Predictive Maintenance of Manned Spacecraft Through Remaining Useful Life Estimation Technique

Manned spacecraft pose challenges in terms of extremely high safety and reliability, and with the growth of system complexity and longer on-orbit operation time, the traditional management mode, such as monitoring the threshold of parameter passively, is difficult to meet the required safety standards. Predictive maintenance, which analyzes the system heath trend and estimates remaining useful life(RUL) to establish maintenance strategies ahead of time before failure occurs, is a new mode to approach maintenance tasks. Here, a predictive maintenance strategy for complex manned spacecraft is proposed based on the remaining useful life estimation technique. Firstly, a health index is established based on an abundance of telemetry data, reflecting the system's current health state. Secondly, we map the health index to the remaining useful life through system degradation modelling, taking into consideration both the system's stochastic deterioration and uncertainty. The maintenance and management strategies are then made based on the calculated distribution of RUL time. Finally, a case study on Chinese space station energy system predictive maintenance is presented.

Adaptive augmentation of gain-scheduled controller for aerospace vehicles

This paper proposes an adaptive augmentation control design approach of the gain-scheduled controller.This extension is motivated by the need for augmentation of the baseline gainscheduled controller.The proposed approach can be utilized to design flight control systems for advanced aerospace vehicles with a large parameter variation.The flight dynamics within the flight envelope is described by a switched nonlinear system,which is essentially a switched polytopic system with uncertainties.The flight control system consists of a baseline gain-scheduled controller and a model reference adaptive augmentation controller,while the latter can recover the nominal performance of the gainscheduled controlled system under large uncertainties.By the multiple Lyapunov functions method,it is proved that the switched nonlinear system is uniformly ultimately bounded.To validate the effectiveness of the proposed approach,this approach is applied to a generic hypersonic vehicle,and the simulation results show that the system output tracks the command signal well even when large uncertainties exist.

Finite element modeling of the shaped charge jet and design of the reusable perforating gun

Finite element method is used to study the formations of the penetration jet,the bulge,and the burr in the designed reusable perforating gun.The attached layer of the soft metal on the perforator is studied for the controlling of the bulge height on the casing of the reusable perforating gun.Results indicate that the shaped charge jet is initially formed in the center of the shaped charge liner and then the material of the liner is driven to the centerline of the liner by the detonation wave.The attachment of the soft metal layer to the cartridge of the perforator can be beneficial to control the bulge height.The design on the blind holes on the casing can affect the burr height formed by the collision between the jet and the casing.With the increase in the liner angle,the penetration width on the cement wall of the wellbore is increased.

Analysis and comparison of potential power and thermal management systems for high-speed aircraft with an optimization method

Under the dual effects of aerodynamic heating and high-power electronic equipment heating,the heat sink and power demand of advanced high-speed aircraft have been exponentially rising,which seriously restricts the aircraft performance.To improve system cooling and power supply performance and reduce engine performance loss,a power and thermal management system(PTMS)with high performance,low energy consumption,and light weight urgently needs to be developed.In this paper,three modes of a potential PTMS with different heat sinks and bleed air sources are further discussed to analyze and compare the optimal matching with the flight mission at Mach 1-4.4.The equivalent mass method is used to uniformly assess the costs of the fixed weight,bleed,resistance,etc.as a function of the fuel weight penalty,which is chosen as the optimization objective.The optimization variables consist of the compressor outlet temperature,cooling air flow rate,and fan duct heat exchanger structure size.The results show that the intermediate-stage bleed air and fan duct heat sink are more suitable when the Mach number is less than 2,but the ram air bleed is highly suitable for flight missions at a high Mach number.Especially at Mach 3.4-4.4,the ram air bleed mode can respond to the cooling and power demands with a simple architecture.

A NEW DAMAGE MECHANICS BASED APPROACH TO FATIGUE LIFE PREDICTION AND ITS ENGINEERING APPLICATION

An approach based on continuum damage mechanics to fatigue life prediction for structures is proposed. A new fatigue damage evolution equation is developed, in which the pa- rameters are obtained in a simple way with reference to the experimental results of fatigue tests on standard specimens. With the utilization of APDL language on the ANSYS platform, a finite element implementation is presented to perform coupling operation on damage evolution of mate- rial and stress redistribution. The fatigue lives of some notched specimens and a Pitch-change-link are predicted by using the above approach. The calculated results are validated with experimental data.

