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It is an indispensable part of airworthiness certification to evaluate the fuel tank flammability exposure time for transport aircraft. There are many factors and complex coupling relationships affecting the fuel tank flammability exposure time. The current work not only lacks a comprehensive analysis of these factors but also lacks the significance of each factor, the interaction relationship and the prediction method of flammability exposure time. The lack of research in these aspects seriously restricts the smooth development of the airworthiness forensics work of domestic large aircraft. This paper aims to clarify the internal relationship between user input parameters and predict the flammability exposure time of fuel tanks for transport aircraft.

Based on the requirements of airworthiness certification for large aircraft, an in-depth analysis of the Monte Carlo flammability evaluation source procedures specified in China Civil Aviation Regulation/FAR25 airworthiness regulations was made, the internal relationship between factors affecting the fuel tank flammability exposure time was clarified and the significant effects and interactions of input parameters in the Monte Carlo evaluation model were studied using the response surface method. And the BP artificial neural network training samples with high significance factors were used to establish the prediction model of flammability exposure time.

The input parameters in the Monte Carlo program directly or indirectly affect the fuel tank flammability exposure time by means of the influence on the flammability limit or fuel temperature. Among the factors affecting flammability exposure time, the cruising Mach number, balance temperature difference and maximum range are the most significant, and they are all positively correlated with flammability exposure time. Although there are interactions among all factors, the degree of influence on flammability exposure time is not the same. The interaction between maximum range and equilibrium temperature difference is more significant than other factors. The prediction model of flammability exposure time based on multifactor interaction and BP neural network has good accuracy and can be applied to the prediction of fuel tank flammability exposure time.

The flammability exposure time prediction model was established based on multifactor interaction and BP neural network. The limited test results were combined with intelligent algorithm to achieve rapid prediction, which saved the test cost and time.

The assessment of fuel tank flammability exposure time for transport aircraft is one of the indispensable links in the airworthiness certification process. According to published literature, many factors can affect the flammability exposure time, while systematic analysis and calculations addressing these factors are in shortage.

Based on the requirements for airworthiness certification of domestic large aircraft, the fuel tank flammability exposure time of transport aircraft is calculated with the Monte Carlo evaluation model specified by Federal Aviation Administration. Meanwhile, the influence of each input parameter on the flammability exposure time is obtained by taking user input parameters in the model as independent variables and freezing other factors at the same time. The significance degree of the influence of each factor is discussed by the orthogonal test method. Subsequently, the interaction between the input parameters is studied by response surface method, and a multiple linear regression method is used to establish the functional relationship between the flammability exposure time and the influence parameters.

Research studies show that among the many factors that affect the flammability exposure time, the cruising Mach number, the equilibrium temperature difference and the maximum range are more significant and much attention should be paid to in the airworthiness certification; although there are interactions among various factors, they have different influence on the flammability exposure time, among which the interactions between maximum range and equilibrium temperature difference are the most significant compared with others; established by applying multiple linear regression equation and based on the test data of response surface method, the functional relationship between flammability exposure time and influence parameters is of sufficient reliability and can be used for preliminary prediction of fuel tank flammability exposure time for transport aircraft.

The research achievements of this paper can provide much useful reference for the certification of domestic large aircraft.

Determining the variation law of the oxygen concentration in the ullage space of the fuel tank is the key to the design of the inert system. Among various factors affecting the oxygen concentration in the ullage space of the fuel tank, the temperature difference between day and night shows particular importance while relevant analysis and calculation are scarce.

This study establishes a theoretical simulation model of the central wing fuel tank of an aircraft according to the relevant provisions of day-night temperature variation in FAR25 airworthiness regulations, verifies the model with the existing experimental data and discusses the corresponding relationship between the oxygen concentration in the ullage space of the fuel tank and the day-night temperature difference. The influence of day and night temperature difference, fuel type, fuel load rate, initial oxygen concentration, dissolved oxygen evolution and other factors on the oxygen concentration in the ullage space of the fuel tank were analyzed, and the limit of initial oxygen concentration of the fuel tank before the shutdown at night meeting the requirements of the airworthiness provisions was proposed.

The results show that the temperature difference between day and night, fuel load rate, initial oxygen concentration and other factors have different effects on the oxygen concentration in the ullage space of fuel tank. The initial oxygen concentration limit before shutdown shall be 2% below the 12% oxygen concentration stipulated by FAA.

The research results in this paper will be of good reference value to the design of the inert system and the calculation of the flammability exposure evaluation time. This paper aims to be good reference of the design of the inert system and the calculation of the flammability exposure evaluation time.

The research results of this paper can provide practical guidance for the current civil airworthiness certification work.

This study aims to seek a new economic and environmental protection fuel tank inerting method.

The principle that serves as the basis for the cooling inerting process is described, the workflow of the cooling inerting system is designed, the mathematical model of the cooling inerting system is established, and the important performance changes of cooling inerting in the flight package line and the influence of key parameters on it are simulated by using Modelica software.

The results show that the cooling inerting system can be turned on to quickly reduce the vapour concentration in the gas phase in the fuel space and reduce the temperature below the flammability limit. Within a certain range of pumping flow, the inerting effect is more obvious when the pumping flow is larger. Simply running the cooling inerting system on the ground can remain the tank in an inert state throughout the flight envelope.

However, cooling inerting is suitable for models with fewer internal heat sources. An excessive number of internal heat sources will lead to inerting failure.

This study provides theoretical support for the feasibility of cooling inerting. Cooling inerting does not require engine air, and the cooling is mainly accomplished with air, which places a small load on the cooling system and has a much lower cost than the airborne hollow fibre film inerting technology widely used at present. It is a promising new inerting technology.

