Dynamic stability index and vibration analysis of a flexible Stewart platform

2007 ◽  
Vol 307 (3-5) ◽  
pp. 495-512 ◽  
Author(s):  
Parthajit Mukherjee ◽  
Bhaskar Dasgupta ◽  
A.K. Mallik
Keyword(s):  
Dynamic Stability ◽  
Vibration Analysis ◽  
Stability Index ◽  
Stewart Platform

Development of a Dynamic Stability Simulator for Articulated and Conventionaltractors Useful for Real-Time Safety Devices

2013 ◽  
Vol 394 ◽  
pp. 546-553 ◽  
Author(s):  
Fabrizio Mazzetto ◽  
Marco Bietresato ◽  
Renato Vidoni
Keyword(s):  
Real Time ◽  
Dynamic Stability ◽  
Stability Problem ◽  
Stability Index ◽  
Real Field ◽  
Circular Trajectory ◽  
Safety Devices ◽  
Test Platform ◽  
Agricultural Tractors ◽  
The Stability

The safety of agricultural tractors drivers is a very actual topic, especially when tractors operate on side slopes, such as in terraced vineyards. This work approaches the stability problem of articulated tractors by modelling, simulating and quantifying the safety of the driver with respect to both roll and pitch overturns. First of all, an articulated tractor has been modelled and simplified, after that a stability index has been defined and calculatedin several simulated slope conditions when the tractor travels along a circular trajectory; then, the obtained results have beencompared with respect to a conventional tractor. This work is a preliminary studyfor a tilting test platform for real vehicles, capable to reproduce real field conditions (slope, obstacles, roughness). Finally, some directives on how exploiting the obtained results for real-time safety devices have been formulated.

Dynamic stability and nonlinear vibration analysis of a rotor system with flexible/rigid blades

2016 ◽  
Vol 105 ◽  
pp. 633-653 ◽  
Author(s):  
Saeed Bab ◽  
Siamak E. Khadem ◽  
Amirhassan Abbasi ◽  
Majid Shahgholi
Keyword(s):  
Nonlinear Vibration ◽  
Dynamic Stability ◽  
Vibration Analysis ◽  
Rotor System

Effects of Peroneal Muscles Fatigue on Dynamic Stability Following Lateral Hop Landing: Time to Stabilization Versus Dynamic Postural Stability Index

2019 ◽  
Vol 28 (1) ◽  
pp. 17-23 ◽  
Author(s):  
Kazem Malmir ◽  
Gholam Reza Olyaei ◽  
Saeed Talebian ◽  
Ali Ashraf Jamshidi ◽  
Majid Ashraf Ganguie
Keyword(s):  
Dynamic Stability ◽  
Postural Stability ◽  
Force Plate ◽  
Stability Index ◽  
Voluntary Contraction ◽  
Lower Extremity Injury ◽  
Resultant Vector ◽  
Time To Stabilization ◽  
Quasi Experimental ◽  
Dynamic Postural Stability

Context: Dynamic stability is a necessary requirement in many sports competitions. Muscle fatigue, which can impair stability, may be occurred in many sports competitions in which lateral movements and landing repeated frequently. Objective: To assess the effects of peroneal muscles fatigue on dynamic stability following lateral hop landing through measuring time to stabilization (TTS) and dynamic postural stability index (DPSI). Design: Quasi-experimental. Setting: Laboratory study. Participants: A total of 20 recreationally active, healthy males with no lower-extremity injury during the previous 6 months participated in this study. Intervention: Participants performed a lateral hop on a force plate before and immediately after a fatigue intervention using a Biodex dynamometer. For inducing fatigue, the participant made a prolonged eversion effort with 40% of the maximal voluntary contraction. Fatigue was met when the eversion torque declined by 50% of the initial value. TTS and DPSI were calculated using sequential averaging method and relevant formulas, respectively. Main Outcome Measures: Premeasures and postmeasures of TTS in the anteroposterior, mediolateral and vertical directions, resultant vector of TTS, stability indices in the anteroposterior, mediolateral and vertical directions, and DPSI. Results: Means of the DPSI or its components did not change significantly due to fatigue (P > .05). Means of the TTS in the anteroposterior and mediolateral directions, and the mean of the resultant vector of the TTS increased significantly after fatigue (P < .05). Conclusions: The question that the dynamic stability is affected or not affected by fatigue depends on which of the TTS or DPSI is used for analysis. The TTS may be a sensitive measure to detect subtle changes in postural stability due to fatigue. But, the DPSI which may be changed after a more strenuous fatigue may be related to actual fatiguing situations.

scholarly journals Increase in Stability of an X-Configured AUV through Hydrodynamic Design Iterations with the Definition of a New Stability Index to Include Effect of Gravity

