the Surface Properties in Superplastically Boronized Duplex Stainless Steel (DSS)." Defect and Diffusion Forum 283-286 (March 2009): 458–63. http://dx.doi.org/10.4028/www.scientific.net/ddf.283-286.458.
Повний текст джерелаАнотація:
It was reported that superplastic boronizing process (SPB) provides a much faster boronizing rate than the conventional boronizing process (CB). This process was conducted on duplex stainless steel (DSS) which exhibit superplasticity. The study concentrated on the effect of strain rate and compression strain on SPB. The process was conducted under four different strain rates and three diferent strains condition. Boronizing was successfully conducted with the best result obtained under the high strain rate range of 5 x 10-5 s-1 to 1 x 10-3 s-1 which is associated with the superplastic region. Through SPB, movement of atoms into the specimen was highly accelerated by the grain boundary sliding process leading to a formation of thick and hard boronized layer in extraordinarily short period of time.
34
Kremser, G., J. Woch, K. Mursula, P. Tanskanen, B. Wilken, and R. Lundin. "Origin of energetic ions in the polar cusp inferred from ion composition measurements by the Viking satellite." Annales Geophysicae 13, no. 6 (June 30, 1995): 595–607. http://dx.doi.org/10.1007/s00585-995-0595-9.
Повний текст джерелаАнотація:
Abstract. The magnetospheric ion composition spectrometer MICS on the Swedish Viking satellite provided measurements of the ion composition in the energy range 10.1 keV/e\\leqE/Q\\leq326.0 keV/e. Data obtained during orbit 842 were used to investigate the ion distribution in the northern polar cusp and its vicinity. The satellite traversed the outer ring current, boundary region, cusp proper and plasma mantle during its poleward movement. H+ and He++ ions were encountered in all of these regions. He+ ions were present only in the ring current. The number of O+ and O++ ions was very small. Heavy high-charge state ions typical for the solar wind were observed for the first time, most of them in the poleward part of the boundary region and in the cusp proper. The H+ ions exhibited two periods with high intensities. One of them, called the BR/CP event, appeared at energies up to 50 keV. It started at the equatorward limit of the boundary region and continued into the cusp proper. Energy spectra indicate a ring current origin for the BR/CP event. Pitch angle distributions show downward streaming of H+ ions at its equatorward limit and upward streaming on the poleward side. This event is interpreted as the result of pitch angle scattering of ring current ions by fluctuations in the magnetopause current layer in combination with poleward convection. The other of the two periods with high H+ ion intensities, called the accelerated ion event, was superimposed on the BR/CP event. It was restricted to energies \\leq15 keV and occurred in the poleward part of the boundary region. This event is regarded as the high-energy tail of magnetosheath ions that were accelerated while penetrating into the magnetosphere. The cusp region thus contains ions of magnetospheric as well as of magnetosheath origin. The appearance of the ions depends, in addition to the ion source, on the magnetic field configuration and dynamic processes inside and close to the cusp.
35
Uddin, Emad, Wei-Xi Huang, and Hyung Jin Sung. "Interaction modes of multiple flexible flags in a uniform flow." Journal of Fluid Mechanics 729 (July 24, 2013): 563–83. http://dx.doi.org/10.1017/jfm.2013.314.
Повний текст джерелаАнотація:
AbstractFish schooling is not merely a social behaviour; it also improves the efficiency of movement within a fluid environment. Inspired by the hydrodynamics of schooling, a group of flexible bodies was modelled as a collection of individuals arranged in a combination of tandem and side-by-side formations. The downstream bodies were found to be strongly influenced by the vortices shed from an upstream body, as revealed in the vortex–vortex and vortex–body interactions. To investigate the interactions between flexible bodies and vortices, the present study examined flexible flags in a viscous flow by using an improved version of the immersed boundary method. Three different flag formations were modelled to cover the basic structures involved in fish schooling: triangular, diamond and conical formations. The drag coefficients of the downstream flags could be decreased below the value for a single flag by adjusting the streamwise and spanwise gap distances and the flag bending coefficient. The drag variations were influenced by the interactions between vortices shed from the upstream flexible flags and those surrounding the downstream flags. The interactions between the flexible flags were investigated as a function of both the gap distance between the flags and the bending coefficients. The maximum drag reduction and the trailing flag position were calculated for different sets of conditions. Single-frequency and multifrequency modes were identified and were found to correspond to constructive and destructive vortex interaction modes, which explained the variations in the drag on the downstream flags.
