A Paratrooper Model Sensitivity Analysis for Personnel Airdrop

The location and orientation of a rigid body in space can be defined in terms of three noncollinear points in the body. As the rigid body is moved through space, the motion may be described by a series of rotations and translations. The sequence of displacements may be conveniently represented in matrix form by a series of displacement matrices that describe the motion of the body between successive positions. If the rotations and translations (and hence the displacement matrix) are known then succeeding positions of a rigid body may be easily calculated in terms of the initial position. Conversely, if successive positions of three points in the rigid body are known, it is possible to calculate the parameters of the corresponding rotation and translation. In this paper, a new solution is presented which provides explicit formulas for the rotation and translation of a rigid body in terms of the initial and final positions of three points fixed in the rigid body. The rotation matrix is determined directly whereupon appropriate rotation angles and other information can subsequently be calculated if desired.

This paper presents a new flight trajectory optimisation method, based on genetic algorithms, where the selected optimisation criterion is the minimisation of the total cost. The candidate flight trajectories evaluated in the optimisation process are defined as flight plans with two components: a lateral flight plan (the set of geographic points that define the flight trajectory track segments) and a vertical flight plan (the set of data that define the altitude and speed profiles, as well as the points where the altitude and/or speed changes occur). The lateral components of the candidate flight plans are constructed by selecting a set of adjacent nodes from a routing grid. The routing grid nodes are generated based on the orthodromic route between the flight trajectory’s initial and final points, a selected maximum lateral deviation from the orthodromic route and a selected grid node step size along and across the orthodromic route. Two strategies are investigated to handle invalid flight plans (relative to the aircraft’s flight envelope) and to compute their flight performance parameters. A first strategy is to assign a large penalty total cost to invalid flight profiles. The second strategy is to adjust the invalid flight plan parameters (altitude and/or speed) to the nearest limit of the flight envelope, with priority being given to maintaining the planned altitude. The tests performed in this study show that the second strategy is computationally expensive (requiring more than twice the execution time relative to the first strategy) and yields less optimal solutions. The performance of the optimal profiles identified by the proposed optimisation method, using the two strategies regarding invalid flight profile performance evaluation, were compared with the performance data of a reference flight profile, using identical input data: initial aircraft weight, initial and final aircraft geographic positions, altitudes and speed, cost index, and atmospheric data. The initial and final aircraft geographic positions, and the reference flight profile data, were retrieved from the FlightAware web site. This data corresponds to a real flight performed with the aircraft model used in this study. Tests were performed for six Cost Index values. Given the randomness of the genetic algorithms, the convergence to a global optimal solution is not guaranteed (the solution may be non-optimal or a local optima). For a better evaluation of the performance of the proposed method, ten test runs were performed for each Cost Index value. The total cost reduction for the optimal flight plans obtained using the proposed method, relative to the reference flight plan, was between 0.822% and 3.042% for the cases when the invalid flight profiles were corrected, and between 1.598% and 3.97% for the cases where the invalid profiles were assigned a penalty total cost.

The paper presents a six-degree of freedom mathematical model of a light sport aircraft and analytically reveals aircraft dynamic response both longitudinal and lateral-directional stability. The model composes of both the kinematics equations of motion and the kinetics equations of aerodynamic forces and moments, known as the aerodynamic model equations. Simulation results show responses of the perturbed dynamic system at trim condition, which indicates dynamic stability of both short-period pitching oscillation and phugoid in longitudinal axes. The spiral, roll subsidence, and dutch roll modes in lateral-directional axes are also dynamic stable as well. These are essential to understand and evaluate the dynamic behavior, stability, safety, and other aspects of the designed aircraft through a mathematical model before conducting an operational flight test.  

