scholarly journals Impact Force of Free-fall Lifeboats at Water Entry

1994 ◽  
Vol 90 (0) ◽  
pp. 165-173
Author(s):  
Kazuo HITOMI ◽  
Osamu MIYATA
Keyword(s):  
Impact Force ◽  
Free Fall ◽  
Water Entry

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

2000 ◽  
Vol 214 (2) ◽  
pp. 359-370 ◽  
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.

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

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.

Analysis of Parameters Affecting Impact Force Attenuation during Landing in Human Vertical Free Fall

1982 ◽  
Vol 11 (3) ◽  
pp. 141-147 ◽  
Author(s):  
J Mizrahi ◽  
Z Susak
Keyword(s):  
Early Phase ◽  
Impact Force ◽  
Body Position ◽  
Free Fall ◽  
Muscle Action ◽  
Impact Forces ◽  
Ground Roll ◽  
Vertical Landing

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.

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

2012 ◽  
Vol 10 (6) ◽  
pp. 490-497 ◽  
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.

scholarly journals Water Entry Simulation of Free-fall Lifeboat

1996 ◽  
Vol 1996 (179) ◽  
pp. 205-211 ◽  
Author(s):  
Makoto Arai ◽  
M. Reaz H. Khondoker ◽  
Yoshiyuki Inoue
Keyword(s):  
Free Fall ◽  
Water Entry

Numerical Analysis of Impact Loads on Subsea Structures During Water Entry in Presence of Waves

2020 ◽  
Author(s):  
Gustavo Garcia Momm ◽  
Ivan Fábio Mota de Menezes
Keyword(s):  
Constant Velocity ◽  
Oil And Gas ◽  
Free Fall ◽  
Water Entry ◽  
Gas Production ◽  
Rigid Bodies ◽  
Bottom Surface ◽  
Impact Loads ◽  
Flat Bottom ◽  
The Impact

Abstract Subsea structures employed on offshore oil and gas production systems are likely to be subject to severe loads during deployment. Lowering these structures through the wave zone is a critical operation and the prediction of the loads associated is complex as it involves accelerations of these bodies induced by the vessel motion and the sea surface displacements. This work presents a numerical approach to assessment of the effect of waves on the impact loads that subsea structures are subject to during water entry. A 2D one degree of freedom model using the SPH method was developed to estimate slamming loads on rigid bodies during water entry considering both calm and wavy surfaces. Initially the model was employed to simulate the water entry of wedge considering both free fall and constant velocity cases, obtaining loads profile similar to experiments and numerical simulations from the literature. Later, the constant velocity model was configured to a flat bottom surface rigid body in order to represent a subsea manifold. A regular waves generator provided different wavelength, height and phase enabling slamming load assessment in various situations.

Free Fall Water Entry of a Two-Dimensional Asymmetric Wedge in Oblique Slamming: A Numerical Study

2020 ◽  
Author(s):  
Saeed Hosseinzadeh ◽  
Mohammad Izadi ◽  
Kristjan Tabri
Keyword(s):  
Numerical Study ◽  
Experimental Studies ◽  
Free Fall ◽  
Water Entry ◽  
Vertical Acceleration ◽  
Two Dimensional ◽  
Pile Up ◽  
Real Phenomenon ◽  
Precise Simulation ◽  
Good Agreement

Abstract This paper examines the hydrodynamic problem of a two-dimensional symmetric and asymmetric wedge water entry through freefall motion. The gravity effect on the flow is considered and because of precise simulation close to the real phenomenon, the oblique slamming is analyzed. The defined problem is numerically studied using SIMPLE and HRIC schemes and by implementing an overset mesh approach. In order to evaluate the accuracy of the numerical model, the present results are compared and validated with previous experimental studies and showed good agreement. The results are presented and compared for each symmetry and asymmetry in different deadrise angles, drop heights and heel angles. Based on a comparison of the measured vertical acceleration of the experimental wedge data, it is determined that the proposed numerical method has relatively good accuracy in predicting the slamming phenomenon and wedge response. The influence of viscous regime on water entry simulations is investigated, in according to results, effect of viscosity is negligible. Results show that the heel angle dramatically affects the wedge dynamics, pile-up evolution, and pressure distribution. These results suggest evidence for a complex interaction between geometric parameters on the water entry of rigid wedges, which could finally develop our understanding of planing vessels operating in real sea conditions.

Free fall water entry of a cone in three degrees of freedom

2020 ◽  
Vol 101 ◽  
pp. 102273 ◽  
Author(s):  
Shi-Li Sun ◽  
Yong Cheng ◽  
Jie Cui ◽  
Shi-Yan Sun
Keyword(s):  
Degrees Of Freedom ◽  
Free Fall ◽  
Water Entry ◽  
Three Degrees Of Freedom
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