Hasil untuk "Motor vehicles. Aeronautics. Astronautics"

Wang Wendi, Chen Xin, Zhang Jing

Aiming at the problems of large loss of RF coaxial cable used in traditional RF communication of airborne weapons, large frequency bandwidth of RF signal sent inside weapons, and limited allocation of resources inside weapons, a four-channel WDM optical RF signal transmission system based on carrier suppression modulation is designed by combining optical RF technology in microwave photonics and wavelength division multiplexing technology. Firstly, the transmission link of the 2-fold frequency RF signal normally generated by carrier suppression modulation is simulated. Then NRZ code is used to simulate the digital signal and load the signal generation rate at 10 Gbit/s to the optical carrier that modulates different frequency RF signals for transmission. After recovery by the photodetector, the bit error rate of the system is measured to determine the communication quality. Analyze the signal transmission of RoF system. Finally, a four-channel optical radio frequency transmission system is designed. The feasibility of the system is verified by identifying the signal-to-noise ratio of different radio frequency signals transmitted by each channel at the signal transmission rate of 10 Gbit/s and the bit error rate of modulated digital signals.

Zhihao Zhang, Jiaxi Zhao, Tingting Liu et al.

To improve the accuracy of the wind tunnel test, relying on the high-pressure gas source of the China Aerodynamic Research and Development Center, a secondary flow standard facility based on a sonic nozzle array was developed, with a pressure range of (1~6) MPa and a flow range of (0.12~5.55) kg/s. Currently, most facilities use the average temperature measured by the temperature array to represent the upstream temperature of the sonic nozzle array. However, the small flow calibration test results showed that the maximum temperature difference upstream of the standard sonic nozzle array was 1.97 K, and the temperature field upstream of the sonic nozzle array showed non-uniformity, so the above method cannot accurately obtain the upstream temperature. To solve this problem, each nozzle used in the standard sonic nozzle array was accurately measured by temperature sensors. The uncertainty of the facility and the discharge coefficient of the calibrated nozzle between the two methods were compared. The results showed that compared with the discharge coefficient obtained using the temperature sensor array of 0.9902, the accurate measurement of 0.9904 was closer to the National Institute of Metrology, China (NIM) traceable result of 0.9907, and the relative uncertainty of the facility was reduced from 0.124% (<i>k</i> = 2) to 0.120% (<i>k</i> = 2).

mohamad ali amirifar, alireza rajabi, nooredin ghadiri masoom et al.

In this study, the pulse mode performance of a monopropellant hydrazine thruster has been studied. For this purpose, a laboratory sample of a monopropellant hydrazine thruster under atmospheric pressure was fabricated and tested. The catalyst of this thruster is synthesized natively. The pulse mode performance of this monopropellant hydrazine thruster has been evaluated experimentally and the results have been presented. The results of this study show that the monopropellant hydrazine thruster made with a synthesized catalyst produces reproducible impulses for pulses less than 10 milliseconds wide. The minimum impulse of this monopropellant hydrazine thruster is measured at 32 mNS. Also, the standard deviation of the impulse is less than 6% for 100 pulses. The thruster response time is also very reproducible. The results of this study showed that the centroid of the thruster changes linearly with the pulse width. However, the transient behavior of the chamber pressure is relatively slow, leading to a large centroid

Bin Li, Zixuan Hang, Ting Dai

Corrugated core sandwich structures have great potential in the application to thermal protection system of aerospace vehicles. However, the traditional layout of web plates could inevitably lead to thermal short effects and high risk of buckling failure of the integrated thermal protection system (ITPS). In this paper, a novel double-layer ITPS is proposed by splitting and reorganizing a classical corrugated sandwich structure without additional introducing of weight. Distribution types of parallel, symmetric, and orthogonal of the double layers are designed and studied in detail. Basic theory of the thermomechanical problem as well as finite element simulation is carried out to study the responses of the ITPS. Numerical results show that the orthogonal type has more excellent yield resistance at high temperature and large temperature gradient than the others, while the parallel type has a relatively stronger buckling resistance. In addition, the structural stiffness variation caused by temperature dependencies of material parameters is greater than that caused by thermal stress, which shows the significance of consideration of temperature-dependent material properties in structure vibration analysis.

Qingcai Zhang, Qinqin Wang, Xiaoming Tan et al.

