Semi-active stabilisation of a pipe conveying fluid using eddy-current dampers: state-feedback control design,experimental validation

An application of electromagnetic devices of the motional type (i.e. eddy-current dampers) to improve the dynamic stability of a cantilever pipe discharging fluid is proposed. When the flow velocity reaches a critical value, this system loses stability through the flutter. A contactless damping device is used. This actuator is made of a conducting plate attached to the pipe that moves together with it within the perpendicular magnetic field that is generated by the controlled electromagnets. During the motion the eddy currents in the plate and a resultant drag force of a viscous character are generated. First, an optimal control problem that aims to stabilise the system with the optimal rate of decrease of the system’s energy is posed and solved. Then a state-feedback parametrization of the obtained optimal control, which can be used in a closed-loop scheme is proposed. The effectiveness of the designed optimal controller is validated by making a comparison with the corresponding passive solutions on the specially designed and constructed experimental test stand of a pipe conveying air.

     

Stabilization of a cantilever pipe conveying fluid using electromagnetic actuators of the transformer type

The article presents an investigation of the stabilization of a cantilever pipe discharging fluid using electromagnetic actuators of the transformer type. With the flow velocity reaching a critical value, the straight equilibrium position of the pipe becomes unstable, and self-excited lateral vibrations arise. Supplying voltage to the actuators yields two opposite effects. First, each of the actuators attracts the pipe, thus introduces the effect of negative stiffness which destabilizes the middle equilibrium. Second, lateral vibrations change the gap in magnetic circuits of the actuators, which leads to oscillations of magnetic field in the cores and the electromagnetic phenomena of induction and hysteresis that impede the motion of the pipe. The combination of these two non-linear effects is ambiguous, so the problem is explored both theoretically and experimentally. First, a mathematical model of the system in form of a partial differential equation governing the dynamics of the pipe coupled with two ordinary differential equations of electro-magnetodynamics of the actuators is presented. Then, the equation of the pipe’s dynamics is discretized using the Galerkin procedure, and the resultant set of ordinary equations is solved numerically. It has been shown that the overall effect of actuators action is positive: the critical flow velocity has been increased and the amplitude of post-critical vibrations reduced. These results have been validated experimentally on a test stand.

     

Electronic Properties of Nanocrystalline Layers of Wide-Band-Gap Materials

The study presents an analysis of the properties of nanocrystalline wide-band-gap materials—diamond, BN, AlN, CN, GaN—as films produced by various plasma deposition techniques. The results of investigating their bulk as well as interface (i.e. layer–substrate) properties are shown and discussed. The influence of the nanocrystalline structure of the films on their electrophysical and optical characteristics, as well as on their phase composition and energy band diagrams configuration, was determined. Another phenomenon investigated was the influence of the plasma process parameters (like ion bombardment energy) on the structure of the layers, the dielectric strength of a layer, the substrate–interface region width, the density of states and of the electronic charge present in the bulk of the material and in the material–substrate transition zone. The choice of substrate type was dependent on the requirements imposed by the research method employed or by the fact of its usability in such fields of application as optoelectronics, optics, mechanics and bioengineering. From the above point of view the usage of various technological processes (selective etching, doping and fabrication of metal contacts) was also analyzed     

Reversible hydrogen absorption in neutron generating tubes

The operation of neutron generating tubes is presented. The real system is described. Some aspects of reversible absorption of hydrogen isotope by metals are analyzed. A model describing decisive phenomena and letting us to avoid undesirable situations is proposed. Analogies with other chemical systems are pointed out.