查看更多>>摘要：In order to further achieve the balance between the calculation accuracy and efficiency of the transient analysis of the aero-engine disc cavity system,an Optimized Time-adaptive Aerother-mal Coupling calculation(OTAC)method has been proposed.It combines one-dimensional tran-sient calculation of air system,Conventional Sequence Staggered(CSS)method,Time-adaptive Aerothermal Coupling calculation(TAC)method and differential evolution optimization algorithm to obtain an efficient and high-precision aerothermal coupling calculation method of air system.Considering both the heat conduction in the solid domain and the flow in the fluid domain as unsteady states in the OTAC,the interaction of fluid-solid information within a single coupling time step size was implemented based on the CSS method.Furthermore,the coupling time step size was automatically adjusted with the number of iterations by using the Proportional-Integral-Deri vative(PID)controller.Results show that when compared with the traditional loosely coupling method with a fixed time step size,the computational accuracy and efficiency of the OTAC method are improved by 8.9％and 30％,respectively.Compared with the tight coupling calculation,the OTAC method can achieve a speedup of 1 to 2 orders of magnitude,while the calculation error is maintained within 6.1％.
查看更多>>摘要：The human factors and their interaction with other factors play an important role in the flight safety of transport aircraft.In this paper,a paradigm of risk assessment for transport aircraft interacting with piloting behaviors is proposed,with focus on landing which is the most accident-prone flight stage in aviation safety statistics.Model-based flight simulation serves as our data source for landing risk analysis under uncertainties.A digital pilot in the loop that reflects the human piloting behaviors is employed to facilitate simulation efficiency.Eight types of unsafe events in landing are identified from statistics.On this basis,the landing safety boundary is extracted via stochastic simulation to divide safety and hazardous flight status domains,which con-tributes to flight status management and risk warning.The simulation results indicate that appro-priate piloting behavior,which is active response and fast target acquisition with minimum overshoot and fluctuation,shows benefit to landing safety.The subset simulation technique is employed to further refine the boundary with less computational workload.Furthermore,the effect of airspeed,windspeed,and other factors on landing risk is also discussed.The proposed risk assess-ment method would help optimize operation procedure and develop targeted pilot training pro-gram.
查看更多>>摘要：For the conceptual design phase of Unmanned Aerial Vehicles(UAVs),a process for conceptual design and configuration selection of Solar/Hydrogen powered UAVs(S/H-UAVs)is proposed.The design requirements of S/H-UAVs were analyzed firstly.The proposed process used Fuzzy Quality Function Deployment(FQFD)to establish logical and quantitative standards.Moreover,in order to appropriately describe the hesitancy of experts while making decision,it used Q-Rung Dual Hesitant Fuzzy Sets(QRDHFS)to score the correlationships.In addition,a decision-making framework is proposed to perform a logical selection of typical layouts based on defuzzi-fication method and Technique for Order Preference by Similarity to the Ideal Solution(TOPSIS).The present process has been applied for S/H-UAVs.The resulting set of design requirements con-sists of three categories:Mission Requirements(MRs),Engineering Characteristics(ECs)and Tech-nical Indicators(TIs).Four typical layouts of S/H-UAVs were sorted and determined.The performance of four typical layouts were evaluated and the Strut-Braced Wing(SBW)with external hydrogen storage was selected as the best layout for S/H-UAVs.
查看更多>>摘要：Distributed Propulsion Wing(DPW)technology offers significant advantages in terms of flight energy savings,but the strong aerodynamic coupling between the propulsive internal flow and aerodynamic external flow brings significant design challenges.As the primary DPW profile design is of great significance,this paper proposes a hybrid method to solve the inverse problem mainly based on the formula relationship between the required aerodynamic loads and the profile shape,which is more direct and instructive compared with traditional parametric iterative methods.The aerodynamic characteristics are described by the circulation distribution in the Fourier series form,then the mean camber line of the profile is solved through the re-derived airfoil theory considering disk's influence.Further CFD correction methods are also proposed.To validate the effectiveness and feasibility of the proposed hybrid inverse method,several DPW profile design tests are then conducted.Finally,the relationship between 2D and realistic 3D unit shape is also researched.The results show that the proposed inverse design method has great accuracy and convergence speed in the design tests,and shows good robustness against changes of the design parameters.The 2D profile shape and the actual 3D shape of DPW unit can establish an aerodynamic-propulsion equivalent relationship based on the same internal mass fluxes.
查看更多>>摘要：The voluminous stratospheric non-rigid airship is very sensitive to the external thermal environment.The temperature change of internal gas caused by the variation in the external ther-mal environment and wind speed will lead to a change in the shape and buoyancy of the airship,thereby affecting its flight control.The traditional static analysis method is difficult to accurately reflect this fluid-thermal-structural coupling process.In this paper,the iterative analysis method was established for the fluid-thermal-structural coupling effect of stratospheric non-rigid airship based on the models of fluid,thermal,and structural deformation.Considering the load such as the internal thermal effect and external flow field of the airship,the simulation of the thermo-induced structural deformation effect was conducted using Fluent and Abaqus software.The influ-ence of local time and external wind speed on the structural deformation,volume,and equilibrium altitude of the airship was analyzed.The results demonstrate that,at low wind speed,the influence of aerodynamic pressure on the deformation of the airship is negligible.However,a great amount of heat is carried away by the wind,then the structural deformation caused by internal and external pressure difference is alleviated and the equilibrium altitude of the airship change obviously.This can serve as a guideline for the design and flight test of the long-endurance stratospheric non-rigid airship.
