This paper aims at studying the axial vibration response characteristics of Fluid-Structure Interaction (FSI) vibration of aircraft hydraulic pipe when considering the friction coupling. Based on the Brunone empirical model and the Zielke weighting function, an expression of fluid shear stress of the hydraulic pipeline is presented for a wide range of Reynolds number, and the friction model of the FSI 14-equation for high-speed and high-pressure hydraulic pipeline is modified. On this basis, a left-wing hydraulic pipeline of the C919 airplane is taken as the verification object and modeled, then the FSI vibration 14-equation is solved using frequency-domain transfer matrix method in MATLAB to analyze the modal and the axial vibration characteristics of the pipeline. Ultimately, a test experiment is given and discussed by being compared with the numerical simulation results, which confirmed the correctness of the friction model and demonstrated that the analytic accuracy of axial velocity response of FSI vibration could be improved by considering the friction coupling.

With regard to the rear-drive in-wheel motor vehicle, this paper studies the joint estimation method for the vehicle state and road adhesion coefficient. A nonlinear seven degrees of freedom vehicle estimation model and a tire estimation model are established. A vehicle driving state estimator and a road adhesion coefficient estimator based on the generalized high-order cubature Kalman filter (GHCKF) algorithm are designed. The vehicle state estimator combines the vehicle model and the tire model to calculate the vehicle state parameters, provides the state parameters for the road adhesion coefficient estimator, and realizes the real-time estimation of the road adhesion coefficient. The exponential fading memory adaptive algorithm is used to update the measurement noise variance, and we upgrade the GHCKF to the adaptive generalized high-order cubature Kalman filter (AGHCKF), which estimates the vehicle state and road adhesion coefficient. The typical working conditions using the double GHCKF/AGHCKF estimation algorithm were simulated and analyzed. Then, high-and low-speed driving experiments based on typical working conditions were carried out. An integrated navigation system (INS), global positioning system (GPS), and real-time kinematic positioning (RTK) were used to collect the real-time data of the vehicle, and compare them with the estimated values of the joint estimator, to verify the feasibility of the vehicle-state–road-adhesion-coefficient joint estimator. We compared a high-order GHCKF algorithm, high-order improved AGHCKF algorithm, and a cubature Kalman filter (CKF) algorithm, and the simulation and experimental results show that the joint estimator using the CKF, GHCKF, and AGHCKF algorithms can realize the real-time estimation of the vehicle state and the road adhesion coefficient. The AGHCKF algorithm shows the best effectiveness and robustness of the three algorithms.

The previous sensitivity analysis researches are not accurate enough and also have the limited reference value, because those mathematical models are relatively simple and the change of the load and the initial displacement changes of the piston are ignored, even experiment verification is not conducted. Therefore, in view of deficiencies above, a nonlinear mathematical model is established in this paper, including dynamic characteristics of servo valve, nonlinear characteristics of pressure-flow, initial displacement of servo cylinder piston and friction nonlinearity. The transfer function block diagram is built for the hydraulic drive unit closed loop position control, as well as the state equations. Through deriving the time-varying coefficient items matrix and time-varying free items matrix of sensitivity equations respectively, the expression of sensitivity equations based on the nonlinear mathematical model are obtained. According to structure parameters of hydraulic drive unit, working parameters, fluid transmission characteristics and measured friction-velocity curves, the simulation analysis of hydraulic drive unit is completed on the MATLAB/Simulink simulation platform with the displacement step 2 mm, 5 mm and 10 mm, respectively. The simulation results indicate that the developed nonlinear mathematical model is sufficient by comparing the characteristic curves of experimental step response and simulation step response under different constant load. Then, the sensitivity function time-history curves of seventeen parameters are obtained, basing on each state vector time-history curve of step response characteristic. The maximum value of displacement variation percentage and the sum of displacement variation absolute values in the sampling time are both taken as sensitivity indexes. The sensitivity indexes values above are calculated and shown visually in histograms under different working conditions, and change rules are analyzed. Then the sensitivity indexes values of four measurable parameters, such as supply pressure, proportional gain, initial position of servo cylinder piston and load force, are verified experimentally on test platform of hydraulic drive unit, and the experimental research shows that the sensitivity analysis results obtained through simulation are approximate to the test results. This research indicates each parameter sensitivity characteristics of hydraulic drive unit, the performance-affected main parameters and secondary parameters are got under different working conditions, which will provide the theoretical foundation for the control compensation and structure optimization of hydraulic drive unit.

A bionic hydraulic pipeline (BHP) with a three-layer structure is designed innovatively on the basis of an animal’s biological mechanism. Its intermediate layer is rubber material. Its middle layer is the same as the middle layer of the blood vessels at the outlet of a cheetah’s heart and has good viscoelasticity. Which is used to absorb the flow pressure pulsation of the hydraulic system. Besides, a dynamic model of a BHP and the effect of absorption pulsation are further studied. It includes a rubber material model and the FSI (fluid’structure interaction) dynamic equation of the relationship between the liquid and rubber material. For rubber materials, the Mooney-Rivlin model is selected to describe the dynamic characteristics. After testing the stress and strain data through experiments, C10 and C01 of the rubber material are obtained. After determining the constitutive model of rubber and its parameters, the FSI model of the BHP is established. The natural frequency of the BHP is obtained when we solve the model with Matlab. Furthermore, to evaluate the accuracy of the model, hammer mode experiments are performed. They show that the accuracy of the model’s evaluation is within 5.

To explore the problem of parameter optimization for complex nonlinear function, a chaos wolf optimization algorithm (CWOA) with self-adaptive variable step-size was proposed. The algorithm was based on the swarm intelligence of wolf pack, which fully simulated the predation behavior and prey distribution way of wolves. It possessed three intelligent behaviors such as migration, summons and siege. And the competition rule as “winner-take-all” and the update mechanism as “survival of the fittest” were also the characteristics of the algorithm. Moreover, it combined the strategies of self-adaptive variable step-size search and chaos optimization. The CWOA was utilized in parameter optimization of twelve typical and complex nonlinear functions. And the obtained results were compared with many existing algorithms, including the classical genetic algorithm, the particle swarm optimization algorithm and the leader wolf pack search algorithm. The investigation results indicate that CWOA possess preferable optimization ability. There are advantages in optimization accuracy and convergence rate. Furthermore, it demonstrates high robustness and global searching ability.

This paper focuses on the frequency domain fluid–structure interaction (FSI) vibration characteristics of aircraft hydraulic pipe with complex constraints. The linear partial differential fourteen-equation model is applied to describe the nonlinear FSI dynamics of pipes conveying fluid with high-speed, high-pressure, a wide Reynolds number, and the vibration frequency range. The excitation, complex boundary, and middle constraint models of liquid-filled pipes are analytically established and added into the global model of the pipe system. These resulting models are solved by the improved Laplace transform transfer matrix method (LTTMM) in the frequency domain. Then, the dynamic response characteristics of an aircraft hydraulic pipe containing diverse constraints are investigated numerically and experimentally under four types of working conditions, and the improvement conditions for the numerical instabilities are presented. In general, the present method is highly efficient and convenient for rapid model parameter modifications, in order to be fully applicable to different pipe systems and analysis cases. The results reveal the complex resonant laws regarding aircraft hydraulic pipes with complex constraints in the broad frequency band, which can also provide theoretical reference and technical support for FSI vibration analysis and the control of aircraft hydraulic pipes.