Descent Mode Research Articles

Flight Stability of Spinning Projectiles at High Angles of Attack

The flight behavior of the spin-stabilized 105 mm M1 artillery projectile, when fired with high quadrant elevation, is studied using six-degrees-of-freedom trajectory simulations and theoretical methods of stability analysis. Trajectory simulation results confirm the known effect of overstabilization at the apogee, leading to high angles of attack (AoA), drift to the left, and base-forward descent. For quadrant elevations between nose-forward and base-forward descent, a previously unknown descent mode was discovered, with projectiles performing a low-frequency coning motion at high angles of attack of 73 and 104 deg, respectively. An exhaustive theoretical description of such high-AoA limit cycles is given that overcomes the limitation to small angles of attack prevalent in traditional concepts of projectile stability. Based on a formulation of the angular motion in spherical coordinates, conditions for the existence of limit cycles are identified and stability criteria are derived using Lyapunov’s first method of linearization around equilibrium and eigenvalue analysis of the resulting Jacobian. The resulting criteria indicate that limit cycle flight is primarily governed by the Magnus moment coefficient. The method is applied to the 105 mm M1 projectile, and the coning motions observed in the trajectory simulations are accurately reproduced by the theory.

Computational investigations of Ka-226T helicopter coaxial rotor aerodynamics in the vortex ring state

The vortex ring states are observed when the rotor is flowed at positive angles of attack. For the main rotor, these conditions are realized during a steep descent of the helicopter at low speeds. The rotor vortex ring states are affected by significant phenomena related to the behavior of its aerodynamics, including negative phenomena. The latter is, firstly, referred to decrease in rotor thrust, increase in the required power, pulsations of thrust and torque, unsteady flapping blade motion, etc. In terms of helicopter piloting, it means a sharp loss of altitude, increase in the control force, a high level of vibration, defocusing attenuation of rotor spinning cone, as well as controllability deterioration. All these factors determine the relevance of research on these modes and the importance of solving a problem of defining their boundaries. Recently, due to the rapid development of computer technologies and computational models, it has become practical to perform numerical research of the rotor aerodynamics in vortex ring states. The paper presents the study results of Ka-226T helicopter coaxial rotor aerodynamics in steep descent modes in the field of vortex ring states. The angles of rotor attack αВ = 90...30° and the range of vertical descent velocities Vу = 0...26 m/s are considered. The original nonlinear bladed vortex model of the rotor developed at the Moscow Aviation Institute (MAI) was used. The total and distributed aerodynamic rotor characteristics were calculated. The shapes of the vortex wake and the rotor flow patterns were analyzed. The boundaries of the vortex ring states in velocity coordinates “Vx − Vу” were constructed according to various criteria reflecting the known features of these states. The results obtained significantly complement the existing experience of experimental and numerical research in this field.

Survey of the flight efficiency of a long-haul aircraft under uncertainty of tasks

The article considers the problem of optimizing a long-haul aircraft flight under uncertainty of objectives and tasks. Based on the analysis of the well-known flight mode selection criterion, two main objectives of the flight were identified minimizing fuel consumption and flight endurance. The study of this criterion based on a multi-purpose approach made it possible to develop an analytical model of the performance indicator containing two objective functions and a weight coefficient as a measure of comparative importance between the identified objectives. It is shown that the weight coefficient in the tasks of flight efficiency research is a measure of the uncertainty of the tasks. Consideration of the weight coefficient role in the optimization problem objective function made it possible to develop operational and trajectory methods for selecting flight modes. In the developed statement of the problem, the problems of cruise flight optimization and climb and descent modes are considered. The paper introduces the concept of the optimal cruise range as a vertical separation criterion, which allows you to rationally design the flight path at different flight levels under the uncertainty of tasks. The procedure for researching the efficiency and optimization of flight has been conducted and demonstrated by the method of mathematical modeling. The results of optimizing the flight mode are compared with the typical flight modes recommended by the flight manual. The introduced methods of flight efficiency investigation can be helpful in developing recommendations of long-haul aircraft operation. The methods and principles of a multi-purpose approach, operations research and decision theory were used in the paper. The long-haul aircraft IL-96-300 was selected as the object of research.