36
Liljegren, S., S. Höfner, B. Freytag, and S. Bladh. "Atmospheres and wind properties of non-spherical AGB stars." Astronomy & Astrophysics 619 (November 2018): A47. http://dx.doi.org/10.1051/0004-6361/201833203.
Повний текст джерелаАнотація:
Context. The wind-driving mechanism of asymptotic giant branch (AGB) stars is commonly attributed to a two-step process: first, gas in the stellar atmosphere is levitated by shockwaves caused by stellar pulsation, then accelerated outwards by radiative pressure on newly formed dust, inducing a wind. Dynamical modelling of such winds usually assumes a spherically symmetric star. Aims. We explore the potential consequences of complex stellar surface structures, as predicted by three-dimensional (3D) star-in-a-box modelling of M-type AGB stars, on the resulting wind properties with the aim to improve the current wind models. Methods. Two different modelling approaches are used; the CO5BOLD 3D star-in-a-box code to simulate the convective, pulsating interior and lower atmosphere of the star, and the DARWIN one-dimensional (1D) code to describe the dynamical atmosphere where the wind is accelerated. The gas dynamics of the inner atmosphere region at distances of R ∼ 1−2 R⋆, which both modelling approaches simulate, are compared. Dynamical properties and luminosity variations derived from CO5BOLD interior models are used as input for the inner boundary in DARWIN wind models in order to emulate the effects of giant convection cells and pulsation, and explore their influence on the dynamical properties. Results. The CO5BOLD models are inherently anisotropic, with non-uniform shock fronts and varying luminosity amplitudes, in contrast to the spherically symmetrical DARWIN wind models. DARWIN wind models with CO5BOLD-derived inner boundary conditions produced wind velocities and mass-loss rates comparable to the standard DARWIN models, however the winds show large density variations on time-scales of 10–20 yr. Conclusions. The method outlined in this paper derives pulsation properties from the 3D star-in-a-box CO5BOLD models, to be used in the DARWIN models. If the current grid of CO5BOLD models is extended, it will be possible to construct extensive DARWIN grids with inner boundary conditions derived from 3D interior modelling of convection and pulsation, and avoid the free parameters of the current approach.
37
Dieckmann, M. E., D. Folini, I. Hotz, A. Nordman, P. Dell’Acqua, A. Ynnerman, and R. Walder. "Structure of a collisionless pair jet in a magnetized electron–proton plasma: flow-aligned magnetic field." Astronomy & Astrophysics 621 (January 2019): A142. http://dx.doi.org/10.1051/0004-6361/201834393.
Повний текст джерелаАнотація:
Aims. We study the effect a guiding magnetic field has on the formation and structure of a pair jet that propagates through a collisionless electron–proton plasma at rest. Methods. We model with a particle-in-cell (PIC) simulation a pair cloud with a temperature of 400 keV and a mean speed of 0.9c (c - light speed). Pair particles are continuously injected at the boundary. The cloud propagates through a spatially uniform, magnetized, and cool ambient electron–proton plasma at rest. The mean velocity vector of the pair cloud is aligned with the uniform background magnetic field. The pair cloud has a lateral extent of a few ion skin depths. Results. A jet forms in time. Its outer cocoon consists of jet-accelerated ambient plasma and is separated from the inner cocoon by an electromagnetic piston with a thickness that is comparable to the local thermal gyroradius of jet particles. The inner cocoon consists of pair plasma, which lost its directed flow energy while it swept out the background magnetic field and compressed it into the electromagnetic piston. A beam of electrons and positrons moves along the jet spine at its initial speed. Its electrons are slowed down and some positrons are accelerated as they cross the head of the jet. The latter escape upstream along the magnetic field, which yields an excess of megaelectronvolt positrons ahead of the jet. A filamentation instability between positrons and protons accelerates some of the protons, which were located behind the electromagnetic piston at the time it formed, to megaelectronvolt energies. Conclusions. A microscopic pair jet in collisionless plasma has a structure that is similar to that predicted by a hydrodynamic model of relativistic astrophysical pair jets. It is a source of megaelectronvolt positrons. An electromagnetic piston acts as the contact discontinuity between the inner and outer cocoons. It would form on subsecond timescales in a plasma with a density that is comparable to that of the interstellar medium in the rest frame of the latter. A supercritical fast magnetosonic shock will form between the pristine ambient plasma and the jet-accelerated plasma on a timescale that exceeds our simulation time by an order of magnitude.
