Modeling a Viscoelastic Gymnastics Landing Mat during Impact

2006 ◽  
Vol 22 (2) ◽  
pp. 103-111 ◽  
Author(s):  
Chris Mills ◽  
Matthew T.G. Pain ◽  
Maurice R. Yeadon
Keyword(s):  
High Speed ◽  
Force Plate ◽  
System Model ◽  
Video Cameras ◽  
Key Characteristics ◽  
Single Mass ◽  
Force Time ◽  
Mass Spring ◽  
The Impact ◽  
Landing Mat

Landing mats that can undergo a large amount of area deformation are now essential for the safe completion of landings in gymnastics. The objective of this study was to develop an analytical model of a landing mat that reproduces the key characteristics of the mat-ground force during impact with minimal simulation run time. A force plate and two high-speed video cameras were used to record the mat deformation during vertical drop testing of a 24-kg impactor. Four increasingly complex point mass spring-damper models, from a single mass spring-damper system, Model 1, to a 3-layer mass spring-damper system, Model 4, were constructed using Matlab to model the mat's behavior during impact. A fifth model composed of a 3-layer mass spring-damper system was developed using visual Nastran 4D. The results showed that Models 4 and 5 were able to match the loading phase of the impact with simulation times of less than 1 second for Model 4 and 28 seconds for Model 5. Both Models 4 and 5 successfully reproduced the key force-time characteristics of the mat-ground interface, such as peak forces, time of peak forces, interpeak minima and initial rates of loading, and could be incorporated into a gymnast-mat model.

scholarly journals Biomechanical assessment of various punching techniques

2020 ◽  
Author(s):  
Jiri Adamec ◽  
Peter Hofer ◽  
Stefan Pittner ◽  
Fabio Monticelli ◽  
Matthias Graw ◽  
...  
Keyword(s):  
High Speed ◽  
Vertical Wall ◽  
Force Plate ◽  
Physical Parameters ◽  
Time Curve ◽  
Biomechanical Assessment ◽  
Sports Science ◽  
General Terms ◽  
Force Time ◽  
The Impact

Abstract Punches without the use of instruments/objects are a common type of body violence and as such a frequent subject of medicolegal analyses. The assessment of the injuries occurred as well as of the potential of the assault to produce severe body harm is based on objective traces (especially the documented injuries of both parties involved) as well as the—often divergent—descriptions of the event. Quantitative data regarding the punching characteristics that could be used for the assessment are rare and originate mostly in sports science. The aim of this study was to provide physical data enabling/facilitating the assessment of various punching techniques. A total of 50 volunteers took part in our study (29 males and 21 females) and performed severe punches with the fist, with the small finger edge of the hand (karate chop), and with the open hand with both the dominant and the non-dominant hands in randomized order. The strikes were performed on a boxing pad attached to a KISTLER force plate (sampling frequency 10,000 Hz) mounted on a vertical wall. The punching velocity was defined as the hand velocity over the last 10 cm prior to the contact to the pad and ascertained by using a high-speed camera (2000 Hz). Apart from the strike velocity, the maximum force, the impulse (the integral of the force-time curve), the impact duration, and the effective mass of the punch (the ratio between the impulse and the strike velocity) were measured/calculated. The results show a various degree of dependence of the physical parameters of the strikes on the punching technique, gender, hand used, body weight, and other factors. On the other hand, a high degree of variability was observed that is likely attributable to individual punching capabilities. In a follow-up study, we plan to compare the “ordinary” persons with highly trained (boxers etc.) individuals. Even though the results must be interpreted with great caution and a direct transfer of the quantitative parameters to real-world situations is in general terms not possible, the study offers valuable insights and a solid basis for a qualified forensic medical/biomechanical assessment.

scholarly journals Experimental analysis of high velocity impacts of composite fragments on aluminium plates

2021 ◽  
Vol 250 ◽  
pp. 01011
Author(s):  
Jorge López-Puente ◽  
Jesús Pernas-Sánchez ◽  
José Alfonso Artero-Guerrero ◽  
David Varas ◽  
Joseba Múgica ◽  
...  
Keyword(s):  
High Velocity ◽  
High Speed ◽  
Woven Composites ◽  
Residual Velocity ◽  
Video Cameras ◽  
High Speed Video ◽  
High Velocity Impacts ◽  
Deformable Structure ◽  
The Impact ◽  
Composite Blades

The improvement of engines is one of the ways to diminish the fuel consumption in civil aircrafts, and Open Rotors engines are one of the best promises in order to achieve a sensible efficiency increment. These engines have large composite blades that could, in the event of failure, impact against the fuselage, totally or partially. In this case, composite fragments could behave as impactors. In order to design fuselages for this event and adopt these new engines in the future, it is necessary to understand the impact behaviour of a composite fragment against a deformable structure. To this end, unidirectional and woven composites fragments were impacted at high velocity (up to 150 m/s) against aluminium panels at different impact velocities. The composite fragments were made using AS4/8552 (UD) and AGP-193PW (woven) prepregs manufactured by Hexcel Composites, both using AS4 fibres and 8552 epoxy matrix. High speed video cameras were used to record the impact process and to measure both the impact and the residual velocity and hence the energy absorbed.