A rim seal is often used to prevent the ingress of high-temperature gas into the turbine disk cavity and protect the turbine disk from damage. Based on the overlapping rim seal (Seal-A), this paper proposes two more composite sealing structures (Seal-B and Seal-C) to show the effects of a deep cavity in the static disk and a modified platform in the rotating disk. Three-dimensional unsteady Reynolds-averaged Navier–Stokes equations and the shear stress transfer (SST) k-ω turbulence model were used to reveal the flow field characteristics and the sealing efficiency. The results show that the rotor–stator interaction plays a dominant role in the sealing outlet pressure, and the sealing efficiency in the outflow area obtained by the transient calculation is lower than that of the steady-state calculation. The rise in the cooling air flow enhances the reverse vortex in the sealing cavity, and the disk cavity’s sealing efficiency is also improved. When the cooling air flow ratio increases from 0.6% to 1.8%, the sealing efficiency at the high radius increases by 30%. The shape of the deep cavity produces a new return vortex at the lower part of the sealing cavity, which improves the sealing efficiency. The shark nose platform in Seal-C aggravates the gas ingress at the sealing outlet but improves the sealing efficiency at the sealing cavity. In general, compared with Seal-A, the sealing efficiency of Seal-B and Seal-C is increased by 13.5% and 10%, respectively, at a cooling air flow ratio of 0.6%.

Bing Hua, Xiaosong Wei, Yunhua Wu et al.

The velocity and acceleration of geostationary transfer orbit (GTO) satellites change dramatically and periodically, and the operating area extends from hundreds of kilometers to 36,000 km above the Earth’s surface. This leads to the limitation of navigation methods of GTO satellites, the complexity of perturbation components and the increase of sensor measurement noise. Therefore, in this paper, a celestial navigation system/Beidou navigation system (CNS/BDS) integrated navigation method based on the adaptive spherical simplex unscented transformation federated Kalman filter (ASSUT-FF) algorithm is designed for GTO satellite high-precision autonomous navigation, considering the integrated navigation method and filtering algorithm. A Beidou observation model based on the relative pseudorange/pseudorange rate is established. Even when the GTO satellite moves to the high orbit region, it can still use BDS navigation information to determine the orbit. In addition, the designed adaptive algorithm can still ensure the filter stability in a complex space environment. The CNS/BDS integrated navigation method based on the ASSUT-FF algorithm proposed in this paper can realize continuous and high-precision autonomous navigation of GTO satellites. The simulation results show that the orbit determination accuracy of the proposed navigation method is 96.23% and 84.06% higher than that of the single celestial navigation method and the traditional Beidou geometric positioning correction celestial navigation method, respectively. The performance test results of the adaptive algorithm also show that the ASUT-FF algorithm has good robustness.

Philippe Jardin, Ioannis Moisidis, Kürsat Kartal et al.

Driving style classification does not only depend on objective measures such as vehicle speed or acceleration, but is also highly subjective as drivers come with their own definition. From our perspective, the successful implementation of driving style classification in real-world applications requires an adaptive approach that is tuned to each driver individually. Within this work, we propose a transfer learning framework for driving style classification in which we use a previously developed rule-based algorithm for the initialization of the neural network weights and train on limited data. Therefore, we applied various state-of-the-art machine learning methods to ensure robust training. First, we performed heuristic-based feature engineering to enhance generalized feature building in the first layer. We then calibrated our network to be able to use its output as a probabilistic metric and to only give predictions above a predefined neural network confidence. To increase the robustness of the transfer learning in early increments, we used a synthetic oversampling technique. We then performed a holistic hyperparameter optimization in the form of a random grid search, which incorporated the entire learning framework from pretraining to incremental adaption. The final algorithm was then evaluated based on the data of predefined synthetic drivers. Our results showed that, by integrating these various methods, high system-level performance and robustness were met with as little as three new training and validation data samples in each increment.

Aniekan Ikpe

In this study, CAD model was developed for reciprocating piston of an IC engine using SOLIDWORKS (2017 version) modelling tool and was simulated at a speed of 600-3000 RPM. Reaction forces and linear velocity at different combustion time, thermal stresses, equivalent strains, resultant and displacement on the piston were determined. At an engine speed of 3000 RPM and 224NM torque, maximum displacement of 8.03x10-1mm, maximum equivalent strain of 2.152x10-2 and maximum thermal stress of 24.465N/mm^2. The maximum thermally induced stress value fell below the yield strength (460 N/mm^2) of the low alloy steel piston material, indicating that the material still has the capacity to accommodate stresses and deformations before its yield strength is exceeded. It was observed that the higher the engine speed, the higher the reaction forces and resultant displacements on the piston. The highest deformation value was recorded as 13,004.927 N/mm^2 which occurred at the point where the piston pin and one end of the connecting rod interlocks. Specific attention should be given to the selection of piston material and the intricate environment it operates, as it serves as the heart of a given IC engine.

