Robust Nonlinear Control Scheme for Electro-Hydraulic Force Tracking Control with Time-Varying Output Constraint

This paper presents a robust nonlinear control scheme with time-varying output constraint for the electro-hydraulic force control system (EHFCS). Two typical double-rod symmetrical hydraulic cylinders are employed to simulate force environments in the EHFCS. Therefore, in order to improve the performance of the EHFCS, firstly, the model of the EHFCS is established with taking external disturbances, parameter uncertainties as well as structural vibrations into consideration. Secondly, in order to estimate external disturbances, parameter uncertainties and structural vibrations in the EHFCS and compensate them in the following robust controller design, two disturbance observers (DOs) are designed according to the nonlinear system model. Thirdly, with two estimation values from two DOs, a time-varying constraint-based robust controller (TVCRC) is presented in detail. Moreover, the stability of the proposed controller is analyzed by defining a proper Lyapunov functions. Finally, in order to validate the performance of the proposed controller, a series of simulation studies are conducted using the MATLAB/Simulink software. These simulation results give a fine proof of the efficiency of the proposed controller. What’s more, an experimental setup of the EHFCS is established to further validate the performance. Comparative experimental results show that the proposed controller exhibits better performance than the TVCRC without two DOs and a conventional proportional integral (PI) controller.

Hidroituango Intake Gate Closure - Emergency Conditions

This article presents the investigation, analysis, and results of the intake gate closure of two vertical fixed-wheel gates at the hydroelectric project Ituango in Colombia (2400 MW) under free- flow conditions. This atypical operation was considered successful notwithstanding adverse conditions, and therefore, it can be classified as a unique operation in the field of hydraulic gates. In this article, some relevant parameters, such as the hydraulic force of the servomotor during the operation of the gate, were measured before and after the operation and analyzed, and the results were presented. A new chart is proposed for the downpull coefficient based on the collected data, which could be implemented in the closure of gates against the free flow. Considering the abovementioned factors, the authors propose some recommendations and present drawn conclusions contributing to state of the art on design, manufacturing, and operation of this type of hydraulic gates and structures for large and small dams under adverse and extreme conditions.

Calibration of CFD grid for simulating the impeller clearance flow and axial hydraulic force of centrifugal pump

The axial hydraulic force of centrifugal pump is an important parameter affecting pump performance. The force mainly includes the force inside impeller and in clearance. Due to the special structural characteristics of the clearance, the influence of grid discretization method on the calculation of axial force in the clearance is not fully understood. Therefore, based on the Reynolds-averaged method with shear stress transport turbulence model, an orthogonal experiment was designed to compare the correlation coefficient of velocity and pressure distribution between shear stress transport model and large eddy simulation models. A more suitable grid discretization strategy was found by artificial neural network for grid calibration. When the strategy is applied to the entire centrifugal pump, the prediction of axial force has high accuracy. The range analysis shows that the grid node number in the wall-wall direction has the greatest impact on velocity distribution. When the mesh parameters are in a certain range, it can compromise between the simulation accuracy and computational resource. The Reynolds-averaged model based simulation is proved accurate in capturing the complex velocity and pressure field inside clearance. The entire pump model is also used for the verification after the calibration of grid. The typical axial force law can be found under different flow rate conditions. This study provides a significant guidance in determining the grid scheme for accurate prediction of centrifugal pump’s axial force. It makes the computational fluid dynamics simulation feasible in the initial design of centrifugal pump which specifically considers the axial force problem.

Optimization of Nonlinear Pressure-flow Characteristics of a Spring- Loaded Pressure Relief Valve Based on CFD Simulation

In this study, the nonlinear pressure-flow characteristics of a spring-loaded pressure relief valve (PRV) which is used in the automotive fuel supply system for pressure control is analyzed, and its characteristics are improved by means of geometrical modifications of the valve structure. Given the complexity of the coupling mechanism between the valve internal flow characteristics and spring system, a quasi-steady computational fluid dynamics (CFD) method is introduced to predict the nonlinear pressure-flow characteristic curve of the valve and the accuracy is validated by experimental data. The total hydraulic force on the valve spool and diaphragm are divided into three parts according to the position of action and the correlation between the internal flow characteristics, hydraulic force, and pressure-flow characteristics of the valve are explained by CFD analysis and visualization. The result shows that the quasi-steady CFD method can accurately predict the trends of the valve nonlinear pressure-flow characteristic curve which is mainly determined by the hydraulic force produced in the middle chamber of the valve, when the valve opening reaches a certain value, a main vortex would be formulated in the middle chamber and lead to the sudden increase of hydraulic force which causes the fluctuation of the pressure-flow characteristic curve of the valve. It was also found that by increasing the round corner size, the valve opening value of flow pattern change will be promoted and the valve pressure-flow characteristic can be optimized.

