To improve the pressure capacity of the magnetic fluid seal with a large sealing gap, a new type of stepped magnetic fluid seals was firstly proposed based on magnetic fluid seal with multiple magnetic sources or stepped labyrinth seals. A universal magnetic fluid seal with two permanent magnets and a diverging stepped magnetic fluid seal have been investigated by experimental methods. The experimental results of the both sealing structures have been compared and analyzed. The results indicate that the diverging stepped magnetic fluid seal shows good performance compared to the universal magnetic fluid seal without stepping structure and it is an effective method to improve magnetic fluid sealing capacity with a large gap.

A large gap structure device of the magnetic fluid static sealing have been designed, and this structure was made to test the anti-pressure, the experimental station and process was discussed, the factors that affect the experiment result were also been analyzed. The pressure capacity and the size of the leak rate have been measured when the sealing gap were 0.4mm, 0.5mm, 0.6mm and 0.7mm respectively. Experiments show that the design of the sealing structure can solve the problem of large gaps in the magnetic sealing, and for the gap of 0.4mm, its anti-pressure capacity is 70 percent more than the pressure of the typical sealing gap (0.15mm).

Stress-sensitive widely exists in fractured reservoir. In this paper, a mathematical model of flow in stress-sensitive reservoir with horizontal well is established based on experimental data and with process of linearization. By using of Lord Kelvin point-source solution, Bessel function integration and Poisson superimpose formula, the dimensionless pressure response function of horizontal well in infinite stress-sensitive reservoir is obtained. And then the derivative type curve is calculated. Based on the type curve, the characteristics and influencing factors of the fluid flow through porous medium of horizontal well in stress-sensitive gas reservoir are analyzed.

Magnetic fluid is the key core of magnetic fluid sensor. Here magnetic model of magnetic fluid is analyzed. The magnetic curve of magnetic fluid is divided into 3 parts and the liner area is presented to make magnetic fluid sensor more sensitively. The magnetic force of magnetic fluid in magnetic field is calculated and analyzed. The magnetic permeability of magnetic fluid in sensor could be treated as a constant in the linear area of magnetization curve. And the magnetic force of magnetic fluid in magnetic field could be ignored if the length to diameter ratio of the solenoid is large enough.

Two different structure of dampers based on the principle of second-order buoyancy were designed in this paper. In order to verify the reduction of the vibration, a test rig was set up. On the test rig, the reduction effect of two different dampers was studied by adjusting the amount of the magnetic fluid. The experiment results indicate the relationship between the damping effect of magnetic fluid damper and the amount of magnetic fluid and this analysis result is benefit to the design of the dampers.