<sec> The topologically protected edge states of elastic waves in phononic crystal plates have the outstanding characteristics in wave manipulation such as the strong suppression of back-scattering and defect immunity, which can be used for controlling vibration and noise, detecting the structural damage, conducting the material nondestructive test and other engineering practices, and therefore have received much attention. But for plate structures, the propagation of elastic waves is complicated due to the coexistence and coupling of different types of wave modes, resulting in a challenge in designing topologically protected states. </sec><sec>In this paper, a simple phononic crystal plate with triangular holes is designed for elastic wave manipulation based on topologically protected edge states. The band structure characteristics of the unit cell are studied by varying the rotation angle <i>θ</i> of the triangular holes around their geometric centers from the initial positions. It is found that the band structure of the initial unit cell with rotation angle <i>θ</i> = 0° has two pairs of degenerate modes. At <inline-formula><tex-math id="M6">\begin{document}$ \theta = \pm 33^\circ $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20200542_M6.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20200542_M6.png"/></alternatives></inline-formula>, a double Dirac cone appears at the center <i>Γ</i> point of the Brillouin zone without requiring the lattices to fold, and a band inversion occurs on both sides of <inline-formula><tex-math id="M7">\begin{document}$ \pm 33^\circ $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20200542_M7.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20200542_M7.png"/></alternatives></inline-formula> which can be characterized as a topological phase transition. </sec><sec>The elastic band gap and two kinds of pseudospin states with clockwise or counterclockwise circulating mechanical energy flux patterns in the band structure are found by calculating the projected band structures of a supercell which is composed of phononic crystals with different topological phases. Based on this finding, different constructions of phononic waveguide are used for implementing the numerical analysis to demonstrate the back-scattering immunity of the edge states when disorder, tortuosity and cavity are introduced into the waveguide. Unidirectional robust propagation and multichannel waveguide switch due to the pseudospin-dependent one-way edge modes are also validated with numerical models. The phononic crystal plate presented in this paper provides a simple realizable method of designing the topologically protected elastic edge states. </sec>

Signal injection degrades the starting performance of the brushless synchronous starter/generator (BSSG), and reversible magnetic saliency of the main generator (MG) leads to failure for most traditional sensorless methods. A novel full-speed sensorless starting control method of BSSG is proposed to solve these problems. The main exciter (ME), mechanically coupled to MG, is used as a position sensor of MG at low speed. The position of ME is extracted from the hexagonal trajectory of the rotor current space vector and then converted into the rotation angle of MG. At standstill, a fast initial position detection of MG is conducted with the electromotive force (EMF) of MG, induced by the establishment of the field current of MG. Then, the continuous position of MG is the sum of the estimated rotation angle and initial position. At high speed, flux weakening of MG is achieved by changing the structure of ME, invalidating the approach dependent on ME. Thus, estimations at low speed are replaced by ones based on extended EMF of MG gradually before the structure change. Signal injection is not needed and effects of reversible magnetic saliency are avoided in this approach. The effectiveness of this method is verified by experiments.

PurposeThis paper aims to present a concept of an automatic directional control system of remotely piloted aerial system (RPAS) during the taxiing phase. In particular, it shows the initial stages of the control laws synthesis-mathematical model and simulation of taxiing aircraft. Several reasons have emerged in recent years that make the automation of taxiing an important design challenge including decreased safety, performance and pilot workload.Design/methodology/approachThe adapted methodology follows the model-based design approach in which the control system and the aircraft are mathematically modelled to allow control laws synthesis. The computer simulations are carried out to analyse the model behaviour.FindingsChosen methodology and modelling technique, especially tire-ground contact model, resulted in a taxiing aircraft model that can be used for directional control law synthesis. Aerodynamic forces and moments were identified in the wind tunnel tests for the full range of the slip angle. Simulations allowed to compute the critical speeds for different taxiway conditions in a 90° turn.Practical implicationsThe results can be used for the taxi directional control law synthesis and simulation of the control system. The computed critical speeds can be treated as a safety limits.Originality/valueThe taxi directional control system has not been introduced to the RPAS yet. Therefore, the model of taxiing aircraft including aerodynamic characteristics for the full range of the slip angle has a big value in the process of design and implementation of the future auto taxi systems. Moreover, computed speed safety limits can be used by designers and standards creators.