EFFECT OF THE FLUID ON THE IMPACT FORCE OF THE WET MISSILE

2015 ◽  
Vol 2 (1) ◽  
Author(s):  
Duc-Kien Thai ◽  
Seung-Eock Kim
Keyword(s):  
Impact Force ◽  
Force Plate ◽  
Time History ◽  
Research Centre ◽  
Element Analysis ◽  
Time Histories ◽  
Target Wall ◽  
Force Time ◽  
Missile Test ◽  
The Impact

In this paper, the force-time histories of soft missiles, with and without filled water, impacting the target wall were investigated using finite element analysis. The force plate tests, with a dry missile (test FP8) and a wet missile (test FP16) carried out by Technical Research Centre of Finland (VTT), were used. The numerical analysis results were verified by comparing with those of experiments. A parametric analysis with different missile velocities was also performed to investigate the force-time history and impulse of the missile impact on target plate. Based on a comparison with the Riera approach, the coefficients were proposed to modify the Riera function. The analysis results show that, the Riera function accurately predicted the impact force time history in the case of the dry missile. However, in the case of the wet missile, the coefficients α from 1.24 to 1.45 are recommended to be added to the second term of the Riera function in the case in which the impact velocity is in the range of 70 m/s to 200 m/s.

Analysis of Dynamic Response of Simply-Supported Girder Bridge in High-Speed Railway Based on the Moving Rows Mass-Spring Model

2012 ◽  
Vol 193-194 ◽  
pp. 919-924
Author(s):  
Jin Feng Wu ◽  
Zhi Jun Zhang ◽  
Xiao Zhen Li
Keyword(s):  
High Speed ◽  
Damping Ratio ◽  
Spring Model ◽  
Simply Supported ◽  
Mass Spring Model ◽  
Girder Bridge ◽  
Set Up ◽  
Mass Spring ◽  
The Impact ◽  
Bridge System

The vibration theory of beam and D’Alembert principle are used to set up vehicle-bridge system for a simply-supported girder bridge under the moving rows mass-spring model. The kinematic equations of vehicle and bridge are derived separately. And with the force balanced relationship and the displacement compatibility conditions between wheels and rail, the equations of vehicle-bridge system are established. A calculating program is complicated with MATLAB language and solved by Newmark-β method. Results show that the effect of the damping ratio on the impact factor is significant and running speed of the vehicle is one of the main actors resulting in vibration of the system.

scholarly journals Vibration Excitation and Control of a Pedestrian Walkway by Individuals and Crowds

2005 ◽  
Vol 12 (5) ◽  
pp. 333-347 ◽  
Author(s):  
James Mark William Brownjohn ◽  
Tao Neng Fu
Keyword(s):  
Force Plate ◽  
Low Frequency ◽  
Modal Parameters ◽  
Modal Parameter ◽  
Low Frequency Vibration ◽  
Lateral Response ◽  
Single Mass ◽  
The Subject ◽  
Mass Spring ◽  
And Control

As part of a continuing study on effects of humans on loading and dynamic response of footbridges, a steel frame walkway has been the subject of studies on the effects of multiple pedestrians with respect to loading and response mitigation. Following finite element modeling and experimental modal analysis to identify the low frequency vibration modes likely to be excited by normal walking, the variation of response with pedestrian density and of system damping and natural frequency with occupancy by stationary pedestrians were both studied. The potentially mitigating effect of stationary occupants is still not well understood and the study included direct measurement of damping forces and absorbed energy using a force plate. The various tests showed that energy dissipation measured directly was consistent with the observed change in damping, that vertical and lateral response both varied approximately with square root of number of pedestrians, and that the simple model of a human as a single mass-spring-damper system may need to be refined to fit observed changes in modal parameters with a crowd of humans present. Modal parameter changes with moving pedestrians were small compared to those with stationary pedestrians indicating that within limits, modal parameters for the empty structure could be used in analysis.

scholarly journals Soft projectile impact forces measurement using Hopkinson bars: application to ice, artificial bird and rubber

2021 ◽  
Vol 250 ◽  
pp. 01008
Author(s):  
Ramón del Cuvillo ◽  
Jose Alfonso Artero-Guerrero ◽  
Jesús Pernas-Sánchez ◽  
Jorge López Puente
Keyword(s):  
Kinetic Energy ◽  
High Speed ◽  
Soft Materials ◽  
Peak Force ◽  
Video Cameras ◽  
Impact Forces ◽  
Compression Strain ◽  
Experimental Campaign ◽  
The Impact ◽  
Semiconductor Strain

