ANALYTICAL SOLUTION OF WEDGE WATER ENTRY BY USING SCHWARTZ–CHRISTOFFEL CONFORMAL MAPPING

2011 ◽  
Vol 02 (03) ◽  
pp. 337-354 ◽  
Author(s):  
PARVIZ GHADIMI ◽  
AMIR SAADATKHAH ◽  
ABBAS DASHTIMANESH
Keyword(s):  
Conformal Mapping ◽  
Impact Force ◽  
Offshore Structures ◽  
Water Entry ◽  
The Body ◽  
Water Impact ◽  
Local Pressure ◽  
Maximum Impact Force ◽  
The Impact ◽  
First Time

Water impact is one of the most critical phenomena from the viewpoint of the structural design of ships and offshore structures. The impact force can impose a large load with high local pressure on the body surface. On the other hand, determination of the maximum impact force during impact and acting point itself is very important in the design of floats. In this paper, the water entry of a two-dimensional wedge section is considered. This study is carried out in the framework of a potential-flow assumption. In particular, water impact on a dropping wedge with a constant velocity is pursued analytically by using the Schwartz–Christoffel conformal mapping. In order to determine a position of the wedge where the instantaneous effective force is largest during the impact, a particular equation is introduced here for the first time. The pressure distribution and maximum impact force are also calculated. The obtained results are compared against other numerical and experimental works and favorable agreement is displayed.

Nonlinear Computation of Water Impact of Axisymmetric Bodies

2011 ◽  
Vol 55 (01) ◽  
pp. 29-44
Author(s):  
Hongmei Yan ◽  
Yuming Liu
Keyword(s):  
Free Surface ◽  
Flow Separation ◽  
Impact Force ◽  
Surface Profile ◽  
The Body ◽  
Gravity Effect ◽  
Water Impact ◽  
Free Surface Profile ◽  
Axisymmetric Bodies ◽  
The Impact

A fully nonlinear numerical simulation based on a boundary element method was used to investigate water impact of axisymmetric bodies that strike vertically the horizontal free surface from the air. The main objective was to understand the gravity effect on flow/wave kinematics and dynamics and to quantify the range of validity of existing theories and computations that are based on the infinite Froude number assumption. Two body geometries were considered: inverted cone and sphere. For the inverted cone, we obtained detailed dependencies of free-surface profile and impact pressure and load on the body on the generalized Froude number (Fr(V/gt)1/2, where V is the impact velocity, g is the gravitational acceleration, and t is time) and deadrise angle a. Based on these, we developed an approximate formula for evaluating the contribution of the gravity effect to the total impact force on the body in terms of a similarity parameter Fr/a1/2. For the sphere, we developed and applied a pressure-based criterion to follow the evolution of flow separation on the body and to obtain an appropriate description of the free-surface profile near the body and accurate evaluation of the impact pressure and load on the body during the entire impact process. The numerical result of impact force on the body agreed well with existing experimental measurements. We confirmed that the gravity effect is unimportant in initial impact of the sphere. Significantly, we found that in a later stage of impact, flow separation remains at an almost fixed position at an angle u 62.5 deg to the bottom of the sphere for a wide range of Froude numbers, Fr V/(gR)1/2 1, where R is the radius of the sphere.

Slamming Loads on a Wedge Elastically Suspended on a Marine Structure

2015 ◽  
Author(s):  
Hui Sun ◽  
Jens B. Helmers
Keyword(s):  
Free Surface ◽  
Impact Force ◽  
Water Entry ◽  
The Body ◽  
Water Impact ◽  
Surface Conditions ◽  
Marine Structure ◽  
Nonlinear Free Surface ◽  
Stiffness And Damping ◽  
Water Exit

Slamming loads on a two-dimensional wedge elastically suspended on a marine structure are analyzed by using either a combined Wagner and von Karman method (W-vK) or a boundary element method (BEM). Fully nonlinear free surface conditions are satisfied in the BEM. Hydroelasticity effects are considered in both methods. A sinusoidal free surface motion relative to the marine structure is specified for the slamming event. Both the water entry phase and the water exit phase are simulated. The numerical results by the two different methods are compared. The W-vK method can generally predict the same trend of the variation of the body motions and the water forces, although the predicted maximum forces are larger than those by the BEM. The influence of the stiffness and damping of the elastic connection on the water impact force are discussed.

