Nonlinear systems are modeled as piecewise linear systems at multiple operating points, where the operating points are modeled as switches between constituent linearized systems. In this paper, adaptive piecewise linear switch controller is proposed for improving the response time and tracking performance of the hydraulic actuator control system, which is essentially piecewise linear. The controller composed of PID and Model Reference Adaptive Control (MRAC) adaptively chooses the proportion of these two components and makes the designed system have faster response time at the transient phase and better tracking performance, simultaneously. Then, their stability and tracking performance are analyzed and evaluated by the hydraulic actuator control system, the hydraulic actuator is controlled by the electrohydraulic system, and its model is built, which has piecewise linear characteristic. Then the controller results are compared between PID and MRAC and the switch controller designed in this paper is applied to the hydraulic actuator; it is obvious that adaptive switch controller has better effects both on response time and on tracking performance.
Impedance
spectroscopy (IS) is a widely used nondestructive and
high-throughput experimental technique for the characterization of
electrical properties of materials. In the petroleum industry, IS
is frequently employed to determine the electrical properties of asphaltenes
and resins. The electrical properties of waxy crude oils, which correlate
significantly with the flowability, however, have received little
to no attention in the existing investigations. In this work, we inspected
the influence of wax precipitation on IS of waxy crude oil for the
first time. The investigation was carried out in a frequency range
of 2 × 10–1 to 2 × 104 Hz and
a temperature range of 5–60 °C. It was discovered that
the Nyquist diagram representing the electrical response of waxy oil
evolves from one semicircle to two semicircles as wax molecules precipitate
at temperatures below the wax appearance temperature. IS of waxy crude
oil can be reproduced by an equivalent circuit model composed of two
serially connected constant phase element-ideal resistance combinations
(R
bulk|Q
bulk – R
wax|Q
wax). It was found that the resistor-like contribution from
wax in the equivalent circuit model, R
wax, increases with the amount of precipitated wax, whereas the capacitor-like
contribution in the equivalent circuit model, Q
wax, decreases with the amount of precipitated wax. Furthermore,
the flow property of waxy oil, such as viscosity, can be related to
the conductivity according to the fractional Walden rule. The entire
viscosity–conductivity relationship can be divided into three
regions, and each segment of the relationship can be fitted by the
fractional Walden rule.
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