METHOD OF RESEARCH ON THE DYNAMIC VISCOSITY OF MAGNETIC FLUIDS AT HIGH SHEAR RATE

Magnetic fluids have an important position in the design of technical systems due to their unique properties. They are used primarily in mechanical energy dissipation systems, i.e. brakes and vibration dampers, as well as in the design of seals. In many applications, the magnetic fluid operates at high flow velocities through narrow slots. Therefore, there is a need to determine the rheological properties of this type of substance at high shear rates. Due to the high density of magnetic fluids and the associated occurrence of mass forces, as well as the requirements regarding the distribution of the magnetic field, the measurement of the viscosity of magnetic fluids at high shear rates is extremely difficult when conventional measuring systems are used. The paper presents a proposal for a new measuring system and a method to determine the viscosity of magnetic fluids at high shear rates, as well as the results of research on the possibility of using the presented structure in the case of ferrofluids.

Dependence of Modified Butterworth Van-Dyke Model Parameters and Magnetoimpedance on DC Magnetic Field for Magnetoelectric Composites

This study investigates the impedance curve of magnetoelectric (ME) composites (i.e., Fe80Si9B11/Pb(Zr0.3Ti0.7)O3 laminate) and extracts the modified Butterworth–Van Dyke (MBVD) model’s parameters at various direct current (DC) bias magnetic fields Hdc. It is interesting to find that both the magnetoimpedance and MBVD model’s parameters of ME composite depend on Hdc, which is primarily attributed to the dependence of FeSiB’s and neighboring PZT’s material properties on Hdc. On one hand, the delta E effect and magnetostriction of FeSiB result in the change in PZT’s dielectric permittivity, leading to the variation in impedance with Hdc. On the other hand, the magnetostriction and mechanical energy dissipation of FeSiB as a function of Hdc result in the field dependences of the MBVD model’s parameters and mechanical quality factor. Furthermore, the influences of piezoelectric and electrode materials properties on the MBVD model’s parameters are analyzed. This study plays a guiding role for ME sensor design and its application.

Mechanical Behavior of Active and Passive Strain Sections in CFRP Laminate under Uniaxial Tension

This study investigates the nonlinear behavior of quasi-isotropic CFRP laminate under uniaxial tension. To verify the convergence of the calculated and experimental deviations, the approximating nonlinear equations describing the upper and lower hysteresis loop branches were found. The formation of a hysteresis loop in the active and passive strain sections in CFRP laminate has been studied. The open hysteresis loop development stages are shown from maximum expansion to stabilization, and to the tendency of branches to connect and narrow the loop. The point of the maximum angle between the upper and lower branches of the loop is determined – the apex of the hysteresis loop at maximum deformation. The strain region is found, in which the branches of the loop are parallel. The equations are determined, describing the nonlinear behavior of modules of Ex(ε) in the sections of increasing and decreasing strain. The dependence between mechanical energy dissipation per unit volume and strain was obtained.

A preliminary study about gravitational wave radiation and cosmic heat death

ABSTRACT We study the role of gravitational waves (GW) in the heat death of the Universe. Due to the GW emission, in a very long period, dynamical systems in the universe suffer from persistent mechanical energy dissipation, evolving to a state of universal rest and death. With N-body simulations, we adopt a simple yet representative scheme to calculate the energy loss due to the GW emission. For current dark matter systems with mass ∼1012−1015 M⊙, we estimate their GW emission time-scale as ∼1019−1025 yr. This time-scale is significantly larger than any baryon processes in the Universe, but still ∼1080 times shorter than that of the Hawking radiation. We stress that our analysis could be invalid due to many unknowns such as the dynamical chaos, the quadrupole momentum of haloes, the angular momentum loss, the dynamic friction, the central black hole accretion, the dark matter decays or annihilations, the property of dark energy, and the future evolution of the Universe.