XMAM:X-raying models with a matrix to reveal backdoor attacks for federated learning

Federated Learning (FL), a burgeoning technology, has received increasing attention due to its privacy protection capability. However, the base algorithm FedAvg is vulnerable when it suffers from so-called backdoor attacks. Former researchers proposed several robust aggregation methods. Unfortunately, due to the hidden characteristic of backdoor attacks, many of these aggregation methods are unable to defend against backdoor attacks. What's more, the attackers recently have proposed some hiding methods that further improve backdoor attacks' stealthiness, making all the existing robust aggregation methods fail.To tackle the threat of backdoor attacks, we propose a new aggregation method, X-raying Models with A Matrix (XMAM), to reveal the malicious local model updates submitted by the backdoor attackers. Since we observe that the output of the Softmax layer exhibits distinguishable patterns between malicious and benign updates, unlike the existing aggregation algorithms, we focus on the Softmax layer's output in which the backdoor attackers are difficult to hide their malicious behavior. Specifically, like medical X-ray examinations, we investigate the collected local model updates by using a matrix as an input to get their Softmax layer's outputs. Then, we preclude updates whose outputs are abnormal by clustering. Without any training dataset in the server, the extensive evaluations show that our XMAM can effectively distinguish malicious local model updates from benign ones. For instance, when other methods fail to defend against the backdoor attacks at no more than 20% malicious clients, our method can tolerate 45% malicious clients in the black-box mode and about 30% in Projected Gradient Descent (PGD) mode. Besides, under adaptive attacks, the results demonstrate that XMAM can still complete the global model training task even when there are 40% malicious clients. Finally, we analyze our method's screening complexity and compare the real screening time with other methods. The results show that XMAM is about 10–10000 times faster than the existing methods.

Thermodynamic characteristics of CO2 adsorption on β-cyclodextrin based porous materials: Equilibrium capacity function with four variables

This work focuses on establishing a kind of extended adsorption model equation including four variables relevant to preparation conditions (activation temperature and heating rate) except adsorption situations (adsorption temperature and adsorption pressure). And the equation is used for thermodynamic analysis of CO2 adsorption on a promising cyclodextrin based porous material. Novelty, those isotherms of CO2 adsorption on the porous materials prepared at different activation temperatures and heating rates are experimentally obtained to investigate the effects of activation temperature and heating rate on CO2 adsorption. Then the parameters of the model equation are quantified based on 589 data points from the isotherms by the least squares regression method combined with the steepest descent mode. Research results indicate that high performance for CO2 uptake appears on the porous material prepared at high activation temperature and low heating rate. Differently with the previous studies, the adsorption site energy distribution is found to exhibit an asymmetrical peak and the peak site energy increases with an increase of activation temperature but the decrease of heating rate. Moreover, a series of interesting phenomena of those thermodynamic state parameters via adsorption temperature and pressure are verified based on both extended Slip model and D-R model, which have not been reported before.

Numerical Study of Coaxial Main Rotor Aerodynamics in Steep Descent

Numerical studies of the aerodynamic characteristics of the coaxial main rotor of the Kamov Ka-32 helicopter in steep descent modes, including the area of the vortex ring state (VRS) modes, have been performed. Used in this paper is an original free vortex wake model of the rotor developed by the authors. The angles of attack of the rotor αR = 30 – 90° and the rate of descent in the range of Vy = 0–30 m/s are considered. The calculations have been carried out under the condition of a fixed time-average thrust of the rotor. The visualization of the rotor wake shapes the flow structures using streamlines, and the flow velocities have been received and analyzed. The VRS boundaries in “Vx–Vy” coordinates have been constructed. The criteria used in this paper are: rotor thrust and torque pulsations, rise of rotor torque and induced velocity relative to the hovering mode. The results of the calculations are compared with the experimental and calculated data of other authors, and a satisfactory match has been obtained. The new results presented in this paper can supplement the existing experience of experimental and numerical research in this field.

