Rudder Surface Research Articles

A Self-Supervised Fault Detection for UAV Based on Unbalanced Flight Data Representation Learning and Wavelet Analysis

This paper aims to build a Self-supervised Fault Detection Model for UAVs combined with an Auto-Encoder. With the development of data science, it is imperative to detect UAV faults and improve their safety. Many factors affect the fault of a UAV, such as the voltage of the generator, angle of attack, and position of the rudder surface. A UAV is a typical complex system, and its flight data are typical high-dimensional large sample data sets. In practical applications such as UAV fault detection, the fault data only appear in a small part of the data sets. In this study, representation learning is used to extract the normal features of the flight data and reduce the dimensions of the data. The normal data are used for the training of the Auto-Encoder, and the reconstruction loss is used as the criterion for fault detection. An Improved Auto-Encoder suitable for UAV Flight Data Sets is proposed in this paper. In the Auto-Encoder, we use wavelet analysis to extract the low-frequency signals with different frequencies from the flight data. The Auto-Encoder is used for the feature extraction and reconstruction of the low-frequency signals with different frequencies. To improve the effectiveness of the fault localization at inference, we develop a new fault factor location model, which is based on the reconstruction loss of the Auto-Encoder and edge detection operator. The UAV Flight Data Sets are used for hard-landing detection, and an average accuracy of 91.01% is obtained. Compared with other models, the results suggest that the developed Self-supervised Fault Detection Model for UAVs has better accuracy. Concluding this study, an explanation is provided concerning the proposed model’s good results.

함정의 평판형 방향타 캐비테이션 침식에 대한 모형 시험 연구

In the present study, a method of performing cavitation erosion test directly on the anodized surface of the rudder model is proposed, not applying ink or paint on its surface. An image processing technique is newly developed to quantitatively evaluate the erosion damages on the rudder model surface after erosion test. The preprocessing saturation image, image smoothing, adaptive hysteresis thresholding and eroded area detection algorithms are in the image processing program. The rudder cavitation erosion tests are conducted in the rudder deflection angle range of 0SUPo/SUP to -4SUPo/SUP, which is used to maintain a straight course at the highest speed of the targeted navy ship. In the case of the conventional flat-type full-spade rudder currently being used in the target ship, surface erosion can occur on the model rudder surface in the above rudder deflection angle range. The bubble type of cavitation occurs on rudder surface, which is estimated to be the main reason of erosion damage on the rudder surface.

Vortex dynamics impact on the wake flow of a marine rudder with leading-edge tubercles

The impact of two tubercle leading-edge (TLE) modifications on the turbulent wake of a reference marine rudder at Reynolds number 2.26 × 106 was analysed numerically using Detached Eddy Simulations (DES). This paper studies the counter-rotating vortex pair formation around the TLE and their impact on the wake structures behind the rudder to find out if the vortex interaction can accelerate the tip vortex dissipation. According to the results, the tubercles enhanced lift for angles of attack (AOA) 10º and above, but at the cost of a drag penalty which reduced the rudders’ lift-to-drag ratio. The formation of the distinctive stream-wise counter-rotating vortex pairs occurred behind the tubercles, which then interacted with the dominant tip vortex. Due to the inherent spanwise flow component of finite-span lifting surfaces the counter-rotating vortex pairs were generated at unequal strength and soon merged into singular vortices co-rotating with the tip vortex. The vortices facilitated flow compartmentalisation over the rudder suction side which broke up the trailing-edge vortex sheet and confined the spanwise flow separation over the rudder surface as AOA increased. The tubercles confined flow separation closer to the rudder tip which reduced the lift generation in the tip area and minimised the initial tip vortex strength. Large elements of stream-wise counter-rotating vorticity formed around the localised stall cells of the TLE rudders that interacted with the tip vortex downstream, introducing elliptical instabilities further weakening the tip vortex and changing its trajectory.

Study on tolerance control of flying-wing layout vectored thrust UAV

The flying-wing layout vectored thrust UAV often uses multiple sets of aerodynamic rudder surfaces and vector nozzles to jointly generate the required control force and torque, which belongs to a typical overdrive system. Multiple sets of rudder surfaces give UAV a higher redundancy configuration, but also result in multiplying the rudder surface failure rate. Especially for the statically unstable flying-wing UAV in lateral direction, the moment imbalance caused by the failure of the executive rudder will seriously affect the flight safety. Therefore, this paper takes the failure of elevator and rudder damage as an example, and proposes a kind of control distribution method of aerodynamic-based control and vectored thrust as auxiliary. The binary vector deflection mechanism is used to generate vector thrust, compensate damaged actuator mechanism rudder effect, release the control margin of the rudder actuator, and restore the maneuverability of the aircraft. Under the failure of the aerodynamic rudder actuator damage, the stable control UAV is realized.