Path planning is the key technology for UAV to achieve autonomous flight. Considering the shortcomings of path planning based on the conventional potential field method, this paper proposes an improved optimization algorithm based on the artificial potential field method and extends it to three-dimensional space to better achieve flight constrained 3D online path planning for UAVs. The algorithm is improved and optimized aiming at the three problems of goal nonreachable with obstacle nearby (GNWON), easy to fall into local minimum, and path oscillation in traditional artificial potential field method. First, an improved potential field function with relative distance is used to solve the GNWON, and an optimized repulsive potential field calculation method based on different obstacles or threat models is proposed to optimize the planned path. Secondly, in order to make the drone jump out of the local minimum trap, a method of setting heuristic sub-target points is proposed. For local path oscillation, a method using memory sum force was proposed to improve the oscillation. The simulation results show that the improved optimization algorithm in this paper effectively makes up for the shortcomings of the traditional artificial potential field method, and the designed 3D online path planning algorithm for the UAV is practical and feasible.

María del Pilar García-Chitiva

Los avances tecnológicos han permeado todas las formas de enseñanza y aprendizaje. Por lo tanto, la instrucción y la capacitación también forman parte de los estudios en los que se documenta el uso de los Entornos Virtuales de Aprendizaje (eva) para determinar el alcance de las tecnologías virtuales en todos los niveles de aprendizaje (desde el aprendizaje de un contenido de una materia en la educación superior hasta la construcción de un barco en la capacitación técnica y laboral). Este artículo tiene dos propósitos. El primero es analizar el estado de la investigación sobre procesos de instrucción mediados por herramientas virtuales. Para ello, se realiza un análisis bibliométrico de las publicaciones realizadas entre 1997 y el 2018, indexadas en la base de datos scopus. El segundo propósito es examinar los principales avances presentados en la literatura científica revisada para así determinar los desafíos que enfrentan estudios posteriores, principalmente en lo que respecta a procesos de Instrucción, Entrenamiento y Evaluación en el Puesto de Trabajo (ieept). Dentro de los hallazgos de esta revisión, se estableció que el incipiente proceso de investigación de la instrucción mediada por tecnología explica la falta de publicaciones sobre el tema indexadas en bases de datos internacionales. También se estableció que, mediante el empleo de las herramientas disponibles para los procesos de instrucción, como simuladores y software, se pueden adelantar procesos de investigación similares a los documentados en este artículo.

Selin Aradag, Kubra Asena Gelisli, Elcin Ceren Yaldir

Supersonic flow over cavities has been of interest since 1960s because cavities represent the bomb bays of aircraft. The flow is transient, turbulent, and complicated. Pressure fluctuations inside the cavity can impede successful weapon release. The objective of this study is to use active and passive control methods on supersonic cavity flow numerically to decrease or eliminate pressure oscillations. Jet blowing at several locations on the front and aft walls of the cavity configuration is used as an active control method. Several techniques are used for passive control including using a cover plate to separate the flow dynamics inside and outside of the cavity, trailing edge wall modifications, such as inclination of the trailing edge, and providing curvature to the trailing edge wall. The results of active and passive control techniques are compared with the baseline case in terms of pressure fluctuations, sound pressure levels at the leading edge, trailing edge walls, and cavity floor and in terms of formation of the flow structures and the results are presented. It is observed from the results that modification of the trailing edge wall is the most effective of the control methods tested leading to up to 40 dB reductions in cavity tones.

V. V. Savtseva

Philosophical meaning of the category "quality" is defined, the role of quality control in the evaluation of quality is justified, ontological, axiological, phenomenological aspects of quality control are characterized.

D. V. Tikhonov, V. N. Tikhonov

The article is devoted to an assessment of danger degree of a flight situation with the engine failure on the ascending maneuvers using natural- model approach and expert evaluation in the absence of the possibility of using a pilotage stand.

