Angle Velocity Research Articles

Longitudinal dynamic envelope solution and transition path optimization based on reachability analysis for fixed-wing VTOL UAVs

Flight velocity and tilt angle are commonly employed to define the safe region for fixed-wing vertical take-off and landing (FW-VTOL) UAVs as they undergo tilting, referred to as the transition corridor. Nevertheless, the transition corridor only considers the aircraft's limitations in a quasi-stationary condition and ignores the additional constraints introduced by the aircraft's kinematic behavior. To obtain a more accurate safe state space, the concept of the dynamic envelope was proposed by previous researchers. The dynamic envelope of UAV represents the safe state space taking into account aerodynamic constraints and kinematic constraints. Solving the dynamic envelope has consistently remained a focal point of research in the field. This study introduces an innovative approach that employs reachability analysis to solve the dynamic envelope of the FW-VTOL UAV during the transition stage. Building upon this, it proposes a safety index for the transition path, optimized to determine the safest transition path. Subsequently, specific case studies verified the effectiveness of the solution process and optimization method. The designed optimal path enhances safety by 9.71% compared to the basic path, signifying its practical significance in mitigating risk during the transition stage of FW-VTOL UAVs. Furthermore, the attributes of the transition path are analyzed based on two aspects: (A) a comparison between the optimal transition path and the two-dimensional transition path with a constant angle of attack; (B) an examination of how key UAV design parameters influence the transition path's safety. Overall, the methodology and general rules proposed in this study provide a theoretical basis and technical support for improving the security of FW-VTOL UAVs in the transition stage.

Residual deficits of knee and hip joint coordination and clinical performance after return to sports in athletes with anterior cruciate ligament reconstruction

BackgroundBiomechanical changes and neuromuscular adaptations have been suggested as risk factors of secondary injury in individuals after anterior cruciate ligament reconstruction (ACLr). To achieve a better understanding of preventive mechanisms, movement quality is an important factor of consideration. Few studies have explored time-series analysis during landing alongside clinical performance in injured and non-injured individuals. The purpose of the study was to investigate the biomechanical risks of recurrent injury by comparing clinical and jump-landing performance assessments between athletes with ACLr and healthy controls.MethodThis study was observational study. Sixteen athletes with and without ACLr voluntarily participated in clinical and laboratory measurements. Single-leg hop distance, isokinetic tests, landing error score, and limb symmetry index (LSI) were included in clinical report. Lower limb movements were recorded to measure joint biomechanics during multi-directional landings in motion analysis laboratory. Hip-knee angle and angular velocity were explored using discrete time-point analysis, and a two-way mixed analysis of variance (2 × 4, group × jump-landing direction) was used for statistical analysis. Time series and hip-knee coordination analyses were performed using statistical parametric mapping and descriptive techniques.ResultsSignificantly lower single-leg hop distance was noted in ACLr group (158.10 cm) compared to control group (178.38 cm). Although the hip and knee moments showed significant differences between four directions (p < 0.01), no group effect was observed (p > 0.05). Statistical parametric mapping showed significant differences (p ≤ 0.05) between groups for hip abduction and coordinate plot of hip and knee joints. Athletes with ACLr demonstrated a higher velocity of hip adduction. Time-series analysis revealed differences in coordination between groups for frontal hip and knee motion.ConclusionsAthletes with ACLr landed with poor hip adduction control and stiffer knee on the involved side. Multi-directions landing should be considered over the entire time series, which may facilitate improved movement quality and return to sports in athletes with ACLr.

Analisis Gerak Biomekanika (Kinovea Software) Untukmengembangkan Kemampuan Akurasi Shooting Sepakbola Pada Mahasiswa Fakultas Ilmu Ke Olahragawaan Universitas Negeri Makassar

Research assesses movement, shooting accuracy and knee angle in football. Using a biomechanics approach with Kinovea’s software, the study aims to evaluate the process of recording such movements, focusing on the advantages and disadvantages of the method. The sample consisted of 30 fourth semester students in the Physical Education, Sports, and Recreation Study Program at (UNM). This study used a survey method with an observational approach to analyze the relationship between knee angle and ball speed in the context of football shooting techniques. Visual recording of shooting motion techniques is done with a camera and analyzed using Kinovea’s software. The research sample consisted of 30 Physical Education, Health, and Recreation (PJKR) students who had the best shooting accuracy and were male at Makassar State University. Data on ball velocity and knee angle were analyzed using the SPSS program version 25. The results showed a Pearson correlation coefficient of 0.591, with a significance (2-tailed) of 0.001, indicating a positive and significant relationship between knee angle and ball speed. However, it should be noted that correlation does not imply causality. The first model has a coefficient of determination (R Square) of 0.349, indicating that about 34.9% of the variability in ball velocity can be explained by knee angle. An Adjusted R Square value of 0.326, indicating that the addition of predictor or sample variables will not provide a significant improvement in explaining ball velocity variability. Although there is a strong and significant relationship between knee angle and ball speed, other factors such as player technique and environmental factors can also influence this relationship. Therefore, more research is needed to understand the additional factors that influence this relationship as well as to establish a causal relationship between the two variables.