The purpose of this paper is to determine thermal behaviour of wing fuel tank wall via heating by external heat sources.

A 3D finite element model of the structure has been created that takes into account convection, conduction and radiation effects. In addition, a 3D finite volume model of the air inside the leading edge is created. Through a computational fluid dynamics approach, the flow of air and thermal behaviour of the air is modelled. The structure and fluid model are coupled via a co-simulation engine to exchange heat flux and temperature. Different ventilation cases of the leading edge and their impact on the thermal behaviour of the tank wall (corresponding to the front spar) are investigated.

Results of 3D analysis illustrate good insight into the thermal behaviour of the tank wall. Furthermore, if regions exist in the leading edge that differs significantly from the overall thermal picture of the leading edge, these are visible in a 3D analysis. Finally, the models can be used to support a flammability analysis assessment.

Provided that the bleed pipe is located far enough from the spar and covered with sufficient thermal heat isolation, the composite leading edge structure will not reach extremely high temperatures.

These detailed simulations provide accurate results which can be used as reliable input for the fuel tank flammability analysis.

To reduce the flammability exposure assessment time and meet the requirements of airworthiness regulations of transport aircraft, inerting system has become the standard configuration of modern civil aircraft. Therefore, airworthiness regulations put forward definite quantitative index requirements for the safety of inerting system, and to obtain the quantitative data of the safety of inerting system, it is necessary to solve the calculation method. As one of the quantitative/qualitative evaluation techniques for system safety, fault tree analysis is recognized by international airworthiness organizations and national airworthiness certification agencies. When fault tree analysis technology is applied to quantitative analysis of the safety of inerted system, there are still some problems, such as heavy margin of constructing fault tree, great difficulty, high requirement for analysts and poor accuracy of solving when there are too many minimum cut sets. However, based on tens of thousands of flight simulation tests, Monte Carlo random number generation method can solve this problem.

In this paper, the fault tree of airborne inerting system is established, and the top event is airborne inerting system losing air separation function. Monte Carlo method based on random number generation is used to carry out system security analysis. The reliability of this method is verified.

The static fault tree analysis method based on Monte Carlo random number generation can not only solve the problem of quantitative analysis of inerting system, but can also avoid the defects of complicated solution and inaccurate solution caused by the large number of minimum cut sets, and its calculation results have good reliability.

The research results of this paper can be used as supporting evidence for airworthiness compliance of airborne inerting system.

The research results of this paper can provide practical guidance for the current civil airworthiness certification work.

The rest-to-rest movements for a spacecraft, such as attitude adjustment and orbital manoeuver, are likely to excite residual vibration of flexible appendages, which may affect the attitude accuracy and even result in severe structural damage. The purpose of this paper is to present an approach to attenuating the vibration of flexible solar array by using reaction flywheel.

The reaction flywheel installed on solar array served as an actuator to provide reaction torque to a structure according to a designed feedback control law. This torque can be considered as an artificial damping. Experiment on a scale model of the solar array is first performed to verify the effectiveness of this method. Numerical simulation on finite element model of a full-scale solar array is subsequently carried out to confirm the validity of this method for practical engineering application.

The vibration suppression effect on the structure using a reaction flywheel is deduced by theoretical analysis. Results from both experiment and numerical simulation reveal that the efficiency of vibration attenuation is promoted.

Improvements on control law are left for further study. Additionally, only the first-order bending vibration of the flexible solar array is attenuated, and further study is required for other types of vibration suppression.

An effective method is proposed for spacecraft designers to actively suppress the vibration of the flexible solar array.

A novel active vibration reduction scheme is proposed using a reaction flywheel to suppress vibration of the flexible solar array. This paper fulfils a source of theoretical analysis and experimental studies for vibration reduction measure design and provides practical help for the spacecraft designers.

The objective of this study is to model the propagating front in the interaction of gases in an aircraft fuel tank. To this end, we introduce a nonlinear parabolic operator, for which solutions are shown to be regular.

The authors provide an analytical expression for the propagating front, that shifts any combination of oxygen and nitrogen, in the tank airspace, into a safe condition to avoid potential explosions. The analytical exercise is validated with a real flight.

According to the flight test data, the safe condition, of maximum 7% of oxygen, is given for a time t = 45.2 min since the beginning of the flight, while according to our analysis, such a safe level is obtained for t = 41.42 min. For other safe levels of oxygen, the error between the analytical assessment and the flight data was observed to be below 10%.

The interaction of gases in a fuel tank has been little explored in the literature. Our value consists of introducing a set of nonlinear partial differential equations to increase the accuracy in modeling the interaction of gasses, which has been typically done via algebraic equations.

The purpose of this study is to improve the performance of hollow fiber membrane and improve the separation efficiency.

By establishing a mathematical model of hollow fiber membrane gas separation, the influences of parameters such as pressure difference between the inside and outside of the filament, initial oxygen concentration of intake air, intake air flow rate and back pressure outside the filament on the polarization coefficient were analyzed, so as to explore the degree of influence of operating parameters on the concentration polarization, and put forward a technical scheme to reduce the concentration polarization.

Factors such as pressure difference between the inside and outside of the filament, initial oxygen concentration of intake air, intake air flow rate and back pressure outside the filament have a certain effect on the polarization coefficient. Among them, the polarization coefficient is positively correlated with pressure difference inside and outside the filament, initial oxygen concentration of intake air and back pressure outside the filament, and is negatively correlated with intake air flow.

Negative pressure suction on the permeation side can be used to increase the membrane permeation flow rate and reduce the concentration polarization.

The influence of concentration polarization on membrane performance is reduced by controlling various factors.