scholarly journals Analysis of SamSat-218D nanosatelite motion acording to trajectory measurements

2020 ◽  
Vol 18 (4) ◽  
pp. 18-28
Author(s):  
I. V. Belokonov ◽  
I. A. Timbai ◽  
P. N. Nikolaev ◽  
U. M. Orazbaeva
Keyword(s):  
Center Of Mass ◽  
Angle Of Attack ◽  
Angular Acceleration ◽  
Average Density ◽  
Rectangular Parallelepiped ◽  
Transient Motion ◽  
Ballistic Coefficient ◽  
Maximum Value ◽  
Angular Velocities ◽  
Aerodynamic Moment

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.

Laboratory and field evaluation of a small form factor head impact sensor in un-helmeted play

2017 ◽  
Vol 232 (3) ◽  
pp. 242-254 ◽  
Author(s):  
Derek Nevins ◽  
Kasee Hildenbrand ◽  
Jeff Kensrud ◽  
Anita Vasavada ◽  
Lloyd Smith
Keyword(s):  
Form Factor ◽  
Center Of Mass ◽  
False Negative ◽  
Angular Acceleration ◽  
Linear Acceleration ◽  
Field Evaluation ◽  
Head Impact ◽  
Sensor Data ◽  
Small Form ◽  
Small Form Factor

Head impact sensors are increasingly used to quantify the frequency and magnitude of head impacts in sports. A dearth of information exists regarding head impact in un-helmeted sport, despite the substantial number of concussions experienced in these sports. This study evaluated the performance of one small form factor head impact sensor in both laboratory and field environments. In laboratory tests, sensor performance was assessed using a Hybrid III headform and neck. The headform assembly was mounted on a low-friction sled and impacted with three sports balls over a range of velocities (10–31 m/s) at two locations and from three directions. Measures of linear and angular acceleration obtained from the small form factor wireless sensor were compared to measures of linear and angular acceleration obtained by wired sensors mounted at the headform center of mass. Accuracy of the sensor varied inversely with impact magnitude, with relative differences across test conditions ranging from 0.1% to 266.0% for peak linear acceleration and 4.7% to 94.6% for peak angular acceleration when compared to a wired reference system. In the field evaluation, eight male high school soccer players were instrumented with the head impact sensor in seven games. Video of the games was synchronized with sensor data and reviewed to determine the number of false positive and false negative head acceleration event classifications. Of the 98 events classified as valid by the sensor, 20.5% (20 impacts) did not result from contact with the ball, another player, the ground or player motion and were therefore considered false positives. Video review of events classified as invalid or spurious by the sensor found 77.8% (14 of 18 impacts) to be due to contact with the ball, another player or player motion and were considered false negatives.

scholarly journals Non-coplanar interplanetary flight simulation considering motion relative to the center of mass peculiarities of solar sail spacecraft

2020 ◽  
Vol 4 (3) ◽  
pp. 141-150
Author(s):  
R. M. Khabibullin ◽  
O. L. Starinova
Keyword(s):  
Thin Film ◽  
Center Of Mass ◽  
Control Program ◽  
Solar Sail ◽  
Flight Simulation ◽  
Light Pressure ◽  
Second Stage ◽  
Third Stage ◽  
Angular Velocities ◽  
The Hill

The paper is devoted to the non-coplanar interplanetary Earth–Venus flight of a spacecraft equipped with a non-perfectly reflecting solar sail, the magnitude and direction of acceleration from which is calculated taking into account specular and diffuse reflections, absorption and transmission of photons by the surface of the solar sail. The goal of the heliocentric motion is to transfer the solar sail spacecraft into the Hill sphere of Venus with zero hyperbolic excess of speed. A feature of the paper is the study of the motion of a non-perfectly reflecting solar sail spacecraft taking into account the motion relative to the center of mass. The problem is divided into three stages. At the first stage, a nominal program for controlling the motion of the spacecraft center of mass is formed. At the second stage, sufficient angular velocities are determined to ensure the obtained nominal control program and the parameters of the spacecraft controls – thin-film controls located along the perimeter of the solar sail – are calculated. The operating principle of the thin-film controls is quite simple. When the voltage applied to the thin-film controls changes, they become transparent or opaque, there is a difference in the normal components of the light pressure forces, which provides a control torque for changing the orientation of the spacecraft in space. At the third stage, the joint motion of the center of mass and relative to the center of mass of the spacecraft is simulated to demonstrate the feasibility of the obtained control program. As a result, a comparison is made of non-coplanar interplanetary Earth–Venus flights with and without thin-film control elements.

