Angular Acceleration Research Articles

Simulation and kinematic analysis of a 3-DOF marine antenna pedestal focusing on singularity avoidance and its effects on angular velocity and angular acceleration

Simulation and kinematic analysis of a 3-DOF marine antenna pedestal focusing on singularity avoidance and its effects on angular velocity and angular acceleration

Head Kinematics Associated with Off-Field Head Injury Assessment (HIA1) Events in a Season of English Elite-Level Club Men's and Women's Rugby Union Matches.

The purpose of this study was to investigate head kinematic variables in elite men's and women's rugby union and their ability to predict player removal for an off-field (HIA1) head injury assessment. Instrumented mouthguard (iMG) data were collected for 250 men and 132 women from 1865 and 807 player-matches, respectively, and synchronised to video-coded match footage. Head peak resultant linear acceleration (PLA), peak resultant angular acceleration (PAA) and peak change in angular velocity (dPAV) were extracted from each head acceleration event (HAE). HAEs were linked to documented HIA1 events, with ten logistical regression models for men and women, using a random subset of non-case HAEs, calculated to identify kinematic variables associated with HIA1 events. Receiver operating characteristic curves (ROC) were used to describe thresholds for HIA1 removal. Increases in PLA and dPAV were significantly associated with an increasing likelihood of HIA1 removal in the men's game, with an OR ranging from 1.05-1.12 and 1.13-1.18, respectively. The optimal values to maximise for both sensitivity and specificity for detecting an HIA1 were 1.96krad⋅s-2, 24.29 g and 14.75 rad⋅s-1 for PAA, PLA and dPAV, respectively. Only one model had any significant variable associated with increasing the likelihood of a HIA1 removal in the women's game-PAA with an OR of 8.51 (1.23-58.66). The optimal values for sensitivity and specificity for women were 2.01 krad⋅s-2, 25.98 g and 15.38rad⋅s-1 for PAA, PLA and dPAV, respectively. PLA and dPAV were predictive of men's HIA1 events. Further HIA1 data are needed to understand the role of head kinematic variables in the women's game. The calculated spectrum of sensitivity and specificity of iMG alerts for HIA1 removals in men and women present a starting point for further discussion about using iMGs as an additional trigger in the existing HIA process.

Angular Bloch oscillations and their applications

Abstract To advance inertial navigation, we present the scheme for a compact quantum sensor which is based on the quantum phenomenon of the angular Bloch oscillations and measuring exclusively the angular acceleration of slow external rotation. We study the dynamics of ultra-cold atoms confined in a toroidal trap with a ring-lattice along the azimuth angle, realized with the superposition of two copropagating Laguerre–Gaussian beams. In the presence of external rotation with a small angular acceleration, or a prescribed linear chirp between the two beams, the measured angular momentum of the trapped atoms exhibits a specific periodic behaviour in time, which we call as the angular Bloch oscillations. This quantum phenomenon is shown to be a key element of fruitful applications for (i) an efficient transfer of quantized angular momentum from the light to the atoms by controlling the chirp, and (ii) the direct determination of the angular acceleration of external rotation by measuring the Bloch period.

Modeling and analysis of nonlinear dynamics of axisymmetric vector nozzle based on deep neural network

Abstract The axisymmetric nozzle mechanism is the core part for thrust vectoring of aero engine, which contains complex rigid-flexible coupled multibody system with joints clearance and significantly reduces the efficiency in modeling and calculation, therefore the kinematics and dynamics analysis of axisymmetric vectoring nozzle mechanism based on deep neural network is proposed. The deep neural network model of the axisymmetric vector nozzle is established according to the limited training data from the physical dynamic model and then used to predict the kinematics and dynamics response of the axisymmetric vector nozzle. This study analyses the effects of joint clearance on the kinematics and dynamics of the axisymmetric vector nozzle mechanism by a data-driven model. It is found that the angular acceleration of the expanding blade and the driving force are mostly affected by joint clearance followed by the angle, angular velocity and position of the expanding blade. Larger joint clearance results in more pronounced fluctuations of the dynamic response of the mechanism, which is due to the greater relative velocity and contact force between the bushing and the pin. Since axisymmetric vector nozzles are highly complex nonlinear systems, traditional numerical methods of dynamics are extremely time-consuming. Our work indicates that the data-driven approach greatly reduces the computational cost while maintaining accuracy, and can be used for rapid evaluation and iterative computation of complex multibody dynamics of engine nozzle mechanism.