Experimental insight into dynamics of water droplet impacting on solid surface and theoretical prediction for maximum spreading coefficient at low Weber number

The hydrodynamics of a droplet impacting solid surface at low Weber number has been studied comprehensively by using a high-speed camera and a theoretical approach based on the improved models of surface energy and viscous dissipation. The impact process is elucidated by analyzing quantitatively the interface evolution of droplet impact solid surface, and the effects of glycerol solution concentration, surfactant concentration, impact velocity, and wall contact angle on spreading width and rebounding height are extensively investigated, respectively. Four stages, namely, approaching, spreading, retracting and stabilizing stages are identified visually during a complete droplet collision. Increasing the concentration of glycerol solution can simultaneously reduce droplet spreading width and rebounding height. However, improving surfactant concentration or enhancing impact velocity can promote droplet spread but hinder its rebound. Decreasing wall contact angle is beneficial to droplet propagation, whereas disadvantageous to droplet rebound. Both surface energy and viscous dissipation are accurately considered based on a real geometric shape and an improved spreading time at the maximum spreading, and thus a novel theoretical formula for the maximum spreading coefficient of droplet impacting at low Weber number has been developed and proved to have a higher prediction accuracy than the previous models under present experimental conditions.

Rock fragmentation mechanism of PDC cutter from the insight of cutting chips

To meet the global energy needs and demands, obtaining oil and gas resources from deep strata plays an increasingly important role in energy supply. However, it is difficult to drill since the special properties of rocks in deep formation. To further improve the breaking efficiency of polycrystalline diamond compact (PDC) bit in deep hard rock, this paper conducted several groups of experiments on cutting granite with PDC cutters. By changing the cutting depth, rake angle and linear velocity, the relationship between the mass proportion, fractal dimension and roughness index of cuttings and the mechanical specific energy (MSE) is explored, and the following conclusions are obtained: When cutting depth HC exceeds 0.8 mm, massive chips with particle size r > 2 mm begin to form and the brittle failure begins to occur, and the probability of brittle failure will increase with the further increase of cutting depth. With the increase of rake angle, more energy will be used to form new surfaces of cutting chips, resulting in a decrease in the roughness index and an increase in MSE. More massive chips will be formed with the increasing linear velocity, but MSE only decrease slightly. The variation of the fractal MSE (FMSE) that based on the fractal dimension of cutting chips is extremely consistent with the MSE. The relevant conclusions in this paper can provide some reference for the structural design of PDC bit, so as to improve the drilling efficiency in deep hard rock.

LES on wind turbines by comparison of Vortex Particle Method and Finite Volume Method codes

The aim of this paper is to compare two different computational methods that analyse the flow around wind turbine using Large-Eddy-Simulations (LES). The first method uses a three-dimensional unsteady Lagrangian Vortex Particle method (VP) associated to a lifting-line (LL) approach providing radial loads, integrated thrust and power coefficients, circulations and angle of attack across the turbine blades. The second method solves the incompressible Navier-Stokes equations with the classical Finite Volume (FV) method coupled to the Actuator Line (AL) method to model the rotor blades. Both methods are compared by means of a benchmark consisting in a single full-scale NREL5MW wind turbine and the results are thus compared to Martínez-Tossas et al (2018). The comparisons involve loads, angle of attack and velocity along the blade. Wakes downstream of the turbine are analysed via the evolution of flow fields as mean velocity and vorticity. Results are found to be in good agreement with the verification case. A comparison is also performed on the evaluation of the numerical cost, precision and efficiency of both computational methods.

