The Influence of Shaft Eccentricity on the Magnetic Fluid Sealing Performance

Shicong Li,Decai Li,Shuangxi Li 한국자기학회 2023 Journal of Magnetics Vol.28 No.2

This manuscript delves into the impact of shaft eccentricity and diameter on the pressure resistance and magnetic force of a magnetic fluid seal (MFS), through both magnetic circuit analysis method (MCAM) and finite element method (FEM). The study proposes a systematic approach to enhance the performance of eccentric MFS based on MCAM. The results show a near-linear decrease in the pressure resistance of the MFS with increasing eccentricity, with a maximum decline of 65 %. However, the MFS model with a 100 mm shaft diameter renders more precise results in predicting the sealing performance for larger shaft diameters since the pressure resistance decrease remains below 5 % as shaft diameter is increased. The optimal range of pole tooth structure parameters has also been determined. Remarkably, the proposed method affords a precise analysis of the performance of large-diameter eccentric MFS, which is not feasible using two-dimensional axisymmetric magnetic field models.

Study of Spaceborne W-band Millimeter Wave Radiometer

Jing, Li,Shengwei, Zhang,Maohua, Sun,Decai, Kong,Heguang, Liu,Jingshan, Jiang 대한원격탐사학회 2001 International Symposium on Remote Sensing Vol.17 No.1

The W-band millimeter wave radiometer has been studied under the support of Chinese Academy of Science (CAS) and it is successfully studied for the first time in China. Its technical index is suitable for the use in space. The main characteristics of the W-band millimeter wave radiometer are introduced in this paper.

Experiment Study and Machine Learning Prediction of Damping Performance of Ferrofluid Dynamic Vibration Absorber

Xiao Liu,Decai Li 한국자기학회 2022 Journal of Magnetics Vol.27 No.1

In this research, we study four influence factors of the damping performance of ferrofluid dynamic vibration absorber, as well as predict and optimize the damping performance by machine learning method. The vibration absorber in our research is based on the second order buoyancy principle, which consists of a non-magnetic container, a small amount of ferrofluid and a permanent magnet. The effects of the initial amplitude, the cone angle of the cover, the thickness of the gasket and the mass of the ferrofluid on the damping performance are investigated by experiments. Based on the experiment data, we use BP neural network to establish a prediction model between the four influence factors and the damping performance. The prediction error of damping efficiency predicted by BP neural network is mainly within ± 0.4%. Meanwhile, the determination coefficient R² of test data is 0.96242. The both indicate that BP neural network has a good performance in predicting the damping efficiency. Furthermore, we use the search algorithm to find the optimized values of each influence factor through the prediction model and the high damping efficiency is confirmed by experiments. Our work introduces machine learning into the field of vibration absorber designing, which provides an innovative method for the rapid design of high efficiency vibration absorber.

Analysis on Seal Capacity of Magnetic Fluid Seal Using Ring Magnet

Jiawei Liu,Decai Li 한국자기학회 2022 Journal of Magnetics Vol.27 No.1

Magnetic fluid seal is one of the most mature applications of magnetic fluid. When the shaft has a large radial runout, the classical pole piece is easily damaged. Due to its small size, the commonly used pole piece structure harbors problems like poor seal performance under a large gap and poor processability. By exploring the distribution law of the magnetic field on the magnet’s surface, we provided theoretical support for the magnetic fluid seal using axially-magnetized ring magnets. New structures for the magnetic fluid seal using axially-magnetized slotted ring magnets and the magnetic fluid seal using radially-magnetized ring magnets were proposed. Then, comparisons were made between the classical magnetic fluid seal and the magnetic fluid seal using ring magnets. The results revealed that the magnetic fluid seal using axially-magnetized slotted ring magnets and the magnetic fluid seal using radially-magnetized ring magnets exhibited a certain seal capacity, which could replace the classical magnetic fluid seal structure.

Research on the Axial Magnetic Levitation Force Acting on the Ring Magnet Suspended in Magnetic Fluid : Considering a Radial Eccentricity

Jun Yu,Decai Li,Nannan Di,Ningning Guo 한국자기학회 2019 Journal of Magnetics Vol.24 No.2

The self-suspension of magnet in magnetic fluid has been widely used in micromechanical systems, sensors, and dampers. The magnetic field associated with the ring magnet is obtained by numerical calculation and simulation through which the axial magnetic levitation force is calculated, and the numerical calculation, simulation, and experimental results agree with each other. The influence of the radial eccentricity of the ring magnet on the axial magnetic levitation force is studied, the ring magnet will experience a maximum axial magnetic levitation force without radial eccentricity. With the increase of radial eccentricity and the decrease of the distance between the bottom of the ring magnet and container, the axial magnetic levitation force will continue to decrease. But it is worth noting that the magnitude of the change caused by radial eccentricity is negligible compared to that of the axial magnetic levitation force.

