PATHS OF FREELY FALLING DISKS

2009 ◽  
Vol 23 (03) ◽  
pp. 373-376 ◽  
Author(s):  
HONGJIE ZHONG ◽  
CUNBIAO LEE
Keyword(s):  
Degrees Of Freedom ◽  
Center Of Mass ◽  
Vertical Plane ◽  
Stereoscopic Vision ◽  
Six Degrees Of Freedom ◽  
Mass Distributions ◽  
First Case ◽  
The Mean ◽  
Thin Disks ◽  
Free Falling

The free falling motion of round thin disks in quiescent water was investigated experimentally. The mean density of the disks were about 1.05 g/cm3, slightly larger than water, and thickness to diameter ratio is 0.1. In this letter, We reported two cases with different mass distributions, in one case the disk's center of mass coincided with the geometry center and in another case it was deviated. Two CCD cameras were used to photograph the falling disk simultaneously, the disk's six degrees of freedom were obtained via a stereoscopic vision method. In the first case fluttering motion was observed, the disk's oscillatory motion confined in a vertical plane, and the pitching motion occurred about an axis normal to the plane. In the second case, steady helical falling was observed, the disk moved in a helical path at constant speed, the attacking angle is constant.

Maximum Total Point Motion of Five Points Versus All Points in Assessing Tibial Baseplate Stability

2021 ◽  
Author(s):  
Abigail Niesen ◽  
Anna L Garverick ◽  
Maury Hull
Keyword(s):  
Degrees Of Freedom ◽  
Stability Limit ◽  
3D Models ◽  
Six Degrees Of Freedom ◽  
Percent Error ◽  
Model Based ◽  
Point Motion ◽  
The Mean ◽  
The Difference ◽  
Total Point

Abstract Maximum total point motion (MTPM), the point on a baseplate that migrates the most, has been used to assess the risk of tibial baseplate loosening using radiostereometric analysis (RSA). Two methods for determining MTPM for model-based RSA are to use either 5 points distributed around the perimeter of the baseplate or to use all points on the 3D model. The objectives were to quantify the mean difference in MTPM using 5 points vs. all points, compute the percent error relative to the 6-month stability limit for groups of patients, and to determine the dependency of differences in MTPM on baseplate size and shape. A dataset of 10,000 migration values was generated using the mean and standard deviation of migration in six degrees of freedom at 6 months from an RSA study. The dataset was used to simulate migration of 3D models (two baseplate shapes and two baseplate sizes) and calculate the difference in MTPM using 5 virtual points vs. all points and the percent error (i.e. difference in MTPM/stability limit) relative to the 6-month stability limit. The difference in MTPM was about 0.02 mm, or 4% percent relative to the 6-month stability limit, which is not clinically important. Furthermore, results were not affected by baseplate shape or size. Researchers can decide whether to use 5 points or all points when computing MTPM for model-based RSA. The authors recommend using 5 points to maintain consistency with marker-based RSA.

Development of a 6-DOF Testing Platform for Multirotor Flying Vehicles with Suspended Loads

Aerospace ◽  
2021 ◽  
Vol 8 (11) ◽  
pp. 355
Author(s):  
Saad M. S. Mukras ◽  
Hanafy M. Omar
Keyword(s):  
Degrees Of Freedom ◽  
Center Of Mass ◽  
Performance Testing ◽  
Flight Performance ◽  
Testing Platform ◽  
Six Degrees Of Freedom ◽  
Mass Properties ◽  
Test Platform ◽  
Suspended Loads

The development of multirotor vehicles can often be a dangerous and costly undertaking due to the possibility of crashes resulting from faulty controllers. The matter of safety in such activities has primarily been addressed through the use of testbeds. However, testbeds for testing multirotor vehicles with suspended loads have previously not been reported. In this study, a simple yet novel testing platform was designed and built to aid in testing and evaluating the performances of multirotor flying vehicles, including vehicles with suspended loads. The platform allows the flying vehicle to move with all six degrees of freedom (DOF). Single or three-DOF motions can also be performed. Moreover, the platform was designed to enable the determination of the mass properties (center of mass and moments of inertia) of small multirotor vehicles (which are usually required in the development of new control systems). The applicability of the test platform for the in-flight performance testing of a multirotor vehicle was successfully demonstrated using a Holybro X500 quadcopter with a suspended load. The test platform was also successfully used to determine the mass properties of the vehicle.

scholarly journals Investigating the Influence of Shaft Balance Point on Clubhead Speed: A Simulation Study