This work presents an experimental campaign of impacts of soft projectiles to measure the induced force during the impact. Three different materials acting as soft impactors that could strike against a aeronautical structural component: ice, artificial bird and rubber have been impacted at several velocities against an aluminium Hopkinson bar. This device has been instrumented with semiconductor strain gauges that allow to obtain the induced compression strain. Additionally, all the impacts were recorded using high-speed video cameras, allowing the kinematic analysis of the projectile during the impact. After the results study, it has been concluded that there is a linear dependency between the kinetic energy and the peak force for all three materials. Added to that, it has been proved that the higher peak force corresponds to ice, despite the kinetic energy, followed by rubber and finally the artificial bird. In addition, while ice and artificial bird projectiles get radially dispersed after the impact, rubber spheres rebound due to its different behaviour. The obtained data is of great interest to design structures which could be subjected to impacts of soft materials such as aeronautic structures

Comparative Study of Fiber Metal Laminates (FMLs) and Aluminum Skins for Polypropylene (PP) Honeycomb Core Sandwich Structure under Low Velocity Impact Loads

2011 ◽  
Vol 471-472 ◽  
pp. 524-529
Author(s):  
Md Akil Hazizan ◽  
C.Y. Tan
Keyword(s):  
High Speed ◽  
Sandwich Structure ◽  
Pure Aluminum ◽  
Low Velocity Impact ◽  
Honeycomb Core ◽  
Low Velocity ◽  
Time Histories ◽  
Force Time ◽  
Impact Energies ◽  
The Impact

In this study, the impact responses of sandwich structure with both FML and aluminum skins were compared. The force-time histories from the low-velocity drop weight impact tester were recorded under various impact energies. Energy absorbed from the two types of sandwich structures under various impact energies were also calculated by measuring its initial velocity before impact from a series of recorded high speed camera pictures and force-time histories. Based on results obtained, pure aluminum skins with PP honeycomb core that being impacted by lower impact energies shows higher absorbed energies as compared to FML skins. However with higher impact energies the FML skins shows improvement over the aluminum with higher energy absorption capacity. Damages created were also being characterized under optical microscope for further investigation.

Landing Strategy Adjustments Made by Female Gymnasts in Response to Drop Height and Mat Composition

1993 ◽  
Vol 9 (3) ◽  
pp. 173-190 ◽  
Author(s):  
Jill L. McNitt-Gray ◽  
Takashi Yokoi ◽  
Carl Millward
Keyword(s):  
Angular Position ◽  
Force Plate ◽  
Vertical Force ◽  
Drop Height ◽  
Time To Peak ◽  
Impact Peak ◽  
Force Time ◽  
Female Gymnasts ◽  
Landing Mat ◽  
Vertical Impact

In this study, drop height and landing mat composition were hypothesized to influence the landing strategies preferred by female gymnasts. Adjustments in strategy in response to changes in drop height and mat composition were identified by comparison of mechanical variables characterizing two-foot competition-style drop landings from three heights onto two different mats varying in composition (i.e., soft vs. stiff). Force-time characteristics of the landings were quantified (1000 Hz) by a force plate fully supporting the mat. Segment kinematics were recorded simultaneously with shuttered video (60 Hz). Significant differences (ANOVA; p < .05) in peak vertical force, landing phase time, time to peak vertical force, and lower extremity kinematics were found across drop heights. Only time to vertical impact peak and minimum knee angular position produced significant differences between the soft and stiff mats. These results indicate changes in drop height and mat composition may elicit changes in landing strategies of female gymnasts.

Modeling of Tread Block Contact Mechanics Using Linear Viscoelastic Theory3

2008 ◽  
Vol 36 (3) ◽  
pp. 211-226 ◽  
Author(s):  
F. Liu ◽  
M. P. F. Sutcliffe ◽  
W. R. Graham
Keyword(s):  
High Speed ◽  
Slip Rate ◽  
Material Model ◽  
Contact Forces ◽  
Block Modeling ◽  
Rate Dependent ◽  
Linear Viscoelastic Material ◽  
Linear Viscoelastic ◽  
The Impact ◽  
Good Agreement

Abstract In an effort to understand the dynamic hub forces on road vehicles, an advanced free-rolling tire-model is being developed in which the tread blocks and tire belt are modeled separately. This paper presents the interim results for the tread block modeling. The finite element code ABAQUS/Explicit is used to predict the contact forces on the tread blocks based on a linear viscoelastic material model. Special attention is paid to investigating the forces on the tread blocks during the impact and release motions. A pressure and slip-rate-dependent frictional law is applied in the analysis. A simplified numerical model is also proposed where the tread blocks are discretized into linear viscoelastic spring elements. The results from both models are validated via experiments in a high-speed rolling test rig and found to be in good agreement.

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