Research of Servo Control with Microcontroller

Servos are widely used in aeromodelling and other model sports as a device that receives PWM signals to drive the rudder surface by controlling elements such as the transmission rod. By referring to previous experiences in developing quadruped robots and reviewing relevant books and papers, this essay summarizes the main methods of controlling a servo with a microcontroller. This will help the beginner in rudder control to acquire the relevant knowledge.

Improved Adaptive Fault-Tolerant Control of a Variable Structure Fighter with Multiple Faults Based on an Extended Observer

In this paper, an improved adaptive fault-tolerant control (FTC) scheme is presented based on an extended state observer (ESO) for a highly maneuverable variable structure fighter (VSF) with simultaneous faults of the rudder surface and sensor. The feedback linearization model of the attitude system with faults and external disturbances is introduced. In order to realize the real-time observation of the rudder and sensor faults, a neural network estimator is used to approximate sensor faults, and the ESO is designed to estimate the rudder surface fault and attitude variables. On this basis, the estimated value is used to replace the measured value for state variables to design the adaptive fault-tolerant controller for the inner and outer loop, combined with the second-order command filter to offset the phenomenon of backstepping differential amplification system noise. Finally, the proposed FTC scheme realizes the variable structure self-repairing of multiple positions, multiple types of faults in VSF using fault estimation. The Lyapunov theory and Barbalat’s lemma prove the stability of the designed observer and controller. The effectiveness of the FTC scheme is verified by a simulation experiment.

Experimental investigation of flow control of a curved-surface jet at Mach 5 hypersonic flow

Jet flow-control technology is a promising area of fluid research. In this work, the flow-control effect of a curved-surface jet in an incoming flow of Mach = 5 and its underlying control mechanism are experimentally studied using high-speed photography and dynamic force measurement. From the establishment of complete stability of the flow field, the evolutionary process can be roughly divided into five stages: two equilibrium stages (short and long term), jet acceleration stage, bow shock formation stage, interference removal stage, and stable state. By defining the pressure ratio (PR) as an independent variable, it is found that the flow control of the jet occurs through different wave-system structures. The interaction between the jet and the incoming flow produces an oblique shockwave and expansion waves. The shockwave generates thrust and forms a virtual rudder surface; the expansion waves interact with the backflow region and the separated shear layer to generate lift. Moreover, PR has an optimal solution of PRopt. When PR < PRopt, the effect of flow control is related to α, Ve, and ρe, and the greater the PR, the stronger the flow-control effect. When PR > PRopt, the flow-control effect is related to α and ρe, and the larger the PR, the weaker the effect of the shockwave and the stronger the effect of the expansion waves but the slower the growth. In experiments, the thrust, pitching moment, and lift increased by 17.43%, 17.75%, and 9.45%, respectively, because of the appearance of wave-system structure when PRopt = 201.32.

Experimental study on the frequency characteristics of cloud cavitation on a full-spade rudder of a ship

The frequency characteristics of cloud cavitation on a full-spade rudder are investigated using a cavitation image processing technique and cavitation noise analysis. The rudder deflection angle is varied from −8° to −15° to generate cloud cavitation on the rudder surface. For images recorded at 103 fps (frame per second), reference values for detecting cavitation are defined and calculated in red–green–blue and hue–saturation–lightness color spaces to quantitatively analyze the amount of cavitation. At a rudder deflection angle of −12°, the amount of cavitation generated by a three-dimensional (3D) twisted full-spade rudder is found to be reduced by ∼60% compared with that generated by a flat-type full-spade rudder. The intrinsic frequency characteristics of cloud cavitation are also obtained from time-series data of the cavitation amount and are found to be the same through analysis of the noise signal measured by a hydrophone. The peak value of acoustic noise appears in the frequency band 30–50 Hz in the flat-type full-spade rudder; however, it is substantially decreased in the 3D twisted full-spade rudder at rudder angles of from −8° to −15°, where a noise-reduction effect is observed in the frequency band corresponding to the peak value.