scholarly journals Density Variations in Alpine Snow

1967 ◽  
Vol 6 (46) ◽  
pp. 495-503 ◽  
Author(s):  
Donald Alford
Keyword(s):  
Physical Property ◽  
Average Density ◽  
Western Montana ◽  
Snow Pack ◽  
Snow Layer ◽  
Near Surface ◽  
Annual Layer ◽  
Maximum Value ◽  
Air Temperatures ◽  
Density Values

AbstractStratigraphic studies of the annual snow layer in the Beartooth Mountains of south-western Montana and on Mount Logan in the St. Elias Range have disclosed a similiar distribution of at least one physical property of the snow pack in the two areas. The average density of the pack, obtained by integrating a series of measurements taken at 5–10 cm. vertical intervals over the total thickness of the annual layer, reaches a maximum value near a mid-point of the total elevation covered by each traverse and decreases linearly toward the elevation extremes. A preliminary hypothesis, relating the distribution of average snow-density values along slopes to a semi-stable zonation of near-surface air temperatures, is presented.

Gyroscope-Free Link Parameter Measurement Using Accelerometers and Magnetometer

2014 ◽  
Author(s):  
Vishesh Vikas ◽  
Carl D. Crane
Keyword(s):  
Angular Velocity ◽  
Joint Angle ◽  
Inertial Sensors ◽  
Angular Acceleration ◽  
Parameter Measurement ◽  
Joint Angles ◽  
Symmetry Constraint ◽  
Estimation Techniques ◽  
Angular Velocities ◽  
Joint Parameters

Knowledge of joint angles, angular velocities is essential for control of link mechanisms and robots. The estimation of joint angles and angular velocity is performed using combination of inertial sensors (accelerometers and gyroscopes) which are contactless and flexible at point of application. Different estimation techniques are used to fuse data from different inertial sensors. Bio-inspired sensors using symmetrically placed multiple inertial sensors are capable of instantaneously measuring joint parameters (joint angle, angular velocities and angular acceleration) without use of any estimation techniques. Calibration of inertial sensors is easier and more reliable for accelerometers as compared to gyroscopes. The research presents gyroscope-less, multiple accelerometer and magnetometer based sensors capable of measuring (not estimating) joint parameters. The contribution of the improved sensor are four-fold. Firstly, the inertial sensors are devoid of symmetry constraint unlike the previously researched bio-inspired sensors. However, the accelerometer are non-coplanarly placed. Secondly, the accelerometer-magnetometer combination sensor allows for calculation of a unique rotation matrix between two link joined by any kind of joint. Thirdly, the sensors are easier to calibrate as they consist only of accelerometers. Finally, the sensors allow for calculation of angular velocity and angular acceleration without use of gyroscopes.

scholarly journals Quantification of vibrissal mechanical properties across the rat mystacial pad

2019 ◽  
Vol 121 (5) ◽  
pp. 1879-1895 ◽  
Author(s):  
Anne En-Tzu Yang ◽  
Hayley M. Belli ◽  
Mitra J. Z. Hartmann
Keyword(s):  
Mechanical Properties ◽  
Center Of Mass ◽  
Distal Region ◽  
Density Variation ◽  
Average Density ◽  
Proximal Region ◽  
Moment Of Inertia ◽  
Radius Of Gyration ◽  
Mass Moment ◽  
Mass Moment Of Inertia