Development of a method for the impact performance characterization of commonly worn helmets in rodeo bull-riding

As the rodeo sport of bull-riding increases in popularity, dangers to bull-rider athlete safety continue to pose serious health risks. Despite frequent occurrences of head trauma in the sport, current test methods for evaluating helmets commonly worn in bull-riding fail to consider rotational head acceleration, which is correlated to concussive events in impact sports. Additionally, the second most prevalent mechanism contributing to head trauma in bull-riding is bull kick impacts, which have yet to be accurately modeled in a test method. Researchers aim to enhance bull-rider athlete protection through the development of a helmet test method that simulates bull kicks with a pneumatic linear impactor. The proposed test method considers impacts at two impact velocities and six impact locations using a flat and Equestrian Hazard Anvil. Two commonly worn helmets in bull-riding are evaluated in this study, and an adequate sample size is determined from analyzing variation between repeated impacts. The proposed test method is statistically validated, and researchers show that impacts at higher kicking velocities and impacts with the flat anvil result in increased rotational head accelerations. Ultimately, this study emphasizes the need for helmets designed specifically for the unique impacts of bull-riding by simulating bull kicks through pneumatic linear impactor testing to reduce rotational head kinematics and hoof penetration.

System Tautochronic Path for Pendulum Vibration Absorber Based on Simple Harmonic Oscillator Transformation

Abstract Centrifugal pendulum vibration absorbers (CPVAs) are essentially collections of pendulums attached to a rotating component or components within a mechanical system for the purpose of mitigating the typical torsional surging that is inherent to internal combustion engines and electric motors. The dynamic stability and performance of CPVAs are highly dependent on the motion path defined for their pendulous masses. Assemblies of absorbers are tuned by adjusting these paths such that the pendulums respond to problematic orders (multiples of average rotation speed) in a way that smooths the rotational accelerations arising from combustion or other nonuniform rotational acceleration events. For most motion paths, pendulum tuning indeed shifts as a function of the pendulum response amplitude. For a given motion path, the tuning shift that occurs as pendulum amplitude varies produces potentially undesirable dynamic instabilities. Large amplitude pendulum motion that mitigates a high percentage of torsional oscillation while avoiding instabilities brought on by tuning shift introduces complexity and hazards into CPVA design processes. Therefore, identifying pendulum paths whose tuning order does not shift as the pendulum amplitude varies, so-called tautochronic paths, may greatly simplify engineering design processes for generating high-performing CPVAs. To illustrate this new approach and results, a tautochronic cutout shape producing constant period system motion is obtained for a simplified problem involving a mass sliding in the cutout of a larger mass that is free to translate horizontally without friction in a constant gravitational field, where the translating base mass replaces the rotating rotor in the centrifugal field.

Poincaré tornados.

We show that Poincaré polarization singularities, spiraling like a tornado, can be generated by superimposing two orthogonally polarized, abruptly auto-focusing ring-Airy beams that carry orbital angular momentum (OAM). Seeded by phase vortices of the same helicity, which are adapted to the high-intensity rings of one of the superimposing beams, these polarization singularities follow trajectories that twist and shrink in an accelerating fashion along their propagation. Reaching angular acceleration that exceeds 120 rad/mm2, these Poincaré tornados can find application in singular optics, wavefront shaping, polarization engineering, and imaging through complex media.

Comparison of three different ice hockey helmets using an ice hockey specific test protocol

Although there are currently no standard tests measuring rotational head motion for ice hockey, researchers have proposed test methods which induce rotational head motion from an impact and may reflect more closely how concussions occur in the sport. Recently, Meehan et al. developed a test method for ice hockey helmets to represent concussive injuries associated with ice hockey. While that provided a method that used impact parameters closer to what may be experienced, the research did not evaluate if different helmets would produce differing results under those loading conditions. The purpose of this study is to use the methods developed by Meehan et al. to evaluate the protective capacity of three different ice hockey helmet designs. This research used monorail drop rig and pneumatic ram systems to follow the protocol of Meehan with a bare headform condition and three different helmet designs, allowing for differences in linear and rotational acceleration, rotational velocity, and maximum principal strain to be determined. The results of this research found that the test method developed by Meehan et al. does result in significant differences between different helmets and helmet designs under identical impact conditions. However, these differences were limited which may be a reflection of the test method as well as commonality in terms of how ice hockey helmets are designed; the different models may not be sufficiently different enough to provide different results under these loading conditions.