38
Samal, Sneha, and Ignazio Blanco. "Investigation of Dispersion, Interfacial Adhesion of Isotropic and Anisotropic Filler in Polymer Composite." Applied Sciences 11, no. 18 (September 15, 2021): 8561. http://dx.doi.org/10.3390/app11188561.
Повний текст джерелаАнотація:
The movement of isotropic and anisotropic particles of iron and graphite within the polymer matrix was predicted and examined by the COMSOL simulation method. The interfacial adhesion of filler particles within the matrix was investigated under surface features observation. Carbonyl Iron (CI) particles, considered to be regular with a uniform size of (1–5 µm), were mixed with irregular particles of graphite (20–150 µm) with 30 V% in quantity in a silicone rubber matrix. The particle–matrix and particle–particle interactions were analyzed from the inner surface features. The drag of non-spherical particles and particle Reynolds numbers (Rep) were taken into consideration in point force models for both the Stokes (Rep ≪ 1) and Newton regime for particle shape. Newton regime is based on the aspect ratio for particles with regular and irregular shapes. The boundary area of the irregular particles holds like an anchor inside the polymer matrix for strong adhesion; however, regular particles have partial attachment due to the gravitational pull of attraction from the bottom contact points. However, uniform distribution of isotropic particles has been observed in comparison to the anisotropic particles within the polymer matrix.
39
Bhayadia, Amit, Anthony Olivett, Tarunraj Singh, and M. Amin Karami. "Input shaping for travelling wave generation." Smart Materials and Structures 31, no. 5 (March 22, 2022): 055006. http://dx.doi.org/10.1088/1361-665x/ac5c89.
Повний текст джерелаАнотація:
Abstract Travelling wave patterns observed in the movement of certain aquatic animals has motivated research in the modification of flow behavior, especially to deal with boundary layer separation in airplane wings. Research has shown that inducing travelling waves on the top surface of the wing can generate sufficient momentum to prevent boundary layer separation without increasing the drag. Due to this effect of propagating waves on the aerodynamics, generation of travelling waves on solid surfaces is being widely studied. Recently, methods such as two-mode excitation, active sink and impedance matching have shown promise in generation of uniform travelling waves in solids with the help of piezo electric actuators. Unfortunately, there are some challenges involved in the experimental application of these methods. Although these techniques have shown to be adequate in laboratory settings, they require laborious tuning procedures which do not guarantee desired trajectories and are followed in light of interference from unwanted modes and their transients. Some methods rely on selective mode excitation, which can cause interference from unwanted modes if the transient behavior of the system is not accounted for. Feed-forward input shaping control methods are proposed that augment the open-loop piezo actuation method (two-mode excitation) and provide a more robust method for generating uniform travelling waves. The input shaping control alters the reference signal such that the parasitic behavior of unnecessary modes is cancelled out. The combination of the mode suppression and selective mode excitation through input shaping is verified experimentally for generation of a smooth travelling waves in finite structures.
40
Wu, Xin Hua, Joaquin Del Prado, D. Hu, A. Huang, M. Q. Chu, and M. H. Loretto. "Ageing of C-Containing and C-Free Ti-15Cr and Ti-15-3." Materials Science Forum 539-543 (March 2007): 3595–600. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.3595.
Повний текст джерелаАнотація:
Samples of Ti-15Cr and Ti-15V-3Sn-3Al-3Cr (wt%) containing controlled additions of carbon up to 0.2wt% and different oxygen contents have been quenched and aged at temperatures between 400 and 600°C. Optical, scanning and analytical transmission electron microscopy have been used to characterise the microstructures of the quenched and aged samples. Hardness testing has been used to follow the kinetics and extent of age hardening, which are accelerated in Ccontaining samples. The addition of carbon results in the formation of Ti(CxOy) precipitates which pin grain boundaries in forged samples so that the grain size in the quenched C-containing samples is about a factor of ten less than that in the C-free samples. In the C-free samples coarse grain boundary alpha tends to form, but in the C-containing samples alpha precipitation is more uniform throughout the beta grains. The extent of omega precipitation is very different in the two alloys; the Ti-15Cr alloy forms athermal omega in the as-quenched samples and large omega precipitates are formed on ageing at 400°C. No evidence for omega has been obtained in the Ti-15-3. The hardening responses and microstructural observations are interpreted in terms of the different grain boundary oxygen contents in the C-containing and C-free samples and the different roles of omega and of carbon in the two alloys.
