Force balance in current sheets in collisionless plasma

In this paper, we derive a divergent form of the force balance equation for collisionless plasma in the quasineutrality approximation, in which the electric field and current density are excluded. For a stationary spatially one-dimensional current sheet with a constant normal component of the magnetic field and magnetized electrons, the general form of the force balance equation has been obtained for the first time in the form of a conservation law. An equation in this form is necessary for the correct formulation of boundary conditions when modeling asymmetric current sheets, as well as for the control of the stationarity of the numerical solution obtained in the model. Furthermore, the fulfillment of this equation is considered for two types of stationary configurations of a thin current sheet, which are obtained using a numerical model. The derived equation makes it possible to develop models of asymmetric current sheets, in particular current sheets on the magnetopause flanks in the magnetotail.

Force balance in current sheets in collisionless plasma

In this paper, we derive a divergent form of the force balance equation for collisionless plasma in the quasineutrality approximation, in which the electric field and current density are excluded. For a stationary spatially one-dimensional current sheet with a constant normal component of the magnetic field and magnetized electrons, the general form of the force balance equation has been obtained for the first time in the form of a conservation law. An equation in this form is necessary for the correct formulation of boundary conditions when modeling asymmetric current sheets, as well as for the control of the stationarity of the numerical solution obtained in the model. Furthermore, the fulfillment of this equation is considered for two types of stationary configurations of a thin current sheet, which are obtained using a numerical model. The derived equation makes it possible to develop models of asymmetric current sheets, in particular current sheets on the magnetopause flanks in the magnetotail.

Features of the Behavior of a Polymer Solution Jet in Electrospinning

Using the numerical analysis of the force balance equation and the rheological equation of the model of finitely extensible chains, the dynamics of a charged jet during the electrospinning of a polymer solution and the orientation of macromolecules in the jet are studied. In fairly weak electric fields, the jet always remains rectilinear, while in strong fields the straight section of the jet has a finite length, after which the motion of the jet becomes unstable. This behavior is due to the competition between inertial and viscoelastic forces, with viscoelasticity dominating in strong fields. It is found that polymer chains in the jet are strongly stretched along the flow direction.

Force balance in current sheets

<p>A new form of the proton force balance equation for the plasma consisting of collisionless protons and magnetized electrons is obtained. In the equation, the electric field is expressed through the magnetic field and the divergence of electron pressure tensor. The latter is reqiured for the correct determination of boundary conditions in models of current sheets to control the force balance in the models of that type. From this, a general form of the force balance equation in a one-dimensional current sheet is obtained, and effects of electron pressure anisotropy are considered. We reproduce realistic stationary configurations of current sheets using novel methods of numerical simulations and the Vlasov equation solving. </p>

Velocity Analysis of a Single Vertically Falling Non-Spherical Particle in Newtonian and Non-Newtonian Fluids

An analytical investigation is applied for the velocity of a vertically falling non-spherical particle in Newtonian and nonNewtonian fluid. The velocity of vertically falling non-spherical particle can be described by the force balance equation (BassetBoussinesq-Ossen equation). Variational Iterations Method (VIM) and Runge- Kutta 4th order method are used to solve the existing problem. The results were compared those obtained from VIM by R-K 4th order method. We obtained that VIM which was used to solve such non-linear differential equation with fractional power is simpler and more accurate than other methods. Analytical results indicate that the velocity in a falling procedure is significantly increased and more in Newtonian fluid. Also particle’s velocity in Newtonian fluid reaches early at terminal velocity as compare to non-Newtonian fluid. To obtain the results for all different methods, the symbolic calculus software MATLAB is used.

Study of up–down poloidal density asymmetry of high- impurities with the new impurity version of XGCa

Addition of multispecies impurity ions to the total-f gyrokinetic particle-in-cell code XGCa is reported, including a cross-verification of neoclassical physics against the NEO code. This new version of the neoclassical gyrokinetic code XGCa is used to benchmark and confirm the previous reduced-equation-based prediction that high- $Z$ impurity particles in the Pfirsch–Schlüter regime can exhibit a significant level of up–down poloidal asymmetry, through the large parallel friction force, and thus influence the radial plasma transport significantly. The study is performed in a plasma with weak toroidal rotation. In comparison, when the impurity particles are in the plateau regime, the up–down poloidal asymmetry becomes weak, with the parallel friction force becoming weaker than the parallel viscous force. It is also found that the linearization of the perturbed distribution function, based on the small poloidal asymmetry assumption, can become invalid. Using the numerical data from XGCa, each term in the parallel fluid force-balance equation have been analysed to find that both the main ions and the electrons respond to the poloidal potential variation adiabatically when the high- $Z$ tungsten possesses large poloidal variation.