2021 ◽  
Vol 9 (9) ◽  
pp. 942
Author(s):  
Lakshmi Miller ◽  
Stefano Brizzolara ◽  
Daniel J. Stilwell
Keyword(s):  
Dynamic Stability ◽  
Autonomous Underwater Vehicle ◽  
Fluid Dynamic ◽  
Vertical Plane ◽  
Stability Index ◽  
Lumped Parameter Model ◽  
Restoring Force ◽  
Baseline Design ◽  
Course Stability ◽  
Hull Design

A study about the effect of different configurations of stationary and movable appendages on the dynamic stability of an autonomous underwater vehicle (AUV) is presented. A new stability index that can be used to assess dynamic stability in the vertical plane is derived. It improves upon the vertical plane stability index by accurately accounting for the contribution of hydrostatic forces to dynamic stability, even at low speeds. The use of the new stability index is illustrated by applying it to a set of AUV configurations based on an AUV initially designed at Virginia Tech and built by Dive Technologies. The applicability of this index depends on the speed of the craft. The range of applicability in terms of speed is presented for the DIVE craft as an example. The baseline design of the DIVE craft has asymmetry in the vertical plane and symmetry in the horizontal plane. A virtual planar motion mechanism (VPMM) is used to obtain the hydrodynamic coefficients of the hull. Design iterations are performed on the baseline design by varying the appendages in shape and size, adding appendages and adding features on appendages. The best and the baseline design from this effort are incorporated in a 6 DOF lumped-parameter model (LPM) to compare results of a straight line maneuver. A computational fluid dynamic (CFD) tool is used to obtain the trajectory comparison of turn-circle maneuver for these two designs. A principal conclusion is the important contribution of a hydrostatic restoring force at low-moderate speeds by using GVgrav and the influence of design of control surfaces, both stationary and non-stationary, in the achievement of control-fixed course stability.

scholarly journals Parametric Vibration Analysis of a Six-Degree-of-Freedom Electro-Hydraulic Stewart Platform

2021 ◽  
Vol 2021 ◽  
pp. 1-27
Author(s):  
Xiaoming Yuan ◽  
Yue Tang ◽  
Weiqi Wang ◽  
Lijie Zhang
Keyword(s):  
Natural Frequency ◽  
Vibration Analysis ◽  
Dominant Frequency ◽  
Stewart Platform ◽  
Sixth Order ◽  
Equivalent Stiffness ◽  
Main Resonance ◽  
Hydraulic Oil ◽  
Coupling Parameters ◽  
Vibration Time

Electro-hydraulic Stewart 6-DOF platform is a 6-DOF parallel mechanism combined with the electro-hydraulic servo control system, which is widely used in the field of construction machinery. In actual working conditions, the flow and pressure pulsation of the hydraulic oil output from the hydraulic leg of the electro-hydraulic Stewart platform are inevitable, so the equivalent stiffness of the platform leg will change, and the stiffness parameters of the transmission system will change, resulting in vibration, which will affect the accuracy of the platform. This paper considering the fluid unit equivalent stiffness cyclical fluctuations and leg, on the basis of the relationship between hydraulic stiffness, constructs the electric hydraulic Stewart platform machine vibration dynamics equation, fluid coupling parameters of vibration parameters using the method of the multiscale approximate analytic formula of the main resonance and combination resonance are derived, and the system parameters vibration time-domain response and frequency response under two different poses are discussed. Results show that the system first to six order natural frequency and the first to the sixth order natural frequency and frequency of hydraulic oil equivalent stiffness of the combination of frequency will have an effect on the parameters of the system vibration. In the main resonance, the dominant frequency is mainly the first to sixth order natural frequency of the system; in the combined resonance, the dominant frequency is the combined frequency. Through the parameter vibration analysis of two different positions of the platform, it is concluded that when the platform is in an asymmetric position, each leg of the system is more involved in vibration. This study can provide the reference for the subsequent dynamic optimization and reliability analysis of the electro-hydraulic Stewart platform.

scholarly journals How Does Functional Soccer Training on Uneven Ground Affect Dynamic Stability of Lower Limbs in Young Soccer Players

2014 ◽  
Vol 2 (11_suppl3) ◽  
pp. 2325967114S0015
Author(s):  
Marcin Plenzler ◽  
Natalia Mrozińska ◽  
Anna Mierzwińska ◽  
Olga Korbolewska ◽  
Daria Mejnartowicz ◽  
...  
Keyword(s):  
Dynamic Stability ◽  
Stability Index ◽  
Core Stability ◽  
Lower Limbs ◽  
Soccer Players ◽  
Control Group ◽  
Preparatory Period ◽  
Overall Stability ◽  
Soccer Training ◽  
Stability Results