41
Zhou, Haiping, Chengcai Zhang, Baokun Han, Jianfeng Qiu, Shengxue Qin, Kuidong Gao, Jie Liu, Shuai Sun, and Hongbin Zhang. "Microstructures and Mechanical Properties of Nanocrystalline AZ31 Magnesium Alloy Powders with Submicron TiB2 Additions Prepared by Mechanical Milling." Crystals 10, no. 6 (June 26, 2020): 550. http://dx.doi.org/10.3390/cryst10060550.
Повний текст джерелаАнотація:
In this work, nanocrystalline AZ31 magnesium alloy powders, reinforced by submicron TiB2 particles, were prepared via mechanical milling. It was found that TiB2 particles stimulated the fracture and welding of AZ31/TiB2 powders, leading to the acceleration of the milling process. Meanwhile, the TiB2 particles were refined to submicron-scale size during the milling process, and their distribution was uniform in the Mg matrix. In addition, the matrix was significantly refined during the milling process, which was also accelerated by the TiB2 particles. The formation of grain boundary segregation layers also led to the weakened TiB2 peaks in the XRD patterns during the mechanical milling. The grain sizes of AZ31–2.5 wt % TiB2, AZ31–5 wt % TiB2 and AZ31–10 wt % TiB2 powders were refined to 53 nm, 37 nm and 23 nm, respectively, after milling for 110 h. Under the combined effect of the nanocrystalline matrix and the well-dispersed submicron TiB2 particles, the AZ31/TiB2 composites exhibited excellent micro-hardness. For the AZ31–10 wt % TiB2 composite, the micro-hardness was enhanced to 153 HV0.5.
42
Tang, Meng, Kaiming Wu, Jing Liu, Lin Cheng, Xian Zhang, and Yan Chen. "Mechanism Understanding of the Role of Rare Earth Inclusions in the Initial Marine Corrosion Process of Microalloyed Steels." Materials 12, no. 20 (October 15, 2019): 3359. http://dx.doi.org/10.3390/ma12203359.
Повний текст джерелаАнотація:
In this study, the corrosion behavior of rare earth (RE) microalloyed steels was first evaluated through potentiodynamic polarization tests and corrosion weight loss experiments, and then the corrosion morphologies were observed by scanning electron microscope (SEM). After immersion in a NaCl solution, the sulfides (or oxygen sulfides) dissolved preferentially, followed by corrosion at the boundary between the Fe matrix and oxides. Afterwards, the inclusions fell off as a whole, which promoted pitting nucleation. The first principle modeling demonstrated that the work functions of various kinds of inclusions descended in the following order: La2Zr2O7 > LaAlO3 > (La2O3 ≈ Fe ≈ La2O2S) > La2S3, which provided a theoretical explanation to the dissolution behaviors of inclusions. That is, inclusions containing sulfur tend to dissolve preferentially, whereas the oxides do not dissolve easily. Subsequently, the surface current distributions were detected by the scanning vibrating electrode technique (SVET), which provided more microscopic insight into the role of inclusions in the corrosion propagation. Results showed that the active sites of pitting nucleation accelerated the transverse propagation of corrosion. Finally, local corrosion spread to the whole surface as uniform corrosion.
43
Wang, Ping, Jian Ping Li, Yong Chun Guo, Zhong Yang, and Feng Xia. "Effect of Tin on Microstructure and Electrochemistrical Properties of Mg-Al-Sn-Zn Magnesium Alloys Anodic Materials." Advanced Materials Research 197-198 (February 2011): 1129–34. http://dx.doi.org/10.4028/www.scientific.net/amr.197-198.1129.
