Efficient numerical computation of the steady-state response and stability analysis of the rotor systems with squeeze film dampers

The aim of this paper is to demonstrate capabilities of the created numerical procedure, which is based on harmonic balance method. Furthermore, the procedure incorporates the alternating frequency-time domain technique and the arc-length parameterization to solve the steady-state response of nonlinear systems in efficient manner, including unstable branches. The stability of the motion was assessed by two methods: the 2n-pass method and Hill’s method. The procedure was verified on an example from literature to prove its sufficient accuracy and subsequently, the procedure was applied on the finite element model of the rotor systém mounted on the squeeze film dampers. The carried out computational simulations confirmed that the created procedure is efficient for the strongly nonlinear response and it gives similar results as the time integration

Demonstration of the developed procedure for the computation of the nonlinear steady-state response on practical examples

project “IT4Innovations excellence in science - LQ1602”, by the Student’s Grant Competition project SP2019/97“, and by the grant project 19-06666S of the Czech Science Foundation

New test device design for static ferrofluid magnetic sealing

This work has been supported by the grant project 19-06666S of the Czech Science Foundation, the doctoral grant VSB-TUO, reg. no. CZ.02.2.69/0.0/0.0/19_073/0016945 within the Operational Programme Research, Development and Education, under project DGS/TEAM/2020-033, and by the National Programme of Sustainability (NPU II) project “IT4Innovations excellence in science - LQ1602”

The fuzzy approach for investigation of the steady-state response of rotors excited by loading effects of uncertain magnitude

the grant projects 19-06666S, LQ1602 (NPU II

The Effect of Sonication on Acoustic Properties of Biogenic Ferroparticle Suspension

Superparamagnetic iron oxide nanoparticles (SPION) synthesised chemically usually need the modification of the particle surface. Other natural sources of magnetic particles are various magnetotactic bacteria. Magnetosomes isolated from magnetotactic bacteria are organelles consisting of magnetite (Fe3O4) or greigite (Fe3S4) crystals enclosed by a biological membrane. Magnetotactic bacteria produce their magnetic particles in chains. The process of isolation of magnetosome chains from the body of bacteria consists of a series of cycles of centrifugation and magnetic decantation. Using a high-energy ultrasound it is possible to break the magnetosome chains into individual nanoparticles – magnetosomes. This study presents the effect of sonication of magnetosome suspension on their acoustic properties, that is speed and attenuation of the sound. Acoustic propagation parameters are measured using ultrasonic spectroscopy based on FFT spectral analysis of the received pulses. The speed and attenuation of ultrasonic waves in magnetosome suspensions are analysed as a function of frequency, temperature, magnetic field intensity, and the angle between the direction of the wave and the direction of the field

Influence of Magnetic Field on Dielectric Breakdown in Transformer Oil Based Ferrofluids

In this paper the experimental study of the breakdown field strength in a transformer oil based ferrofluid is reported. The experiments are conducted on five ferrofluid samples with different magnetic volume fraction. The influence of external magnetic field on the breakdown field strength is investigated, when a quasi-homogenous magnetic field was applied in parallel and perpendicular configuration in regard to the electric field. The obtained results are analysed in accordance to the electron charging of ferrofluid nanoparticles theory

Properties of Magnetosome Suspension under the Influence of Magnetic Field

The magnetotactic bacteria synthesize chains of nanosized magnetic particles that function as a compass needle to navigate in the direction of the earth's magnetic field. Magnetosomes are bacterial magnetic nanoparticles containing iron mineral crystals of magnetite or greigite, enveloped by a natural biological membrane. The objective of the work is to study the influence of magnetic field on rheology and acoustic properties of magnetosome suspension. Experimental results show a clear effect of the external magnetic field on the acoustic parameters such as velocity and attenuation of ultrasonic wave, and the viscosity of the suspension, arising from the biogenic magnetic particles aggregation

Properties of Magnetosome Suspension under the Influence of Magnetic Field

The magnetotactic bacteria synthesize chains of nanosized magnetic particles that function as a compass needle to navigate in the direction of the earth's magnetic field. Magnetosomes are bacterial magnetic nanoparticles containing iron mineral crystals of magnetite or greigite, enveloped by a natural biological membrane. The objective of the work is to study the influence of magnetic field on rheology and acoustic properties of magnetosome suspension. Experimental results show a clear effect of the external magnetic field on the acoustic parameters such as velocity and attenuation of ultrasonic wave, and the viscosity of the suspension, arising from the biogenic magnetic particles aggregation

Magnetodielectric anisotropy in magnetic fluids in temperature interval from 20 °C to 80 °C

Substitution of transformer oil as insulator medium by magnetic fluid in transformers requires observation of electric properties of magnetic fluids at temperatures higher than 20 °C. That´s why important physical quantities were measured at temperature in interval from 20 °C to 80 °C. The magnetodielectric anisotropy was studied at the same temperature region. Two important quantities have been measured: specific electric conductivity and dielectric breakdown strength of magnetic fluids at volume concentrations from 0,185 % to 2 %. So the behavior of magnetic fluids as insulator medium could be observed at working conditions of transformers