Design and Analysis of a Plane Vibration-based Electromagnetic Generator Using a Magnetic Spring and Ferrofluid

Siqi Wang,Decai Li 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.5

This paper describes the design and characterization of a plane vibration-based electromagnetic generator that is capable of converting low-frequency vibration energy into electrical energy. A magnetic spring is formed by a magnetic attractive force between fixed and movable permanent magnets. The ferrofluid is employed on the bottom of the movable permanent magnet to suspend it and reduce the mechanical damping as a fluid lubricant. When the electromagnetic generator with a ferrofluid of 0.3 g was operated under a resonance condition, the output power reached 0.27 mW, and the power density of the electromagnetic generator was 5.68 μW/cm2. The electromagnetic generator was also used to harvest energy from human motion. The measured average load powers of the electromagnetic generator from human waist motion were 0.835 mW and 1.3 mW during walking and jogging, respectively.

Numerical Analysis and Experiment Study of Magnetic Fluid Boundary in Seals

Yibiao Chen,Decai Li,Yanjuan Zhang,Anmin Xi 한국자기학회 2018 Journal of Magnetics Vol.23 No.2

Magnetic fluid seals are widely used technical applications of magnetic fluid. This paper presents a numerical simulation model to obtain the boundary of magnetic fluid in seals. The magnetic field in the seal is solved by finite element method, and the boundary is calculated by using Navier-Stokes equations in magnetic fluid. In order to observe the surface and obtain the seal capacity, the plane magnetic fluid seal experiment is carried out. The relationship between the seal capacity and the magnetic fluid volume is presented. The seal capacity which is obtained by the theoretical analysis has well congruence with the result of the experiment. The displacement of boundary with the pressure difference is quantitatively depicted.

Investigation on the Influence of Temperature on Starting Torque of Magnetic Fluid Seal

Jiawei Chen,Decai Li,Du Hao 한국자기학회 2018 Journal of Magnetics Vol.23 No.3

The widest application of magnetic fluid is in magnetic fluid seals. The starting torque varying with temperature of magnetic fluid seal has limited its application in special seal field such as military industry. This paper firstly measure the starting torque of magnetic fluid seals under different temperature conditions from −55 oC to 70 ℃ after holding for 2.5 hours in a closed environment with uniform temperature. And the law of starting torque with temperature change is studied experimentally. The results show that the starting torque of the magnetic fluid seal changes unobvious at 25 ℃ or higher temperature. The starting toque of magnetic fluid seal increases with the decrease of temperature, and the causes of which are analyzed. The results of this study provide experimental and theoretical reference for reducing the staring torque of magnetic fluid seal in low temperature environment.

Non-uniform Distribution of Magnetic Fluid in Multistage Magnetic Fluid Seals

Wang Zhongzhong,Li Decai,Zhou Jing 한국자기학회 2017 Journal of Magnetics Vol.22 No.2

Magnetic fluid, a new type of magnetic material, is a colloidal liquid constituted of nano-scale ferromagnetic particles suspended in carrier fluid. Magnetic fluid sealing is one of the most successful applications of magnetic fluid. As a new type of seal offering the advantages of no leakage, long life and high reliability, the magnetic fluid seal has been widely utilized under vacuum- and low-pressure-differential conditions. In practical applications, for improved pressure capacity, a multistage sealing structure is always used. However, in engineering applications, a uniform distribution of magnetic fluid under each tooth often cannot be achieved, which problem weakens the overall pressure capacity of the seals. In order to improve the pressure capacity of magnetic fluid seals and broaden their applications, the present study theoretically and experimentally analyzed the degree of non-uniform distribution of multistage magnetic fluid seals. A mathematical model reflecting the relationship between the pressure capacity and the distribution of magnetic fluid under a single tooth was constructed, and a formula showing the relationship between the volume of magnetic fluid and its contact width with the shaft was derived. Furthermore, the relationship of magnetic fluid volume to capacity was analyzed. Thereby, the causes of non-uniform distribution could be verified: injection of magnetic fluid; the assembly of magnetic fluid seals; the change of magnetic fluid silhouette under pressure loading; the magnetic fluid sealing mechanism of pressure transmission, and seal failure. In consideration of these causes, methods to improve the pressure capacity of magnetic fluid seals was devised (and is herein proposed).

Influence of Particle Size Distribution of Magnetic Fluid on the Resistance Torque of Magnetic Fluid Seal

Siyu Chen,Decai Li 한국자기학회 2017 Journal of Magnetics Vol.22 No.4

Magnetic fluid seal is widely used in military and aerospace industry owing to its zero leakage property, long life and reliability. The resistance torque is often required to be small and stay within allowable scope with the standing time expanding and the working environment changing. In this paper, we discussed the influence of the particle size distribution of magnetic fluid on the resistance torque of magnetic fluid seal. Samples of magnetic fluid of different particle size distribution were processed by applying a magnetic field gradient. Afterwards, the rheological property of different samples was analyzed using rheometer. Besides, the resistance torque of magnetic fluid seal on different occasions was measured. We explained these results from the point of formation and destruction of magnetic aggregations based on the theory of magnetoviscous effect, thus provided feasible ways to improve the performance of magnetic fluid seal.