Spreading model of single droplet impacting the banana leaf surface and computational fluid dynamics simulation analysis

The droplet deposition behavior is an important indicator of precision agriculture and sustainable agriculture 4.0. Comprehensive analysis of the behavior and modeling of pesticide droplets impacting target leaves is an important basis for achieving efficient spray deposition. In this study, banana leaves were taken as the research object, the spreading model and computational fluid dynamics (CFD) model of single droplet impacting on the target leaf surface were studied from the micro and macro perspectives. The aim is to clarify and obtain the quantitative mapping relationship between droplet deposition performance and related operating parameters. The results showed that the pesticide droplets were asymmetrically spread and slipped on the surface of the inclined banana leaves. The maximum lateral spreading diameter Dnmax was only affected by the normal component of Weber number Wen, while the maximum tangential spreading diameter Dtmax and slip distance L were affected by the normal component of Weber number Wen and the inclination angle α. As the impact velocity increases, the pesticide droplets interact with the non-smooth morphology of the banana leaf surface to form a large number of pinning sites on the edge contact line. Combining the microscopic characteristics of banana leaves with the physicochemical characteristics of the droplets, a CFD model was established to carry out single-drop impact simulation verification. The impact velocity and inclination angle were set as variables to carry out CFD simulation of the dynamic process. The numerical simulation results are consistent with the spreading model obtained from the experimental study, which can quantitatively reflect the impact process of pesticide droplets. The spreading model and CFD model of pesticide droplets impacting on the banana leaf surface established in this study, can provide guidance for the selection of pesticide application for the spray droplet deposition behavior. At the same time, it can also provide methodological reference for other crop spray research and spray technology research in other fields.

Dynamics of a bouncing capsule: An impulse model vs a Hertzian model

A capsule-shaped object, unlike a sphere, can rebound to a higher height than it is dropped from if it has an initial spin. In this paper, we compare two quantitative models of this phenomenon: an impulse-based analytic model and a force-based Hertzian model. We experimentally studied the effects of impact angular velocity and contact angle on the capsule's rebounding velocity and angular velocity. Our experimental findings showed successful agreement with our Hertzian model but not with our impulse model. We attribute the comparative success of the Hertzian model to its intricate treatment of the slip–stick behavior of friction during the collision.

Design and analysis of a lower limb assistive exoskeleton robot.

In recent years, exoskeleton robot technology has developed rapidly. Exoskeleton robots that can be worn on a human body and provide additional strength, speed or other abilities. Exoskeleton robots have a wide range of applications, such as medical rehabilitation, logistics and disaster relief and other fields. The study goal is to propose a lower limb assistive exoskeleton robot to provide extra power for wearers. The mechanical structure of the exoskeleton robot was designed by using bionics principle to imitate human body shape, so as to satisfy the coordination of man-machine movement and the comfort of wearing. Then a gait prediction method based on neural network was designed. In addition, a control strategy according to iterative learning control was designed. The experiment results showed that the proposed exoskeleton robot can produce effective assistance and reduce the wearer's muscle force output. A lower limb assistive exoskeleton robot was introduced in this paper. The kinematics model and dynamic model of the exoskeleton robot were established. Tracking effects of joint angle displacement and velocity were analyzed to verify feasibility of the control strategy. The learning error of joint angle can be improved with increase of the number of iterations. The error of trajectory tracking is acceptable.

Simultaneous rotation-nutation suppression for a tumbling satellite via a flexible rod

Effectively capturing a malfunctioning tumbling satellite by a servicing spacecraft is nowadays a worldwide challenge. Because of the potential collision between the chaser and the target spacecraft, it is risky to directly capture the tumbling satellite. An innovative approach is to use a flexible brush/rod as the end-effector of a chaser to tackle the tumbling target. However, almost all studies are confined to reducing the pure rotational motion without considering the inevitable nutation motion. To ensure safe capture, it is necessary to suppress both the nutation and rotation simultaneously to the desired low level. There are two difficulties with the simultaneous suppression problem: i) the ideal contact point between the rod and the target is difficult to pinpoint for simultaneous suppression, and ii) the solution of the rod-target dynamic system (described by nonlinear partial differential equations) is extremely time-consuming especially with the limited computing capability of the on-board computer. To conquer these difficulties, a simultaneous rotation-nutation suppression (SRNS) method based on the equal ratio principle is proposed to simultaneously reduce angular velocity and nutation angle. Besides, a highly efficient simplified rod-target model is established based on machine learning. Numerical simulations have been carried out to verify the effectiveness and efficiency of the proposed method.

Trajectory Optimization and Multiple-Sliding-Surface Terminal Guidance in the Lifting Atmospheric Reentry

AbstractIn this paper, the problem of guiding a vehicle from the entry interface to the ground is addressed. The Space Shuttle Orbiter is assumed as the reference vehicle and its aerodynamics data are interpolated to properly simulate its dynamics. The transatmospheric guidance is based on an open-loop optimal strategy which minimizes the total heat input absorbed by the vehicle while satisfying all the constraints. Instead, the terminal phase guidance is achieved through a multiple-sliding-surface technique, which is able to drive the vehicle toward a specified landing point with desired heading angle and vertical velocity at touchdown, even in the presence of nonnominal initial conditions. The terminal guidance strategy is successfully tested through a Monte Carlo campaign, in the presence of stochastic winds and wide dispersions on the initial conditions at the terminal area energy management, in more critical scenarios with respect to the orbiter safety criteria.