Numerical visualization of drop and opening process for parachute-payload system adopting fluid\u2013solid coupling simulation

In order to study the fluid–solid coupling dynamic characteristics of parachute-payload system during drop process and analyze the unsteady aerodynamic characteristics under finite mass opening conditions, an adaptive moving fluid mesh method is developed on the basis of the existing arbitrary Lagrangian–Eulerian (ALE) fluid–solid coupling method. The calculation results of open force and drop velocity on the C-9 parachute demonstrate the effectiveness of this method. On this basis, the effect of canopies with three different permeability on parachute-payload system motion characteristic including opening property, steady descent property and stability is studied. Comparative analysis is conducted for structures and characteristics of vortex with different canopy materials, and interference mechanism of unsteady flow for parachute-payload system in unsteady oscillation is revealed. The results show that the adaptive moving fluid mesh method can effectively eliminate restrictions of existing simulation methods for parachute-payload system and significantly reduce calculation time. For the lightweight parachute, permeability has significant effect on kinetic characteristic of parachute-payload system. Canopy with large permeability has small opening load and structural stress in opening stage. After opening, there are mainly small vortexes distributed evenly behind the canopy with good stability. However, canopy with small permeability has obvious breath behavior and oscillation in opening stage. The main vortexes periodically shed off after opening. With the change of permeability from small to large, Parachute-payload system eventually presents three steady descent modes: conical descent, gliding descent and stable vertical descent.Graphical abstract

Numerical study of the main rotor steep descent modes in the vortex ring state area

The research has been focused on aerodynamic characteristics of the Mi-8 helicopter main rotor in the hover and steep descent modes at rotor angles of attack αR = 90-30º, including vortex ring state area. The research is based on the original free wake model developed by the authors at Moscow Aviation Institute. Total and distributed aerodynamic characteristics, rotor wake shapes and streamlines have been calculated and analyzed. The vortex ring state area borders in the Vx-Vy (horizontal and vertical flight speed components) coordinates have been defined. Five criteria are used: growth of the required rotor blade pitch angle; growth of rotor power consumption with a fixed rotor thrust; increase of the averaged value of the induced velocities and amplitudes of the rotor thrust and torque pulsations. The calculation results have been compared with experimental and calculation data of other authors and indicate sufficient reliability and applicability of used free wake model for calculation and analysis of the vortex ring state modes of helicopter rotor. The results presented in the paper can also significantly supplement the available results of experimental and computational studies of the helicopter rotor operation at steep descent modes in the vortex ring state area.

Eccentric disks falling in water

The freely falling of solid bodies in viscous liquids is an interesting issue concerned with many hydrodynamics and engineering problems. The eccentricity of the solid bodies may lead to new dynamic behaviors and complex paths of falling. Eccentric annular disks with holes covered by transparent tapes are used to study the effect of eccentricity on the descent flight. This paper experimentally investigates the falling regimes of the eccentric disks in water with Reynolds number between 4000 and 21 000 and classifies the descent modes into three types, i.e., the fluttering, chaotic, and tumbling motions, the transition motion, and the new stable descending motion. Finally, we map out the three descent modes of eccentric disks in a two-dimensional phase space of eccentricity e and dimensionless moment of inertia I*. It is found that eccentricity is a significant parameter when describing the descent modes of eccentric disks. Enough large eccentricity stabilizes freely falling disks, while small eccentricity (e < 0.06) leads to the rotation of disk in an arc in the x-y plane accompanied by chaotic and tumbling motions or asymmetric zigzag motion. The descent modes are mainly dependent on e for I* higher than 0.02, and dependent on both e and I* for I* lower than 0.02.

Numerical investigation of full scale coaxial main rotor aerodynamics in hover and vertical descent

The original free vortex wake model was used for numerical investigation. Calculation of the aerodynamic characteristics in hover and vertical descent modes in the range of vertical descent speed of 0–30 m/s including the Vortex Ring State (VRS) area was performed. The calculations were carried out under the condition of variable blade pitch angle values providing a fixed time-average thrust value. Visualization data of free vortex wake shapes, flow structures, and velocity fields were obtained and analyzed. The time-dependences of the rotor’s thrust and torque coefficients were obtained and analyzed. The obtained data allows determining the boundaries of the VRS area by various criteria such as rotor thrust and torque pulsations, growth of rotor power consumption relative to the hover, growth of rotor induced velocities relative to the hover, and growth of the required rotor blade pitch angles values. The results of the study are compared with experimental and calculated data of other authors and can significantly supplement the available results of experimental and computational studies in this area.