Research on Abnormal Geometric Similarity Design Method of a Missile with Tail Rudder Model in High Speed Wind Tunnel

Abstract Geometric similarity is an important similarity laws for the experimental study on aerodynamic characteristics of wind tunnel models. General aspect the ratio of missile body length to rudder surface aspect length is large. The test model is designed according to the complete geometric similarity scale. It is often difficult to match the length aspect ratio size in the limited space of the wind tunnel test section. Based on this problem, the abnormal geometric similarity design method of the missile body under the condition of fixed tail rudder is studied by numerical simulation. The results show that When truncated to 0.625, 0.7, 0.8 and 0.9 times the original projectile length, the change of the inflow conditions at the leading edge of the rudder surface is small, which can meet the research needs of the aerodynamic characteristics of the tail rudder, and lay a theoretical foundation for the design of relevant wind tunnel test models.

AERODYNAMIC ANALYSIS OF MORPHING WING.

This thesis presents a modelling and design exploration study of a novel twisting wing whose motion is enabled by a tensegrity mechanism. First, the aerodynamic characteristics of the twisting wing, which does not require control surfaces to modulate its shape, are compared with those of a conventional wing having a control surface. It is shown via computational fluid dynamics analyses that the twisting wing displays higher lift-to-drag ratio than the conventional wing and hence the twisting wing is more aerodynamically efficient. In addition, due to the reduction of discontinuous rudder surfaces, morphing wings can further improve the stealth performance. A finite element model with geometrical nonlinear effects is then proposed to correct the errors of the linear analysis and verify the effectiveness of the optimization method. This design is shown to be able to reduce the overall weight of the structure and achieve control of the macro mechanical performance of the wing. The work provides a general optimization design method for similar modular structures, allowing independent programmable adjustment of the parameters of each single structural cell.

An Adaptive Operational Modal Analysis under Non-White Noise Excitation Using Hybrid Neural Networks

To adaptively identify the modal parameters for time-invariant structures excited by non-white noise, this paper proposes a new operational modal analysis (OMA) method using hybrid neural networks. In this work, taking the acceleration response directly as the input data of the networks not only simplifies the data processing, but also retains all the characteristics of the data. The data processed by the output function is the output data of the network, and its peak corresponds to the modal frequency. The proposed output function greatly reduces the computational cost. In addition, a small sample dataset ensures that the hybrid neural networks identify the modal parameters with the highest accuracy in the shortest possible time. Interestingly, the hybrid neural networks combine the advantages of the convolutional neural network (CNN) and gate recurrent unit (GRU). To illustrate the advantages of the proposed method, the cantilever beam and the rudder surface excited by white and non-white noise are taken as examples for experimental verification. The results reveal that the proposed method has a strong anti-noise ability and high recognition accuracy, and is not limited by ambient excitation type.

The Influence of Leading-Edge Tubercles on the Wake Flow Dynamics of a Marine Rudder

The impact of two tubercle leading-edge (TLE) modifications on the turbulent wake of a representative marine rudder at Reynolds number 2.26×106 was analysed numerically using Detached-Eddy Simulations. TLE have been shown to alter the flow profile over aero/hydrofoils through the generation of streamwise counter-rotating vortex pairs behind the tubercles, which can enhance the lifting performance. This paper studies the formation of these vortex pairs and their impact on the wake structures behind the rudder to find out if vortex interaction can reduce the tip vortex. The tubercles enhanced lift for angles of attack (AOA) 10o and above, but at the cost of a large drag penalty that reduced the rudders' lift-to-drag ratio. The formation of the distinctive streamwise counter-rotating vortex pairs behind the tubercles was shown. Due to the inherent spanwise flow component of finite-span lifting surfaces the vortices were generated at unequal strength and only positive vortices were maintained in the wake. The vortices facilitated flow compartmentalisation over the rudder suction side which broke up the trailing-edge vortex sheet and confined the spanwise flow separation over the rudder surface as AOA increased. The tubercles confined flow separation closer to the rudder tip which caused a tip-offloading effect that minimised the initial tip vortex strength. Large elements of streamwise counter-rotating vorticity formed around the localised stall cells of the TLE rudders that interacted with the tip vortex downstream, introducing elliptical instabilities further weakening the tip vortex and changing its trajectory.

