Search Results

Abstract The ground vibration test (GVT) is an important phase in a new aircraft development program, or the structural modification of a certified aircraft, to experimentally determine the structural vibrational modes of the aircraft and their modal parameters. These modal parameters are used to validate and correlate the dynamic finite element model of the aircraft to predict potential structural instabilities (such as flutter), assessing the significance of modifications to research vehicles by comparing the modal data before and after the modification and helping to resolve in-flight anomalies. Due to the high cost and the extensive preparations of such tests, a new method of vibration testing called the taxi vibration test (TVT) rooted in operational modal analysis (OMA) was recently proposed and investigated as an alternative method to conventional GVT.

Abstract This research was initiated with the goal of developing a significantly stronger aircraft transparency design that would reduce transparency failures from bird strikes. The objective of this research is to demonstrate the fact that incorporating high-strength tempered glass into cockpit window constructions for commercial aircraft can produce enhanced safety protection from bird strikes and weight savings. Thermal glass tempering technology was developed that advances the state of the art for high-strength tempered glass, producing 28 to 36% higher tempered strength. As part of this research, glass probability of failure prediction methodology was introduced for determining the performance of transparencies from simulated bird impact loading. Data used in the failure calculation include the total performance strength of highly tempered glass derived from the basic strength of the glass, the temper level, the time duration of the load, and the area under load.

Abstract In the given work the design and stress–strain calculation of housing parts of large machines during operation are considered. At the same time, both classical electromagnetic forces and technological operations necessary for mechanical processing and assembly of such objects as well as transportation processes are taken into account for the first time. The task of analyzing of the stress–strain state of the framework was solved in the three-dimensional setting using the finite element method by the SolidWorks software complex. The three-dimensional analysis of the stress–strain state of the structure for technological operations, namely tilting, lifting, and moving the large DC machines frame without poles and with poles, showed that the values of mechanical stresses that arise in the connections of the frame exceed the permissible limits, resulting in significant deformation of the structure.

Abstract For spacecraft with high power consumption, it is reasonable to build the thermal control system based on a two-phase mechanically pumped loop. The heat-controlled accumulator is a key element of the two-phase mechanically pumped loop, which allows for the control of pressure in the loop and maintains the required level of coolant boiling temperature or cavitation margin at the pump inlet. There can be two critical modes of loop operation where the ability to control pressure will be lost. The first critical mode occurs when the accumulator fills with liquid at high heat loads. The second critical mode occurs when the accumulator is at low heat loads and partial loss of coolant, for example, due to the leak caused by micrometeorite breakdown. Both modes are caused by insufficient accumulator volume or working fluid charge.

Abstract This work describes an investigation of measurement techniques for the indicated mean effective pressure (IMEP) on a 55 cc single-cylinder, 4.4 kW, two-stroke, spark ignition (SI) engine intended for use on Group 1 and Group 2 remotely piloted aircraft (RPAs). Three different sensors were used: two piezoelectric pressure transducers (one flush mount and one measuring spark plug) for measuring in-cylinder pressure and one capacitive sensor for determining the top dead center (TDC) position of the piston. The effort consisted of three objectives: to investigate the merits of a flush mount pressure transducer compared to a pressure transducer integrated into the spark plug, to perform a parametric analysis to characterize the effect of the variability in the engine test bench controls on the IMEP, and to determine the thermodynamic loss angle for the engine.

Abstract Previous artificial lightning strike direct effect research has examined a broad range of specimen design parameters. No works have studied how such specimen design parameters and electrical boundary conditions impact the dissipation of electric current flow through individual plies. This article assesses the influence of carbon fiber composite specimen design parameters (design parameters = specimen size, shape, and stacking sequence) and electrical boundary conditions on the dissipation of current and the spread of damage resulting from Joule heating. Thermal-electric finite element (FE) modelling is used and laboratory scale (<1 m long) and aircraft scale (>1 m long) models are generated in which laminated ply current dissipation is predicted, considering a fixed artificial lightning current waveform. The simulation results establish a positive correlation between the current exiting the specimen from a given ply and the amount of thermal damage in that ply.

Abstract In view of the structural accidental events in the ongoing airworthiness stage of civil aircraft, it is necessary to conduct a risk assessment to ensure that the risk level is within an acceptable range. However, the existing models of risk assessment have not effectively dealt with the risk of accidental structural damage due to random failure. This article focuses on probabilistic risk assessment using the Transport Airplane Risk Assessment Methodology (TARAM) of accidental structural damage of civil aircraft. Based on the TARAM and probability reliability integral, a refined failure frequency probability calculation model is established to elaborate on composite structure failure frequency. A case study is analyzed for the outer wing plane of an aircraft having impact damage of composite materials. Finally, results of the risk assessment without correction and risk assessment with correction are presented for detailed visual inspection and general visual inspection.