Michail Zhelamskij

This article highlights both theoretical and experimental experiences in the field of helmet-mounted cueing systems. The current state of these systems is described as optical and hybrid. The adventures of the positioning under local magnetic field are considered, and the directions for further improvement of magnetic technology are identified. A new method is proposed for the local magnetic field creation to increase update rate, to reduce the influence of the Earth’s magnetic field, and to reduce energy consumption of helmet-mounted cueing systems in relation to known prototypes. A mathematical model of positioning field is offered. The accuracy of the field mathematical description is studied for different shapes of windings. The transients are investigated in the source of positioning field and in the interior of the cockpit. In addition, a mathematical model of magnetic measurements is proposed, and the main sources of measurement and positioning errors are investigated. The calculation algorithm of the helmet’s coordinates is considered based on the results of magnetic measurements. The results of physical models research are given, and the operation of a sample in the full range of angles is shown. The trial mapping is conducted for the field created by the source with a ferromagnetic core. Positioning of the helmet’s movement on specified paths is performed, and the results make it possible to figure out the next generation of helmetmounted cueing systems with extended angles range, higher angular and linear accuracy, increased update rate (200 Hz),and minimized influence of Earth’s magnetic field.

E. A. Bolelov, Yu. M. Ermoshenko

The article considers the elaboration of the problem of optimal algorithm synthesis of complex signal processing of satellite GLONASS/GPS systems navigation relayed from the Board of the upper-air radiosonde and the output data upper-air radar to determine the spatial coordinates of upper-air radiosonde. The upper-air sounding is performed with the help of technical means of radio sounding system of atmosphere, including the upper-air radiosonde, manufactured in free flight, and ground supporting equipment, which includes devices for signal processing of upper-air radiosonde and preparation of the operational upper-air messages. The peculiarity of atmosphere radio sounding of domestic system is the measurement with method of radar slant range to upper-air radiosonde, the viewing angles of the antenna upper-air radar to determine azimuth and elevation of upper-air radiosonde. The disadvantage of the radar method of radiosonde support is the relatively low accuracy of determining the coordinates of the radiosonde and the possible disruption of automatic tracking in angular coordinates. Satellite navigation system based on the microwave sensors has clear advantages in terms of efficiency, size, mobility, and use on mobile objects, however, with significant drawbacks associated primarily with the geometric factor and the error propagation of the navigation signal. The article presents a mathematical model useful incoherent GLONASS/GPS signals, relayed by the upper-air radiosonde, and interference on the input receiver ground point for complex information processing, and mathematical models of output data in upper-air radars.

Alexandru DUMITRACHE, Florin FRUNZULICA, Horia DUMITRESCU et al.

The goal of this paper is to provide a numerical flow analysis based on RANS equations in two directions: the study of augmented high-lift system for a cross-section airfoil of a wing up to transonic regime and the circulation control implemented by tangentially blowing jet over a highly curved surface due to Coanda effect on a rotor blade for a wind turbine. This study were analyzed the performance, sensitivities and limitations of the circulation control method based on blowing jet for a fixed wing as well as for a rotating wing. Directions of future research are identified and discussed.

Joshua W. Batterson, E. Jacob

Ibrahim Abdulwehab A., Abidin Ezrann Zharif B. Zainal, Aziz Rashid A. et al.

A linear engine type with piston assembly that swings between two oppositely placed combustion chambers considered in this study. The study investigated the effect of injection timing on starting of the engine. The injection position varied at five different positions (17mm to 27mm) before the maximum switching limit of the engine reached. It was observed that advancing the injection position in free-piston engine slows down the compression stroke and increases the combustion duration. Furthermore, lower peak pressure and rate of heat release occurred at 17 mm, 20 mm, and 23 mm injection timing. Relatively stable operation of the engine was achieved at 25 mm.

Adam Bry

Édgar Leonardo Gómez Gómez, Jorge Eduardo Ortiz Triviño

En este artículo se analiza el protocolo de comunicaciones por enlaces de datos en VHF (VDL), el cual, junto con técnicas de posicionamiento satelital, es uno de los pilares fundamentales dentro del concepto CNS/ATM planteado por la Organización de Aviación Civil Internacional (OACI), el cual busca la implantación de nuevas tecnologías para la prestación de los servicios de tránsito aéreo en las áreas de comunicaciones, navegación y vigilancia de aeronaves a nivel mundial. Se presenta el tipo de sistemas usados actualmente por la Unidad Administrativa Especial de Aeronáutica Civil (UAEAC) para la prestación de estos servicios en Colombia, y se hace un comparativo para establecer las ventajas que tiene la implantación de las nuevas tecnologías planteadas en el concepto CNS/ATM, teniendo en cuenta las condiciones particulares de terreno y de flujo de tránsito aéreo que presenta Colombia. Además, se presentan los proyectos de implementación de subredes basadas en enlaces de datos VDL más relevantes a nivel mundial, los cuales permiten obtener resultados de pruebas de funcionamiento, como un paso fundamental hacia la consolidación a nivel mundial de este tipo de tecnología.