Helmets with lattice liners can mitigate traumatic brain injury from impacts

This study explores the effectiveness of architected lattice structures, specifically made of PA12 material, as potential helmet liners to mitigate traumatic brain injuries (TBI), with a focus on rotational acceleration. Evaluating three lattice unit cell topologies (simple cubic, dode-medium, and rhombic dodecahedron), the research builds upon prior investigations indicating that PA12 lattice liners may outperform conventional EPS liners. Employing a high-fidelity finite element male head model and utilizing direct and oblique impact scenarios, mechanical quantities, such as maximum principal strain (MPS) and shear strain, cumulative strain damage measure and intracranial pressure were measured at the tissue level in different brain regions, Results indicate that lattice liners, especially with dode-medium topology, exhibit promising reductions in brain tissue strains. On average, during oblique impacts, less than 1 % of the brain volume experienced an MPS level of 0.4 when the lattice liners were adopted, whereas that percentage was above 70 % with the expandable polystyrene (EPS) foam liners. Pressure-based assessments suggest that lattice liners may outperform EPS liners in oblique impacts, showcasing the limitations of EPS for effective TBI mitigation. Despite certain model limitations, this study emphasizes the need for advancements in helmet technology, particularly in the development of commercial lattice liners using additive manufacturing, to address the limitations of existing EPS liners in preventing rotational consequences of impacts and reducing TBI.

Analyze the moment of inertia of an object in uniformly accelerated linear motion and angular motion

Abstract. In studying particle kinematics, calculus plays an important role in analyzing and solving motion problems as a key mathematical tool. This paper mainly discusses the application of calculus in uniformly accelerated linear motion (LM) and angular motion (AM), focusing on the relationship between position, velocity, and acceleration and the analysis of the rate of change of motion. Through the study of uniformly accelerated LM, this paper guides researchers to use calculus to establish the mathematical relationship between position, velocity, and acceleration and verifies the accuracy of these formulas through practical cases. Similarly, in AM, this paper provides an in-depth understanding of the dynamic behavior of an object rotating around a fixed axis through calculus and calculates and applies important parameters in AM to solve practical problems by analyzing angular velocity and acceleration. In addition, this paper demonstrates the potential of calculus for a wide range of applications in dealing with variable speed motion and rate of change analysis. By integrating the rate of change of displacement and acceleration, it provides a precise tool for the optimization and resolution of engineering problems. In conclusion, calculus not only enriches the theory of kinematics but also demonstrates its important value in practical applications.

Analysis of the third class mechanism using the modeling method in the Mathcad software environment

Purpose. To carry out a kinematic analysis of a flat twelve-link hinged mechanism with three leading links, the basis of which is a structural group of links of the third class of the fourth order with rotational kinematic pairs, which is used in technological equipment. Methodology. The kinematic study of a flat complex mechanism of the third class with three leading links was performed using the mathematical modeling method in the Mathcad software environment. Findings. Using the method of mathematical modeling, the mechanism was presented in the form of free vectors built on its links, for which, taking into account the presence of three leading links, three vector contours were selected, which made it possible to draw up a system of vector equations of their closedness with further solving by a numerical method in the Mathcad software environment. The functions of the rotation angles of the mechanism links, their angular velocities and accelerations were obtained in analytical and graphical form depending on the rotation angle of the first driving crank of the mechanism, the calculation of the angular velocities and accelerations of all the driven links of the mechanism was performed. Originality. A sequence was developed and a kinematic study of a complex planar mechanism of the third class with three leading links was done, the basis of which is a structural group of links of the third class of the fourth order. Schematic modeling of the mechanism with three leading links was performed, a visualization schedule of its kinematic scheme was built, and a valid version of its assembly was obtained from many possible ones, for which the values of kinematic parameters of all its links were determined. Practical value. An analysis of the effect of the kinematic parameters of the three leading links of the third-class mechanism on the movement of the working body of the technological equipment was carried out. From the analysis of the obtained research results for the cycle of the mechanism the reason was found for the incomplete technological stoppage of the link, which should provide the working body of the machine for the required period of time. Recommendations of the elimination were made to identify the deficiency and proposals for the need to improve the drive of this equipment.