Tension-Torsion High-Cycle Fatigue Life Prediction of 2A12-T4 Aluminium Alloy by Considering the Anisotropic Damage:Model, Parameter Identification, and Numerical Implementation

To consider the anisotropic damage in fatigue, an improved boom-panel model is presented to simulate a representative volume element (RVE) in the framework of continuum damage mechanics. The anisotropic damage state of the RVE is described by the continuity extents of booms and panels, whose damage evolutions are assumed to be isotropic. The numerical implementation is proposed on the basis of damage mechanics and the finite element method. Finally, the approach is applied to the fatigue life prediction of 2A12-T4 aluminium alloy specimen under cyclic loading of tension-torsion. The results indicate a good agreement with the experimental data.

Experimental method for and theoretical research on defect tolerance of fxed plate based on damage mechanics

An experimental method and a theoretical analysis based on continuum damage mechan- ics are applied for the defects tolerance of fixed plate. The defects type studied in this article is scratch, which is considered a typical defect on fixed plate according to the engineering practice. The general approach to the defects tolerance analysis of scratched fixed plate is presented. The method of fatigue life prediction for standard notched specimens has been established on the basis of continuum damage mechanics. For the purpose of obtaining the influence law of fatigue life in consequence of scratches, fatigue experiments of standard notched specimens and scratched specimens have been done. Evalu- ation of the fatigue life of scratched fixed plate has been carried out. And the value of scratch defects permissible to the condition of safety service life has been worked out. According to the results of the- oretical calculations, the fatigue experiment of scratched fixed plate has been performed. The outcome shows that the theoretical prediction tallies with the experimental results.

Application analysis of efficient heat dissipation of electronic equipment based on flexible nanocomposites

The efficient heat dissipation of electronic equipment is very important,its heat dissipation performance directly determines the life of the equipment itself.A hand-held electronic communications equipment,when used in surface temperature is exorbitant,need to heat dissipation equipment efficiently,to ensure that the use of comfort in the handheld.In accordance with this requirement,this article presents a flexible composite material based on nano-efficient cooling methods that can keep the layout,through the improvement of internal thermal path,it can achieve the effective heat dissipation.The network thermal resistance method is used to analyze the heat transfer in the equipment,and the thermal analysis of the local thermal resistance is carried out.At the same time,through the modeling of electronic equipment and the analysis of finite elements,the temperature drop of the equipment after improvement is accurately judged.Finally,the device experimental performance comparison before and after the optimization of the standby mode and working mode is verified.The results show that the optimized equipment heat source temperature can be reduced by up to 8.5℃,the surface temperature of the equipment can be reduced by about 5℃~7℃,and the final control equipment in the steady standby state of the temperature of about 39±0.5℃,to ensure the comfort of use,and also improved the service life of the equipment.The efficient thermal design of electronic equipment based on flexible nanocomposites can provide a convenient and reliable cooling solution for high-heat flow density devices.

Study on interference suppression based on joint fractional Fourier domain and time domain

An interference suppression algorithm is proposed to meet challenges of the traditional technique in dealing with the linear frequency modulation(LFM) interference,such as high loss of signal-to-noise ratio(SNR),the output signal-to-interfer-ence-plus-noise ratio(SINR) sensitive to input interference-to-signal ratio(ISR) that results in an unstable synchronization,and the spectrum leakage serious in strong ISR situation.This approach firstly makes use of the windowed and lapped technique to the fractional Fourier transform(FRFT) to enhance the ISR improvement and lower the SNR loss.Then by weakening the interference and a secondary threshold process,interference energy can be suppressed as much as possible and the output SINR is less sensitive to the ISR.Finally,a joint fractional Fourier domain and time domain technique is proposed to overcome the residual interference energy caused by the strong interference or the discontinuous-phase interference.Theoretical analysis and simulation results show that the proposed algorithm can achieve better performance than the conventional methods in suppressing both the multi period LFM interference and the multi chirp-rate LFM interference,especially in the strong interference environment.

Non-fragile switched H_∞ control for morphing aircraft with asynchronous switching

This paper deals with the problem of non-fragile linear parameter-varying（LPV） H_∞ control for morphing aircraft with asynchronous switching.The switched LPV model of morphing aircraft is established by Jacobian linearization approach according to the nonlinear model.The data missing is taken into account in the link from sensors to controllers and the link from controllers to actuators,which satisfies Bernoulli distribution.The non-fragile switched LPV controllers are constructed with consideration of the uncertainties of controllers and asynchronous switching phenomenon.The parameter-dependent Lyapunov functional method and mode-dependent average dwell time（MDADT） method are combined to guarantee the stability and prescribed performance of the system.The sufficient conditions on the solvability of the problem are derived in the form of linear matrix inequalities（LMI）.In order to achieve higher efficiency of the designing process,an algorithm is applied to divide the whole set into subsets automatically.Simulation results are provided to verify the effectiveness and superiority of the method in the paper.