Modeling and analysis of windmilling operation during mode transition of a turbine-based-combined cycle engine

Mode transition control is a critical issue of Turbine-Based-Combined Cycle (TBCC) engines when the primary thrust providers change from gas turbine engines to ramjets/scramjets. During mode transition, windmilling operation is inevitable when the fuel mass flow rate of the turbojet engine is decreasing to zero gradually. Existed research on mode transition control of TBCC engines usually neglect this process or simplify this process to a rapid thrust loss due to lacking a windmilling model. However, the absence of the windmilling model might cause critical problems unconsidered at the control system design stage and increase the risk of mission abortion. This paper provides a method of modeling the windmilling operation of a TBCC engine. Sub-idle compressor component maps are obtained by the interpolation method based on a zero-speed line to consider the characteristics that the total pressure ratio is below one. Friction torque is added in the torque balance relationship to achieve the free windmilling operation state when both the compressor and the turbine provide positive torques. The inlet start/unstart status coupled with the operating point of the turbojet engine is also considered. Results show that this model could reflect the characteristics that the total pressure ratio of the compressor is below one, and it provides a positive torque instead of a negative one when the turbojet engine operates at some sub-idle states. Moreover, inlet unstart would happen at some point when the turbojet engine is shutting down to the free windmilling state, under which the turbojet engine would bring in the flight drag instead of a positive thrust. In the descent mode transition when the turbojet engine is accelerating to be restarted, an inappropriate rotating speed of the inlet splitter could result in a fail inlet restart.

Experiments on fall of open tori

Fall of open tori horizontally dropped in quiescent water is experimentally investigated. The fall is controlled by the Galileo number, the torus aspect ratio and the solid to fluid density ratio. The dependence of the descent velocity and of the drag coefficient on the control parameters is first analyzed. As the control parameters are varied, vertical translation, zigzagging and spiraling descent are observed. These different descent modes are characterized and a phase diagram of the falling tori are presented as function of the three control parameters.

Simulation Model of Releasing a Symmetric Auto-rotating Body in the Air

В работе построена математическая модель тела сложной конфигурации, состоящего из стержня и двух прямоугольных пластинок, ортогональных к стержню, которое представляет собой рабочий элемент ветротурбины Дарье. Тело совершает плоскопараллельное снижение под действием силы тяжести и аэродинамических сил. Аэродинамические силы, приложенные к пластинкам, приняты в соответствии с эмпирической теорией стационарного обтекания плоской пластины. Исследуется вопрос о существовании различных стационарных режимов спуска и их устойчивости. Сначала рассматриваются простейшие стационарные режимы, при которых тело движется поступательно. Указаны наиболее характерные простейшие режимы поступательного движения. Найден режим планирования под углом восемьдесят семь градусов. Наибольший интерес в работе представляет режим авторотации, при котором тело быстро вращается и осуществляет снижение по вертикали или наклонной прямой подобно свободно вращающемуся несущему винту. При помощи метода осреднения получены оценки средней угловой скорости, средней скорости центра масс и среднего угла планирования тела в режиме авторотации доказано, что режим авторотации является притягивающим. Показано, что спуск в режиме авторотации происходит с наименьшей скоростью по сравнению с другими режимами, что позволяет применять эту конструкцию в качестве системы спуска или аэродинамического тормозного устройства, либо как систему планирования. Численно решены уравнения равновесия и построены зависимости угла планирования от установочного угла и вертикальной проекции скорости от установочного угла. Написаны программы, в которых проводится численное интегрирование уравнений движения рассматриваемого тела и результаты численного интегрирования сравниваются с полученными теоретическими оценками для оценки точности рассматриваемых методов. The article presents the creation of a mathematical model of a body with a complex configuration, consisting of a rod and two rectangular plates orthogonal to the rod, which is a working element of the Darier wind turbine. The body makes a plane-parallel decrease under the action of gravity and aerodynamic forces. The aerodynamic forces applied to the plates are adopted in accordance with the empirical theory of stationary flow around a flat plate. The question of the existence of various stationary descent modes and their stability is investigated. First, we consider the simplest stationary modes in which the body moves translationally. The most salient simplest modes of translational motion are indicated. A volplaning mode at an angle of eighty-seven degrees is found. The most interesting point in this article is the autorotation mode, when the body rotates rapidly and decreases vertically or in an inclined straight line like a freely rotating rotor. Using the homogenization method, estimates of the average angular velocity, the average velocity of the mass center and the average glide angle of the body in the autorotation mode are obtained it is proved that the autorotation mode is attracting. It is shown that the descent in autorotation mode occurs at the lowest speed compared to other modes, which allows you to use this design as a descent system or aerodynamic braking device, or as a planning system. The equilibrium equations are numerically solved the functional relationship between the glide angle and the rigging angle and functional relationship between the vertical projection of speed on the rigging angle are constructed. Programs are written that numerical integrate the equations of the body motion and the results of numerical integration are compared with the theoretical estimates to evaluate the accuracy of the methods under consideration.

