ИСТИНА

The deformation of a magnetic fluid in an applied magnetic field can be used to create directional motion. In this work, the statics and motion of a spherical body with magnetizable material (body), partially immersed in a magnetic fluid (MF) with a free surface, on a horizontal plane in a uniform vertical applied magnetic field H are considered experimentally and theoretically. The statics experiments are made with water-based MF and the body in a non-magnetic medium in a rectangular vessel. The vessel with fluids is placed in a uniform vertical magnetic field H of Helmholtz coils. The maximum H is turned on, and the body levitates in the MF (see Fig. 1). Then the field value H is decreased by some step. The dependencies of the levitation height of the body on H are plotted. The dynamic experiment is carried out as follows: the body, which levitates in the MF drop (~ 0.01 ml) in uniform vertical H, is displaced for some distance from the initial position. A thin MF layer remains behind the body (see Fig. 2). Then we free the body and observe a horizontal motion along the layer. The problem of the equilibrium of the spherical magnetizable body in the MF drop is solved, considering the gravity, the dependence of the magnetization on the magnetic field, without surface tension. An analytical expression for the magnetic force acting on the body in a non-inductive approximation is found. A program for calculation of this force and the MF shape is written. The dependence of the levitation height on the applied field H is plotted numerically. The expression for the horizontal component of the magnetic force acting on the body from the thin rectangular MF layer is obtained analytically. Using this expression, the motion of the body along a MF layer is calculated taking into account the viscous force. A comparison of theoretical and experimental results is made. This work was supported by the RFBR grants 18-31-00066 (experimental and numerical investigations), 18-501-12011.