This paper presents the modeling, optimization, and validation of a hollow plunger type solenoid for high speed On/Off valve. In the preliminary design, an accurate equivalent magnetic circuit model of the proposed solenoid is carried out, and the magnetic circuit is arranged in Kirchhoffs voltage law matrix form for the convenience of computer calculation. An iterative method is applied to obtain accurate permeability of the nonlinear magnetic material. To optimize the design parameters, a multiobjective optimization process is developed, and the multiobjective particle swarm optimization method is used to obtain the Pareto front of the desired objectives. An approved solution in Pareto front is selected by analytic hierarchy process and validated by the finite element analysis (FEA) method. A prototype based on the final optimized design is manufactured and tested. The experiment results verified the validation proposed design and optimization process.

An enhanced bandwidth nonlinear resonant electromagnetic energy harvester has been designed to harness low frequency energy from basic human motion. Some vertical stacked cylindrical permanent magnets (PMs) constitute the inertial mass of the proposed harvester, which is suspended axially by two magnetic-springs and circumferentially by ferrofluid within a carbon fiber tube. In order to widen the frequency band and improve harvesting efficiency, two PMs are respectively fixed on the two end caps of the carbon fiber tube, so as to form two magnetic-springs with variable stiffness by cooperating with the PM stack. The self-assembled ferrofluid around the PM stack acts as its bearing system to minimize any friction during its movement. Copper wire are wrapped outside the tube to form the armature winding. The stiffness characteristic of the magnetic-springs and the optimum equilibrium position and number of windings have been determined by finite element method (FEM) analysis. As a proof of concept, a portable prototype of the proposed energy harvester that weighs 110g and with a volume of only 37.7cm $^3$ is fabricated. A series of experiments are carried out and the results show that the frequency band of the harvester becomes wider as the external vibration intensity increases. In addition, the effectiveness of ferrofluid in reducing friction is demonstrated under walking and running conditions. Without ferrofluid, the maximum average outputs are 10.15 mW and 32.53 mW respectively for walking and running. With ferrofluid, the maximum outputs are 17.72 mW and 54.61 mW, representing an increase of 74.58% and 67.88%, respectively. Furthermore, the prototype exhibits an average power density of 1.45 mW/cm $^3$ during running motions, which compares favorably with existing harvesters used in low power wearable devices.

The aircraft braking system is a critical system used to slow down and stop the aircraft. Typically, the aircraft braking system usually uses the electro-hydraulic pressure servo-valve (EHPSV) to regulate the braking pressure of the aircraft. However, the pilot stage of EHPSV which has very precise orifice is easy to be blocked and leads to terrible fault. The on / off valve is robust to oil contamination and has better stability, but it is challenging to achieve high-precision pressure regulation. In order to guarantee the braking efficiency of aircraft, a high-precision pressure regulation algorithm is required. In this study, a algorithm with on / off valve array unit is studied to optimize the pressure regulation performance. The characteristics of the on / off valve under different actuation times and pressures are derived. Based on this characteristics, a novel algorithm which can predict the required number of on / off valves and actuation time obtained by the unknown input state observer. Then the proposed algorithm is validated both by simulations and experiments. The results show that the proposed regulation algorithm in this study can achieve high-precision pressure regulation for aircraft braking application, which the regulation precision is better than 0.2 MPa, and the overshoot is less than 2.5%.

To overcome the adverse effects of time-varying parametric uncertainties and strong disturbances in aircraft antiskid braking systems (ABS), achieving efficient antiskid braking control and shortening the braking distance. This article proposes a modified super-twisting sliding mode control (MSSMC)-based aircraft ABS controller with gain adaptive schedule and disturbance compensation. In this article, MSSMC is obtained by substituting the discontinuous term in the conventional super-twisting sliding mode control (SSMC) with a continuous fractional power term, which can alleviate the chattering and improve the tracking performance. The developed controller is derived by effectively integrating MSSMC, extended state observer (ESO) and gain adaptive techniques, preserving the advantages of these approaches while effectively overcoming their practical performance limitations. The time-varying disturbances and unmodeled dynamics in aircraft ABS are estimated by ESO and compensated in a feedforward way, which significantly decreases the residual uncertainties handled by the MSSMC, thus alleviating the burden on the MSSMC and avoiding the high-gain feedback. In addition, a novel gain adaptive protocol for MSSMC is proposed, which can minimize the control gain and the chattering amplitude without the prerequisite of uncertain upper boundary required for conventional SSMC. Theoretical analysis based on the Lyapunov approach shows that the designed ABS controller ensures that the sliding variable converges to the desired accuracy near the origin in a finite time. Comparative experimental results demonstrate the effectiveness of the proposed approach.

Electro-hydrostatic actuator is generally regarded as the preferred solution for more electrical aircraft actuation systems. It is of importance to optimize the weight, efficiency and other key design parameters, during the preliminary design phase. This paper describes a multi-objective optimization preliminary design method of the electro-hydrostatic actuator with the objectives of optimizing the weight and efficiency. Models are developed to predict the weight and efficiency of the electro-hydrostatic actuator from the requirements of the control surface. The models of weight prediction are achieved by using scaling laws with collected data, and the efficiency is calculated by the static energy loss model. The multi-objective optimization approach is used to find the Pareto-front of objectives and relevant design parameters. The proposed approach is able to explore the influence of the level length of linkage, displacement of pump and torque constant of motor on the weight and efficiency of the electro-hydrostatic actuator, find the Pareto-front designs in the defined parameter space and satisfy all relevant constraints. Using an electro-hydrostatic actuator for control surface as a test case, the proposed methodology is demonstrated by comparing three different conditions. It is also envisaged that the proposed prediction models and multi-objective optimization preliminary design method can be applied to other components and systems.