Investigating the influence of Taekwondo body protectors size on shock absorption

2020 ◽  
pp. 1-9
Author(s):  
Hee Seong Jeong ◽  
Sae Yong Lee ◽  
Hyung Jun Noh ◽  
David Michael O’Sullivan ◽  
Young Rim Lee
Keyword(s):  
Impact Strength ◽  
Impact Force ◽  
Impact Load ◽  
The Body ◽  
Shock Absorption ◽  
Significance Level ◽  
The Difference ◽  
Maximum Impact Force ◽  
Impact Energies ◽  
The Impact

OBJECTIVE: This study aims to compare and analyze the difference of impact force attenuation according to size and impact location on a Taekwondo body protector. METHODS: Body protectors sized 1 to 5, were impact tested by equipment based on the specifications in the European standard manual (EN 13277-1, 3). The impactor release heights were set to match impact energies of 3 and 15 J. The impactor was made from a 2.5 kg cylindrically cut piece of aluminum. Each body protector was impacted 10 times at the two impact energies and two locations. The differences in performance for each body protector size were compared using a two-way analysis of variance with a significance level of p< 005. The effect sizes were investigated using a partial eta squared value (η2). RESULTS: The significant mean differences between the body protector size and impact area (p< 005) and the average impact time of impact strengths 3 and 15 J were 0.0017 and 0.0012 s, respectively In addition, when an impact strength of 15 J was applied, the maximum resulting impact force exceeded 2000 N for both locations on all sizes. Furthermore, at an impact strength of 3 J size 3 significantly reduced the impact force more than the other sizes; however, size 1 showed the greatest shock absorption at an impact of 15 J. CONCLUSION: The results of this study show that the shock absorption of body protectors does not increase according to size; i.e., a larger body protector does not reduce the impact load more effectively. To improve safety performance, we recommend a maximum impact force of 2000 N or less for all body protectors.

scholarly journals Experimental Study of the Debris Flow Slurry Impact and Distribution

2018 ◽  
Vol 2018 ◽  
pp. 1-15 ◽  
Author(s):  
Haixin Zhao ◽  
Lingkan Yao ◽  
Yong You ◽  
Baoliang Wang ◽  
Cong Zhang
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Impact Force ◽  
Influence Factors ◽  
Flume Experiment ◽  
Middle Point ◽  
Laboratory Flume ◽  
Critical Issues ◽  
Maximum Impact Force ◽  
The Impact

In this study, we present a new method to calculate debris flow slurry impact and its distribution, which are critical issues for designing countermeasures against debris flows. There is no unified formula at present, and we usually design preventive engineering according to the uniform distribution of the maximum impact force. For conducting a laboratory flume experiment, we arrange sensors at different positions on a dam and analyze the differences on debris flow slurry impact against various densities, channel slopes, and dam front angles. Results show that the force of debris flow on the dam distributes unevenly, and that the impact force is large in the middle and decreases gradually to the both sides. We systematically analyze the influence factors for the calculation of the maximum impact force in the middle point and give the quantitative law of decay from the middle to the sides. We propose a method to calculate the distribution of the debris flow impact force on the whole section and provide a case to illustrate this method.

Theoretical Study of the Water Entry of a Body in Waves: Application to Safety of Occupants in Free-Fall Lifeboats

2009 ◽  
Author(s):  
Thomas Sauder ◽  
Se´bastien Fouques
Keyword(s):  
Water Waves ◽  
Degrees Of Freedom ◽  
Mass Matrix ◽  
Free Fall ◽  
Theoretical Method ◽  
Emergency Evacuation ◽  
Momentum Conservation ◽  
The Body ◽  
Water Impact ◽  
The Impact

The safety of occupants in free-fall lifeboats (FFL) during water impact is addressed. The first part of the paper describes a theoretical method developed to predict the trajectory in six degrees of freedom of a body entering water waves. Slamming forces and moments are computed, based on momentum conservation, long wave approximation and a von Karman type of approach. The added mass matrix of the body is evaluated for impact conditions by a boundary element method. The second part of the paper focuses on the application of the method to free-fall lifeboats, which are used for emergency evacuation of oil platforms or ships. Acceleration loads on FFL occupants during water impact are dependent on numerous parameters, especially the hull shape, the mass distribution, the wave heading relative to the lifeboat, and the impact point on the wave surface. Assessing operational limits of FFL by means of model tests only has therefore been costly and time consuming. This issue is addressed here by applying the theoretical method described in the first part. The model has been validated for FFL through extensive model testing in calm water and regular waves, and statistical estimates of acceleration levels for lifeboat occupants, as well as acceleration time series were obtained that can be used as inputs to numerical human response models.