Numerical Investigation of Aeroelastic Characteristics of Grid Fin

Grid fin is widely used in the field of aerospace because of its unique advantages in the aerodynamic and structural performance. Meanwhile, the aerodynamic and structural characteristics of the grid fin are quite different from those of the conventional rudder. Deep understanding of the aeroelastic characteristics and mechanism of the grid fin is of great reference value for the fine design of grid fin. In this paper, an efficient reduction-order-method-based aeroelastic analysis method is established, and the method is verified by the flutter case of AGARD 445.6 wing. Finally, based on this method, the flowfield characteristics and the variation of flutter characteristics with Mach number are studied in detail. The results show that in the subsonic region, the transonic flutter “dip” of the grid fin occurs earlier than that of the conventional wing due to the acceleration effect of the grid fin on the airflow. In the transonic region, when the flowfield is characterized by a bow shock wave, the critical flutter speed increases slightly with the increase of Mach number. However, in the supersonic region, when the flowfield is characterized by an oblique shock wave, the flutter critical velocity increases substantially with the increase of Mach number. It is found that the variation law of the flutter boundary with Mach number is very similar to that of the normal force and the pitching moment with Mach number, and there is a close relationship between them. The ratio of flutter speed of the grid fin to the freestream velocity will reach the minimum value near . At the same time, it is discovered that the flutter instability of the grid fin is mainly caused by the coupling of the bending mode and torsional mode of the grid fin, and the instability mode is the torsional mode. Meanwhile, it should be noted that the flutter coupling characteristics of the grid fin differ greatly from those of the conventional rudder surface due to the great difference in structural characteristics and unsteady aerodynamic characteristics.

Experimental and numerical investigations on the unsteady thrust of a propeller in presence of an upstream rudder

The unsteady thrust of a propeller in presence of an asymmetric upstream rudder is experimentally and numerically studied. First, a high-resolution dynamometer is utilized to measure the unsteady thrust of the propeller downstream of a rudder in the water tunnel. Second, by means of the large eddy simulation, a CFD model including both rudder and propeller is established to predict the flow field and the unsteady thrust of the propeller. After verifying the accuracy of the numerical method, the influences of rudder angle on the unsteady thrust of propeller are numerically studied. It is shown that for the flow field, the separation location of vortices moves upstream on the rudder surface with the increase of rudder angle. For the tonal forces, the tonal thrust increases with the rudder angle, and the transverse tonal force increases rapidly due to the increased asymmetry of the flow field. For the broadband forces, the force spectrum in the low-frequency range increases and humps appear at the blade passing frequencies.

함정용 방향타에서 발생하는 구름(cloud) 캐비테이션의 주파수 특성에 대한 실험적 연구

In this study, the amount and frequency characteristics of cloud cavitation formed on a navy ship rudder were investigated through cavitation image processing technique and cavitation noise analysis. A high-speed camera with high time resolution was used to observe the cavitation on a full-spade rudder. The deflection angle range of the full-spade rudder was set to 8 to 15 degrees so that cloud cavitation was generated on the rudder surface. For images taken at 104 fps (frame per second), reference values for detecting cavitation were defined and detected in Red, Green, Blue and Hue, Saturation, Lightness color spaces to quantitatively analyze the amount of cavitation. Intrinsic frequency characteristics of cloud cavitation were detected from the time series data of the amount of cavitation. The frequency characteristics of cloud cavitation obtained by using the image processing technique were found to be the same through the analysis of the noise signal measured by the hydrophone installed on the hull above the rudder, and its peak value was in the frequency band of 30~60Hz.

Aerodynamic characteristics of hypersonic airfoils based on jet flow control technology

Hypersonic aircraft represent an important area of aerospace development. Raising the aircraft lift-to-drag ratio, improving the efficiency of attitude control, and optimizing aerodynamic performance are important goals. Active flow control technology can improve the aerodynamic performance of the aircraft while optimizing its control attitude. In the field of low speed, subsonic speed, and supersonic speed, many experiments and numerical simulations have been carried out to verify the excellent auxiliary or control effects of active flow control technology on aircraft. In this paper, a two-dimensional hypersonic airfoil is selected to analyze the feasibility and control effect of jet flow control technology under hypersonic inflow, and a flow control scheme is designed to make the jet eject from the wing surface. First, the influence of different jet excitation parameters on the scheme is explored through numerical simulation, mainly including the Mach number, the jet location, the jet angle, and the change with the angle of attack. After that, typical excitation states of numerical simulation are selected for hypersonic wind tunnel experiment verification, whose results are in good agreement with those of the numerical simulation. The results prove that, under the condition of high altitude and low pressure, if jet excitation is applied on the surface of the hypersonic airfoil, a local high pressure area will be formed in front of the excitation port, and the differential pressure between upper and lower wings will be changed. It can optimize the aerodynamic characteristics, increase or reduce lift, produce pitching moment simultaneously, enhance the efficiency of the rudder surface, and assist attitude control.