This note is presented as an idea to be criticised rather than as a description of a fully developed experimental technique. There are weaknesses in the method which will prevent it from giving absolutely correct answers, for example, the twist imparted to the boundary layer when a body of revolution is rolled cannot be represented. But some of the major effects can be represented, and the idea may possibly be developed to be of practical significance.It is standard wind tunnel practice to measure the aerodynamic derivatives CYβ, C1β, Cnβ, CMβ, CLβ and CDβ by having a wind stream of constant direction, and measuring aerodynamic forces and moments on a model aircraft placed at angles of yaw and pitch to the stream.

Ten stable male non-ventilated coronary artery bypass patients (mean age 59 f 12 years) were comparatively studied with thermodilution (T.D.) and bioelectric impedance (Z) 24-48 hrs. post surgery, in the Open Heart Recovery (OHR) Unit. Cardiac outputs (CO) were compared, after blinded measurements were obtained in three sequential positions (supine, 45 degree head-up tilt and supine). (Z) cardiac outputs were compared to (T.D.) using the actual value for resistivity @) of blood (sampled at the time of the study) and assumed values of 135.5 ohm-an and 150 ohm-an. The results indicate high correlations (range = .W to 99) in the initial supine position for all resistivity conditions followed by a progressive dedine when body position is changed to 45 degrees and supine (range = .74 to 30). The highest overall correlations and closest mean CO values were obtained when (p) was measured. Signifcant (p<.02) mean differences between 2 and T.D. were observed when (p) was assumed to be 150 ohm-cm. In this spedic group of patients, impedance CO is highly correlated to T.D. CO with mean values not significantly different when (p) is measured or assumed to be 135.5 ohm-cm, yet absolute mean values are closest when (p) is not assumed.

The objective of this work was to validate a recently developed automated-chimera, domain-decomposition algorithm for the aerodynamic analysis of aircraft escape systems. This automated-chimera methodology was incorporated into the CFD-FASTRAN flow solver, which also includes a six-degree-of- freedom (6DOF) model. In particular, the methodology was demonstrated and validated by reproducing: 1) a half-scale wind tunnel test of an ACES-II ejection seat separating from an F-16 forebody, and 2) a full-scale sled test of an F/A-18 jettisonable canopy. Comparisons of CFD predictions and test data were made for six-component balance data, surface pressure data, and trajectory data.

Motion capture technology finds wide application in various fields such as entertainment, sports analysis, and biomechanics, enabling accurate digitization of real-world movements for replication in digital environments. There exist diverse motion capture systems utilizing different technologies, supported by software tools for marker movement extraction. Further processing of acquired data requires additional investment in software development. This paper presents the human motion estimator application developed using GUI in MATLAB App Designer. This application aims to generate human movement based on recorded marker data obtained from motion capture systems (MCS), currently supporting two MCSs: Vicon and ART. The developed application aims to become a universal tool for estimating human movements, supporting data from ART or Vicon MCS. The application provides visual instructions for mounting markers on the body and initialization position, while data processing is based on optimization algorithms for defined criteria functions. The application targets research institutions by providing essential software support for ART or Vicon MCSs, thus enhancing data analysis capabilities for estimating upper body movement. The application is a framework, a starting point, to be upgraded and future developed with additional MCS and features.

The motion of the SamSat-218D nanosatellite is analyzed by trajectory measurements. Special features of nanosatellite behavior in low orbits were experimentally confirmed. These features are due to both the influence of the atmosphere and the nanosatellites inherent mass-inertia characteristics: the orbital lifetime of nanosatellites is shorter, whereas angular acceleration generated by the aerodynamic moment couple is much higher than that of satellites with large sizes and masses. Variation of the ballistic coefficient in time is estimated from known trajectory measurements and information on the average density of the atmosphere at the points of trajectory measurements. The ballistic coefficient of the SamSat-218D nanosatellite having the shape of a rectangular parallelepiped depends on the spatial angle of attack and the angle of proper rotation. The ratio of the maximum value of the ballistic coefficient to the minimum value is 4.75. This made it possible to evaluate the nature of possible motion relative to the nanosatellite center of mass by the behavior of the ballistic coefficient. The most probable motion relative to the center of mass of the SamSat-218D nanosatellite is the transient motion between different equilibrium positions, due to commensurate aerodynamic and gravitational moments and insignificant angular velocities.