Hydrodynamic calculation of wedge-shaped system «slider-guide» operating on compressible lubricant in presence of melt on surface of guide

In the article on the basis of the equation of motion of the compressible lubricant for the «thin layer», continuity, state, and the equation describing the profile of the molten contour taking into account the formula of mechanical energy dissipation the asymptotic and self-similar solution is found for the extreme (when the speed tends to infinity) and non-extreme case. As a result of solving the problem, a refined mathematical calculation model of a wedgeshaped sliding support with a low-melting metal coating on a movable contact surface is obtained, which compensates for an emergency lack of lubricant and provides a stable hydrodynamic lubrication mode

The Effect of Root Clearance on Mechanical Energy Dissipation for Axial Flow Pump Device Based on Entropy Production

The axial flow pump is a low head, high discharge pump usually applicable in drainage and irrigation facilities. A certain gap should be reserved between the impeller blade root and the impeller hub to ensure the blade adjustability to broaden the high-efficiency area. The pressure difference between its blade surface induces leakage flow in the root clearance region, which decreases hydraulic performance and operational stability. Therefore, this study was carried out to investigate the effect of root clearance on mechanical energy dissipation using numerical simulation and entropy production methods. The numerical model was validated with an external characteristics test, and unsteady flow simulations were conducted on the axial flow pump under four different root clearance radii. The maximum reductions of 15.5% and 6.8% for head and hydraulic efficiency are obtained for the largest root clearance of 8 mm, respectively. The dissipation based on entropy theory consists of indirect dissipation and neglectable direct dissipation. The leakage flow in the root clearance led to the distortion of the impeller’s flow pattern, and the indirect dissipation rate and overall dissipation of the impeller increased with increasing root clearance radius. The inflow pattern in the diffuser was also distorted by leakage flow. The diffuser’s overall dissipation, indirect dissipation rate on the blade surface, and indirect dissipation rate near inlet increased with increasing root clearance radius. The research could serve as a theoretical reference for the axial flow pump’s root clearance design for performance improvement and operational stability.

HYDRAULIC PROPERTIES OF SAND SLURRY FLOW IN A PIPE

The sand slurry flow in a cylindrical pipe is investigated using the Ostwald de Waele model. The dependence of the fluid flow rate on the pressure drop is determined, dependencies for the radial distribution of velocity and effective viscosity of flow are obtained. It is shown that the distribution of effective viscosity is characterized by a monotonic increase as it approaches the pipe walls. As the consistency increases, the mechanical energy dissipation of the flow also increases leading to an increase in hydraulic resistance. During the flow of dilatant media with the low nonlinearity index, the hydraulic resistance decreases with increasing pressure drop. When this index is 2, the hydraulic resistance does not depend on the pressure drop and is determined only by the liquid properties and the channel size. At highe values of the nonlinearity index, the increased pressure drop leads to an increase in hydraulic resistance. Keywords

Numerical Analysis of Mechanical Energy Dissipation for an Axial-Flow Pump Based on Entropy Generation Theory

Mechanical energy dissipation is a major problem affecting hydraulic machinery especially under partial-load conditions. Owing to limitations of traditional methods in evaluating mechanical energy dissipation, entropy generation theory is introduced to study mechanical energy dissipation with varying discharge and tip clearance intuitively through numerical simulations in an axial-flow pump. Results show that the impeller and diffuser are the main domains of mechanical energy dissipation, respectively accounting for 35.32%–55.51% and 32.61%–20.42% of mechanical energy dissipation throughout the flow passage. The mechanical energy dissipation of the impeller has a strong relation with the hump characteristic and becomes increasingly important with decreasing discharge. Areas of high turbulent dissipation in the impeller are mainly concentrated near the blades’ suction sides, and these regions, especially areas near the shroud, extend with decreasing discharge. When the pump enters the hump region, the distributions of turbulent dissipation near the shroud become disordered and expand towards the impeller’s inlet side. Unstable flows, like flow separation and vortices, near the blades’ suction sides lead to the high turbulent dissipation in the impeller and hump characteristic. Turbulent dissipation at the tip decreases from the blade leading edge to trailing edge, and regions of high dissipation distribute near the leading edge of the blade tip side. An increase in tip clearance for the same discharge mainly increases areas of high turbulent dissipation near the shroud and at the tip of the impeller, finally reducing pump performance.