Proceedings ◽  
2020 ◽  
Vol 49 (1) ◽  
pp. 156
Author(s):  
William McNally ◽  
John McPhee
Keyword(s):  
Total Mass ◽  
Center Of Mass ◽  
Golf Club ◽  
Physical Interaction ◽  
Balance Point ◽  
Mass Distributions ◽  
Biomechanical Models ◽  
Significant Difference ◽  
The Mean ◽  
Simulation Results

In this study, a dynamic golfer model was used to investigate the influence of the golf shaft’s balance point (i.e., center of mass) on the generation of clubhead speed. Three hypothetical shaft designs having different mass distributions, but the same total mass and stiffness, were proposed. The golfer model was then stochastically optimized 100 times using each shaft. A statistically significant difference was found between the mean clubhead speeds at impact (p < 0.001), where the clubhead speed increased as the balance point moved closer to the grip. When comparing the two shafts with the largest difference in balance point, a 1.6% increase in mean clubhead speed was observed for a change in balance point of 18.8 cm. The simulation results have implications for shaft design and demonstrate the usefulness of biomechanical models for capturing the complex physical interaction between the golfer and golf club.

scholarly journals Kinematic Analysis of a Six-Degrees-of-Freedom Model Based on ISB Recommendation: A Repeatability Analysis and Comparison with Conventional Gait Model

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Magdalena Żuk ◽  
Celina Pezowicz
Keyword(s):  
Degrees Of Freedom ◽  
External Rotation ◽  
Transverse Plane ◽  
Analysis Model ◽  
Range Of Movement ◽  
Current Standard ◽  
Six Degrees Of Freedom ◽  
Model Based ◽  
The Mean ◽  
Landmark Position

Objective. The purpose of the present work was to assess the validity of a six-degrees-of-freedom gait analysis model based on the ISB recommendation on definitions of joint coordinate systems (ISB 6DOF) through a quantitative comparison with the Helen Hays model (HH) and repeatability assessment.Methods. Four healthy subjects were analysed with both marker sets: an HH marker set and four marker clusters in ISB 6DOF. A navigated pointer was used to indicate the anatomical landmark position in the cluster reference system according to the ISB recommendation. Three gait cycles were selected from the data collected simultaneously for the two marker sets.Results. Two protocols showed good intertrial repeatability, which apart from pelvic rotation did not exceed 2°. The greatest differences between protocols were observed in the transverse plane as well as for knee angles. Knee internal/external rotation revealed the lowest subject-to-subject and interprotocol repeatability and inconsistent patterns for both protocols. Knee range of movement in transverse plane was overestimated for the HH set (the mean is 34°), which could indicate the cross-talk effect.Conclusions. The ISB 6DOF anatomically based protocol enabled full 3D kinematic description of joints according to the current standard with clinically acceptable intertrial repeatability and minimal equipment requirements.

scholarly journals Clinical experience of craniospinal intensity-modulated spot-scanning proton therapy using large fields for central nervous system medulloblastomas and germ cell tumors in children, adolescents, and young adults

2019 ◽  
Vol 60 (4) ◽  
pp. 527-537
Author(s):  
Takayuki Hashimoto ◽  
Shinichi Shimizu ◽  
Seishin Takao ◽  
Shunsuke Terasaka ◽  
Akihiro Iguchi ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Germ Cell Tumors ◽  
Adolescent And Young Adult ◽  
Hematological Toxicity ◽  
Six Degrees Of Freedom ◽  
Intensity Modulated ◽  
Patient Table ◽  
Biological Effectiveness ◽  
The Mean ◽  
Beam Delivery

Abstract The outcomes of intensity-modulated proton craniospinal irradiation (ipCSI) are unclear. We evaluated the clinical benefit of our newly developed ipCSI system that incorporates two gantry-mounted orthogonal online X-ray imagers with a robotic six-degrees-of-freedom patient table. Nine patients (7–19 years old) were treated with ipCSI. The prescribed dose for CSI ranged from 23.4 to 36.0 Gy (relative biological effectiveness) in 13–20 fractions. Four adolescent and young adult (AYA) patients (15 years or older) were treated with vertebral-body-sparing ipCSI (VBSipCSI). Myelosuppression following VBSipCSI was compared with that of eight AYA patients treated with photon CSI at the same institution previously. The mean homogeneity index (HI) in the nine patients was 0.056 (95% confidence interval: 0.044–0.068). The mean time from the start to the end of all beam delivery was 37 min 39 s ± 2 min 24 s (minimum to maximum: 22 min 49 s – 42 min 51 s). The nadir white blood cell, hemoglobin, and platelet levels during the 4 weeks following the end of the CSI were significantly higher in the VBSipCSI group than in the photon CSI group (P = 0.0071, 0.0453, 0.0024, respectively). The levels at 4 weeks after the end of CSI were significantly higher in the VBSipCSI group than in the photon CSI group (P = 0.0023, 0.0414, 0.0061). Image-guided ipCSI was deliverable in a reasonable time with sufficient HI. Using VBSipCSI, AYA patients experienced a lower incidence of serious acute hematological toxicity than AYA patients treated with photon CSI.

