Search

Protected areas are widely recognized as crucial for biodiversity conservation and ecosystem service maintenance. In recent decades, countries worldwide have made great progress in expanding the scope of protected areas. However, the evaluation of conservation effectiveness is insufficient due to limited resource inputs. In this study, we assessed the nature reserves’ effectiveness in conserving biodiversity and ecosystem services for the Three-river Source of the Tibetan Plateau in China over the past 20 years at multiple scales. Our findings revealed substantial improvements in biodiversity value, habitat quality, water retention carbon storage, and a slight decline in soil retention. Furthermore, implementing conservation measures within the nature reserves has resulted in better ecological conditions than areas outside. In terms of the different protection zones within the nature reserves, the core areas showed the highest improvement in ecological conditions, followed by the buffer areas and experimental areas. These results indicate a positive influence of ecological projects on conservation objectives. Additionally, the study indicated the effectiveness of more stringent conservation management. Limiting human activities and taking measures to protect soil retention in the Three-river nature reserves is urgent.

Airbreathing aero-engines are regarded as excellent propulsion devices from ground takeoff to hypersonic flight, and require control systems to ensure their efficient and safe operation. Therefore, the present paper aims to provide a summary report of recent research progress on airbreathing aero-engine control to help researchers working on this topic. First, five control problems of airbreathing aero-engines are classified: uncertainty problem, multi-objective and multivariable control, fault-tolerant control, distributed control system, and airframe/propulsion integrated control system. Subsequently, the research progress of aircraft gas turbine engine modelling, linear control, nonlinear control, and intelligent control is reviewed, and the advantages and disadvantages of various advanced control algorithms in aircraft gas turbine engines is discussed. Third, several typical hypersonic flight tests are investigated, and the modelling and control issues of dual-mode scramjet are examined. Fourth, modelling, mode transition control and thrust pinch control for turbine-based combined cycle engines are introduced. Followed, significant hypersonic airframe/propulsion integrated system control is analysed. Finally, the study provides specific control research topics that require attention on airbreathing aero-engines.

The generalization ability and robustness of data-driven models deteriorate when samples are scarce or input features are outside the training sample space. This research focuses on building a data assimilation (DA) framework that embeds the time sequence prediction model and improves the prediction results by constructing an enhanced system state vector that incorporates model bias parameters and new observation data to achieve the deviation correction and improve the robustness of the model. The DA framework proposed in this study includes three steps: prediction model inference, ensemble Kalman filter (EnKF) online deployment, and model parameter update. Wind tunnel experiments of a supersonic cascade are performed to obtain the original data for training the prediction model and optimizing the DA framework. Long short-term memory network (LSTM) was chosen as the prediction model. The testing set is distributed outside the sample space of the training set to verify the effectiveness of the DA framework for enhancing the time sequence prediction model. The improvement effects of the EnKF-enhanced LSTM model on the time sequence prediction results of the wall pressure in the oscillating flow field and the non-oscillating flow field are studied. The optimization results indicate that the LSTM model embedded in the DA framework can significantly improve the wall pressure prediction results. Thus, the results of this study lay a solid foundation for the condition monitoring and margin determination of the supersonic cascade flow field.

Aimed at diversity of hypersonic flight mission, this paper discusses the multivariable control of regeneratively-cooled scramjet engine with two-stage kerosene injection for both safety operation and high performance. Firstly, the multivariable control strategy is proposed to solve the inlet unstart and overtemperature control issues. There are two linear models identified for different control objects because of the control strategy. Among them, the inputs are two-stage fuel equivalence ratios, and the outputs are thrust, inlet steady margin, and thrust and kerosene temperature at cooling channels outlet, respectively. Secondly, H∞ multivariable control method is introduced. The standard H∞ control problem with structural uncertainty is constructed in detail. In order to settle the issue that the control strategy selects various controlled output variables under different flight missions, a switching controller based on controller output reset is proposed. Lastly, not only thrust and steady margin control loop, but also thrust and fuel temperature control loop of the regeneratively-cooled scramjet engine are established. Simultaneously, the switching system with the two control loops is designed in this paper. Simulation results indicate that rapid responses of control system, smooth and steady switching between different loops are realized. The engine with control system can operate steadily with high performance at both specific and variable operating conditions.

This paper investigates the control-oriented modeling for turbofan engines. The nonlinear equilibrium manifold expansion (EME) model of the multiple input multiple output (MIMO) turbofan engine is established, which can simulate the variation of high-pressure rotor speed, low-pressure rotor speed and pressure ratio of compressor with fuel flow and throat area of the nozzle. Firstly, the definitions and properties of the equilibrium manifold method are presented. Secondly, the steady-state and dynamic two-step identification method of the MIMO EME model is given, and the effects of scheduling variables and input noise on model accuracy are discussed. By selecting specific path, a small amount of dynamic data is used to identify a complete EME model. Thirdly, modeling and simulation at dynamic off-design conditions show that the EME model has model accuracy close to the nonlinear component-level (NCL) model, but the model structure is simpler and the calculation is faster than that. Finally, the linearization results are obtained based on the properties of the EME model, and the stability of the model is proved through the analysis of the eigenvalues, which all have negative real parts. The EME model constructed in this paper can meet the requirements of real-time simulation and control system design.