查看更多>>摘要：Traditional centralized Proportional Integral(PI)controller design methods based on Equivalent Transfer Functions(ETFs)have poor decoupling effect in turboprop engines.In this paper,a centralized PI design method based on dynamic imaginary matrix and equivalent transfer function is proposed.Firstly,a method for solving equivalent transfer functions based on the dynamic imaginary matrix is proposed,which adopts dynamic imaginary matrix to describe the dynamic characteristics of the system,and obtains the equivalent transfer function based on the dynamic imaginary matrix characteristics.Secondly,for the equivalent transfer function,a central-ized PI control gain is designed using the Taylor expansion method.Meanwhile,this paper further proves that the centralized PI design method proposed in this paper has integral stability.Consid-ering the impact of altitude and Mach number on turboprop engines,a linear feedforward control method based on the transfer function matrix is further proposed based on the centralized PI con-troller,and the stability of the entire comprehensive control method is proved.Finally,to ensure the safe and effective operation of the turboprop engine,a temperature and torque limiting protection controller is designed for the turboprop engine.Simulation results show that the centralized PI con-troller design method and linear feedforward control method proposed can effectively improve the control quality of turboprop engine control systems.
查看更多>>摘要：The identification of aerodynamic parameters is accomplished through the test data of the dynamic movement of scaled aircraft models flying dynamically in wind tunnel,which can real-ize the accurate acquisition of the aerodynamic model of the aircraft in the preliminary stage for aircraft design,and it is of great significance for improving the efficiency of aircraft design.How-ever,the translational motion of the test model in the wind tunnel virtual flight is subject to con-straints that result in distinct flight dynamics compared to free flight.These constraints have implications for the accuracy of aerodynamic derivatives obtained through the identification of wind tunnel test data.With this issue in mind,the research studies the differences in longitudinal dynamic characteristics between unconstrained free flight and wind tunnel virtual flight,and inno-vatively proposes an online correction test based wind tunnel virtual flight test technique.The lon-gitudinal trajectory and velocity changes of the model are solved online by the aerodynamic forces measured during the test,and then the coupled relationship between aircraft translation and rota-tion is used to correct the model's pitch attitude motion online.For the first time,the problem of solving the data approximation for free flight has been solved,eliminating the difference between the dynamics of wind tunnel virtual flight and free flight,and improving the accuracy of the aero-dynamic derivative identification results.The experiment's findings show that accurate aerodynamic derivatives can be identified based on the online correction test data,and the observed behaviour of the identified motion model has similarities to that of the free flight motion model.
查看更多>>摘要：The issue of nonlinear structural freeplays in aircraft has always been a significant con-cern.This study investigates the aeroelastic characteristics of a twin-tail boom Unmanned Aerial Vehicle(UAV)with simultaneous freeplay nonlinearity in its left and right rudders.A comprehen-sive Limit Cycle Oscillation(LCO)solution route is proposed for complex aircraft with multiple freeplays,which can consider both accuracy and efficiency.For the first time,this study reveals the unique LCO characteristics exhibited by twin-tail boom UAVs with rudder freeplays and pro-vides simulations and explanations of interesting phenomena observed during actual flight.The governing equations are established using the free-interface component mode synthesis method,and the LCOs of the system are mainly solved through the improved time-domain numerical con-tinuation method and frequency-domain numerical continuation method.Furthermore,the study investigates the influence of the left and right rudder freeplay size ratio on the LCO characteristics.The results demonstrate that the twin-tail boom UAV exhibits two stable LCO types:close and dif-fering left and right rudder amplitudes.The proposed method successfully describes the complete LCO behaviors of the system.Overall,this study makes significant contributions to our understand-ing of the aeroelastic behavior of twin-tail boom UAVs with rudder freeplays.
查看更多>>摘要：The Complementary Metal-Oxide Semiconductor(CMOS)image sensor is a critical component with the function of providing accurate positioning in many space application systems.Under long-time operation in space environments,there are radiation related degradation and var-ious uncertainties affecting the positioning accuracy of CMOS image sensors,which further leads to a reliability reduction of CMOS image sensors.Obviously,the reliability of CMOS image sensors is related to their specified function,degradation,and uncertainties;however,current research has not fully described this relationship.In this paper,a comprehensive approach to reliability modelling of CMOS image sensors is proposed based on the reliability science principles.Firstly,the perfor-mance margin modelling of centroid positioning accuracy is conducted.Then,the degradation model of CMOS image sensors is derived considering the dark current increase induced by the total ionizing dose effects.Finally,various uncertainties are analyzed and quantified,and the measure-ment equation of reliability is proposed.A case study of a CMOS image sensor is conducted to apply the proposed method,and the sensitivity analysis can provide suggestions for design and use of CMOS image sensors to ensure reliability.A simulation study is conducted to present the advantages of the proposed comprehensive approach.
查看更多>>摘要：This paper examines the longitudinal tensile behavior and failure mechanism of a new unidirectional carbon fiber reinforced aluminum composite through experiments and simulations.A Weibull distribution model was established to describe the fiber strength dispersion based on single-fiber tensile tests for carbon fibers extracted from the composite.The constitutive models for the matrix and interface were established based on the uniaxial tensile and single-fiber push-out tests,respectively.Then,a 3D micromechanical numerical model,innovatively considering the fiber strength dispersion by use of the weakest link and Weibull distribution theories,was estab-lished to simulate the progressive failure behavior of the composite under longitudinal tension.Due to the dispersion of fiber strength,the weakest link of the fiber first fractures,and stress concentra-tion occurs in the surrounding fibers,interfaces,and matrix.The maximum stress concentration fac-tor for neighboring fibers varies nonlinearly with the distance from the fractured fiber.Both isolated and clustered fractured fibers are present during the progressive failure process of the composite.The expansion of fractured fiber clusters intensifies stress concentration and material degradation which in turn enlarges the fractured fiber clusters,and their mutual action leads to the final collapse of the composite.
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