Impact of gradient microstructure on strain hardening via activation of multiple deformation mechanisms in CoCrNi medium entropy alloy

Abstract Face centered cubic (FCC) structural medium/high entropy alloys (MEAs), characterized by excellent strength and ductility, have attracted significant attention by the research community. The incorporation of gradient structures (GSs) further can enhance their mechanical properties. In the present research, we employ the rotation acceleration shot peening technique to introduce a GS within the CoCrNi FCC MEA to investigate underlying mechanisms governing the physical deformation processes during the generation of GSs through processing, which the primary goal is mitigating the intrinsic trade-off between strength and ductility. Through the microstructures analysis along the depth direction, both pre and post uniaxial tensile plastic deformation, we unveiled that the low stacking fault (SF) energy characteristic of the CoCrNi MEA triggered the emergence of diverse defects in the core region. The presence of nanoscale deformation twins, SFs, Lomer–Cottrell dislocation locks and phase transformation from FCC to hexagonal close-packed at twin boundaries synergistically enhanced the strain hardening capacity of the material.

Development of the numerical differentiation method for approximating pitch acceleration using sensor fusion approach

In this paper, a novel algorithm is proposed to accurately estimate pitch acceleration that is crucial for moment coefficient estimation of the mathematical model of aircraft and control design in the presence of measurement noise. The angular velocity of the body as well as the Euler angles provided by the navigation system are used to interpolate the attitude trajectories using an algorithm based on the Hermite-spline polynomial. By differentiating the resultant trajectory function, the angular acceleration can be estimated accurately. This paper also analyzes a well-known method-Poplavski method based on polynomial regression, developed by the Russian scientist B.K. Poplavski to estimate derivatives. The simulation results obtained from the novel algorithm are compared with those obtained using the Poplavski method. The results verified that the novel algorithm that uses both pitch angle and angular velocity provides better accuracy in estimating pitch acceleration than the Poplavski method does, regardless of the sampling rate, which is very important in numerical differentiation and the noise level.

A joint acceleration planning method for inverse kinematics of manipulator based on second-order system with variable impedance

The paper presents an angular acceleration planning method for joint space of manipulator to achieve real-time tracking tasks under joint constraint. To improve the performance of the algorithm and ensure the joint limit, the proposed method establishes a Second-order System with Variable Impedance (SSVI). The Second-order System is introduced in the joint space through the joint angular acceleration in second derivative of kinematics. The impedance parameters vary with different states of joint and the variable impedance produced virtual repulsive force to ensure that the joint motions are within the specified ranges when they are close to limits. The damping impedance contained in the system can improve convergence speed and suppress system oscillation and vibration caused by factors such as the visual noise. Simulation and experiment results verify that the method is effective and has faster convergence speed and more smooth motion compared with other methods.

The influence of sand content on dynamic behaviors of ballast bed from a multiscale perspective

In desert regions, sand intrusion into the ballast bed is unavoidable, leading to a reduction in the elasticity of the ballast bed and posing potential risks to the service safety. Previous studies have focused on the behaviors of sandy ballast beds in 2D planes using discrete element method (DEM), where sand content is typically calculated utilizing sand areas within the ballast voids, different from that using sand volumes or mass in 3D space. Therefore, the impacts of sand content on the multiscale responses of the ballast bed are not fully addressed. In this paper, 3D full-scale half-sleeper models with various sand contents are established via DEM. Multiscale responses of sandy ballast bed obtained by laboratory tests are utilized to verify the reliability of established models. Simulation results show that macroscopically, sand intrusion increases the stiffness and consequently reduces the elasticity of the ballast bed. Microscopically, sand contaminant restricts the translational acceleration of ballast particles, while simultaneously intensifying the angular acceleration. In terms of particle contact, the anisotropy of the directional distribution of contact force among ballast particles is weakened by sand contaminant. Therefore, the inter-particle contact force among ballast particles becomes more uniform, particularly beneath the rail. A normalized parameter is proposed to quantify the filling effect of sand contaminant, based on which the relationships between multiscale dynamic responses and sand content are linearized. The linearization results indicate that the sand intrusion has more significant impacts on the multiscale responses of the ballast bed under higher loading magnitude.

