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The inconsistency in acceleration and deceleration performance between high and low altitudes is a significant challenge in aircraft engine control today. In the past, neither open-loop fuel–air ratio control nor closed-loop N-dot control could resolve this issue perfectly; the difference in acceleration and deceleration performance between high and low altitudes is even more than three times. The operational characteristics of aircraft engines vary significantly between high and low altitudes, posing challenges for transient state control in high-performance aircraft engines. To address these transient performance inconsistencies due to altitude uncertainties, a μ-synthesis adaptive tracking transition control design method with hybrid open-loop and closed-loop direct thrust control is proposed. The main innovation lies in proposing a new segmented hybrid control scheme. Under a high-power state, it employs a dual closed-loop μ-synthesis adaptive tracking framework, using fuel flow to control thrust and nozzle area to control the turbine pressure ratio. In a low-power state, a single-variable closed-loop and open-loop control architecture is applied. Simulation results show that the hybrid open/closed-loop control method can suppress the inconsistency of acceleration and deceleration performance caused by altitude uncertainties in turbofan engines, ensuring consistent robustness in acceleration and deceleration performance across different altitudes. From the ground to an altitude of 11 km, the new method has an acceleration time range of 3.44 s–3.84 s and a deceleration time range of 4.83 s–5.98 s; compared with the previous fuel–air ratio acceleration time of 4.17 s–9.12 s and deceleration time of 6.12 s–14.48 s, its high and low-altitude acceleration and deceleration consistency performance is greatly improved. [ABSTRACT FROM AUTHOR]

As the power unit of an aircraft, the engine's primary task is to provide the demanded thrust, making research on direct thrust control crucial. However, being a complicated multivariable system, effective multivariable direct thrust control methods are currently lacking. The main content of this paper is threefold. First, it presents a dual-loop multivariable μ-synthesis direct thrust control scheme for mixed-exhaust low-bypass turbofan engines, which is a typical rotationally symmetric machine. The scheme adjusts fuel flow for thrust control and nozzle area to control the turbine pressure ratio, ensuring thrust tracking while maintaining the engine's key parameters within safe limits. Second, a fast, accurate thrust estimation algorithm based on aerodynamic thermodynamics and component characteristics is introduced. At last, considering the model uncertainties between off-design and design points, a weight function frequency shaping μ-synthesis control design method is proposed to address internal loop coupling and external disturbance suppression. Nonlinear simulations within the flight envelope show that μ-synthesis direct thrust control achieves robust servo tracking and disturbance rejection, with a maximum steady-state thrust error of no more than 0.1%, and the key parameters are not over their safety boundaries. [ABSTRACT FROM AUTHOR]

Model Predictive Control (MPC) has many advantages in controlling an aero-engine, such as handling actuator constraints, but the computational burden greatly obstructs its application. The current multiplex MPC can reduce computational complexity, but it will significantly decrease the control performance. To guarantee real-time performance and good control performance simultaneously, an intelligent reduced-dimensional scheme of MPC is proposed. The scheme includes a control variable selection algorithm and a control sequence coordination strategy. A constrained optimization problem with low computational complexity is first constructed by using only one control variable to define a reduced-dimensional control sequence. Therein, the control variable selection algorithm provides an intelligent mode to determine the control variable that has the best control effect at the current sampling instant. Furthermore, a coordination strategy is adopted in the reduced-dimensional control sequence to consider the interaction of control variables at different predicting instants. Finally, an intelligent reduced-dimensional MPC controller is designed and implemented on an aero-engine. Simulation results demonstrate the effectiveness of the intelligent reduced-dimensional scheme. Compared with the multiplex MPC, the intelligent reduced-dimensional MPC controller enhances the control quality significantly by 34.06%; compared with the standard MPC, the average time consumption is decreased by 64.72%. [ABSTRACT FROM AUTHOR]

To solve the modeling problem of altitude ground test facility (AGTF) exhaust systems, which is caused by nonlinearity along the gas path and the difficulty of ejection factor calculation, a multi-cavity iterative modeling method is presented. The components of exhaust systems, such as the exhaust diffuser and cooler, are built with a series of volumes. It overcomes the disadvantage that traditional lumped-parameter models have, whereby they cannot calculate the dynamic parameters along the gas path. The exhaust system model is built with an iterative method based on multi-cavity components, and simulations are carried out under experimental conditions. The simulation results show that the maximum error of pressure is 2 kPa in the steady state and less than 6 kPa in the transient process compared with experimental data. Closed-loop simulations are also carried out to further verify the accuracy and effectiveness of the multi-cavity iterative exhaust system modeling method. [ABSTRACT FROM AUTHOR]