Abstract For Chinese low-cost airlines network, this article employed two indicators: network topology indexes, to evaluate the current status of the network, and economic performance indexes, to analyze the development potential of the network. From the topology indexes, each airline has its own different characteristics, advantages, and disadvantages, while from economic and socio-demographic indexes, Spring Airlines, West Air, and China United Airlines have obvious advantages and other airlines have distinct shortcomings. Then, the TOPSIS (Technique for Order Preference by Similarity to an Ideal Solution) method was used to comprehensively evaluate Chinese low-cost airlines. The results show that the ranking in terms of network is: Spring Airlines, Western Airlines, China United Airlines, Lucky Air, 9 Air, Chengdu Airlines, and also show Chinese low-cost airlines network is in initial and growth stage.

Abstract The electric propulsion system plays an important role during the operation of a satellite, i.e., maintaining the position of the north-south poles, adjusting the attitude, and transferring the orbit, where vector adjustment device is a key part of the system. We developed a new large-angle device to transfer thruster orbital, which has three driving motors and the failure of a single motor cannot affect the operation. The posture angle and linear pair displacement of this mechanism are simulated using forward and inverse kinematics solutions. In the following, the actual adjustment angle was measured with a three-coordinates measuring instrument and a gradiometer to compare with the simulated values. This design has been successfully applied in China’s asteroid exploration mission.

Abstract This article reports a reduced-order modeling framework of bladed disks on a rotating shaft to simulate the vibration signature of faults in different components, aiming toward simulated data-driven machine learning. We have employed lumped and one-dimensional analytical models of the subcomponents for better insight into the complex dynamic response. The framework addresses some of the challenges encountered in analyzing and optimizing fault detection and identification schemes for health monitoring of aeroengines and other rotating machinery. We model the bladed disks and shafts by combining lumped elements and one-dimensional finite elements, leading to a coupled system. The simulation results are in good agreement with previously published data. We model and analyze the cracks in a blade with their effective reduced stiffness approximation.

Abstract With the growing number of cross-sea flights, the occurrence of maritime-related accidents, which have a high fatality rate, has become increasingly critical. This study is aimed at highlighting the causes of maritime-related accidents and identifying the risk factors that led to fatal crashes in the period 2009-2019. A total of 207 maritime-related accidents, the final reports of which are available in the online database of the National Transportation Safety Board, were considered. The accident cause distribution was obtained from the final reports. A two-step approach, involving uni-variable and multi-variable analysis logistic regression, was implemented to select the significant risk factors from 27 parameters. Results showed that the four main causes of maritime-related accidents were personnel issues (69.6%), aircraft-related aspects (60.4%), environmental issues (36.7%), and organizational issues (3.9%).

Abstract Laminated composites are extensively used in the aerospace industry. However, structures made from laminated composites are highly susceptible to delamination failures. It is therefore imperative to consider a structure tolerance to delamination during design and operation. Hybrid composites with laminas containing different fibers were used earlier in laminates to achieve certain benefits in strength, stiffness, and buckling. However, the concept of mixing laminas with different fibers was not explored by researchers to enhance delamination tolerance levels. This article examines the above aspect of hybridization by employing machine learning algorithms and proposes a reliable method of analysis to study delamination, which is crucial to ensure the safety of airframe composite panels.

Abstract This article presents a numerical solution to the problem of delamination in a separable Metal Composite High-Pressure Vessel (MC HPV). This problem is associated with local buckling of the inner metal shell (liner) surrounded by an outer rigid composite shell. A geometrically and physically nonlinear MC HPV deformation model is constructed considering the three-dimensional stress-strain state, real-time mode, and technological deviations inherent in real vessel designs. The model combines the deformation of the vessel end domes and the cylindrical part. A unilateral constraint is believed to exist on the interface between the liner and the composite shell, allowing the liner to delaminate from the latter when bending. Calculations are performed using the finite element method in the LS-DYNA software package in a dynamic formulation. The vessel is divided into solid finite elements such as TSHELL and SOLID.

