Reproducible SPT hammer impact force with an automatic free fall SPT hammer system

The characteristics of impact forces on the legs during vertical landing of human vertical free fall in different falling conditions were studied to reveal the parameters which take part in the attenuation of these impact forces. The following parameters were investigated: body position during landing, range of flexion of the joints of the legs at impact, usage of ground-roll immediately after impact and softness of the ground. The results indicate that joint movements and muscle action play a major role in reducing peak forces during landing. This emphasizes the importance of adequate training to improve the pre-programmed non-reflex muscle action, necessary in the early phase of impact.

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Performance analysis of the protective effects of bicycle helmets during impact and crush tests in pediatric skull models

Journal of Neurosurgery Pediatrics ◽

10.3171/2012.8.peds12116 ◽

2012 ◽

Vol 10 (6) ◽

pp. 490-497 ◽

Cited By ~ 18

Author(s):

Tobias A. Mattei ◽

Brandon J. Bond ◽

Carlos R. Goulart ◽

Chris A. Sloffer ◽

Martin J. Morris ◽

...

Keyword(s):

Impact Force ◽

Compressive Force ◽

Free Fall ◽

Protective Effects ◽

Human Cadaver ◽

Bicycle Helmet ◽

Bicycle Helmets ◽

Drop Tests ◽

Flat Steel ◽

Human Skulls

Object Bicycle accidents are a very important cause of clinically important traumatic brain injury (TBI) in children. One factor that has been shown to mitigate the severity of lesions associated with TBI in such scenarios is the proper use of a helmet. The object of this study was to test and evaluate the protection afforded by a children's bicycle helmet to human cadaver skulls with a child's anthropometry in both “impact” and “crushing” situations. Methods The authors tested human skulls with and without bicycle helmets in drop tests in a monorail-guided free-fall impact apparatus from heights of 6 to 48 in onto a flat steel anvil. Unhelmeted skulls were dropped at 6 in, with progressive height increases until failure (fracture). The maximum resultant acceleration rates experienced by helmeted and unhelmeted skulls on impact were recorded by an accelerometer attached to the skulls. In addition, compressive forces were applied to both helmeted and unhelmeted skulls in progressive amounts. The tolerance in each circumstance was recorded and compared between the two groups. Results Helmets conferred up to an 87% reduction in so-called mean maximum resultant acceleration over unhelmeted skulls. In compression testing, helmeted skulls were unable to be crushed in the compression fixture up to 470 pound-force (approximately 230 kgf), whereas both skull and helmet alone failed in testing. Conclusions Children's bicycle helmets provide measurable protection in terms of attenuating the acceleration experienced by a skull on the introduction of an impact force. Moreover, such helmets have the durability to mitigate the effects of a more rare but catastrophic direct compressive force. Therefore, the use of bicycle helmets is an important preventive tool to reduce the incidence of severe associated TBI in children as well as to minimize the morbidity of its neurological consequences.

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A comparative study on the behaviour of free-fall lifeboat launching from a skid and from a hook

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1243/0954406001523029 ◽

2000 ◽

Vol 214 (2) ◽

pp. 359-370 ◽

Cited By ~ 2

Author(s):

M Reaz H Khondoker ◽

M Arai

Keyword(s):

Numerical Simulation ◽

Dynamic Response ◽

Comparative Study ◽

Impact Force ◽

Free Fall ◽

Water Entry ◽

Hydrodynamic Forces ◽

Response Criteria ◽

Risk Of Injury ◽

Tremendous Impact

There are two commonly used launching methods of free-fall lifeboats: from a skid and from a hook. A free-fall lifeboat, whether it is released from a skid or from a hook, experiences tremendous impact when it enters the water. This impact force, together with other hydrostatic and hydrodynamic forces and moments, affects the motions and accelerations of the boat considerably. In this paper, a comparative study on the behaviours of the skid and hook launching of free-fall lifeboats has been presented. Numerical simulation for different launching methods has been used as a tool to obtain trajectories of the lifeboat for different launching conditions. Also polar diagrams of accelerations are drawn using the data computed for the same conditions. Dynamic response criteria have been used in order to evaluate the risk of injury to the occupants during water entry of the lifeboat.

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Parametric Study on the Free-Fall Water Entry of a Sphere by Using the RANS Method

Journal of Marine Science and Engineering ◽

10.3390/jmse7050122 ◽

2019 ◽

Vol 7 (5) ◽

pp. 122

Author(s):

Pengyao Yu ◽

Cong Shen ◽

Chunbo Zhen ◽

Haoyun Tang ◽

Tianlin Wang

Keyword(s):

Impact Velocity ◽

Impact Force ◽

Free Fall ◽

Water Entry ◽

Time Step ◽

Measuring Device ◽

Mesh Density ◽

The Impact ◽

Peak Value ◽

Rans Method

Motivated by the application of water-entry problems in the air-drop deployment of a spherical oceanographic measuring device, the free-fall water entry of a sphere was numerically investigated by using the transient Reynolds-averaged Navier–Stokes (RANS) method. A convergence study was carried out, which accounts for the mesh density and time-step independence. The present model was validated by the comparison of non-dimensional impact force with previous experimental and numerical results. Effects of parameters, such as impact velocity, radius, and mass of the sphere on the impact force and the acceleration of the sphere, are discussed. It is found that the peak value of the non-dimensional impact force is independent of the impact velocity and the radius of the sphere, while it depends on the mass of the sphere. By fitting the relationship between the peak value of the non-dimensional impact force and the non-dimensional mass, simplified formulas for the prediction of peak values of the impact force and the acceleration were achieved, which will be useful in the design of the spherical oceanographic measuring device.

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Some insights into slamming forces: Compressible and incompressible phases

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1243/0954406001523867 ◽

2000 ◽

Vol 214 (6) ◽

pp. 881-888 ◽

Cited By ~ 4

Author(s):

E F Campana ◽

A Carcaterra ◽

E Ciappi ◽

A Iafrati

Keyword(s):

Impact Force ◽

Mass Parameter ◽

Free Fall ◽

The Body ◽

Body Motion ◽

Closed Form Expression ◽

Surface Evolution ◽

Entry Velocity ◽

Wetted Area ◽

The Impact

In the present paper the slamming force occurring in the free-fall impact of cylindrical bodies over the water surface is analysed in both compressible and incompressible stages. In the compressible phase the hydrodynamic analysis is carried out by the acoustic approximation and a closed-form expression for the impact force is recovered. The incompressible stage is approached through an unsteady boundary element method to compute the free surface evolution and the slamming force on the body. In both cases the hydrodynamic force is coupled to the rigid body motion to update the entry velocity of the body. The combined effect of the increasing wetted area and the reducing entry velocity leads to a maximum in the impact force that depends on the body mass. A parametric investigation shows that in the impact of a wedge section, if the maximum is reached either in the compressible or in the incompressible stages, a similar square root trend characterizes the dependence of this maximum on a non-dimensional mass parameter.

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Free fall

AccessScience ◽

10.1036/1097-8542.271400 ◽

2015 ◽

Keyword(s):

Free Fall

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