scholarly journals ANALYSIS OF THE RESPONSE OF OFFSHORE-MOORED SHIPS TO WAVES

1964 ◽  
Vol 1 (9) ◽  
pp. 46
Author(s):  
Jan L. Leendertse
Keyword(s):  
Degrees Of Freedom ◽  
Vertical Plane ◽  
Longitudinal Axis ◽  
Mooring Line ◽  
Wave System ◽  
Sea Waves ◽  
Mooring Lines ◽  
Six Degrees Of Freedom ◽  
General Terms ◽  
Relationship Of

A vessel moored at sea will experience complicated series of translational and rotational oscillations due to sea waves. These motions can be considered as the summation of six components, three translational and three rotational. In the presently available analyses of motions of unmoored ships, differential equations can be written for each mode of movement. Unfortunately, motions in one of these modes are coupled to motions of other modes, and the analysis becomes rather complicated. Generally, the problem is simplified by neglecting some of the coupling effects and by specifying the position of the vessel in the wave system. This study develops and analyzes a model for a moored ship restrained by mooring lines, using the presently available mathematical models for the free ship and the force-displacement relationship of the cable-holding points on the ship. The coupled movement (three degrees of freedom) in a vertical plane through the longitudinal axis of the vessel and the generated mooring-line forces are considered in detail. The general case of six degrees of freedom in arbitrary heading is discussed briefly in general terms.

Experiences in the development of a teleoperated parallel robot for aerial line maintenance

Robotica ◽  
2011 ◽  
Vol 29 (6) ◽  
pp. 873-881 ◽  
Author(s):  
Cecilia Garcia ◽  
Roque Saltaren ◽  
Rafael Aracil
Keyword(s):  
Degrees Of Freedom ◽  
Laboratory Experiments ◽  
Parallel Robot ◽  
Stereoscopic Vision ◽  
Six Degrees Of Freedom ◽  
Experimental Prototype ◽  
Inspection And Maintenance ◽  
Force Reflection ◽  
Local Station ◽  
Stewart Gough Platform

SUMMARYThis paper presents the teleoperation of a parallel robot based on the Stewart–Gough platform. The robot is an experimental prototype capable of sliding along electrical lines in order to carry out different inspection and maintenance tasks. The paper also describes the kinematic equations of the parallel robot and their solution. The teleoperation of the prototype took place in a testing bank developed in the laboratory and containing the basic elements of electrical lines. The operator who performs the task uses a six degrees-of-freedom master-arm with force reflection, which also has an image-viewing system providing the operator with stereoscopic vision and allowing him/her to calibrate the information of the local station simulator with the real environment through the blending of images. The paper also presents the results of the laboratory experiments of the robot sliding along a line.

The motion of a lunar orbiter

1966 ◽  
Vol 25 ◽  
pp. 373
Author(s):  
Y. Kozai
Keyword(s):  
Degrees Of Freedom ◽  
Dimensional Space ◽  
Artificial Satellite ◽  
Equations Of Motion ◽  
Triaxial Ellipsoid ◽  
The Moon ◽  
Secular Motion ◽  
The Earth ◽  
Close Satellite ◽  
The Mean

The motion of an artificial satellite around the Moon is much more complicated than that around the Earth, since the shape of the Moon is a triaxial ellipsoid and the effect of the Earth on the motion is very important even for a very close satellite.The differential equations of motion of the satellite are written in canonical form of three degrees of freedom with time depending Hamiltonian. By eliminating short-periodic terms depending on the mean longitude of the satellite and by assuming that the Earth is moving on the lunar equator, however, the equations are reduced to those of two degrees of freedom with an energy integral.Since the mean motion of the Earth around the Moon is more rapid than the secular motion of the argument of pericentre of the satellite by a factor of one order, the terms depending on the longitude of the Earth can be eliminated, and the degree of freedom is reduced to one.Then the motion can be discussed by drawing equi-energy curves in two-dimensional space. According to these figures satellites with high inclination have large possibilities of falling down to the lunar surface even if the initial eccentricities are very small.The principal properties of the motion are not changed even if plausible values ofJ3andJ4of the Moon are included.This paper has been published in Publ. astr. Soc.Japan15, 301, 1963.

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