Повний текст джерелаАнотація:
Morphologies, microstructure and composition distribution of the magnesium anodic materials were studied by metallographic microscopy, x-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The corrosion behavior and electrochemical properties of Mg alloy were also investigated by constant current method, potential polarization, collecting gas through drainage. The results show that tin restrained β-Mg17Al12 phase precipitation along the grain boundary. With the content of tin increasing, granular Mg2Sn phase was improved. After uniform heat treatment, most of β-Mg17Al12 phase was dissolved, but most of Mg2Sn was not dissolved. Tin could improve self-corrosion potential and release hydrogen rate. Magnesium alloy anode with 1% tin content had high discharge potential and current efficiency. With the current density increasing, the release hydrogen rate augmented. The current efficiency reached 82 % at 20mA/cm2. The main composition of the corrosion products were MgO and Al2O3 which were easily peeled off. As a result, more negative and stable work potential was produced and the reaction was accelerated continuously.
44
Gu, Ning, Zhiliang Lu, and Tongqing Guo. "Simulation of Viscous Flows Around A Moving Airfoil by Field Velocity Method with Viscous Flux Correction." Advances in Applied Mathematics and Mechanics 4, no. 03 (June 2012): 294–310. http://dx.doi.org/10.4208/aamm.10-m1167.
Повний текст джерелаАнотація:
AbstractBased on the field velocity method, a novel approach for simulating unsteady pitching and plunging motion of an airfoil is presented in this paper. Responses to pitching and plunging motions of the airfoil are simulated under different conditions. The obtained results are compared with those of moving grid method and good agreement is achieved. In the conventional field velocity method, the Euler solver is usually used to simulate the movement of the airfoil. However, when viscous effect is considered, unsteady Navier-Stokes equations have to be solved and the viscous flux correction must be taken into account. In this work, the viscous flux correction is introduced into the conventional field velocity method when non-uniform grid speed distribution is occurred. Numerical experiments for the flow around NACA0012 airfoil showed that the proposed approach can well simulate viscous moving boundary flow problems.
45
Tang, Qianlong, Fudong Chen, Mingfeng Lei, Binbin Zhu, and Limin Peng. "Study on the Generalized Displacement Boundary and Its Analytical Prediction for Ground Movements Induced by Shield Tunneling." Advances in Civil Engineering 2021 (March 23, 2021): 1–18. http://dx.doi.org/10.1155/2021/8858874.
Повний текст джерелаАнотація:
The process of shield tunnel excavation would inevitably cause surrounding ground movement, and excessive displacement in the soil could lead to large deformation and even collapse of the tunnel. The methods estimating convergence deformation around tunnel opening is summarized. Then, a universal pattern of displacement boundary condition around the tunnel cavity is originally introduced, which is solved as the combination of three fundamental deformation modes, namely, uniform convergence, vertical translation, and ovalization. The expression for the above-mentioned displacement boundary condition is derived, by imposing which the analytical solution for ground movements, based on the stress function method, is proposed. The reliability and applicability of this proposed solution are verified by comparing the observed data in terms of surface settlement, underground settlement, and horizontal displacement. Further parametric analyses indicate the following: (1) the maximum settlement increases linearly with the gap parameter and the tunnel radius, while it is negatively related to the tunnel depth; (2) the trough width parameter is independent of the gap parameter and the radius, while it is proportional to the tunnel depth. This study provides a new simple and reliable method for predicting ground movements induced by shield tunneling.
46
Hu, Gaoquan, Zhaohui Wang, Yiwei Fan, Hongmei Yuan, and Quanjie Gao. "Study on the disturbance effect of pulsating flow and heat transfer in self-excited oscillation shear layer." Thermal Science, no. 00 (2021): 347. http://dx.doi.org/10.2298/tsci210611347h.