Computational Research of the Main Rotor Steep Descent Modes Based on the Nonlinear Blade Vortex Model

The main rotor operation is studied of the Mi-8 single-rotor helicopter in steep descent modes at the rotor angles of attack αR = 90−30 deg. The study resulted in total and distributed aerodynamic performance, rotor wake patterns and flow patterns. The vortex ring state area is designed based on the result analysis in terms of some features. The calculation results are compared with the experimental data and calculations of other authors.

From feed-in tariff to renewable portfolio standards: An evolutionary game theory perspective

China is experiencing renewable energy support schemes evolution from feed-in tariff (FIT) to renewable portfolio standards (RPS) scheme, which can be significantly influenced by renewable and conventional electricity producers strategies. This paper applies evolutionary game theory and system dynamics (SD) model to examine electricity producers strategies in this scheme context. We utilize the data from Chinese wind power industry for simulation to represent evolution of strategies, and research impacts of scheme parameters (subsidy, quota, and fine) on electricity producers and tradable green certificate (TGC) market operation. The results show that, to ensure all the electricity producers willing to trade TGC, scheme parameters should be within a reasonable range. Moreover, the stage descent mode of subsidy and higher level of fine will help the electricity producers accept the RPS scheme as soon as possible and promote the scale of TGC transaction, but the quota requirement should be avoided too low. At the end of the paper, policy implications are offered as references for the government.

Monocular Vision SLAM-Based UAV Autonomous Landing in Emergencies and Unknown Environments

With the popularization and wide application of drones in military and civilian fields, the safety of drones must be considered. At present, the failure and drop rates of drones are still much higher than those of manned aircraft. Therefore, it is imperative to improve the research on the safe landing and recovery of drones. However, most drone navigation methods rely on global positioning system (GPS) signals. When GPS signals are missing, these drones cannot land or recover properly. In fact, with the help of optical equipment and image recognition technology, the position and posture of the drone in three dimensions can be obtained, and the environment where the drone is located can be perceived. This paper proposes and implements a monocular vision-based drone autonomous landing system in emergencies and in unstructured environments. In this system, a novel map representation approach is proposed that combines three-dimensional features and a mid-pass filter to remove noise and construct a grid map with different heights. In addition, a region segmentation is presented to detect the edges of different-height grid areas for the sake of improving the speed and accuracy of the subsequent landing area selection. As a visual landing technology, this paper evaluates the proposed algorithm in two tasks: scene reconstruction integrity and landing location security. In these tasks, firstly, a drone scans the scene and acquires key frames in the monocular visual simultaneous localization and mapping (SLAM) system in order to estimate the pose of the drone and to create a three-dimensional point cloud map. Then, the filtered three-dimensional point cloud map is converted into a grid map. The grid map is further divided into different regions to select the appropriate landing zone. Thus, it can carry out autonomous route planning. Finally, when it stops upon the landing field, it will start the descent mode near the landing area. Experiments in multiple sets of real scenes show that the environmental awareness and the landing area selection have high robustness and real-time performance.