Chip breakage in silk microfibre production using elliptical vibration turning

To overcome the precision limitation and environmental impact of current chemical-based production methods for manufacturing silk microfibres used for targeted drug delivery, this paper presents a high-precision, scalable, eco-friendly mechanical machining approach to produce such microfibres in the form of discontinuous chips obtained through elliptical vibration turning of silk fibroin film using a diamond tool. The length and waist width of fabricated microfibres can be precisely controlled. As each vibration cycle will produce one silk microfibre, complete and deterministic chip breakage becomes an essential and challenging task in this approach due to its unique two-phase structure. Thus, the hybrid FE-SPH numerical simulations and machining experiments were conducted to gain a pioneering and in-depth exploration of the chip-breaking mechanism in this process. It was found that applying a low depth ratio (ratio of the nominal depth of cut to the tool path vertical amplitude) and a high horizontal speed ratio (the nominal cutting speed versus the critical workpiece velocity) could effectively reduce the average tool velocity angle (the angle from the deepest cut to the tool exit point along the cutting direction). A smaller angle would enhance the diamond tool's shearing action and led to the reduction of hydrostatic pressure in the cutting zone and a consequent decrease in the ductility of silk fibroin due to its unique structure dominated by beta-sheet crystallites. The above adjustments collectively facilitated chip breakage. This paper, therefore, established a governing rule for the controlled and repeatable formation of microfibres based on the average tool velocity angle for the first time and revealed that the cutting chips would undergo complete and deterministic breakages once the angle approached below 22.6°. On this basis, the high-precision and scalable manufacturing of silk microfibres with precisely controllable length and waist width was ultimately achieved.

Event-triggered consensus tracking control of flexible manipulators with nonlinear time-varying fault-tolerant actuators and input constraint

This paper introduces a novel event-triggered consensus control strategy for a multi-agent system composed of underactuated flexible manipulators. Most existing research on consensus tracking control assumes that the model targeted is fully actuated, the control signal is continuous, and that both time-varying actuator failures and input constraints are managed separately. These challenges were tackled in this study within the context of multi-agent systems, addressing input constraints and nonlinear time-varying actuator failures simultaneously. Moreover, an event-triggered mechanism is proposed to reduce signal communication. A double closed-loop consensus tracking method is designed based on the multi-agent topology, enabling all flexible manipulators to track the angle and angular velocity of the leader and an adaptive control law is designed to solve actuator faults. Finally, the simulation results demonstrate the effectiveness of the proposed control scheme.

Elastic-plastic collision mechanism of micron-sized particle impacting rough surfaces

The interaction between micron-sized particles and rough surfaces represents a common natural phenomenon. Diverse Gaussian rough surfaces are reconstructed by utilizing inverse Fourier transformation, and the impact of surface roughness on the collision of micron-sized particles is investigated, scrutinized through the sizes of RMS roughness and correlation length from 0.025 μm to 0.2 μm. Given the relevance of surface roughness to particle size, it focuses on 1 μm particles collision—a dimension representative size ingested in the turbine blade cooling passage. The results indicate that RMS roughness primarily influences the height of asperities, whereas correlation length predominantly affects the density of asperities. COR diminishes with increasing roughness, and does not exhibit a decline with escalating speed, when the correlation length is small. The maximum contact area remains relatively constant with the larger roughness. Rotational velocity and rebound angle are predominantly impacted by the RMS roughness, less influence of the correlation length.

Numerical Simulation of Extreme Ice Loads on Complex Pile Legs of Offshore Substation Structures

The sea ice failure mode and ice force amplitude depend on the structural form at the point of interaction, but the impacts of ice load when interacting with marine engineering structures with additional attachments are not yet clear. This study conducts numerical simulations using the discrete element method to investigate the interaction between sea ice and cable pipes attached to offshore substation structures. Various operating conditions such as ice velocity, ice thickness, and ice attack angle are selected to simulate the interaction between sea ice and such structures, clarifying the variations in the sea ice failure mode and ice force amplitude. The results indicate that crushing failure mainly occurs when sea ice interacts with such structures, and the presence of cable pipes does not alter the sea ice failure mode at the legs of offshore substation structures. The preliminary action of sea ice with cable pipes effectively reduces the ice load on the structure, and the minimum ice force amplitude occurs at an ice attack angle of 90°, with the ice force amplitude increasing with the ice thickness but showing no clear correlation with the ice velocity. The findings of this study provide a reference for the ice-resistant design of offshore substation structures in cold regions.