Numerical simulation of structural response during propeller-rudder interaction

The propeller wake can cause vibrations on the rudder surface, which worsen the noise and reliability. The vibration monitoring of the rudder operating in the propeller wake with fluid-structure interaction (FSI) method is still challenging. In the present study, the structural response during propeller-rudder interaction is investigated using detached eddy simulation. Three-dimensional distributions of loads, stresses, and deformations are discussed. The leading and trailing edges exhibit the strongest deformations in opposite directions, which are S-shaped. The strongest lateral deformation occurs between the tip vortex and hub vortex regions. In the tip vortex region, the dominant lateral vibrations fluctuate at the blade passing frequency (BPF) and shaft frequency (SF). However, the 75 Hz-fluctuation becomes significant at the trailing edge of the rudder. In the hub vortex region, the lateral deformation fluctuates mainly at 75 Hz except the area near the leading edge. There are weak vibrations occurring at the natural frequencies of the rudder when the natural frequencies of the rudder are much higher than the SF and BPF. However, the plate in the propeller suffers intense vibrations at the frequencies near the natural frequencies, where the natural frequencies of the plate are close to SF and BPF.

Research on control effectiveness of fluidic thrust vectoring.

In view of the control effects of fluidic thrust vector technology for low-speed aircraft at high altitude/low density and low altitude/high density are studied. The S-A model of FLUENT software is used to simulate the flow field inside and outside the nozzle with variable control surface parameters, and the relationship between the area of control surface and the deflection effect of main flow at different altitudes is obtained. It is found that the fluidic thrust vectoring nozzle can effectively control the internal flow in the ground state and the high altitude/low density state. and the mainstream deflection angle can be continuously adjusted. The maximum deflection angle of the flow in the ground state is 21.86°, and the maximum deviation angle of the 20 km high altitude/low density state is 18.80°. The deflecting of the inner flow of the nozzle is beneficial to provide more lateral force and lateral torque for the aircraft. The high altitude/low density state is taken as an example. When the internal flow deflects 18.80°, the lateral force is 0.32 times the main thrust. For aircraft with high altitude and low density, sufficient lateral and lateral torque can make the flying aircraft more flexible, which can make up the shortcomings of the conventional rudder failure and even replace the conventional rudder surface.

Analysis and Experimental Research on Test Method of Initial Guidance Thrust

With the gradual development of aerospace industry, the demand for missile performance is also growing. The steering gear, as one of the main implementing agencies of the missile guidance and control system, can adjust the actual thrust size through the closed-loop control system during missile guidance the deflection angle of the rudder surface, in order to change the missile's flight speed and flight attitude. The missile during the flight attitude correction and speed adjustment are through the electric servo output power to change the size of the output to complete. In this paper, the unsteady turbulent analysis theory is used to analyze the thrust test mechanism of jet. Through the simulation of the flow field, the influence of bearing wall position on the impact jet backflow zone location is studied, and the position of the bearing wall whose pressure value is the closest to the true value is determined. In addition, a simplified test system of jet thrust test was designed. The relationship between wall position and pressure was verified through experiments, which verified the accuracy of simulation results.

Flow over a hydrofoil in the wake of a propeller

Large Eddy Simulations are reported on the flow around a rudder operating in the wake of a propeller. Results demonstrate the production of important spanwise flows within the boundary layer on the hydrofoil, mainly tied to the behavior of the largest coherent structures populating the propeller wake. The two branches of the hub vortex are shifted from the pressure towards the suction sides of the rudder. The pressure and suction side branches of the tip vortices move outward and inward, respectively. This phenomena increase the asymmetry between pressure and suction sides, with wider areas of the rudder surface affected by the propeller wake on the pressure sides. In the vicinity of the leading edge the main sources of turbulent fluctuations within the boundary layer on the hydrofoil are the two branches of the hub vortex, with also an evident signature of the tip vortices, especially on the suction sides, where they experience a stronger stretching. Moving from the leading edge towards the trailing edge both momentum and turbulence within the rudder boundary layer become obviously higher on the pressure sides than on the suction sides, because of the impingement operated by the propeller wake, whose azimuthal velocity is directed towards the pressure sides of the hydrofoil. Such effect is evident across the whole spanwise extent affected by the propeller wake, involving also the outer radii populated by the tip vortices. However, moving away from the surface of the hydrofoil the turbulent stresses become higher on the suction sides, due to the shear generated by the contraction of the propeller wake, which is instead expanding on the pressure sides.