Повний текст джерелаАнотація:
The fluid movement motion has an important influence on the evolution of the pulsating flow in the hot runner. Using the Large Eddy Simulation numerical method, the instantaneous velocity, wall shear stress, boundary layer thickness and Nu number of hot runner section under different structural parameters at an inlet pressure of 5000 Pa were studied. The research results showed that the backflow vortex can be formed in the hot runner, and the fluid at the axis center of hot runner can form a pulsating flow under the squeezing action of the backflow vortex. The pulsating flow had a strong disturbance effect on the fluid around the axis center and accelerated the heat exchange between the fluid around the axis center and the wall. The disturbance effect of pulsating flow gradually strengthened with the flow of the main flow to the downstream. When d2/d1 was 1-1.8, the wall shear stress first increased and then decreased, and the wall heat transfer efficiency first increased and then decreased. The maximum wall shear stress was 36.4Pa. When L/D was 0.45-0.65, the boundary layer thickness first decreased and then increased, and the heat transfer efficiency first increased and then decreased. The minimum boundary layer thickness was 0.392mm and the maximum Nu number was 138. When d2/d1=1.4 and L/D=0.55, the maximum comprehensive evaluation factor reached 1.241, and the heat transfer efficiency was increased by 24.1%.
47
Koshel, S., and G. Koshel. "ANALYSIS OF THE REVERSING MECHANISM OF LIGHT INDUSTRY EQUIPMENT." Odes’kyi Politechnichnyi Universytet Pratsi 1, no. 63 (2021): 38–43. http://dx.doi.org/10.15276/opu.1.63.2021.04.
Повний текст джерелаАнотація:
To create reliable and highly efficient, en- ergy-saving machines for light industry, it is necessary to study the dynamic processes of movement of the links of the mechanisms of which they are composed. Especially such studies should be given attention for machines, the mechanisms of which have a cyclic nature of action. During the execution of a technological operation in light industry machines with a periodic cyclic movement of the working bodies, an uneven movement of the main shaft occurs. This is caused by the movement of the links of the mechanism with certain accelerations and taking into account the periodic nature of the action of technological loads, which vary in magnitude and direction. The uneven nature of the movement leads to the appearance of additional loads in the kinematic pairs of mechanisms, mechanical vibrations in the mechanical trans- mission systems of motion, leads to the appearance of vibrations and violations in the positioning of the working bodies, affects the techno- logical process of the equipment. Uniform and stable tension of the threads is the key to a high-quality performance of the loop formation process in knitwear. Additional dynamic loads affect the technological tension of textile threads during equipment operation. These loads are caused by the accelerated movement of the links of the mechanism, which is especially important for technological equipment with the pres- ence of a reverse working stroke of its links. In such mechanisms, the values of the angular acceleration of the links and the linear accelera- tion of their individual points can acquire critically permissible values. It is possible to ensure the movement of the working bodies of the machine according to the law for which the tension of the threads will be optimally necessary. To do this, you need to choose the right type of mechanism that sets them in motion. The aim of the work is to conduct a structural-kinematic research of the mechanism of the reversible movement of the needle drum of a knitting machine, which will justify the selection of the required type of mechanism for such equipment. The confirmation of the improvement of the conditions for the formation of loops when knitting on a knitting machine with a reversible needle drum movement, made on the basis of a rocker mechanism, has been obtained.
48
Courcoubetis, George, Manasi S. Gangan, Sean Lim, Xiaokan Guo, Stephan Haas, and James Q. Boedicker. "Formation, collective motion, and merging of macroscopic bacterial aggregates." PLOS Computational Biology 18, no. 1 (January 4, 2022): e1009153. http://dx.doi.org/10.1371/journal.pcbi.1009153.
Повний текст джерелаАнотація:
Chemotactic bacteria form emergent spatial patterns of variable cell density within cultures that are initially spatially uniform. These patterns are the result of chemical gradients that are created from the directed movement and metabolic activity of billions of cells. A recent study on pattern formation in wild bacterial isolates has revealed unique collective behaviors of the bacteria Enterobacter cloacae. As in other bacterial species, Enterobacter cloacae form macroscopic aggregates. Once formed, these bacterial clusters can migrate several millimeters, sometimes resulting in the merging of two or more clusters. To better understand these phenomena, we examine the formation and dynamics of thousands of bacterial clusters that form within a 22 cm square culture dish filled with soft agar over two days. At the macroscale, the aggregates display spatial order at short length scales, and the migration of cell clusters is superdiffusive, with a merging acceleration that is correlated with aggregate size. At the microscale, aggregates are composed of immotile cells surrounded by low density regions of motile cells. The collective movement of the aggregates is the result of an asymmetric flux of bacteria at the boundary. An agent-based model is developed to examine how these phenomena are the result of both chemotactic movement and a change in motility at high cell density. These results identify and characterize a new mechanism for collective bacterial motility driven by a transient, density-dependent change in motility.