Hydraulic force is a novel mechanism of diastolic function that may contribute to decreased diastolic filling in HFpEF and facilitate filling in HFrEF

It is a previously unrecognized physiological mechanism of the heart that diastolic filling occurs with the help of hydraulics. In patients with heart failure with preserved ejection fraction, atrial dilatation may cause the net hydraulic force to work against cardiac filling, thus further augmenting diastolic dysfunction. In contrast, it may work favorably in patients with dilated ventricles, as in heart failure with reduced ejection fraction.

Investigation of the Starting-Up Axial Hydraulic Force and Structure Characteristics of Pump Turbine in Pump Mode

During the starting up of the pump mode in pump turbines, the axial hydraulic force acting on the runner would develop with the guide vane opening. It causes deformation and stress on the support bracket, main shaft and runner, which influence the operation security. In this case, the axial hydraulic force of the pump turbine is studied during the starting up of pump mode. Its influences on the support bracket and main shaft are investigated in detail. Based on the prediction results of axial hydraulic force, the starting-up process can be divided into “unsteady region” and “Q flat region” with obviously different features. The mechanism is also discussed by analyzing pressure distributions and streamlines. The deformation of the support bracket and main shaft are found to have a relationship with the resultant force on the crown and band. A deflection is found on the deformation of the runner with the nodal diameter as the midline in the later stages of the starting-up process. The reason is discussed according to pressure distributions. The stress concentration of the support bracket is found on the connection between thrust seating and support plates. The stress of the runner is mainly on the connection between the crown and the blade’s leading-edge. This work will provide more useful information and strong references for similar cases. It will also help in the design of pump turbine units with more stabilized systems for reducing over-loaded hydraulic force, and in the solving of problems related to structural characteristics.

Optimization Design of Actuator Parameters with Stepless Capacity Control System Considering the Effect of Backflow Clearance

The actuator is the key to the stepless capacity control system of a reciprocating compressor. The coupling effect between the actuator and the reciprocating compressor was not considered in the traditional design, and the large design margin led to low system reliability, high cost and low safety. In this paper, a reciprocating compressor and actuator were taken as research objects. The backflow clearance of the suction valve was simulated by CFD (computational fluid dynamics), The relationship between backflow clearance and resultant gas force of the valve plate was discussed. By building a mathematical model of actuators considering backflow clearance and impact rebound, the relationship between the parameters of actuators was studied. Based on the mathematical model and CFD analysis, the hydraulic force and spring stiffness were taken as the design variables, the impact velocity of ejection or withdrawal and the backflow clearance were taken as objective functions, and the actuator parameters were optimized with NSGA-II (Non-dominated Sorting Genetic Algorithm – II). The optimization results show that when the backflow clearance is 0.0065 mm, the hydraulic force is 94.25 N, and the spring stiffness is 11,575.84 N/m, the objective functions are optimized, the parameters are significantly improved, and a good effect is achieved on the experimental table of a 2D reciprocating compressor.

Proportional–Integral–Derivative Controller Design Using an Advanced Lévy-Flight Salp Swarm Algorithm for Hydraulic Systems

To improve the control ability of proportional–integral–derivative (PID) controllers and increase the stability of force actuator systems, this paper introduces a PID controller based on the self-growing lévy-flight salp swarm algorithm (SG-LSSA) in the force actuator system. First, the force actuator system model was built, and the transfer function model was obtained by the identification of system parameters identifying. Second, the SG-LSSA was proposed and used to test ten benchmark functions. Then, SG-LSSA-PID, whose parameters were tuned by SG-LSSA, was applied to the electro-hydraulic force actuator system to suppress interference signals. Finally, the temporal response characteristic and the frequency response characteristic were studied and compared with different algorithms. Ten benchmark function experiments indicate that SG-LSSA has a superior convergence speed and perfect optimization capability. The system performance results demonstrate that the electro-hydraulic force actuator system utilized the SG-LSSA-PID controller has a remarkable capability to maintain the stability and robustness under unknown interference signals.

Numerical Investigation on the Mechanism of Double-Volute Balancing Radial Hydraulic Force on the Centrifugal Pump

Double-volute is an effective technique to reduce radial hydraulic force on the centrifugal pump and thereby mitigate the pump-casing vibration induced by unsteady flow characteristics. The mechanism of the double-volute structure balancing radial force on the impeller and volute was investigated on the basis of volute cross-sections by using Computational Fluid Dynamics (CFD) method. The tested performances and simulated inner-flow characteristics of two pumps with single-volute and double-volute were compared in this paper. The performance-test results verify the veracity of CFD method and illustrate that double-volute pump has some losses in terms of pump head and operation efficiency. The numerical simulations reveal that double-volute pump has smaller radial-force magnitude than single-volute pump on the abnormal conditions. Steady pressure field and transient pressure variations of pumps were explored to account for radial-force characteristics of double-volute pump. Compared with the single-volute structure, obvious pressure increases were found in the upper chamber (single part) of the double-volute, while the static pressure decreased in the lower chamber (double chambers). This situation reduces the pressure difference between two volute cross-sections in the collinear radial direction, resulting in smaller radial hydraulic force. Moreover, the transient simulations present the same phenomenon. The radial-forces distribute more uniformly in the double-volute pump, which can alleviate some vibrations.