Exploring the impact of sepak takraw ball heading on brain injury risk: An analytical and experimental investigation

Sepak takraw, a unique sport resembling volleyball but played with the legs, is popular in Asia. Players often use their foreheads to receive the ball, exposing them to potential brain injuries. This research evaluates the potential for brain injuries from heading in sepak takraw. Using both analytical and experimental approaches, we developed a mathematical model adapted from soccer-related studies to predict peak linear acceleration (PLA). We also conducted laboratory experiments to measure PLA and peak rotational acceleration (PRA) using a ball launcher and an Anthropomorphic Test Device (ATD). The mathematical model demonstrated a high level of accuracy in PLA prediction, confirming its reliability. Comparative analysis with soccer and water polo studies revealed that the measured PLA, PRA, and Head Injury Criteria (HIC) values for sepak takraw are below suggested concussion thresholds, indicating a lower risk of brain injury. However, this assessment does not account for the cumulative effects of repetitive head impacts, which increase the risk of brain injury over time. Despite sepak takraw’s distinct play style, the findings indicate that while the inherent risk of head injury from single impacts may be low, the potential long-term effects of repetitive impacts warrant further investigation. This study enhances the understanding of sports-related brain injuries and highlights the need for further research into subconcussive impacts and the development of protective measures. Our research paves the way for more comprehensive investigations, including field experiments, which are crucial for a nuanced understanding of sepak takraw’s impact dynamics.

Study of the Mechanism of Perceived Rotational Acceleration of a Bionic Semicircular Canal on the Basis of the "Circular Geometry Hypothesis".

Academia often uses the "circular geometry hypothesis" to explain the sensing principle of the human semicircular canal (SCC) system for angular acceleration, which is widely accepted as an important angular acceleration sensor in the human balance system. On the basis of this hypothesis and the anatomical structure of human SCCs, a series of physical SCC models with different geometries at 4× magnification were prepared via three-dimensional printing and modification of hydrogels. Theoretical models of the SCC perception mechanism were established. Then, impulse angular acceleration, sinusoidal rotation, and sinusoidal linear stimulation were applied to the models, and their responses were visually observed and analyzed in detail. As a result, the circular SCC model had a larger system gain and a smaller phase difference for angular acceleration stimulation but a smaller system gain and a larger phase difference for linear acceleration stimulation. These results verified that the circular semicircular canal was more sensitive to angular acceleration. Our bionic model is hoped to be used for demonstrating the human SCC working process, facilitating researchers in better understanding of the working mechanism of the human SCC, or as a manual model for medical staff to simulate the diagnosis and treatment of human SCC.

Determination of the dynamic stiffness matrix of a rail damper and application to vibration decay rate

In this paper, the 6×6 dynamic stiffness matrix of a rail damper seen by a short section of rail is defined based on the force simplification theory, and a method to determine the matrix is presented. According to the method, frequency response functions (FRFs) between specific points on the rail as a rigid body are measured with hammer testing. These FRFs are then used to express the acceleration of the mass center of the rail as well as the rail's angular acceleration. As the third step, the equations of motion of the rail are established based on the laws of momentum and moment of momentum, from which the dynamic stiffness matrix can be worked out. The method is then applied to determine the dynamic stiffnesses of a typical damper, and the determined dynamic striffnesses are combined with an infinite periodic track model to stduy the effect of the damper on the verical and lateral vibration decay rates of the rail.

Player and match characteristics associated with head acceleration events in elite-level men’s and women’s rugby union matches

ObjectiveTo examine the likelihood of head acceleration events (HAEs) as a function of previously identified risk factors: match time, player status (starter or substitute) and pitch location in elite-level men’s...

Analysis and optimization of quantitative casting motion of a casting and pouring robot

According to the specifications of a 20 kg load for the casting barrel, we have crafted a three-dimensional model of the robot and scrutinized the three phases of liquid level variation within the casting barrel throughout the casting procedure. Following our analysis, it has been ascertained that the relationship between time and angle is an implicit function, rendering the discovery of an analytical expression for time in terms of angle unattainable. The dynamics of the casting barrel have been emulated using MATLAB, revealing the presence of critical points in the function plot. Upon fitting the original function with a fifth-degree polynomial interpolation, the resultant fifth-degree polynomial function depicting time against angular acceleration exhibits significant oscillations, particularly at the critical points. To address this, a proportional integral derivative algorithm, predicated on the discretization of time and acceleration functions, has been implemented for rectification. The outcomes demonstrate that this approach effectively diminishes the oscillation amplitude of the function plot and enhances its alignment with the original function.