49
Matao, Paul, Bijjula Prabhakar Reddy, and Jefta Sunzu. "Hall and Rotation Effects on Radiating and Reacting MHD Flow past an Accelerated Permeable Plate with Soret and Dufour Effects." Trends in Sciences 19, no. 5 (February 24, 2022): 2879. http://dx.doi.org/10.48048/tis.2022.2879.
Повний текст джерелаАнотація:
This article investigates numerically the effects of Hall current and rotation effects on radiating and chemically reacting unsteady MHD natural convection flow past an accelerated infinite vertical permeable plate in the presence of Soret and Dufour effects. The dimensionless coupled non-linear governing partial differential equations of the problem are solved numerically by employing finite element method. The influence of various physical parameters influencing the flow on the primary velocity, secondary velocity, temperature and the species concentration are displayed graphically whilst the numerical results of the primary skin friction, secondary skin-friction, Nusselt number and the Sherwood number are presented in tabular form. Results reveals that magnetic parameter, radiation parameter and chemical reaction rate tends to depreciate both primary and secondary velocity components whilst Hall, Soret and Dufour effects have reverse trend. Rotation parameter tends to retard fluid flow in the primary flow direction and accelerate fluid flow in the secondary flow direction. Thermal boundary layer thickness decreases with increasing radiation parameter whilst the reverse trend is noticed with increasing Dufour effect. Thermal diffusion effect causes to improve concentration boundary layer thickness whilst chemical reaction rate has reverse impact. These parameters have similar effect on the primary and secondary skin-frictions whilst opposite effect was noticed on the Nusselt and Sherwood numbers. This model problem finds an important in engineering and industrial application such as MHD generators, food processing, heat exchangers devices and internal rotation rate of the sun.
HIGHLIGHTS
The problem investigate the effects of Hall current and rotation effects on radiating and reacting on unsteady magnetohydrodynamics (MHD) natural convection heat and mass transfer flow over an infinite vertical porous plate embedded in a uniform porous medium taking Soret and Dufour effects into account
The resulting partial differential equations governing the fluid flow are solved numerically using the finite element method. In order to determine the effects of various pertinent parameters and to investigate the important flow features, the numerical calculations for fluid velocity, temperature and species concentration are computed and shown graphically whereas skin friction, Nusselt number and Sherwood number at the plate are evaluated and depicted in tabular form
The model problem finds an important in engineering and industrial application
GRAPHICAL ABSTRACT
50
Popov, I. P. "COMBINATION OF CIRCULAR MOTIONS IN MACHINES AND MECHANISMS." Frontier materials & technologies, no. 4 (2021): 48–56. http://dx.doi.org/10.18323/2782-4039-2021-4-48-56.
Повний текст джерелаАнотація:
In technical systems, including aviation and space technology, and in particular, in aircraft transmissions, bearings, orbital systems, helicopter mechanisms, and many others, the combined rotational movements are widespread, and when designing, it is important to understand the nature of joint motion. The paper aimed at the generalization of the principle of the combination of motions in circular movements. The author considered the x'0'y' coordinate system that rotates in the x0y coordinate system without angular acceleration with the velocity ω. The radius of rotation is equal to ρ1. Wherein 0x || 0'x', 0y || 0'y'. An object a rotates in the x'0'y' coordinate system without angular acceleration with the velocity ±ω. The radius of rotation is equal to ρ2. The study identified that at reverse rotations, the trajectory of joint motion represents an ellipse. The author determined all standard ellipse characteristics relating to the case under the study and identified the elliptical trajectory inclination. The study shows that if the joint motion trajectory is elliptical and the semi-axes are equal (ρ1+ρ2) and |ρ1−ρ2|, then an object a undergoes circular motion in the x'0'y' coordinate system without angular acceleration with the velocity −ω. Just as the result of the superposition of two non-accelerated straight movements is also non-accelerated, i.e. a uniform and rectilinear movement, at the one-way rotations, the joint motion trajectory represents a circle. At circular motions with multiple speeds, the joint motion trajectory represents a snail. The practical aspect of the study is determined by the fact that the resulting formulas can be directly used in the CAD system when performing design works.