To support the advanced controller design and verification of the Aeropropulsion System Test Facility (ASTF), it is necessary to establish a mathematical model of ASTF with high precision and replace the current lumped parameter model. Therefore, a quasi-one-dimensional flow model of ASTF is established considering friction, localized losses, heat transfer, etc. Moreover, a generic modeling method is proposed for quasi-one-dimensional flow. With this method, all component models of ASTF are composed of staggered central control volume (CCV) and boundary control volume (BCV) and connected through virtual control volume. Thus, the properties of quasi-one-dimensional flow, such as spatial effect and time delay, can be easily addressed during the modeling process. The simulation results show that the quasi-one-dimensional flow model has higher accuracy than the lumped parameter model. Comparing the simulation results of the quasi-one-dimensional flow model with the test data, the relative errors of flow and pressure are less than 2.2% and 1.4%, respectively, further verifying the correctness of the proposed modeling method. [ABSTRACT FROM AUTHOR]

Modelica is an open-source, object-oriented equation-based modeling language. It is suitable for describing sophisticated dynamic systems (symmetry/asymmetry) as it uses mathematical acausal equations to express physical characteristics. The hydraulic mechanical units (HMU) of gas turbine engine control systems couple the contents of mechanical, hydraulic, symmetry, and other multidisciplinary fields. This paper focuses on the Modelica description method of those HMU models. The content of this work is threefold: firstly, the division form of basic elements in HMU is defined, and the method for describing these element models with Modelica is proposed; secondly, the organization of the element models is defined by using the inheritance characteristics of Modelica, and a lightweight (small code scale) component model is designed; and finally, the causal/acausal connections are designed according to bond graph theory, and the elements and components are integrated into a prototype modeling library. In this paper, the modeling library is verified by comparing simulation results of five typical HMU subsystem models with commercial modeling and simulation software. [ABSTRACT FROM AUTHOR]

The Flight Environment Simulation System (FESS) at Altitude Ground Test Facilities (AGTF) is used to test aircraft engines. The FESS model is the basis of research and verification of advanced control algorithms. To further improve the steady and dynamic accuracy of the FESS model, a modeling method based on quasi-one-dimensional flow is proposed. Firstly, based on the unified inlet/outlet boundary specifications, the component models of test equipment, such as the quasi-one-dimensional flow model of pipe, the regulating valve model considering the heat transfer process, the multi-inlet and multi-outlet volume model reflecting the mixing characteristics of air flow, and the air source model and engine model, were established. Secondly, according to the real structure and working mechanism of the FESS, the above component models were used to build the numerical simulation model of the FESS. The simulation results showed that the relative deviation of mass flow and pressure were less than 4.4% and 0.9%, respectively, which verifies the correctness of the modeling method. In addition, the PI controller was designed for the FESS, and the simulation results show that the model is able to support controller development and verification. [ABSTRACT FROM AUTHOR]

In this work, a new strategy is developed to design and synthesize quaternary catalysts NiS/CdS/MIL-101/PTCs (MIL = Materials of Institute Lavoisier, PTCs = polyoxo-titanium clusters) with excellent photocatalytic activity for H 2 evolution. PTCs and NiS can be successfully integrated into CdS/MIL-101 system by multi-step solvothermal in situ reaction method. The as-synthesized photocatalysts integrated with NiS and PTCs exhibit the dramatically enhanced photocatalytic activity for hydrogen evolution, which is approximately 230 times higher than that of uncoupled catalyst CdS/MIL-101. It is more interesting that the photocatalytic activity can be tuned by structural evolution of PTCs. The photoelectrochemical characteristics of catalysts confirm that the drastic enhancement for photocatalytic H 2 -production activity was predominantly attributed to PTCs and NiS contributing to matching energy gap and improving visible-light response, respectively, and both inhibiting recombination of photogenerated electron-hole pairs. More importantly, this work can flourish the design idea derived from the relation of structure and application for photocatalysts. Image 1 • Two NiS/CdS/MIL-101/PTCs show excellent photocatalytic activity for H 2 evolution. • Integrating PTCs can well match energy gap and accelerate charges transfer. • Doping NiS can improve visible-light response and enhance electron-hole separation. • The photocatalytic activity can be tuned by evolving the intrinsic structure of PTCs. • This work should flourish the design idea of photocatalysts on molecule level. [ABSTRACT FROM AUTHOR]

A high in-stent restenosis rate and thrombosis have compromised clinical benefits after vascular stent placement. Exercise rehabilitation after stenting emerges as a promising and practical therapeutic strategy to improve the clinical performance of this therapy, although it remains controversial. The present study aimed to explore the impact of exercise training on hemodynamic performance after vascular stent implantation. Different 3-dimensional computational models based on the patient-specific carotids were constructed to calculate hemodynamic parameters, including flow velocity, time-averaged wall shear (TAWSS), oscillatory shear index (OSI) and relative residence time (RRT). The results demonstrated that exercise training increased TAWSS but decreased OSI and RRT in some cases after the intervention, and high-intensity exercise further suppressed the adverse blood flow. However, exercise training remarkably reduced TAWSS and elevated OSI and RRT in patients with mild stenosis at upstream of stented segment. Additionally, we discovered that the hemodynamic environment change induced by exercise training was not significant compared to the stent position in some cases. Exercise had a less beneficial impact on the disturbed blood flow after the distal common carotid artery (CCA) stenting. These findings highlighted that exercise-induced hemodynamic changes differ under different conditions. The exercise training for the intervention patients should only be performed after a comprehensive vascular function assessment.