Recent work has quantified the geometric parameters of individual rat vibrissae (whiskers) and developed equations that describe how these parameters vary as a function of row and column position across the array. This characterization included a detailed quantification of whisker base diameter and arc length as well as the geometry of the whisker medulla. The present study now uses these equations for whisker geometry to quantify several properties of the whisker that govern its mechanical behavior. We first show that the average density of a whisker is lower in its proximal region than in its distal region. This density variation appears to be largely attributable to the presence of the whisker cuticle rather than the medulla. The density variation has very little effect on the center of mass of the whisker. We next show that the presence of the medulla decreases the deflection of the whisker under its own weight and also decreases its mass moment of inertia while sacrificing <1% stiffness at the whisker base compared with a solid whisker. Finally, we quantify two dimensionless parameters across the array. First, the deflection-to-length ratio decreases from caudal to rostral: caudal whiskers are longer but deflect more under their own weight. Second, the nondimensionalized radius of gyration is approximately constant across the array, which may simplify control of whisking by the intrinsic muscles. We anticipate that future work will exploit the mechanical properties computed in the present study to improve simulations of the mechanosensory signals associated with vibrissotactile exploratory behavior. NEW & NOTEWORTHY The mechanical signals transmitted by a whisker depend critically on its geometry. We used measurements of whisker geometry and mass to quantify the center of mass, mass moment of inertia, radius of gyration, and deflection under gravity of the whisker. We describe how variations in these quantities across the array could enhance sensing behaviors while reducing energy costs and simplifying whisking control. Most importantly, we provide derivations for these quantities for use in future simulation work.

Comparative Analyses of the Dominant and Non-Dominant Upper Limbs during the Abduction and Adduction Motions

2020 ◽  
Author(s):  
Haemi JEE ◽  
Jaehyun PARK
Keyword(s):  
Range Of Motion ◽  
Angular Acceleration ◽  
Movement Analysis ◽  
Upper Limbs ◽  
Phase 0 ◽  
Natural Movement ◽  
Acceleration And Deceleration ◽  
Angular Velocities ◽  
Later Phase ◽  
Dominant Side

Background: Asymmetry in repeated motion may lead to dyskinesia through imbalance in the involved musculoskeletal structures. The dominance sides are also involved greater movement involvement over the nondominant sides. The upper limbs with multiple joints and largest range of motion are prone for unsynchronized coordination. Natural movement analysis is required for application to everyday activities. Methods: Thirty participants were first recruited from Inha University, Incheon, Korea in 2019. Twenty subjects were assessed for comparisons of asymmetrical motion between the dominant and non-dominant arms during the abduction and adduction lateral raises after excluding ten subjects for shoulder pain and lefthandedness. Results: The abduction and adduction motions of the bilateral arms were compared for the angular locations, velocity, and acceleration for every 10 degrees. The angular locations of the dominant side occurred significant earlier in the initial (10°, 20°, 30°) phase and later in the last (10°, 20°) phase of abduction and adduction in comparison to the non-dominant side (P<.05). The angular accelerations of the dominant side were also significantly greater during the initial phase (0°, 10°, 30°) and last phase (0°, 10°, 30°) (P <.05). The angular velocities were significantly greater during the later phase (40, 50, 60°) of abduction (P <.04). Conclusion: Comparative dominant side indicated more controlled movements through the range of motion with greater stability in angular acceleration and deceleration especially during the initial and last phase of abduction and adduction, respectively. Training for control of the specific angular points should be considered during abduction and adduction motions to prevent asymmetry of the bilateral arms.

The Mechanism Optimization Design of Multifunctional Mobile Electric Bed-Chair

2012 ◽  
Vol 184-185 ◽  
pp. 201-205
Author(s):  
Shao Jie Xin ◽  
Huan Huan Zhang
Keyword(s):  
Human Body ◽  
Optimization Design ◽  
Angular Acceleration ◽  
Mapping Method ◽  
Work Space ◽  
Mechanism Optimization ◽  
Mobile Bed ◽  
Maximum Value ◽  
Geometric Mapping

Multifunctional mobile bed-chair is designed base on human body engineering principles, it has several functions such as mobility, sitting up, bend knees and sleeping flat. We determine the size of components in both back raising mechanism and bend knees mechanism with geometric mapping method to satisfy the requirements of movement and work space. With the soft of ADAMS to optimize and simulate the motion of the bed-chair, the optimization goal is minimization of maximum value of the angular acceleration of both the back rod in back raising mechanism and leg rod in bend knees mechanism. Finally, we got the satisfied size of mechanisms.