Metabolic features of cosmonauts after ballistic descent from the Earth orbit

The features of metabolic reactions in five cosmonauts after long-term flights on the International Space Station (ISS) and landing along a ballistic trajectory and in the cosmonauts returning to Earth in the mode of automatic controlled descent were studied. Venous blood samples were collected, and 50 biochemical parameter values that reflect the functional state of organs and tissues and characterize the main metabolic pathways were determined. On the first day of the recovery period after ballistic descent, the activity of the myocardial, liver, and gastrointestinal enzymes in the blood serum of cosmonauts was increased 1.3- to 2.1-fold; a number of the parameter values exceeded the upper normal limit. The level of C-reactive protein increased fivefold as compared with the preflight values. Marked signs of glycolysis, glycogenolysis and lipolysis activation as well as disorders of acid–base balance were observed. Changes in the biochemical parameter values in cosmonauts after landing along a ballistic trajectory differed significantly from those revealed in the same cosmonauts after long-term missions followed by automatic controlled descent to Earth. Negative metabolic changes tendency after landing along a ballistic trajectory remained for at least 14 days of the recovery period. It was concluded that changes in the metabolic reactions of cosmonauts after long-term missions to the ISS depend on the flights final stage conditions. After landing on Soyuz spaceships in the ballistic descent mode, the cosmonauts had adverse prognosis changes in the biochemical values characterizing the state of the cardiovascular system and marked shifts in the activity of the liver and gastrointestinal constellation enzymes. The dynamics of carbohydrate, lipid, and protein metabolism as well as acid–base balance indicates a significant tension of all body systems and exhaustion of its functional reserves.

Trustable UAV for higher level control architectures

Future unmanned air vehicles (UAVs) are expected to operate under the supervision of higher level control architectures that give instructions to engage and direct the UAV to perform a certain task. These instructions allow the UAV to make decisions along any point of its trajectory and then modify its flight path by using a sequence of reconfigurable controllers at the decision points. Assume that the UAV is flying with a transient and with a steady state contributing to a flight control mode (FCM) such as an altitude hold, an ascent and a descent mode when only longitudinal aircraft dynamics is considered. At the time of a decision, if the UAV bifurcates from its original (or parent) FCM in an effort to acquire a new (or a child) FCM and comply with a higher level instruction, then the UAV is said to be trustable. Mathematically, at the time of bifurcation where controller reconfiguration takes place, trustable UAV with the child trajectory must originate from a region where the stability regions of the parent and child trajectories intersect. In this paper, a procedure to reconfigure such FCMs and their controllers that develop the trustable UAV are presented. A three degree of freedom UAV is considered to illustrate the trustable UAV.

Detection of Gait Modes Using an Artificial Neural Network during Walking with a Powered Ankle-Foot Orthosis.

This paper presents an algorithm, for use with a Portable Powered Ankle-Foot Orthosis (i.e., PPAFO) that can automatically detect changes in gait modes (level ground, ascent and descent of stairs or ramps), thus allowing for appropriate ankle actuation control during swing phase. An artificial neural network (ANN) algorithm used input signals from an inertial measurement unit and foot switches, that is, vertical velocity and segment angle of the foot. Output from the ANN was filtered and adjusted to generate a final data set used to classify different gait modes. Five healthy male subjects walked with the PPAFO on the right leg for two test scenarios (walking over level ground and up and down stairs or a ramp; three trials per scenario). Success rate was quantified by the number of correctly classified steps with respect to the total number of steps. The results indicated that the proposed algorithm's success rate was high (99.3%, 100%, and 98.3% for level, ascent, and descent modes in the stairs scenario, respectively; 98.9%, 97.8%, and 100% in the ramp scenario). The proposed algorithm continuously detected each step's gait mode with faster timing and higher accuracy compared to a previous algorithm that used a decision tree based on maximizing the reliability of the mode recognition.

A feasibility study of depth image based intent recognition for lower limb prostheses.

This paper presents our preliminary work on a depth camera based intent recognition system intended for future use in robotic prosthetic legs. The approach infers the activity mode of the subject for standing, walking, running, stair ascent and stair descent modes only using data from the depth camera. Depth difference images are also used to increase the performance of the approach by discriminating between static and dynamic instances. After confidence map based filtering, simple features such as mean, maximum, minimum and standard deviation are extracted from rectangular regions of the frames. A support vector machine with a cubic kernel is used for the classification task. The classification results are post-processed by a voting filter to increase the robustness of activity mode recognition. Experiments conducted with a healthy subject donning the depth camera to his lower leg showed the efficacy of the approach. Specifically, the depth camera based recognition system was able to identify 28 activity mode transitions successfully. The only case of incorrect mode switching was an intended run to stand transition, where an intermediate transition from run to walk was recognized before transitioning to the intended standing mode.