DYNAMIC CHARACTERISTICS MEASUREMENTS OF A FORCE TRANSDUCER AGAINST SMALL AND SHORT-DURATION IMPACT FORCES

2014 ◽  
Vol 21 (1) ◽  
pp. 59-66 ◽  
Author(s):  
Mitra Djamal ◽  
Kazuhide Watanabe ◽  
Kyohei Irisa ◽  
Irfa Aji Prayogi ◽  
Akihiro Takita ◽  
...  
Keyword(s):  
Short Duration ◽  
Dynamic Characteristics ◽  
Impact Force ◽  
Inertial Force ◽  
Small Mass ◽  
Force Transducer ◽  
Force Transducers ◽  
Impact Forces ◽  
Maximum Impact Force ◽  
The Impact

Abstract A method for evaluating the dynamic characteristics of force transducers against small and short-duration impact forces is developed. In this method, a small mass collides with a force transducer and the impact force is measured with high accuracy as the inertial force of the mass. A pneumatic linear bearing is used to achieve linear motion with sufficiently small friction acting on the mass, which is the moving part of the bearing. Small and short-duration impact forces with a maximum impact force of approximately 5 N and minimum half-value width of approximately 1 ms are applied to a force transducer and the impulse responses are evaluated.

Impact of Elastic Body on the Deep and Shallow Water

2013 ◽  
Author(s):  
Alexander A. Korobkin ◽  
Tatyana I. Khabakhpasheva
Keyword(s):  
Shallow Water ◽  
Elastic Body ◽  
Water Depth ◽  
The Body ◽  
Complex Structures ◽  
Water Impact ◽  
One Dimensional ◽  
Mode Method ◽  
Bending Stresses ◽  
The Impact

Two-dimensional unsteady problem of elastic body impact on liquid free surface is considered. The water is either of infinite depth or shallow. We are concerned with the effect of the water depth on the bending stresses in the structure caused by the fluid-structure interaction. The Wagner model is used for infinite water depth. In the case of shallow water impact, the hydrodynamic problem is one-dimensional but nonlinear. Both problems for deep and shallow waters are solved numerically by the normal mode method. Two shapes of the body, cylindrical shell and elastic wedge, are considered. The impact conditions and the structural characteristic are identical. The bending stresses in the structure are investigated. It is shown that the bending stresses for impact on shallow water are greater than those for the infinite water depth. The developed methods and approaches can be combined with FFM to include complex structures.

A Comparative Study on the Effect of Mechanical Compliance for a Safe Physical Human–Robot Interaction

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Yu She ◽  
Siyang Song ◽  
Hai-Jun Su ◽  
Junmin Wang
Keyword(s):  
Impact Force ◽  
Variable Stiffness ◽  
Human Robot Interaction ◽  
Design Parameters ◽  
Robot Dynamics ◽  
Robot Interaction ◽  
Promising Alternative ◽  
Mechanical Compliance ◽  
Maximum Impact Force ◽  
The Impact

Abstract In this paper, we study the effects of mechanical compliance on safety in physical human–robot interaction (pHRI). More specifically, we compare the effect of joint compliance and link compliance on the impact force assuming a contact occurred between a robot and a human head. We first establish pHRI system models that are composed of robot dynamics, an impact contact model, and head dynamics. These models are validated by Simscape simulation. By comparing impact results with a robotic arm made of a compliant link (CL) and compliant joint (CJ), we conclude that the CL design produces a smaller maximum impact force given the same lateral stiffness as well as other physical and geometric parameters. Furthermore, we compare the variable stiffness joint (VSJ) with the variable stiffness link (VSL) for various actuation parameters and design parameters. While decreasing stiffness of CJs cannot effectively reduce the maximum impact force, CL design is more effective in reducing impact force by varying the link stiffness. We conclude that the CL design potentially outperforms the CJ design in addressing safety in pHRI and can be used as a promising alternative solution to address the safety constraints in pHRI.

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.

Size Effects in the Impact of Carbon Fiber Reinforced Composite Structures

2018 ◽  
Vol 789 ◽  
pp. 155-160
Author(s):  
Yi Ou Shen ◽  
Yan Li
Keyword(s):  
Size Effects ◽  
Composite Structures ◽  
Impact Force ◽  
Flexural Rigidity ◽  
Experimental Results ◽  
Target Size ◽  
Mass Model ◽  
Energy Impact ◽  
Maximum Impact Force ◽  
The Impact

In this study, target size effects in the low energy impact response of plain CFRP plateswere investigated. It was found that increase the target size leads to a reduction in the maximumimpact force recorded during the test. This is due to the reduction on flexural rigidity of the largerpanels. The experimental results indicated that at energies above the first failure threshold, themaximum impact force does not coincidence with the predicting value. Two mathematical modelswere used to predict the maximum impact force including single degree of freedom (SDOF)spring-mass model and Energy-Balance (E-B) model. The predicting results were then comparedwith the experimental results, and both of the two models show good agreement with theexperimental results in elastic deformation region. In addition, the level of agreement between thepredictions and the experimental results indicate that both models are capable of modelling theimpact response of these CFRP panels at elastic regime.

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