In acoustic power transfer systems, a receiver is displaced from a transmitter by an axial depth, a lateral offset (alignment), and a rotation angle (orientation). In systems where the receiver’s position is not fixed, such as a receiver implanted in biological tissue, slight variations in depth, orientation, or alignment can cause significant variations in the received voltage and power. To address this concern, this paper presents a computationally efficient technique to model the effects of depth, orientation, and alignment via ray tracing (DOART) on received voltage and power in acoustic power transfer systems. DOART combines transducer circuit equivalent models, a modified version of Huygens principle, and ray tracing to simulate pressure wave propagation and reflection between a transmitter and a receiver in a homogeneous medium. A reflected grid method is introduced to calculate propagation distances, reflection coefficients, and initial vectors between a point on the transmitter and a point on the receiver for an arbitrary number of reflections. DOART convergence and simulation time per data point is discussed as a function of the number of reflections and elements chosen. Finally, experimental data is compared to DOART simulation data in terms of magnitude and shape of the received voltage signal.

The aim of this paper is to investigate the aerodynamic interference effects of typical devices supporting aircraft models during wind tunnel tests by means of CFD tools. This work proposes the use of steady RANS simulations of the flow field in order to predict the interference produced by two different models of struts: (1) one that is made up of two parts and is solidal with the wind-tunnel model for variation of the angles of incidence (α) and of the angles of sideslip (β) and (b) the second that is made up of one part and is fixed for α variations and is solidal with the model for β variations. Low and high Reynolds flow conditions are considered and a typical cruise configuration of a scaled model of regional aircraft is addressed in both power-off and power-on conditions. The strut effect is investigated for several angles of incidence and sideslip. From the numerical point of view, the flow field and forces disturbance caused by the struts are derived by comparing simulations with and without the support. The interference is analysed in terms of global forces and moments coefficients and local quantities, such as pressure coefficients distributions. The main result regarding the comparison between the two models of strut is that the corrections to be applied to experimental data and the effect of both ventral struts on the global aerodynamic forces and moments are small.

The purpose of this paper is to present linear parameter varying modeling and simulation of a folding-wing morphing aircraft in the wing-folding process. Morphing aircraft can alter the shape to adapt to mission environment changing. When the wing shape is varying, the dynamic responses of the morphing aircraft will be dependent on the time-varying aerodynamic forces and moments, which will be a function of the wing shape change by the morphing command. The folding-wing morphing aircraft is regarded as a variable geometry rigid body, and the six-degree-of-freedom nonlinear dynamic model in the wing-folding process is founded. The decoupled longitudinal dynamic equation of the morphing process is deduced by simplification, and the longitudinal dynamic responses of the wing morphing process are numerically simulated by the quasi-steady aerodynamic assumption. Furthermore, using the Jacobian linearization approach, the longitudinal nonlinear dynamics equations of morphing aircraft are linearized, and the longitudinal linear parameter varying model of the morphing aircraft in the wing-folding process is obtained. Finally, the linear parameter varying model is validated by the open-loop time responses compared to the nonlinear aircraft responses. The research results can be as great reference for the linear parameter varying controller design for the morphing aircraft in the wing shape varying.

The wind tunnel balance signal detection system is widely employed in aerospace applications for the accurate and automated measurement of aerodynamic forces and moments. However, measurement errors arise under different environmental temperature. This paper addresses the issue of measurement accuracy under different temperature conditions by proposing a temperature compensation method based on an improved gray wolf optimization (IGWO) algorithm and optimized extreme learning machine (ELM). The IGWO algorithm is enhanced by improving the initial population position, convergence factor, and iteration weights of the gray wolf optimization algorithm. Subsequently, the IGWO algorithm is employed to determine the optimal network parameters for the ELM. The calibration decoupling experiment and high-low temperature experiment are designed and carried out. On this basis, ELM, GWO-ELM, PSO-ELM, GWO-RBFNN and IGWO-ELM are used for temperature compensation experiments. The experimental results show that IGWO-ELM has a good temperature compensation effect, reducing the measurement error from 20%FS to within 0.04%FS. Consequently, the accuracy and stability of the wind tunnel balance signal detection system under different temperature environments are enhanced.