INERTIA PARAMETERS ESTIMATION OF PLANAR OBJECT ON ROBOT PUSHING OPERATION

2009 ◽  
Vol 06 (04) ◽  
pp. 239-247 ◽  
Author(s):  
YONG YU ◽  
TETSU ARIMA ◽  
SHOWZOW TSUJIO
Keyword(s):  
Experimental Verification ◽  
Center Of Mass ◽  
Point Contact ◽  
Parameters Estimation ◽  
Moment Of Inertia ◽  
Inertia Parameters ◽  
Angular Velocities ◽  
Unknown Object

This paper proposes a technique that can estimate the inertia parameters of a graspless unknown object, which is pushed by robot fingers. Using the fingertip different accelerations (or angular accelerations), velocities (or angular velocities) and forces information measured in pushing operations, the algorithms to estimate the object mass (or moment of inertia) are described. Then, a line called C.M. Line, is defined in this paper. The line contains the center of mass and is between two fingertips which are in point-contact with an object side. By using two or more orientation-different C.M. lines, an algorithm to estimate the center of mass of the object is given. Lastly, experimental verification on the proposed approach is performed and its results are outlined.

scholarly journals Analysis on Flow Field Characteristics of Airfoil in Pitching Motion

2021 ◽  
Vol 2076 (1) ◽  
pp. 012069
Author(s):  
Rui Yin ◽  
Jing Huang ◽  
Zhi-Yuan He
Keyword(s):  
Flow Field ◽  
Drag Coefficient ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Decisive Role ◽  
Aerodynamic Characteristics ◽  
Pitching Motion ◽  
Maximum Value ◽  
Flow Field Characteristics ◽  
Lift And Drag

Abstract Based on CFD, the flow field characteristics of NACA4412 airfoil are analyzed under pitching motion, and its aerodynamic characteristics are interpreted. The results show that streamline changes on the upper surface of the airfoil play a decisive role in the aerodynamic characteristics. The interaction between the vortex leads to fluctuations in the lift and drag coefficients. Under a big angle of attack, the secondary trailing vortex on the upper surface of the airfoil adheres to the trailing edge of the airfoil, resulting in an increased drag coefficient. Under a small angle of attack, the secondary trailing vortex can break away from the airfoil. The lift coefficient reaches the maximum value of 2.961 before the airfoil is turned upside down, and the drag coefficient reaches the maximum value of 1.515 after the airfoil is turned upside down, but the corresponding angles of attack of the two are equal.

Intrasubject Variability of Upper Extremity Angular Kinematics in the Tennis Forehand Drive

1990 ◽  
Vol 6 (4) ◽  
pp. 415-421 ◽  
Author(s):  
Duane V. Knudson
Keyword(s):  
Upper Extremity ◽  
Angular Position ◽  
Angular Acceleration ◽  
Intrasubject Variability ◽  
Tennis Players ◽  
Forward Stroke ◽  
Coefficients Of Variation ◽  
Subject Variability ◽  
Position Data ◽  
Angular Velocities

The intra subject variability of the angular kinematics of the wrist and elbow joints in the tennis forehand drive were studied. Two varsity tennis players were filmed as they performed flat forehand drives. The DLT method of 3-D reconstruction was used to measure the angular motion of the upper extremity for eight strokes to assess the intra subject variability of selected kinematic variables. Curves were synchronized to impact and averaged. Wrist and elbow angular position data were quite consistent, with curve coefficients of variation (CV) less than 5.9%. The consistent angular positions during the forward stroke did not result from highly consistent patterns of angular velocities or accelerations. For both the wrist and elbow joints, intra subject variability increased for the angular velocity (CV = 90.6%) and angular acceleration (CV = 129.5%) curves. Biomechanical studies comparing derivatives or kinetic variables across subjects may have to be interpreted with reference to intra subject variability.

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