Abstract The general English speech recognition is based on the techniques of n-grams where the words before and after are predicted and the utterance prediction is produced. At the same time, having a significantly lengthier n-gram has its own impact in training and the accuracy. Shorter n-grams require the utterances to be split and predicted than using the complete utterance. This article discusses specific techniques to address the specific problems in Air Traffic Speech, which is a medium length utterance domain. Moving from the adapted language models (LMs) to rescored LM, a combined technique of syntax analysis along with a deep learning model is proposed, which improves the overall accuracy. It is explained that this technique can help to adapt the proposed method for different contexts within the same domain and can be successful.

Abstract To ensure the ongoing safety of aircraft, it is necessary to conduct risk assessment for those events that occurred during routine operations. Consequently, the corresponding corrective actions should be accomplished within the compliance time if the event was ascertained to be unsafe. However, the existing models of risk assessment and determination of the correction time limit have not dealt with the time-varying failure rate of components. Based on the Gunstone method, this article considers the event risks of the fleet at different correction time limits, combined with the Monte Carlo method to establish a model of risk assessment and determination of the correction time limit. Based on the event risk level and the risk per flight hour, the risks of the event under the condition of no corrective actions and corrective actions with different time limits were assessed, respectively.

Abstract Loose particles inside the additional pipe of a rocket engine are an important factor that causes propulsion system failure. For loose particles inside the additional pipe, it is necessary not only to determine whether they exist or not but also to locate them for subsequent processing. Due to the complex structure of the additional pipe, the medium used for sound wave transmission is nonuniformity, and the speed of sound is anisotropic. So it is difficult to determine the locations of loose particles by using the traditional time difference localization method. Aiming at this problem, this article proposed a localization method of loose particles based on Chaos Theory and Particle Swarm Optimization-Back-Propagation Neural Network (PSO BP Neural Network). First, chaotic characteristics of collision signals generated by loose particles are studied.

Abstract Water droplet size variation has been established in the literature as an important variable that influences the behavior and characteristics of water in fuel emulsion. However, with the growing demand for sustainable aviation fuels (SAF), no data is available that shows how these fuels will affect the size of dispersed water droplets and their frequency distribution. To address this lack of knowledge, this study explores and presents experimental results on the characterization of dispersed water droplets in alternative fuels and Jet A-1 fuel under dynamic conditions. The alternative fuels comprised of two fully synthetic fuels, two fuels synthesized from bio-derived materials, and one bio-derived fuel. The data and statistics presented reveal that water droplet frequency and size distribution are sensitive to changes in fuel composition.

Abstract The increase in worldwide awareness of environmental issues has necessitated the air transport industry to drastically reduce carbon dioxide emissions. To meet this goal, one solution is the electrification of aircraft propulsion systems. In particular, single-aisle aircraft with partial turboelectric propulsion with approximately 150 passenger seats in the 2030s are the focus. To develop a single-aisle aircraft with partial turboelectric propulsion, an air-cooled interior permanent magnet (IPM) motor with an output of 2 MW is desired. In this article, mathematical system equations that describe heat transfer inside the target air-cooled IPM motor are formulated, and their mathematical analytical solutions are obtained.

Abstract The purpose of the present article is to develop a Finite Element Method (FEM) for steady potential flows over a range of bluff bodies like cylinders to streamlined profiles such as airfoils. In contrast to conventional panel methods, Laplace’s equation describing the potential flow is solved here for the velocity-potential function using the Galerkin method. A brief discussion on edge singularities in potential flows has also been presented using a half-cylinder case study. A novel method for implementing Kutta condition over airfoils to have lifting flow is explained. Compared with other Finite Difference Methods (FDM) and Finite Volume Methods (FVM), the present methodology has proven to be computationally faster for airfoils with both a finite angle trailing edge and cusped trailing edge. The results obtained have demonstrated excellent accuracy compared to analytical and panel methods.

Abstract In this article, we study the problem of axial and radial coupling rub-impact faults based on a full degree-of-freedom rotor system, which has not been extensively discussed in previous literature. An improved magnetorheological (MR) damper configuration is proposed in order to study its effect on the inhibition of coupling rub-impact faults. The Lagrange method is used to establish the finite element model of a rotor-bearing system under radial, axial, and radial-axial coupling rub-impact. At the same time, based on the bilinear constitutive equation of the MR fluid, the dynamic model of the MR damper is established. Through using the Newmark-β method to present a numerical solution, the nonlinear dynamic behaviors of the rotor system under different rub-impact faults are studied; also, the influence of the MR damper on the rub-impact fault dynamic behavior is investigated.