Objectives: The aim of the study was to assess the level of lower limbs’ stability under dynamic conditions in soccer players before and after the preparatory period. The results of young players were compared with the control group’s records. The analysis included, both, the dominant (the one kicking the ball) and the non-dominant (supporting) limb. Methods: 13 players from AGAPE Soccer Academy in Białołęka (year 2002), participated in this study. The control group were 18 young, healthy, and active volunteers (14 male, and 4 female; mean age = 21,4±1,2 years). The dynamic stabilography was recorded on Biodex Balance System device. For data analysis, the bending dispersion in the medial/lateral plane, and anterior/posterior plane, along with the overall stability index (OSI) were tested. The measurements were taken in single-leg stance on the right and left leg respectively. Each testing included 3 repetitions in 30 seconds intervals on the platform’s second level of testing. The preliminary study was performed before the beginning of the season’s preparatory period. During the preparatory period, which lasted 16 weeks, the motor activity training programme was completed (90 minutes, once a week). The programme included elements such as: functional soccer training and stabilization training on an unstable ground, core stability training, dynamic stability exercises, and lower limbs coordination and strength training. After the preparatory period, the health examinations were performed. Test results were statistically analysed using the Wilcoxon signed-rank test in order to establish parameters’ changes within the study group, and the U-Mann-Whitney test was applied in order to estimate the variances between the study and control groups. The statistical significance threshold was p≤0,05. Results: The study showed a significant statistical improvement of stability parameters expressed by the overall stability index (OSI) and A/P stability index for the supporting limb after the preparatory period, during which a stability and proprioception training was completed. The significance of these results is even greater when the parallel substantial increase of the physical body height of these young players is taken into account (the taller the player is, the harder it is for him to keep the balance). The players’ tests results are, also, statistically lower than the control group’s data. That, in turn, means that the players had better stability in comparison to the control group. This co-dependence regarding the overall stability was mainly affected by the A/P stability indexes taken in a sagittal plane. Also, no new injuries were recorded within the young players group. Conclusion: 1. The exercised functional training significantly improved stability results of the supporting limb among the young players. 2. The results encourage to continue the study, and, in the later stage, check whether there is an actual relationship between the dynamic stability results and sports achievements combined with the frequency of injuries.

On the Measurement of Dynamic Stability of Human Locomotion

1994 ◽  
Vol 116 (1) ◽  
pp. 30-36 ◽  
Author(s):  
Yildirim Hurmuzlu ◽  
Cagatay Basdogan
Keyword(s):  
Dynamic Stability ◽  
Complex Dynamics ◽  
Stability Index ◽  
Normal Subjects ◽  
Human Locomotion ◽  
Heel Strike ◽  
Analytical Methodology ◽  
Gait Patterns ◽  
Kinematic Data ◽  
The Stability

The main focus of the present investigation is the development of quantitative measures to assess the dynamic stability of human locomotion. The analytical methodology is based on Floquet theory, which was developed to investigate the stability of nonlinear oscillators. Here the basic approach is modified such that it accommodates the study of the complex dynamics of human locomotion and differences among various individuals. A quantitative stability index has been developed to characterize the ability of humans to maintain steady gait patterns. Floquet multipliers of twenty normal subjects were computed from the kinematic data at Poincare´ sections taken at four instants of the gait cycle, namely heel strike, foot flat, heel off, and toe off. Then, an averaged stability index was computed for each subject. Statistical analysis was performed to demonstrate the utility of the stability indices as quantitative measures of dynamic stability of gait for the subject population tested during the present study.

Dynamic Knockdown of Canting Keel Yachts in Breaking Waves

2009 ◽  
Vol 46 (02) ◽  
pp. 99-106
Author(s):  
Jonathan R. Binns ◽  
Oscar Palos ◽  
Paul Brandner ◽  
Giles Thomas
Keyword(s):  
Experimental Investigation ◽  
Dynamic Stability ◽  
Stability Index ◽  
Breaking Waves ◽  
Experimental Results ◽  
Towing Tank ◽  
Video Cameras ◽  
Regulatory Authorities ◽  
Righting Moment

Yacht canting keel configurations have been developed to maximize the available righting moment by rotating their keel bulb to windward. Regulatory authorities have been required to establish rules covering the design and operation of such systems; however, significant dynamic investigations into their behavior have not been performed. This paper presents results from a theoretical and experimental investigation into the dynamic stability of canting keel sailing yachts when experiencing a knockdown by large breaking waves. Towing tank experiments were conducted on a yacht model with a fixed keel and two canted keel configurations, beam-on to large solitary breaking waves. The motion of the model during the tests was recorded by four video cameras and analyzed using photogrammetry. A comparison of the hydrostatic predictions and experimental results indicate that the traditional GZ approach of assessing the energy required to heel may not be appropriate for yachts with canting keels. In addition, a correlation of the experimental results with the ISO stability index highlights that this index may be unsuitable for categorizing yachts with canting keels with respect to their ability to recover after a knockdown event.

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