Prescribed-time integrated guidance and control for bank to turn reentry vehicle

In this paper, a novel prescribed-time integrated guidance and control (IGC) with spiral maneuvering deceleration (SMD) method is developed for bank to turn (BTT) reentry vehicle with the consideration of elevation angle and terminal velocity constraints. First, a strict feedback form IGC model is established for BTT reentry vehicle under multiple constraints. Second, a prescribed-time sliding mode controller (SMC) based on prescribed-time extended state observer (ESO) is designed to hit the ground fixed target with the desired line of sight (LOS) elevation angle. Then in order to make the reentry vehicle achieve a better strike effect, it is necessary to constrain the terminal velocity of the reentry flight, a SMD scheme is proposed to achieve the desired terminal velocity. Finally, the efficiency of the proposed scheme is verified by six–degree–of–freedom (6DoF) numerical simulations.

Generation of Propagation-Dependent OAM Self-Torque with Chirped Spiral Gratings

The application of non-uniform spiral gratings to control the structure, topological parameters and propagation of orbital angular momentum (OAM) beams was studied experimentally with coherent near-infrared light. Adapted digital spiral grating structures were programmed into the phase map of a high-resolution liquid-crystal-on-silicon spatial light modulator (LCoS-SLM). It is shown that characteristic spatio-spectral anomalies related to Gouy phase shift can be used as pointers to quantify rotational beam properties. Depending on the sign and gradient of spatially variable periods of chirped spiral gratings (CSGs), variations in rotation angle and angular velocity were measured as a function of the propagation distance. Propagation-dependent self-torque is introduced in analogy to known local self-torque phenomena of OAM beams as obtained by the superposition of temporally chirped or phase-modulated wavepackets. Applications in metrology, nonlinear optics or particle trapping are conceivable.

Simulations of beta-induced Alfvén eigenmode mitigation by off-axis energetic particle distribution

The effect of different off-axis energetic particle (EP) slowing down distribution on beta-induced Alfvén eigenmode (BAE), driven by the on-axis EP distribution, is systematically studied using kinetic-magnetohydrodynamic code M3D-K. The aim is to analyze the optimal parameter region for controlling AEs via varying EP distribution parameters. The simulation results reveal that by modifying the gradients of the EP distribution, the off-axis EP can further destabilize or mitigate the on-axis EP driven BAE, depending on the off-axis EP distribution’s parameters: deposition profile, EP beta, pitch angle, injection velocity and direction. When the off-axis EP is deposited outside the mode center, and its injection velocity is sufficiently large to satisfy the resonance with BAE, the stabilization of BAE is achieved. This stabilizing effect is directly proportional to the off-axis EP beta, while excessive off-axis EP beta can trigger a new EP-driven instability located outside the BAE. Furthermore, to achieve a stronger stabilizing effect, the pitch angle distribution and velocity direction of the off-axis EP should be close to those of the on-axis EP. For instance, compared to the off-axis counter-passing EP, the off-axis co-passing EP can lead to a more effective mitigation of the BAE driven by the on-axis co-passing EP.

High–speed train crash safety assessment for Train–moose collisions

High–speed train crash safety assessment for Train–moose collisions

A VISION-BASED SYSTEM DESIGN AND IMPLEMENTATION FOR ACCIDENT DETECTION AND ANALYSIS VIA TRAFFIC SURVEILLANCE VIDEO

This study aims to test the entire framework on an AI demo board and investigate the issue of automatically and effectively recognizing and analyzing traffic incidents captured by surveillance cameras. To begin, the motion interaction field (MIF) method, which is capable of detecting collisions in video, is used to locate damaged automobiles based on the interactions of various moving objects. Second, the location of the destroyed vehicles is determined using the YOLO v3 model. Using a hierarchical clustering method, the vehicle trajectories prior to the collision are recovered, and the related trajectories are reconstructed. Finally, a perspective transformation is used to project the trajectory into a vertical view to help traffic cops make better decisions. The unbiased finite impulse response (UFIR) method, which does not require statistical information about the external noise, is used to estimate the vehicle's velocity. The estimated velocity and impact angle from the vertical view can then be used to investigate the traffic accident. Finally, a Huawei AI demo board called HiKey970, which was used to code all of the aforementioned algorithms, is used in an experiment to show how useful and effective the proposed method is in practice. A few mishap observation recordings are sent onto the demo board. Mishaps are recognized and the proper vehicle directions are gathered.