Mechanism of Steady and Unsteady Piping in Coastal and Hydraulic Structures with a Sloped Face

Coastal and hydraulic structures, such as revetments, embankments and levees—as well as their underlying soil—may experience piping when exposed to outward pressure gradients. The aim of the present study is twofold: (1) to derive the force-balance equation for soils with a sloping surface exposed to a steady hydraulic gradient (relevant to hydraulic structures) and to seek a criterion for piping, including the friction terms; (2) to study the case of unsteady hydraulic gradient forcing (relevant to coastal structures) by means of a series of experiments. The derived force-balance equation is compared with the available experimental and numerical model data from the literature and extended to soils protected by a filter/armour layer or rip rap. The experiments conducted to study the mechanism of piping under unsteady hydraulic gradients involved two types of loadings; sudden and oscillatory. The results show that although the mechanism of steady and unsteady piping has some similar aspects, the soil is generally more prone to piping in the unsteady hydraulic loading compared to the steady case, attributed to the inertia terms. The hydraulic conductivity of the soil becomes more distinctive for the unsteady piping case. Finally, remarks are made about practical applications.

Influence of parameters of PM controller on vibration performance of liquid hydrostatic guide-way system

The vibration of liquid hydrostatic guide-way system during the working process makes a full impact on the machining precision of the numerically-controlled machine tool. The hydrostatic guide-way under the regulation of PM (Progressive Mengen) controller is taken as the research object. First, based on the force balance equation of hydrostatic guide-way, two kinds of vibration model of hydrostatic guide-way are established, respectively, and oil film stiffness equation and damping coefficient formula are derived. Second, the inherent frequency and amplitude of the guide-way system are derived. Third, the influence of PM controller parameters on the inherent frequency and amplitude of the guide-way system is analysed theoretically. The result indicates that the inherent frequency of the guide-way system changes with PM controller parameter and it makes a full impact on the active vibration amplitude of the hydrostatic guide-way system, but not the passive vibration amplitude. This article is provided a reference for the practical application of PM controller.

A METHOD FOR STATIC ANALYSIS OF CABLE-STAYED STRUCTURES SUBJECTED TO IN-PLANE LOADS

Present cable theory which formulated from force balance equation of single cable under self-weight and forms a catenary shape of deflection, that is nonlinear; therefore to determine displacement, deformation and tension forces of the cable and cable-stayed structures we need to provide some additional assumptions of cables and use iteration calculation. This paper presents a new method for static analysis of cable-stayed structures subjected to in-plane loading. By combination of the Gaussian Extreme Principle method and virtual displacement principle, authors to formulate and solve nonlinear equation system of cable-stayed structures, which ensured forces balancing as well as continuity of displacements and deformations of structures. This method allows for simultaneous determination of displacement, deformation and internal forces of cable-stayed structures without any other additional hypothesis, which is different from present cable theory.

Evaluation of the search and rescue LEEWAY model in the Tyrrhenian Sea: a new point of view

The trajectories' prediction of floating objects above the sea surface represents an important task in search and rescue (SAR) operations. In this paper we show how it is possible to estimate the most probable search area by means of a stochastic model, schematizing the shape of the object appropriately and evaluating the forces acting on it. The LEEWAY model,a Monte Carlo-based ensemble trajectory model, has been used; here, both statistical law to calculate the leeway and an almost deterministic law inspired by the boundary layer theory have been considered. The model is nested within the subregional hydrodynamic model TSCRM (Tyrrhenian Sicily Channel Regional Model) developed in the framework of PON-TESSA (Programma Operativo Nazionale; National Operative Program – TEchnology for the Situational Sea Awareness) project. The main objective of the work is to validate a new approach of leeway calculation that relies on a real person in water (PIW) event, which occurred in the Tyrrhenian Sea in July 2013. The results show that by assimilating a human body to a cylinder and estimating both the transition from laminar to turbulent boundary layer and the drag coefficients, it can be possible to solve a force balance equation, which allows the search area to be estimated with good approximation. This new point of view leads to the possibility of also testing the same approach for other different categories of targets, so as to overcome the limitations associated with the calculation of the leeway in the future by means of standard statistical law.